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whose senior Professor he was from 1868 to 1903

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THE

MICROSCOPE:

REVELATIONS.

WORKS BY DR. CARPENTER.

i
PRINCIPLES OF COMPARATIVE PHYSIOLOGY.

A New American, FRoM THE FourtH anp Revisep Loxpon Enition.

With more than three hundred beautiful illustrations. In one large and hand-
some octavo volume of 752 pages.

Without pretending to it, it is an Ency- | could have brought to so successful an issue
clopzdia of the subject, accurate and com- | as Dr. Carpenter. We feel that this ab-
plete in all respects—a truthful reflection | stract can give the reader a very imperfect
of the advanced state at which the science | idea of the fulness of this work, and no
has now arrived—Dublin Quarterly Jour- | idea of its unity, of the admirable manner
nal of Medical Science. in which material has been brought, from

A truly magnificent work—in itself a | the most various sources, to conduce to its
perfect physiological study.—Ranking’s | completeness, of the lucidity of the reason-
Abstract. ing it contains, or of the clearness of lan-

This work stands without its fellow. It | guage in which the whole is clothed.—
is one, few men in Europe could have | Medical Times.
undertaken ; itis one, no man, we believe,

Ii.
PRINCIPLES OF HUMAN PHYSIOLOGY.

WITH THEIR CHIEF APPLICATIONS TO

PSYCHOLOGY, PATHOLOGY, THERAPEUTICS, HYGIENE, AND
FORENSIC .MEDICINE.

A new American, from the last and revised London Edition, with nearly three
hundred illustrations. Edited, with additions, by F. Gurney Smith, M.D. In one
large and handsome volume of about nine hundred pages.

The most complete work on the science A complete cyclopeedia of this branch of
in our language.—.4m. Med. Journal. science—NV. Y. Med. Times.

The most complete work now extant in The most complete exposition of physio-
our language—N. O. Med. Register. logy which any language can at present

The best text-book in the language on | give—Brit. and For. Med.-Chirurg. Review.
this extensive subject.— London Med. Times.

I.
ELEMENTS (OR MANUAL) OF PHYSIOLOGY.

INCLUDING PHYSIOLOGICAL ANATOMY.

Second American, from the last and revised London Edition, with one hundred
and ninety illustrations. In one handsome octavo volume of 566 pages.

In his former works it would seem that Those who have occasion for an elemen-
he had exhausted the subject of Physiology. | tary treatise on Physiology, cannot do bet-
In the present, he gives the essence, as it | ter than to possess themselves of the manual
were, of the whole.—N. Y. Journal of | of Dr. Carpenter.—Medical Examiner.
Medicine.

PREPARING

PRINCIPLES OF GENERAL PHYSIOLOGY, including ORGANIC CHEM.
ISTRY, and HISTOLOGY. With a general sketch of the Vegetable and Animal
Kingdoms. With several hundred illustrations. In one large and handsome
octavo volume.

In his last edition of the ‘Comparative Physiology” and ‘Human Physiology,”
the author found it desirable to omit the chapters connected with “ General Physio-
logy.” He has therefore undertaken to prepare a volume devoted exclusively to
that subject, forming an introduction to the other works, or, taken in conjunction
ihe ee constituting a complete and extended system of Physiology, in all its

ranches.

THE

MICROSCOPE:

AND ITS

REVELATIONS,

BY

WILLIAM B. CARPENTER, M.D., F.R.S., F.G.S.,

dh siece IN PHYSIOLOGY AND COMPARATIVE ANATOMY IN THE UNIVERSITY OF LONDON ;
PROFESSOR, OF MEDICAL JURISPRUDENCE IN UNIVERSITY COLLEGE ;
PRESID OF THE MICROSCOPICAL SOCIETY OF LONDON; ETC.

WITH AN APPENDIX

CONTAINING THE

AfPLications OF THE MICROSCOPE TO CLINICAL MEDICINE, ETC.

BY

FRANCIS GURNEY SMITH, M.D.,

PROFESSOR OF THE INSTITUTES OF MEDICINE
IN THE MEDICAL DEPARTMENT OF PENNSYLVANIA COLLEGE, ETC.

ILLUSTRATED BY FOUR HUNDRED AND THIRTY-FOUR
Gngrabings on Wood.

PHILADELPHIA:
BLANCHARD AND LEA.

1856.
~)

Cuno

C28]

CUlboy
Entered, according to Act of Congress, in the year 1856,
BY BLANCHARD AND LEA,

In the Clerk's Office of the District Court for the Eastern District of Pennsylvania.

C. SHERMAN & SON, PRINTERS,

19 St. James Street.

PREFACE TO THE AMERICAN EDITION.

Tue American Edition of Dr. Carpenter’s Work has been
reprinted with the Author’s sanction, from advance sheets fur-
nished by him to.the American publishers. In assuming the
supervision of the press, the Editor has been careful to leave the
work as it came from the Author’s hands. Such additions as
seemed most required by the Students of this country have been
made in the form of an Appendix. The reader will find Dr.
Carpenter’s reasons for omitting the Clinical Applications of
the Microscope, fully detailed in his Preface; but as the various
works on this subject are not readily accessible on this side of
the Atlantic, it was thought that a selection from them, in a
compendious form, might enhance the usefulness of the work.
Free use has been made, therefore, of the excellent manuals of
Beale and Bennett; and the various kindred treatises and jour-
nals have also been drawn upon. All that this portion of the
work claims is to present a general view of those subjects which
seem to be most required by the student of the Microscope.
The growing interest in this important field of inquiry will,

it is hoped, afford sufficient apology for its introduction.

v1 PREFACE TO THE AMERICAN EDITION.

A short account of American Microscopes, their modifications
and accessories, has also been added, and the whole Appendix
has been fully illustrated, through the liberality of the Pub-
lishers, by the addition of upwards of one hundred wood-
engravings.

Francis Gurney Situ, M.D.

428 Watnout STREET,
June, 1856.

PREFACE.

THE rapid increase which has recently taken place in the use
of the Microscope,—both as an instrument of scientific research,
and as a means of gratifying a laudable curiosity and of obtain-
ing a healthful recreation,—has naturally led to a demand for
information, both as to the mode of employing the instrument
and its appurtenances, and as to the objects for whose minute
examination it is most appropriate. And as none of the existing
Treatises, either British or Foreign, on the Microscope and its
Uses, have seemed to the Author fully adapted to meet this
demand (some of them being almost exclusively concerned with
the Microscope itself, and others with some special branch or
branches of Microscopic study), he has felt encouraged to carry
out a plan which he had formed several years since; by endea-
voring to combine, within a moderate compass, that information
in regard to the use of his ‘tools’ which is most essential to the
working Microscopist, with such an account of the objects best
fitted for his study, as might qualify him to comprehend what
he observes, and might thus prepare him to benefit science,
whilst expanding and refreshing his own mind.

In his account of the various forms of Microscopes and Acces-
sory Apparatus, the Author has not attempted to describe every-
thing which is in use in this country; still less, to go into details
respecting the construction of foreign instruments. He is satis-
fied that in all which relates both to the mechanical and the
optical arrangements of their instruments, the chief English
Microscope-makers are decidedly in advance of their Conti-
nental rivals; and on this point he speaks not only from his
own conviction, but from the authority of a highly accomplished
German Microscopist, who has recently visited London for the

vill PREFACE.

express purpose of making the comparison. Even among the
products of English skill, it was necessary for him to make a
selection ; and he trusts that he will be found to have done ade-
quate justice to all those who have most claim to an honorable
mention.

The great objection to English Microscopes, especially on the
western side of the Atlantic, seems to be their costliness; and
as it can be affirmed with truth, that the instruments of Nachet,
Oberhauser, and other Continental makers, are adequate for all
essential purposes, a general preference is given to the latter (as
the Author understands) among the Microscopists of the United
States. He feels sure, however, that no one who has ever been
accustomed to work with a well-constructed English Microscope
will ever give the preference to a foreign instrument; and he is
glad to be able to announce that one of the best London firms
is now prepared to supply a Microscope of excellent quality at a
price very little exceeding that paid for Continental instruments,
of far superior capabilities. (See p. 1038, note.)

In treating of the Applications of the Microscope, the Author
has constantly endeavored to meet the wants of those who come
to the study of the minute forms of Animal and Vegetable life
with little or no previous scientific preparation, but who desire
to gain something more than a mere sight of the objects to which
their observation may be directed. Some of these may perhaps
object to the general tone of his work as too highly pitched, and
may think that he might have rendered his descriptions simpler
by employing fewer scientific terms. But he would reply to
such, that he has had much opportunity of observing, among
the votaries of the Microscope, a desire for such information as
he has attempted to convey (of the extent of which desire, the
success of the “ Quarterly Journal of Microscopical Science” is a
very gratifying evidence); and that the use of scientific terms
cannot be dispensed with, since there are no others in which the
facts can be expressed. As he has made a point of explaining
these, in the places where they are first introduced, he cannot
think that any of his readers need find much difficulty in appre-
hending their meaning.

The proportion of space allotted to the various departments,
has been determined, not so much by their Physiological im-
portance, as by their special interest to the Microscopist; and
the remembrance of this consideration will serve to account for

PREFACE. ix

much that might otherwise appear strange. The Author has
thought it particularly needful to restrain himself, in treating of
certain very important subjects which are fully discussed in trea-
tisey expressly devoted to them (such, for example, as the struc-
ture of Insects, and the Primary Tissues of Vertebrata), in order
that he might give more space to those on which no such sources
of information are readily accessible. For the same reason he
has omitted all reference to the applications of the Microscope
to Pathological inquiry; a subject which would interest only
one division of his readers, and on which it would have been
impossible for him to compress, within a sufficiently narrow
compass, a really useful summary of what such readers can
readily learn elsewhere. So again, the application of the Micro-
scope to the detection of Adulterations in Food, &c., is a topic
of such a purely special character, and must be so entirely based
on detailed descriptions of the substances in question, that he
has thought it better to leave this also untouched.

It has been the Author's object throughout, to guide the pos-
sessor of a Microscope to the intelligent study of any department
of Natural History, that his individual tastes may lead him to
follow out, and his particular circumstances may give him faci-
lities for pursuing. And he has particularly aimed to show,
under each head, how small is the amount of reliable knowledge
already acquired, compared with that which remains to be
attained by the zealous and persevering student. Being satis-
fied that there is a large quantity of valuable Microscope “power
at present running to waste in this country,—being applied in
such desultory observations as are of no service whatever to
science, and of very little to the mind of the observer,—he will
consider the labor he has bestowed upon the production of this
Manual as well repaid, if it should tend to direct this power to
more systematic labors, in those fertile fields which only await
the cultivator to bear abundant fruit.

In all that concerns the working of the Microscope, the Author
has mainly drawn upon his own experience, which dates back
almost to the time when Achromatic Object-glasses were first
constructed in this country. He would be ungrateful, however,
if he were not to acknowledge that he has derived many valu-
able hints from the Practical Treatises of Mr. Quekett and Dr.
Beale, and from the Micrographic Dictionary of Messrs. Griffith
and Henfrey. And among the works by which he has been

x PREFACE,

specially aided in treating of the Applications of the instrument,
he would especially name Mr. Quekett’s valuable Lectures on
Histology (Vegetable and Animal), Mr. Ralfs’s beautiful Mono-
graph on the British Desmidiex, Prof. W. Smith’s on the Diato-
mace (which will, when complete, be quite worthy to take
rank with the preceding), and the Micrographic Dictionary.

All the Illustrations have been drawn by Mr. W. Bagg, and
have been engraved under his superintendence; and the Author
ventures to affirm, that for fidelity as well as for beauty of
execution, they will bear comparison with any Microscopic de-
lineations yet executed on wood. A large proportion of the
subjects are original ; the sources of all that are not so, are spe-
cified in the list (p. xvii).

The Author feels that some apology is due for the long delay
which has attended the appearance of this work. When it was
first announced as forthcoming, his full intention was to apply
himself immediately to its production; but the unexpected de-
mand for new editions of his two large Treatises on Physiology,
required that the whole of his disposable time and attention
should be given up during two years to carrying these through
the press. When he at last found himself free to apply himself
to the “Microscope,” he fully expected that the forward state of
his preparations would enable him to complete it by October,
1855. But in this expectation he has been disappointed by the
occurrence of two severe attacks of indisposition, which com-
pelled him for a time to suspend all mental exertion, and have
rendered it necessary for him carefully to abstain from overtask-
ing himself; so that he feels assured that those who have kindly
waited for the appearance of this volume, will not, when ac-
quainted with these circumstances, blame him for a delay, the
causes of which have lain so completely beyond his control.

University Haut, Lonpon,
Feb. 9, 1856.

TABLE OF CONTENTS.

INTRODUCTION.

History of the Microscope and Microscopic Research,

; CHAPTER I.
Optical Principles of the Microscope,

CHAPTER II.

CONSTRUCTION OF THE MICROSCOPE.

General Principles, . 5 . . .
Simple Microscopes, ‘ ‘ .
Ross's, 5
Gairdner’s, . : ‘ ‘ ‘ .
Field’s,
Quekett’s,
Compound Microscopes,
Field’s,
Highley’s,
Nachet’s, . 3 .
. Smith and Beck’s Student’s,
Do. Dissecting,
Warington’s Universal, . : 5 .
Ross’s, 5 ‘

Powell and Lealand’s
Smith and Beck’s,
Nachet’s Binocular,

CHAPTER III.
ACCESSORY APPARATUS.

Draw-Tube,

Erector,

Micrometer,

Goniometer, . : i :
Indicator,

Camera Lucida,

Object-Glass Holder, .

PAGE

33

65

xii CONTENTS.

Object-Marker,

Lever Stage, . ; : : : :
Object-Finder,

Magnetic Stage,
Diaphragm-Plate,

Achromatic Condenser,
Reflecting Prisms, .
White-Cloud Iuminator,
Oblique Illuminators,
Black-Ground Illuminators,
Polarizing Apparatus,
Tuminators for Opaque Orjects,

Stage-Forceps, .

Glass Stage-Plate, . ‘

Aquatic Box, . : 5 ‘ . . E

Zoophyte Trough,

Compressorium,

Dipping-Tubes,

Forceps, . . . ‘ ‘ .
CHAPTER IV.

MANAGEMENT OF THE MICROSCOPE.
Support, : ‘ : . : 5
Light, . . ‘ ‘i

Position of die:

Care of the Eyes, .

Care of the Microscope,

General Arrangements, :

Arrangement for Transparent Objects,

Arrangement for Opaque Objects,

Errors of Interpretation,

Comparative Values of Object- GTassees Test- Objects,
Determination of Magnifying Power, : .

CHAPTER V.

PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS.

‘Microscopic Dissection,

Cutting Sections of Soft Sulistanees,,

Cutting Sections of Harder Substances,
Grinding and Polishing of ee
Chemical Actions,

Glass Slides,

Thin Glass,

Varnishes and Cements, .

Mousting Objects Dry, ‘
Mounting Objects in Canada Balsam, . ‘i
Preservative Fluids, . : ,
Mounting Objects in Fluid,

Cement-Cells,

Thin-Glass Cells,

PAGE
127
128
129
130
131
131
133
134
135
138
140
143
146
147
148
149
150
152
153

154
154
157
158
159
160
168
175
180
192
199

201
204
205
207
211
214
214
217
221
224
232
234
235
236

CONTENTS.
Plate-Glass and Shallow Cells, ‘ i : ‘ :
Deep and Built-up Cells, . . F . * ‘ .
Mounting Objects in Cells, . . . . . .
Importance of Cleanliness, . . : . . .
Labelling and Preserving of Objects, : . 7 ;
Collection of Objects, . ; : . . : ;

CHAPTER VI.
MICROSCOPIC FORMS OF VEGETABLE LIFE.—PROTOPHYTES,

Boundary between Animal and Vegetable a al

Characters of Vegetable Cell, . : . .

Life-History of Simplest Protophytes

Volvocines, Fi . : d :

Desmidiacez, . . : > ‘i

Diatomacez,

Palmellacez, . . : : . . .

Ulvacese, . A ‘ F é : : : .
Oscillatoriacez, é : : . 7

Siphonacez, : c : . .

Confervacee,

Conjugatez, : - . : . .
Chatophoracee,

Batrachospermez, : . z : . : .
Characez,

CHAPTER VII.
MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

Alge, ‘ : : 7 : .
Lichens, .

Fungi,

Hepatic,

Mosses, : . ‘ . : .

Ferns, . : : 7

Equisetacee, . : ‘ : ‘i . i:

CHAPTER VIII.
MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS.

Elementary Tissues, .

Structure of Stem and Root,

Structure of Cuticle and Leaves,

Structure of Flowers, . A 5 ‘

CHAPTER IX.

MICROSCOPIC FORMS OF ANIMAL LIFE:—-PROTOZOA}; ANIMALCULES.

Protozoa, , . .

Rhizopoda, i : ‘

Infusoria, : : s ‘i . .
Rotifera, . 5 fi . 3 Fi : ‘ .

xiv CONTENTS.

CHAPTER X.
FORAMINIFERA, POLYCYSTINA, AND SPONGES.
Foraminifera,
Polycystina,
Sponges,
CHAPTER XI.
ZOOPHYTES.
Hydra,
Hydrozoa,
Acalepha,
Anthozoa,

CHAPTER XII.
ECHINODERMATA.

Structure of Shell and Spines,
Echinoderm Larve,

CHAPTER XIII.
POLYZOA AND COMPOUND TUNICATA.
Polyzoa, .
Compound Tunicata,
CHAPTER XIV.
MOLLUSCOUS ANIMALS GENERALLY.

Shells of Mollusca,

Tongues of Gasteropods, .
Development of Gasteropods,
Ciliary motion on Gills,

Organs of Sense of Mollusks,
Chromatophores of Cephalopods,

CHAPTER XV.
ANNULOSA OR WORMS.
Entozoa,
Turbellaria,
Annelida,
CHAPTER XVI.
CRUSTACEA.
Pycnogonide,
Entomostraca,
Suctoria,
Cirrhipeda,

Shell of Decapoda,
Metamorphosis of Decapoda,

PAGE
436
449
452

457
461
467
472

ATT
486

492
500

506
517
521
526
527
528

527
533
535

539
541
547
548
550
551

CONTENTS.

CHAPTER XVII.

INSECTS AND ARACHNIDA.

Great number and variety of Objects afforded by Insects,
Structure of Integument, . ‘ ‘ ‘
Tegumentary Appendages,

Parts of the Head, a

Circulation of the Blood,

Respiratory a al

Wings,

Feet,

Stings and Oripositore,

Eggs, :

Acarida, :

Parts of Spiders, . .

CHAPTER XVIII.
VERTEBRATED ANIMALS.

Primary Tissues,

Bone,

Teeth, . 2 . .

Scales of Fish, = . .

Hairs, . . :

Feathers, . . . .
Hoofs, Horns, &c., £ : ‘i F
Blood, : : :
White and Yellow Fibres, :

Skin, Mucous, and Serous Membranes,
Epidermis, . . :
Pigment-Cells, : ‘ .
Epithelium,
Fat, .
Cartilage, A 3 2 .
Glands, 3 . . . . .
Muscle, :
Nerve,

Circulation of the Blood,

Injected Preparations,

Vessels of Respiratory Organs,

CHAPTER XIX.

APPLICATIONS OF THE MICROSCOPE TO GEOLOGY.

Fossilized Wood, Coal,
Fossil Foraminifera, Chalk,
Nummulites,
Orbitoides, j
Organic materials of Rocks, ‘
Structure of Fossil Bones, Teeth, &c.,

XV

PAGE
554
555
556
561
569
570
574
576
578
579
581
583

584
584
588
591
594
597
598
598
602
604
605
605
606
607
608
609
611
614
616
619
624

625
631
634
637
639
641

Xvi CONTENTS.

CHAPTER XX.

INORGANIC OR MINERAL KINGDOM.—POLARIZATION.

PAGE

Mineral objects, ‘ : . : : ‘ F . 644

Crystallization of Salis, . : ; : ; P : 645

Objects suitable for Polariscope, . : F ‘ j . 645
APPENDIX.

Microscope as a means of Diagnosis, : . : - 650

Examination of the Nervous System, . Z . : : 653

Muscular System, 2 : ‘ . » 655

Respiratory System, : : . ‘ 657

Morbid Lung, : . ‘ F . 658

Examination of the @lacdatar System, ‘ 4 ‘ ‘ : 662

Liver, : . : : : 3 : . - 662

Kidney, . ‘ é : i F : : : 663

Morbid Kidney, : . : . : . . - 664

Salivary Glands, . ‘ : ; . . . 664

Thymus and Thyroid Glands : , 5 a . . 664

Adipose Tissue, . . : . : : : 664

Fatty Degeneration, . Q 5 : . 665

Examination of Vaséular ae Mose sates : : , 666

Skin, Mucous and Serous Membrane, : j . 667

The Eye, : : : : 671

The Hard eeiee ‘ 7 7 : . - 672

Morbid Growths, F i ‘ : 2 674

Animal Fluids, . 4 F : . - 681

Serous and Dropsical Fluids, - : . : . . 699

Injections, . : ; . : - 700

Microscopes a ineneal Nianpbiekirs: ; : : : , 704

OOIMONRYEN

LIST OF ILLUSTRATIONS,

. Refraction of Parallel Rays by Plano-convex Lens,
Ditto by Double-convex Lens,
. Refraction of Converging Rays,

. Refraction of Diverging Rays,

. Formation of Images by Convex Lenses,
- Spherical Aberration, .

. Chromatic Aberration,

. Section of the Achromatic Object. glass,
. Effect of Covering-glass,

- Action of Simple Microscope,

. Simplest form of Compound Microscope,
- Complete Compound Microscope,

. Huyghenian Eye-piece, . :

. Ross’s Simple Microscope,

. Gairdner’s Simple Microscope, .

. Field’s Simple Microscope, .

- Quekett’s Dissecting Microscope,

. Field’s Compound Microscope,

. Highley’s Hospital Microscope,

. Nachet’s Compound Microscope,

. Smith and Beck’s Student’s Microscope,

Ditto Dissecting Microscope,

. Warington’s Universal Microscope,

Ditto Ditto, .
Ditto Ditto,
Ditto Ditto,

- Ross’s Large Compound Microscope, .
. Powell and Lealand’s Ditto, .

. Smith and Beck's Ditto,

. Arrangement of Binocular Prisms, .
- Nachet’s Binocular Microscope, .

. Draw-tube with Erector,

3. Jackson’s Hye-piece Micrometer,

. Microscope arranged for Drawing, .
35. Ross’s Achromatic Condenser, .

. Smith and Beck’s Ditto,

- Powell and Lealand’s Ditto, .

. White-Cloud ee

. Amici’s Prism,

. Parabolic Illuminator,

. Fitting of Polarizing Prism,

. Fitting of Analyzing Prism,

43. Selenite Object-Carrier, .
44, Bull’s-Kye Condennen .
45. Ordinary Condensing Lens,
46. Side Reflector, 7 .

XV LIST OF ILLUSTRATIONS.

47.
48.
49.
50.
51.
52.
53.
54,
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
. Built-up Cells,

. Palmoglea macrococca, after Braun,

. Protococcus pluvialis, after Cohn,

. Volvox globator, after Ehrenberg,

. Development of Volvox, after Williamson, .

. Various species of Staurastrum, after Ralfs,

. Closterium lunula, after 8S. G. Osborne,

. Development of Pediastrum granulatum, after Braun,
. Various forms of Pediastrum, after Ralfs, . f

. Conjugation of Cosmarium botrytis, after Ralfs,

Stage-Forceps, : ‘ - .

Aquatic Box, : F : . : é

Zoophyte-Trough,

Compressorium, ;

Dipping-Tubes, . .

Forceps, . ‘

Section of Adjusting Object- Glass,

Arrangement of Microscope for Transparent Objects,
Ditto Ditto Opaque Objects,

Spring Scissors, : : :

Curved Scissors, 4 ‘ ‘

Valentin’s Knife,

Section-Instrument, : : . .

Lever of Contact,

Slider-Forceps,

Spring-Press,

Turn-Table, :

Plate-glass Cells, ‘ . ‘i :

Tube-Cells, . F a ‘ . .

Ditto of Closterium, after Ralfs,

. Didymoprium Grevillii, after Ralfs,

. Portion of Isthmia nervosa, after Smith,

. Triceratium favus, after Smith, ‘

. Pleurosigma angulatum, after Wenham,

. Biddulphia pulchella, after Smith,

. Conjugation of Epithemia, after Thwaites, .

3. Conjugation of Au/acosetra, after Thwaites,

. Actinocyclus undulatus, after Smith,

. Heliopelta, :

. Arachnoidiscus Ehrenbergii, after Smith,

. Campylodiscus costatus, after Smith,

. Surirella constricta, after Smith,

. Gomphonema geminatum, after Smith, .
Ditto, more highly magnified, after ‘Smith,
. Liemophora flabellata, after Smith, ‘

. Meridion circulare and Bacilluria ‘paradoxa, after Smith,
. Achnanthes longipes, after Smith,

. Diatoma vulgare, after Smith, .

. Grammatophora serpentina, after Smith, ;

. Isthmia nervosa, after Smith,

. Meloseira subflexilis, after Smith,

. Meloseira varians, after Smith,

. Mastogloia Smithit, after Smith,

. Mastogloia lanceolata, after Smith,

. Fossil Diatomacee from Oran, after Ehrenberg,

2. Fossil Diatomacee from Mourne Mountain, after r Bhrenberg,
3. Hematococcus sanguineus, after Hassal, ;
. Development of Ulva, after Kiitzing,

. Zoospores of Ulva, after Thuret,

. Zoospores of Achlya, after Unger, :

. Cell-multiplication of Conferva, after Mohl,

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286
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318

108.

109.
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lil.
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116.
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118,
119,
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12).
122.
123.
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155.
156,
157.
158.
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160.
161,

162.
163.
164.
165.
166,
167.
168.

LIST OF ILLUSTRATIONS,

Zygnema quininum, after Kiitzing, : . .
Cheetophora elegans, after Thuret,
Batrachospermum moniliforme, .

Nitella flexilis, after Slack, . :

Antheridia of Chara, after Thuret,

Mesogloia vermicularis, after Payer,

Sphacelaria cirrhosa,

Receptacle of Fucus, after Thuret,

Antheridia and antherozoids of Fucus, after Thuret,
Tetraspores of Carpocaulon, after Kiitzing,
Torula Cerevisic, after Mandl, 3
Sarcina ventricult, after Robin,

Botrytis bassiana, after Robin,

Enterobryus spiralis, after Leidy,

Structure of Hnterobryus, after Leidy,

Fungoid Vegetation, from Passulus, after Leidy,
Stysanus caput-meduse, after Payer

Puccinia graminis, .

Heidium tussilaginis, after Payer,

Clavaria crispula, after Payer, :
Fructification of Marchantia, after Payer,
Stomata of Marchantia, after Mirbel,
Conceptacles of Marchantia, after Mirbel,
Archegonia of Marchantia, after Payer,

Elater and spores of Marchantia, after Payes
Portion of Leaf of Sphagnum,

Structure of Mosses, after Jussieu,

Antheridia and antherozoids of Polytrichum, after Thuret, .

Mouth of Capsule of Funaria,
Peristome of Fontinalis, after Payer,
Ditto of Bryum, | ditto,

Ditto of Cinclidium, ditto,
Petiole of Fern, .
Sori of Polypodium, after Payer,
Ditto of Hemionitis, ditto,
Sorus and Indusium of Aspidium, .

Ditto of Deparia, after Payer, .
Development of Prothallium of Pteris, after Suminski,
Antheridia and antherozoids of Preris, after Suminski,
Archegonium of Pteris, after Suminski,

Spores of Hquisetum, after Payer,

Section of leaf of Agave, after Hartig,

Section of Aralia (rice-paper),

Stellate Parenchyma of Rush,

Cubical parenchyma of Nuphar,

Circulation in hairs of Tradescantia, after Slack,
Testa of Star-Anise, ‘
Section of Cherry-stone,

Section of Coquilla-nut, .

Spiral cells of Oncidium,

Spiral fibres of Collomia,

Cells of Paony, filled with starch,

Starch-grains, under polarized light,

Glandular fibres of Coniferous Wood, :
Vascular tissue of Italian Reed, after Schleiden,
Transverse Section of stem of Palm,

Ditto of Wanghie Cane,
Ditto of Clematis,
Ditto of Cedar,

Ditto of Buckthorn,

Ditto Ditto more highly magnified,

xix

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820
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B51
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xX

169.
170.
tri.
172.
173.
174,
175.
176.
*177.
178.
179.
180.
181.
182.
183.
184,
185.
186.
187.
188.
189.
190.
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192.
193.
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195.
196.
197.
198.
199,
200.
201.
202.
203.
204.
205.
206.
207.
208.
209.
210.
#11,
212.
213.
214.
215.
216.
21%,
218.
219.
220.
221,
292.
223.
224,
225.
226.
20%.
228.
229,

LIST OF ILLUSTRATIONS.
Transverse Section of Hazel, i
Ditto of Fossil Conifer,
Vertical section of Fossil Conifer, radial,
Ditto Ditto, tangential,
Ditto of Mahogany, é
Transverse Section of Fossil-wood, .

Vertical Section of Ditto, i 7
Transverse Section of Fossil-wood, .

Vertical Section Ditto, ‘
Transverse Section of Aristolochia, (?)

Ditto of eyeeh
Cuticle of Yucca,
Ditto of Indian Cor ny
Ditto of Apple, after Brongniart, .
Ditto of Rochea,
Vertical Section of leaf of Rochea, after ‘Bronguiart,

Cuticle of Lrés, Ditto,
Vertical Section of leaf of Tris, Ditto,
Longitudinal Section of ditto, Ditto,
Cuticle of Petal of Geranium, ;

Pollen-grains of Althea, &c.,

Seeds of Poppy, &e.,

Amaba princeps, after Ehrenberg,

Actinophrys sol, after Clarapéde,

Various forms of Rhizopods, after Ebrenber .
Kerona silurus, after Milne-Edwards,
Paramecium caudatum, Ditto, .

Group of Vorticella, after Ehrenberg,

Fissiparous Multiplication of Chilodon, after Ehrenberg,

Metamorphoses of Vorticella, after Stein,

Ditto of Trichoda, after Haime,
Brachionus pala, after Milne-Edwards,
Rotifer vulgaris, after Ehrenberg, :
Stephanoceros Eichornii, Ditto, ? 7 ,
Noteus quadricornis, Ditto, .
Gromia oviformis, after Schulze,
Rosalina ornata, after Schulze,
Orbitolites complanatus,
Animal of simple type of ditto,
Animal of complex type of ditto,
Section of Faujusina, after Williamson,
Podocyrtis Schomburgkii, after Ehrenberg,
Rhopalocanium ornatum, Ditto,
Haliomma Humboldtii, Ditto, .
Perichlamydium preetextumn, Ditto,

Polycystina from Barbadoes, Ditto, : ge te
Stylodictya gracilis, Ditto,
Astromma Aristotelis, Ditto,

Structure of Grantia, after Dobie,
Portion of Hulichondri ia,
Siliceous spicules of Pachymatisma,
Hydra fusca, after Milne-Edwards,

Ditto in gemmation, after Trembley,
Medusa-buds of Syncoryna, after Sars,
Campanularia gelatinosa, after Van Beneden,

Sertularia cupressina, after Johnston,
Thaumantias pilosella, after E. Forbes, ‘
Development of Medusa-buds, after Dalyell.
Development of Meduse, Ditto, . -

Cydippe and Beroe, after Milne-Edwards,
Noctilucu miliaris, after Quatrefages,

230.
231.
232.
233.
234,
235.
236.
237.
238.
239.
240.
241.
242,
243.
244,
245.
246.
247,
248.
249.
250.
251.
252.
253.
254,
255.
256.
257.
258.
259.
260.
261.
262.
263.
264.
265.
266.
267.
268.
269.
270.
271.
272.
273.
274.
275.
276.
277,
278.
279.
280.
281.
282.
283.
284,
285.
286.
287.
288.
289.
290.

LIST OF ILLUSTRATIONS.

Spicules of Alcyonium and Gorgonia, .

Ditto of Gorgonia guttata,
Spicules of Muricea elongata, .
Filiferous capsules of Actinia, &c., after Gosse,
Section of Shell of Hchinus,
Calcareous reticulation of Spine of Echinus,
Ambulacral disk of Echinus,
Transverse Section of Spine ‘of Acrocladia, .
Spines of Spatangus, . :
Calcareous skeleton of Astrophyton,

Ditto of Holothuria,
Ditto of Synapia,
Ditto ‘of Chirodota,

Bipinnarian larva of Starfish, after Muller, .
Pluteus-larva of Echinus, after Miller, .

Cells of Lepralie, after Johnston,

Laguncula repens, after Van Beneden, .

Bird’s-head processes of Cellularia and Bugula, after Johnston and Busk,

Amaroucium proliferum, after Milne- Edwards,
Botryllus violaceus, Ditto
Perophora, after Lister, .

Transverse Section of Pinna,

Membranous basis of Ditto

Vertical Section of Ditto 2
Oblique Section of Ditto i 4 .
Section of hinge-tooth of Mya,

Nacre of Avicula,

Tubular shell- structure of Anomia, .

Vertical Section of shell of Unio,

Internal surface of shell of Terebratula,

External Ditto Ditto

Vertical Sections of Ditto . :

Horizontal Section of shell of Zerebratula bullata,
Ditto Ditto of Megerlia lima, ‘
Ditto Ditto of Spiriferina rostrata,

Palate of Helix hortensis, . : é

Ditto of Zonites cellarius,

Ditto of Trochus zizyphinus,

Ditto of Doris tuberculata,

Ditto of Buccinwm, under polarized light, .
Embryoes of Nudibranchs, after Alder and Hancock,
Embryonic development of Purpura,

Latter stages of the same,

Structure of Polycelis, after Quatrefages,
Circulation of Terebella, after Milne-Edwards, .
Ammothea pycnogonoides, after Quatrefages,
Cyclops quadricornis, after Baird, .
Development of Balanus, after Bate,
Metamorphoses of Carcinus, after Couch,

Scale of Morpho Menelaus, .

Battledoor scale of Polyommatus argus, after r Quekett ‘

Scales of Podura plumbea, . .

Hairs of Myriapod and Dermestes, .

Head and eyes of Bee,

Section of Kye of Melolontha, after Strauss- -Durekbeim,
Antenna of Cockchafer,

Portions of _ ditto more highly magnified

Tongue of Fly, F

Tongue, &c., of Honey Bee,

Proboscis of Vanessa,

Tracheal system of Nepa, after Milne- Edwards,

Xxi

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472
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475
478
478
478
479
481
482
485
486
486
487
489
492
493
498
501
502
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507
507
507
508
509
510
512
512
513
513
514
514
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518
519
519
521
522
523
525
534
535
540
543
549
551
557
557
558
560
561
562
565
565
566
567
568
571

Xxil LIST OF ILLUSTRATIONS.

PAGE
291. Trachew of Dytiscus, . r A . . . 571
292. Spiracle of Fly, . . : : : - 572
293. Spiracle of Larva of Cockchaffer, ; 2 ‘ . 5 572
294. Foot of Fly, after Hepworth, . . : . . SIT
295. Foot of Dytiscus, . : . . . : 517
296. Eggs of Insects, after Burmeister, : . . : - 580
297. Foot, with combs, of Spider, ; : . . 583
298. Ordinary and glutinous threads of Spider, : i: . - 583
299, Minute Structure of Bone, after Wilson, . 6 < ‘ 585
300. Lacune of Ditto, highly magnified, after Mand], : : - 586
301. Section of Bony scale of Lepidosteus, ‘ . : . 587
302. Vertical Section of Tooth of Lamna, after Owen, , ; - 588
303. Trausverse Ditto of Pristis, ditto, i . : 588
304. Ditto Ditto of Myliobates, F e . 589
305. Vertical Section of Human Tooth, after Mandl, | . : . 590
306. Portion of Skin of Sole, . é . . : . 592
307. Scale of Sole, : ‘ - 2 , j . 592
308. Hair of Musk-Deer, ‘ : i : ‘ ‘ - 595
309. Hair of Sable, . ‘ A . F ‘ 595
310. Hairs of Squirrel and Indian Bat, E : F : - 695
311. Transverse section of Hair of Pecari, 3 . . ‘ 595
312. Structure of Human Huir, after Wilson, 3 ‘ . » 596
313. Transverse section of Horn of Rhinoceros, . 2 : a 598
314. Blood-corpuscles of Frog, after Donne, . 3 ‘ ‘ . 599
315. Ditto of Man, Ditto, : . : 599
316. Fibrous Membrane of Egg-shell, ; A : . - 603
317. White Fibrous Tissue, : ‘ é : 3 1 603
318. Yellow Fibrous Tissue, . : . : . - 603
319. Pigment-cells of Choroid, after Henle, ‘i zi ‘ . 605
320. Pigment- cells of Tadpole, after Schwann, F j . . 606
321. Ciliated Epithelium, after Mandl, . : : : : 607
322. Areolar and Adipose Tissue, after Mandl, i: : i - 608
323. Cartilage of Ear of Mouse, . . : ‘ ‘ 609
324. Cartilage of Tadpole, after Schwann, . : 7 : - 609
325. Striated Muscular F Fibre, . 5 7 . a e 612
326. Ultimate fibrille of Ditto, s . 612
327. Capillary Circulation in Web of Frog og's foot, after Wagner ‘ 618
328. Intestinal villi of Monkey, : ‘ - 622
329. Various forms of Capillary network, after Berres, . : . 623
330. Portion of Gill of Hel, . ‘ ’ ; . 624
331. Interior of Lung of Frog, . z . : F ‘ 624
332. Section of Lung of Fowl, . : F : : . 625
333. Section of Human Lung, ‘ P 3 626
334. Microscopic organisms in Levant Mud, after Williamson, . 630
335. Ditto in Chalk from Gravesend, after Ehrenberg, 631
336. Ditto Ditto from Meudon, Ditto . . 632
337. Vertical section of Nimmutite, i ‘ Z Fi 635
338. Portion of Ditto, more highly magnified, ‘ - : . 636
339. Horizontal section of Ditto, . : . 637
340. Section of Orbitoides Prati parallel to its surface, ‘ : . 637
341. Portions of Ditto, more highly magnified, . - < : 638
342. Vertical section of Ditto, 3 $ 3 a . 638
343. Hye of Trilobite, after Buckland, é . é : 640
344. Section of Tooth of Labyr inthodon, after Owen, : ? . 641
345. Crystallized Silver, . : : 645
346. Oily Matter in Fibres of Brain (Todd and Bowman), ‘ ‘ . 653
347. Corpora Amylacea of Pineal Gland (Sieveking and Jones), A 654
348. Fatty Degeneration of Nerve-Fibre, : 3 ‘ 3 . 6-4
349. Striated Muscular Fibre, . ‘ : ‘ ' 654
350, Elongated Muscle-Cells nae Striated) i ; F . 656

351. Sarcolemma, j . . . : 656

352.

353.
354,
355.
356.
357.
358.
359.
360.
361.
362.
363.
364.
365.
366.
367.
368.
369,
370.
371.
372,
373.
374,
375.
376.

377. \
378.
379.
380.
381.
382.
383.
384,
385.
386. \
387,
388.
389.
390.
391.
392.
393,
394,
395.
396.
397.
398.
399.
400.
401.
402.
403,
404,
405,
406.
407.
408,
409,
410,
411,
412.

LIST OF ILLUSTRATIONS.

Structure of Lung, . : . .
Capillaries of Lung, . . . .
Tubercle Corpuscles, . . : ‘
Yellow Tubercle (Bennett),

Scrofulous Pus (Bennett), . F é .

Section of Gray Granulations,
Cretaceous and Cheesy Variety of Tubercle (Bennett),
Pigmentary Matter mixed with Tubercle (Bennett),

Structure of Tubercular Mass from Cerebellum,

Tubercle Corpuscle from Lung,
Plastic or Pyoid Corpuscle, :
Granular Corpuscle from Cerebral Swelling,
Corpuscles from Reticulum of Cancer,
Lung in first Stage of Pneumonia (Da Costa),

Ditto 2d Ditto Ditto

Ditto Ditto Ditto

Ditto 3d Ditto Ditto . .
Transverse Section of Lobule of Human Liver (Leidy),
Hepatic Cells (Leidy), . 4 : ;
Urine from tube and Epithelial Cell,
Adipose Tissue,
Fatty Degeneration of Vessels of Brain,

Atheromatous Deposits in Vessels, . .

Fibre-Cells passing into Fibres,
Fibrous Tissue formed from Fibre-Cell, .
Altered Epithelial Cells from Ulcer of Lip,
Epithelial and Fibre-Cells from same, :
Pus Corpuscles, _.. . i

Ditto after Acetic Acid,
Free Cancer Nuclei, .

Polygonal Cancer-Cells eiscaatiteoss

Caudate Cancer-Cells (Donaldson),
Fusiform Cells, . - ‘

Concentric Cancer-Cells,

Compound, a Mother Cell, .

Agglomerated Nuclei (Donaldson),

Corpuscles of Blood,

Same after exposure to Air, .

Colorless Corpuscles,

Blood in Leucocythemia,

Caudate Blood-Corpuscles,

Milk and Colostrum-Granules,

Healthy Milk-Globules, .

Salivary Corpuscles, Epithelial Scales and Granules,
Tubercle-Corpuscles (Bennett), ‘
Sputum of Calcareous Matter,

Sputum in Acute Pneumonia, .

Pus-Globules,

Scrofulous Pus, .

Mucous Corpuscles and Epithelium i in Urine,
Secreting Canal and Epithelium from Kidney, .
Mucus, Pus, Blood, and,Epithelium in Leucorrhea,
Fibrinous Casts from Tubuli Uriniferi, .

Ditto —_ Ditto Ditto in : Brights Disease
Tube containing a Homogeneous Cast, ;
Spermatozoa, .

Torula from Urine of Diabetes, .

XXIV LIST OF ILLUSTRATIONS.

413.
Al4,
415.
Al6.
417.
418.
419,
420.
421.
422.
423,
424.
425.
426.
427,
428,
429,
430.
431.
432.
433.
434.

Oil-Globules from Urine,

Lithic Acid Crystals,

Various forms of Lithates,

Crystal of Cystine,

Oxalate of Lime,

Same (various forms),

Dumb-Bell Crystals,

Urate of Ammonia,

Triple Phosphate,

Stellar form of Triple Phosphate,

Starch Corpuscles after Partial Digestion, .

Microscopic Appearance of Cancerous Juice from Urine,

Fibres and Corpuscles from Ovarian Fluid,.

Spencer’s Trunnion Microscope,

Queen’s Student's Microscope,

Grunow’s Student’s Microscope, :
Ditto Ditto smaller size,
Ditto first-class Microscope, .

Diagram of Smith’s Inverted Microscope,

Dr. J. L. Smith’s Inverted Microscope, .

} Dr. J. L. Smith’s Goniometer and Micrometer,

THE MICROSCOPE.

INTRODUCTION.

No one who attentively examines the progress of any depart-
ment of Science, save such as are (like Mathematics or Meta-
physics) of a purely abstract character, can fail to perceive how
much it is dependent upon the perfection of its instruments.
There are few instances, in fact, in which the invention of a new
instrument, or the improvement of an old one, has not given a
fresh stimulus to investigation ; even where it has done no more
than afford that degree of precision to the results of inquiries
already in progress, which alone could enable them to be made
available as data for philosophical reasoning. But there are
many cases in which such inventions or improvements have
opened out entirely new paths of scientific research, leading to
fertile fields of investigation whose very existence had been pre-
viously unknown, to rich.mines of discovery whose treasures had
lain uncared for because entirely unsuspected. A few examples
of this general truth may not be inappropriate, by way of pre-
face to the brief notice which it is intended to give in the present
Introduction, of the most important epochs in the history, as
well of the Microscope itself, as of its application to the purposes
of scientific research.

Thus in taking a retrospective survey of the history of Astro-
nomy, we find that every great advance in our knowledge of the
Celestial Universe, has been preceded by improvements, either
in those instruments for measuring space and time, by which the
places of the Heavenly Bodies are determined, the rate of their
movements estimated, and a basis for the computation of their
distances ascertained; or, again, in the telescope, by which our
power of sight is so wonderfully augmented, that we are enabled,
when gazing through it into the unfathomable depths of space,
to take cognizance of world beyond world and system beyond
system, whose remoteness cannot be expressed by any form of
words that shall convey a distinct idea to the mind, and to bring
the members of our own group within such visual proximity to

3

34 INTRODUCTION,

ourselves, that we can scrutinize their appearance nearly as well]
as if they had actually been brought a thousand times nearer to
us. For it was the increased precision of celestial observations
on the places and movements of the Planets, which furnished the
data whereon Kepler was enabled to base his statement of the
laws of their motion. It was the application of the pendulum to
the measurement of short intervals of time, that enabled Galileo
to ascertain the law of Falling Bodies. And it was not until the
precise measurement of a degree upon the surface of the Earth
had furnished the means of determining both its own diameter
and its distance from the Moon, that Newton was enabled to
verify and establish his grand conception, of the identity of that
force which deflects the planets from a rectilineal course into
elliptical orbits, with that which draws a stone to the ground;
and thus to establish that Law of Universal Gravitation, which
still remains the most comprehensive, as well as the most simple,
of all the generalizations, within which the intellect of man has
been able to comprehend the phenomena of Nature. So, again,
it was only when the elder Herschel had developed new powers
in the telescope, that Sidereal Astronomy could be pursued with
any view much higher than that of mapping the distribution of
the stars in the celestial sphere; and the present state of our
knowledge of double, triple, and other combinations of stars,
with their mutually adjusted movements, of the multiform clus-
ters of luminous points which seem like repetitions of our own
firmament in remote depths of space, and of those nebulous films
which may be conceived to be new worlds and systems in pro-
cess of formation, has only been rendered attainable by the im-
provements which have been subsequently made in the construe-
tion of that majestic instrument.

If we glance at the mode in which the fabric of our existing
Chemistry has been upreared, we at once see that it could not
have attained its present elevation and stability, but for the in-
strumentality of the perfected balance; by whose unerring indi-
cations it was that the first decisive blow was given to the old
“phlogistic” theory, that the foundation was laid for true ideas of
chemical combination, that the Laws of that Combination were
determined, and that the Combining Equivalents of different
elementary substances were ascertained; and by whose means
alone can any of those analytical researches be prosecuted, which
are not only daily adding to our knowledge of the composition
of the bodies which surround us, and suggesting the most im-
portant applications of that knowledge to almost every depart-
ment of the Arts of Life, but which are preparing a broad and
secure foundation for a loftier and more comprehensive system
of Chemical Philosophy.

So, again, the balance of torsion, the ingenious invention of
Cavendish and Coulomb, enables the Physical philosopher not
merely to render sensible, but to subject to precise measurement

VALUE OF INSTRUMENTS OF RESEARCH. 35

and subdivision, degrees of force that are far too fecble to affect
the nicest balance of the ordinary construction, even if it were
possible to bring them to act upon it; and strange as it may
seem, it has been in such a balance that the Earth itself has been
weighed, and that a basis has been thus afforded for the compu-
tation of the weights of the different Planets and even of the
Sun; whilst in the opposite direction it is employed to furnish
those data in regard to the intensity of the electric and magnetic
forces, on which alone can any valid theory of their operation be
constructed.

The galvanometer, again, in which the minutest Electric dis-
turbances are rendered sensible by the deflection of the magnetic
needle, has not only brought to light a vast class of most inte-
resting electric changes which were previously unsuspected (one
of the most remarkable of these being the existence of electric
currents in the nerves of living animals, first ascertained by M.
du Bois-Reymond), but has enabled those changes to be esti-
mated with a marvellous amount of exactness; thus furnishing
to observations made by its means, a precision which is quite
unattainable in any other mode, and which is absolutely essential
to the establishment of any valid theory of electric action. And
this same instrument is scarcely less valuable, as serving, by a
particular modification of it, for the detection and estimation of
changes of Temperature far too minute to be measured by the
ordinary thermometer; thus affording the requisite means of ex-
actness to observation, in a department of science to which at
first sight it appeared to have no relation.

‘What an important influence,” says Sir John Herschel, “may
be exercised over the progress of a single branch of science, by
the invention of a ready and convenient mode of executing a
definite measurement, and the construction and common intro-
duction of an instrument adapted for it, cannot be better exem-
plified than by the instance of the reflecting goniometer ; this
simple, cheap, and portable little instrument has changed the
whole face of Mineralogy, and given it all the characters of one
of the exact sciences.”

Of all the instruments which have been yet applied to scien-
tific research, there is perhaps not one which has undergone such
important improvements within so brief a space of time, as the
Microscope has received during the second quarter of the present
century; and there is certainly none whose use under its im-
proved form has been more largely or more rapidly productive of
most valuable results. As an optical instrument, the Microscope
is now at least as perfect as the Telescope; for the 6-feet para-
bolic speculum of Lord Rosse’s gigantic instrument, is not more
completely adapted to the Astronomical survey of the heavenly
bodies, than the achromatic combination of lenses so minute that
they can scarcely be themselves discerned by the unaided eye, is
to the scrutiny of the Physiologist into the mysteries of life

36 INTRODUCTION.

and organization. Nor are the revelations of the one less sur-
prising to those who find their greatest charm in novelty, or less
interesting to those who apply themselves to the study of their
scientific bearings, than are those of the other. The universe
which the Microscope brings under our ken, seems as unbounded
in its limit as that whose remotest depths the Telescope still
vainly attempts to fathom. Wonders as great are disclosed in a
speck of whose minuteness the mind can scarcely form any dis-
tinct conception, as in the most mysterious of those nebule whose
incalculable distance baffles our hopes of attaining a more inti-
mate knowledge of their constitution. And the general doctrines
to which the labors of Microscopists are manifestly tending, in
regard to the laws of Organization and the nature of Vital Action,
seem fully deserving to take rank in comprehensiveness and im-
portance with the highest principles yet attained in Physical or
Chemical Science.

As the primary object of this treatise is to promote the use of
the Microscope, by explaining its construction, by instructing
the learner in the best methods of employing it, and by pointing
out the principal directions in which these may be turned to
good account, any detailed review of its A¢story would be mis-
placed. It will suffice to state, that whilst the s¢mple microscope
or magnifying-glass was known at a very remote period, the
compound microscope,—the powers of which, like those of the
telescope, depend upon the combination of two or more lenses,—
was not invented until about the end of the sixteenth century ;
the earlier microscopes having been little else than modified tele-
scopes, and the essential distinction between the two not having
been at first appreciated. Still, even in the very imperfect form
which the instrument originally possessed, the attention of scien-
tific men was early attracted to the Microscope; for it opened to
them a field of research altogether new, and promised to add
largely to their information concerning the structure of every
kind of organized body. The Transactions of the Royal Society
contain the most striking evidence of the interest taken in mi-
croscopic investigations two centuries ago. Their early volumes,
as Mr. Quekett truly remarks, “literally teem” with improve-
ments in the construction of the Microscope, and with discoveries
made by its means. The Micrographia of Robert Hooke, pub-
lished in 1667, was, for its time, a most wonderful production ;
but this was soon surpassed by the researches of Leeuwenhoek,
whose name first appears in the Philosophical Transactions, in
the year 1678. That with such imperfect instruments at his
command, this accurate and pains-taking observer should have
seen se much and so well, as to make it dangerous for any one
even now to announce a discovery, without having first con-
sulted his works, in order to see whether some anticipation of it
may not be found there, must ever remain a marvel to the micro-
scopist. This is partly to be explained by the fact, that he

EARLY REVELATIONS OF THE MICROSCOPE. 37

trusted less to the compound microscope, than to single lenses
of high power, the use of which is attended with difficulty, but
which are comparatively free from the errors inseparable from
the first-named instrument in its original form. The names of
Grew and Malpighi, also, appear as frequent contributors to the
early volumes of the Philosophical Transactions; the researches
of the former having been chiefly directed to the minute struc-
ture of Plants, and those of the latter to that of Animals. Both
were attended with great success. The former laid the founda-
tion of our anatomical knowledge of the Vegetable tissues, and
described their disposition in the roots and stems of a great
variety of plants and trees; besides making out many important
facts in regard to their physiological actions. The latter did the
same for the Animal body; and seems to have been the first to
witness the marvellous spectacle of the movement of Blood in
the capillary vessels of the Frog’s foot,—thus verifying by ocular
demonstration that doctrine of the passage of blood from the
smallest arteries to the smallest veins, which had been pro-
pounded as a rational probability by the sagacious Harvey.
Glimpses of the invisible world of Animalcular life were oc-
casionally revealed to the earlier Microscopists, by which their
curiosity must have been strongly excited; yet they do not ap-
pear to have entered on this class of investigations, with any
large portion of that persevering zeal which they devoted to
the analysis of the higher forms of organic structure. Its won-
ders, however, were gradually unfolded; so that in the various
treatises on the Microscope published during the eighteenth
century, an account of the plants and animals (but especially ot
the latter) too minute to be seen by the unaided eye, occupies a
conspicuous place. It was towards the middle of that period,
that M. Trembley of Geneva first gave to the world his researches
on the “Fresh-water Polype”’ or Hydra; the publication of which
may be considered to have marked a most important epoch in the
history of microscopic inquiry. For it presented to the natu-
ralist the first known example of a class of animals (of which the
more delicate and flexible Zoophytes are, so to speak, the ske-
letons) whose claim to that designation had been previously
doubted or even denied, the terms ‘‘sea-mosses,”’ “ sea ferns,” &c.,
having been applied to them, not merely as appropriately indicat-
ing their form and aspect, but as expressive of what even the most
eminent Zoologists, as well as Botanists, considered to be their
vegetable nature. ‘And it presented to the Physiologist an en-
tirely new type of animal life; the wonderful nature of which
was fitted not only to excite the liveliest interest, but also to
effect a vast extension in the range of the ideas entertained up to
that time regarding its nature and capacities. For what animal
previously known, could propagate itself by buds like a plant,—
could produce afresh any part that might be cut away,—could
form any number of new heads by the completion of the halves

38 INTRODUCTION.

into which the previous heads had been slit (thus realizing the
ancient fable of the Hydra),—could even regenerate the whole
from a minute portion, so that when the body of one individual
was positively minced into fragments, each of these should grow
into a new and complete polype,—could endure being turned
inside out, so that what was previously the external surface
should become the lining of the stomach, and vice versé,—and
could sustain various other kinds of treatment not less strange
(such as the grafting of two individuals together, head to head,
or tail to tail, or the head of the one to the tail of another), not
only without any apparent injury, but with every indication, in
the vigor of its life, of being entirely free from suffering or
damage? (See Chap. XI).—It was by our own countryman, Ellis,
that the discoveries of Trembley were first applied to the elucida-
tion of the real animal nature of the so-called Corallines ;? the
structure of which was so carefully investigated by him, that
subsequent observers added little to our knowledge of it, until a
comparatively recent period.

The true animaleules were first systematically studied, in the
latter part of the last century, by Gleichen, a German micro-
scopist, who devised the ingenious plan of feeding them with
particles of coloring matter, so as to make apparent the form and
position of their digestive cavities; and this study was after-
wards zealously pursued by the eminent Danish naturalist, Otho
Fred. Miller, to the results of whose labors in this field but little
was added by others, until Professor Ehrenberg entered upon the
investigation with the advantage of greatly improved instruments.
It was at about the same period with Miiller, that Vaucher, a
Genevese botanist, systematically applied the Microscope to the
investigation of the lower forms of Vegetable life; and made
many curious discoveries in regard both to their structure and
to the history of their lives. He was the first to notice the ex-
traordinary phenomenon of the spontaneous movement of the
Zoospores of the humbler aquatic plants, which is known to be the
means provided by nature for the dispersion of the race (Chaps.
VI, VII); but being possessed with the idea (common to all Natu-
ralists of that period and still very generally prevalent) that spon-
taneous motion evinces Animal life, he interpreted the facts which
he observed, as indicating the existence of a class of beings which
are Plants at one phase of their lives, and animals at another,—
a doctrine which has since been completely set aside by the ad-
vance of physiological knowledge. Notwithstanding this and
other errors of interpretation, however, the work of Vaucher on
the “‘ Fresh-water Conferve’’ contains such a vast body of accu-
rate observation on the growth and reproduction of the Micro-
scopic Plants to the study of which he devoted himself, that it is
quite worthy to take rank with that of Trembley, as havin g laid

' The structures to which this term is now scientifically restricted, are really vege-
table.

SUPPOSED FALLACIES OF THE MICROSCOPE. 39

the foundation of all our scientific knowledge of these very inte-
resting forms. Although the curious phenomenon of “ conju-
gation” had been previously observed by Miiller, yet its con-
nection with the function of Reproduction had not been even
suspected by him; and it was by Vaucher that its real import
was first discerned, and that its occurrence (which had been re-
garded by Miiller as an isolated phenomenon, peculiar to a single
species) was found to be common to a large number of humble
aquatic forms of vegetation. But little advance was made upon the
discoveries of Vaucher in regard to these, save by addition to the
number of their specific forms, until a fresh stimulus had been
given to such investigations by the improvement of the instru-
ment itself. At present, they are among the most favorite ob-
jects of study among a large number of observers, both in this
country and on the Continent ; and are well deserving of the
attention which they receive.

Less real progress seems to have been made in Microscopic
inquiry, during the first quarter of the present century, than
during any similar period since the invention of the instrument.
The defects inseparable from its original construction, formed a
bar to all discovery beyond certain limits ; and although we are
now continually meeting with new wonders, which patient and
sagacious observation would have detected at any time and with
any of the instruments then in use, yet it is not surprising that
the impression should have become general, that almost every-
thing which it could accomplish had already been done. The
instrument fell under a temporary cloud from another cause ;
for having been applied by Anatomists and Physiologists to the
determination of the elementary structure of the aninal body,
their. results were found to be so discordant, as to give rise to a
general suspicion of a want of trustworthiness in the Microscope,
and in everything announced upon its authority. Thus both
the instrument and its advocates were brought into more or less
discredit ; and as they continue to lie under this, in the estima-
tion of many, to the present day, it will be desirable to pause
here for awhile, to inquire into the sources of that discrepancy, to
consider whether it is avoidable, and to inquire how far it should
lead to a distrust of Microscopic observations, carefully and saga-
ciously made, and accurately recorded.

It is a tendency common to all: observers, and not by any
means peculiar to Microscopists, to describe what they believe and
infer, rather than what they actually witness. The older Micro-
scopic observers were especially liable to fall into this error; since
the want of definiteness in the images presented to their eyes,
left a great deal to be completed by the imagination. And
when, as frequently happened, Physiologists began with theorizing
on the elementary structure of the body, and allowed them-
selves to twist their imperfect observations into accordance with
their theories, it was not surprising that their accounts of what

40 INTRODUCTION.

they professed to have seen should be extremely discordant. But
from the moment that the visual image presented by a well-con-
structed Microscope, gave almost as perfect an idea of the object,
as we could have obtained from the sight of the object itself, if
enlarged to the same size and viewed with the unassisted eye,
Microscopic observations admitted of nearly the same certainty as
observations of any other class; it being only in a comparatively
small number of cases, that a doubt can fairly remain about any
question of fact, as to which the Microscope can be expected to
inform us.!

Another fallacy, common like the last to all observations, but
with which the Microscopie observations of former times were
perhaps especially chargeable, arises from a want of due atten-
tion to the conditions under which the observations are made.
Thus one observer described the Human Blood-corpuscles as
flattened disks resembling pieces of money, another as slightly
concave on each surface, a third as slightly convex, a fourth as
highly convex, and a fifth as globular; and the former preva-
lence of the last opinion, is marked by the habit which still
lingers in popular phraseology, of designating these bodies as
“pblood-globules.”” Yet all microscopists are now agreed, that
their real form, when examined in freshly drawn blood, is that of
circular disks, with slightly concave surfaces; and the diversity
in previous statements was simply due to the alteration effected
in the shape of these disks, by the action of water or other
liquids added for the sake of dilution; the effect of this being to
render their surfaces first flat, then slightly convex, then more
highly convex, at last changing their form to that of perfect
spheres. But microscopical inquiries are not in themselves more
liable to fallacies of this description, than are any other kinds of
scientific investigation; and it will always be found here, as well
as elsewhere, that—good instruments and competent observers
being presupposed—the accordance in results will be precisely
proportional to the accordance of conditions, that is, to the simi-
larity of the objects, the similarity of the treatment to which they
may be subjected, and the similarity of the mode in which they
may be viewed.?

The more completely, therefore, the statements of Microscopic
observers are kept free from those fallacies, to which observa-
tions of any kind are liable, wherein due care has not been taken

1 One of the most remarkable of the questiones verate at present agitated, is the
nature of the markings on the siliceous valves of Diatomacee (Chap. VI); some ob-
servers affirming those spots of the surface to be elevations, which others consider to
be depressions. ‘The difference is here one of interpretation, rather than of direct odserva-
tion ; the nature of the case preventing that kind of view of the object, which could
leave no doubt as to the fact; and the conclusion formed being one of inference from a
variety of appearances, which will differently impress the minds of different individuals.

2 In objects of the most difficult class, such as the Diatomacee, this last point is one of
fundamental importance; very different appearances being presented by the same object,
according to the mode in which it is illuminated, and the focal adjustment of the object-
glass under which it is examined.—See Chap. VI.

MODERN REVELATIONS OF THE MICROSCOPE. 41

to guard against them, the more completely will it be found that
an essential agreement exists among them all, in regard to the
facts which they record. And although the influence of precon-
ceived theories still too greatly modifies, in the minds of some, the
descriptions they profess to give of the facts actually presented to
their visual sense, yet on the whole it is remarkable to what a
unity of doctrine the best Microscopists of all countries are con-
verging, in regard to all such subjects of this kind of inquiry, as
have been studied by them with adequate care and under simi-
lar ‘conditions. Hence it is neither fair to charge upon the
Microscopists of the present day the errors of their predecessors ;
nor is it just to lay to the account of the instrument, what
entirely proceeds from the fault of the observer, in recording, not
what he sees in it, but what he fancies he can see.

It was at the commencement of the second quarter of the
present century, that the principle of Achromatic correction, which
had long before been applied to the Telescope, was first brought
into efficient operation in the construction of the Microscope;
for although its theoretical possibility was well known, insupera-
ble difficulties were believed to exist in its practical application.
The nature of this most important improvement will be explained
in its proper place (Chap. I); and at present it will be sufficient
to say, that within eight or ten years from the date of its
first introduction, the character of the Microscope had been in
effect so completely transformed, that it became an altogether
new instrument; and from being considered but little better
than a scientific toy, it soon acquired the deserved reputation of
being one of the most perfect instruments ever devised by Art
for the investigation of Nature. To this reputation it has a still
greater claim at the present time; and though it would be ha-
zardous to deny the possibility of any further improvement, yet
the statements of theorists as to what may be accomplished, are
so nearly equalled by what has been effected, that little room for
improvement can be considered to remain, unless an entirely
new theory shall be devised, which shall create a new set of
possibilities.

Neither Botanists or Zoologists, Anatomists or Physiologists,
were slow to avail themselves of the means of perfecting and. ex-
tending their knowledge, thus unexpectedly put into their hands ;
and the records of Scientific Societies, and the pages of Scientific
Journals, have ever since teemed, like the early Transactions of
the Royal Society, with discoveries made by its instrumentality.
All really philosophic inquirers soon came to feel, how vastly
the use of the improved Microscope must add to their insight
into every department of Organic Nature; and numbers forth-
with applied themselves diligently to the labor of investigation.
Old lines of research, which had been abandoned as unlikely to
lead to any satisfactory issue, were taken up again with the con-
fident expectation of success, which the result has shown to have.

42 INTRODUCTION.

been well grounded; and new paths were soon struck out, each
of which, leading into some region previously unexplored, soon
cleared the way to others which became alike productive; thus
laying open an almost unlimited range of inquiry, which the
time that has since elapsed has served rather to extend than to
contract, and which the labor that has been devoted to it has
rather amplified than exhausted. A slight sketch of what has
already been accomplished by the assistance of the Microscope,
in the investigation of the phenomena of Life, seems an appro-
priate Introduction to the more detailed account of the instru-
ment and its uses, which the present Treatise is designed to
embrace.

The comparative simplicity of the structure of Plants, and the
relatively large scale of their elementary parts, had allowed the
Vegetable Anatomist, as we have seen, to elucidate some of its
most important features, without any better assistance than the
earlier Microscopes were capable of supplying. And many of those
humbler forms of Cryptogamic vegetation, which only manifest
themselves to the unaided eye when by their multiplication they
aggregate into large masses, had been made the objects of care-
ful study, which had yielded some most important results. Hence
there seemed comparatively little to be done by the Microscopist
in Botanical research; and it was not immediately perceived
what was the direction in which his labors were likely to be
most productive. Many valuable memoirs had been published,
from time to time, on various points of vegetable structure; the
increased precision and greater completeness of which, bore
testimony to the importance of the aid which had been atforded
by the greater efficiency of the instrument employed in such re-
searches. But it was when the attention of Vegetable Physiolo-
gists first began to be prominently directed to the history of
development, as the most important of all the subjects which pre-
sented themselves for investigation, that the greatest impulse
was given to Scientific Botany; and its subsequent progress has
been largely influenced by that impulse, both in the accelerated
rate at which it has advanced, and in the direction which it has
taken. Although Robert Brown had previously observed and
recorded certain phenomena of great importance, yet it is in the
Memoir of Prof. Schleiden, first published in 1887, that this new
movement may be considered to have had its real origin; so
that, whatever may be the errors with which his statements
(whether on that occasion, or subsequently) are chargeable, there
cannot be any reasonable question as to the essential service he
has rendered to science, in pointing out the way to others, on
whose results greater reliance may be placed. It was by Schlei-
den that the fundamental truth was first broadly enunciated, that
as there are as many among the lowest orders of Plants, in
which a single cell constitutes the entire individual, cach living
for and by itself alone, so each of the cells, by the aggregation of

MICROSCOPIC STUDY OF THE CRYPTOGAMIA. 43

which any individual among the higher Plants consists, has an
independent life of its own, besides the “incidental” life which it
possesses as a part of the organism at large: and that the
doctrine was first proclaimed, that the life-history of the indi-
vidual cell is therefore the very first and absolutely indispensable
basis, not only for Vegetable Physiology, but (as was even then
foreseen by his far-reaching mental vision) for Comparative
Physiology in general. The first problem, therefore, which he
set himself to investigate, was—how does the cell itself originate ?
It is unfortunate that he should have had recourse for its solu-
tion, to some of those cases in which the investigation is attended
with peculiar difficulty, instead of making more use of the means
and opportunities which the “single-celled”’ plants afford; and
it is doubtless in great part to this cause, that we are to attribute
certain fallacies in his results, of which subsequent researches
have furnished the correction.

In no department of Botany, has recent Microscopy been
more fertile in curious and important results, than in that which
relates to the humblest forms of Cryptogamia that abound not

only in our seas, rivers, and lakes, but even more in our marshes,
pools, and ditches. For, in the first place, these present us with
a number of most beautiful and most varied forms, such as on
that account alone are objects of great interest to the Micro-
scopist; this is especially the case with the curious group (ranked
among Animalcules by Prof. Ehrenberg), which, from the bipar-
tite form of their cells, has received the designation of Desmidiew.
In another group, that of Diatomacee (also still regarded as Ani-
malcules, not only by Ehrenberg, but by many other Naturalists),
not only are the forms of the plants often very remarkable, but
their surfaces exhibit markings of extraordinary beauty and
symmetry, which are among the best ‘‘test-objects” that can be
employed for the higher powers of the instrument (Chap. IV):
moreover, the membrane of each cell being coated externally
with a film of silica, which not only takes its form, but receives
the impress of its minutest markings, the siliceous skeletons
remain unchanged after the death of the plants which formed
them, sometimes accumulating to such an amount, as to give rise
to deposits of considerable thickness at the bottoms of the lakes
or pools which they inhabit; and similar deposits, commonly
designated as beds of “ fossil animalcules,” are not unfrequently
found at a considerable distance from the surface of the ground,
on the site of what must have probably once been a lake or estu-
ary, occasionally extending over such an area, and reaching to
such a depth, as to constitute no insignificant part of the crust
of the globe.—It is not only in these particulars, however,
that the foregoing and other humble Plants have special attrac-
tions for the Microscopist; for the study of their living actions
brings to view many phenomena, which are not only well caleu-
lated to excite the interest of those who find their chicf pleasure

44 INTRODUCTION.

in the act of observing, but are also of the highest value to the
Physiologist, who seeks to determine from the study of them
what are the acts wherein Vitality may be said essentially to
consist, and what are the fundamental distinctions between Ani-
mal and Vegetable life. Thus it is among these plants, that we
can best study the history of the multiplication of cells by
“binary subdivision,” which seems to be the most general mode
of growth and increase throughout the Vegetable kingdom ; and
it is in these, again, that the process of sexual generation is pre-
sented to us under its simplest aspect, in that curious act of
“conjugation” to which reference has already been made (p. 39).
But further, nearly all these Plants have at some period or other
of their lives, a power of spontaneous movement ; which in many
instances so much resembles that of Animalcules, as to seem un-
mistakably to indicate their animal nature, more especially as
this movement is usually accomplished by the agency of visible
cilia: and the determination of the conditions under which it
occurs, and of the purposes it is intended to fulfil, is only likely
to be accomplished after a far more extensive as well as more
minute study of their entire history, than has yet been prose-
cuted, save in a small number of instances. It is not a little
remarkable, that in several of the cases in which the life-history
of these plants has been most completely elucidated, they have
been found to present a great variety of forms and aspects at
different periods of their existence, and also to possess several
different methods of reproduction; and hence it can be very
little doubted, that numerous forms which are commonly reputed
to be distinct and unrelated species, will prove in the end to be
nothing else than successive stages of one and the same type.
One of the most curious results attained by Microscopie inquiry
of late years, has been the successive transfer of one group of
reputed Animalcules after another, from the Animal to the Vege-
table side of the line of demarcation between the two kingdoms;
and although, as to the precise points across which this line
should be drawn, there is not yet a unanimous agreement, yet
there is now an increasing accordance as to its general situation,
which, even a few years since, was energetically canvassed.
Those who are acquainted with the well-known Jolvox (com-
monly termed the “ globe-animalcule”’) will be surprised to learn
that this, with its allies, constituting the family Volvocinee, is
now to be considered as on the Vegetable side of the boundary.
(On the subjects of this paragraph, see Chap. VI.)

Not only this lowest type of Vegetable existence, but the Cryp-
togamie series as a whole, has undergone of late years a very
close scrutiny, which has yielded results of the highest impor-
tance; many new and curious forms having been brought to
light (some of them in situations in which their existence might
have been least anticipated), and some of the most obscure por-
tions of their history having received an unexpectedly clear eluci-

MICROSCOPIC STUDY OF THE CRYPTOGAMIA. 45

dation. Thus the discovery was announced by M. Audouin in
1837, that the disease termed muscardine, which annually carried
off large numbers of the silkworms bred in the south of France,
really consists in the growth of a fungous vegetation in the interior
of their bodies, the further propagation of which may be almost
entirely prevented by appropriate means; in the succeeding
year, the fact was brought forward by several Microscopists, that
yeast also is composed of vegetable cells, which grow and multi-
ply during the process of fermentation; and subsequent re-
searches have shown that the bodies of almost all animals, not
even excepting Man himself, are occasionally infested by Vege-
table as well as by animal Parasites, many of them remarkable
for their beauty of configuration, and others for the variety of
the forms they assume. The various parasites which attack our
cultivated plants, again,—such as the “blights” of corn, the po-
tato fungus, and the vine fungus,—have received a large measure
of attention from Microscopists, and much valuable information
has been collected in regard to them. It is still a question, how-
ever, which has to be decided upon other than microscopic evi-
dence, how far the attacks of these fungi are to be considered as
the causes of the diseases to which they stand related, or whether
their presence (as is undoubtedly the case in many parallel in-
stances) is the effect of the previously unhealthy condition of the
plants which they infest; the general evidence appears to the
author to incline to the latter view.

Of all the additions which our knowledge of the structure and
life-history of the higher types of Cryptogamic vegetation has
received, since the achromatic microscope has been brought to
bear upon them, there is none so remarkable as that which re-
lates to their Reproductive function. For the existence in that
group of anything at all corresponding to the sexual generation
of Flowering Plants, was scarcely admitted by any Botanists;
and those few who did affirm it were unable to substantiate their
views by any satisfactory proof, and were (as the event has
shown) quite wrong as to the grounds on which they based them.
Various isolated facts, the true meaning of which was quite un-
recognized, had been discovered from time to time,—such as the
existence of the moving filaments now termed ‘“antherozoids,” in
the “ globules” of the Chara (first demonstrated by Mr. Varley in
1834), and in the “antheridia” of Mosses and Liverworts (as shown
by Unger and Meyen in 1887), and the presence of “antheridia”
upon what had been always previously considered the embryo-
frond of the Ferns (first detected by Nageli in 1844); but of the
connection of these with the generative function, no valid evi-
dence could be produced, and the sexual reproduction of the
Cryptogamia was treated by many Botanists of the greatest
eminence, as a doctrine not less chimerical, than the doctrine
of the sexuality of Flowering Plants had appeared to be to
the opponents of Linneus. It was by the admirable researches

46 INTRODUCTION.

of Count Suminski upon the development of the Ferns (1848),
that the way was first opened to the right comprehension
of the reproductive process in that group; and the doctrine
of the fertilizing powers of the “antherozoids,” once established
in a single case, was soon proved to apply equally well to
many others. Not a year has since elapsed, without the pro-
duction of new evidence of the like sexuality in the several
groups of the Cryptogamic series; this having been especially
furnished by Hofmeister in regard to the higher types, by Thuret
and Decaisne as to the marine Algw, and by Tulasne with re-
spect to Lichens and Fungi; and the doctrine may now be con-
sidered as established beyond the reach of cavil from any but
those, who, having early committed themselves dogmatically to
the negative opinion, have not the candor to allow due weight
to the evidence on the affirmative side. With the study of the
Reproduction of these plants, that of the history of their Develop-
ment has naturally been connected; and some of the facts already
brought to light, especially by the study of certain forms of Fun-
gous vegetation, demonstrate the extreme importance of this
inquiry in settling the foundations of Classification. For whereas
the arrangement of Fungi, as of other Plants, has been based
upon the characters furnished by their fructification, these charac-
ters have been found by Tulasne to be frequently subject to varia-
tions so wide, that one and the same individual shall present two
or more kinds of fructification, such as had been previously con-
sidered to be peculiar to distinct orders. In this department of
study, which has been scarcely at all cultivated by Microscopists
of our own country, there is a peculiarly wide field for careful’
and painstaking research, and a sure prospect of an ample har-
vest of discovery. (On the subjects of the two preceding para-
graphs, see Chap. VII.)

Although it has been in Cryptogamic Botany, that the zealous
pursuit of Microscopic inquiry has been most conducive to scien-
tific progress, yet the attention of Vegetable Anatomists and
Physiologists has been also largely and productively directed to
the minute structure and life-history of Flowering Plants. For
although some of the general features of that structure had been
made out by the earlier observers, and successive additions had
been made to the knowledge of them, previously to the new era
to which reference has so often been made, yet all this knowledge
required to be completed and made exact, by a more refined ex-
amination of the Elementary Tissues than was before possible;
and little was certainly known in regard to those processes of
growth, development, and reproduction, in which their activity
as living organisms consists. All the researches which have
been made upon this point, tend most completely to bear out
the general doctrine so clearly set forth by Schleiden, as to the
independent vitality of each integral part of the fabric; and
among the most curious results of the inquiries which have been

MICROSCOPIC STUDY OF FLOWERING PLANTS. 47

prosecuted in this direction, may be mentioned the discovery,
that the movement of “rotation” of the protoplasma (or the viscid
granular fluid at the expense of which the nutritive act seems to
take place) within the cells, which was first observed by the
Abbé Corti in the Chara in 1776, is by no means a unique or
exceptional case; for that it may be detected in so large a num-
ber of instances, among Phanerogamia no less than among Cryp-
togamia, as apparently to justify the conclusion that it takes
place in Vegetable cells generally, at some period or other of
their evolution. In studying the phenomena of Vegetable Nu-
trition, the Microscope has been most effectually applied, not
merely to the determination of changes in the form and arrange-
ment of the elementary parts, but also to the detection of such
changes in their composition, as ordinary Chemistry would be
quite at fault to discover; each individual cell being (so to speak)
a laboratory in itself, within which a transformation of organic
compounds is continually taking place, not only for its own
requirements, but for those of the economy at large; and these
changes being at once made apparent by the application of
chemical reagents to microscopic specimens whilst actually under
observation. Hence the Vegetable Physiologist finds, in this
Microscopic Chemistry, one ot his most valuable means of tracing
the succession of the changes in which Nutrition consists, as
well as of establishing the chemical nature of particles far too
minute to be analyzed in the ordinary way; and he derives
further assistance in the same kind of investigation, from the
application of Polarized Light (§ 68), which immediately enables
him to detect the presence of mineral deposits, of starch-granules,
and of certain other substances which are peculiarly affected by
it. One of the most interesting among the general results of
such researches, has been the discovery that the true cell-wall of
the Plant (the “ primordial utricle’’ of Mohl) has the same albwmi-
nous composition as that of the Animal; the external cellulose
envelope, which had been previously considered as the distinc-
tive attribute of the Vegetable cell, being in reality but a secre-
tion from its surface. Of all the applications of the Microscope,
however, to the study of the life-history of the Flowering plant,
there is none which has excited so much interest, or given rise
to so much discussion, as the nature of the process by which the
Ovule is feeundated by the penetration of the pollen-tube. This
question, in the opinion of the author, may be considered as now
determined ; and the conclusion arrived at is one so strictly in
harmony with the general results obtained by the study of the
(apparently) very different phenomena presented by the Genera-
tive process of the Cryptogamia, that it justifies the Physiologist
in advancing a general doctrine as to the nature of the function,
which proves to be no less applicable to the Animal kingdom
than it is to the Vegetable. (See Chap. VIII.)

Among the objects of interest so abundantly offered by the

48 INTRODUCTION.

Animal Kingdom to the observation of Microscopists furnished
with vastly improved instruments of research, it was natural that
those minuter forms of Animal life which teem in almost every
stationary collection of water, should engage their early atten-
tion; and among those Naturalists who applied themselves to
this study, the foremost rank must undoubtedly be assigned to
the celebrated German Microscopist, Prof. Ehrenberg. For al-
though it is now unquestionable that he has committed numer-
ous errors,—many doctrines which at first gained considerable
currency on the strength of his high reputation, having now been
abandoned by almost every one save their originator,—yet when
we look at the vast advances which he unquestionably made in
our knowledge of Animalcular life, the untiring industry which
he has displayed in the study of it, the impulse which he has
given to the investigations of others, and the broad foundation
which he has laid for their inquiries in the magnificent works in
which his own observations are recorded, we cannot but feel that
his services have been almost invaluable, since, but for him, this
department of microscopic inquiry would certainly have been in
a position far behind that to which it has now advanced. Yet,
great as has been the labor bestowed by him and by his followers
in the same line of pursuit, it has become increasingly evident
of late years that our knowledge of Infusory Animalcules is still
in its infancy; that the great fabric erected by Prof. Ehrenberg
rests upon a most insecure foundation; and that the Anatomy,
Physiology, and systematic arrangement of these beings need to
be restudied completely, ab initio. For, in the first place, there
can be no doubt whatever, that a considerable section of the so-
called Animalcules belongs to the Vegetable kingdom; consist-
ing, as already pointed out, of the motile forms of the humbler
Plants, of which a very large proportion pass, at some period of
their existence, through a stage of activity that serves for their
diffusion. Moreover, in another group, whose character has been
entirely misconceived by the great German Microscopist, and
was first clearly discriminated by M. Dujardin, there is neither
mouth nor stomach of any kind; the minute plants and animals
which serve it as food, being incorporated, as it were, with the
soft animal jelly, which constitutes the almost homogeneous
body; and this jelly further extending itself into “ pseudopodial”
prolongations, whereby these alimentary particles are laid hold
of and drawn in. It was by the same distinguished French Mi-
eroscopist, that the important fact was first discovered, that
animals of this Rhizopod type are really the fabricators of those
minute shells, which, from their Nautilus-like aspect, had been
previously regarded as belonging to the highest class of the Mol-
luscous Sub-Kingdom; and the whole of this most interesting
group, which had received from M. D’Orbigny (who first per-
ceived the speciality of its nature, and made a particular study
of it) the designation of Foraminifera, has thus had its place in

MICROSCOPIC STUDY OF ANIMALCULES. 49

the Animal scale most strangely reversed; being at once de-
graded from a’ position but little removed from Vertebrated ani-
mals, to a level in some respects even lower than that of the
ordinary Animalcules.

But even when Prof. Ehrenberg’s class of Polygastrica has
been thus reduced, by the removal of those forms which are true
Plants, and by the detachment of such as belong to the Rhizopod
group, we find that our knowledge of its real nature is almost
wholly to be gained; since little else has yet been accomplished than
a description of a multitude of forms, of whose history as living
beings scarcely anything else is known, than that they take food
into the interior of their bodies by means of an oral orifice, that
they digest this food and appropriate it to their own growth,
and that they multiply themselves by binary subdivision. Now
there is a very strong analogical probability, that many even of
the most dissimilar forms of these Animalcules will prove to be
different states of one and the same; for their multiplication by
binary subdivision being nota true generative process, but being
merely (so to speak) the growth of the individual, we may be al-
most certain that sooner or later a new phase will present itself,
consisting in the evolution of proper sexual bodies, which will
perform a true generative act, the products of which may be
very probably quite different from the forms we are accustomed
to regard as peculiar to each species. The attention of several
eminent Microscopists at the present time is strongly fixed upon
this part of the inquiry ; which can only be efficiently prosecuted,
by limiting the range of observation for a time to @ small number
of forms, and pursuing these through all the phases of their ex-
istence.

Among the most important of Prof. Ehrenberg’s unquestioned
discoveries, we are undoubtedly to place that of the compara-
tively high organization of the Rotifera, or Wheel-Animalcules
and their allies ; for which, though previously confounded with
a similar Infusoria, he asserted and vindicated a claim to a far
more elevated rank. Yor although in this instance, too, some of
his descriptions have been shown to be incorrect, and many of
his inferences to be erroneous, and although subsequent observ-
ers are not agreed among themselves as to many important par-
ticulars, yet all assent to the general accuracy of Prof. Ehrenberg’s
statements, and recognize the title of the Rotifera to a place not
far removed from that of the Vermiform tribes. A parallel dis-
covery was made about the same time by MM. Audouin and
Milne Edwards, in regard to the Flustre and their allies, which
had previously ranked among those flexible Zoophytes popularly
known as “ corallines,” andare often scarcely to be distinguished
from them in mode of growth or general aspect ;’ but which

' “You go down,” says Mr. Kingsley, “to any shore after a gale of wind, and pick
up a few delicate little sea-ferns. You have two in your hand (Sertularia operculata

and Gemellaria loriculata), which probably look to you, eyen under a good pocket mag-
nifier, identical or nearly so. But you are told, to your surprise, that however like the

50 INTRODUCTION.

were separated as a distinct order by these observers, on account
of their possession of a second orifice to the alimentary canal,
and the general tendency of their plan of organization to that
which characterizes the inferior Mollusca. The importance of
this distinction was at once recognized ; and the group received
the designation of Polyzoa from Mr. J. V. Thompson, and of
Bryozoa from Prof. Ehrenberg. The organization of this very
interesting group was further elucidated, some years subsequent-
ly, by the admirable observations of Dr. Arthur Farre upon a
newly-discovered form (named by him Bowerbankia), the trans-
parence of whose envelopes allowed its internal structure to be
distinctly made out ; and the additional features which he de-
tected, were all such asto strengthen the idea already entertained
of its essentially Molluscan character. This ideareceived its final
and complete confirmation from the admirable researches of
M. Milne Edwards on the Compound Ascidians, which are the
lowest animals whose Molluscous nature had been previously ac-
knowledged ; these having been discovered by him to agree with
Zoophytes in their plant-like attribute of extension by “ gemma-
tion” or budding, and to present, in all the most important fea-
tures of their organization, an extremely close approximation to
the Bryozoa. Thus whilst Microscopic research has degraded
the Foraminifera from their supposed rank with the Nautilus
and Cuttle-fish, to the level of the Sponge, it has raised the
Wheel-Animalcules into proximity with the aquatic Worms,
and the humble “ Sea-Mat,” formerly supposed to be a Plant, to
a position not much below that of the Oyster and Mussel.'
Another most curious and most important field of microscopic
inquiry has been opened up in the discovery of the Transforma-
tions which a large proportion of the lower animals undergo,
during the early stages of their existence ; and notwithstanding
that it has even yet been very imperfectly cultivated, the unexpect-
ed result has been already attained, that the fact of “metamor-
phosis,”—previously known only in the cases of Insects and Tad-
poles, and commonly considered as an altogether exceptional phe-
nomenon,—is almost wnzversal among the inferior tribes ; it being
a rare occurrence for the offspring to come forth from the egg in
a condition bearing any resemblance to that which characterizes
the adult, and the latter being in general attained only after a
long series of changes, in the course of which many curious
phases are presented. One of the earliest and most remarkable
discoveries which was made in this direction,—that of the meta-
morphosis of the Cirrhipeds (Barnacles and their allies) by Mr. J.
V. Thompson,—proved of most important assistance in the de-
termination of the true place of that group, which had previously
been a matter of controversy; for although in their outward

dead horny polypidoms which you hold may be, the two species of animal which have
formed them, are at least as far apart in the scale of creation as a quadruped is from a
fish.”

sn reference to the subjects of the three preceding paragraphs, see Chaps. IX
I y
?

MICROSCOPIC STUDY OF LOWER ANIMALS. 51

characters they bear such a resemblance to Mollusks, that the
Barnacles which attach themselves to floating timber, and the
Acorn-shells which incrust the surfaces of rocks, are unhesitat-
ingly ranked by Shell-collectors among their “ multivalves,” yet
the close resemblance which exists between their early forms and
the little Water-Fleas which swarm in our pools, makes it quite
certain that the Barnacles not only belong to the Articulated in-
stead of tothe Molluscous series, but that they must be ranked in
close proximity to the Entomostracous division of the Crustacea,
if not actually asmembers of it. To the same discoverer, moreover,
we owe the knowledge that even the common Crab undergoes
metamorphoses scarcely less strange, its earliest form being a lit-
tle creature of most grotesque shape, which had been previously
described as an adult and perfect Entomostracan; so that, al-
though scarcely any two creatures can apparently be more uhlike
than a Barnacle and a Crab, they have (so to speak) the same
starting-point; the difference in their ultimate aspect chiefly
arising from the difference in the proportionate development of
parts which are common to both. A still more remarkable series
of Metamorphoses has recently been shown by Prof. Miiller to
exist among the Echinoderms (Star-fish, Sea-urchings, &c.) ; whose
development he has studied with great perseverance and sagacity.
Thus the larva of the Star-fish is an active free-swimming animal,
having a long body with six slender arms on each side, from one
end of which the young star-fish is (so to speak) budded off; and
when this has attained a certain stage of development, the long
twelve-armed body separates from it and dies off, its chief func-
tion having apparently been, to carry the young Star-fish to a
distance from its fellows, and thus to prevent overcrowding by
the accumulation of individuals in particular spots, which would
be liable to occur if they never had any more active powers of
locomotion than they possess in their adult state. Scarcely less
remarkable are the changes which are to be witnessed in the
greater number of aquatic Mollusks, almost all of which, however
inert in their adult condition, possess active powers of locomotion
in their larval state ; some being propelled by the vibratile move-
ment of cilia disposed upon the head somewhat after the fashion
of those of Wheel-animalcules, and others by the lateral strokes
of a sort of tail which afterwards disappears like that of a tadpole.
Among the Annelids or marine worms, again, there is found
to be an extraordinary dissimilarity, though of a somewhat dif-
ferent nature, between the larval and the adult forms: for they
commonly come forth from the egg in a condition but little ad-
vanced beyond that of Animalcules; and, although they do not
undergo any metamorphosis comparable to that of Insects, they
pass through a long series of phases of development (chiefly
consisting in the successive production of new joints or segments,
and of the organs appertaining to these) before they acquire their
complete type. In nearly all the foregoing cases it may be re-

52 INTRODUCTION.

marked, that the larval forms of different species bear to one
another a far stronger resemblance than exists among adults,
the distinguishing characters of the latter being only evolved in
the course of their development; and every new discovery in
this direction only gives fresh confirmation to the great law of
development early detected by the sagacity of Von Baer, that the
more special forms of structure arise out of the more general, and this
by a gradual change. The meaning of this law will become ob-
vious hereafter, when some of the principal cases to which it
applies shall have been brought in illustration of it (Chap. XII).
A still more curious series of discoveries has been made, by
means of the Microscope, in regard to the early development of
the Mcdusan Acalephs (jelly-fish, &c.), and the relationship that
exists between them and the Hydraform Zoophytes ;—two groups
of animals, which had been previously ranked in different classes,
and had not been supposed to possess anything in common.
For it has been clearly made out by the careful observations of
Sars, Siebold, Dalyell, and others, that those delicate arborescent
Zoophytes, each polype of which is essentially a Hydra, not only
grow by extending themselves into new branches, like plants,
sometimes also budding off detached gemme, which multiply
their kind by developing themselves into Zoophytic forms like
those whence they sprang; but also produce peculiar buds hav-
ing all the characters of Medusce, which contain the proper gene-
rative organs of the Zoophyte, but which, usually detaching
themselves from the stock that bore them, swim freely through
the ocean as minute jelly-fish, without exhibiting the slightest
trace of their originally attached condition. The Meduse in due
time produce fertile eggs; and each egg developes itself, not into
the form of its immediate progenitor, ‘but into that of the Zoo-
phyte from which the Medusa was budded off. And thus a most
extraordinary alteration of forms is presented, between the Zoo-
phyte, which may be compared to the growing or vegetating stage
of a Plant (its polypes representing the leaf-buds), and the
Medusa, the development of which marks its flowering stage.
So again, from the investigation of the early history of those
larger forms of “jelly-fish’’ with which every visitor to the sea-
coast is familiar, it has been rendered certain that they too are
developed from Polype larvee, usually of very minute size, which
give off Medusa buds; so that whilst they are best known to us
in their Medusan state, and the Hydraform Zoophytes in their
polypoid state, each of these groups is the representative of a
certain stage in the life-history of one and the same tribe of
these curious beings, which, when complete, includes both states,
as will hereafter be shown in more detail (Chap. XI). Changes
very similar in kind, and in many respects even more remark-
able, have been found by microscopic inquiry to take place
among the Hntozoa (intestinal worms); but being interesting
only to professed Naturalists and scientific Physiologists, they
scarcely call for particular notice in a treatise like the present.

MICROSCOPIC STUDY OF LOWER ANIMALS, 53

It has not been among the least important results of the new
turn which Zoological inquiry has thus taken, that a far higher
spirit has been introduced into the cultivation of this science,
than previously pervaded it. Formerly it was thought, both in
Zoology and in Botany, that Classification might be adequately
based on external characters alone; and the scientific acquire-
ments of a Naturalist were estimated rather by the extent of his
acquaintance with these, than by any knowledge he might
possess of their internal organization. The great system of
Cuvier, it is true, professed to rest upon organization as its
basis; but the acquaintance with this which was considered
requisite for the purpose, was very limited in its amount and
superficial in its character; and no Naturalist formerly thought
of studying the history of Development as a necessary adjunct
to the Science of Classification. How essential a knowledge of
it has now become, however, if only as a basis for any truly
natural arrangement of Animals, must have become apparent
from the preceding sketch; and it has thus come to be felt and
admitted amongst all truly philosophic Naturalists, that the com-
plete study of any particular group, even for the purposes of
classification, involves the acquirement of a knowledge, not only
of its intimate structure, but of its entire life-history. And thus
Natural History and Physiology,—two departments of the great
Science of Life, which the Creator inextricably blended, but
which Man has foolishly striven to separate,—are now again
being brought into their original and essential harmony; and it
is coming to be thought more credible, to give a complete eluci-
dation of the history of even a single species, than to describe
any number of new forms, about which nothing else is made out
save what shows itself on the surface.

Thus every Microscopist, however limited may be his oppor-
tunities, has a wide range of observation presented to him in the
study of the lower forms of Animal life; with the strongest incite-
ment to persevering and well-directed inquiry, that the anticipation
of novelty, and the expectation of valuable results, can afford. For,
notwithstanding the large number of admirable records which
have been already publighed (chiefly, we must admit with regret,
by Continental Naturalists) upon the developmental history of
the lower tribes of Animals, there is no one of the subjects that
have been just passed in review, of which the knowledge hith-
erto gained can be regarded as more than a sample of that which
remains to be acquired. Records like those already referred to,
might easily be multiplied a hundred fold, with infinite advan-
tage to Science; if those Microscopists who spend their time in
desultory observation, and in looking at some favorite objects
over and over again, would but concentrate their attention upon
some particular species or group, and work out its entire history
with patience and determination. And the observer himself
would find this great advantage in so doing,—that an inquiry

54 INTRODUCTION.

thus pursued gradually becomes to him an object of such attrac-
tive interest, that he experiences a zest in its pursuit to which the
mere dilettante is an entire stranger,—besides enjoying all the
mental profit, which is the almost necessary result of the thorough
performance of any task that is not in itself unworthy. And
what can be a more worthy occupation, than the attempt to gain
an insight, however limited, into the operations of Creative
Wisdom ?—these being not less wonderfully displayed among
the forms of Animal life which are accounted the simplest and
least attractive, than in those which more conspicuously solicit the
attention of the Student of Nature, by the beauty of their aspect
or the elaborateness of their organization.

It has not been, however, in the study of the minuter forms of
Animal life alone, that the Microscope has been turned to valu-
able account; for the Anatomists and Physiologists who had
made the Human fabric the especial object of their study, and
who had been led to believe that the knowledge accumulated
by their repeated and persevering scrutiny into every portion
accessible to their vision, was all which it lay within their power
to attain, have found in this new instrument of research, the
means of advancing far nearer towards the penetralia of Organ-
ization, and of gaining a much deeper insight into the mysteries
of Life, than had ever before been conceived possible. For
every part of the entire organism has been, so to speak, decom-
posed into its elementarg tissues, the structure and actions of each
of which have been separately and minutely investigated; and
thus a new department of study, which is known as Histology (or
Science of the Tissues), has not only been marked out, but has
already made great advances towards completeness. In the
pursuit of this inquiry, the Microscopists of our day have not
limited themselves to the fabric of Man, but have extended their
researches through the entire range of the Animal kingdom;
and in so doing, have found, as in every other department of
Nature, a combination of endless variety in detail, with a mar-
vellous simplicity and uniformity of general plan. Thus the
bones which constitute the skeleton of the Vertebrated animal,—
however different from each other in their external configura-
tion, in the arrangement of their compatt and their cancellated
portions, and other such particulars as specially adapt them for
the purposes they have to perform in each organism,—all consist
of a certain kind of tissue, distinguished under the microscope
by features of a most peculiar and interesting kind; and these
features, whilst presenting (like those of the Human counte-
nance) a certain general conformity to a common plan, exhibit
(as Prof. Quekett has shown) such distinctive modifications of
that plan in the different classes and orders of the Vertebrated
series, that it is generally possible by the microscopic examina-
tion of the merest fragment of a bone, to pronounce with great
probability as to the natural family to which it has belonged. “Still

MICROSCOPIC STUDY OF ANIMAL TISSUES. 55

more is this the case in regard to the Teeth, whose organic struc-
ture (originally detected by Leeuwenhoek) has been newly and
far more completely elucidated by Profrs. Purkinje, Retzius,
Owen, and Tomes; for the inquiry into the comparative struc-
ture of these organs, which has been prosecuted™by Prof. Owen,
in particular, through the entire range of the Vertebrated series,
has shown that, with an equally close conformity to a certain
general plan of structure, there are at the same time still wider
diversities in detail, which are so characteristic of their respective
groups, that it is often possible to discriminate, not only families,
but even the genera and species, by careful attention to the
minute features of their structure. Similar inquiries, with
results in many respects analogous, have been carried out by the
Author, in regard to the Shells of Mollusks, Crustaceans, and
. Echinoderms; his researches having not only demonstrated the
regularly-organized structure of these protective envelopes (which
had been previously affirmed to be mere inorganic exudations,
presenting in many instances a crystalline texture), but having
shown that many natural groups are so distinctively character-
ized by the microscopic peculiarities they present, that the in-
spection of a minute fragment of Shell will often serve to deter-
mine, no less surely than in the case of bones and teeth, the
position of the animal of which it formed a part. The soft parts
of the Animal body, moreover, such as the cartilages which
cover the extremities of the bones and the ligaments which hold
them together at the joints, the muscles whose contraction deve-
lopes motion and the tendons which communicate that motion,
the nervous ganglia which generate nervous force and the nerve-
fibres which convey it, the skin which clothes the body and the
mucous and serous membranes which line its cavities, the asstm7-
lating glands which make the blood and the secreting glands which
keep it in a state of purity,—these, and many other tissues that
might be enumerated, are severally found to present character-
istic peculiarities of structure, which are more or less distinctly
recognizable throughout the Animal series, and which bear the
strongest testimony to the Unity of the Design in which they all
originated. As we descend to the lower forms of Animal life,
however, we find these distinctions less and less obvious; and
we at last come to fabrics of such extreme simplicity and homogene-
ousness, that every part seems to resemble every other in struc-
ture and action; no provision being made for that “ division of
labor” which marks the higher types of organization, and which,
being the consequence of the development of separate organs
each having its special work to do, can only be effected where
there is a “differentiation” of parts, that gives to the entire
fabric a character of heterogeneousness.

The Microscopic investigation whose nature has thus been
sketched, has not only been most fruitful in the discovery of
individual facts, but has led to certain general results, of great

56 INTRODUCTION.

value in Physiological Science. Among the most important of
these, is the complete metamorphosis which has been effected in
the ideas previously entertained regarding living action ; such
having been essentially based on the Circulation of the blood, as
the only vital fhenomenon of which any direct cognizance could
be gained through the medium of the senses. For it gradually
came to be clearly perceived, that in the Animal as in the Plant,
each integral portion of the Organism possesses an independent Life
of its own, in virtue of which it performs a series of actions pe-
culiar to itself, provided that the conditions requisite for those
actions be supplied to it; and that the Life of the body as a
whole (like a symphony performed by a full orchestra) consists
in the harmonious combination of its separate instrumental acts,
—the circulation of the blood, instead of making the tissues, sim-
ply affording the supply of prepared nutriment, at the expense
of which they evolve themselves from germs previously existing.
This general doctrine was first put prominently forwards by
Schwann, whose “ Microscopical Researches into the Accordance
in the Structure and Growth of Animals and Plants,” published
in 1839, marks the commencement of a new era in all that
department of Animal Physiology, which comprises the simply
vegetative life of the organized fabric. These researches, avow-
edly based upon the ideas advanced by Schleiden, were prose-
cuted in the same direction as his had been; the object which
this admirable observer and philosophic reasoner specially pro-
posed to himself, being the study of the development of the
‘Animal tissues. He found that although their evolution cannot
be watched while in actual progress, its history may be traced
out by the comparison of the successive stages brought to light
‘by Microscopic research; and in so far as this has been accom-
plished for each separate part of the organism, the structure and
actions of its several components, however diverse in their fully
developed condition, are found to resemble each other more and
more closely, the more nearly these parts are traced back to their
earliest appearance. Thus we arrive in our retrospective survey,
at a period in the early history of Man, at which the whole em-
bryonic mass is but a congeries of cells, all apparently similar and
equal to each other; and going still further back, it is found
that all these have had their origin in the subdivision of a single
primordial cell, which is the first defined product of the generative
act. On this single cell, the Physiologist bases his idea of the
most elementary type of Organization ; whilst his actions present
him with all that 1s essential to the notion of Life. And in pur-
suing the history of the germ, from this, its simplest and most
homogeneous form, to the assumption of that completed and per-
fected type which is marked by the extreme heterogeneousness of
its different parts, he has another illustration of that law of pro-
gress from the general to the special, which is one of the highest
principles yet attained in the science of Vitality...

MICROSCOPIC STUDY OF ANIMAL DEVELOPMENT. 57

But, further, the Physiologist, not confining his inquiries to
Man, pursues the like researches into the developmental history
of other living beings, and is soon led to the conclusion that the
same is true of them also; each Animal, as well as each Plant,
having the same starting-point in the single cell; and the dis-
tinctive features by which its perfected form is characterized,
how striking and important soever these may be, arising in the
course of its development towards the condition it is ultimately
to present. In the progress of that evolution, those fundamental
differences which mark out the great natural divisions of the
Animal and the Vegetable kingdoms respectively, are the first
to manifest themselves; and the subordinate peculiarities which
distinguish classes, orders, families, genera, and species, succes-
sively make their appearance, usually (but not by any means
constantly) in the order of importance which Systematists have
assigned to them. And it is in thus pursuing, by the aid which
the Microscope alone can afford to his visual power, the history
of the Organic Germ, from that simple and homogeneous form
which seems common to every kind of living being, either ‘to
that complex and most heterogeneous organism which is the
mortal tenement of Man’s immortal spirit, or only to that hum-
ble Protophyte or Protozoon, which lives and grows and multi-
plies witlout showing any essential advance upon its embryonic
type,—that the Physiologist is led to his grandest conception of
the Unity and All-Comprehensive nature of that Creative Design,
of which the development of every individual Organism, from
the lowest to the highest, is a separate exemplification, at once
perfect in itself, and harmonious with every other.

It has been the purpose of the foregoing sketch, to convey an!
idea, not merely of the services which the Microscope has already
rendered to the collector of facts in every department of the Sci-
ence of Life, but also of the value of these facts as a foundation
for philosophical reasoning. For it is when thus utilized, that.
observations, whether made with the Microscope or with the
Telescope, or by any other instrumentality, acquire their highest
value, and excite the strongest interest in the mind. But as it
is not every one who is prepared by his previous acquirements
to appreciate such researches, according to the scientific estimate
of their importance, it may be well now to address ourselves to
that large and increasing number, who are disposed to apply
themselves to Microscopic research as amateurs, following the
pursuit rather as a means of wholesome recreation to their own
minds, than with a view to the extension of the boundaries of
existing knowledge; and to those in particular who are charged,
whether as parents or as instructors, with the direction and train-
ing of the youthful mind.

All the advantages which have been urged at various times,

58 INTRODUCTION.

with so much sense and vigor,! in favor of the study of Natural
History, apply with full force to Microscopical inquiry. What
better encouragement and direction can possibly be given to the
exercise of the observing powers of a child, than to habituate him
to the employment of this instrument upon the objects which
immediately surround him, and then to teach him to search out
novelties among those less immediately accessible? The more
we limit the natural exercise of these powers, by the use of those
methods of education which are generally considered to be spe-
cially advantageous for the development of the Intellect,—the
more we take him from fields and woods, from hills and moors,
from river-side and sea-shore, and shut him up in close school-
rooms and narrow play-grounds, limiting his attention to ab-
stractions, and cutting him off even in his hours of sport from
those sights and sounds of Nature which seem to be the ap-
pointed food of the youthful spirit,—the more does it seem im-
portant that he should in some way be brought into contact with
her, that he should have his thoughts sometimes turned from the
pages of books to those of Creation, from the teachings of Man
to those of God. Now if we attempt to give this direction to
the thoughts and feelings in a merely dédactie mode, it loses that
spontaneousness which is one of its most valuable features. But
if we place before the young a set of objects which cam scarcely
fail to excite their healthful curiosity, satisfying this only so far
as to leave them still inquirers, and stimulating their interest
from time to time by the disclosure of such new wonders as
arouse new feelings of delight, they come to look upon the pur-
suit as an ever-fresh fountain of happiness and enjoyment, and
to seek every opportunity of following it for themselves.

There are no circumstances or conditions of life, which need
be altogether cut off from these sources of interest and improve-
ment. Those who are brought up amidst the wholesome influ-
ences of a country life, have, it is true, the greatest direct oppor-
tunities of thus drawing from the Natural Creation the appropriate
nurture for their own spiritual life. But the very familiarity of
the objects around them, prevents these from exerting their most
wholesome influence, unless they be led to see how much there
is beneath the surface even of what they seem to know best; and
in rightly training them to look for this, how many educational
objects,—physical, intellectual, and moral,—may be answered at
the same time! ‘A walk without an object,” says Mr. Kings-
ley, “unless in the most lovely and novel scenery, is a poor
exercise; and as a recreation utterly nil. If we wish rural walks
to do our children any good, we must give them a love for rural
sights, an object in every walk; we must teach them—and we
can teach them—to find wonder in every insect, sublimity in
every hedge-row, the records of past worlds in every pebble, and

' By none more forcibly than by Mr. Kingsley, in his recent little volume entitled
“ Glaucus, or the Wonders of the Shore.”

EDUCATIONAL VALUE OF THE MICROSCOPE. 59

boundless fertility upon the barren shore; and so, by teaching
them to make full use of that limited sphere in which they now
are, make them faithful in a few things, that they may be fit
hereafter to be rulers over much.” What can be a more effectual).
means of turning such opportunities to the best account, than
the employment of an aid which not only multiplies almost
infinitely the sources of interest presented by the objects with
which our eye® are most familiar, but finds inexhaustible life
where all seems lifeless, ceaseless activity where all seems motion-
less, perpetual change where all seems inert? Turn, on the other
hand, to the young who are growing up in our great towns, in
the heart of the vast Metropolis, whose range of vision is limited
on every side by bricks and mortar, who rarely see a green leaf
or a fresh blade of grass, and whose knowledge of animal life is
practically limited to the dozen or two of creatures that every-
where attach themselves to the companionship of Man, and shape
their habits by his. To attempt to inspire a real love of Nature
by books and pictures, in those who have never felt her influences,
is almost hopeless. A child may be interested by accounts of her
wonders, as by any other instructive narrative; but they have
little of life or reality in his mind,—far less than has the story of
adventure which appeals to his own sympathies, or even than the
fairy tale which charms and fixes his imagination. But here the ,
Microscope may be introduced with all the more advantage, as
being almost the only means accessible under such circumstances,
for supplying what is needed. A single rural or even suburban
walk will afford stores of pleasurable occupation for weeks, in
the examination of its collected treasures. A large glass jar may
be easily made to teem with life, in almost as many and as varied
forms as could be found by the unaided eye in long and toilsome
voyages over the wide ocean; and a never-ending source of
amusement is afforded by the observation of their growth, their
changes, their movements, their habits. The school-boy thus
trained, looks forward to the holiday which shall enable him to
search afresh in some favorite pool, or to explore the wonders of
some stagnant basin, with as much zest as the keenest sportsman
longs for a day’s shooting on the moors, or a day’s fishing in the
best trout stream; and with this great advantage over him,—
that his excursion is only the beginning of a fresh stock of
enjoyment, instead of being in itself the whole.
This is no imaginary picture, but one which we have constantly
“under our eyes; and no argument can be needed to show the
value of such a taste, to such, at least, as have set clearly before
their minds the objects at which they should aim in the great
work of Education. For we have not merely to train the intel-
lectual powers and to develope the moral sense ; but to form those
tastes—those “likes and dislikes’’—which exercise a more abiding
and amore cogent influence on the conduct, than either the
reason or the mere knowledge of duty. It is our object to foster

60 INTRODUCTION,

all the higher aspirations, to keep in check all that is low and de-
grading. But the mind must have recreation and amusement ;
and the more closely it is kept by the system of education adopted,
to the exercise of any one set of powers, the more potent will be
that reaction which will urge it, when restraint is removed, to
activity of some other kind; and the more important is it, that
this reaction should receive a direction to what is healthful and
elevating, instead of to what is weakening and @egrading. It is
quite a mistake to imagine that those evil habits which result
from a wrong exercise of the natural powers, a wrong direction
of the natural tendencies, can be effectually antagonized by the
simple effort at repression. The constant exercise either of ex-
ternal coercion or of internal restraint, tends to keep the atten-
tion directed towards the forbidden object of gratification ; the
malady is only held in check, not cured; and it will break out,
perhaps with augmented force, whenever the perpetually-present
impulses shall derive more than ordinary strength from some
casual occurrence, or the restraining power shall have been tem-
porarily weakened. The only ettectual mode of keeping in
check the wrong, is by making use of these same powers and
tendencies in a right mode ; by finding out objects whereon they
may be beneficially exercised; and by giving them such a direc-
tion and encouragement, as may lead them to expend themselves
upon these, instead of fretting and chafing under restraint, ready.
to break loose at the first opportunity. There is no object on
which the youthful energy can be employed more worthily, than
in the pursuit of Knowledge; no kind of knowledge can be
made more attractive, than that which is presented by the Works
of Creation; no source is more accessible, no fountain more
inexhaustible ; and there is none which affords, both in the mode
of pursuing it, and in its own nature, so complete and beneficial
a diversion from the ordinary scholastic pursuits.

If there be one class more than another, which especially needs
to have its attention thus awakened to such objects of interest,
as, by drawing its better nature into exercise, shall keep it free
from the grovelling sensuality in which it too frequently loses
itself, it is our Laboring population; the elevation of which is
one of the great social problems of the day. On those who are
actively concerned in promoting and conducting its education,
the claims and advantages of the Study of Nature can scarcely
be too strongly urged; since experience has fully proved,—what
might have been a priori anticipated,—that where the taste for
this pursuit has been early fostered by judicious training, it be-
comes so completely a part of the mind, that it rarely leaves the
individual, however unfavorable his circumstances may be to
its exercise, but continues to exert a refining and elevating in-
fluence through his whole subsequent course of life. Now for
the reasons already stated, the Microscope is not merely a most
valuable adjunct in such instruction, but its assistance is essential

EDUCATIONAL USES OF THE MICROSCOPE. 61

in giving to almost every Natural object its highest educational .
value ; and whilst the country Schoolmaster has the best oppor-
tunities of turning it to useful account, it is to the ety School-
master that, in default of other opportunities, its importance as
an educational instrument should be the greatest. It was from
feeling very strongly how much advantage would accrue from
the introduction of a form of Microscope, which should be at
once good enough for Educational purposes, and cheap enough to
find its way into every well-supported School in town and coun-
try, that the Author suggested to the Society of Arts in the
summer of 1854, that it should endeavor to carry out an object
so strictly in accordance with the enlightened purposes which it
is aiming to effect; and this suggestion having been considered
worthy ofadoption, a Committee, chiefly consisting of experienced
Microscopists, was appointed to carry it into effect. It was de-
termined to aim at obtaining two instruments ;—a simple and
low-priced microscope for the use of Scholars, to whom it might
be appropriately given as a reward for zeal and proficiency in the
pursuit of Natural History, not in books, but in the field ;—and
a compound Microscope for the use of Teachers, of capacity sufii-
cient to afford a good.view of every kind of object most likely to
interest the pupil or to be within the reach of the instructor.
Notwithstanding the apprehensions generally expressed, that no
instruments at all likely to answer the intended purpose could
possibly be produced at the prices specified, the result has proved
the fallacy; for among several instruments of greater or less
efficiency, sent in competition for the award, the Committee was
able to select a Simple and a Compound Microscope fully an-°
swering their expectations, and henceforth to be supplied to the
public at a cost so low as to place these instruments (it may be
hoped) within the reach of almost every one to whom they are
likely to be of service. An account of these two Microscopes
will be given hereafter. (Chap. II, §§ 29, 31.)

It is not alone, however, as furnishing an attractive object of
pursuit for the young—fitted at once to excite a wholesome taste
for novelty, ever growing with what it feeds on, and to call forth
the healthful exercise of all those powers, both physical and
mental, which can minister to its gratification,—that Natu-
ral History studies in general, and Microscopie inquiry in
particular, are to be specially commended as a means of intel-
lecttal and moral discipline; for there is no capacity, however
elevated, to which they do not furnish ample material for the
exercise of all its best powers, no period of life which may not
draw from them its purest pleasures. Even to observe well is not:
so easy a thing as some persons imagine. Some are too hasty,
imagining that they can take in everything at a glance, and
hence often forming very erroneous or imperfect notions, which
may give an entirely wrong direction not only to their own views
but to those of others, and may thus render necessary an amount

62 INTRODUCTION.

\of labor for the ultimate determination of the truth, many times
as great as that which would have sufficed in the first instance,
had the original observations been accurately made and faithfully
recorded. Others, again, are too slow and hesitating ; and fix
their attention too much upon details, to be able to enter into
the real significance of what may be presented to the vision.
Although ignorance has doubtless much to do in producing both
these faults, yet they both have their source in mental tendencies
which are not corrected by the mere acquisition of knowledge,
and which are very inimical, not merely to its fair reception, but
also to the formation of a sound judgment upon any subject
whatever. The habit of guarding against them, therefore, once
acquired in regard to Microscopic observation, will be of invalu-
able service in every walk of life. Not less important is it (as
‘has been already shown), to keep our observations free alike
from the bias of preconceived ideas, and from the suggestive
influence of superficial resemblances; and here, too, we find the
training which Microscopical study affords, especially when it is
prosecuted under the direction of an experienced guide, of the
highest value in forming judicious habits of thought and action.
To set the young observer to examine and investigate for him-
self, to tell him merely where to look and (in general terms) what
to look for, to require from him a careful account of what he
sees, and then to lead him to compare this with the descriptions
of similar objects by Microscopists of large experience and un-
questionable accuracy, is not only the best training he can receive
as a Microscopist, but one of the best means of preparing his
mind for the exercise of its powers in any sphere whatever.

It cannot be too strongly or too constantly kept in view, that
the value of the results of Microscopic inquiry will depend far
more upon the sagacity, perseverance, and accuracy of the ob-
server, than upon the elaborateness of his instrument. The most
perfect Microseope ever made, in the hands of one who knows
not how to turn it to account, is valueless; in the hands of a
careless, a hasty, or a prejudiced observer, it is worse than value-
less, as furnishing new contributions to the already large stock
of errors that pass under the guise of scientific truths. On the
other hand, the least costly Microscope that has ever been con-

' structed, how limited soever its powers, provided that it gives no
false appearances, shall furnish to him who knows what may be
done with it, a means of turning to an account, profitable alike
to science and to his own immortal spirit, those hours which
might otherwise be passed in languid ennu?, or in frivolous or
degrading amusements,' and even of immortalizing his name by
the discovery of secrets in Nature as yet undreamed of. A very

1 “T have seen,” says Mr. Kingsley, “the cultivated man, craving for travel and suc-
cess in life, pent up in the drudgery of London work, and yet keeping his spirit calm,
and his morals perhaps all the more righteous, by spending over his Microscope even-
ings which would too probably have gradually been wasted at the theatre.”

EDUCATIONAL USES OF THE MICROSCOPE. 63

large proportion of the great achievements of Microscopic re-
search that have been noticed in the preceding outline, have
been made by the instrumentality of microscopes which would
be generally condemned in the present days as utterly unfit for
any scientific purpose; and it cannot for a moment be supposed,
that the field which Nature presents for the prosecution of in-
quiries with instruments of comparatively limited capacity, has
been in any appreciable degree exhausted. On the contrary,’
what has been done by these ‘and scarcely superior instruments,
only shows how much there is to be done. The author may be
excused for citing, as an apposite example of his meaning, the
curious results he has recently obtained from the study of the
development of the Purpura lapillus (rockwhellx), which will be
detailed in their appropriate anes (Chap. XII); for these were
obtained almost entirely by the aid of single lenses, the Compound
Microscope having been only occasionally applied to, for the
verification of what had been previously worked out, or for the
examination of such minute details as the power employed did
not suffice to reveal.

But it should be urged upon such as are anxious to do service
to science, by the publication of discoveries which they suppose
themselves to have made with comparatively imperfect instru-
ments, that they will do well to refrain from bringing these for-
ward, until they shall have obtained the opportunity of verifying
them with better. It is, as already remarked, when an object is
least clearly seen, that there is most room for the exercise of the
imagination; and there was sound sense in the reply once made
by a veteran observer, to one who had been telling him of won-'
derful discoveries which another was said to have made “zn spite
of the badness of his Microscope,”—“ No, sir, it was in conse-
quence of the badness of his Microscope.” If those who observe,
with however humble an instrument, will but rigidly observe the
rule of recording only what they can elearly see, they can neither
go far astray themselves, nor seriously mislead others.

Among the erroneous tendencies which Microscopic inquiry
seems especially fitted to correct, is that which leads to the esti-
mation of things by their merely sensuous or material greatness,
instead of by their value in extending our ideas and elevating
our aspirations. For we cannot long scrutinize the “world of
small” to which we thus find access, without having the convic-
tion forced upon us, that all size is but relative, and that mass
has nothing to do with real grandeur. There is something in
the extreme of minuteness, which is no less wonderful,—might
it not almost be said, no less majestic ?—than the extreme of
vastness. If the mind loses itself in the contemplation of the
immeasurable depths of space, and of the innumerable multi-
tudes of stars and systems by which they are peopled, it is equally
lost in wonder and admiration, when the eye is turned to those
countless multitudes of living beings which a single drop of

64 INTRODUCTION.

water may c8ntain, and when the attention is given to the won-
drous succession of phenomena which the life-history of every
individual among them exhibits, and to the order and constancy
‘which this presents. Still more is this the case, when we direct
our scrutiny to the penetration of that universe which may be
said to be included in the body of Man, or of any one of the
higher forms of organized being, and survey the innumerable
assemblage of elementary parts, each having its own independent
life, yet each working in perfect harmony with the rest, for the
completion of the wondrous aggregate which the life of the whole
presents. In the study of the one class of phenomena, no less
than in the survey of the other, we are led towards that Infinity,
in comparison with which the greatest and the least among the
objects of Man’s regard are equally insignificant; and in that
Infinity alone can we seek for a Wisdom to design, or a Power
to execute, results so vast and so varied, by the orderly co-opera-
tion of the most simple means.

e
CHAPTER I.
OPTICAL PRINCIPLES OF THE MICROSCOPE.

1. Att Microscopes in ordinary use, whether simple or com-
pound, depend for their magnifying power on that influence
exerted by lenses in altering the course of the rays of light pass-
ing through them, which is termed refraction. This influence
takes place in accordance with the two following laws, which
are fully explained and illustrated in every elementary treatise
on. optics.?

I. A ray of light passing from a rarer into a denser medium,
is refracted towards a line drawn perpendicularly to the plane
which divides them; and vice versa.

II. The sines of the angles of inetdence and refraction (that. is,
of the angles which the ray makes with the perpendicular before
and after its refraction) bear to one another a constant ratio for
each substance, which is known as its index of refraction.

It follows from the first of these laws, that a ray of light enter-
ing any denser medium perpendicularly, undergoes no refraction,
but continues in its straight course; and from the second, that
the rays nearest the perpendicular are refracted less than those
more distant from it. The “index of refraction” is determined
for different substances, by the amount of the refractive influence
which they exert upon rays passing into them, not from air, but
from a vacuum; and in expressing it, the sine of the angle of
refraction is considered as the unzt, to which that of the angle of
incidence bears a fixed relation. Thus when we say that the
“index of refraction” of Water is 1:336, we mean that the sine
of the angle of incidence of a ray passing into water from a
-vacuum, is to that of the angle of refraction, as 1:336 to 1, or
almost exactly as 14 to 1, or as 4to 3. And thus, the angle of
incidence being given, that of the angle of refraction may be
found by dividing it by the index of refraction.

2. On the other hand, when a ray emerges from a dense
medium into a rare one, it is bent from the perpendicular, accord-

‘It is not considered necessary in the present Treatise, to describe the reflecting
Microscope of Amici; since this, although superior to the Microscopes in use previously
to its introduction, has been completely superseded by the application of the Achromatic
principle to the ordinary Microseope.

2 See especially Dr. Golding Bird's “ Manual of Natural Philosophy,” Chap, XXII.
5

e

66 OPTICAL PRINCIPLES OF THE MICROSCOPE,

ing to the same ratio; and to find the course of the emergent
ray, the sine of the angle of incidence must be multiplied by the
“index of refraction,” which will give the sine of the angle of
refraction. Now when an emergent ray falls very obliquely upon
the surface, the refraction which it woyld sustain in passing
forth, tending as it does to deflect it still farther from the per-
pendicular, becomes so great that the ray cannot pass out at all,
and is reflected back from the plane which separates the two
media, into the one from which it was emerging. This internal
reflection will take place, whenever the product of the sine of the
angle of incidence, multiplied by the index of refraction, exceeds
the sine of 90°, which is the radius of the circle; and therefore
the “limiting angle,” beyond which an oblique ray suffers in-
ternal reflection, varies for different substances in proportion to
their respective indices of refraction. Thus, the index of refrac-
tion of water being 1-336, no ray can pass out of it into a vacuum,"
if its angle of incidence exceed 48° 28’, since the sine of that
angle, multiplied by 1-336, equals the radius; and in like manner,
the “limiting angle” for flint-glass, its index of refraction being
1:60, is 88° 41’. This fact imposes certain limits upon the
performance of microscopic Lenses; whilst at the same time it
enables the optician to make most advantageous use of glass
Prisms for the purpose of reflection; the proportion of the light
which they throw back being much greater than that returned
from the best polished metallic surfaces, and the brilliancy of the
reflected image being consequently higher. Such prisms are of
great value to the Microscopist for particular purposes, as will
hereafter appear (§§ 40, 41, 57, 60).

3. The lenses employed in the construction of Microscopes are
chiefly convex ; those of the opposite kind, or coneave, being only
used to make certain modifications in the course of the rays pass-
ing through convex lenses, whereby their performance is rendered
more exact (§§ 10, 12). It is easily shown to be in accordance
with the laws of refraction already cited, that when a “pencil” of
parallel rays, passing through air, impinges upon a conver surface
of glass, the rays will be made to converge; for they will be bent
towards the centre of the circle, the radius being the perpendicu-
lar to each point of curvature. The central or axial ray, as it
coincides with the perpendicular, will undergo no refraction; the
others will be bent from their original course in an increasing *
degree, in proportion as they fall at a distance from the centre of
the lens; and the effect upon the whole will be such, that they
will be caused to meet at a point, called the focus, some distance
beyond the centre of curvature. This effect will not be materi-

‘ The reader may easily make evident to himself the internal reflection of water, by
nearly filling a wineglass with water, and holding it at a higher level than his eye, so
that he sees the surface of the fluid obliquely from beneath; no object held above the
water will then be visible through it, if the eye be placed beyond the limiting angle;

whilst the surface itself will appear as if silvered, through its reflecting back to the eye
the light which falls upon it from beneath.

REFRACTION BY CONVEX LENSES. 67

ally changed by allowing rays to pass into air again through
a plane surface of glass, perpendicular to the axial ray (Fig. 1);
a lens of this description is called a plano-convex lens; and it
will hereafter be shown to possess properties, which render it
very useful in the construction of microscopes. But if, instead
of passing through a plane surface, the rays re-enter the air
through a second convex surface, turned in the opposite direction,
as in a double-convex lens, they will be made to converge still
more. This will be readily comprehended, when it is borne in
mind that the contrary direction of the second surface, and the

Fic. 1. Fie. 2.

a

Parallel rays, falling on a plano-convez lens, Parallel rays, falling on a double-convex lens,
brought to a focus at the distance of its diameter; brought to a focus in its centre ; conversely, rays

and conversely, rays diverging from that point, diverging from that point, rendered parallel.
rendered parallel. .

contrary direction of its refraction (this being from the denser me-
dium instead of into it), antagonize each other ; so that the second
convex surface exerts an influence on the course of the rays pass-
ing through it, which is almost exactly equivalent to that of the
first. Hence the focus of a double-convex lens will be just half
the distance, or (as commonly expressed) will be at half the
length, of the focus of a plano-convex lens having the same cur-
vature on one side (Fig. 2).

4. The distance of the focus from the lens will depend, not
merely upon its degree of curvature, but also upon the refracting
power of the substance of which it may be formed; since the
lower the index of refraction, the less will the oblique rays be
deflected towards the axial ray, and the more remote will be their
point of meeting ; and conversely, the greater the refractive index,
the more will the oblique rays be deflected towards the axial ray,
and the nearer will be their point of convergence. A lens made
of any substance whose index of refraction is 1:5, will bring
parallel rays to a focus at the distance of its diameter of curva-
ture, after they have passed through one convex surface (Fig. 1),
and at the distance of its radius of curvature, after they have
passed through éwo convex surfaces (Fig. 2); and as this ratio
almost exactly expresses the refractive power of ordinary Glass,
we may for all practical purposes consider the “principal focus”
(as the focus for parallel rays is termed), of a double-convex lens

68 OPTICAL PRINCIPLES OF THE MICROSCOPE,

to be at the distance of its radius, that is, in its centre of ctirva-
ture, and that of a plano-convex lens to be at the distance of twice
its radius, that is, at the other end of the diameter of its sphere of
curvature.

5. It is evident from what has preceded, that as a double-con-
vex lens brings parallel rays to a focus in its centre of curvature,
it will on the other hand cause those rays to assume a parallel
direction, which are diverging from that centre before they im-
pinge upon it (Fig. 2); so that, if a luminous body be placed in the
principal focus of a double-convex lens, its divergent rays, falling
on one surface of the lens as a cone, will pass forth from its other
side as a cylinder. Again, if rays already converging fall upon a
double-convex lens, they will be brought together at a point
nearer to it than its centre of curvature (Fig. 3); whilst, if the
incident rays be diverging from a distant point, their focus will
be more distant from the lens than its principal focus (Fig. 4).

Fia. 3. Fia. 4.

Rays already converging. brought to- Rays diverging from points more distant than the
gether at a point nearer than the principal principal focus on either side, brought to a focus be-
focus; and rays diverging from a point yond it; if the point of divergence be within the circle
within the principal focus, still diverging, of curvature, the focus of convergence will be beyond
though in a diminished degree. it; and vice versa,

The further from the point from which they diverge, the more
nearly will the rays approach the parallel direction; until, at
length, when the object is very distant, its rays in effect become
parallel, and are brought together in the principal focus. If the
rays which fall upon a double-convex lens, be diverging from the
farther extremity of the diameter of its sphere of curvature, they
will be brought to a focus at an equal distance on the other side
of the lens; but the more the point of divergence is approximated
to the centre or principal focus, the further removed on the other
side will be the point of convergence, until, the point of diver-
gence being at the centre, there is no convergence at all, the rays
being merely rendered parallel. If the point of divergence be
within the principal focus, they will neither be brought to eon-
verge nor be rendered parallel, but will diverge in a diminished
degree (Fig. 3). The same principles apply equally to a plano-
convex lens; allowance being made for the double distance of its
principal focus. They also apply to a lens whose surfaces have

REFRACTION BY CONVEX AND CONCAVE LENSES. 69

different curvatures; the principal focus of such a lens is found
by multiplying the radius of one surface by the radius of the
other, and dividing this product by half the sum of the same
radii. The rules by which the foci of convex lenses may be
found, for rays of different degrees of convergence and diver-
gence, will be found in works on Optics.

6. The refracting influence of concave lenses will evidently be
precisely the opposite of that of convex. Rays which fall upon
them in a parallel direction, will be made to diverge as if from
the principal focus, which is here called the negative focus. This
will be, for a plano-concave lens, at the distance of the diameter
of the sphere of curvature; and for a double-concave, in the
centre of that sphere. In the same manner, rays which are con-
verging to such a degree, that, if uninterrupted, they would have
met in the principal focus, will be rendered parallel; if con-
verging more, they will still meet, but at a greater distance ; and
if converging less, they will diverge as from a negative focus at
a greater distance than that for parallel rays. If already diverg-
ing, they will diverge still more, as from a negative focus nearer
than the principal focus; but this will approach the principal
focus, in proportion as the distance of the point of divergence
is such, that the direction of the rays approaches the parallel.

7. If a lens be convex on one side and concave on the other,
forming what is called a meniscus, its effect will depend upon the
proportion between the two curvatures. If they are equal, as
in a watch glass, no perceptible effect will be produced; if the
convex curvature be the greater, the effect will be that of a less
powerful conver lens: and if the concave curvature be the more
considerable, it will be that of a less powerful concave lens. The
focus of convergence for parallel rays in the first case, and of
divergence in the second, may be found by dividing the product,
of the two radii by half their difference.

8. Hitherto we have considered only the effects of lenses upon
a “pencil” of rays issuing from a single luminous point, and
that point situated in the line of its axis. Ifthe point be situated
above the line of its axis, the focus will be below it, and vice versd.
The surface of every luminous body may be regarded as compre-
hending an infinite number of such points, from every one of
which a pencil of rays proceeds, and is refracted according to the
laws already specified; so that a perfect but inverted image or
picture of the object is formed upon any surface placed in the
focus, and adapted to receive the rays. It will be evident from
what has gone before, that if the object be placed at twice the
distance of the principal focus, the image, being formed at an
equal distance on the other side of the lens (§ 5), will be of the
same dimensions with the object: whilst, on the other hand, if
the object (Fig. 5, a 6) be nearer the lens, the image 4 B will be
farther from it, and of larger dimensions; but if the object a B
be farther from the lens, the image ad will be nearer to it, and

70 OPTICAL PRINCIPLES OF THE MICROSCOPE.

smaller than itself. Further, it is to be remarked, that the
larger the image in proportion to the object, the less bright it

Fic. 5. will be, because the same
amount of light has to be
spread over a greater sur-
face ; whilst an image that
is smaller than the object,
will be more brilliant in
the same proportion.

9. The knowledge of
these general facts will en-
able us readily to under-
stand the ordinary opera-
tion of the Microscope; but the instrument is subject to cer-
tain optical imperfections, the mode of remedying which can-
not be comprehended without an acquaintance with their
nature. One of these imperfections results from the une-
qual refraction of the rays which have passed through lenses,
whose curvatures are equal over their whole surfaces. If
the course of the rays passing through an ordinary convex
lens be carefully laid down (Fig. 6), it will be found that

Fic. 6. they do not all meet exactly

_in the foci already stated,

AWB but that the focus F of the
»- ~ rays AB, AB, which have

“—ren F passed through the periphe-
= F SSS ral portion of the lens, is
much closer to it than that

B of the rays ad, a5, which are
nearer the line of its axis;

Diagram illustrating Spherical Aberration. so that, if a sereen be held
in the former, the rays which have passed through the central
portion of the lens will be stopped by it before they have come
to a focus; and if the screen be carried back into the focus of the
latter, the rays which were most distant from the axis will have
previously met and crossed, so that they will come to it in a state
of divergence, and will pass to¢ and d. In either case, there-
fore, the image will have a certain degree of indistinctness ; and
there is no one point to which all the rays can be brought by a
single lens of spherical curvature. The difference between the
focal points of the central and of the peripheral rays, is termed
the Spherical Aberration. Itis obvious that, to produce the de-
sired effect, the curvature requires to be increased around the
centre of the lens, so as to bring the rays which pass through it
more speedily to a focus; and to be diminished towards the cir-
cumference, so as to throw the focus of the rays influenced by it
to a greater distance. The requisite conditions may be theoreti-
cally fulfilled by a lens, one of whose surfaces, instead of being
spherical, should be a portion of an elfipsoid or hyperboloid of

Formation of Images by convex lenses.

SPHERICAL AND CHROMATIC ABERRATION, 71

certain proportions; but the difficulties in the way of the mecha-
nical execution of lenses of this description are such, that, for
practical purposes, this plan of construction is altogether un-
available.

9 a. Various means have been devised for reducing the Aber-
ration of lenses of spherical curvature. It may be considerably
diminished, by making the most advantageous use of ordinary
lenses. Thus, the aberration of a plano-convex lens, whose con-
vex side is turned towards parallel rays, is only jy ths of its
thickness; whilst, if its plane side be turned towards them, the
aberration is 44 times the thickness of the lens. Hence, in the
employment of a plano-convex lens, its convex surface should be
turned towards a distant object, when it is used to form an image
by bringing to a focus parallel or slightly diverging rays; but it
should be turned towards the eye, when it is used to render
parallel the rays which are diverging from a very near object.
The single lens having the least spherical aberration, is a.double-
convex whose radii are as one to six: when its flattest face is
turned towards parallel rays, the aberration is nearly 34 times
its thickness; but when its most convex side receives or trans-
mits them, the aberration is only ;3,ths of its thickness. The
aberration is further diminished, by reducing the aperture or
working-surface of the lens, so as to employ only the rays that
pass through the central part, which, if sufficiently small in pro-
portion to the whole sphere, will bring them all to nearly the
same focus. The use of this may be particularly noticed in the
object-glasses of common (non-achromatic) Microscopes; in
which, whatever be the size of the lens itself, the greater portion
of its surface is rendered inoperative by a stop, which is a plate
with a circular aperture interposed between the lens and the rest
of the instrument. If this aperture be gradually enlarged, it
will be seen that, although the image becomes more and more
illdminated, it is at the same time becoming more and more in-
distinct; and that, in order to gain defining power, the aperture
must be reduced again. Now this reduction is attended with
two great inconveniences ; im the first place, the loss of intensity
of light, the degree of which will depend upon the quantity
transmitted by the lens, and will vary, therefore, with its aper-
ture; and, secondly, the diminution of the “angle of aperture,”’
that is, of the angle (a6, Fig. 8) made by the most diverging of
the rays of the pencil issuing from any point of an object, which
can enter the lens; on the extent of which angle depend some
of the most important qualities of a Microscope (§ 100).

10. The Spherical Aberration may be got rid of altogether,
however, by making use of combinations of lenses, so disposed
that their opposite aberrations shall correct each other, whilst
magnifying power is still.gained. For it is easily seen that, as
the aberration of a concave lens is just the opposite of that of a
convex lens, the aberration of a convex lens placed in its most

ee OPTICAL PRINCIPLES OF THE MICROSCOPE.

favorable position may be corrected by a concave lens of much
less power in its most unfavorable position; so that, although
the power of the convex lens is weakened, all the rays which
pass through this combination will be brought to one focus. It
is by a method of this kind, that the Optician aims to correct the
spherical aberration, in the construction of those combinations
of lenses which are now employed as object-glasses, in all Com-
pound Microscopes that are of any real value as instruments of
observation. But it sometimes happens that this correction is
not perfectly made; and the want of it becomes evident, in the
fog by which the distinctness of the image of the object, and
especially the precision of its outlines, is obscured.

11. But the spherical aberration is not the only imperfection
with which the optician has to contend in the construction of
microscopes. A difficulty equally serious arises from the unequal
refrangibility of the several colored rays, which together make
up white or colorless light,' so that they are not all brought to
the same focus, even by a lens free from spherical aberration.
It is this difference in their refrangibility, which causes their
complete separation by the prism into a spectrum; and it mani-
fests itself, though in a less degree, in the image formed by a
convex lens. For if parallel rays of white light fall upon a con-
vex surface, the most refrangible of its component rays, namely,
the violet, will be brought to a focus at a point somewhat nearer
to the lens than the principal focus, which is the mean of the
whole; and the converse will be true of the red rays, which are
the least refrangible, and whose foeus will therefore be more dis-
tant. Thus in Fig. 7, the rays of white light, az, a B, which fall

on the peripheral portion

of the lens, are so far de-
composed, that the violet

FE rays are brought to a focus
y == p> at co, and crossing thére,
ad = diverge again and pass on
el ee = towards FF. On the other
* hand, the red rays are not

brought to a focus until D,

Diagram illustrating Chromatic Aberration. and cross the diverging
violet rays atu E. The foci of the intermediate rays of’ the spec-
trum (indigo, blue, green, yellow, and orange) are intermediate
between these two extremes. If the image be received upon a
sereen placed at c, the focus of the violet rays, violet will pre-
dominate in its own color, and it will be surrounded by a pris-
matic fringe in which blue, green, yellow, orange, and red may
be successively distinguished. If, on the other hand, the screen
be placed at p, the focus of the red rays, the image will have a

Fia, 7.

‘It has been deemed better to adhere to the ordinary phraseology, when speaking of
this fact, as more generally intelligible than the language in which it might be more
scientifically described, and at the same time leading to no practical error.

CHROMATIC ABERRATION. 73

predominantly red tint, and will be surrounded by a series of
colored fringes in inverted order, formed by the other rays of the
spectrum, which have met and crossed.! The line £ £, which
joins the points of intersection between the red and the violet
rays, marks the “mean focus,” that is the situation in which the
colored fringes will be narrowest, the “‘dispersion’’ of the colored
rays being the least; whilst the interval c p, which separates the
foci of the extreme rays, is termed the Chromatic Aberration of
the lens. As the axial ray a’ B’ undergoes no refraction, neither
does it sustain any dispersion; and the nearer the rays are to
the axial ray, the less dispersion do they suffer. Again, the
more oblique the direction of the rays, whether they pass through
the central or the peripheral portion of the lens, the greater will
be the refraction they undergo, and the greater also will be their
dispersion; and thus it happens that when, by using only the
central part of a lens (§ 12), the chromatic aberration is reduced
to its minimum, the central part of a picture may be tolerably
free from false colors, whilst its marginal portion shall exhibit
broad fringes.’

12. The Chromatic Aberration of a lens, like the Spherical,
may be diminished by the contraction of its aperture, so that
only its central portion is employed. But the error cannot be
got rid of entirely by any such reduction, which, for the reasons
already mentioned, is in itself extremely undesirable. Hence it
is of the ‘first importance in the construction of a really efficient
Microscope, that the chromatic aberration of its “object-glasses”
(in which the principal dispersion is liable to occur) should be
entirely corrected, so that the largest possible aperture should be
given to these lenses, without the production of any false colors.
No such correction can be accomplished even theoretically in a
single lens; but it may be effected by the combination of two or
more, advantage being taken of the different relations which the
refractive and the dispersive powers bear to each other in different
substances. For if we can unite with a convex lens, whose dis-
persive power is dow as compared with its refractive power, a
concave of lower curvature, whose dispersive power is relatively
high, it is obvious that the dispersion of the rays occasioned by
the convex lens may be effectually neutralized by the opposite
dispersion of the concave (§ 6); whilst the refracting power of
the convex is only lowered by the opposite refraction of the con-
cave, in virtue of the longer focus of the latter. No difficulty
stands in the way of carrying this theoretical correction into
practice. For the “dispersive” power of flint-glass bears so
much larger a ratio to its refractive power than does that of

! This experiment is best tried with a lens of Jong focus, of which the central part is
eovered with an opaque stop, so that the light passes only through a peripheral ring;
since, if its whole aperture be in use, the regular formation of the fringes is interfered
with by the spherical aberration, which gives a different focus to the rays passing through

each annular zone. 2
2 This is well seen in the large pictures exhibited by Oxy-hydrogen Microscopes.

74 OPTICAL PRINCIPLES OF THE MICROSCOPE.

erown-glass, that a convex lens of the former, the focal length of
which is 72 inches, will produce the same degree of color as a
convex lens of crown-glass, whose focal length is 43 inches.
Hence a concave lens of the former material and curvature, will
fully correct the dispersion of a convex lens of the latter; whilst
it diminishes its refractive power only to such an extent as to
make its focus 10 inches. The correction for chromatic aberra-
tion in such a lens would be perfect, if it were not that, although
the extreme rays, violet and red, are thus brought to the same
focus, the dispersion of the rest is not equally compensated; so
that what is termed a secondary spectrum is produced, the images
of objects seen through such a lens being bordered on one side
with a purple fringe, and on the other with a green fringe.
Moreover such a lens is not corrected for spherical aberration ;
and it must of course be rendered free from this, to be of any
real service, however complete may be the freedom of its image
from false colors. The double correction may be accomplished
theoretically by the combination of three lenses, namely, a double-
concave of flint placed between two double-convex of crown,
ground to certain curvatures; and this method has long been
employed in the construction of the large object-glasses of Tele-
scopes, which are, by means of it, rendered Achromatic,—that is,
are enabled to exert their refractive power without producing
either chromatic or spherical aberration.

13. It has only been of late years, however, that the construc-
tion of Achromatic object-glasses for Microscopes has been con-
sidered practicable; their extremely minute size having been
thought to forbid the attainment of that accuracy which is neces-
sary in the adjustment of the several curvatures, in order that
the errors of each separate lens which enters into the combina-
tion, may be effectually balanced by the opposite errors of the
rest. The first successful, attempt was made in this direction, in
the year 1823, by M. Selligues of Paris; the plan which he
adopted being that of the combination of two or more pairs of
lenses, each pair consisting of a double-convex of crown-glass,
and a plano-concave of flint. In the next year, Mr. Tulley of
London, without any knowledge of what M. Selligues had ac-
complished, applied himself (at the suggestion of Dr. Goring) to
the construction of achromatic object-glasses for the microscope ;
and succeeded in producing a single combination of three lenses
(on the telescope plan), the corrections of which were extremely
complete. This combination, however, was not of high power,
nor of large angular aperture; and it was found that these ad-
vantages could not be gained, without the addition of a second
combination. Prof. Amici at Modena, also, who attempted the
construction of microscopic object-glasses as early as 1812, but,
despairing of success, had turned his attention to the application
of the reflecting principle to the Microscope, resumed his original
labors on hearing of the success of M. Selligues; and, by work-

ACHROMATIC OBJECT-GLASS. 75

ing on his plan, he produced, in 1827, an achromatic combination
of three pairs of lenses, which surpassed anything of the same
kind that had been previously executed. From that time, the
superiority of the plan of combining three pairs of lenses (Fig. 8;
1, 2, 3), which should be so adjusted as to correct each other’s
errors, to the telescopic combinations adopted
by Mr. Tulley, may be considered to have been
completely established; and English opticians,
working on this method, soon rivalled the best
productions of Continental skill.

14. It was in this country that the next im-
portant improvements originated; these being
the result of the theoretical investigations of
Mr. J. J. Lister,’ which led him to the discovery
of certain properties in achromatic combinations,
that had not been previously detected. Acting
upon the rules which he laid down, practical b
opticians at once succeeded in producing com- Section of an Achromatic
binations far superior to any which had been = M18
previously executed, both in wideness of aperture, flatness of
field, and perfectness of correction; and continued progress has
been since made in the same direction, by the like combination
of theoretical acumen with manipulative skill.2 For the subse-
quent investigations of Mr. Lister have led him to suggest new
combinations, which have been speedily carried into practical
execution; and there is good reason to believe that the limit of
perfection has now been nearly reached, since almost everything
which seems theoretically possible has been actually accom-
plished. The most perfect combinations at present in use for
high powers, consist of as many as ezght distinct lenses; namely,
in front, a triplet composed of two plano-convex lenses of crown-
glass, with a plano-concave of dense flint between them; next,
a doublet, composed of a double-convex of crown, and a double-

Fig. 8.

1 See his Memoir in the “ Philosophical Transactions,” for 1829.

2 The first British Opticians (after Mr. Tulley) who applied themselves to the con-
struction of Achromatic object-glasses for microscopes, were Mr. Ross and Mr. Powell.
Mc. James Smith did not enter the field until] some time afterwards; but, having the
advantage of Mr. Lister's special superintendence, he soon equalled, in the lower
powers at least, the best productions of his predecessors. With Mr. Ross, his son bas
been subsequently associated: with Mr. Powell, his brother-in-law, Mr. Lealand ; and
with Mr. Smith, Mr. Beck, a nephew of Mr. Lister. These three firms have constantly
kept up an honorable rivalry, which has been very advantageous to the perfectionnement
of the Microscope; and have maintained a position which is still far in advance of that
of all other manufacturing Opticians in this country or the Continent. The lenses pro-
duced by each are distinguished by excellencies of their own; and it would be scarcely
possible fairly to assign an absolute preference to either above the others. Among the
amateurs who have occupied themselves in the construction of microscopic Achromatics,
Mr. Wenham has been the most successful. An American rival has recently been
announced, in the person of Mr. Spencer; who, taking advantage of all that had been
previously accomplished, is said to have produced combinations not only equalling, but,
in some important particulars, surpassing those of English makers. Only one of these,
however, has found its way (the author believes) 10 this country; and not having had
the opportunity of seeing it himself, be can only judge of it by report. (See Appendix.)

76 OPTICAL PRINCIPLES OF THE MICROSCOPE.

concave of flint; and at the back, another triplet, consisting of
two double-convex lenses of crown, with a double-concave of
flint interposed between them. By the use of this combination,
an angular aperture of no less than 170° has been obtained with
an objective of 1-12th inch focus; and it is obvious that as an
increase of divergence of no more than 10° would bring the ex-
treme rays into a straight line with each other, they would not
enter the lens at all; so that no further enlargement of the aper-
ture can be practically useful.

15. The enlargement of the angle of aperture, and the greater
‘completeness of the corrections, first obtained by the adoption of
| Mr. Lister’s principles, soon rendered sensible an imperfection in
‘the performance of these lenses under certain circumstances
which had previously passed
unnoticed ; and the important
discovery was made by Mr.
Ross, that a very obvious dif:
ference existed in the precision
of the image, according as the
object is viewed with or with-
out a covering of tale or thin
glass; an object-glass which is
perfectly adapted to either of
these conditions, being sensi-
bly defective under the other.
The mode in which this differ
ence arises, is explained by
Mr. Ross as follows.! Let 0,

Fig. 9, be any point of an object; o p the axial ray of the pencil
that diverges from it; and o1, 01’, two diverging rays, the one
near to, the other remote from, the axialray. Now ife@e@aeé
* represent the section of a piece of thin glass, intervening between
the object and the object-glass, the rays o T and o 1’ will be re-
fracted in their passage through it, in the directions TR, 1’ RB’;
and on emerging from it again, they will pass on towards E and
BE’, Now if the course of these emergent rays be traced back-
wards, as by the dotted lines, the ray ZR will seem to have issued
from x, and the ray 8’ R’ from y; and the distance x y is an
aberration quite sufficient to disturb the previous balance of the
aberrations of the lens composing the object-glass. The requi-
site correction may be effected, as Mr. Ross pointed out, by giv-
ing to the front pair (Fig. 8,1) of the three of which the objective
is composed, an excess of positive aberration (7. e. by under-cor-
recting it), and by giving to the other two pairs (2, 3) an excess of
negative aberration (¢.e. by over-correcting them), and by making
the distance between the former and the latter susceptible of
alteration. For when the front pair is approximated most nearly
to the other two, and its distance from the object is increased,

Fig. 9.

' “ Transactions of the Society of Arts,” vol. li.

CORRECTION FOR COVERING OF THE OBJECT. 17

its positive aberration is more strongly exerted upon the other
pairs, than it is when the distance between the lenses is increased,
and the distance between the front pair and the object is dimi-
nished. Consequently, if the lenses be so adjusted that their cor-
rection is perfect for an uncovered object, the front pair being
removed to a certain distance from the others, its approximation
to them will give to the whole combination an excess of positive
aberration, which will neutralize the negative aberration occa-
sioned by covering the object with a thin plate of glass.1' It is
obvious that this correction will be more important to the perfect
performance of the combination, the larger is its angle of aper-
ture; since, the wider the divergence of the oblique rays from
the axial ray, the greater will be the refraction which they will
sustain in passing through a plate of glass, and the greater there-
fore will be the negative aberration produced, which will, if un-
corrected, seriously impair the distinctness of the image. And
it is consequently not required for low powers, whose angle of
aperture is comparatively small; nor even for the higher, so long
as their angle of aperture does not exceed 50°. As a large pro-
portion of the lenses made by foreign Opticians do not range
beyond this, the adjustment in question may be dispensed with;
and even where the angle is much larger, if the corrections be
made perfect for a thickness of glass of 1-100th of an inch (which
is about an average of that with which objects of the finer kind
are usually covered), they will not be much deranged by a dif
ference of a few hundredths of an inch, more or less, in that
amount. .

16. We are now prepared to enter upon the application of the
optical principles which have been explained and illustrated in
the foregoing pages, to the construction of microscopes. These
are distinguished as simple, and compound ; each kind having its
peculiar advantages to the Student of Nature. Their essential
difference consists in this ;—that in the former, the rays of light
which enter the eye of the observer proceed directly from the
object itself, after having been subject only to a change in their
course; whilst in the latter, an enlarged image of the object is
formed by a lens, which image is viewed by the observer through
a simple microscope, as if it were the object itself. The simple
* microscope may consist of one lens; but (as will be presently
shown) it may be formed of two, or epyen three; these, however,
are so disposed as to produce an action upon the rays of light
corresponding to that of a single lens. In the compound micro-
scope, on the other hand, not less than two lenses must be em-
ployed; one to form the enlarged image of the object, and this,
being nearest to it, is called the object-glass; whilst the other
again magnifies that image, being interposed between it and the
eye of the observer, and is hence called the eye-glass. A perfect

! The mode in which this adjustment is effected, will be more fitly described here-
after (§ 82).

78 OPTICAL PRINCIPLES OF THE MICROSCOPE.

object-glass, as we have seen, must consist of a combination of
lenses ; and the eye-glass, as we shall presently see (§ 21), is best
constructed by placing two lenses in a certain relative position,
forming what is termed an eye-piece. These two kinds of in-
strument need to be separately considered in detail. _

17. Simple Microscope.—In order to gain a clear notion of the
mode in which a single lens serves to “magnify” minute objects,
it is necessary to revert to the phenomena of ordinary vision.
An eye free from any defect has a considerable power of adjust-
ing itself, in such a manner as to gain a distinct view of objects
placed at extremely varying distances; but the image formed
upon the retina will of course vary in size with the distance of
the object; and the amount of detail perceptible in it will fol-
low the same proportion. To ordinary eyes, however, there is
a limit within which no distinct image can be formed, on account
of the too great divergence of the rays of the different pencils
which then enter the eye ; since the eye is usually adapted to re-
ceive, and to bring to a focus, rays which are parallel or but
slightly divergent. This limit is variously stated at from five to
ten inches; we are inclined to think from our own observations,
that the latter estimate is nearest the truth; that is, although a
person with an ordinary vision may see an object much nearer to
his eye, he will see little if any more of its details, since what is
gained in size will be lost in distinctness. Now the utility of a
convex lens interposed between a near object and the eye, con-
sists in its reducing the divergence of the rays forming the seve-
ral pencils which issue from it; so that they enter the eye ina
state of moderate divergence, as if they had issued from an ob-
ject beyond the nearest limit of distinct vision; and a well-de-
fined picture is consequently formed upon the retina. But not
only is the course of the several rays in each pencil altered as
regards the rest, by this refracting process, but the course of the
pencils themselves is changed, so that they enter the eye under
an angle corresponding with that at which they would have ar-
rived from a larger object situated ata greater distance. The
picture formed upon the retina, therefore, by any object (Fig. 10),

Fic. 10. corresponds in all respects
with one which would have
been made by the same ob-
ject a 6 increased in its di-
mensions to A B, and view-
ed at the smallest ordinary
distance of distinct vision.
A “short-sighted” person,
however, who can see ob-
jects distinctly at a distance
of two or three inches, has
the same power in his eye
Diagram illustrating the action of the Simple Microscope. alone, by reason ‘of ve

greater convexity, as that which the person of ordinary vision

SIMPLE MICROSCOPE. 79

gains by the assistance of a convex lens which shall enable him
to see at the same distance with equal distinctness. It is evident,
therefore, that the magnifying power of a single lens, depending
as it does upon the proportion between the distance at which it
renders the object visible, and the nearest distance of unaided.
distinct vision, must be different to different eyes. ‘It is usually
estimated, however, by finding how many times the focal length
of the lens is contained in ten inches; since, in order to render
the rays from the object nearly parallel, it must be placed nearly
in the focus of the lens (Fig. 2); and the picture is referred by
the mind to an object at the ordinary distance. Thus, if the
focal length of a lens be one inch, its magnifying power for each
dimension will be ten times, and consequently a hundred super-
ficial ; if its focal distance be only one-tenth of an inch, its mag-
nifying power will be a hundred linear, gr ten thousand superti-
cial. ‘The use of the convex lens has the further advantage of
bringing to the eye a much greater amount of light, than would
have entered the pupil from the enlarged object at the ordinary
distance, provided its own diameter be greater than that of the
pupil; but this can only be the case when its magnifying power
is low.

18. It is obviously desirable, especially when lenses of very
high magnifying power are being employed, that their aperture
should be as large as possible; since the light issuing from a
minute object has then té be diffused over a large picture, and
will be proportionally diminished in intensity. But the shorter
the focus, the less must be the diameter of the sphere of which
the lens forms a part ; and unless the aperture be proportionally
diminished, the spherical and chromatic aberrations will inter-
fere so much with the distinctness of the picture, that the ad-
vantages: which might be anticipated from the use of such lenses
will be almost negatived. Nevertheless, the Simple Microscope
has been an instrument of extreme value in anatomical research,
owing to its freedom from those errors to which the Compound
Microscope, as originally constructed, was necessarily subject ;
the greater certainty of its indications being evident from the
fact, that the eye of the observer receives the rays sent forth by
the object itself, instead of those which proceed from an image
of that object. A detail of the means employed by different
individuals,#for procuring lenses of extremely short focus, though
possessing much interest in itself, would be misplaced here;
since recent improvements, as will presently be shown, have
superseded the necessity of all these. It may be stated, how-
ever, that Leeuwenhoeck, De la Torre, and others among the
older microscopists, made great use of small globules procured
by fusion of threads or particles of glass. The most important
suggestion for the improvement of the Simple Microscope com-
posed of a single lens, proceeded some years ago from Dr.
Brewster, who proposed to substitute diamond, sapphire, garnet,

80 OPTICAL PRINCIPLES OF THE MICROSCOPE

and other precious stones of high refractive power, for glass, as
the material of single lenses. A lens of much longer radius of
curvature might thus be employed, to gain an equal magnifying
power ; and the aperture would admit of great extension, with-
out a proportional increase in the spherical and chromatic aber-
rations. This suggestion has been carried into practice with
complete success, as regards the performance of lenses executed
on this plan; but the difficulties of various kinds in the way of
their execution, are such as to render them very expensive; and
as they are not superior to the combination now to be described,
they have latterly been quite superseded by it. This combina-
tion, first proposed by Dr. Wollaston, and known as his doublet,
consists of two plano-convex lenses, whose focal lengths are in
the proportion of one to three, or nearly so, having their convex
sides directed towards the eye, and the lens of shortest focal
length nearest the objéct. In Dr. Wollaston’s original combina-
tion, no perforated diaphragm (or “ stop’) was interposed; and
the distances between the lenses was left to be determined by ex-
periment in each case. A great improvement was subsequently
made, however, by the introduction of a “stop” between the
lenses, and by the division of the power of the smaller lens be-
tween two (especially when a very short focus is required) so as
to form a triplet, as was first suggested by Mr. Holland.* When
combinations of this kind are well constructed, both the spheri-
cal and the chromatic aberrations are so much reduced, that the
angle of aperture nay be considerably enlarged without much
sacrifice of distinctness; and hence for all powers above 1-4th
inch focus, doublets and triplets are far superior to single lenses.
The performance of even the best of these forms of Simple mi-
croscope, however, is so far inferior to that of a good Compound
microscope as now constructed upon the achromatic principle,
that no one who has the command of the latter form of instru-
ment would ever use the higher powers of the former. It is for
the prosecution of observations, and for the carrying on of dis-
sections, which only require low powers, that the Simple micro-
scope is to be preferred; and, consequently, although doublets
and triplets afforded the best means of obtaining a high magni-
fying power, before Achromatic lenses were brought to their pre-
sent perfection, they are now comparatively little used.

19. Another form of simple magnifier, possessing certain ad-
vantages over the ordinary double-convex lens, is that commonly
known by the name of the “Coddington” lens. The first idea
of it was given by Dr. Wollaston, who proposed to cement to-
gether two plano-convex, or hemispherical lenses, by their plane
sides, with a stop interposed, the central aperture of which should
be equal to 1-5th of the focal length. The great advantage of
such a lens is, that the oblique pencils pass, like the centre ones,
at right angles with the surface ; and that they are consequently
but little subject to aberration. The idea was further improved

1 « Transactions of the Society of Arts,” vol. xlix.

STANHOPE LENS—COMPOUND MICROSCOPE, 81

upon by Mr. Coddington, who pointed out that the same end
would be much better answered by taking a sphere of glass, and
grinding a deep groove in its equatorial part, which should. be
then filled with opaque matter, so as to limit the central aper-
ture. Such a lens gives a large field of view, admits a considera-
ble amount of light, and is equally good in all directions ;. but
its powers of definition are by no means equal to those of an
achromatic lens, or even of a doublet. This form is chiefly use-
ful, therefore, as a hand magnifier, in which neither high power
nor perfect definition is required; its peculiar qualities rendering
it supetior to an ordinary lens of the same power, for the class
of objects for which such lenses are applied in this mode. We
think it right to state that many of the magnifiers sold as “ Cod-
dington”’ lenses are not really (as we have satisfied ourselves)
portions of spheres, but are manufactured out of ordinary double-
convex lenses, and will be destitute, therefore, of many of the
above advantages. It may be desirable to allude to the magni-
fier known under the name of the “Stanhope” lens, which some-
what resembles the “Coddington” in appearance, but differs
from it essentially in properties. It is nothing more than a
double-convex lens, having two surfaces’of unequal curvatures,
separated from each other by a considerable thickness of glass ;
the distance of the two surfaces from each other being so ad-
justed, that when the most convex is turned towards the eye,
minute objects placed on the other surface shall be in the focus
of the lens. This is an easy mode of applying a rather high
magnifying power to scales of butterflies’ wings and other similar
flat and minute objects, which will readily adhere to the surface
of the glass; and it also ‘serves to detect the presence of the
larger animalcules, or of crystals in minute drops of fluid, to ex-
hibit the “eels” in paste or vinegar, &. &c. ; but it is almost en-
tirely destitute of value as an instrument of scientific research,
and can scarcely be regarded in any higher light than as an in-
genious philosophical toy.!

20. Compound Microscope.—In its most simple form, this instru-
ment consists of only two lenses, the “‘object-glass” and the “eye-
glass:” the former, ¢ p (Fig. 11), receiving the rays of light direct
from the object, 4 B, which is brought into near proximity to it,
forms an enlarged and inverted image a’ 8’ at a greater distance
on the other side; whilst the latter, L M, receives the rays which
are diverging from this image, as if they proceeded from an
object actually occupying its position and enlarged to its dimen-
sions, and these it brings to the eye at £, so altering their course
as to make that image appear far larger to the eye, precisely as
in the case of the simple microscope (§ 16). It is obvious that
by the use of the very same lenses, a considerable variety of
magnifying power may be obtained, simply by altering their

'The principal forms of construction of Simple Microscopes, will be described in the
next chapter. ; :

6

82 OPTICAL PRINCIPLES OF THE MICROSCOPE.

position in regard to each other and to the object; for if the eye-
glass be carried further from the object-glass, whilst the object is
approximated nearer to the latter, the image a’ 8B’ will be formed
at a greater distance from it, and its dimensions will consequently
be augmented. If on the other hand, the eye-glass be brought
nearer to the object-glass, whilst the object is removed further
from it, the distance of the image will be shortened, and its
dimensions proportionably diminished. We shall hereafter see
that this mode of varying the magnifying power of compound
microscopes may be turned to good account in more than one.
fee. a Fie. 1 mode (§§ 43, 44); but there are
_ limits to the use which can be
advantageously made of it.—
The amplification may also be
varied by altering the magni-
fying power of the eye-glass;
but here, too, there are limits
to the increase; since defects
of the object-glass, which are
not perceptible when its image
is but moderately enlarged, are
brought into injurious promi-
nence when the imperfect im-
age is amplified to a much
greater extent. In practice, it
is generally found much better
to vary the power, by employ-
ing object-glasses of different
foci; an object-glass of long
focus forming an image, which
is not at many times the dis-
tance of the object from the
other side of the lens, and
which, therefore, is not of
many times its dimension;
whilst an object-glass of short
focus requires that the object
should be so nearly approxi-
mated to it, that the distance
of the image is a much higher
ae of that of the object,
; and its dimensions are propor-
ee ee ee aly liom, Uk ae
scope. scope. ever mode additional amplifica-
tion be obtained, two things must always result from the change:
the portion of the surface of the object, of which an image can be
formed, must be diminished; and the quantity of light spread
over that image must be proportionably lessened.
21. In addition to the two lenses of which the Compound
Microscope essentially consists, another (Fig. 12, r F) is usually

CONSTRUCTION OF COMPOUND MICROSCOPE. 83

introduced between the object-glass and the image formed by it.
The ordinary purpose of this lens is to'change the course of the
rays in such a manner, that the image may be formed of dimen-
sions not too great for the whole of it to come within the range of
the eye-piece; and as it thus allows more of the object to be seen
at once, it is called the field-glass. It is now usually considered,
however, as belonging to the ocular end of the instrument,—the
eye-glass and the field-glass being together termed the Hye-piece.
Various forms of this eye-piece have been proposed by different
opticians; and one or another will be preferred, according to the
purpose for which it may be required. That which it is most
advantageous, to employ with Achromatic object-glasses, to the
performance of which it is desired to give the greatest possible
effect, is termed the “‘Huyghenian;” having been employed by
Huyghens for his telescopes, although without the knowledge of
all the advantages which its best construction renders it capable
of affording. It consists of two plano-convex lenses (EE and F F,
Fig. 12), with their plane sides towards the eye; these are placed
at a distance equal to half the sum of their focal lengths; or, to
speak with more precision, at half the sum of the focal length of
the eye-glass, and of the distance from the field-glass at which an
image of the object-glass would be formed by it. A “stop” or
diaphragm, B B, must be placed between the two lenses, in the
visual focus of the eye-glass, which is, of course, the position
wherein the image of the object will be formed, by the rays
brought into convergence by their passage through the field-glass.
By Huyghens, this arrangement was in-
tended merely to diminish the spherical
aberration; but it was subsequently
shown by Boscovich, that the chromatic
dispersion was also in a great part cor-
rected by it. Since the introduction
of Achromatic object-glasses for Com-
pound Microscopes, it has been further
shown that all error may be avoided by
aslight over-correction of these; so that
the blue and red rays may be caused
to enter the eye in a parallel direction
(though not actually coincident), and
thus to produce a colorless image.
Thus let p M Nn (Fig. 18), represent
the two extreme rays of three pencils,
which, without the field-glass, would — gooion or suygnenian Bye-piece
form a blue image convex to the eye- adapted to over-corrected Achro-
glass, at BB, and a red one at RR; then, ™ate oblectives.

by the intervention of the field-glass, a blue image, concave to
the eye-glass, is formed at B’ 8’, and a red one at R’ RB’. As the
focus of the eye-glass is shorter for blue rays than for red rays,
by just the difference in the place of these images, their rays,
after refraction by it, enter the eye in a parallel direction, and

84 OPTICAL PRINCIPLES OF THE MICROSCOPE.

produce a picture free from false color. If the object-glass had
been rendered perfectly achromatic, the blue rays, after passing
through the field-glass, would have been brought to a focus at}, and
the red at 7; so that an error would be produced, which would have
been increased instead of antagonized by the eye-glass. Another
advantage of a well-constructed Huyghenian eye-piece is that
the image produced by the meeting of the rays after passing
through the field-glass, is by it rendered concave towards the
eye-glass, instead of convex, so that every part of it may be in
focus at the same time, and the field of view thereby rendered flat.

22. Two or more Huyghenian eye-pieces, of different magni-
fying powers, known as Nos. 1, 2, 3, &c., are usually supplied
with a Compound Microscope.. The utility of the higher powers
will mainly depend upon the excellence of the objectives; for
when an achromatic combination of small aperture, which is
sufficiently well corrected to perform very tolerably with a low
eye-piece, is used with an eye-piece of higher magnifying power
(commonly spoken of as a ‘deeper’ one), the image may lose
more in brightness and in definition, than is gained by its ampli-
fication; whilst the image given by an objective of large angular
aperture and very perfect corrections, shall sustain so little loss
of light or of definition by ‘“‘ deep eye-piecing,” that the increase
of magnifying power shall be almost all clear gain. Such an
objective, therefore, though of far inferior power in itself, is
practically more valuable (as giving a much greater range of
power with equal efficiency) than a lens of higher power which
can only be used effectively with the shallower eye-pieces. Hence
the mode in which different achromatic combinations of the same
power, whose performance with shallow eye-pieces is nearly the
same, are respectively affected by deep eye-pieces, afford a good test
of their respective merits; since any defect in the corrections is
sure to be brought out by the higher amplification of the image,
whilst a deficiency of aperture is manifested by the want of light.

23, An Hye-piece is sometimes furnished with achromatic
microscopes, especially for micrometrie purposes, which, though
composed of only two plano-convex lenses, differs essentially in
its construction from the Huyghenian; the field-glass having its
convex side upwards, and being so much nearer to the eye-glass,
that the image is not formed above it (as at BB, Fig. 12), but
below it. This eye-piece, which is known as Ramsden’s, gives a
very distinct view in the central portion of the field; but, as it
does not, like the Huyghenian, correct the convexity of the image
formed by the objéct-glass, but rather increases it, the marginal
portions of the field of view, when the centre is in focus, are quite
indistinct. Hence this eye-piece cannot be recommended for
ordinary use; and its chief value to the Microscopist has resulted

'Those who desire to gain more information upon this subject than they can from the
above notice of it, may be referred to Mr. Varley’s investigation of the properties of the
Huyghenian eye-piece, in the 51st volume of the “ Transactions of the Society of Arts;”
and to the article “ Microscope,” by Mr. Ross, in the “ Penny Cyclopedia.”

CONSTRUCTION OF EYE-PIECES. 85

from its adaptation to receive a divided glass micrometer, which
may be fitted into the exact plane wherein the image is formed
by the object-glass, so that its scale and that image are both
magnified together by the lenses interposed between them and
the eye. We shall hereafter see, however, that the same end
may be so readily attained with the Huyghenian eye-piece (§ 46),
that no practical advantage is gained by the use of that of Rams-
den. It is affirmed by Mr. Ross, that if the Achromatic princi-
ple were applied to the construction of Eye-pieces, the latter is
the form with which the greatest perfection would be obtained.
That such an adaptation might be productive of valuable results,
appears from the success with which Mr. Brooke has employed
a triplet objective of one-inch focus, as an eye-piece; the defini-
tion obtained by it being very superior to that afforded by the
ordinary Huyghenian eye-piece.

24. In the Eye-pieces of compound microscopes of older con-
struction, it was customary to employ a pair of plano or double-
convex lenses of longer focus, for the eye-glass, instead of a
single plano-convex of shorter focus; the advantage being, that a
larger and flatter field could be thereby obtained. A brighter
image, a flatter field, and a greater freedom from aberration, than
are afforded by any ordinary eye-piece of this kind, may be ob-
tained by the substitution of a combination nearly resembling
Herschel’s ‘aplanatic doublet”-—namely, a meniscus, having its
concave side next the eye, and a double-convex of the form of
least aberration,’ with its flattest side next the object—for the
plano-convex eye-glass; and the substitution of a double-con-
vex lens of the form of least aberration, with its flattest side
next the object, for the plano-convex field-glass. With such
an eye-piece, a field of fourteen inches in diameter (measured at
the usual distance of ten inches) may be obtained perfectly flat,
and equally distinct and well illuminated over every part. When
such an eye-piece, however, is used in conjunction with achroma-
tic objectives, it impairs the definition of their image to such a
degree, that their finest qualities are altogether sacrificed. Still
there are certain large transparent objects, such as transverse
sections of wood, wings of insects, &c., in viewing which a large
and flat field is of more importance than perfect definition; since
their structure is so coarse, that there is no minute detail to be
brought out. Nothing is so effective for the exhibition of these,
as an eye-piece of the kind just alluded to, with an objective of
about 8 or 4 inches focus; and this may either be a single lens
(which, when of such low power, will perform sufficiently well for
objects of this class), or a single pair of lenses forming part of a
perfect achromatic combination, having its aperture somewhat
contracted by a stop.

1 The “ form of least aberration” is when the radii of the two surfaces are to each other
*. nee the lowest French Achromatics answer extremely well for this purpose; and
the front pair of the lowest set usually made in this country (that, namely, of 2 inches

focus) is sometimes made removable, so that the back pair, which also is very suitable to
the class of objects mentioned above, may be employed by itself.

CHAPTER II.
CONSTRUCTION OF THE MICROSCOPE.

25. THE optical principles whereon the operation of the Micro-
scope depends, having now been explained, we have next to
consider the mechanical provisions, whereby they are brought to
bear upon the different purposes which the instrument is
destined to serve. And first it will be desirable to state those
general principles, which have received the sanction of universal
experience, in regard to the best arrangement of its constituent
parts. Every complete Microscope, whether Simple or Compound,
must possess, in addition to the lens or combination of lenses
which affords its magnifying power, a stage whereon the object
may securely rest, a concave mirror for the illumination of trans-
parent objects from beneath, and a condensing-lens for the illumi-
nation of opaque objects from above.

I. Now in whatever mode these may be connected with each
other, it is essential that the optical part and the stage should be so
disposed, as either to be altogether free from tendency to vibration, or
to vibrate together ; since it is obvious that any movement of one,
in which the other does not partake, will be augmented to the
eye of the observer in proportion to the magnifying power
employed. In a badly-constructed instrument, even though
placed upon a steady table resting upon the firm floor of a well-
built house, when high powers are used, the object is seen to
oscillate so rapidly at the slightest tremor, such as that caused by
a person walking across the room, or by a carriage rolling by in
the street, as to be frequently almost indistinguishable: whereas
in a well-constructed microscope, scarcely any perceptible effect
will be produced by even greater disturbances.

II. The next requisite is a capability of accurate adjustment to
every variety of focal distance, without movement of the object. It is
now a principle almost universally recognized in the construction
of good Microscopes, that the stage whereon the object is placed
should be a fixture; the movement by which the focus is to be
adjusted, being effected in the lenses or optical portion. Several
reasons concur to establish this principle; of which one of the
most important is, that, if the stage be made the movable part,

MECHANICAL REQUIREMENTS. 87

the adjustment of the illuminating apparatus must be made
afresh for every change of magnifying power; whilst if the
stage be a fixture, the illumination having been“ once well
adjusted, the object may be examined under a great variety of
magnifying powers, without its being changed in any respect.
Moreover, if the stage be the movable part, it can never have
that firmness given to it which it ought to possess; for it is
almost impossible to make a movable stage free from some
degree of spring, so that, when the hands bear upon it in adjust-
ing the position of an object, it yields in a degree, which, how-
ever trifling in itself, becomes unpleasantly apparent with high
powers. The mode of effecting the focal adjustment should be
such as to allow free range from a minute fraction of an inch to
three or four inches, with equal power of obtaining a delicate
adjustment at any part. It should also be so accurate, that the
optical axis of the instrument should not be in the least altered
by movement in a vertical direction; so that, if an object be
brought into the centre of the field with a low power, and a
higher power be then substituted, it should be found in the centre
of cts field, notwithstanding the great alteration in the focus. In
this way much time may often be saved, by employing a low
power as a finder for an object to be examined by a higher one;
and when an object is being viewed by a succession of powers,
little or no readjustment of its place on the stage should be
required. For the Simple Microscope, in which it is seldom
advantageous to use lenses of shorter focus than 1-4th inch (save
where doublets are employed, § 18), a rack-and-pinion adjustment
answers sufficiently well; and this is quite adequate, also, for the
focal adjustment of the Compound body, when objectives of low
power only are employed. But for any lenses whose focus is less
than half an inch, a “fine adjustment,” by means of a screw move-
ment operating either on the object-glass alone or on the entire
body, is of great value; and for the highest powers it is quite
indispensable. In some Microscopes, indeed, which are provided
with a “fine adjustment,” the rack-and-pinion movement is
dispensed with: the “coarse adjustment” being given by merely
sliding the body up and down in the socket which grasps it. But
this plan is objectionable, inasmuch as it involves the use of both
hands in making the “coarse adjustment,” for which only one
should be required ; and even then the adjustment cannot be made
with nearly the same facility, as by a smooth well-cut rack. The
Author’s experience, therefore, would lead him to recommend,
that if one of these adjustments is to be dispensed with, it should
be the “screw” or “fine” adjustment, rather than the “rack”
or “coarse,” unless the instrument is to be almost exclusively
employed for the examination of objects requiring high magnify-
ing powers.!
1Jn the Microscopes constructed by Mr. Ladd, a chain-movement is substituted for the

rack-and-pinion; and this has the advantage of being smoother and more sensitive, of
being less likely to become unequal by wear, and of being easily tightened if it should

88 CONSTRUCTION OF THE MICROSCOPE.

II. Scarcely less important than the preceding requisite, in
the case of the Compound Microscope, though it does not add
much to tle utility of the Simple, is the capability of being placed
in either a vertical or a horizontal position, or at any angle with the
horizon, without deranging the adjustment of its parts to each
other, and without placing the eye-piece in such a position as to
be inconvenient to the observer. It is certainly a matter of sur-
prise, that Opticians, especially on the Continent, should have
so long neglected the very simple means which are at present
commonly employed in this country, of giving an inclined posi-
tion to microscopes; since it is now universally acknowledged,
that the vertical position is, of all that can be adopted, the very
worst. An inclination of about 55° to the horizon will generally
be found most convenient for unconstrained observation; and
the instrument should be so constructed, as, when thus inclined,
to give to the stage such an elevation above the table, that when
the hands are employed at it, the arms may rest conveniently
upon the table. In this manner a degree of support is attained,
which gives such free play to the muscles of the hands, that
movements of the greatest nicety may be executed by them;
and fatigue of long-continued observation is greatly diminished.
Such minutie may appear too trivial to deserve mention; but
no practised microscopist will be slow to acknowledge their value.
The stage must of course be provided with some means of sup-
porting the object, when it is itself placed in a position so in-
clined that the object would slip down unless sustained. There
are some objects, however, which can only be seen in a vertical
microscope, as they require to be viewed in a position nearly or
entirely horizontal; such are dissections in water, urinary de-
posits, saline solutions undergoing crystallization, &c. For other
purposes, again, the microscope should be placed horizontally, as
when the camera lucida is used for drawing or measuring. It
ought, therefore, to be made capable of every such variety of
position.

IV. The last principle on which we shall here dwell, is simpli-
city in the construction and adjustment of every part. Many in-

enious mechanical devices have been invented and executed,
or the purpose of overcoming difficulties which are in them-
selves really trivial. A moderate amount of dexterity in the use
of the hands is sufficient to render most of these superfluous;
and without such dexterity, no one, even with the most complete
mechanical facilities, will ever become a good microscopist.
Among the conveniences of simplicity, the practised Microsco-
pist will not fail to recognize the saving of time effected by being

“Jose time ;” whilst its delicacy and smoothness admit of an exact adjustment being
made by its means alone, even when high powers are employed. Still, as will be shown
hereafter (§ 81), the use of the “fine adjustment” is by no means restricted to this pur-
pose; and it cannot be advantageously dispensed with in a Microscope, which is to be
used for any but the most common purposes,

MECHANICAL REQUIREMENTS. 89

able quickly to set up and put away his instrument. Where a
number of parts are to be screwed together before it can be
brought into use, interesting objects (as well as time) dre not un-
frequently lost; and the same cause will often occasion the in-
strument to be left exposed to the air and dust, to its great detri-
ment, because time is required to put it away; so that a slight
advantage on the side of simplicity of arrangement, often causes
an inferior instrument to be preferred by the working microsco-
pist to a superior one. Yet there is, of course, a limit to this
simplification; and no arrangement can be objected to on this
score, which gives advantages in the examination of difficult ob-
jects or the determination of doubtful questions, such as no
simpler means can afford. The meaning of this distinction will
become apparent, if it be applied to the cases of the “traversing
stage” (§ 37) and the “achromatic condenser” (§ 56). For al-
though the traversing stage may be considered a valuable aid in
observation, as facilitating the finding of a minute object, or the
examination éf the entire surface of a large one, yet it adds
nothing to the clearness.of our view of either; and its place may
in great degree be supplied by the fingers of a good manipulator.
On the other hand, the use of the achromatic condenser not only
contributes very materially, but is absolutely indispensable, to
the formation of a perfect image, in the case of many objects of
a difficult class; the want of it cannot be compensated by the
most dexterous use of the ordinary appliances ; and consequently,
although it may fairly be considered superfluous, as regards a
large proportion of the purposes to which the Microscope is di-
rected, whether for investigation or for display, yet as regards
the particular objects just alluded to, it must be considered as no
less necessary a part of the instrument than the achromatic ob-
jective itself. Where expense is not an object, the Microscope
should doubtless be fitted with both these valuable accessories ;
where, on the other hand, the cost is so limited that only one
can be afforded, that one should be selected which will make the
instrument most useful for the purposes to which it is likely to
be applied. (See Introduction, pp. 60, 61.)

In the account now to be given, of the principal forms of
Microscope readily procurable in this country, it will he the
Author’s object, not so much to enumerate and describe the vari-
ous patterns which the several makers of the instrument have
produced, as, by selecting from among them those examples
which it seems to him most desirable to make known, and by
specifying the peculiar advantages which each of these presents,
to guide his readers in the choice of the kind of Microscope best
suited, on the one hand, to the class of investigations they may
be desirous of following out, and on the other, to their pe-
cuniary ability. He is anxious, however, that he should not be
supposed to mark any preference for the particular instruments

90 CONSTRUCTION OF THE MICROSCOPE.

he has selected, over those constructed upon the same general
plan by other makers; to have enumerated them all, would ob-
viously be quite incompatible with the plan of his treatise ; but
he has considered it fair (save in one or two special cases) to give
the preference to those makers who have worked out their own
plans of construction, and have thus furnished (to say the least)
the general designs, which have been adopted with more or less
of modification by others.

Simple Microscope.

26. Under this head, the common hand-magnifier or pocket-
lens first claims our attention ; being in reality a Simple Micro-
scope, although not commonly accounted as such. Although
this little instrument is in every one’s hands, and is indispensable
to the Naturalist,—as affording him the means of at once making
such preliminary examinations as often afford him most important
guidance,—yet there are comparatively few who know how to
handle it to the best advantage. The chief difficulty lies in the
steady fixation of it at the requisite distance from the object, es-
pecially when the lens employed is of such short focus, that the
slightest want of exactness in this adjustment produces evident
indistinctness of the image. By carefully resting the hand which
carries the glass, however, against that which carries the object,
so that both, whenever they move, shall move together, the ob-
server, after a little practice, will be able to employ even high
powers with comparative facility. The lenses most generally
serviceable for hand-magnifiers, range in focal length from two
inches to half an inch; and a combination of two or three of
such in the same handle, with an intervening perforated plate
of tortoise-shell (which serves as a diaphragm when they are
used together), will be found very useful. When such a mag-
nifying power is desired, as would require a lens of a quarter of
an inch focus, it is best obtained by the substitution of a “‘ Cod-
dington” (§ 19) for the ordinary double-convex lens. The handle
of the magnifier may be pierced with a hole at the end most dis-
tant from the joint by which the lenses are attached to it; and
through this may be passed a wire, which, being fitted vertically
into a stand or foot, serves for the support of the magnifying
lenses in a horizontal position, at any height at which it may be
convenient to fix them. Such a little apparatus is a rudimentary
form (so to speak) of what is commonly understood as a Simple
Microscope ; the term being usually applied to those instruments
in which the magnifying powers are supported otherwise than
in the hand, or, in which, if the whole apparatus be supported
by the hand, the lenses have a fixed bearing upon the object (§ 28).

27. Ross’s Simple Microscope.—This instrument holds an in-
termediate place between the hand-magnifier and the complete
Microscope; being, in fact, nothing less than a lens supported
in such a manner, as to be capable of being readily fixed ina

HAND-MAGNIFIER—ROSS8’S SIMPLE MICROSCOPE. 91

variety of positions suitable for dissecting and for other manipu-
lations. It consists of a circular brass foot, wherein is screwed
a short tubular pillar (Fig. 14), whichis “sprung” at its upper
end, so as to grasp a second tube, also “sprung,” by the drawing
out of which the pillar may be elongated to about three inches.
This carries at its upper end a jointed socket, through which a
square bar about 33 inches long slides rather stiffly ; and one end.
of this bar carries another joint, to which is attached a ring for
holding the lenses. By lengthening or shortening the pillar, by
varying the angle which the square bar makes with its summit,
and by sliding that bar through its socket, almost any position
and elevation may be given to the lens, that can be required for
the purposes to which it may be most usefully applied; care
being taken in all in-
stances, that the ring
which carries the lens
should (by means of its
joint) be placed horizon-
tally. At A is seen the
position which adapts it
best for picking out mi-
nute shells or for other si-
milar manipulations; the
sand or dredgings to be
examined being spread
upon a piece of black
paper, and raised upon a
book, a box, or some
other support, to such a
height, that when the
lens is adjusted thereto,
the eye may be applied to
it continuously without
unnecessary fatigue. It
will be found advantage-
ous that the foot of the
microscope should not
stand upon the paper
over which the objects
are spread, as it is de-
sirable to shake this from’
time to time, in order to
bring a fresh portion of
the matters to be ex-
amined into view; and,
generally speaking, it
will be found convenient ; ;
to place iton the opposite Ross’s Simple Microscope.
side of the object, rather than on the same side with the ob-

Fria. 14,

fi
——-

92 CONSTRUCTION OF THE MICROSCOPE.

server, At B is shown the positionin which it may be most con-
veniently set, for the dissection of objects contained in a plate or
trough, the sides of which, being higher than the lens, would
prevent the use of any magnifier mounted on a horizontal arm.
The powers usually supplied with this instrument, are one lens
of an inch focus, and a second of either half or a quarter of an
inch. By unscrewing the pillar, the whole is made to pack into
a small flat case, the extreme portability of which is a great re-
commendation. Although the uses of this little instrument are
greatly limited by its want of stage, mirror, &c., yet for the class
of purposes to which it 2s suited, it has advantages over perhaps
every other form that has been devised.

28. Gairdner’s Simple Microscope.—This little instrument, dis-
tinguished like the preceding for its simplicity and portability,
is adapted to quite a different class of purposes; namely, the
examination of minute transparent objects, especially those con-
tained in fluid, such as Animaleules, Desmidiew and Diatomacee,
Urinary deposits, &c. It consists (Fig. 15) of a Wollaston’s
doublet (§ 18), supported upon a handle, with which is also con-
nected an elastic slip of brass, carrying a
ring which surrounds the projecting centre
of the under side of the doublet; this ring
is made to approach nearer to, or to recede
further from, the doublet, by means of a
milled-headed screw which passes through
the stem that supports the latter, and bears
upon the slip of brass that carries'the former;
and to the side of it which is furthest from
the doublet, a disk of very thin glass is
cemented. In using this little instrument,
a minute drop of the liquid to be examined
is to be placed on the under side of the thin
| glass disk,—that is, on the side away from
i@ the doublet,—and it is to be covered by
another disk, which will be drawn to the
fixed disk, and supported in its place by the
capillary attraction of the fluid for both.
The instrument is then to be so held, that
the eye, when applied to the doublet, looks
at the light through the film of liquid; and
when the focal adjustment is made by means
of the milled head, any particles this may
contain, of a size to be brought into view by the magnifying
power employed, will be distinctly discerned. The instrument
is usually constructed with but a single power, adapted to the
class of objects for which it is to be employed; thus for the pur-
poses of the botanical or zoological, collector, a power of from 70
to 100 diameters is sufficient; whilst for the examination of uri-
nary deposits, a power of 200 or more is desirable. It would not

Fra. 15.

Gairdner’s Simple Microscope.

GAIRDNER’S AND FIELD’S SIMPLE MICROSCOPES. 93

be difficult so to modify it, however, by making the doublet to
screw into a socket, instead of fixing it on the stem, that one
power might be substituted for another on the same instrument;
and the adjusting screw might then perhaps be dispensed with,
since the focal adjustment might probably be made sufficiently
well, by turning round the doublet itself in its screwed socket.
The object-holder, too, might be so constructed as to receive a
greater variety of objects, and even to hold preparations mounted
on slips of glass; which would often be a matter of great con-
venience for class demonstration. All this, however, would add
to the complexity and the cost of the instrument; the simplicity
and low price of which at present constitute its chief reeommen-
dation. Though not suited for the higher purposes of a Micro-
scope (the view of any object afforded by a doublet magnifying
100 or 200 diameters, being far inferior to that presented by only
a tolerable achromatic), yet there is a certain class of observations
for which it is particularly convenient,—those, namely, which
only require a recognition of known forms. Thus, the collector
of Diatomacee, Animalcules, &c., may by its means at once test
the general value of the sample he has taken up, and may decide
whether to throw it away as worthless, or to reserve it for more
minute examination. And the Medical practitioner who is
familiar with the aspect of Urinary deposits, may, by this little
instrument (which he can carry in his waistcoat-pocket), discrimi-
nate on the spot the nature of almost any sediment whose charac-
ter he may wish to know, without being obliged to have recourse
to a more elaborate apparatus.}

29. Field’s Simple Microscope.—The general purposes of a sim-
ple Microscope are satisfactorily answered by the instrument,
which has recently gained the premium awarded by the Council
of the Society of Arts, and which is capable of being very effec-
tively used in the examination of most of the objects for which
such an instrument is suited. It consists (Fig. 16) of a tubular
stem, about five inches high, the lower end of which screws
firmly into the lid of the box wherein the instrument is packed
when not in use. To the upper end of this stem, the stage is
firmly fixed; while the lower ‘end carries a concave murror.
Within the tubular stem is a round pillar, having a rack cut into
it, against which a pinion works that is turned by a milled head;
and the upper part of this pillar carries a horizontal arm which
bears the lenses; so that, by turning the milled head, the arm
may be raised or lowered, and the requisite focal adjustment ob-
tained. Three magnifiers are supplied with this instrument; and
by using them either separately or in combination (the lens of
shortest focus being placed at the bottom, whenever two, or
all three, are used together), a considerable range of powers,

! This Microscope, the invention of Dr. William Gairdner, of Edinburgh, is made by
Mr. Bryson, optician, of that city. :

94 CONSTRUCTION OF THE MICROSCOPE.

from about five to forty diameters, is obtained. The stage is
perforated with a hole at each corner; into any one of which may
be fitted a condensing
lens for opaque objects
(§ 64), or a pair of
stage-forceps (§ 66). An
aquatic-box for the ex-
amination of objects in
water (§ 68) is also sup-
plied.’ This instrument
is peculiarly adapted for
educational purposes ;?
being fitted in every
particular for the ex-
amination of botanical
specimens, small insects
or parts of insects, water
flies, the larger animal-
cules, and other such
objects as young people
may readily collect and
prepare for themselves;
and such as_ have
trained themselves in

Field’s Simple Microscope. the application of it
to the study of Nature, are well prepared for the advantageous
use of the Compound Microscope. But it also affords to the
scientific inquirer all that is.essential to the pursuit of such
investigations, as are best followed out by the concurrent em-
ployment of a Simple and a Compound Microscope, the former
being most fitted for the preparation, and the latter for the
examination, of many kinds of objects;?—and it may be easily
adapted to the purposes of dissection, by placing it between arm-
rests (§ 104), or blocks of wood, or books piled one on another, so
as to give a support for the hand on either side, at or near the
level of the stage.

30. Quekett’s Dissecting Mieroscope.—To the scientifie investi-
gator, however, it is generally more convenient to have a larger
stage than the preceding instrument affords; and in this respect
an arrangement devised by Mr. Quekett (Fig. 17) will be found
extremely convenient. The stage, which constitutes the princi-
pal part of the apparatus, is a plate of brass (bronzed) nearly six
inches square, screwed to a piece of mahogany of the same size
and about éths of an inch thick; underneath this a folding flap

Fia. 16,

' The price of the instrument, with all these appurtenances, packed in a neat ma-
hogany box, is only half a guinea ; and the maker, Mr. G. Field, of Birmingham, is
bound by his agreement with the Society of Arts to keep it always in stock. See also
Say

2 See Introduction, pp. 60, 61. 5 See Introduction, p. 63.

QUEKETT’S DISSECTING MICROSCOPE. 95

four inches broad is attached by hinges on each side; and the
two flaps are so shaped, that, when closed together, one lies
closely upon the other, as shown in Fig. 17,8. These flaps,
when opened, and kept asunder by a brass bar, as shown in Fig.
17, 4, give a firm support to the stage at a convenient height;

Fig. 17.

ear
IY ——

SS ]]]S==

Quekett’s Dissecting Microscope.

and the bar also carries a socket, into which the stem of the
mirror-frame is inserted. At the back of the stage-plate is a
round hole, through which a tubular stem slides vertically, that
carries at its summit the horizorital arm for the magnifying pow-
ers; this stem may or may not be furnished with a rack-and-
pinion movement; but the author’s experience leads him strongly
to recommend that it should be provided with this means of
making the focal adjustment; since the sliding action, indepen-
dently of the greater trouble it always involves, is apt to become
uneven and difficult, especially if the surface of the stem should
have become roughened by the corrosion of sea-water, or by the
action of acids, salines, &., used as reagents. The same frame
which carries the mirror, is also made to carry a lens which serves
as a condenser for opaque objects; its stem being then fitted into

$6 CONSTRUCTION OF THE MICROSCOPE.

a hole in the stage, at one side, or in front of, its central perfora-
tion. The instrument is usually furnished with three magnifiers,
namely, an inch and half-inch ordinary lenses, and a quarter-inch
Coddington (§ 19); and these will be found to be the powers
most useful for the purposes to which this instrument is specially
adapted. The lenses, mirror, condenser, cross-bar, vertical stem,
and milled head, all fit into hollows cut for their reception on
the under side of the stage, and are then covered and kept in
place by the side flaps; so that, when packed together, and the
flaps kept down by an elastic band, as shown in Fig. 17, B, the
instrument is extremely portable, furnishing (so to speak) a case
for itself. It may be easily made to serve as a Compound micro-
scope, by means of an additional stem and horizontal arm, car-
rying a light “body.” The principal disadvantages of this very
ingenious and otherwise most convenient arrangement, are that
it must be always used with the light zn front of the observer, or
nearly so, since the side-flaps interfere with the access of side-
light to the mirror; and that the obstruction of the side-flaps also
prevents the hands from having that ready access to the mirror,
which is convenient in making its adjustments. These incon-
veniences, however, are trifling, when compared with the great
facilities afforded for scientific investigation by the size and firm-
ness of the stage; and the author can confidently recommend
the instrument for all such purposes, from much personal experi-
ence of its utility.

Compound Microscope.

The various forms of Compound Microscope may be grouped
with tolerable definiteness into two principal classes; one con-
sisting of those instruments, whose size and general plan of con-
struction adapt them only for the ordinary methods of observa-
tion; whilst the other includes those which are suited to carry
the various accessories, whose use enables the observer not only
to work with more facility and certainty, but, in some instances,
to gain information respecting the object of his examination,
which he could not obtain without them. It is true that some
of the most important of these accessories may be applied to the
smaller and lighter kind of Microscopes; but when it is desired
to render the instrument complete by the addition of them, it is
far preferable to adopt one of those larger and more substantial
patterns, which has been devised with express reference to their
most advantageous and most convenient employment. In nearly
all the instruments now to be described, the same basis of sup-
port is adopted, namely, a triangular “foot,” from which arise
two uprights ; and between these the microscope itself is swung,
in such a manner that the weight of its different parts may be as
nearly as possible balanced above and below the centres of sus-
pension, in all the ordinary positions of the instrument. This
double support was first introduced by Mr. George Jackson, who

FIELD’S EDUCATIONAL MICROSCOPE. 97

substituted two pillars (a form which Messrs. Smith and Beck
still retain in their Large Compound Microscope, Fig. 29) for
the single pillar connected with the microscope itself by a “‘ cra-
dle-joint” (as in Fig. 20) which was previously in use; but in
place of pillars screwed into the tripod base, a pair of flattened
uprights, cast in one piece with it, is now generally adopted,
with a view both to greater solidity and to facility of construc-
tion. Messrs. Powell and Lealand, it will be observed, adopt a
tripod support of a different kind (Fig. 28), still, however, carry-
ing out the same fundamental principle, of swinging the micro-
scope itself between two centres. Two different modes of giving
support and motion to the “body” will be found to prevail.
One consists in its attachment at its base to the transverse “arm,”
which is borne on the summit of the movable stem, whose rack
is acted on by the pinion of the milled head, as in Figs. 18, 27,
28; whilst in the other, the body is supported along a great part
of its length by means of a solid “limb,” to which is attached
the pinion that acts on a rack fixed to the body itself, as in Figs.
21, 22, and 29. The former method has the advantage of ena-
bling the body to be turned aside by the rotation of the trans-
verse arm upon the summit of the stem,—a movement which is
often convenient, both as leaving the stage clear for dissection,
&e., and as enabling the objectives to be more readily exchanged ;
but it is subject to the disadvantage, that unless the transverse
arm and the body are constructed with great solidity, the absence
of support along the length of the latter leaves it subject to vi-
bration, which may become unpleasantly apparent when high
powers are used, giving a dancing motion to the objects. With
a view of preventing this vibration, Messrs. Powell and Lealand
connect the top of the “body” with the back of the transverse
arm, by a pair of oblique “stays” (Fig. 28). The second method
of support is decidedly superior in steadiness, a perfect freedom
from tremor being obtained with less solidity, and therefore with
less cumbrousness ; the mode in which the rack is applied, more-
over, in the microscopes of Messrs. Smith and Beck (most of
which are constructed upon this plan) gives to it a peculiar
smoothness and easiness of working; but the traversing move-
ment of the body is sacrificed. Although some attach considera-
ble importance to this movement, the author’s experience of
instruments constructed upon both plans, leads him to give a
preference to the second.

31. Field’s Compound Microscope.—The first of the simpler
forms which we shall more particularly describe, is that to which
the medal of the Society of Arts has been recently awarded, not.
as a testimony to the perfection of its construction, but as mark-
ing the highest degree of excellence among the instruments sent
in competition, that seemed consistent with the cheapness’ which

1 The, price of this instrument, complete, with two eye-pieces and two achromatic
objectives giving a range of power from about 25 to 200 diameters, condenser on a

98 CONSTRUCTION OF THE MICROSCOPE.

was the fundamental requirement (see Introduction, p. 61). The
tripod foot (Fig. 18), with its pair of uprights, is of cast iron; and
affords a very firm and steady basis of support. The centres of
suspension by which the microscope is swung between these up-
Fia. 18. rights, are attached to the hol-

low pillar that bears all the
other parts. Just above them,
when the instrument is in a
vertical position, is a milled
head on either side, which
acts on a rack cut into the
stem that rises from the pillar,
and carries the body on a
transverse arm, thus giving
the “coarse” adjustment for
focal distance; whilst the
“fine” adjustment is given by
another milled head (seen
edgeways in the figure) in the
transverse arm, which turns
a screw whose extremity acts
upon a lever that produces a
slight change in the distance
between the object-glass and
the object, by elevating or de-
pressing a tube that carries
BIEIE SOUEMIEE HEESEESP Es the former,—this tube being

so fitted to the lower end of the body as to slide freely within it,
and being pressed downwards by a spring, whilst it is raised up-
wards by the lever-action just named. The additional advantage
is gained by this arrangement (which is the one adopted with
some modification by most Microscope makers), namely, that if
the object-glass should be carelessly forced down so as to press
upon the object, the yielding of the spring-tube prevents any
serious injury to the one, and to a certain extent protects the
other. The stage, which is firmly attached to the pillar, is fur-
nished on its upper surface with a movable brass ledge, against
which the object rests when the stage is inclined in any degree
to the horizon; this ledge should slide smoothly and easily from
the back to the front of the stage, but should have at the same
time sufficient hold upon it to retain its position and to support °
the object, at whatever point it may be left. At a little distance
beneath the stage, there is attached to it a “diaphragm plate,”
perforated with holes of various sizes for the regulation of the
quantity of light admitted to transparent objects (§ 55), and also
affording, in one of its positions, a dark background, which is

separate stand, stage-forceps, and live-box, in a mahogany case, is only three guineas;
and the maker, Mr. G. Field, of Birmingham, is bound by his agreement with the
Society of Arts to keep it always in stock, so as to supply any purchaser at once.

HIGHLEY’S HOSPITAL MICROSCOPE. 99

useful when opaque objects are being viewed. The stage is per-
forated at one of its front corners with a hole, into which fits a
pair of stage-forceps (§ 66). The mirror, which is concave on
one side and plane on the other, is attached, not to the pillar, but
to a tube which slides upon it, so that its distance from the under
side of the stage may be increased or diminished. The con-
denser for opaque objects is mounted on a separate stand (§ 64).
The simplicity of the constrtiction of this Microscope, and the
facility with which all those adjustments may be made that are
required for the purposes which it is intended to fulfil, should
constitute, with its low price, a great recommendation to those
who value a Microscope rather as a means of interesting recrea-
tion for themselves, or of cultivating a taste for the study of na-
ture and a habit of correct observation in the yeung, than as an
instrument of scientific research. It is not, of course, to be ex-
pected that it should bear comparison, in regard either to the
mechanical finish of its workmanship, or to the perfection of its
optical effects, with Micro-
scopes of many times its cost;
but it is infinitely superior to
the best Microscope ever con-
structed on the old (non-achro-
matic) plan; and it is greatly
to be preferred in its mecha-
nical arrangements to any of
the earlier achromatic micro-
scopes, which it at least equals
in optical performance.

82. Highley’s Hospital Micro-
scope.—The scale of this in-
strument is somewhat larger
than that of the preceding,
and its workmanship more
finished and substantial. The
tripod stand, the stage and its
fittings, and the mirror, al-
most exactly resemble those
first described; but the body,
which is longer, is supported
in a different manner. The
pillar to which the stage and
the mirror are attached, is pro-
longed upwards, and then
forms a kind of “limb,” to
which is affixed a tube slit
down in front; and within
this tube the “body” slides up and down, with sufficient freedom
to allow of being easily moved, yet with sufficient stiffness to
remain firm in any position in which it may be left. In the sim-
ple form of this instrument here delineated, the sliding action

Fig. 19.

Highley’s Hospital Microscope.

100 CONSTRUCTION OF THE MICRCGSCOPE.

affords the only means of making the “coarse” adjustment (§ 25,
II); but a rack-and-pinion movement may be introduced ata
trifling additional cost. The “fine” adjustment is made bya
milled head in front of the lower end of the body, which acts
directly upon a tube sliding within it that carries the objectives,
This instrument is particularly adapted, by the roominess of its
stage, for the examination of pathological specimens; and, when
the body is provided with a rack movement, it forms an unex-
ceptionable microscope for general purposes, and may even be fur-
nished with a movable stage, achromatic condenser, polarizing
apparatus, &c.!

33. Nachet’s Microscope-—Until a comparatively recent period,
all save the most elaborate and expensive forms of Compound
Microscope constructed by Continental opticians, were adapted
for use in the vertical position only. M. Nachet, however, has
now so modified his ordinary pattern, that the instrument may
be inclined (like the preceding) at any angle; and he has thus
rendered it a very convenient, as well asa cheap and portable Mi-
croscope. The basis consists of a somewhat oval foot, with a
single pillar rising from a little behind its centre; and at the top
of this pillar is a “cradle-joint,” which supports the stage and
the upright steth that carries the body. The transverse arm, how-
ever, is attached, not directly to the summit of this stem, but to
a tube which slides over it; and this tube can be raised or
lowered by turning the milled head at its summit (which acts
upon a screw that enters the stem), whereby a “fine” adjustment
is obtained, that acts through the transverse arm upon the body
which it carries. The “coarse” adjustment is effected, as in the
preceding case, by sliding the body through an outer tube which
grasps it; the latter being fixed into the transverse arm. The
mode in which the object issupported upon the stage, when this
is inclined, is very simple and ingenious, and is in some repects
preferable to the sliding-ledge generally used by English makers.
Near each side of the stage is seen a somewhat elastic strip or
tongue of sheet brass, the front extremity of which is free, but
which is attached at its hinder end to a pin that passes through
a hole in the stage, in which it works very easily. This pin is
prolonged for about #ths inch beneath the stage, and then termi-
nates in a broad flat head; and it is surrounded by a slender
spiral spring, which, bearing at its two ends against the under
side of the stage and the head of the pin, tends to depress the
latter, and thus to bring the brass tongue into close apposition
with the stage when nothing intervenes, and to bind down any-
thing that may be placed between them. In making use of
this little apparatus, 1t is most convenient to employ both hands,
in such a manner that the thumb and forefinger of each shall

' The cost of this instrument essentially depends npon the number and magnifying
power of the objectives supplied with it; it is usually provided, however, with a 1-inch
and }-inch; and is then sold (without the rack movement) at £6 10s. This sum, how-
ever, does not include either a case or any accessory apparatus.

NACHET’S MICROSCOPE. 101

hold one end of the slip of glass whereon is placed the object
under examination, whilst one of the other fingers of each
hand is used to push up the
head at the end of the pin,
so as to lift the tongue from
the stage; the slip of glass
can then be moved from side
to side, or up and down,
with the most perfect free-
dom, and may be firmly se-
cured at any point by ceasing
to press upon the heads of
the pins, which will then be
forced down by the springs,
so as to bring the tongues to
bear on the slip of glass.
When the microscope is used
in a vertical position, for the
examination of urinary de-
posits, &c., no means of fix-
ing the object being requir-
ed, it is convenient to turn
the tongues backwards, so
as not to occupy any part of
the stage. The advantages
of this arrangement are the
perfect freedom with which
the slip of glass can be moved >
under the objective, either in a

finding a minute object, or Nachet’s Compound Microscope.

in examining the surface of a larger one; and the facility and
exactness with which it is retained at any point, at which it may
be desired to fix it. The disadvantages are, the necessity of
using both hands to move the object; and the interference of the
tongues with the movement of the object from side to side, when
it is large enough to require a considerable range; on which
last account the plan is unsuited to the use of an aquatic box.
The stage is furnished on its under surface witha diaphragm
plate, not mounted as a wheel, but sliding in a straight line,
which is a less convenient arrangement ; and to its lower side is
also attached a stem that carries the mirror, the distance of which
from the stage is not capable of variation. This instrument is
distinguished by its simplicity and cheapness, and by its adapta-
tion to many of the wants of the scientific inquirer.'. One of its
chief disadvantages is the small size (especially the narrowness)
of its stage, which cramps the operations of the observer; and
hence it will not be found nearly so convenient to the young
microscopist, as the equally simple patterns in common use in

1 With three objectives and three eye-pieces, giving a range of magnifying powers
from about 50 to about 500 diameters, it is sold in Paris for 190 francs.

Fic. 20.

102 CONSTRUCTION OF THE MICROSCOPE.

this country. Those, however, who are carrying on researches
upon objects too minute to make this objection felt (such, for
example, as urinary deposits), and who need high magnifying
powers, without requiring these to possess the greatest attainable
perfection, will find this Microscope extremely well suited to
their wants. Another instrument constructed by M. Nachet
upon the same general plan, but upon a larger scale, is capable
of being fitted with Achromatic condenser, Polarizing apparatus,
Micrometer eye-piece, Stage movements, &c.; in the arrange-
ment of which accessories, much skilful contrivance is shown.
The Binocular Microscope of the
Fig. 21. same ingenious Optician will

be described further on (§ 40).
34. Smith and Beck's Stu-
dent’s Microscope.—Of the pat-
terns yet devised for a micro-
scope of simple construction,
which shall yet be capable of
answering every essential pur-
pose whether of display or of
investigation, that of Messrs,
Smith and Beck appears to
the Author to be (to say the
least) among the best; and he
recommends it with the more
confidence, since he has for
many years employed one of
these Microscopes as his own
working instrument. There
is nothing distinctive in the
tripod support, or in the mode
in which the microscope itself
is suspended between the up-
rights. But the “body” rests
for a great part of its length
upon a “limb” of solid brass,
ploughed into a groove for the
reception of the rack which is
attached to the body; this
groove being of such a form,
that the rack is firmly held in
it, whilst it slides smoothly
through it. The great advan-
tage of this method of construction over any other in which the
rack-and-pinion movement is made to act directly on the body, is
that it renders impossible any of that tevdst which tends to throw
the object more or less completely out of the field, and secures
that exact centering which is essential to the optical perfection of
the instrament. The upper end of the body is furnished with a
“draw tube,” by which its length can be increased; and one side

Smith and Beck’s Student’s Microscope.

SMITH AND BECK’S STUDENT’S MICROSCOPE. 103

of this is graduated to inches and tenths. The advantages of' this
arrangement will be explained hereafter (§ 48). The “fine” ad-
justment is effected by means of a milled head, situated just be-
hind the base of the stem that bears the limb; this acts on a
screw, the turning of which (by a contrivance that need not be
described in detail) depresses the stem with the limb and body
attached to it, so as to bring the objective nearer to .the object ;
whilst if the pressure of the screw be withdrawn, by turning the
milled head in the opposite direction, the tubular stem (with the
limb and body) is carried upwards by a spiral spring in its in-
terior, thus increasing the distance of the objective from the ob-
ject. This adjustment is remarkable for its sensitiveness, and
for its freedom from any displacing action upon theimage. The
only other peculiarity that need be noticed in this instrument,
is the mode in which the object is borne upon the stage ; for, in-
stead of resting against a ledge, it lies upon a kind of fork,
which slides in grooves ploughed out of the stage, and which
moves with such facility, that the pressure of a single finger upon’
one of the upright pins at the back of the fork 1s sufficient to
push it in either direction. At the extremity of one of the
prongs of this fork, is a “spring clip” for securing the object by
a gentle pressure, which is particularly useful when the micro-
scope is placed in a horizontal position for drawing with the
camera lucida (§ 49), the stage being then vertical. And at the
extremity of the other prong is a hole for the insertion of the pin
of the stage-forceps, which thus gains the advantage of the sliding
movement of the fork, in addition to its own actions. This in-
strument can easily be made to receive the addition of an achro-
matic condenser and of a polarizing apparatus; it may also be
fitted with a traversing stage, but there is scarcely sufficient room
for its working, to render such an addition worth its cost.’

35. Smithand Beck's Dissecting Microscope.—A modification of
the preceding pattern has been made for the special purpose of
carrying on dissections under the Compound Microscope, without
any interference, however, with the use of the instrument for all
ordinary purposes. The general plan of the instrument (Fig. 22),
as will be at once apparent, is essentially the same as that of the

1 No working Physiologist or Naturalist can reguire, in the Author’s opinion, a better
instrument than the above ; unless he be directing his attention to some particular class
of objects, which need the very highest microscopic refinements for their elucidation.
The cost of the instrument, fitted with two eye-pieces, condenser for opaque objects,
aquatic box, and stage-forceps, is (with case) about £7; the cost of the objectives de-
pends upon their magnifying power and upon their angular aperture. Those most
serviceable for ordinary purposes are the 14 inch, 3 inch, 4, inch, and 4 inch, whose
respective prices are £3, and 3,5, and 6 guineas; the first and third, or the second
and fourth, of these may be selected in the first instance, and the others added at any
time ; the addition of the 4 inch (which the unpractised microscopist is scarcely likely
to employ to advantage, and which is ‘only useful for a very limited set of purposes)
may be postponed until it is really needed and can be effectually employed. Morecan
be seen of most objects by the proper management of such a } inch as Messrs. 8. and
B. now supply, than could have been made out by the $ of a few years back. These
opticians are now constructing a new pattern of Student’s Microscope, complete in
itself, with two good powers, which will be well adapted to the most important uses of

104 CONSTRUCTION OF THE MICROSCOPE.

Student’s Microscope; but the stage is much longer from back to
front, so as to give more room; and from the back of it rises a
strong curved limb for the support of the body, which is made to
slide upon it, as in the previous case, by a rack-and-pinion move-
ment. A second milled head is seen above that by which the
focal adjustment is made; and this acts by means of a rack
upon the draw-tube, which it brings out or shuts in, without the
necessity of holding the body with the other hand,—a movement
which will be found of very great advantage, when the “erecting
Fie. 22. - eye-piece” (§ 44) is employed
for varying the magnifying
power. The chief use of
this erecting eye-piece, which
screws into the lower end of
the draw-tube (Fig. 32), in the
Dissecting Microscope, is to
erect the image (as its designa-
tion implies), and thus to facili-
tate the employment of dissect-
ing instruments upon an object
under inspection, the selection
of minute shells, &e., or other
manipulations, which cannot
be so conveniently carried on,
save after long practice, when
the object is inverted. Asthe
“fine” adjustment cannot, in
this pattern, be applied to the
“limb,” it is attached (if re-
quired) to the lower end of the
body itself, as in Messrs. Smith
and Beck’s larger Microscope
(Fig. 29); but for the purposes
to which such an instrument’
as this is usually applied, the
fine adjustment is seldom need-
ed, the rack-movement being
sufficiently exact and sensitive
to furnish all that is needed
for low and medium powers.

the Physiologist and Medical Practitioner, without exceeding ten pounds in price. To
those, however, who, though obliged to limit their first outlay, contemplate making sub-
sequent additions, the Author would strongly recommend the choice of the instrument
described in the text, as one on which such additional expenditure may be more pro-
fitably bestowed. Since the above were written, Messrs. Smith and Beck have brought
out the “ Educational Microscope” there alluded to; and after a careful examination of it,
the Author can strongly recommend it as admirably adapted to the purposes for which
it is intended. It is fitted with two eyepieces and two objectives, giving a range of
powers from 55 to 350 diameters; and may also be furnished with an extra low power
for large opaque objects, at a small additional cost. For the additional sum of £5, a Lie-
berkthn, Parabolic Hluminator, Polarizing Apparatus, Camera Lucida Prism, Aquatic
Box, and Zoophyte Trough are supplied; all fitted into the saine very portable case, and
rendering the instrament extremely complete.

WARINGTON’S UNIVERSAL MICROSCOPE. 105

When this addition is made, however, the instrument is adapted
to any kind of work to which the preceding can be applied ; it
can receive the same fittings; and in consequence of the larger
dimensions of the stage, a traversing movement may be readily
added to it. This Microscope may thus be rendered a very com-
plete instrument; but it will scarcely be so convenient in use, as
the instruments which are specially planned for a greater range
of adaptations; and the particular advantage it possesses, is for
the purpose indicated by its designation.

36. Warington’s Universal Microscope-—A new set of adapta-
tions for special purposes, called for by new requirements, has
been recently devised by Mr. Warington ; who, by different com-
binations of the same very simple materials, has produced an in-
strument which may be used in four different modes, and which
may fairly, therefore, be designated a “ universal’ microscope.
Mr. Warington’s original object was to provide an arrangement,
whereby the Compound Microscope should be brought to bear
upon living objects in an Aquarium, when these might be either
in contact with one of the glass sides, or be not far removed from
it. This he accomplished by making use of the body of a Stu-
dent’s microscope (§ 34), with the grooved limb in which it slides,
and attaching the latter by a strong cradle-joint to a tubular
stem, which could be fixed at any height upon the edge of the
table that. supports the Aqua-
rium, by means of a clamp with Fra. 28.

a binding screw. Subsequently
Mr. W. dispensed with the rack ;
attaching the cradlejoint at the
top of the tubular stem to an
outer tube, within which the
sliding of the body acts as a
“coarse” adjustment; and pro-
viding a “fine” adjustment (by
‘an ingenious plan of his own)
at the object end of the body
itself. To the Author, how-
ever, it has seemed far more
convenient to retain the rack;
and this he has combined with
the sliding tube, thus obtaining ‘Warington’s Universal Microscope, as arranged
great facility of adjustment with for viewing objects in au Aquarium.

no perceptible “twist; and

the arrangement of the apparatus, with this modification, is
shown in Fig. 23. If the rack be well cut, there will be no oc-
casion for a “fine” adjustment; since the purposes to which this
arrangement is adapted, only require low or moderate powers.
When the instrument is set up in the above position, the body
may be moved like a swivel from side to side, and it may be
inclined downwards at any degree of obliquity; but its most

106 CONSTRUCTION OF THE MICROSCOPE.

suitable position will generally be the horizontal, with its axis

Fig. 24,

Wartngton’s Universal Microscope, as arranged for Dis-
section in a large trough. (N.B.—By drawing the stem a
through the elamp, the body may be shifted to sucha dis-
tance fromthe wooden hase, that the latter need not interfere

with the dissecting trough.)

Fig. 25.

.

Warington’s Universal Microscope, arranged for ordinary use.

3 Sgih tas :
LX 8

directed at right angles
to the flat side of the
Aquarium. It is obvi-
ous that the very same
instrument, turned from
the horizontal into the
vertical position, by at-
taching the clamp (as
in Fig. 24) to the edge
ofa wooden strutt rising
vertically from a hori-
zontal slab, instead of
to the edge of a hori-
zontal table, becomes
extremely well suited
for examining objects
which are in course of
dissection in a trough
too large to be con-
veniently transferred to
the stage of the micro-
scope, for looking over
minute shells spread out
on a sheet of paper, and
for other purposes for
which a special form of
dissecting microscope
has been devised by
Messrs. Powell and Lea-
land. But again, by
turning up the L shaped
support constructed for
the last-named purpose,
so that it shall rest (as it
were) on two legs like
the Greek 2, and then
clamping the stem that
carries the body to its
highest edge, the instru-
ment acquires a position
very suitable for ordi-
nary microscope work ;
and nothing is wanted
to adapt it to this, save

. the addition of a stage

and a mirror, each of
which may be so con-
structed as to fit into a

WARINGTON’S UNIVERSAL MICROSCOPE. 107

brass socket let into the wooden support, thus completing the
Microscope in the form represented in Fig. 25. This is not the
last of the adaptations of which the instrument is capable; for the
wooden support remaining at the same inclination, the body may
be brought to the perpendicular, by shifting its stem in the clamp
and by altering its angle at the cradlejoint; whilst a horizontal po-
sition may be given to the stage, by fitting it into another socket
(Fig. 26); in this arrangement, Fria 96"

moreover, the stage acquires an ree
increase of firmness, from the
bearing of a plate that projects
at right angles from its under
surface, upon the inclined face
of the wooden support. Thusa
dissecting microscope is form-
ed, which has many of the ad-
vantages of that of Messrs.
Smith and Beck; being subject,
however, to the important
drawback, that the mirror can-
not be so placed as to reflect
the light upwards through the
axis of the microscope. (A
means of remedying this, how-
ever, might perhaps be con-
trived without much difficulty
or cost.) On the left side of
the slanting support, at a short
distance above the stage, is a :
hole into which may be fitted Warington’s Universal Microscope, arranged for
either the stem of a condens- se ae

ing lens for opaque objects, or the stem of the stage-forceps ;
either or both of which may also be fitted into holes in the front
corners of the stage. The stage is provided with a sliding ledge
for the support of objects in an inclined position; and it might
also be furnished, if required, with a diaphragm plate. One of
the chief merits of the instrument, however, being lightness and
portability, it would not be desirable to encumber it with many
accessories. or convenience of packing, the shorter portion of
the 1 piece may be connected with the longer by strong pins
fitted into sockets, instead of being permanently fixed, so that the
two can be readily disconnected and one part laid flat upon the
other; and the whole apparatus will then lie within a very small
compass.. The distinctive peculiarity of this instrument consists
in the extreme simplicity of the means by which a variety of
useful ends are obtained. It is scarcely one that should be re-
commended to the beginner ; since it is in several respects not
so well adapted for ordinary work, as the forms already described.
But itis a most valuable addition to the Microscopic apparatus of

108 CONSTRUCTION OF THE MICROSCOPE.

the Naturalist ; and may be constructed at so trifling an expense,
to work with any objectives he already may possess, that a con-
siderable’demand may be anticipated for it.!

37. We now pass to an entirely different class of instruments,
—those of which the aim is, not simplicity but perfection ; not
the production of the best effect with limited means, but the at-
tainment of everything that the Microscope can accomplish, with-
out regard to cost or complexity. This object has been certainly
carried out by the Opticians of our own country, niuch more com-
pletely than by those of the Continent; and it seems but fair to-
wards the three principal London makers, by whose labors the
present admirable results have been attained, that the pattern
finally adopted by each should be here delineated and described.
Without any invidious preference, the first place may fairly be

7 assigned to the Large
Compound Microscope
of Mr. Ross; not
only as being the
one which was first
brought (in all essen-
tial features at least) to
its present form, but
also because it is that
which contains the
greatest number of
provisions for investi-
gating objects in a
variety of different
modes. The general
plan of Mr. Ross’s Mi-
croscope will be seen
to be essentially the
same with that which
has been followed by
Mr. Fieldin the simple
form of this instru-
ment first described
‘(§ 31), as well as by
many other makers;
but it is carried out
with the greatest at-
tention to solidity of
construction, in those
parts especially which
are most liable to tremor; and we are informed by Mr. Ross,
that every part has been tested by the “inverted pendulum”

4

eM _

Ross’s Large Compound Microscope.

'This instrument has been made for Mr. Warington and for the Author by Mr.
Salmon, 100 Fenchurch Street; who supplies it, on either plan, without objectives or
case, but with condenser and stage-forceps, for 3 guineas.

ROSS’S LARGE COMPOUND MICROSCOPE. 109

(an instrument contrived to indicate otherwise insensible vibra-
tions), and either strengthened or reduced as might be found
necessary, so as to obtain an equality of vibration between the
stage and the optical part, which will prevent any percepti-
ble tremor in the image. The “coarse” adjustment 1s made by
the large milled head situated just behind the summit of the up-
rights, which turns a pinion working into arack cut on the back
of a very strong flattened stem, that carries the transverse arm at
its summit; a second milled head (which is here concealed by
the stage fittings) is attached to the other end of the axis of the
pinion (as in Fig. 18), so as to be worked with the left hand. The
“‘ fine” adjustment is effected by the milled head on the transverse
arm just behind the base of the “body;” this acts upon the
“nose” or tube projecting below the arm, wherein the objectives
are screwed. The other milled head seen at the summit of the
stem, serves to secure the transverse arm to this, and may be
tightened or slackened at pleasure, so as to regulate the travers-
ing movement of the arm; this movement is only allowed to
take place in one direction, namely, towards the right side, being
checked in the opposite by a “stop,” which secures the coinci-
dence of the axis of the body with the centre of the stage and
with the axis of the illuminating apparatus beneath it. It is in
the movements of the stage, that the greatest contrivance is
shown ; these are three, namely, a traversing movement from
side to side, a traversing movement from before backwards, and
a rotatory movement. The traversing movements, which allow
the platform carrying the object to be shifted about an inch in
each direction, are effected by the two milled heads situated at
the right of the stage; and these are placed side by side, in such
a position that one may be conveniently acted on by the fore-
finger, and the other by the middle finger, the thumb being
readily passed from one to the other. The traversing portion
of the stage carries the platform whereon the object is ]aid, which
has a ledge at the back for it to rest against; and this platform
has a sliding movement of its own, from before backwards, by
which the object is first brought near to the axis of the micro-
scope, its perfect adjustment being then obtained by the traversing
movement. To this platform, and to the traversing slides which
carry it, ‘a rotatory movement is imparted by a milled head,
placed underneath the stage on the left hand side ; for this milled
head turns a pinion which works against the circular rack (seen
in the figure) whereby the whole apparatus above is carried round
about a third of a revolution, without in the least disturbing the
place of the object,.or removing it from the field of the micro-
scope. This rotatory movement is useful for two purposes ; first,
in the examination of very delicate objects by oblique lights, in
order that, without disturbing the illuminating apparatus, the
effect of the light and shadow may be seen in every direction,
whereby important additional information is often gained; and,

110 CONSTRUCTION OF THE MICROSCOPE.

secondly, in the examination of objects under polarized light, a
class of appearances being produced by the rotation of the object
between the prisms, which is not developed by the rotation of
either of the prisms themselves. Below the stage, and in front
of the stem that carries the mirror, is a dovetail sliding bar,
which is moved up and down by the milled head shown at its
side ; this sliding bar carries what is termed by Mr. Ross the
“secondary stage” (omitted in the figure for the sake of simpli-
city), which consists of a cylindrical tube for the reception of the
achromatic condenser, the polarizing prism, and other fittings;
to this secondary stage, also, a rotatory motion is communicated
by the turning of a milled head; and a traversing movement of
limited extent is likewise given to it by means of two screws,
one on the front and the other on the left hand side of the frame
which carries it, in order thatits axis may be brought into perfect
coincidence with the axis of the “ body.” The special advantages
of this instrument consist in its perfect steadiness, in the admirable
finish of its workmanship, and in the variety of movements
which may be given both to the object and to the fittings of the
secondary stage. Its disadvantages consist in the want of porta-
bility, necessarily arising from the substantial mode of its con-
struction; and in the multiplicity of its movable parts, which
presents to the beginner an aspect of great complexity. This
complexity, however, is much more apparent than real ; for each
of these parts Has an independent action of its own, the nature
of which is very soon learned; and the various milled heads are
so disposed, that the hand readily (and at last almost instine-
tively) finds its way from one to the other, so as to make any re-
quired adjustment, whilst the eye is steadily directed to the ob-
ject. To the practised observer, therefore, this multiplication of
adjustments is a real saving of time and labor, enabling him to
do perfectly and readily what might otherwise require much
trouble, besides affording him certain capabilities which he would
not otherwise possess at all.

38. Powell and Lealand’s Compound Microscope.—This instru-
ment, represented in Fig. 28, is far lighter than the preceding in
its general “ build,” without being at all deficient in steadi-
ness; it has not, however, some of those improvements for
which Mr. Ross’s plan of construction is especially adapted.
The three-legged stand gives a firm support to the trunnions
that carry the tube to which the stage is attached, and from
which a triangular stem is raised, by the rack-and-pinion
movement set in action by the double milled head, whereby the
“coarse” adjustment of the focus is obtained. The triangular
stem carries at its summit the transverse arm, which contains
(as in Mr. Ross’s Microscope) the lever action of the “fine”
adjustment; and this is acted on by the milled head at the back
of the arm, whence also pass two oblique stays, which, being
attached to the upper part of the body, assist in preventing its

POWELL AND LEALAND’S MICROSCOPE. 111

vibration. The stage is provided with a traversing movement
in each direction, to the extent of about three-quarters of an
inch; this is effected on the plan known as Turrell’s, in which
the two milled heads Fra. 28

are placed on the, =
same axis, instead of
side by side, one of
them being also re-

peated on the left

hand of the stage, so

that the movements

may be communi-

cated either by the

right hand alone, or

by both hands in com-

bination. The plat-

form which carries

the object is made to

slide, asin the preced-

ing case, on the sum-

mit of the traversing

apparatus ; and it has

not only a_ ledge

whereon the object

may rest, but also a
“spring clip” for se-

curing it whenever
the stage may be

placed in a vertical

position. This plat-

form, moreover, is so

connected with the

traversing apparatus,

that it may be turned

round in the direction

of its plane; but as

this rotation takes place above instead of beneath the traversing
apparatus, there is no security that the centre of rotation shall
coincide with the axis of the optical portion of the instrument; so
that, unless this adjustment have been previously made, the object
will’ be thrown completely out of the field of view when the
platform is made to revolve. Hence, although this movement is
of great use in facilitating the full examination of an object,
by enabling the observer to bring it into the field of view in
every variety of position, it does not serve, like the rotatory
movement of Mr. Ross’s stage, to change the position of the
object in regard to the illuminating apparatus, without disturb-
ing the observer’s view of it. The condenser for transparent
objects, the polarizing apparatus, &c., are here fitted to the under

Powell and Lealand’s Large Compound Microscope.

112 CONSTRUCTION OF THE MICROSCOPE.

side of the principal stage itself, instead of to an independent
or secondary stage; an arrangement which, though convenient
as regards compactness, admits of less variety of adjustment
than is afforded by the latter plan. The mirror, instead of being
swung loosely upon two centres, is pivofed to one end of a
quadrant of brass, of which the other end is pivoted to a strong
pin that projects from the sliding tube; a spring being s0 at-
tached to each of these pivots, as to give to the movements of
the mirror that suitable degree of stiffness, which shall prevent
it from being disturbed by a passing touch. No instrument can
be better adapted than this to all the ordinary wants of the Mi-
croscopist ; there are very few purposes which it cannot be made
to answer; and there are many who will consider that its defi-
ciency as to these is counterbalanced (to say the least) by its
comparative simplicity and portability, as well as by its lower
cost. For the sake, however, of such as may desire the power
of obtaining a more oblique illumination, than is permitted by
the construction of the stage in the instrument just described,
Messrs. P. and L. have recently brought out a new pattern, in
which the thickness of the stage is greatly reduced, a sub-stage
is provided for the reception of the condenser and other fittings,
and the mirror is mounted on a doubly extending arm.

39. Smith and Beck's Large Microscope.—The general plan of
this instrument (Fig. 29) nearly resembles that of the “ dissecting
microscope” of the same makers, already noticed (§ 35), so far,
at least, as regards the mode of supporting the body, and of
effecting the focal adjustments; whilst in the construction of the
stage, and in the arrangement of the fittings beneath, it differs
from all the microscopes hitherto described. The stage is fur-
nished with the usual traversing movements; but it is distin-
guished by its thinness; and this is of importance in certain
cases, as admitting of a more oblique illumination than could
otherwise be obtained, and also as allowing the construction of
the achromatic condenser (§ 56) to be much simplified. The
platform for the object is fitted upon the traversing apparatus, in
the same mode asin the microscope last described, and possesses
the same kind of rotatory movement. Beneath the stage isa
continuation of the gun-metal “limb” which carries the body;
and this is ploughed out into a groove for the reception of a
sliding-bar, which carries what may be termed the “secondary
body,” namely, a short tube (seen beneath the stage), capable of
being moved up and down by a milled head, and fitted for the
reception of the achromatic condenser, polarizing apparatus, &e.
This “secondary body” consequently answers the same purpose
as the “secondary stage” of Mr. Ross’s microscope, and its rela-
tions to the other parts of the instrument are essentially the
same; but it differs in the following particulars :—first, that by
being made to work in a groove which is in perfect correspon-
dence with that wherein the principal “ body” works (this corre-

SMITH AND BECK’S LARGE MICROSCOPE. 113

spondence being secured by the action of the planing machine
that ploughs both grooves), the “secondary” body always has
its axis so perfectly continuous with that of the first, that no
special adjustment is need- Fig. 29.

ed to “centre” the greater
part of the illuminating
apparatus; and, secondly,
that the tube will carry the
achromatic condenser at
its upper end, the polaris-
ing prism at its lower, and
the selenite plates between
the two, a combination
that cannot be made in
any other instrument (§
63). Moreover, as all
these fittings are received
into a tube of which the
exact size and position are
assured, the makers of this
instrument can supply ad-
ditional apparatus at any
time, with the certainty of
its accurate adjustment.
This “secondary body,”
however, has not the rota-
tory movement possessed
by Mr. Ross’s “‘ secondary
stage ;”’ and to the limited
class of purposes, there-
fore, which that move-
ment is adapted to serve,
it cannot be adapted. Smith and Beck’s Large Compound Microscope.
The mirror is hung in the usual way between two centres;
but the semicircle that carries these, instead of being at once
pivoted to the tube which slides upon the cylindrical stem,
is attached to an intermediate arm; and by means of this
it may be placed in such a position as to reflect light very ob-
liquely upon the object,-and thus to bring out a new set of ap-
pearances, with which it is very important in certain cases to be
acquainted. In regard to weight and complexity, this instrument
holds.a position intermediate between the two last described.
The mode in which the body is supported, appears to the author
decidedly preferable to that adopted by the other makers; and
though it has the disadvantage of separating the focal adjust-
ments from each other and from the stage motions more widely
than is the case in the two preceding instruments, yet the differ-
ence is scarcely perceptible in practice. The milled heads acting
on the former are both of them in positions in which they are

8

114 CONSTRUCTION OF THE MICROSCOPE.

easily reached by the left hand, when the elbow is resting on the
table; whilst the right hand finds the milled heads of the travers-
ing stage and of the secondary body in close proximity to each
other. The imperfection of the means of giving rotation to the
object, constitutes in this, as in Powell and Lealand’s microscope,
a point of inferiority to Ross’s; the number of cases in which
such a movement is important, however, is by no means consi-
derable. On the other hand, the arrangement of the illuminating
apparatus in Smith and Beck’s Microscope, seems to the author
to present some decided advantages over that adopted by either
of the other makers; and in point of general excellence of work-
manship, this instrument cannot be surpassed.

Without any invidious comparisons, it may be safely said that
whoever desires to possess a first-class Microscope, cannot do bet-
ter than select one of the three instruments last described; the
excellence of the optical performance of the lenses supplied by
their respective makers, being so nearly on a par, that the choice
may be decided chiefly by the preference which the taste of the
purchaser, or the nature of the researches on which he may be
engaged, may lead him to entertain, for one or other of the plans
of construction which has now been brought under notice.

40. Nachet’s Binocular Microscope.—Since that remarkable
invention of Prof. Wheatstone, the Stereoscope, has led to a
general appreciation of the value of binocular vision, in conveying
to the mind a notion of the solid forms of bodies, various attempts
have been made to apply the same principle to the Microscope.
To any one who understands the principle of the Stereoscope, a
little consideration will make it obvious that this end might be
theoretically attained, by placing, two microscope-bodies at such
an angle of inclination, that their respective object-glasses should
point to the same object, whilst their eye-pieces should be at the
ordinary distance of the right and left cyes from each other; but
this practical difficulty will obviously and necessarily arise, in
bringing the two microscopes into the requisite convergence,—
that the axes of the instruments cannot be approximated suffi-
ciently closely at their lower ends, unless the objectives employed
should be of a focus so long, that the value of such an instrument
would be extremely limited. It was early seen, therefore, that
the only feasible method would be to use but a single objective
for both bodies; but to bisect the pencils of rays emerging from
this lens, so as to cause all those which have issued from the ob-
ject in such a direction as to pass through either half of it, to be
refracted into the body situated on that side; so that the two
eyes, applied to the two eye-pieces respectively, shall receive
through the two halves of the objective, two magnified images
of the object differing from each other in perspective projection,
as if the object, actually enlarged to the dimensions of its image,
had been viewed by both eyes at once at a moderate distance.

NACHET’S BINOCULAR MICROSCOPE. 115

‘That such a method would produce the Stereoscopic effect, might
be anticipated from the result of the very simple experiment of
covering the right-hand or the left-hand half of an object-glass of
low power, during the examination of any object that lies in
oblique perspective; for the two views of it thus obtained, will
be found to present just the kind and degree of difference which
is observable in stereoscopic pictures. The first attempt to put
this plan into execution, seems to have been that of Prof. Riddell,
of New Orleans; but the results of his method, as followed by
opticians on the European side of the Atlantic, were far from
answering the expectations excited by his own description of
them. The subject was both theoretically and practically inves-
tigated by Mr. Wenham, with much ability (Transactions of the
Microscopical Society, new series, Vol. I, p. 1); and a Binocular
Microscope on a pattern suggested by him, was constructed by
Messrs. Smith and Beck. This, too, was far from satisfactory in
its performance, having two capital defects; namely, first, that
the view which it gave was often pseudoscopic, the projecting por-
tions of the object appearing to be depressed, and vice versé ; and
second, that the two bodies being united at a fixed angle of con-
vergence, the distance between their axes could not be con-
veniently adapted to the varying distances of the eyes of different
individuals. The construction adopted by M. Nachet, however,
is much more successful. His method is to divide the pencil of
rays issuing from the objec- Fra. 30.

tive, by means of a prism

(Fig. 80, p) whose section is

an equilateral triangle; for

the rays a6 on the right side, .
which enter the flattened sur- |
face presented to them, are
reflected, by impinging very
obliquely against one of the |
internal faces of the prism, i
towards the left, emerging es
again from the prism, as they .
had entered it, almost at right ‘
angles; and in like manner

Ly “Ne
the rays a’ 0’ on the left side |
are reflected towards the \

6: wu

right. Each of these pencils
is received by a similar prism,
: which again changes its direc- Arrangement of Prisms in Nachet’s Binocular

tion, so as to render it parallel TEEDES EEE

to its original course; and thus the two halves a 6 and a’ b! of
the original pencil are completely separated from each other to
any interval that may be required, this interval being determined
by the distance between the central and the lateral prisms. In

116 CONSTRUCTION OF THE MICROSCOPE.

Fig. 81 is shown the Binocular Microscope constructed by M.

Fic. 31. Nachet upon this plan. The arrangement
of the base and stage is that commonly
employed in French vertical Microscopes ;
and a stem rises from the back of it, with
which the double body is connected by a
rack-and-pinion movement that gives the
focal adjustment. The apparatus of prisms
shown in Fig. 30, is placed between the
object-glass and the lower ends of the
bodies; and by means of a double-threaded
screw acted on by a milled head between
the two bodies, they may be separated
from, or approximated towards, each other;
so that the distance between their axes
may be brought to coincide with the dis-
tance between the axes of the eyes of the
individual observer. The author can con-
firm by his own experience the statement
of M. Nachet, that this instrument is en-
tirely free from that tendency to produce
pseudoscopic effects, which is the great
drawback in Prof. Riddell’s and in Mr.
Wenham’s arrangements; and it comes so
near the theoretical standard of perfection,
when used with low powers of moderate
Nachet's Binocular Microscope. anerture, that its performance may be con-
sidered highly satisfactory. Its definition, however, when used
with higher powers of larger angular aperture, has not yet been
rendered sufficiently good, to enable it to afford a satisfactory
view of the more difficult class of test-objects; and it may be
doubted whether, considering the number of deflections which
the rays undergo in their course, such perfect definition is to be
anticipated. For although their general course on entering and
emerging from each prism may be perpendicular to its surfaces,
so that they suffer no refraction, many of them will be slightly
oblique, and will therefore undergo not only refraction, but also
some amount of chromatic dispersion. And it is moreover to be
recollected, that when high powers are being employed, and
especially such as are of large angular aperture, the smallest de-
parture from exactitude in the focal adjustment gives indistinct-
ness to the image. Now the special object of this instrument
being to convey to the mind the notion of the solid forms of
objects, of which some parts project more than others, it is obvi-
ous that the rays proceeding from the projecting parts cannot be
so nearly brought to the same focus with those from the receding,
as to produce an even tolerably distinct image of both at once.
It seems likely to be only with objectives of comparatively low
power and small angular aperture, that images suitable for the

NACHET’S BINOCULAR MICROSCOPE, 117

production of Stereoscopic effects will be produced; but for cer-
tain classes of objects, this mode of exhibition is most admirably
adapted, the solid forms of the Polycystina (Chap. X), for example,
being brought out by it (especially when they are viewed as
opaque, not as transparent objects) with such a reality, as to
make them resemble carved ivory balls which the hand feels
ready to grasp.

41, The same method of dividing the pencil of rays issuing
from the object glass, by a separating prism placed in its course,
has been applied by M. Nachet to another purpose,—that of en-
abling two or more observers to look at the same object at once,
which is often a matter not only of considerable convenience,
but also of great importance, especially in the demonstration of
dissections. The account given by M. Nachet of the construc-
tion of this instrument, as adapted for two persons, will be found
in the “Quarterly Journal of Microscopical Science,” Vol. II,
p. 72; he has subsequently devised another arrangement, by
which the form of the separating prism is adapted to divide the
pencil into three or even four parts, each of which may be di-
rected into a different body, so as to give to several observers at
one time a nearly identical image of the same object. Of course,
the larger the number of secondary pencils into which the pri-
mary pencil is thus divided, the smaller will be the share of light
which each observer will receive ; but this reduction does not in-
terfere with the distinctness of the image, and may be in some
degree compensated by a greater intensity of illumination. (See

Appendix for a description of American instruments and mo-
difications.) ,

CHAPTER ILI.
ACCESSORY APPARATUS.

42. In describing the various pieces of accessory apparatus
with which the Microscope may be furnished, it will be con-
venient in the first place to treat of those which form (when in
use) part of the instrument itself, being Appendages either to its
Body or to its Stage, or serving for the Hlumination of the ob-
jects which are under examination ; and secondly to notice such
as have for their function to facilitate that examination, by en-
abling the microscopist to bring the Objects conveniently under
his inspection.

Section 1. APPENDAGES TO THE Microscope.

43. Draw-Tube.—It is advantageous for many purposes, that
the Eye-piece should be fitted, not at once into the “ body” of
the Microscope, but into an intermediate tube ; the drawing out
of which, by augmenting the distance between the object-glass
and the image which it forms in the focus of the eye-glass, still
further augments the size of the image in relation to that of the
object (§ 20). For although the magnifying power cannot be
thus increased with advantage to any considerable extent, yet, if
the corrections of the object-glass have been perfectly adjusted,
its performance is not seriously impaired by a moderate lengthen-
ing of the body ; and this may be conveniently had recourse to on
many occasions, in which some amplification is desired, inter-
mediate between the powers furnished by any two objectives.
Thus if one object-glass give a power of 80 diameters, and
another a power of 120, by using the first and drawing the eye-
piece, its power may be increased to 100. Again, itis often very
useful to make the object fill up the whole, or nearly the whole,
of the field of view: thus if an object that is being viewed by
transmitted rays, is so far from transparent as to require a strong
light to render its details visible, the distinctness of its details 1s
very much interfered with, if, through its not occupying the
peripheral part of the field, a glare of light enter the eye around
its margin ; and the importance of this adjustment is even greater,
if opaque objects mounted on black disks are being viewed by

DRAW-TUBE—ERECTOR. 119

the Lieberkthn (§ 65), since if any light be transmitted to the

eye direct from the mirror, in consequence of the disk failing to
‘ occupy the centre field, it greatly interferes with the vividness
and distinctness of the image of the object. In the use of the
Micrometric eye-pieces to be presently described (§§ 45, 46), very
great advantage is to be derived from the assistance of the draw-
tube; as enabling us to make a precise adjustment between the
divisions of the stage micrometer, and those of the eye-piece mi-
crometer; and as.admitting the establishment of a more con-
venient numerical relation between the two, than could be other-
wise secured without far more elaborate contrivances. More-
over, if, for the sake of saving room in packing, it be desired to
reduce the length of the body, the draw-tube affords a ready
means of doing so; since the body may be made to “shut up,”
like a telescope, to little more than half its length, without any
impairment of the optical performance of the instrument when
mounted for use.

44, Hrector.—It is only, however, in the use of the Erector,
that the full value of the draw-tube, and the advantage of giving
to it a rack-and-pinion movement of its own (§ 35),
come to be fully appreciated. This instrument, first
applied to the Compound Microscope by Mr. Lister,
consists of a tube about three inches long, having a
meniscus at one end and a plano-convex lens at
the other (the convex sides being upwards in each
case), with a diaphragm nearly half way between
them; and this is screwed into the lower end of the
draw-tube, as shown in Fig. 32. Its effect is (like
the corresponding erector of the Telescope), to an-
‘tagonize the reversion of the image formed by the
object-glass, by producing a second reversion, so as
to make the image presented to the eye correspond
in position with the object. The passage of the rays
through two additional lenses, of course occasions a
certain loss of light by reflection from their surfaces,
besides subjecting them to aberrations whereby the
distinctness of the image is somewhat impaired; but
this need not be an obstacle to its use for the
class of purposes for which it is especially adapted in
other respects (§ 35), since these seldom require a Pran-tube iltea
very high degree of defining power. By the position
given to the Erector, it is made subservient to another pur-
pose, of great utility; namely, the procuring a very extensive
range of magnifying power, without any change in the objective.
For when the draw-tube, with the erector fitted to it, is com-
pletely pushed in, the acting length of the body (so to speak) is
so greatly reduced by the formation of the first image much
nearer the objective, that, if a lens of 8-10ths of an inch focus be
employed, an object of the diameter of 1 inch can be taken in,

Fig. 32,

120 ACCESSORY APPARATUS.

and enlarged to no more than 4 diameters; whilst, on the other
hand, when the tube is drawn out to its whole length, the ob-
ject is enlarged 100 diameters. Of course every intermediate
range can be obtained, by drawing out the tube more or less;
and the facility with which this can be accomplished, renders
such an instrument most useful in various kinds of research,
especially those in which it is important, after finding an object
with a lower power, to examine it under a higher amplification ;
since this may be done, without either a change of objectives, or
a transfer of the object to another microscope fitted with a dif:
ferent power. It is when the draw-tube is thus made subservient
to the use of the Erector, that the value of its rack-and-pinion
adjustment is most felt; for by giving motion to the milled head
which acts upon this (Fig. 22) with one hand, whilst the other
hand is kept upon the milled head which moves the whole body
(it being necessary to shorten the distance between the object
and the objective, in proportion as the distance of the image
from the objective is increased), the observer—after a little prac-
tice in the working together of the two adjustments—may al-
most instantaneously alter his power to any amount of amplifica-
tion which he may find the object to require, without ever losing
a tolerably distinct view of it. This can scarcely be accomplished
without the rack movement; since, if both hands be required to
make the alteration of the draw-tube, the readjustment of the
focus must be effected subsequently.

45. Micrometer.—Although some have applied their micro-
metric apparatus to the stage of the microscope, yet it is to the
Eye-piece that it may be most advantageously adapted.1 The
cobweb micrometer, invented by Ramsden for Telescopes, is pro-
bably, when well constructed, the most perfect instrument that
the Microscopist can employ. It is made by stretching across
the field of a “positive” eye-piece (§ 23) two very delicate paral-
lel wires or cobwebs, one of which can be separated from the
other by the action of a fine-threaded screw, the head of which
is divided at its edge into a convenient number of parts, which
successively pass by an index as the milled head is turned. A por-
tion of the field of view on one side is cut off at right angles to
the cobweb threads, by a scale formed of a thin plate of brass
having notches at its edge, whose distance corresponds to that
of the threads of the screw, every fifth notch being made deeper
than the rest for the sake of ready enumeration. The object
being brought into such a position that one of its edges seems to
touch the stationary thread, the other thread is moved by the
micrometer screw, until it appear to lie in contact with the other
edge of the object; the number of entire divisions on the scale

1 The Stage-micrometer constructed by Fratinhofer is employed by many continental
Microscopists; but it is subject to this disadvantage,—that any error in its performance
is augmented by the whole magnifying power employed; whilst a like error in the Eye-
piece-micrometer is increased by the magnifying power of the eye-piece alone.

MICROMETER EYE-PIECE. 121

shows how many complete turns of the screw must have been
made in thus separating the threads ; while the number to which
the index points on the milled head, shows what fraction of a
turn may have been made in addition. It is usual, by employ-
ing a screw of 100 threads to the inch, to give to each division
of the scale the value of 1-100th of an inch, and to divide the
milled head into 100 parts; but the absolute value of the divi-
sions is of little consequence, since their micrometric value de-
pends upon the objective with which the instrument may be em-
ployed. This must be determined by means of a ruled slip of
glass laid upon the stage; and as the distance of the divisions
even in the best ruled slip is by no means uniform,’ it is advisa-
ble to take an average of several measurements, both upon dif-
ferent slips, and upon different parts of the same slip. Here the
draw-tube will be of essential use, in enabling the microscopist
to bring the value of the divisions of his Micrometer to even num-
bers. Thus, suppose that with a 1-4th-inch object-glass, the tube
being pushed in, a separation of the lines by one entire turn
and 37-100ths of another were needed to take in the space be-
tween two lines on the ruled slip, whose actual distance is
1-1000th of an inch; then it is obvious that 137 divisions on the
milled head are equivalent with that power to a dimension of
1-1000th of an inch, or the value of each division is 1-137,000th
of aninch. But as this is an awkward number for calculation,
the magnifying power may be readily increased by means of the
draw-tube, until the space of 1-1000th of an inch shall be repre-
sented by a separation of the cobweb threads to the extent of
150 divisions; thus giving to each division the much more con-
venient value of 1-150,000th of an inch. The Microscopist who
applies himself to researches requiring micrometric measure-
ment, should determine the value of his Micrometer with each
of the objectives he is likely to use for the purpose ; and should
keep a table of these determinations, recording in each case the
extent to which the tube has been drawn out, as marked by the
graduated scale of inches which it should possess. The accuracy
with which measurements may be made with this instrument, is
not really quite so minute as it appears to be; for itis found
practically that when the milled head is so graduated, that, by
moving it through a single division, the cobweb threads are se-
parated or approximated by no more than 1-10,000th of an inch,
it needs to be moved through four divisions, for any change in
the position of the threads to be made sensible to the eye. Con-
sequently, if three entire turns, or 300 divisions, were found to
separate the threads so far as to coincide with a distance of
1-1000th of an inch on the ruled glass under a 1-8th of an inch

' OF the degree of this inequality, some idea may be formed from the statement of
Hannover, that the value of the different divisions of a glass ruled by Chevalier to
1-100th of a millimetre, varied between the extreme ratios of 31°36, the mean of all
being 34.

122 ACCESSORY APPARATUS.

objective, although each division of the milled head, will thus
represent 1-300,000th of an inch, yet the smallest measurable
space will be four times that amount, or 1-75,000th of an inch.
With the 1-12th inch objective, the smallest measurable space
may be about 1-100,000th of an inch. ;

46. The expensiveness of the cobweb-micrometer being an im-
portant obstacle to its general use, a simpler method is more com-
monly adopted, which consists in the insertion of a transparent
scale into the focus of the eye-piece, on which the image of the
object is seen to be projected. By Mr. Ross, who first devised
this method, the “ positive” eye-piece was employed, and a glass
plate ruled in squares was attached beneath its field-glass, at such
a distance that it and the image of the object should be in focus
together ; and the value of these squares having been determined
with each of the objectives, in the manner already described, the
size of the object was estimated by the proportion of the square
that might be occupied by its image. While the use of the posi-
tive eye-piece, however, renders the definition of the ruled lines
peculiarly distinct, it impairs the definition of the object; and
the “ negative” or common Huyghenian eye-piece is now gene-
rally preferred. The arrangement devised by Mr. G. Jackson
allows the divided glass to be introduced into the ordinary eye-
piece (thus dispensing with the necessity for one specially adapted
for micrometry), and greatly increases the facility and accuracy
with which the eye-piece scale may be used. This scale is ruled
like that of an ordinary measure (7. e. with every tenth line long,
and every fifth line half its length), on a slip of glass, which is
so fitted into a brass frame (Fig. 33, B), as to have a slight motion
towards either end;
one of its extremities
is pressed upon by a
small fine milled-head-
ed screw which works
through the frame, and
the other by a spring
(concealedin the figure)
which antagonizes the
screw. The scale thus
mounted is introduced
through a pair of slits
in the eye-piece tube,
B immediately above the
diaphragm (Fig. 33, 4),

so as to oceupy the

¥ centre of the field ; and
| it is brought accurately

into focus by unscrew-
: ing the glass nearest to
the eye, until the lines of the scale are clearly seen. The value

Fig. 83.

Mr, Jackson’s Eye-piece Micrometer.

MICROMETER EYE-PIECE. 133

of the divisions of this scale must be determined, as in the for-
mer instance, by means of a ruled stage-micrometer, for each
objective employed in micrometry (the drawing out of the eye-
piece tube enabling the proportions to be adjusted to even and
convenient numbers); and this having been accomplished, the
scale is brought to bear upon the object to be measured, by moving
the latter as nearly as possible into the centre of the field, and
then rotating the eye-piece in such a manner, that the scale may
lie across that diameter which it is desired to measure. The push-
ing-screw at the extremity of the scale being then turned, until
one edge of the object is.in exact contact with one of the long
lines, the number of divisions which its diameter occupies is at
once read off by directing the attention to the other edge,—the
operation, as Mr. Quekett justly remarks, being nothing more
than laying a rule across the body to be measured. This method
of measurement may be made quite exact enough for all ordi-
nary purposes, provided, in the first place, that the eye-piece
scale be divided with a fair degree of accuracy; and secondly,
that the value of its divisions be ascertained (as in the case of
the cobweb-micrometer) by several comparisons with the scale
laid upon the stage. Thus if; by a mean of numerous observa-
tions, we establish the value of each division of the eye-piece
scale to be 1-12,500th of an inch, then, if the image of an object
be found to measure 33 of those divisions, its real diameter will
be 32 x yaéy5 or 1-8571st of an inch... Now as, with an objec-
tive of 1-12th inch focus, the value of the divisions of the eye-
piece scale may be reduced to 1-25,000th of an inch, and as the
eye can estimate a fourth ‘part of one of ‘the divisions with tole-
rable accuracy, it follows that a magnitude of as little as
1-100,000th of an inch can be measured with a near approach to
exactness, and that this instrument cannot be fairly considered as
ranking much below the cobweb-micrometer in minute accuracy.
At any rate, it is sufficiently precise (when due care is employed)
for all ordinary purposes; and it has the great advantage of
cheapness and simplicity. Whatever method be adopted, if the
measurement be made in the Eye-piece, and not on the stage,
it will be necessary to make allowance for the adjustment of the
object-glass to the thickness of the glass that covers the object,
since its magnifying power is considerably affected by the separa-
tion of the front pair of lenses from those behind it (§ 83). It
will be found convenient to compensate for this alteration, by
altering the draw-tube in such a manner as to neutralize the
effect. produced by the adjustment of the objective; thus giving
one uniform value to the divisions of the eye-piece scale, what-

1 The calculation of the dimensions is most simplified by the adoption of a decimal
scale ; the value of each division being made, by the use of the draw-tube adjustment,
to correspond to some aliquot part of a ten-thousandth or a hundred-thousandth of an
inch, and the dimensions of the object being then found by simple multiplication :—Thus
(to take the above example) the value of each division in the decimal scale is ‘00008,
and the diameter of the object is 00028.

1é4 ACCESSORY APPARATUS.

ever may be the thickness of the covering-glass: the amount of
the alteration required for each degree must of course be deter-
mined by a series of measurements with the stage-micrometer,
and should be recorded on the table of the micrometric values of
the several objectives.

47. Goniometer—When the Microscope is employed in re-
searches on minute crystals, a means of measuring their angles
is provided by the adaptation of a goniometer to the eye-piece,
The simplest form (contrived by Schmidt and made by Ross)
which answers sufficiently well for all ordinary purposes, essen-
tially consists merely of a “‘positive’’ eye-piece, with a single
cobweb-thread stretched across it diametrically in a circular frame
capable of rotation; the edges of this frame are graduated in de-
grees, and a vernier is also attached to the index, whereby frac-
tional parts of degrees may be read off. By rotating the frame
carrying the thread, so that it shall lie successively in the direc-
tions of the two sides of the crystal, the angle which they form
is at once measured by the difference of the degrees to which the
index points on the two occasions. For the cobweb-thread, a
glass plate, ruled with parallel lines at about the 1-50th of an
inch asunder, may be advantageously substituted; since it is not
then necessary to bring the crystal into such a position as to lie
along the diametrical thread, but its angle may be measured by
means of any one of the lines to which it happens to be nearest.
If a higher clegree of precision be required than this instrument
is fitted to afford, the Doudble-refracting Goniometer, invented by
Dr. Leeson, may be substituted; for a description of which (too
long to be introduced here) the reader is referred to Dr. L.’s ac-
count in the “ Proceedings of the Chemical Society,” Part xxxiii,
and to Mr. Quekett’s ‘“ Practical Treatise on the Microscope.”
(See Appendix for a description of a Micrometer and Goniometer,
by Prof. J. L. Smith.)

48. Inedicator.—When the Microscope is used for the purpose
of demonstrating to others such objects as may not be at once
distinguished by the uninitiated eye, it is very useful to introduce
into the eye-piece, just over the diaphragm, a small steel hand
pointing to nearly the centre of the field; to whose extremity
the particular portion of the image which the observer is intended
to look at, is to be brought by moving the object. The hand
may be so attached, as to be readily turned back when not re-
quired; leaving the field of the eye-piece quite free. This little
contrivance, which was devised by Mr. J. Quekett, is appropri-
ately termed by him the indicator.

49. Camera Lucida.—Various contrivances may be adapted to
the eye-piece, in order to enable the observer to see the image
projected upon a surface whereon he may trace its outlines. The
one most generally employed is the Camera Lucida prism con-
trived by Dr. Wollaston for the general purposes of delineation;
this being fitted on the front of the eye-piece, in place of the

CAMERA LUCIDA. 125

“cap”: by which it is usually surmounted. The Microscope being
placed in a horizontal position, as shown in Fig. 34, the rays
which pass through the eye-piece into the prism, sustain such a
total reflection
from its oblique
surface, that they
come to its upper
horizontal —sur-
face at right an-
gles to their pre-
vious direction ;
and the eye being
so placed over
the edge of this
surface, that it
receives _ these
rays from the
prism through
part of the pupil,
whilst it looks
beyond the
prism, down to a
white-paper surface on the table, with the other half, it sees the
image so strongly and clearly projected upon that surface, that
the only difficulty in tracing it arises from a certain incapacity
which seems to exist in some individuals, for seeing the image
and the tracing-point at the same time. This difficulty (which
is common to all instruments devised for this purpose) is lessened
by the interposition of a slightly convex lens in the position
shown in the figure, between the eye and the paper, in order
that the rays from the paper and tracing-point may diverge at
the same angle as those which are received from the prism; and
it may be generally got over altogether, by experimentally modi-
fying the relative degrees of light received from the object and
from the paper. If the image be too bright, the paper, the
tracing-point, and the outline it has made, are scarcely seen; and
either less light may be allowed to come from the object, or
more light (as by a taper held near) may be thrown on the paper
and tracing-point. Sometimes, on the other hand, measures of
the contrary kind must be taken. Instead of the prism, some
microscopists prefer a speculum of polished steel, of smaller size
than the ordinary pupil of the eye, fixed at an angle of 45° in
front of the eye-piece ; and this answers exactly the same purpose
as the precéding, since the rays from the eye-piece are reflected
vertically upwards to the central part of the pupil placed above
the mirror, whilst, as the eye also receives rays from the paper
and tracer, in the same direction, through the peripheral portion
of the pupil, the image formed by the microscope is visually pro-
jected downwards, as in the preceding case. This disk, the in-

Fre, 34,

Microscope arranged with Camera Lucida for Drawing or Micrometry.

126 ACCESSORY APPARATUS,

vention of the celebrated anatomist Soemmering, is preferred by
some microscopic delineators to the caimera lucida. The fact is,
however (as the author can testify from his own experience), that
there is a sort of “knack” in the use of each instrument, which
is commonly acquired by practice alone; and that a person habi-
tuated to the use of either of them, does not at first work well
with another. <A different plan is preferred by some micro-
scopists, which consists in the substitution of a plate of neutral-
tint or darkened glass for the oblique mirror; the eye receiving
at the same time the rays of the microscopic image, which are
obliquely reflected to it from the surface of the glass, and those
of the paper, tracing-point, &c., which come to it through the
glass. It is so extremely useful to the microscopist, to be able to
take outlines with one or other of these instruments, that every
one would do well to practise the art. Although some persons
at once acquire the power of sceing the image and the tracing-
point with equal distinctness, the case is more frequently other-
wise; and hence no one should allow himself to be bafiled by the
failure of his first attempt. It will sometimes happen, especially
when the prism is employed, that the want of power to see the
pencil is due to the faulty position of the eye, too large a part of
it being over the prism itself. When once a good position has
been obtained, the eye should be held there as steadily as possi-
ble, until the tracing shall have been completed. It is essential
to keep in view, that the proportion between the size of the
tracing and that of the object, is affected by the height of the eye
above the paper; and hence that if the microscope be placed
upon a support of different thickness, or the eye-piece be elevated
or depressed by a slight inclination given to the body, the scale
will be altered. This it is of course peculiarly important to bear
in mind, when a series of tracings is being made of any set of
objects which it is intended to delineate on a uniform scale; or
when the camera lucida (or any similar arrangement) is employed
for the purpose of Micrometry. All that is requisite to turn it to
this account, is an accurately divided stage-micrometer, which,
being placed in the position of the object, enables the observer
to see its lines projected upon the surface upon which he has
drawn his outline; for if the divisions be marked upon the paper,
the average of several be taken, and the paper be then divided
by parallel lines at the distance thus ascertained (the spaces being
subdivided by intermediate lines, if desirable), a very accurate
scale is furnished, by which the dimensions of any objects drawn
in outline under the same power may be minutely determined.
Thus if the divisions of a stage-micrometer, the real value of each
of which is 1-200th of an inch, should be projected with such a
magnifying power, as to be at the distance of an inch from one
another on the paper, it is obvious that an ordinary inch-scale
applied to the measurement of an outline, would give its dimen-
sions in two-hundredths of an inch, whilst each fifth of that scale

OBJECT-GLASS HOLDER—OBJECT-MARKER. 127

would be the equivalent of a thousandth of an inch. When a
sufficient magnifying power is used, and the scale thus made is
minutely divided, great accuracy may be obtained. It has been
by the use of this method, that Mr. Gulliver has made his admi-
rable series of measurements of the diameters of the Blood-cor-
puscles of different animals.

50. Object-Glass Holder.—In Microscopes of the old construc-
tion, whose objectives were single lenses, these were not unfre-
quently mounted near the periphery of a circular disk pivoted
to the lower end of the body, in such a manner that any desired
power might at once be brought into use by merely rotating the
disk. Since the introduction of achromatic object-glasses, this
method has been until recently abandoned ; every “power” being
separately connected with the extremity of the body, so as not to
admit of any substitution, save by screwing off one objective and
screwing on another. The old method, however, has been par-
tially reverted to by Mr. C. Brooke; who has contrived a holder
into which two objectives may be screwed, and which, being
attached to the “‘nose’’ of the body, enables either of them to be
brought into position, by simply turning the arm on its pivot.
This is an extremely convenient arrangement, and might easily
be carried further if desired; since, by having a tri-radiate or
quadri-radiate arm, three or four powers might be thus brought
into use successively, with as much facility as two. The principal
objection to the general use of such an appendage, lies in the
nicety of workmanship that is required to obtain that exact
“centering,” which is needed to bring the axis of the objective
into precise continuity with that of the body; and unless this be
attained, the performance of the instrument is greatly impaired.
In microscopes of the old construction, the other imperfections
were so great, that none but an excessive deficiency in this
respect would attract attention.- The convenience of such an
instantaneous change in the power of the objective is very great;
since it is continually desirable to obtain a general view of an
object with a low power, and to examine the parts of it in detail
under a higher amplification, with as little expenditure of time
and trouble as possible.

51. Object-Marker.—All Microscopists occasionally, and some
continually, feel the need of a ready means of finding, upon a
glass slide, the particular object or portion of an object, which
they desire to bring into view; and various contrivances have
been suggested for the purpose. Where different magnifying
powers can be readily substituted one for another, as by the use
of the Erector (§ 44) or of the Object-glass holder (§ 50), no special
means are required; since, when the object has been found by
a low power, and brought into the centre of the field, it is rightly
placed for examination by any other objective. Even this slight
trouble, however, may be saved by the adoption of more special
methods; among the simplest of which is marking the position of

128 ACCESSORY APPARATUS.

the object on the surface of the thin glass which covers it. The
readiest mode of doing this, when the object is large enough to
be distinguished by the naked eye, is to make asmall ring round
it with a fine camel-hair pencil dipped in Indian ink; but when
the object is not thus visible, the slide must be laid in position
on the stage, the object “found” in the microscope, the con-
denser adjusted to give a bright and defined circle of light, and
then, the microscope-body being withdrawn, the black ring is to
be marked around the illuminated spot. The same end, how-
ever, may be more precisely as well as more neatly accomplished,
by attaching an object-marker to the objective itself. That of
Mr. Tomes consists simply of an ivory cap, fitting over the 1-4th-
inch objective, having its extremity narrowed down (like that of
the objective itself), but perforated in the centre, so as to form a
minute ring; the object having been “ found” and brought into
the centre of the field, the cap is placed upon the objective, the
ring is blackened with Indian ink, and then, being carefully
brought by the focal adjustment into contact with the surface of
the glass, it stamps on this a minute circle enclosing the object.
A more elaborate contrivance of a similar kind, for marking a
circle round the object by a diamond point, attached to a cap
fitting on the objective, has been recently described by Mr. Bridg-
man (“ Quarterly Microscopical Journal,” vol. iii, p. 237); this
has the advantage of admitting a variation in the size of the
circle, and also of substituting a delicate line for the broad ring
which may partly obscure some neighboring object; but, on the
other hand, the very delicacy of the diamond marks prevents
them from being readily distinguished, and some kinds of glass.
are so apt to “star’’ when marked with a diamond point, that
cracks or splinters may extend from the circle over the object it
is intended to indicate. The most unobjectionable and satisfac-
tory mode of “finding” an object, however, is, in the Author's
opinion, that which is afforded by a graduation of the movable
parts of the stage, in the manner to be presently described (§ 53).
52. Lever Stage.—The general arrangement of the Traversing
Stage, now usually adapted to all high class Microscopes, has
been already explained (§§ 87-39); and though the details are
differently constructed by the several makers, yet the general
principle is, that a lateral or horizontal movement is given to the
object-platform by one milled head, and a front to back or verti-
cal movement (the microscope being supposed to be placed in an
inclined position) by another. The stage may be so constructed,
however, that motion shall be given to the object-platform by
means of a lever acting upon it in any required direction ; this
being accomplished by making the object-platform slide laterally
on an intermediate plate, and by making the latter slide verti-
cally upon the fixed stage-plate which forms the basis of the
whole; each pair of plates being connected by dovetailed slides
and grooves. Thus the object-platform may be readily made to

LEVER STAGE—OBJECT- FINDER. 129

traverse, not merely horizontally or vertically, but, by the simul-
taneous sliding of both plates, in any intermediate direction.
This is especially convenient in following the movements of Ani-
malcules, &c., for which purpose this lever-stage is to be pre-
ferred to the ordinary form: its use being attended with this
particular facility, that, as the motion of the hand is reversed by
the lever, so that the object moves in the opposite direction, and
as the motion of the object is again reversed to the eye by the
microscope, the image moves in the same direction as the hand;
and thus, with a little practice, even the most rapid swimmer
may be kept within the field by the dexterous management of
the lever. For general purposes, however, the ordinary tra-
versing stage will be found most convenient.

58. Odject-Finder.—Hither kind of movable stage admits of a
simple addition, which very much facilitates the “finding” of
minute objects mounted in slides, that are not distinguishable by
the naked eye; such, for example, as the particular forms that
present themselves in Diatomaceous deposits. This “finder”
consists of two graduated scales, one of them vertical, attached
to the fixed stage-plate, and the other horizontal, attached to an
arm carried by the intermediate plate; the first of these scales
enables the observer to “set” the vertically sliding plate to any
determinate position in relation to the fixed plate, while the
second gives him the like power of setting the horizontally sliding
plate by the intermediate. In order to make use of these scales, it
is of course necessary that the sliding and rotating platform on
which the object immediately rests, should be always brought
into one constant position upon the traversing plates beneath ;
this is accomplished by means of a pair of stops, against which it
should be brought to bear. So, again, this sliding plate or ob-
ject-platform should itself be furnished with a “stop” for the
glass slide to abut against, so as to secure this being always laid
in the same position. These stops may be made removable, so
as not to interfere with the ordinary working of the stage. Now
supposing an observer to be examining a newly-mounted slide,
containing any objects which he is likely to wish to find on some
future occasion; he first lays the slide on the object-platform,
with its lower edge resting on the ledge, and its end abutting
against the lateral stop, and brings the object-platform itself into
its fixed place against the stops; then if, on sweeping through
the slide, he meet with any particular form worthy of note, he
reads off its position upon the two scales, and records it in any
convenient mode. The scale may be divided to 50ths of an inch,
and each of these spaces may be again halved by the eye; the
record may perhaps be best made thus,— Triceratium favus 28; ;—
the upper number always referring to the upper scale, which is
the horizontal, and the lower to the vertical. Now whenever
the Microscopist may wish again to bring this object under exa-
mination, he has merely to lay the slide in the same position on

180 ACCESSORY APPARATUS.

the platform, to bring the platform itself into its fixed place on the
traversing plate below, and then to adjust the traversing plates
themselves by their respective scales. Even a non-movable stage
may have a similar pair of scales adapted to it; the vertical scale
being so placed, as to mark the position into which the object-
platform is brought by sliding it up or down; and the horizontal
scale being marked upon the object-platform itself, so as to allow
the observer to note the precise position of the end @f the glass
slide. Thus let it be supposed that, by shifting the slide from
side to side, and by moving the object-platform up or down, a
certain object has been brought into the field; if the place of
the object-platform and of the slide be then noted by the vertical
and the horizontal scales, the object may be found at any future
time without difficulty, by readjusting the slide and the object-
platform to the same numbers.'' The numbers referring to each
object may either be marked upon the slides themselves, like
the names of the objects, or may be recorded with these in a
separate list, referring to the slides by figures alone. The gene-
ral adoption of such a plan, though involving a little more labor
at first, would prove in the end to be a great saving both of time
and trouble.

54. Magnetic Stage.—If a stage be unprovided with a travers-
ing movement of any kind, there is no means of allowing the
object to be moved in all directions with smoothness and facility,
and yet of holding it in any position in which the Microscopist
desires to retain it, more convenient and more ready of applica-
tion, than is furnished by magnetic attraction. A magnetic
stage was originally proposed by Mr. King of Bristol ; but seems
to have been first brought into efficient practical action by Mr.
G. Busk. His plan consists in attaching two semicircular mag-
nets to the under side of the stage, so as nearly to surround its
aperture, and in inserting, for the conveyance of the magnetic
force to the upper side, four soft iron pegs, which slightly pro-
ject above its surface ; over these an object-bearer of soft iron,
with its under surface ground smooth and true, will slide so
readily, as to admit of very easy and precise adjustment of the

1 The first of the above plans, to the utility and accuracy of which the Author can
bear strong testimony, was suggested by Mr. Okeden in the “Quart. Microsc. Journal,”
vol. iii, p. 166. The second had been previously suggested by Mr. E. G. Wright in the
same Journal, vol. i, p. 302; the descriptions of both are made clear by figures. Other
“ finders” are described and figured by Mr. J. Tyrrel, Mr. T. E. Amyot, and Mr. Bridg-
man, at pp. 234 and 302-304 of the last-named volume. It appears to the Author that
Mr. Okeden’s plan might be adopted with very little tronble or expense in every Mi-
croscope possessed of a stage movement, and Mr. Wright’s in every Microscope with a
fixed stage but movable object-carrier; and that it would be very desirable for every
microscope thatmay be made hereafter, to be furnished with such scales. If the dif
ferent makers could agree upon some common system of graduation, in the same way
as Microscopists have adopted 3 inches by 1 as the standard dimension of object-
slides, much trouble would be saved to observers at a distance from one another, who
might wish to examine each others’ objects; for the numerical reference attached to

each object would then enable it to be found by every observer, whose stage should be
graduated upon the same method.

MAGNETIC STAGE—DIAPHRAGM-PLATE. 131

place of the object by a steady and practised hand. Another ar-
rangement, which has some advantages over the preceding, has
been proposed by Mr. J. B. Spencer; this consists in surround-
ing the aperture of the stage by a ring of soft iron, the surface
of which projects very slightly above the brass plate, the mag-
nets (cut out of sheet-steel) being attached to the under side of
the object-bearer. This method is perhaps more readily applica-
ble than Mr. Busk’s to the stage of any microscope, and will pro-
bably interfere less with its other fittings.'

55. Diaphragm-Plate.-—No microscope stage should ever be
without a diaphragm-plate fitted to its under surface, for the sake
of restricting the amount of light reflected from the mirror, and
of limiting the angle at which its rays impinge on the object
(see Figs. 18 and 21). This plate should always be at least half
an inch below the object, since it is otherwise comparatively in-
operative ; and thus, whilst it may be fixed immediately beneath
a movable stage whose thickness serves to remove it sufficiently
far, it should be fixed on the end of ashort tube forming a sort of
well on the under side of the stage, when this consists of but a
single fixed plate. The diaphragm-plate should be perforated
with holes of several different sizes, in the largest of which it is
convenient to fit a ground-glass (this, by means of a screw-socket,
may be made removable at pleasure), the use of which is to dif-
fuse a soft and equable light over the field, when large trans-
parent objects (such as sections of wood) are under examination ;
between the smallest and the largest aperture, there should be an
unperforated space, to serve as a dark background for opaque
objects. The diaphragm-plate itself, the “well” of the stage, in
fact every part through which light passes to the object from be-
neath, should be blackened, in order to avoid the interference
that would be occasioned by irregularly reflected rays. The edge
of the diaphragm-plate should be notched at certain intervals,
and a spring catch fitted so as to drop into the notches, in order
that each aperture may be brought into its proper central posi-
tion. This simple arrangement, in combination with the mirror
(which should be concave on one side and plane on the other)
and side-condenser (§ 64), affords to the Microscopist all the
means of illuminating his objects, whether transparent or opaque,
which are ordinarily requisite: to bring out the highest powers
of the instrument, however, more refined methods of illumina-
tion are required ; and a far greater variety of treatment is needed
in the case of many objects, the determination of whose true
characters is a matter of difficulty, even under every advantage
which can be derived from assistance of this kind.

56. Achromatic Condenser.—In almost every case in which an
objective of 1-4th inch or any shorter focus is employed, its per-

‘ For a more detailed description, with illustrative figures, of Mr. Busk’s Magnetic

Stage, see “Quarterly Microsc. Journal,” vol. ii, p. 280; and for Mr. Spencer's, vol.
iii, p. 173.

1382 ACCESSORY APPARATUS.

formance is greatly improved by the interposition of an achro-
matic combination between the mirror and the object, in such a
manner that the rays reflected from the former shall be brought
to a focus in the spot to which the objective is directed. This
may be accomplished sufficiently well for ordinary purposes, by
adapting a French triple combination of about 1-4th inch focus,
to the end of a tube 1} inch long, which shall slide within an-
other tube fitted to the opening in the stage, by the bayonet
catch or any similar connection that gives attachment to the
diaphragm-plate. If this be correctly centred in the first in-
stance, and the workmanship of the microscope be good, no more
expensive arrangement will be required, by such at least as ma

be satisfied with that degree of perfection, which suffices for the
clear discernment of all but the most difficult objects. The slid-
ing movement of the tube, especially if it be accomplished by a
lever-action (as suggested by Mr. Quekett), is quite sufficient for
the adjustment of the focus; and the removal of the outer lens
adapts it for use with objectives below 1-4th inch, to whose per-
formance it often affords important assistance. In the most per-
fect arrangement of the Achromatic Condenser, however, such
as is now adapted to all first-class instruments made in this
country, the achromatic combination is one specially adapted to
the purpose; and is so mounted as to insure the greatest ac-
curacy of its adjustments. By Mr. Ross it is supported by what
he terms the “secondary stage” (§ 37); and by Messrs. Smith
and Beck it is carried upon the summit of the “ cylindrical fit-
ting’ which answers the same purpose (§ 39); whilst by Messrs.
Powell and Lealand, it is attached by a bayonet-catch to the
under side of the fixed stage-plate (§ 388). In either case it is
provided with a pair of milled-headed screws (Fig. 36), which give
it a slight degree of horizontal motion in transverse directions,
for the purpose of procuring an accurate centring; and where,
as in Messrs. Powell and Lealand’s instrument, the focal adjust-
ment is not given by the movement of the carriage which bears
it, a rack and pinion is attached for this purpose to the tube of
the condenser itself. In order that the Achromatic Condenser
should be made to afford the greatest possible variety of modifi-
cations of the illuminating pencil, it requires to be furnished
with a diaphragm-plate (as first suggested by Mr. Gillett) imme-
diately behind its lenses ; and this should be pierced with holes
of such a form and size, as to be adapted to cut off in various
degrees, not merely the peripheral, but also the central parts of
the illuminating pencil. The former of these purposes is of
course accomplished, by merely narrowing the aperture which
limits the passage of the rays through the central part of the lens;
the latter, on the other hand, requires an aperture as large as
that of the lens, having its central part more or less completely
occupied by a solid disk, which may so nearly fill the circle, as to
leave but a mere ring through which the light may pass. Such

ACHROMATIC CONDENSER. 133

apertures are shown in the diaphragm-plates in Figs. 35 and 36.
The Condenser thus completed is constructed on three different
plans by the three principal makers, in accordance with the differ-
ent arrangements of their respective stages. By Mr. Ross, who ori-
ginally carried Mr. Gillett’s plans into operation, the diaphragm-
plate has the shape of a short frustrum of a cone (Fig. 35), so at-
tached to the condenser, that the portion of the plate which passes
through it shall cut it transversely; each
aperture is indicated by a number on the
dial; and a spring-catch is so arranged, as
to mark when any one of the apertures is
in its right place, and to show its number.
The thinness of the stage in Messrs. Smith
and Beck’s microscope, allows the dia-
phragm-plate to be made upon the ordinary
plan (Fig. 36), since it can be brought
sufficiently near to the lenses of the con-
denser, without coming into too close con-
tiguity with the stage; and this is obvi-
ously the simplest and most convenient
arrangement. By Messrs. Powell and Lea-
land, again,—their stage being too thick to
allow of the diaphragm-plate being placed
beneath it, without removing that Fie. 36.
plate from its proper position be-
hind the lenses of the + condenser,
—the diaphragm-plate is made so
small that it can be received into
the interior of the stage (Fig. 37),
but is rotated by a milled head be-
neath; and the edge of this is
marked by numbers, each signify-
ing a particular aperture, and thus
marking by its position which aper-
ture is in use. As, however, the
smallness of the diaphragm-plate
so limits the number of apertures, that the desirable variety
could not be afforded by it alone, a second plate is made to ro-
tate immediately beneath it upon the same axis (like the hour
andeminute hands of a watch), by means of a second milled
head, numbered at its edge like the first; and the apertures in
the diaphragm-plate being simple circles, the centres of these
are covered by stops of different sizes, supplied by the second or
“stop’-plate; by which very ingenious arrangement, a great
variety of combinations may be obtained, all of them indicated
by the numbering on the two milled heads. “

57. Reflecting Prisms.—Every mirror composed of glass silvered
at the back, gives, as is well known, a double reflection ; namely,
a principal image from the metallic surface, and a secondary im-

Fig. 35.

Smith and Beck’s Achromatic Condenser.

184 ACCESSORY APPARATUS.

age from the surface of the glass in front of it. This secondary
image, it has been thought, interferes with the perfect perform-
ance of the achromatic condenser; and hence, for obtaining the

Fra. 37,

Powell and Lealand’s Achromatic Condenser.

most satisfactory definition, some Microscopists prefer to direct
the axis of the microscope to the source of light (the mirror being
turned aside); whilst others, feeling the inconvenience of the
position thus required, have recourse to a prism which shall give
the required reflection with only a single image. The prism
usually employed (having been originally applied to this purpose
by M. Dujardin) has plane surfaces, and acts, therefore, as the
equivalent of a plane mirror. A reflecting prism has been de-
vised, however, by Mr. Abraham (optician of Liverpool), which
is intended by him to take the place both of mirror and achro-
matic condenser, though its action (as it seems to the author)
must rather be that of the ordinary concave mirror; this has one
of its surfaces hollowed out to receive one side of a double-con-
vex lens, the other side of which acts as the emergent surface of
the prism, causing the rays as they pass through it to converge;
and the prism itself being composed of flint-glass, whilst the lens
is of crown, no chromatic dispersion of the rays is produced,
though the spherical aberration is not corrected.

58. White-Cloud Iluminators.—It being universally admitted
that the light of a bright white cloud is the best of all kinféls of
illumination for nearly every kind of Microscopic inquiry, various
attempts have been made to obtain such light, from the direct
rays either of the sun or of a lamp, by what may be called an
artificial cloud. Some have replaced the plane mirror by a sur-
face of pounded glass or of carbonate of soda, or (more com-
monly) by a disk of plaster of Paris, the latter being decidedly
the preferable method; but a sufficiently bright light is not thus
obtained, unless a condenser be employed to intensify the illumi-
nation of the mirror. Such a condenser may be most conveni-

WHITE-CLOUD AND OBLIQUE ILLUMINATORS. 135

ently attached by a jointed arm to the frame which carries the
disk, according to the method of Messrs. Powell and Lealand,
shown in Fig. 38; the frame itself being made to fit upon the
mirror, and to turn with it in every direction. Another very
simple, and for many purposes very efli- Fi. 38.
cient mode of obtaining a white-cloud
illumination (invented by Mr. Handford)
consists in coating the back of a concave
plate of glass, like that employed in the
ordinary concave mirror, with white zine __|
paint, instead of silvering it; and then “ =
mounting this in a fame, which may be a a ‘
fitted (like the plaster of Paris disk just © W™*Cloud Muminator.
described) over the ordinary mirror. A concave surface of plas-
ter of Paris, moreover, might easily be obtained by casting it
when fluid upon the convex surface of such a plate. When a
concavity is thus given to the white surface, its performance with
low powers is much improved; but with high powers, a special
condensation of the light must be adopted, and the arrangement
above described seems the simplest that could be devised. It is
open, however, to certain objections, which become apparent
when very high powers are used and difficult objects are under
examination; and to obtain the most perfect white-cloud illumi-
nation possible, is the object of the apparatus devised by Mr.
Gillett. This consists of a small camphine lamp, placed nearly
in the focus of a parabolic speculum, which reflects the rays
either at once upon a disk of roughened enamel or upon a second
(hyperbolic) speculum which reflects them upon such a disk. A
very pure and concentrated light is thus obtained; and as the
forms of the incident pencils are broken up by the roughened
surface, that surface takes the place of the lamp, as the source
from which the rays primarily issue. The advantage of this illu-
mination is specially felt, in the examination of objects of the
most difficult class under the highest powers.

59. Oblique Illuminators.—It is frequently desirable to obtain
a means of illuminating transparent objects with rays of more
obliquity than can be reflected to them from the mirror, even
when this is thrown as much as its mounting will permit out of
the axis of the Microscope (§ 39), or than can be transmitted by
the ordinary achromatic condenser, even when all but its mar-
ginal aperture is stopped out. Such oblique light may be used
in two entirely different modes. The rays, although very far out
of the axis of the microscope, may still not make too great an
angle with it to fall beyond the aperture of the objective; and
thus, entering its peripheral portion after their passage through
the object, they will form the image in the ordinary way. The
advantage of such oblique illumination, arises from its power of
bringing out markings which cannot be seen when only direct
rays are employed; and when the rays come only from one side,

136 ACCESSORY APPARATUS.

so as to throw a strong shadow, and either the stage or the illu-
minator is made to rotate, so that the light shall fall upon the
object. successively in every azimuth, information may often be
gained respecting the nature of these markings, which can be
acquired in no other mode. But the direction given to the rays
may be so oblique, that they shall not enter the object-glass at
all; in this case, they serve to illuminate the object itself, which
shines by the light whose passage it has interrupted; and as the
observer then receives no other light than that which radiates
from it, the object (provided it be of a nature to stop enough
light) is seen bright upon a dark field. Hach of these methods
has its advantages for particular classes of objects; and it is ad-
visable, in all doubtful cases, to have recourse to every variety of
oblique illumination that shall present the object under a different
aspect. Almost every Microscopist who has especially devoted
his attention to the more difficult ined or dotted objects, has de-
vised his own particular arrangement for oblique illumination,
and feels confident of its superiority to others. To give a full
description of all, would be quite unsuitable to our present ob-
ject; those, therefore, will be specially noticed, which have al-
ready acquired general approval; whilst such as have only been
recommended by ¢ndividuals, will be simply referred to. As
they have little in common, save their purpose, it seems scarcely
possible to classify them according to any other character, than
that afforded by the direction which they give to the oblique rays;
some of them bringing these to bear on the object from one side
alone, and others from all sides.

60. One of the earliest methods devised for obtaining oblique
light, was the eccentric prism of M. Nachet; which, occupying
the place of the achromatic condenser, and like it receiving its
light from the mirror, has its surfaces so arranged, as to throw a
converging pencil of rays on the under side of the object, whose
axis is at an angle of about 40° with the axis of the microscope.
One great convenience of this instrument lies in the power of
giving revolution to the prism, by simply turning it in its socket,
so as to direct the oblique rays upon the object from every side
successively, without moving the stage. Its principal disadvan-
tages consist in the limitation of its aperture (producing a de-
ficiency of light), in the want of correction for its chromatic aber-
ration, and in the absence of any power of varying the obliquity
of the illuminating pencil.’ All these disadvantages seem to be
remedied by the plan of oblique illumination recently proposed
by Mr. Sollitt, of Hull, which consists in the employment of an
Achromatic condenser of very long focus and large aperture,
mounted in such a manner as to enable its axis to be inclined to
that of the microscope through a wide angular range; a con-

‘A full description of M. Nachet's prism, and a mathematical investigation of its
properties, by Mr. G. Shadbolt, will be found in the “ Transactions of the Microscopical
Society” (1st series), vol. iii, p. 74, e¢ seq.

PRISMS FOR OBLIQUE ILLUMINATION. 137

denser of this description he states to be suitable also for all ordi-
nary purposes. (“ Quart. Microse. Journ.,” vol. ili, p. 87.) Such
an instrument, when its axis does not form a very large angle
with that of the microscope, may receive its light from the plane
mirror, especially if this be so-mounted as to be capable of being
turned considerably out of the visual axis; but when its position
is too oblique for the light to be thus supplied to it, recourse
must be had to rays either proceeding direct from their source
(such as a lamp or a bright cloud), or directed at the requisite
angle by a reflector placed in a suitable position. For this latter
purpose, a rectangular prism (§ 57), mounted on a separate stand,
will be found very convenient. By many observers, a combina-
tion of the reflecting and refracting powers of a prism is preferred,
which causes the rays to be at once reflected by a plane surface,
and concentrated by lenticular surfaces; so that the prism an-
swers the purpose of mirror and condenser at the same time.
Such a prism was first constructed by Amici; and it may be
either mounted on a separate base, or attached to some part of
the microscope-stand. The mounting adopted by Messrs. Smith
and Beck, and shown in Fig. 39, is a very simple and convenient
one; this consists in attaching the frame Fia. 39.

of the prism to a sliding bar, which
works in dovetail grooves on the top of
a cap that may be set on the cylindrical
fitting beneath the stage; the slide
serves for the regulation of the distance
of the prism from the axis of the micro-
scope, and consequently of the obliquity
of the illumination; whilst its distance
beneath the stage is adjusted by the = heck eee
rack-movement of the cylindrical fit- Amici’s Prism for oblique illumination.
ting. In this manner, an illuminating pencil of almost any de-
gree of obliquity may be readily obtained; but there is no pro-
vision for the correction of its aberrations. Such a provision is
afforded by the achromatic prism of Mr. Abraham (§ 57), which
may be mounted in the manner just described. And the same
object is attained by an arrangement devised by Mr. Grubb, a
Dublin optician, of which Dr. Robinson, of Armagh, speaks very
highly; the prism having its aberrations corrected for a lamp
placed at a given distance in the plane of the stage; and being
mounted in such a manner as to be capable of travelling (like Mr.
Sollitt’s condenser) through an angular range of as much as 120°
( Quart. Microsc. Journ.,” vol. iii, p. 166). In all of these me-
thods, the obliquity of the illumination is practically limited by
the construction of the stage, and especially by the relation
which its thickness bears to the diameter of its lower aperture.
The thinner the stage, and the larger its lower aperture, the
more oblique will be the rays which may be transmitted through
it; and in admitting an extreme obliquity of illumination, the

188 ACCESSORY APPARATUS.

thin stage recently introduced into some of the best Microscopes
(§§ 88, 39) possesses a great advantage over all whose thickness
is greater. On the other hand, it is when the rays are most
oblique, that the greatest advantage is gained by making them
fall upon the object from every side in succession ; and where
this cannot be accomplished (as in the case of Nachet’s prism) by
the rotation of the illuminating apparatus, the rotatory movement
must be given to the object. It is obvious that, for this purpose,
a revolving stage which keeps the object constantly in the field
(§ 87), is decidedly preferable to one which does not possess such
a movement; but the means have not yet been found of obtain-
ing this advantage without some sacrifice of the other.

61. Whenever the rays are directed with such obliquity, as
not to be received into the object-glass at all, but are sufficiently
retained by the object, to render it (so to speak) selfluminous,
we have what is known as the black ground illumination ; to which
the attention of Microscopists generally was first drawn by the
Rev. J. B. Reade, in the year 1838, although it had been prac-
tised some time before, not only by the Author but by several
other observers. For low powers whose angular aperture is small,
and for such objects as do not require any more special provision,
a sufliciently good “black ground” illumination may be obtained
by means of the concave mirror alone, especially when it is so
mounted as to be capable of a more than ordinary degree of ob-
liquity. In this manner it is often possible, not merely to bring
into view features of structure that might not otherwise be dis-
tinguishable, but to see bodies of extreme transparency (such,
for instance, as very minute Animalcules) that are not visible
when the field is flooded (so to speak) by direct light; these pre-
senting the beautiful spectacle of phosphorescent points rapidly
sailing through adark ocean. Where the mirror cannot be placed
in a position oblique enough to give this effect, a black ground
illumination sufficiently good for many purposes may be ob-
tained by Mr. Reade’s original method; which consisted in dis-
pensing with the mirror altogether, and in placing the lamp and
ordinary condensing-lens (§ 64) in such a position beneath and
to one side of the stage, as to throw upon the under side of the
object a pencil of rays too oblique to enter the object-glass after
passing through it. Another very simple mode, which answers
sufficiently well for low powers and for the larger objects which
these are fitted to view, consists in the substitution, for the
achromatic condenser, of a plano-convex lens of great convexity,
forming a large segment of its sphere, with a central stop to cut
off the direct rays; for the rays passing through the marginal
portion of this Spotted Lens, being strongly refracted by its high
curvature, are made to converge at an angle too wide for their
entrance into an objective of moderate aperture, and thus the
field is left dark ; whilst all the light stopped by the object serves
(as it were) to give it a luminosity of its own. Neither of the

PARABOLIC AND ANNULAR CONDENSERS, 1389

foregoing plans, however, will answer well for objectives of high
power, having such large angles of aperture that the light must
fall very obliquely to pass beyond them altogether. Thus if the
pencil formed by the “spotted lens” have an angle of 60°, its rays
will enter a 1-4th-inch objective of 70°, and the field will not be
darkened. For obtaining a greater degree of obliquity, Mr.
Wenham has contrived a Parabolic Speculum,’ having its apex
cut off, so that the object might be placed in the focus, to which
all rays parallel to its axis are reflected ; andthe direct rays being
checked by a stop placed behind it, the object is illuminated only
by those which are reflected to it from all sides of the interior
of the parabola at avery oblique angle. As the thickness of the
glass slide on which the object is mounted, was found by Mr.
'W. to produce a very sensible aberration in the rays converging
towards it, he interposed a meniscus lens, having such a curva-
ture as to produce a counteracting aberration of an opposite kind.
The circular opening at the bottom of the wide tube (Fig. 40)
that carries the speculum, may be fitted with a diaphragm,
adapted to cover any portion of it that may be desired ; and by
giving rotation to this diaphragm, rays of great obliquity may
be made to fall upon the object from every azimuth in succes-
sion (§ 60). A like purpose was aimed at in the Annular Con-
denser of Mr. Shadbolt,? which consists of a ring of glass, whose
surface was so shaped as to present a prismatic section; the in-
clination of the outer side being such as to produce a total re-
flection of the rays impinging on it, and to direct these through
the inner side of the ring, so as to fall at a very oblique angle
upon the object, from every azimuth of the circle. A combina-
tion of both methods is adopted in the Parabolic Illuminator
(Fig. 40), now supplied by Messrs. Smith and Beck; for this
consists of a paraboloid of glass, resembling Fie. 40,

a cast of the interior of Mr. Wenham’s para-
bolic speculum, but reflecting the rays which
fall upon the outer surface of the glass, like
Mr. Shadbolt’s annular prism. It has the ad-
vantage of being more easily constructed than
the parabolic speculum, and is little, if at all,
inferior to it in performance; but it requires
that an appropriate “stop” should be adapted
to it, for each objective with which it is to be
used: whilst in Mr. Wenham’s speculum, the
requisite adaptation for the angular aperture
of the objective is made by altering the posi-
tion of the stop by means of the central stem;
the effect of which alteration is to cut off a
larger and larger proportion of the least ob- — Patabolie Illuminator.
lique rays, the more nearly the stop is approximated to the ob-

'« Transactions of the Microscopical Society” (1st Series), vol. iii, p. 85.
2 Op. cit. p. 132.

140 ACCESSORY APPARATUS.

ject; and thus to illuminate it more and more exclusively by
those which meet at the widest angle. In using either of these
illuminators, the rays which are made to fall upon them should
be parallel, consequently the plane mirror should always be em-
ployed; and when, instead of the parallel rays of daylight, we
are obliged to use the diverging rays of a lamp, these should be
rendered as parallel as possible, previously to their reflection
from the mirror, by the interposition of the “bull’s eye” con-
denser (§ 64) so adjusted as to produce this effect.

62. For the exhibition of those classes of objects which are
suitable for “black ground” illumination, and which are better
seen by light sent into them from every azimuth, than they are
by a pencil, however bright, incident in one direction only, no
more simple, convenient, and efficient means could probably be
found, than that which is afforded by the “spotted lens” for low
powers, and by the ‘parabolic illuminator” for powers as high
as 1-4th or 1-5th of an inch focus ;—the use of the latter with
the highest powers, being rendered disadvantageous by the great
reduction in the amount of light, occasioned by the necessity for
cutting off of all the rays reflected from the paraboloid, which
fall upon the object within the limits of their angle of aperture.
One of the great advantages of this kind of illumination consists
in this: that, as the light radiates from each part of the object as
its proper source, instead of merely passing through it from a more
remote source, its different parts are seen much more in their
normal relations to one another, and it acquires far more of the
aspect of solidity. The rationale of this is easily made apparent
by holding up a glass vessel with a figured surface between one
eye anda lamp or a window, so that it is seen by transmitted
light alone; for the figures of its two surfaces are then so blended
together to the eye, that unless their form and distribution be
previously known, it can scarcely be said with certainty which
markings belong to either. If, on the other hand, an opaque
body be so placed behind the vesscl, that no rays are transmitted
directly through it, whilst it receives adequate illumination from
the circumambient light, its form is clearly discerned, and the
two surfaces are differentiated without the least difficulty.

68. Polarizing Apparatus.—In order to examine transparent
objects by polarized light, it is necessary to employ some means
of polarizing the rays before they pass through the object, and to
apply to them, in some part of their course between the object
and the eye, an analyzing medium. These two requirements
may be provided for in different modes. The polarizer may be
either a bundle of plates of thin glass, used in place of the
mirror, and polarizing the rays by reflection; or it may be a
“single image” or “Nicol” prism of Iceland Spar, which is so
constructed as to transmit only one of the two rays into which a
beam of ordinary light is made to divaricate on passing through
this substance; or it may be a plate of Tourmaline, or one of

POLARIZING APPARATUS. 141

the artificial tourmalines composed of the disulphate of iodine
and quinine, now known by the designation of “ Herapathite,”
after the name of their discoverer. Of these methods, the
“Nicol” prism is the one generally preferred ; the objection to
the reflecting polarizer being, that it cannot be made to rotate ;
the tourmaline being undesirable, on account of the color
which it imparts when sufficiently thick to produce an effective
polarization; and the crystals of Herapathite being seldom
obtained perfect, of sufficient size to afford a good illumination.
The polarizing prism is usually fitted into a tube (Fig. 41, 4, a)
with a large milled head (c) at the bottom, by which it is made
to rotate in a collar (6) that is attached ‘to the microscope; this
collar may be fitted to the under side of the stage-plate, or,
where a seeondary stage is provided, it may be attached to this;
in the microscope of Messrs. Smith and Beck, it screws into the
lower part (0) of a tube (Fig. 41, B),that slides into the “ cylin-
drical fitting” beneath the stage (Fig. 29). The analyzer, which

Fie. 41, Fig, 42.

Fitting of Polarizing Prism in Smith and Beck's Fitting of Analyzing Prism
Microscope. upon the Eye-piece.

may be either a “ Nicol” prism, a Tourmaline, or a crystal of
Herapathite, is usually placed either in the interior of the micro-
scope, or between the eye-piece and the eye. If it be a prism,
it is mounted in a tube, which may either be screwed into the
lower end of the body in the situation of the erector (Fig. 32),
or may be fitted over the eye-piece in place of its ordinary cap
(Fig. 42); in the former situation it has the advantage of not
limiting the field, but it stops a considerable proportion of the
light ; in the latter, it detracts much less from the brightness of
the image, but cuts off a good deal of the margin of the field.
A plate of Tourmaline or Herapathite, if obtainable of sufficient
size and freedom from color, has a decided advantage above the
Nicol prism, as an analyzer, in being free from both these
inconveniences ; and it may be set in a cap which fits over the
ordinary cap of the eye-piece. For bringing out certain effects
of color by the use of Polarized light (Chap. XX), it is desir-
able to interpose a plate of Selenite beneath the polarizer and

142 ACCESSORY APPARATUS.

the object; and it is advantageous that this should be made
to revolve. A very convenient mode of effecting this, is to
mount the selenite plate in a revolving collar, which fits into the
upper end (a) of the tube (Fig. 41, 8) that receives the polarizing
rism. In order to obtain the greatest variety of coloration
with different objects, films of selenite of different thickness
should be employed; and this may be accomplished by sub-
stituting one for another in the revolving collar. A still greater
variety may be obtained by mounting three films, which sepa-
rately give three different colors, in a frame resembling that in
which hand-magnifiers are usually mounted, so that they may
be used singly or in double or triple combinations ; as many as
thirteen different tints may thus be obtained; but the advantage
of revolution is sacrificed. When the construction of the
microscope does not readily admit of the connection of the
selenite plate with the polarizing prism, it is convenient to make
use of a plate of brass (Fig. 48) somewhat larger than the glass
slides in which objects are
Fig, 43. ordinarily mounted, with a
ledge near one edge for the
slide to rest against, and a
large circular aperture into
which a glass is fitted, having
a film of selenite cemented
to it; this “selenite stage”
or object-carrier being laid
upon the stage of the micro-
scope, and the slide containing the object being placed upon it,
the effect of the selenite is obtained, as in the previous arrange-
ment; and by an ingenious modification contrived by Dr.
Leeson, the ring into which the selenite plate is fitted being
made movable, one plate may be substituted for another, whilst
rotation may be given to the ring by means of a tangent-screw
fitted into the brass plate. Such a “selenite stage’’ answers
every purpose that can be required; but as there is no provision
for using two or three plates in combination, it is necessary to
have a distinct selenite plate for every modification of colors
that may be desired.

A very beautiful effect may be obtained with certain kinds of
semi-opaque objects, by illuminating them by means of a “spotted
lens” (§ 61), with a polarizer of Herapathite placed at such a dis-
tance above it as to receive the converging hollow pencil near its
termination in the object, and an analyzer of the usual descrip-
tion,—a combination devised by Mr. Furze;! for the solidity
which this mode of oblique illumination imparts to certain ob-
jects, is remarkably heightened by the play of colors afforded by
the polarization of the light. When the polarizing apparatus 1s
being employed with any but the lowest powers, it is very advan-

Selenite Object-Carrier.

' «Transactions of the Microscopical Society” (2d series), vol. iii, p. 63.

BULL’S-EYE CONDENSER. 143

tageous to use the achromatic condenser in combination with it;
this combination, which cannot be made in ordinary microscopes,
is provided for in that of Messrs. Smith and Beck, by the “cylin-
drical fitting” so often referred to, which can receive the polar-
izing prism at its lower end, and the achromatic condenser at its
upper, whilst the selenite plate or plates may be interposed be-
tween them.

64. Illuminators for Opaque Objects.—All objects through which
sufficient light cannot be transmitted to enable them to be viewed
in the modes already described, require to be illuminated by
rays, which, being thrown upon the surface under examination,
shall be reflected from it into the microscope; and this mode of
viewing them may often be
advantageously adopted in Fie. 44.
regard to semi-transparent or
even transparent objects, for
the sake of the diverse aspects
it affords. Among the various
methods devised for this pur-
pose, the one most generally
adopted consists in the use of
a condensing lens, either at-
tached to the microscope, or
mounted upon a separate
stand, by which the rays pro-
ceeding from a lamp or from
a bright sky are made to con-
verge upon the object. For
the efficient illumination of
large opaque objects, such as
injected preparations, it is
desirable to employ a “ bull’s-
eye’ condenser ‘(which is a
plano-convex lens of short
focus, two or three inches in
diameter), mounted upon a
separate stand, in such a man-
ner as to allow of being placed
in a great variety of positions.
The mounting shown in Fig.
44 ig perhaps one of the best Bull’s-Eye Condenser.
that can be adopted: the
frame which carries the lens is borne at the bottom upon aswivel-
joint, which allows it to be turned in any azimuth ; whilst it-may
be inclined at any angle to the horizon, by the revolution of

’ For an account of the nature and properties of Polarized Light, which would be
out of place in the present treatise, see the chapters on that subject in Dr. Golding Bird's
“ Manual of Natural Philosophy,” Dr. Pereira’s “ Lectures on Polarized Light,” New Ed.,
edited by Prof. Baden Powell, or any modern treatise on Optics.

144 ACCESSORY APPARATUS.

the horizontal tube to which it is attached, around the other
horizontal tube which projects from the stem ; by the sliding of
one of these tubes within the other, again, the horizontal arm may
be lengthened or shortened ; the lens may be secured in any posi-
tion (as its weight is apt to drag it down when it is inclined, unless
the tubes be made to work, the one into the other, more stiffly
than is convenient) by means of a tightening collar milled at its
edges; and finally the horizontal arm is attached to a spring
socket, which slides up and down upon a vertical stem. The
optical effect of such a lens differs according to the side of it
turned towards the light, and the condition of the rays which fall
upon it. The position of least spherical aberration, is when its
convex side is turned towards parallel or towards the least diverging
rays ; consequently, when used by daylight, its plane side should be
turned towards the odject ; and the same position should be given to
it, when it is used for procuring converging rays from a lamp, the
lamp being placed four or five times farther off on one side, than
the object ison theother. Butit may also be employed for the pur-
pose of reducing the diverging rays of the lamp to parallelism, for
use either with the parabolic illuminator (§ 61), or with the side-
reflector to be presently described; and the plane side is then to
be turned towards the lamp, which must be placed at such a dis-
tance from the condenser, that the rays which have passed through
the latter shall form a lumin-
Fra. 45, ous circle equal to it in size,
at whatever distance from the
lens the screen may be held.
Even where the large “ bull’s-
eye” condenser is provided, it
is well to have a smaller con-
densing lens in addition ; and
this, which is usually a double-
convex lens, may either be
mounted on a separate base
(Fig. 45), or may be attached
to some part of the micro-
scope. (In Messrs. Smith and
Beck’s large microscope, Fig.
29, two sockets with binding-
screws, one for the condensing
lens, the other for the side-re-
flector, are seen in the ‘limb.”)
This condensing lens is sufli-
Ordinary Condensing Lens. cient by itself for most ordi-
nary purposes; and it may
also be used to obtain a greater concentration of the rays already
brought into convergence by the bull’s-eye (§ 98).
65. The illumination of opaque objects may be effected by re-
flection, as well as by refraction ; and a very advantageous means

SIDE-REFLECTOR FOR OPAQUE OBJECTS. 145

of using the light of a lamp for this purpose, is afforded by the
Side-Reflector contrived by Mr. Ross. This is a highly polished
concave speculum (Fig. 46), which can be placed above and to
one side of the object; and which is so mounted as to be capable
of being placed in every kind of position, according to the place
of the lamp, and the degree of obliquity
of the illumination required. The squared
stem, with which the speculum is con-
nected by several intermediate joints, may
be fitted to a socket, either in the stage or
in some part of the microscope-stand, like
that of the smaller condensing lens. The
light reflected by the speculum upon the
object, may be either that which falls on
it direct from the lamp, or may come to it
through the intervention of the bull’s-eye,
arranged so as to throw parallel rays upon
the speculum (§ 64). The prisms already
described as in use for the illumination of
transparent objects by the reflection of
light from beneath, may also be employed,
by an inversion of their position, for the
illumination of opaque objects from above.
In Continental Microscopes, the prism is
frequently attached to the lower end of the
body; but this is an undesirable mode of
supporting it, since the illumination is dis-
turbed by every alteration in the distance
between the body and the object. This
seems to be provided against by the mount-

ing of the prism in Mr. Grubb’s micro-

scope (§ 60), which allows it to be used at

any angle either above or below the stage.

Fie, 46.

A mode of illuminating opaque objects by
a small concave speculum reflecting the
light directly down upon it, was formerly Side-Reflector.

much in use, but is now comparatively

seldom employed. This concave speculum, termed a “ Lieber-
ktihn” from the celebrated Microscopist who invented it, is made
to fit upon the end of the objective, having a perforation in the
centre for the passage of the rays from the object to the lens;
and it receives its light from the mirror beneath, the object being
so mounted as only to stop out the central portion of the rays
that are reflected upwards. The curvature of the speculum isso
adapted to the focus of the object-glass, that, when the latter is
duly adjusted, the rays reflected up to it from the mirror shall
be made to converge strongly upon the part of the object that
is in focus; consequently, unless (as is sometimes done) the spe-
culum should be mounted on a tube sliding over the “nose” of

10

146 ACCESSORY APPARATUS.

the microscope, and capable of being adjusted to the different
distances required by the several objectives, a separate speculum
is required for every object-glass. The disadvantages of this
mode of illumination are chiefly these :—first, that by sending
the light down upon the object almost perpendicularly, there is
scarcely any shadow, so that the inequalities of its surface, and
any minute markings which it may present, are but faintly or
not at all seen; second, that the size of the object must be so
limited by that of the speculum, as to allow the rays to pass to
its marginal portion; and third, that a special mode of mounting
is required, to allow the light to be reflected from the mirror
around the margin of the object. The first objection may be in
some degree removed, by turning the mirror considerably out of
the axis, so as to reflect its light obliquely upon the Lieberkithn,
which will then send it down obliquely upon the object; the
illumination, however, will not even then be so good as that
which is afforded by the side-reflector. The mounting of opaque
objects in wooden slides (Chapter V), which affords in many
cases the most convenient means of preserving them, completely
prevents the employment of the Lieberkiihn in the examination
of them; and they must either be set, for this purpose, upon
disks which afford them no protection, or in glass cells witha
blackened background. The cases wherein the Lieberkiihn is
most useful, are those in which it is desired to examine small
opaque objects, such as can be held in the stage-forceps (§ 66),
or laid upon a slip of glass, with lenses of half inch focus or less;
since a stronger light can be thus concentrated upon them, than
can be easily obtained by side-illumination. In every such case,
a black background must be provided, of such a size as to fill
the field, so that no light shall come to the eye direct from the
mirror, and yet not large enough to create any unnecessary ob-
struction to the passage of the rays from the mirror to the specu-
lum. With each Licberkiihn is commonly provided a blackened
stop of appropriate size, having a well-like cavity, and mounted
upon a pin which fits into a support connected with the under
side of the stage; but though the “dark well” serves to throw
out a few objects with peculiar force, yet, for all ordinary pur-
poses, a spot made with black paper or black sealing-wax-varnish
upon a slip of glass will answer the required purpose very
effectually, the slip being simply laid upon the stage beneath
the object.

Section 2. APPARATUS FOR THE PRESENTATION oF OBJECTS.

66. Stage-Forceps.—Every Microscope should be furnished with
a pair of Stage-foreeps (Fig. 47) for holding minute objects
beneath the object-glass. They aremounted by means of a joint
upon a pin, which fits into a hole either in the corner of the stage
itself, ov in the object-platform ; the object is inserted by pressing
the pin that projects from one of the blades, whereby it is sepa-

STAGE-FORCEPS—GLASS STAGE-PLATEI. 147

rated from the other; and the blades close again, so as to retain
the object when the pressure is withdrawn. By sliding the wire
stem which bears the forceps through its socket, and by moving
that socket vertically upon its joint, and the joint horizontally

Fig. 47.

Stage-Forceps.

upon the pin, the object may be brought into the field precisely
in the position required; and it may be turned round and
round, so that all sides of it may be, examined by simply giving
a twisting movement to the wire stem. The other extremity of
the stem often bears a small brass box filled with cork, and per-
forated with holes in its side; this affords a secure hold to com-
mon pins, to which disks of card, &c., may be attached, whereon
objects are mounted for being viewed with the Lieberkihn.
This method of mounting was formerly much in vogue, but has
been less employed of late, since the Lieberkiihn has fallen into
comparative disuse.

67. Glass Stage-Plate.—Every Microscope should be furnished
with a piece of plate-glass, about 4 in. by 1} in., to one margin
of which a narrow strip of glass is cemented, so as to form a
ledge. This is extremely useful, both for laying objects upon
(the ledge preventing them from sliding down when the micro-
scope is inclined), and for preserving the stage from injury by
spilling of sea-water or other saline or corrosive liquids, when
such are in use. Such a plate not only serves for the examina-
tion of transparent, but also of opaque objects; the dark back-
ground being furnished by the diaphragm-plate (§ 55), and the
condensing-lens being so placed as to throw a side-light upon
them. A small addition may be conveniently made to the glass
stage-plate, which adapts it for use asa Growing-Slide. A circu-
lar aperture, of about the diameter of a test-tube, is made near
one end of the plate (the length of which, for this purpose, had
better be not less than 5 inches), and in this is to be fitted a
little cup, formed of the end of a test-tube, about three-quarters
of an inch deep, in such a manner that its rim shall project a little
above the surface of the plate. The cup may be closed by an
ordinary cork, or (to avoid the danger of splitting it) by a disk
of glass cemented to a ring of cork which shall embrace the ex-
terior of the tube; but a small aperture must be left, by grind-
ing a notch in the rim of the cup, sufficient to admit the passage
of two or three threads of lamp-cotton. The manner in which the
“ srowing-slide” is used, is this:—Supposing we wish to follow
the changes undergone by some minute Alga or Infusorium, which

148 ACCESSORY APPARATUS.

we have just detected in a drop of liquid under examination
upon an ordinary slip of glass (and covered with thin glass),—
we transfer this slip to the “growing-slide,” fill the cup with
distilled water mixed with a small proportion of the water in
which the organism was found, and then so arrange the threads
(previously moistened with distilled water), that they shall pass
from the cup to the edge of the liquid in which the object is con-
tained. Thus, as the water evaporates from beneath the thin
glass, the threads will afford a continuous supply; and the
threads will not become dry, until the whole of the liquid has
been absorbed by them and has been dissipated by evaporation.
Fresh supplies may, of course, be introduced into the cup from
time to time, as may be needed, so as to prevent any loss of
liquid from beneath the thin glass; and in this manner, the most
important requisite for the continued growth of aquatic or-
ganisms,—a constant supply of liquid, without an exclusion of
air,—may be secured.'

68. Aquatic Box or Animaleule Cage.—This, also, is an ap-
pendage with which every Microscope should be provided, so
varied and so constant is its utility. It consists of a short piece of
wide brass tube, fixed perpendicularly at one end into a flat plate
of brass (Fig. 48) which is perforated by an aperture equal in

Fia. 48.

TT

nM

Aquatic Box or Animalcule Cage, as seen in perspective at a, and in section at B.

diameter to that of the tube, and having its opposite extremity
closed by a disk of glass (B 6); over this fits a cover, formed of
a piece of tube just large enough to slide rather stiffly upon that
which forms the box, closed at the top by another disk of glass
(pa). The cover being taken off, a drop of the liquid to be
examined, or any thin object which can be most advantageously
looked at in fluid, is placed upon the lower plate; the cover is
then slipped over it, and is pressed down until the drop of liquid
be spread out, or the object be flattened, to the degree most con-
venient for observation. If the glass disk which forms the lid
be cemented or burnished into the brass ring which carries it, a
small hole should be left for the escape of air or superfluous
fluid; and this hole may be closed up with a morsel of wax, if

‘See the “ Micrographic Dictionary,” by Dr. Griffith and Mr. Henfrey, Introduction,
p. xx.

AQUATIC BOX OR ANIMALCULE CAGE, 149

it be desired to prevent the included fluid from evaporating.
But as it is desirable that this glass should be thin enough to
allow a 1-4th-inch objective to be employed for the examination
of Animalcules, &c., and as such thin glass is extremely apt to
be broken, it is a much better plan to furnish the brass cover
with a screw-cap, which holds the brass disk with sufficient
firmness, but permits it to be readily replaced when broken ;
and as the looseness of this fitting gives ample space for the
escape of air or fluid around the margin of the disk, no special
aperture is needed. It is always desirable, if possible, to prevent
the liquid from spreading to the edge of the disk; since any
objects it may contain are very apt, in such a case, to be lost
under the opaque ring of the cover; this is to be avoided by
limiting the quantity of the liquid introduced, by laying it upon
the centre of the lower plate, and by pressing down the cover
with great caution, so as to flatten the drop equally on all sides,
stopping short when it is spreading too close to the margin.
With a little practice, this object may in general be successfully
attained ; but if so much superfluous liquid should have been in-
troduced, that it has flooded the circumference of the inclosed
space, and exuded around the edge of the disk, it is better to
wipe the whole perfectly dry, and then to introduce a fresh drop,
taking more care to limit its quantity and to restrain it within
convenient bounds. If the box be well constructed, and the
glass disks be flat, they will come into such close contact, that
objects of extreme thinness may be compressed between them;
hence not only may such small animals as Water-fleas (Hntomo-
straca) be restrained from the active movements which preclude
any careful observation of their structure,—and this without any
permanent injury being inflicted upon them,—but much smaller
creatures, such as Wheel-Animalcules (Rotifera), or Bryozoa,
may be flattened out, so as to display their internal organization
more clearly, and even the larger Infusoria may be treated in
like manner. The working Microscopist will find it of great
advantage to possess several of these aquatic boxes, of different
sizes; and one or two of them may have the glass cover of
stronger glass than the rest, and firmly fixed in its rim, so that,
if the cover be made to slide equably on the box, the instrument
(in hands accustomed to careful manipulation) may be made to
answer the purpose of a compressorium (§ 70).

69. Zoophyte Trough.—For the examination of living aquatic
objects, too large to be conveniently received into the Aquatic
Box, the Zoophyte trough contrived by Mr. Lister may be em-
ployed with great advantage. This consists of a trough of the
shape represented in Fig. 48, formed of plates and slips of plate-
glass cemented together by marine glue; of a loose vertical plate
of glass, just so much smaller than the front or back of the in-
side of the trough, as to be able to move freely between its sides;
and of a horizontal slip of glass, whose length equals that of the

150 ACCESSORY APPARATUS.

inside bottom of the trough, but whose breadth is inferior by the
; thickness of the plate just men-
a tioned. The trough being filled
with water (fresh or salt, as the
case may be), the horizontal slip is
laid at the bottom, and the vertical
plate is placed in contact with the
front of the trough, its lower mar-
gin being received into the space
left at the front edge of the hori-
zontal slip, which serves to hold it
— there, acting as a kind of hinge; a
Foswhyty Trae, small ivory wedge is then inserted
between the front glass of the trough
and the upper part of the vertical plate, which it serves to press
backwards; but this pressure is kept in check by a little spring of
bent whalebone, which is placed between the vertical plate and
the back glass of the trough. By moving the ivory wedge up or
down, the amount of space left between the upper part of the
vertical plate and the front glass of the trough can be precisely
regulated; and as their lower margins are always in close appo-
sition, it is evident that the one will incline to the other, with a
constant diminution of the distance between them, from above
downwards. Hence a Zoophyte, or any similar body, dropped
into this space, will descend until it rests against the two sur-
faces of glass, and will remain there in a situation extremely
convenient for observation; and the regulating-wedge, by in-
creasing or diminishing the space, serves to determine the level
to which the object shall fall. Of these troughs, again, it is con-
venient for the working Microscopist to be furnished with
several, of different sizes; and in one of them Chara or Mitella
may be kept growing in a state very convenient for observation.
A similar trough may be provided for this last purpose, however,
by dispensing with the vertical plate and horizontal slip alto-
gether, and approximating the front and back plates so that only
a very narrow space is contained between them ; in this case it
is convenient to let the upper lip of the back plate project con-
siderably beyond that of the front plate, as objects may then be
much more readily inserted between them; and the back plate
may also be conveniently made to project beyond the sides of
the trough, as would be useful, too, in the case of larger troughs.
If it be wished to grow Chara, &c., in a thin trough of this kind,
the trough, whenever it is not under observation, should be im-
mersed in a tumbler or jar of water, since the plant will not
flourish in a very limited supply.

70. Compressorium.—The purpose of this instrument is to
apply a graduated: pressure to objects, whose structure can only
be made out when they are thinned by extension. For such as
will bear tolerably rough treatment, a well-constructed Aquatic
Box may be made to answer the purpose of a compressor; but

COMPRESSORIUM. 151

there is a very large class, whose organization is so delicate as
to be confused or altogether destroyed by the slightest excess of
pressure; and for the examination of such, an instrument in
which the degree of compression can be regulated with pre-
cision, is almost indispensable. Various plans of construction
have been proposed; but none among them appears to the
Author-to present so many advantages as the one represented in
Fig. 50, the general plan of which was originally devised by
Schiek of Berlin, but the details of which have been modified
by M. de Quatrefages, who has constantly employed this instru-
ment in his elaborate and most successful researches on the
organization of the Marine Worms. It consists of a plate of
brass between 3 and 4

inches long, and from Fia, 50.

134 to 14 inch broad,
having a central aper-
ture of from 4 to 2 of
an inch. This central
aperture is covered on
its upper side by a Compressorium.

disk of thin glass,

which may be cemented to the brass plate by Canada balsam ;
and the under side of it is bevelled away, so that the thickness
of the edge shall not interfere with the approach of the objective
to its margin, when that side is made the uppermost. Near one
extremity of the plate is a strong vertical pin, that gives support
to a horizontal bar which turns on it as on a swivel; through
the end of this bar that projects beyond the plate, there passes a
screw with a milled head; and at the other end is jointed a
second bar, against one end of which the screw bears, whilst the
other carries a frame holding a second disk of thin glass. This
frame is a small circular plate of glass, having an aperture equal
in size to that of the large plate ; to its under side, which is flat,
a disk of thin glass is cemented by Canada balsam, while its
upper side is bevelled off as it approaches the opening, for the
purpose just now specified; and by being swung between pivots
in a semicircle of brass, which is itself pivoted to the movable
arm, it is made capable of a limited movement in any direction.
The upper disk with the apparatus which supports it, having
been completely turned aside round the swivel-joint, the object
to be compressed is laid upon the lower disk; the upper disk is
then turned back so as to lie precisely over it, and by the action
of the milled-head screw, is gradually approximated to the
lower, to which the pivot movements of its frame allow it to
take up a parallel position, whatever may be the inclination of the
bar. As it is frequently of great importance to be able to look
at either side of the object under compression, the principal
plate is provided with two pins at the extremity farthest from
the milled head, which, being exactly equal in length to the
swivel-pin, afford, with it, a support to the instrument, when it

152 ACCESSORY APPARATUS.

is so turned that the side represented as undermost in the figure,
shall be uppermost; and it is in order that high powers may be
used in this case as in the other, that the disk which then covers
the object is made of thin glass, instead of being (as in the
original form of the instrument) a piece of thick glass plate.
That a thin glass disk is more liable to fracture under pressure,
than a thick one, is no serious objection to its use for this pur-
pose; since the lower one is not more likely to break than the
upper one; and either may be replaced with extreme facility,
by simply warming the part of the instrument to which it is
attached, so as to loosen the cement that holds it. And the
advantage of being able to view an object under a high
power, from either side, will be most fully appreciated by
every one who has been much engaged in the
Fia. 51. class of observations, which this instrument is
specially adapted to facilitate. IPf this Compres-
sorium be made of sufficient size to admit an or-
dinary glass slide between the vertical pins, an
object may be subjected to compression, and
afterwards removed for examination out of the
| compressor, without transferring it from one glass
| to another, which is frequently an advantage.
| In this case, it will be convenient that the thin
| glass disk should be “countersunk” into the upper
| | | surface of the principal plate, so as to form one
i |, | level with it.
id | i 71. Dipping Tubes—In every operation in
| which small quantities of liquid, or small ob-
jects contained in liquid, have to be dealt
with by the Microscopist, he will find it a very
great convenience to be provided with a set of
tubes of the forms represented in Fig. 51, but of
somewhat larger dimensions. These were for-
merly designated as “ fishing tubes;” the purpose
| for which they were originally devised having
been the fishing out of Water-Fleas, aquatic
Insect-Larve, the larger Animalcules, or other
living objects distinguishable cither by the un-
aided eye or by the assistance of a magnifying
glass, from the vessels that may contain them.
But they are equally applicable, of course, to the
MI selection of minute Plants; and they may be

A B C

yy oS OTD

turned to many other no less useful purposes,
some of which will be specified hereafter. When
Fishing Tubes. it, is desired to secure an object which can be seen
either with the eye alone or with a magnifying

glass, one of these tubes is passed down into the liquid, its upper
orifice having been previously closed by the forefinger, until
its lower orifice is close above the object; the finger being then
removed, the liquid suddenly rises into the tube, probably carrying

a

FISHING TUBES—FORCEPS. 153

the object up with it; and, if this is seen to be the case, by put-
ting the finger again on the top of the tube, its contents remain
in it when the tube is lifted out, and may be deposited on a
slip of glass or on the lower disk of the aquatic box, or, if too
copious for either receptacle, may be discharged into a watch-glass.
In thus fishing for any but the minutest objects, it will be
generally found convenient to employ the open-mouthed tube c;
and when its contents have been discharged, if they include but
a single object of the desiderated kind, this may be taken up by
one of the finer tubes, 4, B, or, if more convenient, the whole
superfluous fluid may be sucked up by the mouth, and the
object left with no more than is suitable; or, if there be many
of the desired objects in the fluid first selected, these may be
taken up from it, one by one, by either of the finer tubes.

72. Forceps.—Another instrument so indispensable to the Mi-
croscopist as to be commonly considered an appendage to the
Microscope, is the Forceps for taking up minute objects ; many
forms of this have been devised, of which one of the most con-
venient is represented in Fig. 52, of something less than the

Fia. 52.

Lo- : EP.)

Forceps.

actual size. As the forceps, in marine researches, have continu-
ally to be plunged into sea-water, it is better that they should be
made of brass or of German silver, than of steel, since the latter
rusts far more readily; and as they are not intended (like dis-
secting forceps) to take a firm grasp of the object, but merely to
hold it, they may be made very light, and their spring part
slender. As it is essential, however, to their utility, that their
points should meet accurately, it is well that one of the blades
should be furnished with a guide-pin, passing through a hole in
the other.

The foregoing constitute, it is believed, all the most important
pieces of Apparatus, which can be considered in the light of Ac-
cessories to the Microscope. Those which have been contrived
to afford facilities for the preparation and mounting of Objects,
will be described in a future chapter (Chap. V). It may be
thought that some notice ought to be taken of the Mrog Plate and
Fish Pan, with the former of which many Microscopes are sup-
plied, whilst the latter has scarcely yet gone altogether out of
use. But the Author having been accustomed to gain all the
advantages of these, by methods far more simple, whilst at least
equally efficacious, does not consider them as presenting any ad-
vantages which render it desirable to expend time or space in
giving a detailed account of them; and he will explain the
methods alluded to, under the appropriate head.

CHAPTER IV.
MANAGEMENT OF THE MICROSCOPE.

73. Support—The Table on which the Microscope is placed,
when in use, should be one whose size enables it also to receive
the various appurtenances which the observer finds it convenient
to have within his reach, and whose steadiness is such as to allow
of his arms being rested upon it without any yielding; it should,
moreover, be so framed, as to be as free as possible from any
tendency to transmit the vibrations of the building or floor
whereon it stands. The manner in which the Microscope itself
is constructed, however, will have a great influence on the effect
of any such disturbing cause; since, if the whole instrument
move together, scarcely any tremulousness will be produced in
the image, by vibrations which cause it to dance” most un-
pleasantly, if the body and stage of the Microscope oscillate in-
dependently of each other. Hence, in choosing a Microscope,
it should always be subjected to this test, and should be unhesi-
tatingly rejected if the result be unfavorable. It is of course
to be borne in mind, that any vibration, either of the object or
of the optical apparatus, in which the other does not partake,
will be much more apparent when high magnifying powers are
used, than when the object is amplified in a much less degree,
the motion of the object being magnified in precisely the same
ratio with the object itself; hence if, when the microscope is
thus tested with high powers, it is found to be free from fault,
its steadiness with low powers may be assumed; but, on the
other hand, a Microscope which may give an image free from
perceptible tremor when the lowest powers only are employed,
may be quite unfit for use with the highest.

74. Light.—Whatever may be the purposes to which the Mi-
croscope is applied, it is a matter of the first importance to secure
a pure and adequate illumination. There is scarcely any class

1 The working Microscopist will find ita matter of great convenience to have a Table
specially set apart for this purpose; furnished with drawers in which are contained the
various accessories he may require for the preparation and mounting of objects. If the
Microscope be one which is not very readily taken out from and put back into its case,
it is very convenient to cover it with a large bell-glass; which may be so suspended
from the ceiling, by a cord carrying a counterpoise at its other end, as to be raised or
lowered with the least possible trouble, and to be entirely out of the way when the
Microscope is in use. Similar but smaller bell-glasses are also useful for the protection
of objects, which are in course of being examined or prepared, and which it is desirable
to seclude from dust,

ARTIFICIAL LIGHT—-LAMPS. 155

of objects, for the examination of which good daylight is not to
be preferred to any other kind of light; but good lamplight is
preferable to bad daylight. When daylight is employed, the
Microscope should be placed near a window, whose aspect should
be (as nearly as may be convenient) opposite to the side on which
the sun is shining; for the light of the sun reflected from a
bright cloud, is that which the experienced Microscopist will
almost always prefer, the rays proceeding from a cloudless blue
sky being by no means so well fitted for his purpose, and the
dull lurid reflection of a dark cloud being the worst of all. The
direct rays of the sun are far too powerful to be used with ad-
vantage, unless its intensity be moderated, either by reflection
from a plaster-of-paris or some other “white-cloud” mirror (§ 58),
or by passage through some imperfectly transparent medium.’
The moderator contrived by Mr. Rainey for lamp or gas-light
(§ 75), has been found to answer equally well for direct sun-
light ; the glare and heating power of which it so effectually sub-
dues, as to destroy all tendency to injure the most delicate ob-
ject, or to confuse the observer's view of it; whilst an illumina-
tion is obtained by its means, whose intensity renders it superior
for certain purposes to anything else. The young Microscopist
is earnestly recommended to make as much use of daylight as
possible; not only because, in a large number of cases, the view
of the object which it affords is more satisfactory than that which
can be obtained by any kind of lamp-light, but also because it is
much less “trying” to the eyes. So great, indeed, is the dif-
ference between the two in this respect, that there are many
who find themselves unable to carry on their observations for
any length of time by lamp-light, although they experience
neither fatigue nor strain from many hours’ continuous work by
daylight.

75. When recourse is had to Artificial light, it is of great im-
portance, not only that it should be of good quality, but that the
arrangement for furnishing it should be suitable to the special
wants of the Microscopist. Thus, although a wax or composi-
tion candle affords a very pure light, yet its use is attended with
two inconveniences, which render its use very undesirable when
any better light can be obtained ;—namely, the constant flicker-
ing of the flame, which is not sufficiently prevented by surround- -
ing it with a chimney; and the continual alteration in its level,
which is occasioned by the consumption of the candle. The
most useful light for ordinary use, is that furnished by the steady
and constant flame of the lamp, fed either with oil, camphine, or
gas; the wick or burner should be cylindrical or “argand;” it
should be capable of adjustment to any height above the table;
and a movable shade should be provided, by which the light may
be prevented from coming direct to the observer’s eyes, or from
diffusing itself too widely through the room. These requisites
are supplied by the lamp commonly known as the “ University”

156 MANAGEMENT OF THE MICROSCOPE.

or “reading” lamp, which has a circular foot with a vertical
stem, on which the oil-reservoir (carrying with it the burner) and
the shade, can be fixed at any convenient height. French and
German lamps on the same general construction, but having the
reservoir contrived on the “ bird-fountain” principle, are also to
be obtained, being largely imported for the use of watch-makers ;
these have the advantage of burning out all their oil, which is
not the case with the ordinary “reading’’-lamp, as 7 does not
burn well except when full or nearly so; but they are usually
destitute of a shade, which, however, can be easily added.
Lamps of either kind are sometimes constructed on the “solar”
principle, which increases the purity and intensity of the light,
but at the same time not only diminishes the diameter of the
flame, but also produces an inconvenient transverse “ break”
near its lower part. The best kind of light which an oil-lamp
can furnish, is that yielded by the ‘Moderator’ lamps which
have of late come into such general use; but they have this im-
portant drawback, that they contain in themselves no adjustment
for varying the elevation of the burner, and that their construc-
tion is such as to give no facilities for any arrangement of this
kind. The same objection applies to the Camphine-lamps in
ordinary use; but a small camphine-lamp has been constructed
for the special use of Microscopists, which is capable of being
placed on an adjustable stand, so that its flame may be raised or
lowered to any desired level. The light of this lamp is whiter
and more intense than that of any other, and it may be used with
advantage for certain very delicate observations (§ 58); but for
the ordinary purposes of the Microscopist it is not so convenient,
the surface of flame from which the light can be received by the
mirror or condenser, being limited by the peculiar construction
which the combustion of camphine requires. To every one who
has a supply of gas at command, the use of it for his microscope-
lamp (by means of a flexible tube) strongly recommends itself,
on account of its extreme convenience, and its freedom from any
kind of trouble. The lamp should be constructed on the general
plan already described, the burner being made to slide up and
down on a stem rising perpendicularly from a foot, which also
carries a shade; and the burner should be one which affords a
_ bright and steady cylindrical flame, either “ Leslie’s’” or the
“cone’’-burner being probably the best. Even the best light
supplied by a gas-lamp, however, is inferior in quality to that of
a good oil-lamp ; and is more injurious and unpleasant to the
eye. Hence the interposition of some kind of artificial medium,
adapted to keep back the yellow rays, whose predominance in
the lamp-flame is the chief source of its injurious action, is es-
pecially required when gas-light is used. This may be partly
effected, by the simple expedient of using a chimney of bluish
glass, known as “ Leblond’s ;” but, in addition, it is advantageous
to cause the light to pass through a screen of bluish-black or

POSITION OF THE LIGHT. 157

neutral-tint glass; and it will then be nearly purified as to
quality, though much reduced in intensity.!. Mr. Rainey, who
has paid great attention to the best means of obtaining a good
illumination by artificial light, recommends, as the best moderator,
one piece of dark blue glass, free from any tint of red, another
of very pale blue with a slight shade of green, and two of thick
white plate-glass, all cemented together with Canada balsam ;
this, as already stated, may be used with sun-light, as well as
with lamp-light. The Microscopist who wishes to render the
artificial light which he may be in the habit of using, as pure as
possible, will do well to compare with daylight (as suggested by
Dr. Griffith, who seems to have been the first to employ tinted
glass with this object); furnishing himself with several pieces of
glass of different shades, substituting one for another, and alter-
ing their distances from the lamp,? until he has succeeded in so
tempering its rays, that the field of his Microscope, or the object
under view, is not more colored when illuminated by the artificial
light reflected from the mirror, than it is-when the mirror is so
turned as to reflect good light from a white cloud.

76. Position of the Light—When the Microscope is used by
daylight it will usually be found most convenient to place it in
such a manner, that the light shall be at the left hand of the ob-
server. It is most important that no light should enter his eye,
save that which comes to it through the Microscope; and the
access of direct light can scarcely be avoided, when he sits with
his face to the light. Of the two sides, it is more convenient to
have the light on the deft; first, because it is not interfered with
by the right hand, when this is employed in giving the requisite
direction to the mirror, or in adjusting the illuminating appara-
tus; and secondly, because, as most persons employ the right
eye rather than the left, the projection of the nose serves to cut
off those lateral rays, which, when the light comes from the right
side, glance between the eye and the eye-piece. In order to pre-
vent, still more completely, the access of false light, it is desirable,
if it be otherwise convenient, that when daylight is employed,
its source should be a little behind the observer: but as it will
then, by falling upon the stage, interfere with the view of any
object which is imperfectly transparent (§ 87), it may be necessary
to keep it from doing so, by the interposition of a screen. When
Artificial light is employed, the same general precautions should
be taken. The lamp should always be placed on the left side,

1 A gas-lamp provided with these and other appurtenances for regulating the illumi-
nation, and also with a water-bath and mounting-plate, is supplied by Mr. S. Highley,
Fleet Street.

2 The nearer the colored glass is approximated to the flame, the less modification will
it produce in its rays; since their intensity varies in different parts of their course, in-
versely with the square of their distance from the illuminating centre, whilst is in-
fluence is a constant quality. “Hence a pale-blue glass placed near the mirror, or be-
tween the mirror and the stage, bas more effect than a chimney of much deeper blue
immediately surrounding the flame.

158 MANAGEMENT OF THE MICROSCOPE.

unless the use of the mirror be dispensed with, or some special
reason exist for placing it otherwise. Ifthe object under exami-
nation be transparent, the lamp should be placed at a distance
from the eye about midway between that of the stage and that of
the mirror; if on the other hand, the object be opaque, it should
be at a distance about midway between the eye and the stage;
so that its light may fall, in the one case upon the mirror, in the
other case upon the stage, at an angle of about 45° with the axis
of the microscope. The passage of direct rays from the flame to
the eye, should be guarded against by the interposition of the
lamp-shade ; and no more light should be diffused through the
apartment, than is absolutely necessary for other purposes. If
observations of a very delicate nature are being made, it is desi-
rable, alike by daylight and by lamp-light, to exclude all lateral
rays from the eye, as completely as possible; and this may be
readily accomplished, by means of a shade attached to the eye-
piece of the microscope. Such a shade may be made most simply
of an oblong piece of card-board, having a circular hole cut in it,
by which it may fit upon the eye-piece or the upper part of the
body; its two ends should be turned up, so as to cut off all
lateral light; its upper side should also be turned up, so as to
cut off the light from the front; and a notch should be eut in
its lower edge, in the proper position to receive the nose. It
may be either painted black, or may be covered with black cloth
or velvet.

TT. Care of the Hyes.— Although most Microscopists acquire a
habit of employing only one eye (generally the right), yet it will
be decidedly advantageous to the beginner, that he should learn
to use either eye indifferently; since by employing and resting
each alternately, he may work much longer, without incurring un-
pleasant or injurious fatigue, than when he always employs the
same. Whether or not he do this, be will find it of great im-
portance to acquire the habit of keeping open the unemployed eye.
This, to such as are unaccustomed to it, seems at first very em-
barrassing, on account of the interference with the microscopic
image, which is occasioned by the picture of surrounding objects,
formed upon the retina of the second eye; but the habit of re-
stricting the attention to that impression only which is received
through the microscopic eye, may generally be soon acquired;
and when it has once been formed, all difficulty ceases. Those
who find it unusually difficult to acquire this habit, may do well
to learn it in the first instance with the assistance of the shade
just described; the employment of which will permit the second
eye to be kept open without any confusion. The advantage of
the practice, in diminishing the fatigue of long-continued obser-
vation, is such, that no pains are ill bestowed by the Microscopist,
which are devoted to early habituation to it. There can be no
doubt that the habitual use of the Microscope for many hours
together, especially by lamp-light, and with high magnifying

CLEANSING OF THE LENSES, ETC. 159

powers, has a great tendency to injure the sight. Every Micro-
scopist who thus occupies himself, therefore, will do well, as he
values his eyes, not merely to adopt the various precautionary
measures already specified, but rigorously to observe the simple
rule of not continuing to observe, any longer than he can do so without
fatigue.

78. Care of the Microscope.—Before the Microscope is brought
into use, the cleanliness and dryness of its glasses ought to be
ascertained. If-dust or moisture should have settled on the
Mirror, this can be readily wiped off. If any spots should show
themselves on the field of view, when it is illummated by the
mirror, these are probably due to particles adherent to one of the
lenses of the Eye-piece; and this may be determined by turning
the eye-piece round, which will cause the spots also to rotate, if
their source lies in it. It may very probably be sufficient to
wipe the upper surface of the eye-glass (by removing its cap), and
the lower surface of the field-glass;- but if, after this has been
done, the spots should still present themselves, it will be neces-
sary to unscrew the lenses from their sockets, and to wipe their
inner surfaces ; taking care to screw them firmly into their places
again, and not to confuse the lenses of ditterent eye-pieces.
Sometimes the eye-glass is obscured by dust of extreme fineness,
which may be carried off by a smart puff of breath; the vapor
which then remains upon the surface being readily dissipated, by
rapidly moving the glass backwards and forwards a few times
through the air. And it is always desirable to try this plan in
the first instance; since, however soft the substance with which
the glasses are wiped, their polish is impaired in the end by the
too frequent performance of the process. The best material for
wiping glass, is a piece of soft wash-leather, from which the dust
it generally contains has been well beaten out. If the Object-
glasses be carefully handled, and be kept in their boxes when
not in use, they will not be likely to require cleansing. One of
their chief dangers, however, to which they are liable in the
hands of an inexperienced Microscopist, arises from the neglect
of precaution in using them with fluids; which, when allowed to
come in contact with the surface of the outer glass, should be
wiped off as soon as‘possible. In screwing and unscrewing them,
great care should be taken to keep the glasses at a distance from
the surface of the hands; since they are liable not only to be
soiled by actual contact, but to be dimmed by the vaporous ex-
halation from skin which they do not touch. This dimness will
be best dissipated, by moving the glass quickly through the air.
It will sometimes be found, on holding an object-glass to the
light, that particles either of ordinary dust, or more often of the
black coating of the interior of the microscope, have settled upon
the surface of its back lens; these are best removed by a clean
and dry camel-hair pencil. If any cloudiness or dust should still
present itself in an object-glass, after its front and back surfaces

160 MANAGEMENT OF THE MICROSCOPE,

have been carefully cleansed, it should be sent to the maker (if
it be of English manufacture) to be taken to pieces, as the ama-
teur will seldom succeed in doing this without injury to the work;
the foreign combinations, however, being usually put together
in a simpler manner, may be readily unscrewed, cleansed, and
screwed together again. Not unfrequently an objective is ren-
dered dim by the cracking of the cement by which the lenses are
united, or by the insinuation of moisture between them; this
last defect occasionally arises from a fault in the quality of the
glass, which is technically said to ‘sweat.’ In neither of these
cases has the Microscopist any resource, save in an Optician ex-
perienced in this kind of work; since his own attempts to remedy
the defect are pretty sure to be attended with more injury than
benefit.

79. General Arrangement of the Microscope for Use.—The in-
clined position of the instrument, already so frequently referred
to, is that in which Observation by it can be so much more ad-
vantageously carried on than it can be in any other, that this
should always be had recourse to, unless particular circumstances
render it unsuitable. The precise inclination that may prove to
be most convenient, will depend upon the “build” of the Micro-
scope, upon the height of the observer’s seat as compared with
that of the table on which the instrument rests, and lastly, upon
the tallness of the individual; and it must be determined in each
ease by his own experience of what suits him best,—that which
he finds most comfortable, being that in which he will be able not
only to work the longest, but to see most distinctly. The selec-
tion of the object-glasses and eye-pieces to be employed, must be
entirely determined by the character of the object. Large ob-
jects presenting no minute structural features, should always be
examined in the first instance by the lowest powers, whereby a
general view of their nature is obtained; and since, with lenses
of comparatively long focus and small angle of aperture, the pre-
cision of the focal adjustment is not of so much consequence as
it is with the higher powers, not only those parts can be seen
which are exactly in focus, but those also can be tolerably well
distinguished, which are not precisely in that plane, but are a
little nearer or more remote. When the general aspect of an
object has been sufficiently examined through low powers, its
details may be scrutinized under a higher amplification ; and this
will be required in the first instance, if the object be so minute,
that little or nothing can be made out respecting it, save when 4
very enlarged image is formed. The power needed in each par-
ticular case, can only be learned by experience; that which is
most suitable for the several classes of objects hereafter to be
described, will be specified under each head. In the general ex-
amination of the larger class of objects, the range of power that is
afforded by the “erector” in combination with the ‘draw-tube”
($44), will be found very useful; whilst for the ready exchange

USE OF DIFFERENT EYE-PIECES. 161

of a low power for a high one, great convenience is afforded by
Mr. Brooke’s object-glass holder (§ 50).

80. When the Microscopist wishes to augment his magnifying
power, he has a choice between the employment of an Objective
of shorter focus, and the use of a deeper Hye-piece. If he pos-
sess a complete series of objectives, he will generally find it best
to substitute one of these for another, without changing the eye-
piece for a deeper one; but if his “‘ powers” be separated by wide
intervals, he will be able to break the abruptness of the increase
in amplification which they produce, by using each objective
first with the shallower, and then with the deeper eye-piece.
Thus if a Microscope be only provided with two objectives, of
1 inch and 1-4th inch focus respectively, and with two eye-
pieces, one nearly double the power of the other (as is the case
with Messrs. Smith and Beck’s new Educational Microscope, p.
103, note), such a range as the following may be obtained,—55,
100, 200, 350 diameters; or, with two objectives of somewhat
shorter focus, and with deeper eye-pieces (as is the case with an
instrument in the Author’s possession, constructed by Kellner
of Wetzlar, whose Microscopes have acquired for themselves a
deservedly high reputation),—88, 176, 850, 700 diameters. The
use of the “ draw-tube” (§ 48) enables the Microscopist still fur-
ther to vary the magnifying power of his instrument, and thus
to obtain almost any exact number of diameters he may desire,
within the limits to which he is restricted by the focal length of
his objectives. The advantage to be derived, however, either
from “deep eye-piecing,” or from the use of the draw-tube, will
mainly depend upon the quality of the object-glass. For if it
be imperfectly corrected, its errors are so much exaggerated,
that more is lost in definition than is gained in amplification ;
whilst, if its aperture be small, the loss of light is an equally
serious drawback. On the other hand, a combination of perfect
construction and wide angle of aperture, will sustain this treat-
ment with so little impairment in the perfection of its image,
that a magnifying power may be obtained by its use, such as,
with an inferior instrument, can only be derived from an object-
ive of much shorter focus combined with a shallow eye-piece.!
In making any such comparisons, it must be constantly borne
in mind that the real question is, what can be seen ? It is always
desirable for the purposes of research, to employ the lowest power
with which the details of structure can be clearly made out;
since, the lower the power, the less is the liability to error from
false appearances, and the better can the mutual relations of the
different parts of the object be appreciated. Hence in testing
the optical quality of a Microscope, the question should always

! The 4-10ths object-glass of Messrs. Smith and Beck was specially distinguished by
the Jurors of the Great Exhibition, as affording, by the use of deep eye-pieces and the
draw tube, a power fully equivalent in the resolution of difficult tests, to that which, a
few years previously, could only have been given by an objective of 1-8th inch.

ll

162 MANAGEMENT OF THE MICROSCOPH,

be,—not, what is its greatest magnifying power,—but, what is
the least magnifying power under which it will show objects of
a given degree of difficulty.

81. In making the Focal Adjustment, when low powers are
used, it will scarcely be necessary to employ any but the coarse
movement ; provided that the rack be well cut, the pinion work
in it smoothly and easily, without either “spring,” “loss of
time,” or “twist,” and the milled head be large enough to give
the requisite leverage. All these are requisites which should be
found in every well-constructed instrument; and its possession
of them should be tested, like its freedom from vibration, by the
use of high powers, since a really good coarse adjustment should
enable the observer to “focus” an objective of 1-8th inch with
precision. What is meant by “spring” is the alteration which
may often be observed to take place on the withdrawal of the
hand; the object which has been brought precisely into focus,
and which so remains as long as the milled head is between the
fingers, becoming indistinct when the milled head islet go. The
source of this fault may lie either in the rack-movement itself,
or in the general framing of the instrument, which is so weak
as to allow of displacement by the mere weight or pressure of
the hand; should the latter be the case, the ‘‘ spring” may be in
great degree prevented, by carefully abstaining from bearing on
the milled head, which should be simply rotated between the fin-
gers. By “loss of time” is meant the want of sufficient readiness
in the action of the pinion upon the rack, so that the milled head
may be moved a little in either direction, without affecting the
body; thus occasioning a great diminution in the sensitiveness
of the adjustment. This fault may sometimes be detected in
Microscopes of the best original construction, which have gradu-
ally worked loose, from the constancy with which they have
been in employment; and it may often be corrected by tighten-
ing the screws that bring the pinion to bear against the rack.
And by “twist” it is intended to express that apparent move-
ment of the object across the field, which results from a real
displacement of the axis of the body to one side or the other,
owing to a want of correct fitting in the working parts. As this
last fault depends entirely upon bad original workmanship, there
is no remedy for it; but it is one which most seriously interferes
with the convenient use of the instrument, however excellent
may be its optical performance. In the use of the coarse adjust-
ment with an objective of short focus, extreme care is necessary
to avoid bringing it down upon the object, to the injury of one
or both; for although the spring with which the tube for the
reception of the object-glass is furnished, whenever the fine
adjustment is immediately applied to this (§ 31), takes off the
violence of the crushing action, yet such an action, even when
thus moderated, can scarcely fail to damage or disturb the object,
and may do great mischief to the lenses. Where no such spring-

ADJUSTMENT OF FOCUS. 163

tube is furnished, the fine adjustment being otherwise provided
for, or being not supplied at all, still greater care is of course
required. It is here, perhaps, well to notice, for the guidance of
the young Microscopist, that the actual distance between the
object-glass and the object, when a distinct image is formed, is
always considerably less than the nominal focal length of the
object-glass; thus, the distance of the 1 inch or 2-3 inch object-
glass may be little more than halfan inch; that of the 4-10 inch
may be but little more than one-tenth of an inch; that of a 1-4
ora 1-5 inch may scarcely exceed one-twentieth; that of a 1-8
inch may not be one-fortieth; and that of a 1-12 or a 1-16 inch
may be so close as not to admit the intervention of a piece of
glass no more than one-hundredth of an inch in thickness. The
reason of this is, that the focal length of an Achromatic objective
is estimated by that of the Single lens with which it agrees in
the size of the image it forms, and therefore in magnifying power "
(e. g., it is said to be of 1 inch focus, when its power is equiva-
lent to that of a single lens, which brings parallel rays to a point
at an inch distance); whilst from its being composed of a com-
bination of lenses, the point from which that focal distance has
really to be measured, is not at the surface of its front lens, but
at some distance behind it, in the interior of the combination.
One more precaution it may be well to specify ;—namely, that
either in changing one object for another, or in substituting one
objective for another, save when powers of such focal length are
employed as to remove all likelihood of injury, the “body”
should be turned to one side, where the construction of the Mi-
croscope admits of this displacement, or (where it does not)
should have its distance from the stage increased by the “coarse
movement.” This precaution is absolutely necessary, when ob-
jectives of short focus are in use, to avoid injury either to the
lenses or to the object; and when it is habitually practised with
regard to these, it becomes so much like an “acquired instinct,”
as to be almost invariably practised in other cases.

82. In obtaining an exact Focal Adjustment with object-
glasses of less than half an inch focus, it will be generally found
convenient to employ the fine movement ; and as recourse will
frequently be had to its assistance for other purposes also, it is
very important that it should be well constructed and in good
working order. The points to be particularly looked to in test-
ing it, are for the most part the same with those already noticed
in relation to the coarse movement. It should work smoothly
and equably, producing that graduated alteration of the distance
of the object-glass from the object, which it is its special duty to
effect, without any jerking or irregularity. It should be so sensi-
tive, that any movement of the milled head should at once make
its action apparent, by an alteration in the distinctness of the
image, when high powers are employed, without any “loss of

164 MANAGEMENT OF THE MICROSCOPE.

time.’? And its action should not give rise to any twisting or
displacing movement of the image, which ought not to be in the
least degree disturbed by any number of rotations of the milled
head, still less, by a rotation through only a few degrees. One
great use of the “fine adjustment” consists in bringing into view
different strata of the object, and this in such a gradual manner
that their connection with one another shall be made apparent,
Whether an opaque or a transparent object be under examina-
tion, only that part can be perfectly discerned under any power,
which is exactly in focus; and when high powers of large aper-
ture are employed, this is the only part that can be seen at all.
A minute alteration of the focus often causes so entirely different
a set of appearances to be presented, that, if this alteration be
made abruptly, their relation to the preceding can scarcely be
even guessed at; and the gradual transition from the one to the
other, which the fine adjustment alone affords, is therefore ne-
cessary to the correct interpretation of either. To take a very
simple case:—The transparent body of a certain animal being
traversed by vessels lying in different planes, one set of these
vessels is brought into view by one adjustment, another set by
“ focussing” to a different plane; and the connection of the two
sets of vessels, which may be the point of most importance in
the whole anatomy of the animal, may be entirely overlooked,
for want of a fine adjustment, the graduated action of which
shall enable one to be traced continuously into the other. What
is true even of low and medium powers, is of course true to a
still greater degree of high powers; for although the “ coarse
movement’ may enable the observer to bring any stratum of the
object into accurate focus, it is impossible for him by its means
to secure that transitional “focussing,” which is often so much
more instructive than an exact adjustment at any one point. A
clearer idea of the nature of a doubtful structure is, in fact, often
derived from what is caught sight of in the act of changing the
focus, than by the most attentive study and comparison of the
different views obtained by any number of separate “ focussings.”
The experienced Microscopist, therefore, when examining an
object of almost any description, constantly keeps his finger
upon the milled head of the “fine movement,” and watches the
effect produced by its revolution upon every feature which he
distinguishes ; never leaving off, until he be satisfied that he has
scrutinized not only the entire surface, but the entire thickness of
the object. It will often happen, that, where different structural
features present themselves on different planes, it will be difficult
or even impossible to determine which of them is the nearer and

11t will sometimes happen that the “fine movement” will seem not to act, merely
because it has been so habitually worked in one direction rather than the other, that its
screw has been turned too far. In that case, nothing more is required for its restoration
to good working order, than turning the screw in the other direction, until it shall have
reached about the middle of its range of action.

ADJUSTMENT OF THE OBJECT-GLASS. 165

which the more remote (it being the special result of the ordinary
mode of viewing objects by transmitted light, that such differ-
ences are obliterated), unless, by the use of the “ fine movement,”
it be ascertained, when they are successively brought into focus,
whether the object-glass has been moved towards or away from
the object. Even this, however, will not always succeed in cer-
tain of the most difficult cases, in which the difference of level
is so slight as to be almost inappreciable ;—as, for instance, in
the case of the markings on the siliceous lorice of the Diatomacese
Fig. 80).

3. When objectives of short focus and of wide angular aper-
ture are being employed, something more is necessary than exact
focal adjustment; this being the Adjustment of the Odject-glass
itself, which is required to neutralize the disturbing effect of the
glass cover upon the course of the rays proceeding from the ob-
ject (§ 15). For this adjustment, it will be recollected, a power
of altering the distance between the front pair and the remainder
of the combination is required; and this power is obtained in
the following manner. The front pair of lenses is fixed into a
tube (Fig. 58, a), which slides over an interior tube (B) by which
the other two pairs are

held; and it is drawn up

or down by means of a

collar (c), which works in

a furrow cut in the inner

tube, and upon a screw-

thread cut in the outer,

so that its revolution in

the plane to which it is pcovered
fixed by the one tube, Covered
gives a vertical movement

to the other. In one part

of ‘the outer tube, an ob-

long slit is made, as seen

at D, into which projects

a small tongue, screwed =
on the inner tube 5 at the Section of an Adjusting Object-Glass.
side of the former two

horizontal lines are engraved, one pointing to the word “un-
covered,” the other to the word “ covered;” whilst the latter is
crossed by a horizontal mark, which is brought to coincide with
either of the two lines by the rotation of the screw-collar, which
moves the outer tube up or down. When the mark has been
made to point to the line “uncovered,” it indicates that the dis-
tance of the lenses of the object-glass is such, as to make it suita-
ble for viewing an object without any interference from thin
glass; when, on the other hand, the mark has been brought, by
the revolution of the screw-collar, into coincidence with the line
“covered,” it indicates that the front lens has been brought into

Fig. 52.

166 MANAGEMENT OF THE MICROSCOPE.

such proximity with the other two, as to produce a “positive
aberration” in the objective, fitted to neutralize the “negative
aberration” produced by the interposition of a glass cover of a
certain thickness. It is evident, however, that unless the par-
ticular thickness of glass for which this degree of alteration ig
suited, be always employed for this purpose, the correction can-
not be exact; and means must he taken for adapting it to every
grade of thickness, which may be likely to present itself in the
glass covers. Unless this correction be made with the greatest
precision, the enlargement of the angle of aperture, to which our
Opticians have of late applied themselves with such remarkable
success, becomes worse than useless; being a source of dimi-
nished instead of increased distinctness in the details of the ob-
ject, which are far better seen with an objective of greatly inferior
aperture, possessing no special adjustment for the thickness of
the glass. The following general rule is given by Mr. Wenham,
for securing the most efficient performance of an object-glass
with any ordinary object :—‘‘ Select any dark speck or opaque
portion of the object, and bring the outline into perfect focus;
then lay the finger on the milled head of the fine motion, and
move it briskly backwards and forwards in both directions from
the first position. Observe the expansion of the dark outline of
the object, both when within, and when without, the focus. If
the greater expansion, or coma, is when the object is wzthout the
focus, or furthest from the objective, the lenses must be placed
further asunder, or towards the mark ‘uncovered.’ If the
greater coma is when the object is within the focus, or nearest to
the objective, the lenses must be brought closer together, or
towards the mark ‘ covered.’ When the object-glass is in proper
adjustment, the expansion of the outline is exactly the same both
within and without the focus.” A different indication, however,
is afforded by such “ test-objects’’ as present (like the Podura-
scale and the Diatomaces) a set of distinct dots or other mark-
ings. For “if the dots have a tendency to run into lines when
the object is placed without the focus, the glasses must be brought
closer together; on the contrary, if the lines appear when the
object is within the focal point, the object must be further sepa-
rated.| When the angle of aperture is very wide, the difference
in the aspect of any severe test under different adjustments be-
comes at once evident; markings which are very distinet when
the correction has been exactly made, disappearing almost
instantaneously when the screw-collar is turned a little way
round.’”?

1See “ Quart. Journ. of Microse. Science,” vol. ii, p. 138.

2 Mr. Wenham remarks (loc. cit.), not without justice, upon the difficulty of making
this adjustment, even in the Objectives of our best Opticians; and he states that he has
himself succeeded much better, by making the outer tube the fixture, and by making
the tube that carries the other pairs slide within this; the motion being given by the

action of an inclined slit in the revolving collar, upon a pin that passes through a longi-
tudinal slit in the outer tube, to be attached to the inner. The whole range of adjust

ADJUSTMENT OF THE OBJECT-GLASS. 167

84. Although the most perfect correction required for each par-
ticular object (which depends, not merely upon the thickness of
its glass cover, but upon that of the fluid or balsam in which it
may be mounted) can only be found by experimental trial, yet
for all ordinary purposes, the following simple method, first de-
vised by Mr. Powell, will suffice. The object-glass, adjusted to
“uncovered,” is to be “‘ focussed” to the object; its screw-collar
is next to be turned, until the surface.of the glass cover comes
into focus, as may be perceived by the spots or striee by which it
may be marked; the object is then to be again brought into
focus by the “fine movement.” The edge of the screw-collar
being now usually graduated, the particular adjustment which
any object may have been found to require, and of which a
record has been kept, may be made again without any difficulty.
By Messrs. Smith and Beck, however, who first introduced this
graduation, a further use is made of it. By experiments such as
those described in the last paragraph, the correct adjustment is
first found for any particular object, and the number of divisions
observed, through which the screw-collar must be moved in order
to bring it back to 0°, the position suitable for an uncovered ob-
ject. The thickness of the glass cover must then be measured
by means of the “ fine movement:” this is done by bringing into
exact focus, first the object itself, and then the surface of the
glass cover, and by observing the number of divisions through
which the milled head (which is itself graduated) has passed in
making this change. A definite ratio between that thickness of
glass, and the correction required in that particular objective, is
thus established ; and this serves as the guide to the requisite
correction for any other thickness, which has been determined
in like manner by the “fine movement.”” Thus, supposing a
particular thickness of glass to be measured by 12 divisions of
the milled head of the fine movement, and the most perfect per-
formance of the object-glass to be obtained by moving the screw-
collar through 8 divisions, then a thickness of glass measured by
9 divisions of the milled head, would require the screw-collar to
be adjusted to 6 divisions in order to obtain the best effect. The
ratio between the two sets of divisions is by no means the same
for different combinations; and.it ought to be determined for
each objective by its maker, who will generally be the best judge
of the best “points” of his lenses; but when this ratio has been
once ascertained, the adjustment for any thickness of glass with
which the object may happen to be covered, is readily made by
the Microscopist himself. Although this method appears some-
what more complex than that of Mr. Powell, yet it is more per-
fect; and when the ratio between the two sets of divisions has
been once determined, the adjustment does not really involve

ment is thus performed within a third part of a revolution, with scarcely any friction,
and with such an immediate transition from good to bad definition, that the best point
is made readily apparent.

168 MANAGEMENT OF THE MICROSCOPE.

more trouble. Another use is made of this adjustment by Messrs.
Smith and Beck; namely, to correct the performance of the ob-
jectives, which is disturbed by the increase of distance between
the objective and the eye-piece, that is occasioned by the use of
the draw-tube (§ 43). Accordingly, they mark a scale of inches
on the draw-tube (which is useful for many other purposes), and
direct that for every inch the body is lengthened, the screw-collar
of the objective shall be moved through a certain number of
divisions.

85. Arrangement for Transparent Objects.—If the object be
already “‘ mounted” in a slide, nothing more is necessary, in
order to bring it into the right position for viewing it, than to
lay the slide upon the object-platform of the stage, and to sup-
port it in such a position (by means of the sliding ledge or other
contrivance) that the part to be viewed is, as nearly as can be
guessed, in the centre of the aperture of the stage, and therefore
in a line with the axis of the body. If the object be not
‘“‘mounted,” and be of such a kind that it is best seen dry, it
may be simply laid upon the glass stage-plate (§ 67), the ledge of
which will prevent it from slipping off when the microscope is
inclined, and a plate of thin glass may be laid over it for its pro-
tection, if its delicacy should seem to render this desirable. If,
again, it be disposed to curl up, so that a slight pressure is
needed to flatten or extend it, recourse may be had to the use of
the aquatic box (§ 68), or of the compressorium (§ 70), no liquid,
however, being introduced between the surfaces of glass. In a
very large proportion of cases, however, either the objects to be
examined are already floating in fluid, or it is preferable to
examine them in fluid, on account of the greater distinctness
with which they may be seen; if such objects be minute, and
the quantity of liquid be small, the drop is simply to be laid on
a slip of glass, and covered with a plate of thin glass; if the
object or the quantity of liquid be larger, it will be better to
place it in the aquatic box; whilst, if the objects have dimen-
sions which render even this inconvenient, the zoophyte trough
(§ 69) will afford the best medium for its examination. If it be
wished to have recourse to compression, for the expansion or
flattening of the object, this may be made upon the ordinary
slide, by pressing down the thin glass cover with a pointed
stick; and this method, which allows the pressure to be applied
where it may chance to be most required, will generally be
found preferable for delicate.portions of tissue which are easily
spread out, and which, in fact, require little other compression
than is afforded by the weight of the glass cover, and by the
capillary attraction which draws it into proximity with the slide
beneath. A firmer and more enduring pressure may be exerted
by the dexterous management of a well-constructed aquatic
box; and this method is peculiarly valuable for confining the
movements of minute animals, so as to keep them at rest under

ARRANGEMENT FOR TRANSPARENT OBJECTS. 169

the field of the microscope, without killing them. It is where a
firm but graduated pressure is required, for the flattening out of the
bodies of thin semi-transparent animals, without the necessity of re-
moving them from the field of the microscope, that the compresso-
rium is most useful. Wherever the first and simplest of the above
methods can be had recourse to, it is the preferable one; since
the object, when on a glass slide, can be subjected to the Achro-
matic Condenser, Polarisecope, Oblique Illumination, &., with
far more convenience than when removed to a plane above the
stage, as it must be when the aquatic box is used. Whether
the object be submitted to examination on a slip of glass, or in
the aquatic box or compressorium, it must be first payaeh
approximately into position, and supported there, just as if it
were in a mounted slide. The precise mode of effecting this
will differ, according to the particular plan of the instrument
employed; thus in some, it is only the ledge itself that slides
along the stage ; in others, it is a carriage of some kind, whereon
the object-slide rests; in others, again, it is the entire platform
itself that moves upon a fixed plate beneath.

86. Having guided his object, as nearly as he can do by the
unassisted eye, into its proper place, the Microscopist then
brings his light (whether natural or artificial) to bear upon it, by
turning the mirror in such a direction as to reflect upon its
under surface the rays which are received by itself from the sky
or the lamp. The concave mirror is that which should always be
first employed, the plane being reserved for special purposes ;
and it should bring the rays to convergence in or near the plane
in which the object
lies (Fig. 54). The Fia. 54.
distance at which it f
should be ordinarily
set beneath the stage,
is that at which it
brings parallel rays
to a focus; but this
distance should be
capable of elongation,
by the lengthening of
the stem to which the
mirror is attached;
since the rays diverg-
ing from a lamp at a
short distance, are not
so soon brought to a ——
focus. The correct Arrangement of Microscope for Transparent Objects.
focal adjustment of
the mirror may be judged of, by its formation of images of
window-bars, chimneys, &c., upon any semi-transparent medium
placed in the plane of the object. It is only, however, when

170 MANAGEMENT OF THE MICROSCOPE.

small objects are being viewed under high magnifying powers,
that such a concentration of the light reflected by the mirror is
either necessary or desirable ; for with large objects, seen under
low powers, the field would not in this mode be equably
illuminated. The diffusion of the light over a larger area may
be secured, either by shifting the mirror so much above or so
much below its previous position, that the pencil will fall upon
the object whilst still converging or after it has met and
diverged; or, on the other hand, by the interposition of a plate
of ground glass in the course of the converging pencil,—this
last method, which is peculiarly appropriate to lamp-light, being
very easily had recourse to, if the diaphragm plate, as formerly
recommended (§ 55), have had its largest aperture filled with
such a diffused medium. The eye being now applied to the
Hye-piece, and the body being “focussed,” the object is to be
brought into the exact position required, by the use of the
traversing movement, if the stage be provided with it; if not,
by the use of the two hands, one moving the object-slide from
side to side, the other pushing the ledge, fork, or holder that
carries it, either forwards or backwards, as may be required. It
is always to be remembered, in making such adjustments by the
direct use of the hands, that, owing to the inverting action of
the microscope, the motion to be given to the object, whether
lateral or vertical, must be precisely opposed to that which
its image seems to require, save when the Erector (§ 44) is
employed. When the object has been thus brought fully into
view, the Mirror may require a more accurate adjustment.
What should be aimed at, is the diffusion of a clear and equable
light over the entire field; and the observer should not be
satisfied, until he has attained this object. If the field should
be darker on the one side than on the other, the mirror should
be slightly turned in such a direction as to throw more light
upon that side; perhaps in so doing, the light may be withdrawn
from some part previously illuminated; and it may thus be
found that the pencil is not large enough to light up the entire
field. This may be owing to one of three causes: either the cone
of rays may be received by the object too near to its focal apex,
the remedy for which lies in an alteration in the distance of the
mirror from the stage; or, from the very oblique position of the
mirror, the cone is too much narrowed across one of its diame-
ters, and the remedy must be sought in a change in the position
either of the microscope or of the lamp, so that the face of the
mirror may not be turned so much away from the axis of vision;
or, again, from the centre of the mirror being out of the optical
axis of the instrument, the illuminating cone is projected
obliquely, an error which can be rectified without the least
difficulty. If the cone of rays should come to a focus in the
object, the field is not unlikely to be crossed by the images of
window-bars or chimneys, or the form of the lamp-flame may be

REGULATION OF TRANSMITTED LIGHT. 171

distinguished upon it; the former must be got rid of by a slight
change in the inclination of the mirror; and if the latter cannot
be dissipated in the same way, the lamp should be brought a
little nearer.

87. The equable illumination of the entire field having been
thus obtained, the quantity of light to be admitted should be re-
gulated by the Diaphragm-plate (§ 55). This must depend very
much upon the nature of the object, and upon the intensity of
the light. Generally speaking, thé more transparent the object,
the less light does it need for its most perfect display; and its
most delicate markings are frequently only made visible, when
the major part of the cone of rays has been cut off. Thus the
movement of the cilia,—those minute vibratile filaments, with
which almost every Animal is provided in some part of its or-
ganism, and which many of the humbler Plants also possess,—
can only be discerned in many instances, when the light is ad-
mitted through the smallest aperture. On the other hand, the
less transparent objects usually require the stronger illumination
which is afforded by a wider cone of rays; and there are some
(such as semi-transparent sections of fossil teeth) which, even
when viewed with low powers, are better seen with the intenser
light afforded by the Achromatic Condenser. In every case in
which the object presents any considerable obstruction to the
passage of the rays through it, great care should be taken to pro-
tect it entirely from ineident light; since this extremity weakens
the effect of that which is received into the microscope by trans-
mission. Itis by daylight that this interference is most likely
to occur : since, if the precautions already given (§ 76) respecting
the use of lamp-light be observed, no great amount of light can
fall upon the upper surface of the object. The observer will be
warned that such an effect is being produced, by perceiving that
there is a want, not only of brightness, but of clearness, in the
image ; the field being veiled, as it were, by a kind of thin vapor ;
and he may at once satisfy himself of the cause, by interposing
his hand between the stage and the source of light, when the
immediate increase of brilliancy and of distinctness will reveal
to him the occasion of the previous deficiency in both. Nothing
more is necessary for its permanent avoidance, than the inter-
position of an opaque screen (blackened on the side towards the
stage) between the window and the object; care being of course
taken, that the screen does not interfere with the passage of
light to the mirror. Such a screen may be easily shaped and
adapted either to be carried by the stage itself, or by the stand
for the condenser; but it is seldom employed by Microscopists,
as it interferes with access to the left side of the stage’ and the
interposition of the hand, so often as it may be needed, is more
frequently had recourse to in preference, as the more convenient
expedient. The young Microscopist who may be examining
transparent objects by daylight, is recommended never to omit

172 MANAGEMENT OF TIE MICROSCOPE.

ascertaining, whether the view which he may obtain of them, is
in any degree thus marred by incident light.

88. Although the illumination afforded by the mirror alone is
quite adequate for a very large proportion of the purposes for
which the Microscope may be profitably employed (nothing else
having been used by many of those who have made most valua-
ble contributions to Science by means of this instrument), yet,
when high magnifying powers are employed, and sometimes even
when but a very moderate amplification is needed, great advan-
tage is gained from the use of the Achromatic Condenser. The
various modes in which this may be constructed, and may be
fitted to the Microscope, have been already described (§ 56); we
have now to speak of the manner of using it. The lenses with
which the Condenser is provided should be made to separate
from each other, in such a manner that two or three distinct
powers should be afforded ; the complete combination should be
used with objectives of 1-5th inch focus or less; the front lens
should be removed with objectives of from half to a quarter of
an inch focus; and the second lens may be removed, so that the
back lens will be alone employed, when it is desired to use the
condenser with objectives of less than half an inch focus. It is
of the greatest importance that the Condenser should be ac-
curately adjusted, both as to the coincidence of its optical axis
with that of the Microscope itself, and as to its focal distance
from the object. The centring may be most readily accom-
plished, by so adjusting the distance of the condenser from the
stage (by the rack-and-pinion action, or the siding movement,
with which it is always provided), that a sharp circle of light
shall be thrown on any semi-transparent medium laid upon it;
then, on this being viewed through the Microscope with an ob-
jective of sufficiently low power to take in the whole of it, if
this circle be not found to be concentric with the field of view,
the axis of the condenser must be altered by means of the milled-
head tangent screws with which it is provided. The focal adjust-
ment, on the other hand, must be made under the objective which
is to be employed in the examination of the object, by turning
the mirror in such a manner as to throw upon the visual image
of the object (previously brought into the focus of the Micro-
scope) an image of a chimney or window-bar, if daylight be em-
ployed, or of the top, bottom, or edge of the lamp-flame, if lamp-
light be in use; such a vertical movement should be given to the
condenser, as may render the view of this as distinct as possible;
and the direction of the mirror should then be sufficiently
changed to displace these images, and to substitute for them the
clearest light that can be obtained. It will generally be found,
however, that although such an exact focussing gives the most
perfect results by daylight, yet that by lamp-light the best illu-
mination is obtained, when the condenser is removed to a some-
what greater distance from the object, than that at which it gives

USE OF ACHROMATIC CONDENSER. 173

a distinct image of the lamp. In every case, indeed, in which
it is desired to ascertain the effect of variety in the method of
illumination, the effects of alterations in the distance of the con-
denser from the object should be tried; as it will often happen
that delicate markings become visible when the condenser is a
little owt of focus, which cannot be distinguished when it is pre-
cisely in focus.. The diaphragm-plate with which all the best
forms of Achromatic Condenser are now furnished, enables the
observer not only to vary the angle of his illuminating pencils
through a range of from 20° to 80°, but also to stop off the
central portion of the pencil, so as to allow only its most oblique
rays to pass; and the contrast presented by the aspect of many
objects, according as the size and form of the aperture in the
diaphragm-plate Timits the rays transmitted by the condenser to
those of the central or those of the peripheral portion of the
pencil, is often so marked, as to show beyond question the great
importance of this mode of varying the illumination. When
the condenser is employed, the plane Mirror may often be sub-
stituted with advantage for the concave; the chief effect of this
exchange being to diminish the quantity of light, without alter-
ing the angle of the illuminating pencil. It must be borne in
mind, in making such an alteration, that the plane mirror reflects
parallel or (if from a lamp) diverging rays, instead of the con-
verging rays reflected by the concave mirror; so that the focus
of the condenser is likely to require readjustment. For objects
of great delicacy and transparency, the “ white-cloud”’ illumina-
tion (§ 58) may be had recourse to with advantage; or, if it be
desired that the illuminating pencil should be free from the error
imparted by the double reflection of the mirror, the mirror may
be turned aside, and in its stead the lamp (if the observation be
made by artificial light) may be placed in the axis of the micro-
scope; or the mirror may be replaced by ‘“ Dujardin’s prism”’
(§ 57), which will be equally available either by daylight or by
lamp-light.

89. Should it be desired, however, to try the effect of very
oblique light upon an object, the Achromatic Condenser must
be removed (unless, as in Mr. Sollitt’s arrangement, § 130, it be
so constructed as to be capable of inclination to the axis of the
Microscope), and other means must be employed. The simplest
method, where the mirror is mounted on an “arm” (Fig. 29), is
to turn it to one side so as to reflect the rays at a considerable
angle; and where this cannot be done, nearly the same effect is
produced by placing the lamp in the direction from which it is
desired that the oblique rays should proceed, and interposing an
ordinary condensing lens between it and the object. Or, if the
Microscopist be provided with the means of mounting a “ Du-
jardin’s prism” on a separate stand, he may place it in such a
position as to reflect light from any point required: and he may
concentrate that light by an ordinary condenser. The possession

/

174 MANAGEMENT OF THE MICROSCOPE.

of Amici’s prism, however (which serves both as mirror and con-
denser, § 60), will save the necessity of any other provision of
this kind. It is when objects are thus illuminated by oblique
light, and when their markings are of such a kind as to be best
or to be only shown by light falling upon them in one particular
direction, that we derive the greatest advantage from the power
of giving a rotatory movement either to the object or to the illu-
minating apparatus. Thus suppose that an object be
A marked by longitudinal strize, too faint to be seen by
| ordinary direct light; the oblique light most fitted to
D bring them into view, will be that proceeding in
| either of the directions c or p; that which falls upon
B it in the directions 4 and B, tending to obscure the
striae rather than to disclose them. But, moreover,
if the strie should be due to furrows or prominences which have
one side inclined and the other side abrupt, they will not be
brought ‘into view indifferently by light from c or from pb, but
will be shown best by that which makes the strongest shadow;
hence if there be a projecting ridge, with an abrupt side looking
towards o, it will be best seen by light from p; whilst if there
be a furrow with a steep bank on the side of ©, it will be by
light from that side that it will be best displayed. But it is not
at all unfrequent for the longitudinal striz to be crossed by
others ; and these transverse strie will usually be best seen by
the light that is least favorable for the longitudinal; so that, in
order to bring them into distinct view, either the illuminating
pencil or the object must be moved a quarter round. The re-
volving action with which the stage of Mr. Ross’s Microscope is
provided (§ 37), enables this movement to be given to the object
without any displacement of its image, which, of course, exe-
cutes, to the eye of the observer, a rotation in the opposite di-
rection. In other microscopes, however, it is difficult to give a
rotation to the object, by causing the object-platform to turn
upon its axis, without throwing the object out of the field (§ 38);
though this may be accomplished, by such an adjustment of the
traversing movement, as shall bring the centre of the tube on
which that platform turns round, into the visual axis of the
microscope—or, if this adjustment cannot be conveniently made
in the first instance, by keeping the right hand constantly in
action upon the milled heads of the stage movement, whilst the
left hand rotates the object-platform, so as, by means of the
former, to correct the displacement of the object occasioned by
the latter. It may be sufficient, however, to examine the object
in several different positions, so that the appearances it presents
in each may be compared, without thus watching the transition
from one to the other.
90. There are many kinds of transparent objects, especially
such as either consist of thin plates, disks, or spicules of siliceous
or calcareous matter, or contain such bodies, which are peculiarly

ARRANGEMENT FOR OPAQUE OBJECTS. 175

well seen under the black-ground illumination (§§ 61, 62) ; for not
only does the brilliant luminosity which they then present, con-
trasting remarkably well with the dark ground behind them,
show their forms to extraordinary advantage; but this mode of
illumination imparts to them an appearance of solidity, which
they do not exhibit by ordinary transmitted light (§ 62); and it
also frequently brings out surface-markings, which are not other-
wise distinguishable. Hence, when any object is under exami-
nation, that can be supposed to be a good subject for this method,
the trial of it should never be omitted. For the low powers, the
use of the “spotted lens” will be found sufficiently satisfactory ;
for the higher, the paraboloid should be employed (§ 61). Similar
general remarks may be made, respecting the examination of ob-
jects by polarized light. Some of the most striking effects of
this kind of illumination, are produced upon bodies whose par-
ticles have a crystalline aggregation ; and hence it may often be
employed with great advantage to bring such bodies into view,
when they would not otherwise be distinguished ; thus, for ex-
ample, the raphides of Plants are much more clearly made out by
its means, in the midst of the vegetable tissues, than they can be
by any other. But the peculiar effects of polarized light are also
exerted upon a great number of other organized substances, both
Animal and Vegetable; and it often reveals differences in the
arrangement or in the relative density of their component par-
ticles, the existence of which would not otherwise have been
suspected ; hence, the Microscopist will do well to have recourse
to it, whenever he may have the least suspicion that its use can
ive him an additional power of discrimination.

91. Arrangement for Opaque Objects—Although a large pro-
portion of the objects best suited for Microscopic examination
are either in themselves sufficiently transparent to admit of being
viewed by light transmitted through them, or may be made so by
appropriate means, and although that method (where it can be
adopted) is generally the one best fitted for the elucidation of the
details of their structure, yet there are many objects of the most
interesting character, the opacity of which entirely forbids the
use of this method, and of which, therefore, the surfaces only
can be viewed, by means of the incident rays which they reflect.
These are, for the most part, objects of comparatively large di-
. mensions, for which a low magnifying power suffices; and it is
specially important, in the examination of such objects, not to
use a lens of shorter focus than is absolutely necessary for dis-
cerning the details of the structure; since, the longer the focus
of the objective employed, the less is the indistinctness produced
by inequalities of the surface, and the larger, too, may be its aper-
ture, so as to admit a greater quantity of light, to the great im-
provement of the brightness of the image. It is surprising how
little attention has been given by Opticians to the construction of
objectives suitable for this purpose. In their zeal for the im-

176 MANAGEMENT OF THE MICROSCOPE.

provement of the higher powers of the Microscope, they have
thought comparatively little of the lower; and in Continental
Microscopes, it is rare to meet with an objective which will give
even a tolerable view of alarge opaque object. The Author, in-
deed, well remembers the time, when it was not thought worth
while, even by English Opticians, to construct Achromatic ob-
ject-glasses of less than an inch focus; and the production of
objectives of 14 inch and 2 inch focus has been chiefly called
for, in consequence of their value in displaying anatomical pre-
parations in which the bloodvessels have been injected with
coloring matter. The view which is afforded of large opaque
objects, however, by a Compound Microscope, furnished with
even an imperfectly corrected Achromatic object-glass, giving a
magnifying power of 20 or 25 diameters, is so greatly preferable
to that which is given by any Simple Microscope, that no instru-
ment that is intended for general research should be unfurnished
with such a power. It is especially required in Microscopes that
are to be used for Educational purposes; since it is most im-
portant that the young should be trained in a knowledge of the
wonders and beauties of the familiar objects around them ; and
an objective of low power and wide aperture, adapted to the
examination of a large surface at once, affords a means of dis-
playing these, such as can be afforded in no other way, save by
the use of the Erector and draw-tube (§ 44). A microscope fur-
nished with these appendages, need not be supplied with an ob-
jective of longer focus than 1 inch or 8-10ths inch; but the
Author would strongly recommend to such as do not possess
them, that they should give to a “dividing” 12 inch or 2 inch
(in which the front lens is removable, and is replaced by a per-
forated cap that limits the aperture of the back lens, which is
then employed by itself, having a focus of about 3 inches) a pre-
ference over such as do not thus supply the extremely low power
which he recommends.’

92. The mode of bringing opaque objects under view, will
differ according to their “mounting,” and to the manner in
which it is desired to illuminate them. If the object be mounted
in a “slide” of glass or wood, upon a large opaque surface, the
slide must be laid on the stage in the usual manner, and the
object brought as nearly as possible into position by the eye
alone (§ 84). If it be not so mounted, it may be simply laid upon ,
the glass stage-plate, resting against its ledge; and the diaphragm-
plate must then be so turned, as to afford it a black background.

‘A single pair (flint and crown) of about 2 inch focus, was constructed at the
Author’s request, some years since, by Messrs. Smith and Beck, for the special purpose
of exbibiting injected preparations, and other opaque objects; and its performance has
been so satisfactory to him, that he was induced to urge upon the Microscopic Committee
appointed by the Society of Arts, that the Educational Microscope for whicl they in-
vited competition (§ 31), should be furnished with such a power. This reeommenda-
tion having been adopted, the instrument selected has been specially fitted for the
class of olijects above alluded to,

ILLUMINATION FOR OPAQUE OBJECTS. 177

For all ordinary purposes, a plano or double-convex lens, of
about 14 inch diameter, and 2 inches focus, either mounted upon
a separate stand (as in Fig. 45), or so attached by a jointed
support to the Microscope itself as to admit of being placed in
any required position,
willanswer extremely
well as a Condenser.
If Daylight be em-
ployed, the micro-
scope should be so
placed that the strong-
est light may fall
obliquely upon the
stage, and preferably
from the left hand
side; there will then
be no difficulty in so
disposing this con-
denser, as to afford
an illumination suffi-
cient for almost any
kind of object, pro-
vided the quality of
the light itself be good. Direct sunlight cannot be here em-
ployed, without the production of an injurious glare, and the
risk of burning the object; but the sunlight reflected from a
bright cloud is the best light possible. The condenser should
always be placed at right angles to the direction of the illumi-
nating rays, and at a distance from the object which will be de-
termined by the size of the surface to be illuminated and by the
kind of light required. If the magnifying power employed be
high, and the field of view be consequently limited, it will be
desirable so to adjust the lens, as to bring the cone of rays to a
point upon the part of the object under examination; and this
adjustment can only be rightly made whilst the object is kept in
view under the microscope, the condenser being moved in va-
rious modes, until that position has been found for it in which
it gives the best light. If, on the other hand, the power be low,
and it be desired to spread the light equably over a large field,
the condenser should be placed either within or beyond its focal
distance; and here, too, the best position will be ascertained by
trial. It will often be desirable, also, to vary both the obliquity
of the light, and the direction in which it falls upon the object;
the aspect of which is greatly affected by the manner in which
the shadows are projected upon its surface, and in which the
lights are reflected from the various points of it. There are
many objects, indeed, distinguished by their striking appearance
when the light falls upon them on one side, which are entirely

destitute both of brilliancy of color and of sharpness of outline,
12

Fig. 55,

Arrangement of Microscope for Opaque Objects.

178 MANAGEMENT OF THE MICROSCOPE.

when illuminated from the opposite side. Hence it is always
desirable to try the eflect of changing the position of the object;
which, if it be “mounted,” may be first shifted by merely re-
versing the place of the two ends of the slide, and then, if this
be not satisfactory, may be more completely as well as more
gradually altered, by making the object-platform itself revolve,
where the stage is fitted with such a movement: if, however, the
object be not mounted, but be simply resting on the stage-plate, it
may be readily shifted by hand. With regard to the obliquity
of the illuminating rays, it is well to remark, that if the object
be “mounted” under a glass cover, and the incident rays fall at
too great an angle with the perpendicular, a large proportion of
them will be reflected, and the brilliancy of the object will be
greatly impaired.

93. The same general arrangement must be made, when
Artificial light is used for the illumination of opaque objects;
the lamp being placed in such a position in regard to the stage,
that its rays may fall in the direction indicated in Fig. 55; and
these rays being collected and concentrated by the condenser, as
already directed. As the rays proceeding from a lamp within a
short distance are already diverging, they will not be brought by
the condenser to such speedy convergence, as are the parallel
rays of daylight; and it must, therefore, be further removed
from the object, to produce the same effect. By modifying the
distance of the condenser from the lamp and from the object
respectively, the cone of rays may be brought nearly to a focus,
or it may be spread almost equally over a large surface, as may
be desired. In the illumination of opaque objects, the inferiority
of artificial to solar light is not so perceptible as in the case of
transparent objects; and the former has the advantage of being
more easily concentrated to the precise degree, and of being
more readily made to fallin the precise direction, that may be
found most advantageous. Moreover, the contrast of lght
and shadow will be more strongly marked, when no light falls
upon the object except that proceeding from the lamp used for
its illumination, than it can be when the shadows are partially
lightened by the rays which fall upon the object from every
quarter, as must be the case if it be viewed by daylight. If the
ordinary condensing lens do not afford a sufficient illumination,
the large ‘“bull’s-eye’” condenser (§ 64) may be employed ; its
convex side being turned towards the lamp, when it is desired to
bring its rays into the most complete convergence. And, if a
still more concentrated light be required for the illumination of
a small object under a high power, the small condenser may be
so placed as to receive the cone where it is reduced to its own
size; since, by its means, the rays may be brought to a more
exact convergence than they can be by the bull’s-eye alone. In
this manner, very minute bodies may be viewed as opaque objects
under a tolerably high magnifying power; provided that the

EXAMINATION OF OPAQUE OBJECTS. 179

brasswork of the extremities of the objectives be so bevelled off,
as to allow the illuminating cone to have access to the object.
No method of illuminating large opaque objects by lamp-light
is more effective, than the reflection of light. from a concave
speculum placed near the side of the object (§ 65); this not only
affords a brilliant light, which may be equably spread over as
large a surface as may be required, but may, by the mode in
which it is jointed to its supports, be made to throw its rays
upon the object at a great variety of angles, without the neces-
sity of moving the lamp, whereby the direction in which the
best illumination can be gained, is readily ascertained. If a
more intense light and a greater concentration be required, than
the speculum will afford by reflecting the diverging rays of the
lamp, these may be rendered parallel or slightly convergent by
the interposition of the bull’s-eye condenser, which, for such a
purpose, must have its plane side turned towards the lamp. This
speculum cannot be so advantageously used by daylight, the
ordinary condensing lens being then decidedly preferable.

94. If the object which it is desired to examine be of small
size, and of a shape and character that render it unsuitable to be
laid upon the glass stage-plate, or to be turned over so as to bring
each side in turn into the most advantageous position,—as is the
case, for example, with the capsules of Mosses, the mouths ot
which cannot be conveniently brought into view in this mode,—
it may be grasped in the stage-forceps (§ 66), which afford great
facility for this kind of manipulation; or, if it be too minute or
delicate to be thus held, it may be taken up upon the head of a
small pin, by moistening this with saliva or with a little thin
gum-water; and the pin may then be either held in the stage-
forceps, or may be run into the cork at its opposite extremity.
By careful manipulation, every part of such an object may be
brought under view successively, and may be exposed to every
variety of illumination. It is in viewing objects supported in
this mode, that the utility of the Lieberkiihn (§ 65) is chiefly felt;
for, as the stage-forceps needs to be shifted into different po-
sitions, so that the object is sometimes raised above and some-
times depressed. below the level of the stage, in order to present
it under a different aspect, the side illumination, whatever be its
source, needs to be newly adjusted with each change in the po-
sition of the object; whilst the Lieberkiihn adjusts itself, so to
speak, when the object is brought into focus. If the mirror be
so mounted that it can be turned considerably out of the axis of
the microscope, and the aperture of the stage be sufficiently large,
a light of considerable obliquity may be reflected from the Lie-

1 Since the introduction of the Parabolic illuminator, the occasions on which
advantageous recourse can be had to the examination of minute objects with high
powers by incident light, have become much less numerous; since these objects are for
the most part sufficiently transparent to admit of being illuminated by that instrument ;

and when they are so, the view of them which it affords is generally much superior to
any that can be gained by the method of illumination described above.

180 MANAGEMENT OF THE MICROSCOPE.

berkiihn ; thus enabling it to afford a kind of illumination, which,
as already remarked, is usually much more valuable than that
produced by the nearly perpendicular rays sent down by it on
the object, when the mirror is placed in the axis. Whenever the
Lieberktihn is employed, care must be taken that the direct light
from the mirror be entirely stopped out by the interposition ofa
“‘ dark well” or of a black disk, of such a size as to fill the field
given by the particular objective employed, but not to pass much
beyond it. An ingenious combination of a hemispherical Lie-
berktihn with the Paraboloid (§ 61) has been devised by Mr.
Wenham, for the illumination of minute opaque objects by very
oblique rays,! and Mr. C. Brooke has attached a small plane spe-
culum to objectives of 1-8th and 1-12th inch focus (which cannot
be otherwise advantageously employed with that illuminator), in
such a manner that its surface is level with, or very little below,
that of the outer lens, so as to reflect downwards upon the object
those extreme pencils of rays which pass by the aperture of the
object-glass. In either case, an oblique illumination from one
side only may be obtained, by shuttmg off either half of the lower
aperture of the paraboloid. These contrivances for the examina-
tion of minute objects with high powers by incident light, have
scarcely yet received the attention they deserve.

95. Errors of Interpretation.—The correctness of the conclu-
sions which the Microscopist will draw, regarding the nature of
any object, from the visual appearances which it presents to him,
when examined in the various modes now specified, will neces-
sarily depend in great degree upon his previous experience in
microscopic observation, and upon his knowledge of the class of
bodies to which the particular specimen may belong. Not only
are observations of any kind liable, as already remarked (Intro-
duction, pp. 89-41), to certain fallacies arising out of the previous
notions which the observer may entertain, in regard to the con-
stitution of the objects or the nature of the actions to which his
attention is directed; but even the most practised observer is
apt to take no note of such phenomena as his mind is not pre-
pared to appreciate. Thus, for example, it cannot be doubted
that many Physiologists must have seen those appearances in
thin slices of Cartilage, which are now interpreted as denoting
its cellular organization, without in the least degree suspecting
their real import, which Schwann was the first to deduce from
the study of the development of that tissue; it was not known
before his time, “ what cells mean” in Animal organization ; and
the retinal pictures which now suggest the idea of them to the
mind of even the tyro in the study of Histology (p. 54), passed
almost entirely unnoticed by keen-sighted and intelligent Micro-
scopists previously to 1839. Errors and imperfections of this
kind can only be corrected, it is obvious, by general advance in
scientific knowledge; but the history of them affords a useful

1“ Quart. Journ. of Microsc. Science,” vol. ii, p. 155.

ERRORS OF INTERPRETATION. 181

warning against hasty conclusions drawn from a too cursory ex-
amination. If the history of almost any scientific investigation
were fully made known, it would generally appear, that the sta-
bility and completeness. of the conclusions finally arrived at, had
only been attained after many modifications, or even entire altera-
tions, of doctrine. And it is, therefore, of such great importance
to the correctness of our conclusions, as to be almost essential,
that they should not be finally formed and announced, until they
have been tested in every conceivable mode. It is due to Science,
that it should be burdened with as few false facts and false doc-
trines as possible. It is due to other truth-seekers, that they
should not be misled, to the great waste of their time and pains,
by our errors. And it is due to ourselves, that we should not
commit our reputation to the chance of impairment, by the pre-
mature formation and publication of conclusions, which may be
at once reversed by other observers better informed than our-
selves, or may be proved to be fallacious at some future time,
perhaps even by our own more extended and careful researches.
The suspension of the adjudgment, whenever there seems room for
doubt, is a lesson inculeated by all those Philosophers who have
gained the highest repute for practical wisdom; and it is one
which the Microscopist cannot too soon learn, or too constantly
practise.

96. Besides these general warnings, however, certain special
cautions should be given to the young Microscopist, with regard
to errors into which he is liable to be led, by the misinterpreta-
tion of appearances peculiar to objects thus viewed, even when
the very best instruments are employed. Thus the sharpness
of the outline of any transparent object is impaired by a change
in the course of the rays that’ merely pass by it, which is termed
Inflection or Diffraction. If any opaque object be held in the
course of a cone of rays diverging from a focus, the shadow
which it will form upon a screen held to receive it, will not
possess ,a well-defined edge, but will have as its boundary a
shaded band, gradually increasing in brightness from the part of
the sereen on which the shadow is most intense, to that on which
the illumination is most complete. If the light be homogeneous
in its quality, the shaded band will possess no colors of its own ;
but if the light be decomposable, like the ordinary solar beam,
the band will exhibit prismatic fringes. It is obvious that such
a diffraction must exist in the rays transmitted through the sub-
stance, as well as along the edges, of transparent objects; and
that it must interfere with the perfect distinctness, not merely
of their outlines, but of their images, the various markings of
which are shadows of portions: that afford obstacles, more or

! This phenomena is explained on the Undulatory Theory of light, by the disturbance
which takes place in the onward propagation of waves, when subsidiary centres of
undulation are developed by the impact of the principal undulations on obstacles in

their course; the chromatic dispersion being due to the inequality in the lengths of the
undulations proper to the severally colored rays.

182 MANAGEMENT OF THE MICROSCOPE.

less complete, to the perfectly free transmission of the rays,
There are many objects of great delicacy, in which the “ diffrac.
tion-band”’ is liable to be mistaken for the indication of an actual
substance; on the other hand, the presence of an actual sub-
stance of extreme transparency, may sometimes be doubted or
denied, through its being erroneously attributed to the “ diffrac.
tion-band.”' No rules can be given for the avoidance of such
errors, since they can only be escaped by the discriminative
power which education and habit confer. ‘The practised Micro-
scopist, indeed, almost instinctively makes the requisite allow-
ance for diffraction; and seldom finds himself embarrassed by
it, in the interpretation of the visual appearances which he
obtains through a good instrument. Besides this unavoidable
result of the inflection of the rays of light, there is a peculiar
phenomenon attendant upon oblique illumination at certain
angles in one direction; which consists in the production of a
double image, or a kind of overlying shadow, sometimes pre-
senting markings equally distinct with those of the object itself.
This image, which is not unlike the secondary spectrum formed
by reflection from the outer surface of a silvered-glass mirror,
has been called the “ diffracting spectrum ;” but its origin does
not really lie in the diffraction of the luminous rays, since on the
one hand it cannot be explained according to the laws of diffrac-
tion, and on the other it may be traced to an entirely different
cause. An object thus illuminated is seen by two different sets
of rays; those, namely, of transmitted light, which pass through
it obliquely from the source of the illumination to the opposite
side of the object-glass ; and those of radiated light, which, being
intercepted by the object, are given off from it again in all di-
rections. (The latter alone are the rays whereby the images are
formed in any kind of “black-ground” illumination, §§ 61, 62.)
Two different images will be formed, when the illuminating
pencil is very oblique, and the angular aperture of the object-
glass is wide; one of them by the light transmitted to one ex-
treme of its aperture, the other by the light radiated to its gene-
ral surface ; and one or the other of these images may be stopped
out, by covering that portion of the lens which receives, or that
which does not receive, the transmitted pencil. This “ diffract-
ing-spectrum” may be produced at pleasure, in an object illu-
minated by direct light and seen with a large aperture, by hold-
ing a needle or a horse-hair before the front lens, so as to split
the aperture into two parts.

97. Errors of interpretation arising from the imperfection of
the Focal adjustment, are not at all uncommon amongst young

1 Thus the account given by Prof. Sharpey and the Author, of the structure of Muscu-
lar Fibre (Chap. XVIII), has been called in question by observers who had not seen
their preparations, on the ground that the “ diffraction-band” had not been allowed for.
To whatever the appearance in question (Fig. 326) may be due, there cannot be the
slightest question that it does not arise from diffraction.

ERRORS OF INTERPRETATION, 183

Microscopists. With lenses of high power, and especially with
those of large angular aperture, it very seldom happens that all
the parts of an object, however small and flat it may be, can be
in focus together; and hence the focal adjustment being exactly
made for one part, everything that is not in exact focus is not
only more or less indistinct, but is often wrongly represented.
The indistinctness of outline will sometimes present the appear-
ance ofa pellucid border, which, like the diffraction-band, may
be mistaken for actual substance. But the most common error
is that which is produced by the reversal of the lights and
shadows, resulting from the refractive powers of the object itself;
thus, the bi-concavity of the blood-disks of Human (and other
Mammalian) blood, occasions their centres to appear dark, when
in the focus of the Microscope, through the dispersion of the
light which it occasions; but when they are brought a little
within the focus, by a slight approximation of the object-glass,
the centres appear brighter than the peripheral parts of the disks
(Fig. 815). The same reversal presents itself in the case of the
markings of the Diatomacee; for these, when the surface is ex-
actly in focus, are seen as light hexagonal spaces, separated by
dark partitions; and yet, when the surface is slightly beyond the
focus, the hexagonal are are dark, and the intervening parti-
tions light (Fig. 80). The best means of avoiding errors of in-
terpretation arising from this source, lies in the employment of
the lowest powers with which the particular structures can be
distinguished ; since, if the different parts of the surface and
margin of the object can be simultaneously brought so nearly
into focus that a distinct view may be gained of all of them at
once, no false appearances will be produced, and everything will
be seen in its real aspect.

98. A very important and very frequent source of error, which
sometimes operates even on experienced Microscopists, lies in
the refractive influence exerted by certain peculiarities in the
form or constitution of objects, upon the rays of light trans-
mitted through them; this influence being of a nature to give
rise to appearances in the image, which suggest to the observer
an idea of their cause that may be altogether different from the
reality. A very characteristic illustration of the fallacy resulting
from external configuration, is furnished by the notion which
long prevailed among Microscopic observers, and which still
lingers in the public mind, of the tubular structure of the Human
hair. This notion has no other foundation, than the existence
of a bright band down the axis of the hair, which is due to the
convergence of the rays of light occasioned by the convexity of
its surface, and which is equally.shown by any other transparent
cylinder; and it is unmistakably disproved by the appearances
presented by thin transverse sections of Hair, which show that
it is not only filled up to its centre with a medullary substance,
but that its centre is sometimes even darker than the surrounding

184 MANAGEMENT OF THE MICROSCOPE.

part (Fig. 311). Of the fallacy which may sometimes arise from
diversities in the refractive power of the internal parts of an ob-
ject, we have an equally “pregnant instance” in the misinter-
pretation of the nature of the lacune and canaliculi of Bone
(Fig. 300), which were long supposed to be solid corpuscles with
radiating filaments of peculiar opacity, instead of being, as is
now universally admitted, minute chambers with diverging pas-
sages, excavated in the solid osseous substance. For just as the
convexity of its surfaces will cause a transparent cylinder to
show a bright axial band, so will the concavity of the internal
surfaces of the cavities or tubes hollowed out in the midst of
highly refracting substances, occasion a divergence of the rays
passing through them, and consequently render them so dark
that they are easily mistaken for opaque solids. That such is
the case with the so-called “bone-corpuscles,” is shown by the
effects of the infiltration of Canada balsam through the osseous
substance; for when this fills up the excavations,—being nearly
of the same refractive power with the bone itself, and being also
quite transparent, and (in thin laminee) quite colorless,—it ob-
literates them altogether. So, again, if a person who is unac-
customed to the use of the microscope should chance to have his
attention directed to a preparation mounted in liquid or in bal-
sam, that might chance to contain azr-bubdles, he will be almost
certain to be so much more strongly impressed by the appear-
ance of these, than by that of the object, that his first remark
will be upon the number of strange-looking black rings which
he sees, and his first inquiry will be in regard to their meaning.

99. No experienced Microscopist could now be led astray by
such obvious fallacies as those alluded to; but it is necessary to.
dwell upon them, as warnings to those who have still to go
through the same education. The best method of learning to
appreciate the class of appearances in question, is the comparison
of the aspect of globules of Oil in water, with that of globules of
Water in oil, or of bubbles of Air in water or Canada-balsam.
This comparison may be very readily made by shaking up some
oil with water to which a little gum has been added, so as to form
an emulsion; or by simply placing a drop of oil of turpentine
and a drop of water together on a slip of glass, laying a thin glass
cover upon them, and then moving the cover several times back-
wards and forwards upon the slide.t. Now when such a mixture
is examined with a sufficiently high magnifying power, all the
globules present nearly the same appearance, namely, dark mar-
gins with bright centres; but when the test of alteration of the
focus is applied to them, the difference is at once revealed; for
whilst the globules of Oil surrounded by water become darker as
the object-glass is depressed, and lighter as it is ratsed, those of

‘If this latter mode be adopted, it is preferable, as suggested by the authors of the
“ Micrographiec Dictionary” (Introduction, p. xxxii), to color the oil of turpentine with
alkanet, or some similar substance, for itsymore ready distinction.

APPEARANCES OF GLOBULES OF AIR, ETC. 185

Water surrounded by oil become more luminous as the object-
glass is depressed, and darker as it is raised. The reason of this
lies in the fact, that the high refracting power of the oil causes
each of its globules to act like a double-convex lens of very short
focus ; and as this will bring the rays which pass through it into
convergence above the globule (7. e. between the globule and the
objective), its brightest image is given, when the object-glass is
removed somewhat further from it than the exact focal distance
of the object. On the other hand, the globule of water in oil, or
the minute bubble of air in water or balsam, acts, in virtue of its
inferior refractive power, like a double-concave lens; and _as the
rays of this diverge from a virtual focus below the globule (2. e.
between the globule and the mirror), the spot of greatest lumi-
nosity will be found, by causing the object-glass to approach
within the proper focus. Now in the “protoplasm” of the cells
of the lower Plants, and in the “‘sarcode” of the lower animals,
oil-particles and vacuoles (or void spaces) are often interspersed ;
and present, at first sight,so very striking a resemblance, that
the inexperienced observer may well be pardoned for mistaking
the “vacuoles” for larger globules of a material more refractive
than the gelatinous substance around them. But the difference
in the effects of alterations of focus on the two sets of appear-
ances, at once serves to make evident the difference of their
causes; and this, moreover, is made obvious by the effect of
oblique light, which will cause the strongest shadow to exhibit
itself on opposite sides, in the two cases respectively. It will be
obvious that minute elevations and depressions of the surface of
the object will exert an influence upon the course of the rays
which it transmits, very similar to that. which proceeds from the
presence of globular spaces, filled with transparent substances of
greater or less refracting power, in its interior; and that the dis-
crimination between the two may be made by the same means.
For if the dots appear more luminous as the object-glass is raised,
and darker as it is depressed, they may be interpreted as being
due to convexities upon the surface; but if the contrary is the
case, they may be referred to concavities.

100. Among the sources of fallacy by which the young Micro-
scopist is liable to be misled, one of the most curious is the Mole-
cular Movement which is exhibited by the particles of nearly all
bodies that are sufficiently finely divided, when suspended in
water or other fluids. This movement was first observed in the
fine granular particles, which exist in great abundance in the
contents of the pollen-grains of plants (sometimes termed the
fovilla), and which are set free by crushing these grains; and it
was imagined that they indicated the possession of some special
vital endowment of these particles, analogous to that of the sper-
matozoa of animals. In the year 1827, however, it was an-
nounced by Dr. Robert Brown, that numerous other substances,
organic and inorganic, when reduced to a state of equally minute

186 MANAGEMENT OF THE MICROSCOPE.

division, exhibit a like movement, so that it cannot be regarded
as indicative of any endowment peculiar to the fovilla-granules ;
-and subsequent researches have shown, that there is no known ex-
ception to the rule, that such motion takes place in the particles of
all substances, though some require to be more finely divided
than others, before they will exhibit it. Nothing is better adapted
to show it, than a minute portion of gamboge, indigo, or carmine,
rubbed up with water ; for the particles of these substances, which
are not dissolved, but only suspended, are of sufficiently large
size to be easily distinguished with a magnifying power of 250
diameters, and are seen to be in perpetual locomotion. Their
movement is chiefly of an oscillatory kind; but they also rotate
backwards and forwards upon their axes, and they gradually
change their places in the field of view. It may be observed that
the movement of the smallest particles is the most energetic, and
that the largest are quite motionless, whilst those of intermediate
size move, but with comparative inertness. The movement is
not due (as some have imagined) to evaporation of the liquid;
for it continues, without the least abatement of energy, in a drop
of aqueous fluid that is completely surrounded by oil, and is
therefore cut off from all possibility of evaporization; and it has
been known to continue for many years, in a small quantity of
fluid enclosed between two glasses in an air-tight case. It is,
however, greatly accelerated, and rendered more energetic, by
Heat; and this seems to show that it is due, either directly to
some calorical changes continually taking place in the fluid, or
to some obscure chemical action between the solid particles and
the fluid, which is indirectly promoted by heat. It is curious
that the closer the conformity between the specific gravity of the
solid particles and that of the liquid, the less minute need be
that reduction in their size which is a necessary condition of their
movement; and it is from this that the substances just named
are so favorable for the exhibition of it. On the other hand, the
particles of metals, which are from seven to twelve times as heavy
as water, require to be reduced to a minuteness many times
greater than that of the particles of carmine or gamboge, before
they become subject to this curious action. In any case in which
the motions of very minute particles, of whatever kind, are in
question, it is necessary to make allowance for this “ molecular
movement;”’ and the young Microscopist will therefore do well
to familiarize himself with its ordinary characters, by the careful
observation of it in such cases as those just named, and in any
others in which he may meet with it.

101. Comparative Values of Object-Glasses; Test Obdjects.—In
estimating the comparative values of different object-glasses, re-
gard must always be had to the purpose for which each is de-
signed; since it is impossible to construct a combination, which
shall be equally serviceable for every requirement. It is com-
monly assumed, that an Objective which will show certain test-

DEFINING AND PENETRATING POWERS. 187

objects, must be very superior, for everything else, to a glass which
will not show these; but this is known to every practical Micro-
scopist to be a great mistake,—the very qualities which enable it
to resolve the more difficult ‘tests’ being incompatible with
those which make it most useful in all the ordinary purposes of
scientific investigation. Four distinct attributes have to be
specially considered, in judging of the character of an object-
glass, viz.: (1) its defining power, or power of giving a clear and
distinct image of all well-marked features of an object, especially
of its boundaries ; (2) its penetrating power, or power of enabling
the observer to look into the structure of objects;' (8) its resolving
power, by which it enables closely-approximated marking to be
distinguished ; and (4) the flatness of the field which it gives.

I. The “ Defining power’’of an objective mainly depends upon
the perfection of its correctness, both for Spherical and for Chro-
matic aberration (§§ 9, 15) ; and it is'an attribute essential to the
satisfactory performance of any objective, whatever be its other
qualities. Good definition may be more easily obtained with
lenses of small or moderate, than with lenses of large angular
aperture; and in the aim to extend the aperture, the perfection
of the definition is not unfrequently impaired. An experienced
Microscopist will judge of the defining power of a lens by the
quality of the image which it gives of almost any object with
which he may be familiar; but there are certain “tests,” to be
presently described, which are particularly appropriate for the
determination of it. Any imperfection in defining power is ex-
aggerated, as already pointed out (§§ 22, 80), by the use of “ deep”
eye-pieces ; so that, in determining the value of an objective, it
is by no means sufficient to estimate its performance under a low
eye-piece, an image which appears tolerably clear when mode-
rately magnified, being often found exceedingly deficient in
sharpness when more highly amplified. The use of the draw-
tube (§ 43) affords an additional means of testing the defining
power; but this cannot be fairly had recourse to, unless an altera-
tion be made in the adjustment for the thickness of the glass
that covers the object (§ 84), in proportion to the lengthening of
the body, and the nearer approximation of the object to the ob-
jective which this involves.

Il. The “ Penetrating power” of an object-glass (good defini-
tion being of course presupposed) mainly depends upon the

’ The Author is aware that he is here employing the term “ Penetration” in a sense
very different from that which it was intended to convey by Dr. Goring, who first ap-
plied it to designate a certain quality of Microscopic objectives. But he considers that
what was termed “penetration” by Dr. Goring may be far more appropriately desig-
nated as resolving power ; this term having been long in use to express the parallel attri-
bute of Telescopes, as regards the separation of the diffused luminosity of Nebule into
distinct points of light. The term Penetration, having been thus set free, may well be
applied (as above) in what seems its natural meaning; and the Author (who has long
been in the habit of employing it in this sense) may refer to the Report of the Jury of
the “ Great Exhibition” of 1851, as giving an authoritative sanction to the above use of it

188 MANAGEMENT OF THE MICROSCOPE.

degree of distinctness with which parts of the object that are a
little out of focus can be discerned ; and this will be found to vary
greatly in different objectives, being, within certain limits, in an
inverse proportion to the extent of the angle of aperture. This
is very easily understood on optical principles. The central rays
of any pencil undergo the least refraction or change in their
course; the peripheral rays, the most. The greater the change,
the greater is the difference between the amounts of refraction
respectively undergone by rays coming off from points at slightly
different distances; and the greater, when the focal adjustment
is correct for one of these points, will be the indistinctness of the
image of the other. Hence an objective of comparatively limited
aperture may enable the observer to gain a view of the whole of
an object, the several parts of whose structure lie at different dis-
tances from it, sufficiently good to afford an adequate idea of the
relation of those parts to each other; whilst if the same object
be looked at with an objective of very wide angle of aperture,
which only enables what is precisely in focus to be seen at all,
each part can only be separately discerned, and the mutual re-
lations of the whole cannot be brought into view. The want of
this “ penetrating power” is a serious drawback in the perfor-
mance of many objectives, which are distinguished by the pos-
session of other admirable qualities. The possession of a high
measure of it is so essential, in the Author’s opinion, to the
satisfactory performance of those objectives which are to be em-
ployed for the general purposes of scientifie investigation, that he
cannot consider its deficiency to be compensated by the posses-
sion of any degree of the resolving power, whose use is compara-
tively limited.

Il. The “ Resolving power,” by which very minute markings,
—whether lines, striee, or dots,—are discerned and clearly sepa-
rated from each other, may be said to stand in direct relation (a
perfect definition being presupposed) to the extent of its angle
of aperture, and consequently to the obliquity of the rays which
it can receive from the several points of the surface of the ob-
ject. This is not so much the case, where the markings depend
upon the interposition of opaque or semi-opaque particles in the
midst of a transparent substance, so that the lights and shadows
of the image represent the absolute degrees of greater or less
transparency in its several parts; as it is where, the whole sub-
stance being equally transparent, the markings are due to the
refracting influence which inequalities of the surface exert upon
the course of the rays that pass through it. It may be readily
perceived, on a little reflection, that the information given about
such inequalities by rays of light transmitted axially through the
object, must be very inferior to that which can be gained from
rays of light transmitted obliquely; and thus it happens that,
as already explained, many such markings are seen by oblique
illumination (as, for instance, by the use of the central stop in

RESOLVING POWER—FLATNESS OF FIELD. 189

the condenser, § 56), which could not be seen, under the same
object-glass, by light transmitted more nearly in the axis of the
microscope. When an object, however, is seen by transmitted
light, no degree of obliquity in the illuminating rays can be use-
ful, which exceeds that at which the object-glass can receive
them: but the illumination of objects which are seen by radiated
light (§ 62), depends upon these very rays; and thus it is that
the “black-ground” illumination by the paraboloid or by any
other effective contrivance (§ 61), will often bring surface-mark-
ings into view, which cannot be seen by transmitted light. An
object-glass of very wide aperture, however, will receive, even
with ordinary illumination, so many rays of great obliquity, that
the same kind of effect will be produced, as by oblique illumina-
tion with an objective of smaller aperture; but when, with such
an objective, oblique illumination is used, a greater resolving
power is obtained, than any combination of smaller angular aper-
ture can possess. In comparing the resolving power of different
object-glasses, it is obviously essential to a correct judgment,
that the illumination should be the same ; for it will often happen
that an observer who knows the “points” of his own instru-
ment, will “bring out” tests, which another, with object-glasses
of much greater capability, does not resolve, simply for want of
proper management. Moreover, it must be borne in mind that
great resolving power may exist, even though the definition may
be far from exact; since the former depends more upon angle
of aperture, than upon the perfection of the corrections : and yet
there cannot be the slightest question, that, of two objectives ot
the same focal length, one perfectly corrected up to a moderate
angle of aperture, the other with the wider aperture but less per-
fectly corrected, the former will be the one most suitable to the
general purposes of the Microscopist.

IV. The “ Flatness of the field” afforded by the object-glass,
is a condition of great importance to the advantageous use of
the Microscope ; since the real extent of the field of view prac-
tically depends upon it. Many objectives are so constructed,
that, even with a perfectly flat object, the foci of the central and
of the peripheral parts of the field are so different, that when
the adjustment is made for one, the other is entirely indistinct.
Hence, when the central portion is being looked at, no more in-
formation is gained respecting the peripheral, than if it had been
altogether “stopped out.” With a really good object-glass, not
only should the image be distinct even to the margin of the
field, but the marginal portion should be as free from chromatic
fringes or from indistinctness of outline, as the central portion.
In many microscopes of inferior construction, the imperfection
of the objectives in this respect, is masked by the contraction of
the aperture of the diaphragm in the eye-piece (§ 21), which
limits the dimensions of the field; and the performance of one
objective within this limit may scarcely be distinguishable from

190 MANAGEMENT OF THE MICROSCOPE.

that of another, although, if the two were compared under an
eye-piece of larger aperture, their difference of excellence would
be at once made apparent, by the perfect correctness of one to
the margin of the field, and by the entire failure of the other in
every part save its centre. In estimating the relative merits of
two lenses, therefore, as regards this condition, the comparison
should of course be made under the same Hye-piece.

V. It may be safely affirmed, that the most perfect Object-glass
is that which combines all the preceding attributes, in the highest
degree in which they are compatible one with another. But, as
has just been shown, two of the most important, namely—pene-
trating power and resolving power,—stand in such opposite re-
lations to the angular aperture, that the highest degree of which
each is in itself capable, can only be attained by some sacrifice of
the other; and, therefore, of two objectives which are respec-
tively characterized by the predominance of these opposite
qualities, one or the other will be preferred by the Microscopist,
according to the particular class of researches which he may be
carrying on ; just as a man who is about to purchase a horse, will
be guided in his choice by the kind of work for which he destines
the animal. Hence it shows, in the Author’s estimation, just as
limited an appreciation of the practical applications of the in-
strument, to estimate the merits of an object-glass by its capa-
bility of showing certain lined or dotted “tests,” without any
reference to its penetrating or defining power; as it would be if
a man should estimate the merits of a horse merely by the num-
ber of seconds within which he couldrun a mile, or by the num-
ber of pounds he could draw; without any reference, in the first
case, either to the weight he could carry, or to the length of time
during which he could maintain his speed; and in the second
case, either to the rate of his draught, or to his power of con-
tinuing the exertion. The greatest capacity for speed alone, the
power of sustaining it not being required, and burden being
reduced almost to nothing, is that which is sought in the Racer;
the greatest power of steady draught, the rate of movement being
of comparative little importance, is that which is most valued in
the cart-horse; but for the ordinary carriage-horse or roadster,
the highest merit lies in such a combenation of speed and power
with endurance, as cannot coexist with the greatest perfection of
either the two first. The Author feels it the more important
that he should express himself clearly and strongly on this sub-
ject, as there is a great tendency at present, both among amateur
Microscopists and among Opticians, to look at the attainment of
that ‘resolving power’ which is given by angular aperture, as
the one thing needful; those other attributes which are of far
more importance in almost every kind of scientific investigation,
being comparatively little thought of; and he therefore ventures
here to repeat the remarks he made upon this subject in his re-
cent Presidential Address to the Microscopical Society, of the

REAL VALUE OF ANGULAR APERTURE, 191
correctness of which he has been since assured, by the approval
of many of those who have most successfully employed the Mi-
croscope in Physiological investigations. “The superiority in
resolving power possessed. by object-glasses of large angular aper-
ture, is obtained at the expense of other advantages. For even
granting that there is no sacrifice of that most important ele-
ment defining power (which can only be secured, with a very
wide angle, by the utmost perfection in all the corrections), yet
the adequate performance of such a lens can only be secured by
the greatest exactness in the adjustments. Only that portion of
the object which is precisely in focus, can be seen with an ap-
proach to distinctness, everything that is in the least degree
out of it being imbedded (so to speak) in a thick fog; it is re-
quisite, too, that the adjustment for the thickness of the glass
that covers the object, should exactly neutralize the effect of its
refraction ; and the arrangement of the mirror and condenser
must be such as to give to the object the best possible illumina-
tion. If there be any failure in these conditions, the perfor-
mance of a lens of very wide angular aperture is very much in-
ferior to that of a lens of moderate aperture ; and except in very
experienced hands, this is likely to be generally the case. Now
to the working Microscopist, unless he be studying the particu-
lar classes of objects which expressly require this condition, it is
a source of great inconvenience and loss of time to be obliged
to be continually making these adjustments; and a lens, which,
when adjusted for a thickness of glass of 1-100”, will perform
without much sensible deterioration with a thickness either of
1-80” or of 1-120”, is practically the best for all ordinary pur-
poses. Moreover, a lens of moderate aperture has this very great
advantage, that the parts of the object which are less perfectly in
focus, can be much better seen; and therefore that the relation
of that which is most distinctly discerned, to all the rest of the
object, is rendered far more apparent. Let me remind you, fur-
ther, that almost all the great achievements of Microscopic re-
search have been made by the instrumentality of such objectives
as [amrecommending. There can be no question about the large
proportion of the results which Continental microscopists may
claim, in nearly all departments of minute anatomical, physiolo-
gical, botanical, or zoological investigation, since the introduc-
tion of this invaluable auxiliary ; and it is well known that the
great majority of their instruments are of extremely simple con-
struction, and that their objectives are generally of very mode-
rate angular aperture. Moreover, if we look at the date of some
of the principal contributions which this country has furnished
to the common stock, such as the ‘Odontography’ of Professor
Owen, the ‘Researches into the Structure of Shell’ carried out
by Mr. Bowerbank and myself, the ‘Physiological Anatomy’ of
Messrs. Todd and Bowman, the first volume of the ‘ Histologi-
cal Catalogue,’ by Professor Quekett, and the ‘ British Desmi-

192 MANAGEMENT OF THE MICROSCOPE.

dee’ of Mr. Ralfs, we find sure reason to conclude that these re-
searches must have been made with the instrumentality of lenses,
which would in the present day be regarded as of very limited
capacity. I hope that, in these remarks, I shall not be under.
stood as in any way desirous to damp the zeal of those, who are
applying themselves to the perfectionizing of achromatic objec-
tives. I regard it asa fortunate thing for the progress of science,
that there are individuals whose tastes lead them to the adoption
of this pursuit; who stimulate our instrument-makers to go on
from one range to another, until they have conquered the diffi-
culties which previously baffled them ; and then apply themselves
to find out some new tests, which shall offer a fresh difficulty to be
overcome. But it is not the only, nor can I regard it as the chief
work of the Microscope, to resolve the markings upon the Diato-
macere, or tests of the like difficulty; and although I should con-
sider this as the highest object of ambition to our makers, if the
performances of such lenses with test-objects were any fair mea-
sure of their general utility, yet as I think that I have demon-
strated that the very conditions of their construction render them
inferior in this respect for the purposes of ordinary microscopic
research, I would much rather hold out the reward of high ap-
preciation (we have no other to give) to him who should produce
the best working microscope, adapted to all ordinary requirements,
at the lowest cost. It does not seem to me an unapt simile, to
compare the devotees of large angular apertures to the gentle-
man of the ‘turf.’ It is, I believe, generally admitted, that the
breeding of a class of horses distinguished by speed and ‘blood,’
which is kept up by the devotion of a certain class of our country-
men to the noble sport of racing, is an advantage to almost
every breed of horses throughout the country; tending, as it
does, to develope and maintain a high standard in these particu-
lars. But no one would ever think of using a race-horse for a
roadster or a carriage-horse ; knowing well that the very qualities
which most distinguish him asa racer, are incompatible with
his suitableness for ordinary work. And so I think that the
‘breeders’ of first-class Microscopes (if I may so designate
them) are doing great service, by showing to what a pitch of per-
fection certain kinds of excellence may be carried, and by thus
improving the standard of ordinary instruments ; notwithstand-
ing that, for nearly all working purposes, the latter may be prac-
tically superior.”

102. Test Odjects.—It is usual to judge of the optical perfection
of a Microscope, by its capacity for exhibiting certain objects,
which are regarded as tests of the merits of its object-glasses ;
these tests being of various degrees of difficulty ; and that being
accounted the best instrument, which shows the most difficult
of such tests. Now it must be borne in mind, that only two out
of the four qualities which have been just enumerated,—namely,
defining power, and. resolving power,—can be estimated by any

TEST-OBJECTS. 193

of these tests; and the greater number of them, being objects
whose surface is marked by lines, strie, or dots, are tests of re-
solving power, and thus of angular aperture only. Hence, as
already shown, an objective may show very difficult test-objects,
and yet may be very unfit for ordinary use. Moreover, these
test-objects are only suitable to object-glasses of very short focus
and high magnifying power; whereas the greater part of the
real work of the Microscope is done with objectives of compara-
tively low power; and the enlargement of the angular aperture,
which "enables even these to resolve (under deep eye-pieces)
many objects which were formerly considered adequate tests for
higher powers, is by no means an unmixed good. In estimating
the value of an object-glass, it should always be considered for
what purpose it is intended; and its merits should be judged of
according to the degree in which it fulfils that purpose. We
shall therefore consider, what are the attributes proper to the
several “powers” of object-glasses,—low, medium, and high ;—
and what are the objects by its mode of exhibiting which, it
may be fairly judged.

I. By object-glasses of low power, we may understand any
whose focal length is greater than half an inch. The “ powers”
usually made in this country are of 2 in. or 14 in. focus (these
being sometimes made to divide, so as to leave a power of about
3 in. focus), 1 in., and 8-10ths or 2-3ds in.; and they give a range
of amplification of from 12 to 60 diameters with the shallower
eye-piece, and of from 18 to 90 diameters with the deeper. These
are the objectives which are most used in the examination of
opaque objects, and of transparent objects of large size and of
comparatively coarse texture; and the qualities most desirable
in them, are a sufficiently large aperture to give a bright image,
combined with such accurate definition as to give a clear image,
with penetrating power sufficient to prevent any moderate in-
equalities of surface from seriously interfering with the distinct-
ness of the entire picture, and with perfect flatness of the image
when the object itself is flat. For the 2 in. or 1} in. objective,
no ground of judgment is better, than the manner in which it
shows such an “injected” preparation as the interior of a Frog’s
lung (Fig. 831) or a portion of the villous coat of the Monkey’s
intestine (Fig. 828); for the aperture ought to be sufficient to
give a bright image of such objects, by ordinary daylight, with-
out the use of a condensing-lens; the border of every vessel
should be clearly defined, without any thickness or blackness of
edge; every part of such an object that comes within the field,
should be capable of being made out when the focal adjustment
is adapted for any other part; whilst, by making that adjustment
a medium one, the whole should be seen without any marked
indistinctness. If the aperture be too small, the image will be
dark; if it be too large, details are brought into view (such as
the separateness of the particles of the vermilion injection) which

13

194 MANAGEMENT OF THE MICROSCOPE.

it is of no advantage to see, whilst, through the sacrifice of pene-
tration, those parts of the object which are brought exactly into
focus being seen with over-minuteness, the remainder are en-
veloped in a thick fog, through which even their general contour
ean scarcely be seen to loom; and if the corrections be imper-
feetly made, no line or edge will be seen with perfect sharpness,
For defining power, the Author has found the pollen-grains of
the Hollyhock, or any other flower of the Mallow kind (Fig. 189),
viewed as an opaque object, a very good test; the minute spines
with which it is beset, being but dimly seen with any save a good
object-glass of these long foci, and being really well exhibited
only by adding such power to the eye-piece, as will exaggerate
any want of definition on the part of an inferior lens. or flat-
ness of field, no test is better than a section of Wood (Fig. 165)
or a large Echinus-spine (Fig. 237), under an eye-piece that will
give a field of the diameter of from 9 to 12 inches. Such objects
ought to be very well shown by the divided lens of 2 in. or 3 in,
focus; but, as its corrections are rendered imperfect by the re-
moval of the front pair, its defining power is necessarily impaired,
and cannot be made even tolerable, save by such a curtailment
of the aperture as detracts from the brightness of the image.
The general performance of object-glasses of 1 in. and 8-10ths
in. focus, may be partly judged of by the manner in which they
show such injections as those of the Gill of the Eel (Fig. 330) or
of the Bird’s Lung (Fig. 332), which require a higher magnifying
power for their resolution than those previously named; still
better, perhaps, by the mode in which they exhibit a portion of
the wing of some Lepidopterous insect, having well-marked
scales; the same qualities should here be looked for, as in the
case of the lowest powers; and a want of either of them is to be
distinguished in a similar manner. The increase of angular
aperture which these lenses may advantageously receive, should
render them capable of resolving all the easier “test’’ scales of
Lepidoptera, such as those of the Morpho menelaus (Fig. 279), in
which, with the deeper eye-piece, they should show the trans-
verse as well as the longitudinal markings. The tongue of the
common Fly (Fig. 287) is one of the best transparent objects for
enabling a practised eye to estimate the general performance of
object-glasses of these powers; since it is only under a really
good lens, that all the details of its structure can be clearly made
out; and an objective which shows this well, may be trusted to
for any other object of its kind. For flatness of field, sections
of small Echinus-spines are very good tests. The exactness of
the corrections in lenses of these foci, may be judged of by the
examination of objects which are almost sure to exhibit color,
if the correction be otherwise than perfect; this is the case, for
example, with the glandule of Coniferous wood (Fig. 161), the
centres of which ought to be clearly defined under such objec-
tives, and ought to be quite free from color; and also with the

TEST-OBJECTS FOR LOW AND MEDIUM POWER. 195

trache of Insects (Fig. 291), the spires of which ought to be
distinctly separated from each other, without any appearance of
intervening chromatic fringes.

II. We may consider as object-glasses of medium power, those
which range from half to one-fifth of an inch focus; whose
magnifying power is from about 100 to 250 diameters under the
shallower eye-piece, and from about 150 to 375 diameters with
the deeper. These cannot be advantageously employed in the
examination of opaque objects, save of such as are of unusual
minuteness; but their great value lies in the information they
enable us to obtain, regarding the details of organized structures
and of living actions, by the examination of properly prepared
transparent objects by transmitted light. It is to these lenses,
that the remarks already made respecting angular aperture (§ 101)
especially apply; since it is in them that the greatest difference
exists, between the ordinary requirements of the scientific in-
vestigator, and the special needs of those who devote themselves
to the particular classes of objects for which the greatest resolv-
ing power is required. A moderate amount of such power is
essential to the value of every objective within the above-named
range of foci; thus, even a good half-inch should enable the
markings of the larger scales of the Polyommatus argus (azure-
blue butterfly) to be distinguished, these being of the same kind
with those of the Menelaus, but more delicate, and should clearly
separate the dots of the small or “battledoor” scales (Fig. 280) of
the same insect, which, if unresolved, are seen as coarse longitu-
dinal lines; a good 4-10ths in. should resolve the larger scales of
the Podura (Fig. 281) without difficulty; and a good 1-4th or
1-5th in. should bring out the markings on the smaller scales of
the Podura, and should resolve the markings on the Pleurosigma
hippocampus into longitudinal and transverse lines. Even the
4-10ths (a power for which Messrs. Smith and Beck have attained
a deserved celebrity) may be made with an angle of aperture
sufficiently wide to resolve the objects named as fair tests for the
powers above it; and so the 1-4th inch may, by the enlargement
of its angular aperture to 120° (which has been accomplished by
Mr. Saar! be made to exhibit the more difficult Diatomacez.
But it will be found that, in such object-glasses, the difficulty of
making the most advantageous use of them, and the loss of
penetrating power which necessarily attends the excessive exten-
sion of their angular aperture, are most serious drawbacks to
their practical utility in the hands of the Anatomical or Physio-
logical investigator; for whose purposes, such a resolving power
as will show the easier tests first enumerated, combined with
perfect definition, with a fair amount of penetrating power, and
with flatness of field, constitute the best combination. For de-
fining power, very good tests are found in the complex hairs of
many animals, such as the Indian Bat (Fig. 310, c), and the
Dermestes (Fig. 282, 8). And for that combination of the seve-

196 MANAGEMENT OF THE MICROSCOPE.

ral attributes which the Author thinks most important, he has
found no test more valuable and positive, as regards objectives
of from 4-10ths to 1-5th inch focus, than Mr. Lealand’s prepara-
tions of Muscular fibre (Fig. 826). In every case, the objective
should be tested with the ‘deeper, as well as with the shallower
eye-piece; and the effect of this will be a fair test of its merits.
Where markings are indistinguishable under a certain objective,
merely because of their minuteness or their too close approxima-
tion, they may be enlarged or separated by a deeper eye-piece,
provided that the objective be well corrected. But if, in such a
case, the image be darkened or blurred, so as to be rather deteri-
orated than improved, it may be concluded that the objective is
of inferior quality, having either an insufficient angular aperture,
or being imperfectly corrected, or both.

III. All object-glasses of less than 1-5th of an inch focus, may
be classed as high powers; the focal lengths to which they are
ordinarily constructed are 1-6th, 1-8th, 1-12th, and 1-16th of an
inch respectively; and the magnifying powers they are fitted to
afford, range from about 320 to 850 diameters with the shallower
eye-piece, and from 480 to 1300 diameters with the deeper. By
the use of still deeper eye-pieces, a power of 2000 or more may
be easily obtained; but nothing seems to be really gained by
such high amplification. Moreover, as the 1-12th inch object-
glass may have its angular aperture extended to the utmost limits
compatible with the reception of rays from any object, it does
not seem that anything can be gained by a reduction of the focal
distance to the 1-16th inch; and the latter being a more difficult
combination, as well to construct as to use, both Opticians and
Microscopists have of late years found it advantageous to limit
themselves to the 1-12th, which gives an amplification of about
650 diameters with the shallower eye-piece, and of about 1000
with the deeper. The use of this class of objectives is much
more restricted than that of the preceding. They are not em-
ployed for the ordinary purposes of scientific investigation ; and
their value chiefly lies in the power which they afford, of tracing
out certain points of minute structure, which the objectives ot
medium power may only doubtfully indicate, and of exhibiting
certain classes of very difficult striated or dotted objects, which
they cannot resolve. Hence it is obvious that, with regard to
object-glasses of this class, ‘resolving power” (coupled with “de-
fining power’’) is the highest requisite, “‘ penetration” and “ flat-
ness of field” being of secondary account; and that the value of
an objective may here be fairly estimated by its angular aperture,
provided that its aberrations be exactly corrected. Of angular
aperture and definition, very good tests are afforded by the lines
artificially ruled by M. Nobert, and by the more “ difficult”
species of Diatomacese. What is known as “Nobert’s Test’ is
a plate of glass, on a small space of which, not exceeding a fiftieth
of an inch in breadth, are ruled ten or more series of lines, form-

TEST-OBJECTS FOR HIGH POWERS. 197

ing as many separate bands of equal breadth; in each of these
bands, the lines are ruled at a certain known distance; and the
distances are so adjusted in the successive bands, as to form a
regularly diminishing series, and thus to present a succession of
tests of progressively increasing difficulty. The distances of the
lines differ on different plates ; all the bands in some series being
resolvable under a good objective of 1-4th inch focus, whilst the
closest bands in others defy the resolving power of a 1-12th inch
objective of large aperture. Thus a “test-plate’” whose widest
lines are at a distance from each other of 1-1000th of a Paris line,
or of 1-11,200th of an English inch, and whose closest lines are at
1-5000th of a line, or 1-56,000th of an inch, from each other, will
serve as a very fair test for the angular aperture and defining
power of object-glasses below 1-4th inch focus; the superiority
of each in these particulars, being judged of by the number of
bands which it will resolve into well-defined lines, and by the
sharpness and clearness of these lines; while the performance of
a 1-4th inch: objective may be accounted very satisfactory, if it
will enable them all to be clearly distinguished. But if the first
of the bands should have an interval of only 1-4000th of a Paris
line, or 1-45,000th of an English inch, between its lines, and the
last should have its lines approximated to 1-10,000th of a Paris
line, or 1-112,000th of an English inch, then only a few of the
easier bands will be resolved by the 1-4th inch, a few more by
the 1-8th inch, and even the 1-12th inch will probably not enable
any band to be distinctly resolved, whose lines are closer than
1-7000th of a Paris line, or 1-79,000th of an English inch. At
present, therefore, the existence of separate lines of a narrower
interval than this, is a matter of faith rather than of sight; but
there can be no reasonable doubt that the lines do exist; and the
resolution of them would evince the extraordinary superiority of
any objective, or of any system of illumination, which should
enable them to be distinguished. The mathematical certainty
with which the degree of approximation of these lines may be
ascertained, and the gradation of the series which they present,
gives to M. Nobert’s test-plate a very high value for the determi-
nation of the relative merits of different objectives, of that class,
at least, in which angular aperture and definition are of the first
importance; whilst it also serves to test the degree in which
these capabilities are possessed by object-glasses of medium
power, in which other attributes also have to be considered.
The value of the minuter Diatomacee, as furnishing, in their sur-
face-markings, admirable test-objects for the highest powers of
the Microscope, was first made known by Messrs. Harrison and
Sollitt, of Hull, in 1841; and it cannot be questioned that this
discovery has largely contributed to the success of the endeavors
which have since been so effectually made, to perfect this class
of objectives, and to find out new methods of using them to the
best advantage. The nature of these markings will be described

198 MANAGEMENT OF THE MICROSCOPE.

hereafter; and it will be sufficient in this place to give a table of
the average distances of the lineation of different species,’ which
will serve to indicate their respective degrees of difficulty as
“tests.” The greater part of those which are now in use for this
purpose, are. comprehended in the genus Pleurosigma of Prof. W.
Smith, which includes those Mavicule whose “frustules” are dis-
tinguished by their sigmoid (S-like) curvature (§ 184).

Lines in 1-1000th of an inch.
. Pleurosigma littorale, . 7 24

1 , :
2. Pleurosigma Hippocampus, . : ; 30 long., 40 trans.
3. Pleurosigma strigile, : ; ‘ : 36
4. Pleurosigma strigosum, . i : : 44
5. Pleurosigma elongatum, . : 48
6. Pleurosigma angulatum, . . F : 52
7. Pleurosigma Spenceri, . : : 3 55 long., 50 trans.
8. Pleurosigma fasciola, : : : 64
9. Pleurosigma obscurum, . 4 ‘ - 75
10. Pleurosigma macrum, . : . : 85
1]. Nitzschia sigmoidea, 4 ; : RB
12. Navicula rhomboides, . F : . 85

The first seven of the foregoing may be resolved, with judi-
cious management, by good 1-4th or 1-5th in. objectives; the
remainder require the 1-8th or 1-12th in., for the satisfactory ex-
hibition of their markings. Several very difficult tests of this
description have been furnished by Prof. Bailey of West Point
(U. 8.), among them the very beautiful Grammatophora subtilis-
sima and the Ayalodiscus subtilis; the latter, being of discoid
form, and having markings which radiate in all directions, very
much like those of an engine-turned watch, is a useful test for
observers who have not facilities for obtaining oblique light in
any direction; since, whatever may be the azimuth from which the
oblique pencil may proceed, some portion of the disk will always

' This table is taken from Prof. W. Smith’s admirable Monograph on the Diatomacee;
and it includes most of the species usually employed as tests. These should always be
mounted between two pieces of thin glass, according to the method hereafter to be
described (§ 122), in order to avoid, as much as possible, the production of aberrations
in the illuminating pencil. The number of lineations must be considered as an average,
the extremes sometimes varying to a considerable amount on either side. A much
higher estimate is given by Messrs, Harrison and Sollitt in the “ Quart. Journ. of Mi-
crosc, Science,” vol. ii, p. 62; the Pleurosigma fasciola being reckoned by them to contain
90 lines in 1-1000th of an inch, the Mitzschia sigmoidea 100 lines, and a species cited as
Navicula arcus (which can scarcely be the one so named by Ehrenberg, and termed by
Prof. W. Smith Eunolia arcus) no less than 130. The last they speak of as “so ex-
tremely difficult, that, in order even ‘to catch a glimpse of its delicate markings, the
observer must be in possession of glasses of a very large angle of aperture and the finest
definition, have the most careful management of oblique light, and in addition be pos
sessed of a large share of patience.” The Author cannot but believe that there is some
error in these measurements; since, as the well-defined lines upon Nobert's test-plate
have not yet been resolved, when they have approximated more closely than the highest
numbers mentioned in Prof. W. Smith’s table, it can scarcely be imagined possible that
the delicate markings of a Navicula should even be “glimpsed,” if they be as much
closer than those of the species previously accounted most difficult, as those of the latter
are than those of the easiest,

DETERMINATION OF MAGNIFYING POWER. 199

be in the best possible position in regard to the light, whereas,
in the case of other finely-lined tests, it is only when the most
favorable position has been attained, perhaps after tedious and
troublesome trials, that the markings are displayed."

103. Determination of Magnifying Power.—The last subject to
be here adverted to, is the mode of estimating the magnifying
power of Microscopes, or, in other words, the number of times
that any object is magnified. This will of course depend upon
a comparison of the real size of the object, with the apparent size
of the image; but our estimate of the latter will depend upon
the distance at which we assume it to be seen, since, if it be
projected at different distances from the eye, it will present very
different dimensions. Opticians generally, however, have agreed
to consider ten inches as the standard of comparison; and when,
therefore, an object is said to be magnified 100 diameters, it is
meant that its visual image, projected at 10 inches from the
eye (as when thrown down by the Camera Lucida, § 49) upon a
surface at that distance beneath, has 100 times the actual dimen-
sions of the object. The measurement of the magnifying power
of Simple or Compound Microscopes by this standard is attended
with no difficulty. All that is required is a stage-micrometer
accurately divided to a small fraction of an inch (the 1-100th
will answer very well for low powers, the 1-1000th for high), and
acommon foot-rule divided to tenths of an inch. The micro-
meter being adjusted to the focus of the objective, the rule is
held parallel with it, at the distance of ten inches from the eye.
If the second eye be then opened, whilst the other is looking at
the object, the circle of light included within the field of view,
and the object itself, will be seen faintly projected upon the
rule; and it will be very easy to mark upon the latter the appa-
rent distances of the divisions on the micrometer, and thence to
ascertain the magnifying power. Thus, supposing each of the
divisions of 1-100th of an inch to correspond with 13 inch upon
the rule, the linear magnifying power is 150 diameters; if it cor-
respond with half an inch, the magnifying power would be 50
diameters. If, again, each of the divisions of the 1-1000th inch
micrometer correspond to 6-10ths of an inch upon the rule, the
magnifying power is 600 diameters; and if it correspond to 175
inch, the magnifying power is 1200 diameters. In this mode of
measurement, the estimate of parts of tenths on the rule can
only be made by guess; but greater accuracy may be obtained
by projecting the micrometer-scale with the Camera Lucida at
the distance of ten inches from the eye, marking the intervals
on paper, taking an average of these, and repeating this with the
compasses ten times along the inch-scale. Thus, if the space
given by one of the divisions of the 1-1000th-inch micrometer,

' See Prof. Bailey’s interesting memoirs in Vols. II and VII of the “Smithsonian Con-
tributions to Knowledge.”

200 MANAGEMENT OF THE MICROSCOPE,

repeated ten times along the rule, gave 6 inches and 2 tenths,
the value of each division would be :625 of an inch, and the
magnifying power 625. The superficial magnifying power is of
course estimated by squaring the linear; but this is a mode of
statement never adopted by scientific observers, although often
employed to excite popular admiration, or to attract customers,
by those whose interest is concerned in doing so,!

‘ An ingenious method has been devised by Prof. Harting, of Utrecht, for determining
“the utmost limits of penetrating and separating power possessed by a Microscope,”
by using as test-objects the very reduced images of various bodies formed by air-bubbles
in gum-mucilage. The mode of obtaining and employing these images for the above
purpose, will be found in the “ Quarterly Journal of Microscopical Science,” vol. i, p. 292,

CHAPTER YV.
PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS.

Unoer this head it is intended to give such general directions
respecting the preparation, mounting, and collection of Objects,
as will supersede the necessity of frequent repetition when each
particular class is described ; and also to enumerate the materials
and appliances, which will be required or found advantageous.

Section 1. PREPARATION OF OBJECTS.

104. Microscopic Dissection The separation of the different
parts of an Animal or Vegetable structure by dissection, so as
to prepare any portion for being minutely examined under the
Microscope should be accomplished, so far as may be found
practicable, with the naked eye; but the best mode of doing
this, will depend in great degree upon the size and character
of the object. Generally speaking, it will be found advantageous
to carry on the dissection under water, with which alcohol should
be mingled where the substance has been long immersed in
spirit. The size and depth of the vessel should be proportioned
to the dimensions of the object to be dissected; since, for the
ready access of the hands and dissecting instruments, it is con-
venient that the object should neither be far from its walls, nor
lie under any great depth of water. Where there is no occasion
that the bottom of the vessel should be transparent, no kind of
dissecting-trough is more convenient, than that which every one
may readily make for himself, of any dimensions he may desire,
by taking a piece of sheet gutta percha of adequate size and
stoutness, warming it sufficiently to render it flexible, and then
turning up its four sides, drawing out each corner into a sort of
spout, which serves to pour away its contents when it needs
emptying. The dark color of this substance enables it to furnish
a background, which assists the observer in distinguishing deli-
cate membranes, fibres, &c., especially when magnifying lenses
are employed; and it is hard enough, without being too hard,
to allow of pins being fixed into it, both for securing the object,
and for keeping apart such portions as it is useful to put on the
stretch. When glass or earthenware troughs are employed, a
piece of sheet-cork, loaded with lead, must be provided, to an-

202 PREPARATION OF OBJECTS.

swer the same puposes. In carrying on dissections in such a
trough, it is frequently desirable to concentrate additional light
upon the part which is being operated on, by means of the
smaller condensing lens (Fig. 45); and when magnifying power
is wanted, it may be supplied either by a single lens, mounted
after the manner of Ross’s Simple Microscope (Fig. 14, B), or by
a Compound body mounted as in one of Mr. Warington’s ar-
rangements (Fig. 24). Portions of the body under dissection,
being floated off when detached, may be conveniently taken up
from the trough by placing a slip of glass beneath them (which
is often the only mode in which delicate membranes can be satis-
factorily spread out); and may be then placed under the micro-
scope for minute examination, being first covered with thin
glass, beneath the edges of which is to be introduced a little of
the liquid wherein the dissection is being carried on. Where the
body under dissection is so transparent, that more advantage is
gained by transmitting hght through it, than by looking at it as
an opaque object, the trough should have a glass bottom; and
for this purpose, unless the body be of unusual size, some of the
glass ‘cells’ to be hereafter described (§§ 186, 137) will usually
answer very well. The finest dissections may often be best
made upon ordinary slips of glass; care being taken to keep the
object sufficiently surrounded by fluid. For work of this kind,
no simple instrument is more generally serviceable than Mr.
Quekett’s Dissecting Microscope (Fig. 17); but if higher magni-
fying powers be needed than this will conveniently afford, re-
course may be had to Smith and Beck’s Dissecting Microscope
(Fig. 29), which for this purpose should always be furnished with
the Erector (Fig. 32). A particular arrangement of the light,
devised many years since by the Author, will enable an expert
dissector to prosecute his work with the naked eye, to an extent
for which a lens would otherwise be required. This consists in
giving to the object the same kind of black-ground illumination,
as is now in common use for a very different purpose; and
nothing more is necessary to afford it, than to attach to the under
side of the stage a sort of “ well,” composed of a tube blackened
in its interior, about 13 inch long, of the same diameter as the
opening of the stage-plate, into the lower extremity of which a
diaphragm or a ground-glass may be fitted, for the purpose of
diminishing or of softening the light. The slide being laid upon
the stage, and the mirror being so turned as to illuminate the
object, the eye is to be so placed (the arm carrying the magnifiers
being turned to one side) that the object is seen against the dark
background afforded by the side of the well. In this manner,
fibres of extreme minuteness, or other particles of extraordinary
delicacy, can be clearly distinguished, such as could otherwise
be scarcely discerned at all without the assistance of a magnifier.
And the further the dissection can be carried in this mode, the
less difficulty will be found in completing it, when the simple or

INSTRUMENTS FOR MICROSCOPIC DISSECTION. 2038

compound Microscope is brought to bear upon it. Whenever'a
dissection is being made upon the stage of a microscope, it is
desirable that support should be provided for the hands on either
side. This may be given by books or blocks of wood piled up
to the requisite height; but in place of flat “rests,” it 1s much
more convenient to provide a pair of inclined planes, sloping
away from the stage at an angle of about 30° below the horizon.
These may be either solid blocks of wood, or (which is much
less cumbrous) they may be made of two boards hinged together,
one giving the inclined plane, which rests at one end upon the
table, while the other, standing vertically, affords the requisite
elevation to the extremity which abuts against the stage.

105. The instruments used in Microscopic dissection, are for
the most part of the same kind as those which are needed in
ordinary minute Anatomical research, such as scalpels, scissors,
forceps, &c.; the fine instruments used in operations upon the
eye, however, will commonly be found most suitable. A pair of
delicate scissors curved to one side, is extremely convenient for
cutting open tubular parts; these should have their points
blunted; but other scissors should have fine points. A pair of
fine-pointed scissors (Fig. 56), one leg of which is fixed in a light
handle, and the other kept
apart from it by a spring, so
as to close by the pressure of
the finger and to open of it-
self, will be found (if the
blades be well sharpened on Scting-Relscors.

a hone) much superior to any

kind of knives, for cutting through delicate tissues with as little
disturbance of them as possible: Swammerdam is said to have
made great use of this instrument in his elaborate insect-dissec-
tions. Another cutting instrament much used by some dissectors,
may be designated as a miniature of the shears used in shearing
sheep, or as a cutting-forceps; the blades of such an instrument
may be prevented from springing too far asunder, by means of
a regulating-screw (as in the “ microtome” of M. Strauss-Durek-
heim) or by some other kind of check; and the cutting action,
being executed by the opposed pressure of the finger and thumb,
may be performed with great precision. A pair of small straight
forceps, with fine points, and another pair of curved forceps, will
be found useful in addition to the ordinary dissecting-forceps.
Of all the instruments contrived for delicate dissections, how-
ever, none are more serviceable than those which the Microsco-
pist may make for himself out of ordinary needles. These should
be fixed in light wooden handles! (the cedar sticks used for

' Special needle-holders (like miniature port-crayons) have been made for this pur-
pose; and although they afford the facility of lengthening or shortening the acting point
of the needle at will, and also of carrying a reserve store of needles at the other end,

yet the Author would decidedly recommend the use of the wooden handles, of which
a large stock may be obtained for a trifle.

Fic, 56,

204 PREPARATION OF OBJECTS.

eamel-hair pencils, or the handles of steel-pen-holders, will
answer extremely well), in such a manner that their points
should not project far,! since they will otherwise have too much
“spring: much may be done by their mere tearing action; but
if 1t be desired to use them as cutténg instruments, all that is ne-
cessary is to give them an edge upon a hone. It will sometimes
be desirable to give a finer point to such needles, than they ori-
ginally possess; this also may be done upon a hone. A needle
with its point bent to a right angle, or nearly so, is often useful;
and this may be shaped by simply heating the point in a lamp or
candle, giving to it the required turn with a pair of pliers, and
then hardening the point again by reheating it and plunging it
into cold water or tallow.

106. Cutting Sections of Soft Substances.—Most important in-
formation respecting the structure of many substances, both
Animal and Vegetable, may be obtained by cutting sections of

them, thin enough to be viewed as transparent

Fie. 57. objects. Where the substances are soft, no other
instrument is necessary for this purpose, than a
sharp knife, which may be best made with a thin
two-edged blade like that of a lancet; conside-
rable practice is needed, however, to make effec-
tual use of it; and some individuals acquire a
degree of dexterity, which others never succeed
in attaining. In cutting sections of Animal tis-
sues, which, owing to the quantity of water they
contain, do not present a sufficiently firm resis-
tance, it is often desirable to halfdry these, by
exposing small pieces freely to the air, with the
aid of a gentle warmth if required; when this
desiccating process has been carried sufficiently
calling Thin Seetons, £4, thinner sections can be cut, than could pos-
sibly have been made in the original state of the

tissue; and the texture, after a short maceration in water, almost
entirely recovers its pristine characters. There are certain tis-
sues, however, which will not bear to be thus treated, and of
which it is sufficient to examine an extremely minute portion;
and for making sections of these, such a pair of scissors as is re-
presented in Fig. 57 will often be found very useful; since,
owing to the curvature of the blades,? the two extremities of a

1 The following is the mode in which the Author has found it convenient to mount
his needles for this and other purposes:—The needle being held firmly im a pair
of pliers grasped by the right hand, its poiat may be forced into the end of a cedar or
other stick held in the left, until it has entered to the depth of half an inch or more; the
needle is then cut off to the desired length (the eye end being thus got rid of) ; and
being then drawn out, the truncated end is forced into the hole previously made by the
point, until it cannot be made to penetrate further, when it will be found to be very se-
curely fixed. The end of the handle which embraces it, may then be bevelled away
round its point of insertion,

2 It is difficult to convey by a drawing the idea of the real curvature of this instru-
ment, the blades of which, when it is held in front view, curve—not to either side—

CUTTING THIN SECTIONS. 205

section taken from a flat surface will generally be found to thin
away, although the middle of it may be too thick to exhibit any
structure. Where only a moderate degree of thinness is re-
quired, either in consequence of the transparence of the tissue,
or because it is not desired to exhibit its minutest details, the
two-bladed knife contrived by Prof. Valentin (Fig. 58) may be
employed with advantage. The blades are attached to each
other at their lower end by a screw, in such a manner that their
“ spring’ tends to keep them apart; and their distance is regu-
lated by pushing the little rivet backwards or forwards in the

Fig. 58.

Valentin’s Knife.

slit through which it works. The knife should be dipped in
water before using, or, still better, the section should be made
under water, as the instrument works much better when wet;
after use, it should be carefully washed and dried, a piece of soft
leather -being passed between the blades. If any water have
found its way into the part through which the rivet works, the
movable blade should be detached by taking out its screw, and
éach blade should be cleaned separately."

107. Cutting Sections of Harder Substances.—There is a large
class of substances, both Animal and Vegetable, which are too
hard to admit of sections being made in the manner just de-
scribed, but of which extremely thin slices can be made by a
sharp cutting instrument, if only they be properly held and sup-
ported, more especially when the thickness of the section can be
regulated by a mechanical contrivance; such are, in particular,
the Stems and Roots of Plants, and the Horns, Hoofs, Cartilages,
and similarly firm structures of Animals. Various costly ma-
chines have been devised for this purpose, some of them charac-
terized by great ingenuity of contrivance and beauty of work-
manship; but every purpose to which these are adapted, will be
found to be answered by a very simple and unexpensive little
instrument, which may either be held in the hand, or (which is
preferable) may be firmly attached by means of a T-shaped piece
of wood (as in Fig. 59), to the end of a table or work-bench.
but towards the observer; these scissors being, as the French instrument-makers say,
courbés sur le plat. As an example of the utility of such an instrument to the Micro-
scopist, the Aushor may cite the curious demonstration given a few years since, by Dr.
Aug. Waller, of the structure of the gustative papillze, by snipping off the papille from
the living human tongue, which may be done with no more pain than the prick of a pin
would occasion,

' An improved form of this instrument is constructed by Mr. Matthews of Portugal
Street; the blades being made with a convex instead of a straight edge, their distance

from each other being regulated by a milled-head screw, and their separation for clean-
ing being more easily accomplished. ;

206 PREPARATION OF OBJECTS.

This instrument essentially consists of an upright hollow cylinder
of brass, with a kind of piston
which is pushed from below
upwards by a fine-threaded
_ screw, turned by a large milled
head; at the upper end, the
cylinder terminates in a brass
table, which is made to present
a perfectly flat surface. At one
side is seen a small milled head,
which acts upon a “binding-
screw,” whose extremity pro-
jects into the cavity of the cylin-
der, and serves to compress and
steady anything that it holds.
A. cylindrical stem of wood, a
piece of horn, whalebone, carti-
lage, &e., is to be fitted to the
interior of the cylinder, so as to project a little above its top, and
is to be steadied by the “ binding-screw ;” it is then to be cut to
a level by means of a sharp knife or razor, laid flat upon the
table. The milled head is next to be moved through such a por-
tion of a turn, as may very slightly elevate the substance to be
cut, so as to make it project in an almost insensible degree above
the table ; and this projecting part is to be sliced off with a knife,
previously dipped in water. The best knife for this purpose is a
razor, ground flat (instead of concave) on one side, but having
still a concave surface on the other; the flat side is to be laid
downwards upon the table; and the motion given to the edge
should be a combination of drawing and pressing. (It will be
generally found that better sections are made, by working the
knife from the operator, than towards him.) When one slice has
been thus taken off, it should be removed from the blade by
dipping it into water, or by the use of a camel-hair brush; the
milled head should be again advanced, and another section taken;
and so on. Different substances will be found both to bear: and
to require different degrees of thickness; and the amount that
suits each can only be Pund by trial. It is advantageous to have
the large milled head graduated, and furnished with a fixed
index; so that this amount having been once determined, the
screw shall be so turned as to always produce the exact elevation
required. Where the substance of which it is desired to obtain
sections by this instrument, is of too small a size or of too soft a
texture to be held firmly in the manner just described, it may be
placed between the two vertical halves of a cork of suitable size
to be pressed into the cylinder; and the cork, with the object it
grasps, is then to be sliced in the manner already described, the
small section of the latter being carefully taken off the knife, or
floated away from it, on each occasion, to prevent it from being

Section Instrument.

CUTTING AND GRINDING THIN SECTIONS. 207 .

lost amopg the lamelle of cork which are removed at the
same time. The special methods of preparation which are re-
quired in the case of the various substances, of which sections
may be conveniently cut by this instrument, will be described
under their several heads.

108. Grinding .and Polishing of Sections.—Substances which
are too hard to be sliced with a cutting instrument in the manner
last described,—such as bones, teeth, shells, corals, fossils of all
kinds, and even some recent vegetable tissues,—can only be re-
duced to the requisite thinness for Microscopical examination,
by grinding down thick sections, until they become so thin as
to be transparent. The general method of making such pre-
parations will be here described; but those special details of
management which particular substances may require, will be
given when these substances, are respectively described. The
first thing to be done, will usually be to procure a section of the
substance, as thin as it can be safely cut. Most substances not
siliceous may be divided by the fine saws used by artisans for
cutting brass; but there are some bodies (such as the enamel of
teeth, and porcellanous shells), which, though merely calcareous,
have their mineral particles arranged in such a peculiar state of
aggregation, as to make it very difficult. and tedious to divide
them in this mode; and.it is much the quicker operation to slit

them with a disk of soft iron (resembling that used by the lapi-
* dary) charged at its edge with diamond-dust, which may be
driven in an ordinary lathe. Where waste of material is of no
account, a very expeditious method of obtaining pieces fit to
grind down, is to detach them from the mass with a strong pair
of “ cutting-pincers,”’ or, if it be of small dimensions, with “ cut-
ting-pliers ;” and.a flat surface must then be given to it, either
by holding it to the side of an ordinary grindstone, or by rubbing
it on a plate of lead (cast or planed to a perfect level) charged with
emery, or by a strong toothed file, the former being the most
suitable for the hardest substances, the latter for the toughest.
There are certain substances, especially calcareous fossils of
wood, bone, and teeth, in which the greatest care is required in
the performance of these preliminary operations, on account of
their extreme friability ; the vibration produced by the working
of the saw or the file, or by grinding on a rough surface, being
sufficient to disintegrate even a thick mass, so that it falls to
pieces under the hand; such specimens, therefore, it is requisite
to treat with great caution, dividing them by the smooth action
ot the wheel, and then rubbing them down upon nothing rougher
than a very fine “grit.” Where (as often happens) such speci-
mens are sufficiently porous to admit of the penetration of
Canada balsam, it will be desirable, after soaking them in tur-

'The following directions do not apply to Siliceous substances; as sections of these

can only be prepared by those who possess a regular Lapidary’s apparatus, and who
have been specially instructed in the use of it.

208 PREPARATION OF OBJECTS.

pentine for a while, to lay some liquid balsam upon,the parts
through which the section is to pass, and then to place the speci-
men before the fire or in an oven for some little time, so as first to
cause the balsam to run in, and then to harden it; by this means
the specimen will be rendered much more fit for the processes it
has afterwards to undergo. It not unfrequently happens, that
the small size, awkward shape, or extreme hardness of the body,
occasions a difficulty in holding it either for cutting or grinding;
in such a case, it is much better to attach it to the glass in the
first instance, by any side that happens to be flattest; and then
to rub it down by means of the “hold” of the glass upon it, until
the projecting portion has been brought to a plane, and has been
prepared for permanent attachment to the glass. This is the
method which is generally most convenient to pursue with re-
gard to small bodies; and there are many which can scarcely be
treated in any other way, than by attaching a number of them
to the glass at once, in such a manner as to make them mutually
support one another.'

109. The mode in which the operation is then to be proceeded
with, depends upon whether the section is to be ultimately set
up in Canada balsam (§ 125), or is to be motinted dry (§ 122), or
in fluid (§ 132). In the former case, the following is the plan
to be pursued. The flattened surface is to be polished, by rub-
bing it with water on a “ Water-of-Ayr’ stone, on a hone or
“Turkey” stone, or on a new stone recently introduced under
the name of the “ Arkansas” stone; the first of the three is the
best for all ordinary purposes; but the two latter, being much
harder, may be employed for substances which resist it.2 When
this has been sufficiently accomplished, the section is to be at-
tached with Canada balsam to a slip of thick, well-annealed glass;
and, as the success of the final result will often depend upon the
completeness of its adhesion to this, the means of most effec-
tually securing that adhesion will now be described in detail.
Some Canada balsam, previously rendered somewhat stiff by the
evaporation of part of its turpentine, is to be melted on the glass
slip, so as to form a thick drop, covering a space somewhat larger
than the area of the section; and it should then be set aside to
cool, during which process, the bubbles that may have formed in
it will usually burst. When cold, its hardness should be tested,
which is best done by the edge of the thumb-nail; for it should
be with difficulty indented by its pressure, and yet should not be

! Thus, in making horizontal and vertical sections of Foraminifera, as it would be im-
possible to cut them through, they must be laid close together in a bed of hardened
Canada balsam on a slip of glass, in such positions, that, when rubbed down, the plane
of section shaJl traverse them in the desired directions; and one flat surface having
been thus obtained for each, this must be turned downwards, and the other side ground
away.

2 As the flatness of the polished surface is a matter of the first importance, that of the
stones themselves should be tested from time to time ; and whenever they are found
to have been rubbed down on any one part more than on another, they should be flat-
tened ona paving-stone with fine sand, or on the lead-plate with emery.

GRINDING AND POLISHING THIN SECTIONS. 209

so resinous as to be brittle. If it be too soft, as indicated by its
too ready yielding to the thumb nail, it should be boiled a little
more; if too hard, which will be shown by its chipping, it should
be re-melted and diluted with more fluid balsam, and then set
aside to cool as before. When it is found to be of the right con-
sistence, the section should be laid upon its surface, with the
polished side downwards; the slip of glass is next to be gradu-
ally warmed until the balsam is softened, special care being taken
to avoid the formation of bubbles; and the section is then to be
gently pressed down upon the liquefied balsam, the pressure
being at first applied rather on one side than over its whole area,
so as to drive the superfluous balsam in a sort of wave towards
the other side, and an equable pressure being finally made over
the whole. If this be carefully done, even a very large section
may be attached to glass, without the intervention of any air-
bubbles ; if, however, they should present themselves, and they
cannot be expelled by increasing the pressure over the part be-
neath which they are, or by slightly shifting the section from side
to side, it is better to take the section entirely off, to melt a little
fresh balsam upon the glass, and then to lay the section upon it
as before.

110. When the section has been thus secured to the glass, and
the attached part thoroughly saturated (if it be porous) with hard
Canada balsam, it may be readily reduced in thickness, either by
grinding or filing as before, or, if the thickness be excessive, by
taking off the chief part of it at once by the slitting-wheel. So
soon, however, as it approaches the thinness of a piece of ordi-
nary card, it should be rubbed down with water on one of the
smooth stones previously named, the glass slip being held be-
neath the fingers with its face downwards, and the pressure being
applied with such equality, that the thickness of the section shall
be (as nearly as can be discerned) equal over its entire surface.
As soon as it begins to be translucent, it should be placed under
the Microscope (particular regard being had to the precaution
specified in § 86), and note taken of any inequality; and then,
when it is again laid upon the stone, such inequality may be
brought down, by making special pressure with the fore-finger
upon the part of the slide above it. When the thinness of the
section is such as to cause the water to spread around it between
the glass and the stone, an excess of thickness on either side may
often be detected, by noticing the smaller distance to which the
liquid extends. In proportion as the substance attached to the
glass is ground away, the superfluous balsam which may have
exuded around it will be brought into contact with the stone;
and this should be removed with a knife, care being taken, how-
ever, that a margin be still left round the edge of the section.
As the section approaches the degree of thinness which is most
suitable for the display of its organization, great care must be

taken that the grinding process be not carried too far; and fre-
14

210 PREPARATION OF OBJECTS.

quent recourse should be had to the Microscope, which it is con-
venient to have always at hand, when work of this kind is being
carried on. There are many substances whose intimate structure
can only be displayed in its highest perfection, when a very little
more reduction would destroy the section altogether; and every
Microscopist who has occupied himself in making such prepara-
tions, can tell of the number which he has sacrificed in order to
attain this perfection. Hence if the amount of material be limited,
it is a good rule to stop short as soon as a good section has been
made, and to lay it aside—‘ letting well alone’’—whilst the at-
tempt is being made to procure a better one; if this should fail,
another attempt may be made, and so on, until either success
has been attained, or the whole of the material has been con-
sumed,—the first section, however, still remaining: whereas, if
the first, like every successive section, be sacrificed in the attempt
to obtain perfection, no trace will be left to “show what has
been.” In judging of the appearance of sections in this stage
under the Microscope, it is to be remembered that its transpa-
rence will subsequently be considerably increased by mounting
in Canada balsam. (§ 125) ; this is particularly the case with fossils,
to which a deep hue has been given by the infiltration of some
coloring matter; and with any substances whose particles have a
molecular aggregation, that is rather amorphous than crystalline,
When a sufficient thinness has been attained, the section may
generally be “mounted” in Canada balsam; and the mode in
which this must be managed, will be detailed hereafter (§ 129),

111. As there are certain substances, however, the view of
whose structure is impaired by mounting in Canada balsam, and
which should therefore be mounted either dry or in fluid, a dif-
ferent method of procedure must be adopted with them. If
tolerably thin sections of them can be cut in the first instance, or
if they are of a size and shape to be held in the hand whilst
they are being roughly ground down, there will be no occasion
to attach them to glass at all; is is frequently convenient to do
this at first, however, for the purpose of obtaining a “hold”
upon the specimen; but the surface which has been thus at-
tached, must afterwards be completely rubbed away, in order to
bring into view a stratum which the Canada balsam shall not
have penetrated. As none but substances possessing considera-
ble toughness, such as bones and teeth, can be treated in this
manner, and as these are the substances which are most quickly
reduced by a coarse file, and are least liable to be injured by its
action, it will be generally found possible to bring the sections to
a considerable thinness, by laying them upon a piece of cork or
soft wood held in a vice, and operating upon them first witha
coarser and then with a finer file. When this cannot safely be
carried further, the section must be rubbed down upon that one
of the fine stones already mentioned (§ 109), which is found best
to suit it; as long as the section is tolerably thick, the finger
may be used to press and move it: but as soon as the finger

USE OF CHEMICAL REAGENTS. 211

itself begins to come into contact with the stone, it must be
guarded by a flat slice of cork, or by a piece of gutta percha, a
little larger than the object. Under either of these, the section
may be rubbed down until it has been reduced to the requisite
degree of tenuity ; but even the most careful working, on the
finest-grained stone, will leave its surface covered with scratches,
which not only detract from its appearance, but prevent the de-
tails of its internal structure from being as readily made out, as
they can be in a polished section. This polish may be imparted,
by rubbing the section with putty powder (peroxide of tin) and
water, upon a leather strap, made by covering the surface of a
board with buff-leather, having three or four thicknesses of cloth,
flannel, or soft leather beneath it; this operation must be per-
formed on both sides of the section, until all the marks of the
scratches left by the stone shall have been rubbed out; when the
specimen will be fit for mounting, after having been carefully
cleansed from any adhering particles of putty powder.

112. Chemical Actions.—One important part of the preparation
of Microscopic objects, is often effected by the use of Chemical
Reagents. These may be employed, either for the sake of re-
moving substances of which it is desired to get rid, in order to
bring something else into view; or for the sake of detecting the
presence of particular substances in the object under examina-
tion. Thus, in order to obtain the animal basis of Shell, Bone,
Tooth, &c., itis necessary to dissolve away the calcareous portion
of these tissues by the use of acids; a mixture of nitric and
muriatic acids is preferable; and this should be added, little by
little, to a considerable bulk of water, until a disengagement of
gas be perceived to commence from the surface of the specimen.
Care should always be taken not to hurry the process by adding
too much acid, since, when the animal membrane is of very deli-
cate consistence, it is liable to be dissolved; and in some cases
it is better to allow the action to go on for many weeks, adding
only a drop or two of acid at a time. When siliceous particles
are to be removed (such as those which form the lorice of the
Diatomacez), for the sake of leaving the organic membrane in a
state adapted to separate examination, hydrofluoric acid must be
employed as the menstruum. It is sometimes necessary, on the
other hand, to get rid of the organic matter, for the sake of ob-
taining the mineral particles in a separate state, as in the case of
the spicules of Sponges, Gorgonie, &c., this may be done either
by incineration, or (which is generally preferable) by boiling or
macerating for a long time in a solution of caustic potash. In
separating from Guano, again, the siliceous skeletons of Diato-
maceex, &c., which it may contain, muriatic and nitric acids are
largely used, to dissolve away every part of the mass on which
they will act; the microscopic organisms for which search is
made, being contained in a few grains of sediment which are
left when a pound of pure guano is thus treated.

212 PREPARATION OF OBJECTS.

113. In applying Chemical Reagents to Microscopie objects
for the purpose of testing, it is necessary to use great care not to
add too much at once; and it is better that the test-bottle itself
should afford the means of regulating the quantity, than that an
additional rod or tube should be required. Two modes have
been devised for this purpose. One consists in drawing the neck
of the test-bottle to a capillary orifice, and covering it with a cap
which fits around it; and the fluid is caused to flow from this,
drop by drop, by the warmth of the hand applied to the bottle,
which causes an expansion of the air it may contain.'! When
these bottles are emptied, they must be refilled by expelling the
air by heat, and placing the capillary orifice under the surface of
the fuid to be introduced, which will then be forced in as the
bottle cools; this process may need to be repeated two or three
times (care being taken that the heat applied be not so great as
to crack the bottle); but it is better not to fill the bottle more
than half-full, in order that air enough may be left for the warmth
of the hand to act upon. The other arrangement for applying
minute quantities of test-liquids, consists in the elongation of the
stopper, which is drawn to a fusiform point, so as to serve as the
test-rod for its own bottle. This enables either a mere trace, or
several ordinary drops, of the reagent to be applied at once; for
the elongated stopper will take up a considerable quantity, a
larger or smaller proportion of which (as desired), may be left
behind, by bringing the lower part of the stopper into contact
with the inside of the neck of the bottle, as it is being withdrawn.
Whichever plan is made use of, great care should be taken to
avoid carrying away from the slide to which the test-liquid is
appled, any loose particles which may be upon it, and which
may be thus transferred to some other object, to the great per-
plexity of the Microscopist. It is better, indeed, not to deposit
the drop of test-liquid on the slide in immediate contact with the
substance to which it is to be applied; but to bring the two into
contact after the test-bottle has been withdrawn.

114. The following are the Test-Liquids most frequently
needed.

1. Solution of Jodine in water (1 gr. of iodine, 3 grs. of iodide
of potassium, 1 oz. of distilled water) turns starch blue, and cel-
lulose brown; it also gives an intense brown to albuminous sub-
stances.

2. Dilute Sulphuric Acid (one of acid to two or three parts of
water) gives to cellulose that has been previously dyed with
iodine, a blue or purple hue; also, when mixed with a solution
of sugar, it gives a rose-red hue, more or less deep, with nitro-
genous substances and with bile (Pettenkofer's test).

' A set of 12 test-bottles on this plan, packed in a box, is supplied by Mr. Highley, of
Fleet Street.

? Bottles of this pattern, which was devised by Dr. Griffith, are sold by Mr, Ferguson
of Giltspur Street. .

TEST-LIQUIDS—MOUNTING OF OBJECTS. 213

3. Solution of chloride of zine, iodine, and iodide of potassium,
made in the following way :—Zine is dissolved in hydrochloric
acid, and the solution is permitted to evaporate, in contact with .
metallic zine, until it attains the thickness of a syrup; this syrup «
is then saturated with iodide of potassium, and iodine is last
added. This solution (which is known as Schultz’s test) serves,
like the preceding, to detect the presence of cellulose, and has
the advantage over sulphuric acid of being less destructive to the
tissues. Each will sometimes succeed where the other fails ; con-
sequently, in doubtful cases, both should be employed.

4. Concentrated Mitrie Acid gives to albuminous substances
an intense yellow; when diluted with about two or three parts
of water, it is very useful in separating the elementary parts
of many Animal and Vegetable tissues, when these are boiled
in it.

5. Acetie Acid (diluted with from three to five parts of water)
is a most useful test-liquid to the Animal Histologist, from its
power of dissolving, or at least of reducing to a state of such
transparency that they can no longer be distinguished, certain
membranes, fibres, &c.; whilst others are brought strongly into
view.

6. Acid Nitrate of Mercury (Millon’s test) colors albuminous
substances red.

7. Solution of caustic Potash or Soda (the latter being gene-
rally preferable) has a remarkable solvent effect upon many or-
ganic substances, both Animal and Vegetable.

8. Alcohol dissolves resinous substances and many vegetable
coloring matters, and renders most vegetable preparations more
transparent; on the other hand, by its coagulating action, it
renders many animal tissues (as nerve-fibres) more opaque, and
thus brings them into greater distinctness.

9. Ether dissolves not only resins, but oils and fats.

Sxction 2. Mountine or OBpsercts. “

115. The Microscopist not merely desires to prepare objects ‘
for examination, but, where possible, to preserve them in such a
manner that they may be inspected at any future time. This*
may be so effectually accomplished in regard to many substances,
that they undergo no kind of change, however long they may be
retained ; and even delicate structures whose composition renders
them peculiarly liable to decay, may often be kept, by complete
seclusion from the air, and by immersion in a preservative fluid,
in a state so nearly resembling that in which they were at first
prepared, that they will continue, during an indefinite length of
time, to exhibit their original characters with scarcely any de-
terioration. The method of “ mounting” objects to be thus pre-
served, will differ, of course, both according to their respective
natures, and also to the mode in which they are to be viewed,

214 MOUNTING OF OBJECTS.

whether as transparent or as opaque objects. Thus they may be
set up dry, or in Canada balsam, or in some preservative liquid;
they may need to be simply covered with thin glass, or they may
require to be surrounded by a “cell;” if they are to be viewed
by transmitted light, they must always have glass below them ;
but if they are to be seen by the light reflected from their sur.
faces, they may often be preterably mounted on wood, card, or
some other material which itself affords a black background.
In almost all cases in which transparent objects are to be
mounted, use will have to be made of the slips of glass techni-
cally called slides or sliders, and of covers of thin glass, and it will
therefore be desirable to treat of these in the first instance.

116. Glass Slides —The kind of glass usually employed for
mounting objects, is that which is known as “flatted crown;”
and it is now almost invariably cut, by the common consent of
Microscopists in this country, into slips measuring 8 in. by 1 in;
for objects too large to be mounted on these, the size of 3 in. by
13 in. may be adopted. Such slips may be purchased, accurately
cut to size, and ground at the edges, for so little more than the
cost of the glass, that few persons to whom time is an object
would trouble themselves to prepare them; it being only when
glass slides of some unusual dimensions are required, or when it
is desired to construct “built up cells” (§§ 186, 137), that a facility
of cutting glass with a glazier’s diamond becomes useful. The
glass slide prepared for use, should be free from veins, air bubbles,
or other flaws, at least in the central part on which the object is
placed; and any whose defects render them unsuitable for ordi-
nary purposes, should be selected and laid aside for uses to which
the working Microscopist will find no difficulty in putting them.
As the slips vary considerably in thickness, it will be advanta-
geous to separate the thick from the thin,and both from those of
medium substance: the last may be employed for mounting or-
dinary objects; the second for mounting delicate objects to be
viewed by the high powers, with which the achromatic condenser

is to be used, so as to avoid any unnecessary refraction of the
‘illuminating pencil by the thickness of the plate which it has to

, traverse beneath the object; whilst the first should be set aside

“for the attachment of objects which are to be ground down, and
for which, therefore, a stronger mounting than usual is desirable.
Where very hard substances have to be thus operated on, it is
advantageous to attach them in the first instance to pieces of
very thick plate-glass; only transferring them to the ordinary
slides, when they have been reduced to nearly the requisite thin-
ness (§ 129).

117. Thin Glass—The older Microscopists were obliged to
employ thin lamine of tale, for covering objects to be viewed
with lenses of short foci; but this material, which was in many
respects objectionable, is now entirely superseded by the thin
glass manuiactured for this express purpose by Messrs. Chance

CUTTING THIN GLASS. 215

of Birmingham, which may be obtained. of various degrees of
thickness, from 1-20th to 1-250th of an inch. This glass, being
unannealed, is very hard and brittle; and much care and some
dexterity are required in cutting it. This should be done with
the writing diamond ; and it is advantageous to lay the thin glass
upon a piece of wetted plate-glass, as its tendency to crack and
“star” is thereby diminished. For cutting square or other rect-
angular covers, nothing but a flat rule is required. For cutting
rounds or ovals, on the other hand, it is necessary to have
“ouides’” of some kind. The simplest, which are as effective as
any, consist of pieces of flat brass plate, perforated with holes
of the various sizes desired; or curtain-rings, with a piece of
wire soldered on eitherside: these being held firmly down on
the thin glass with two fingers of the left hand, the writing-
diamond is carried round the inner margin of the aperture with
the right; care being taken that, in so doing, the diamond be
made to revolve on its own axis, which is needful both that it
may mark the glass, and also that the beginning and the end of
the cut may join. Wherea number of such “rounds” are being
cut at once, it saves much trouble, as well as risk of loss by
breakage in separating them, to cut the glass first into strips,
whose breadth shall equal the diameter of the rounds. But it is
very convenient to use up for this purpose any odd pieces of
glass, whose shape may render them unsuitable for being cut
into “squares” without much waste. The pieces of thin glass
thus prepared for use, should be sorted, not only according to
size and shape, but also according to thickness. The thinnest
glass is of course most difficult to handle safely, and is most
liable to fracture from accidents of various kinds; and hence it
should only be employed for the purpose for which it is abso-
lutely needed,—namely, the mounting of objects which are to be
viewed by the highest powers. The thickest pieces, again, may
be most advantageously employed as covers for large cells in
which objects are mounted in fluid (§§ 186, 187), to be viewed
by the low powers, whose performance is not sensibly affected by
the aberration thus produced. And the pieces of medium thin-
ness will be found those most serviceable for all ordinary pur-
poses; neither being, on the one hand, difficult to handle; nor,
on the other, interfering with the clearness of the image formed
by medium powers of moderate aperture, even when no special
adjustment is made for the aberration they produce (§ 101).

' A very elegant little instrument, for the purpose of cutting thin glass rounds, con-
trived by Mr. Shadbolt, and another, of a more substantial character, invented by Mr.
Darker, will be found described in Mr, Quekett’s “‘ Practical Treatise.” These imstru-
ments, however, are rather adapted for the use of those who have occasion to prepare
such rounds in large quantities, than for the ordinary working Microscopist, who will
find the method above described answer his requirements sufficiently well. Indeed it
is in some respects superior; since a firm pressure made by the ring or plate on the
glass round, tends to prevent the crack from spreading into it. Toevery one to whom
the saving of time is a greater object than the expenditure of a few shillings, it is strongly
recommended that these “rounds” should be purchased ready cut; as they may be
obtained of any required size and thinness, at a very moderate cost.

216 MOUNTING OF OBJECTS.

118. The exact thickness of any piece of glass may be deter.
mined without difficulty, by placing it edgeways on the stage ot
the microscope (holding it in the stage-forceps), and measuring
its edge by the eye-piece micrometer (§ 46). A much more ready
means is afforded, however, by the Lever of Contact (Fig. 60) de-
vised by Mr. Ross for this express purpose. This instrument

Fig. 60.

Lever of Contact.

consists of a small horizontal table of brass, mounted upon a
stand, and having at one end an are graduated into 20 divisions,
each of which represents 1-1000th of an inch, so that the entire
are measures 1-50th of an inch; at the other end is a pivot, on
which moves a long and delicate lever of steel, whose extremity
points to the graduated arc, whilst it has very near its pivot a sort
of projecting tooth, which bears at * against a vertical plate ot
steel that is screwed to the horizontal table. The piece of thin
glass to be measured, being inserted between the vertical plate
and the projecting tooth of the lever, its thickness in thousandths
of an inch is given by the number on the graduated arc, to which
the extremity of the lever points. Thus, if the number be 8, the
thickness of the glass is ‘008, or 1-125th of an inch. A very
elegant little instrument, which is used by watchmakers for mea-
suring the thickness of thin plates and wires, may be obtained
at a much less cost from the dealers in Swiss tools; this answers
the purpose equally well; but the “value” of its scale must be
determined by gauging the thickness of a piece of glass, or the
diameter of a fine wire, and comparing the number of divisions
which it indicates, with the micrometrical measurement of the
same body obtained by the microscope. When the glass covers
have been sorted according to their thickness, it will be found
convenient to employ those of one particular thickness for each
particular class of objects; since, when one object is being ex-
amined after another, no readjustment of the objective will then
be required for each. This will be found a great saving of time
and trouble, when high powers are in use. It is undesirable to
employ glass covers of greater thickness than 1-140th (-007) of
an inch, with any object-glass whose aperture exceeds 75°; and
for object-glasses of 120° and upwards, the glass cover should not
exceed 1-250th (-004) of an inch.

119. On account of the extreme brittleness of the thin glass,
it is desirable to keep the pieces, when cut and sorted, in some

CLEANING THIN GLASS COVERS. 217

fine soft powder, such as starch. Before using it, however, the
Microscopist should be careful to clean it thoroughly ; not merely
for the sake of removing foulnesses which would interfere with
the view of the object, but also for the sake of getting rid of
adherent starch-grains, the presence of which might lead to
wrong conclusions, and also of freeing the surface from that
slight greasiness, which, by preventing it from being readily
wetted by water, frequently occasions great inconvenience in the
mounting of objects in fluid. The thicker pieces may be washed
and wiped without much danger of fracture, if due care be em-
ployed ; but the thinner require much precaution ; and in cleans-
ing these, the simple method devised by Mr. Spencer will be
found very useful. This consists in the use of a pair of round
flat disks, about 14 inch in diameter, made of wood or metal
covered with chamois leather, and furnished with handles; for
when a piece even of the thinnest glass is laid upon one of these,
it may be rubbed clean with the other, and any amount of pres-
gure may be used, without the least risk of breaking it. Pre-
viously to doing this, however, it will be advantageous to soak
the pieces for a time in strong sulphuric acid, and then to wash
them in two or three waters; if greasiness, however, be their
chief fault, they should be soaked in a strong infusion of nut-
galls; with which it will be also advantageous to cleanse the
surface of glass slides that are to be used for mounting objects
in liquid.

120. Varnishes and Cements.—There are three very distinct
purposes, for which cements that possess the power of holding
firmly to glass, and of resisting, not merely water, but other pre-
servative liquids, are required by the Microscopist ; these being
(1) the attachment of the glass covers to the slides or cells con-
taining the object, (2) the formation of thin cells of cement only,
and (3) the attachment of the glass plate or tube-cells to the
slides. The two former of these purposes are answered by liquid
cements or varnishes, which may be applied without heat; the
last requires a solid cement of greater tenacity, which can only
be used in the melted state. The Varnishes used for mounting
objects in liquid, should always be such as contain no mizture of
solid particles. This is a principle on which the Author, from an
experience of many years, is disposed to lay great stress ; having
often made trial, at the recommendation of friends, of varnishes
which were said to have been greatly improved by thickening
with litharge or lamp-black ; and having always found that, al-
though they might stand well for a few weeks or months, they
became porous after a greater lapse of time, allowing the evapo-
ration of the liquid and the admission of air. He has himself
found none more durable than that known as japanner’s Gold-
size, which may be obtained at almost every color-shop ; for al-
though this, when newly made, is apt to be somewhat too thin,
so as to tend to run in beneath the glass cover, it may be easily

218 MOUNTING OF OBJECTS.

prevented by employing very liquid Gold-size, and by using it in
extremely small quantity in the first instance; since whenever
the glass cover lies perfectly flat on its bed, and the fluid be-
neath extends to the edges, the thin Jayer of this varnish dries
very quickly, without any tendency to runin. When this has
completely set, a second layer should be applied ; and a layer of
Asphalte over the whole will add to its security, and improve
the appearance of the mounting. The danger of running in
appears to the Author to be the greatest, when, in consequence
of the use of old and viscid gold-size, the layer is too thick,
and is long in drying. His experience leads him to distrust
Asphalte when used alone, as being liable to admit air after a
lengthened period of drying. He has recently learned from
Mr, Tomes, that he finds saturated solution of arsenious acid to
be a very good medium for mounting delicate preparations of
animal structures. If it be allowed to become so thick, how-
ever, as not to be easily worked by the brush, it is quite unfit
for use. There are few preservative liquids with which gold-
size may not be employed ; since it is not acted on by any aque-
ous solution, and resists moderately diluted spirit; oil of turpen-
tine being its only true solvent.!. Many Microscopists prefer the
solution of shell-lac in naphtha, which is sold under the name
of Liquid Glue; this dries more quickly than gold-size, but is
more brittle when completely hardened, and does not, in the
Author’s opinion, adhere so firmly and enduringly to glass; and
it is, moreover, more easily acted on by diluted alcohol than the
preceding. Of late, a solution of Asphalte in drying-oil or tur-
pentine, sometimes known under the name of ‘“ Brunswick-
black,” has come much into use. It is extremely easy and
pleasant to work with, and dries quickly; but it is brittle when
dry, and is disposed to crack, not merely when subject to any
“jar,” but also (after some time) spontaneously. This evil may
be corrected, according to Mr. Brooke, by adding to it a little
solution of Caoutchouc in mineral naphtha. Oil of turpentine
is the solvent for this varnish, as for gold-size; and brushes
which have been used with either, may be cleansed by that
menstruum; those which have been used with liquid glue, may
be cleansed with naphtha. For mounting objects dry (§ 122), or
for giving a finished appearance to mountings which have been
made by one or other of the foregoing cements, varnishes may
be used, which, from containing coloring particles, or from being
acted on by the preservative liquids employed, could not be safely
laid on in the first instance. Among the most convenient of
this kind, are varnishes made by dissolving red or black or any
other colored Sealing-wax in strong alcohol; these are more to
be recommended for their appearance, however, than for their

' The Author has preparations mounted with gold-size as much as twelve years ago,
which have remained perfectly free from leakage; the precaution having been taken,
to lay on a thin coat of varnish every two or tliree years,

VARNISHES AND CEMENTS. 219

tenacity, being very apt to lose their hold upon the glass after a
time; and the Author, having suffered much injury to his pre-
parations from trusting to them, would recommend that, even in
mounting objects dry, some other cement should be first used,
by which the glass cover should be attached to the slide, the
sealing-wax varnish being only laid on as a finish. If a black
varnish be desired for such a purpose, it may be readily made by
mixing gold-size with a small quantity of lamp-black; this dries
quickly, and is free from brittleness; but, for the reason already
mentioned, it should not be used in the first instance to mount
objects in fluid, although it may be laid as a finish over gold-size
or asphalte. For making cement-cells (§ 184), either asphalte,
gold-size, or liquid glue may be employed, the first being on the
whole preferable; the varnish termed Black Japan also makes
very good and durable cells, if the glasses to which it has been
applied be exposed to the heat of an oven, not raised so high as
to cause them to “ blister.”’

121. Although Canada balsam has been sometimes used as
a cement, and has the advantage of being worked with extreme
convenience, yet it is so apt to crack when hardened by time,
that a slight “jar’’ will cause the cell to spring away from the
glass to which it has been attached. Hence, if employed at all
for fixing cells to glass slides, its use should be limited to those
plate-cells which attord a large surface of attachment (§ 186), or
to those very thin tube-cells (§ 135), which cannot be so con-
veniently attached with marine glue, and of which the cover
may be secured to the slide by spreading the ring of gold-size
round the margin of the cell itself (§ 188). Care should be taken,
in applying the Canada balsam, that it be sufficiently hardened
by heat, but that it be not so heated as to become brittle (§ 109):
the general method of using it for this purpose, is the same as
that which must be practised in the case of marine glue. The
superfluous balsam left after pressing down the cell, is to be re-
moved, first by scraping with a heated knife, and then with a rag
dipped in oil of turpentine, after which it is desirable to give the
glass surface a final cleansing with alcohol. For all kinds of cells
(§§ 185, 187) except those just mentioned, the proper cement is
Marine Glue, which is a mixture of shell-lac, caoutchouc, and
naphtha, now extensively employed ; being distinguished by its
extraordinary tenacity, and by its power of resisting solvents of
almost every kind. Different qualities of this substance are
made for the several purposes to which it is applied; that which
is most suitable to the wants of the Microscopist, is known in
commerce as GK 4. As this cement can only be applied hot, and
as it is a great saving of trouble to attach a considerable number
of cells at the same time, a Mounting-Plate should be provided,
which will furnish the requisite heat to several slides at once.
Such a surface may be afforded by the top of a stove; but it is
better to have one which can be used at all seasons, and the heat

220 MOUNTING OF OBJECTS.

of which can be precisely regulated at pleasure. A very simple
apparatus much used for this purpose, consists of a small table
of brass or iron plate, about 6 inches long and 2 broad, with legs
about 4 inches high, either screwed into its four corners, or so
jointed to them as to fold down; this is set over a small spirit-
lamp, the flame of which is regulated to give the heat required.
The Author has found it much preferable, however, to lay the
plate on one of the rings of a small “retort-stand’’ (used in
Chemical operations), which admits of being shifted to any
height that may be desired, so that the heat applied may be pre-
cisely graduated ; or, if a gas lamp be employed for the ordinary
purposes of illumination, its stem may be fitted with a sliding-
ring, which will carry either a hot plate or a water-bath.' It is
more convenient, however, to have two such plates, laid on two
rings; one being allowed to cool with the slides upon it, whilst
the other is being heated. The glass slides and cells which are
to be attached to each other, must first be heated on the mount-
ing-plate; and some small cuttings of marine-glue are then to
be placed, either upon that surface of the cell which is to be at-
tached, or upon that portion of the slide on which it is to lie,
the former being perhaps preferable. When they begin to melt,
they may be worked over the surface of attachment by means of
a needle-point ; and in this manner, the melted glue may be uni-
formly spread, care being taken to pick out any of the small
gritty particles which this cement sometimes contains. When
the surface of attachment is thus completely covered with lique-
fied glue, the cell is to be taken up witha pair of forceps, turned
over and deposited in its propcr place on the slide; and it is
then to be firmly pressed down with a stick (such as the handle
of the needle) or with a piece of flat wood, so as to squeeze out
any superfluous glue from beneath. If any air-bubbles should
be seen between the cell and the slide, these should if possible
be got rid of by pressure, or by slightly moving the cell from
side to side; but if their presence results, as is sometimes the
case, from deficiency of cement at that point, the cell must be
lifted off again, and more glue applied at the required spot.
Sometimes, in spite of care, the glue becomes hardened and
blackened by overheating; and as, in this case, it will not stick
well to the glass, it is preferable not to attempt to proceed, but
to lift off the cell from the slide, to let it cool, and then to repeat
the process. When the cementing has been satisfactorily accom-
plished, the slides should be allowed to cool gradually, in order
to secure the firm adhesion of the glue; and this is readily ac-
complished, in the first instance, by pushing each, as it is finished,
towards one of the extremities of the plate, which is of course
cooler than the centre. If two plates are in use, the heated plate
may then be readily moved away upon the ring which supports

1 Both these fittings are adapted to the Gas lamp supplied for the use of Microscopists
by Mr. 8. Highley (§ 75).

1

MOUNTING TRANSPARENT OBJECTS DRY. 221

it, the other being brought down in its place ; and as the heated
plate will be some little time in cooling, the firm attachment of
the cells will be secured. If, on the other hand, there be only a
single plate, and the operator desire to proceed at once in mount-
ing more cells, the slides already completed should be carefully
removed from it, and laid upon a wooden surface, the slow con-
duction of which will prevent them from cooling too fast. Be-
fore they are quite cold, the superfluous glue should be scraped
from the glass with a small chisel or awl; and the surface should
then be carefully cleansed with a solution of potash, which may
be rubbed upon it with a piece of rag covering a stick shaped
like a chisel. The cellsshould next be washed with a hard brush
and soap and water, and may be finally cleansed by rubbing with
a little weak spirit and a soft cloth. In cases in which appearance
is not of much consequence, and especially in those in which the
cell is to be used for mounting large opaque objects, it is de-
cidedly preferable not to scrape off the glue too closely round
the edges of attachment, as the “hold” is much firmer, and
the probability of the penetration of air or fluid much less, if
the immediate margin of glue be left, both outside and inside
the cell.

122. Mounting Objects Dry.—There are certain objects, which,
even when they are to be viewed by transmitted light, are more
advantageously seen when simply laid on glass, than when they
are immersed either in fluid or in balsam. This is the case
especially with sections of bones and teeth, much of whose in-
ternal structure is obliterated by the penetration of fluid; and
also with the scales of Lepidopterous and other Insects, whose
minute surface-markings are far more distinct when thus ex-
amined, than when treated in any other way.’ For preserving
such objects, it is of course desirable that they should be pro-
tected by a cover; and this must be so attached to the glass
slide, as to keep the object in place, besides being itself secured.
For this purpose sealing-wax varnish is often used, but is unsuit-
able on account of its brittleness when dry; gold size mixed with
lamp-black is much to be preferred, and, if carefully laid on, will
not tend to run in between the cover and the slide. If the object
have any tendency to curl up, or to keep off the cover from the
slide by its own “spring,” it will be useful, while applying the
varnish, to make use of pressure, such as that afforded by the
little implement represented in Fig. 62. This pressure should

"Tt is affirmed by two high authorities on all that relates both to the theoretical and
practical action of Object-glasses of large aperture (namely, Prof. Robinson and Mr.
Wenbam), that the effect of mounting delicate test-objects in Canada balsam is practi-
cally to reduce the aperture, since no rays can diverge after passing through a stratum
of this substance, at a greater angle than 85° or 90°. Hence they recommend that the
“difficult” Diatomacee should not be mounted in balsam, if they are to be viewed by
objectives of 120° or 130°. Their position is disputed, however, by Prof. Bailey (U. S.),
who affirms that balsam-mounted specimens are preferable as test-objects. Those who

are interested in this question, will do well to consult the papers of these gentlemen, in
the 2d and 3d volumes of the “ Quart. Journ. of Microsc. Science.”

200 MOUNTING OF OBJECTS.

not be remitted, until the varnish is dry enough to hold down
the cover by itself. For mounting delicate objects, the thinner
slides should be selected (§ 116); and for very difficult test-objects,
it is advantageous to employ thin glass below as well as above
the specimens, for the sake of diminishing the aberration which
the illuminating pencil sustains in its passage to the object, and
for allowing the achromatic condenser to approach the object as
closely as possible. For this purpose, the simplest method is to
take a slip of wood, of the ordinary size of the glass slide (3 in.
by 1 in.), with a central aperture of from 3 to 5-8ths of an inch;
to cover this aperture with a “square” or “round” of thin glass
of sufficient size to project considerably beyond it; to lay the
object upon this glass, and to protect it with a cover of rather
smaller size, which should be fastened down all round by var-
nish, to prevent the entrance of moisture; and finally to secure
both glasses to the wooden slide, by gumming down over them
a piece of paper, with a perforation of the same size as that of
the slide itself.

123. For dry-mounting opaque objects, the method adopted
must vary with the mode in which the object is to be illuminated;
since, if a side-condenser or reflector is to be employed, the whole
slide may be opaque; whereas if the Lieberkiihn is preferred,
the object should be placed on a disk of appropriate size (§ 65),
supported in such a mode as to admit the light all around it.
For the former purpose, the Author has devised the following
simple method, which he has found to afford peculiar con-
veniences. Let there be provided a cedar slide of the kind just
described, a piece of card of the same dimensions, and a piece of
dead-black paper, rather larger than the aperture of the slide, ifa
dark mounting be desired, which is preferable for most objects;
this piece of paper is to be gummed to the middle of the card,
and then, some stiff gum having been previously spread over one
side of the slide (care being taken that there is no superfluity of
it immediately around the aperture), this is to be laid down upon
the card, and subjected to pressure.!. An extremely neat “cell”
will thus be formed for the reception of the object, the depth of
which will be determined by the thickness of the slide, and the
diameter by the size of the perforation ; and it will be found con-
venient to use slides of various thicknesses and having apertures
of different sizes. The cell should always be deep enough for its
wall to rise above the object; but, on the other hand, if it be too
deep, its wall will interfere with the oblique incidence of the
light upon any object that may be near its periphery. The ob-
ject, if flat or small, may be attached by ordinary gum-mucilage;
if, however, it be large, and the part of it to be attached have an
irregular surface, it is desirable to afford a “bed” to this by gum

* Tt will be found a very convenient plan, to prepare a large number of such sliles at
once; and this may be done in a marvellously short time, if the slips of card have been
previously cut to the exact size in a bookbinder'’s press.

MOUNTING OPAQUE OBJECTS FOR LIEBERKUHN. 228

thickened with starch. The complete protection thus given to
the object, is the great recommendation of this method; since,
when objects are simply fastened on black paper gummed on a
slip of glass, their protection from its surface renders them con-
stantly liable to accidents; as many know, to their cost, who
have used that mode of mounting. But this is by no means
its only convenience. It is far cheaper than mounting objects
in glass cells, which is the only other mode of affording them
protection, save the use of pill-boxes in the manner to be pre-
sently described. It allows the slides, not only to range in
the ordinary cabinets, but also to be laid one against another,
and to be packed closely in cases or secured by elastic bands ;
and this last plan is extremely convenient, not merely for the
saving of space, but also for preserving the objects from dust.
Should any more special protection be required, a thin glass
cover may be laid over the top of the cell, and secured there by
gummed paper; but this will, of course, occasion a slight pro-
jection, which will expose the glass cover to the risk of fracture
when the slide is pressed against others; and the Author’s ex-
perience leads him to conclude, that the mode of packing just
described affords a security from dust, that is scarcely less effec-
tual than a thin glass cover. Further, the card on the under sur-
face affords a great convenience for writing on the slide the name
and other particulars of the object. If the object be so large as
to project above the surface, even when the thickest slides are
used which it is convenient to employ, an additional protection
may be afforded, by gluing a couple of strips of wood of adequate
thickness along the edges of the slide ;? or by gumming a second
slide to the face of the first, taking care that its aperture be large
enough to prevent obstruction to oblique light. Very delicate,
flat objects, on the other hand, even when to be viewed by inci-
dent light, should be mounted on glass and protected by a cover,
in the same manner as transparent objects; a dark background
being furnished to them, either by the “dark well” (§ 65) or by
the closed diaphragm (§ 55).

124. Objects which are to be viewed by the Lieberkiihn should
be mounted either on flat disks of card or cork, or, if protection
be desired, in cups of proper depth, resembling very shallow pill-
boxes, which may be made with or without covers,’ of any size

1A very convenient kind of slide, for mounting large opaque objects, is made by
Messrs. Carpenter and Westley, 24 Regent Street, by ploughing out a groove in a strip
of wood, so that its section presents this form LI. The object may be mounted upon
the bottom of the groove; or upon a disk of card fitted into an aperture in the slide, and
so held there by a brass ring, that it may be taken out and held between the stage-for-
ceps, so as to be viewed with the Lieberktihn. These slides are commonly made five
inches long, and are fitted for the reception of four objects; for the sake of uniformity,
however, as well as for preventing them from overbalancing on the stage, it might be
convenient that they should be made three inches long, and that each should only
receive one or (at most) two objects.

2 Round boxes with glass covers are now coming into very extensive use for the pre-
servation of Natural History specimens of various kinds, in such a manner that the con-

224 MOUNTING OF OBJECTS.

desired, and lined with black paper, by any pill-box maker,
The disks or pill-box cells may be attached to glass slides by
gum, so as to range in an ordinary object-cabinet ; and this mode
will be generally adopted by such as lay stress upon uniformity,
and prefer the easiest methods of exhibiting their objects. As
there are many opaque objects, however, which can only be well
judged of when different sides are presented to the Microscope,
there is a great advantage in mounting these in such a manner,
as to admit of their being turned at various angles; and this
may be done by attaching the disk with sealing-wax or some other
cement, to a pin, which may be either held between the blades
of the stage-forceps, or passed into the cork box at its other ex-
tremity (§ 66). Ifthe Microscopist should be pursuing the study
of any class of objects which renders it desirable to mount a
large number in this mode, the most convenient plan is to glue
two pieces of cardboard to the two sides of a piece of rather thick
chamois leather; one of the surfaces of this sandwich-like board
should be covered with dead-black paper; and disks of any de-
sired diameter may then be cut out with a punch, and mounted
upon a pin by simply passing it through the stratum of leather.
The pill-box mounting will be less advantageous for this pur-
pose, since, if the object be completely buried in the cell, there
will be less power of seeing it on any but its upper surface; a
pin may be secured to the bottom of such a box, however, by
gumming over it a piece of stout paper. Disks may easily be
punched, also, out of sheet gutta percha of any convenient thick-
ness; or short cylinders may be made, by cutting up the thick
cords made for lathe-bands; these are all readily penetrated by
a heated pin, and no further trouble is necessary to attach them
to it. Protective wells may also be made by cutting off short
pieces from a gutta percha tube, and attaching these to the disks
by a gentle heat. For the reception of boxes or disks thus
mounted on pins, a drawer should be provided with a thick cork
bottom, into which the pin is to be inserted far enough to pre-
vent risk of displacement.

125. Mounting Objects in Canada Balsam.—This method of
mounting is suitable to a very large proportion of those objects,
which are to be viewed by transmitted light, and whose texture
is not affected by the loss of the aqueous fluid they may contain ;
and it has many advantages over the mounting of the like ob-
jects dry. For, in the first place, as it fills up the little inequali-
ties of their surface, even where it does not actually penetrate
their substance, it increases their transparence by doing away
with irregular refractions of the light in its way through them,

tents ofeach box, whilst protected and kept together, are at the same time presented to the
eye. The Author has found the smallest and shallowest boxes of this kind that can be
made, especially when lined with black paper, extremely useful for keeping Foramini-
fera and other Microscopic organisms in quantities; and also for mounting larger speci-
mens for the Microscope as above described. :

MOUNTING OBJECTS IN CANADA BALSAM. 225

and gives them the aspect of perfect smoothness ; this is well seen
in the case of sections of Shell, &c., which, when thus mounted,
do not require a high polish (§ 110). But, secondly, where the
structure, although itself hard, is penetrated by internal vacuities,
the balsam, by filling these, prevents that obscuration resulting
from the interposition of air-spaces, and from additional internal
surfaces of reflection, by which the transmitted rays are distorted,
and a large proportion of them lost: this is well seen in the case
of the Foraminifera, and of sections of the “test’’ and “spines”’
of Echinida, whose intimate structure can be far better made
out, when they are thus mounted, than when mounted dry,
although their substance is (for the most part at least) itself so
dense, that the balsam cannot be imagined to penetrate it; and
likewise with dry Vegetable preparations, which are perhaps also
affected in the manner to be next described. Thirdly, there are
very many structures of great interest to the Microscopist, whose
appearance is extraordinarily improved by this method of mount-
ing, in consequence of a specific effect which the balsam has in
combining (so to speak) with their component elements, so as
to render them far more transparent than before: this effect is
seen in the case of all dry preparations of Insect structure, espe-
cially of such as consist of their hard external tegument or of
parts derived from this; also in the various horny tissues (hairs,
hoof, horn, &c.) of the higher animals; and likewise in many or-
ganized substances, both recent and fossil, which are penetrated
by calcareous matter in an amorphous condition. Besides these
advantages, the mounting of objects in Canada balsam affords
one of the easiest methods of fixing and preserving them; and
consequently, it is almost always had recourse to, in the case of
such transparent objects as do not need to be preserved in fluid;
save where, in virtue of the action just described, it impairs the
distinctness of surface-markings, or obliterates internal cavities
a canals, which constitute the most important features of the
object.

126. Canada Balsam, being nothing else than a very pure
Turpentine, is a natural combination of resin with the essential
oil of turpentine. In its fresh state, it is a viscid liquid, easily
poured out, but capable of being drawn into fine threads; and
this is the condition in which the Microscopist will find it most
desirable to use it for the mounting of objects generally. The
balsam may be conveniently kept in a glass bottle or jar with a
wide mouth, being taken up as required by a small glass rod
drawn to a blunt point, such as is used by Chemists as a “stirrer ;”
and if, instead of a cork or stopper, this bottle should be pro-
vided with a tall hollow “cap,” the glass rod may always
stand in the balsam, with its upper end projecting into the cap.
In taking out the balsam, care should be taken not to drop it
prematurely from the rod; and not to let it come into contact with
the interior of the neck or with the mouth of the jar. Both

15

226 MOUNTING OF OBJECTS.

these mischances may be avoided, by not attempting to take up
on the rod more than it will properly carry; and by holding it
in a horizontal position, after drawing it out from the bottle,
until the slip on which it is to deposit the balsam, is just beneath
its point. The Author has himself been in the habit of employ-
ing, instead of a hollow cap to his balsam Jar, a disk of light
wood, simply lying on its mouth; the centre of this disk is per-
forated with a hole, just large enough to allow the glass rod to
fit it rather stiffly ; and the rod is to be passed into the jar, only
so far as to dip by its point into the balsam, being pushed fur-
ther down as the level of the balsam is lowered. In this manner,
a small quantity of balsam may be taken up with far less risk of
messing it, than when the rod dips into it for two or three inches;
if due care be taken not to allow the balsam to come into con-
tact with the lip of the jar, the cover never sticks to it, but is
readily lifted off upon the rod; and although it might seem an
incumbrance in the use of the rod, yet it is not practically found
to be so. If the balsam be kept too long, it becomes, through
the loss of part of its volatile oil, too stiff for convenient use, and
may be thinned by mixing it ata gentle heat with pure oil of
turpentine; this mixture, however, does not produce that
thorough incorporation of the constituents which exists in the
fresh balsam ; and it is consequently preferable to use in other
ways the balsam which has become somewhat too stiff, and to
have recourse to a fresh supply of liquid balsam for mounting
purposes. When Canada balsam is to be employed as a cement,
as for attaching sections, &c., to glass slides (§ 109), it should be
in a much stiffer condition ; since, if it be dropped on the slide
in too liquid a state, it will probably spread much wider, and
will lie in a thinner stratum than is desirable. This hardening
process may be carried to any extent that may be desired, by
exposing the balsam in an uncorked jar (the mouth of which:
however, should be covered with paper, for the sake, of keep-
ing off dust) to a continual gentle heat, such as that of a water-
bath.

127. In mounting objects in Canada balsam, it is convenient
to be provided with certain simple instruments, the use of which
will save much time and trouble. For the heat required, a

Slider Forceps.

Spirit lamp is by far the best source ; both as admitting of easy
regulation, and as being perfectly free from smoke. Where a
number of objects are being mounted on the same occasion, it
will be found convenient to employ either a water-bath covered

MOUNTING OBJECTS IN CANADA BALSAM. 297

with a flat plate of metal, or a similar metal plate supported at
such a distance above the lamp flame (§ 121), as not to become
more heated than it would be through a water-bath. For hold-
ing the slide, either whilst it is being heated over the flame, or
whilst it is being subsequently cooled, the Wooden Forceps
(Fig. 61) contrived for this purpose by Mr. Page, will be found
extremely convenient; this, by its elasticity, affords a secure
grasp to a slide of any ordinary thickness, the wooden blades
being separated by pressure upon the brass studs ; and the lower
stud, with the bent piece of brass at the junction of the blades,
affords a level support to the forceps, which thus, while resting
upon the table, keeps the heated glass from contact with its sur-
face. Besides a pair of fine-pointed Metal forceps for holding
the object to be mounted, there should be another of a com-
moner kind for taking up the glass cover, the former being liable
to be soiled with balsam. A pair of stout needles mounted in
wooden handles (§ 105), will be found indispensable, both for
manipulating the object, and for breaking or removing air-bub-
bles ; and if these handles be cut to a flat surface at the other
extremity, they will serve also to press down the glass covers,
for which purpose a pointed stick also is useful. For holding
down these covers, whilst the balsam is cooling, if the elasticity
of the objects should tend to make them spring up, nothing is
more simple or convenient than a compressor made by a slight
alteration of the “ American clothes peg,” which is now in ge-
neral use in this country for a variety of purposes; all that is
necessary being to rub down the opposed surfaces of the “ clip”
with a flat file, so that they shall be parallel to each other when
an ordinary slide with its cover is interposed between them (Fig.
62). Great care should be taken to keep these implements free
from soils of balsam; since the
slides and glass covers are certain Fie. 62.
to receive them. The readiest
mode of cleansing the needles
(their “temper” being a matter
of no consequence for these pur-
poses) is to heat them red hot
in the lamp, so as to burn off the Spring Press.

‘balsam; and then carefully to
wipe them. The forceps, both of wood and of metal, should be
cleansed with oil of turpentine or with rectified spirit.

128. Much of the success of mounting objects in this mode
will depend upon their previous preparation. They should have
been previously well cleansed with water, from which they should
be transferred into proof-spirit, as this will dry out much more
readily than water. If they have any greasiness of surface or of
substance, this should be removed by maceration in ether or in
oil of turpentine; and maceration in turpentine is also very use-
ful in preparing the way for the penetration of the balsam into

228 MOUNTING OF OBJECTS.

substances which are unusually opaque. A long-continued mace-
ration in turpentine, moreover, assists in freeing the specimen
from air-bubbles; as it gradually creeps into spaces which are
otherwise unoccupied, and, when the object is transferred to the
balsam, the free miscibility of the two substances causes its place
to be partly taken by the latter. In mounting an ordinary ob-
ject, a sufficient quantity of liquid balsam should be laid in the
centre of the slide; this should be warmed, but not boiled; and
any air-bubbles which may make their appearance, should either
be caused to burst by touching them with the needle-point, or
should be drawn to one side. The object, if it can be held in
the fine-pointed forceps, should then be plunged into the drop
of balsam; and, if it be not completely covered, a little more
balsam should be applied over it, care being taken as before to
prevent over-heating, and to get rid of the bubbles as they rise.
If, on the other hand, the object be in a finely divided condition
(such, for example, as a collection of fossil Infusoria, of Sponge-
spicules, &c.), it is better to place it first in the position it is to
oceupy on the slide, then to place near it a drop of balsam, which
is to be warmed and freed from bubbles as before; the slide is
then to be so inclined, as to cause the balsam to run towards the
object, through and over which it will probably diffuse itself
without any air-bubbles; but if any should arise, they may be
broken by a heated needle-point. Ifthe object contain numerous
large air-spaces with free openings, and be one whose texture is
not injured by heat, as is the case with Foraminifera, the air
may often be got rid of by boiling it in the balsam ; for the heat,
causing the air to expand, drives out a large proportion of it;
this will be replaced, if it be allowed partly to cool, by the en-
trance of balsam; and then, by a second heating, the balsam
being boiled within the cavities, its vapor expels the remaining
air, and, on the condensation of the vapor, the liquid balsam runs
in and takes its place. For this method to succeed, however, it
is essential that the balsam be prevented from becoming hard
through boiling, by the addition of fresh liquid balsam from
time to time; and it will often be found that, should vacuities
remain which boiling does not remove, these contract or alto-
gether disappear if the slide be kept for a few days at a gentle
heat, the semi-fluid balsam being gradually forced into their
place by the pressure of the surrounding air. There are many
textures, however, which are extremely injured by a very slight
excess of heat, having a tendency to curl up and to become stiff
and brittle; and objects containing these are at once spoiled by
boiling them in balsam. In such cases, it is much better to
have recourse to the assistance of the air-pump; for by placing
the slide, with the object immersed in very liquid balsam, upon
a tin or copper vessel filled with hot water, under the receiver,
and then exhausting this, the air-bubbles will be drawn forth,
and, on the readmission of the air, the balsam is forced by its

MOUNTING OBJECTS IN CANADA BALSAM. 999

pressure into the place which they occupied. Some objects,
however, retain the air with such tenacity, as to require the re-
petition of the exhausting process two or three times: and in
this case it is preferable to use camphine or oil of turpentine in-
stead of balsam, on account of its greater fluidity, and to warm
even this to a temperature of about 100°. There are certain
cases, on the other hand, in which it is desirable to retain, instead
of expelling, the air contained within the cavities of the object.
Thus, if minute insects (such as Fleas) be displayed as transparent
objects to show the ramifications of the trachee, or if it be wished
that a section of Tooth or Bone should be so mounted in balsam
as to exhibit its canaliculi, the previous maceration in oil of tur-
pentine should be never employed, and the balsam employed
should be some which has been previously hardened ; this being
melted without the use of more heat than is necessary, the object
should be surrounded by it, and the cover put on as quickly as
possible; and the slide should then be laid upon a surface ot
stone or metal, the good conducting power of which causes the
balsam to cool rapidly, and thus diminishes its tendency to pene-
trate into the substance of the object.

129. When the object is already attached to the glass slide,
the mounting in Canada balsam is usually a matter of very little
difficulty. If it be a soft tissue which has been spread out and
allowed to dry upon the glass for the purpose of securing it in its
place, all that is necessary in the first instance is to dry it tho-
roughly, to shave or scrape it with a sharp knife if it should seem
too thick, and to moisten its surface with oil of turpentine if it
should not readily “take’’ the balsam. ‘The slide is then very
gently warmed, a sufficient quantity of balsam is spread over the
surface of the specimen, care being taken that it “takes” it in
every point, and the glass cover is put on. If the preparation
cover a large area, great care should be taken in letting down the
cover gradually from one side, so as to drive a wave of balsam
before it which shall sweep away air-bubbles; raising it a little,
and introducing a small quantity of fresh balsam, if any vacuity
present itself as it descends. The preferable mode, however, ot
mounting thin sections of hard bodies, will depend in great de-
gree upon the size of the section and the tenacity of its substance.
Where its area is great and its texture brittle, its removal from
the glass on which it has been ground down, to another slip,
cannot be accomplished, even by the most dexterous manage-
ment, without considerable risk of breaking it; and although, by
the friction of the glass upon the stone, the edges of this will
probably have been scratched or roughened, yet this is a dis-sight
about which the scientific Microscopist will care but little, as it
only affects the saleable value of such objects. Nothing more
will in this case be necessary, than to lay some liquid Canada
balsam on the surface of the section, to warm it gently, and then
to place on it a thin glass cover of suitable dimensions, gently

230 MOUNTING OF OBJECTS.

pressing this down wherever the balsam happens to be thickest,
and endeavoring to drive all air-bubbles before a wave of liquid,
until they are entirely expelled, or at any rate are driven beyond
the margin of the section. If this operation be not at once suc-
cessful,—either a few large air-bubbles, or a great number of
smaller ones, which cannot be got rid of by gentle pressure,
being visible between the surface of the section and the cover-
ing-glass,—it is better at once to remove the cover by gentle
warmth, and to repeat the operation with an additional supply of
balsam, rather than to attempt to drive out the bubbles by any
manipulation. Whatever treatment be adopted, special care
should always be taken not to apply so much heat as to melé the
hard balsam beneath the section,! or to boil the thin balsam above ;
in the former case, the loosening of the section from the glass is
very apt to be followed by the detachment of some portions of it
from the rest, whilst the glass cover is being pressed down ; and
in the latter, the production of bubbles very seriously embar-
rasses the operation. Ifthe heat should unfortunately be carried
so far as to boil the cement bencath the section, there will be little
chance, if its area be large, of getting rid of the bubbles thus
produced, without removing it altogether from the glass to which
it was attached, or, at any rate, without pushing it along the
glass, in such a way as to slide it away from the bubbles; in that
case, the part towards which it is moved should always be well
supplied with balsam, and the bubbles that remain should be
drawn away or broken with the needle-point; after which, the
section being slid hack to its original position, it is probable that
no bubbles may be found beneath it. In cases, however, in
which the appearance of the preparations is an object of much
consideration, and in which the tenacity of the substance and
the small size of the section prevent much risk of its breaking
in the transfer, it may be loosened from the glass to which it
was first attached, either by heat, or by soaking in ether. The
former being the simplest and readiest method, is the one most
commonly practised; the only difficulty lies in lifting off the
specimen without breaking it; and this may best be done, by
means of a camel-hair brush dipped in oil of turpentine. The
glass to which the section is to be transferred, should have a
large spot of liquid balsam laid in the proper place; the object
is to be laid on this, and its upper surface covered with the like
balsam ; and then, the thin glass cover being placed upon it, this
is to be gently pressed down in the manner already described.
If ether be had recourse to, the slide should be placed in a wide-
mouthed bottle of that liquid, which should then be corked or
stopped ; and after a time, the section will be found to be lying
detached in it, whence it may be taken up either by the forceps

‘Tt will often be found convenient to turn the slide with the face downwards, and
to apply a gentle heat directly to the thin glass cover, and to the balsam above the object,
instead of heating this through the glass slide and the balsam beneath it.

MOUNTING OBJECTS IN CANADA BALSAM. 231

or camel-hair brush. Such a transfer will often be found advan-
tageous, before the final completion of the reducing process; for
it will oceasionally happen that we find something in the struc-
ture of the specimen, which will be best displayed by rubbing it
down afresh on the side first attached to the glass; and, when a
number of small sections are being made at once (which it is
often very convenient to do, not only in the case already men-
tioned, § 108, but in many others), it not only saves time, but
insures the accurate flattening of the surface in grinding, to fix
several-upon the same slip, and to work them down together,
until the requisite thinness has been nearly attained, when they
must be transferred to separate slips, and finished one by one.
In either case, the reattachment must of course be made like
the original attachment, with balsam which has been first har-
dened (§ 109).

130. When the Balsam employed in mounting has remained
in the liquid condition here recommended, the glass cover will
not be secure from displacement until the balsam has become
harder. This change it will require a long time to undergo,
unless the aid of a gentle continuous warmth be afforded.
Nothing is more suitable for this purpose, than the warmth of
a chimney-piece immediately above the fire-place ; as it is quite
sufficient to produce the effect in the course of a few days, whilst
there is no danger of its becoming excessive; but in default of
this convenience, an oven carefully regulated, or (still better) a
water-bath, may be employed. Whether either of these means
be adopted, or the slides be put aside for the balsam to be
hardened by time, they should always be laid in the horizontal
position, that their covers may not be caused by gravitation to
slip down from their places. It may be better, before submitting
the slides to this hardening process, to scrape from their surface
any superfluous balsam that does not immediately surround the
glass cover; but the knife should never be carried so near to the
edge of this, as to run any risk of displacing it; and it is much
better to defer the final cleaning of the slide, until the attach-
ment of the cover has become firm. The remaining balsam may
then be scraped away with a knife or small chisel, the imple-
ment being warmed if the balsam be very stiff; the slide should
then be rubbed with a rag dipped in oil of turpentine, until
every perceptible soil of balsam 1s removed, especial care being
taken to cleanse the surface and edges of the glass cover; and as
this will itself leave a certain resinous film, it is better to give
the slide a final cleansing with Alcohol. If its surface should
have been considerably smeared with balsam, it is very con-
venient, after scraping away all that can be removed in that
manner, to scrub it with a tooth-brush or nail-brush, first letting
fall on it a few drops of turpentine or spirit of wine; and there
is less risk of displacing the glass cover in this mode, than in
rubbing it in any other way. The menstrua which serve thus to

232 MOUNTING OF OBJECTS.

cleanse the slides, of course answer equally well for cleansing
the hands. The most ready. solvent for balsam is Ether; but
the ordinary use of this being interdicted by its costliness, and
by the quickness with which it is dissipated by evaporation,
Alcohol or Oil of Turpentine may be used in its stead.

131. Preservative Fluids.—Objects which would lose their cha-
racters in drying, can of course only be preserved in anything
like their original condition, by mounting in fluid; and the
choice of the fluid to be employed in each case will depend upon
the character of the object, and the purpose aimed at in its pre-
servation. As specific directions will be given hereafter in re-
gard to most of the principal classes of Microscopic preparations,
little more will be required in this place, than an enumeration
of the preservative fluids, with a notice of their respective quali-
ties. For very minute and delicate Vegetable objects, especi-
ally those belonging to the orders Desmidiacez and Diatomacee,
nothing seems to produce less alteration in the disposition ot
the endochrome, or serves better to preserve their color, than
Distilled Water ; provided that, by the complete exclusion of air,
the vital processes and decomposing changes can be alike sus-
pended. This method of mounting, however, is liable to the ob-
jection that confervoid growths sometimes make their appear-
ance in the preparation; and it is preferable to make some
addition to the water, which shall be unfavorable to their de-
velopment. Saturation with camphor, or shaking up with a few
drops of ereasote, will sometimes answer; but if the preservation
of color be not an object, nothing is better than the addition ot
about a tenth part of alcohol; and where the loss of color would
be objectionable, the solution of a grain of bay-salt and a grain
of alum in an ounce of water will give it the requisite qualities.
For larger preparations of Algs, &c., what is called Thivaites’s
Fluid may be employed; this is prepared by adding to one
part of rectified spirit as many drops of creasote as will saturate
it, and then gradually mixing up with it in a mortar some
prepared chalk with 16 parts of water; an equal quantity of
water saturated with camphor is then to be added, and the mix-
ture, after standing for a few days, is to be carefully filtered. A
liquid of this kind also serves well for the preservation of many
animal preparations; but it is said by Dr. Beale to become tur-
bid when thus employed in large quantity ; and he recommends
the following modification. Mix 8 drachms of creasote with 6
ounces of wood naphtha, and add in a mortar as much prepared
chalk as may be necessary to form a smooth thick paste; water
must be gradually added to the extent of 64 ounces, a few lumps
of camphor thrown in, and the mixture allowed to stand for two or
three weeks in a lightly covered vessel, with occasional stirring ;
after which it should be filtered, and preserved in well-stopped
bottles. Of late years, Glycerine has been much employed as a pre-
servative fluid; it allows the colors of vegetable substances to be

PRESERVATIVE FLUIDS. 233
retained, but, unless much diluted, it alters the disposition of the
endochrome; and confervoid growths are apt to make their ap-
pearance in it. The best proportion seems to be one part of
glycerine to two parts of camphor-water. The preparation
known as Deane’s Gelatine is one of the most convenient media
for preserving the larger forms of Confervee and other Micro-
scopic Algee, as well as sections of such as are still more bulky.
This is prepared by soaking 1 oz. of gelatine in 4 oz. of water
until the gelatine is quite soft, and then adding 5 oz. of honey
previously raised to boiling heat in another vessel; the whole is
then to be made boiling hot, and when it has somewhat cooled,
but is still perfectly fluid, 6 drops of creasote and } oz. of spirit
of wine, previously mixed together, are to be added, and the
whole is to be filtered through fine flannel. This composition,
when cold, forms a very stiff jelly ; but it becomes perfectly fluid
on the application of a very slight warmth, and may then be used
like any other preservative liquid, care being taken, however,
that the slide and the glass cover are themselves gently warmed
before it comes into contact with them. A mixture of gelatine
and glycerine has been employed for the same purpose. Some
Vegetable Anatomists make great use of a solution of Chloride
of Calcium (muriate of lime) in three parts of water; its chief ad-
vantage being, that owing to its deliquescent property, it does
not dry up, even when the cell is not perfectly closedin. It has,
however, the disadvantages of not preserving colors, and of al-
tering the disposition of the cell-contents by its endosmotic
power. For the preservation of microscopic preparations of
Animal tissues, a mixture of one part of Alcohol and five of
water will generally answer very well, save in regard to the re-
moval of their colors. Where the preservation of these is aimed
at, the best medium will usually be Goadby’s Solution, which is
made by dissolving 4 oz. of bay salt, 2 oz. of alum, and 4 grains
of corrosive sublimate, in 4 pints of boiling water; this should
be carefully filtered before it is used; and for all delicate pre-
parations it may be diluted with an equal bulk, or even with
twice its bull of water. This solution must not be used where
any calcareous texture, such as shell or bone, forms part of the
preparation; and one of Mr. Goadby’s other solutions (8 oz. of
bay salt and 2 grs. of corrosive sublimate, to a quart of water,—
or, in cases where the coagulating action of corrosive sublimate
on albuminous matters would be an objection, the substitution
of 20 grains of arsenious acid) may be used in its stead; or
Thwaites’s fluid, or Dr. Beale’s modification of it, or Deane’s
Gelatine may be tried. It is often quite impossible to predicate
beforehand what preservative fluid will answer best for a particu-
lar kind of preparation; and it is consequently desirable, where
there is no lack of material, always to mount the same object in
two or three different ways, marking on each slide the method

234 MOUNTING OF OBJECTS.

employed, and comparing the specimens from time to time, so
as to judge how each is affected.

132. Of Mounting Objects in Fluid.—As a general rule, it is
desirable that objects which are to be mounted in fluid, should
be soaked in the particular fluid to be employed, for some little
time before mounting; since, if this precaution be not taken,
air-bubbles are very apt to present themselves. It is sometimes
necessary, in order to secure the displacement of air contained
in the specimen, to employ the air-pump in the mode already
directed (§ 128); but it will sometimes be found sufficient to im-
merse the specimen for a few minutes in alcohol (provided that
this does not do any detriment to its tissues), which will often
penetrate where water will not make its way; and when the
spirit has driven out the air, the specimen may be removed back
to water, which will gradually displace the spirit. When Deane’s
Gelatine is used, however, all that can be done, will be to drain
the object of its superfluous water before applying the liquefied
medium ; but as air-bubbles are extremely apt to arise, they must
be removed by means of the air-pump, the gelatine being kept
in a liquid state by the use of a vessel of hot water, as in the
case of Canada balsam. In dealing with the small quantities of
fluid required in mounting microscopic objects, it is essential for
the operator to be provided with the means of transferring very
small quantities from the vessel containing it, to the slide, as
well as of taking up from the slide what may be lying superfluous
uponit. The straight and curved-pointed “dipping-tubes”’ (Fig.
ol, A, B) may be made to answer this purpose; but it is much
better that tubes for this purpose be furnished with a bulb, like
that of the Chemist’s “ pipette,” and that their orifices be drawn
toa fine point. The fluid is drawn into the tubes by suction,
and expelled by the pressure of the breath; the curved-pointed
tube will generally be the best for introducing fluid beneath the
glass cover, and the straight-pointed for simply filling cells or
for taking up superfluous fluid. The Author has of late found
very great convenience in the use of a small glass syringe, the
orifice of which is slightly curved and drawn to a fine capillary
point; for as the syringe works independently of the mouth, its
orifice may be applied in any way that may be found convenient;
and when the mouth is freed from the efforts of suction and
ejection, the eyes can be better employed in watching the opera-
tion. Besides the pipettes and the syringe, some blotting-paper,
of the most bibulous kind that can be procured, will be found
very useful.

133. There are certain objects of extreme thinness, which re-
quire no other provision for mounting them in fluid, than an
ordinary glass slide, a thin glass cover, and some gold-size or
asphalte (§ 120). The object having been laid in its place, and
a drop of the fluid laid upon it (care being taken that no air-
space remains beneath the under side of the object and the sur-

MOUNTING OBJECTS IN FLUID. 235

face of the slide), the glass cover is then to be laid upon it, one
side being first brought into contact with the slide, and the other
being gradually lowered, in such a manner that the air shall be
all displaced before the fluid. If any air-bubbles remain in the
central part of the space between the cover and the slide, the
former must be raised again, and more fluid should be introduced ;
but if the bubbles be near the edge, a slight pressure on that
part of the cover will often suffice to expel them, or the cover
may be a little shifted so as to bring them to its edge. There
are some objects, however, whose parts are liable to be displaced
by the slightest shifting of this kind; and it is more easy to avoid
making air-bubbles, by watching the extension of the fluid as the
cover is lowered, and by introducing an additional supply when
and where it may be needed, than it is to get rid of them after-
wards without injury to the object. When this end has been
satisfactorily accomplished, all that is needed is first to remove
all superfluous fluid from the surface of the slide, and from around
the edge of the cover, with a piece of blotting-paper, taking care
not to draw away any of the fluid from beneath the cover, or (if
any have been removed accidentally) to replace what may be
deficient; and then to make a circle of asphalte or gold-size
around the cover, taking care that it “‘ wets” its edges, and ad-
vances a little way upon its upper surface. When this first coat
is dry, another should be applied, particular care being taken
that the cement shall fill the angular furrow at the margin of the
cover. In laying on the second coat, it will be convenient, if the
cover be round, to make use of the whirling-table (Fig. 63); and
if the slide be so carefully laid upon it, that the glass cover is
exactly concentric with its axis, the whirling-table may be used
even for the first application of the varnish; a slight error in this
respect, however, may occasion the displacement of the cover.
By far the greater number of preparations which are to be pre-
served in liquid, however, should be mounted in a “Cell” of
some kind, which forms a well of suitable depth, wherein the
preservative liquid may be retained. This is absolutely necessary
in the ease of all objects, whose thickness is such as to prevent
the glass cover from coming into close approximation with the
slide; and it is descrable, wherever that approximation is not
such as to.cause the cover to be drawn to the glass slide by ca-
pillary attraction, or wherever the cover is sensibly kept apart
from the slide by the thickness of any portion of the object.
Hence itis only in the case of objects of the most extreme tenuity,
that the “cell” can be advantageously dispensed with ;—the dan-
ger of not employing it, in many cases in which there is no diffi-
culty in mounting the object without it, being that after a time
the cement is apt to run in beneath the cover, which process is
pretty sure to continue, when it may have once commenced.
134. Cement-Cells.—When the Cells are required for mounting
very thin objects, they may be advantageously made of varnish

236 MOUNTING OF OBJECTS.

only, by the use of the ingenious little instrument (Fig. 63) con-
trived by Mr. Shadbolt. This consists of a small slab of ma-
hogany, into one end of
which is fixed a pivot,
whereon a circular turn-
table of brass, about three
inches in diameter, is
made to rotate easily, a
rapid motion being given
Shadbolt’s Turn-table for making Cement-Cells. to it by the application
of the fore-finger to the
milled head seen beneath. The glass slide being laid upon the
turn-table, in such a manner that its two edges shall be equidis-
tant from the centre (a guide to which is afforded by a circle of
an inch in diameter, traced upon the brass), and being held by
the springs with which it is furnished, a camel-hair pencil dipped
in the varnish to be used (Brunswick black or Asphalte is the
best) is held in the right hand, so that its point comes into con-
tact with the glass, a little within the guiding circle just named.
The turn-table being then put into rotation with the left hand,
a ring of varnish of suitable breadth is made upon the glass;
and if the slide be set aside in a horizontal position, this ring
will be found, when dry, to have lost the little inequalities it may
have at first presented, and to present a very level surface. Ifa
greater thickness be desired than a single application will con-
veniently make, a second layer may be laid on.after the first is
dry. It is convenient to prepare a number of these cells at once,
since, when “the hand is in,” they will be made more dexter-
ously than when the operation is performed only once; and it
will be advantageous to subject them to the warmth of a slightly
heated oven, whereby the flattening of their surface will be more
completely assured. The Microscopist will find it a matter ot
great convenience to have a stock of these cells always by him,
ready prepared for use.

135. Thin Glass Cells —For the reception of objects too thick
for varnish cells, but not thicker than ordinary thin glass, it is
advantageous to construct cells of glass; and these may be made
in one of two ways, either by grinding down the cross sections
of glass tubes (§ 137) until they have been reduced to the desired
thinness, or by perforating a plate of thin glass with an aperture
of the desired size ; and then cementing the ring or the plate to
the glass slide with marine glue. The former plan is hable to
the objection, that in reducing the glass rings to the desired
thinness, they are extremely liable to crack or break, and that
their attainable forms are limited. The latter will generally
answer very well, if care be taken in the selection of a flat piece
of thin glass; and the perforation, if due precaution be em-
ployed, may be made of any size or form that may be desired.
For making round cells, the perforated pieces that sometimes re-

PLATE GLASS CELLS. 237

main entire after the cutting of disks (§ 117) may be employed,
the disks often falling out of themselves when the glass is laid
aside for a few days; and thus the same piece of thin glass may
afford a plate, which, when cemented to a glass slide forms a
cell, and a disk suitable as the cover to a cell of somewhat
smaller size. There is great danger, however, of the cracking of
the surrounding glass, especially when the disk is of large size ;
and it will generally be found a saving of trouble, to employ the
method recommended by Dr. L. Beale. This consists in attach-
ing a piece of thin glass to one of the glass rings of which the
deeper cells are made G 187), of any form that may be desired,
by means of marine glue, first laid upon the latter, and melted
upon the hot plate; when the glue is quite cold, the point of a
round or semicircular file is sharply thrust through the centre of
the thin glass, which is carefully filed to the size of the interior
of the ring; and the ring being then heated a second time on the
hot plate, the thin glass plate may be readily detached from it,
and at once cemented upon the glass slide. The success of this
simple process depends upon the very firm and intimate ad-
hesion of the thin glass to the ring, which prevents any crack
from running into the part of the thin glass that is attached to
it, however roughly the file may be used. By having many of
the rings on the hot plate at once, and operating with them in
turn, a great number of cells can be made in a short time; and
such large thin cells may be made in this mode, as could scarcely
be fabricated (on account of the extreme brittleness of this glass)
by any other. A press, consisting of two plates of brass screwed
together, holding the thin glass between them, has been devised
by Mr. C. Brooke for the same purpose; but the foregoing
method has the advantage, not only of requiring no special ap-
paratus, but also of enabling the form and size of the perforation
to be readily varied. After the thin glass has been cemented to
the slide, it is desirable to roughen its upper surface, by rubbing
it upon a leaden or pewter plate (§ 108) with fine emery; since
the gold-size or other varnish adheres much more firmly to
a “ground” than to a polished surface. Although the thin
glass cell requires much more trouble in its preparation than the
cement cell, yet it is decidedly to be preferred for any very
choice objects; since, if any air should find admission, it 1s more
readily detected; and the remounting of the object may be
accomplished in the same cell, with very little disturbance of its
position.

136. Plate Glass and Shallow Cells—For mounting objects of
somewhat greater thickness than can be included within thin glass
cells, shallow cells may be made by drilling apertures of the de-
sired size in pieces of plate-glass of the requisite thickness, and
by attaching these with marine glue to glass slides (Fig. 64).
Such holes may be made not merely circular (A) but oval (c);
and a very elongated perforation may be made, by drilling two

238 MOUNTING OF OBJECTS.

holes at the required distance and then connecting them by cut-
ting out the intermediate space(s). These operations, however,
can scarcely be performed by any but regular glass-cutters, and,
being troublesome, are expensive; hence the plate-glass cells
have been generally superseded, either by tube-cells (§ 137) or by
built-up cells. Although the
former may be reduced to
any degree of shallowness
that may be desired, and are
made of most of the sizes and
forms that can be ordinarily
needed, yet for extra sizes or
peculiar forms, shallow cells
may be easily built up after
the following very simple and
effective method. A piece of
plate glass, ofa thickness that
shall give the desired depth
to the cell, is to be cut to the
dimensions of its outside
p Wall; and a strip is then to
. be cut off with the diamond
' from each of its edges, of such
breadth as shall leave the in-
terior piece equal in its dimensions to the cavity of the cell, that
is desired. This piece being rejected, the four strips are then to
be cemented upon the glass slide in their original position, so
that the diamond cuts shall fit together with the most exact pre-
cision; and the upper surface is then to be ground flat with
emery upon the pewter plate, and left rough as before. This
plan answers admirably for constructing such large shallow cells
as are required for the mounting of Zoophytes and similar ob-
jects.
; Having had occasion, during the last few months, to mount a
large number of objects in shallow cells, the Author has adopted
the recommendation of a friend, to make use of cells which are
sunk by grinding out a concave in the thickness of a glass plate.
These, until recently, were costly; but they are now made in
large quantities, and their price has been so much reduced, that
they can be obtained more cheaply than any other kind. For
objects whose shape adapts them to the form and depth of the
concavity, these cells will be found peculiarly advantageous ; since
they do not hold air-bubbles so tenaciously as do those with per-
pendicular walls; and there is no cemented plate or ring to be
loosened from its attachment, either by a sudden jar or by the
lapse of time. For transparent objects, however, they are less
suitable (unless manufactured with more care than is usually given
to them) than they are for opaque; since the concave bottom 1s
seldom so highly polished, as to be free from scratches and rough-

Fig. 64,

Plate Glass Cells.

TUBE-CELLS. 239

nesses, which greatly interfere with the appearance of the picture.
Cells of this kind may be obtained, from Messrs.: Jackson, Ox-
ford Street, either of round or oval form, and not only ground
out of slides of the usual size (3 in. by 1) and thickness, but also
hollowed in pieces of plate-glass of larger dimensions.

137. Deep and Built-up Cells——The deep cells which are re-
quired for mounting Injections and other microscopic prepara-
tions of considerable size and thickness, may be made by drilling
through a piece of thick plate glass (Fig. 64, p); but for the reason
already given, the drilled cells are now seldom used, their place
having been taken, either by tube-cells, or by the deep built-up
cells to be presently described. The tube-cells are made by cut-
ting transverse sections of thick-walled glass tubes of the required
size, grinding the surfaces of these rings to the desired thinness,
and then cementing them to the glass slides with marine glue.
Not only may round cells (Fig. 65, a, B), of any diameter and any
depth that the Microscopist can possibly require, be made by this
simple method, but oval,
square-shaped, or oblong
cells (c, D) are now made, of
the forms and sizes that he
is most likely to want, by
flattening the round glass-
tube whilst hot, or by blow-
ing it within amould. The
facility with which such cells
may be made, and the se-
curity they afford, have
caused the deep cells built
up of separate strips of glass
(Fig. 66) to be comparatively
little employed, except in
cases where some very un-
usual size or shape (A) may
be required, or where it is ?
necessary that not merely
the top and bottom, but also nr Seren ae
the sides of the object, should sei a edie
be clearly seen (B). The perfect construction of these requires
a nicety of workmanship which few amateurs possess, and the
expenditure of more time than Microscopists generally have to
spare ; and as it is consequently preferable to obtain them ready
made, directions for making them need not here be given. A
new plan of making deep cells, however, has been lately intro-
duced by Dr. L. Beale; which, though it does not give them
side walls possessing the same flatness with those of the built-up
cells, adapts them to serve most of the purposes for which these
are required, and makes them more secure against leakage;
whilst it has the advantage of being so easy and simple, that

Fia. 65.

240 MOUNTING OF OBJECTS.

any one may put it into practice. A long strip of plate glass is
to be taken, whose breadth is equal to the desired depth of the
cell, and whose length must be
Fie. 66. equal to the sum of that of all
aa its sides. This strip is to be
carefully bent to a right angle
in the blow-pipe flame, at three
points previously indicated by
marks so placed as to show
where the angles should fall;
and the two ends, which will
thus be brought into contact
at right angles, are to be fused
Built-up Cells. together. Thus a large square
well, slightly rounded at the
angles, will be formed; and this, being very brittle, should be
allowed to cool very gradually, or, still better, should be annealed
in an oven. It must then be ground quite true on its upper and
lower edges, either on the lead plate with emery, or on a flat
stone with fine sand; and it may then be cemented to a glass
slide in the usual way.

138. Mounting Oljects in Cells—In mounting an object in a
cell, the first attention will of course be given to the cleanness
of the interior of the cell, and of the glass cover which is to be
placed on it; this having been secured, the cell is to be filled
with fluid by the pipette or syringe ; and any minute air-bubbles
which may be seen adhering to its bottom or sides, must be
removed by the needle: the object, previously soaked in fluid
resembling that with which the cell is filled, is then to be placed’
in the cell, and should be carefully examined for air-bubbles on
all sides, and also by looking up from below. When every pre-
caution has been taken to free it from these troublesome in-
truders, the cover may be placed on the cell, one side being first
brought down upon its edge and then the other; and if the cell
have been previously brimming over with fluid (as it ought to
be) it is not likely that any air-space will remain. If, however,
any bubbles should present themselves beneath the cover, the
slide should be inclined, so as to cause them to rise towards the
highest part of its circumference, and the cover slipped away
from that part, so as to admit of the introduction of a little ad-
ditional fluid by the pipette or syringe; and when this has
taken the place of the air-bubbles, the cover may be slipped
back into its place.t All superfluous fluid is then to be takeu

' Mr. Quekett and some other practised manipulators recommend that thé edges of
the cell and that of the disk of glass be smeared with the gold-size or other varnish em-
ployed, before the cell is filled with fluid; but the Author has found this practice ob-
jectionable, for two reasons,—first, because it prevents the cover from being slipped to
one side (which is often desirable), without its being soiled by the varnish,—and se-
cond, because when the ede of the cell has been thus mace to “take” the varnish, that

which is afterwards applied for the closure of the cell is more likely to run in, than if
the whole of the surface covered by the glass is moistened with water.

MOUNTING OBJECTS IN CELLS. 241

up with blotting-paper; and particular care should be taken
thoroughly to dry the surface of the cell and the edge of the
cover, since the varnish will not hold to them if they be in the
least damp with water. Care must also be taken, however, that
the fluid be not drawn away from between the cover and the
edge of the cell on which it rests; since any deficiency here is
sure to be filled by varnish, the running in of which is particu-
larly objectionable. These minutie having been attended to,
the closure of the cell may be at once effected, by carrying athin
layer of gold-size or asphalte around and upon the edge of the
glass cover, taking care that it touches every point of it, and fills.
the angular channel which is left around its margin. If the wall’
of the cell be very thin, it will be advantageous to include it in
the ring of varnish; so that this shall hold down the cover, not
only on the cell, but on the slide beneath. The Author has
found it advantageous, however, to delay closing the cell for
some little time after the superfluous fluid has been drawn off;
for as soon as evaporation beneath the edges of the cover begins
to diminish the quantity of fluid in the cell, air-bubbles often
begin to make their appearance, which were previously hidden
in the recesses of the object; and in the course of half an hour,
a considerable number are often collected. The cover should
then be slipped aside, fresh fluid be introduced, the air-bubbles
removed, and the cover put on again ; and this operation should
be repeated, until it fails to draw forth any more air-bubbles.
It will, of course, be observed, that, if the evaporation of fluid
should proceed far, air-bubbles will enter beneath the cover; but
these will show themselves on the surface of the fluid; whereas
those which arise from the object itself, are found in the deeper
parts of the cell. Much time may be saved, however, and the
freedom of the preparation from air-bubbles may be most effec-
tually secured, by placing the cell, after it has been filled in the
first instance, in the vacuum of an air-pump; and if several ob-
jects are being mounted at once, they may all be subjected to the
exhausting process at the samé time. The application of the
varnish should be repeated after the lapse of a few hours, and
may be again renewed with advantage several times in the
course of a week or two; care being taken that each layer
covers the edges, as well as the whole surface, of that which pre-
ceded it.

139. The presence of air-bubbles, in any preparation mounted
in fluid, is to be particularly avoided, not merely on account of
its interference with the view of the object, but also because,
when air-spaces, however small, once exist, they are almost cer-
tain to increase, until at last they take the place of the entire
fluid, and the object remains‘dry. Even with the most ex-
perienced manipulators, however, this misfortune not unfre-
quently occurs; being sometimes due to the obstinate entangle-
ment of air-bubblesin the object, when it was originally mounted ;

16

242 MOUNTING OF OBJECTS.

and sometimes to the perviousness of some part of the cement,
which has allowed a portion of the contained fluid to escape, and
air to find admission. In either case, so soon as an air-bubble
1g seen in such a preparation, the attempt should be made to
prevent its increase, by laying on an additional coat of varnish;
but if this should not be successful, the cover should be taken
off, and the specimen remounted, so soon as the fluid hag
escaped to such a degree as to leave any considerable portion of
it uncovered.

140. Importance of Cleanliness.—The success of the result of
any of the foregoing operations is greatly detracted from, if, in
consequence of the adhesion of foreign substances to the glasses
whereon the objects are mounted, or to the implements used in
the manipulations, any extraneous particles are brought into
view with the object itself. Some such will occasionally present
themselves, even under careful management; especially fibres
of silk, wool, cotton, or linen, from the handkerchiefs, &c., with
which the glass slides may have been wiped, and grains of starch,
which often remain obstinately adherent to the thin glass covers
kept in it. But a careless and uncleanly manipulator will allow
his objects to contract many other impurities than these ; and espe-
cially to be contaminated by particles of dust floating through
the air, the access of which may be readily prevented by proper
precautions. It is desirable to have at hand a well-closed cup-
board furnished with shelves, or a cabinet of well-fitted drawers,
or a number of bell-glasses upon a flat table, for the purpose of
securing our glasses, objects, &c., from this contamination, in
the intervals of the work of preparation; and the more readily
accessible these receptacles are, the more use will the Microsco-
pist be likely to make of them. Great care ought, of course, to
be taken, that the liquids employed for mounting should be
freed, by effectual filtration, from all floating particles; and both
these and the Canada balsam should be kept in well-closed
bottles.

141. Labelling and Preserving of Objects—Whenever the
mounting of an object has been completed, its name ought to
be at once marked on it, and the slide should be put away in its
appropriate place. Some inscribe the name on the glass itself,
with a writing diamond; whilst others prefer to gum a label! on
the slide; and others, again, cover one or both surfaces of the
slide with colored paper, and attach the label to it. In the case
of objects mounted dry or in balsam, the latter method has the
advantage of rendering the glass cover more secure from dis-
placement by a slight blow or “jar,” when the varnish or balsam
may have become brittle by the lapse of years. Instead, how-
ever, of attaching the white label on which the name of the ob-
ject is written, outside the colored paper with which the slide is

1 Very neat gummed labels, of various sizes and patterns suitable to the wants of the
Microscopist, are sold by the “ Drapers’ Stationers” in the City.

COLLECTION OF OBJECTS. 243

covered, it is better to attach the label to the glass, and to punch
a hole out of the colored paper, sufficiently large to show the
name, in the part corresponding to it; in this manner the label
is prevented from falling off, which it frequently does when
attached to the glass without protection, or to the outside of the
paper cover. Wien objects are mounted in fluid, either with or
without cells, paper coverings to the slides had better be dis-
pensed with; and besides the name of the object, it is desirable
to inscribe on the glass that of the fluid in which it is mounted.
For the preservation of objects, the pasteboard boxes now made
at a very reasonable cost, with wooden racks, to contain 6, 12,
or 24 slides, will be found extremely useful. In these, however,
the slides must always stand upon their edges; a position which,
besides interfering with that ready view of them which is re-
quired for the immediate selection of any particular specimen, is
unfavorable to the continued soundness of preparations mounted
in fluid. Although such boxes are most useful, indeed almost
indispensable, to the Microscopist, for holding slides which he
desires (for whatever purpose) to keep for a while constantly at
hand, yet his regularly classified series is much more conve-
niently stored in a Cabinet containing numerous very shallow
drawers, in which they lie flat and exposed to view. Such
cabinets are now prepared for sale under the direction of our
principal Opticians, with all the improvements that experience
has suggested. In order to prevent the warping of the thin
wood of which,the bottoms of the drawers are usually made,
whereby their sliding action is obstructed, it has been found ad-
vantageous to substitute strained canvas or papier mache. Again,
in order to antagonize the disposition of the slides to slip one
over another in the opening or shutting of the drawers, it has
been found preferable to arrange them in such a manner, that
they lie with their ends (instead of their long sides) towards the
front of the drawer, and to interpose a cross-strip of wood, lying
parallel to the front of the drawer, between each row. It is very
convenient, moreover, for the front of the drawer to be furnished
with a little tablet of porcelain, on which the name of the group
of objects it may contain can be written in pencil, so as to be
readily rubbed out; or a small frame may be attached to it, into
which a slip of card may be inserted for the same purpose.

«
Section 3. CoLLECTION oF OBJECTS.

142. A large proportion of the objects with which the Micro-
scopist is concerned, are derived from the minute parts of those
larger organisms, whether Vegetable or Animal, the collection
of which does not require any other methods than those pursued
by the ordinary Naturalist. With regard to such, therefore, no
special directions are required. But there are several most in-
teresting and important groups, both of Plants and Animals,

244 COLLECTION OF OBJECTS.

which are themselves, on account of their minuteness, essentially
microscopic; and the collection of these requires peculiar methodg
and implements, which are, however, very simple,—the chief
element of success lying in the knowledge where to look, and
what to look for. In the present place, general directions only
will be given; the particular details relating to the several groups,
being reserved for the account to be hereafter given of each. |
148. All the Microscopic organisms in question, being aquatic,
must be sought for in pools, ditches, streams, or other collections
of water ; through which some of them freely move, whilst others
attach themselves to the stems and leaves of aquatic plants, or
even to pieces of stick or decaying leaves, &c., that may be float-
ing on the surface or submerged beneath it, while others, again,
are to be sought for in the-muddy sediments at the bottom. Of
those which have the power of free motion, some keep near the
surface, whilst others swim in the deeper waters; but the situa-
tion of many depends entirely upon the light, since they rise to
the surface in sunshine, and subside again afterwards. The Col-
lector will therefore require a means of obtaining samples of
water at different depths, and of drawing to himself portions of
the larger bodies to which the microscopic organisms may be
attached. For these purposes, nothing is so convenient as a rod
about five feet long, which may be divided into two pieces jointed
together; and the farther extremity of this rod should be pierced
with a hole, passing for some distance into its length.’ Into this
hole, as a socket, may be fitted either of the three implements
which the Collector may happen to require. If he desires to
take up samples of the water, he will need a wide-mouthed bottle,
containing about 2 0z. This may be attached to the extremity
of the rod, by simply passing round its neck a strap of thin whale-
bone or sheet gutta percha, the two ends of which are to be
brought together and inserted into the socket, in which they may
be secured by a plug of soft wood or cork. The bottle being
held sideways with its mouth partly below the water, the surface
may be skimmed; or, if it be desired to bring up a sample of the
liquid from below, or to draw into the bottle any bodies that may
be loosely attached to the submerged plants, the bottle is to be
plunged into the water with its mouth downwards, carried into
the situation in which it is desired that it should be filled, and
then suddenly turned with its mouth upwards. If, again, the
organisms which it may be desired to collect, are of sufficient
size to be strained out of the water by a piece of fine muslin, a
ring-net should be fitted into the socket of the rod. This may
be made by sewing the muslin bag to a ring of stout wire, fur-
nished with a projecting stem which may be inserted by means
of a cork into the socket of the rod. But it is more convenient
1 Cheap fishing-rods are now sold at the toy shops, which answer this purpose ex-

tremely well, the last or slenderest joint being laid on one side; its socket in the last
joint but one, being well adapted to receive the tittings above described.

COLLECTION OF OBJECTS. 245

that the muslin should be made removable; and this may be pro-
vided for (as suggested in the “ Micrographic Dictionary,” Intro-
duction, p. xxiv) by the substitution of a wooden ring, grooved
on its outside, for the wire ring; the muslin being strained upon
it by a ring of vulcanized India rubber, which lies in the groove,
and which may be readily slipped off and on, so as to allow a
fresh piece of muslin to be put in the place of that which has
been last used. For bringing up portions of larger Plants, either
for the sake of examining their own structure, or for obtaining
the growths which may be parasitic upon them, a cutting-hook,
shaped somewhat like a sickle, may be fitted into the socket of
the rod.

144. The Collector should also be furnished with a number of
bottles, into which he may transfer the samples thus obtained.
These it will be convenient to have of two kinds; one set wide-
mouthed, and capable of being closely corked, for minute Plants ;
the other set with narrower mouths, having short pieces of tube
passed through the corks, for the purpose of containing Animal-
cules without depriving them of air. The former kind, however,
may be safely employed for Animalcules, if they be not above’
two-thirds filled (so as to leave an adequate air-space), and be not
kept long closed. Such bottles should be fitted into cases, in
which several may be carried at once without risk of breakage.
Whilst engaged in the search for Microscopic objects, it is desi-
rable for the collector to possess a means of at once recognizing
the forms which he may gather, where this is possible, in order
that he may decide whether the “ gathering”’ is, or is not, worth
preserving; for this purpose either a powerful “‘ Coddington” or
‘“‘Stanhope”’ lens (§ 19), or a Gairdner’s Simple Microscope (§ 28),
will be found most useful, according to the class of objects of
which the collector is in search. The first will answer very well
for Zoophytes and the larger Diatomacer; but the second or
third will be needed for Desmidiacex, the smaller Diatomacez,
and Animalcules.

1 The bottles in which smelling-salts are now commonly sold, having the corks fitted
into disks of turned wood, are very convenient, both in size and shape, for the purposes
of the Microscopist ; cases containing 3, 4, 6, or 8 such bottles, are made by Mr. Ferguson,
of Giltspur Street. The wide-mouthed bottles with screw caps, made by the York Glass
Company, are also extremely convenient.

CHAPTER VI.
MICROSCOPIC FORMS OF VEGETABLE LIFE.—PROTOPHYTES.

145. In commencing our survey of these wonders and beav-
ties of Life and Organization, which are revealed to us by the
assistance of the Microscope, it seems on every account the most
appropriate to turn our attention in the first instance to the
Vegetable Kingdom; and to begin with those humblest mem-
bers of that kingdom, whose form and structure, and whose
very existence, in many cases, are only known to us through its
use. For those who desire to make themselves familiar with
microscopic appearances, and to acquire dexterity in microscopic
manipulation, cannot do better than educate themselves by the
study of those comparatively simple forms of organization, which
the Vegetable fabric presents; since a facility in minute dissec-
tion and in microscopic analysis may be thus acquired, which
will save much expenditure of time and labor, that might be
unprofitably applied, without such apprenticeship, to the attempt
to unravel the complexities of Animal organization. But fur-
ther, the scientific Histologist (p. 49) looks to the careful study
of the structure of the simplest forms of Vegetation, as furnish-
ing the key (so to speak) that opens the right entrance to the
study of the elementary Organization, not merely of the higher
Plants, but of the highest Animals. And in like manner, the
scientific Physiologist looks to the complete knowledge of their
life history, as furnishing the surest basis for those general no-
tions of the nature of Vital Action, which the advance of science
has shown to be really well founded, only when they prove
equally applicable to both kingdoms. But further, a peculiar
interest attaches itself at the present time, to everything which
throws light upon the debated question of the boundary between
the two kingdoms; a question which is not less keenly debated
among Naturalists, than that of many a disputed frontier has
been between adjacent Nations. For many parts of this border
country have been taken and retaken several times; their inha-
bitants (so to speak) having first been considered, on account of
their general appearance, to belong to the Vegetable Kingdom,—
then, in consequence of some movements being observed in them,
being claimed by the Zoologists,—then, on the ground of their

DISTINCTION BETWEEN PLANTS AND ANIMALS, 247

evidently plant-like mode of growth, being transferred back to
the Botanical side,—then, owing to the supposed detection of
some new feature in their structure or physiology, being again
claimed as members of the Animal Kingdom,—and lastly, on
the discovery of a fallacy in these arguments, being once more
laid hold of by the Botanist, with whom, for the most part, they
now remain. For the attention which has been given of late
years to the study of the humblest forms of Vegetation, has led
to the knowledge of so many phenomena, among what must be
undoubtedly regarded as Plants, which would formerly have been
considered unquestionable marks of animality, that the discovery
of the like phenomena among the doubtful beings in question,
so far from being any evidence of their animality, really affords
a probability of the opposite kind.

146. In the present state of Science, it would be very difficult,
and is perhaps impossible, to lay down any definite line of de-
marcation between the two kingdoms; since there is no single
character by which the Animal or Vegetable nature of any or-
ganism can be tested. Probably the one which is most generally
applicable, among those lowest organisms which most closely
approximate to one another, is—not, as formerly supposed, the
presence or absence of spontaneous motion, but the dependence
of the being for nutriment upon organic compounds already:
formed, which it takes (in some way or other) into the interior
of its body, or its possession of the power of obtaining its own
alimentary matter by absorption, from the inorganic elements on
its exterior, The former is the characteristic of the Animal
Kingdom as a whole ; the latter is the attribute of the Vegetable ;
and although certain apparently exceptional cases may exist, yet
these do not seem to occur among the group in which such a
means of distinction is most useful to us. For we shall find
that those Protozoa, or simplest Animals, which seem to be com-
posed of nothing else than a mass of living jelly (Chaps. IX, X),
are supported as exclusively, either upon other Protozoa, or upon
Protophyta, which are humble Plants of equal simplicity, as the
highest Animals are upon the flesh of other animals, or upon
the products of the Vegetable Kingdom; whilst these Pro-
tophytes, in common with the highest Plants, draw their nourish-
ment from water, carbonic acid, and ammonia, and are distin-
guished by their power of liberating oxygen, through the
decomposition of carbonic acid, under the influence of sunlight.
And we shall, moreover, find, that even such Protozoa as have
neither stomach nor mouth, receive their alimentary matter
direct into the very substance of their bodies, in which it under-
goes a kind of digestion; whilst the Protophyta absorb through
their external surface only, and take in no solid particles of any
description. With regard to motion, which was formerly con-
sidered the distinctive attribute of animality, we now know, not
merely that many Protophytes (perhaps all, at some period or

248 MICROSCOPIC FORMS OF VEGETABLE LIFE,

other of their lives) possess a power of spontaneous movement,
but also that the instruments of motion, when these can be dis-
covered, are of the very same character in the Plant as in the
Animal; being little hair-like filaments termed cilia (from the
Latin ciliwm, an eyelash), by whose rhythmical vibration the
body of which they form part is propelled in definite directions.
The peculiar contractility of these cilia cannot be accounted for
in either case, any better than in the other; all we can say is,
that it seems to depend upon the continued vital activity of the
living substance of which these filaments are prolongations ; and
that this contractile substance has a composition essentially the
same in the Plant as in the Animal.

147. The plan of organization throughout the Vegetable
kingdom presents this remarkable feature of uniformity,—that
the fabric of the highest and most complicated Plants, consists
of nothing else than an aggregation of the bodies termed cells,
every one of which, amongst the lowest and simplest forms ot
Vegetation, may maintain an independent existence, and may
multiply itself most indefinitely, so as to form vast assemblages
of similar bodies. And the essential difference between the
plans of structure in the two cases lies in this,—that the cells
produced by the self-multiplication of the primordial cell of the
Protophyte, are all mere repetitions of it and of one another,
each living by and for itself,—whilst those produced by the like
self-multiplication of the primordial cell in the Oak or Palm, not
only remain in mutual connection, but undergo a progressive
“ differentiation,” a fabric being thereby developed, which is
composed of a number of distinct organs (stem, leaves, roots,
flowers, &c.), each of them characterized by specialities not
merely of external form but of intimate structure (the ordinary
type of the cell undergoing various modifications, to be described
in their proper place, Chap. VIII), and performing actions pe-
culiar to itself, which contribute to the life of the Plant as a whole.
Hence, as was first definitely stated by Schleiden (see Introduc-
tion, p. 43), it is in the life-history of the individual cell, that we
find the true basis of the study of Vegetable Life in general.
And we shall now inquire, therefore, what information on this
point we derive from Microscopie research. In its most com-
pletely developed form, the Vegetable Cell may be considered as
a closed membranous bag or vesicle, containing a fluid cell-sap;
and thus we have to consider separately the cell-wall and the cell-
contents. The “cell-wall’” is composed of two layers, of very
different composition and properties. The inner of these, which
has received the name of primordial utricle, appears to be the one
first formed, and most essential to the existence of the cell; it is
extremely thin and delicate, so that it escapes attention so long
as it remains in contact with the external layer; and it is only
brought into view when separated from this, either by develop-
mental changes (Fig. 107), or by the influence of reagents which

CHARACTERS OF THE VEGETABLE CELL. 949

cause it to contract by drawing forth part of its contents (Fig.
175). Its composition is indicated, by the effects of reagents, to
be albuminous; that is, it agrees with the formative substance of
the Animal tissues, not only in the proportions of oxygen, hydro-
gen, carbon, and nitrogen which it contains, but also in the
nature of the compound formed by the union of these elements.
The external layer, on the other hand, though commonly re-
garded as the proper “ cell-wall,” is generated on the surface of
the primordial utricle, after the latter has completely inclosed
the cavity and its contents, so that it takes no essential part in
the formation of the cell. It is usually thick and strong in com-
parison with the other, and may often be shown to consist of
several layers. In its chemical nature it is altogether dissimilar
to the primordial utricle ; for it is essentially composed of cellu-
lose, a substance containing no nitrogen, and nearly identical
with starch. The relative offices of these two membranes are
very different; for whilst there are many indications that the
primordial utricle continues to participate actively in the vital
operations of the cell, it seems certain that the cellulose-wall
takes no concern in them, but is only their product; its function
being simply protective. The contents of the vegetable-cell,
being usually more or less deeply colored, have received the col-
lective designation of endochrome (or internal coloring substance) ;
and they essentially consist of a layer of colorless “‘ protoplasm”
(or organizable fluid, containing albuminous matter in combina-
tion with dextrine or starch-gum) in immediate contact with the
primordial utricle, within which is the more watery cell-sap,
particles of chlorophyll or coloring substance being diffused
through both, or through the former only.

148. But although these component parts may be made out
without any difficulty in a large proportion of Vegetable cells,
yet they cannot be distinguished in some of those humble organ-
isms, which are nearest to the border ground between the two
kingdoms. For in them we find the “‘cell-wall” very imperfectly
differentiated from the “cell-contents;’’ the former not having by
any means the firmness of a perfect membrane, and the latter
not possessing the liquidity which elsewhere characterizes them.
And in some instances, the cell appears to be represented only
by a mass of endochrome, so viscid as to retain its external form
without any limitary membrane, though the superficial layer
seems to have a firmer consistence than the interior substance ;
and this may or may not be surrounded by a gelatinous-looking
envelope, which is equally far from possessing a membranous
firmness, and yet is the only representative of the cellulose-wall.
This viscid endochrome consists, as elsewhere, of a colorless
protoplasm, through which coloring particles are diffused, some-
times uniformly, sometimes in local aggregations, leaving parts
of the protoplasm uncolored. The superficial layer, in particular,
is frequently destitute of color; and the “primordial utricle” ap-

250 MICROSCOPIC FORMS OF VEGETABLE LIFE.

pears to be formed by its solidification. In the interior of the
viscid mass, are commonly found vacuoles, which are distinguished
from the surroundihg substance by their difference in refracting
power ; these, however, are not usually void spaces, but are cavi-
ties in the protoplasm occupied by fluid of a more watery con-
sistence ; and this “‘ vacuolation” of the interior, which increases
until the cell-contents have almost entirely lost their original
viscidity and are of a more watery character, seems to take place
part passu with the consolidation of the exterior into distinct
membranous walls; so that the development of a perfect cell out
of a rudimentary mass of endochrome, may be stated to consist
essentially in the gradual differentiation of its substance, which
was at first a nearly homogeneous viscid mass, into the solid
cell-wall and the liquid cell-contents. It is interesting to ob-
serve, at the very outset of our inquiry into the nature of Organ-
ization and Vital action, so characteristic an illustration of the
great law of Von Bar, already referred to (pp. 52, 55).

149. Now among the Protophytes or simplest Plants, on the
examination of which we are about to enter, there are many, of
which every single cellis not only capable of living in a state of
isolation from the rest, but even normally does so; and thus, in
the ordinary phraseology, every cell is to be accounted a * dis-
tinct individual.” There are others, again, of which shapeless
masses are made up by the aggregation of contiguous cells, which,
though quite capable of living independently, remain attached
to each other by the mutual fusion (so to speak) of their gela-
tinous investments. And there are others, moreover, in which
a definite adhesion exists between the cells, and in which regular
plant-like structures are thus formed, notwithstanding that every
cell is still but a repetition of every other, and is capable of living
independently if detached, so as to answer to the designation of
a “unicellular” or single-celled plant. These different conditions
we shall find to arise out of the mode in which each particular
species multiplies by binary subdivision (§ 150): for where the
pair of cells that is produced by the segmentation of the previous
cell, undergo a complete separation from one another, they will
henceforth live quite separately; but if, instead of undergoing
this complete fusion, they should be held together by the inter-
vening gelatinous envelope, a shapeless mass results from re-
peated subdivisions not taking place on any determinate plan;
and if, moreover, the binary subdivision should always take
place in a determinate direction, a long narrow filament (Fig.
104, p), or a broad flat leaf-like expansion (Fig. 104, @), may be
generated. To such extended fabrics, the term “ unicellular
plants” can scarcely be applied with propriety, since they may
be built up of many thousands or millions of distinct cells, which
have no disposition to separate from each other spontaneously.
Still they correspond with those which are strictly unicellular,
in the absence of any differentiation, either in structure or in

GENERAL CHARACTERS OF PROTOPHYTES. 251

actions, between their component cells; each one of these being
a repetition of the rest, and no relation of mutual dependence
existing among them. All such organisms may well be included
under the general term of Protophytes, by which it is convenient
to designate the primitive or alsineniaty forms of Vegetation ;
and we shall now enter, in such detail as the nature of the pre-
sent Treatise allows, into the history of those forms of the group,
which present most of interest to the Microscopist, or which best
serve to illustrate the general doctrines of Physiology.

150. The life-history of one of these Unicellular Plants, in
its most simple form, can scarcely be better exemplified than in
the Palmoglea macrococea (Kiitzing); one of those humble kinds
of vegetation which spreads itself as a green slime over damp
stones, walls, &c.

When this slime is Fig, 67.

examined with the
microscope, it is
found to consist of a
multitude of green
cells (Fig. 67, a), each
surrounded by a ge-
latinous envelope;
the cell, which does
not seem to have any
distinct membranous
wall, is filled with
granular particles of
a green color; and a
‘nucleus’ may some-
times be distin uish- arious ses of development of Pulmoglea macrococes ;
ed through fia tnldee ete cy ees oer of binary
ofthess: When treat. aie te aan
ed with tincture of jaconjaetion, eee
iodine, however, the

green contents of the cell are turned to a brownish hue, and a
dark-brown nucleus is distinctly shown (¢). Other cells are seen
(8), which are considerably elongated, some of them beginning
to present a sort of hour-glass contraction across the middle; in
these is commencing that curious multiplication by duplicative
subdivision, which is the mode in which increase nearly always
takes place throughout the Vegetable kingdom; and when cells
in this condition are treated with tincture of iodine, the nucleus
is seen to be undergoing the like elongation and constriction (H).
A more advanced state of the process of subdivision is seen at c,
in which the constriction has proceeded to the extent of com-
pletely cutting off the two halves of the cell, as well as of the
nucleus (1) from each other, though they still remain in mutual
contact; but in a yet later stage, they are found detached from
each other (p), though still included within the same gelatinous

252 MICROSCOPIC FORMS OF VEGETABLE LIFE.

envelope. Hach new cell then begins to secrete its own gela-
tinous envelope; so that, by its intervention, the two are usually
soon separated from one another (£). Sometimes, however, this
is not the case; the process of subdivision being quickly re-
peated, before there is time for the production of the gelatinous
envelope, so that a series of cells (F), hanging on one to another,
is produced. There appears to be no definite limit to this kind
of multiplication; and extensive areas may be quickly covered,
in circumstances favorable to the growth of the plant, by the
products of the duplicative subdivision of one primordial cell,
This, however, is simply an act of Growth, precisely analogous
to that by which any one of the higher forms of Vegetation ex-
tends itself, and differing only in this, that the cells produced by
each act of cell-subdivision in the present case exactly resemble
that from which they sprang; whilst in the case of more highly
organized Plants, they gradually become differentiated to a
greater or less degree, so that special ‘“ organs’ are evolved,
which take upon themselves dissimilar yet mutually dependent
parts, in the economy of the entire organism.

151. The process which represents the Generation of the higher
Plants is here performed in a manner so simple, that it would
not be recognized as such, if we were not able to trace it up
through a succession of modes of gradually increasing complexity,
until we arrive at the elaborate operations which are concerned
in the production and fertilization of the seeds of Flowering
Plants. For it consists in nothing else than the reunion or
fusion together of any pair of cells (K),—a process which is termed
Conjugation; and it is characteristic of this humble plant, and
shows how imperfect must be the consistence of its cell-mem-
brane, that this seems to enter into the fusion, no less completely
than the cell-contents. The communication is at first usually
made by a narrow neck or bridge (Kk); but before long it extends
through a large part of the contiguous boundaries (1); and at
last the two cells are seen to be completely fused into one mass
(m); which is termed the spore. Each “spore” thus formed is
the “primordial cell” of a new generation, into which it evolves
itself by successive repetitions of the process of binary subdivi-
sion. It is curious to observe, that during the conjugating pro-
cess, a production of oil-particles tales place in the cells; these
at first are small and distant, but gradually become larger and
approximate more closely to each other, and at last coalesce so
as to form oil-drops of various sizes, the green granular matter
disappearing; and the color of the conjugated body changes,
with the advance of this process, from green to a light yellowish-
brown. When the spore begins to vegetate, on the other hand,
producing a pair of new cells by binary subdivision, a converse
change takes place; the oil-globules disappear, and green granu-
lar matter takes their place. Now this is precisely what occurs
in the formation of seed among the higher Plants; for starchy

STILL AND MOTILE CONDITIONS OF PROTOPHYTES. 2853

substances are transformed into oil, which is stored up in the
seed for the nutrition of the embryo, and is applied, during ger-
mination, to the purposes which are at other times answered by
starch or chlorophyll. The growth of this little plant appears to
be favored by cold and damp; its generation, on the other hand,
is promoted by heat and dryness; and it is obvious that the
spore-cell must be endowed with a greater power of resisting
this, than the vegetating plant has, since the species would other-
wise be destroyed by every drought.

152. If the preceding sketch really comprehends the whole
life-history of the humble plant to which it relates, this history
is much more simple than that of other forms of vegetation,
which, without appearing to possess an essentially higher struc-
ture, present themselves under a much greater variety of forms
and conditions. One of the most remarkable of these varieties
is the motile condition, which seems to be common, in some
stage or other of their existence, to a very large proportion of
the lower forms of aquatic vegetation; and which usually de-
pends upon the extension of the primordial utricle into one or
two thread-like filaments (Fig. 68, H-1), endowed with the power
of executing rhythmical contractions, whereby the cell is im-
pelled through the water. As an illustration of this peculiar
mode of activity, which was formerly supposed to betoken Ani-
mal life, a sketch will be given of the history of a plant, the
Protococeus pluvialis, which is not uncommon in collections of
rain-water,' and which, in its motile condition, has been very

1 The Author had under his own observation, about eight years ago, an extraordinary
abundance of what he now feels satisfied must have been this plant, in a rain-water
cistern, which had been newly cleaned out. His notice was attracted to it, by seeing
the surface of the water covered with a green froth, whenever the sun shone upon it.
On examining a portion of this froth under the Microscope, he found that the water was
crowded with green cells in active motion; and although the only bodies at all re-
sembling them, of which he could find any description, were the so-called Animaicules,
constituting the genus Chlamydomonas of Prof. Ehrenberg, and very little was known at
that time of the “ motile” conditions of Plants of this description, yet of the vegetable
nature of these bodies he could not entertain the smallest doubt. They appeared in
freshly collected rain-water, and could not, therefore, be deriving their support from
organie matter; under the influence of light, they were obviously decomposing carbonic
acid and liberating oxygen, and this influence he found to be essential to the continu-
ance of their growth and development, which took place entirely upon the Vegetative
plan. Not many days after the Protophyte first appeared in the water, a few Wheel-
“Animalcules presented themselves; these fed greedily upon it, and increased so rapidly
(the weather being very warm) that they soon became almost as crowded as the cells
of the Protococcus had been; and it was probably due in part to their voracity, that the
plant soon became less abufidant, and before long disappeared altogether. Had the
Author been then aware of its assumption of the “ still” condition, he might have found
itat the bottom of the cistern, after it had ceased to present itself at the surface. The
account of this Plant given above, is derived from that of Dr. Cohn, in the “ Nova
Acta Acad. Nat. Curios.” (Bonn, 1850), tom. xxii; of which an abstract by Mr. George
Busk is contained in the “ Botanical and Physiological Memoirs,” published by the Ray
Society for 1853. This excellent observer states that he kept his plants for observation
in little glass vessels, having the form of a truncated cone, about two inches deep, and
one inch and a quarter in diameter. with a flat bottom polished on both sides, and
filled with water to the depth of from two to three lines. “It was only in vessels of
this kind,” he says, “that he was able to follow the development of a number of various

254 MICROSCOPIC FORMS OF VEGETABLE LIFE,

commonly regarded as an Animalcule, its different states having
been described under several different names.

153. In the first place, the color of these cells varies consider-
ably; since, although they are usually green at the period of
their most active life, they are sometimes red; and their red
form has received the distinguishing appellation of Hematococeus.
Very commonly the red coloring matter forms only a central
mass of greater or less size, having the appearance of a nucleus
(as shown in Fig. 68, z); and sometimes it is reduced to a single

ranular point, which has been erroneously represented by Prof.
hrenberg as the eye of these so-called Animalcules. It is quite
certain that the red coloring substance is very nearly related in

Fia. 68.

Various phases of development of Protococcus pluvialis:—a, an encysted cell, which has passed
into the “still” condition; B, division of a “still” cell into two; c, another mode of division into two,
each primordial vesicle having developed a cellulose envelope around itself, whilst yet within the
original cell; D, division of an encysted cell into four; £, division of an encysted cell into eight; F,
division of an encysted cell into thirty-two segments; 6, motile gonidia (zoospores) after their escape
from the original cell; u, a primordial utricle, without cellulose envelope, furnished with two cilia;
1, a similar primordial utricle, with distinct cellulose envelope, and threads of protoplasm extending
towards it; x, an encysted primordial utricle, pointed at both ends, and furnished with two cilia; l,
an encysted primordial utricle, of which nearly half is composed of a colorless granular substance,
enclosing a red body resembling a nucleus.

its chemical character to the green, and that the one may be
converted into the other; though the conditions under which
this conversion may take place are not precisely known. In the
still form of the cell, with which we may commence the history

cells throughout its whole course.” Probably he would have found the glass tube cells
represented in Fig. 65, if he had been acquainted with them, to answer his purpose Just
as well as these specially constructed vessels.

STILL AND MOTILE CONDITIONS OF PROTOCOCCUS. 255

of its life, we find a mass of endochrome, consisting of a color-
less protoplasm, through which red or green colored granules
are more or less uniformly diffused; on the surface of this
endochrome, the colorless protoplasm is condensed into a more
consistent layer, forming an imperfect “ primordial utricle;” and
this is surrounded by a tolerably firm layer, which seems to con-
sist of cellulose or of some modification of it. Outside this (as
shown in Fig. 68, a), when the “still” cell is formed by a change
in the condition of a cell that has been previously “ motile,’”’ we
find another envelope, which seems to be of the same nature,
but which is separated by the interposition of aqueous fluid;
this, however, may be altogether wanting. The multiplication
of the “still” cells by self-division takes place as in the previous
instance; the endochrome, enclosed in its primordial utricle,
first undergoing separation into two halves (as seen at B), and
each of these halves subsequently developing a cellulose enve-
lope around itself, and undergoing the same division in its turn.
Thus 2, 4, 8, 16 new cells are successively produced; and these
are sometimes set free by the complete dissolution of the enve-
lope of the original cell; but they are more commonly -held
together by its transformation into a gelatinous investment, in
which they remain imbedded. Sometimes the contents of the
primordial utricle subdivide at once into four segments (as at D),
of which every one forthwith acquires the characters of an inde-
pendent cell; but this, although an ordinary method of multi-
plication among the “motile” cells, is comparatively rare in the
“still” condition. Sometimes, again, the cell-contents of the
“still” form subdivide at once into eight portions, which, being
of small size, and endowed with motile power, may be con-
sidered as “ zoospores;’’ it is not quite clear what becomes of
these; but there is reason to believe that some of them retain
their motile powers, and, after increasing in size, develope an
investing cyst, like the free primordial utricles to be presently
described; that others produce a firm cellulose envelope, and
become “still” cells; and that others (perhaps the majority)
perish without any further change.

154. When the ordinary self-division of the “still” cells into
two segments has been repeated four times, so as to produce 16
cells—and sometimes at an earlier period—the new cells thus
produced assume the “ motile” condition ; being liberated before
the development of the cellulose envelope, and becoming fur-
nished with two long vibratile filaments, which appear to be
extensions of the primordial utricle (a). In this condition, it
seems obvious that the colorless protoplasm is more developed
relatively to the coloring matter, than it is in the “still” cells;
it generally accumulates in the part from which the vibratile
filaments or cilia proceed, so as to form a sort of transparent
beak (H, K, L); and it usually contains “vacuoles,” occupied only
by clear aqueous fluid, which are sometimes so numerous as to

*

256 MICROSCOPIC FORMS OF VEGETABLE LIFE.

take in a large part of the cavity of the cell, so that the colored
contents seem only like a deposit on its walls. Before long, this
“motile” primordial utricle acquires a peculiar saccular invest-
ment, which seems to correspond with the cellulose envelope of
the “still” cells, but which is not so firm in its consistence (1, x,
L). Thread-like extensions of the protoplasm, sometimes con-
taining colored globules, are not unfrequently seen to radiate
from the primordial utricle towards the exterior of this envelop-
ing bag (1); these are rendered more distinct by iodine, and can
be made to retract by means of reagents; and their existence
seems to show, on the one hand, that the transparent space
through which they extend themselves is only occupied bya
watery liquid, and on the other, that the layer of protoplasm
which constitutes the primordial utricle, is far from possessing
the tenacity of a completely formed membrane. The vibratile
filaments pass through the cellulose envelope, which invests them
with a sort of sheath; and in the portion that is within this
sheath, no movement is seen. During the active life of the
‘“‘ motile” cells, the vibration, of these cilia is so rapid, that it can
be recognized only by the currents it produces in the water,
through which the cells are rapidly propelled ; but when the mo-
tion becomes slacker, the filaments themselves are readily dis-
tinguishable; and they may be made more obvious by the addition
of iodine. The multiplication of these motile cells may take
place in various modes, giving rise to a great variety of appear-
ances. Sometimes they undergo a regular binary subdivision,
whereby a pair of motile cells is produced (c), each resembling
its single predecessor in possessing the cellulose investment, the
transparent beak, and the vibratile filaments, before the solution
of the original investment. Sometimes, again, the contents of
the primordial cell undergo a segmentation in the first instance
into four divisions (D); which may either become isolated by the
dissolution of their envelope, and may separate from each other
in the condition of free primordial utricles (a), developing their
cellulose investments at a future time; or may acquire their cel-
lulose investments (as in the preceding case) before the solution
of that of the original cell; and sometimes, even after the disap-
pearance of this, and the formation of their own independent in-
vestments, they remain attached to each other at their beaked
extremities, the primordial utricles being connected with each
other by peduncular prolongations, and the whole compound
body having the form of a+. This quaternary segmentation
appears to be a more frequent mode of multiplication among the
“motile” cells, than the subdivision into two; although as we
have seen, it is less common in the “still” condition. So, also,
a primary segmentation of the entire endochrome of the “mo-
tile” cells, into 8, 16, or even 82 parts, may take place (z, F), thus
giving rise to as many minute primordial cells. These, when
they are set free, and possess active powers of movement, rank

VARIOUS CONDITIONS OF PROTOCOCCUS. 257

as “zoospores” (G): which may either develope a loose cellulose
investment or cyst, so as to attain the full dimensions of the or-
dinary motile cells (1, K), or may become clothed with a dense
envelope, and lose their vibratile cilia, thus passing into the
“still” condition (a); and this last transformation may even take
place, before they are set free from the envelope within which
they were produced, so that they constitute a mulberry-like mass,
which fills the whole cavity of the original cell, and is kept in
motion by its cilia.

155. All these varieties, whose relation to each other has been
clearly proved by watching the successional changes that make
up the history of this one Plant, have been regarded as consti-
tuting, not merely distinct species, but distinct genera of Animal-
cules; such us, Chlamydomonas, Huglena, Trachelomonas, Gyges,
Gonium, Pandorina, Botryocystis, Uvella, Syncrypta, Monas, As-
tasia, Bodo, and probably many others.’ Certain forms, such as
the “motile” cells (1, K, L), appear in a given infusion, at first
exclusively and then principally; they gradually diminish, be-
come more and more rare, and finally disappear altogether, being
replaced by the “still” form. After some time, the number of
the “ motile’ cells again increases, and reaches, as before, an ex-
traordinary amount; and this alteration may be repeated several
times in the course of a few weeks. The process of segmentation
is often accomplished with great rapidity. Ifa number of motile
cells be transferred from a larger glass into a small capsule, it
will be found, after the lapse of a few hours, that most of them
have subsided to the bottom; in the course of the day, they will
all be observed to be upon the point of subdivision; on the fol-
lowing morning, the divisional brood will have become quite
free; and on the next, the bottom of the vessel will be found
covered with a new brood of self-dividing cells, which again pro-
ceed to the formation of a new brood, and so on. The activity
of motion and the activity of multiplication, seem to stand, in
some degree, in a relation of reciprocity to each other; for the
self-dividing process takes place with greater rapidity in the
“still” cells, than in the “ motile.”

1Tn the above sketch, the Author has presented the facts described by Dr. Cohn,
under the relation which they seemed to him naturally to bear; for the membrane
which immediately surrounds the primordial utricle of the “still” cells, appears to him
to be essentially the same with the sacculated investment of the “ motile” form, since it
differs only in its greater density, and in the absence of the interposed Muid. It is dis-
tinctly stated by Cohn, towards the conclusion of his Memoir, that the one like the other
consists of cellulose, since both alike give the characteristic blue color with a very dilute
solution of iodine, and with moderately diluted sulphuric acid; yet he speaks of what
he terms the “ encysted zoospore’ (1, K, L), as being formed by one cell within another,
the outer cel] having a true cell-membrane and aqueous contents, but being destitute of
primordial utricle ; whilst the inner céll has denser, colored contents, but is without thé
true cell-membrane. Having enjoyed, since the above was written, the opportunity of
personally communicating with Dr. Cohn with regard to the question to which it refers,
the Author is glad to be able to state, that Dr. Cohn’s Jater observations have led him to
adopt a view of the relationship of the “ still” and “ motile” forms, which is in essential
accordance with his own. .
17

¥

*258 MICROSCOPIC FORMS OF VEGETABLE LIFE

156. What are the precise conditions which determine the
transition from one state to the other, cannot yet be precisely
stated; but the influence of certain agencies can be predicted
with tolerable certainty. Thus it is only necessary to pour the
water containing these organisms, from a smaller and deeper
into a larger and shallower vessel, at once to determine segmen-
tation in numerous cells,—a phenomenon which is observable
also in many other Protophytes. The “motile” cells seem to be
favorably affected by light, for they collect themselves at the sur-
face of the water and at the edges of the vessel; but when they
are about to undergo segmentation, or to pass into the “still”
condition, they sink to the bottom of the vessel, or retreat to that
part of it in which they are least subjected to light. When kept
in the dark, the “motile” cells undergo a great diminution of
their chlorophyll, which becomes very pale, and is diffused, in-
stead of forming definite granules; they continue their move-
ment, however, uninterruptedly, without either sinking to the
bottom, or passing into the still form, or undergoing segmenta-
tion. A moderate warmth, particularly that of the vernal sun,
is favorable to the development of the ‘‘ motile” cells; but a tem-
perature of excessive elevation prevents it. Rapid evaporation
of the water in which the “ motile” forms of Protococcus may be
contained, kills them at once; but a more gradual loss, such as
takes place in deep glasses, causes them merely to pass into the
“still” form; and in this condition,—especially when they have
assumed a red hue,—they may be completely dried up, and may
remain in a state of dormant vitality for many years. It is in
this state that they are wafted about in atmospheric currents, and
that, being brought down by the rain into pools, cisterns, &c., they
may present themselves where none had been previously known
to exist; and there, under favorable circumstances, they may
undergo a very rapid multiplication, and may maintain them-
selves until the water is dried up, or some other change occurs
which is incompatible with the continuance of their vital activity.
They then very commonly become red throughout, the red coloy-
ing substance extending itself from the centre towards the cir-
cumference, and assuming an appearance like that of oil-drops;
and these red cells, acquiring thick cell-walls and a mucous en-
velope, float in flocculent aggregations on the surface of the
water. This state seems to correspond with the “winter spores”
of other Protophytes; and it may continue until warmth, air,
and moisture, cause the development of the red cells into the
ordinary “still” cells, green matter being gradually produced,
until the red substance forms only the central part of the endo-
chrome. After this occurs the cycle of changes which has been
already described; and the Plant may pass through a long series
of these, before it returns to the state of the red thick-walled cell,
in which it may again remain dormant for an unlimited period.
Even this cycle, however, cannot be regarded as completing the

' VOLVOCINES. 259

history of the species before us; since it does not include the
performance of any true Generative act. There can be little
doubt that, in some stage of its existence, a “conjugation” of two
cells occurs, as in the preceding case; and the attention of ob-
servers should be directed to its discovery, as well as to the de-
tection of other varieties in the condition of this interesting little
Plant, which will be probably found to present themselves before
and after the performance of that act.

157. From the composite motile forms of the preceding type,
the transition is easy to the group of Vol-
vocinee,—an assemblage of minute Plants Fra. 69.
of the greatest interest to the Microscopist,
on account both of the Animalcule-like
activity of their movements, and of the

reat beauty and regularity of their forms.

he most remarkable example of this group,
is the well-known Volvox globator (Fig. 69),
or “globe-animaleule ;” which is not un-
common in fresh-water pools, and which,
attaining a diameter of 1-30th of an inch,
may be seen with the naked eye, when the
drop containing it is held up to the light, Volvox Globator.
swimming through the water which it in-
habits. Its onward motion is usually of a rolling kind; but it
sometimes slides smoothly along, without turning on its axis ;
whilst sometimes, again, it rotates like a top, without changing
its position. When examined with a sufficient magnifying
power, the Volvor is seen to consist of a hollow sphere, com-
posed of a very pellucid material, which is studded at regular
intervals with minute green spots, and which is often (but not
constantly) traversed by green threads connecting these spots to-
gether. From each of the spots proceed two long cilia; so that
the entire surface is beset with these vibratile filaments, to whose
combined action its movements are due. Within the external
sphere, there may generally be seen from two to twenty other
globes, of a darker color, and of varying sizes; the smaller of
these are attached to the inner surface of the investing sphere,
and project into its cavity; but the larger lie freely within the
cavity, and may often be observed to revolve by the agency of
their own ciliary filaments. After a time, the original sphere
bursts, the contained sphericles swim forth and speedily develope
themselves into the likeness of that within which they have been
evolved; their component particles, which are at first closely
aggregated together, being separated from each other by the in-
terposition of the transparent pellicle. It was long supposed
that the Volvor was a single Animal; and it was first shown to
be a composite fabric, made up of a repetition of organisms in
all respects similar to each other, by Prof. Ehrenberg ; who,
however, considered these organisms as Monads, and described

260 MICROSCOPIC FORMS OF VEGETABLE LIFE.

them as each possessing a mouth, several stomachs, and an eye!
Our present knowledge of their nature, however, leaves no doubt
of their Vegetable character; and the peculiarity of their history
renders it desirable to describe it in some detail.

158. Each of the so-called “ Monads” is in reality a some-
what flask-shaped mass of endochrome, about 1-3000th of an
inch in diameter; consisting, as in the previous instances, of
chlorophyll-granules, diffused through a colorless protoplasm
(Fig. 70, 1, 1); and bounded by a layer of condensed protoplasm,
which represents a primordial utricle, but is obviously far from
having attained a membranous consistence. It is prolonged out:
wardly (or towards the circumference of the sphere) into a sort
of colorless peak or proboscis, from which proceed two long
vibratile cilia (L); and it is invested by a pellucid or “ hyaline”
envelope (1, d) of considerable thickness, the borders of which
are flattened against those of other similar envelopes (g, ¢ e),
but which does not appear to have the tenacity of a true mem-
brane. Itis impossible not to recognize the precise similarity
between the structure of this body, and that of the motile “ en-
cysted” cell of Protococeus pluvialis (Fig. 68, &); there is not,
in fact, any perceptible difference between them, save that which
arises from the regular aggregation, in Volvoz, of the cells which
normally detach themselves from one another in Protococcus.
The presence of cellulose in the hyaline substance is not indi-
cated, in the ordinary condition of Volvor, by the iodine and
sulphuric acid test, though the use of “‘ Schulz’s solution” gives
to it a faint blue tinge; there can be no doubt of its existence,
however, in the hyaline envelope of what has been termed Vol-
vox aureus, which is in reality nothing but the “ winter spore”
of Volvox globator. The cilia and endochrome, as in the motile
forms of Protococcus, are tinged of a deep brown by iodine,
with the exception of one or two particles in each cell, which,
being turned blue, may be inferred to be starch ; and when the
contents of the cell are liberated, bluish flocculi, apparently in-
dicative of the presence of cellulose, are brought into view by
the action of sulphuric acid and iodine. All these reactions are
strictly vegetable in their nature. When the cell is approaching
maturity, its endochrome always exhibits one or more “ vacuoles”
(Fig. 70, 1, a a), of a spherical form, and usually about one-third
of its own diameter ; and these “ vacuoles” (which are the so-called
“stomachs” of Prof. Ehrenberg) have been observed by Mr. G.
Busk to undergo a very curious rhythmical contraction and dila-
tation at intervals of about 40 seconds; the contraction (which
seems to amount to complete obliteration of the cavity of the
vacuole) taking place rapidly or suddenly, whilst the dilatation
is slow and gradual. This curious action ceases, however, as the
cell arrives at its full maturity ; a condition which seems to be
marked by the greater consolidation of the primordial utricle, by
the removal or transformation of some of the chlorophyll (the

STRUCTURE OF VOLVOX GLOBATOR. 261

greater part of the coloring matter contracting into a small irre-
gular mass, which adheres to the bottom or side of the cell,
leaving the rest of the cavity clear and transparent), and the
formation of the red spot (6), which obviously consists, as in
Protococcus, of a peculiar modification of chlorophyll.

159. Each mass of endochrome normally communicates with
those in nearest proximity with it, by extensions of its own sub-
stance, which are sometimes single and sometimes double (g, d
6); and these connecting processes necessarily cross the lines of
division between their respective hyaline investments. The
thickness of these processes varies very considerably ; for some-
times they are broad bands, and in other cases mere threads;
whilst they are occasionally wanting altogether. This difference
seems partly to depend upon the age of the specimen, and partly
upon the abundance of nutriment which it obtains; for, as we
shall presently see, the connection is most intimate at an early
period, before the hyaline investments of the cells have increased
so much as to separate the masses of endochrome to a distance
from one another (B, ¢, D); whilst in a mature individual, in
which this separation has taken place to its full extent, and the
nutritive processes have become less active, the masses of endo-
chrome very commonly assume an angular form, and the con-
necting processes are drawn out into threads (as seen at £), or
they retain their globular form, and the connecting processes
altogether disappear. The influence of reagents, or the infiltra-
tion of water into the interior of the hyaline investment, will
sometimes cause the connecting processes (as in Protococcus, §
154), to be drawn back into the central mass of endochrome;
and they will also retreat on the mere rupture of the hyaline in-
vestment; from these circumstances it may be inferred, that they
are not enclosed in any definite membrane. On the other hand,
the connecting threads are sometimes seen as double lines, which
seem like tubular prolongations of a consistent membrane, with-
out any protoplasmic granules in their interior. It is obvious,
then, that an examination of a considerable number of specimens,
exhibiting various phases of conformation, is necessary to de-
monstrate the nature of these communications; but this may be
best made out by attending to the history of their development,
which we shall now describe.

160. The spherical body of the young Volvor (Fig. 78, A) is
composed of an aggregation of somewhat angular masses of en-
dochrome (6), separated by the interposition of hyaline substance ;
and the whole seems to be enclosed in a distinctly membranous
envelope, which is probably the distended hyaline investment of
the primordial cell, within which, as will presently appear, the
entire aggregation originated. In the midst of the polygonal
masses of endochrome, one mass (a), rather larger than the rest,
is seen to present a circular form ; and this, as will presently
appear, is the originating cell of what is hereafter to become a

262 MICROSCOPIC FORMS OF VEGETABLE LIFE.

new sphere. The growing Volvox at first increases in size, not
only by the interposition of new hyaline substance between its
component masses of endochrome, but also by an increase in
these masses themselves (B, a), which come into continuous con-
nection with each other by the coalescence of processes (6) which

Vurious Stages in the Development of Volvoxz Globator.

they severally put forth; at the same time, an increase is ob-
served in the size of the globular cell (c), which is preliminary
to its binary subdivision. A more advanced stage of the same
developmental process is seen at c; in which the connecting pro-
cesses (a a) are so much increased in size, as to establish a most
intimate union between the masses of endochrome, although the
increase of the intervening hyaline substance carries these masses
apart from one another; whilst the endochrome of the central

DEVELOPMENT OF VOLVOX GLOBATOR. 268

globular cell has undergone segmentation into two halves. In
the stage represented at p, the masses of endochrome have been
still more widely separated by the interposition of hyaline sub-
stance; each has become furnished with its pair of ciliary fila-
ments; and the globular cell has undergone a second segmenta-
tion. Finally at z, which represents a portion of the spherical
wall of a mature Volvox, the endochrome masses are observed
to present a more scattered aspect, partly on account of their
own reduction in size, and partly through the interposition of a
greatly increased amount of hyaline substance, which is secreted
from the surface of each mass; and that portion which belongs
to each cell, standing to the endochrome mass in the relation of
the cellulose coat of ordinary cells to their primordial utricle, is
frequently seen to be marked out from the rest by delicate lines
of hexagonal areolation (e, c), which indicate the boundaries of
each, Of these it is often difficult to obtain a sight, a nice
management of the light being usually requisite with fresh spe-
cimens; but the prolonged action of water (especially when it
contains a trace of iodine), or of glycerine, will often bring them
into clear view. The prolonged action of glycerine, moreover,
will often show that the boundary lines are double, being formed
by the coalescence of two contiguous cell-walls; and they some-
times retreat from each other so far, that the hexagonal areole
-become rounded.

161. As the primary sphere approaches maturity, the second-
ary germ, whose origin has been traced from the beginning, also
‘advances in development; its contents undergoing multiplica-
tion by successive segmentations, so that we find it to consist ot
8, 16, 32, 64, and still more numerous divisions, as shown in
Fig. 70, F, ¢, H. Up to this stage, at which first the sphere
appears to become hollow, it is retained within the hyaline enve-
lope of the cell within which it has been produced; a similar
envelope can be easily distinguished, as shown at x, just when
the segmentation has been completed, and at that stage the cilia
pass into it, but do not extend beyond it; and even in the
mature volvox, it continues to form an investment around the
hyaline envelopes of the separate cells, as shown at x. It seems
to be by the adhesion of the hyaline investment of the new
sphere to that of the old, that the secondary sphere remains for
a time attached to the interior. wall of the primary; at what
exact period, or in what precise manner, the separation between
the two takes place, has not yet been determined. At the time
of the separation, the developmental process has generally
advanced as far as the stage represented at a; the foundation of
one or more tertiary spheres being usually distinguishable in the
enlargement of certain of its cells. And thus the cycle of
development is completed, in so far as regards the increase of
cells by subdivision. But,-as already pointed out, the life-his-
tory of no organism can be considered as complete, unless it

254 MICROSCOPIC FORMS OF VEGETABLE LIFE,

includes an act of “conjugation,” or some other form of the
true Generative process; and as none such has yet been observed
in Volvor, there is strong ground to suspect that we are not
acquainted with its whole life, but that conjugation may occur
in some condition not yet known to us, which may only present
itself after a long succession of repetitions of that process ot
gemmation, by which the Volvox spheres are multiplied and
reproduced.

162. Certain curious varieties, however, occasionally present
themselves in the preceding cycle. Thus, the young Volvox
globe which has attained the size and has undergone the degree
of segmentation indicated at a or H, sometimes becomes at first
deep green and then yellow; its hyaline envelope acquires an
unusual firmness, and a second coat is formed within the first,
the colored contents undergoing some retraction ; and eventually
a considerable space intervenes between the two coats, which is
occupied by a clear fluid. The protoplasmic contents of the
inner envelope consist chiefly of starch grains, mixed with a
bright yellow and apparently oily fluid. In this and other
respects, the body in question corresponds so closely with the
“still” or “winter” spore of other Protophytes, which is adapted
to resist influences that are fatal to the more actively vegetating
forms of these organisms, that it seems most probable (as was
first suggested by Mr. G. Busk) to stand in this relation to Vol-
vox globator, although the ultimate mode of its development is
not known; and thus the Volvor aureus, as the kind that pro-
duces these golden yellow spheres has been designated, is nothing
else than an ordinary Volvox preparing its brood for the winter
state of inactivity. The Volvor stellatus of Ehrenberg, again,
seems to be nothing more than a variety of the same specific
type; its peculiarity consisting in the presence of numerous
‘conical eminences, formed of the hyaline substance only, on the
secondary globules, giving them a stellate aspect. The endo-
chrome segments resemble those of the globules of Volvox aureus,
both in color and composition; and these two forms of second-
ary globules, the stellate and the smooth, having been observed
by Mr. Busk to coexist in the very same sphere, are certainly to
be regarded as varieties of one and the same type.' The same
excellent observer has also pointed out the probability, that the

1“Tn the month of August last,” says My. Bnsk (Op. cit. p. 44), “ when, in a certain
pond on Blackheath, there was the most incredible abundance of Volvox, so great, 1n
fact, as to render the water at the lee side of the pond in certain spots of a deep green
color, and to cause it to afford, when collected, a very strong herbaceous or confervoid
smell, the majority of the plants exhibited the stellate form of spores, or rapidly acquired
spores of that character, and very many were in, or soon assumed, the form of V. aureus.
They seemed, in fact, to be entering on their hibernating state. Many among them,
however, though all small and starved-looking, were of the common kind, in all these,
Prof. Williamson's hexagonal areolation was very distinct. In the month of October,
however, upon returning to the same pond,I was able to find very few Volvoces at all,
and all of the usual kind; in none of these could I detect the least appearance of the
same arrangement.’ Prof. Williamson has noticed analogous variations, in the speci
mens taken at different seasons from one locality (Op. cit. p. 56).

DESMIDIACEZ—GENERAL CHARACTERS. 265

body designated by Prof. Ehrenberg Spherosira volvox, is an
ordinary Volvox in a different phase of development. For it
does not present any marked feature of dissimilarity, except that
a large proportion of the green cells, instead of being single (as
in the ordinary form of Volvox) save where they are developing
themselves into young spheres, are very commonly double,
quadruple, or multiple; and the groups of ciliated cells thus
produced, instead of constituting a hollow sphere, form by their
aggregation discoid bodies, of which the separate fusiform cells
are connected at one end, whilst at the other they are free, each
being furnished with a single cilium. These clusters separate
themselves from the primary sphere, and swim forth freely,
under the forms which have been designated as Uvella and
Synerypta by Prof. Ehrenberg. The further history of these
has not been traced; and it does not seem improbable that more
than one intermediate stage may be passed through, before a
return is made to the type of Volvox globator.'

163. Desmidiacew.—Among the simplest tribes of Protophytes,
there are two which are of such peculiar interest to the Micro-
scopist, as to need a special notice; these are the Desmidiew (or
more properly Desmidiacee), and the Diatomacee. Both of them
have been ranked by Ehrenberg, and by many other Naturalists,
as Animalcules; but the fuller knowledge of their life-history,
and the more extended acquaintance with the parallel histories
of other simple forms of Vegetation, which have been gained
during the last ten years, can scarcely be considered by judges
who are at once competent and unprejudiced, as otherwise than
decisive in regard to their vegetable nature. The Desmidiaceee
are minute plants of a green color, growing in fresh water;
generally speaking, the cells are independent of each other (Figs.
71, 75, 76); but sometimes those which have been formed by
duplicative subdivision from a single primordial cell, remain
adherent one to another in linear series, so as to form a filament
(Fig. 77); whilst in other instances, they constitute beautiful
star-like groups (Figs. 73, 74). This tribe is distinguished by
two peculiar features; one of these being the semblance of a
subdivision into two symmetrical halves, which is seen in the
cells of most species, and which is sometimes so decided as to
have led to the belief that the cell is really double (Fig. 75 a),

'The doctrine of the vegetable nature of the Volvox, which had been suggested hy
Siebold, Braun, and other German Naturalists, was first distinctly enunciated by Prof.
Williamson, on the basis of the history of its development, in the “Transactions of the
Philosophical Society of Manchester,” vol. ix. Subsequently Mr. G. Busk, whilst ad-
ducing additional evidence of the Vegetable nature of Volvox. in his extremely valuable
Memoir in the “ Transactions of the Microscopical Society,” 2d Series, vol. i, called in
question some of the views of Prof. Williamson, which were justified by that gentle-
man in his “ Forther Elucidations” in the same Transactions. The Author has endea-
vored to state the facts in which both these excellent observers agree (and which he
has himself had the opportunity of verifying), with the interpretation that seems to him
most accordant with the phenomena presented by other Protophytes; and he believes

that this interpretation harmonizes with what is most essential in the doctrines of both,
their differences having been to a certain degree reconciled by their mutual admissions.

266 MICROSCOPIC FORMS OF VEGETABLE LIFE.

though in other cases it is merely indicated by a slight notch on
one side (as in the marginal cells of Fig. 73, a, £); whilst the
other is the frequency of projections from their surface, which
are sometimes short and inconspicuous (Fig. 75), but are often
elongated into spines, presenting a very symmetrical arrangement
(Fig. 71). These projections are generally formed by the outer

Various species of Slaurasirum :—a, S. vestitum; B, S. Ue 3 ¢, S. parad ;
D, «, S. brachiatum.

coat alone, which possess an almost horny consistence, so as to
retain its form after the discharge of its contents (Figs. 74, g, 75,
B), but which does not include any mineral ingredient, either
calcareous or siliceous, in its composition. This outer coat is
surrounded by a very transparent sheath of gelatinous substance,
which is sometimes very distinct (as shown in Fig. 77), whilst in
other cases its existence is only indicated by its preventing the
contact of the cells. The outer coat encloses an inner mem-
brane, which is not always, however, closely adherent to it; and
this immediately surrounds the colored substance which occupies
the whole interior of the cell. It is quite certain that the Desmi-
diacez, like the Confervoid Plants in general, grow at the ex-
pense of the inorganic elements which surround them, instead
of depending upon other living beings for their subsistence ; and
that they decompose carbonic acid, and give off oxygen, under
the influence of sunlight. They have the power of generating
from these materials the organic compounds which they require
for their own development; and these are such as are formed by
other undoubted Protophytes, as is proved by the application of
the appropriate tests. Thus the outer coat is colored blue by
sulphuric acid and iodine, and is therefore composed of cellulose.
The “endochrome” derives its color from the same green sub-
stance “chlorophyll,” as that which imparts it to Plants gene-
rally; and this is mingled with a protoplasmic fluid, in which
“vacuoles” are frequently to be seen. At certain stages in the

ROTATION OF FLUID IN CLOSTERIUM. 267

growth of these plants, as in other Algw, starch is produced ; the
presence of which is made obvious by the application of iodine.
There is no one essential point, therefore, in which the Desmi-
diacee differ from other Protophytes, or really approach the
Animal kingdom. Some of the arguments that have been ad-
vanced in support of their Animal affinities,—such as their mul-
tiplication by transverse subdivision, and their generation by a
process of conjugation,—are really, now that the physiology of
the unicellular plants is better understood, much more strongly
indicative of their Vegetable alliances. The assertion of Prot.
Ehrenberg, that Closterium possesses organs which it protrudes
through apertures in its extremities, and keeps in continual
motion, is (like too many of his statements) simply untrue. And
although many of these plants have a power of slowly changing
their place, so that they approach the light side of the vessel in
which they are kept, and will even traverse the field of the
microscope under the eye of the observer, yet this faculty is in
no respect different from that which many undoubted Proto-
phytes (such as Oseillatorie, § 196) possess.

164. A very peculiar feature which has recently attracted much
attention, is the circulation of fluid which may be seen to take
place in the Closteriwm, both between its “cellulose” coat and its
“primordial utricle,” and within the latter; and the edliary action
by which, according to the testimony of some good observers,
this circulation is maintained. It is not difficult to distinguish
this movement along the convex and concave edges of the cell of
any vigorous specimen of Closterium, if it be examined under a
magnifying power of 250 or 300 diameters; and a peculiar whirl-

Fic. 72.

Economy of Closterium lunula :—a, frond showing central separation at a, in which large globules.
b, are not seen ;—s, one extremity enlarged, showing at @ the double row of cilia, at U the internal
current, and ate the external current;—c, external jet produced by pressure on the froud ;—p, frond
in a state of self-division.

ing movement may also be distinguished, in the large rounded
space which is left at each end of the cell by the retreat of the

268 MICROSCOPIC FORMS OF VEGETABLE LIFE.

endochrome from the primordial utricle (Fig. 72, a, B). Accord-
ing to Mr. 8. G. Osborne, however, by using the “‘ Rainey mode-
rator” (§ 74), with direct sunlight and an achromatic condenser,
and. by increasing the power to about 500 diameters (Mr. Ross’s
objective of 1-6th in., with a deep eye-piece, being the combina-
tion employed), a very distinct action of cilia may be discerned,
both along the inner edge of the primordial utricle, between this
membrane and the endochrome, and along its outer edge, be-
neath the cellulose coat; the action being in opposite directions
in these two situations, and producing two opposite currents.
By careful focussing, the circulation may be seen in broad streams
over the whole surface of the endochrome; and these streams
detach and carry with them, from time to time, little oval or
globular bodies (4, 6), which are put forth from it, and which are
earried by the course of the flow to the chambers at the extremi-
ties, where they join a crowd of similar bodies (8). In each of
these chambers, a current may be seen from the somewhat abrupt
termination of the endochrome, towards the obtuse end of the
cell (as indicated by the interior arrows); and the globules it
contains are kept in a sort of twisting movement by the action
of the cilia on the znner side of the primordial utricle, which can
here be distinctly seen as at a. Other currents are seen externally
to it, which seem to be kept up by the outer set of cilia; these
form three or four distinct courses of globules, passing towards
and away from ¢ (as indicated by the outer arrows), where they
seem to encounter a fluid jetted towards them through an aper-
ture in the primordial utricle at the apex of the chamber; and
here some communication between the inner and the outer cur-
rents takes place. A corresponding aperture seems also to exist
in the outer cellulose coat; for if the endochrome be forced by
pressure into closer proximity than usual to the obtuse termina-
tion of the cell, the current from its extremity may be seen to
spread into the surrounding fluid. This circulation is by no
means peculiar to Closterium ; having been seen by Mr. Osborne
in many other Desmidiacez, in several of which he has also de-
tected what he believes to be ciliary action.!

165. When the single cell has come to its full maturity, it
commonly multiplies itself by duplicative subdivision ; but the
plan on which this takes place is often peculiarly modified, in
order to maintain the symmetry characteristic of the tribe. In
a cell of the simple cylindrical form of those of Didymoprium
(Fig. 77), little more is necessary than the separation of the two
halves, and the formation of a partition between them by the
infolding of the primordial utricle, according to the plan already

1See Mr. S. G. Osborne's commmnnications to the “ Quarterly Journal of Microscopical
Science,” vol. ii, p. 234, and vol. iii, p. 54. Although the Circulation is an unquestion-
able fact, it may be doubted whether the appearance of Ciliary action is not an optical
illusion, due to the play of the peculiar light employed, among the moving particles of

the fluid. See Mr. Wenham’s paper on the Circulation in the Leaf-Cells of Anacharis,
in the same Journal, vol. ili, p. 278.

MULTIPLICATION OF DESMIDIACEA 269

described (§ 150); and in this manner, out of the lowest cell of
the filament a, a double cell Bis produced. But it will be ob-
served that each of the simple cells has a bifid wart-like projec-
tion of the cellulose coat on either side, and that the half of this
projectian, which has been appropriated by each of the two new
cells, is itself becoming bifid, though not symmetrically; in process
of time, however, the increased development of the sides of the
cells which remain in contiguity with each other, brings up the
smaller projections to the dimensions of the larger, and the
symmetry of the cell is restored. In Closterium (Fig. 72, p), the
two halves of the endochrome first retreat from one another at
the middle line, and a constriction takes place round the cellu-
lose coat; this constriction deepens until it becomes an hour-
glass contraction, which proceeds until the cellulose coat entirely
closes round the primordial utricle of the two segments ; in this
state, one half commonly remains passive, whilst the other has
a motion from side to side, which gradually becomes more
active; and at last one segment quits the other with a sort of
jerk. At this time, a constriction is seen across the middle: of
the primordial utricle of each segment; but there is still only a
single chamber, which is that belonging to one of the extremities
of the original entire frond. The globular circulation, for some
hours previously to subdivision, and for a few hours afterwards,
runs quite round the obtuse end a of the endochrome; but
gradually a chamber is formed, like that at the opposite extre-
mity, by a separation between the cellulose coat and the primor-
dial utricle ; whilst at the same time, the obtuse form becomes
changed to a more elongated and contracted shape. Thus, in
five or six hours after the separation, the aspect of each extremity
becomes the same, and each half resembles the perfect frond in
whose self-division it originated; and the globular circulation
within the newly-formed chamber comes into connection with
the general circulation, some of the free particles which are
moving over the surface of the primordial utricle, being drawn
into its vortex and tossed about in its eddies. The process is
seen to be performed after nearly the same method in Stauras-
trum (Fig. T1, D, E); the division taking place across the central
constriction, and each half gradually acquiring the symmetry
of the original. In such forms as Cosmarium, however, in which
the cell consists of two lobes united together by a narrow isthmus
(Fig. 75), the division takes place after a different method; for
the central region of the isthmus expands, and displays two
globular enlargements, separated from each other and from the
two halves of the original cell (which their interposition carries
apart) by a narrow neck; and these enlargements increase, until
they assume the appearance of the half-segments of the original
cell. In this state, therefore, the plant consists of a row of four
segments, lying end to end, the two old ones forming the ex-
tremes, and the two new ones (which do not usually acquire the
full size or the characteristic markings of the original, before the

270 MICROSCOPIC FORMS OF VEGETABLE LIFE,

division occurs) occupying the intermediate place. At last the
central fusion becomes complete, and two bipartite fronds are
formed, each having one old and one young segment ; the young
segment, however, soon acquires the full size and characteristic
aspect of the old one; and the same process, the whole of which
may take place within twenty-four hours,’ is repeated ere long,
In Spherozosma, the cells thus produced remain connected in
rows within a gelatinous sheath, like those of Didymoprium
(Fig. 77); and different stages of the process may commonly be
observed in the different parts of any one of the filaments thus
formed. In any such filament, it is obvious that the two oldest
segments are found at its opposite extremities, and that each
subdivision of the intermediate cells must carry them further
and further from each other. This is a very different mode of
increase from that of the Confervacee, in which the terminal cell
alone undergoes subdivision (§ 198), and is consequently the last
formed.

166. Many of the Desmidiacee multiply after another method;
namely, by the subdivision of their endochrome into a multitude
of granular particles, termed gonidia; which are set free by the
rupture of the cell-wall, and of which every one may develope
itself into a new cell. These “ gonidia’” may be endowed with
cilia, and may possess an active power of locomotion, in which
case they are known as “ zoospores;” or they may be destitute
of any such power, and may become enclosed in a firm cyst or
envelope that seems destined for their long-continued preserva-
tion, in which case they are designated as ‘“‘resting-spores.” The
movement of the zoospores, first within the cavity of the cell
that gives origin to them, and afterwards externally to it, has
frequently been observed in the various species of Cosmarium;
and has been described under the title of “the swarming of the
granules,” from the extraordinary resemblance which the mass
of moving particles bears to a swarm of bees. The subsequent
history of their development, however, has not been fully traced
out; and this is a point to which the attention of Microscopists
should be specially directed. In Pediastrum, a plant whose frond
normally consists of a cluster of cells, the zoospores are not
emitted separately, but those formed by the subdivision of the
endochrome of one cell, which may be 4, 8, 16, 32, or 64 in
number, escape from the parent frond still enclosed in the inner
tunic of the cell; and it is within this that they develope them-
selves into a cluster, resembling that in which they originated.
This is well shown in the accompanying series of illustrations of
the developmental history of Pediastrum granulatum (Fig. 78, A-F),
a species whose frond normally consists of 16 cells, but may be

! See the observations of Mrs. Herbert Thomas on Cosmarium margaritiferwm, in
“Microscopical Transactions,” Second Series, vol. iii, pp. 33-36. Several varieties in
the mode of subdivision are described in this short record of long-continued observa-
tions, as of occasional occurrence.

MULTIPLICATION OF DESMIDIACES. 271

composed of either of the just mentioned multiples or sub-mul-
tiples of that number. At a is seen an old disk, of irregular
shape, nearly emptied by the emission of its gonidia, which had

Various phases of development of Pediastrum granulatum.

been seen to take place, within a few hours previously, from the
cells a, 6, c, d, e; most of the empty cells exhibit the cross slit
through which their contents had been discharged; and where
this does not present itself on the side next the observer, it oc-
curs on the other. Three of the cells still possess their colored
contents, but in different conditions. One of them exhibits an
early stage of the subdivision of the endochrome, namely, into
two halves, one of which already appears halved again. Two
others are filled by sixteen very closely crowded gonidia, only
half of which are visible, as they form a double layer. Besides
these, one cell is in the very act of discharging its gonidia; nine
of which have passed forth from its cavity, though still enveloped
in a vesicle formed by the extension of its innermost membrane;
whilst seven yet remain in its interior. The new-born family,
as it appears immediately on its complete emersion, is shown at
B; the gonidia are actively moving within the vesicle; and they
do not as yet show any indication either of symmetrical arrange-
ment, or of the peculiar form which they are subsequently to
assume. Within a quarter of an hour, however, the gonidia are
observed to settle down into one plane, and to assume some kind
of regular arrangement, most commonly that seen at c, in which
there is a single central body, surrounded by a circle of five, and
this again by a circle of ten; they do not, however, as yet adhere
firmly together. The gonidia now begin to develope themselves
into new cells, increase in size, and come into closer approxima-
tion (D); and the edge of each, especially in the marginal row,
presents a notch, which foreshadows the production of its charac-

272 MICROSCOPIC FORMS OF VEGETABLE LIFE.

teristic “horns.” Within about four or five hours after the
escape of the gonidia, the cluster has come to assume much
more of the distinctive aspect of the species, the marginal cells
having grown out into horns (g); still, however, they are not
very closely connected with each other; and between the cells of
the inner row, considerable spaces yet intervene. It is in the
course of the second day, that the cells become closely applied
to each other, and that the growth, of the horns is completed, so
as to constitute a perfect disk, like that seen at ¥, in which,
however, the arrangement of the interior cells does not follow
the typical plan.

167. The varieties which present themselves, indeed, both as
to the number of cells in each cluster, and the plan on which
they are disposed, are such as to baffle all attempts to base spe-
cific distinctions on such grounds: and the more attentively the
life-history of any one of these plants is studied, the more evident
does it appear that many reputed species have no real existence.
Some of these, indeed, are nothing else than mere transitory
forms; thus it can scarcely be doubted that the specimen repre-
sented in Fig. T4, p, under the name of Pediastrum pertusum, is
in reality nothing else than a young frond of P. granulatum, in
the stage represented in Fig. 78, B, but consisting of 32 cells.
On the other hand, in Fig. 74, B, we see an emptied frond of P.
granulatum, exhibiting the peculiar surface-marking from which
the name of the species is derived, but composed of no more

Fia. 74.

Various species (2) of Beueuatrian s—a, P. tetras; B, c, P. birudiutum; b, P. pertusum ; , emply
frond of P. granulatum.

than 8 cells. And instances every now and then occur, in which
the frond consists of only 4 cclls, each of them presenting the
two-horned shape. So, again, in Fig. 74, B and c, are shown two
varieties of Pediastrum biradiatum, whose frond is normally com-

MODES OF MULTIPLICATION OF DESMIDIACER 273

posed of sixteen cells; whilst at a is figured a form which is
designated as P. tetras, but which may be strongly suspected to
be merely a 4-celled variety of B and c.

168. Many similar cases might be cited ; and the Author would
strongly urge those Microscopists who have the requisite time
and opportunities, to apply themselves to the determination of
the real species of this group, by studying the entire life-history of
whatever forms may happen to lie within their reach, noting all
the varieties which present themselves among the offsets from
any one stock. It must not be forgotten that this process of
multiplication is analogous to the propagation of the higher Plants
by budding, and to the subsequent separation of the buds, either
spontaneously, or by the artificial operations of grafting, layer-
ing, &c.; and just as in all these cases, the particular variety is
propagated, whilst only the characters of the species are trans-
mitted by the true generative operation to the descendants raised
from seed, so does it come to pass that the characters of any par-
ticular variety which may arise among these unicellular Plants,
are diffused by the process of duplicative subdivision, amongst
vast multitudes of so-called individuals. Thus it happens that,
as Mr. Ralfs has remarked, “one pool may abound with indi-
viduals of Staurastrum dejectum or Arthrodesmus incus, having
the mucro curved outwards; in a neighboring pool, every speci-
men may have it curved inwards; and in another, it may be
straight. The cause of the similarity in each pool no doubt is,
that all its plants are offsets from a few primary fronds.’’ Hence
the universality of any particular character, in all the plants of
one gathering, is by no means sufficient to entitle these to take
rank as a distinct species; since they are, properly speaking, but
repetitions of the same form by a process of simple multiplication,
really representing, in their entire aggregate, the one plant or
tree that grows from a single seed.’ In the genus Celastrum, the
frond of which, like that of Pediastrum, is composed of clusters
of cells, the endochrome subdivides into segments, as if for the
formation of zoospores; but no motion takes place. These seg-
ments acquire cellulose coats, and arrange themselves within the
parent-cells according to the typical pattern; and then the wall
of the parent-cell splits and peels off, leaving them as the founda-
tion of a new cluster (Pringsheim). A somewhat parallel phe-
nomenon has been observed and figured in Closterium by Focke;
the entire endochrome being retracted from the walls, and break-
ing up into a number of globules, every one of which acquires a
very firm envelope, resembling that of the “resting-spores” or
‘‘winter-spores” of many other Protophytes. Probably the fol-
lowing observation of Mr. Jenner’s refers to a more limited pro-
duction of these “ resting-spores :’-—“In all the Desmidiacee,

1 For a discussion of the question what really constitutes individuality in this and
similar cases, see the Author’s “ Principles of Comparative Physiology,” Chap. XI, Sec-
tion 2.—.Am, Ed.

18

274 MICROSCOPIC FORMS OF VEGETABLE LIFE.

but especially in Clostertwm and Micrasterias, small, compact,
seed-like bodies of a blackish color are at times to be met with,
Their situation is uncertain, and their number varies from one to
four. In their immediate neighborhood the endochrome is want-
ing, as if it had been required to form them; but in the rest of
the frond it retains its usual color and appearance.” It seems
likely that, when thus enclosed in a firm cyst, the gonidia are
more capable of preserving their vitality, than they are when
destitute of such a protection; and that in this condition they
may be taken up and wafted through the air, so as to convey the
species into new localities.

169. The proper Generative process in the Desmidiacee is
always accomplished by the act of “ conjugation ;” and this takes
place after a manner very different from that which we have

seen to occur in Palmoglea. For

Fie. 75 each cell here possesses, it will be

recollected, a firm external enve-
lope, which cannot enter into coa-
lescence with that of any other;
and this membrane dehisces more
or less completely, so as to sepa-
rate each of the conjugating cells
into two valves (Fig. 75, o, D; Fig.
76, c). The contents of each cell,
being thus set free, without (as it
appears) any distinct investment,
blend with those of the other; and
a mass is formed by their union,
which so acquires a truly mem-
branous envelope.’ This envelope
is at first very delicate, and is

Cosmarium botrytis:—a, mature frond; filled with green and granular Gone

8, empty frond; c, transverse view; 2, tents; by degrees the envelope ac-
sporangium with empty fronds. quires increased thickness, and the
contents of the spore-cell become
brown or red. The surface of the sporangium, as this body is
now termed, is sometimes smooth, as in Closteriwm and its allies
(Fig. 76), and in the Desmidiee proper (Fig. 77); but in the
Cosmariec, it acquires a granular, tuberculated, or even spinous
surface (Fig. 75), the spines being sometimes simple and some-
times forked at their extremities.”

170. The mode in which conjugation takes place in the fila-
mentous species constituting the Desmidiew proper, is, however,
in many respects different. The filaments first separate into
their component joints; and when two cells approach in con-

1 In Closterium lineatum, as in many of the Dialomacee (§ 178), the act of conjugation
gives origin to two sporangial cells. ;

2 Bodies precisely resembling these, and almost certainly to be regarded as of this
kind, are often found fossilized in flint, and have been described by Ehrenberg under
the name of Nanthidia.

CONJUGATION OF FILAMENTOUS DESMIDIACER 275

jugation, the outer cell-wall of each splits or gapes at that part
which adjoins the other cell,
and a new growth takes
place, which forms a sort of
connecting tube, uniting the
cavities of the two cells(Fig. |
TT, D, E). Through this tube GP __
the entire endochrome of ¢
one cell passes over into the
cavity of the other (p), and
the two are commingled so
as to form a single mass (8),
as is the case in many of the
Conjugatee (§ 199). The
joint which contains the
sporangium can scarcely be
distinguished at first (after
the separation of the empty — ctosierium striatolum:—a, ordinary frond; 8,
cell), save by the greater empty frond; c, two fronds in conjugation.
density of its contents; but
the proper coats of the sporangium gradually become more dis-
tinct, and the enveloping cell-wall disappears. The subsequent
history of the sporangia is still obscure; since, although it can-
not be doubted that they give origin to new plants resembling
those by whose conjugation they are formed, it is not known
whether each sporangium in the first instance developes a single
cell, or a brood of cells. The latter seems, from the observa-
tions of Jenner and Focke, to be the case with Closterium ;
whilst those of Mrs. H. Tho-
Fie, 77. mas (loc. cit.) indicate that it is
likewise in Cosmarium, whose
sporangium has been seen by
her to emit large numbers of
bodies resembling zoospores.
This part of the history of
the group is yet involved in
much mystery; more espe-

Didymoprium Grevillii :—a, portion of filament, surrounded by gelatinous envelope ; B, dividing
joint; c, single joint viewed transversely ; D, two cells in conjugation ; £, formation of sporangium.

cially since, according to the observations of Mr. Ralfs, there

276 MICROSCOPIC FORMS OF VEGETABLE LIFE,

are several Desmidiacese which never make their appearance in
the same pools for two years successively, although their spo-
rangia are abundantly produced,—a circumstance which would
seem to indicate that their sporangia give origin to some dif.
ferent forms. It is a subject, therefore, to which the attention
of Microscopists cannot be too sedulously directed.

171. The Desmidiacee are not found in running streams,
unless the motion of the water be very slow; but are to be
looked for in standing, but not in stagnant waters. Small shal-
low pools that do not dry up in summer, especially in open ex-
posed situations, such as boggy moors, are most productive.
The larger and heavier species commonly lie at the bottom of
the pools, either spread out as a thin gelatinous stratum, or col-
lected into finger-like tufts. By gently passing the fingers be-
neath these, they may be caused to rise towards the surface of
the water, and may then be lifted out by a tin box or scoop.
Other species form a greenish or dirty cloud upon the stems and
leaves of other aquatic plants; and these also are best detached
by passing the hand beneath them, and “stripping” the plant
between the fingers, so as to carry off upon them what adhered
to it. If, on the other hand, the bodies of which we are in search
should be much diffused through the water, there is no other
course than to take it up in large quantities by the box or scoop,
and to separate them by straining through a piece of linen. At
first nothing appears on the linen but a mere stain or a little
dirt; but by the straining of repeated quantities, a considerable
accumulation may be gradually made. This should be then
scraped off with a knife, and transferred into bottles with fresh
water. If what has been brought up by hand be richly charged
with these forms, it should be at once deposited in a bottle; this
at first seems only to contain foul water; but by allowing it to
remain undisturbed for a little time, the Desmidiaces will sink
to the bottom, and most of the water may then be poured off, to
be replaced by a fresh supply. If the bottles be freely exposed
to solar light, these little plants will flourish, apparently as well
as in their native pools; and their various phases of multiplica-
tion and reproduction may be observed during successive months
or even years. If the pools be too deep for the use of the hand
and the scoop, a collecting-bottle attached to a stick (§ 148) may
be employed in its stead. The ‘“ring-net’’ may also be advanta-
geously employed, especially if it be so constructed as to allow
of the ready substitution of one piece of muslin for another
($143). For by using several pieces of previously-wetted muslin
in succession, a large number of these minute organisms may be
separated from the water; the pieces of muslin may be brought
home, folded up in wide-mouthed bottles, separately, or several
in one, according as the organisms are obtained from one or from
several waters; and they are then to be opened out in jars of
filtered river-water, and exposed to the light, when the Desm1-
diacese will detach themselves from it.

GENERAL CHARACTERS OF DIATOMACEA, 277

172. Diatomacee.—Notwithstanding the very close affinity,
which, as will be presently shown, exists between this group and
the preceding, many Naturalists who do not hesitate inregarding
the Desmidiace as Plants, persist in referring the Diatomacese
to the Animal kingdom. For this separation, no valid reason
can be assigned ; the curious movements which the Diatomacez
exhibit, being certainly not of a nature to indicate the possession
of any truly animal endowment; and all their other characters
being unmistakably vegetable. Like the Desmidiacese, they are
simple cells, having a firm external coating, within which is in-
cluded a mass of endrochrome whose superficial layer seems to
be consolidated into a sort of primordial utricle. The external
coat, however, though it seems to have a basis of organic mem-
brane,’ is consolidated by szlex; the presence of which in this
situation is one of the most distinctive characters of the group.
The endochrome, instead of being bright green, is of a yellowish-
brown; and its peculiar color seems to be in some degree de-
pendent upon the presence of zron, which is assimilated by the
plants of this group, and which may be detected even in their
colorless silicified envelopes. The coloring substance appears to
be a modification of ordinary chlorophyll; it takes a green or
greenish-blue tint with sulphuric acid; and often assumes this
hue in drying. The endochrome consists, as in other Plants, of
a viscid protoplasm, in which float the granules of coloring
matter. In the ordinary condition of the cell, these granules are
diffused through it with tolerable uniformity, except in the cen-
tral spot which is occupied by a nucleus; round this nucleus
they, commonly form a ring, from which radiating lines of
granules may be seen to diverge into the cell-cavity. At certain
times, oil-globules are observable in the protoplasm; these seem
to represent the starch-granules of the Desmidiacese (§ 163) and
the oil-globules of other Protophytes (§ 151). A distinct move-
ment of the granular particles of the endochrome, closely re-
sembling the circulation of the cell-contents of the Desmidiaces
(§ 164), has been noticed by Prof. W. Smith in some of the larger
species of Diatomacee, suchas Surirella biseriata, Niteschia scalaris,
and‘ Campylodiscus spiralis; and although this movement has
not the regularity so remarkable in the preceding group, yet its
existence 18 important, as confirming the conclusion that each
Diatom is a single cell (the endochrome moving freely from one
part of its interior to another), and that it does not contain in its

! A membrane bearing all the markings of the siliceous envelope has been found by
Prof. Bailey to remain, after the removal of the silex by hydrofluoric acid; and this
membrane seems to have been presumed by him, as also by Prof. W. Smith, to lie
beneath the siliceous envelope, and to secrete this on its surface as a sort of epidermis,
The Author agrees, however, with the authors of the “Micrographic Dictionary” (p.
200), in considering it much more likely that this membrane is the proper “ cellulose
coat” interpenetrated by silex; especially since it has been found by Schmidt, that after
removing the protoplasm of Frustulia salina by potash, and the oil by ether, a substance
remained identical in composition with the cellulose of Lichens.

278 MICROSCOPIC FORMS OF VEGETABLE LIFE.

interior the aggregation of separate organs which have been
imagined to exist in it.

173. The Diatomaces seem to have received their name from
the readiness with which those forms that grow in coherent
masses (which were those with which Naturalists first became
acquainted) may be cut or broken through ; hence they have been
also designated by the vernacular term “‘brittle-worts.” Of this
we have an example in the common Diatoma (Fig. 94), whose
component cells (which in this tribe are usually designated as
frustules) are sometimes found adherent side by side (as at 5) so
as to form filaments, but are more commonly met with in a state
of partial separation, remaining connected at their angles only
(usually the alternate angles of the contiguous frustules) so as to
form a zigzag chain. A similar cohesion at the angles is seen
in the allied genus Grammatophora (Fig. 95), in Isthmia (Fig. 96),
and in many other Diatoms; in Biddulphia (Fig. 81), there even
seems to be a special organ of attachment at these points. In
some Diatoms, however, the cells produced by successive acts of
binary subdivision, habitually remain adherent one to another;
and thus are produced filaments or clusters of various shapes.
Thus it is obvious that, when each cell is a short cylinder, an
aggregation of such cylinders, end to end, must form a rounded
filament, as in Melosetra (Figs. 97, 98); and whatever may be the
form of the sides of the cells, if they be parallel one to the other,
a straight filament will still be produced, as in Achnanthes (Fig.
93). But if, instead of being parallel, the sides be somewhat
inclined towards each other, a curved band will be the result;
this may not continue entire, but may so divide itself as to form
fan-shaped expansions, as those of Lichmophora flabellata (Fig.
91); or the cohesion may be sufficient to occasion the band to
wind itself (as it were) round a central axis, and thus, not merely
to form a complete circle, but a spiral of several turns, as in Me-
ridion circulare (Fig. 92, B). Many Diatoms, again, possess a
stipes or stalk-like appendage, by which they are attached to
other plants or to stones, pieces of wood, &c., and this may be a
simple foot-like appendage, as in Achnanthes longipes (Fig. 98),
or it may be a composite plant-like structure, as in Lichmophora
(Fig. 91), Gomphonema (Fig. 89), and Mastogloia (Fig. 99). Little
is known respecting the nature of this stipes; it is, however,
quite flexible; and may be conceived to be an extension of the
cellulose coat unconsolidated by silex, analogous to the prolonga-
tions which have been seen in the Desmidiacee (§ 168), and to the
filaments which sometimes connect the cells of the Palmellacee
(§ 194). Some Diatoms, again, have a mucous or gelatinous 1n-
vestment, which may even be so substantial that they lie as it
were in a bed of it, as in Mastogloia (Figs. 99, 100), or which
may form a sort of tubular sheath, as in Schizonema. Ina large
proportion of the group, however, the frustules are always met
with entirely free; neither remaining in the least degree coherent

SILICEOUS ENVELOPE OF DIATOMACESA. 279

one to another, after the process of duplicative subdivision has
once been completed; nor being in any way connected, either
by a stipes, or by a gelatinous investment. ‘This is the case, for
example, with J'riceratium (Fig. 79), Pleurosigma (Fig. 80), Acti-
nocyclus (Figs. 84, 101, 6 6), Heliopelta (Fig. 85), Arachnotdiseus
(Fig. 86), Campylodiscus (Fig. 87), Surirella (Fig. 88), Coscenodiscus
(Fig. 101, a, a, a), and many others. The discoid forms, how-
ever, when obtained in their living state, are commonly found
cohering to the surface of seaweeds.

174. We have now to examine more minutely into the curious
structure of the siliceous envelope, which constitutes the charac-
teristic feature of the Diatomaces, and the presence of which
imparts a peculiar interest to the group, not merely on aecount
of the elaborately marked pattern which it often exhibits, but
also through the perpetuation of the minutest details of that
pattern, in the specimens obtained from fossilized deposits (Figs.
101, 102). The siliceous envelope of every Diatomaceous “ frus-
tule” or cell, consists of two valves or plates, usually of the most
perfect symmetry, closely applied to each other, like the two
valves of a Mussel or other bivalve shell, along a line of fracture
or suture; and each valve being more or less concavo-convex, a
cavity is left between the two, which is occupied by the cell-con-
tents. The form of this cavity, however, differs very greatly ;
for sometimes each valve is hemispherical, so that the cavity is
globular; sometimes it is a smaller segment of a sphere, re-
sembling a watch-glass, so that the cavity is lenticular; some-
times the central portion is completely flattened, and the sides
abruptly turned up, so that the valve resembles the cover of a
pill-box, in which case the cavity will be cylindrical; and these
and other varieties may coexist with any modifications of the
contour of the valves, which may be square, triangular (Fig. 79),
heart-shaped (Fig. 87), boat-shaped (Fig. 88, a), or very much
elongated (Fig. 80, a), and may be furnished (though this is rare
among the Diatomacee) with projecting outgrowths (Fig. 81).
Tn all instances, the frustule is considered to present its “front”
view, when its suture is turned towards the eye, as in Fig. 88, B,
Cc; whilst its “‘side” view is seen, when the centre of either valve
is directly beneath the eye (a). Although the two valves meet
along the suture, in those newly formed frustules which have
been just produced by binary subdivision (as shown in Fig. 81,
A, e), yet as soon as they begin to undergo any increase, the
valves separate from one another, and the cell-membrane which
is thus left exposed, immediately becomes consolidated by silex,
and thus forms a sort of hoop that intervenes between the valves
(as seen at B); this hoop becomes broader and broader with the
increase of the cell in length; and it sometimes attains a very
considerable width (Fig. 81, a, 4). As growth and self-division
are continually going on when the frustules are in a healthy
vigorous condition, it is rare to find a specimen in which the
valves are not in some degree separated by the interposition of

280 MICROSCOPIC FORMS OF VEGETABLE LIFE.

the “hoop.” The impermeability of the siliceous envelope ren-
ders necessary some special aperture, through which the sur-
rounding water may communicate with the contents of the cell.
Such apertures are found along the whole line of suture in disk-
like frustules; but when the Diatom is of an elongated form,
they are found at the extremities of the frustules only. They
do not appear to be absolute perforations in the envelope, but
are merely points at which its siliceous impregnation is wanting;
and these are usually indicated by slight depressions of its sur-
face. In some Diatoms, as Surirella (Fig. 88) and Campylodiscus
(Fig. 87), these interruptions are connected with what seem to
be minute canals hollowed out between the siliceous envelope
and the membrane investing the endochrome. In many genera,
the surface of each valve is distinguished by the presence of a
longitudinal band, on which the usual markings are deficient;
and this is widened into small expansions at the extremities, and
sometimes at the centre also, as we see in Pleurosigma (Fig. 80)
and Gomphonema (Fig. 89). This band seems to be merely a
portion in which the siliceous envelope is thicker than it is else-
where, forming a sort of rib that seems designed to give firmness
to the valve; and its expansions are solid nodules of the same
substance.?

175. The nature of the delicate and regular markings, with
which probably every Diatomaceous valve is beset, has been of
late years a subject of much discussion among Microscopists, and
cannot be said to be even yet settled, although (in the Author's
opinion) the weight of evidence now decidedly preponderates on

one side. In the first place

Fra. 78. it may be remarked, that

there is a much greater uni-
formity in the general cha-
racter of these markings,
than was supposed when at-
tention was first directed to
them; for what were at first
supposed to be denes, are now
resolved by objectives of
large angular aperture into
j i j aS. rows of dots ; and these dots,
OPRGOROS3O8I0Z805 0 3" when sufficiently magnified,
Portion of Cell of Isthnia nervosa, highly magnified. €@YC found to bear a close
resemblance to the coarser

markings on the larger species. It is to the latter, therefore.

'These nodules were mistaken by Prof. Ehrenberg for apertures; and in this error
he has been followed by Kitzing. There cannot any longer, however, be a doubt a>
to their real nature. As Prof. W. Sinith has justly remarked :—“ The internal contents
of the frustule never escape at these points when the frustule is subjected to pressure.
but invariably at the suture or at the extremities, where the foramina already described
exist. Nor does the valve, when fractured, show any disposition to break at the ex-
pansions of the central line, as would necessarily be the case were such points perfo-
rations and not nodules,”

NATURE OF SURFACE MARKINGS OF DIATOMACES. 281

that we should have recourse for the determination of the nature
of these markings; and we cannot resort to better illustrations,
than those which are afforded by Jsthmia (Fig. 78), Triceratium
(Fig. 79), and Biddulphia (Fig. 81), in all of which the structure
of the valve can be distinctly seen under a low magnifying
power and with ordinary light. In each of these instances, we
see a number of areole, rounded,

oval, or hexagonal, with intervening Fra. 79.

spaces symmetrically disposed; and
the idea at once suggests itself, that
these areole are portions of the sur-
face either elevated above or depressed
below the rest. That the latter is
their true condition, is suggested by
the appearances they present when
the light is obliquely directed; and
it may also be inferred from the as-
‘pect presented by these objects when
viewed by the black ground illumi-
nation (§ 61), since the areole are
then less bright than the interven-
ing spaces, less light being stopped
by their thinner substance. More-
over, when a valve is broken, the
line of fracture corresponds to what,
on this supposition, is its weakest
portion ; since it passes through the
areole, instead of through the inter-
vening spaces, which last would be
the weaker portions if the areole
were prominences. But the most satisfactory proof that the
areole are depressions, is perhaps that which is afforded by a
side view of them, such as may be obtained by examining the
curved edges of the valves in IJsthmza; this, 1t may be safely
affirmed, can leave no doubt in the mind of any competent and
unprejudiced observer, as to the nature of the markings in that
genus; and analogy would seem to justify the extension of the
same view to the other cases in which the microscopic appear-
ances correspond. Now, it would not be difficult to bring
together a connected series of Diatomacex, in which the mark-
ings, still exhibiting the same general aspect, become more and
more minute, requiring for their resolution the use of oblique

'It is considered by Prof. W. Smith, that this areolation is indicative of a cellular
structure in the siliceous envelope. But when it is borne in mind that the entire frus-
tule constitutes a single cell, such an hypothesis seems altogether inadmissible. The
Author would rather consider the markings in question as analogous to those which are
presented by the surface of many pollen-grains (Fig. 189), of whose single-celled nature
no doubt can exist; and in his researches on the Foraminifera, he has met with several
instances, in which the calcareous investments of those segments of sarcode which must
be considered as the representatives of single cells, are marked with a like areolation,

the areole being here unquestionably depressions, formed by the thinning away of the
envelope at those parts.

Triceratium favus:—a, side view; B, front
view.

282 MICROSCOPIC FORMS OF VEGETABLE LIFE,

light or of stops with a central diaphragm, and of objectives of
larger and larger angular aperture ; until we come to those species
which present the greatest difficulty, and the nature of whose
markings seem most obscure. The more perfectly these mark-
ings can be defined, however, in any case, the more decidedly
are they found to correspond with what has been already seen.
Thus, if we examine Pleurosigma angulatum, one of the easier
tests (§ 102), with an objective of 1-4th inch focus and 75° aper-
ture, we shall see very much what is represented in Fig. 80, a;
namely, a double series of somewhat interrupted lines, crossing
each other at an angle of 60 degrees, so as to have between them
imperfectly defined lozenge-shaped spaces.’ When, however,

A Fia. 80.

Pleurosigma angulatum:—a, entire
frustule, as seen under a power of 500
diam.; B, hexagonal areolation, as seen
under a power of 1800 diam.; c, the
same, as seen under a power of 16,000
diam.

the valve is examined with an objective of 1-12th inch focus,
having an angular aperture of 130°, and is illuminated by oblique
rays, its hexagonal areolation becomes very distinct, as shown at
zg. And if a photographic representation obtained by such a
power be itself enlarged by photography, as has been accom-

) This representation is taken from a Photograph by Mr, Delves, which is imitated as

closely as Wood-engraving can imitate on a scale of such minuteness, but with a reversal
of the lights and shades,

DUPLICATIVE SUBDIVISION IN DIATOMACEA. 283.

plished by Mr. Wenham, the appearance represented at c is
obtained ; which is in all respects comparable with that presented
under a low power by the valve of Triceratium or Isthmia. At the
upper part of this figure, which represents a portion of the object
that was accurately in focus, the hexagonal ares are seen to be
light, and the intervening spaces dark; the reverse is the case with
the lower portion, which was out of focus; and a curious transition
from one condition to the other is seen in the intermediate part.
176. The process of multiplication by self-division takes place
among the Diatomace on the same general plan as in the Des-
midiacex, but with some modifications incident to the peculiari-
ties of the structure of the former group. The first stage con-
sists in the elongation of the cell, and the increase in the breadth
of the “hoop,” which is well seen in Fig. 81; for in the newly-
formed cell e, the two valves are
in immediate apposition, in d Fig. 81.
a hoop intervenes, in a this
hoop has become much wider,
and in é the increase has gone
on until the original form of
the cell is completely changed.
At the same time, the endo-
chrome separates into two halves
so that its granules form two
layers, applied to the opposite
sides of the frustule; the nu-
cleus also subdivides, in the
manner formerly shown (Fig.
67, 6, H, 1); and (although the
process has not been clearly
made out in this group) it may
be pretty certainly concluded
that the primordial utricle folds
in, first forming a mere con-
striction, then an hour-glass
contraction, and finally a com-
plete double partition, as in Biddulphia puichella. ;—a, chain of cells in
other instances (§ 165). From different states; a, full size; b, elongating
each of these two surfaces a Preparatory to subdivision; ¢, formation of
new siliceous valve is formed, eee cee ay eal uae
as shown at Fig. 81, a,c, just — magnifiea
as a new cellulose wall is gene-
rated in the subdivision of other cells; and this valve is usually

} The Author does not think it necessary to go more in full into the discussion of the
nature of these markings, which some have represented to be due to hemispherical
elevations on the valves; as he thinks that no argument is likely to convince those,
whose minds are prepossessed with a conception which influences their interpretation
of what they see. To those who come fresh to the question, he would strongly recom-
mend the education of their judgment upon the larger and more closely marked Diatoms,
as above described, before they commit themselves to an opinion on either side. A
fuller statement of the question will be found in the “ Micrographic Dictionary,” * Intro-
duction,” p. xxxiii, and Arts, “ Angular Aperture” and “ Diatomacee.”

284 MICROSCOPIC FORMS OF VEGETABLE LIFE.

the exact counterpart of the one to which it is opposed, and
forms with it a complete cell, so that the original frustule is
replaced by two frustules. Sometimes, however, the new valves
seem to be a little larger than their predecessors; so that, in the
filamentous species, there may be an increase sufficient to occa-
sion a gradual widening:of the filament, although not percepti-
ble when two contiguous frustules are compared; whilst, in the
free forms, frustules of different sizes may be met with, of which
the larger are more numerous than the smaller, the increase in
number having taken place in geometrical progression, whilst
that of size was uniform. It is not always clear what becomes
of the “hoop.” In Biddulphia and Isthmia (Fig. 96) the two
young cells slip out of it, and the hoop at last becomes com-
pletely detached; and the same thing happens with many other
Diatoms; so that the “hoops” are to be found in large numbers,
in the settlings of water in which they have been growing for
some time. In Meloseira (Figs. 97, 98), and perhaps in the fila-
mentous species generally, on the other hand, the “hoops”
appear to keep the new frustules united together for some time.
But in some other eases, all trace of it is lost; and it may be
questioned whether it has ever been properly silicified, and
whether it does not become fused (as it were) into the gelatinous
envelope. During the healthy life of the Diatom, the process of
self-division is continually being repeated; and a very rapid
multiplication of frustules thus takes place, all of which (as in
the cases already cited, §§ 150, 165) must be considered to be
repetitions of one and the same individual. Hence it may hap-
pen (as among the Desmidiacee, § 168) that myriads of frustules
may be found in one locality, uniformly distinguished by some
peculiarity of form, size, or marking; which may yet have had
the same remote origin as another collection of frustules, found
in some different locality, and alike distinguished by some pecu-
liarity of its own.. For there is strong reason to believe, that
such differences spring up among the progeny of any true gene-
rative act (§ 178); and, when that progeny is dispersed by cur-
rents into different localities, each will continue to multiply its
own special type, so long as the process of self-division goes on.

177. It is uncertain whether the Diatomacee also multiply by
the breaking up of their endochrome into “gonidia,” and by
the liberation of these, either in the active condition of “zo0-
spores,” or in the state of “still” or “resting” spores. Certain
recent observations by Focke,’ however, taken in connection
with the analogy of other Protophytes, and with the fact that
the sporangial frustules undoubtedly thus multiply by gonidia
(§ 178), seem to justify the conclusion that such a method of
multiplication does obtain in this group. And it is not at all
improbable, that very considerable differences in the size, form,

1“ Physiologisch. Studien,” Heft ii, 1853; quoted in “ Micrographical Dictionary,”
p. 201.

CONJUGATION OF DIATOMACEA, 285

and markings of the frustules, such as many consider sufficient
to establish a diversity of species, have their origin in this mode
of propagation. It is probable that, so long as the vegetating
processes are in full activity, multiplication takes place in pre-
ference by self-division ; and that it is when deficiency of warmth,
of moisture, or of some other condition, gives a check to these,
that the formation of encysted gonidia, having a greater power
of resisting unfavorable influences, will take place; whereby the
species is maintained in a dormant state, until the external con-
ditions are favorable to a renewal of active vegetation (§ 156).
178. The process of “conjugation,” or true Generation, has
been observed to take place among the ordinary Diatomacer,
almost exactly as among the Desmidiacee. Thus in Surirella
(Fig. 88), the valves of two free and adjacent frustules separate
from each other at the sutures, and the two endochromes (proba-
bly included in their primordial utricle) are discharged; these
coalesce, and form a single sporangial mass, which becomes
enclosed in a gelatinous envelope; and in due time this mass
shapes itself into a frustule resembling that of its parent, but of
larger size. In Epithemia (Fig. 82, a, B), however,—the first
Diatom in which the conjugating process was observed, by Mr.
Thwaites,—the endochrome of each of the conjugating frustules
(Cc, D) appears to divide at the time of its discharge, into two
halves; each half coalesces
with half of the other endo- Fie, 82.
chrome; and thus two spo-
rangial frustules (&, F) are
formed (as in Closteriwm linea-
tum, § 169, note), which, as in
the preceding case, become
invested with a gelatinous
envelope, and gradually as-
sume the form and markings
of the parent frustules, but
grow to a very much larger
size, the sporangial masses
having obviously a power of
self-increase up to the time
when their envelopes are con-
solidated. This double conju-
gation seems to be the ordi-
nary type of the process hier ce
among the Diatoms, A eu- ,Cavuein of Aptis copes a ou
rious departure from the same; ¢, ae ete steht tetE concave sur-
usual plan is observed in faces in close apposition; D, front view of one
some of the filamentous spe- of the frustules, showing the separation of its
+ : valves along the suture; =, #,.side and front
C1ES 5 for their component views afterthe formation of the sporangia.
cells, instead of conjugating

with those of another filament (as is the case with the filamen-

286 MICROSCOPIC FORMS OF VEGETABLE LIFE,

tous Desmidiacee, § 170, and usually but not invariably with the
Zygnemacee, § 199), conjugate with each other; and this may
take place even before they have been completely separated by
self-division. Thus in Melosezra (§ 188) and its allies, the endo-
chrome of particular frustules, after separating as if for the
formation of a pair of new cells, moves back from the extremi-
ties towards the centre, rapidly increasing in quantity and aggre-
gating into a sporangial mass (Fig. 83, 2, a, b,c), and around

Fig. 83.

Self-Conjugation of Aulacoseira crenulata:—1, simple filament; 2, filament developing sporangia;
a, b, ¢, successive stages in the formation of sporangia; 3, embryonic frustules, in successive stages;
a, b, c, of multiplication,

this a new envelope is developed, which may or may not resem-
ble that of the ordinary frustules, but which remains in conti-
nuity with them, giving rise to a strange inequality in the size of
the different parts of the filaments (Figs. 97, 98). Of the subse-
quent history of the sporangial frustule, much remains to be
learned; and it is probably not the same in all cases. It has
been already shown that the sporangial frustule, even where it
precisely resembles its parent in form and marking, greatly
exceeds it in size; and this excess seems to render it improbable
that it should reproduce the race by ordinary self-division.
Appearances have been seen, which make it probable that the
contents of each sporangial frustule break up into “ gonidia;”
and that it is from these that the new generation originates.
These gonidia, if each be surrounded (as in many other cases)
by a distinct cyst, may remain undeveloped for a considerable
period; and they must augment considerably in size, before they
attain the dimensions of the parent frustule. It is in this stage
of the process, that the modifying influence of external agencies
is most likely to exert its effects; and it may be easily conceived
that (as in higher Plants and Animals) this influence may give
rise to various diversities among the respective individuals of
the same brood; which diversities (as we have seen) are trans-
mitted to all the repetitions of each, that are produced by the

MOVEMENTS OF DIATOMACESA, 287

self-dividing process. Hence a very considerable latitude is to
be allowed to the limits of species, when the different forms of
Diatomacez are compared; and here, as in many other cases, a
most important question arises as to what are those limits,—a
question which can only be answered by such a careful study of
the entire life-history of every single type, as may advantage-
ously occupy the attention of many a Microscopist, who is at
present devoting himself to the mere detection of differences,
and to the multiplication of reputed species.’

179. Most of the Diatoms which are not fixed by a stipes, pos-
sess some power of spontaneous movement; and this is especially
seen in those, whose frustules are of a long narrow form, such as
that of the Navicule generally. The motion is of a peculiar kind,
being usually a series of jerks, which carry forward the frustule
in the direction of its length, and then carry it back through
nearly the same path. Sometimes, however, the motion is smooth
and equable; and this is especially the case with the curious Ba-
cillaria paradora (Fig. 92, B), whose frustules slide over each
other in one direction, until they are all but detached, and then
slide as far in the opposite direction, repeating this alternate
movement at very regular intervals.? In either case, the motion
is obviously quite of a different nature from that of beings pos-
sessed of a power of self-direction. ‘ An obstacle in the path,”
says Prof. W. Smith, “is not avoided, but pushed aside; or, if it
be sufficient to avert the onward course of the frustule, the latter
is detained for a time equal to that which it would have occupied
in its forward progression, and then retires from the impediment
as if it had accomplished its full course.” The character of the
movement is obviously similar to that of those motile forms of
Protophyta which have been already described; but it has not
yet been definitely traced to any organ of impulsion; and the
cause of it is still obscure. By Prof. W. Smith it is referred to

' See on this subject a valuable Paper by Prof. W. Smith “On the Determination of
Species in the Diatomacee,” in the “ Quart. Journ. of Microsc. Science,” vol. iii, p. 130:
a Memoir by Prof. W. Gregory “On shape of Outline as a specific character of Diato-
macee,” in “Trans. of Microsc. Soc.,” 2d Series, vol. iii; and the Author's Presidential
Address in the same volume, pp. 44-50. ;

? This curious phenomenon, the Author has himself more than once had the oppor-
tunity of witnessing.

3 Prof. Smith says:—“ Among the hundreds of species which I have examined in
every stage of growth and phase of movement, aided by glasses which have never been
surpassed for clearness and definition, I have never been able to detect any semblance
of a motile organ; nor have I, by coloring the fluid with carmine or indigo, been able to
detect in the colored particles surrounding the Diatom, those rotary movements, which
indicate, in the various species of true Infusorial animalcules, the presence of cilia.”
(Synopsis of British Diatomaces, Introduction, p. xxiv.)—Mr. Jabez Hogg, however, has
recently stated (“ Quart. Journ. of Microsc. Science,” vol. iii, p. 235) that by the employ-
ment of the same mode of illumination as that by which the ciliary action may be dis-
cerned in Closterium, &c. (§ 164), a ciliary movement may be detected at the orifices
which have already been described as existing in the siliceous envelope of the Diato-
maceons frustule (§ 174). It may be questioned, however, whether this be anything
else than an optical illusion, arising from the existence of currents at these orifices, pro-
duced by the vital actions going on within the cell, as noticed above.

288 MICROSCOPIC FORMS OF VEGETABLE LIFE.

forces operating within the frustule, and originating in the vital
operations of growth, &c., which may cause the surrounding fluid
to be drawn in through one set of apertures, and expelled through
the other.' “If,” as he remarks, “the motion be produced by
the exosmose taking place alternately at one and the other ex-
tremity, while endosmose is proceeding at the other, an alterna-
ting movement would be the result in frustules of a linear form;
whilst in others of an elliptical or orbicular outline, in which
foramina exist along the entire line of suture, the movements, if
any, must be irregular or slowly lateral. Such is precisely the
ease. The backward and forward movements of the Navicule
have been already described ; in Surirella (Fig. 88) and Campylo-
discus (Fig. 87), the motion never proceeds further than a languid
roll from one side to the other; and in Gomphonema (Fig. 89), in
which a foramen, fulfilling the nutritive office, is found at the
larger extremity only, the movement (which is only seen when
the frustule is separated from its stipes) is a hardly perceptible
advance in intermitted jerks in the direction of the narrow end.”

180. The principles upon which this interesting group should
be classified, cannot be properly determined, until the history of
the Generative process,—of which nothing whatever is yet known
in a large proportion of Diatoms, and very little in any of them,—
shall have been thoroughly followed out. As already stated,
there is a strong probability that many of the forms which are at
present considered as distinct from each other, would prove to be
but different states of the same, if their whole history were ascer-
tained. On the other hand, it is by no means impossible that
some which appear to be nearly related in the structure of their
frustules and in their mode of growth, may prove to have quite
different modes of reproduction. At present, therefore, any clas-
sification must be merely provisional; and in the notice now to
be taken of some of the most interesting forms of the Diatomacez,
the method of Prof. W. Smith, which is based upon the degree
of connection that remains between the several frustules after
self-division, will be adopted, since it possesses the advantage of
being in accordance with the general “ physiognomies”’ of these
organisms, as it brings together those forms which correspond
most closely in plan of growth; but it cannot be regarded as a
truly natural classification, since it often separates genera which
are closely allied in the structure of the individual frustules, as,
for example, Coscinodiscus and Meloseira. The whole order is
thus grouped, in the first instance, under two Tribes; the first
including those which have the frustules naked, that is, neither

‘It has been objected to this view, by the authors of the “ Micrographic Dictionary,”
that, if such were the case, the like movements would be frequently met with in other
minute unicellular organisms. They seem to have forgotten, however, that there are
no other such organisms, in which the cell is almost entirely enclosed in an impermeable
envelope, which limits the imbibition and expulsion of fluid to a small number of defi-
nite points, instead of allowing it to take place equally (as in other unicellular organisms)
over the entire surface.

CLASSIFICATION OF DIATOMACEA, 289

imbedded in gelatine, nor enclosed in a membranaceous tube;
whilst the second is composed of those forms, whose frustules
have a gelatinous or membranaceous envelope. The frustules of
the Diatoms belonging to the first tribe, however, may have
various degrees of connection; for whilst, in some (a), the union
is dissolved almost immediately upon the completion of self-
division, there are others (6) in which a gelatinous cushion or a
stipes, to which the frustules are attached by a small portion of
their surface, maintains a partial connection between the divided
frustules, and others (¢), again, in which the frustules remain in
more or less complete cohesion, and form filaments, which, if
the cohesion be limited to the angles of the frustules, are mere
zigzag chains, but, if the cohesion extend to the entire surfaces
of their sides, are continuous filaments, either flattened or cylin-
drical.

181. That section of the first tribe, in which the frustules are
entirely disconnected from each other after the completion of
their self-division, includes anumber of beautiful discoidal forms,
which seem to constitute a natural group, and may therefore be
appropriately noticed in connection with each other. The genus
Coscinodiscus is one of great interest, from the vast abundance
of its valves in certain fossil deposits (Fig. 101, a a a), especially
the Infusorial earth of Richmond in Virginia, of Bermuda, and
of Oran, as also in Guano. Each frustule is of discoidal shape,
being composed of two nearly flattened valves, united by a hoop;
so that, if the frustules remained in adhesion, they would form
a filament resembling that of Meloseira (Fig. 97). The regu-
larity of the hexagonal divisions on the valves, renders them
beautiful microscopic objects; in some species, the areole are
smallest near the centre, and gradually increase in size towards
the margin ; in others, a few of the central areolee are the largest,
and the rest are of nearly uniform size. Most of the species are
either marine, or are inhabitants of brackish water; when living,
they are most commonly found adherent to sea-weeds or zoo-
phytes; but when dead, the valves fall as a sediment to the
bottom of the water. In both
these conditions, they were found Fig. 84.
by Prof. J. Quekett in connec-
tion with Zoophytes which had
been brought home from Melville
Island by Sir E. Parry; and
the species seemed to be identi-
cal with those of the Richmond
earth. Nearly allied to the pre-
ceding is the beautiful genus

Actinocyclus undulatus :—a, side view ;

Actinocyclus (Fig. 84), of which z, front view.

also the frustules are discoidal in

form, but of which each valve, instead of being flat, has an undulat-

ing surface, as is seen in front view (B); giving to the side view (a)
19

290 MICROSCOPIC FORMS OF VEGETABLE LIFE.

the appearane of being marked by radiating bands. Owing to thig
peculiarity of shape, the whole surface cannot be brought into
focus at once, except with a lower power; and the difference of
aspect which the different radial divisions present in Fig. 84, is sim-
ply due to the fact, that one set is out of focus, whilst the other ig
in it, since the appearances are reversed by merely altering the
focal adjustment. The number of radial divisions has been con-
sidered a character of sufficient importance to serve for the dis-
tinction of species; but this is probably subject to variation ;
since we not unfrequently meet with disks, of which one has
(say) 8 and another 10 such divisions, but which are so pre-
cisely alike in every other particular, that they can scarcely be
accounted as specifically different. The valves of this genus are
very abundant in the infusorial earths of Richmond, Bermuda,
and Oran (Fig. 101, 5, 6, 6); and many of the same species have
been found recent in guano, and in the seas of various parts of
the world. The frustules in their living state appear to be ge-
nerally attached to sea-weeds or zoophytes.

182. The Bermuda earth also contains the very beautiful form
(Fig. 85), which, though scarcely separable from <Actinocyclus

Fig. 85,

Heliopelta.

except by its marginal spines, has received from Prof. Ehrenberg
the distinctive appellation of Heliopelta (sun-shield). In the re-
presentation here given, the object is delineated as seen by the
parabolic illuminator (§ 61), which brings into view certain fea-
tures that can scarcely be seen by ordinary transmitted light.
Four of the radial divisions are seen to be marked out into
circular areole; but in the four which alternate with them, a
minute granular structure is observable. This may be shown
by careful adjustment of the focus, to exist over the whole of
the valve, even on the divisions in which the circular areolation

DIATOMACEHZ—ARACHNOIDISCUS. 291

is here displayed; and it hence appears that this marking is
superficial, and that the circular areolation exists in a deeper
layer of the siliceous lorica. In the alternating divisions whose
surface is here displayed, the subjacent areolation, when brought
into view by focussing down to it, is seen to be formed of equi-
lateral triangles; it is not, however, nearly so well marked as the
circular areolation of the first-mentioned divisions. The dark
spots seen at the ends of the rays, like the dark centre, appear
to be solid tubercles of silex, not traversed by markings, as in
many other Diatoms; most assuredly they are not orifices, as
supposed by Prof. Ehrenberg. Of this type, again, specimens
are found presenting 6, 8, or 10 radial divisions, but in other
respects exactly similar; on the other hand, two specimens
agreeing in their number of divisions, may exhibit minute dif-
ferences of other kinds; in fact it is rare to find two that are
precisely alike. It seems probable, then, that we must allow a
considerable latitude of variation in these forms, before attempt-
ing to separate any of them as distinct species. Another very

Arachnoidiscus Ehrenbergii.

beautiful discoidal Diatom, which occurs in guano, and is also
found attached to sea-weeds from different parts of the world
(especially to a species employed by the Japanese in making
soup), is the Arachnoidiscus (Fig. 86), 80 named from the resem-
blance which the beautiful markings on its disk cause it to bear
to a spider’s web. According to Mr. Shadbolt,’ who has care-
fully examined its structure, each valve consists of two layers;
the outer one, a thin flexible horny membrane, indestructible by

1“ Transactions of Microscopical Society,” 1st Series, vol. iii, p. 49.

292 MICROSCOPIC FORMS OF VEGETABLE LIFE.

boiling nitric acid; the inner one, siliceous. It is the former
which has upon it the peculiar spider’s web-like markings;
whilst it is the latter that forms the supporting framework,
which bears a very strong resemblance to that of a circular
Gothic window. The two can occasionally be separated entire,
by first boiling the disks for a considerable time in nitric acid,
and then carefully washing them in distilled water. Even with-
out such separation, however, the distinctness of the two layers
can be made out by focussing for each separately under a 1-4th
or 1-5th in. objective; or by looking at a valve as an opaque
object (either by the Parabolic illuminator, or by the Lieberkiihn,
or by a side light) with a 4-10ths in. objective, first from one
side, and then trom the other.

183. Nearly allied to the preceding in general characters, but
differing in the triangular shape of its valves, is the Triceratium ;
of which striking form a considerable number of species are
met with in the Bermuda and other Infusorial earths, while
others are inhabitants of the existing ocean and of tidal rivers.
The Z. favus (Fig. 79), which is one of the largest and most re-
gularly marked of any of these, occurs in the mud of the
Thames and in various other estuaries on our own coast; it has
been found, also, on the surface of the large sea-shells from
various parts of the world, such as those of Hippopus and Halio-
tis, before they have been cleaned; and it presents itself like-
wise in the infusorial earth of Petersburg (U. 8.) Although the
triangular form, when the frustule is looked at sideways, is that
which is characteristic of the genus, yet in some of the species
there seems a tendency to produce quadrangular and even penta-
gonal forms; these being marked as varieties, by their exact
correspondence in sculpture, color, &c., with the normal trian-
gular forms.’ This departure is extremely remarkable, since it

breaks down what

Fia. 87. seems at first to be

= i the most distinctive

: character of the ge-
nus; and its occur-
rence is an indication
of the degree of lati-
tude which we ought
to allow in other cases.
The genus Campylo-
discus (Fig. 87) 18
distinguished by its
saddle-shaped curva-
Campylodiscus costatus :—a, front view ; B, side view. ture, and by its rib-

bed markings, which

seem to indicate the presence of canals excavated in or beneath

' See Mr. Brightwell’s excellent memoir “On the genus Triceratium,” in “ Quart. Mi-
crose. Journal,” vol. i, p. 245,

DIATOMACEHZ—SURIRELLA, NAVICULA. 293

the valves, for the passage of fluid between the orifices in the
siliceous envelope and the soft cell-membrane beneath. The
form of the valves, in most of the species, is circular, or nearly
so; some are nearly flat, whilst in others the twist is greater than
in the species here represented. Some of the species are marine,
whilst others occur in fresh water; a very beautiful form, the C.
clypeus, exists in such abundance in the Infusorial stratum dis-
covered by Prof. Ehrenberg at Soos near Ezer in Bohemia, that
the earth seems almost entirely composed of it. Some of the
forms of the last genus lead towards Surirella (Fig. 88), which,
like it, presents the appear-
ance of possessing a canali- Fie. 88.
cular system, though thisis 4 = ,
by no means equally con- 4
spicuous in all the species.
The distinctive character of
the genus, in addition to the |
presence of the canaliculi, is |
derived from the longitudi- |
nal line down the centre of
each valve (4), and the pro-
t

aa

y
“Wy
PUTTS

LL

iain

ANT

me

cir

2
longation ofthe marginsinto 4 ie
“ alee.”” Numerous species Gi
are known, which are mostly

of a somewhat ovate form, Surirella constricta :—a, side view ; B, front view;
some being broader and 0, binary subdivision.

others narrower than S. con-

stricta; the greater part of them are inhabitants of fresh or
brackish water, though some few are marine; and several occur
in those infusorial earths, which seem to have been deposited at
the bottoms of lakes, such as that of the Mourne Mountains in
Treland (Fig. 102, 8, ¢, hk).

184. We now come to that interesting series of forms, which
has been ranked under the genus Navicula, until its recent sub-
division by Prof. W. Smith into the three genera Navicula, Pin-
nularia, and Pleurosigma, each of which still comprehends a ve
large number of species. They are all distinguished by the ob-
long or lanceolate form of their valves, by the convexity of their
surfaces, by the presence of a longitudinal line along the middle
line of each valve, dilating into nodules at the centre and extre-
mities, and by the more or less conspicuous marking of the
valves with transverse or oblique striz, which, under a sufficient
magnifying power, are resolvable into a regular areolation, re-
sembling, though on a very minute scale, that of the more coarsely
marked Diatoms (§ 175). The genus Navicula, as now constituted,
is distinguished by these stri, and by the appearance of rows of
circular dots which they present, when sufficiently magnified.
In Pinnularia (Fig. 102, h), the strie are not resolvable into dots,
and are so strongly marked as almost to resemble the “ribs” of

294 MICROSCOPIC FORMS OF VEGETABLE LIFE.

Surirella, The genus Pleurosigma is at once distinguished by
the peculiar curvature of its valves (Fig. 80); and it is further
remarkable for the extreme closeness of their striation, and for
the consequent “difficulty” which attends its resolution into a
regular areolation. The species of the first two of these genera
are for the most part inhabitants of fresh water; and they con-
stitute a large part of most of the Infusorial Earths which were
deposited at the bottoms of lakes. Among the most remarkable
of such deposits, are the substances largely used in the arts for
the polishing of metals, under the names of Tripoli and rotten-
stone; these consist in great part of the frustules of Navicule
and Pinnularie. The Polierschiefer or polishing-slate of Bilin
in Bohemia, the powder of which is largely used in Germany for
the same purpose, and which also furnishes the fine sand used
for the most delicate castings in iron, occurs in a series of beds
averaging fourteen feet in thickness ; and these present appear-
ances which indicate that they
Fic. 89. have been at some time exposed
to a hightemperature. The well-
known Turkey-stone, so gene-
rally employed for the sharpen-
ing of edge tools, seems to be
essentially composed of a similar
aggregation of frustules of Na-
vicule, &c., which has been con-
solidated by heat. The species
of Pleurosigma, on the other
hand, are for the most part either
marine, or are inhabitants of
? brackish water; and they compa-
ratively seldom present themselves
in a fossilized state. The genus
Stauroneis, which belongs to the
same group, differs from all the
preceding forms, in having the
central nodule of each valve
dilated laterally into a band free
from strie, which forms a cross
with the longitudinal band; of
this very beautiful form, some
species are fresh water, others
marine; and the former present
Gomphonema geminatum : its frustules con- themselves frequently in certain
nected by stipes. infusorial earths.
185. The group we have next
to notice, consists of those genera which have the frustules,
' For some very curious examples of the extent to which variation in form, size. and
distance of strimw, may take place in this group, among individuals which must be ac-

counted as of the same species, see the memoirs of Profrs. W. Smith and W. Gregory
already referred to (p. 287, note),

FORMS WITH CONNECTED FRUSTULES. 295

after self-division, attached by a gelatinous cushion, or by a
dichotomous stipes (Fig. 89). Many of these present a strong re-
semblance to some of the preceding, so far as the structure of
their frustules is itself concerned; so that when, as frequently
happens, they are found unattached, the difference is not appa-
rent. In Synedra (Fig. 102, 7), which is not unlike a long nar-
row Navicula (an imperfect longitudinal line, with central and
terminal dilatations, being often, but not always, apparent), the
frustules are at first invariably attached to larger Alge, or other
aquatic plants, by a cushion-like gelatinous basis; and when they
remain adherent to this after repeated subdivision, they some-
times form a fan-like band of frustules, not unlike that of Lic-
mophora (Fig. 91), or even a stellate cluster, the appearance of
which is extremely characteristic. So again, the frustules of
Gomphonema (Fig. 90) in a side view, are not unlike those of
Navicula; but they are distinguished in front view by their
cuneate (wedge-like) form, which arises chiefly from the une-
qual development of the membrane connecting the valves, at the
upper and lower ends. The stipes seems to be formed by an
exudation from the frustule, which is secreted only during the
process of self-division ; hence when this process has been com-
pleted, the extension of the single filament below the frustule
ceases; but when it recom-
mences, a sort of joint or articu-
lation is formed, from which a
new filament begins to sprout g@==E
for each of the half-frustules ;
and when these separate, they
carry apart the peduncles which
support them, as far as their
divergence can take place; and
it is in this manner that the
dichotomous character is given
to the entire stipes (Fig. 89).
The species of Gomphonema :
are, with scarcely an exception, Gomphonema geminatum :—a, side view of frus-
inhabitants of fresh water; and {ule more hisbly magnified; s, front views ¢,
areamongthecommonestforms

of Diatomacee. In Licmophora (Fig. 91) we meet with a dif
ferent mode of growth; for the newly formed part of the stipes,
instead of itself becoming double with each act of self-division
of the frustule, increases in breadth, while the frustules them-
selves remain coherent; so that a beautiful fan-like arrangement
is produced. A splitting away of a few frustules seems occasion-
ally to take place, from one side or the other, before the elonga-
tion of the stipes; so that the entire plant presents us with a more
or less complete flabella or fan upon the summit of the branches,
with imperfect flabelle or single frustules irregularly scattered
throughout the entire length of the footstalk. This beautiful
plant is marine, and is parasitic upon sea-weeds and zoophytes.

296 MICROSCOPIC FORMS OF VEGETABLE LIFE.

186. Inthe group at which we now arrive, there is more or less
of permanent connection between the frustules themselves; and
this may depend merely upon the cohesion of their surfaces, or may

Fia. 91.

Licmophora flabellata.

be occasioned by the persis-
tence of the connecting
membrane of the valves after
the completion of the self.
division ofthe frustules. To
the former division belong
several genera, the form of
whose frustules is more or
less elongated, so that the
filament formed by their co-
hesion is a flattened band.
If the two extremities of the
frustule be of equal breadth,
as in Baeillaria, the band
will be straight; but if one
be broader than the other,
so that the frustule in front
view has a cuneate or wedge-
like form, the filament will
be curved, as in the beauti-
ful Meridion cireulare (Fig.
92, a). Although these,
when gathered and placed
under the microscope, pre-

sent the appearance of circles overlying one another, they really
grow in a helical (screw-like) form, making several continuous

4, Meridion circulare :—, Bacillaria paradoaa.

turns. This Diatom abounds in many localities in this country;
but there is none in which it presents itself in such rich luxu-
riance, as in the mountain brooks about West Point in the
United States, the bottoms of which, according to Prof. Bailey,

FRAGILLARIA—ACHNANTHES. 297

“are literally covered in the first warm days of spring with a
ferruginous colored mucous matter, about a quarter of an inch
thick, which on examination by the microsgope, proves to be
filled with millions and millions of these exquisitely beautiful
siliceous bodies. Every submerged stone, twig and spear of
grass is enveloped by them; and the waving plume-like appear-
ance of a filamentous body covered in this way is often very ele-
gant.” The genus Bacillaria, so named from the stafflike form
of its frustules, is now limited to the species B. paradora (Fig.
92, B), whose remarkable movements have been already de-
scribed (§ 179). Owing to this displacement of the frustules, its
filaments seldom present themselves with straight parallel sides,
but nearly always in forms more or less oblique, such as those
represented above. This curious object is an inhabitant of salt
or of brackish water. Many of the species formerly ranked under
this genus are now referred to the genus Diatoma (§ 187); to
which also the genus Fragillaria is nearly allied, the difference
between them lying chiefly in the mode of adhe-

sion of the frustules. These in Fragillaria form Fig. 93.
long straight filaments with parallel sides; the
filaments, however, as the name of the genus im-
plies, very readily break up into their component
trustules, often separating at the slightest touch.
Its various species are very common in pools
and ditches. Among the numerous ‘genera be-
longing to this group, we may stop to notice
Achnanthes ; some of the species of which, par-
ticularly A. longipes (Fig. 93), are furnished
with a single nearly straight stipes, attached to
one end of the lower margin of the first frustule
of the filament. There is a curious difference
in the markings of the valves of the upper and
lower frustules; for while both are traversed by
strie, which are resolvable under a sufficient
power into rows of dots, as well as by a longitu-
dinal line, which sometimes has a nodule at
each end (as in Navicula), the lower valve (a),
has also a transverse line, forming a stauros or
cross, which is wanting in the upper valve (e).
A persistence of the connecting membrane may
sometimes be observed in this genus, so as to
form an additional connection between the
cells; thus, in Fig. 93, it not only holds to-
gether the two new frustules resulting from the —Achnanthes tongipes :-—
subdivision of the lowest cell, a, which are not ©, % @ successive
yet completely separated the one from the other, stages of selfdivision.
but it may be observed to invest the two frus-

tules 6 and e, which have not merely separated, but are them-
selves beginning to undergo binary subdivision; and it may also

RT
nee

298 MICROSCOPIC FORMS OF VEGETABLE LIFE.

be observed to invest the frustule d, from which the frustule e,
being the terminal one, has more completely freed itself.

187. It is by the,persistence of the connecting membrane, not-
withstanding the dissolution of the adhesion between the sur-
faces of the valves, that the frustules are so held together after
self-division as to form zigzag chains in the next group; of
which the genus Diatoma (Fig. 94), that gives the name (‘“cut-
ting through”) to the whole order, is a typical example. Its

Fra. 96.
Fia. 94, Fig. 95.

Fig. 94. Diatoma vulgare :—a, side view of frustule; b, frustule undergoing self-division.

Fig. 95. Gr tophora serpentina:—a, front and side views of single frustule; }, 6, front and end
views of divided frustule; c, a frustule about to undergo self-division; d, a frustule completely
divided.

Fig. 96. Isthmia nervosa.

valves, when turned sideways, are seen to be strongly marked
by transverse striae, which extend into the front view. The
proportion between the length and the breadth of each valve is
found to varyso considerably, that, if the extreme forms only were
compared, there would seem adequate ground for regarding them
as belonging to different species. This genus inhabits fresh
water, preferring gently running streams, in which it is some-
times very abundant. The genus Grammatophora (Fig. 95) is
nearly allied to the preceding; but its transverse strive are ex-
tremely faint and difficult of detection, so that its valves serve a8
“‘test-objects” (§ 102, ITI); and the frustules, when seen in front
view, are marked by peculiar bands, usually sinuous, which are
termed witte. The curious Biddulphia, whose self-division has
already been described (§ 176), belongs to this group; its frus-
tules have a very peculiar external form (Fig. 81), and they are
believed to be divided internally by partitions which correspond

DIATOMACEZ—MEMBRANACEOUS FRONDS. 299

to the external ribbings. So far as is yet known, it is exclusively
marine. Nearly allied to it, is the beautiful genus Isthmia (Fig.
96), which is also marine, and which grows attached to larger
sea-weeds, the basal frustule being very commonly attached by a
stipes. In this, as in the preceding genus, the areolated structure
of the surface is very conspicuous (Fig. 78), both in the valves
and in the connecting “hoop;” and this hoop, being silicified,
not only connects the two new frustules (as at 6), until they have
separated from each other, but, after such separation, remains
for a time round one of the frustules, so as to give it a truncated
appearance (a, ¢).

188. It is by the complete persistence of the siliceous hoop,
that the frustules are held together in that curious group of
Diatomacese, which consists of a few genera whose cylindrical
filaments bear a close external resemblance to those of Confer-
vacee. The most important of these is Meloseira (Figs. 97, 98),
long since characterized as a plant by the Swedish algologist
Agardh, but taken from
the Vegetable kingdom Fig. 97, Fig, 98.
with other Diatoms by Prof.
Ehrenberg, who included
its species in his genus
Gallionella. Some of its
species are marine, others
fresh water; one of the lat-
ter, the WM. ochracea, seems
to grow best in boggy pools
containing a ferruginous
impregnation; and it is
stated by Prof. Ehrenberg
to take up from the water,
and to incorporate with its
own substance, a consider-
able quantity of iron. The
filaments of Meloseira very
commonly fall apart at the
slightest touch; and in the wcoseira subylenitis.
infusorial earths, in which
some species abound, the frustules are always found detached
(Fig. 102, @ a, dd). The meaning of the remarkable difference
in the sizes and forms of the frustules of the same filaments
(Fig. 97, 98) has not yet been fully ascertained; but it seems to
be related to the curious process of self-conjugation already
described (§ 178). The sides of the valves are often marked
with radiating strie (Fig. 102, dd); and in some species they
have toothed or serrated margins, by which the frustules lock
together.

189. The Second tribe of Diatomacee, in which the frustules
are completely enveloped by a gelatinous or membranaceous

HMeloseira varians.

800 MICROSCOPIC FORMS OF VEGETABLE LIFE.

envelope, does not contain many forms so interesting as those
which have been already described ; and it will not be requisite
to dwell long upon it. This envelope forms a frond, that holds
together all the frustules which have originated in the self-divi-
sion of one individual; and it may either consist of an indefi-
nite gelatinous mass, or rather aggregation of masses, in which
the frustules are imbedded (Fig. 100), or of an indefinite cluster

Fig, 99. Fig. 100.

Fig. 99. Mastogloia Smithii:—a, entire stipes; 3B, frustule in its gelatinous envelope; c—#, dif-
ferent forms of frustule as seen in front view; G, side view; 4, frustule undergoing subdivision.
Fig. 100. Mastogloia lanceolata.

of such masses, supported by a stipes (Fig. 99), as in the genus
Mastogloia ; or it may have a definite shape, either globular, com-
pressed, or filamentous, within which the frustules either lie
scattered, as in Dickieia and Berkeleyia, or in rows, as in Schizo-
nema, or in bundles, as in Homeocladia. These are all, or nearly
all, marine forms; and many of them present so strong a re-
semblance to the smaller filamentous Alge, that they might
easily be mistaken for such. Their frustules, however, when
taken out of their containing tubes, frequently present so near
an approximation, both in structure and markings, to members
of the preceding groups of Diatomacee, that their close relation-
ship to them cannot be questioned. Very strongly marked
varieties sometimes present themselves within the limits of
a single species; thus the valves c, p, z, F (Fig. 99), would’
scarcely have been supposed to belong to the same specific
type, were they not found upon the same stipes. The careful
study of these varieties, in every instance in which any dispos!-

GENERAL DISTRIBUTION OF DIATOMACEA. 801

tion to variation shows itself, so as to reduce the enormous num-
ber of species with which our systematic treatises are loaded, is
a pursuit of far greater real value, than the multiplication of
species by the detection of such minute differences as may be
presented by forms discovered in newly explored localities ; such
differences, as already pointed out, being probably, in a large
proportion of cases, the result of the multiplication of some
one form, which, under modifying influences that we do not yet
understand, has departed from the ordinary type. The more
faithfully and comprehensively this study is carried out, in any
department of Natural History, the more does it prove that the
range of variation is far more extensive than had been previ-
ously imagined; and this is especially likely to be the case with
such humble organisms as those we have been considering ; since
they are obviously more influenced than are those of higher
types, by the conditions under which they are developed ; whilst,
from the very wide geographical range through which the same
forms are diffused, they are subject to very great diversities of
such conditions.

190. The general habits of this most interesting group cannot
be better stated than in the words of Prof. W. Smith, from
whose admirable Monograph the Author has drawn the greater
part of his materials for the foregoing account of it! “The
Diatomacez inhabit the sea, or fresh water; but the species pe-
culiar to the one, are never found in a living state in any other
locality ; though there are some which prefer a medium of a
mixed nature, and are only to be met with in water more or less
brackish. The latter are often found in great abundance and
variety in districts occasionally subject to marine influences, such
as marshes in the neighborhood of the sea, or the deltas of
rivers, where, on the occurrence of high tides, the freshness of
the water is affected by percolation from the adjoining stream,
or more directly by the occasional overflow of its banks. Other
favorite habitats of the Diatomacese are stones of mountain
streams or waterfalls, and the shallow pools left by the retiring
tide at the mouths of our larger rivers. They are not, how-
ever, confined to the localities I have mentioned,—they are, in
fact, most ubiquitous, and there is hardly a roadside ditch,
water-trough, or cistern, which will not reward a search, and
furnish specimens of the tribe.” Such is their abundance in
some rivers and estuaries, that their multiplication is affirmed
by Prof. Ehrenberg to have exercised an important influence in
blocking up harbors and diminishing the depth of channels!

'The Author has great pleasure in here acknowledging the liberality of Messrs.
Smith and Beck, who have allowed him, not only to make free use of this volume, but
also to copy as many as he desired of the admirable series of illustrations which have
been executed for it by Mr. Tuffen West, many of them still unpublished. All the
figures of Diatomacez, given in‘ this Manual, except Figs. 80 and 85, which are drawn
from nature, and Figs. 101, 102, which are copied from Prof. Ehrenberg, are as exact
copies of Mr. West's lithographs as the best Wood-engraving can produce.

802 MICROSCOPIC FORMS OF VEGETABLE LIFE.

Of their extraordinary abundance in certain parts of the ocean,
the best evidence is afforded by the observations of Dr. W. J,
Hooker upon the Diatomacex of the southern seas; for within
the Antarctic Circle, they are rendered peculiarly conspicuous
by becoming enclosed in the newly-formed ice, and by being
washed up in myriads by the sea on to the “ pack” and “ bergs,”
everywhere staining the white ice and snow of a pale ochreous
brown. A deposit of mud, chiefly consisting of the siliceous
loricze of Diatomacer, not less than 400 miles long and 120 miles
broad, was found at a depth of between 200 and 400 feet, on
the flanks of Victoria Land in 78° south latitude; of the thick-
ness of this deposit no conjecture could be formed; but that it
must be continually increasing is evident, the silex of which it
is in a great measure composed being indestructible. A fact of
peculiar interest in connection with this deposit, is its extension
over the submarine flanks of Mount Erebus, an active volcano
of 12,400 feet elevation; since a communication between the
ocean-waters and the bowels of a voleano, such as there are
other reasons for believing to be occasionally formed, would ac-
count for the presence of Diatomacee in volcanic ashes and
pumice, which was discovered by Prof. Ehrenberg. It is re-
marked by Dr. Hooker, that the universal presence of this in-

Fig. 101.

Fossti Diatomacee, &c., from Oran:—a, a, a, Coscinodisens; b, b, b, Actinocyclus; ¢, Dictyochya
fibula; d, Lithasteriscus radiatus; e, Spongolithis acicularis; Jf, f, Grammatophora parallela (side
view) ; g,g) Grammatophora angulosa (front view).

visible vegetation throughout the South Polar Ocean, is a most
important feature; since there is a marked deficiency, in this
region, of higher forms of vegetation ; and were it not for them,

DIATOMACHA—FOSSILIZED DEPOSITS. 803

there would neither be food for aquatic animals, nor (if it were
possible for these to maintain themselves by preying on one
another) could the ocean-waters be purified of the carbonic acid
which animal respiration and decomposition would be continually
imparting to it. It is interesting to observe, that some species
of marine Diatomacee are found through every degree of lati-
tude between Spitzbergen and Victoria Land ; whilst others seem
limited to particular regions. One of the most singular instances
of the preservation of Diatomaceous forms, is their existence in
Guano; into which they must have passed from the intestinal
canals of the birds of whose accumulated excrement that sub-
tance is composed, those birds having received them, it is pro-
bable, from shell-fish, to which these minute organisms serve as
ordinary food (§ 192.)

. 191. The indestructible nature of the epiderms of Diatomacee
has also served to perpetuate their presence in numerous locali-
ties, from which their living forms have long since disappeared ;
for the accumulation of sediment formed by their successive pro-
duction and death, either on the bed of the ocean, or on the bot-
toms of fresh-water lakes, gives rise to deposits which may attain
considerable thickness, and which, by subsequent changes of
level, may come to form part of the dry land. Thus very exten-
sive siliceous strata, consisting almost entirely of marine Diato-
mace, are found to alternate, in the neighborhood of the Medi-
terranean, with calcareous strata, chiefly formed of Foraminifera
(Chap. X); the whole series being the representative of the Chalk
formation of Northern Europe, in which the silex that was pro-
bably deposited at first in this form, has undergone conversion
into flint, by agencies hereafter to be considered (Chaps. X, XTX).
Of the Diatomaceous composition of these strata, we have a
characteristic example in Fig. 101, which represents the fossil
Diatomacee of Oran, in Algeria. The so-called “infusorial
earth” of Richmond, in Virginia, and that of Bermuda, also ma-
rine deposits, are very celebrated among Microscopists for the
number and beauty of the forms they have yielded; the former
constitutes a stratum of 18 feet in thickness, underlying the whole
city, and extending over an area whose limits are not known.
Several deposits of more limited extent, and apparently of fresh-
water origin, have been found in our own islands; as for instance
at Dolgelly, in North Wales, at Lough Mourne, in Ireland (Fig.
102), and in the island of Mull, in Scotland. Similar deposits in
Sweden and Norway are known under the name of berg-meAl or
mountain flour; and in times of scarcity, the inhabitants of those
countries are accustomed to mix these substances with their
dough in making bread. This has been supposed merely to have
the effect of giving increased bulk to their loaves, so as to render
the really nutritive portion more satisfying. But as the berg-
mehl has been found to lose from a quarter to a third of its
weight by exposure to a red-heat, there seems a strong proba-

304 MICROSCOPIC FORMS OF VEGETABLE LIFE.

bility that it contains organic matter, which renders it nutritious
in itself. When thus occurring in strata of a fossil or sub-fossil
character, the Diatomaceous deposits are generally distinguisha-
ble as white or cream-colored powders of extreme fineness.

192. For collecting fresh Diatomacee, three general methods
are to be had recourse to, which have been already described
(§ 148,171). “Their living masses,” says Prof. W. Smith, “ pre-

Fia. 102.

Fossil Diatomacee, &c., from Mourne Mountain, Ireland :—a, a,a, Gaillonella (Meloseira) procera,
and G. granulata; d, d,d, G. biseriata (side view); },b, Surirella plicata; ¢,S. craticula; k, 8. cale-
donica; e, Gomphonema gracile; 7, Cocconema fusidium; g, Tabellaria vulgaris; A, Pinnularia dac-
tylus; 2, P. nobilis; l, Synedra ulna.
sent themselves as colored fringes attached to larger plants, or
forming a covering to stones or rocks in cushion-like tufts—or
spread over their surface as delicate velvet—or depositing them-
selves as a filmy stratum on the mud, or intermixed with the
scum of living or decayed vegetation floating on the surface of
the water. Their color is usually a yellowish-brown of a greater
or less intensity, varying from a light chestnut, in individual spe-
cimens, to a shade almost approaching black in the aggregated
masses. Their presence may often be detected without the aid
of a microscope, by the absence, in many species, of the fibrous
tenacity which distinguishes other plants; when removed from
their natural position, they become distributed through the
water, and are held in suspension by it, only subsiding after
some little time has elapsed.” Notwithstanding every care, the
collected specimens are liable to be mixed with much foreign
matter; this may be partly got rid of by repeated washings 1
pure water, and, by taking advantage, at the same time, of the
different specific gravities of the Diatoms and of the intermixed

MODE OF COLLECTING DIATOMACES. 805

substances, to secure their separation. Sand, being the heaviest,
will subside first; fine particles of mud, on the other hand, will
float after the Diatoms have subsided. The tendency which the
Diatomacere have, to make their way towards the light, will
afford much assistance in procuring the free forms in a tolerably
clean state; for if the gathering which contains them be left un-
disturbed for a sufficient length of time, in a shallow vessel ex-
posed to the sunlight, they may be skimmed from the surface.
The marine forms must be looked for upon sea-weeds, and in
the fine mud or sand of soundings or dredgings; they are fre-
quently found also, in considerable numbers, in the stomachs of
the oyster, scallop, whelk, and other Mollusks, especially the
‘bivalves,’ in those of the crab and lobster, and even in those
of the sole, turbot, and other “flat-fish.” ‘Several species,”’
says Prof. W. Smith, “rarely or never occurring in my usual
haunts, have been supplied in abundance by the careful dissec-
tion of the above microphagists.” The separation of the Diatoms
from the other contents of these stomachs, must be accomplished
by the same process as that by which they are obtained from
Guano or the calcareous Infusorial Earths; of this, the following
are the most essential particulars. The guano or earth is first to
be washed several times in pure water, which should be well
stirred, and the sediment then allowed to subside for some hours
before the water is poured off, since, if it be decanted too soon,
it may carry the lighter forms away with it. Some kinds of earth
have so little impurity, that one washing suffices; but in any
case it is to be continued so long as the water remains colored.
The deposit is then to be treated, in a flask or test tube, with
hydrochloric (muriatic) acid; and after the first effervescence is
over, a gentle heat may be applied. -As soon as the action has
ceased, and time has been given for the sediment to subside, the
acid should be poured off, and another portion added; and this
should be repeated as often as any effect is produced. When
hydrochloric acid ceases to act, strong nitric Acid should be sub-
stituted; and after the first effervescence is over, a continued
heat of about 200° should be applied for some hours. When
sufficient time has been given for subsidence, the acid may be
poured off, and the sediment treated with another portion; and
this is to be repeated, until no further action takes place. The
sediment is then to be washed, until all trace of the acid is re-
moved ; and if there have been no admixture of siliceous sand in
the earth or guano, this sediment will consist almost entirely of
Diatomacee, with the addition, perhaps, of Sponge-spicules. The
separation of siliceous sand, and the subdivision of the entire
aggregate of Diatoms into the larger and the finer kinds, may
be accomplished by stirring the sediment in a tall jar of water,
and then, while it is still in motion, pouring off the supernatant
fluid as soon as the coarser particles have subsided; this fluid
should be set aside, and, as soon as a finer sediment has subsided,
20

306 MICROSCOPIC FORMS OF VEGETABLE LIFE,

it should again be poured off; and this process may be repeated
three or four times at increasing intervals, until no further sedi-
ment subsides after the lapse of half an hour. The first sediment
will probably contain all the sandy particles, with, perhaps, some
of the largest Diatoms, which may be picked out from among
them; and the subsequent sediments will consist almost exclu-
sively of Diatoms, the sizes of which will be so graduated, that
the earliest sediments may be examined with the lower powers,
the next with the medium powers, while the latest will require
the higher powers,—a separation which is attended with great
convenience.)

198. The mode of mounting specimens of Diatomacez, will
depend upon the purpose which they are intended to serve. If
they can be obtained quite fresh, and it be desired that they
should exhibit, as closely as possible, the appearance presented
by the living plants, they should be put up in distilled water
within cement cells (§ 134); but if they are not thus mounted
within a short time after they have been gathered, about a sixth
part of alcohol should be added to the water. If it be desired
to exhibit the stipitate forms in their natural parasitism upon
other aquatic plants, the entire mass may be mounted in Deane’s
gelatine (§ 131), in a deeper cell; and such a preparation is a
very beautiful object for the black-ground illumination. If, on
the other hand, the minute structure of the siliceous envelopes
is the feature to be brought into view, the fresh Diatoms must
be boiled in nitric or hydrochloric acid, which must then be
poured off (sufficient time being allowed for the deposit of the
residue), and the sediment, after repeated washings, is to be
either mounted in balsam in the ordinary manner (§ 128), or, if
the species have markings that are peculiarly difficult of resolu-
tion, is to be set up dry between two pieces of thin glass (§ 122).
In order to obtain a satisfactory view of these markings, object-
glasses of very wide angle of aperture are required, and all the
refinements which*have recently been introduced into the me-
thods of Illumination, need to be put in practice. (Chaps. II,
IV.) It will often be convenient to mount certain particular
forms of Diatomacee separately from the general aggregate ; but
on account of their minuteness, they cannot be selected and re-
moved by the usual means. The larger forms, which may be
readily distinguished under a simple microscope, may be taken
up by a camel-hair pencil, which has been so trimmed as to
leave two or three hairs projecting beyond the rest. But the
smaller can only be dealt with by a single fine bristle or stout
sable-hair, which may be inserted into the cleft end of a slender
wooden handle; and if the bristle or hair should be split at its
extremity in a brush-like manner, it will be particularly useful.

' A somewhat more complicated method of applying the same principle, is described

by Mr. Okeden in the “ Quart. Journ. of Microsc. Science,” vol. iii, p. 158. The Author
believes, however, that the method above described will answer every purpose.

PALMELLACEAS. 307

Such split hairs (as Dr. Redfern first noticed) may always be
found in a shaving brush which has been for some time in use.
Those should be selected, which have thin split portions so
closely in contact, that they appear single until touched at their
ends. When the split extremity of such a hair touches the
glass slide, its parts separate from each other to an amount pro-
portionate to the pressure; and, on being brought up to the
object, first pushed -to the edge of the fluid on the slide, may
generally be made to seize it. Supposing that we wish to select
certain particular forms, from a Diatomaceous sediment which
has been obtained by the preceding processes; either of the two
following modes may be put in practice. A small portion of
the sediment being taken up in the dipping-tube, and allowed
‘to escape upon the slide, so as to form a long narrow line upon
it, this is to be examined with the lowest power with which
the object we are in search of can be distinguished (the erector
and draw-tube, §§ 43, 44, will here be very useful); and when
one of the specimens has been found, it may be taken up,
if possible, on the point of the hair, and transferred to a new
slide, to which it may be made to adhere by first breathing on
its surface. But if it be found impracticable thus to remove the
specimens, on account of their minuteness, they may be pushed
to one side of the slide on which they are lying; all the remain-
der of the sediment which it is not desired to preserve, may be
washed off; and the objects may then be pushed back into the
middle of the slide, and mounted in any way that may be desired.

194. Palmellacee.—To the little group of Plants which is
ranked under this designation, those two genera belong, which
have been already cited as illustrations of the humblest types of
vegetation (§§ 150, 152); and the other forms which are asso-
ciated with these, are scarcely less simple in their essential
characters, though sometimes attaining considerable dimensions.
They all grow either on damp surfaces, or in fresh or salt water;
and they may either form (1) a mere powdery layer, of which the
component particles have little or no adhesion to each other, or
they may present themselves (2) in the condition of an indefinite
slimy film, or (8) in that of a tolerably firm and definitely
bounded membranous “frond.” The first of these states we
have seen to be characteristic of Palmoglea and Protococcus : the
new cells which are originated by the process of duplicative sub-
division, usually separating from each other after a short time ;
and even where they remain in cohesion, nothing like a frond
or membranous expansion being formed. The “red snow,”
which sometimes colors extensive tracts in Arctic or Alpine re-
gions, penetrating even to the depth of several feet, and vege-
tating actively at a temperature which reduces most plants to a
state of torpor, is generally considered to be a species of Proto-
coecus; but as its cells are connected by a tolerably firm gela-
tinous investment, it would rather seem to be a Palmella. The

308 MICROSCOPIC FORMS OF VEGETABLE LIFE

second is the condition of the genus Palmella; of which one spe-
cies, the P. cruenta, usually known under the name of “ gory
dew,” is common on damp walls and shady places, sometimes
extending itself over a considerable area as a tough gelatinous
mass, of the color and general appearance of coagulated blood,
A characteristic illustration of it is also afforded by the Hemato.
coccus sanguineus (Fig. 103), which chiefly differs from Palmella
in the partial persist-
Fra. 103. ence of the walls of the
parent cells, so that the
whole mass is gubdi-
vided by partitions,
which enclose a larger
or smaller number of
cells originating in the
subdivision of their
contents. Besides in-
creasing in the ordi-
nary mode of bina
multiplication, the Pal-
, mella cells seem occa-
sionally to rupture and
diffuse their granular
contents through the

gelatinous stratum,

Hematococcus sanguineus, in various stages of development:— : oi os
a, single cells, enclosed in their mucous envelope; }, c, clusters and thus to give origin
formed by subdivision of parent cell; d, more numerous cluster. to a whole cluster at

its ee ne = various stages of division; e, large mass of once, as seen at e, after
young cells, formed by the continuance of the same process, and
the manner of other

enclosed within a common mucous envelope.

: simple Plants to be
presently described (§ 195), save that these minute segments of
the endochrome, having no power of spontaneous motion, can-
not be ranked as Zoospores. The gelatinous masses of the Pal-
mellee are frequently found to contain parasitic growths, formed
by the extension of other plants through their substance; but
numerous branched filaments sometimes present themselves,
which, being traceable into absolute continuity with the cells,
must be considered as properly appertaining to them. Some-
times these filaments radiate in various directions from a single
central cell, and must at first be considered as mere extensions
of this; their extremities dilate, however, into new cells; and,
when these are fully formed, the tubular connections close up,
and the cells become detached from each other. This is ob-
viously an additional mode of increase by gemmation ; analogous
to that which we shall meet with among the Confervaceee (§ 198).

' Although the Authors of the “ Micrographie Dictionary” throw doubt upon this fact,
yet the writer, having had the opportunity of verifying the observations of that most
accurate Algologist, Mr. Thwaites, can entertain no doubt of their correctness. (See
“Ann. of Nat. Hist.” N.S. vol. ii, p. 313.)

ULVACEH—THEIR MODE OF DEVELOPMENT. 309

Of the third condition, we have an example in the curious Pal-
modictyon described by Kiitzing; the frond of which appears to
the naked eye like a delicate network consisting of anastomosing
branches, each composed of a single or double row of large vesi-
cles, within every one of which is produced a pair of elliptical
cellules that ultimately escape as “zoospores.” The alternation
between the “motile” form and the “still” or resting form, which
has been described as occurring in Protococcus (§§ 1538-155), has
been observed in several other forms of this group; and it seems
obviously intended, like the production of “zoospores,” to secure
the dispersion of the plant, and to prevent it from choking itself
by overgrowth in any one locality. No other form of the true.
Generative process, than the “conjugation” of two cells, and the
formation of a spore by the reunion of their contents, has yet been
observed among the members of this family; and as this has only
been witnessed in a few of them, it is probable that we do not yet
know by any means the whole of their life-history. And from
the close resemblance which many reputed Palmellacee bear to
the early stages of higher
Plants (Fig. 104, a, B, c), Fra. 104.
there is considerable doubt
whether they ought to be
regarded in the light of dis-
tinct and complete organ-
isms, or whether they are
anything else than embryo-
nic forms of more elevated
types. Here, again, there-
fore, there is an ample field
for investigation to the Mi-
croscopist who desires to
employ himself in extending
the boundaries of Science,
and in perfecting our very |, poor tics
imperfect acquaintance with @Uaee¢uen sant 98
thesé humble but most in- ““*****s##=ssn as
teresting and instructive ee

Li

G

types of Vegetation. sta ce ae Sasi sore
195. Notwithstanding the

very definite form and large
size attained by the fronds
or leafy expansions of the
Ulvacee, to which group be-
long the grass-green sea-
weeds (or “lavers’’) found on
every coast, yet their essen- Successive stages of development of Uiva.

tial structure differs but very

little from that of the preceding group; and the principal
advance is shown in this, that the cells, when multiplied by

310 MICROSCOPIC FORMS OF VEGETABLE LIFE.

binary subdivision, not only remain in firm connection with
each other, but possess a very regular arrangement (in virtue of
the determinate plan on which the subdivision takes place), and
form a regular membranous stratum. The mode in which this
frond is produced, is best understood by studying the history of
its development, some of the principal phases of which are seen
in Fig. 104; for the isolated cells (a), in which it originates,
resembling in all points those of a Protococcus, give rise, by their
successive subdivisions in determinate directions, to such regular
clusters as those seen at B and ¢, or to such confervoid filaments
as that shown at p. A continuation of the same regular mode
of subdivision, taking place alternately in two directions, may at
once extend the clusters B and c into leaf-like expansions; or, if
the filamentous stage be passed through (different species present-
ing variations in the history of their development), the filament in-
creases in breadth as well as in length (as seen at £), and finally be-
comes such a frond asigshown at F, ¢. In the simple membranous
expansions thus formed, there is no approach to a “ differentia-
tion” of parts, by even the semblance of a formation of root, stem,
and leaf, such as the higher Alge present; every portion is the
exact counterpart of every other; and every portion seems to take
an equal share in the operations of growth and reproduction. Each
cell is very commonly found to exhibit an imperfect partitioning

Fra, 104,

4 WUT
OCI. Cel aS
een

AO!

Formation of Zoospores in Phycoseris gigantea (Ulva latissima) ;—a, portion of the ordinary frond:
b, cells in which the endochrome is beginning to break up into segments; ¢, cells from the boundary
hetween the colored and colorless portion, some of them containing zoospores, others being empty:
d, ciliated zoospores, as in active motion; ¢, subsequent development of the zoospores.

into four parts, preparatory to multiplication by double subdivi-
sion; and the entire frond usually shows the groups of cells
arranged in clusters containing some multiple of four. Besides
this continuous increase of the individual frond, however, we

OSCILLATORIACESR. 811

find in most species of Ulva a provision for extending the plant
by the dispersion of “ zoospores ;”’ for the endochrome (Fig. 105,
a) subdivides into numerous segments (as at 6 and ec), which at first
are seen to lie in close contact within the cell that contains them,
then begin to exhibit a kind of restless motion, and at last pass
forth through an aperture in the cell-wall, acquire four or more
cilia (d), and swim freely through the water for some time. At
last, however, they come to rest, attach themselves to some fixed
point, and begin to grow into clusters or filaments (e), in the
manner already described. The walls of the cells which have
thus discharged their endochrome, remain as colorless spots on
_ the frond; sometimes these are intermingled with the portions
still vegetating in the usual mode; but sometimes the whole
endochrome of one portion of the frond may thus escape in the
form of zoospores, thus leaving behind it nothing but a white
flaccid membrane. If the Microscopist who meets with a frond
of an Ulva in this condition should examine the line of separa-
tion between its green and its colored portion, he may not
improbably meet with cells in the very act of discharging their
zoospores, which “swarm” around their points of exit, very
much in the manner that Animalcules are often seen to do
around particular spots of the field of view, and which might
easily be taken for true Infusoria; but on carrying his observa-
tions further, he would see that similar bodies are moving within
cells a little more remote from the dividing line, and that a little
further still, they are obviously but masses of endochrome in
the act of subdivision.! Of the true Generative process in the
Ulvacez, nothing whatever is known; and it is consequently
altogether uncertain whether it takes place by simple conjuga-
tion, or according to that more truly sexual method which will
be presently described. Here, again, therefore, is an unsolved
problem of the greatest physiological interest, which probably
requires nothing more for its solution, than patient and discrimi-
nating study. And the Author would point out, that it is by no
means unlikely that the generative process may not be performed
in the complete plant, but, as in the Ferns (§ 219), in the early
product of the development of the zoospore. Although the
typical Ulvacee are marine, yet there are several fresh-water
species; and there are some which can even vegetate on damp
surfaces, such as those of rocks or garden-walls kept moist by
the percolation of water.

196. The Osczllatoriacee constitute another tribe of simple
Plants, of great interest to the Microscopist, on account both of
the extreme simplicity of their structure, and of the peculiar
animal-like movements which they exhibit. They are conti-
nuous tubular filaments, formed by the elongation of their pri-

‘Such an observation the Author had the good fortune to make in the year 1842,
when ‘the emission of zoospores from the Ulvacez, although it had been described by
the Swedish algologist Agardh, had not been seen (he believes) by any British naturalist.

312 MICROSCOPIC FORMS OF VEGETABLE LIFE.

mordial cells, usually lying together in bundles or in strata, some-
times quite free, and sometimes invested by a gelatinous matrix,
The endochrome which they contain usually exhibits some degree
of transverse striation, as if breaking up into short segments by
the division of the tube into cells; but this division is never
perfected by the formation of complete partitions; and the fila-
ments ultimately break up into distinct joints, the fragments of
endochrome, which are to be regarded as gonidia, usually escaping
from their sheaths, and giving origin to new filaments. These
plants are commonly of some shade of green, often mingled,
however, with blue; but not unfrequently they are of a purplish
hue, and are sometimes so dark, as, when in mass, to seem nearly
black. They occur not only in fresh, stagnant, brackish, and
salt waters (certain species being peculiar to each), but also in
mud, on wet stones, or on damp ground. Their very curious
movements constitute the most remarkable feature in their his-
tory. These are described by Dr. Harvey’ as of three kinds;
first, a pendulum-like movement from side to side, performed by
one end, whilst the other remains fixed so as to form a sort of
pivot; second, a movement of flexure of the filament itself, the
oscillating extremity bending over first to one side and then to
the other, like the head of a worm or caterpillar seeking some-
thing on its line of march; and third, a simple onward move-
ment of progression. ‘The whole phenomenon,” continues Dr.
H., “may perhaps be resolved into a spiral onward movement of
the filament. Ifa piece of the stratum of an Oseillatoria be
placed in a vessel of water, and allowed to remain there for some
hours, its edge will first become fringed with filaments, radiating
as from a central point, with their tips outwards. These fila-
ments by their constant oscillatory movements, are continually
loosened from their hold on the stratum, east into the water, and
at the same time propelled forward; and as the oscillation con-
tinues after the filament has left its nest, the little swimmer
gradually moves along, till it not only reaches the edge of the
vessel, but often, as if in the attempt to escape confinement—
continues its voyage up the sides, till it is stopped by dryness.
Thus in avery short time, a small piece of Oscillatoria will spread
itself over a large vessel of water.” This rhythmical movement,
impelling the filaments in an undeviating onward course, is
evidently of a nature altogether different from the truly sponta-
neous motions of Animals; and must be considered simply as
the expression of certain vital changes taking place in the inte-
rior of the cells. It is greatly influenced by temperature and
light, being much more active in warmth and sunshine than in
cold and shade; and it is checked by any strong chemical agents.
The true Generation of Oscillatoriacee is as yet completely un-
known; and it does not seem at all unlikely that these plants
may be the “motile” forms of some others, which, in their “still

1« Manual of British Marine Alge,” p. 220.

OSCILLATORIACEH—NOSTOCHACES, 313

condition, present an aspect altogether different. Nearly allied
to the preceding, is the little tribe of Nostochacew ; which consists
of distinctly beaded filaments, lying in firmly gelatinous fronds
of definite outline. The filaments are usually simple, though
sometimes branched; and are almost always curved or twisted,
often taking a spiral direction. The masses of jelly in which
they are imbedded are sometimes globular or nearly so, and
sometimes extend in more or less regular branches; they fre-
quently attain a very considerable size ; and as they occasionally
present themselves quite suddenly (especially in the latter part of
the autumn, on damp garden walks), they have received the
name of “fallen stars.” They are not always so suddenly pro-
duced, however, as they appear to be; for they shrink up into
mere films in dry weather, and expand again with the first
shower. These plants multiply themselves, like the Oscillatorie,
by the subdivision of their filaments, the portions of which escape
from the gelatinous mass wherein they are imbedded, and move
slowly through the water in the direction of their length; after
a time they cease to move, and a new gelatinous envelope is
formed around each piece, which then begins not only to increase
in length by the transverse subdivision of its segments, but also
to double itself by longitudinal fission, so that each filament
splits lengthways (as it were) into two new ones. By the repeti-
tion of this process, a mass of new filaments is produced, the parts
of which are at first confused, but afterwards become more dis-
tinctly separated by the interposition of the gelatinous substance
developed between them. Besides the ordinary cells of the
beaded filaments, two other kinds are occasionally observable;
namely, ‘vesicular cells’ of larger size than the rest (sometimes
occurring at one end of the filaments, sometimes in their centre,
and sometimes at intervals along their whole length), which are
destitute of endochrome, and are sometimes furnished with cilia;
and “sporangial cells,” which seem like enlarged forms of the
ordinary cells, and which are usually found in the neighborhood
of the preceding. There is very strong evidence from analogy,
that the “vesicular cells” are ‘antheridia’” or sperm-cells, and
that the “sporangial cells” contain germs, which, when fertilized
by the antherozoids, and set free, become “ resting-spores,” as in
certain members of the family to be next noticed.

197. Although many of the plants belonging to the family
Siphonacee attain a considerable size, and resemble the higher
Sea-weeds in their general mode of growth, yet they retain a
simplicity of structure so extreme, that it apparently requires
them to be ranked among the Protophytes. They are inhabi-
tants both of fresh water and of the sea, and consist of very large
tubular cells, which commonly extend themselves into branches,
so as to form an arborescent frond.‘ These branches, however,
are seldom separated from the stem by any intervening partition ;
but the whole frond is composed -of a simple continuous tube,

314 MICROSCOPIC FORMS OF VEGETABLE LIFE.

the entire contents of which may be readily pressed out through
an orifice made by wounding any part of the wall. The Vau-
cheria, named after the Genevese botanist whose admirable re-
searches on the fresh-water Confervee have been already referred
to (p. 88), may be selected as a particularly good illustration of
this family ; its history having been pretty completely made out.
Most of its species are inhabitants of fresh water; but some are
marine, and they commonly present themselves in the form of
cushion-like masses, composed of irregularly branching filaments,
which, although they remain distinct, are densely tufted together,
and variously interwoven. The formation of moving gonidia or
‘zoospores’ may be readily observed in these plants, the whole
process usually occupying but a very short time. The extremity
of one of the filaments usually swells up in the form of a club,
and the endochrome accumulates in it, so as to give it a darker
hue than the rest; a separation of this part from the remainder
of the filament, by the interposition of a transparent space, is
next seen; a new envelope is then formed around the mass thus
cut off; and at last the membranous wall of the investing tube
gives way, and the “zoospore”’ escapes, not, however, until it
has undergone marked changes of form, and exhibited curious
movements. Its motions continue for some time after its escape,
and are then plainly seen to be due to the action of the cilia with
which its whole surface is clothed. If it be placed in water in
which some carmine or indigo has been rubbed, the colored
granules are seen to be driven 1n such a manner as to show that
a powerful current is produced by their propulsive action, and a
long tract is left behind it. When it meets with an obstacle, the
ciliary action not being arrested, the zoospore is flattened against
the object; and it may thus be compressed, even to the extent
of causing its endochrome to be discharged. The cilia are best
seen, when their movements have been retarded or entirely ar-
rested by means of opium, iodine, or other chemical reagents.
The motion of the spore continues for about two hours ; but after
the lapse of that time it soon comes to an end, and the spore
begins to develope itself into a new plant. It has been observed
by Unger, that the escape of the zoospores generally takes place
towards 8 a.M.; to watch this phenomenon, therefore, the plant
should be gathered the day before, and its tufts examined early
in the morning. It is stated by Dr. Hassall, that he has seen the
same filament give off two or three zoospores successively. Their
emission is obviously to be regarded as a method of increase by
gemmation, rather than as a generative act; and recent disco-
veries have shown that there exists in this humble plant a true
process of Sexual Generation, as was, indeed, long ago suspected
by Vaucher, though upon no sufficient grounds. The branching
filaments are often seen to bear at their sides peculiar globular
or oval capsular protuberances, sometimes separated by the in-
terposition of a stalk, which are filled with dark endochrome;

SIPHONACEZ—REPRODUCTION OF VAUCHERIA. 3815

and these have been observed to give exit to large bodies covered
with a firm envelope, from which, after a time, new plants arise.
In the immediate neighborhood of these “capsules” are always
found certain other projections, which, from being usually pointed
and somewhat curved, have been named “horns;” and these
were supposed by Vaucher to fulfil the function of the anthers of
flowering-plants. The recent observations of Pringsheim have
shown that such is really the case; for the “horns” are ‘‘anthe-
ridia,” which, like those of the Characew (§ 202), produce anthero-
zoids in their interior; whilst the capsules are ‘“ germ-cells,”
whose aggregate mass of endochrome is destined to become,
when fertilized, the primordial cell of a new generation. The
antherozoids, when set free from the antheridium, swarm over
the exterior of the capsule, and have actually been seen to pene-
trate its cavity, through an aperture which opportunely forms
in its wall, and to come into contact with the surface of its endo-
chrome-mass,: over which they diffuse themselves; there they
seem to undergo dissolution, their contents mingling themselves
with those of the germ-cell; and the endochrome mass, which
had previously no proper investment of its own, soon begins to
form an envelope, which increases in thickness and strength,
until it has acquired such a density as enables it to afford a firm
protection to its contents. This body, possessing no power of
spontaneous movement, is known as a “resting-spore,” in con-
tradistinction to the “zoospores” already described; and it an-
swers the purpose of a seed, in laying the foundation for a new
generation, whilst the “‘zoospores’’ merely multiply the individual
by a process analogous to budding. The Microscopist who
wishes to study the development of zoospores, as well as several
other phenomena.of this low type of vegetation, may advanta-
geously have recourse to the little plant termed Achlya prolifera,
which grows parasitically upon the bodies of dead flies lying in
the water, but also not unfrequently attaches itself to the gills ot
fish, and is occasionally found on the bodies of frogs. Its tufts
are distinguishable by the naked eye, as clusters of minute co-
lorless filaments; and these are found, when examined by the
microscope, to be long tubes devoid of all partitions, extending
themselves in various directions. The tubes contain a colorless
slightly granular protoplasm, the particles of which are seen to
move slowly in streams along the walls, as in Chara, the currents
occasionally anastomosing with each other (Fig. 106, c). Within
about thirty-six hours after the first appearance of the parasite
on any body, the protoplasm begins to accumulate in the dilated
ends of the filaments, each of which is cut off from the remainder
by the formation of a partition; and within this dilated cell, the
movement of the protoplasm continues for a time to be distin-
guishable. Very speedily, however, its endochrome shows the
appearance of being broken up into a large number of distinct
masses, which are at first in close contact with each other and

316 MICROSCOPIC FORMS OF VEGETABLE LIFE.

with the walls of the cell (Fig. 106, a), but which gradually be-
come more isolated, each seeming to acquire a proper cell-wall;
they then begin to move about within the parent cell; and, when
quite mature, they are set free by the rupture of its wall (8), to
go forth and form new attachments, and to develope themselves
into tubiform cells resembling those from which they sprang,
Each of these “motile gonidia” is possessed of only two cilia;
their movements are not so powerful as those of the zoospores of
Vaucheria; and they come to an end sooner. This plant forms
‘‘resting-spores’”’ also, like those of Vaucheria; and there is every
probability that they are generated by a like sexual process.
They may remain unchanged

Fia. 106. for along time in water, when

no suitable nidus exists for
them; but will quickly ger-
minate, if a dead insect or
other suitable object be
thrown in. One of the most
curious forms of this group,
is the Hydrodictyon utricula-
tum, which is found in fresh-
water pools in the midland
and southern counties of
England. Its frond consists
of a green open network of
filaments, acquiring, when
full grown, a length of from
four to six inches, and com-
posed of a vast number of
cylindrical tubular cells,
which attain the length of
four lines or more, and ad-
here to each other by their
rounded extremities, the
eae ay ele of eds ee eae dilated extre- points of junction correspond-
mity ofa lament, separated fom he rex bY PH ing to the knots or intersec-
formation;—B, conceplacle discharging itself, and tions of the network. Each
setting free young cells, a, b ¢;—c, portion of filament, of these cells may form with-
showing the course of the circulation of granular pro- . . ‘
toplasm. in itself an enormous multi-
tude (from 7000 to 20,000) of

“gonidia;” which, at a certain stage of their development, are
observed in active motion in its interior; but of which groups
are afterwards formed by their mutual adhesion, that are set
free by the dissolution of their envelopes, each group giving
origin to a new plant-net. Besides these bodies, however, cer-
tain cells produce from 30,000 to 100,000 more minute bodies of
longer shape, each furnished with four long cilia and a red spot,
which are termed by Braun “microgonidia:” these escape from
the cell in a swarm, move freely in the water for some time, and

¢

CELL-MULTIPLICATION IN CONFERVA. 317

then come to rest and sink to the bottom, where they remain
heaped in green masses. What is their future history, has not
yet been ascertained; but there is evidence from analogy that
they are “antheridial’”’ cells, which have for their office to fecun-
date the true germ-cells by contained antherozoids. No develop-
ment of “resting-spores,” however, has yet been observed. The
rapidity of the growth of this curious plant, is not one of the
least remarkable parts of its history. The individual cells of
which the net is composed, at the time of their emersion as
gonidia, measure no more than 1-2500th of an inch in length ;
but in the course of a few weeks, they grow to a length of from
1-12th to 1-3d of an inch.

198. Almost every pond and ditch contains some members of
the family Confervacee ; but they are especially abundant in
moving water; and they constitute the greater part of those
green threads, which are to be seen attached to stones, with their
free ends floating in the direction of the current, in every run-
ning stream, and upon almost every part of the sea-shore, and
which are commonly known under the name of “ silk-weeds”’ or
“crow-silk.” Their form is usually very regular; for each
thread is a long cylinder, made up by the union of a single file
of short cylindrical cells united to each other by their flattened
extremities; sometimes these threads give off lateral branches,
which have the same structure. The endochrome, though
usually green, is occasionally of a brown or purple hue; it is
sometimes distributed uniformly throughout the cell (as in Fig.
107), whilst in other instances it is arranged in a pattern of some
kind, as a network or a spiral; but this may be only a transi-
tional stage in its development. The plants of this order are
extremely favorable subjects for the study of the method of cell-
multiplication by binary subdivision. This process usually takes
place only in the terminal cell; and it may be almost always
observed there, in some one of its stages. The first step is seen
to be the subdivision of the endochrome, and the inflection of
the primordial utricle around it (Fig. 107, a, a); and thus there
is gradually formed a sort of hour-glass contraction across the
cavity of the parent cell, by which it is divided into two equal
halves (8). The two surfaces of the infolded utricle produce a
double layer of cellulose membrane between them; this is not
confined, however, to the contiguous surfaces of the young cell,
but takes place over the whole exterior of the primordial utricle,
so that the new septum is continuous with new layers that are
formed throughout the interior of the cellulose wall of the original
cell (c). Sometimes, however, asin Conferva glomerata (a common
species), new cells may originate as branches from any part of the
surface, by a process of budding; which, notwithstanding its
difference of mode, agrees with that just described in its essential
character, being the result of the subdivision of the original cell.
A certain portion of the primordial utricle seems to undergo

318 MICROSCOPIC FORMS OF VEGETABLE LIFE.

increased nutrition, for it is seen to project, carrying the cellulose
envelope before it, so as to form a little protuberance; and this
sometimes attains a considerable length, before any separation of
its cavity from that of the cell which gave origin to it, begins
to take place. This separation is gradu-

Fig. 107. ally effected, however, by the infolding

of the primordial utricle, just as in the
preceding case; and thus the endo-
chrome of the branch cell is com-
pletely severed from that of the stock.
The branch then begins to elongate
itself by the subdivision of its first-
formed cell; and this process may be
repeated fora time in all the cells of the
filament, though it usually comes to be
restricted at last to the termina! cell.
The Confervacee multiply themselves
by “zoospores,” which are produced
within their cells, and are then set
free, just as in the Ulvacee (§ 195); in
most of the genera, the endochrome
of each cell divides into numerous
BY zoospores, which are of course very mi-
Process of cell-multiplication in nute 3 but in idogonium,—a fresh-water
lala ka Seam I distinguished by the circular
lion at a, all se onion markings which form rings round the
at b; B, the separation completed, extremities of many of the cells, and
formed ala; e formation of sage, ©«PY Many interesting peculiarities of
tional layers of cellulose wall, ¢, growth and reproduction,’— only a
se BL single large zoospore is set free from
cle, a, which encloses the endo. @2ch cell; and its liberation is accom-
chrome, b. plished by the almost complete fis-
sion of the wall of the cell through

one of these rings, a small part only remaining uncleft, which
serves as a kind of hinge, whereby the two parts of the fila-
ment are prevented from being altogether separated. Some-
times the zoospore does not completely extricate itself from
the parent cell; and it may begin to grow in this situation, the
root-like processes which it puts forth being extended into the
cavity. -A true sexual generation has been observed in several
Contervacee ; and is probably universal throughout the group.
Thus in Spheroplea annulina, according to the recent observa-
tions of Dr. Cohn,? the ring-like masses of endochrome, of which
several are found in each cell, resolve themselves in certain of
the cells into minute bodies resembling the antherozoids of
Chara (Fig. 112, 4), which, after moving freely within these
cells, escape through apertures in their walls, and then penetrate

! See the account of these processes in the “ Micrographic Dictionary,” p. 468.
% Monatsberichte der Konig], Akad. der Wissenschaften,” Mai, 1855.

GENERATION OF CONFERVACER AND CONJUGATES. 319

apertures in the walls of certain other cells, within each of which
the endochrome has coalesced into a globular mass; over this
mass the antherozoids spread themselves, and seem to dissolve
away upon its.surface; and after this process has taken place,
the mass of endochrome acquires a firm envelope, and becomes
a “‘resting-spore,” which, when set free by the rupture of the
parent cell-wall, germinates into a new plant. A curious varia-
tion of this process is seen in Gdogonium; for instead of the
antherozoids escaping freely from the “sperm-cells’’ which pro-
duced them, they are discharged en masse, included within a
capsule which is furnished with cilia, and which so resembles a
“ zoospore”’ as to be easily mistaken for it; and it is only when
this has attached itself, and has set free its contents by the fall-
ing off of a sort of lid, that the antherozoids are enabled to
perform their fertilizing office. The same thing happens in
some other Confervacee; in which, however, the antheridial
capsules, being smaller than the zoospores, are distinguished as
macrogonidia, whilst the latter are known as macrogonidia. The
offices of these different classes of reproductive bodies are only
now beginning to be understood; and the inquiry is one so
fraught with Physiological interest, and, from the facility of
growing these plants in artificial Aquaria, may be so easily pur-
sued, that it may be hoped that Microscopists will apply them-
selves to it so zealously, as not long to leave any part of it in
obscurity.

199. The family Conjugatee agrees with that of the Confervacew
in its mode of growth, but differs from it in the plan in which
its generative process is performed; this being accomplished by
an act of “conjugation,” resembling that which has been de-
scribed in the simplest Protophytes. These plants are not found
so much in running streams, as in waters that are perfectly still,
such as those in ponds, reservoirs, ditches, or marshy grounds;
and they are for the most part unattached, floating freely at or
near the surface, especially when buoyed up by the bubbles of
gas which are liberated from the midst of them under the influ-
ence of solar light and heat. In an early stage of their growth,
whilst as yet the cells are undergoing multiplication by subdi-
vision, the endochrome is commonly diffused pretty uniformly
through their cavities (Fig. 109, a); but as they advance towards
the stage of conjugation, the endochrome ordinarily arranges,
itself in regular spirals (8), but occasionally in some other forms.
The act of “conjugation” usually occurs between the cells of two
distinct filaments, that happen to lie in proximity to each other;
and all the cells of each filament generally take part in it at:
once. The adjacent cells put forth little protuberances, which .
come into contact with each other, and then coalesce by the
breaking down of the intervening partitions, so as to establish a
free passage between the cavities of the conjugating cells. In
some genera of this family (such as Mesocarpus), the conjugating

320 MICROSCOPIC FORMS OF VEGETABLE LIFE.

cells pour their endochromes into a dilatation of the passage that
has been established between them; and itisthere that they com-
mingle, so as to form the spore or the embryo-cell. But in the
Zygnema (Fig. 108), which is among the commonest and best
known forms of Conjugates, the endochrome of one cell passes
over entirely into the cavity of the other; and it is within the
latter that the spore is formed (c), the two endochromes coa-

Fia. 108.

Various stages of the history of Zygnema quininum :—a, three cells, a, b,¢, of a young filament, of
which 6 is undergoing subdivision ; B, two filaments in the first stage of conjugation, showing the
spiral disposition of their endochromes, and the protuberances from the conjugating cells; c, com-
pletion of the act of conjugation, the endochromes of the cells of the filament a having entirely passed
over to those of filament }, in which the sporangia are formed.
lescing into a single mass, around which a firm envelope gradu-
ally makes its appearance. Further, it may be generally observed,
that all the cells of one filament thus empty themselves, whilst
all the cells of the other filaments become the recipients ; here,
therefore, we seem to have a foreshadowing of the sexual dis-
tinction of the generative cells into “sperm-cells” and “ germ-
cells,” which we have just seen to exist in the Confervacee
(§ 198). And this transition will be still more complete, if (as
Itzigsohn has aflirmed) the endochrome of certain filaments of
Spirogyra breaks up before conjugation into little spherical
aggregations, which are gradually converted into nearly color-
less spiral filaments, having an active spontaneous motion, and
therefore corresponding precisely to the antherozoids of the truly
sexual Protophytes.’

' This group of plants seems to serve as the connecting link between those simple
Protophytes in which the sexes are not yet differentiated, and those higher forms in
which the distinction between the “sperm-cells” and “ germ-cells” is very apparent.
For let it be supposed that in Spheroplea (§ 198) a conjugation of two adjacent cells
were to take place, at that stage in their development in which the endochrome 1s
uniformly arranged in rings, no differentiation of sexes yet showing itself,—the process
would in all respects correspond with that of the ordinary Conjugate. Again, whilst
in Mesocarpus, the two conjugating cells appear to take (as in the Desmidee, § 169) a
precisely similar share in the formation of their product, the first stage of differentiation

REPRODUCTION OF CHEATOPHORACESR. 321

200. The Chetophoracee constitute another beautiful and in-
teresting little group of Confervoid plants, of which some species
inhabit the sea, whilst others are found in fresh and pure water,
rather in that of gently mov-
ing streams, however, than in Fia. 109.
strongly flowing currents. Ge-
nerally speaking, their filaments
put forth lateral branches, and
extend themselves into arbo-
rescent fronds; and one of the
distinctive characters of the
group is afforded by the fact,
that the extremities of these
branches are usually prolonged
into bristle-shaped processes
(Fig. 109). As in many pre-
ceding cases, these plants mul-
tiply themselves by the con-
version of the endochrome of
certain of their cells into “ zoo-
spores; and these, when set
free, are seen to be furnished
with four large cilia. ‘ Rest-
ing-spores” have also been
seen in many species; and it is Sadie miele

. rauches of Chetophora elegans, i the act
probable that these, as In Con- of discharging ciliated zoospores, which
fervacee, are true generative are seen, as in motion, on the right.
products of the fertilization of
the contents of “germ-cells” by ‘“antherozoids’ developed
within “sperm-cells” (§ 198). Nearly allied to the preceding
are the Batrachospermee, whose name is indicative of the strong
resemblance which their beaded filaments bear to frog-spawn ;
these exhibit a somewhat greater complexity of structure, and
afford objects of extreme beauty to the Microscopist. The
plants of this family are all inhabitants of fresh water, and they
are chiefly found in that which is pure and gently flowing.
“They are so extremely flexible,” says Dr. Hassall, ‘that they
obey the slightest motion of the fluid which surrounds them ;
and nothing can surpass the ease and grace of their movements.
into sperm-cells and germ-cells is manifested in Zygnema, by the passage of the whole
endochrome of those of one filament into the cavities of the other, and by the formation .
of the spores within the latter. In Spirogyra, moreover, the endochrome of one set of
cells becomes converted into antherozoids before conjugation, whilst that of the other
aggregates into a sporangial mass; thus exhibiting the second stage of differentiation.
Further, there are certain species which agree with the ordinary Conjugate in their
general habit, and which form “ resting-spores” like theirs, but in which no conjugation
has been observed; and it seems not improbable that in these, as in Sphzroplea, the
aotherozoids make their way out of thé sperm-cell by minute apertures in its wall, and.
swim freely about before finding their way into the germ-cell through the apertures in
us wall;—still, however, performing by this means the very same act, as that which is
accomplished by the more direct process of conjugation,—viz., the introduction of the
contents of the sperm cell into the interior of the germ-cell.

21

322 MICROSCOPIC FORMS OF VEGETABLE LIFE,

When removed from the water, they lose all form, and appear
like pieces of jelly, without trace of organization ; on immersion,
however, the branches quickly resume their former disposition.”
Their color is for the most part of a brownish-green ; but some-
times they are of a reddish or bluish purple. The central axis
of each plant is originally composed of a single file of large
cylindrical cells laid end to end; but this is subsequently in-
vested by other cells, in the manner to be presently described.
It bears, at pretty regular intervals, whorls of short radiating
branches, each of them composed of rounded cells arranged in a
bead-like row (Fig. 110), and sometimes subdividing again into
two, or themselves giving off lateral branches. Each of the pri-
mary branches originates ina little protuberance from the primi-
tive cell of the central axis, precisely after the manner of the
lateral cells of Conferva glomerata (§ 198); as this protuberance
increases in size, its cavity is
Fia, 110. cut off by a septum, so as to
render it an independent cell;
and by the continual repetition
of the process of duplicative
subdivision, this single cell be-
comes converted into a beaded
filament. Certain of these
branches, however, instead of
radiating from the main axis,
grow downwards upon it, so
as to form a closely fitting in-
vestment, that seems properly
to belong to it. Some of the
radiating branches grow out
into long transparent points,
like those of Cheetophoracee ;
and it does not seem by any
Batrachospermum moniliforme. means improbable, that these,
. like the “horns” of Vaucheria
(§ 197), are really antheridia. For within certain cells of other
branches, “ resting-spores” are formed ; by the agglomeration of
which are produced the large dark bodies, that are seen in the
midst of the whorls of branches (Fig. 110).

201. This seems the most appropriate place to consider a group
of humble plants, having a peculiar interest for Microscopists,—
that, namely, of Characew ; in which we have a vegetative appa-
ratus as simple as that of the Protophytes already described,
whilst their reproductive apparatus is even more highly developed
than that of the proper Alge. They are for the most part in-
habitants of fresh waters, and are found rather in such as are
still, than in those which are in motion; one species, however,
may be met with in ditches whose waters are rendered salt by
communication with the sea. They may be easily grown for

ROTATION IN CELLS OF CHARA. 323

the purposes of observation, in large glass jars exposed to the
light; all that is necessary being to pour off the water occasion-
ally from the upper part of the vessel (thus carrying away a film
that is apt to form on its surface), and to replace this by fresh
water. Each plant is composed of an assemblage of long tubi-
form cells, placed end to end; with a distinct central axis, around
which the branches are disposed at intervals with great regular-
ity (Fig. 111, a). In one of the genera, Nitella, the stem and

Fig. 111.

Nitella flexilis:—a, stem and branches of the natural size; a, b, c, d, four verticils of branches
issuing from the stem; e¢, f, subdivision of the branches ;—x, portion of the stem and branches en-
larged; a, 6, joints of stem; ¢, d, verticils; e, 7, new cells sprouting from the sides of the branches;
g, h, new cells sprouting at the extremities of the branches.

branches are simple cells, which sometimes attain the length of
several inches; whilst in the true Chara, each central tube is
surrounded by an envelope of smaller ones, which is formed as
in Batrachospermee, save that the investing cells grow upwards
as well as downwards from each joint, and meet each other on
the stem half-way between the joints. Some species have the
power of secreting carbonate of lime from the water in which
they grow, if this be at all impregnated with calcareous matter;
and by the deposition of it beneath their teguments, they have
gained their popular name of “ stone-worts.’”’ These humble
plants have attracted much attention, in consequence of the
facility with which the “rotation,” or movement of fluid in the
interior of the individual cells, may be seen in them. Each cell,

324 MICROSCOPIC FORMS OF VEGETABLE LIFE.

in the healthy state, is lined by a layer of green oval granules,
which cover every part, except two longitudinal lines that remain
nearly colorless (Fig. 111, 8); and a constant stream of semi-fluid
matter, containing numerous jelly-like globules, is seen to flow
over this green layer, the current passing up one side, changing
its direction at the extremity, and flowing down the other side,
the ascending and descending spaces being bounded by the
transparent lines just mentioned. That the currents are in
some way directed by the layer of granules, appears from the
fact noticed by Mr. Varley,' that if accident damages or removes
them near the boundary between the ascending and descending
currents, a portion of the fluid of the two currents will inter-
mingle by passing the boundary; whilst, if the injury be repaired
by the development of new granules on the part from which
they had been detached, the circulation resumes its regularity,
no part of either current passing the boundary. In the young
cells, however, the rotation may be seen, before their granular
lining is formed. The rate of the movement is affected by any-
thing which influences the vital activity of the plant; thus, it is
accelerated by moderate warmth, whilst it is retarded by cold;
and it may be at once checked bya slight electric discharge
through the plant. The moving globules, which consist of
starchy matter, are of various sizes; being sometimes very small,
and of definite figure, whilst in other instances they are seen as
large irregular masses, which appear to be formed by the aggre-
gation of the smaller particles... The production of new cells,
for the extension of the stem or branches, or the origination of
new whorls, is not here accomplished by the subdivision of the
parent cell, but takes place by the method of out-growth (Fig.
111, B, e, f, g, h), which, as already shown (§ 198), is nothing but
a modification of the usual process of cell-multiplication ; in this
manner, the extension of the individual plant is effected with
considerable rapidity. When these plants are well supplied
with nutriment, and are actively vegetating under the influence
of light, warmth, &c., they not unfrequently develope “ bulbels,”
or gonidia of a peculiar kind, which serve the same purpose in
multiplying the individual, as is answered by the zoospores of

1“ Transactions of the Microscopical Society” (First Series), vol. ii, p. 99.

2 This interesting phenomenon may be readily observed, by taking a small portion
of the plant out of the water in which it is growing, and either placing it in a large
aquatic box (% 68) or in the zoophyte-trough (§ 69), or laying it on the glass stage-plate
(§ 67) and covering it with thin glass. The modification of the stage-plate which is
termed the “ growing-slide,” will enable the Microscopist to keep a portion of Chara
under observation for many days together; and this is a much simpler and more con-
venient arrangement than the method devised by Mr. Varley for growing Chara in
bottles ; since the bottle requires a special “ phial-holder” for fixing it on the Microscope
stage, and the convexity of its surface produces some distortion of the image. The Jat-
ter method, however, has its advantages for those who wish to make a special study or
a frequent exhibition of the phenomenon in question; and such should consult Mr.
Varley’s memoir in the “ Transactions of the Society of Arts,” vols. xlviii, xlix, 1; some
parts of which are cited by Mr, Quekett in his “ Practical Treatise on the Microscope;
Third Ed, pp. 166, 397, et seq.

GENERATIVE APPARATUS OF CHARACES. 825

the simpler Protophytes; these are little clusters of cells, filled
with starch, which sprout from the sides of the central axis, and
then, falling off, evolve the long tubiform cells characteristic of
the plant from which they were produced.' The Characee may
also be multiplied by artificial subdivision; the separated parts
continuing to grow, under favorable circumstances, and de-
veloping themselves into the typical form. :

202. The generative apparatus of Characee consists of two sets
of bodies, both of which grow at the bases of the branches Cig,
112, a, B); one set is known by the designation of “ globules,”

Fig. 112.

Antheridia of Chara fragilis :—a, antheridium or “ globule” developed at the base of pistillidium or
“nucule;"—s, nucule enlarged, globule laid open by the separation of its valves; c, one of the
valves, with its group of antheridial filaments, each composed of a linear series of cells, within
every one of which an antherozoid is formed j—in p, 8, and ¥, the successive stages of this formation
are seenj;—and at c is shown the escape of the mature antherozoids, H.

the other by that of “nucules.” The globules are really anthe-
ridia; whilst the nucules contain the germ-cells. The “globules,”
which are nearly spherical, have an envelope made up of eight

' This multiplication by bulbels was described by Amici in 1827; but his observa-

tions seem to have been forgotten by Botanists, until the rediscovery of the fact by M.
Montague.

326 MICROSCOPIC FORMS OF VEGETABLE LIFE.

triangular valves (3, c), often curiously marked, which enclose a
nucleus of a light reddish color; this nucleus is principally com-
posed of a mass of filaments rolled up compactly together; and
each of these filaments (c) consists, like a Conferva, of a linear
succession of cells. In every one of these cells there is formed,
by a gradual change in its contents (the successive stages of
which are seen at D, E, F), a spiral thread of two or three coils,
which, at first motionless, after a time begins to move and re-
volve within the cell; and at last the cell-wall gives way, and
the spiral thread makes its way out (@), partially straightens
itself, and moves actively through the water for some time (a),
in a tolerably determinate direction, by the lashing action of two
long and very delicate filaments with which they are furnished.
The exterior of the “nucule” (4, B) is formed by five spirally
twisted tubes, that give it a very peculiar aspect; and these en-
close a central sac containing protoplasm, oil, and starch-globules.
At a certain period, the spirally twisted tubes, which form a kind
of crown around the summit, separate from cach other, leaving
a canal that leads down to the central cell; and it is probable
that through this canal the antherozoids make their way down,
to perform the act of fertilization. Ultimately the nucule falls
off like a seed, and gives origin to a single new plant by a kind
of germination. The complete specialization of the Generative
apparatus which we here observe (the organs of which it is com-
posed being distinctly separated from the ordinary vegetating
structure of the plant), as well as the complex structure of the
organs themselves, mark out this group, in spite of the simplicity
of the rest of its structure, as belonging to a grade very much
above that of the other families that have been treated of in this
chapter; but as scarcely any two Botanists agree upon the exact
place which ought to be assigned to it, the convenience of asso-
ciating it with other forms of vegetation of which the Micro-
scopist especially takes cognizance, is a sufficient reason for so
arranging it in a work like the present.

CHAPTER VII.

MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

203. From those simple Protophytes, whose minuteness causes
their entire fabrics to be fitting objects for Microscopic examina-
tion, we pass to those higher forms of Vegetable life, whose
larger dimensions require that they should be analyzed (so to
speak) by the examination of their separate parts. And in the
present chapter, we shall bring under notice some ofthe princi-
pal points of interest to the Microscopist, which are presented
by the Cryptogamie series ; commencing with those simpler Alge,
which scarcely rank higher than some of the Protophytes already

- described; and ending with the Ferns and their allies, which
closely abut upon the Phanerogamia or Flowering Plants. In
ascending this series, we shall have to notice a gradual differentia-
tion of organs; those set apart for Reproduction being in the
first place separated from those appropriated to Nutrition (as we
have already seen them tobe in the Characez) ; and the principal
parts of the Nutritive apparatus, which are at first so blended
together that no real distinction exists between root, stem, and
leaf, being progressively evolved on types more and more pecu-
liar to each respectively, and having their functions more and
more limited to themselves alone. Hence
we find a differentiation, not merely in
the external form, but also in the inti-
mate structure of organs; its degree bear-
ing a close correspondence to the degree
in which their functions are respectively
specialized or limited to particular actions.
Thus in the simple Ulva (Fig. 104), what-
ever may be the extent of the frond, every
part has exactly the same structure, and
performs the same actions, as every other
part; living for and by itself alone. In
Batrachospermum (Fig. 110), we have
seen a delinite arrangement of branches
upon an axis of growth; and while the Mesogloia vermicularis.
branches are formed of simple necklace-
like rows of rounded cells, the cells of the stem are elongated
and adhere to one another by flattened ends. This kind of dif-

328 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

ferentiation is seen to be carried to a still greater extent in Meso-
gloia (Fig. 113); a plant which may be considered as one of the
connecting links between such Protophytes as Batrachospermes
—which it resembles in general plan of structure,—and the
Fucoid Alge, which it resembles in fructification.

204. When we pass to the higher Sea-weeds, such as the com-
mon Fucus and Laminaria, we observe a certain foreshadowing
of the distinction between root, stem, and leaf; but this distine-
tion is but very imperfectly carried out, the root-like and stem-like
portions serving for little else than the mechanical attachment
of the leaf-like part of the plant, and each still absorbing and
assimilating its own nutriment, so that no transmission of fluid
takes place from one portion of the fabric to another. Hence
we find that there is not yet any departure from the simple cellu-
lar type of structure; the only modification being, that the
several layers of cells, where many exist, are of different sizes
and shapes, the texture being usually closer on the exterior and
looser within ; and that the texture of the stem and roots is denser
than that of the expanded fronds. This simple cellular type of
structure is maintained through all but the highest Cryptogamia;
for it is not until we come to the Mosses, that the differentiation
of stem, root, and leaf is established; and even in these it is not
so fully carried out, as to require a provision for the free trans-
mission of fluid from one part to another; whilst the scale of
their fabrics is not such as to render it necessary that their softer
parts should be supported by a tissue of peculiar density. But
in the group of Ferns, which, notwithstanding their complete
adhesion to the Cryptogamic type of Reproduction, have the
general form of the higher plants, and even attain the size
and bearing of trees, we find the leaves separated from the roots
by the intervention of a stem; and in this stem, as also in the
leaf-stalks prolonged from it, we find, interposed in the midst of
the cellular tissue which forms their principal substance, two
new forms of structure,—namely, woody fibre which serves to
give strength and support to the stem and to the organs it bears,
and ducts through which the liquid absorbed by the roots may
be readily conveyed to the leaves.

205. The group of Melanospermous or olive-green Sea-weeds,
which, in the family Fucacee, exhibits the highest type of Algal
structure, presents us with the lowest in the family Hetocarpacee ;
which, notwithstanding, contains some of the most elegant and
delicate structures that are anywhere to be found in the group,
the full beauty of which can only be discerned by the micro-
scope. Such is the case, for example, with the Sphacelaria, a
small and delicate sea-weed, which is very commonly found
parasitic upon larger Alge, either near low-water mark, or alto-
gether submerged; its general form being remarkably charac-
terized by a symmetry that extends also to the individual
branches (Fig. 114), the ends of which, however, have a decayed

GENERATIVE ORGANS OF FUCACEA. 329

look, that seems to have suggested the name of the genus (from
the Greek cyazeioc, gangrene). The study of the higher and
larger members of this group, has recently come to present a
new and very attractive source of interest to the Microscopist,
in consequence of the discovery of the truly sexual nature of
their fructification ; and we shall take that of a common species
of Fucus as the type of that of the order generally. The
“receptacles” which are borne at the extremities of the fronds,
here contain both “sperm-cells” and “ germ-cells;’’ in some
other species, however, they are disposed in different receptacles
on the same plant; whilst in the commonest of all, F. vesiculosus
(bladder-wrack), they are limited to different individuals... When
a section is made through

one of the flattened recep- Fie. 115.

tacles of F. platycarpus,
its interior is seen to be a
nearly globular cavity (Fig.
115), lined with filament-

Fig. 114, Terminal portion of branch of Sphacelaria cirrhosa.
Fig. 115. Vertical Section of receptacle of Fucus platycarpus, lined with filaments, among which
lie the antheridial cells, and the sporangia containing octospores.

ous cells, some of which are greatly elongated, so as to project
through the pore by which the cavity opens on the surface.
Among these are to be distinguished, towards the period of their

a It was at first stated by MM. Thuret and Decaisne, that this species was sometimes
diwecious, sometimes hermaphrodite ; but they now consider the hermaphrodite form to
be a distinct species, the F. platycarpus described above.

330 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

maturity, certain filaments (Fig. 116, 4) whose granular contents
acquire an orange hue, and gradually shape themselves into oval
bodies (8), each with an orange-colored spot, and two long

Fig. 116.

Antheridia and antherozoids of Fucus plutycarpus :—a, branching articulated hairs, detached from
the walls of the receptacle, bearing antheridia in different stages of development; B, antherozoids,
some of them free, others still included in their antheridial cells.

thread-like appendages, which, when discharged by the rupture
of the containing cell, have for a time a rapid undulatory motion,
whereby these antherozoids are diffused through the surrounding
liquid. Lying amidst the filamentous mass, near the walls of
the cavity, are seen (Fig. 115) numerous dark pear-shaped bodies,
which are the sporangia, or parent cells of the “ germ-cells.”
Each of these sporangia gives origin, by duplicative subdivision,
to a cluster of eight cells, which is thence known as an “ octo-
spore ;” and these are liberated from their envelopes, before the
act of fertilization takes place. This act consists in the swarm-
ing of the antherozoids over the surface of the germ-cells, to
which they communicate a rotatory motion by the vibration of
their own filaments; it takes place within the receptacles in the
hermaphrodite Fuci, so that the spores do not make their exit
from the cavity until after they have been fecundated ; but in
the monecious and diccious species, each kind of receptacle
separately discharges its contents, which come into mutual con-
tact on their exterior. The antheridial cells are usually ejected
entire, but soon rupture, so as to give exit to their filaments; the
sporangia of the female receptacles discharge their globular
octospores within the receptacle; and these, soon after passing
forth, liberate their separate spores, which speedily meet with
antherozoids and are fecundated by them. The spores, when
fertilized, soon acquire a new and firmer envelope; and under
favorable circumstances they speedily begin to develope them-
selves into new plants. The first change that is seen in them, 1s

‘ GENERATIVE ORGANS IN FLORIDESA. 3831

the projection and narrowing of one end into a kind of footstalk,
by which the spore attaches itself, its form passing from the
globular to the pear-shaped; a partition is speedily observable
in its interior, its single cell being subdivided into two; and by
a continuation of a like process of duplication, first a filament,
and then a frondose expansion, is produced, which gradually
evolves itself into the likeness of the parent plant. The whole
of this process may be watched without difficulty, by obtaining
specimens of F. vesiculosus at the period at which the fructifica-
tion is shown to be mature, by the recent discharge of the con-
tents of the conceptacles in little gelatinous masses on their
orifices; for if some of the spores, which have been set free
from the olive-green (female) receptacles, be placed in a drop of
sea-water in a very shallow cell, and a small quantity of the mass
of antherozoids set free from the orange-yellow (male) recepta-
cles, be mingled with the fluid, they will speedily be observed,
with the aid of a magnifying power of 200 or 250 diameters, to
go through the actions just described; and the subsequent pro-
cesses of germination may be watched by means of the “ grow-
ing-slide.”! The winter months, from December to March, are
the most favorable for the observation of these phenomena; but
where the Fuci abound, some individuals will usually be found
in fructification at almost any period of the year. Even in the
Fucacee, according to recent observations, a multiplication by
zoospores, like that of the Ulvaceze (§ 195), still takes place ;
these bodies being produced within certain of the cells that
form the superficial layer of the frond, and swimming about
freely for a time after their emission, until they fix themselves
and begin to grow. That they are to be considered gemme,
and not as generative products, appears certain from the fact
that they will vegetate without the assistance of any other bodies;
whereas the antherozoids of themselves never come to anything,
and the octospores undergo no further changes, but decay away
(as M. Thuret has experimentally ascertained), if not fecundated
by the antherozoids.

206. Among the Rhodospermee, or red Sea-weeds, also, we find
various simple but most beautiful forms, which connect this
group with the more elevated Protophytes, especially with the
family Chetophoracee ; such delicate feathery or leaf-like fronds
belong, for the most part to the family Ceramzacee, some members
of which are found upon every part of our coasts, attached either
to rocks or stones, or to larger Algee, and often themselves afford-
ing an attachment to Zoophytes and Bryozoa. They chiefly live
in deeper water than the other sea-weeds; and their richest tints
are only exhibited, when they grow under the shade of project-
ing rocks or of larger dark-colored Alge. Hence in growing

‘If a cell be not employed, the drop should not be covered, unless some precaution
be taken to keep the pressure of the thin glass from the minute bodies beneath, whose
movements it will otherwise impede.

332 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

them artificially in Aquaria, it is requisite to protect them from
an excess of light; since otherwise they become unhealthy. The
nature of the fructification of the Rhodospermece (or Floridec) is less
perfectly understood than that of the Fucoid Alge. It is certain,
however, that antheridia exist among them; these being de-
veloped in individuals that do not produce spores, and in pretty
much the same situations. The products of these antheridia,
however, do not exhibit the spontaneous motion of ordinary an-
therozoids. Of the spores there are two kinds, of which one set
are probably “ gemme,” whilst the other are “ germ-cells;” but
it is not yet determined to which of the two these characters
respectively belong. The ‘“tetraspores,”—which are peculiarly
characteristic of the group, being found in every one of its sub-
divisions,—are usually imbedded in the general substance of the
frond, though they sometimes congregate in particular parts, or
are restricted to a special branch. Hach group (Fig. 117, 8) seems

Fig. 117.

Arrangement of tretraspores, in Carpocaulon mediterraneum :—a, entire plant; B, longitudinal section
of branch. (N. B. Where only three tetraspores are seen, it is merely because the fourth did not hap-
pen to be so placed as to be seen at the same view.)

to be evolved within one of the ordinary cells of the frond, which
undergoes a duplicative subdivision; the four secondary cells,
however, remain enclosed within their primary cell until the
period of maturity, a new envelope, the “perispore,” being
formed around them. In the Corallines, which are sea-weeds
whose tissue is consolidated by calcareous deposit, the tetra-
spores are included within hollow conceptacles; but generally
speaking, it is the simple spores only which are thus specially

STRUCTURE AND REPRODUCTION OF LICHENS. 333

protected. These are never scattered through the frond, like the
tetraspores; and are commonly developed within a ceramidium,
which is an urn-shaped case, furnished with a pore at its summit,
and containing a tuft of pear-shaped spores arising from the base
of its cavity. The resemblance of these bodies in position to the
“ octospores” of Fuci, would seem to justify the conclusion that
they are the true generative spores, whilst the tetraspores are
gemme, as Harvey and Thwaites consider them; but a different
view is taken by Decaisne, Agardh, and other eminent Algolo-
gists, who regard the tetraspores as the true generative spores,
and consider the simple spores to be gemme. It is, therefore, a
point of much interest to determine by careful observation and
experiment which is the right view; and Microscopists who have
the opportunity of studying these plants, either in their native
haunts, or in artificial Aquaria, can scarcely apply themselves to
a better subject of investigation.

207. The class of Lichens, which consists of plants that closely
correspond with Algee in simplicity of organization, but differ
from them widely in habit, does not present so many objects of
attractive interest to the Microscopist; and the peculiar density
which usually characterizes their structure, renders a minute ex-
amination of it more than ordinarily difficult. Lichens are com-
monly found growing upon the trunks or branches of trees, upon
rocks or stones, upon hard earth, or in other situations in which
they are sparingly supplied with moisture, but are freely ex-
posed to light and air. In the simpler forms of this group, the
primordial cell gives origin, by the ordinary process of subdivi-
sion, to a single layer of cells, which may spread itself over the
surface to which it is attached, in a more or less circular form;
and one or more additional layers being afterwards developed
upon its free surface, a thallus is formed, which has no very de-
fined limit, and which, in consequence of the very slight adhesion
of its component cells, is said to be “ pulverulent.” Sometimes,
however, the cells of the thallus are rather arranged in the form
of filaments, which penetrate the superficial layers of the bark
whereon such Lichens grow, and which are sometimes also so
interwoven at the outer surface, as to form a sort of cuticle.
Interposed among the ordinary cells of the thallus, we very com-
monly find certain green globular cells, arranged in single bead-
like filaments; these, which are termed gonidia, being found to
be capable of reproducing the plant when detached, must be
considered as gemme. In the higher tribes of Lichens, we find
the interlacing filaments forming a tough cortical envelope to
both surfaces; whilst in the interior of the firm “crustaceous”
thallus, the gonidial cells are found in regular layers. Some-
times these increase in particular spots, and make their way
through the upper cortical layer, so as to appear on the surface
as little masses of dust, which are called soredia. Besides these,
Lichens contain proper Generative organs, by which a true sexual

3384 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

reproduction seems to be effected. In addition to the “ fructifi-
cation” which is commonly recognized by its projection from
the surface of the thallus, the researches of M. Tulasne have de-
tected a set of peculiar organs of much smaller size, not unlike
the male receptacles of Fuci (§ 205), to which he has given the
appellation of spermogonia. From the exterior of the cellular
filaments which line these cavities, a vast number of minute
oval bodies termed spermatia are budded off, which, when mature,
escape in great numbers from the orifices of the spermogonia.
They differ from ordinary antherozoids in being destitute of any
power of spontaneous movement; but in this respect they are
paralleled by the spermatoid bodies of the Floridec (§ 206). As
their participation in the production of fertile spores has not yet
been demonstrated, we cannot yet indubitably assign to them
the character of “sperm-cells;” although various considerations
concur to render their possession of this attribute highly probable.
The female portion of the generative apparatus, though some-
times dispersed through the thallus, is usually collected into
special aggregations, which form projections of various shapes;
these, although they have received a variety of designations ac-
cording to their particular conformation, may all be included
under the general term apothecia. When divided by a vertical
section, these bodies at their maturity are found to contain a
number of ase? or spore-cases, arranged vertically in the midst of
straight elongated cells or filaments, which are termed paraphyses.
Each of the asci contains a definite number of spores (usually
eight, but always a multiple of two), which are projected from
the apothecia with some force, the emission being kept up con-
tinuously for some time; this discharge seems to be due to the
different effect of moisture upon the different layers of the
apothecium. When and how the act of fecundation is accom-
plished, is a matter still hidden in obscurity; and the problem
is one which, owing to the difficulties arising out of the dense
structure of the organs, will only be resolved by a combination
of sagacity, manipulative skill, and perseverance, on the part of
Microscopic observers who may devote themselves to the study.

208. In the simplest forms of Fung, we again return to the
lowest type of Vegetable existence, namely, the single cell; and
such, if perfect plants, would properly take rank among the low-
est Protophytes. But there is good reason for regarding many
—perhaps all—of those which seem most simple, as the imper-
fectly developed states of other Plants, which, if they attained
their full evolution, would present a much more complex struc-
ture. This is the case, for example, with the Torula cerevisie or
Yeast-plant, which so abounds in Yeast, that this substance may
be said to be almost entirely made up of it. When a small
quantity of yeast is placed under the Microscope, and is magn
fied 800 or 400 diameters, it is found to be full of globules, which
are clearly cells; and these cells vegetate, when placed in a fer-

SIMPLER FORMS OF FUNGI—YEAST-PLANT. 335

mentable fluid containing some form of albuminous matter in
addition to sugar, in the manner represented in Fig. 118. Each

Fig. 118.

Torula Cerevisie, or Yeast-Plant, as developed during the process of fermentation :—a, 8, ¢, d, suc-
cessive stages of Cell-multiplication.

cell puts forth one or two projections, which seem to be young
cells developed as buds or offsets from their predecessors; these,
in the course of ashort time, become complete cells, and again per-
form the same process ; and in this manner the single cells of yeast
develope themselves, in the course of a few hours, into rows of
four, five, or six, which remain in continuity with each other
whilst the plant is still growing, but which separate if the fer-
menting process be checked, and return to the isolated condition
of those which originally constituted the yeast. Thus it is, that
the quantity of yeast first introduced into the fermentable fluid,
is multiplied six times or more, during the changes in which it
takes part. The full development of the Plant, however, and
the evolution of its apparatus of fructification, only occur, when
the fermenting process is allowed to go on without check; and
it seems capable of producing a considerable variety of forms,
whose precise relationship to each other has not yet been made
clear. In fact, with regard to the Fungi generally, it has been
made apparent by recent observations, that different individuals
of the very same species may not only develope themselves ac-
cording to a great number of very dissimilar modes of growth,
but that they may even bear very dissimilar types of fructification ;
and further, that even the same individual may put forth, at dif-
ferent periods of its life, those two kinds of fructification,—the
basidio-sporous, in which the spores are developed by out-growth
from free points (dasidia), and the theca-sporous, in which they are
developed in the interior of cases (theee or asci, Fig. 125),—which
had been previously considered as separately characterizing the
two principal groups, into which the class is primarily divided.
209. Many of the simpler forms of Fungi are inhabitants of
the interior of the bodies of other animals, and are only known
as living in these situations. Among these may first be men-
tioned the Sarcina ventriculi (Fig. 119), which is most frequently
found in the matters vomited by persons suffering under disorder
of the stomach, but has also been met with in other diseased
parts of the body. The plant has been detected in the con-
tents of the stomach, however, under circumstances which
seem to indicate that it is not an uncommon tenant of that
organ even in health, and that it may accumulate there to a

336 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

considerable amount without producing any inconvenience ;
it seems probable, therefore, that its presence in disease is
rather to be considered as fa-

Fig. 119. vored by the changed state of

the fluids which the disease
induces (either an acid or a
fermentable state of the con-
tents of the stomach having
been generally found to exist
in the cases in which the plant
has been most abundant), than
to be itself the occasion of the
disease, as some havesupposed,
The Sarcina presents itself in
the form of clusters of adhe-
rent cells arranged in squares,
each square containing from
4 to 64, and the number of cells being obviously multiplied
by duplicative subdivision in directions transverse to each
other. In fact, its general mode of growth would indicate
a near relationship to Gonium, one of the Volvocinex, which
presents itself in similar quadripartite aggregations; and many
Botanists, looking to this circumstance, and to the residence
of the plant in liquid, regard it as belonging to the group
of Alge. It agrees with the Fungi, however, in not living
elsewhere than in liquids containing organic matter; and there
can be little doubt that, as no fructification has yet been seen
in it, only its earlier and simpler condition is yet known to
us. Its true place cannot be determined, until its whole life-
history shall have been followed out. There is a form of
Fungous vegetation that is prone to develope itself within the
living body, which is of great economic importance, as well as
of scientific interest; this is the Botrytis bassiana (Fig. 120), a
kind of “mould,” the growth of which is the real source of a
disease termed Muscardine, that sometimes carries off Silk-worms
in large numbers, just when they are about to enter the chrysalis
state, to the great injury of their breeders. The sporules of this
fungus, floating in the air, enter the breathing-pores which open
into the tracheal system of the silk-worm (Chap. XVII); they first
develope themselves within the air-tubes, which are soon blocked
up by their growth; and they then extend themselves through
the fatty mass beneath the skin, occasioning the destruction of
this tissue, which is very important as a reservoir of nutriment
to the animal, when it is about to pass into a state of complete
inactivity. The disease invariably occasions the death of the
silk-worm which it attacks ; but it seldom shows itself externally
until afterwards, when it rapidly shoots forth from beneath the
skin, especially at the junction of the rings of the body. Although
it spontaneously attacks only the larva, yet it may be communl-

&

Surcina ventricult.

FUNGOUS VEGETATION IN SILK-WORMS. 337

cated by inoculation to the Chrysalis and the Moth, as well as to
the worm; and it has been also observed to attack other Lepi-
dopterous Insects. A careful investigation of the circumstances
which favor the development of this disease, was made by Au-
douin, who first discovered its real nature; and he showed that
its spread is favored by the overcrowding of the worms in the
breeding establishments, and particularly by the practice of
throwing the bodies of such as die, into a heap in the immediate
neighborhood of the living worms; this heap speedily becomes
covered with this kind of “mould,” which finds upon it a most
congenial soil; and it keeps up a continual supply of sporules,
which, being diffused through the atmosphere of the neighbor-
hood, are drawn into the breathing pores of individuals pre-
viously healthy. Wherever the precautions obviously suggested
by the knowledge of the nature of the disease thus afforded by

Fig. 120.

Botrytis bassiana :—a, the fungus as it first appears at the orifices of the stigmata; 8, tubular fila-
ments bearing short branches, as seen two days afterwards; ©, magnified view of the same; c, D,
appearance of filaments on the fourth and sixth days; F, masses of mature spores falling off the
branches, with filaments proceeding from them.

the Microscope have been duly put in force, its extension has
been kept within comparatively limited bounds. The plant pre-
22

338 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.,

sents itself (Fig. 120) under a considerable variety of forms; all
of which, however, are of extremely simple structure, consisting
of elongated or rounded cells, connected in necklace-like fila-
ments, very nearly as in the ordinary “‘ bead-moulds.”’

210. Again, it is not at all uncommon in the West Indies to see
individuals of a species of Polistes (the representative of the
Wasp of our own country) flying about with plants of their own
length projecting from some part of their surface, the germs of
which have been probably introduced (as in the preceding case)
through the breathing-pores at their sides, and have taken root
in their substance, so as to produce a luxuriant vegetation. In
time, however, this fungous growth spreads through the body,
and destroys the life of the insect ; it then seems to grow more
rapidly, the decomposing tissue of the dead body being still
more adapted than the living structure to afford it nutriment.
A similar growth of different species of the genus Spheria takes
place in the bodies of certain caterpillars in New Zealand,
Australia, and China; and being thus completely pervaded by a
dense substance, which, when dried, has almost the solidity ot
wood, these Caterpillars come to present the appearance of
twigs, with long slender stalks that are formed by the projection

of the fungus itself. The Chinese

Fig. 121. species is valued as a medicinal

drug. The stomachs and intes-
tines of many Worms and Insects
are infested with Entophytic Fun-
gi, which grow there with great
luxurianee. Inthe accompanying
illustrations (Figs. 121, 122) are
shown some of the forms of the
Enterobryus,' which has been found
by Dr. Leidy to be so constantly
present in the stomach of certain
species of Julus (gally-worm), that
Growth of Enterobryus spiralis from mu- It 18 extremely rare to meet with
cous membrane of stomach of Julus:—a, individuals whose stomachs do not
epics’ te not teow meatanes & -pontain it, ‘The Enterobryusiorigt
celle; dye, secondary cells. ally consists of asingle long tubu-
lar cell, which sometimes grows In

a spiral mode (Fig. 121), sometimes straight and tapering (Fig.
122, a); in its young state, the cell contains a transparent pro-
toplasma, with granules and globules of various sizes; but in its
more advanced condition, the tube of the filament is occupied
by cells in various stages of development; these distend the

1 This plant, also, has much affinity to Alge in its general type of structure, and is re-
ferred to that group by many Botanists; but the conditions of its growth, asin the case of
Sarcina, seem rather to indicate its affinity to the Fungi; and until its proper fructification
shall have been made out, its true place in the scale must be considered as undetermined.

FUNGOUS VEGETATION IN LIVING INSECTS, 8389

terminal part of the cell (Fig. 122, 8), and press so much against
each other that their walls become flattened; whilst nearer the
middle of the same filament (c), we find them retaining their
rounded form, and merely lying in contact with each other; and

Fia, 122.

Structure of Enterobryus :—A, growth of £. attenuatus, from mucous membrane of the stomach of
Passulus ; 8, dilated extremity of primary cell of E. elegans, filled with secondary cells, whieh, near
its termination, become mutually flattened by pressure; c, lower portion of the same filament, con-
taining cells mingled with granules; p, base of the same filament, containing globules interspersed
among granules.

at the base (p) they lie detached in the midst of the granular
protoplasma. In JH. spiralis, the primary cells (Fig. 121, 6, ¢)
very commonly have secondary and even ternary cells (d) de-
veloped at their extremities; but this is rarely seen in H. attenua-
tus (Fig. 122). It may be considered as next to certain that the
tubular filaments rupture, when the contained cells have arrived
at maturity, and give them exit; and that these cells are de-
veloped, under favorable circumstances, into tubular filaments
like those from which they sprang; but the process has not yet
been thoroughly made out. This is obviously not the true
Generation of the plant, but is analogous to the development of
zoospores in Achlya (§ 197). It is not a little curious, moreover,
that the Entozoa or parasitic worms infesting the alimentary
canal of these animals, should be frequently clothed ezternally
with an abundant growth of such plants; in one instance Dr.
Leidy found an Ascaris bearing twenty-three filaments of Hntero-
bryus “which appeared to cause no inconvenience to the animal,
as it moved and wriggled about with all the ordinary activity of
the species.” The presence of this kind of vegetation seems to
be related to the peculiar food of the animals in whose stomachs
it is found; for Dr. Leidy could not discover a trace of these or
of any other parasitic plants in the alimentary canal of the carni-
vorous Myriapods which he examined; whilst he met with a
constant and most extraordinary profusion of vegetation (Fig.

340 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

123) in the stomach of an herbivorous beetle, the Passulus cornutus,
which lives, like the Tuli,
Fig, 123. in stumps of old trees,
and feeds as they do on
decaying wood. Of this
vegetation, some parts
present themselves in
tolerably definite forms,
which have been de-
scribed under various
names; whilst other por-
tions have the indefinite-
ness of imperfectly de-
veloped organisms, and
can scarcely be charac-
terized in the present
state of our knowledge
of them. With regard
to several forms, indeed,
Dr. Leidy expresses a
y i doubt whether they are
Fungoid Vegetation, clothing membrane of stomach of parasitic plants, or whe-
Passulus, intermingled with brush-like hairs. ther they are outgrowths
of the membrane itself.
There are various diseased conditions of the Human skin and
mucous membranes, in which there is a combination of fungoid
vegetation and morbid growth of the animal tissues; this is the
case, for example, with the Tinea favosa, a disease of the scalp,
in which yellow crusts are formed, that consist almost entirely
of the mycelium, receptacles, and sporules of a fungus; and the
like is true also of those white patches (Aphthe) on the lining
membrane of the mouth of children, which are known as Thrush.
In these and similar cases, two opinions are entertained as to
the relation of the fungi to the diseases in which they present
themselves; some maintaining that their presence is the essential
condition of these diseases, which originate in the introduction
of the vegetable germs; and others considering their presence to.
be secondary to some morbid alteration of the parts wherein the
fungi appear, which alteration favors their development. The
first of these doctrines derives a strong support from the fact,
that the diseases in question may be communicated to healthy in-
dividuals, through the introduction of the germs of the fungi by
inoculation ; whilst the second is rather consistent with general
analogy, and especially with what is known of the conditions
under which the various kinds of fungoid “blights” develope
themselves in or upon growing Plants (§ 212). ;
211. There are scarcely any Microscopic objects more beauti-
ful, than some of those forms of “mould” or “mildew,” which
are so commonly found growing upon the surface of jams and

GROWTH OF MOULD ON DECAYING SUBSTANCES. 38341

other preserves; especially when they are viewed with a low
magnifying power, by reflected light. For they present them-
selves as a forest of stems and branches of extremely varied and
elegant forms (Fig. 124), loaded with fruit of singular delicacy of
conformation, all glistening brightly on a dark ground. In re-
moving a portion of the “mould” from the surface whereon it
grows, for the purpose of microscopic examination, it is desirable
to disturb it no more than can be helped, in order that it may be
seen as nearly as possible in its natural condition; and it is there-
fore preferable to take up a portion of the membrane-like sub-
stance whereon it usually rests, which is,
in fact, a mycelium composed of interlacing ae oe
filaments of the vegetative part of the plant,
the stems and branches being its reproduc-
tive portion (§ 213). The universality of the
appearance of these simple forms of Fungi
upon all spots favorable to their develop-
ment, has given rise to the belief that they
are spontaneously produced by decaying
substances; but there is no occasion for
this mode of accounting for it; since the
extraordinary means adopted by Nature
for the production and diffusion of the
germs of these plants, adequately suffices
to explain the facts of the case. The num-
ber of sporules which any one Fungus
may develope, is almost incalculable; a single individual of the
putt-ball tribe has been computed to send forth no fewer than ten
millions. And their minuteness is such, that they are scattered
through the air in the condition of the finest possible dust; so
that it is difficult to conceive of a place from which they should
be excluded. This mode of explanation has received further
confirmation from the facts recently ascertained, in regard to the
great number of forms under which a single germ may develope
itself; the particular form being determined, it seems likely, by
the soil whereon each germ happens to grow. Hence we are not
obliged to suppose that distinct germs are floating about in the
atmosphere, for all the forms of fungous vegetation which appear
to be of different species, and which are only found in particular
situations,—the Puccinia rose, for example, only upon rose-
bushes, Jsaria felina only upon the dung of cats deposited in
humid and obscure situations, and Onygena exigua upon the hoofs
of dead horses ;—but are warranted in believing that the real va-
riety of germs is comparatively small, and that the facts just
stated, with others of the same order, only indicate the modify-
ing influence of the circumstances under which they are de-
veloped.

212. The parasitic Fungi which infest some of the Vegetables
most important to Man, as furnishing his staple articles of food,

Stysanus caput-meduse.

3842 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

constitute a group of special interest to the Microscopist; of
which a few of the chief examples may here be noticed. The
mildew, which is often found attacking the straw of Wheat, shows
itself externally in the form of circular clusters of pear-shaped
spore-cases (Fig. 125), each containing two compartments filled
with sporules; these (constituting the

Fre. 125. Puceinia graminis) arise from a filamen-

tous tissue constituting the mycelium, the
threads of which interweave themselves
with the tissue of the straw; and they
generally make their way to the surface
through the ‘stomata’ or breathing-
pores of its epidermis. The rust, which
makes its appearance on the leaves and
chaft-scales of Wheat, has a fructification
that seems essentially distinct from that
just described, consisting of oval spore-
cases, that grow without any regularity
of arrangement from the threads of the
mycelium; and hence it has been con-
sidered to belong to a different genus and
species, Uredo rubigo. But from the ob-
servations of Prof. Henslow, it seems cer-
tain that the ‘rust’ is only an earlier form of the ‘“ mildew;”
the one form being capable of development into the other, and
the fructiffcation characteristic of the two supposed genera having
been evolved on one and the same individual. Another reputed
species of Uredo (the U. segetum) it is, which, when it attacks the
flower of the wheat, reducing the ears to black masses of sooty
powder, is known as “smut” or “dust-brand.’”’ The corn-grains
are entirely replaced by aggregations of spores; and these being
of extreme minuteness, they are very easily and very extensively
diffused. The “bunt” or “stinking rust’ is another species of
Uredo (the U. fetida), which is chiefly distinguished by its dis-
gusting odor. The prevalence of these “blights” to any con-
siderable extent, seems generally traceable to some seasonal in-
fluences unfavorable to the healthy development of the wheat
plant; but they often make their appearance in particular locali-
ties, through careless cultivation, or want of due precaution in
the selection of seed. It may be considered as certain that an
admixture of the spores of any of these fungi with the grains,
will endanger the plants raised from them; but it is equally cer-
tain that the fungi have little tendency to develope themselves in
plants that are vegetating with perfect healthfulness. The wide
prevalence of such blights in bad seasons is not difficult to ac-
count for, if it be true (as the observations of Mr. John Marshall,
a few years since, rendered probable) that there are really very
few wheat-grains, near the points of which one or two sporules
of Fungi may not be found, entangled among their minute hairs;

Puceinia graminis.

GENERATION OF FUNGI. 343

and it may be fairly surmised that these sporules remain dor-
mant, unless an unfavorable season should favor their develop-
ment, by inducing an unhealthy condition of the wheat-plant.
The same general doctrine probably applies to the Botrytis, which,
from 1847 to the present time, has had a large share in the pro-
duction of the “ Potato-disease ;” and to the Ozdiwm, which has
a like relation to the “ Vine-disease” that has been extending
itself for some years past through the south of Europe. There
seems no doubt that, in the fully developed disease, the Fungus
is always present; and that its growth and multiplication have a
large share in the increase and extension of the disorder, just as
the growth of the Yeast-plant excites and accelerates fermenta-
tion, and its reproduction enables this action to be indefinitely
extended through its instrumentality. But just as the Yeast-
plant will not vegetate save in a fermentable fluid, that is, in a
solution which, in addition to sugar, contains some decomposable
albuminous matter,—so does it seem probable, on a consideration
of all the phenomena of the Potato and Vine diseases, that
neither the Botrytis of the one, nor the Oidium of the other will
vegetate in perfectly healthy plants; but that a disordered con-
dition, induced either by forcing and therefore unnatural systems
of cultivation, or by unfavorable seasons, or by a combination of
both, is necessary as a “ predisposing” condition.

213. In those lower forms of this class to which our notice of
it has hitherto been chiefly restricted, there is not any very com-
plete separation between its nutritive or vegetative, and its Re-
productive portions ; every cell, as in the simplest Protophytes,
being equally concerned in both. But such a separation makes

Fig. 126,

Aicidium tussilaginis :—a, portion of the plant magnified; B, section of one of the conceptacles
with its spores.

itself apparent in the higher; and this in a very curious mode.
For the ostensible Fungi of almost every description (Fig. 126)
consist, in fact, of nothing else than the organs of fructification ;

344 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.,

the nutritive apparatus of these plants being composed of an
indefinite myceliwm, which is a filamentous expansion (Fig. 127),
composed of elongated branching cells (a), interlacing amongst
each other, but having no intimate connection ; and this “ myce-
lium”’ has such an indefiniteness of form, and varies so little in

Fig, 127.

Clavaria crispula :—a, portion of the mycelium magnified.

the different tribes of Fungi, that no determination of species,
genus, or even family, could be certainly made from it alone.
The recent observations of Tulasne render it probable that a
true sexual generation exists among the Fungi; since he has
ascertained that the presence of bodies resembling the spermatia
of Lichens (§ 207) may be regarded as universal in the organs of
fructification, at an early period of their development. These
are budded off (so to speak) from ramifying filaments, which
are sometimes developed in the midst of those that bear the
spores, and are sometimes found on other parts of the plant,
being occasionally included in distinct conceptacles or spermo-
gonta, as in Lichens. The whole history of the development of
the Fungi, and the question of the relationship of its ditterent
forms to each other, is one that most urgently calls for re-exami-
nation at the present time, under the guidance of our recently
acquired knowledge, and with the assistance of improved in-
struments of Microscopic investigation; and whilst there is a
wide field for the labors of those who possess only instruments
of very moderate capacity, there are several questions which can
only be worked out by means of the highest powers and the
most careful appliances which the practised Microscopist can
bring to bear upon them.

214. The little group of Hepatice or “ Liverworts,” which is
intermediate between Lichens and Mosses,—rather agreeing with
the former in its general mode of growth, whilst approaching
the latter in its fructification,—presents numerous objects of
great interest to the Microscopist; and no species is richer in
these, than the very common Marchantia polymorpha, which may
often be found growing between the paving-stones of damp
court-yards, but which particularly luxuriates in the neighbor-
hood of springs or water-falls, where its lobed fronds are found
covering extensive surfaces of moist rock or soil, adhering by
the radical (root) filaments which arise from their lower surface.

STOMATA AND CONCEPTACLES OF MARCHANTIA. 845

At the period of fructification, these fronds send up stalks, which
carry at their summit either round shield-like disks, or radiating
bodies that bear some resemblance to a wheel without its tire
(Fig. 128) ; the former carry the male organs or antheridia, and
the latter, at an early period, the female organs or archegonia,
which afterwards give place to the sporangia or spore-cases.' But
besides these, the frond usually bears upon its surface (as shown
in Fig. 128) a number of little

open basket-shaped ‘ concep- Fig. 128.

tacles,’’ whose nature and pur-
pose will be presently explained.
The green surface of the frond
of this Liverwort is seen under
a low magnifying power to be
divided into minute diamond-
shaped spaces (Fig. 129, a, a, a)
bounded by raised bands (e, e);
every one of these spaces has in
its centre a curious brownish-
colored body (6, 6), with an open- eta

ing in its middle, which allows pipsrous onceptactes; and lobed receptacles
a few small green cells to be seen bearing pistillidia.

through it. When athin vertical

section is made of the frond (B), it is seen that each of the
lozenge-shaped divisions of its surface corresponds with an air-
chamber in its interior; which is bounded below by a floor (a, a)
of closely set cells (from whose under surface the radical fila-

Fig, 129.

EX y i
en OOI Ee

A, Portion of frond of Marchantia polymorpha seen from above; a, a, lozenge-shaped divisions ;
6, b, stomata seen in the centre of the lozenges; c¢, c, greenish bands separating the lozenges:—s,
vertical section of the frond, showing a, a, the dense layer of cellular tissue forming the floor of the
cavity d,d; b, d, cuticular layer, forming its root; c,¢, its walls; f, f, loose cells in its interior; g,
stoma divided perpendicularly ; h, rings of cells forming its wall; 7, cells forming the obturator
ring.

ments arise), at the sides by walls (¢, e) of similar solid paren-
chyma, the projection of whose summits forms the raised bands
on the surface, and above by a cuticle (6, 6) formed of a single
layer of cells; whilst its interior is occupied by a very. loosely

1In some species, the same shields bear both sets of organs; and in Marchantia

androgyna, we find the upper surface of one half of the pelta developing antheridia,
whilst the under surface of the under half bears archegonia.

846 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

arranged parenchyma, composed of branching rows of cells
(f, f) that seem to spring from the floor,—these cells being what
are seen from above, when the observer looks down through the
central aperture just mentioned. If the vertical section should
happen to traverse one of the peculiar bodies which occupies
the centres of the divisions, it will bring into view a structure of
remarkable complexity. Hach of these stomata (as they are
termed, from the Greek ozo»a, mouth) forms a sort of shaft (9),
composed of four or five rings (like the “ courses” of bricks in
a chimney) placed one upon the other (h) every ring being made
up of fouf or five cells; and the lowest of these rings (¢) appears
to regulate the aperture, by the contraction or expansion of the
cells which compose it, and it is hence termed the “ obtura-
tor ring.’ In this manner, each of the air-chambers of the frond
is brought into communication with the external atmosphere;
the degree of that communication being regulated by the limita-
tion of the aperture. We shall hereafter find (§ 245) that the
leaves of the higher plants contain intercellular spaces, which
also communicate with the exterior by “stomata ;’’ but that the
structure of these organs is far less complex in them, than it is
in this humble Liverwort.

215. The basket-shaped “ conceptacles” which are borne upon
the surface of the frond (Fig. 180, 4), and which may often be

Fig. 130.

Gemmiparous conceptacles of Marchantia polymorpha:—as, conceptacle fully expanded, rising
from the surface of the frond, a, a, and containing disks already detached ;—x, first appearance of
conceptacle on the surface of the frond, showing the formation of its fringe by the splitting of the
cuticle.

found in all stages of development, are structures of singular
beauty. They contain, when mature, a number of little green
round or oblong disks, each composed of two or more layers of
cells; and their wall is surmounted by a glistening fringe of
“teeth,” whose edges are themselves regularly fringed with
minute outgrowths. This fringe is at first formed by the split-
ting up of the epidermis, as seen at B, at the time when the con-
ceptacle and its contents are first making their way above the
surface. The little disks (sometimes termed “bulbels,” from
their analogy to the bulbels or detached buds of Flowering

GENERATIVE APPARATUS OF MARCHANTIA. 347

Plants) are at first evolved as single globular cells, supported
upon other cells which form their footstalks; these single cells
gradually undergo multiplication by duplicative subdivision, until
they evolve themselves into the disks; and these disks, when
mature, spontaneously detach themselves from their footstalks,
and lie free within the cavity of the conceptacle. Most com-
monly they are at last washed out by rain, and are thus carried
to different parts of the neighboring soil, on which they grow
very rapidly when well supplied with moisture; sometimes, how-
ever, they may be found growing whilst still contained within
the conceptacles, forming natural grafts (so to speak) upon the
stock from which they have been developed and detached; and
many of the irregular lobes which the frond of the Marchantia
puts forth, seem to have this origin. When this plant vegetates
in damp shady situations, which are favorable to the nutritive
processes, it does not readily produce the true fructification,
which is to be looked for rather in plants growing in more ex-
posed places. ach of the stalked peltate (shield-like) disks con-
tains a number of flask-shaped cavities opening upon its upper
surface, which are brought into view by a vertical section; and
in each of these cavities is lodged an “ antheridium,’’ composed
of a mass of “sperm-cells,” within which are developed “ anthero-
zoids” like those of Chara (§ 202), surmounted by a long neck
that projects through the mouth of the flask-shaped cavity. The
wheel-like receptacles (Fig. 128) on the other hand, bear on their
under surface, at an early stage, concealed between membranes
that connect the origins of the lobes with one another, a set of
“archegonia,” shaped like flasks with elongated necks (Fig. 131);
each of these has in its interior a “ germ-cell,” to which a canal
leads down from the extremity of the

neck; and there is every reason to be- Fia. 131,

lieve that, as in Ferns, the germ-cell
is fertilized by the penetration of the
antheridia through this canal, until
they reach it. Instead, however, of at
once evolving itself into a new plant
resembling its parent, the fertilized
germ-cell, or embryo-cell, developes
itself into a mass of cells enclosed {
within a capsule, which is termed a
“sporangium ;” and thus the mature
receptacle, in place of archegonia,
bears capsules or sporangia, which
finally burst open, and discharge their contents. These contents
consist of “spores,” which are isolated cells, enclosed in firm
yellow-envelopes; and of “laters,” which are ovoidal cells, each
containing a double spiral fibre coiled up in its interior. This
fibre is so elastic, that, when the surrounding pressure is with-
drawn by the bursting of the sporangium, the spires extend

oH
SEN,
e im
Archegonia of Marchantia polymorpha, in
successive slages of development.

348 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA.

themselves (Fig. 132), tearing apart the cell-membrane; and they
do this suddenly, so as to jerk forth the spores which may be
adherent to their coils, and thus to assist in their dispersion.
The spores, when subjected to moisture, with a moderate amount
of light and warmth, develope themselves into little collections
of cells, which gradually assume the form of a flattened frond;
and thus the species is very extensively multiplied, every one of
the mass of spores, which is the product of a single germ-cell,
being capable of giving origin to an independent individual,
216. The tribe of Mosses is as remarkable from the
Fie. 132. delicacy and minuteness of all the plants composing it,
as other orders of the Vegetable Kingdom are for the
majesty of their forms, the richness of their foliage, or
the splendor of their blossoms. There is not one of
this little tribe, whose external organs do not serve as
beautiful objects, when viewed with low powers of the
Microscope; while their more concealed wonders are
admirably fitted for the detailed scrutiny of the prac-
tised observer. The Mosses always possess a distinct
axis of growth, commonly more or less erect, on which
the minute and delicately formed leaves are arranged
with great regularity. The stem shows some indication
of the separation of a cortical or bark-like portion, from
the medullary or pith-like, by the intervention of acircle
of bundles of elongated cells, which seem to prefigure
the woody portion of the stem of higher plants, and
from which prolongations pass into the leaves, so as to
afford them a sort of midrib. The leaf usually consists
of either a single or a double layer of cells, having
flattened sides by which they adhere one to another;
they rarely present any distinct epidermic layer; but
such a layer, perforated by stomata of simple structure,
is commonly found on the sete or bristle-like footstalks
bearing the fructification, and sometimes on the midribs
of the leaves. The leaf-cells of the Sphagnum (bog
moss) exhibit a very curious departure from the ordi-
nary type; for instead of being small and polygonal,
Swoeewt they are large and elongated (Fig. 133); they contain
Marchantia. spiral fibres loosely coiled in their interior; and their
membranous walls have large rounded apertures, by
which their cavities freely communicate with one another, as is
sometimes curiously evidenced by the passage of Wheel Ani-
malcules, that make their habitation in these chambers. Be-
tween these coarsely spiral cells, are some thick-walled narrow
elongated cells, which give to the leaf its firmness; these, in the
very young leaf (as Mr. Huxley has pointed out). do not differ
much in appearance from the others; the peculiarities of both
being evolved by a gradual process of “differentiation.” The
chief interest of the Mosses, however, to the Microscopist, lies

STRUCTURE AND REPRODUCTION OF MOSSES. 849

in their fructification; which recent discoveries have invested
with a new character. What has been commonly regarded in
that light, namely, the “capsule” or “urn,” borne at the top
of a long footstalk, which springs from

the centre of a cluster of leaves (Fig. b
134, a), is not the real fructification, but
its product; for Mosses, like Liverworts,
possess both antheridia and pistillidia,
although these are by no means con-
spicuous. These organs are sometimes
found in the same envelope (or peri-
gone), sometimes on different parts of
the same plants, sometimes only on
different individuals ; but in either case,
they are usually situated close to the
axis, among the bases of the leaves.
The antheridia are globular, oval, or
elongated bodies (Fig. 135, 4) composed
of aggregations of cells, of which the
exterior form a sort of capsule, whilst Portion of the leaf of Sphag-
the interior are “sperm-cells,” each of ee eee ee eee and
which, as 1t comes to maturity, deve- communicating apertures; and
lopes within itself an “antherozoid” (B, the intervening bands, >, >,
c, D); and the antherozoids, set free by A aaa

Fia. 133.
b b

cells.

Fie. 134.

Structure of Mosses:—a, Plant of Funaria hygrometrica, showing f, the leaves, u, the urs sup-
ported upon the setz or footstalks, s, closed by the operculum, 0, and covered by the calyptra, c:—B,
urns of Encalyptra vulgaris, one of them closed and covered with the ealyptra, the other open; U,
u, the urns; 0, 0, the opercula; ¢, calyptra; p, peristome; s, s, seta2:—c, longitudinal section of very
young urn of Splachnum ; a, solid tissue forming the lower part of the capsule; ¢, columella; J, Jocu-
lus or space around it for the development of the spores; e, epidermic layer of cells, thickened at

the top to form the operculum, 0; p, two intermediate layers, from which the peristome will be formed ;
s, inner layer of cells forming the wall of the loculus.

the rupture of the cells within which they are formed, make

850 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

their escape by a passage that opens for them at the summit of
the antheridium. The antheridia are generally surrounded by a
cluster of hair-like fila-

Fra. 135. ments, composed of cells

a joined together (Fig. 134,

sgt 4), and called “ paraphy-

ses.” The archegonia bear
a general resemblance to
those of Marchantia (Fig.
131); and there is every
reason to believe that the
fertilization of their con-
tained germ-cells is ac-
complished in the manner
already described; for
antherozoids have been
observedswimming about
around the archegonia
within their involucrum,!
and the evolution of cap-
sules from archegonia has
been ascertained not to
take place in those Mosses
which bear the two sets
of organs on separate in-
dividuals, unless an an-
theridial plant be in the
neighborhood. The fer-
tilized embryonal cell
becomes gradually deve-
loped by cell division into
a conical body elevated
upon a stalk; and this at
Q a) length tears across the
Antheridia and Antherozoids of Polytrichum com- walls of the flask-shaped
mune: a,group of antheridia, mingled with hairs and archegonium by @ circu.
sterile filaments (paraphyses); of the three antheridia, lar fissure, carrying the

the ceutral one isin the act of discharging its contents: : d
. é F rds as a
that on the left is not yet mature, while that on the higher part upwa

right has already emptied itself, so that the cellular calyptra or hood (Fig.
structure of its walls becomes apparent;—s, cellular 135, B, c) upon its sum-

contents of an antheridium, previously to the develop- & ee he lower art
ment of the antherozoids;—c, the same, showing the mit, AN hile t P

first appearance of the antherozoids;—p, the same, remains to form a kind

mature and discharging the antherozoids. of eollar round the pase
of the stalk.

217. The “urns” or spore-capsules of Mosses, which are thus

the immediate product of the Generative act, and which must

really be considered as the offspring of the plants that bear them

1 The detection of the antherozoids within the canal of the archegonium, and upon
the surface of the germ-cell, is a point well worthy of Microscopic research.

SPORE-CAPSULES AND PERISTOME OF MOSSES. 351

(although grafted on to these, and drawing their nourishment
from them), are closed at their summit by opercula or lids (Fig.
185, B, 0, 0), which fall off when the contents of the capsules are
mature, so as to give them free exit; and the mouth thus laid
open is surrounded by a beautiful toothed fringe, which is termed
the peristome. This fringe, as seen in its original undisturbed
position, is shown in Fig. 186; whilst in Figs. 187-139 are shown

Fig. 136, Fig. 137,

Mouth of capsule of Funaria, showing the Double Peristome of Fontinalis
Peristome in situ. antipyretica,

three different forms of it, spread out and detached, illustrating
the varieties which it exhibits in different genera of Mosses,—
varieties whose existence and readiness of recognition render
them characters of extreme value to the systematic Botanist,
whilst they furnish objects of great interest and beauty for the

Fia. 138. Fia. 139.

Double Peristome of Bryum Double Peristome of Cinclidium
intermedium. arcticum.

Microscopist. The peristome seems always to be originally
double, one layer springing from the outer, and the other from
the inner, of two layers of cells which may be distinguished in
the immature capsule (Fig. 135, c, p); but frequently, at the time
of maturity, one or other of these is wanting, and sometimes

5352 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

both are obliterated, so that there is no peristome at all. The
number of the “teeth” is always a multiple of 4, varying from 4
to 64; sometimes they are prolonged into straight or twisted hairs,
The spores are contained in the upper part of the capsule, where
they are clustered round a central pillar, which is termed the
columella. In the young capsule, the whole mass is nearly solid
(Fig. 185, c), the space (2) in which the spores are developed
being very small; but this gradually augments, the walls be-
coming more condensed; and at the time of maturity, the inte-
rior of the capsule is almost entirely occupied by the spores, in
the dispersion of which the peristome seems in some degree to
answer the same purpose as the elaters of Hepatice. The deve-
lopment of the spores into new plants, commences with the rup-
ture of their outer walls, and a protrusion of their inner coats;
and from the projecting extremity new cells are put forth bya
process of outgrowth, which form a sort of confervoid filament
(as in Fig. 145, c). At certain points of this filament, its compo-
nent cells multiply by subdivision, so as to form rounded clus-
ters, from every one of which an independent plant may arise;
so that several individuals may be evolved from a single spore.
A numerous aggregation of spores may be developed, as we have
seen, from a single germ-cell; so that the immediate product of
each act of fertilization does not consist (as in the higher Plants)
of a single seed, that afterwards developes itself into a composite
fabric, whence are put forth a multitude of leaf buds, every one
of which is capable (under favorable circumstances) of evolving
itself into a complete Plant; but divides itself at once into a
mass of isolated cells (spores), of which every one may be con-
sidered in the light of a bud or gemma of the simplest possible
kind, and one of the first acts of which is to put forth other buds,
whereby the rapid extension of these
Fra. 140. plants 1s secured, although no separate
individual ever attains more than a very
limited size.

218. In the Ferns we have in many
respects a near approximation to
Flowering plants; but this approxima-
tion does not extend to their Reproduc-
' ’ tive apparatus, which is formed upon a

‘type essentially the same as that of
Mosses, but is evolved at a very different
period of life. As the component tis-
sues of which their fabrics are com-
posed, are essentially the same as those
ote section of ootsialk of 2m which will be described in the next chap-
eee ay ares ter, it will not be requisite here to dwell

upon them. The stem (where it exists)
is for the most part made up of cellular parenchyma, which 18
separated into a cortical and a medullary portion, by the inter-

FRUCTIFICATION OF FERNS. 858

position of a circular series of fibro-vascular bundles containing
true woody tissue and ducts. These bundles form a kind of irre-
gular network, from which prolongations are given off that pass
into the leaf-stalks, and thence into the midrib and its late-
ral branches; and it is their peculiar arrangement in the leaf-
stalks, which gives to the transverse section of these the fig-
ured marking commonly known as “King Charles in the
oak.’ A thin section, especially if somewhat oblique (Fig.
140), displays extremely well the peculiar character of the

Fie. 141. Fie. 142.

Leaflet of Polypodium, with sori. Portion of Frond of Hemionitis, with sori.

ducts of the Fern; which are termed “scalariform,” from the
resemblance of the regular markings on their walls to the rungs
of a ladder. What is usually considered the “fructification” of
the Ferns, affords a most beautiful and readily prepared class of
opaque objects for the lowest powers of the Microscope; nothing
more being necessary, than to lay a fragment of the frond that
bears it on its under surface, upon the glass stage-plate, or to
hold it in the stage-forceps, and to throw an adequate light upon
it by the side-condenser. It usually presents itself in the form
of isolated spots, termed sori, as in the common Polypodium (Fig.
141), and in the Aspidiwm (Fig. 143); but sometimes these “sori”
are elongated into bands, as in the common Scolopendrum (Harts
tongue): and these bands may coalesce with each other, so as
almost to cover the surface of the frond with a network, as in
Hemionites (Fig. 142); or they may form merely a single band
along its borders, as in the common Pteris (brake-fern). The
sori are sometimes naked on the under surface of the fronds;
23

3854 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

but they are frequently covered with a delicate membrane,
termed the indusium, which may either form a sort of cap upon
the summit of each sorus, as in Aspidium (Fig. 148), or a long
fold, as in Scolopendrum and Pteris, or a sort of cup, as in De-
paria (Fig. 144). Each of these sori, when sufficiently magnified,
1s found to be made up of a multitude of capsules or thece (Figs,
148, 144), which are sometimes closely attached to the surface of
the leaf, but more commonly spring from it by a pedicel or foot-
stalk. The wall of the capsule is composed of flattened cells,
applied to each other by their edges; but there is generally one
row of these, thicker and larger than the rest, which springs from
the pedicel, and is continued over the summit of the capsule, so
as to form a projecting ring, which is known as the annulus,
This ring has an elasticity superior to that of all the rest of the
capsular wall, causing it to split across, when mature, so that the
contained spores may escape; and in many instances carrying
the two halves of the capsule widely apart from each other (Fig.
141), the fissure extending to such a depth as to separate them
completely. It will frequently happen, that specimens of Fern-
fructification gathered for the Microscope, will be found to have
all the capsules burst and the spores dispersed, whilst in others,
less advanced, the capsules may all be closed; others, however,
may often be met with, in which some of the capsules are closed
and others are open; and if these be watched with sufficient at-
tention, the rupture of some of the thecee and the dispersion of
the spores may be observed to take place, whilst the specimen is
under observation in the field of the microscope. In sori whose
capsules have all burst, the annuli connecting their two halves
are the most conspicuous objects, looking, when a strong light is
thrown upon them, like strongly banded worms of a bright
brown hue. This is particularly the case in Scolopendrum,

Fia. 143.

Sis 4 7
a =
Sorus and indusium of Aspidium. Sorus and cup-shaped indusium of Deparia prolifera.

whose elongated sori are remarkably beautiful objects for the
microscope in all their stages ; until quite mature, however, they
need to be brought into view by turning back the two indusial
folds that cover them. The commonest Ferns, indeed, which
are found in almost every hedge, furnish objects of no less beauty

GENERATIVE ORGANS OF FERNS. 855

than those yielded by the rarest exotics ; and it is in every respect
a most valuable training to the young, to teach them how much
there may be found to interest, when looked for with intelligent
eyes, even in the most familiar and therefore disregarded speci-
mens of Nature’s handiwork. ;

219. The spores (Fig. 145, a) set free by the bursting of the
thecse, usually have a somewhat angular form, and are invested
by a yellowish or brownish outer coat, which is marked, very
much in the manner of pollen-grains (Fig. 187), with points,
streaks, ridges, or reticulations. When placed upon a damp sur-
face, and exposed to a sufficiency of light and warmth, the spore
begins to “germinate,” the first indication of its vegetative ac-
tivity being a slight enlargement, which is manifested in the

Fig. 145.

Development of Prothallium of Pteris serrulata :—a, spore set free from the theca;—B, spore begin-
ning to germinate, putting forth the tubular prolongation a from the principal cell, b ;—c, first formed
linear series of cells;—p, prothallium taking the form of a leaf-like expansion}; a first, and b second
radical fibre; c, d, the two lobes, and e the indentation between them; /, 7, first formed part of the
prothallium; g, external coat of the original spore; h, 2, antheridia.

rounding off of its angles; this is followed by the putting forth
of a tubular prolongation (8, a) of the internal cell-wall, through
an aperture in the outer spore-coat; and by the absorption of
moisture through this root-fibre, the inner cell is so distended,
that it bursts the external unyielding integument, and soon
begins to elongate itself in a direction opposite to that of the
root-fibre. A production of new cells by subdivision then takes
place from its growing extremity ; this at first proceeds in a single
series, so as to form a kind of confervoid filament (c); but the
multiplication of cells by subdivision soon takes place transversely
as well as longitudinally, so that a flattened leaf-like expansion
(D) is produced, so closely resembling that of a young Marchantia
as to be readily mistaken for it. This expansion, which is termed
the prothallium, varies in its configuration in different species;

356 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

but its essential structure always remains the same. From its
under surface are developed, not merely the root-fibres (a, 3)
which serve to fix it in the soil, and at the same time to supply
it with moisture, but also the antheridia and archegonia, which
constitute the true representatives of the essential parts of the
flower of higher Plants. Some of the antheridia may be dis-
tinguished at an early period of the development of the prothal-
lium (A, h); and at the time of its complete evolution these bodies
are seen in considerable numbers, especially about the origins of
the root-fibres. Each has its origin in a peculiar protrusion that
takes place from one of the cells of the prothallium (Fig. 146, a, a)

?

Fia. 146.

Development of the Autheridia and Antherozoids of Pteris serruluta :—a, projection of one of the
cells of the prothallium, showing the antheridial cell, b, with its sperm cells, e, within the cavity of
the original cell, a ;—s, antheridium completely developed; a, wall of antheridial cell; e, sperm-
cells, each enclosing an antherozoid ;—c, one of the antherozoids more highly magnified, showing a,
its large extremity, b, its small extremity, d, d, its cilia.
this is at first entirely filled with chlorophyll-granules; but soon
a peculiar free cell (6) is seen in its interior, filled with mucilage
and colorless granules. This cell gradually becomes filled with
another brood of young cells (c), and increases considerably in its
dimensions, so as to fill the projection which encloses it; this
part of the original cavity is now cut off from that of the cell of
which it was an offshoot, and the antheridium henceforth ranks
as a distinct and independent organ. Each of the secondary cells
(B) contained within its primary cell, is seen, as it approaches
maturity, to contain a spirally coiled filament; and whien they
have been set free by the bursting of the antheridium, they them-
selves burst and give exit to their “ antherozoids’” (c), which exe-
cute rapid movements of rotation on their axes, partly dependent
on the six long cilia with which they are furnished. The arehe-
gonia are fewer in number, and are found upon a different part
of the prothallium. Each of them at its origin presents itself
only as a slight elevation of the cellular layer of the prothallium,
within which is a large intercellular space containing a peculiar
cell (the ‘“germ-cell’”’), and opening externally by an orifice at
the summit of the projection ; but when fully developed (Fig. 147),
it is composed of from ten to twelve cells built up in layers of
four cells each, one upon another, so as to form a kind of chim-
ney or shaft, having a central passage that leads down to the
cavity at its base, wherein the germ-cell is contained. Into this
cavity the antherozoids penetrate, so as to come into contact with

GENERATIVE ORGANS OF FERNS. 857

the “germ-cell;” and, by the softening of the membrane at its
apex, they are even enabled to enter its cavity, within which a
minute “embryonic vesicle’ was previously distinguishable.
This embryonic vesicle, when fertilized by the antherozoids which

Fra. 147,

Archegonium of Pleris serrulata :—A, as seen from above; @, u, u, cells surrounding the base of the
cavity; b, c, d, successive layers of cells, the highest enclosing a quadrangular orifice :—s, side
view, showing, A, A, cavity containing the germ-cell; 8, B, walls of the archegonium, made up of the
four layers of cells, b, c,d, e, and having an opening on the summit; c, c, antherozoids within the
cavity; g, large extremity; h, thread-like portion; <, small extremity in contact with the germ-cell
and dilated.

move actively round it, becomes the primordial cell of a new
plant, the development of which speedily commences.’ By the
usual process of duplicative subdivision a globular homogeneous
mass of cells is at first formed; but rudiments of special organs
soon begin to make their appearance; the germ grows at the
expense of the nutriment prepared for it by the prothallium ; and
it soon bursts forth from the cavity of the archegonium, which
organ in the meantime is becoming atrophied. In the very be-
ginnitg of its development, the tendency is seen in the cells of
one extremity to grow upwards, so as to evolve the stem and
leaves, and in those of the other extremity to grow downwards,

! See Hofmeister, in “ Ann. of Nat. Hist.,” 2d Ser. vol. xiv, p. 272. The study of the de-
velopment of the spores of Ferns, and of the act of fertilization and of its products, may
be conveniently prosecuted as follows:—Let a frond of a Fern, whose fructification is
mature, be laid upon a piece of fine paper, with its spore-bearing surface downwards;
in the course of a day or two, this paper will be found to be covered with a very fine
brownish dust, which consists of the discharged spores. This must be carefully col-
lected, and should be spread upon the surface of a smoothed fragment of porous sand-
stone; the stone being placed in a saucer, the bottom of which is covered with water,
and a glass tumbler being inverted over it,'the requisite supply of moisture is insured,
and the spores will germiuate luxuriantly. Some of the prothallia soon advance beyond
the rest; and at the time when the advanced ones have long ceased to produce anthe-
ridia, and bear abundance of archegonia, those which have remained behind in their
growth are beginning to be covered with antheridia. If the crop be now kept with
little moisture for several weeks, and then suddenly watered, a large number of anthe-
ridia and archegonia simultaneously open; and in a few hours afterwards, the surface
of the larger prothallia will be found almost covered with moving antherozoids. Such
prothallia as exhibit freshly opened archegonia, are now to be held by one lobe between
the forefinger and thumb of the left hand, so that the upper surface of the prothallium
lies upon the thumb; and the thinnest possible sections are then to be made, with a thin
narrow-bladed knife, perpendicularly to the surface of the prothallium. Of these sec-
tions, which, after much practice, may be made no more than 1-1 5th of a line in thick-
ness, some will probably lay open the canals of the archegonia; and within these, when
examined with a power of 200 or 300 diameters, antherozoids may be occasionally dis-
tinguished.

358 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA,

to form the root; and when these organs have been sufficiently
developed to absorb and prepare the nutriment which the young
plant requires, the prothallium, whose functions as a “nurse” is
now discharged, decays away.

220. The little group of Hguisetacee (Horsetails), which seem
nearly allied to the Ferns in the type of their generative apparatus,
though that of their vegetative portion is very different, affords
certain objects of considerable interest to the Microscopist. The
whole of their structure is penetrated to so extraordinary a degree
by silex, that, even when the organic portion has been destroyed
by prolonged maceration in dilute nitric acid, a consistent skele-
ton still remains. This mineral, in fact, constitutes in some
species not less than 13 per cent. of the whole solid matter, and
50 per cent. of their inorganic ash. The cuticle, which is used
by cabinet-makers for smoothing the surface of wood, becomes,
through the peculiar arrangement of its siliceous particles, an
extremely beautiful object under polarized light. Of these par-
ticles (each of which has a regular axis of double refraction),
some are distributed in two lines, parallel to the axis: others,
however, are grouped into oval forms, connected with each other,
like the jewels of a necklace, by a chain of particles forming a
sort of curvilinear quadrangle; and these (which are, in fact, the
particles occupying the cells of the stomata) are arranged in pairs.
‘What is usually designated as the fructification of the Equise-
tacese, forms a cone or spike at the extremity of certain of the
stem-like branches (the real stem being a horizontal rhizoma);

Fig. 148,

and consists of a cluster of shield-like disks, each of which car-
ries a circle of thecw or spore-cases, that open by longtitudinal
slits to set free the spores. Each of these bodies has, attached
to it, a pair of elastic filaments (Fig. 148), that are originally
formed as spiral fibres on the interior of the wall of the primary
cell within which the spore is generated, and are set free by its
rupture ; these are at first coiled up closely around the spore,
in the manner represented at a, though more closely applied to
the surface; but, on the slightest application of moisture, they
suddenly extend themselves in the manner shown at B; and this
motion, like the extension of the spiral elaters of Marchantia,
probably serves to assist in the dispersion of the spores. Ifa
number of the spores be spread out on a slip of glass under the
field of view, and, whilst the observer watches them, a bystander

GENERAL SUMMARY OF CRYPTOGAMIC GENERATION. 3859

breathe gently upon the glass, all the filaments will be instan-
taneously put in motion,—thus presenting an extremely curious
spectacle,—and will almost as suddenly return to their previous
condition, when the effect of the moisture has passed off. These
spores are to be regarded in the same light as those of Ferns;
namely, as gemme or rudimentary buds, not as seeds. They
evolve themselves after the like method into a prothallium ; and
this developes antheridia and archegonia, by the conjoint action
of which an embryo is produced.

221. In ascending, as we have now done, from the lower to the
higher Cryptogamia, we have seen a gradual change in the gene-
ral plan of structure, so that the superior forms present a close
approximation to the Flowering Plant, which is undoubtedly the
highest type of Vegetation. But we have everywhere en-
countered a mode of Generation, which, whilst essentially the
same throughout the series, is essentially distinct from that of
the Phanerogamia; the fertilizing material of the “ sperm-cell”
being embodied, as it were, in self-moving filaments, which find
their way to the germ-cells by their own independent movements ;
and the “embryo-cell” being destitute of that store of prepared
nutriment, which surrounds it in the true seed, and serves as
the pabulum for its early development. In the lower Crypto-
gamia, we have seen that the embryo-cell, after fertilization, is
thrown at once upon the world (so to speak) to get its own
living; but in the Liverworts, Mosses, and Ferns, the embryo-
cell is nurtured by the parent-plant, for a period that varies in
each case according to the nature of the fabric into which it
evolves itself. While the true reproduction of the species is
effected by the proper Generative act, the multiplication of the
individual is accomplished by the production and dispersion of
spores ; and this production, as we have seen, takes place at very
different periods of existence in the several groups, dividing the
life of each into two separate epochs, in which it presents itself
under two very distinct phases that contrast remarkably with
each other. Thus, the frond of the Marchantia, bearing its anthe-
ridia and archegonia, is that which seems naturally to constitute
the plant; but that which represents it in the Ferns, is the mi-
nute Marchantia-like prothallium. On the other hand, the pro-
duct into which the fertilized: embryo-cell evolves itself in the
Ferns, is that which is commonly regarded as the plant; and this
is represented in the Liverworts and Mosses by the spore-capsules
alone. We shall notice, in the next Chapter (§ 256), the repre-
sentation of these two phases in the life of the Flowering
Plant, which is traceable by means of the study of the Lycopo-
diacee and Conifere ; two groups that form the link of transition
between these two great divisions of the Vegetable kingdom,
the former being probably to be regarded as the highest of
the Cryptogamia, and the latter as the lowest of the Phanero-
gamia.'

' See the Author’s “Principles of Comparative Physiology,” Am. ed. 1854, §§ 499-505,

CHAPTER VIII.
OF THE MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS.

222. Elementary Tissues.—In passing from the Cryptogamiec
division of the Vegetable Kingdom, to that larger and more
ostensibly important province which includes the Flowering
Plants, we do not meet with so wide a departure from those
simple types of structure we have already considered, as the
great differences in general aspect and external conformation
might naturally lead us to expect. For a very large proportion
of the fabric of even the most elaborately formed Tree, is made
up of components of the very same kind with those which con-
stitute the entire organisms of the simplest Cryptogamia; and
that proportion always includes the parts most actively con-
cerned in the performance of the vegetative functions. For
although the stems, branches, and roots, of trees and shrubs, are
principally composed of woody tissue, such as we do not meet
with in any but the highest Cryptogamia, yet the special office
of this is to afford mechanical support; when it is once formed,
it takes no further share in the vital economy, than to serve for
the conveyance of fluid from the roots, upwards through the stem
and branches, to the leaves; and even in these organs, not only
the pith and the bark, with the “medullary rays” which serve to
connect them, but that “cambium-layer’’ intervening between
the bark and the wood (§ 240), in which the periodical formation
of the new layers both of bark and wood takes place, are com-
posed of cellular substance. This tissue is found, in fact,
wherever growth is taking place; as, for example, in the spon-
gioles or growing points of the root-fibres, in the leaf-buds and
leaves, and in the flower-buds and sexual parts of the flower; it
is only when these organs attain an advanced stage of develop-
ment, that woody structure is found in them,—its purpose (as in
the stem) being merely to give support to their softer textures;
and the small proportion of their substance which it forms, being
at once seen in those beautiful skeletons, which, by a little skill
and perseverance, may be made of leaves, flowers, and certain
fruits. All the softer and more pulpy tissue of these organs 18
composed of cells more or less compactly aggregated together,

CELLULAR TISSUE, 361

and having forms which approximate more or less closely to the
globular or ovoidal, which may be considered as their original
type.
7593, As a general rule, the rounded shape is preserved only
when the cells are but loosely aggregated, as in the parenchy-
matous (or fleshy) substance of leaves (Fig. 149); and it is then
only, that the distinctness of the walls becomes evident. When
the tissue becomes more
solid, the sides of the vesi-
cles are pressed against each
other, so as to flatten them
and to bring them into close
apposition; and they then
adhere to one another in
such a manner, that the par-
titions appear, except when
carefully examined, to be
single, instead of being (as
they really are) double. Fre-
quently it happens that the
pressure is exerted more in
go direction than in an- Section of leaf of Agave, treated with dilute nitric acid
other, so that the form pre- showing the pricioiel utricle contracted in ihaditeriat
sented by the outline of the of the cells:—a, epidermic cells; b, boundary cells of
cell varies according to the A ae ¢, cells of parenchyma; d, their primordial
direction in which the sec-

tion is made. This is well shown in the pith of the young shoots
of Elder, Lilac, or other rapidly growing trees; the cells of which,
when cut transversely, generally exhibit circular outlines, whilst,
when the section is made vertically, their borders are straight,
so as to make them appear like cubes or elongated prisms, as in
Fig. 152. A very good example of such a cellular parenchyma
is to be found in the substance known as “ Rice-paper ;”’ which
is made by cutting the herbaceous stem of a Chinese plant
termed Aralia papyrifera,! vertically round and round, with a
long sharp knife, so that its tissue may be (as it were) unrolled
ina sheet. The shape of the cells, as seen in the rice-paper thus
prepared, is irregularly prismatical, as shown in Fig. 150, 8; but
if the stem be cut transversely, their outlines are seen to be cir-
cular or nearly so (A). When, as often happens, the cells have a
very elongated form, this elongation is in the direction of their
growth, which is that, of course, wherein there is least resistance.
Hence their greatest length is nearly always in the direction of
the axis; but there is one remarkable exception,—that, namely,
which is afforded by the “ medullary rays” of Exogenous stems
(§ 239), whose cells are greatly elongated in the horizontal direc-
tion (Fig. 161, a), their growth being from the centre of the stem

1 The schynomene, which is sometimes named as the source of this article, is an
Indian plant, employed for a similar purpose. ‘

362 STRUCTURE OF PHANEROGAMIC PLANTS.

towards its circumference. It is obvious that fluids will be more
readily transmitted in the direction of greatest elongation, being
that in which they will have to pass through the least number of
partitions; and whilst their ordinary course is in the direction of

Fra. 150.

Sections of Cellular Parenchyma of Aralia. or Rice-paper Plant;—a, transversely to the axis of the
stem; 8, in the direction of the axis.

the length of the roots, stem, or branches, they will be enabled,
by means of the medullary rays, to find their way in the trans-
verse direction. One of the most curious varieties of form which
Vegetable cells present is that represented in Fig. 151, which
constitutes the stellate cell. This

modification, to which we have Fie. 152.

already seen an approximation in
the Volvor (§ 159), is found in the
spongy parenchymatous sub-
stance where lightness is an ob-
ject; as in the stems of many

Section of Cellular parenchyma of Rush. Cubical parenchyma, with stellate cells, from
petiole of Nuphar lutea.

aquatic plants, such as the Rush, which need to be furnished
with air-spaces. In other instances, these air-spaces are large
cavities, which are altogether left void of tissue; such is the case

ag
ROTATION IN VALLISNERIA AND ANACHARIS. 3863

in the Nuphar lutea (Yellow water-lily), the footstalks of whose
leaves contain large air-chambers, the walls of which are built
up of very regular cubical cells, whilst some curiously formed
large stellate cells project into the cavity which they bound (Fig.
152). The dimensions of the component vesicles of Cellular
tissue are extremely variable; for although their diameter is very
commonly between 1-300th and 1-500th of an inch, they occa-
sionally measure as much as 1-30th of an inch across, whilst in
other instances they are not more than 1-3000th.

224, The component cells of Cellular tissue are usually held
together by an intercellular substance, which may be considered
analogous to the “ gelatinous” layer that intervenes between the
cells of the Alge. There are many cellular substances, how-
ever, in which, in consequence of the loose aggregation of their
component cells, these may be readily isolated, so as to be pre-
pared for separate examination without the use of reagents
which alter their condition; this is the case with the pulp of
ripe fruits, such as the Strawberry or Currant (the Snowberry is
a particularly favorable subject for this kind of examination),
and with the parenchyma of many fleshy leaves, such as those
of the Carnation (Dianthus caryophyllus) or the London Pride
(Saxifragra crassifolia). Such cells usually contain evident
nuclei, which are turned brownish-yellow by iodine, whilst their
membrane is only turned pale-yellow; and in this way the
nucleus may be brought into view, when, as often happens, it is
not previously distinguishable. Ifa drop of the iodized solution
of chloride of zine be subsequently added, the cell-membrane
becomes of a beautiful blue color, whilst the nucleus and the
granular protoplasm that surrounds it, retain their brownish-
yellow tint. The use of dilute nitric or sulphuric acid, of alco-
hol, of syrup, or of several other reagents, serves to bring into
view the “primordial utricle’”’ of Mohl; its contents being made
to coagulate and shrink, so that it detaches itself from the cellu-
lose wall with which it is ordinarily in contact, and shrivels up
within its cavity, as shown in Fig. 149.

225. It is probable that all cells, at some stage or other of their
growth, exhibit, in a greater or less degree of intensity, that
curious movement of “rotation,” which has been already de-
scribed as occurring in the Charace (§ 201), and which consists
in the steady flow of one or of several currents of protoplasm
over the inner wall of the cell; this being rendered apparent by
the movement of the particles which the current carries along
with it. The best examples of it are found among submerged
plants, in the cells of which it continues for a much longer
period than it usually does elsewhere; and among these there
are two, the Vallisneria spiralis and the Anacharvs alsinastrum,
which are peculiarly fitted for the exhibition of this interesting
phenomenon. The former is an aquatic plant that grows abun-
dantly in the rivers of the south of Europe, but is not a native

364 STRUCTURE OF PHANEROGAMIC PLANTS.

of this country; it may, however, be readily grown in a tall
glass jar having at the bottom a couple of inches of mould,
which, after the roots have been inserted into it, should be
closely pressed down, the jar being then filled with water, of
which a portion should be occasionally changed.’ The jar should
be freely exposed to light, and should be kept in as warm but
equal a temperature as possible. The long grass-like leaves of
this plant are too thick to allow the transmission of sufficient
light through them for the purpose of this observation ; and it
is requisite to make a thin slice or shaving with a sharp knife.
If this be taken from the surface, so that the section chiefly con-
sists of the superficial layer of cells, these will be found to be
small, and the particles of chlorophyll, though in great abun-
dance, will rarely be seen in motion. But if, after the removal
of this layer, a deeper stratum be sliced off, this will be found to
consist of larger cells, some of them greatly elongated, with
particles of chlorophyll in smaller number, but carried along in’
active rotation by the current of protoplasm; and it will often
be noticed, that the rotation takes place in contiguous cells in
opposite directions. If the movement (as is generally the case)
be checked by the shock of the operation, it will be revived
again by a gentle warmth; and it may continue under favorable
circumstances, in the separated fragment, for a period of weeks
or even of months. Hence when it is desired to exhibit the
phenomenon, the preferable method is to make the sections a
little time before they are likely to be wanted, and to carry them
in asmall vial of water in the waistcoat pocket, so that they may
receive the gentle and continuous warmth of the body. In
summer, when the plant is in its most vigorous state of growth,
the section may be taken from any one of the leaves; but in
winter, it is preferable to select those which are a little yellow?
The Anacharis alsinastrum is a water-weed, which, having been
accidentally introduced into this country about twelve years ago,
has since spread itself with such rapidity through our canals and
rivers, as, in many instances, seriously to impede the navigation.
It does not require to root itself in the bottom, but floats in any
part of the water it inhabits; and it is so tenacious of life, that
even small fragments are sufficient for the origination of new
plants. The leaves have no distinct cuticle, but are for the most
part composed of two layers of cells, and these are elongated
and colorless in the centre, forming a kind of midrib; towards
the margins of the leaves, however, there is but a single layer.
Hence no preparation whatever is required for the exhibition of

1 Mr. Quekett has found it the most convenient method of changing the water in the
jars in which Chara, Vallisneria, &., are growing, to place them occasionally under a
water-tap, and allow a very gentle stream to fall into them for some hours; for by the
prolonged overflow thus occasioned, all the impure water, with the conferva that is apt
to grow on the sides of the vessel, may be readily got 1id of. :

2 An object-glass of 4th inch focus affords the best power for the observation of this
interesting phenomenon. .

ROTATION IN HAIRS AND CUTICLE-CELLS. 365

this interesting phenomenon; all that is necessary being to take
a leaf from the stem (one of the older yellowish leaves being
preferable), and to place it with a drop of water either in the
aquatic box, or on.a slip of glass beneath a thin glass cover. A
higher magnifying power is required, however, than that which
suffices for the examination of the rotation in Chara or Vallis-
neria; the 4th inch object-glass being here preferable to the }th,
and the assistance of the Achromatic condenser: being desirable.
With this amplification, the phenomenon may be best studied in
the single layer of marginal cells; although, when a lower power
is used, it is most evident in the elongated cells forming the
central portion of the leaf. The number of chlorophyll granules
in each cell varies from three or four to upwards of fifty; they
are somewhat irregular in shape, some being nearly circular
flattened disks, whilst others are oval; and they are usually from
1-3000th to 1-5000th of an inch in diameter. When the rotation
is active, the greater number of these granules travel round the
margin of the cells, a few, however, remaining fixed in the
centre; their rate of movement, though only 1-40th of an inch
per minute, being sufficient to carry them several times round
the cell within that period. As in the case of the Vallisneria,
the motion may frequently be observed to take place in opposite
directions in contiguous cells. The thickness of the layer of
protoplasm in which the granules are carried round, is estimated
by Mr. Wenham at no more than 1-20,000th of an inch. A
peculiar undulating appearance is seen in this, under certain
modes of illumination, which suggests the idea of ciliary action;
but this appearance is decidedly affirmed by Mr. Wenham to
‘be an optical illusion. It is a curious circumstance, first re-
marked by Dr. Branson, that the elongated cells along the mar-
gin of the leaf and forming the midrib, contain a large quantity
of silex; as may be readily seen by polarized light, especially
after the leaf has been boiled for a few minutes in equal parts of
nitric acid and water, which removes part of the vegetable sub-
stance, and thus renders the siliceous portion more distinct,
without destroying the form of the leaf.!

226. The phenomena of “rotation,” however, is by no means
restricted to submerged Plants; for it has been witnessed by
numerous observers in so great a variety of other species, that it
may fairly be presumed to be universal. It is especially ob-
servable in the hairs of the epidermic surface; and according to
Mr. Wenham, who has recently given much attention to this
subject, “the difficulty is to find the exceptions, for hairs taken
alike from the loftiest Elm of the forest, to the humblest weed
that we trample beneath our feet, plainly exhibit this circulation.”
Such hairs are furnished by various parts of plants; and what is
chiefly necessary is, that the part from which the hair is gathered

1 See Dr. Branson in “Quart, Journ. of Microsc. Science,” vol. ii, p. 131, and vol. iil,
p. 374; and Mr. Wenham, Op. cit. vol. iii, p. 277.

366 STRUCTURE OF PHANEROGAMIC PLANTS.

should be in a state of vigorous growth. The hairs should be
detached by tearing off, with a pair of fine-pointed forceps, the
portion of the cuticle from which they spring; care being taken
not to grasp the hair itself, whereby such an injury would be
done to it, as to check its circulation. The hair should then be
placed with a drop of water under thin glass; and it will gene-
rally be found advantageous to use a 1-8th in. objective, with an
achromatic condenser having a series of diaphragms. The nature
of the movement in the hairs of

Fie, 153. different species of plants is far

from being uniform. In some in-
stances, the currents pass in sin-
gle lines along the entire length
of the cells, as in the hairs from
the filaments of the Tradescantia
virginica or Virginian spider-wort
(Fig. 158, a); in others, there are
several such currents which retain
their distinctness, as in the jointed
hairs of the calyx of the same
plant (B); in others, again, the
streams coalesce into a network,
the reticulations of which change
their position at short intervals,
asin the hairsof Glaueium luteum;
whilst, lastly, the current may flow
in a sluggish uniformly moving
sheet or layer. Where several dis-
tinct currents exist in one cell,
they are all found to have one com-
mon point of departure and return,
namely the “nucleus” (B, a); from
which it seems fairly to be inferred,
that this body is the centre of the
vital activity of the cell.1 Mr.
Wenham states that in all cases in
baits er vdewnntia Which the sap-motion is seen in
Virgina: s, porion of eutete wit hair the hairs of a plant, the cells of
attached ; a, b, ¢, hcee se cells of the hair; the cuticle also display it, pro-
beaded hair, showing several currents; «, Vided that their walls are not 90
nucleus. opaque or so strongly marked,
as to prevent the rotation from

being distinguished.? The cuticle may be most readily torn off

! The above statement is called in question by Mr. Wenham, who affirms that “ when-
ever he has observed such a ‘nucleus,’ it has either been formed by an accidental con-
glomeration of some of the cell-contents, or by morbid conditions.” The Author is satisfied,
however, from the constancy with which the “ nucleus” is the centre of the diverging
lines of protoplasm, in those cells which have several streams radiating from one point,
that it can neither be an accidental nor a morbid conglomeration.

2 Op. cit. vol. iv. p. 44.

THICKENING DEPOSITS WITHIN CELLS. 367

from the stalk or the midrib of the leaf; and must then be exa-
mined as speedily as possible, since it loses its vitality, when
thus detached, much sooner than do the hairs. Even where no ob-
vious movement of particles is to be seen, the existence of a rota-
tion may be concluded from the peculiar arrangement of the mole-
cules of the protoplasm, which are remarkable fortheir high refrac-
tive power, and which, when arranged in a “ moving train,” ap-
pear as bright lines across the cell; and these lines, on being care-
fully watched, are seen to alter theirrelative positions. The leaf of
the common Plantago (plantain or dock) furnishes an excellent ex-
ample of “rotation ;” the movement being distinguishable at the
same time, both in the cells and in the hairs of the cuticle torn
from its stalk or midrib. It is a curious circumstance, that when
a plant (such as the Anacharis) which exhibits the “rotation,” is
kept in a cold dark place for one ortwo days, not only is the move-
ment suspended, but the moving particles collect together in little
heaps; these being again broken up by the separate motion of their
particles, when the stimulus of light and warmth occasions a
renewal of the circulatory action. It is well to collect the speci-
mens about mid-day, that being the time when the rotation is
most active; and the movement is usually quickened by artificial
warmth, which, indeed, is a necessary condition in some in-
stances to its being seen at all. The most convenient method
of applying this warmth, while the object is on the stage of the
microscope, is to blow a stream of air upon the thin glass cover,
through a glass or metal tube previously heated in a spirit lamp.
227. The walls of the cells of Plants are frequently thickened
by internal deposits, which may present very differentappearances
according to the manner in which they are arranged. In its
simplest condition, such a deposit forms a thin uniform layer
over the whole internal surface
of the cellulose wall (probably Fig. 154,
on the outside of the primor-
dial utricle), scarcely detract-
ing at all from its transparen-
cy, and chiefly distinguishable
sy the “dotted” appearance
which the membrane then pre-
sents (Wig. 150, a). These dots,
however, are not pores, as their
aspect might naturally sug-
gest; but are merely points
at which the deposit is want-
ing, so that the original cell-
wall there remains unthick-

Tissue of the Testa of the seed-coat of Star-
Anise :—a, as seen in section; B, as seen on the

ened. When the cellular surface.

tissue is required to possess

unusual firmness, a deposit of sclerogen (a substance which,
when separated from the resinous and other matters that are

368 STRUCTURE OF PHANEROGAMIC PLANTS.

commonly associated with it, is found to be allied in chemical
composition to cellulose) is formed in successive layers, one
within another (Fig. 154, a), which present themselves as con-
centric rings when the cells containing them are cut through;
and these layers are sometimes so thick and numerous, as almost
to obliterate the original cavity of the cell. By a continuance
of the same arrangement as that which shows itself in the single
layer of the dotted cell,—each deposit being deficient at certain
points, and these points corresponding with each other in the
successive layers,—a series of passages is left, by which the
cavity of the cell is extended at some points to its membranous
wall; and it commonly happens that the points at which the de-
posit is wanting on the walls of two contiguous cells, are coinci-
dent, so that the membranous partition is the only obstacle to
the communication between their cavities (Figs. 154-156). It
is of such tissue that the “stones” of fruit, the gritty substance

Fra. 155,

Zor
is

eee

yA
PAS

om

giant

ped acne

|
y =

oe

Section of Cherry Stone, cutting the Section of Cequilla Nut, in the
cells transversely. direction of the long diameters
of the cells,

which surrounds the seeds and forms little hard points in the
fleshy substance of the pear, the shell of the cocoa-nut, and the
albumen of the seed of Phytelephas (known as “vegetable
ivory’), are made up; and we see the use of this very curious
arrangement, in permitting the cells, even after they have at-
tained a considerable degree of consolidation, still to remain per-
meable to the fluid required for the nutrition of the parts which
such tissue encloses and protects.

228. The deposit sometimes assumes, however, the form of
definite fibres, which lie coiled up in the interior of cells, so a8
to form a single, double, or even a triple or quadruple spire

SPIRAL CELLS. 3869

(Fig. 157). Such “spiral cells” are found most abundantly in
the leaves of certain Orchide-

ous plants, immediately be- Pre 108,

neath the cuticle, where they
are brought into view by ver-

Fig. 157.

Spiral cells of leaf of Oncidium. Spiral fibres of Seed-coat of Collomia,

tical sections, and they may be obtained in an isolated state, by
macerating the leaf and peeling off the cuticle, so as to expose
the layer beneath, which is then easily separated into its com-
ponents. In an Orchideous plant named Saccolabium guttatum,
the spiral cells are unusually long, and have spires winding in
opposite directions; so that, by their mutual intersection, a
series of diamond-shaped markings is produced. Spiral cells
are often found upon the surface of the testa or outer coat of
seeds; and in the Collomia grandiflora, the Salvia verbenaca (wild
clary), and some other plants, the membrane of these cells is so
weak, and the elasticity of their fibres so great, that when the
membrane is softened by the action of water, the fibres suddenly
uncoil and elongate themselves (Fig. 158), springing out, as it
were, from the surface of the seed, to which they give a peculiar
flocculent appearance. This very curious phenomenon, which
greatly preplexes those who are ignorant of its real nature, may
be best observed in the following manner:—A very thin trans-
verse slice of the seed should first be cut, and laid upon the
lower glass of the aquatic box; the cover should then be pressed
down, and the box placed upon the stage, so that the body of
the microscope may be exactly “focussed” to the object, the
power employed being the 1 inch, 2-3ds inch, or the 4 inch ob-
jective. The cover of the aquatic box being then removed, a
small drop of water should be placed on that part of its internal
surface, with which the slice of the seed had been in contact;
and the cover being replaced, the object should be immediately
looked at. It is important that the slice of the seed should be
very thin, for two reasons; first that the view of the spires may
not be confused by their aggregation in too great numbers; and
second, that the drop of water should be held in its place by
24

370 STRUCTURE OF PHANEROGAMIC PLANTS.

capillary attraction, instead of running down and leaving the
object, as it will do if the glasses be too widely separated.

229. In some part or other of most Plants, we meet with cells
containing granules of Starch. These granules are sometimes
minute and very numerous, and are so closely packed together
as to fill the cavity (Fig. 159); in other instances they are of

Fig, 159, Fig. 160.

Cells of Paony, filled with Starch. Granules of Starch, as seen under polarized
light.

much larger dimensions, so that only a small number of them
can be included in any one cell; while in other cases, again,
they are both few and minute, so that they form but a small
proportion of the cell-contents. Their nature is at once detected
by the addition of a solution of iodine, which gives them a
beautiful blue color. Each granule exhibits a peculiar spot termed
the hilum, which marks the point at which, in its early state, it
is attached to the cell-wall; and it also presents, when highly
magnified, a set of circular lines, which are for the most part
concentric (or nearly so) with the hilum. When viewed by po-
larized light (§ 63), each grain exhibits a beautiful dark cross,
the point of intersection being at the hilum (Fig. 160). Regard-
ing the internal structure of the starch grain, opinions are very
much divided; for whilst some affirm the concentric lines to
indicate the existence of a number of concentric lamella, one
enclosing another, others consider that they are due to the
peculiar plaiting or involution of a single vesicular wall;? and
among those who consider it to be concentrically lamellated,
some hold that each lamella is formed outside or upon that which
preceded it, while others consider that each is formed inside or
within its predecessor. The centre of the granule is often oceu-
pied by starchy matter in an unconsolidated state; and it is the
appearance arising from its different refractive power, that has
caused some observers to describe the starch-grain as possessing

1 The first of these opinions is the one which had been generally received until
recently, when Mr. G. Busk supported the latter by new observations made upon the
unfolding of the starch-granule by dilute sulphuric acid; since when, Prof. Allman,
after repeating Mr. Busk’s observations, has been led to affirm them to be fallacious,
and to revert to the first of the above-mentioned doctrines. See Mr. Busk’s memoir in
“Trans. of Microsc. Soc.” ser. 2, vol. i, p. 58; and that of Prof. Allman in “ Quart.
Journ. of Microsc. Sci.” vol. ii, p. 163.

RAPHIDES. 871

anucleus. Although the dimensions of the starch-grains pro-
duced by any one species of Plant are by no means constant, yet
there is a certain average for each, from which none of them
depart very widely; and by reference to this average, the starch-
grains of different plants that yield this product in abundance,
may be microscopically distinguished from one another,—a cir-
cumstance of considerable importanceincommerce. The largest
starch-grains in common use are those of the plant (a species of
Canna) known as Tous les mois; the average diameter of
those of the Potato is about the same. as the diameter of the
smallest of the “tous les mois;” and the size of the ordinary
starch-grains of Wheat and of Sago is about the same as that of
the smallest grains of potato-starch; whilst the granules of
Rice-starch are so very minute, as to be at once distinguished
from any of the preceding.

230. Deposits of mineral matter in a crystalline condition,
known as Raphides, are not unfrequently found in the cells of
Plants; where they are at once brought into view by the use of
polarized light. Their designation (derived from fag:c, a needle)
is very appropriate to one of the most common states in which
these bodies present themselves, that, namely, of bundles of
needle-like crystals, lying side by side in the cavity of the cell;
such bundles are well seen in the cells lying immediately beneath
the cuticle of the bulb of the medicinal Squill. It does not ap-
ply, however, to other forms which are scarcely less abundant;
thus, instead of bundles of minute needles, single large crystals,
octohedral or prismatic, are frequently met with; and the pris-
matic crystals are often aggregated in beautiful stellate groups.
One of the most common materials of raphides, is oxalate of
lime, which is generally found in the stellate form; and no plant
yields these stellate raphides so abundantly as the common Rhu-
bard, the best specimens of the dry medicinal root containing as
much as 35 per cent. of them. In the cuticle of the bulb of the
Onion, the same material occurs under the octohedral or the
prismatic form. In other instances, the calcareous base is com-
bined with tartaric, citric, or malic acid ; and the acicular raphides
are said to consist usually of phosphate of lime. Some raphides
are as long as 1-40th of an inch, while others measure no more
than 1-1000th. They occur in all parts of plants,—the wood,
pith, bark, root, leaves, stipules, sepals, petals, fruit, and even in
the pollen. They are always situated in cells, and not, as some
have stated, in the intercellular passages; the cell-membrane,
however, is often so much thinned away, as to be scarcely dis-
tinguishable. Certain plants of the Cactus tribe, when aged, have
their tissues so loaded with raphides as to become quite brittle;
so that when some large specimens of (. senilis, said to be a
thousand years old, were sent to Kew Gardens, from South
America, some years since, it was found necessary for their pre-
servation during transport, to pack them in cotton, like jewelry.

3872 STRUCTURE OF PHANEROGAMIC PLANTS.

It is not yet known what office the raphides fulfil in the economy
of the Plant; or whether they are to be considered in any other
light, than as non-essential results of the vegetative processes,
For as all these processes require the introduction of mineral
bases from the soil, and themselves produce organic acids in the
substance of the plant, it may be surmised that the accidental
union of the components will occasion the formation of raphides
wherever such union may occur; and this view is supported by
the fact, that the late Mr. E. Quekett succeeded in artificially
producing raphides within the cells of “rice paper” (§ 223), by
first filling these with lime water by means of the air-pump, and
then placing the paper in weak solutions of phosphoric and oxalic
acids. The artificial raphides of phosphate of lime were rhombo-
hedral; while those of oxalate of lime were stellate, exactly re-
sembling the natural raphides of the Rhubarb.'

231. A large proportion of the denser parts of the fabric of the
higher Plants, is made up of the substance which is known as
Ligneous Tissue, or Woody Fibre. This, however, can only be
regarded as a very simple variety of the “cellular ;” for it is com-
posed of peculiarly elongated cells (Fig. 171, a a), usually pointed
at their two extremities so as to become spindle-shaped, whose
walls have a special tendency to undergo consolidation by the
internal deposit of sclerogen. It is obvious that a tissue consist-
ing of elongated cells, adherent together by their entire length,
and strengthened by internal deposit, must possess much greater
tenacity than any tissue in which the cells depart but little from
the primitive spherical form; and we accordingly find Woody
Fibre introduced, wherever it is requisite that the fabric should
possess not merely density, but the power of resistance to tension.
In the higher classes of the Vegetable kingdom, it constitutes
the chief part of the stem and branches, where these have a firm
and durable character; and even in more temporary structures,
such as the herbaceous stems of annual plants, and the leaves
and flowers of almost every tribe, this tissue forms a more or less
important constituent, being especially found in the neighbor-
hood of the spiral vessels and ducts, to which it affords protection
and support. Hence the bundles or fasciculi composed of these
elements, which form the skeletons of leaves, and which give
“‘stringiness” to various esculent vegetable substances, are com-
monly known under the name of fibro-vascular tissue. In their
young and unconsolidated state, the ligneous cells seem to con-
duct fluids with great facility in the direction of their length;
and in the Coniferous tribe whose stems and branches are desti-

!'The materials of the above paragraph are derived from the excellent section on
this subject in Prof. Quekett’s “ Lectures on Histology.” Besides the vegetables therein
named as affording good illustrations of different kinds of Raphides, may be mentioned,
the parenchyma of the leaf of Agave, Aloe, Cycas, Encephalartos, &c., the cuticle of the
bulb of the Hyacinth, Tulip, and Garlic (and probably of other bulbs), the bark of the
Apple, Cascarilla, Cinchona, Lime, Locust, and many other trees, the pith of Eleagnus,
and the testa of the seeds of Anagallis and the Elm.

SPIRAL VESSELS. 873

tute of vessels, they afford the sole channel for the ascent of the
sap. But after their walls have become thickened by internal
deposit, they are no longer subservient to this function ; nor, in-
deed, do they then appear to fulfil any other purpose in the
vegetable economy, than that of affording mechanical support.
It is this which constitutes the difference between the alburnum
or “sap-wood,” and the dwramen or “ heart-wood,” of Exogenous
stems (§ 238). A peculiar set of markings,

seen on the woody fibres of the Conifere, Fra. 161.

and of some other tribes, is represented in
Fig. 161; in each of these spots, the inner
circle appears to mark a deficiency of the
lining deposit, as in the porous cells of
other plants; whilst the outer circle indi-
eates the boundary of a lenticular cavity,
which intervenes between the adjacent
cells at this point, and which contains a
small globular body that may be sometimes
detached. Of the purpose of these minute
bodies interposed between the wood-cells,
nothing is known; there can be no doubt,
however, from the definiteness and con-
stancy of their arrangement, that they
fulfil some important object in the eco- section of Coniferous Wood in
nomy of the plants in which they occur; the direction of the fibres, showing
and there are varieties in this arrangement {uiinn rays evossing the fibres.
so characteristic of different tribes, that it

is sometimes possible to determine, by the microscopic inspec-
tion of a minute fragment, even of a fossil wood, the tribe to
which it belonged. The woody fibre thus marked, is often
designated as “ glandular.”

232. All the more perfect forms of Phanerogamia contain, in
some part of their fabric, the peculiar structures which are known
as Spiral Vessels.' These have the elongated shape of woody
fibres; but the internal deposit, as in the “‘spiral cells” (§ 228),
takes the form of a spiral fibre winding from end to end, remain-
ing distinct from the cell-wall, and retaining its elasticity; this
fibre may be single, double, or even quadruple,—this last charac-
ter presenting itself in the very large elongated fibre-cells of the
Nepenthes (Chinese pitcher-plant). These cells are especially
found in the delicate membrane (‘medullary sheath”) surround-
ing the pith of Exogens, and in the midst of the woody bundles
occurring in the stem of Endogens; thence they proceed in each
case to the leaf-stalks, through which they are distributed to the
leaves. By careful dissection under the microscope, they may
be separated entire; but their structure may be more easily dis-

a

i So long, however, as they retain their original cellular character, and do not coalesce
with each other, these fusiform spiral cells cannot be regarded as having any more
claim to the designation of vessels, than have the elongated cells of the ligneous tissue.

3874 STRUCTURE OF PHANEROGAMIC PLANTS,

played, by cutting round, but not through, the leaf-stalk of the
Strawberry, Geranium, &c., and then drawing the parts asunder.
The membrane composing the tubes of the vessels will thus be
broken across; but the fibres within, being elastic, will be drawn
out and unrolled. Spiral vessels are sometimes found to convey
liquid, whilst in other cases they contain air only; the conditions
of this difference are not yet certainly known.

233. Although fluid generally finds its way with tolerable
facility through the various forms of Cellular tissue, especially
in the direction of the greatest length of its cells, a more direct
means of connection between distant parts is required for an
active circulation. This is afforded by what has been termed
Vasiform tissue, which consists merely of cells laid end to end,
the partitions between them being more or less obliterated, so
that a continuous Duet is formed. The origin of these ducts in
cells is oceasionally very evident, both in the contraction of their
calibre at regular intervals, and in the persistence of the remains
of their partitions (Fig. 175, 6 6); but in most cases it can only
be ascertained by studying the history of their development,
neither of these indications being traceable. The component
cells appear to have been sometimes simply membranous, but
more commonly to have possessed the fibrous type (§ 228).

Some of the ducts formed

Fie. 162. from the latter (Fig. 162, ‘

are so like continuous spira

vessels, as to be scarcely
distinguishable from them,
save in the want of elasticity
-,in the spiral fibre, which
«j causes it to break when the
attempt is made to draw it
out. This would seem to
~ have taken place, in some
‘. Instanees, from the natural
elongation of the cells by
growth; the fibre being bro-
ken up into rings, which
sometimes lie close together,
but more commonly at con-
siderable intervals; such a
duct is said to be annular
(Fig. 162,1). Intermediate
forms between the spiral and
ie annular ducts, which show
econ) stn of sem of Zalun Rel-“«) the derivation of the latter
1, annular duct; 2, spiral duct; 3, dotted duct, with from the former, are very fre-
woody fibre; ¢, cells of the integument. quently to be met with. The
spires are sometimes broken

up still more completely, and the fragments of the fibre extend
in various directions, so as to meet and form an irregular net-

PREPARATION OF VEGETABLE TISSUE. 875

work lining the duct, which is then said to be reticulated. The
continuation of the deposit, however, gradually contracts the
meshes, and leaves the walls of the duct marked only by pores
like those of porous cells (§ 227); and canals upon this plan,
commonly designated as dotted ducts, are among the most com-
mon forms of vasiform tissue, especially in parts of most solid
structure and least rapid growth (Fig. 162, 3). The “scalari-
form’ ducts of Ferns (§ 218) are for the most part of the
spiral type; but spiral ducts are frequently to be met with
also in the rapidly growing leaf-stalks of Flowering plants,
such asthe Rhubarb. Not unfrequently, however, we find all
forms of ducts in the same bundle, as seen in Fig. 162. The
size of these ducts is occasionally so great, as to enable their
openings to be distinguished by the unaided eye. They are
usually largest in stems, whose size is small in proportion to the
surface of leaves which they support, such as the common Cane,
or the Vine; and generally speaking they are larger in woods of
dense texture, such as Oak or Mahogany, than in those of which
the fibres, being softer, can themselves be subservient to the con-
veyance of fluid. They are entirely absent in the Conifers.
234, The Vegetable Tissues, whose principal forms have been
now described, but among which an immense variety of detail
is found, may be either studied as they present themselves in
thin sectzons of the various parts of the plant under examination,
or in the isolated condition in which they are obtained by dissec-
tion. The former process is the most easy, and yields a large
amount of information; but still it cannot be considered that
the characters of any tissue have been properly determined,
until it has been dissected out. Sections of some of the hardest
vegetable substances, such as “‘ vegetable ivory,” the “stones” of
fruit, the “shell” of the cocoa-nut, &e. (§ 227), can scarcely be
obtained except by slicing and grinding (§ 108); and these may
be mounted either in Canada balsam or in weak spirit. In
cases, however, in which the tissues are of only moderate firm-
ness, the section may be readily and most effectually made with
the “Section-Instrument” (§ 107); and there are few parts of the
Vegetable fabric which may not be advantageously examined by
this means, any very soft or thin portions being placed in it
between two pieces of cork. In certain cases, however, in which
even this compression would be injurious, the sections must be
made with a sharp knife, the substance being laid upon a slip of
glass. In dissecting the Vegetable tissues, scarcely any other
instrument will be found really necessary, than a pair of needles
(in handles), one of them ground to a cutting edge. The adhe-
sion between the component cells, fibres, &., is often sufficiently
weakened. by a few hours’ maceration, to allow of their readily
coming apart, when they are torn asunder by the needle points
beneath the simple lens of a dissecting microscope. But if this
should not prove to be the case, it is desirable to employ some

376 STRUCTURE OF PHANEROGAMIC PLANTS,

other method, for the sake of facilitating their isolation. None
is so effectual as the boiling of a thin slice of the substance
under examination, either in dilute nitric acid, or in a mixture
of nitric acid and chlorate of potass. This last method (which
was devised by Schultz) is the most rapid and effectual, requiring
only a few minutes for its performance; but as oxygen is libe-
rated with such freedom as to give an almost explosive character
to the mixture, it should be put in practice with extreme caution.
After being thus treated, the tissue should be boiled in alcohol,
and then in water; and it will then be found very easy to tear
apart the individual cells, ducts, &c., of which it may be com-
posed. These may be preserved by mounting in weak spirit.
235. Structure of the Stem and Root.—It is in the stems and
roots of Plants, that we find the greatest variety of tissues in
combination, and the most regular plans of structure; and sec-
tions of these, viewed under a low magnifying power, are objects
of peculiar beauty, independently of the scientific information
which they afford. The Axis (under which term is included the
Stem with its branches, and the Root with its ramifications)
always has for the basis of its structure a dense cellular paren-
chyma; though this, in the advanced stage of development, may
constitute but a small proportion of it. In the midst of this
parenchyma we generally find fibro-vascular bundles; that is,
fasciculi of woody fibre, with ducts of various kinds, and (very
commonly) spiral vessels. It is in the mode of arrangement of
these bundles, that the fundamental difference exists between
the stems that are commonly designated as Endogenous, and
those which are (more appropriately) termed Hxogenous; for in
the former, the bundles are dispersed throughout the whole
diameter of the axis, without any peculiar plan, the intervals
between them being filled up by cellular parenchyma; whilst in
the latter they are arranged side by side, in such a manner as to
form a hollow cylinder of wood, which includes within it that
portion of the cellular substance which is known as pith, whilst
it is itself enclosed in an envelope of the same substance, that
forms the bark. These two plans of axis formation,—respec-
tively characteristic of those two great groups into which the
Phanerogamia are subdivided, namely the Monocotyledonous, and
the Dicotyledonous,—will now be more particularly described.
236. When a transverse section (Fig. 163) of a Monocotyledo-
nous stem is examined microscopically, it is found to exhibit a
number of fibro-vascular bundles, disposed without any regu-
larity in the midst of the mass of cellular tissue, which forms (as
it were) the matrix or basis of the fabric. Each bundle contains
two, three, or more large ducts, which are at once distinguished
by the size of their openings; and these are surrounded by
woody fibre, and spiral vessels, the transverse diameter of which
is so extremely small, that the portion of the bundles which they
form is at once distinguished in transverse section, by the close-

STRUCTURE OF MONOCOTYLEDONOUS STEM. 377

ness of its texture (Fig. 164). The bundles are least numerous
in the centre of the stem, and become gradually more approxi-
mated towards the circumference: but it frequently happens that
the portion of the area in which they are most compactly

Fra. 163, Fra. 164,

Transverse section of stem of young Palm. Portion of transverse section of stem
of Wanghie Cane.

arranged, is not absolutely at its exterior, this portion being
itself surrounded by an investment composed of cellular tissue
only; and sometimes we find the central portion, also, com-
pletely destitute of fibro-vascular bundles; so that a sort of
indication of the distinction between pith, wood, and bark is
here presented. This distinction, however, is very imperfect ;
for we do not find either the central or the peripheral portions
ever separable, like pith and bark, from the intermediate woody
layer. In its young state, the centre of the stem is always filled
up with cells; but these not unfrequently disappear after a time,
except at the nodes, leaving the stem hollow, as we see in the
whole tribe of Grasses. When a vertical section is made of a
woody stem (as that of a Palm) of sufficient length to trace the
whole extent of the fibro-vascular bundles, it is found that whilst
they pass at their upper extremity into the leaves, they pass at
the lower end, also, towards the surface of the stem, and assist,
by their interlacement with the outer bundles, in forming that
extremely tough investment, which the lower ends of these
stems present. The fibro-vascular bundles once formed, receive
no further additions; and the augmentation of the stem in
diameter depends upon the development of new woody bundles,
in continuity with the leaves which are successively evolved at
its summit. It was formerly supposed that these successively

378 STRUCTURE OF PHANEROGAMIC PLANTS,

formed bundles descend in the interior of the stem through its
entire length, until they reach the roots; and as the successive
development of leaves involves a successive development of new
bundles, the stem was imagined to be continually receiving addi-
tions to its interior, whence the term Endogenous was given to
this type of stem-structure. From the fact just stated, however,
regarding the course of the fibro-vascular bundles, it is obvious
that such a doctrine cannot be any longer admitted; for those
which are most recently formed only pass into the centre of the
stem during the higher part of their course, and usually make
their way again to its exterior at no great distance below; and
thus the lower and older portions of a Palm-stem really do
receive very little augmentation in diameter, while a rapid elon-
gation is taking place at its summit. In fact, the dense unyield-
ing nature of the fabric, which is formed by the interlacement of
the fibro-vascular bundles at or near the surface of the trunk,
would prevent any such augmentation by expanding pressure
from within.

287. In the stems of Dicotyledonous Phanerogamia, we find a
method of arrangement of the several parts, which must be re-
garded as the highest form of the de-
velopment of the axis, being that in
which the greatest differentiation exists.
A distinct division is always seen in a
transverse section, between the three
concentric areze of the pith, the wood,
and the dark ; the first (a) being central
and the last (6) peripheral, and these
having the wood interposed between
them, its circle being made up of wedge-
shaped bundles (d, d), kept apart by the
el eden a bands (¢, ¢) that_pass between the pith
Exogenous stem; a, pith; bb, bark, 20d the bark. The Pith (Fig. 165, a) is
4, plates of cellular tissue (medul- almost invariably composed of cellular
BEY rays) felt between the woody tissue only, which usually presents (in

transverse section) a hexagonal areola-
tion. When newly formed, it has a greenish hue, and its cells
are filled with fluid; but it gradually dries up and loses its color;
and not unfrequently its component cells are torn apart by the
rapid growth of their envelope, so that irregular cavities are
found in it; or, if the stem should increase with extreme rapidity,
it becomes hollow, the pith being reduced to fragments which
are found adhering to its interior wall. The pith is immediately
surrounded by a delicate membrane, consisting almost entirely
of spiral vessels, and termed the “ medullary sheath.”

238. The Woody portion of the stem (Fig. 165, 6, 6) is made
up of woody fibres, usually with the addition of ducts of various
kinds; these, however, are absent in one large group, the Com-

EXOGENOUS STEM. 379

fere or Fir tribe with its allies (Figs. 166, 170-172), in which the
woody fibres are of unusually large diameter, and have the pe-
cul.ar “glandular” markings already described (§ 231). In any
stem or branch of more than one year’s growth, the woody struc-

Fie. 165.

Transverse section of young stem of Clematis:—a, pith; b, b, b, woody bundles; ¢, ¢, v, medullary
rays.

ture presents a more or less distinct appearance of division into
concentric rings, the number of which varies with the age of the
tree (Fig. 167). The composition of the several rings, which are
the sections of so many cylindrical layers, is uniformly the same,
however different their thickness; the arrangement of the two
principal elements, however,—namely the woody fibre and the
ducts,—varies in different species; the ducts being sometimes

Fie. 166.

Portion of transverse section of stem of Cedar :—a, pith; b, b, wood; ¢, bark.

almost uniformly diffused through the whole layer, but in other
instances being confined to its inner part; while in other cases,
again, they are dispersed with a certain regular irregularity (if
such an expression may be allowed), so as to give a curiously
figured appearance to the transverse section (Figs. 167, 168).
The general fact, however, is, that the ducts predominate towards
the inner side of the ring (which is the part of it first formed), and

380 STRUCTURE OF PHANEROGAMIC PLANTS,

that the outer portion of each layer is almost exclusively composed
of woody tissue; such an arrange-
ment is seenin Fig. 165. This alter-
nation of ducts and woody fibre fre-
quently serves to mark the succes.
sion of layers, when, as is not un-
common, there is no very distinct
line of separation between them.
The number of layers is usually
considered to correspond with that
of the years during which the stem
or branch has been growing; and
this is, no doubt, generally true in
regard to the trees of temperate
? climates. There appears strong
Transverse section of stem of Buckthorn reason to believe, however that
(Riiamnus). : 7 ’
such is not the universal rule;
and that we should be more
correct in stating that each
layer indicates an “epoch of
vegetation ;” which, in tempe-
rate climates, is usually (but
not invariably) a year, but
which is commonly much Jess
in the case of trees flourishing
in tropical regions. For ex-
ample, we not unfrequently
meet with stems, in which the
Portion of the — + ae more highly place of a layer of the ordinary
bas breadth is occupied by two nar-
row layers; the line of demarcation between them having appa-
rently been formed by a temporary interruption to the process of
growth, in the middle of the period through which the formation
of wood extends. Such an interruption might occur from heat

Fic. 167.

Fia. 168.

Fie, 169.

a b ¢c

Portion of transverse section of stem of Hazel, showing, in the portion a, b, c, six narrow layers of
wood.

and drought, in a tree that flourishes best in a cold damp atmo-
sphere, or from a fall of temperature in a tree that requires heat;
and in a variable season, it might recur several times. Some-
thing of this kind would appear to have been the cause of the

MEDULLARY RAYS. 3881

peculiar appearance presented by a section of Hazel-stem (in the
Author’s possession), of which a portion is represented in Fig.
169; for between two layers of the ordinary thickness, there in-
tervenes a band whose breadth is altogether less than that of
either of them, and which is yet composed of no fewer than six
layers, four of them (c) being very narrow, and each of the other
two being about as wide as these four together. The inner layers
of wood are the oldest, and the most solidified by matters de-
posited within their component cells and vessels; hence they are
spoken of collectively under the designation duramen or “ heart-
wood.” On the other hand, it is through the cells and ducts of
the outer and newer layers, that the sap rises from the roots
towards the leaves; and these are consequently designated as
alburnum or “‘sap-wood.” The line of demarcation between the
two is sometimes very distinct, as in Lignum-vitee and Cocos
wood; and as a new layer is added every year to the exterior of
the alburnum, an additional layer of the innermost part of the
alburnum is every year consolidated by internal deposit, and is
thus added to the exterior of the duramen. More generally,
however, this consolidation is gradually effected, and the al-
burnum and duramen are not separated by any abrupt line of
division.
239. The Medullary Rays which cross the successive rings of
wood connecting the cellular substance of the pith with that of
the bark, and dividing each ring
Fig. 170. of wood into wedge-shaped seg-
ments, are thin plates of cellular
tissue (Fig. 165, ¢, c), not usually
extending to any great depth in
the vertical direction. It is not
often, however, that their cha-
racter can be so clearly seen in
a transverse section, as it is in
that just referred to; for they
are usually compressed so
: closely, as to appear darker than
Portion of transverse section of large stem of the wedges of woody tissue be-
confused evi, showing, var of tween which they, intervene
very thin bit sinibious Dledullaey Rays. : : (Figs. 166-169) ; and their real
nature is best understood by a
comparison of longitudinal sections made in two different direc-
tions,—namely, radial and tangential,—with the transverse. Three
such sections of a fossil Coniferous wood in the Author’s pos-
session are shown in Figs. 170-172. The stem was of such large
size, that, in so small a part of the area of its transverse section
as is represented in Fig. 170, the medullary rays seem to run
parallel to each other, instead of radiating from a common
centre. They are very narrow; but are so closely set together,
that only two or three rows of woody fibres (no ducts being here

882 STRUCTURE OF PHANEROGAMIC PLANTS,

present) intervene between any pair of them. In the longitu.
dinal section taken in a radial direction (Fig. 171), and conse.

= Fra. 171, Fig, 172,

Fig. 171, Portion of vertical section of the same wood, taken in a radial direction, showing the
glandular woody fibres, without ducts, crossed by the Medullary Rays, a, a.
Fig. 172. Portion of vertical section of the same wood, taken in a tangential direction, so as to
cut across the Medullary Rays.
quently passing in the same course with the medullary rays,
these are seen as thin plates (a, a, a) made up of superposed cells
very much elongated, and crossing, in a hori-
Fig. 173, zontal direction, the glandular woody fibres
which le parallel to one another vertically.
And in the tangential section (Fig. 172),
which passes in a direction at right angles
to that of the medullary rays, and therefore
euts them across, we see that each of the
plates thus formed has a very limited depth
from above downwards, and is composed of
no more than one thickness of horizontal
cells. A section of the stem of Mahogany,
taken in the same direction as the last (Fig.
mele gives a very good view of the cut ends
of the medullary rays, as they pass between
the woody fibres; and they are seen to be
here of somewhat greater thickness, being
composed of two or three rows of cells, ar-
ranged side by side. In another fossil wood,
whose transverse section is shown in Fig.
174, and its tangential section in Fig. 176,
Vertical section of Mahogany. the medullary rays are scen to occupy a
much larger part of the substance of the stem; being seen in the
transverse section as broad bands (aa, a a), intervening between
the closely set woody fibres, among which the large ducts are
scattered; whilst in the tangential, they are observed to be not

EXOGENOUS STEM:—MEDULLARY RAYS. 383

only deeper than the preceding from above downwards, but also
to have a much greater thickness. This section also gives an
excellent view of the ducts 5 6, 6 6, which are here plainly seen

Fig. 174.

eas

||

i
)

Fig. 174. Portion of transverse section of Fossil Wood, showing the Medullary Rays, a a,aa,a 4a,
running nearly parallel to each other, and the openings of the large Ducts in the midst of the woody
fibres.

Fig. 175. Portion of vertical (tangential) section of the same Wood, showing the woody fibres
separated by the Medullary Rays, and by the large Ducts, b b, b b.

to be formed by the coalescence of large cylindrical cells, lying
end to end. In another fossil wood in the Author’s possession,
the medullary rays constitute a still larger proportion of the

Fra. 176. Fie. 177,

8 |
aug

Fig. 176. Portion of transverse section of a Fossil Wood, remarkable for the very large size of
the Medullary Rays, b, b, which separate the woody plates, a, a.

Fig. 177. Vertical (tangential) section of the same wood, showing, u, a, the woody bundles, and
b, b, the Medullary Rays.

stem ; for in the transverse section (Fig. 176), they are seen as
very broad bands (8, 6), alternating with plates of woody struc-

884 STRUCTURE OF PHANEROGAMIC PLANTS.

ture (a, a), whose thickness is often less than their own; whilst
in the tangential section (Fig. 177), the cut extremities of the
medullary rays occupy a very large part of the area, having ap.
parently determined the sinuous course of the woody fibres ;
instead of looking, as in Fig. 172, as if they had forced their wa
between the woody fibres, which there hold a nearly straight and
parallel course on either side of them.

240. The Bark may be usually found to consist of three princi-
pal layers; the external, or epiphlcewm, also termed the suberous
(or corky) layer; the middle, or mesophleum, also termed the
“cellular envelope ;” and the internal, or endophleum, which ig
more commonly known as the liber. The two outer layers are
entirely cellular; and are chiefly distinguished by the form, size,
and direction of their cells. The epiphleum is generally com-
posed of one or more layers of colorless or brownish cells, which
usually present a cubical or tabular form, and are arranged with
their long diameters in the horizontal direction : it is this which,
when developed to an unusual thickness, forms Cork, a substance
which is by no means the product of one kind of tree exclusively,
but which exists in greater or less abundance in the bark of
every exogenous stem. The mesophicum consists of cells, usually
of green color, prismatic in their form, and disposed with their
long diameters parallel to the axis; it is more loosely arranged
than the preceding, and contains “ intercellular passages,” which
often form a network of canals, that have been termed “ latici-
ferous vessels ;” and although usually less developed than the
suberous layer, it sometimes constitutes the chief thickness of
the bark. The liber or inner bark, on the other hand, usually
contains woody fibre in addition to the cellular tissue and latici-
ferous vessels of the preceding; and thus approaches more nearly
in its character to the woody layers, with which it is in close
proximity on its inner surface. The liber may generally be
found to be made up of a succession of thin layers, equalling in
number those of the wood, the innermost being the last formed;
but no such succession can be distinetly traced in the cellular
envelope, or in the suberous layer; although it is certain that
they, too, augment in thickness by additions to their interior,
whilst their external portions are frequently thrown off in the
form of thickish plates, or detach themselves in smaller and
thinner flakes. The bark is always separated from the wood by
the cambium layer, which is the part wherein all new growth
takes place: this seems to consist of mucilaginous semifluid
matter; but it is really made up of cells of a very delicate tex:
ture, which gradually undergo transformations, whereby they
are for the most part converted into woody tissue, ducts, spiral
vessels, &. These materials are so arranged, as to augment the
fibro-vascular bundles of the wood on their external surface;
thus forming a new layer of alburnum, which encloses all those
that preceded it; whilst they also form a new layer of liber, on

BARK. 885

the interior of all those which preceded it; they also extend the
medullary rays, which still maintain a continuous connection be-
tween the pith and the bark; but a portion remains unconverted,
so as always to keep apart the liber and alburnum. This type
of stem structure is termed Exogenous ; a designation which ap-
plies very correctly to the mode of intrease of the woody layers,
although (as we have just seen) the liber is formed upon a truly
endogenous plan.

241. Numerous departures from the normal type are found
in particular tribes of Exogens. Thus in some, the wood is not
marked by concentric circles, their growth not being inter-
rupted by any seasonal change. In other cases, again, each
woody zone is separated from the next, by the interposition of
a thick layer of cellular substance. Sometimes wood is formed
in the bark (as in Calycanthus), so that several woody columns are
produced, which are quite independent of the principal woody
axis, but cluster around it. Occasionally the woody stem is
divided into distinct segments, by the peculiar thickness of cer-
tain of the medullary rays; and in the stem of which Fig. 178
represents a transverse section, these cellular plates form four
large segments, disposed in the manner of a Maltese cross, and
alternating with the four woody segments, which they equal in
size.

242. In its first-developed state, the Exogenous stem con-
sists, like the-so-called endogenous, of cellular tissue only; but

Fig. 179,
Fie. 178.

Fig. 178. Transverse section of the stem of a Climbing-plant (Aristolochia ?) from New Zeuland.
« Fig.179. Portion of transverse section of Burdock (Arctium), showing oue of the fibro-vascular
. bundles, that lies beneath the cellular integument,

after the leaves have been actively performing their functions for
a short time, we find a circle of fibro-vascular bundles, as repre-
sented in the diagram, p. 378, interposed between the central
(or medullary) and the peripheral (or cortical) portions of the

cellular matrix; these fibro-vascular bundles being themselves
25

886 STRUCTURE OF PHANEROGAMIC PLANTS.

separated from each other by plates of cellular tissue, which
still remain to connect the central and the peripheral portions
of the matrix. This first stage in the formation of the Exogen-
ous axis, in which its principal parts—the pith, wood, bark, and
medullary rays—are marked out, is seen even in the stems of
herbaceous plants, which are destined to die down at the end of
the season (Fig. 179); and sections of these, which are ve
easily prepared, are most interesting Microscopic objects. In
such stems, the difference between the ‘“ Endogenous” and the
“ Exogenous’ types is manifested in little else than the disposi-
tion of the fibro-vascular layers; which are scattered through
nearly the whole of the cellular matrix (although most abundant
towards its exterior), in the former case; but are limited toa
circle within the peripheral portion of the cellular tissue, in the
latter. It is in the further development which takes place during
succeeding years in the woody stems of perennial Exogens, that
those characters are displayed, which separate them most com-
pletely from the Ferns and their allies, whose stems contain a
cylindrical layer of fibro-vascular bundles, as well as from (so-
called) Endogens. For whilst the fibro-vascular layers of the
latter, when once formed, undergo no further increase, those of
Exogenous stems are progressively augmented by the metamor-
phosis of the cambium layer ; so that each of the bundles which
once lay as a mere series of parallel cords beneath the cellular
investment of a first year’s stem, may become in time the small
end of a wedge-shaped mass of wood, extending continuously
from the centre to the exterior of a trunk of several feet in
diameter, and becoming progressively thicker as it passes out-
wards. The fibro-vascular bundles of Exogens are therefore
spoken of as “indefinite ;’ whilst those of Exogens and Acro-
gens (Ferns, &c.) are said to be “definite” or ‘“ closed.”

243. The structure of the Roots of Endogens and Exogens is
essentially the same in plan with that of their respective stems.
Generally speaking, however, the roots of Exogens have no pith,
although they have medullary rays; and the succession of dis-
tinct rings is less apparent in them, than it is in the stems from
which they diverge. In the delicate radical filaments which pro-
ceed from the larger root-fibres, a central bundle of vessels will
be seen, enveloped in a sheath of cellular substance; and this
investment also covers in the end of the fibril, which is usually
somewhat dilated, and composed of peculiarly succulent tissue,
forming what is termed the spongiole. The structure of the
radical filaments may be well studied in the common Duckweed,
every floating leaf of which has a single fibril hanging down
from its lower surface.

244. The structure of Stems and Roots cannot be thoroughly
examined in any other way than by making sections in different
directions with the Section-instrument. The general directions
already given (§ 107) leave little to be added respecting this

SECTIONS OF STEMS. 887

special class of objects; the chief points to be attended to being
the preparation of the stems, &c., for slicing, the sharpness of the
knife and the dexterity with which it is handled, and the method
of mounting the sections when made. The wood, if green,
should first be soaked in strong alcohol for a few days, to get rid
of the resinous matter; and it should then be macerated in
water for some days longer, for the removal of its gum, before
being submitted to the cutting process. If the wood be dry, it
should first be softened by soaking for a sufficient length of time
in water, and then treated with spirit and afterwards with water,
like green wood. Some woods are so little affected even by
prolonged maceration, that boiling in water is necessary to
bring them to the degree of softness requisite for making sec-
tions. No wood that has once been dry, however, yields such
good sections, as that which is cut fresh. When a piece, of the
appropriate length, has been placed in the grasp of the Section-
instrument (wedges of deal or other soft wood being forced in
with it, if necessary for its firm fixation), a few thick slices
should first be taken, to reduce its surface to an exact level; the
surface should then be wetted with spirit, the micrometer-screw
moved through a small part of a revolution, and the slice taken
off with the razor, the motion given to which should partake
both of drawing and pushing. A little practice will soon enable
the operator to discover, in each case, how thin he may venture
to cut his sections, without a breach of continuity; and the
micrometer-screw should be turned so as to give the required
elevation. If the surface of the wood has been sufficiently
wetted, the section will not curl up in cutting, but will adhere
to the surface of the, razor, from which it is best detached by
dipping the razor in water, so as to float away the slice of wood,
a camel-hair pencil being used to push it off, if necessary. All
the sections that may be found sufficiently thin and perfect,
should be put aside in a bottle of weak spirit, until they be
mounted. For the minute examination of their structure, it is
generally much better to preserve them in fluid, than to mount
them either dry or in Canada balsam; and no fluid answers
better than weak spirit. Where a mere general view only is
needed, the dry mounting answers the purpose sufliciently well.
It is only in the case of the section being unusually opaque, that
mounting itin Canada balsam can be of any service whatever; and
in general it is rather injurious than useful, making the section
so transparent that its features can scarcely be discerned. Trans-
verse sections, however, when charred by heating between two
plates of glass until they turn brown, may be mounted with
advantage in Canada balsam, and are then very showy specimens
for the solar or gas-microscope. The number of beautiful and
interesting objects which may be thus obtained, at the cost of a
very small-amount of trouble, can scarcely be conceived save by
those who have made a special study of these wonderful struc-

388 STRUCTURE OF PHANEROGAMIC PLANTS,

tures. Even the commonest trees, shrubs, and herbaceous plants,
yield specimens that exhibit a varied elaboration of design,
which cannot but strike with astonishment even the most cursor
observer; and there is none in which a careful study of sections,
made in different parts of the stem, and especially in. the neigh-
borhood of the “ growing point,” will not reveal to the eye of the
scientific Physiologist, some of the most important phenomena of
Vegetation. Fossil Woods, when well preserved, are almost
invariably s:cified, and require, therefore, to be cut and polished
by a Lapidary. Should the Microscopist be fortunate enough to
meet with a portion of a calcified stem, in which the organic
structure is preserved, he should proceed with it after the man-
ner of other hard substances which need to be reduced by grind-
ing (§§ 108-110).

245. Structure of the Cuticle and Leaves.—On all the softer parts
of the higher Plants, save such as grow under water, we find a
superficial layer, different in its texture from the parenchyma
beneath, and constituting a distinct membrane, known as the

Fic. 180. Fie. 181.

ae
a
} ys
: ih
i

Cuticle of Leaf of Pucca. Cuticle of Leaf of Indian Corn (Zea Mais).

Cuticle.’ This membrane is composed of cells, the walls of which
are flattened above and below, whilst they adhere closely to
each other laterally, so as to form a continuous stratum (Fig. 184,
a, a). Their shape is different in almost every tribe of Plants;
thus in the cuticle of the Yucca (Fig. 180), Indian Corn (Fig.
181), Lris (Fig. 183), and most other Monocotyledons, the cells
are elongated, and present an approach to a rectangular contour;
their margins being straight in the Yucca and Iris, but minutely

1 The term epidermis is applied to this membrane by many Vegetable Physiologists,
on account of the analogy it seems to present to the epidermis of Animals; but as
epidermis means a membrane that lies wpon the derm or “ true skin,’ and as no such
subjacent layer exists in the Plant, the transference of the designation is altogether inap-
propriate. It would be much more correct to designate by the name cutis or derm what
is ordinarily denominated the Cuticle; and to reserve the term epidermis for the thin
pellicle which may be sometimes detached from it ($ 247).

STRUCTURE OF THE CUTICLE. 389

sinuous or crenated in the Indian Corn. In most Dicotyledons,
on the other hand, the cells of the cuticle depart less from the
form of circular disks; but their margins usually exhibit large
irregular sinuosities, so that they seem to fit together like the
pieces of a dissected map, as is seen in the cuticle of the Apple
(Fig. 182, 6, 6). Even here, however, the cells of the portion of

Portion of the Cuticle of the inferior surface of the Leaf of the Apple, with the layer of parenchyma
in immediate contact with it:—a, a, elongated cells of the cuticle overlying the veins or nerves of
the leaf; 6, b, ordinary cuticle cells overlying the parenchyma; c, ¢, stomata; d, d, green cells of the
parenchyma, forming a very open network near the lower surface of the leaf.

the cuticle (a, a) that overlies the veins of the leaf, have an elon-
gated form, approaching that of the wood-cells of which these
veins are chiefly composed; and it seems likely, therefore, that
the elongation of the ordinary cuticle-cells of Monocotyledons
has reference to that parallel arrangement of the veins, which
their leaves almost constantly exhibit. The cells of the cuticle
are colorless, or nearly so, no chlorophyll being formed in their
interior; and their walls are generally thickened by secondary
deposit, especially on the side nearest the atmosphere. This
deposit is of a waxy nature, and consequently renders the mem-
brane very impermeable to fluids; the retention of which within
the soft tissue of the leaf is obviously the purpose to be answered
by the peculiar organization of the cuticle. In most European
Plants, the cuticle contains but a single row of cells, which are
usually, moreover, thin-sided; whilst in the generality of tro-
pical species, there exist two, three, or even four layers of thick-
sided cells; this last number being seen in the Oleander, the
cuticle of which, when separated, has an almost leathery firm-
ness. The difference in conformation is obviously adapted to
the conditions of growth under which these plants respectively
exist; since the cuticle of a plant indigenous to temperate
climates, would not afford a sufficient protection to the interior
structure against the rays of a tropical sun ; whilst the diminished
heat of this country would scarcely overcome the resistance
presented by the dense and non-conducting tegument of a

390 STRUCTURE OF PHANEROGAMIC PLANTS.

species formed to exist in tropical climates. A very curious
modification of the cuticle is presented by the Rochea falcata,
commonly known as the “ice-plant;” a designation it owes to

Fia. 183.

Portion of the Cuticle of the upper surlace of the leaf of Roehea falcata, as seen at a from its inner
side, and at B from its outer side :—a, a, small cells forming the inner layer of the cuticle; 6, b, large
prominent cells of the outer layer; c, c, stomata, disposed between the latter.

the peculiar appearance of its surface, which looks as if it were
covered with trozen dewdrops. This appearance is occasioned
by the presence of a layer of very large oval cells (Figs. 183, 184,
6, 6), which lie detached one
Fic. 184. from another upon the surface
of the ordinary cuticle, a, a.
In other instances, the cuticle
is partially invested by a layer
of scales, which are nothing
else than flattened cells, often
having a very peculiar form;
whilst in numerous cases,
again, we find the surface be-
Portion of a vertical section of the same Leaf, set with hairs, which occasion-
showing the small cells, a, a, of the inner layer of ally consist of single elongated
cuticle; the large cells b, b, of the outer layer; ¢, eells but are more commonly
one of the stomata; d, d, cells of the parenchyma; Z . ‘
L, lacuna between the parenchymatous cells, ‘ita made up of a linear serles,
which the stoma opens. attached end to end, as in Fig.
153. Sometimes these hairs
bear little glandular bodies at their extremities, by the secretion
of which a peculiar viscidity is given to the surface of the leaf, as in
the Sundew (Drosera) ; in other instances, the hair has a glandular
body at its base, with whose secretion it is moistened; so that
when this secretion is of an irritating quality, as in the Nettle, it
constitutes a “sting.” A great variety of such organs may be
found, by a microscopic examination of the surface of the leaves
of Plants having any kind of superficial investment to the cuticle.
Many connecting links are found between hairs and scales, such
as the “stellate hairs” of the Deutzia scabra, which a good deal
resemble those within the air-chambers of the Yellow Water-lily
(Fig. 152).

STRUCTURE OF CUTICLE AND STOMATA., 391

246, The Cuticle in many Plants, especially those belonging
to the Grass tribe, has its cell-walls impregnated with silex, like
that of the Equisetum (§ nig so that, when all the organic
matter has been got rid of by heat or by acids, the forms of the
cuticle-cells, hairs, stomata, &c., are still marked out in silex, and
are most beautifully displayed by Polarized light. Such silicified
cuticles are found on the husks of the “grains” yielded by these
plants: and there is none in which a larger proportion of mineral
matter exists, than that of Rice, which contains some curious
elongated cells with toothed margins. The hairs with which
the palee (chaffscales) of most Grasses are furnished, are
strengthened by the like siliceous deposit; and in the Festuca
pratensis, one of the common meadow grasses, the pales are also
beset with longitudinal rows of little cup-like bodies formed of
silica. The cuticle and scaly hairs of Deutzia also contain a large
quantity of silex; and are remarkably beautiful objects for the
Polariscope.

247. Externally to the cuticle, there usually exists a very deli-
cate transparent pellicle, without any decided traces of organiza-
tion, though occasionally somewhat granular in appearance, and
marked by lines that seem to be impressions of the junctions of
the cells with which it was in contact. When detached by
maceration, it not only comes off from the surface of the cuticle,
but also from that of the hairs, &., which this may bear. This
membrane, the proper Hpidermis (p. 388, note), is obviously
formed by the agency of the cells of the cuticle; and it seems to
consist of the external layers of their thickened cellulose walls,
which have coalesced with each other, and have separated them-
selves from the subjacent layers, by a change somewhat analogous
to that which occurs in the Palmellee (§ 194), the outer walls of
whose original cells seem to melt away into the gelatinous in-
vestment, that surrounds the “ broods” which have originated in
their subdivision.

248. In nearly all Plants which possess a distinct Cuticle, this
is perforated by the minute openings termed Stomata (Figs. 182,
188, ¢, ec); which are bordered by cells of a peculiar form, dis-
tinct from those of the cuticle, and more resembling in character
those of the tissue beneath. These boundary-cells are usually
somewhat kidney-shaped, and lie in pairs (Fig. 185, 0, 6), with
an oval opening between them; but by an alteration in their
form, the opening may be contracted or nearly closed. In the
cuticle of Yucca, however, the opening is bounded by two pairs
of cells, and is somewhat quadrangular (Fig. 180); and a like
doubling of the boundary-cells, with a narrower slit between
them, is seen in the cuticle of the Indian Corn (Fig. 181). In
the stomata of no Phanerogamic Plant, however, do we meet
with any conformation at all to be compared in complexity with
that which has been described as existing in the humble Mar-

392
chantia (214).

Fig. 185.

Portion of the Cuticle of the leaf of the Jris
germanica, torn from its surface, ‘and carrying
away with it a portion of the parenchymatous
layer in immediate contact with it:—a, a, elon-
gated cells of the cuticle; 0, b, cells of the stomata ;
¢, ¢, cells of the parenchyma; d, d. impressions
formed by their contact, on the epidermic cells;
e, e, lacune in the parenchyma, corresponding to
the stomata.

STRUCTURE OF PHANEROGAMIC PLANTS,

Stomata are usually found most abundantly (and

sometimes exclusively) in the
cuticle of the lower surfaces of
leaves, where they open into the
air-chambers that are left in the
parenchyma which lies next the
inferior cuticle; in leaves which
float on the surface of water,
however, they are found in the
cuticle of the upper surface
only; whilst, in leaves that ha-
bitually live entirely submerged,
as there is no distinct cuticle,
so there are no stomata. In the
erect leaves of Grasses, the Iris
tribe, &c., they are found equally
(or nearly so) on both surfaces,
As a general fact, they are least
numerous in succulent Plants,
whose moisture, obtained in a
scanty supply, is destined to be

retained in the system; whilst
they abound most in those which exhale fluid most readily, and
therefore absorb it most quickly. It has been estimated that no
fewer than 160,000 are contamed in every square inch of the
under surface of the leaves of Hydrangea and of several other
plants; the greatest number seeming always to present itself in
species, the upper surface of whose leaves is entirely destitute of
these organs. In Iris germanica, each surface has nearly 12,000
stomatain every square inch; and in Vueca, each surface has 40,000.
In Oleander, Banksia, and some other plants, the stomata do not
open directly upon the lower surface of the cuticle, but lie in the
deepest part of little pits or depressions which are excavated in
it, and which are lined with hairs ; the mouths of these pits, with
the hairs that line them, are well brought into view by taking a
thin slice from the surface of the cuticle with a sharp knife; but
the form of the cavities, and the position of the stomata, can only
be well made out in vertical sections of the leaves.

249. The internal structure of Leaves is best brought into
view by making vertical sections, that shall traverse the two
layers of cuticle and the intermediate cellular parenchyma; por-
tions of such sections are shown in Figs. 184, 186, and 187. In
close apposition with the cells of the upper cuticle (Fig. 186, 4,
a), which may or may not be perforated with stomata (¢, ¢, d, 4),
wefind a layer of soft thin-walled cells, containing a large quantity
of chlorophyll; these cells usually press so closely against one
another, that their sides become mutually flattened, and no
spaces are left, save where there isa definite air-chamber into
which the stoma opens (Fig. 184, L); and the compactness of

INTERNAL STRUCTURE OF LEAVES. 393

this superficial layer is well seen, when, as often happens, it ad-
heres so closely to the cuticle, as to be carried away with this
when it is torn away (Fig.
185, ¢, ‘) Beneath this first
layer of leaf-cells, there are
usually several others, rather
less compactly arranged; and
the tissue gradually becomes
more and more lax, its cells
not being in close apposition,
and large intercellular pas-
sages being left amongst
them, until we reach the Vertical section of the Cuticle, and of a portion
lower cuticle, which the par- of the subjacent parenchyma, of a Leaf of Iris
enichyma only touches at cer Son i's ea tie
fee a, Bos BE ela We occa Uae Salas
(Fig. 182, d, d), wi th args - Ba a ed a to the stomata ;
interspaces, into which the

stomata open. It is to this arrangement that the darker
shade of eae almost invariably prewaured by the superior
surfaces of leaves, is principally due; the color of the compo-
nent cells of the parenchyma not being deeper in one part of
the leaf than in another. In ,those plants, however, whose
leaves are erect instead of being horizontal, so that their two
surfaces are equally exposed to light, the parenchyma is arranged
on both sides in the same manner, and their cuticles are fur-
nished with an equal number of stomata. This is the case, for
example, with the leaves of the common Garden Iris (Fig. 187) ;
of which, ‘moreover, we find a central portion (d, d) formed by

Fia. 187.

Portion‘of a vertical longitudinal section of the leaf of Jris, extending from one of its flattened
sides to the other :—a,a, elongated cells of the epidermis; 6, b, stomata cut through longitudinally ;
¢, c, green cells of the parenchyma; d,d, colorless tissue, occupying the interior of the leaf.

thick-walled colorless tissue, very different either from ordinary
leaf-cells or from woody fibre. The explanation of its presence
is probably to be found in the peculiar conformation of the
leaves; for if we pull one of them from its origin, we shall find
that what appears to be the flat expanded blade really exposes
but half its surface; the blade being doubled together longitu-

894. STRUCTURE OF PHANEROGAMIC PLANTS,

dinally, so that what may be considered its under surface ig
entirely concealed. The two halves are adherent together at
their upper part; but at their lower they are commonly separated
by a new leaf, which comes up between them; and it is from
this arrangement, which resembles the position of the legs of a
man on horseback, that the leaves of the Iris tribe are said to be
equitant. Now by tracing the middle layer of colorless cells,
d, d, down to that lower portion of the leat, where its two halves
diverge from one another, we find that it there becomes continv-
ous with the cuticle, to the cells of which (Fig. 185, a) these
bear a strong resemblance, in every respect save the greater pro-
portion of their breadth to their length. Another interesting
variety in leaf-structure is presented by the Water-Lily, and
other plants whose leaves float on the surface ; for here the usual
arrangement is entirely reversed, the closely-set layers of green
leaf-cells being found in contact with the lower surface, whilst
all the upper part of the leaf is occupied by a loose spongy
parenchyma, containing a very large number of air-spaces that
give buoyancy to the leaf; and these spaces communicate with
the external air through the numerous stomata, which, contrary
to the general rule (§ 248), are here found in the upper cuticle
alone.

250. The examination of the foregoing structures is attended
with very little difficulty. Many cuticles may be torn off, by
the exercise of a little dexterity, from the surfaces of the leaves
they invest, without any preparation ; this is especially the case
with Monocotyledonous plants, the “‘ veins” of whose leaves run
parallel, and with such Dicotyledons as have very little woody
structure in their leaves; in those, on the other hand, whose
leaves are furnished with reticulated veins, to which the cuticle
adheres (as is the case in by far the larger proportion), this can
only be detached by first macerating the leaf for a few days in
water; and if the texture of the cuticle should be particularly
firm, the addition of a few drops of nitric acid to the water will
render them more easily separable. If it be desired to preserve
them, they may be advantageously mounted in weak spirit.
Very good sections of most leaves may be made by a sharp knife,
handled by a careful manipulator; but it is generally preferable
to use Valentin’s knife (§ 106) or the section instrument (§ 107);
taking care in the former case to cut down upon a piece of fine
cork; and in the latter not to crush the leaf between the two
pieces of cork that hold it, and to use very soft cork whenever the
delicacy of the leaf renders this desirable. In order to study the
structure of leaves with the fulness that is needed for scientific
research, numerous sections should be made in different direc-
tions; and slices taken parallel to the surfaces, at different dis-
tances from them, should also be examined. There is no
known liquid, in which such sections can be preserved alto-
gether without change; but water with a small dash of spirit,

STRUCTURE OF PARTS OF FLOWER. 895

seems to answer best, provided the cell be air-tight, and the
specimen fresh.

251. Structure of Flowers.—Many of the smaller Flowers are,
when looked at entire, with a low magnifying power, very
striking Microscopic objects; and the interest of the young in
such observations can scarcely be better excited, than by directing
their attention to the new view they thus acquire of the “‘ compo-
site” nature of the humble down-trodden Daisy, or to the beauty
of the minute blossoms of many of those Umbelliferous plants,
which are commonly regarded only as rank weeds. The scientific
Microscopist, however, looks more to the organization of the
separate parts of the flower ; and among these he finds abundant
sources of gratification, not merely to his love of knowledge,
but also to his taste for the beautiful. The general structure of
the Sepals and Petals which constitute the “perianth” or “floral
envelopes,” closely corresponds with that of leaves; the chief
difference lying in the peculiar changes of hue which the chlo-
rophyll almost invariably undergoes in the latter class of organs,
and very frequently in the former also. There are some petals,
however, whose cells exhibit very interesting peculiarities, either
of form or marking, in addition to their distinctive coloration ;
such are those of the Geranium (Pelargonium), of which a small
portion. is represented in Fig. 188. The different portions of
the petal,—when it has been
dried after stripping it of its Fig, 188.
cuticle, immersed for an hour
or two in oil of turpentine,
and then mounted in Canada
balsam,—exhibit a most beau-
tiful variety of vivid colora-
tion,. which is seen to exist
chiefly in the thickened par-
titions of the cells; whilst
the surface of each cell pre-
sents a very curious opaque
spot with numerous divergin
prolon gations, which looks ag Cells from the Petal of the Geranium (Pelargonium).
if formed by a deposit of
sclerogen upon its interior. This method of preparation, how-
ever, does not give a true idea of the structure of the cells; for
each of them has a peculiar mammillary protuberance, the base
of which is surrounded by hairs; and this it is which gives the
pe appearance to the surface of the petal, and which, when
altered by drying and compression, occasions the peculiar spots
represented in Fig. 188. The real character may be brought
into view by Dr. Inman’s method; which consists in drying the
petal (when stripped of its cuticle) on a slip of glass, to which it
adheres, and then placing on it a little Canada balsam diluted
with turpentine, which is to be boiled for an instant over the

396 STRUCTURE OF PHANEROGAMIC PLANTS.

spirit-lamp, after which it is to be covered with a thin glass. The
boiling “blisters” it, but does not remove the color; and on
examination, many of the cells will be found showing the mam-
milla very distinctly, with a score of hairs surrounding its base,
each of these slightly curved, and pointing towards the apex of
the mammilla. The petal of the common Scarlet Pimpernel
(Anagailis arvensis), that of the common Chickweed (Stellaria
media), together with many others of a small and delicate cha-
racter, are also very beautiful microscopic objects; and the two
just named are peculiarly favorable subjects for the examination
of the spiral vessels in their natural position. For the “veins”
which traverse these petals are entirely made up of spiral vessels,
none of which individually attain any great length; but one
follows or takes the place of another, the conical commencement
of each somewhat overlapping the like termination of its pre-
decessor; and where the veins seem to branch, this does not
happen by the bifurcation of a spiral vessel, but by the “ splicing
on” (so to speak) of one to the side of another, or by the “ splic-
ing on”’ of two new vessels diverging from one another, to the
end of that which formed the principal vein.’

252. The Anthers and Pollen-grains, also, present numerous
objects of great interest, both to the scientific Botanist and to
the amateur Microscopist. In the first place, they afford a good
opportunity of studying that “free” cell-development, which
seems peculiar to the parts concerned in the Reproductive pro-
cess, and which consists in the development of a new cell-wall
round an isolated mass of protoplasm forming part of the contents
of a “ parent-cell;” so that the new cell lies free within its cavity,
instead of being developed in continuity with it, as in the ordi-
nary methods of multiplication (§§ 150, 198). If the Anther be
examined, by thin sections, at an early stage of its development
within the young flower-bud, it will be found to be made up of
ordinary cellular parenchyma, in which no peculiarity anywhere
shows itself; but a gradual “ differentiation” speedily takes place,
consisting in the development of a set of very large cells in two
vertical rows, which occupy the place of the loculi or pollen-
chambers that afterwards present themselves; and these cells
give origin to the pollen-grains, whilst the ordinary parenchyma
remains to form the walls of the pollen-chambers. The first
change consists in the multiplication of the cells of the primary
row, by cell-division, in correspondence with the general increase
in the size of the anther; until at length they form masses of
considerable size, composed of large squarish cells, filled with
granular contents, well defined as constituting a distinct tissue
from the walls of the pollen-chambers. The history of the de-
velopment of the pollen-grains in their interior is thus described
by Mr. Henfrey, who has made a special study of it. ‘The con-

1 See Mr. R. H. Solly’s description and figure of the petal of the Anagallis, in “ Trans.
of Society of Arts,” vol. xlviii.

ANTHER-CELLS—POLLEN-GRAINS. 397

tents of each of these cells secrete a layer of cellulose, which does
not adhere to the wall of the parent-cell to form a layer of secon-
dary deposit, but lies free against it, so that a new free cell is
formed within each old one, nearly filling it. The walls of the
old cells then dissolve, so that the free cells become free, no
longer in their parent-cells, but in a cavity which is to constitute
the pollen-chamber or loculus of the anther. These free cells are
the ‘ parent-cells of the pollen’ of authors. A new phenomenon
soon occurs in these. These parent-cells divide into four by or-
dinary cell-division ; either by one or two successive partings, by
septa at right angles to each other, but both perpendicular to an
imaginary axis (as when an orange is quartered); or by simulta-
neously formed septa, which cut off portions in such a manner,
that the new cells stand in the position of cannon-balls piled into
a pyramid (tetrahedrally). These new cells are the ‘special parent-
cells of the pollen ;’ and in each of these the entire protoplasmic
contents secrete a series of layers, which, in the ordinary course,
by the solution of the primary walls of the special parent-cells
upon which they were applied, become the walls of free cells,
which constitute the simple ordinary pollen-cells. These subse-
quently increase in size, and their outer coat assumes its charac-
teristic form and appearance, while free in the chamber of the
anther.’"' This history bears a very close parallel with that of
the development of the spores within the ‘theca’ of the Mosses
(§ 217); and it is not a little curious that the layer of cells which
lines the pollen-chambers, should exhibit, in a considerable pro-
portion of plants, a strong resemblance in structure, though not
in form, to the elaters of the Marchantia (Fig. 182). For they
have in their interior a fibrous deposit; which sometimes forms
a continuous spiral (like that in Fig. 157), as in Narcissus and
Hyoscyamus ; but is often broken up, as it were, into rings, as in
the Iris and Hyacinth; in many instances, forms an irregular
network, as in the Violet and Saxifrage; in other cases, again,
forms a set of interrupted arches, the fibres being deficient on
one side, as in the yellow Water-lily, Bryony, Primrose, &c. ;:
whilst a very peculiar stellate aspect is often given to these cells,
by the convergence of the interrupted fibres towards one point
of the cell-wall, as in the Cactus, Geranium, Madder, and many
other well-known plants. Various intermediate modifications.
exist ; and the particular form presented, often varies in different
parts of the wall of one and the same anther. It seems probable
that, as in Hepaticee, the elasticity of these spiral cells may have
some share in the opening of the pollen-chambers and the dis-
persion of the pollen-grains.

253. The form Of the Pollen-grains seems to depend in part
upon the mode of division of the cavity of the parent-cell into
quarters ; generally speaking it approaches the spheroidal, but
it is sometimes elliptical, and sometimes tetrahedral. It varies

'“ Micrographic Dictionary,” p. 616.

3898 STRUCTURE ‘OF PHANEROGAMIC PLANTS.

more, however, when the pollen is dry, than when it is moist;
for the effect of the imbibition of fluid, which usually takes place
when the pollen is placed in contact with it, is to soften down
angularities, and to bring the cell nearer to the typical sphere.
The pollen-cell (save in a few submerged plants) has a thick
outer coat, surrounding a thin interior wall; and this often
exhibits very curious markings, which seem due to an increased
thickening atsome points, and a thinning away at others. Some-
times these markings give to the surface-layer so close a resem-
blance to a stratum of cells (Fig. 189, B, c, D), that only a very
careful examination can detect the difference. The roughening
of the surface by spines or knobby protuberances, as shown at 4,
is a very common feature ; and this seems to answer the purpose
of enabling the pollen-grains more readily to hold to the surface
whereon they may be cast. Besides these and other inequalities
of the surface, most pollen-grains have what appear to be pores
or slits in the outer coat, varying in number in different species,
through which the inner coat protrudes itself, when the bulk of
its contents has been increased by imbibition ; it seems probable,
however, that the outer coat is not absolutely deficient at these
points, but is only thinned away. Sometimes the pores are
covered by little disk-like pieces, or lids, which fall off when the
pollen-tube is protruded. This action takes place naturally, when
the pollen-grains fall upon the surface of the “stigma,” which is
moistened with a viscid secretion; and the pollen-tubes, at first
mere protrusions of the inner
Fra. 189. coat of their cell, insinuat-
ing themselves between the
loosely packed cells of the
stigma, grow downwards
through the “style,” some-
times even to the length of
several inches, until they
‘reach the ovarium. The first
change,—namely, the pro-
trusion of the inner mem-
brane through the pores of
the exterior,—may be made
to take place artificially, by
moistening the pollen with
water, thin syrup, or dilute
acids (different kinds of pol-
Pollen grains Bi=a, duiea yong: hy Ome len-grains requiring 2, ditfer-
Se MASS Sen eee ent made of treatment); but
_ the subsequent extension by

growth will only take place under the natural conditions.
254. The darker kinds of pollen may be best mounted for the
Microscope in Canada balsam; but this renders the more trans-
parent kinds too faintly distinguishable; and it is better to

STRUCTURE OF OVULES—FERTILIZATION. 899

mount them either dry, or (if they will bear it without rupturing)
in fluid. The most delicate and interesting forms are found, for
the most part, in plants of the Natural families Amarantacee,
Cichoracece, Cucurbitacee, Malvacee, and Passifloree ; others are
furnished also by Convolvolus, Campanula, Enothera, Pelargonium
een, Polygonum, Sedum, and many other Plants. It is
requently preferable to lay down the entire anther with its ad-
herent pollen-grains (where these are of a kind that hold to it),
as an opaque object; this may be done with great advantage in
the case of the common Mallow (Malva sylvestris) or of the Holly-
hock (Althea rosea); the anthers being picked soon after they
have opened, whilst a large proportion of their pollen is yet un-
discharged, and before they have begun to wither, being laid
down as flat as possible between two pieces of smooth blotting-
paper, then subjected to moderate pressure, and finally mounted
upon a black surface. Theyare then, when properly illuminated,
most beautiful objects for the 2 in. objective.

255. The structure and development of the Ovules that are
produced within the ovarium at the base of the pistil, and the
operation in which their fertilization essentially consists, are
subjects of investigation which have a peculiar interest for scien-
tific Botanists, but which,.in consequence of the special difficul-
ties that attend the inquiry, are not commonly regarded as within
the province of amateur Microscopists. The ovule, in its earliest
condition, is, like the anther, a mass of cells, in which no part is
differentiated from the rest; gradually, this body, whieh is
termed the nucleus, is found to be enveloped in one, two, or
three coats, which are formed by the multiplication of cells that
at first constitute merely an annular enlargement at its base;
these coats, however, do not entirely close in around the nucleus,
at the point of which a small aperture always remains, that is
called the mieropyle. In the interior of the nucleus a large cavity
is formed, apparently by the enlargement of one of its cells at the
expense of those which surround it; and this cavity, which is
called the embryo sac, is at first filled only with a liquid proto-
plasm. Some little time before fecundation, however, there are
seen in it a certain number of free cell-nuclei, rarely fewer than
three, and frequently more; around these, free cells of a sphe-
roidal form are developed, which are “ germ-cells,” of which one
only, the embryonal vesicle, is ordinarily destined to be fertilized.
This act is accomplished by the penetration of the pollen-tube,
which, when it has made its way down to the ovarium, enters
the “‘micropyle” of the ovule, and impinges upon the apex of
the “embryo sac,” which it sometimes pushes before it, in such
a manner as to have given origin to the idea that the tube enters
its cavity: no such penetration, however, really exists. By Prof.
Schleiden, and his disciple Schacht, it is affirmed that the embryo
makes its first appearance within the dilated extremity of the
pollen-tube, which speedily becomes filled with a mass of cells ;

400 STRUCTURE OF PHANEROGAMIC PLANTS.

but nearly all other Vegetable Physiologists who have examined
the question with sufficient care, have come to a different con-
clusion,—namely, that the embryo is the product of a cell-multi-
plication within the “embryonal vesicle,” which seems to be
fertilized by the transudation of the contents of the pollen-tube,
just as the embryonal vesicle within the archegonium of the
Ferns is fertilized by the contact of the antherozoids (§ 219).

256. The early processes of development, too, correspond
closely with those which have been described as taking place
through the whole of the inferior tribes; for the primordial cell
that is formed within the embryonal vesicle as the result of its
fecundation, gives origin by transverse fission to a pair; this
again, to four; and so on, it being usually in the terminal cell of
the filament so generated, that the process of multiplication
chiefly takes place, as in the Conferve (§ 198). The filament
then begins to enlarge at its lower extremity, where its cells are
often multiplied into a somewhat globular mass; of this mass,
by far the larger proportion is destined to be evolved into the
“cotyledons,’”’ or seed-leaves, whose function is limited to the
earliest part of the life of the young plant; the small remainder
is the rudiment of the “plumula,” which is to be developed within
the stem and leaves; while the prolonged extremity of the em-
bryonic filament, which is directed towards the micropyle, is the
original of the “radicle” or embryonic root. The mucilaginous
protoplasm filling the “embryo sac,” in which the “embryonal
vesicle’ was imbedded, becomes converted, by the formation of
free cells, soon after fecundation, into a loose cellular tissue,
which constitutes what is known as the ‘‘ endosperm,” this, how-
ever, usually deliquesces again, as the embryonic mass increases
in bulk and presses upon it; and its development is of interest,
chiefly because it may be shown, by the curious intermediate
phase presented by the Lycopodiacew and Conifere (§ 221), that
this endosperm is the equivalent of the “ prothallium” of the
higher Cryptogamia.'

257. In tracing the origin and early history of the Ovule, very
thin sections should be made through the flower-bud, both verti-
cally and transversely ; but when the ovule is large and distinct
enough to be separately examined, it should be placed on the
thumb-nail of the left hand, and very thin sections made with a
sharp razor; the ovule should not be allowed to dry up, and the
sections should be rernoved from the blade of the razor by a
wetted camel-hair pencil. The tracing downwards the pollen-
tubes through the tissue of the style, may be accomplished by

“1 For a more detailed account of the Generative process in ordinary Phanerogamia
and in Conifers, as well as for references to the principal original sources of informa-
tion on this controverted question, the Author may be permitted to refer to his “ Prin-
ciples of Comparative Physiology,” 4th Ed. $§ 501-505. Some recent discussion on
the same subject will be found in the “ Ann. des Sci. Nat.” 4itme Sér. tom. iii, p. 188
et seq.

MICROSCOPIC EXAMINATION OF OVULE 401

sections (which, however, will seldom follow one tube continu-
ously for any great part of its length), or, in some instances, by
careful dissection with needles. Plants of the Orchis tribe are
the most favorable subjects for this kind of investigation, which
is best carried on by artificially applying the pollen to the stigma
of several flowers, and then examining one or more of the styles
daily. “If the style of the flower of an Epipactis (says Schacht),
to which the pollen has been applied about eight days previously,
be examined in the manner above mentioned, the observer will
be surprised at the extraordinary number of pollen-tubes, and
he will easily be able to trace them in large strings, even as far
as the ovules. Viola tricolor (heartsease) and Ribes nigrum and
rubrum (black and red currant) are also good plants for the pur-
pose; in the case of the former plant, withered flowers may be
taken, and branched pollen-tubes will not unfrequently be met
with.” The entrance of the pollen-tube into the micropyle may
be most easily observed in Orchideous plants and in Huphrasia ;
it being only necessary to tear open with a needle the ovary of a
flower which is just withering, and to detach from the placenta
the ovules, almost every one of which will be found to have a
pollen-tube sticking in its micropyle. These ovules, however,
are too small to allow of sections being made, whereby the origin
of the embryo may be discerned; and-for this purpose, 4/nothera
(evening primrose) has been had recourse to by Hoffmeister,
whilst Schacht recommends Lathrea squamaria, Pedicularis pa-
lustris, and particularly Pedicularis sylvatica. There is no kind
of investigation that requires nicer management, and none which
is just now of greater interest to Botanists. Such Microscopists,
therefore, as have qualified themselves for the inquiry, by their
acquirement of the knowledge which is requisite to guide their
dissections, and of the manipulative skill by which alone these
dissections can be successfully made, cannot do a greater service
to science, than by applying themselves perseveringly to it. The
use of high magnifying powers is not at all needed. Much may
be done, in the preparation of the objects, under the Simple
microscope ; and for the examination of the preparations, a power
of 200 diameters with a shallow eye-piece is generally sufficient.
The assistance of the Binocular Microscope would probably be
found peculiarly valuable in this inquiry; since the right inter-
pretation of the appearances presented, mainly depends upon a
precise knowledge of the exact relative position of the pollen-
tube, embryo sac, &c., such as this instrument is peculiarly fitted
to convey.

258. We have now, in the last place, to notice the chief points
of interest to the Microscopist, which are furnished by mature
Seeds. Many of the smaller kinds of these bodies are very curi-
ous, and some are very beautiful, objects, when looked at in their
natural state, under a low magnifying power. Thus the seed of

26

402 STRUCTURE OF PHANEROGAMIC PLANTS.

the Poppy (Fig. 190, a) presents a regular reticulation upon its
surface, pits, for the most

eee part hexagonal, being left

between projecting walls;
that of Caryophyllum (D) is
regularly covered with
curiously jagged divisions,
every one of which has a
small bright black hemi-
spherical knob in its mid-
dle; that of Amaranthus
hypochondriacus has its sur-
face traced with extremely
delicate markings (B); that
of Antirrhinum (?) is
strangely irregular in shape
(c), and looks almost like
a piece of furnace-slag; and
Seeds, as seen under a low magnifying power:—a, that of Bignonia (£) is re-
Poppy ; B, Amaranthus (Prince’s feather); ¢, AnITeR em, markable for the beautiful
ee aaa D, Caryophyllum (Clove-pink); &, structure of the translucent
membrane which _ sur-

rounds it, the radiating lines shown in the figure being found
under a higher magnifying power to consist of rows of elongated
spiral cells. Such are seen, too, in the like delicate membrane
that surrounds several other seeds, as those of Sphenogyne speciosa
and Lophospermum erubescens, which, from possessing this ap-
pendage, are spoken of as ‘“winged.’’ The most remarkable
development of this structure is said by Mr. Quekett to exist in
a seed of Calosanthes Indica, an East Indian plant, in which the
wing extends more than an inch on either side of the seed.
Some seeds are distinguished by a peculiarity of form, which,
although readily discernible by the naked eye, becomes much
more striking when they are viewed under a very low magnify-
ing power; this is the case, for example, with the seeds of the
Carrot, whose long radiating processes make it bear, under the
Microscope, no trifling resemblance to some kinds of star-fish ;
and with those of Cyanthus minor, which bear about the same
degree of resemblance to shaving-brushes. In addition to the
preceding, the following may be mentioned as seeds easily to be
obtained, and as worth mounting for opaque objects :—Anagaillis,
Anethum graveolens, Antirrhinum, Begonia, Carum carui, Coriopsis
tinctoria, Datura, Delphinium, Digitalis, Elatine, Erica, Gentiani,
Gesnera, Hyoscyamus, Hypericum, Lepidium, Limnocharis, Linaria,
Lychnis, Mesembryanthemum, Nicotiana, Orobanche, Petunia, Re-
seda, Saxifraga, Scrophularia, Sedum, Sempervivum, Silene, Stel-
laria, and Verbena. The following may be mounted as trans-
parent objects in Canada balsam :—Drosera, Hydrangea, Mono-

MICROSCOPIC STRUCTURE OF SEEDS. 4038

tropa, Orchis, Parnassia, Pyrola, Saxifraga.! The seeds of Um-
belliferous plants generally are remarkable for the peculiar vitte,
or receptacles for essential oil, which are found in their coats.
Various points of interest respecting the structure of the teste or
envelopes of seeds,—such as the fibre-cells of Cobwa and Collomia,
the stellate cells of the Star-Anise, and the densely consolidated
tissue of the “shells” of the Coquilla-nut, Cocoa-nut; &c.,—having
been already noticed, we cannot here stop todo more than advert -
to the peculiarity of the constitution of the “husk” of the Corn-
grains. In these, as in other Grasses, the ovary itself continues
to envelope the seed, forming a covering to it, that surrounds its
own testa; this covering (which forms the “bran’’ that is de-
tached in grinding) is composed of hexagonal cells of remarkable
regularity and density; and these are so little altered by a high
temperature, as still to be readily distinguishable when the grain
has been ground after roasting,—thus enabling the Microscopist
to detect even a very small admixture of roasted Corn with Coffee
or chicory, without the least difficulty.’

1 These lists have been chiefly derived from the “ Micrographie Dictionary,” p. 572.

2In a case in which the Author was called upon to make such an investigation,
he found as many as thirly distinctly recognizable fragments of this cellular envelope,
in a single grain of a mixture consisting of Chicory with only 5 per cent. of roasted
Corn,

CHAPTER IX.
MICROSCOPIC FORMS OF ANIMAL LIFE:—PROTOZOA; ANIMALCULES.

259. Protozoa.—Passing on, now, to the Animal Kingdom, we
begin by directing our attention to those minute and simple
forms, which correspond, in the Animal series, with the Proto-
phyta in the Vegetable (Chap. VI); and this is the more desira-
ble, since the formation of a distinct group, to which the name
of Protozoa (first proposed by Siebold) may be appropriately
given, is not merely one of the most interesting results of recent
Microscopie inquiry, but is a subject on which it is particularly
important that the Microscopic observer should know what the
Physiologist believes himself to have ascertained. This group,
which must be placed at the very base of the animal scale,
beneath the great subkingdoms marked out by Cuvier, is charac-
terized by the extreme simplicity that prevails in the structure
of the beings composing it; these being either isolated cells, or
aggregations of cells wherein no such differentiation of parts
exhibits itself, as constitutes the ‘“ organs’ of even the simplest
Zoophyte or Worm. We have in the first place to consider,
therefore, what are the essential characters of the Animal cell;
and what are the precise relations of the Protozoa to the Proto-
phyta, to which they seem to bear so close an affinity.

260. The Animal cell, in its most complete form, is compara-
ble in most parts of its structure to that of the Plant; but differs
from it in the entire absence of the “ cellulose-wall,” or of any-
thing that represents it, the cell contents being enclosed in only
a single limitary membrane, the chemical composition of which
(being albuminous) indicates its correspondence with the primor-
dial utricle (§ 147). In its young state, it seems always to con-
tain a semi-fluid plasma, which is essentially the same as the
“protoplasm” of the Plant, save that it does not include chloro-
phyll-granules ; and this may either continue to occupy its cavity
(which is the case in cells whose entire energy is directed to
growth and multiplication), or may give place, either wholly or
in part, to the special product which it may be the function of
the cell to prepare. Like the Vegetable cell, that of Animals
very commonly multiplies by duplicative subdivision; and it
also (especially among Protozoa) may give origin to new cells,

PROTOZOA—AM@BA., 405

by the breaking up of its contents into several particles; but
new cells are not unfrequently to be met with, especially in the
nutritive fluids of such Animals as possess a distinct circulation,
which have not directly originated in either of these modes from
a previously existing cell, but which have been developed by a
process of free cell-formation, namely, by the aggregation of
organic molecules, floating in these fluids, into little masses, of
which the external particles coalesce into a membranous cell-
wall, whilst the interior liquefy into cell-contents. This can
only take place, however, in a liquid which has undergone ela-
boration in the interior of a highly-organized living’body; and
we find no traces of such free cell-formation among the members
of the group we are first to investigate.

261. As we have seen (§ 150) that, among the lowest Proto-
phytes, the general attributes of a cell may exist in a minute
mass of protoplasm which is not bounded by a limitary mem-
brane,—the differentiation between cell-wall and cell-contents
not having yet manifested itself,—so, among the lowest Protozoa,
we find the power of maintaining an independent existence to
be possessed by similar particles of that peculiar blastema, or
formative substance, to which the name of sarcode has been
given by Dujardin (who first drew attention to its extraordinary
endowments), and which may be considered as the basis, not
merely of the entire organisms of Protozoa, but of a large part
of that of higher animals. The properties of this may be most
fully understood by the careful study of a creature, which is by
no means unfrequently to be met with in: fresh and stagnant
waters, vegetable infusions, &., and which, from the great
variety of forms it assumes, has received the designation of Pro-

Fie. 191,

Ameba princeps, in different forms, a, 8, v.

teus. This name, however, having been assigned to an animal
of far higher organization, that with which we are now con-
cerned is properly known as the Ameba (Fig. 191). It may be

406 MICROSCOPIC FORMS OF ANIMAL LIFE.

described as a minute mass of “‘sarcode,” presenting scarcely
any evidence of distinct organization, even of the simplest kind;
for, as in the lowest forms of Vegetable cell (§ 148), there is not
even a complete differentiation between the cell-wall and the
cell-contents; the former not being composed of a distinct
membrane, though obviously possessing more consistence than
the latter, which are semi-fluid. A contractile vesicle (or rather,
perhaps, a “‘ vacuole’) may be observed in some part of the body,
which pulsates at tolerably regular intervals; and ‘vacuoles’ or
clear spaces are seen, surrounding the alimentary particles which
have been ‘received into the midst of the jelly-like substance.
However inert and shapeless this minute body may be when
first noticed, its possession of vital activity is soon made appa-
rent by the movements which it executes, and by the changes of
form which it undergoes; these being, in fact, part of one and
the same set of actions. For the shapeless mass puts forth one
or more finger-like prolongations, which are simply extensions
of its gelatinous substance in those particular directions; and a
continuation of the same action, first distending the prolonga-
tion, and then (as it were) carrying the whole body into it, causes
the entire mass to change its place. After a short time another
prolongation is put forth, either in the same or in some different
direction ; and the body is again absorbed into it. These changes
seem to be connected with a movement of the semi-fluid particles
in the interior of the mass, of which a current may be observed
to “set” in the direction wherein the protrusion is about to take
place, before the surface shows any projection. When the
creature, in the course of its progress, meets with a particle
capable of affording it nutriment, its gelatinous body spreads
itself over or around this, so as to envelope it completely; and
the substance (sometimes animal, sometimes vegetable) thus
taken into this extemporized stomach, undergoes a sort of diges-
tion there, the nutrient material being extracted, and any indigesti-
ble part making its way to the surface and finally being (as it were)
squeezed out. Of the mode of reproduction of Ameba, nothing is
yet known, save that it undergoes multiplication by self-division,
very much in the manner of the Protophytes, and that portions
separated from the jelly-like mass, either by cutting or tearing,
can develope themselves into independent beings. Consequently,
as we are quite in the dark respecting the sexual operation,
which (as all analogy would lead us to believe) must take. place
at some period of its life, it cannot be said that we are
acquainted with more than one phase of its existence; and it is
quite possible that, after many repetitions of the process of multi-
plication by self-division, some entirely new form may present
itself, of which the Ameeba is (as it were) the larva. The com-
pletion of the life-history of this curious creature, therefore, is a
most worthy object of Microscopic inquiry; and its abundance
in many situations should prevent this from being a matter of

PROTOZOA—ACTINOPHRYS. 407

any great difficulty to an observer, who can devote sufficient
attention to the study.!

262. Nearly allied to the preceding, is another curious organism,
on which the attention of many eminent Microscopists has been
recently fixed. This creature, the Actinophrys (Fig. 192), con-
sists like the preceding of a homogeneous, jelly-like contractile
substance, or sarcode, not enclosed in any distinct envelope,
though the outer portion seems to be of firmer consistence than
the inner. Throughout the body, which is usually nearly spheri-
eal in form, but more particularly near its surface, there are ob-
served vacuoles occupied by fluid; these have no definite
boundaries, and may be easily made artificially either to coalesce
into larger ones, or to subdivide into smaller. A “ contractile
vesicle” (0), pulsating rhythmically with great regularity, is
always to be distinguish-
ed either in the midst of Fig. 192.
the jelly-like substance,
or (more commonly),
near its surface; and the
appearance which it pre-
sents in this latter posi-
tion, seems to leave no
doubt of its being in-
cluded within a distinct
though very thin mem-
brane. The “sareode”
extends itself into con-
tractile tentacular fila-
ments, which are called
pseudopodia; and these,
in the Actinophrys sol,
are commonly seen to er beat ot
piston nas doe ee
in such a manner as to aoc ee ai ea oiaed Sens pete
hava suggested the. do. Gasmeeil gartinayt steamy) 5 tame aetonae
signation of the species.

Their degree of extension, however, is extremely variable, and
sometimes they entirely disappear: the creature cannot then be dis-
tinguished with certainty from an Ameeba. For although the form

1 Tt has been recently affirmed by Dr. Hartig, that Amabe@ may be produced by the
transformation of the “ antherozoids” of Chara (§ 202), Marchantia, or Mosses; and
that, in their turn, they become metamorphosed, first into Protococci or other unicellular
Algew, and then into Articulated Alge. But even if jelly like bodies resembling
Amecebe in general appearance and in spontaneous change of form, should be thus pro-
duced, they cannot be said to be true Amebe, unless they should feed in the manner
described above,—which Dr. Hartig does not appear to have witnessed. (See “ Quart.
Journal of Microscopic Science,” vol. iii, p. 51.) However strange Dr. Hartig’s state-
ments may be, they are not more strange than many assertions of the same class first
appeared, which are now admitted as unquestionable truths; and they ought not to be
set aside without disproof, any more than they should be received without further con-
firmation.

408 MICROSCOPIC FORMS OF ANIMAL LIFE

of the latter is generally flattened, yet itsometimes becomes nearly
spherical; so that neither type can be recognized, until the jelly-
like spherule flattens itself out as an Ameeba, or puts forth radi-
ating “pseudopodia” as an Actinophrys. Far less activity is ex-
hibited by Actinophrys, than by Amba; and the slight change
of place which it undergoes from time to time, does not seem at-
tributable either to any change of form of the body, or to any
bending of the tentacles. It is by the agency of these, however,
that its nourishment is obtained ; and this is derived not merely
from vegetable particles, but from various small animals, some
of them (as the young of Crustaceans) possessing great activity,
as well as a comparatively high organization. When any of these
happens to come into contact with one of the tentacular fila-
ments, this usually retains it by adhesion, and forthwith begins
to retract itself; as it shortens, the surrounding filaments also
apply themselves to the captive particle, bending their points
together so as gradually to enclose it, and themselves retracting,
until the prey is brought close to the surface of the body. The
threads of ‘“‘sareode” of which the “pseudopodia” are com-
posed, not being invested (any more than the sarcode of the
body) by any limiting membrane, coalesce with each other and
with it; and thus the particle which has been entrapped by them
becomes actually embedded in the gelatinous mass, and gradually
. passes from the peripheral towards the central part of it, where
its digestible portion undergoes solution, the superficial part of
the body, with its pseudopodial prolongations, in the meantime
recovering their previous condition. Any indigestible portion,
as the shell of a Crustacean, or the hard case of a Rotifer, finds
its way to the surface of the body; and is extruded from it by
a process exactly the converse of that by which it is drawn in
(Fig. 192, p). The number as well as the size of the particles
included by the Actimophrys at any one time is very various;
frequently they are more than ten or twelve. They are not
usually embraced closely by the sarcode, but are surrounded by
fluid in “vacuoles” in its substance; and it was this appearance
which led Prof. Ehrenberg to describe the animalcule as possess-
ing numerous stomachs. The <Aetinophrys, like the Amceba,
multiplies itself by self-division ; but a process which seems to
resemble the “conjugation” of Protophytes (§ 151), has also
been witnessed in it by Prof. Kolliker and Dr. Cohn.t. Two in-
dividuals approximate and coalesce, so as to form what appears
to be a single body; but a “ nucleus” then makes its appearance,
which gradually developes itself into a mass having the charac-
ters of its parent; and the young Actinophrys thus generated
probably escapes. before long from the body within which it

1 It appears probable, from the recent observations of Mr, Weston (Quarterly Journal
of Microsc. Science, Jan 1856), and others, that the supposed “conjugation” of Acti-
nophrys is a mere fusion of two bodies which may separate again unchanged, and is
not a generative phenomenon. The same would appear to be true of it in this respect.
as of Gregarina (§ 358).

COMPARISON OF PROTOZOA AND PROTOPHYTA. 409

originated. As the condition of an Actinophrys undergoing
self-division is to all appearance the same as that of two indivi-
duals in incipient conjugation (Fig. 192, 8), it cannot be deter-
mined in any particular case which operation is in progress,
until the creature has been watched sufficiently long for the ten-
dency of its changes to become apparent. :

263. If, now, we compare the foregoing history with that of
Palmoglewa or any other simple Protophyte, we shall see that
whilst there is a strong analogy between the two sets of pheno-
mena, there are at the same time certain most important dif
ferences. One of the most obvious of these differences, lies in
the movements exhibited by the Amceba and Actinophrys; for
although these are by no means sufficient in themselves (as was
once supposed) to establish the distinction between the Animal
and Vegetable kingdoms, yet, when they do not consist in the
mere vibrations of cilia, such as are executed by zoospores, an-
therozoids, &c., among Plants, but depend upon alterations in a
contractile substance forming the entire body, they bear a much
closer resemblance to the actions of higher Animals; and we
may trace in fact, in the ascending animal scale, a progressive
specialization or setting apart of certain portions of the contrac-
tile substance more peculiarly endowed with this property, until
they take the form of distinct muscular bands. A more positive
and easily defined distinction lies in the nature of the aliment of
the Protophyta and Protozoa respectively, and in the method of
its introduction. For whilst the Protophyte obtains the materials
of its nutrition from the air and moisture that surround it, and
possesses the power of detaching oxygen, hydrogen, carbon, and
nitrogen, from their previous binary combinations, and of uniting
them into ternary, and quaternary organic compounds (chloro-
phyll, starch, albumen, &c.), the simplest Protozoon, in common
with the highest members of the Animal kingdom, seems utterly
destitute of any such power, and is dependent for its support
upon organic substances previously elaborated by other beings.
But further, the Protophyte obtains its nutriment by mere ab-
sorption of liquid and gaseous molecules, which penetrate by
simple imbibition ; whilst the Protozoon, though destitute of any
proper stomach, makes (so to speak) a stomach for itself in the
substance of its body, into which it ingests the solid particles
that constitute its food, and within which it subjects them to a
regular process of digestion. Hence these simplest members of
the two kingdoms, which can scarcely be distinguished from each
other by any structural characters, seem to be physiologically sepa-
rable by the mode in which they perform those actions wherein
their life most essentially consists; for the Protococeus-cell de-
composes carbonic acid under the influence of light, and gene-
rates chlorophyll and proteine compounds, in a manner in all
respects comparable to that in which the same operation is per-
formed by the leaf-cells of the most perfect Plant; whilst the

410 MICROSCOPIC FORMS OF ANIMAL LIFE.

Ameba ingests and digests both Vegetable and Animal food,
and applies it to the nutrition of its body, no less effectively than
an Animal possessing the most complex digestive and circulating
apparatus. And in the present state of our knowledge, we seem
justified in laying it down as the most ready and certain dif-
ferential character we are acquainted with, between the most
closely related Protophyta and Protozoa, that the former (with
the exception of the Fungi) decompose carbonic acid under the
influence of light, and acquire a red or green color from the new
compounds which they form in their interior; whilst the latter,
having no such power,' receive animal and vegetable organisms,
or particles of such, into the interior of their bodies, where they
extract from them the ready prepared nutriment they are fitted
to yield.

364, Rhizopoda.—The two creatures above described as the
types of the simplest form of Protozoic life, are not now regarded
as Infusory Animalcules, among which they were ranked by Prof.
Ehrenberg ; but are considered as the types of a distinct subdi-
vision, to which the name of RAdzopoda has been assigned by M.
Dujardin; this name very appropriately representing the leading
feature in their organization, which consists i the extension of
their sarcode-body into long root-like processes, whereby their
aliment is drawn into its substance. In by far the larger propor-
tion of the animals included in this group, a carapace or shell is
formed, either by the consolidation of the superficial layer of the
sarcode-body through impregnation of its substance with mineral
matter, or (as appears to be the case in some instances) by the
agglutination of particles of sand, &e., with a viscid secretion
exuded from its surface. This “carapace,” in Areedla (Fig. 198,
c, D), has for its basis a layer of dense membrane, which seems
analogous to the firm envelope of the Desmidiacee (§ 164), and
to that which constitutes the basis of the “lorica’” of Diatomacese
(§ 172); and in some species it sends out spinous prolongations
like those of the former; whilst in others its surface exhibits
symmetrical markings that resemble those of the latter. Its ma-
terial differs, however, from that of the cellulose wall of Vegetable
cells, as may be shown by the effects of reagents; and seems to
be rather a modification of horny matter, probably resembling
the chitine which gives solidity to the integuments of Insects.
Not unfrequently it contains particles of sand, minute Diatoms,
&e., imbedded in its substance. The Difflugia (Fig. 193, a, B)
differs in no essential particular from Arcella, save in the form
of its carapace, which is pitcher-shaped, instead of being shield-
like or dish-shaped. In the one case, as in the other, the cara-
pace has but a narrow opening, through which alone can the
“pseudopodia” be projected. The general nature of these ani-

' Many instances have been cited, of Animalcules acquiring a green color by the de-
composition of carbonic acid under the influence of light; but there can be no doubt in

the mind of any one who is familiar with the results of recent microscopic research,
that in all these cases, the supposed Animalcules were really Protophytes.

INFUSORY ANIMALCULES. ‘411

mals seems to be exactly the same as that of Amceba and Actino-
phrys; and their mode of nutrition differs only in this, that their
food can only be drawn into that part of the body which is un-
protected by the carapace. Nothing positive is yet known as to
their Reproduction. Two individuals may not unfrequently be
seen with the apertures of their shells in contact with each other,
the pseudopodial prolongations being apparently common to

Fia. 193.

Various torms of Simple Rhizopods:—a, Difflugia proteiformis: 8, Diflugia oblonga: c, Arcella
acuminata: D, Arcella dentata.

both ; but whether these are in the act of conjugation, or whether
(as the younger aspect of one of the shells sometimes indicates)
the union résults from the production of a bud not yet separated,
cannot yet be certainly affirmed. The most remarkable deve-
lopment of this type of organization presents itself among the
marine Foraminifera and Sponges ; in which composite structures,
often of very large size, are developed by continuous gemmation,
and a complex skeleton is produced. These, not being in them-
selves (for the most part at least) microscopic organisms, will be
more fitly considered under a separate head (Chap. X).

265. Animaleules.—Dismissing the Rhizopods for the present,
we have now to apply ourselves to the special subject of this
chapter; namely, the assemblage of minute forms of Animal
life, which are commonly known under the designation of Ani-
malcules. Nothing can be more vague or inappropriate than
this title, since it only expresses the small dimensions of the
beings to which it is applied, and does not indicate any of their:
characteristic peculiarities: In the infancy of Microscopic
knowledge, it was natural to associate together all those creatures:
which could only be discerned at all under a high magnifying
power, and whose internal structure could not be. clearly made
out with the instruments then in use; and thus the most hetero-
geneous assemblage of Plants, Zoophytes, minute Crustaceans
(water-fleas, &c.), larvee of Worms and Mollusks, &c., came to be
aggregated with the true Animalcules under this head. The
class was being gradually limited by the removal of all such
forms as could be referred to others; but still very little was
known of the real nature of those that remained in it, until the
study was taken up by Prof. Ehrenberg, with the advantage of
instruments which had derived new and vastly improved capa-
Vilities from the application of the principle of Achromatism

412 MICROSCOPIC FORMS OF ANIMAL LIFE.

(p. 48). One of the first and most important results of his study,
and that which has most firmly maintained its ground notwith-
standing the weakening of Prof. Ehrenberg’s authority in other
respects, was the separation of the entire assemblage into two
distinct groups, having scarcely any feature in common except-
ing their minute size, one being of very low, and the other of com-
paratively hégh organization. On the lower group he conferred
thedesignation of Polygastrica (many-stomached), in conse-
quence of having been led to form an idea of their organization,
which the united voice of the most trustworthy observers now
pronounces to be erroneous; and he not only assigned to them
a complex digestive apparatus, but considered them to be en-
dowed with genital organs, nervous ganglia, and organs of
special sense, for none of which can any adequate basis be found
in the appearances that the Microscope brings into view within
their bodies. Hence it seems desirable to abandon the term
“ Polygastrica,” as conveying an erroneous idea of the structure
of these beings; and we may appropriately fall back on the
name Infusoria, or Infusory Animalcules, which simply expresses
their almost universal prevalence in infusions of organic matter.
For although this was applied by the older writers to the higher
group as well as to the lower, yet as these are now distinguished
by an appropriate appellation of their own, and are, moreover,
not found in infusions when in that state of rapid decomposition
which is most favorable to the presence of the inferior kind of
Animalcules, it may very well be withdrawn from them, and be
restricted to the Polygastrica of Ehrenberg, which is the sense
wherein it has been used by many recent writers. To the higher
group, Prof. Ehrenberg’s name fotifera or Rotatorta is on the
whole very appropriate, as significant of that peculiar arrange-
ment of their cilia upon the anterior parts of their bodies, which
in some of their most common forms, gives the appearance
(when the cilia are in action) of wheels in revolution; the group,
however, includes many members, in which the ciliated lobes
are so formed as not to bear the least resemblance to wheels.
In their general organization, these ‘‘ Wheel-animalcules” must
certainly be considered as members of the Articulated division
of the Animal Kingdom; and they seem to constitute a class in
that lower portion of it, to which the designation Worms is now
commonly given. Notwithstanding this wide zoological separa-
tion between the two kinds of Animalcules, it seems most
suitable to the plan of the present work, to treat of them in con-
nection with one another; since the Microscopist continually
finds them associated together, and almost necessarily ranges
them in his own mind under one and the same category.

266. Infusoria.—This term, as now limited by the separation
of the Rotifera, is applied to a far smaller range of forms than
that which was included by Prof. Ehrenberg under the name of
“nolygastric” animalcules. For a large section of these, in-

INFUSORIA, THEIR CONSOLIDATION. 413

cluding the Desmidiacee, Diatomacece, Volvocinew, and many other
Protophytes, have been transferred by the almost concurrent
voice of those Naturalists whose judgment is most to be relied
on, to the Vegetable Kingdom. The Rhizopod group, again,
must be excluded, as being very distinct in its plan of organiza-
tion from the true Infusoria. And, lastly, it is not improbable
that many of the reputed Infusoria may be but larval forms of
some higher organisms, instead of being themselves complete
animals.’ Still an extensive group remains, of which no other
account can at present be given, than that the beings of which it
is composed go through the whole of their lives, so far as we are
acquainted with them, in the condition of isolated cells; differing
from Vegetable cells on the one hand, and from Rhizopods on
the other, in this remarkable particular,—that the alimentary
particles by which they are nourished are taken into their cavity
through a distinct oral aperture, some of them also having an
anal orifice for the ejection of indigestible matters. It has been
imagined by Prof. Ehrenberg, that a distinct alimentary canal
exists; sometimes returning upon itself (as in Vorticella), some-
times proceeding straight from one extremity of the body to the
other (as in Hnchelis), and sometimes passing round and round
in a spiral (as in Leucophrys), having a number of flask-shaped
stomachs connected with it, into which the alimentary particles
find their way, and in which they undergo digestion. But as he
made the like assertions with regard to beings that have been
since undoubtedly proved to belong to the Vegetable Kingdom,
their authority must be explicitly denied; and all the best ob-
servers of the present time would agree (the Author believes) in
the following general account of the organization of Infusoria.
267. Their bodies consist of “sarcode,” of which the outer
layer possesses considerably more consistence than the internal
portion ; the process of differentiation having here advanced sufi-
ciently far to establish a clear distinction between the wail and
its contents. Sometimes, as in Paramecium, a distinct pellicle
may be recognized on the surface of the proper coat of the body;
and this, which is studded with regularly arranged markings
like those of Diatomaces, seems to be the representative of the
carapace of Arcella, &e. (§ 264), as of the cellulose coat of Proto-
phytes. The form of the body is usually much more definite
than that of Ameba or Actinophrys; each species having its
characteristic shape, which is only departed from, for the most
part, when the animalcule is subjected to pressure from without,

1 Professor Agassiz, indeed, goes so far as to assert (“ Ann. of Nat. Hist.” vol. ii, 1850
p. 157) that, as he has satisfied himself by direct observation, Bursaria, Paramecium,
and other Animaleules which are commonly accounted as types of this group, are germs
of fresh-water worms, some of which he has seen hatched from eggs of Planarie. No
confirmation has yet been given to this statement by other observers; and until details
of these observations shall have been published, it cannot be expected that Zoologists
should acquiesce in the entire demolition of this class, which Prof. Agassiz thinks him-
self warranted by them in proposing.

414 MICROSCOPIC FORMS OF ANIMAL LIFE.

or when its cavity has been distended by the ingestion of any
substance above the ordinary size. The body does not seem to
possess much contractile power in its own substance, its move-
ments being principally executed by the instrumentality of loco-
motive appendages; one remarkable instance of contractility,
however, is presented by the stalk of Vorticella (§ 268). The
locomotive appendages, which may all be considered as prolon-
gations of the tegumentary layer, are destitute of any more
minute organization, being, in fact, of the nature of cilia, though
sometimes of much larger dimensions, and employed in a dif
ferent manner. The vibration of ciliary filaments, which are
either disposed along the entire margin of the body, as well as
around the oral aperture (Figs. 194, 195), or are limited to some
one part of it, this being always in the immediate vicinity of the

Fig. 194, Fie. 195.

Fig. 194. Kerona silurus:—a, contractile cavity; 5, mouth; ¢, ¢, animaleules swallowed by the
Kerona, after having themselves ingested particles of indigo.
Fig. 195. Paramecium caudatum :—a, a, contractile cavities; 6, mouth.

mouth (Fig. 196), is the means by far the most frequently em-
ployed by the beings of this class, both for progression through
the water, and for drawing alimentary particles into the interior
of their bodies. In some their vibration is constant, whilst in
others it is only occasional, thus conveying the impression that
the Animalcule has a voluntary control over them ; but there is
strong reason for questioning the existence of any such self-
directing power. These cilia, like those of the zoospores of
Protophytes, can usually be distinctly seen only when their move-
ment is very much slackened in its,rate, or when it has entirely
ceased. Sometimes, however, instead of a multitude of short
cilia, we find a small number of long slender filaments, usually
proceeding from the anterior part of the body (that nearest the
mouth), and strongly resembling the elongated cilia of Proto-
coccus (Fig. 68, #), or of Volvox (Fig. 70, 1, x, 1). But in other

INFUSORIA, THEIR MOVEMENTS. 415

cases, the filaments are comparatively short, and have a bristle-
like firmness; and instead of being kept in vibration, they are
moved (like the spines of Echini) by the contraction of the sub-
stance to which their bases are attached, in such a manner that
the animaleule crawls by their means over a solid surface, as we
see especially in Trichoda lynceus (Fig. 199, p, a). In Chilodon
and Nassula, the mouth is provided with a circlet of these bristles,
which have received the designation of “teeth ;” their function,
however, is rather that of laying hold of alimentary particles by
their expansion and subsequent drawing together (somewhat
after the fashion of the tentacula of Zoophytes), than of reducing
them by any kind of masticatory process.

268. The modes of movement which Infusory Animalcules
execute by means of these instruments, are extremely varied
and remarkable. Some propel themselves directly forwards,
with a velocity which appears, when thus highly magnified, like
that of an arrow, so that the eye can scarcely follow them, whilst
others drag their bodies slowly along like a leech. Some attach
themselves by one of their long filaments to a fixed point, and
revolve around it with great rapidity, whilst others move by
undulations, leaps, or successive gyrations; in short, there is
scarcely any kind of animal movement which they do not
exhibit. There is no sufficient reason, however, to regard such
actions as indicative of consciousness; indeed, the very fact
that they are performed by the instrumentality of ela seems to
imply the contrary; since we know that ciliary action takes
place to a large extent in our own bodies, without the least
dependence upon our consciousness, and that it is also used as a
means of dispersion amoug the zoospores of the lowest Plants,
which cannot for a moment be supposed to be endowed with this
attribute. We can only regard it, therefore, as indicative of a
wonderful adaptation, on the part of these simple ciliated cells,
to a kind of life which enables them to go in quest of their own
nutriment, and to introduce it, when obtained, into the interior
of their bodies. The curious contraction of the footstalk of the
Vorticella, however, is a movement of a very different nature,
and is due to the contractility of the tissue that occupies the
interior of the tubular pedicle. This stalk serves to attach the
bell-shaped body of the Animalcule to some fixed object, such as
the leaf or stem of duckweed; and when the animal is in search of
food, with its cilia in active vibration, the stalk is fully extended.
If, however, the Animalcule should have drawn to its mouth any
particles too large to be received within it, or should be touched by
any other that happens to be swimming near it, or should be
“jarred” by a smart tap on the stage of the microscope, the stalk
suddenly contracts into a spiral, from which it shortly afterwards
extends itself again into its previous condition. Thecentral cord to
whose contractility this action is due, has been described as muscu-
lar; but it does not possess the characteristic structure of either

416 MICROSCOPIC FORMS OF ANIMAL LIFE.

kind of muscular fibre, and is probably nothing else than a portion
of sarcode specially endowed with this property. Nothing but
the rapidity of its contraction and
Pree: relaxation differentiates it from
the pseudopodia of the Rhizo-
pods. There is no reason what-
ever to believe that these Animal-
cules possess any organs of special
sense. The red spots which may
be seen in many of them, and
which have been designated as eyes
by Prof. Ehrenberg, from their sup-
posed correspondence with the eye-
spots of Rotifera (§ 278), really bear
a much greater resemblance to the
red spots which are so frequently
seen among Protophytes (§ 153).
If they are really endowed with
consciousness, as their movements
seem to indicate, though other con-
siderations render it very doubtful,
a they must derive their perceptions
Group of Vorticella nebulifera. showing of external things from the impres-
4, the ordinary form} 8, the same with the gions made upon their general sur-
stalk contracted; c, the same with the a‘ eee)
bell closed; p. 8, F, successive stages of face, but more particularly upon
fissiparous multiplication. their filamentous appendages.

269. The interior of the body does not always seem to consist
of a simple undivided cavity, occupied by soft “sarcode,;”’ for
the tegumentary layer appears in many instances to send pro-
longations across it in different directions, so as to divide it into
chambers of irregular shape, freely communicating with each
other, which may be occupied either by sarcode, or by particles
introduced from without. The alimentary particles which can
be distinguished in the interior of the transparent bodies of
Infusoria, are usually Protophytes of various kinds, either entire
orin a fragmentary state. The Diatomacez seem to be the ordi-
nary food of many; and the insolubility of their lorice enables
the observer to recognize them unmistakably. Sometimes
entire Infusoria are observed within the bodies of others not
much exceeding them in size (Fig. 199, B); but this is only
when they have been recently swallowed, since the prey speedily
undergoes digestion. It would seem as if these creatures do not
feed by any means indiscriminately ; since particular kinds of
them are attracted by particular kinds of aliment; the crushed
bodies and eggs of Entomostracea, for example, are so vora-
ciously consumed by the Coleps, that its body is sometimes quite
altered in shape by the distension. This circumstance, however,
by no means proves, as some have considered it to do, that such
creatures possess a sense of taste and a power of determinate

INFUSORIA, THEIR MODE OF APPROPRIATING FOOD. 417

selection ; for many instances might be cited, in which actions
of the like apparently conscious nature are performed without
any such guidance. The ordinary process of feeding, as well as
the nature and direction of the ciliary currents, may be best
studied by diffusing through the water containing the Animal-
cules, a few particles of indigo or carmine. These may be seen
to be carried by the ciliary vortex into the mouth, and their
passage may be traced for a little distance down a short (usually
ciliated) esophagus. There they commonly become aggregated
together, so as to form a little pellet of nearly globular form;
and this, when it has attained the size of the hollow within
which it is moulded, is projected into the “ general cavity of the
body,” where it lies in a vacuole of the sarcode, its place in the
cesophagus being occupied by other particles subsequently
ingested. This “moulding,” however, is by no means universal ;
the aggregations of colored particles in the bodies of these
animals being often destitute of any regularity of form. One
after another of such particles being thus introduced into the
interior of the body, each aggregation seems to push on its pre-
decessors; and a kind of circulation is thus occasioned in the
contents of the cavity. The pellets that first entered make their
way out after a time (after yielding up their nutritive materials),
generally by a distinct anal orifice, sometimes, however, by any
part of the surface indifferently, and sometimes by the mouth.
A circumstance which seems clearly to indicate that they cannot
be enclosed (as Prof. Ehrenberg maintains) in distinct stomachal
cavities, is that, when the pallets are thus moving round the
body of the Animalcule, two of them sometimes appear to
become fused together, so that they obviously cannot have been
separated by any membranous investment. When the Animal-
cule has not taken food for some time, “vacuoles” or clear
spaces, extremely variable both in size and number, filled only
with a very transparent fluid, are often seen in its sarcode; their
fluid sometimes shows a tinge of color, and this seems to be due
to the solution of some of the vegetable chlorophyll upon which
they may have fed last.

270. Contractile vesicles (Figs. 194, 195, a, a), usually about
the size of the “vacuoles,” are found, either singly or to the
number of from two to sixteen, in the bodies of most Animal-
cules; and may be seen to execute rhythmical movements of
contraction and dilatation at tolerably regular intervals, being so
completely obliterated when emptied of their contents, as to be
quite indistinguishable, and coming into view again as they are
refilled. These vesicles do not change their position in the in-
dividual, and they are pretty constant, both as to size and place,
in different individuals of the same species; hence they are_ob-
viously quite different in character from the “vacuoles.” What
is their purpose in the economy of these creatures can be only

vaguely guessed at; it may be surmised to be the diffusion
27

418 MICROSCOPIC FORMS OF ANIMAL LIFE.

through the body of the liquid product of the digestive opera-
tion,—a surmise which seems in some degree justified by their
unusual complexity in Paramecium. For each of its two globu-
lar vesicles (Fig. 195, a, a), is surrounded by several elongated
cavities, arranged in a radiating manner, so as to give to the
whole somewhat of a starlike aspect; and the liquid contents
are seen to be propelled from the former into the latter, and
vice versd.

271. Of the Reproduction of the Infusoria, our knowledge is
at present very limited ; the attention of observers having, until
a comparatively recent period, been fixed almost exclusively
upon the act of duplicative subdivision, which, though by far the
most frequent method of propagation, is not a true generative
operation. It is effected in the same general mode as the sub-
division of Protophyta; and has been observed in many in-
stances to commence in the ‘nucleus’ which may usually be
distinguished in the cell-bodies of the Infusoria. The division
takes place in some species longitudinally, that is, in the di-
rection of the greatest length of the body (Fig. 196, p, #, F), in
other species transversely (Fig. 199, a, D), whilst in some, as in
Chilodon cucullulus (Fig. 197), it seems to occur in either direc-

Fra. 197.

Fissiparous multiplication of Chilod: Uulus :—a, B, C, ive stuges of longitudinal fission ;
D, E, F, successive stages of transverse fission.

tion indifferently, though there may not improbably be an alter-
nation, as there usually is in the direction of the subdivision of
the component cells of masses that are increasing both in length
and in breadth ( § 195). This operation is performed with such
rapidity, under favorable circumstances, that, according to the
calculation of Prof. Ehrenberg, no fewer than 268 millions might
be produced in a month by the repeated subdivisions of a single
Paramecium. When this fission occurs in Vorticella (Fig. 196),
one of the divisions is usually smaller than the other, sometimes
so much so as to look like a bud; and this usually detaches itself
when mature from the main body, and swims freely about until
it developes a new footstalk for itself. But sometimes the two
parts are equal in size, and the fission extends down the stalk,
which thus becomes double for a greater or less part of its length;
and thus a whole bunch of Vorticelle may spring (by a repetition
of the same process) from one base. In some members of the
same family, indeed, an arborescent structure is produced by the
like processes of division and gemmation.

INFUSORIA—ENCYSTING PROCESS. 419

272. The recent observations of Stein and other Microscopists
have drawn attention to another very curious mode of propaga-
tion, the phenomena of which were completely misapprehended
by Prof. Ehrenberg. Many Infusoria at certain times undergo
an encysting process; that is, their body secretes from its surface
a sort of gelatinous case, which hardens so as completely to
enclose it, the Animalcule, however, still remaining free in the
interior of its coffin-like investment. Previously to the forma-
tion of this cyst, the Animalcule loses its activity, its form
becomes more rounded, and its cilia or other filamentous pro-
longations are lost or re-
tracted, as is well seen in Fie. 198.

Vorticella (Fig. 198, a);
and it was not, perhaps,
very unnatural, that the
encysting process should
have been considered by
Prof. Ehrenberg as the
expiring effort of life. If
the cysts and their con-
tents, however, be atten-
tively watched, it will be
seen that the process is
preliminary to a produc-
tion of new individuals;
and this may take place
in different modes. For
sometimes the substance
of the body appears to
break up (c, D) into nume-
rous ‘gemmules,” which
are analogous to the
‘“* zoospores” of Proto-
phytes, and which, like
them, are set free by the
bursting of the parent
cell(z), swimming forth to Development and Metamorphosis of Vorticella microstoma :
develope themselves into {3 ilo inividualin ts eneysed sate; a rated
new individuals of the a cyst separated from its stalk j—c, the same more advanced,

ame kind. tho bh t first the nucleus broken up into spore-like globules ;—p, the same
. ‘ ug ie more developed, the original body of the Vorticella, d, having

perhaps bearing NO Y= hecome sacculated, and containing many clear spaces ;—z,
semblance to the type of one of the saeculations having burst through the enveloping

cae cyst, a gelatinous mass, e, containing the spores, is dis-
their predecessor. In charged;—rF, transformation of encysted Vorticella (B) into

other instances, however, form of Acineta; 2, nucleus;—G, stalked Acineta form of
] 7 Sq Vorticella, enclosing a young one, the result of the transfor-

only bs single offspring - mation of the nucleus;—H, woung: free Vorticella; a, b, ¢, as

developed from the ‘“ nu- in Fig. 1; g, posterior circlet of cilia.

cleus’ of the original cell- :

body, which offspring may have an entirely dissimilar form; and

this latter change occurs in Vorticella, in conjunction with other

420 MICROSCOPIC FORMS OF ANIMAL LIFE.

peculiarities of a very remarkable kind. For the encysted Vor-
ticella becomes changed into the form of an Acineta (closely re-
sembling that of Actinophrys), as shown in Fig. 198, ¥; and this
may acquire a new stalk, so as to correspond with a Podophrya
(a). At the same time, its band-like nucleus becomes entirely
metamorphosed into a free body of ovate form, which carries at
its narrower end a circlet of long vibrating cilia, while its more
obtuse end is perforated by a mouth which communicates with
a distinct oral cavity. In the interior of this offspring (H), we
already observe a long oval nucleus (6) and a round contractile
vesicle (c), and its whole aspect is that of a young Vorticella-bud
just ready to quit its stock. This body escapes from the interior
of the Acineta by a gap formed in some part of its wall, which,
however, soon closes again, and the Acineta goes on stretching
out and retracting its radiating filaments, and after a time pro-
duces in its interior a new nucleus for a second Vorticella-bud.?
273. Another interesting series of phenomena, of the same
order, is presented in the development of the Animaleule desig-
nated by Miiller as Trichoda lynceus, which has been carefully
studied by M. Jules Haime.? The form which seems most pro-

Fig. 199.

a ce ‘ee @)
ie -

Metamorphoses of Trichoda lynceus :—a, larva (Oxytricha); B, a similar larva, after swallowing the
animalcule represented at M; c, a very large individual on the point of undergoing fission ; p, another
in which the process has advanced further; E. one of the products of such fission; F, the same body
become spherical and motionless; 6, aspect of this sphere fifleen days afterwards; H, later condition
of the same, showing the formation of the cyst; 1, incipient separation between living substance and
exuvial matter; K, partial discharge of the latter, with flattening of the sphere; 1, more distinct for-
mation of the confined animal; mM, its escape from the cyst; N, its appearance some days afterwards:
0, more advanced stage of the same; P, Q, perfect individuals, one as seen sideways, moving on its
bristles, the other as seen from below; these are magnified twice as much as the preceding figures.

perly to be considered as the larval one, is that shown in Fig.
199, a-E, which has been described by Prof. Ehrenberg under

'See Prof. Stein’s Memoir in “Siebold and Kolliker’s Zeitschrift,” Bd. iii, and the
translation of it in “ Ann. of Nat. Hist.” 2d Ser, vol. ix, p. 471.
2 Annales des Sci, Nat.” Sér. 3, tom. xix, p. 109.

INFUSORIA—ENCYSTING PROCESS. 421

the name of Oxytricha. This possesses a long, narrow, flattened
body, furnished with cilia along the greater part of both margins,
and having also at its two extremities a set of larger and stronger
hair-like filaments; and its mouth, which is an oblique slit on
the right hand side of its fore part, has a fringe of minute cilia
on each lip. Through this mouth, large particles are not unfre-
quently swallowed, which are seen lying in the midst of the gela-
tinous contents of the general cavity of the body, without any
surrounding “vacuole; and sometimes even an animalcule of
the same species, but in a different stage of its life, is seen in the
interior of one of these voracious little devourers (B). In this
phase of its existence, the 7richoda undergoes multiplication by
transverse fission, after the ordinary mode (c, D); and it is usually
one of the short-bodied “doubles” thus preduced (z), that passes
into the next phase. This consists in the assumption of the

lobular form, and the almost entire loss of the locomotive appen-

ages (F); in the escape of successive portions of the granular sar-
code, so that “vacuoles” make their appearance (a); and in the
formation of a gelatinous envelope or cyst, which, at first soft,
afterwards acquires increased firmness (H). After remaining for
some time in this condition, the contents of the cyst become
clearly separated from their envelope; and a space appears on
one side, in which ciliary movement can be distinguished (1).
This space gradually extends all round, and a further discharge
of granular matter takes place from the cyst, by which its form
becomes altered (Kk); and the distinction between the newly
formed body to which the cilia belong, and the effete residue of
the old, becomes more and more apparent (L). The former in-
creases in size, whilst the latter diminishes; and at last the former
makes its escape through an aperture in the wall of the cyst, a
part of the latter still remaining within its cavity (m). The body
thus discharged (nN) does not differ much in appearance from that
of the Oxytricha before its encystment (Fr), though only of about
two-thirds its diameter; but it soon developes itself (0, P, Q) into
an Animalcule very different from that in which it originated.
First it becomes still smaller, by the discharge of a portion of its
substance; numerous very stiff bristle-like organs are developed,
on which the animalcule creeps, as by legs, over solid surfaces ;
the external integument becomes more consolidated on its upper
surface, so as to become a kind of carapace; and a mouth is
formed by the opening of a slit on one side, in front of which is
a single hair-like filament, which is made to turn round and
round with great rapidity, so as to describe a sort of inverted
cone, whereby a current is brought towards the mouth. This
latter form has been described by Prof. Ehrenberg under the
name of Aspidisea. It is very much smaller than the larva; the
difference being, in fact, twice as great as that which exists be-
tween A and P, Q (Fig. 199), since the two last figures are drawn
under a magnifying power twice as great as that employed for

422 MICROSCOPIC FORMS OF ANIMAL LIFE.

the preceding. How the Aspidisca-form in its turn gives origin
to the Ozytricha-form, has not yet been made out. A sexual
process, it may be almost certainly concluded, intervenes some-
where; but other transformations may not improbably take place,
before the latter of these types is reproduced.

274. A like succession of phenomena has been observed
among several other forms of Infusoria; so that, considering the
strong general resemblance in kind and degree of organization
which prevails throughout the group, it does not seem unlikely
that the “encysting process’ occurs at some stage of the life of
nearly all these Animalcules, just as the “still” condition alter-
nates with the “ motile” in the most active Protophytes (§§ 152-6).
And it is not improbably in the “ encysted” condition that their
dispersion takes place; since they have been found to endure
desiccation in this state, although, in their ordinary condition of
activity, they cannot be dried up without loss of life. When
this circumstance is taken into account, in conjunction with the
extraordinary rapidity of multiplication of these Animalcules,
and with the fact that a succession of different forms may be
presented by one and the same being, the difficulty of account-
ing for the universality of their diffusion, which has led some
Naturalists to believe in their “spontaneous generation,” and
others to regard them as isolated particles of higher organisms
set free in their decomposition so as to constitute an “ equivocal
generation,” is as readily got over as we have seen it to be in
the case of the Fungi (§ 211). Although it may be stated as a
general fact, that wherever decaying organic matter exists in a
hiquid state, and is exposed to air and warmth, it speedily be-
comes peopled with these minute inhabitants, yet it has been
experimentally proved by Prof. Schultz, that perfectly free access
of air to such infusions, 1s essential to the appearance of Animal-
cules in them. For having kept infusions of decaying animal
and vegetable matter, in air which had been filtered (so to speak)
of any floating germs it might contain, by passing through
either a red-hot tube or strong sulphuric acid, he found that no
Animalcules made their appearance under these circumstances,
even after the lapse of several weeks; although they were seen
in abundance after the free exposure of the same infusions to
the atmosphere for a few hours ‘only. Hence it may be fairly
inferred, that, as seems to be the case with the Fungi, the dried
cysts or the germs of Infusoria are everywhere floating about in
the air, ready to develope themselves wherever the appropriate
conditions are presented ; and all our knowledge of their history,
as well as the strong analogy of the Fungi, seems further to
justify the belief, that the same germs may develope themselves
into several different forms, according to the nature of the liquid
in which they chance to be deposited. This is a subject pe-
culiarly worthy of the attention of Microscopie observers ; who
can scarcely be better employed than in tracing out the succes-

PECULIAR TYPES OF INFUSORIA. 423

sion of phases which any particular type may present, and thus
in making a most important extension of our knowledge of its
life-history, whilst at the same time effecting a most desirable
reduction in the number of reputed species. Such a study, if
perservingly as well as carefully pursued, would be almost certain
to lead to the discovery of the true generative process in these
creatures, of which we cannot at present be said to know any-
thing with certainty. For although an apparent “ conjugation”
has been observed between: the bodies of distinct individuals,
both in the ordinary active states of Infusoria, and in their
Acineta condition, yet this does not seem truly to represent the
sexual union of higher animals; for the blending of the two in-
dividuals is not so complete as to amount to the “fusion” we
have seen to occur in previous instances, the boundaries of each
remaining distinctly traceable; and not only two, but three,
four, or even more, have been found in continuous union.

275. It is obvious that no Classification of Infusoria can be ot
any permanent value, until it shall have been ascertained, by the
study of their entire life-history, what are to be accounted really
distinct forms; and the differences between them, consisting
chiefly in the shape of their bodies, the disposition of their cilia,
the possession of other locomotive appendages, the position of
the mouth, the presence of a distinct anal orifice, and the like,
are matters of such trivial importance as compared with those
leading features of their structure and physiology on which we
have been dwelling, that it does not seem desirable to attempt
in this place to give any account of them. The most remarka-
ble departure from the ordinary type is presented by the Vortv-
celline, the habit of which is to attach themselves to the stems
of aquatic plants or some other supports, either by the apex of
their own conical body,—as is the case with Stentor, one of the
largest of all Infusoria (being visible to the naked eye), which is

.very common in ponds and ditches, attaching itself to duck-
weed, decaying reeds, or other floating bodies, round which it
forms a sort of slimy fringe, but which is often found swimming
freely, its trumpet-shaped body drawn together into the form ot
an egg,—or by a footstalk several times its own length, as is the
case with Vorticella (Fig. 196), which also occasionally quits its
attachment (the stalk apparently dying and being thrown off),
and swims rapidly through the water, being propelled by the
fringe of cilia, which, when the body was fixed by its stalk,
served to produce a vortex in the surrounding fluid, that brought
it both food and air. Another curious departure from the ordi-
nary type is presented by the family Ophrydine ; the animalcules
of which, closely resembling some Vorticelline in their indivi-
dual structure, are usually found imbedded in a gelatinous mass,
of a greenish color, which is sometimes adherent, sometimes
free, and may attain the diameter of four or five inches, pre-
senting such a strong general resemblance to a mass of Nostoc

424 MICROSCOPIC FORMS OF ANIMAL LIFE.

(§ 196) or even of Frogs’ spawn, as to have been mistaken for
such. The mode in which these masses are produced closely
resembles that in which the masses of Mastoloia (§ 189) or of
Palmela (§ 194) are formed; since they simply result from the
fact, that the multitude of individuals produced by a repetition
of the process of self-division, remain connected with each other
for a time by a gelatinous exudation from the surface of their
cell-bodies, instead of at once becoming completely isolated.
From a comparison of the dimensions of the individual Ophrydia,
each of which is about 1-120th of an inch in length, with those
of the composite masses, some estimate may be formed of the
number included in the latter; for a cubic inch would contain
nearly eight millions of them, if they were closely packed; and
many times that number must exist in the larger masses, even
making allowance for the fact that the bodies of the animalcules
are separated from each other by their gelatinous cushion, and
that the masses have their central portions occupied only by
water. Hence we have, in such clusters, a distinct proof of the
extraordinary extent to which multiplication by duplicative sub-
division may proceed, without the interposition of any other
operation. These animalcules, however, free themselves at times
from their gelatinous bed; and have been observed to undergo
an ‘“ encysting process,” corresponding with that of the Vorti-
cellinee (§ 272). It is much to be desired that Microscopic ob-
servers should devote themselves systematically to the continuous
study of even the commonest and best known forms of these
Animaleules; since there is not a single one, whose entire life-
history, from one Generative act to another, is known to us.
And since it cannot be even guessed at, without such knowledge,
what, among the many dissimilar forms that have been described
by Prof. Ehrenberg and others, are to be accounted as truly dis-
tinct species, and what are mere phases in the existence of others
that are perhaps very dissimilar to them in aspect, it is obvious
that no credit is really to be gained by the discovery of any num-
ber of apparently new species, which shall be at all comparable
with that to be acquired by the complete and satisfactory eluci-
dation of the life-history of any one.?

276. As it is among Animalcules that the action of the organs

' The recent memoirs of Prof. Stein in “ Wiegmann’s Archiv,” and in “Siebold and
Kolliker’s Zeitschrift,’ which have been separately published in a collective form
“ Die Infnsionsthiere,” Leipsic, 1854, contain most valuable contributions to the de-
siderated knowledge ; as do also the memoirs of Dr. Cohn in “Siebold and Kolliker’s
Zeitschrift.” The great work of Prof. Ehrenberg, “ Die Infnsionsthierchen,” will always
remain a standard of reference, as the basis of all our higher knowledge of these or-
ganisms ; but its anthority has been completely destroyed by the proof which has been
gradually accumulating, of the erroneous conceptions on which he based his descrip-
tions ; first, as to what are Infusory Animalcules, a very large proportion of those con-
sidered by him as such being undoubtedly Plants ;—second, as to the organization of the
true Infusoria, the complex digestive apparatus, genital organs, nervous system, and
organs of sense, which he believed that he had discovered in them, having no existence
but in bis imagination ;—and, third, as to the relations of his supposed species one to
another, many of these being only different states of the same.

NATURE OF CILIARY MOVEMENT. 425

termed cilia has the most important connection with the vital
functions, it seems desirable to introduce here a more particular
notice of them. They are always found in connection with ceils,
of whose substance, as we have seen among the Protophyta
(§§ 154, 158), they may be considered as extensions. The form
of the filaments is usually a little flattened, and tapering gradu-
ally from the base to the point. Their size is extremely varia-
ble; the largest that have been observed being about 1-500th of
an inch in length, and the smallest about 1-18,000th. When in
motion, each filament appears to bend from its root to its point,
returning again to its original state, like the stalks of wheat when
depressed by the wind; and when a number are affected in suc-
cession with this motion, the appearance of progressive waves
following one another is produced, as when a wheatfield is agi-
tated by successive gusts. When the ciliary action is in full
activity, however, little can be distinguished save the whirl of
particles in the surrounding fluid; but the dack-stroke may often
be perceived, when the forward-stroke is made too quickly to be
seen; and the real direction of the movement is then opposite
tothe apparent. In this back-stroke, when made slowly enough,
a sort of “feathering” action may be observed; the thin edge
being made to cleave the liquid, which has been struck by the
broad surface in the opposite direction. It is only when the rate
of movement has considerably slackened, that the shape and
size of the cilia, and the manner in which their stroke is made,
can be clearly seen. It has been maintained by some, that the
action of the cilia is muscular; but they are often too small to
contain even the minutest fibrille of true muscular tissue, and
no such elements can be discerned around their base; their pre-
sence in Plants, moreover, seems distinctly to negative such an
idea. Hence we must consider them as organs sui generis,
wherein the contractility of the cell to which they belong, is (as
it were) concentrated. We have seen that in the Rhizopods, the
entire mass of whose sarcode is highly contractile, no cilia are
present; whilst in the Infusoria, whose bodies have compara-
tively little contractility, the movements are delegated to the
cilia. Cilia are not confined, however, to Animalcules and
Zoophytes, but exist on some of the free internal surfaces, espe-
cially the walls of the respiratory passages, of all the higher
animals, not excepting Man himself. Our own experience
assures us that their action takes place, not only without any
exercise of will on our own parts, but even without affecting our
consciousness ; and it has been found to continue for many hours,
or even days, after the death of the body at large. How far it is
subject to any conscious control on the part of these Animalcules,
in which the cilia serve as instruments for locomotion as well as
for bringing to them food or oxygen, it is impossible for any one
to say with confidence. In this important respect, however, the
ciliary movement of Animalcules differs from that which is

426 MICROSCOPIC FORMS OF ANIMAL LIFE.

observable in the higher Animals,—that whilst in the latter it is
constant, giving the idea of purely mechanical agency, in the
former it is so interrupted and renewed, as almost necessarily to
suggest to the observer the notion of choice and direction.

211. Rotifera, or Wheel-Animalcules.—We now come to that
higher group of Animalcules, which, in point of complexity of
organization, is as far removed from the preceding, as Mosses
are from the simplest Protophytes; the only point of real resem-
blance between the two groups, in fact, being the minuteness of
size which is common to both, and which was long the obstacle
to the recognition of the comparatively elevated character of the
Rotifera, as it still is to the precise determination of certain
points of their structure. Some of the Wheel-Animalcules are
inhabitants of salt water only, but by far the larger proportion
are found in collections of fresh water, and rather in such as are
free from actively decomposing matter, than in those which
contain organic substances in a putrescent state. Hence when
they present themselves in vegetable infusions, it is usually after
that offensive condition, which is favorable to the development
of many of the Infusoria, has passed away; and they are conse-
quently to be looked for, after the disappearance of many suc-
cessions (it may be) of Animaleules of inferior organization.
Rotifera are more abundantly developed in liquids which have
been long and freely exposed to the open air, than in such as
have been kept under shelter; certain kinds, for example, are
to be met with in the little pools left after rain in the hollows of
the lead with which the tops of houses are partly covered; and
they are occasionally found in enormous numbers in cisterns
which are not beneath roofs or otherwise covered overt. They
are not, however, absolutely confined to collections of liquid ;
for there are a few species which can maintain their existence in
damp earth; and the common Rotifer is occasionally found in
the interior of the leaf-cells of Sphagnum (§ 216). The wheel-
like organs from which the class derives its designation, are
most characteristically seen in the common form just mentioned
(Fig. 201), where they consist of two disk-like lobes or projec-
tions of the body, whose margins are fringed with long cilia;
and it is the uninterrupted succession of strokes given by these
cilia, each ‘row of which nearly returns (as it were) into itself,
that gives rise by an optical illusion to the notion of “wheels.”
This arrangement, however, is by no means universal; in fact, it
obtains in only a small proportion of the group; and by far the
more general plan is that seen in Fig. 200, in which the cilia
form one continuous line across the body, being disposed upon
the sinuous edges of certain lobes or projections which are
borne upon its anterior portion. Some of the chief departures
from this plan will be noticed hereafter (§ 281). The great
transparency of the Rotifera permits their general structure to

! See a remarkable instance of this in p. 253, note,

ROTIFERA, THEIR GENERAL STRUCTURE. 427

be easily recognized. They have usually an elongated form,
similar on the two sides; but this rarely exhibits any traces of
segmental division. The body is covered with a double enve-
lope; both layers of which are extremely thin and flexible in
some species; whilst in others, the outer one seems to possess a
horny consistence. In the former case, the whole integument is
drawn together in a wrinkled manner when the body is short-
ened; in some of the latter the sheath has the form of a polype-
cell, and the body lies loosely in it, the inner layer of the integu-
ment being separated from the outer by

a considerable space (Fig. 202); whilst Fre. 200.

in others, the envelope or lorica is tightly
fitted to the body, and strongly resem-
bles the horny casing of an insect or the
shell of a crab, except that it is not
jointed, and does not extend over the
head and tail, which can be projected
from the openings at its extremities, or
completely drawn within it for protec-
tion (Fig. 203). In those Rotifera in
which the flexibility of the body is not
interfered with by the consolidation of
the external integument, we usually
find it capable of great variation in
shape, the elongated form being occa-
sionally exchanged for an almost globu-
lar one, as is seen especially when the
animals are suffering from deficiency of
water; whilst by alternative movements
of contraction and extension, they can
make their way over solid surfaces, after
the manner of a worm or a leech, with
considerably activity,—some even of the
loricated species being rendered capable of this kind of progres-
sion, by the contractility of the head and tail. All these, too,
can swim readily through the water, by the action of their cilia;
and there are some species which are limited to the latter mode
of progression. The greater number have an organ of attach-
ment at the posterior extremity of the body, which is usually
prolonged into a tail, by which they can affix themselves to any
solid object; and this is their ordinary position, when keeping their
wheels in action for a supply of food or of water. They have no
difficulty, however, in letting go their hold and moving through
the water in search of a new attachment, and may therefore be
considered as perfectly free; the polypoid species, however,*
remain attached by the posterior extremity to the spot on which
they have at first fixed themselves, and their cilia are conse-
quently employed for no other purpose than that of creating
currents in the surrounding water.

Brachionus pala,

428 MICROSCOPIC FORMS OF ANIMAL LIFE.

278. In considering the internal structure of Rotifera, we shall
take as its type the arrangement which it presents in the Rotifer
vulgaris (Fig. 101); and specify the principal variations exhibited
by others. The body of this animal, when fully extended,
possesses greater length in proportion to its diameter than that
of most others of the class; and the tail is composed of three
joints or segments, which are capable of being drawn up, one
within another, like the sliding-tubes of a telescope, each having
a pair of prongs or points at its extremity. Within the external
integument of the body, are seen a set of longitudinal muscular
bands (A), which serve to draw the two extremities towards each
other; and these are crossed by a set of transverse annular bands,
which also are probably muscular, and serve to diminish the
diameter of the body, and thus to increase its length. Between
the wheels is a prominence, bearing two red spots (4), supposed
to be rudimentary eyes, and having the mouth (a) at its extre-
mity; this prominence may be considered, therefore, as a true
head, notwithstanding that it is not clearly distinguishable from
the body. This head also bears upon its under surface a projecting
tubular organ (d), which was thought by Professor Ehrenberg to
be a siphon for the admission of water to the cavity of the body
for the purpose of respiration; this, however, is certainly not
the case, the tube being imperforate at its extremity; and there
seems much more probability in the idea of Dujardin, that it re-
presents the antenne or palpi of higher Articulata, the single
organ being replaced in many Rotifera by a pair, of which each
is furnished at its extremity with a brush-like tuft of hairs that
can be retraced into the tube. The cesophagus, which is narrow
in the Rotifer, but which is dilated into a crop in Stephanoceros
(Fig. 202) and in some other genera, leads to the masticating
apparatus, which in these animals is placed far behind the mouth,
and in close proximity to the stomach. It consists of a pair of
stirrup-shaped jaws (Fig. 201, e) each having from one to five teeth
(in Rotifer, two), which appear to contain mineral matter and to
be of harder texture than the rest of the fabric; these jaws are
put in action by powerful muscles, and are so moved that all the
food which passes into the stomach is subject to be divided and
torn by their teeth. In many Rotifera, the conformation of this
masticating apparatus is extremely complicated. The form of
the alimentary canal varies; this being sometimes a simple tube,
passing without enlargement or constriction from the masticat-
ing apparatus to the anal orifice at the posterior part of the body;
whilst in other instances there is a marked distinction between
the stomach and intestinal tube, the former being a large globu-
lar dilatation immediately below the jaws, whilst the latter is
cylindrical and comparatively small. The alimentary canal of
Rotifer most resembles the first of these types, but presents a
dilatation (2) close to the anal orifice, which may be considered
as a cloaca; that of Brachionus (Fig. 200) is rather formed upon

ROTIFERA, THEIR GENERAL STRUCTURE. 429

the second. Connected with the alimentary canal are various
glandular appendages, more or less developed; sometimes clus-
tering round its walls as a mass of se-

parate follicles, which seems to be the Fre. 201,
condition of the glandular investment
(g) of the alimentary canal in Rotifer ;
in other cases having the form of ccecal
tubuli. Some of these open into the
stomach close to the termination of the
esophagus, and have been supposed
to be salivary or pancreatic in their
character; whilst others, which dis-
charge their secretion into the intesti-
nal tube, have been regarded, and pro-
bably with correctness, as the rudi-
ment of a liver. Ina curious animal-
cule of this class, minutely described
by Mr. Dalrymple,’ although the
mouth, masticating apparatus, and
stomach are constructed upon the re-
gular type of the genus Notommata,
to which it seems nearly allied, yet
there is neither intestine nor anal ori-
fice, and the indigestible matters are
rejected through the mouth. This,
so far as is yet known, is a solitary
example of the existence of this cha-
racter of degradation in the class Ro- RU DOs aE at Fs anh
tifera. There does not appear to be Wheels expanded; mouth; by eye.
any special circulating apparatus in spots; ¢, wheels; d, ealcar (antenna?) ;
these animals; but the nid which Pane et ieee at asin
is contained in the general cavity ieee lates patter "i te aD
of the body, between the exterior water vascular system; %, young ani-
of the alimentary canal and the in- ™™'>°l%™

ner tegumentary membrane, is probably to be regarded as nu-
tritive in its character; and its aeration is provided for by a
peculiar apparatus, which seems to be a rudimentary form of the
‘“‘water vascular system,” that attains a high development in the
class of Worms. On either side of the body there is usually to
be observed a long flexuous tube (Fig. 200), which extends from
a contractile vesicle common to both and opening into the cloaca
(Fig. 201, 2, 7), towards the anterior region of the body, where it
frequently subdivides into branches, one of which may arch over
towards its opposite side, and inosculate with a corresponding
branch from its tube. Attached to each of these tubes are a
number of peculiar organs (usually from two to eight on each
side), in which a trembling movement is seen, very like that of
a flickering flame; these appear to be pear-shaped sacs, attached

1“ Philos, Transact.” 1849, p, 339.

430 MICROSCOPIC FORMS OF ANIMAL LIFE.

by hollow stalks to the main tube, having a long cilium in the
interior of each, that is attached by one extremity to the interior
of the sac, and vibrates with a quick undulatory motion in its
cavity; and there can be little doubt that their purpose is to
keep up a constant movement in the contents of the aquiferous
tubes, whereby fresh water may be continually introduced from
without, for the aeration of the fluids of the body.’ There
is much uncertainty with regard to the structures which Prof.
Ehrenberg has described as ganglia and nerves; and it seems
doubtful if there is more than a single nervous centre in
the neighborhood of the single, double, or multiple red spots,
which are seen upon the head of the Rotifera, and which, cor-
responding precisely in situation with those that in the higher
Articulata are unquestionably eyes, are probably to be regarded
as rudiments of visual organs.

279. The Reproduction of the Rotifera has not yet been com-
pletely elucidated. There is no instance, in this group, in which
multiplication by gemmation or spontaneous fission is certainly
known to take place; but the occurrence of clusters formed by
the aggregation of a number of individuals of Conochilus, adhe-
rent by their tails, and enclosed within a common lorica, would
seem to indicate that these clusters, like the aggregations of
Polygastrica, Bryozoa, and Tunicata, must have been formed by
continuous growth from a single individual. The ordinary
method of multiplication, however, is commonly supposed to be
by a proper generative act; as distinct sexes have been disco-
vered in several individuals, and the act of sexual union has been
witnessed. The condition of the male of the remarkable genus
described by Mr. Dalrymple (loc. cit.) is a most extraordinary
one; for it possesses no mandibles, pharynx, oesophagus, stomach,
nor hepatic glands; having, in fact, no other organs fully deve-
loped, than those of generation. It would appear, therefore,
quite unfit to obtain aliment for itself; and its existence is pro-
bably a very brief one, being continued only so long as the store
of nutriment supplied by the egg remains unexhausted. In
Rotifer, however, as in by far the larger proportion of the class,
no males have been discovered; and it remains doubtful whether
the two sexes are united in the same individual, or whether the
males are produced only at certain times. The female organ
consists but of a single ovarian sac, which frequently occupies a
large part of the cavity of the body, and which opens at its lower
end by a narrow orifice into the cloaca. Although the number
of eggs in these animals is so small, yet the rapidity with which
the whole process of their development and maturation is accom-
plished, renders the multiplication of the race very rapid. The
egg of the Hydatina is extruded from the cloaca within a few

1 See Mr. Huxley's account of these organs, in his description of Lacinularia socialis,
“Transact of Microsc. Soc.” Ser. 2, vol. i, Other observers have supposed that the

pyriform sacs communicate with the general cavity of the body; but the Author has
much confidence in the correctness of Mr. Huxley's statements on this point.

ROTIFERA, THEIR STRUCTURE AND REPRODUCTION. 431

hours after the first rudiment of it is visible; and within twelve
hours more the shell bursts, and the young animal comes forth.
In the Rotifer and several other genera, the development of the
embryo takes place whilst the egg is yet retained within the
body of the parent (Fig. 201, %), and the young are extruded
alive ; whilst in some other instances, the eggs, after their extru-
sion, remain attached to the posterior extremity of the body (Fig.
200), until the young are set free. In general it would seem
that, whether the rupture of the egg-membrane takes place before
or after the egg has left the body, the germinal mass within it is
developed at once into the form of the young animal, which
resembles that of its parent; no preliminary metamorphosis
being gone through, nor any parts developed which are not to
be permanent. The transparency of the egg-membrane, and also
of the tissues, of the parent Rotifer, allows the process of deve-
lopment to be watched, even when the egg is retained within
the body; and it is curious to observe, at a very early period, not
merely the red eye spot of the embryo, but also a distinct ciliary
movement. The multiplication of Hydatina (in which genus three
or four eggs are deposited at once, and their development com-
pleted out of the body) takes place so rapidly, that, according to
the estimate of Prof. Ehrenberg, nearly seventeen millions may be
produced within twenty-four days from a single individual.
Even in those species which usually hatch their eggs within their
bodies, a different set of ova is occasionally developed, which are
furnished with a thick glutinous investment: these, which are
extruded entire, and are laid one upon another, so as at last to
form masses of considerable size in proportion to the bulk of the
animals, seem not to be destined to come so early to maturity,
but very probably remain dormant during the whole winter sea-
son, so as to produce a new brood inthe spring. These “ winter
eggs” are inferred by Mr. Huxley, from the history of their de-
velopment, to be really gemme produced by a non-sexual opera-
tion; while the bodies commonly called ova, he considers to be
true generative products. Dr. Cohn has recently informed the
Author, however, that he has ascertained by direct experiment
upon those species in which the sexes are distinct, that the bodies
commonly termed ova (Figs. 200, 201), are really internal gemme,
since they are reproduced, through many successions, without
any sexual process, just like the external gemmex of Aydra
§ 801), or the internal gemme of Entomostraca and Aphides
Chap. XVI). And this view appears to himself to be more
accordant with general physiological analogy than that of Mr.
Huxley; since, in the other instances referred to, as in the Roti-
fera, the multiplication by gemmation goes on rapidly whilst
food and warmth are abundantly supplied ; but gives place to the
true generative process, when the nutritive activity is lowered by
their withdrawal.
280. Certain Rotifera, among them the common Wheel-Ani-

432 MICROSCOPIC FORMS OF ANIMAL LIFE,

malcule, are remarkable for their tenacity of life, even when re-
duced to the state of most complete dryness; for they can be
kept in this condition for any length of time, and will yet revive
very speedily upon being moistened. Experiments have been
carried still farther with the allied tribe of Tardigrades; indi-
viduals of which have been kept in a vacuum for thirty days,
with sulphuric acid and chloride of calcium (thus suffering the
most complete desiccation that the Chemist can effect), and yet
have not lost their capability of revivification. This fact, taken
in connection with the extraordinary rate of increase mentioned
in the preceding paragraph, removes all difficulty in accounting
for the extent of the diffusion of these animals, and for their oc-
currence in incalculable numbers in situations where, a few days
previously, none were known to exist. For their entire bodies
may be wafted in a dry state by the atmosphere, from place to
place; and their return to a state of active life, after a desiccation
of unlimited duration, may take place whenever they meet with
the requisite conditions,—

Fig, 202, moisture, warmth, and food.

It is probable that the ova are
capable of sustaining treat-
ment even more severe than
the fully developed animals
can bear; and that the race is
frequently continued by them,
when the latter have perished.
281. The principles on
which the various forms that
belong to this class should be
systematically arranged, have
not yet been satisfactorily de-
termined. By Prof. Ehren-
berg, the disposition of the
ciliated lobes or wheel-organs,
and the enclosure or non-en-
closure of the body in a lorica
or case, were taken asthe basis
of his classification ; but as his
ideas on both these points are
inconsistent with the actual
facts of organization, the ar-
rangement founded upon
them cannot be received.
\k Another division of the class
sicittiimammnis has been propounded by M.
: Dujardin, which is based on
the several modes of life of
the most characteristic forms. And in a third, more recently
put forth by Prof. Leydig, the general configuration of the body,

Stephanoceros Eichornii.

ROTIFERA—FLOSCULARIANS AND MELICERTIANS. 483

with the presence, absence, and conformation of the foot (or tail),
are made to furnish the characters of the subordinate groups.
Hither of the two latter is certainly more natural than the first,
as bringing together for the most part the forms which most
agree in general organization, and separating those which differ;
and we shall adopt that of M. Dujardin as most suitable to our
present purpose.

I. The first group includes those that habitually live attached
by the foot, which is prolonged into a pedicle; and it includes
two families, the Floscularians and the Melicertians, both of which
bear a certain general resemblance to the Vorticelline (§ 268) on
the one hand, and to Zoophytes (Chap. XI) on the other. For
they are commonly found attached to the stems and leaves of
aquatic plants, by a long pedicle or footstalk, which bears a
somewhat bell-shaped body; and in one of the most beautiful
species, the Stephanoceros Hichornit (Fig. 202), this body has five
long tentacles, beset with tufts of short bristly cilia, reminding
us of the ciliated tentacles of the Bryozoa (Chap. XIII), whilst
the body seems to be enclosed in a cylindrical cell, resembling
that of Hydrozoa and Bryozoa. A comparison of this with other
forms, however, shows that these tentacles are only extensions of
the ciliated lobes which are common to all the members of these
families; and the so-called “cell” is not formed by a thickening
and separation of the outer tegument, but by a gelatinous secre-
tion from it; so that, as the rest of the organization is essentially
conformable to the Rotiferous type, no such passage is really
established by this animal towards other groups, as it is com-
monly supposed to form. In one respect, Floscularia is still more
aberrant; for the long bristly filaments with which its lobes are
beset, are not capable of rhythmical vibration, and cannot, there-
fore, be properly termed “cilia.” The body of Melicerta is pro-
tected by a most curious cylindrical tube, composed of little
rounded pellets agglutinated together; this is obviously an arti-
ficial construction ; and Mr. Gosse has been fortunate enough to
have an opportunity of watching the animal whilst engaged in
building it up. Beneath a projection on its head which he terms
the chin, there is observed a small disk-like organ, in which,
when the wheels are at work, a movement is seen very much
resembling that of a revolving ventilator. Towards this disk,
the greater proportion of the solid particles that may be drawn
from the surrounding liquid into the vortex of the wheel-organs,
are driven by their ciliary movement, a small part only being
taken into the alimentary canal; and there they accumulate,
until the aggregation (probably cemented by a glutinous secretion
furnished by the organ itself) acquires the size and form of one
of the globular pellets of the case; the time ordinarily required
being about three minutes. The head of the animal then bends
itself down, the pellet-disk is applied to the edge of the tube, the
newly formed pellet is left attached there, and, the head being

28

434 MICROSCOPIC FORMS OF ANIMAL LIFE.

lifted into its former position, the formation of a new pellet at
once commences. ;

II. The next of M. Dujardin’s primary groups (ranged by him,
however, as the third), consists of the ordinary Rotzfer and its
allies, which pass their lives in a state of alternation between the
conditions of those attached by a pedicle, of those which habitu-
ally swim freely through the water, and of those which creep or
crawl over hard surfaces. As these have already been fully de-
scribed, it is not requisite to dwell longer upon them.

III. The next group consists of those Rotifers which seldom or
never attach themselves by the foot, but habitually swim freely
through the water; and putting aside the peculiar aberrant form
Albertia, which has only been found as a parasite in the intestines
of worms, it may be divided into two families, the Brachionians
and the Furcularians. The former are for the most part distin-
guished by the short, broad, and flattened form of the body
(Figs. 200, 203); which is, moreover, enclosed in a sort of cuirass,

Fra. 203.

Noteus quadricornis ; a, dorsal view; 8, side view.

formed by the consolidation of the external integument. This
cuirass is often very beautifully marked on its surface, and may
be prolonged into extensions of various forms, which are some-
times of very considerable length. The latter (corresponding
almost exactly with the Hydatinew of Prof. Ehrenberg) derive
their name from the bifurcation of the foot into a sort of two-
bladed forceps; their bodies are ovoidal or cylindrical, and are
enclosed in a flexible integument, which is often seen to wrinkle
itself into longitudinal and transverse folds, at equidistant lines.
To this family belongs the Hydatina senta, which is one of the
largest of the Rotifera, and which was employed by Prof. Ehren-
berg as the chief subject of his examination of the internal struc-
ture of this group; as does also the Notommata, the curious con-
dition of whose male has been already referred to (§ 279).

ROTIFERA—TARDIGRADA. 435

IV. The fourth of M. Dujardin’s primary orders consists of the
very curious tribe, first carefully investigated by M. Doyére, to
which the name of Tardigrada has been given, on account of the
slowness of their creeping movement. Their relation to the true
Rotifera, however, is not at all clear; and many naturalists regard
them as altogether distinct. They are found in the same loca-
lities with the Rotifers, and, like them, can be revivified after
desiccation (§ 280); but they have a vermiform body, divided trans-
versely into five segments, of which one constitutes the head,
whilst each of the others bears a pair of little fleshy protube-
rances, furnished with four curved hooks, and much eres
the pro-legs of a caterpillar. ‘The head is entirely unpossesse
of ciliated lobes; and it is only in the presence of a pair of jaws
somewhat resembling those of Rotifera, and in the correspon-
dence of their general grade of organization, that they bear any
structural relation to the class we have now been considering.
They may be pretty certainly regarded as a connecting lin
between the Rotifera and the Worms; but they should probably
be ranked on the worm side of the boundary.

282. Notwithstanding that all the best informed Zoologists are
now agreed in ranking the class of Rotifera in the Articulated
series, yet there is still a considerable discordance of opinion as
to the precise part of that series in which they should stand.
For whilst Prof. Leydig, who has recently devoted much atten-
tion to the study of the class, regards them as most allied to the
Crustacea, and terms them “ Ciliocrustaceans,” Mr. Huxley, with
(as it seems to the Author) a clearer insight into their real nature,
has argued that they are more connected with the Annelida,
through the resemblance which they bear to the early larval
forms of that class (Fig. 274). Considered in this light, the Tar-
digrada might seem to represent a more advanced phase of the
same developmental history.’

1 In addition to the classical works of Ehrenberg and Dujardin, the following Me-
moirs should be consulted (besides those already referred to) by such as wish to
acquaint themselves with the best researches upon the Rotifera:—Leydig in “Siebold
and Kolliker’s Zeitschrift,” Band VI, heft 1; Goss on Melicerta ringens, in “ Transact. of
Microsc. Soc.” Ser. I, vol. iii, p. 58; and “Quart. Journ. of Microsc. Sci.” vol. i, p. 7135
Williamson on Melicerta ringens, Op. cit. p.1; and Huxley on Lacinularia socialis, in
“Transact. of Microsc. Soc.” Ser. II, vol. i, p. 1.

CHAPTER X.
FORAMINIFERA, POLYCYSTINA, AND SPONGES.

283. RETURNING now to the lowest or Rhizopod type of Animal
life (§ 264), we have to direct our attention to three very remark-
able series of forms, almost exclusively marine, under which that
type manifests itself; all of them being distinguished by a skeleton
of greater or less density; and this skeleton being generally so
consolidated by mineral deposit, as to retain its form and inti-
mate structure, long after the animal to which it belonged has
ceased to live, even for those undefined periods in which they
have been imbedded as fossils in strata of various geological ages.
In the first of these groups, the Foraminifera, this skeleton con-
sists of a calcareous shell (save in a few exceptional cases, in
which the lorica remains flexible), that invests the sarcode body,
but is usually perforated with numerous minute apertures. In
the second group, also, the Polycystina, there is an investing
shell, perforated with numerous apertures; but this shell is s¢dz-
ceous, instead of calcareous. In the third group, on the other
hand,—that of Portfera, or Sponges,—the skeleton is usually
composed of a network of horny fibres, strengthened either by
calcareous or siliceous spicules, and having the soft animal body,
which is composed of an aggregate of Ameba-like cells, in its
interstices: in this group, moreover, we have a departure from
the Rhizopod type, in the fact that certain parts of the free sur-
faces are furnished with cilia, whereby currents of water are
sustained, that serve both for nutrition and for respiration.

284. Foraminifera.—The beings now known under this desig-
nation, possess, for the most part, polythalamous or “ many-cham-
bered”’ cells (Fig. 336), so strongly resembling those of Nautilus,
Spirula, and other Cephalopod Mollusks, that it is not surprising
that the older Naturalists, to whom the structure of these animals
was entirely unknown, ranked them under that class. As such
they were described by M. D’Orbigny (to whom we owe much of
our knowledge of this group), in all his earlier publications; and
they were distinguished from the ordinary Cephalopods that
possess a single siphon passing from chamber to chamber, by the
designation Foraminifera, which originally imported that the
communications between the chambers are commonly made by

GENERAL ORGANIZATION OF FORAMINIFERA. 437

several such apertures, though it is now more commonly under-
stood as applying to the sieve-like structure often presented by
the external. shell. It was by M. Dujardin, in 1835, that the
structure of these animals was first shown to be conformable to
the Rhizopod type; and notwithstanding the opposition to his
views which has been set up by Prof. Ehrenberg (who, with in-
explicable pertinacity, has con-

tinued to rank them among his Fig. 204.

Bryozoa, Chap. XIII), they have
been confirmed by all subse-
quent observers, and more espe-
cially by the recent researches
of Prof. Schulze,’ who has given
admirable descriptions of the
animals of several different
kinds of Foraminifera, derived
from observation of them during
their living state. The confor-
mity of the Foraminifera to the
ordinary Rhizopod type, is best
seen in those forms, such as
Gromia (Fig. 204), in which
there is no multiplication of
chambers; and it is made ob-
vious by an examination of the
accompanying figure, that there
is no other essential difference
between Gtromia and Arcella or
Diffugia (Fig. 193), than that
which lies in the greater length
and slenderness of the pseudo-
podial prolongations of the sar-
code body in the former, as com-
pared with those of the latter.
The food is obtained by the ex-
tension of these pseudopodia in
various directions from the Gromia oviformis, with its pseudopodia extended.
mouth of the shell; and the ab-

sence of any membrane investing them is clearly indicated by
their fusion or coalescence when two or more happen to come
into contact, as well as by the vagueness of the expansions into’
which they are occasionally seen to spread out. These instru-
ments entangle and lay hold of the minute bodies which serve as
food to the animals, consisting of Diatomacese, Desmidiex, the
smaller forms of Conferve, &c.; and they draw these, by their
contraction, into the substance of the body, within which they
may be seen through the transparent shell. It is not by any
means constantly, that their indigestible residua are cast forth

1« per den Organismus der Polythalamien (Foraminiferen).” Leipzig, 1854,

438 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

again, as we have seen them to be from the surface of the body
of the Actinophrys (§ 262); for they sometimes accumulate in
considerable numbers, so as even to choke up a large part of the
cavity. The sarcode body is occasionally seen to extend itself,
as shown in Fig. 204, around the exterior of the shell; and
pseudopodia are put forth from this extension, as well as from
the ordinary outlet. Although nothing is certainly known of
the mode of propagation of these animals, yet it is probable, from
the analogy of the composite forms, that they multiply them-
selves by the detachment of gemme, composed of portions of
sarcode, which in time form an envelope or shell. Nothing has
-been yet seen, that in the least corresponds to a true Generative
process.

285. By far the greater number of Foraminifera are composite
fabrics, evolved by a process of continuous gemmation, each
gemma remaining in connection with the body by which it was
put forth; and according to the plan on which this gemmation
takes place, will be the configuration of the composite body
thereby produced. Thus if the bud should be put forth from
the aperture of Gromia, in the direction of the axis of its body,
and a second shell should be formed around this bud, in conti-
nuity with the first, and this process should be successionally re-
peated, a straight rod-like shell will be produced, having many
chambers communicating with each other by the openings that
originally constituted their mouths, the mouth of the last formed
chamber being the only aperture through which the sarcode
body, thus composed of a number of segments connected by a
pedunele or “stolon” of the same material, can now project itself
or draw in its food. The successive segments may be all of the
same size, or nearly so, in which case the entire rod will approach
the cylindrical form, or will resemble a line of beads; but it often
happens that each segment is somewhat larger than the pre-
ceding, so that the composite shell has a conical form, the apex
of the cone being the original segment, and its base the one last
formed. The method of growth now described, is common to a
large number of Foraminifera, chiefly belonging to the genera
Nodosaria, Dentalina, Morginulina, which M. D’Orbigny has
ranked together in an order, under the designation of Stichos-
tégues ; it is, however, frequently seen also in the advanced stages
of growth of such as usually begin upon the spiral plan; and
there are various considerations (into which this is not the place
to enter) which satisfy the Author, that the mere direction of in-
crease is a character of very subordinate importance in the group,
instead of being one of such fundamental value as to serve for
the basis of classification.

286. If each of the successively formed segments, instead of
being developed exactly in the axis of its predecessor, should be
directed a little to one side, it is obvious that a curved instead of
a straight rod will be produced ; and this curvature may increase,

COMPOSITE FORMS OF FORAMINIFERA. 439

until it becomes a spiral (Fig. 205). The character of this spiral
will depend in great degree upon the enlargement or non-enlarge-
ment of the successively formed chambers; for sometimes it
opens out very rapidly, every whorl being considerably broader
than that which it surrounds, in consequence of the great excess
of the size of each segment over that of its predecessor, as is ge-
nerally the case in Cristellaria ; whilst in other instances there is
so little difference between the successive segments, after ’the
spiral has made two or three turns, that the breadth of each
whorl scarcely exceeds that of its predecessor, as is well seen in
Faujasina (Fig. 209), as also in Nummulite (Chap. XIX). An
intermediate condition is presented by Rosalina (Fig. 205), which

Fig. 205.

iosalina ornata, with its pseudopodia extended.

may be taken as an example of a very large group of Foramini-
fera, composed of those whose plan of growth is helical or spiral,
and ranged by M. D’Orbigny under the designation Helicostégues.
In this genus, as in a large proportion of its congeners, we find
the shell perforated with numerous apertures, through which
pseudopodia can be extended from any of the segments that are
not enclosed by others, as well as from the mouth or aperture of
the outer segment; and when this is the case, it does not appear
that the sarcode body is so often extended over the exterior of
the shell, as it is when the shell has no perforations for the put-
ting forth of these extensions. There are generally indications,
however, in the structure of the shell itsclf,—new layers being
often formed over the innermost whorls of the spiral, or partial

440 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

deposits being added, sometimes in the shape of bosses, spines,
or other outgrowths,—that a soft substance, capable of originating
such new formation, must occasionally spread itself over the
whole external surface of the previous segments. And it is not
difficult to understand how this may come to pass, when it is
borne in mind that the gelatinous sareode, however fine may be
the threads into which it divides itself, may readily form a con-
tinuous layer by the coalescence of those threads. The group of
Helicostégues is subdivided by M. D’Orbigny into two families,
the Nautiloide, and the Turbinoide ; the first and most important
consisting of those in which the successive whorls all lie in the
same plane, so that the shell is “ equilateral” (like that of a Nau-
tilus), as is the case with Mummulites and their allies (such as
Nonionina, Assilina, Operculina, &c., between which and Num-
mulites the differences are but very slight); whilst the second
contains those in which the spiral passes obliquely round an axis,
so that the shell becomes “inequilateral” (like that of a snail or
periwinkle), as is the case with Motalia (Fig. 835), Fawasina
(Fig. 209) and Rosalina (Fig. 205).

287. Putting aside less important variations in the plan of
gemmation, we have now to notice one that seems essentially dis-
tinct from the preceding; that, namely, in which the new seg-
ments are added in concentric rings, each surrounding its pre-
decessors, so asto form flattened disks. Asan example of this curi-
ous type of Foraminiferous structure, the Orbztolite may be cited ;
which, long known as a very abundant fossil in the early ter-
tiaries of the Paris basin, has lately proved to be scarcely less
abundant in certain parts of the existing ocean. The largest
specimens of it, sometimes attaining the size of a sixpence, have
hitherto been obtained only from the coast of New Holland and
various parts of the Polynesian Archipelago; but disks of com-
paratively minute size (from the diameter of an ordinary pin’s
head, to that of a small pea) and of simpler organization, are to
be found in almost all Foraminiferous sands and dredgings from
the shores of the warmer regions of the globe, being especially
abundant in those of some of the Philippine Islands, of the Red
Sea, of the Mediterranean, and especially of the Hgean. When
such disks are subjected to Microscopic examination, they are
found (if uninjured by abrasion) to present the structure repre-
sented in Fig. 206; where we see on the surface (by incident
light) a number of rounded elevations, arranged in concentric
circles around a sort of nucleus (which has been laid open in the
figure to show its internal structure); whilst at the margin we
observe a row of rounded projections, with a single aperture or
pore in each of the intervening depressions. In very thin disks,
the structure is often brought into view, by mounting them in
Canada balsam, and transmitting light through them, sufliciently
well to render any other mode of preparation unnecessary; but
in those which are too opaque to be thus seen through, it is sufii-

FORAMINIFERA—ORBITOLITE. 441

cient to rub down one of the surfaces upon a stone, and then to
mount the specimen in balsam. Each of the superficial eleva-
tions will then be found
to be the roof or cover Fia. 206,
of an ovate cavity or cell, om
which communicates by
means of a lateral passage
with the cavity on either
side of it in the same
ring; so that each circu-
lar zone of cells might be
described as a continuous
annular passage, dilated
into cavities at intervals.
On the other hand, each
zone communicates with Simple disk ot Orbitokites complanatus, laid open to
the zones that are inter- show its interior structure :—a, central cell; b, cireum-
nal and external to it, by smblen gl sounded by concente zones of cl
means of passages IN 4 passages.

radiating direction; and

it is curious that these passages run, not from the cells of
the inner zone to those of the outer; but from the connect-
ing passages of the former to the cells of the latter; so that
the cells of each zone alternate in position with those of the
zones that are internal and external to it. The radial passages
from the outermost annulus make their way at once to the mar-
gin, where they terminate, forming the ‘pores’ which (as al-
ready mentioned) are to be seen on its exterior. The central
nucleus, when rendered sufficiently transparent by the means
just adverted to, is found to consist of a central cell (a), usually
somewhat pear-shaped, that communicates by a narrow passage
with a much larger cireumambient cell (6), which nearly sur-
rounds it, and which sends off a variable number of radiating
passages towards the cells of the first zone, which forms a com-
plete ring around the nucleus.'

288. The idea of the nature of the living occupant of these
cavities, which might be suggested by the foregoing account of
their arrangement, is fully borne out by the results of the exami-
nation of the sarcode body, that may be obtained by the macera-
tion in dilute acid (so as to remove the shelly investment) of
specimens of Orbitolite, that have been gathered fresh from the
sea-weeds to which in the living state they are found adherent,
and have been kept in spirit. or this body is found to be com-
posed (Fig. 207) of a multitude of segments of ‘“sarcode,” pre-

1 Although the above may be considered the typical form of the Orbitolite, yet, in a
very large proportion of specimens, the first few zones are not complete circles, the
early growth having taken place rather in a spiral than in a radial direction; between
these two plans, there is every variety of gradation ; and even where the spiral is most

distinctly marked in the first instance, the additions soon come to be made in concentric
zones,

442 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

senting not the least trace of higher organization in any part,
and connected together by “stolons” of the like substance. The
“central” pear-shaped segment, a, is seen to have budded off its
“‘circumambient’” segment, , by a narrow footstalk or stolon;
and this circumambient segment, after passing almost entirely
round the central one, has budded off three stolons, which swell
into new segments from which the first annulus is formed.
Scarcely are any two specimens precisely alike, as to the mode
in which the first annulus
Fia. 207, originates from the “ circum-
; ambient” segment; for some-
times a score or more of
radial passages extend them-
selves from every part of the
margin of the latter (and
4, this, as corresponding with
i, the plan of growth afterwards
Wr, followed, is probably the
typical arrangement), whilst
in other cases (as in the ex-
ample before us) the number
of these primary offsets is
extremely small. Each zone
is seen to consist of an as-
x: semblage of ovate segments,
Composite Animal of simple type of Orbitolites whose height (which could
complunatus :—a, central mass of sarcode; 6, eir- not be shown in the figure)
cumambient mass, giving of peduncles, in which corresponds with the thick-
originate the concentric zones of segments con- i
ngeted bytanntlar bande: ness of the disk; these seg-
ments, which are all exactly
similar and equal to one another, are connected by annular
“stolons;’’ and each zone is connected with that on its exterior,
by radial extensions of those stolons, passing off between the
segments. Although no opportunity has yet been obtained, for
a microscopic examination of these animals in their living state,
yet there can be no reasonable doubt that the radial extensions
of the outermost zone issue forth as pseudopodia from the mar-
ginal pores; and that they search for and draw in alimentary
materials, in the same manner as do those of other Foramini-
fera; the whole of the soft body, which has no communication
whatever with the exterior, save through these marginal pores,
being nourished by the transmission of the products of diges-
tion from segment to segment and from zone to zone, through
similar bands of gelatinous substance. In all cases in which the
growth of the disk takes place with normal regularity, it is pro-
bable that a complete circular zone is added at once. When the
sarcode body has increased beyond the capacity of its enveloping
disk, it may be presumed that its pseudopodial extensions, pro-
ceeding from the marginal pores, coalesce, so as to form a com-

FORAMINIFERA—ORBITOLITE. 443

plete annulus of sarcode round the margin of the outermost
zone; and it is probable that it is by a deposit of calcareous
matter in the surface-portion of this annulus, that the new zone
of shelly substance is formed, which constitutes the walls of the
cells and passages occupied by the soft sarcode body. Thus we
find this simple type of organization giving origin to fabrics of
by no means microscopic dimensions, in which, however, there
is no other differentiation of parts than that concerned in the
formation of the shell; every segment and every stolon (with
the exception of the two forming the “ nucleus’) being, so far
as can be ascertained, a precise repetition of every other, and
the segments of the nucleus differing from the rest in nothing
else than their form. The equality of the endowments of the
segments is shown by the fact, of which accident has repeatedly
furnished proof,—that a small portion of a disk, entirely sepa-
rated from the remainder, will not only continue to live, but will
so increase as to form a new disk; the loss of the nucleus not
appearing to be of the slightest consequence, from the time that
active life is established in the outer zones. In what manner
the multiplication and reproduction of the species are accom-
plished, we can as yet do little more than guess; but from
appearances sometimes presented by the sarcode body, it seems
reasonable to infer that “‘gemmules,” corresponding with the
“zoospores” of Protophytes (§ 197), are occasionally formed by
the breaking up of the sarcode into globular masses; and that
these, escaping through the marginal pores, are sent forth to
develope themselves into new fabrics. Of the mode’ wherein
that sexual operation is performed, however, in which alone true
Generation consists, nothing whatever'is known.

289. One of the most curious features in the history of this
animal, is its capacity for developing itself into a form, which,
whilst fundamentally the same as that previously described, is
very much more complex. In all the larger specimens of Orbi-
tolite, we observe that the marginal pores, instead of constituting
but a single row, form many rows, one above another; and be-
sides this, the cells of the two surfaces, instead of being rounded
or ovate in form, are usually oblong and straight-sided, their long
diameters lying in a radial direction. When a vertical section is
made of such a disk, it is found that these oblong chambers
constitute two superficial layers, between which are interposed
columnar chambers of a rounded form; and these last are con-
nected together by a complex series of passages, the arrangement
of which will be best understood from the examination of a part
of the sarcode body that occupies them (Fig. 208). For the ob-
long superficial chambers are occupied by segments of sarcode,
ec, dd, lying side by side so as to form part of an annulus, but
each of them being disconnected from its.neighbors, and com-
municating only by a double footstalk with the two circular sto-
lons aa’; 6b’, which obviously correspond with the single stolon

444 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

of the simple type (Fig. 207). These indirectly connect together,
not merely all the superficial cells
Fra. 208. of each zone, but also the columnar
segments of the intermediate layer;
for these columns (c e, é ¢) terminate
above and below in the annular
stolons, sometimes passing directly
from one to the other, but some-
times going out of the direct course
to coalesce with another column.
The columns of the successive zones
(two sets of which are shown in the
figure) communicate with each
other by threads of sarcode, in such
a manner, that (as in the simple
type) each column is thus brought
@ into connection with two columns
of the zone next interior, to which
Portion of Composite Animal of complex it alternates in position. Similar
une of rls emplaneun;we’ 0¥'K6 threads, passing off from the onter-
centric zones; ce, the upper layer of super- most zone, through the multiple
ficial segments, and dd the lower layer, coll: ranges oft marginal pores, would
vected with the annular bands of both zones; = =
ee, ee’, vertical segments of the two zones. doubtless act as pseudopodia. Now
this plan of growth is so different
from that previously described, that there would at first seem ample
ground for distinguishing the simple and the complex types as two
species. +But the test furnished by the examination of a large
number of spcedmnens, Which ought never to he passed by when it
can possibly be appealed to, furnishes these very singular results :—
1st, That the two forms must be considered as specifically iden-
tical; since there is not only a gradational passage from one to
the other, but they are often combined in the same individual,
the inner and first formed portion of a large disk frequently pre-
senting the simple type, whilst the outer and later formed part
has developed itself upon the complex :—2d, That although the
last mentioned circumstance would naturally suggest that the
change from the one plan to another nay be simply a feature of
advancing age, yet this cannot be the case; since the complex
plan sometimes evolves itself even from the very first (the nueleus,
though resembling that of the simple form, sending out two or
more tiers of radiating threads), whilst, more frequently, the sim-
ple prevails for an indefinite number of zones, and then changes
itself in the course of a few zones into the complex. The mode
in which this change occurs is not a little curious. In the first
place, the short segments, threaded (so to speak) upon their an-
nular stolon, undergo elongation, and the annular stolon itself
becomes double, being first, as it were, split in two, and its upper
and lower halves being separated by the interpolation of a length-

FORAMINIFERA—-NUMMULITES, ETC. 445

ening piece to each columnar segment. These additional pieces
are at first very short; but with the growth of every new zone,
they commonly increase in length; and this interpolated portion
comes to constitute the principal part of the thickness of the disk.
While this change is going on, another is taking place in the
position of the superficial portions of the segments which are
above and below the annular stolons; for these, whilst at first
seeming to be mere continuations of the columns beneath, and
being connected (like them) with the stolons of their own zones
alone, are so displaced, in the course of two or three zones, as to
arch over the space between the zones (as shown in Fig. 208),
and to connect themselves with the stolon, not only of their own
zone, but of the next. It has been thought desirable to enter
into the foregoing detail, since a more striking instance could
scarcely be drawn from any department of Natural History, of
the wide range of variation that may occur within the limits of
one and the same species; and the Microscopist needs to be
specially put on his guard as to this point in respect to the lower
types of Animal, as to those of Vegetable life, since the determi-
nation of form seems to be far less precise among such, than it is
in the higher types.'

290. The type of Foraminiferous structure which has been
just described, is in many respects peculiar, and may be con-
sidered as verging towards the Sponges. Itis obvious, from
what has been said of the extreme freedom with which the
several segments of the sarcode body communicate with each
other, that they form one whole, in a far greater degree than they
do in the ordinary composite Foraminifera, whose segments are
more completely separated, and are very commonly connected
only by a few very slender threads of sarcode. Indeed if we
were to imagine a discoidal mass of sarcode to be traversed by
a reticulated calcareous skeleton, somewhat resembling that open
areolar texture which forms the shell of the Echinida (§ 312), and
this network were to possess somewhat of that regularity in the
disposition of its successively formed parts, which is presented to
us in the spines of that group (Fig. 237), we should have no
unapt representation of the calcareous skeleton of the Orbitolite,
and of its relation to the animal which it envelopes and protects.
Now there are certain Sponges which have a reticular skeleton
composed of mineral matter (§ 296), differing from that of the
Orbitolite in little else than the want of the zonular arrangement
which marks successive epochs of growth; and we shall see that
the constitution of the soft body is essentially the same in one
case asin the other. A remarkable connecting link between the
Orbitolite and certain Sponges, seems, in fact, to be presented

' For a full account of the Organization of the Orbitolite, and of the various conditions
under which it presents itself, see the Author’s memoir upon that genus in “ Philos.
Transact.” 1856.

.

446 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

to us in the curious Thalassicolla,! discovered by Mr. Huxley, and
since observed by Prof. Miiller, which seems also to have rela-
tions to the Polycystina (§ 292).

291. The essential simplicity of the animal, and the absence
of anything like structure in the shell, of the Orbitolite, ob-
viously place it much lower in the scale than those Foraminifera,
which have the segments not only more completely divided, but
enclosed in a shell which is itself distinctly organized. Such is
the case with Nummulites and their nearest allies among the
recent forms. For in these, as will be more fully shown here-
after (Chap. XIX), each segment has its own separate envelope
of shell, so that the partition between any two adjacent chambers
is double; the chambers are so far cut off from one another, as
to communicate only by very narrow passages; but means are
afforded, by which even the innermost chambers are brought into
tolerably direct relation with the exterior. For in this type of
structure, we observe that those parts of their walls which look
towards the outer surfaces, are perforated with immense numbers
of pores resembling those of Fig. 205, but more numerous,
minute, and closely set; and where the walls are thick, these
pores are continued as tubes through their entire substance
(Figs. 209, 838). However fine they may be, the extraordinary
tenuity of the threads into which the sarcode is occasionally seen
to divide itself (Fig. 204), shows that this need not be an ob-
stacle to the passage of pseudopodial prolongations through them.
But further, in the spaces between the walls of contiguous cham-
bers, we find a system of large tubes, which make their way
directly from the central to the peripheral portion of the disk,
and which, communicating on the one hand with the innermost
chambers, and on the other with the margin (being extended
and carried on to it whenever the previous edge is covered by a
new growth), serve to bring the former into a very direct rela-
tion with the external sources of supply of nutriment and oxygen.
A strikingly developed example of this system of ‘“ interseptal”’
canals is presented in the genus Faujasina (Fig. 209) ;2 where the
large size of the canals, and the extreme simplicity of their
arrangement, enable them to be very readily traced out. In
some instances the arrangement becomes extremely complex:

1 See “ Annals of Natural History,” 2d Ser. vol. viii, p. 433; and “Quart. Journ. of
Microsc. Science,” vol. iv, p. 72.

2 See Prof. Williamson's Memoir on the Fawasina, in the “Transact. of Microsc.
Soc.” 2d Ser. vol. i. As the correctness of the account of the interseptal system of
canals, which has been given by the Author (in his Memoir on Nummulite, &c., in
“ Quart. Geol. Journ.” Feb. 1850), and confirmed by the researches of Prof, W. and
himself upon numerous recent types, has been called in question by no less an authority
than Prof, Schulze, who has, in consequence, altogether ignored this important cha-
yacter in his classification, the Author thinks it right to state, that although the above
figure is copied from one of those which illustrate Prof. Williamson’s Memoir, yet it is
the almost precise counterpart of a section of the same species prepared by himself.
The incredulity of Prof. Schulze and others, upon this point, simply depends upon their
want of aptitude in the preparation of sufficiently thin sections.

COLLECTION AND SELECTION OF FORAMINIFERA. 447

this is especially the case, where, as frequently happens, there is
an interstitial calcareous skeleton to be nourished (often extend-
ing itself into outgrowths of

various forms and sizes), in Fra. 209.

addition to the immediate
investments of the seg-
ments; and it becomes ob-
vious from the far greater
development of this canal
system wherever such is the
ease, that this interstitial
skeleton is chiefly if not
entirely maintained through
the instrumentality of the
“stolons” of sarcode which
occupy these canals, and
whose remains may often
be distinctly traced in the
dried shell. Now this, the
highest type of Foramini-
ferous structure, is not only _ Section of Fuxgasina near its base and parallel to
presented by such spiral 17;“towng cathe radiating inerenpal canal; &
forms as Nummulite, but is tubular wall of the chambers.

found also in a genus that is

conformable, in its concentric plan of growth, to Orbitolite.
Hence it is obvious that no arrangement founded, as in that of
M. D’Orbigny, upon a character of such secondary importance
as the direction of gemmation, is likely to be in accordance with
physiological features which a perfect knowledge of the animal
might be expected to afford; and as these can be partly judged
of from the structure of the shell, it seems obvious that this
ought to be made the first consideration. To carry out a classi-
fication on such a basis, however, will involve a large amount of
patient investigation?

292. Many of the Foraminifera attach themselves in the living
state to Sea-weeds, Zoophytes, &c.; and they should, therefore,
be carefully looked for on such bodies, especially when it is de-
sired to observe their internal organization and their habits of
life. They are often to. be collected in much larger numbers,
however, from the sand or mud dredged up from the sea-bottom,
or even from that taken from between the tide marks. Ina
paper containing some valuable hints on this subject,’ Mr. Legg

'The Author has been enabled to make out this curious point completely, in the
Calcarina, a little body resembling a spur-rowel. For he has obtained ample evidence
that the spire with its regularly added segments, and interstitial skeleton extending itself
into radiating spines, may grow quite independently of one another. The proof will be
submitted in future Memoirs to the Royal Society.

2 To this labor, the Author has been for some years devoting a portion of his very
limited leisure, in conjunction with his friend Prof. Williamson, of Manchester ; and the
results of their united labors will appear at the earliest practicable period, in the Ray
Society’s publications.

3 « Transactions of the Microscopical Society,” 2d Series, vol. ii, p. 19.

448 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

mentions that, in walking over the Small Mouth Sand, which is
situated on the north side of Portland Bay, he observed the
sand to be distinctly marked with white ridges, many yards in
length, running parallel with the edge of the water; and upon
examining portions of these, he found Foraminifera in considera-
ble abundance. One of the most fertile sources of supply that
our own coasts afford, is the “ouze” of the Oyster-beds, in which
large numbers of living specimens will be found; the variety of.
specific forms, however, is usually not very great. In separating
these bodies from the particles of sand, mud, &c., with which
they are mixed, various methods may be adopted, in order to
shorten the tedious labor of picking them out, one by one, under
the Simple Microscope; and the choice to be made among these
will mainly depend upon the condition of the Foraminifera, the
importance (or otherwise) of obtaining them alive, and the nature
of the substances with which they are mingled. Thus, if it be
desired to obtain living specimens from the oyster-ouze, for the
examination of their soft parts, or for preservation in a vivarium,
much time will be saved by stirring the mud (which should be
taken from the surface only of the deposit) in a jar with water,
and then allowing it to stand for a few moments; the finer par-
ticles will remain diffused through the liquid, while the heavier
will subside; and as the Foraminifera (in the present case) be-
long to the latter category, they will be found almost entirely
free from extraneous matter, at the bottom of the vessel, after
the operation has been repeated two or three times. It would
always be well to examine the first deposit let fall by the water
that has been poured away; as this may contain the smaller and
lighter forms of Foraminifera. But supposing that it be only
desired to obtain the dead shells from a mass of sand brought up
by the dredge, a very different method should be adopted. The
whole mass should be exposed for some hours to the heat of an
oven, and be turned over several times, until it is found to have
been thoroughly dried throughout; and then, after being al-
lowed to cool, it should be stirred in a large vessel of water.
The chambers of their shells being now occupied by air alone
(for the bodies of such as were alive will have shrunk up almost
to nothing), the Foraminifera will be the lightest portion of the
mass; and they will be found floating on the water, while the
particles of sand, &c., subside. Another method, devised by
Mr. Legg, consists in taking advantage of the relative sizes of
different kinds of Foraminifera and of the substances that ac-
company them. This, which is especially applicable to the sand
and rubbish obtainable from sponges (which may be got in large
quantity from the sponge merchants), consists in sifting the
whole aggregate through successive sieves of wire-gauze, com-
mencing with one of ten wires to the inch, which will separate
large extraneous particles, and proceeding to those of 20, 40, 70,
and 100 wires to the inch, each (especially that of 70) retaining

GENERAL STRUCTURE OF POLYCYSTINA. 449

a much larger proportion of Foraminiferous shells than of the
accompanying particles; so that, a large portion of the extra-
neous matters being thus got rid of, the final selection be-
comes comparatively easy. Certain forms of Foraminifera are
found attached to shells, especially bivalves (such as the Cha-
macece), with foliated surfaces ; and an extensive examination of
those of the Indian Seas, when brought home “in the rough,”
has yielded to Mr. W. K. Parker some most valuable and novel
results, which will be made public in due time.

293. The final selection of specimens for mounting, should
always be made under some appropriate form of Single Micro-
scope (§§ 27-30); a fine camel-hair pencil, with the point wetted
between the lips, being the instrument which may be most con-
veniently and safely employed, even for the most delicate speci-
mens. In mounting Foraminifera as microscopic objects, the
method to be adopted must entirely depend upon whether they
are to be viewed by transmitted or by reflected light. In the
former case, they should be mounted in Canada balsam; the
various precautions to prevent the retention of air bubbles which
have been already described (§ 128), being carefully observed.
In the latter, no plan is so simple, easy, and: effectual, as the
attaching them with a little gum to a blackened disk of card,
and guarding them by a perforated wooden slide (§ 123). They
should be fixed in various positions, so as to present all the dit
ferent aspects of the shell, particular care being taken that its
mouth is clearly displayed ; and where, as will often happen, the
several individuals differ considerably from one another, special
care should be taken to form series illustrative of their range of
variation, and of the mutual connections of even the most di-
verse forms. Tor the display of the internal structure of Fora-
minifera, it will often be necessary to make extremely thin sec-
tions, in the manner already described (§§ 108-110); and much
time will be saved, by attaching a number of specimens to the
glass at once, and by grinding them down together. For the
preparation of sections, however, of the extreme thinness that
is often required, those which have been thus reduced should
be transferred to separate glasses, and finished off each one by
itself.

294. Polycystina.—It is probable that we are to refer to the same
general type, an extensive group of very interesting microscopic
bodies, possessing great beauty and variety of form and structure
(Figs. 210-216) of whose essential character extremely little is
known. These are minute siliceous shells, which appear, from
the recent observations of Prof. Miiller, to contain in the living
state an olive-brown “sarcode,” extending itself into pseudo-
podial prolongations (resembling those of Actinophrys, § 262),
that pass through the large apertures by which the shells are
perforated. The sarcode body does not seem always to fill the
shell; being stated by Prof. Miiller to occupy, in the Hneyrtidiwm

29

450 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

of Messina, only the upper part or vault of the shell, and to be
very regularly divided into four lobes. It is a peculiar feature
in these Polycystine, that

Fig, 210. Fig, 211. their shells are often pro-
longed into spines or other
projections, which are some-
times arranged in such a
manner as to give them a
very singular aspect (Figs.
210, 211). It seems pro-
bable that these creatures
are almost as widely diffused
at the present time as are
the Foraminifera; although,
from their greater minute-
ness, they have not been
so often recognized. For
having been first discovered
by Prof. Ehrenberg at Cux-
Fig. 210. Podocyrtis Schomburgkti, haven on the North Sea,

Fig, 211. Rhopalocanium ornatum. they were afterwards found

by him in collections made

in the Antarctic Seas, and have been recently described by Prof.
Bailey as presenting themselves (with Foraminifera and Diato-
mace) in the deposits brought up by the sounding-lead from the
bottom of the Atlantic Ocean, at depths of from 1000 to 2000
fathoms. They appear to have been much more abundant, how-
ever, during the later geological periods; for not only have
certain forms (among them Haliomma, Fig. 212) been detected by

Fria. 212, Fig. 213.

Fig. 212. Uiliomma ITumbolatii,
Fig. 213. Perichlamydium pretectum.

Prof. Ehrenberg in the chalks and marls of Sicily and Greece,
and of Oran in Africa, and also in the diatomaceous deposits of
Bermuda and Richmond (Virginia); but a large proportion of
the rock that prevails through an extensive district in the island
of Barbadoes, has been found by him to be composed of Poly-

POLYCYSTINA OF BARBADOES. 451

cystina, mingled with Diatomacer, with a few calcareous Fora-
minifera, and with calcareous earth which was probably derived

Fig. 214, -

Fossil Polycystina, &c., from Barbadoes:a, Podocyrtis mitra; 6, Rhabdolithus sceptrum; ¢,
Lychnocanium falciferum; d, Enoyrtidium tubulus; e, Flustrella concentrica; 7, Lychnocanium
lucerna; g, Encyrtidium elegans; h, Dietyospyris clathrus; 7, Encyrtidium mongolfieri; &, Stepha-
nolithis spinescens; 1, 8. nodosa; m, Lithocyclia ocellus; , Cephalolithis sylvina; 0, Podocyrtis
cothurnata; g, Rhabdolithes pipa.

from the decomposition of corals, &c., 80 as to form, according to
the relative proportions of these constituents (which differed in
different parts of the deposit), a tripoli-like sandstone, whitish
and very friable, a compact calcareous sandstone, and strata of a
marly character sometimes containing semi-opal. Previously to
this last discovery, which was made in the year 1846 (the mate-
rials having been furnished by the geological researches of Sir
R. H. Schomburgk), 39 species of Polycystina had been esta-
blished by Prof. E.; but in the Barbadoes deposit, he has detected
no fewer than 282 forms which he considers to be specifically
distinct, besides 25 species of Diatomacee and Foraminifera, and
54 forms which he cannot distinctly determine, but which he
classes under the provisional designations of Geolitharia and
Phytolitharia, making 361 in all, of which more than 300 were
previously unknown. The 282 species of Polycystina are arranged
by Prof. E. in seven families, which include forty-four genera;
but it is obvious that in our present state of almost entire igno-
rance of the structure and physiology of the animals to which
these shells belong, no classification can be otherwise than pro-
visional.—Few Microscopic objects are more beautiful than an
assemblage of the most remarkable forms of Barbadian Polyeys-

452 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

tina, especially when seen brightly illuminated upon a black
ground; since (for the reason formerly explained, § 62) their

Fig, 215, Fia, 216.

Fig. 215. Stylodictya gracilis.
Fig. 216. Astromma Aristotelis.

“solid forms” become much more apparent than they are when
these objects are examined by light transmitted through them.
And the “black ground illumination,” either by the “spotted
lens” or by the “ paraboloid” (§ 61), is much to be preferred for
this purpose, to the ordinary mode of illuminating opaque objects
by incident light from a condenser, although this may be advan-
tageously had recourse to, by the Microscopist who is unprovided
with these appurtenances. No class of objects is more suitable
than these to the “Binocular Microscope” (§ 40); the stereosco-
pic projection of which causes them to be presented to the mind’s
eye in complete relief, so as to bring out with the most marvel-
lous and beautiful effect all their delicate sculpture, reminding
the observer (to compare small things with great) of the finest
specimens of the hollow ivory balls carved by the Chinese.!

295. Sponges.—Although this tribe has been bandied from the
Animal to the Vegetable kingdom, and back again, several times
in succession, yet its claim to a place among the Protozoa may
now be considered as pretty certainly determined, by the infor-
mation derived from Microscopic examination of its minute
structure. For in the living Sponge, the skeleton, usually com-
posed of a fibrous network strengthened by spicules of mineral
matter, is clothed with a soft flesh; and this flesh has been
found by Dujardin and all subsequent observers to consist of an
ageregation of Amcba-like bodies (Fig. 217, 8), some of which
(as Mr. Dobie has shown)’ are furnished with one or more long

! For a fuller description of this group, see Prof. Ehrenberg’s Memoirs in the “ Transac-
tions of the Berlin Academy” for 1846, 1847, and his recently published “ Microgeologie ;”

also “ Ann. of Nat. Hist.” 1847.
2 Goodsir's Annals of Anatomy and Physiology,” No. 2, May, 1852.

GENERAL STRUCTURE OF SPONGES. 453

cilia, closely resembling those of Volvor (Fig. 70, 1), by the
agency of which, a current of water is kept up through the
passages and canals excavated in the substance of the mass.

Fig. 217.

Structure of Grantia conypressu:—a, portion moderately magnified, showing general arrangement
of triradiate spicules and intervening tissue ;—s, small portion highly magnified, showing ciliated
cells.

And from the observations of Mr. Carter’ upon the early
development of Sponges, it*appears that they begin life as soli-
tary Amebe, and that it is only,in the midst of aggregations
formed by the multiplication of these, that the characteristic
Sponge-structure makes its appearance, the formation of spicules
being the first indication of such organization. The ciliated
cells seem to form the walls of the canals by which the whole
fabric of the Sponge is traversed; these canals, which are very
irregular in their distribution, may be said to commence in the
small pores of the surface, and to terminate in the large vents;
and a current is continually entering at the former, and passing
forth from the latter, during the whole life of the Sponge, bring-
ing in alimentary particles and oxygen, and carrying out excre-
mentitious matter.

296. The skeleton which gives shape and substance to the
mass of sarcode particles that constitutes the living animal, is
composed, in the Sponges with which we are most familiar, of
an irregular reticulation of fibres. The arrangement of these
may be best made out, by cutting thin slices of a piece of
Sponge submitted to firm compression, and viewing these slices,
mounted upon a dark ground, with a low magnifying power,
under incident light. Such sections, thus illuminated, are not
merely striking objects, but serve to show, very characteristically,
the general disposition of the larger canals and of the smaller
areole: with which they communicate. In the ordinary Sponge,
the fibrous skeleton is almost entirely destitute of spicules, the
absence of which, in fact, is one important condition of that

1« Annals of Natural History,” Ser. 2, vol. iv.

454 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

flexibility and compressibility on which its uses depend. When
spicules exist in connection with such a skeleton, they are either
altogether imbedded in the fibres, or they are implanted into
them at their bases, as shown in Fig. 218. In the curious and
beautiful Dictyochalix pumiceus of Barbadoes, however, the en-
tire network of fibres is composed of silex, and is so transpa-
rent that it looks as if composed of spun glass. There are many
Sponges in which no fibrous network can be discerned, the
spicules lying imbedded in the midst of the sarcode mass; such
is the case in Grantia (Fig. 217, a), whose triradiate spicules are
composed of carbonate of lime. Sponge-spicules are much more
frequently siliceous than calcareous; and the variety of forms
presented by the siliceous spicules is much greater than that
which we find in the comparatively small number of species in
which they are composed of carbonate of lime. The long
needle-like spicules (Fig. 219) which are extremely abundant in
several Sponges, lying close together in bundles, are sometimes
straight, sometimes slightly curved; they are sometimes pointed
at both ends, sometimes at one only; one or both ends may be
furnished with a head like that of a pin, or may carry three or
more diverging points, which sometimes curve back so as to form
hooks (Fig. 834, H). When the spigules project from the horny
framework, they are usually somewhat conical in form, and their
surface is often beset with little spines, arranged at regular
intervals, giving them a jointed appearance (Fig. 218). Sponge-
spicules frequently occur, however, under forms very different
from the preceding; some being short and many-branched; and
the branches being themselves very commonly stunted into mere
tubercles (some examples of

Fig, 218. which type are presented in Fig.

334, a, c); whilst others are stel-
late, having a central body with
conical spines projecting from it
in all directions (as at D of the
same figure) Great varieties

Fia. 219.

network. ®
Fig. 219, Siliceous Spicules of Pachymatisma,

present themselves in the stellate form, according to the relative
predominance of the body and of the rays; in those represented

SPONGES, MODE OF EXAMINING THEM. 455

in Fig. 219, the rays, though very numerous, are extremely
short; in other instances the rays are much longer, and scarcely
any central nucleus can be said to exist. The varieties in the
form of Sponge-spicules are, in fact, almost endless; and a
single sponge often presents two or more (as shown in Fig. 219),
the stellate spicules usually occurring either in the interspaces
between the elongated kinds, or in the external crust. In one
curious Sponge described by Mr. Bowerbank (the Dusideia fra-
gilis), the spicules are for the most part replaced by particles of
sand, of very uniform size, which are found imbedded in the
horny fibre. The spicules of Sponges cannot be considered,
like the “raphides” of Plants (§ 230), simply as deposits of
mineral matter in a crystalline state. For the forms of many of
them are such as no mere crystallization can produce; many of
them possess internal cavities, which contain organic matter;
and the calcareous spicules, whose mineral matter can be readily
dissolved away by an acid, are found to have a distinct animal
basis. Hence it seems probable, that each spicule was origi-
nally a cell or segment of sarcode, which has undergone calcifica-
tion, and by the self-shaping power of which, the form of the
spicule is mainly determined.

297. Of the Reproductive process in Sponges, much has
yet to be learned. The following is perhaps the most probable
account of it:—Multiplication by gemmation is effected by the
detachment of minute globular particles of sarcode from the
interior of the canals, where they sprout forth as little protu-
berances, whose footstalks gradually become narrower and nar-
rower until they give way altogether; these gemmudles, like the
zoospores of Alge, possess cilia, and issuing forth from the
vents, transport themselves to distant localities, where they may
lay the foundation of new fabrics. But according to the recent
observation§ of Mr. Huxley,! a true sexual generation also takes
place, as might be anticipated; both ova and sperm-cells being
found imbedded in the substance of the Sponge. The bodies
distinguished as capsules, which are larger than the gemmules,
and which usually have their investment strengthened with
siliceous spicules very regularly disposed, are probably the pro-
ducts of this operation. They contain numerous globular par-
ticles of sarcode, every one of which, when set free by the rup-
ture of its envelope, becomes an independent Ameeba-like body,
and may develope itself into a complete-Sponge.

298. With the exception of those that belong to the genus
Spongilla, all known Sponges are marine; but they differ very
much in habit of growth. For whilst some can only be obtained
by dredging at considerable depths, others live near the surface,
whilst others attach themselves to the surfaces of rocks, shells,
&e., between the tide-marks. The various species of Grantia,
in which alone of all the marine Sponges has ciliary movement

1 Ann, of Nat. Hist.” Ser, 2, vol. vii.

456 FORAMINIFERA, POLYCYSTINA, AND SPONGES.

yet been seen, belong to this last category. They have a pecu-
liarly simple structure, each being a sort of bag whose wall is so
thin that no system of canals is required, the water absorbed
by the outer surface passing directly towards the inner, and
being expelled by the mouth of the bag. The cilia may be
plainly distinguished with a 1-8th inch objective, on some of the
cells of the gelatinous substance scraped from the interior of the
bag ; or they may be seen zn situ, by making very thin transverse
sections of the substance of the Sponge.’ It is by such sections
alone, that the internal structure of sponges, and the relation of
their spicular and horny skeletons to their fleshy substance, can
be demonstrated. In order to obtain the spicules in an isolated
condition, however, the animal matter must be got rid of, either
by incineration, or by chemical reagents. The latter method is
preferable, as it is difficult to free the mineral residue from car-
bonaceous particles by heat alone. If (as is commonly the case)
the spicules are siliceous, the Sponge may be treated with strong
nitric or nitro-muriatic acid, until its animal substance is dis-
solved away; if, on the other hand, they be calcareous, a strong
solution of potass must be employed instead of the acid. The
operation is more rapidly accomplished by the aid of heat; but if
the saving of time be not of importance, it is preferable on seve-
ral accounts to dispense with it. The spicules, when obtained
in a separate state, should be mounted in Canada balsam.
Sponge-tissue may often be distinctly recognized in sections of
agate, chalcedony, and other siliceous accretions, as will here-
after be stated in more detail (Chap. XTX).

1See Dobie, loc. cit.; and Bowerbank in “ Transactions of Microscopical Society,” 1st
Ser. vol. iii, p. 137.

CHAPTER XI.

ZOOPHYTES.

299. THE term Zoophyte, although sometimes used in a wider
signification, is properly restricted to the class of Polypifera, or
polype-bearing animals, whose composite skeletons or “ poly-
paries”’ have more or less of a plant-like form ; even the Polyzoa
(or Bryozoa) being now excluded, on account of their truly
Molluscan structure (Chap. XIII), notwithstanding the zoophytic
character of their forms and of their habits of life. The true
Zoophytes may be divided into two primary groups, the Hydrozoa
and the Anthozoa ; the Hydra (or fresh-water polype) standing
as the type of the one, and the Sea-Anemone as the representa-
tive of the other. As the Hydrozoa are essentially microscopic
animals, they need to be described with some minuteness ; whilst
in regard to the Anthozoa, only those points can be dwelt on,
which are of special interest to the Microscopist.

300. The Hydra is to be searched for in pools and ditches,
where it is most commonly to be found attached to the leaves or
stems of aquatic plants, floating pieces of stick, &c. Two species
are common in this country, the H. viridis or green polype, and
the H. vulgaris, which is usually orange-brown, but sometimes
yellowish or red (its color being liable to some variation accord-
ing to the nature of the food on which it has been subsisting);
a third less common species, the H. fusca, is distinguished from
both the preceding by the length of its tentacula, which in the
former are scarcely as long as the body, whilst in the latter they
are, when fully extended, many times longer (Fig. 220). The
body of the Hydra consists of a simple bag or sac, which may
be regarded as a stomach, and which is capable of varying its
shape and dimensions in a very remarkable degree ; sometimes
extending itself in a straight line, so as to form along narrow
cylinder, at other times being seen (when empty) as a minute
contracted globe, whilst, if distended with food, it may present
the form of an inverted flask or bottle, or even of a button. At
the upper end of this sac is a central opening, the “mouth,”
and this is surrounded by a circle of tentacula or “arms,” usually
from six to ten in number, which are arranged with great regu- |
larity around the orifice. The body is prolonged at its lower °

458 ZOOPHYTES.

end into a narrow base, which is furnished with a suctorial disk;
and the Hydra usually attaches itself by this, whilst it allows its
tendril-like tentacula to float

Fria. 220. freely in the water, like so many
fishing-lines. The wall of the
body is composed of cells, im-
bedded in a kind of sarcode;
and it consists of two principal
layers, an outer and more com-
pact, of which the cells form a
tolerably even surface, and an
inner that lines the stomach,
into the cavity of which some of
the cells project. Between these
layers, there is a space chiefly
occupied by “sarcode,” having
many vacuoles or lacune (which
often seem to communicate with
one another) excavated in its
substance. The arms are made
up of the same materials as the
body; but their surface is beset
with little wart-like prominences,
which, when carefully examined,
are found to be composed ot
clusters of small “ thread-cells,”
having a single large cell with
a long spiculum in the centre of
each. The structure of these
thread-cells or ‘“urticating or-
; ans” will be described hereafter

soe orn vineyoutomuhont (310); at present it. will be
enough to point out, that this ap-

paratus, repeated many times on each tentacle, is doubtless in-
tended to give to the organ a great prehensile power ; the minute
filaments forming a rough surface, adapted to prevent the object
from readily slipping out of the grasp of the arm, whilst the
central spiculum is projected into its substance, and probably
conveys into it a poisonous fluid secreted by a vesicle at the base
of the dart. The latter inference is founded upon the oft-re-
peated observation, that if the living prey seized by the tentacles
have a body destitute of hard integument, as is the case with
the minute aquatic Worms which constitute a large part of its
aliment, this speedily dies, even if, instead of being swallowed,
it escapes from their grasp; on the other hand, minute Ento-
mostracous Crustacea, Insects, and other animals with hard en-
velopes, may escape without injury, even after having been de-
tained for some time in the polype’sembrace. The contractility
of the tentacula (the interior of which is traversed by a canal

HYDRA—ITS MULTIPLICATION BY BUDS. 459

which communicates with the cavity of the stomach) is very
remarkable, especially in the Hydra fusca ; whose arms, when
extended in search of prey, are not less than seven or eight
inches in length ; whilst they are sometimes so contracted, when
the stomach is filled with food, as to appear only like little
tubercles around its entrance. By means of these instruments,
the Hydra is enabled to derive its subsistence from animals,
whose activity, as compared with its own slight: powers of loco-
motion, might have been supposed to remove them altogether
from its reach ; for when, in its movements through the water,
a minute worm or a water-flea happens to touch one of the ten-
tacula of the polype, spread out as these are in readiness for
prey, it is immediately seized by this, other arms are soon coiled
around it, and the unfortunate victim is speedily conveyed to the
stomach, within which it may frequently be seen to continue
moving for some little time. Soon, however, its struggles cease,
and its outline is obscured by a turbid film, which gradually
thickens, so that at last its form is wholly lost. The soft parts
are soon completely dissolved, and the harder indigestible por-
tions are rejected through the mouth. A second orifice has
been observed at the lower extremity of the stomach; but this
would not seem to be properly regarded as anal, since it is not
used for the discharge of such exuvie ; itis probably rather to
be considered as representing, in the Hydra, the entrance to that
ramifying cavity, which, in the compound Hydroida, brings ingo
connection the lower extremities of the stomach of all the in-
dividual polypes (Fig. 228). A striking proof of the simplicity
of the structure of the Hydra, is the fact that it may be turned
inside out like a glove; that which was before its external tegu-
ment becoming the lining of its stomach, and vice versd.

301. The ordinary mode of multiplication in this animal, is by
a gemmation resembling that of Plants. Little bud-like pro-
cesses (Fig. 220, 6, c) are developed from its external surface,
which are soon observed to resemble the parent in character,
possessing a digestive sac, mouth, and tentacula; for a long time,
however, their cavity is connected with that of the parent, but at
last the communication is cut off by the closure of the canal of
the footstalk, and the young Polype quits its attachment and
goes in quest of its own maintenance. A second generation of
buds is sometimes observed on the young Polype, before quitting
its parent; and as many as nineteen young Hydre, in different
stages of development, have been seen ¢hus connected with one
original stock (Fig. 221). Another very curious endowment
seems to depend on the same condition,—the extraordinary
power which one portion possesses of reproducing the rest. Into
whatever number of parts a Hydra may be divided, each may
retain its vitality, and give origin to a new and entire fabric; so
that thirty or forty individuals may be formed by the section of
one. The Hydra also propagates itself, however, by a truly

460 ZOOPHYTES.

Sexual process; the fecundating apparatus, or vesicle-producing
“sperm-cells,” and the ovum (containing the “germ-cell,” im-
bedded in a store of nutriment adapted for its early development),
being evolved in the substance of the walls of the stomach, the
former just beneath the arms, the latter nearer to the lower end
of the body. It would appear that sometimes one individual
Hydra developes only the male cysts or sperm-cells, while another
developes only the female cysts or ovisacs; but the general rule
seems to be, that the same individual forms both organs. The
fertilization of the ova, however, cannot take place until after
the rupture of the spermatic cyst and that of the ovisac also; so
that the parent has no further participation in it, than has the
Fucus in the analogous fertilization of its germ-cells after their
discharge (§ 205). Although the production, from such an egg,
of a new Hydra, similar in all respects to its parent, has not yet
been witnessed, there seems no reason to doubt the fact. It
would seem that this alternation in the method of reproduction,
between the gemmiparous and the sexual, is greatly influenced

Fig, 221. Fie. 222.
B

-

lo

ie ‘}

\

Fig. 221. Hydra fusca in gemmation; @, mouth; b, base ; c, origin of one of the buds.

Fig. 222. Development of Medusa-buds in Syncoryna Sarsti:—a, an ordinary polype, with its club-
shaped body covered with tentacula:—s, a polype putting forth medusan gemma; a, avery young
bud; b, a bud more advanced, the quadrangular form of which, with the four nuclei whence the
cirrhi afterwards spring, is shown at d; c, a bud still more advanced.

by external temperature; the eggs being produced at the ap-
proach of winter, and serving to regenerate the species in the

COMPOSITE HYDROZOA—CORYNIDA. 461

spring, the parents not being able to survive the cold season;
whilst the budding process naturally takes place only during the
warmer part of the year, but may be made to continue through
the whole winter, by keeping the water inhabited by the polypes
at a sufficiently high temperature. The Hydra possesses the
power of free locomotion, being able to remove from the spot to
which it has attached itself, to any other that may be more suit-
able to its wants; its changes of place, however, seem rather to
be performed under the influence of light, towards which the
Hydra seeks to move itself, than with reference to the search
after food.

302. Some of the simpler forms of the composite Hydrozoa
may be likened to a Hydra, whose gemme, instead of becoming
detached, remain permanently connected with the parent; and
as these in their turn may develope gemme from their own
bodies, a structure of more or less arborescent character may be
produced. The form which this will present, and the relation of
the component polypes to each other, will depend upon the mode
in which the gemmation takes place; in all instances, however,
the entire cluster is produced by continuous growth from a single
individual; and the stomachs of the several polypes are united
by tubes, which proceed from the base of each other, along the
stalk and branches, to communicate with the cavity of the cen-
tral stem. This is the case with the family Corynide, which are
composite fabrics, sometimes quite arborescent in form, but
unpossessed of any firm investment, the external wall being only
strengthened by a thin horny cuticle. A very beautiful marine
species of this family (the Coryne pusilla), is common on sea-
weeds and stones between the tide-marks; sometimes clustering
parasitically round the stalks of Tubularia so as to form a thick
beard-like mossiness; each aggregate structure, however, not
being more than an inch in length. The tentacula (as in Fig.
222, a) are short, and arise from the whole surface of the body of
the polype, instead of from the margin of the mouth alone; and
at first it seems difficult to understand how they can be of ser-
vice in bringing food to the mouth, which is situated at the very
extremity of the branch. Observation of the living animal,
however, soon removes this difficulty; for the head is so very
flexible, that the mouth can bend itself down towards any of the
tentacula which may have entrapped prey; all its movements are
performed, however, in a very leisurely manner. The fresh-
water genus Cordylophora has yet been only found in a few loca-
lities; and the chief interest attaching to it is derived from the
fact of its having been made the subject of an admirable Memoir
by Prof. Allman,! to which every one should refer, who desires
to acquaint himself with the minute organization of this group
of Zoophytes. The phenomena of the Reproductive process
exhibited by these Hydrozoa, are extremely curious. In Coryne

1“ Philos. Transact.’ 1853.

462 ZOOPHYTES.

and its allies, besides the ordinary gemmation which extends the
original fabric, certain gemme are developed, which gradually
come to present an organization altogether comparable to that of
the simpler Meduse (Fig. 222, B) and which, when detached,
swim freely away. These, there is good reason to believe, stand
in the same relation to the ordinary polype-buds, as the flower-
buds of a plant do to its leaf-buds; each medusa-bud containing
either male or female sexual organs, and performing its part in
the sexual act, after it has been set free from the polype struc-
ture that bore it, just as the male (or staminiferous) flower of the
Vallisneria spiralis discharges its pollen upon the female (or
pistilline) flower, whilst floating on the surface of the water, after
it has broken itself off from the stem. The ova thus fertilized,
being deposited by the free swimming Medusa-buds, evolve
themselves (it is probable) into single polypes, from every one of
which there is gradually produced by continuous gemmation a
composite fabric, that in its turn developes Medusa-buds, whose
offspring resume the polype form. In Cordylophora, instead of
detached Medusa-buds, peculiar capsules sprout forth from the
stem, some of which contain sperm-cells, and others ova; and the
spermatozoa set free from the former enter the ovigerous capsules
and fertilize their ova, after the fashion of Vaucherta (§ 197).
The fertilized ova undergo “segmentation” according to the
ordinary type, the whole yolk-mass subdividing successively into
2, 4, 8, 16, 82 or more parts, until a “ mulberry mass” is formed;
this then begins to elongate itself, the surface becoming smooth,
and showing a transparent margin; and this surface becomes
covered with cilia, by whose agency these little bodies, now called
“ emmules,” first move about within the capsule, and then swim
forth freely when liberated by the opening of its mouth. At this
period, the embryo can be made out to consist of an outer and
an inner layer of cells, with a hollow interior; after some little
time, the cilia disappear, one extremity becomes expanded into
a kind of disk by which it attaches itself to some fixed object; a
mouth is formed, and tentacula sprout forth around it; and the
body increases in length and thickness, so as gradually to acquire
the likeness of one of the parent polypes, after which the plant-
like structure characteristic of the genus is gradually evolved, by
the successive development of polype-buds from the first formed
polype and its subsequent offsets."

303. In the family Tubularide, the long polype-stems are in-
vested by tubular horny sheaths; but these stop short below
the polype-heads, which are consequently unprotected; and the
reproductive gemmee bud forth, as in the preceding case, from
the base of the tentacula. The most common form of this
family is the Tubularia indivisa, which receives its specific name
from the infrequency with which branches are given off from
the stems, these for the most part standing erect and parallel,

' Allman (loc. cit.).

COMPOSITE HYDROZOA—TUBULARIDSE. 463

like the stalks of wheat, upon the base to which they are attached.
This beautiful zoophyte, which sometimes grows between the
tide-marks, but is more abundantly obtained by dredging in
deep water, often attains a size which renders it scarcely a micro-
scopic object; its stems being sometimes no less than a foot in
height, and a line in diameter. Several curious phenomena,
however, are brought into view by microscopic examination.
The polype-stomach is connected with the cavity of the stem by
a circular opening, which is surrounded by a sphincter; and an
alternate movement of dilatation and contraction takes place in
it, fluid being apparently forced up from below, and then ex-
pelled again, after which the sphincter closes, in preparation for
a recurrence of the operation; this, as observed by Mr. Lister,
being repeated at intervals of eighty seconds. Besides the fore-
going movement, a regular flow of fluid, carrying with it solid
particles of various sizes, may be observed along the whole
length of the stem, passing in a somewhat spiral direction, and
a good deal resembling the rotation in Chara (§ 201). The Re-
productive process in this family seems to be effected in various
modes; and the true relation between them has not yet been
clearly made out. The polype-stem sometimes puts forth
branches, at the termination of which new polypes ultimately
make their appearance, as in other composite Hydrozoa; and in
the genus Hudendrium, which is found on many parts of our
coasts, attached to old shells or stones dredged up from deep
water, a beautiful tree-like structure, from three to six inches
high, is thus formed. But around the polype-heads are evolved
gemme of a different kind, as in Coryne ; these being capsules,
within which are formed either one or several ovoid bodies, that
begin to develope themselves into the polype form even before
their escape from their containing cases, and soon fix themselves
after their immersion, shooting up into stems like those of the
parent. Whether this is a method of producing free gemma, or
whether it is a process of sexual generation, is not yet certainly
known; no spermatozoa have been observed in any of these
capsules; and if none should be detected by careful search, the
polypes thus evolved may be presumed to be buds. In several
Tubularide, the evolution of free Medusa-like buds, resembling
those of Syncoryne (Fig. 222), has been observed; and all ana-
logy would indicate that they act as the sexual organs, the de-
velopment of spermatozoa in some, and of ova in others, probably
not taking place until after they have led an independent life
for some time. It is worthy of mention here, that when a Tu-
bularia is kept in confinement, the polype-heads almost always
drop off after afew days, but are soon renewed again by a new
growth from the stem beneath; and this exuviation and re-
generation may take place many times in the same individual.
304. It is in the families Campanularide and Sertularide, that
the horny polypary attains its completest development; since it

464 ZOOPHYTES.

not only affords an investment to the stem, but forms cups or
cells for the protection of the polypes, as well as capsules for
that of the reproductive bodies. In the Campanularide, the
polype-cells are campanulate or bell-shaped, and are borne at the

extremities of ringed stalks (Fig. 228,

¢e); in the Sertularide, on

the other hand, the polype-cells lie along the stem and branches,
attached either to one side only, or to both sides (Fig. 224). In
both, the general structure of the individual polypes (Fig. 223, d)

Fig. 223,

Campanularia gelatinosa :—a, upper part of the stem and
branches, of the natural size; B, a small portion enlarged,
showing the structure of the animal; a, terminal branch
bearing polypes; 0, polype-bud partially developed; c,
horny cell, containing the expanded polype, d; e, ovarian
capsule, containing medusiform gemms in various stages
of development; /, fleshy substance extending through the
stem and branches, and connecting the different polype-
cells and ovarian capsules; g, annular coustrictions at the
base of the branches.

closely corresponds with
that of the Hydra; and
the mode in which they
obtain their food is essen-
tially the same. Of the
products of digestion,
however, a portion finds
its way down into the tu-
bular stem, for the nour-
ishment of the general
fabric; and very much the
same kind of circulatory
movement can be seen in
Campanularia, as in Tu-
bularia, the circulation be-
ing most vigorous in the
neighborhood of growing
parts. Itis from the soft
flesh (f) contained in the
stem and branches, : that
new polype-buds (6) are
evolved; these carry be-
fore them (so to speak) a
portion of the horny in-
tegument, which at first
completely invests the
bud; but as the latter
acquires the organization
of a polype, the case thins
away at its most promi-
nent part and an opening
is formed, through which
the young polype pro-
trudes itself. The origin
of the bodies commonly
but erroneously desig-
nated “ovarian capsules”
(e), is exactly similar; but
their destination is very
different. Within them

are evolved, by a budding process, the generative organs of the

COLLECTION AND OBSERVATION OF HYDROZOA. 465

Zoophyte; and these sometimes develope themselves into the
form of independent Meduse, which completely detach them-
selves from the stock that bore them, make their way out of the
capsule, and swim forth freely, to mature their sexual products
(some developing spermatozoa, and others ova) and give origin
to a new generation of polypes; whilst in other cases, these
flower-buds, whose Medusan structure is less distinctly pro-
nounced, do not completely detach themselves, but expand
one after another at the mouth of the capsule, withering and
dropping off after they have matured their generative pro-
ducts; and in other cases, again, the Medusan conformation is
altogether obscured by want of development, the sexual act
being performed by those bodies whilst they are still enclosed
within their capsules. There is reason to believe that the male
and female Medusoids are always developed within separate cap-
sules, possibly on distinct polypidoms; the males give forth
spermatozoa; whilst the females prepare ova, which, when ferti-
lized by the entrance of spermatozoa, develope themselves into
ciliated “‘ gemmules,”’ and these, escaping from the capsules,
soon evolve themselves into true polypes. This last is the only
mode of generation that has been yet witnessed among the Ser-
tularide ; for no free Medusoids have been observed to make
their way out of the capsules of any members of this family
(Fig. 224), within which may be seen several bodies that are
commonly reputed to be eggs, but are really imperfectly de-
veloped gemme of the Medusan type. It is worthy of notice,
that the horny capsule has been shown by Prof. E. Forbes, to be
essentially a metamorphosed branch, whose numerous small
cells have coalesced (as it were) into a single large one; this is
made obvious by a careful comparison of the forms under which
it presents itself, in different members of these two families.

305. There are few parts of our coasts, which will not supply
some or other of the beautiful and interesting forms of Zoophytic
life which have been thus briefly noticed, without any more
trouble in searching for them, than that of examining the sur-
faces of rocks, stones, sea-weeds, and dead shells between the
tide-marks. Many of them habitually live in that situation; and
others are frequently cast up by the waves from the deeper
waters, especially after a storm. Many kinds, however, can only
be obtained by means of the dredge. For observing them during
their living state, no means is so convenient as.the zoophyte-
trough (§ 69), invented for that express purpose by Mr. Lister,
to whom we owe not.only many improvements in the Microscope
and its appurtenances, but also some of the earliest and best ob-
servations upon this class of Zoophytes which the application of
the Achromatic principle permitted. Before mounting them for
preservation as microscopic objects, the Author has found it best
to keep them for some time in strong spirit; after a prolonged
maceration in which, they may be mounted in spirit sufficiently

30

466 ZOOPHYTES.

dilute to be destitute of any injurious action on the cement.

Goadby’s fluid also may be used; but the preservation of the
soft parts is not quite so

Fa. 224, complete with it as with
spirit. The size of the cell
must of course be propor-

| tioned to that of the object;

y and if it be desired to mount

such a specimen as may serve

for a characteristic illustra-
tion of the mode of growth
of the species it represents,
the large shallow cells, whose
walls are made by cement-
ing four strips of glass to the
plate that forms the bottom

(§ 186), will generally be

found preferable. The horny

polyparies of the Sertularide,
when mounted in Canada
balsam, are beautiful objects
for the Polariscope; but in
order to prepare them suc-
cessfully, somenicety of ma-
nagement is required. The
Sertularia cupressina:—a, natural size; 8, portion following are the outlines of
magnified. the method recommended

by Dr. Golding Bird, who

very successfully practised it. The specimens selected, which
should not exceed two inches in length, are first to be submitted,
while immersed in water of 120°, to the vacuum of an air-pump.

The ebullition which will take place within the cavities, will

have the effect of freeing the polyparies from dead polypes and

other animal matter; and this cleansing process should be re-
peated several times. The specimens are then to be dricd, by
first draining them for a few seconds on bibulous paper, and then
by submitting them to the vacuum of an air-pump, within a thick
earthenware ointment pot fitted with a cover, which has been
previously heated to about 200°; by this means, the specimens
are very quickly and completely dried, the water being evapo-
rated so quickly that the cells and tubes hardly collapse or
wrinkle. The specimens are then to be placed in camphine, and
again subjected to the exhausting process, for the displacement
of the air by that liquid; and when they have been thoroughly
saturated, they should be mounted in Canada balsam in the usual
mode. When thus prepared, they become very beautiful trans-

parent objects for low magnifying powers; and they present a

gorgeous display of colors when examined by polarized hight,

with the interposition of a plate of selenite. These objects are

RELATIONSHIP OF MEDUSZ TO HYDROZOA. 467

peculiarly fitted for Mr. Furze’s combination of the polarizing
plate with the spotted lens (§ 63); as they then exhibit all the
richness of coloration which the former developes, with the pe-
culiar solidity or appearance of projection which they derive from
the use of the latter.

306. No result of Microscopic research has been more unex-
pected, than the discovery of the close relationship subsisting
between the Hydroid Zoophytes and the Medusoid Acalephe (or
jelly-fish). We have seen that many of the small free-swimming
Medusans, belonging to that simple tribe of which Thaumantias
(Fig. 225) may be taken as a representative, are really to be
considered as the detached sexual apparatus of the Zoophytes
from which they have been budded off, endowed with indepen-
dent organs of nutrition and locomotion, whereby they become
capable of maintaining their own ex-
istence and of developing their gene- Fra. 225.
rative products. The general confor- =
mation of these organs will be under-
stood from the accompanying figure. iY
Many of this group are very beautiful <4
objects for Microscopic examination, 4
being small enough to be viewed entire ,Wigs. ff
in the zoophyte-trough. There are few nr
parts of the coast on which they may Thaumantias pilosella, one of the
not be found, especially on a calm «naked-eyed” Meduse :—aa, oral
warm day, by skimming the surface of tentacula; }, stomach; ¢, gastro-
the sea with a fine muslin net attached —Y2seular canals, having the ova.

a 2 fs Ties, , on either side, and ter-
to a ring, which may either be fixed to minating in the marginal canal, ee.
the end of a stick held in the hand, or
may be fastened by a string to the stern of the boat as a tow-net.
In either case, the net should be taken up from time to time,
held so as to allow the water it contains to drain through it, and
then turned inside out (so that what was previously its internal
surface shall now be the external), and moved about in a bucket
of water, so that any minute animals adhering to it may be
washed off. When we turn from these small and simple forms,
to the large and highly-developed Medusans which are com-
monly known as “jelly-tish,” we find that their history is essen-
tially similar; for their progeny have been ascertained to
develope themselves in the first instance under the polype form,
and to lead a life which in all essential respects is zoophytic;
their development into Meduse taking place only in the closing
phase of their existence, and then rather by gemmation from
the original polype, than by a metamorphosis of its own fabric.
The embryo emerges from the cavity of its parent, within which
the first stages of its development have taken place, in the con-
dition of a ciliated gemmule, of rather oblong form, very
closely resembling an’ Infusory animalcule, but destitute of a
mouth. One end soon contracts and attaches itself, however, so

a

468 ZOOPHYTES.

as to form a foot; the other enlarges and opens to form a mouth,
four tubercles sprouting around it, which grow into tentacula;
whilst the central cells melt down to form the cavity of the
stomach. Thus a Hydra-like polype is formed, which soon
acquires many additional tentacula; and this, according to the
observations of Sir J. G. Dalyell, leads in every important par-
ticular the life of a Hydra, propagates like it by repeated gem-
mation, so that whole colonies are formed as offsets from a
single stock, and can be multiplied like it by artificial division,
each segment developing itself into a perfect Hydra. There
seems to be no definite limit to its continuance in this state, or
to its power of giving origin to new polype buds; but under
conditions not yet ascertained, the Strobila (as it is termed)
ceases to propagate by ordinary gemmation, and enters upon an
entirely new series of changes. In the first place, the body
becomes more cylindrical in form than it previously was; then a
constriction or indentation is seen around it, just below the ring
which encircles the mouth and gives origin to the tentacula; and
similar constrictions are soon repeated around the lower parts of
the cylinder, so as to give to the whole body somewhat the
appearance of a rouleau of coins; a sort of fleshy bulb, some-
what of the form of the original polype, being still left at the
attached extremity (Fig. 226, a). The number of circles is

Fig. 226.

DR

Successive Stages of Development of Medusa buds from Strobila larva :—a, polype body; b, it~
original circle of tentacula; ¢, ils secondary circle of tentacula; d, proboscis of most advanced
Medusa disk; e, polype bud from side of polype body.

indefinite, and all are not formed at once, new constrictions
appearing below, after the upper portions have been detached:
as many as 80 or even 40 have thus been produced in one speci-
men. The constrictions then gradually deepen, so as to divide
the cylinder into a pile of saucer-like bodies; the division being
most complete above, and the upper disks usually presenting
some increase in their diameter: and whilst this is taking place,
the edges of the disks become divided into lobes (x), each lobe
soon presenting the cleft with the supposed rudimentary eye
(more probably an auditory organ) at the bottom of it, which is

POLYPOID DEVELOPMENT OF MEDUS4&. 469

to be plainly seen in the detached Medusee (Fig. 227, c). Up to
this period, the tentacula of the original polype surmount the
highest of the disks; but before the detachment of the topmost
disk, this circle disappears, and a new one is developed at the
summit of the bulb which remains at the base of the pile (c, ¢).
At last, the topmost and largest disk begins to exhibit a sort of
convulsive struggle; it becomes detached and swims freely
away; and the same series of changes takes place from above
downwards, until the whole pile of disks is detached and con-
verted into free swimming Meduse. But the original polypoid
body still remains; and may return to its polype-like and original
mode of gemmation (D, e), becoming the progenitor of a new
colony of Strobilee, every one of which may in its turn bud offa
pile of Medusa disks.

307. The bodies thus detached have all the essential characters
of the adult Meduse. Each consists of an umbrella-like disk,
divided at its edge into a variable number of lobes, usually
eight; and of a stomach, which occupies a considerable propor-
tion of the disk, and projects downwards in the form of a pro-
boscis, in the centre of which is the quadrangular mouth (Fig.
227, a, B). As the animal advances towards maturity, the in-

Fia. 227.

B

Development of Meduse from the detached gemmz of Strobila :—a, individual viewed sideways,
and enlarged, showing the proboscis, a, and 0 the bifid lobes; B, individual seen from above, show-
ing the bifid lobes of the margin, and the quadrilateral mouth ; c, one of the bifid lobes still more
enlarged, showing the ocellus (?) at the bottom of the cleft; p, group of young Meduse as seen swim-
ming in the water, of the natural size.

tervals between the segments of the border of the disk gradually
fill up, so that the divisions are obliterated; tubular prolonga-
tions of the stomach extend themselves over the disk; and
from its borders there sprout forth tendril-like filaments, which

470 ZOOPHYTES.

hang down like a fringe around its margin. From the four
angles of the mouth, which, even in the youngest detached
animal, admits of being greatly extended and protruded, pro-
longations are put forth, which form the four large tentacula of
the adult. And finally the generative organs make their ap-
pearance in four chambers disposed around the stomach ; which
are occupied by plaited membranous ribands, containing sperm-
cells in the male, and ova in the female; and the embryoes
evolved from the latter, when they have been fertilized by the
agency of the former, repeat the extraordinary cycle of pheno-
mena which has been now described.

308. In connection with the preceding, it will be convenient
to mention two curious little marine animals of frequent occur-
rence, the true place of which in the scale it seems difficult to
determine, but which, having the free swimming habits and the
soft texture of the Meduse, have been very commonly ranked
as members of the same class. One of these is the Cydippe
pileus (Fig. 228, a) very commonly known as the Beroé, which

Fie. 228.
A
. Ogee!
se AG) ek Wy
of Ry, \ \
7A & ‘X
f oe 7
é wy R d) ae
ot 4 ‘
i\ a
Mi es
Sea ee 2
x Ke
\\

A, Cydippe pileus with its tentacles extended; B, Beroé Forskalii, showing the tubular prolongations
of the stomach.

designation, however, properly appertains to another animal (8)
of the same grade of organization. The body of Cydippe is a
nearly globular mass of soft jelly, usually about three-eighths of
an inch in diameter; and it may be observed, even with the
naked eye, to be marked by eight bright bands, which proceed
from pole to pole like meridian lines, These bands are seen with
the microscope to be formed of rows of large cilia, which are in
a state of pretty constant vibration, though sometimes they are
at rest; and if the sunlight should fall upon them when they
are in activity, they display very beautiful iridescent colors. The
mouth of the animal, situated at one of the poles, leads to a
stomachal cavity of cylindrical shape, which extends about as
far as the centre of the body, and then narrows into an intestinal
tube which terminates at the opposite pole; from this stomach

NOCTILUCA—ANTHOZOA. 471

tubular prolongations pass off beneath the ciliated bands, very
much as in the true Beroé (B). In addition to the rows of cilia,
the Cydippe is furnished with a pair of locomotive organs of a
very peculiar kind; these are long tendril-like filaments, arising
from the bottom of a pair of cavities in the posterior part of
the body, and furnished with lateral branches (a); within these
cavities they are often doubled up, so as not to be visible exter-
nally; and when they are ejected, which often happens quite
suddenly, the main filaments first come forth, and the lateral
tendrils subsequently uncoil themselves, to be drawn in again
and packed up within the cavities, with almost equal suddenness.
The liveliness of this little creature, which may sometimes be
collected in large quantities at once by the muslin net, renders
it a most beautiful subject for observation when due scope is
given to its movements; but for the sake of microscopic exami-
nation, it is of course necessary to confine these. Various
species of true Beroé, some of them even attaining the size of
a small lemon, are occasionally to be met with on our coasts;
in all of which the movements of the body are effected by the
like agency of cilia, arranged in meridional bands. Very dif-
ferent, however, is the structure of another little globular jelly-
like animal, the Moctiluca miliaris (Fig. 229), to which the
diffused luminosity of the sea, a beauti-
ful phenomenon that is of very frequent Fig. 229.
occurrence on our shores, is chiefly at- ;
tributable. This animal is just large
enough to be discerned by the naked
eye, when the water in which it may be
swimming is contained in a glass jar f
exposed to the light; and a tail-like §
appendage, marked with transverse
rings, which is employed by the ani-
mal as an instrument of locomotion,
both for swimming and for pushing, Noctiluea mitiaris.

may also be observed with a hand-

glass. Near the point of its implantation in the body, is a de-
finite mouth, on one side of which a projecting tooth has been
seen by Mr. Huxley; and this mouth leads through a sort of
esophagus, into a large irregular cavity, apparently channelled
out in the jelly-like substance of the body, and therefore con-
sidered by some in the light of a mere “vacuole,” though by
Mr. Huxley it is considered to possess regular walls ; whilst from
its cavity there passes forth a prolongation, which leads, in his
belief, to a distinct anal orifice.’ The external coat is denser
than the contained sarcode; and the former sends thread-like
prolongations through the latter, so as to divide the entire body
into irregular chambers, in some of which “vacuoles” are fre-

1 “Quart. Journ. of Microsc. Science,” vol. iii, p. 49; see also pp. 102, 199,

472 ZOOPHYTES.

quently to be seen. Very little is known about the reproduc-
tion of this animal; and until the mode in which it performs
that important function shall have been made out, and it shall
have also been determined whether it passes through any other
phase of existence, we are scarcely in a position to speak posi-
tively of its true affinities. The nature of its luminosity is
found by microscopic examination to be very peculiar ; for what
appears to the eye to be a uniform glow, is resolvable under a
sufficient magnifying power into a multitude of evanescent
scintillations ; and these are given forth with increased intensity,
whenever the body of the animal receives any mechanical
shock, such as that produced by shaking the vessel or pouring
out its contents, or is acted on by various chemical stimuli, such
as dilute acids, which, however, speedily exhaust the light-pro-
ducing power, occasioning disorganization of the body.

309. Anthozoa.—This group, which constitutes the second
great division of the class of Zoophytes, includes all those larger
forms, whose polypes, when expanded, present the likeness of
“animal flowers:” and it consists of two principal subdivisions,—
the Asteroida, or Aleyonian zoophytes, whose polypes, having
only six or eight broad short tentacula, present a star-like aspect
when expanded,—and the Helianthoida, whose polypes, having
numerous tentacula disposed in several rows, bear a resemblance
to sun-flowers or other composite blossoms. Of the first of these
orders, which contains no solitary species, a characteristic ex-
ample is found in the Alcyonium digitatum of our coasts, which

”

is commonly known under the name of “dead-man’s toes,” or

Fie. 230, Fig. 231. Fia, 232.

230, Spicules of Alcyonium and Gorgonia, Fic. 231. Spicules of Gorgonia guttata. Fie. 232. Spicules
of Muricea elongata.

‘“‘sea-paps.” When a specimen of this is first torn from the rock

to which it has attached itself, it contracts into an unshapely

mass, whose surface presents nothing but a series of slight de-

pressions arranged with a certain regularity. But after being

ASTEROID AND HELIANTHOID POLYPES, 473

immersed for a little time in a jar of sea-water, the mass swells
out again, and from every one of these depressions an eight-
armed polype is protruded, “which resembles a flower of ex-
quisite beauty and perfect symmetry. In specimens recently
taken, each of the petal-like tentacula is seen with a hand-glass
to be furnished with a row of delicately slender pinne or fila-
ments, fringing each margin, and arching outwards; and with a
higher power, these pinne are seen to be roughened, throughout
their whole length, with numerous prickly rings. After a day’s
captivity, however, the petals shrink up into short, thick, un-
shapely masses, rudely notched at their edges” (Gosse). When
a mass of this sort is cut into, it is found to be channelled out,
somewhat like a sponge, by ramifying canals; the vents of which
open into the stomachal cavities of the polypes, which are thus
brought into free communication with each other,—a character
that especially distinguishes this order. A movement of fluid is
kept up within these canals, as may be distinctly seen through
their transparent bodies, by means of cilia lining the internal
surfaces of the polypes; but no cilia can be discerned on their
external surfaces. The tissue of this spongy polypidom is
strengthened throughout, like that of Sponges (§ 296), with mine-
ral spicules (always, however, calcareous), which are remarkable
for the elegance of their forms; these are disposed with great
regularity around the bases of the polypes, and even extend part
of their length upwards on their bodies. The presence of such
spicules is, in fact, a very constant character throughout this
group. Thus in the Gorgonia or Sea-fan, whilst the central part
of the polypidom is consolidated into a horny axis, the soft flesh
which clothes this axis is so full of tuberculated spicules, espe-
cially in its outer layer, that, when this dries up, the spicules
form a thick yellowish or reddish incrustation upon the horny
stem; this is, however, so friable, that it may be easily rubbed
down between the fingers, and, when examined with the Micro-
scope, it is found to consist of spicules of different shapes and
sizes, more or less resembling those shown in Figs. 230-282,
sometimes colorless, but sometimes of a beautiful crimson, yel-
low, or purple. These spicules are best seen by the methods of
illumination that give a black ground, on which they stand out
with great brilliancy. They are, of course, to be separated from
the animal substance in the same manner as the calcareous spi-
cules of Sponges (§ 298); and they should be mounted, like them,
in Canada balsam. It is interesting to remark that the hard cal-
careous stem of the Red Coral, which takes the place of the horny
axis of the Sea-fan, is found, by the examination of very thin
sections, to be made up of a solid aggregation of separate spicules,
closely resembling those of Aleyonian zoophytes in general. The
spicules always possess an organic basis; as is proven by the
fact, that when their lime is dissolved by dilute acid, a gelatinous-

474 ZOOPHYTES.

looking residuum is left, which preserves the form of the spicule,

and is probably to be considered as a cell in an early stage of

esa its wall not yet being differentiated as a distinct mem-
rane.

310. Of the order Helianthoida, the common Actinia or “ Sea-
Anemone” may be taken as the type; the individual polypes of
all the composite structures included in the group being con-
structed upon the same model. In by far the larger proportion
of these Zoophytes, the bases of the polypes, as well as the soft
flesh that connects together the members of aggregate masses,
are consolidated by calcareous deposit into stony corals; and the
surfaces of these are beset with cells, usually of a nearly circular
form, each having numerous lamelle radiating from its centre
towards its circumference, which are formed by the consolidation
of the lower portions of the radiating partitions, that divide the
space intervening between the stomach and the general integu-
ment of the animal into separate chambers. This arrangement
is seen on a large scale in the Fungia or “mushroom coral” of
tropical seas, which is the stony base of a solitary anemone-like
polype; on a far smaller scale, it is seen in thie little Caryophyllia,
a like solitary polype of our own coasts, which is scarcely dis-
tinguishable from an Actinia by any other character than the
presence of this disk, and also on the surface of many of those
stony corals known as “Madrepores;’’ whilst in some of these
the individual polype-cells are so small, that the lamellated ar-
rangement can only be made out when they are considerably
magnified. Portions of the surface of such corals, or sections
taken at a small depth, are very beautiful objects for the lower
powers of the Compound Microscope, the former being viewed
by reflected and the latter by transmitted light. And thin sec-
tions of various fossil Corals of this group are very striking
objects for the lower powers of the Oxyhydrogen Microscope.
The chief point of interest to the Microscopist, however, in the
structure of these animals, lies in the extraordinary abundance
and high development of those “ filiferous capsules,” or ‘‘ thread-
cells,” the presence of which on the tentacles of the Hydraform
polypes has been already noticed (§ 800), and which are also to
be found, sometimes sparingly, sometimes very abundantly, in
the tentacles surrounding the mouth of the Medusa, as well as
on other parts of their bodies. If a tentacle of any of the Sea-
Anemonies, so abundant on our coasts (the smaller and more
transparent kinds being selected in preference), be cut off, and
be subjected to gentle pressure between the two glasses of the
aquatic box or of the compressorium, multitudes of little dart-
like organs will be seen to project themselves from its surface
near its tip; and if the pressure be gradually augmented, many
additional darts will every moment come into view. Not only
do these organs present different forms in different species; but

FILIFEROUS CAPSULES OF POLYPES. AT5

even in one and the same individual very strongly marked diver-
sities are shown, of which a few examples are given in Fig. 238.
At A, B, c, and D, is shown the ap-
pearance of the “‘filiferous capsules,” Fra. 233,
whilst as yet the thread lies coiled.

up in their interior; whilst at z, F, .
G, H, are seen a few of the most |
striking forms which they exhibit,
when the thread or dart has started
forth. The most probable account
of their organization seems to be,
that each is a cell, of which one end
is extended into the thread-like or
dart-like prolongation, but which is
doubled in upon itself, in such a
manner that the armature appears to
be contained in its interior; and that
the springing out of the dart is due
to the eversion of the portion of the
cell which had previously been press-
ed inwards. These thread-cells are
found, however, not merely in the
tentacles and other parts of the ex-
ternal integument of Helianthoid
Zoophytes, but also in the long fila-
ments which lie in coils within the $
chambers that surround the stomach,
in contact with the sexual organs
which are attached to the lamelle
dividing the chambers. It was for-
merly supposed that the last-named
organs were always ovaria, and that
the long and slender filaments con-
tain sperm-cells and are consequently
the male organs. But since it has
been proved that the peculiar “ fili- Filiferous Capsules of Helianthoid Po-
ferous capsules’’ which lie side by (ypes:—a = Corynacits Alimannt; o. &, F,
side in these filaments are really coms, Actinia candida.
identical in structure with those

which are found in the skin, the idea of their sexual nature has
been abandoned; and a more careful examination of the organs
attached to the walls of the chambers has shown that these are
not always ovaries, but that they sometimes contain sperm-cells,
the two sexes being here divided, not united, in the same indi-
vidual. What can be the office of the filiferous filaments thus
contained in the interior of the body, it is difficult to guess at.
They are often found to protrude from rents in the external tegu-
ment, when any violence has been used in detaching the animal
from its base; and when there is no external rupture, they are

476 ZOOPHYTES.

often forced through the wall of the stomach into its cavity, and
may be seen hanging out of the mouth. The largest of these
capsules, in their unprojected state, are about 1-300th of an inch
in length; and the thread or dart, in Corynactis Allmanni, when
fully extended, is not less than 1-8th of an inch, or thirty-seven
times the length of the capsule."

' For the fullest description of these curious bodies, as well as for much other valuable
information upon Zoophytes, see Mr. Gosse’s “ Naturalist’s Rambles on the Devonshire
Coast.” Those who may desire to acquire a more systematic and detailed acquaintance
with this group, may be especially referred to the following Treatises and Memoirs —
Dr. Johnston’s “ History of British Zoophytes,” Prof. Owen’s “ Lectures on the Compara-
tive Anatomy and Physiology of the Invertebrate Animals,” Prof. Rymer Jones’s
“ General Outline of the Organization of the Animal Kingdom,” Prof. Milne Edwards's
“Recherches sur les Polypes,” Prof. Van Beneden “Sur les Tubulaires,” and “ Sur les
Campanulaires,’ in “Mem. de l'Acad. Roy. de Bruxelles,’ tom. xvii. Sir J. G. Dalyell’s
“Rare and Remarkable Animals of Scotland,” vol. i. Trembley’s “Mem pour servir &
Vhistoire d'un genre de Polype d‘Eau douce,” M. Hollard’s “ Monographie du Genre
Actinia,” in “ Ann. des Sci. Nat.” Sér. 3, tom. xv, Mr. Mummery, “On the development
of Tubularia indivisa,” in “Transact. of Microsc. Soc.” 2d Ser. vol. i, p. 28, and Prof.
Max. Schultze, “On the Male Reproductive Organs of Campanularia geniculata,” in
“ Quart. Journ. of Microse. Sci.” vol. iii, p 59. :

CHAPTER XII.

OF ECHINODERMATA.

311. As we ascend the scale of Animal life, we meet with such
a rapid advance in complexity of structure, that it is no longer
possible to acquaint one’s self with any organism by microscopic
examination of it as a whole; and the dissection or analysis
which becomes necessary, in order that each separate part may
be studied in detail, belongs rather to the Comparative Anatomist
than to the ordinary Microscopist. This is especially the case
with the Echinus (sea-urchin), Asterdas (star-fish), and other mem-
bers of the class Echinodermata; since even a general account of
their complex organization would be quite foreign to the purpose
of this work; whilst there are certain parts of their structure,
which furnish microscopic objects of such beauty and interest
that they cannot by any means be passed by; besides which,
recent observations on their embryonic forms have revealed a
most unexpected order of facts, the extension and verification of
which will be of the greatest service to science,—a service that
can only be effectually rendered by well-directed Microscopic
research in fitting localities.

312. It is in the structure of that calcareous skeleton, which
probably exists, under some form or other, in every member of
this class, that the Microscopist finds most to interest him. This
attains its highest development in the Hehinida; in which it
forms a box-like shell, or “test,” composed of numerous polygo-
nal plates jointed to each other with great exactness, and beset
on its external surface with “spines,” which may have the form
of prickles of no great length, or may be stout club-shaped
bodies, or, again, may be very long and slender rods. The inti-
mate structure of the shell is everywhere the same; for it is com-
posed of a network, which consists of carbonate of lime with a
very small quantity of animal matter as a basis, and which ex-
tends in every direction (¢. e. in thickness, as well as in length
and breadth), its areole or interspaces freely communicating with
each other (Fig. 234). These “areole,” and the solid structure
which surrounds them, may bear an extremely variable propor-

478 OF ECHINODERMATA.

tion, one to the other; so that in

Fig. 234, two masses of equal size, the one or
the other may greatly predominate ;
and the texture may have either a
remarkable lightness and porosity, if
the network be a very open one,
like that of Fig. 235, or may possess
a considerable degree of compactness
if the solid portion be strengthened.
Generally speaking, the different
layers of this network, which are
connected together by pillars that
aie pass from one to the other in a di-
caleetcoas weil cr cite eat rection perpéndicalar to their plane,
posed:—a a, portions of a deeper layer. are so arranged that the perforations
in one shall correspond to the inter-

mediate solid structure in the next; and their transparency is
such, that when we are examining a section thin enough to con-
tain only two or three such layers, it

Fia. 235. is easy, by properly “focussing” the
Microscope, to bring either one of
them into distinct view. From this
very simple but very beautiful ar-
rangement, it comes to pass that the
plates of which the entire “test” is
made up, possess a very considerable
degree of strength, notwithstanding
that their porousness is such, that if
a portion of a fractured edge, or any

ronien oF Spine af doedahie shoots, Other part from whieh the investing
its more open network. membrane has been removed, be laid
upon fluid of almost any description,

this will be rapidly sucked up into its substance. A very beau-
tiful example of the same kind of calcareous skeleton, having a
more regular conformation, is

Fra 236. furnished by the disk or ro-

sette which is contained in
the tip of every one of the
tubular suckers put forth by
the living Echinus from the
ambulacral pores of its shell.
If the entire disk be cut off,
and be mounted when dry in
Canada balsam, the caleareous
rosette may be seen sufficiently
well; but its beautiful strue-
ture is better made out, when
One of the segments of the cainenneeins skeleton of an the animal membrane that_en-
Ambulneral disk of Hehinus, closes it has been got rid of

CALCAREOUS SKELETON OF ECHINIDA. 479

by boiling in caustic potass; and the appearance of one of the
five segments of which it is composed, when thus prepared, is
shown in Fig. 236.

313. The most beautiful display of this reticulated structure,
however, is shown in the structure of the “spines” of Echinus,
Cidaris, &e.; in which it is combined with solid ribs or pillars,
disposed in such a manner as to increase the strength of these
organs; a regular and elaborate pattern being formed by their
intermixture, which shows considerable variety in different
species. When we make a thin transverse section of almost any
spine belonging to the genus Hehinus (the small spines of our
British species, however, being exceptional in this respect), we
are at once made aware of the existence of a number of concen-
tric layers, arranged in a manner that strongly reminds us of the
concentric rings of an Exogenous tree (Fig. 167). The number
of these layers is extremely variable; depending not merely
upon the age of the spine, but (as will presently appear) upon
the part of its length from which the section happens to be
taken. The centre is usually occupied by a very open network
(Fig. 235); and this is bounded by a row of transparent spaces
(like those at a a’, b U', ¢ ¢’, Fig. 237), which, on a cursory inspec-
tion, might be supposed to be void spaces, but which on a closer
examination are found to be the sections of solid ribs or pillars,
which run in the direction of the length of the spine, and form
the exterior of every layer. Their solidity becomes very obvi-
ous, when we either examine asection of a spine whose substance
is pervaded (as often happens) with a coloring matter of some

Fig. 237,

Portion of transverse section of Spine of Acrocladia mammillaia.

depth, or when we look at a very thin section by the “black-
ground” illumination. Around the innermost circle of these
solid pillars, there is another layer of the calcareous network,
which again is surrounded by another circle of solid pillars; and
this arrangement may be repeated many times, as shown in Fig.
237, the outermost row of pillars forming the projecting ribs
that are very commonly to be distinguished on the surface of the
spine. Around the cup-shaped base of the spine is a membrane

480 OF ECHINODERMATA.

which is continuous with that covering the surface of the shell,
and which serves not merely to hold down the cup upon the
tubercle over which it works, but also, by its contractility, to
move the spine in any required direction. This membrane is
probably continued onwards over the whole surface of the spine,
although it cannot be clearly traced to any distance from the
base ; and the new formations may be presumed to take place in
its substance. Each new formation completely ensheaths the
old; not merely surrounding the part previously formed, but
also projecting considerably beyond it; and thus it happens that
the number of layers shown in a transverse section, will depend
in part upon the place of the section. For if it cross near the
base, it will traverse every one of the successive layers from the
very commencement; whilst, if it cross near the apex, it will
traverse only the single layer of the last growth, notwithstanding
that, in the club-shaped spines, this terminal portion may be of
considerably larger diameter than the basal; and in any inter-
mediate part of the spine, so many layers will be traversed as
have been formed since the spine first attained that length. The
basal portion of the spine is enveloped in a reticulation of a very
close texture, without concentric layers; forming the cup or
socket which works over the tubercle of the shell. The combi-
nation of elegance of pattern with richness of coloring, renders
well-prepared specimens of these spines among the most beauti-
ful objects that the Microscopist can anywhere meet with. The
large spines of the various species of the genus Aeroeladia fur-
nish sections most remarkable for size and elaborateness as well
as for depth of color (in which last point, however, the deep
purple spines of Echinus lividus are pre-eminent); but for exqui-
site neatness of pattern, there are no spines that can approach
those of Evhinometra heteropora and E. lucunter. The spines of
Heliocidaris variolaris are also remarkable for their beauty. No
succession of concentric layers is seen in the spines of the British
Echini, probably because (according to the opinion of the late
Sir J. G. Dalyell) these spines are cast off and renewed every
year; each new formation thus going to make an entire spine,
instead of making an addition to that previously existing.
Most curious indications are sometimes aftorded by sections of
Echinus-spines, of an extraordinary power of reparation inherent
in these bodies. For irregularities are often seen in the trans-
verse sections, which can be accounted for in no other way, than
by supposing the spines to have received an injury when the
irregular part was at the exterior, and to have had its loss of
substance supplied by the growth of new tissue, over which the
subsequent layers have been formed as usual. And sometimes
a peculiar ring may be seen upon the surface of a spine, which
indicates the place of a complete fracture, all beyond it being a
new growth, whose unconformableness to the older or basal
portion is clearly shown by a longitudinal section.

SPINES OF SPATANGUS. 481

314, The spines of Cidaris present a marked departure from
the plan of structure exhibited in Echinus; for not only are they
destitute of concentric layers, but the calcareous network which
forms their principal substance, is ensheathed in a solid cal-
careous cylinder perforated with tubules, which seems to take
the place of the separate pillars of the Echini. This is usually
found to close in the spine at its tip also; and thus it would
appear that the entire spine must be formed at once, since no
addition could be made either to its length or to its diameter,
save on the outside of this sheath, where it is never to be found.
The sheath itself often rises up in prominent points or ridges on
the surface of these spines; thus giving them a character by
which they may be distinguished from those of Echini. The
slender, almost filamentary spines of Spatangus (Fig. 238), and
the innumerable minute hair-like processes attached to the shell
of Clypeaster, are composed of the like regularly reticulated sub-

Fig. 238,

Spines of Spatangus.

stance; and many of these are very beautiful objects for the
lower powers of the Microscope, when examined by reflected
light, and laid upon a black ground, without any further pre-
paration. It is interesting also to find that the same structure
presents itself in the curious Pedicellarie (forceps-like bodies
mounted on long stalks), which are found on the surface of
many Kchinida, and the nature of which has been a source of
much perplexity to Naturalists, some maintaining that they are
parasites, whilst others consider them as proper appendages of
the Echinus itself. The complete conformity which exists be-
tween the structure of their’skeleton and that of the animal to
which they are attached, would seem to remove all reasonable
doubt of their being truly appendages to it, as observation of
their actions in the living state would indicate. Another ex-
ainple of the same structure is found in the peculiar system of
plates which surrounds the interior of the oral orifice of the
shell, and which gives support to the five teeth that may often
be seen projecting externally through that orifice; the whole
forming what is known as the “lantern of Aristotle.” The
31

482 OF ECHINODERMATA.

texture of the plates or jaws resembles that of the shell in every
respect, save that the network is more open; but that of. the
teeth is much more compact. The latter have been described
by Mr. Quekett as consisting of a substance not altogether un-
like the “ dentine” of the teeth of higher animals, save that the
tubuli, though sometimes parallel, usually have more of a reti-
culated arrangement, and sometimes dilate into irregular “ la-
cuns” or spaces excavated in the hard substance.’ The Author
is not prepared to speak with confidence on this point; but he is
disposed to think that the structure of the teeth is essentially the
same as that of the shell, save in the interspaces of the network
being much narrower; and that the appearance of tubuli (in
which Mr. Quekett has not been able to make out distinct walls)
is due merely to the elongation of these interspaces.
315. The calcareous plates which
Fre. 239. form the less compact skeletons of
the Asteriada (star-fish and their
allies) and of the Ophiurida (sand-
stars and brittle-stars), have the
same texture as those of the shell
of Echinus. And this presents
itself, too, in the spines or prickles
of their surface, when these (as in
the large Gonzaster equestris) are
Calcareous plate and claw of Astrophyton large enough to be furnished with
(Euryale). a caleareous framework, and are
not mere projections of the horny
integument. An example of this kind, furnished by the Astro-
phyton (better known as the Euryale), is represented in Fig. 239.
The spines with which the arms of the species of Ophiocoma
(brittle-star) are beset, are often remarkable for their beauty of
conformation ; that of O. rosula, one of the most common kinds,
might serve (as Prof. E. Forbes justly remarked) in point of
lightness and beauty, as a model for the spire of a cathedral.
316. The calcareous skeleton is very highly developed in the
Crinoidea ; their stems and branches being made up of a cal-
careous network, closely resembling that of the shell of the
Echinus. This is extremely well seen, not only in the recent
Pentacrinus Caput Medusce, a somewhat rare animal of the West
Indian seas, but also ina large proportion of the fossil Crinoidea,
whose remains are so abundant in many of the older geological
formations; for, notwithstanding that these bodies have been
penetrated in the act of fossilization by a mineral infiltration,
which seems to have substituted itself for the original fabric (a
regularly crystalline cleavage being commonly found to exist in
the fossil stems of Encrinites, &c., as in the fossil spines of
Echinidans), yet their organic structure is often most perfectly
preserved. In the circular stems of Encrinites, the texture of

1“ Lectures on Histology,” vol. ii, p. 234.

SECTIONS OF ECHINUS SPINES. 483

the calcareous network is uniform, or nearly so, throughout; but
in the pentangular Pentacrini, a certain figure or pattern is
formed by variations of texture in different parts of the trans-
verse section; and the patterns, though formed upon one gene-
ral plan, are sufficiently diverse in different species, to enable
these to be recognized by the examination of a transverse section
of a single joint of the stem.

317. The structure of the shells, spines, and other solid parts
of the skeleton of Echinodermata can only be displayed by thin
sections, made upon the general plan already described (§§ 109,
110). Buttheir peculiar texture requires that certain precautions
should be taken; in the first place, in order to prevent the sec-
tion from breaking, whilst being reduced to the desirable thin-
ness; and in the second, to prevent the interspaces of the net-
work from being clogged by the particles abraded in the re-
ducing process. A section of the shell, spine, or other portion
of the skeleton, should first be cut with a fine saw, and rubbed
on a flat file until it is about as thin as an ordinary card, after
which it should be smoothed on one side by friction with water
on a Water-of-Ayr stone. It should then be carefully dried, first
on white blotting-paper, afterwards by exposure for some time
to a gentle heat, so that no water may be retained in the inter-
stices of the network, which would oppose the complete pene-
tration of the balsam. Next, it is to be attached to a glass slip
by balsam hardened in the usual manner; but particular care
should be taken, first, that the balsam be brought to exactly the
right degree of hardness, and second, that there be enough, not
merely to attach the specimen to the glass, but also to saturate
its substance throughout. The right degree of hardness is that
at which the cement can be with difficulty indented by the
thumb-nail; if it be made harder than this, it is apt to chip off
the glass in grinding, so that the specimen also breaks away ;
and if it be softer, it holds the abraded particles, so that the
openings of the network becomes clogged with them. If, when
rubbed down nearly to the required thinness, the section appears
to be uniform and satisfactory throughout, the reduction may be
completed without displacing it; but if (as often happens) some
inequality in thickness should be observable, or some minute
air-bubbles should present themselves between the glass and the
under surface, it is desirable to loosen the specimen by the ap-
plication of just enough heat to melt the balsam (special care
being taken to avoid the production of fresh air-bubbles), and to
turn it over so as to attach the side last polished to the glass,
taking care to remove or to break with the needle-point any air-
bubbles that there may be in the balsam covering the part of the
glass on which it is laid. The surface now brought uppermost
1s then to be very carefully ground down; special care being taken
to keep its thickness uniform through every part (which may be
even better judged of by the touch than by the eye), and to

484 OF ECHINODERMATA.

carry the reducing process far enough, without carrying it too
far. Until practice shall have enabled the operator to judge of
this by passing his finger over the specimen, he must have con-
tinual recourse to the microscope during the later stages of his
work; and he should bear constantly in mind, that, as the speci-
men will become much more transparent when mounted in
balsam and covered with glass, than it is when the ground sur-
face is exposed, he need not carry his reducing process so far as
to produce at once the entire transparency he aims at, the
attempt to accomplish which would involve the risk of the de-
struction of the specimen. In “mounting” the specimen, liquid
balsam should be employed, and only a very gentle heat (not
sufficient to produce air-bubbles, or to loosen the specimen from
the glass) should be applied; and if, after it has been mounted,
the section should be found too thick, it will be easy to remove
the glass cover, and to reduce it further, care being taken to
harden the balsam which has been newly laid on, to the proper
degree.

518. If a number of sections are to be prepared at once (and
it is often useful to do this for the sake of economy of time, or
in order to compare sections taken from different parts of the
same spine), this may be most readily accomplished by laying
them down, when cut off by the saw, without any preliminary
preparation save the blowing the calcareous dust from their sur-
faces, upon a thick slip of glass well covered with hardened
balsam ; a large proportion of its surface may thus be occupied
by the sections attached to it, the chief precaution required being
that all the sections come into equally close contact with it.
Their surfaces may then be brought to an exact level, by rubbing
them down, first upon a flat piece of grit (which is very suitable
for the rough grinding of such sections), and then upon a large
Water-of-Ayr stone whose surface is “true.” When this level
has been attained, the ground surface is to be well washed and
dried, and some balsam previously hardened is to be spread over
it, so as to be sucked in by the sections, a moderate heat being
at the same time applied to the glass slide; and this being in-
creased to a sufficient degree to loosen the sections without over-
heating the balsam, the sections are to be turned over one by
one, so that the ground surfaces are now to be attached to the
glass slip, special care being taken to press them all into close
contact with it. They are then to be very carefully rubbed down,
until they are nearly reduced to the required thinness ; and if, on
examining them from time to time, their thinness should be
found to be uniform throughout, the reduction of the entire set
may be completed at once; and when it has been carried sufii-
ciently far, the sections, loosened by warmth, are to be taken up
upon a camel-hair brush dipped in turpentine, and transferred to
separate slips of glass whereon some liquid balsam has been pre-
viously laid, in which they are to be mounted in the usual man-

CALCAREOUS STRUCTURE OF HOLOTHURIDA. 485

ner. It more frequently happens, however, that, notwithstanding
every care, the sections, when ground in a number together, are
not of uniform thickness, owing to some of them being under-
laid by a thicker stratum of balsam than others are; and it is then
necessary to transfer them to separate slips, before the reducin
process is completed, attaching them with hardened balsam, an
finishing each section separately.

319. It now remains for us to notice the curious and often very
beautiful structures, which represent, in the order Holothurida,
the solid calcareous skeleton of the orders already noticed. All
the animals belonging to this order are distinguished by the
flexibility and absence of firmness of their envelopes; and ex-
cepting in the case of certain species which have a set of cal-
careous plates, supporting teeth, disposed around the mouth,
very much as in the Kchinida, we do not find among them any
representation that is apparent to the unassisted eye, of that
skeleton which constitutes so distinctive a feature of the class
generally. Buta microscopic examination of their integument
at once brings to view the existence of great numbers of minute
isolated plates, every one of them presenting the characteristic
reticulated structure, which are set with greater or less closeness
in the substance of the skin. Various forms of the plates which
thus present themselves in Holothuria are shown in Fig. 240; and

Fia. 240.

é &
9 :

Calcareous plates in skin of Holothuria.

at A is seen an oblique view of the kind marked a, more highly
magnified, showing the very peculiar manner wherein one part
is superposed on the other, which is not at all brought into view
when it is merely seen through in the ordinary manner. In the
Synapta, one of the long-bodied forms of this order, which does
not occur upon our own coasts, but is abundant in the Adriatic
Sea, the calcareous plates of the integument have the regular
form shown at 4, Fig. 241; and each of these carries the curious
anchor-like appendage, 0, which is articulated to it by the notched
piece at the foot, in the manner shown (in side view) at 8B. The
anchor-like appendages project from the surface of the skin, and
may be considered as representing the spines of Echinida. Nearly
allied to the Synapta is the Chirodota, of which one species (the
C. digitata), although previously accounted a very rare inhabi-

486 OF ECHINODERMATA.

tant of our seas, has lately been found in considerable numbers
at Torquay (by Mr. Kingsley), and might probably be met with

COA,
Or
rs

Caleareous skeleton of Synapta:—a, plate imbedded in skin ; B, the same, with its anchor-like spine
attached; c, anchor like spine separated.

more frequently if carefully searched for. Not having had the
opportunity of examining a specimen of this animal, the Author
is unable to say whether or not its
integument possesses the very re-
markable wheel-like plates, repre-
sented in Fig. 242, which are found
in the skin of Chirodota violacea, a
species inhabiting the Mediterra-
nean. These plates are objects of
singular beauty and delicacy, being
especially remarkable for the very
minute notching (scarcely to be
discerned in the figures without
the aid of a magnifying glass) which is traceable round the inner
margin of their “tires.” There can be scarcely any reasonable
doubt, that every member of this order has some kind of calca-
reous skeleton, disposed in a manner conformable to the examples
now cited; and it would be very valuable to determine how far
the very marked peculiarities by which they are respectively
distinguished, are characteristic of genera and species. The
plates may be obtained separately, by the usual method of treat-
ing the skin with a solution of potass; and they should be
mounted in Canada balsam. But their position in the skin can
only be ascertained by making sections of the integument, both
vertical and parallel to its surface; and these sections, when dry,
are most advantageously mounted in the same medium, by which
their transparency is greatly increased. All the objects of this
class are most beautifully displayed by the black-ground illumi-
nation (§§ 61, 62); and the same method, when applied to very
thin sections of Echinus-spines, brings out some ettects of mar-
vellous beauty.

320. Echinoderm Larve.—We have now to notice that most
remarkable set of objects, furnished to the Microscopic inquirer
by the larval forms of this class, for our present knowledge of
which, imperfect as it still is, we are almost entirely indebted to

Fie. 242,

Wheel-like plates from skin of Chirodota
violacea.

LARVAL FORMS OF ECHINODERMATA. 487

the painstaking and widely extended investigations of Prof.
Miller. All that our limits permit, is a notice of two of the
most curious forms of these larve, by way of sample of the
wonderful phenomena which his researches have brought to
light; so as (it may be hoped) to excite such an interest among
those Microscopists in particular who may have the opportunity
of pursuing these inquiries, as may induce them to apply them-
selves perseveringly to them, and thus to supply the numerous
links which are at present wanting in the chain of developmental
history. The peculiar feature by which the early history of the
Echinoderms generally seems to be distinguished, is this,—that
the embryonic mass of cells is converted, not into a larva which
subsequently attains the adult form by a process of metamor-
phosis, but into a peculiar zootd, which seems to exist for no
other purpose than to give origin to the Echinoderm by a kind
of internal gemmation, and to carry it to a distance by its active
locomotive powers, so as to prevent the spots inhabited by the
respective species from being overcrowded by the accumulation
of their progeny. The larval zooids are formed upon a type
quite different from that which characterizes the adults; for in-
stead of a radial symmetry, they exhibit a bilateral, the two
sides being precisely alike, and each having a ciliated fringe
along the greater part of the whole of its length. The two
fringes are united by a superior and an inferior transverse ciliated
band; and between the two,
the mouth of the zooid is al-
ways situated. Further, al-
though the adult Star-fish and
Sand-stars have neither intesti-
nal tube nor anal orifice, their
larval zooids, like those of other
Echinoderms, always possess
both. The external forms of
these larve, however, vary in
a ‘fost remarkable degree,
owing to the unequal evolution
of their different parts; and
there is also a considerable di-
versity in the several orders,
as to the proportion of the
fabric of the larva which enters
into the composition of the
adult form. In the fully deve- N
loped Star-fish and Sea-urchin, Uc wehialantr ck. ati Merkelabhen de
the only part retained is a por fact Doha caste io i
tion of the stomach and intes- which the mouth is situated; d d’, bilobed
tine, which is pinched off, so peduncle ; 1, 2, 3, 4, 5, 6, 7, ciliated arms.
to speak, from that of the Larval zooid.

321. One of the most remarkable forms of Echinoderm

Fig. 243.

488 OF ECHINODERMATA.

larvee is that which has received the name of Bipinnaria (Fig.
243), from the symmetrical arrangement of its natatory organs.
The mouth (a), which opens in the middle of a transverse fur-
row, leads through an esophagus 8’ to a large stomach, around
which the body of a Star-fish is developing itself; and on one
side of this mouth is observed the intestinal tube and anus (8).
On either side of the anterior portion of the body, are six or
more narrow fin-like appendages, which are fringed with cilia;
and the posterior part of the body is prolonged into a sort of
pedicle, bilobed towards its extremity, which also is covered
with cilia. The organization of this larva seems completed, and
its movements through the water are very active, before the
mass at its anterior extremity presents anything of the aspect of
the Star-fish ; in this respect corresponding with the movements
of the “pluteus” of the Echinida (§ 322). The temporary
mouth of the larva does not remain as the permanent mouth of
the Star-fish ; for the esophagus of the latter enters on what is
to become the dorsal side of its body, and the true mouth is sub-
sequently formed by the thinning away of the integument on its
ventral surface. The young Star-fish is separated from the
bipinnarian larva, by the forcible contractions of the connecting
pedicle, as soon as the calcareous consolidation of its integument
has taken place, and its true mouth has been formed, but long
before it has attained the adult condition; and as its ulterior
development has not hitherto been observed in any instance, it
is not yet known what are the species in which this mode of
evolution prevails. The larva continues active for several days
after its detachment ; and it is possible, though perhaps scarcely
probable, that it may develope another Asteroid by a repetition
of this process of gemmation.!

322. In the Bipinnaria, as in other larva zooids of the Aste-
riada, there is no internal calcareous framework; such a frame-
work, however, is found in the larvee of the Echinida and Ophi-
urida, of which the form delineated in Fig. 244 is an example.
The embryo issues from the ovum as soon as it has attained, by
the repeated segmentation of the yolk, the condition of the ‘“mul-
berry mass;” and the superficial cells of this are covered with
cilia, by whose agency it swims freely through the water. So
rapid are the early processes of development, that no more than
from twelve to twenty-four hours intervene between fecundation

' See the observations of Koren and Daniellsen (of Bergen) in the “ Zoologiske Bid-
rag,” Bergen, 1847 (translated in the “Ann. des Sci. Nat.” 3e Sér, Zool. tom, iii, p.
347) ; and the Memoir of Prof. Miiller, “ Ueber die Larven und die Metamorphose der
Echinodermen,” in “ Abhaldlungen der Kéniglichen Akademie der Wissenschaften
zu Berlin,” 1848.

2 See Prof. Maller, “Ueber die Larven und die Metamorphose der Ophiuren und
Seeigel,” in “ Abbaldlungen der KGéniglichen Akademie der Wissenschaften zu Berlin,”
1846. See also, for the earlier stages, a Memoir by M. Derbés, in “ Ann. cles Sci. Nat.”
3e Sér. Zool. tom. viii, p. 80; and for the later, Krohn’s “ Beitrag zur Entwickelungs-
geschichte der Seeigillarven,’ Heidelberg, 1849, and his Memoir in“ Miiller’s Archiv.”
1851.

LARVAL FORMS OF ECHINODERMATA.

489

and the emersion of the embryo; the division into two, four, or

even eight segments taking
place within three hours
afterimpregnation. Within
a few hours after its emer-
sion, the embryo changes
from the spherical into a
sub-pyramidal form with a
flattened base; and in the
centre of this base is a de-
pression, which gradually
deepens, so as to form a
mouth that communicates
with a cavity in the interior
of the body, which is sur-
rounded by a portion of the
yolk-mass that has returned
to the liquid granular state.
Subsequently a short intes-
tinal tube is found, with an
anal orifice, opening on one
side of the body. The pyra-
mid is at first triangular, but
it afterwards becomes quad-
rangular; and the angles are
greatly prolonged round the
mouth (or base), whilst the
apex of the pyramid is some-
times much extended in the
opposite direction, but is
sometimes rounded off into
a kind of dome (Fig. 244, a).
All parts of this curious body,
and especially its most pro-
jecting portions, are strength-
ened by a framework of
thread-like calcareous rods
(e). In this condition, the
embryo swims freely through
the water, being propelled
by the action of cilia, which

Fig. 244.

Embryonic development of Echinus :—a, Pluteus
larva at the time of the first appearance of the disk;
@, mouth in the midst of the four-pronged proboscis;
6, stomach; c, echinoid disk; d, d, d, d, four arms
of the Pluteus body; e, calcareous framework; J;
ciliated lobes; g, gy, g, g: ciliated processes of the
proboscis :—8, disk with the first indication of the
cirrhi:—c, disk, with the origin of the spines be-
tween the cirrhi :—p, more advanced disk, with the
cirrhi and spines projecting considerably from the
surface. (N.B. In Figs. b, ¢, and D, the pluteus is
not represented, its parts having undergone no
change, save in becoming relatively smaller.)

clothe the four angles of the pyramid and its projecting arms,
and which are sometimes thickly set upon two or four projecting

lobes (f); and it has received the designation of Pluteus.

The

mouth is usually surrounded by a sort of proboscis, the angles
of which are prolonged into four slender processes (9, 9, 9, 9),
shorter than the four outer legs, but furnished with a similar

calcareous framework.

323. The first indication of the production of the young Echi-

490 OF ECHINODERMATA.

nus from its “pluteus,” is given by the formation of a circular
disk (Fig. 244, a, ¢), on one side of the central stomach (6); and
this disk soon presents five prominent tubercles (8), which sub-
sequently become elongated into tubular cirrhi. The disk gradu-
ally extends itself over the stomach, and between its cirrhi the
rudiments of spines are seen to protrude (c); these, with the
cirrhi, increase in length, so as to project against the envelope of
the “luteus,” and to push themselves through it; whilst, at the
same time, the original angular appendages of the “ pluteus”
diminish in size, the ciliary movement becomes less active, being
superseded by the action of the cirrhi and spines, and the mouth
of the “pluteus” closes up. By the time that the disk has grown
over half of the gastric sphere, very little of the “pluteus’’ re-
mains, except some of the slender calcareous rods ; and the num-
ber of tentacula and spines rapidly increases. The calcareous
framework of the shell at first consists, like that of the Star-
fishes, of a series of isolated networks developed between the
cirrhi; and upon these rest the first formed spines (D). But they
gradually become more consolidated, and extend themselves over
the granular mass, so as to form the series of plates. The mouth
of the Echinus (which is altogether distinct from that of the
“‘pluteus”’) is formed at that side of the granular mass, over
which the shell is last extended; and the first indication of it
consists in the appearance of five calcareous concretions, which
are the summits of the five portions of the framework of jaws
and teeth that surround it. All traces of the original “ pluteus’’
are now lost; and the larva, which now presents the general
aspect of an Echinoid animal, gradually augments in size, multi-
plies the number of its plates, cirrhi, and spines, evolves itself
into its particular generic and specific type, and undergoes various
changes of internal structure, tending to the development of the
complete organism. In collecting the free-swimming larve of
Echinodermata, a fine muslin net should be employed in the
manner already described (§ 306); and the search for them is of
course most likely to be successful in those localities in which
the adult animals of the respective species abound, and on warm
calm days, in which they seem to come to the surface in the
greatest numbers.

324. It is remarkable that the Comatula, one of the most active
of all Echinoderms in its adult state, passes a portion of the early
period of its life in a fixed condition ; being attached by a stem
to sea-weeds or zoophytes, precisely after the manner of the Cyi-
noids or “ lily-stars,’’ which were the most common types of this
class in the older epochs of the world’s history. In this phase of
its life, which was first discovered by Mr. J. V. Thompson, of
Cork, in 1828, it is very minute, and forms a most beautiful ob-
ject for the lower magnifying powers, when viewed in fluid by a
strong incident light, as nearly as possible in its natural condition.
It has hitherto been found so rarely, however, that few Micro-

LARVAL FORMS OF ECHINODERMATA. 491

scopists have been able to become possessed of it; but the Author
has been fortunate enough to discover a locality (Lamlash Bay,
in the Isle of Arran) in which it is so abundant, that it may here-
after find its way into almost every cabinet. It has been made
next to certain, by the observations of Busch, that this fixed stage
is preceded by a free-swimming larval condition; and the pas-
sage from one phase to the other is a problem of the greatest
interest, which the Author hopes to have it in his power to work
out.

CHAPTER XIII.
POLYZOA, AND COMPOUND TUNICATA.

At the lower extremity of the great series of Molluscous
animals we find two very remarkable groups, whose mode of
life has much in common with Zoophytes, whilst their type of
structure is conformable in all essential particulars to that of the
true Mollusks. These animals are for the most part microscopic
in their dimensions ; and as some members of both these groups
are found on almost every coast, and are most interesting
objects for anatomical examination, as well as for observation
in the living state, a brief general account of them will be here.
appropriate.

325. Polyzoa.—The group which is known under this name
to British naturalists, corresponds with that which by Continental

zoologists is designated

Fig. 245. Bryozoa: the former name

(though first used in the
singular instead of the plu-
ral number), having been
introduced by Mr. J. V.
Thompson in a memoir
published in 1830, seems
to have precedence in
point of time over the
latter, which was conferred
by Prof. Ehrenberg in 1831
on a most heterogeneous
group, wherein the Bryo-
zoa, a8 now limited, were
combined with the Fora-
minifera. As the history
of the researches by which

Cells of Lepralie :—a, L. Hyndmanni ; 8, L. figularis ; the Polyzoa have been

cv, ZL, verrucosa. raised from the class of

Zoophytes (in which they

were formerly ranked, for the most part in apposition with the
Hydrozoa), to the Molluscan sub-kingdom, has already been
sketched (p. 49), we may now proceed, without further preface,
to a survey of the leading features of their organization. The

STRUCTURE OF LAGUNCULA.

493

animals of the Polyzoa, in consequence of their universal ten-

dency to multiplication
by gemmation, are sel-
dom or never found soli-
tary, but form clusters
or colonies of various
kinds ; and as each is en-
closed in either a horny
or calcareous sheath, or

“cell,” a composite
structure is formed,
closely corresponding

with the polypidom of
a Zoophyte, which has
been appropriately de-
signated the “ polyzo-
ary.” The individual
cells of the “ polyzoary”
are sometimes only con-
nected with each other
by their common relation
to a creeping stem or
“stolon,” as in Lagun-
cula (Fig. 246); but more
frequently they bud forth
directly, one from an-
other, and extend them-
selves in different direc-
tions over plane surfaces,
as is the case with Flus-
tre, Lepralie, &c. (Fig.
245); whilst not unfre-
quently the Polyzoary de-
velopes itself into an ar-
borescent structure (Fig.
247) which may even pre-
sent somewhat of the den-
sity and massiveness of
the stony Corals. Each
individual is composed
externally of a sort of
sac, of which the outer
or tegumentary layer is
either simply membran-
ous, or is horny, or in
some instances calcified,
so as to form the cell;
this investing sac is lined
by a more delicate mem-

Fie. 246,

Laguncula repens, as seen in its expanded state at A,
and in its contracted state, in two different aspects, at B
andc. The same references answer for each figure :—
@ a, tentacula clothed with vibratile cilia; 6, pharyngeal
cavity ; ¢, valve separating this cavity fromd the cesopha-
gus; e, the stomach, with f its pyloric valve, and g the
circle of cilia surrounding that orifice; A, wall of the -
stomach with biliary follicles; 7, the intestine, contain-
ing k& execrementitious matter, and terminating at 7 the
anus; m, the testicle; n, the ovary; 0, an ovum set free
from the ovary; p, openings for the escape of the ova;
q spermatozoa freely moving in the cavity that surrounds
the viscera; 7, retractor muscle of the angle of the aper-
ture of the sheath; s, retractor of the sheath; ¢, retractor
of the tentacular circle; u, retractor of the oesophagus;
v, Tetractor of the stomach; w, principal extensor
muscle; 2, transverse wrinkles of the sheath; y, fibres
of the sheath, themselves probably muscular; z,
muscles of the tentacula; a (at the base of the tentacular
circle in a), nervous or cesophageal ganglion; @, stem,
—»p, a portion of the tentacular circle shown sepa-
rately on a larger scale; a a, the tentacula clothed with
cilia; 0 8, their internal canals; ¢, muscles of the tenta-
cula; d, transverse muscles forming a ring at the base
of the tentacula: e, muscles of the tentacular circle.

494 POLYZOA AND COMPOUND TUNICATA.

brane, which closes its orifice, and which then becomes continuous
with the wall of the alimentary canal; this lies freely in the visceral
sac, floating (as it were) in the liquid which it contains. The fur-
ther details of the anatomy will be best understood from the exa-
mination of a characteristic example, such as the Laguncularepens ;
which is shown in the state of expansion at a, Fig. 246, and in the
state of contraction at Band. The mouth is surrounded by a
circle of tubular tentacula, which are clothed with vibratile cilia ;
these tentacula, in the species we are considering, vary from ten
to twelve in number; but in some other instances they are more
numerous. By the ciliary investment of their tentacula, the
Polyzoa are at once distinguishable from those Hydraform
polypes to which they bear a superficial resemblance, and with
which they were at one time confounded; and accordingly,
whilst still ranked among the Zoophytes, they were characterized
as Ciliobrachiata. The tentacula are seated upon an annular disk,
which is termed the “lophophore,” and which forms the roof of
the visceral or perigastric cavity; and this cavity extends itself
into the interior of the tentacula, through perforations in the
“‘lophophore.”’ The mouth, situated in the centre of the ‘“ lopho-
phore,” leads to a funnel-shaped cavity, or pharynx, 6, which
is separated from the esophagus, d, by a valve ate; and this
cesophagus opens into the stomach, e, which occupies a con-
siderable part of the visceral cavity. In the Bowerbankia, and
some other Polyzoa, a muscular stomach or gizzard, for the
trituration of the food, ‘intervenes between the csophagus and
the true digestive stomach. The walls of the stomach, A, have
considerable thickness; and they are beset with minute follicles,
which seem to have the character of a rudimentary liver. This,
however, is more obvious in some other members of the group.
The stomach is lined, especially at its upper part, with vibratile
cilia, as seen at c, g; and by the action of these, the food is kept
in a state of constant agitation during the digestive process.
From the upper part of the stomach, which is (as it were)
doubled upon itself, the intestine ¢ opens, by a pyloric orifice f,
which is furnished with a regular valve; within the intestine are
seen at k particles of excrementitious matter; which are dis-
charged by the anal orifice at 2. No circulating apparatus here
exists; but the liquid which fills the cavity that surrounds the
viscera, contains the nutritive matter which has been prepared
by the digestive operation, and which has transuded through
the walls of the alimentary canal; a few corpuscles of irregular
size are seen to float in it. The visceral sacs of the different
individuals put forth from the same stem, appear to communicate
with each other. No other respiratory organs exist than the
tentacula ; into whose. cavity the nutritive fluid is probably sent
from the visceral cavity, for aeration by the current of water
that is continually flowing over them.

326. The production of gemme may take place either from

REPRODUCTION OF LAGUNCULA. 495

the bodies of the animals themselves, which is what always hap-
peus when the cells are in mutual apposition; or from the con-
necting stem or stolon, where the cells are detached from each
other, as in Laguncula. There is first seen a bud-like protube-
rance of the horny external integument, into which the soft
membranous lining prolongs itself; the cavity thus formed, how-
ever, is not to become (as in Hydra and its allies) the stomach of
the new zooid; but it constitutes the chamber surrounding the
digestive viscera, which organs have their origin in a thickening
of the lining membrane, that projects from one side of the cavity
into its interior, and gradually.shapes itself into the alimentary
canal with its tentacular appendages. Of the production of
gemmee from the zooids themselves, the best examples are fur-
nished by the Flustre and their allies. From a single cell of a
Flustra, five such buds may be sent off, which develope them-
selves into new zooids around it; and these, in their turn, pro-
duce buds from their unattached margins, so as rapidly to aug-
ment the number of cells to a very large amount. To this
extension there seems no definite limit; and it often happens
that the cells in the central portion of the leaf-like expansion ot
a Flustra are devoid of contents and have lost their vitality, whilst
the edges are in a state of active growth. Independently of their
propagation by gemmation, the Polyzoa have a true sexual gene-
ration; the sexes, however, being usually, if not invariably,
united in the same individuals. ‘The sperm-cells are developed
in a glandular body, the testicle m, which lies beneath the base
of the stomach; when mature, they rupture, and set free the
spermatozoa q q, which swim freely in the liquid of the visceral
cavity. The ova, on the other hand, are formed in an ovarium n,
which is lodged in the membrane lining the tegumentary sheath,
near its outlet; the ova, having escaped from this into the visce-
ral cavity, as at o, are fertilized by the spermatozoa which they
there meet with; and are finally discharged by an outlet at p,
beneath the tentacular circle.

327. These creatures possess a considerable number of muscles,
by which their bodies may be projected from their sheaths or
drawn within them; of these muscles, 7, s, t, u, v, w, x, the direc-
tion and points of attachment sufficiently indicate the uses; they
are for the most part retractors, serving to draw in and double up
the body, to fold together the circle of tentacula, and to close the
aperture of the sheath, when the animal has been completely
withdrawn into its interior. The projection and expansion of
the animal, on the contrary, appear to be chiefly accomplished
by a general pressure upon the sheath, which will tend to force
out all that can be expelled from it. The tentacula themselves
are furnished with distinct muscular fibres, by which their sepa-
rate movements seem to be governed; the arrangement of these
is seen at p. At the base of the tentacular circle, just above the
anal orifice, is a small body (seen at a, a), which is a nervous

496 POLYZOA AND COMPOUND TUNICATA.

ganglion; as yet no branches have been distinctly seen to be
connected with it in this species; but its character is less doubt-
ful in some other Polyzoa.

828. If we scrutinize the foregoing characters, we shall find
that the most important of them are Molluscan, rather than Zoo-
phytic. In the first place, all true Polypes use their tentacula to
grasp their food and convey it to the mouth; and these tentacula
are destitute of cilia; whilst, on the other hand, in all the Ace-
phalous Mollusea, the nutritive matter is drawn in by a ciliary
current, which also serves to aerate the fluids. Now the latter,
as we have just seen, is the case with the Polyzoa; and thus,
although their arms very commonly present a circular disposition
around the mouth, they may be considered as representing, in
their relation to the economy of the animal, the ciliated branchial
sac of the Ascidians (§ 331). But they do not by any means con-
stantly present this radial symmetry; thus, in the Plumatella, a
beautiful fresh-water genus of Polyzoa, the ciliated arms are set
upon two lobes or projections, one on either side of the mouth.
The structure of the alimentary canal, again, removes the Polyzoa
from the zoophytic series. In no true polype is there a separate
intestine and anal orifice, nor does the whole apparatus hang
freely in the visceral cavity ; and the existence of a gizzard-like
organ, and of a rudimentary liver (closely resembling that found
in the lowest Tunicata), are also characters of elevation. The
most important of all the single characters furnished by the ana-
tomy of these animals, is their nervous system ; which, as already
pointed out, is distinctly Molluscan in its type. The absence of
a heart and a distinct circulating system is, it is true, a Zoophytic
character; but we shall presently find that even in the Tunicata,
which are true Mollusks, the character of the circulating appa-
ratus is extremely degraded. The propagation by gemmation,
although formerly supposed to be a character exclusively Zoo-
phytic, is known to belong also to the greater part of the ‘tuni-
eated” Mollusks; and from this, therefore, no argument can be
drawn in favor of the zoophytic nature of the Polyzoa. And
although many of their composite fabrics have a stony density,
and closely resemble the solid polypidoms of the helianthoid and
asteroid Polypes, yet in others, especially amongst the fresh-
water species, we find a very close resemblance to the gelatinous
bed or leathery crust in which the Compound Ascidians are
lodged; and if we imagine calcareous matter to be deposited in
this bed or crust, we should have a fabric closely resembling that
of many stony polyzoaries.

329. Of all the Polyzoa of our own coasts, the Flustre or “gea-
mats” are the most common; these present flat expanded sur-
faces, resembling in form those of many sea-weeds (for which
they are often mistaken), but exhibiting, when viewed, even with
a low magnifying power, a most beautiful network, which at
once indicates their real character. The cells are arranged on

POLYZOA—FLUSTRA, BOWERBANKIA, 497

both sides; and it has been calculated by Dr. Grant, that as a
single square inch of an ordinary F lustra contains 1800 such cells,
and as an average specimen presents about 10 square inches of
surface, it will consist of no fewer than 18,000 zooids. The want
of transparency in the cell-wall, however, and the infrequency
with which the animal projects its body far beyond the mouth of
the cell, renders the Polyzoa of this genus less favorable subjects
for microscopic examination, than are those of the Bowerbankia,
a Polyzoon with a trailing stem and separated cells like those of
Laguncula, which is very commonly found clustering around the
bases of Flustree. It was in this, that many of the details of the
organization of the interesting group we are considering, were
first studied by Dr. A. Farre, who discovered it in 1837, and sub-
jected it to a far more minute examination than any Polyzoon
had previously received ;1 and it is one of the best adapted of all
the marine forms yet known, for the display of the beauties and
wonders of this type of organization. The Halodactylus (formerly
called Alecyonidium), however, is among the most remarkable of
all the marine forms, for the comparatively large size of the ten-
tacular crowns; these, when expanded, being very distinctly
visible to the naked eye, and presenting a spectacle of the greatest
beauty when viewed under a sufficient magnifying power. The
polyzoary of this genus has a spongy aspect and texture, very
much resembling that of the Aleyonian Zoophytes, for which it
might readily be mistaken when its contained animals are all
withdrawn into their cells; when these are expanded, however,
the aspect of the two is altogether different, as the minute
plumose tufts which then issue from the surface of the Halodac-
tylus, making it look as jf it were covered with the most delicate
downy film, are in striking contrast with the larger, solid-looking
polypes of the Alecyonium. The opacity of the polyzoary of the
Halodactylus renders it quite unsuitable for the examination ot
anything more than the tentacular crown and the esophagus
which it surmounts; the stomach and the remainder of the visce-
ralapparatus being always retained within the cell. Several of
the fresh-water Polyzoa are peculiarly interesting subjects for
microscopic examination; alike on account of the remarkable
distinctness with which the various parts of their organization
may be seen, and the very beautiful manner in which their cili-
ated tentacula are arranged upon a deeply crescentic or horse-
shoe-shaped “lophophore.” By this peculiarity, the fresh-water
Polyzoa are separated as a distinct sub-class from the marine;
the former being designated as Hippocrepia (horseshoe-like), while
the latter are termed Jnfundibulata (funnel-like).

330. The Infundibulata or Marine Polyzoa, constituting by far
the most numerous division of the class, are divided into four

1 See his Memoir in the “ Philosophical Transactions,” for that year.
32

498 POLYZOA AND COMPOUND TUNICATA.

orders, as follows ;—I. Chetlostomata, in which the mouth of the
cell is sub-terminal, or not quite at its extremity (Fig. 245), is
somewhat crescentic in form, and is furnished with a movable
(generally membranous) lip, which closes it when the animal
retreats. This includes a large part of the species that most
abound on our own coasts, notwithstanding their wide differences
in form and habit. Thus the polyzoaries of some (as Flustra) are
horny and flexible, whilst those of others (as Eschara and Rete-
pora) are so penetrated with calcareous matter as to be quite
rigid ; some grow as independent plant-like structures (as Bugula
and Gemellaria), whilst others, having a like arborescent form,
ereep over the surfaces of rocks or stone (as Hippothoa), and
others, again, have their cells in close apposition, and form crusts
which possess no definite figure (as is the case with Lepralia and
Membranipora). A large proportion of the Polyzoa of this order
are furnished with very peculiar motile appendages, which are
of two kinds, avicularia and wbracula. The “avicularia,” or
‘“‘bird’s-head processes,”’ are so named from the striking resem-
blance they present to the head and jaws of a bird (Fig. 247, B).
They are generally “sessile” upon the angles or margins of the
cells, that is, are attached

Fig. 247. at once to them, without

the intervention of a stalk,
as in Fig. 247, a, being
either “projecting” or
“immersed ;’’ but in the
genera Bugula and Bicel-
laria, where they are pre-
sent at all, they are “pe-
dunculate” or mounted on
footstalks (zB). Under one
form or the other, they are
wanting in but few of the
genera belonging to this
order; and their presence
or absence furnishes valu-
able characters for the
discrimination of species.
. Each avicularium has two
’ “mandibles,” of which one
is fixed, like the upper jaw
of a bird, the other mov-
able like its lower jaw ; the
— , letter is opened and closed
aii goslon of Caer ovanet: Neveel te by two seta -of rausdles
magnified, aud seen in the act of grasping another. which are seen in the in-
terior of the “head ;’ and

between them is a peculiar body, furnished with a pencil of

CLASSIFICATION OF POLYZOA. 499

bristles, which is probably a tactile organ, being brought forwards
when the mouth is open, so that the bristles project beyond it,
and being drawn back when the mandible closes. The “avicu-
laria” keep up a continual snapping action, during the life of the
polyzoary ; and they may often be observed to lay hold of minute
worms or other bodies, sometimes even closing upon the beaks
of adjacent organs of the same kind, as shown in Fig. 247, B.
In the pedunculate forms, besides the snapping action, there is a
continual rhythmical nodding of the head upon the stalk; and
few spectacles are more curious than a portion of the polyzoary
of Bugula avicularia (a very common British species) in a state of
active vitality, when viewed under a power sufficiently low to
allow a number of these bodies to be in sight at once. It is still
very doubtful what is their precise function in the economy of
the animal; whether it is to retain bodies that may serve as food
within the reach of the ciliary current, or whether it is, like the
“‘pedicellaria” of Hchini (§ 314), to remove extraneous particles
that may be in contact with the surface of the polyzoary. The
latter would seem to be the function of the vibracula, which are
long bristle-shaped organs, each one springing at its base out of
a sort of cup (Fig. 245, a), that contains museles by which it is
kept in almost constant motion, sweeping slowly and carefully
over the surface of the polyzoary, and removing what might be
injurious to the delicate inhabitants of the cells when their ten-
tacula are protruded. Out of 191 species of Cheilostomatous
Polyzoa described by Mr. Busk, no fewer than 126 are furnished
either with “avicularia,” or with “vibracula,” or with both of these
organs.’ II. The second order, Cyclostomata, consists of those
Polyzoa which have the mouth at the termination of tubular cal-
careous cells, without any movable appendage or lip. This
includes a comparatively small number of genera, of which Crista
and Tubulipora contain the largest proportion of the species that
occur on our own coasts. III. The distinguishing character of
the third order, Ctenosomata, is derived from the presence of a
comb-like circular fringe of bristles, connected by a delicate
membrane, around the mouth of the cell, when the animal is
projected from it; this fringe being drawn in when the animal is
retracted. The polyzoaries of this group are very various in
character, the cells being sometimes horny and separate (as in
Laguncula and Bowerbankia), sometimes fleshy and coalescent (as
in Halodactylus). IV. In the fourth order, Pedicellinece, which
includes only a single genus, Pedicellina, the lophophore is pro-
duced upwards on the back of the tentacles, uniting them at their
base in a sort of muscular calyx, and giving to the animal when
expanded somewhat the form of an inverted bell, like that of

1 See Mr. G Busk’s “ Remarks on the Structure and Function of the Avicularian and
Vibracular Organs of Polyzoa,” in “ Transact. of Microscop. Soc.” Ser. II, vol. ii, p. 26.

300 POLYZOA AND COMPOUND TUNICATA.

Vorticella (Fig. 196). Among the Hippoerepia may be noticed,
as exceptional forms, the Cristatella, whose polyzoary is unat-
tached, so as to be capable of moving freely through the water,
and the Fredericella, the lophophore of which is rather circular
than crescentic, the prolongation being so slight as only to be
discernible on a careful examination. Generally speaking, the
cells are lodged in a sort of gelatinous substratum, which spreads
over the leaves of aquatic plants, sometimes forming masses of
considerable size. As the animals of this group altogether re-
semble the true Zoophytes in their habits, and are found in the
same localities, it is not requisite to add anything to what has
already been said (§ 305) respecting the collection, examination,
and mounting, of this very interesting class of objects.’

331. Compound Tunicata.—The Tunicated Mollusca are so
named from the enclosure of their bodies in a “tunic” which is
sometimes leathery or even cartilaginous in its texture, and
which very commonly includes calcareous spicules, whose forms
are often very beautiful. They present a strong resemblance to
the Polyzoa, not merely in their general plan of conformation,
but also in their tendency to produce composite structures by
gemmation; they are differentiated from them, however, by the
absence of the ciliated tentacula, which form so conspicuous a
feature in the external aspect of the Polyzoa, by the presence of
av distinct circulating apparatus, and by their pecuhar respiratory
apparatus, which may be regarded as a dilatation of their pha-
rynx. In their habits, too, they are more inactive, exhibiting
scarcely anything comparable to those rapid movements of
expansion and retraction, which it is so interesting to watch
among the Polyzoa; whilst, with the exception of the Salpide
and other floating species which are chiefly found in seas warmer
than those that surround our coast, they are rooted to one spot
during all but the earliest period of their lives. The larger
forms of the Ascidian group, which constitutes the bulk of the
class, are always solitary; either not propagating by gemmation
at all, or, if this process does take place, the gemmr being
detached before they have advanced far in their development.
Since these cannot be considered as Microscopic objects (although
no part of their organization can be properly made out without
the assistance of that instrument), our attention will be confined
to those “Compound Ascidians,” the small size and transpa-
rency of whose bodies, when detached from the mass in which
they are imbedded, not only enables their structure to be clearly

' For a more detailed account of the Structure and Classification of this group, see
Prof. Allman’s “ Report on the Fresh-water Polyzoa” in the “ Transactions of the British
Association” for 1850; Prof. Van Beneden’s “ Recherches sur les Bryozoaires de la Cote
d'Ostende,” in “ Mem. de l’Acad. Roy. de Bruxelles,” tom. xvii; Mr. G. Busk’s “ Cata-
togue of the Marine Polyoza in the Collection of the British Museum ;” and Dr. G. Jobn-
ston’s “History of British Zouphytes.”

COMPOUND ASCIDIANS.

501

discerned without dissection, but allows many of their living ac-

tions to be watched. Of these we have a charac-
teristic example in Amaroucium proliferum ; of
which the form of the composite mass and the
anatomy of a single individual are displayed in
Fig. 248. The clusters of these animals pre-
sent themselves on rocks, sea-weeds, &c., very
commonly between the tide-marks. They ap-
pear almost completely inanimate, exhibiting
no very obvious movements when irritated; but
if they be placed when fresh in sea water, a
slight pouting of the orifices will soon be per-

ceptible, and a constant and energetic series of

currents will be found to enter by one set and
to be ejected by the other, indicating that all
the machinery of active life is going on within
these apathetic bodies. In the tribe of Poly-
clinians, to which this genus belongs, the body
is elongated, and may be divided into three
regions, the thorax (4), which is chiefly occupied
by the respiratory sac, the abdomen (8), which
contains the digestive apparatus, and the post-
abdomen (c), in which the heart and generative
organs are lodged. At the summit of the
thorax is seen the oral orifice, e, which leads to
the branchial sac, ¢; thisis perforated by an im-
mense number of slits, which allow part of the
water to pass into the space between the bran-
chial sac and the muscu-
lar mantle, where it is
especially collected in
the thoracic sinus, f. At
k is seen the esophagus,
which is continuous with
the lower part of the
pharyngeal cavity; this
leads to the stomach, J,
which is surrounded by
biliary tubuli; and from
this passes off the intes-
tine, m, which termi-
nates at m in the cloaca.
The long post-abdomen
is principally occupied
by the large ovarium,
p, Which contains ova
in various stages of development.

AG i>

A | anna
PUNY
eo a”)

Fia. 248.

c

yim

liormaMIOO

f TOI
COTTON ia
i)
Y

INCONUOUY

TONY

k—)=>>

JSC

SASS

os
Se

Compound mass of Amaroucitum proliferum, with the
anatomy of a single zooid:—a, thorax; B, abdomen; ¢,
post-abdomen :—e, oral orifice; e, branchial sac; f, tho-
racic sinus; ¢, anal orifice; 7’, projection overhanging it;
j, nervous ganglion; k, cwsophagus; 7, stomach sur-
rounded by biliary tubuli; m, intestine; #. termination
of intestine in cloaca; o, heart; o’, pericardium; p, ova-
tium; p’, egg ready to escape; q, testis; r, spermatic
eanal: 7, termination of this canalin the cloaca.

These, when matured and

set free, find their way into the cloaca; where two large
ova are seen (one marked p’ and the other immediately below

502 POLYZOA AND COMPOUND TUNICATA.

it), waiting for expulsion. In this position they reccive the
fertilizing influence from the testis, g, which discharges its pro-
ducts by the long spermatic canal, r, that opens into the cloaca
at r’. At the very bottom of the post-abdomen, we find the
heart, 0, enclosed in its pericardium, o’. In the tribe we are
now considering, a number of such animals are imbedded toge-
ther in a sort of gelatinous mass, and covered with an integu-
ment common to them all; the composition of this gelatinous
substance is remarkable as including “ cellulose,” which gene-
rally ranks as a purely vegetable product. The mode in which
new individuals are developed in this mass, is by the extension
of “stolons” or creeping stems from the bases of those previ-
ously existing; and from each of these stolons several buds may
be put forth, every one of which may evolve itself into the like-
ness of the stock from which it proceeded, and may in its turn
increase and multiply after the same fashion. A communication
between the circulating systems of the different individuals is
kept up, through their connecting stems, during the whole of
life; and thus their relationship to each other is somewhat like
that of the several polypes on the polypidom of a Campanularia
(§ 304).
332. In the family of Dédemnians, the post-abdomen is absent,
the heart and generative
Fia, 249. apparatus being placed
; by the side of the intes-
tine in the abdominal
portion of the body.
The zooids are fre-
quently arranged in
star-shaped clusters,
their anal orifices being
all directed towards a
common vent which oc-
cupies the centre. This
shortening is still more
remarkable, however, in
Botryllus violaceus :—a, cluster on the surface ofa Fucus the family of Botryllians,
B, portion of the same enlarged. whose beautiful stellate
gelatinous incrustations
are extremely common upon sea-weeds and submerged rocks
(Fig. 249). The anatomy of these animals is very similar to
that of the Amaroucium already described; with this exception,
that the body exhibits no distinction of cavities, all the organs
being brought together in one, which must be considered as
thoracic. In this respect, there is an evident approximation
towards the solitary species.
833. This approximation is still closer, however in the “social”
Ascidians, or Clavellinide ; in which the general plan of structure
is nearly the same, but the zooids are simply connected by their

SOCIAL ASCIDIANS. 503

stolons, instead of being included in a common investment (Fig.
250); so that their relation to each other is very nearly the same
as that of the zooids of Laguncula (§ 822), the chief difference

Fig, 250,

A, Group of Perophora (enlarged), growing from a common stalk:—s, single Perophora; u, test;
b, inner sac; ¢, branchial sac, attached to the inner sac along the line e’ ¢’; e, e, finger-like processes
projecting inwards; f, cavity between test and internal coat; 7, anal orifice or funnel ; g, oral orifice;
g', oral tentacula; hk, downward stream of food ; h/, esophagus; 7, stomach; k, vent; l, ovary (?); 7,
vessels connecting the circulation in the body with that in the stalk.

being that a regular circulation takes place through the stolon
in the one case, such as has no existence in the other. A better
opportunity of studying the living actions of the Ascidians can
scarcely be found, than that which is afforded by the genus Pero-
phora, first discovered by Mr. Lister, which occurs not unfre-
quently on the south coast of England and in the Irish Sea, living
attached to sea-weeds, and looking like an assemblage of minute
globules of jelly, dotted with orange and brown, and linked by
a silvery winding thread. The isolation of the body of each zooid
from that of its fellows, and the extreme transparence of its tunics,
not only enable the movements of fluid within the body to be dis-
tinetly discerned, but also allow the action of the cilia that
border the slits of the respiratory sac to be clearly made out.
This sac is perforated with four rows of narrow oval openings,
through which a portion of the water that enters its branchial ori-
fice (g) escapes into the space between the sac and the mantle,
and is thus discharged immediately by the funnel (f’). What-
ever little particles, animate or inanimate, the current of water
brings, flow into the sac, unless stopped by the tentacula (g’) at
its entrance, which do not appear fastidious. The particles
which are admitted usually lodge somewhere on the sides of the
sac, and then travel horizontally until they arrive at that part of
it down which the current proceeds to the entrance of the sto-

504 POLYZOA AND COMPOUND TUNICATA.

mach (i), which is situated at the bottom of the sac. Minute
animals are often swallowed alive, and have been observed dart-
ing about in the cavity for somé days, without any apparent
injury either to themselves or to the creature which encloses
them. In general, however, particles which are unsuited for re-
ception into the stomach, are ejected by the sudden contraction of
the mantle (or muscular tunic), the vent being at the same time
closed, so that they are forced out by a powerful current through
the branchial orifice. .
334. The circulation of blood, throughout the entire class, is
remarkable for the alternation which it presents, from time to
time, in the direction of its flow; and this curious phenomenon
may be particularly well studied in the Perophora. The creep-
ing-stalk (Fig. 250) that connects the individuals of any group,
contains two distinct canals, which send off branches into each
peduncle. One of these branches terminates in the heart, which*
is nothing more than a contractile dilatation of the principal
trunk ; this trunk subdivides into vessels (or rather s‘nuses, which
are mere channels not having proper walls of their own), of
which some ramify over the respiratory sac, branching off at
each of the passages between the oval slits, whilst others are
first distributed to the stomach and intestines, and to the soft
surface of the mantle. All these reunite, and form a trunk,
which passes to the peduncle, and constitutes the returning
branch. Now whilst at some periods, the heart may be seen
vigorously contracting from behind forwards, so as to propel the
blood along the course just described, the observer, if he con-
tinue to watch, will see its pulsations becoming fainter for a few
beats, and the flow in the vessels becoming slower; and then,
after a slight pause, the whole current in all its windings is re-
versed. The heart gives the opposite impulse, receiving the
blood from the body, and sending it back into the pedunele
through the tube that previously conveyed it thence; while the
tube that had previously served to carry the returning stream,
now brings the blood from the stem, and distributes it to the
branchial sac, mantle, and visceral apparatus, whence it finds
its way back to the heart. After the circulation has continued
for a certain time in this new direction, the intermission is re-
peated; and then a reversal takes place to the first course. The
average time during which the circulation persists in each di-
rection, seems to be about the same for the one as for the other;
but the period between the changes varies as much as from
thirty seconds to two minutes. Although the circulation in the
different bodies is brought into connection by the common stem,
yet that of each is independent of the rest, continuing when the
current through its own footstalk is interrupted by a ligature;
and the stream which returns from the branchial sac and the
viscera is then poured into the posterior part of the heart, instead
of entering the peduncle. This is the course which it takes in

DEVELOPMENT OF THE ASCIDIANS. 505

the “solitary” Ascidians; and also in those composite forms,
whose connecting stolons do not contain bloodvessels.

335. The development of the Ascidians presents some pheno-
mena of much interest to the Microscopist; the early stages of
which are observable, whilst the ova are still within the cloaca
of the parent. After the ordinary repeated segmentation of the
yolk, whereby a “ mulberry mass,” is produced, a sort of ring is
seen, encircling its central portion; but this soon shows itself as
a tapering tail-like prolongation from one side of the yolk, which
gradually becomes more and more detached from it, save at the
part from which it springs. Either whilst the egg is still within
the cloaca, or soon after it has escaped from the vent, its en-
velope bursts, and the larva escapes; and in this condition it
presents very much the appearance of a tadpole, the tail being
straightened out, and propelling the body freely through the
water by its lateral strokes. The centre of the body is occupied
by a mass of liquid yolk; and this is continued into the interior
of three prolongations which extend themselves from the oppo-
site extremity, each terminating in a sort of sucker. After swim-
ming about for some hours with an active wriggling movement,
the larva attaches itself to some solid body by means of one of
these suckers; if disturbed from its position, it at first swims
about as before; but it soon completely loses its activity, and be-
comes permanently attached; and important changes manifest
themselves in its interior. The prolongations of the central yolk-
substance into the anterior processes and tail are gradually drawn
back, so that the whole of it is concentrated into one mass; and
the tail, now consisting only of the gelatinous envelope, is either
detached entire from the body by the contraction of the connect-
ing portion, or withers and is thrown off gradually in shreds.
The shaping of the internal organs out of the yolk-mass, takes
place very rapidly; so that by the end of the second day of the
sedentary state, the outlines of the branchial sac and of the sto-
mach and intestine may be traced ; no external orifices, however,
being as yet visible. The pulsation of the heart is first seen on
the third day, and the formation of the branchial and anal orifices
takes place on the fourth; after which the ciliary currents are
immediately established through the branchial sac and alimentary
canal. The embryonic development of other Ascidians, solitary
as well as composite, takes place on a plan essentially the same
as the foregoing, a free tadpole-like larva being always produced
in the first instance; and in the curious Appendicularia, which
occasionally presents itself on our own coasts, this larval form is -
retained through life.’ ,

1 For more special information respecting the Compound Ascidians, see especially
the admirable Monograph of Prof. Milne Edwards on that group, Mr. Lister’s Memoir
“On the Structure and Functions of Tubular and Cellular Polypi, and of Ascidie,” in
the “ Philos, Transact.” 1834, and Mr. Huxley's Memoir “ On Doliolum and Appendicu-

laria,” in “ Philos, Transact.” 1851; also the Art. Tunicata in the “ Cyclopeedia of Ana-
tomy and Physiology.”

CHAPTER XIV.
MOLLUSCOUS ANIMALS GENERALLY.

Tue various forms of “ Shell-fish,” with their “naked” or shell-
less allies, furnish a great abundance of objects of interest to the
Microscopist; of which, however, the greater part may be
grouped under three heads ;—namely (1), the structure of the
Shell, which is most interesting in the Conehifera or “ Bivalves;”
(2) the structure of the Tongue of the Gasteropoda, most of which
have “Univalve” shells, others, however, being “naked ;’’ and
(8) the Developmental History of the embryo, for the study of which
certain of the Gasteropods present the greatest facilities. These
three subjects, therefore, will be first treated of systematically ;
and a few miscellaneous facts of interest will be subjoined.

336. Shells of Mollusea.—These investments were formerly re-
garded as mere inorganic exudations, composed of calcareous
particles cemented together by animal glue; Microscopie exa-
mination, however, has shown that they possess a distinctly or-
ganic structure; and this structure presents certain very remark-
able variations, in some of the natural groups of which the Mol-
luscous series is composed. We shall first describe that which
may be regarded as the characteristic structure of the ordinary
Bivalves; taking as a type the group of Margaritacee, which in-
cludes the ‘“ Pearl-oyster’ and its allies, the common Pinna
ranking amongst the latter. In all these shells, we readily dis-
tinguish the existence of two distinct layers; an external, of a
brownish-yellow color; and an internal, which has a pearly or
“nacreous” aspect, and is commonly of a lighter hue. The
structure of the outer layer may be conveniently studied in the
shell of Pinna, in which it commonly projects beyond the inner,
and there often forms lamine sufficiently thin and transparent
to exhibit the general nature of its organization without any
artificial reduction. Ifa small portion of such a lamina be exa-
mined with a low magnifying power, even without any prepara-
tion by transmitted light, each of its surfaces will present very
much the appearance of a honeycomb; whilst its broken edge
exhibits an aspect which is evidently fibrous to the eye, but
which, when examined under the microscope with reflected light,
resembles that of an assemblage of basaltic columns (Fig. 334, P).

PRISMATIC SHELL-STRUCTURE OF BIVALVES. 507

The shell is thus seen to be composed of a vast number of
prisms, having a tolerably uniform size, and usually presenting
an approach to the hexagonal shape. These are arranged per-

Fig. 251,

Fig. 251. Section of Shell of Pinna, transversely to the direction of its prisms. Fig. 252. Mem-
branous basis of the same.
pendicularly (or nearly so) to the surface of the lamina of the
shell; so that its thickness is formed by their length, and its two
surfaces by their extremities. A more satisfactory view of these
prisms is obtained by grinding down alamina until it possesses a
high degree of transparency; and it is then seen (Fig. 251) that
the prisms themselves appear to be composed of a very homo-
geneous substance, but they are separated by definite and
strongly marked lines of division. When such a lamina is sub-:
mitted to the action of dilute acid, so as to dissolve away the
carbonate of lime, a tolerably firm and consistent membrane is
left, which exhibits the prismatic structure just as perfectly as
did the original shell (Fig. 252); the hexagonal divisions being
apparently the walls of cells resembling those of the pith or bark
of a plant, in which the cells are frequently hexagonal prisms.
In very thin natural lamine, the nuclei of the cells can often be
plainly distinguished. By making
a section of the shell perpendicu-
larly to its surface, we obtain a
view of the prisms cut in the di-
rection of their length (Fig. 253);
and they are frequently seen to be
marked by delicate transverse striee
(Fig. 254), closely resembling those
observable on the prisms of the
enamel of teeth, to which this
kind of shell-strueture may be
considered as bearing a very close

Section of the Shell of Pinna, in the
resemblance, except as regards the direction of its prisms.

mineralizing ingredient. If a .

similar section be decalcified by dilute acid, the membranous re-
siduum will exhibit the walls of the prismatic cells viewed longi-
tudinally; and these will be seen to be more or less regularly
marked by the transverse strie just alluded to. It sometimes

508 MOLLUSCOUS ANIMALS GENERALLY.

happens in recent, but still more commonly in fossil shells, that
the decay of the animal membrane leaves the contained prisms
without any connecting medium; as they are then quite isolated,
they can be readily detached one from another ; and each one
may be observed to be marked by the like striations, which,
when a sufficiently high magnifying power is used, are seen to
be minute grooves, ap-
Fig. 254. parently resulting from
a thickening of the in-
termediate wall in
those situations. This
thickening seems best
accounted for, by sup-
posing (as first sug-
gested by Prof. Owen)
that each long prisma-
tic cell is made up by
the coalescence of a
pile of flat epidermic
Obligue Section of Prismatic Shell-substance. cells, the transverse
striation marking their
lines of junction; and this view corresponds well with the fact,
that the shell-membrane not unfrequently shows a tendency to
split into thin lamine along the lines of striation; whilst we
occasionally meet with an excessively thin natural lamina, com-
posed of flat pavement-like cells, lying between the thicker
prismatic layers, with one of which it would have probably coa-
lesced, but for some accidental cause which preserved its distinct-
ness, That the prism is not formed in its entire length at once,
but that it is progressively lengthened and consolidated at its
lower extremity, would appear also from the fact, that where the
shell presents a deep color (as in Pinna nigrina), this color is
usually disposed in distinct strata, the outer portion of each laver
being the part most deeply tinged, whilst the inner extremities
of the prisms are almost colorless. This prismatic arrangement
of the carbonate of lime in the shells of Pinna and its allies, has
been long familiar to conchologists; but it has been usually re-
garded as the result of crystallization.

387. It is only in the shells of a few families of Bivalves, that
the combination of organic with mineral components is scen in
this very distinct form; and these families are for the most part
nearly allied to Pinna. In all the genera of the Margaritacee,
we find the external layer of the shell formed upon this plan, and
of considerable thickness ; the internal layer being nacreous. In
the Unionide (fresh-water Mussels), on the contrary, nearly the
whole thickness of the shell is made up of the internal or nacre-
ous layer; but a uniform stratum of prismatic cellular substance
is always found between the nacre and the periostracum.) In

! The periostracum is the yellowish-brown membrane covering the surface of many
shells, which is often (but erroneously) termed the epidermis.

CELLULAR SHELL-STRUCTURE OF BIVALVES. 509

the Ostracee (or Oyster tribe), the greater part of the shell is
composed of a sub-nacreous substance, the successively formed
lamine of which have very little adhesion to each other; but
every one of these laminee is bordered at its free edge by a layer
of the prismatic cellular substance, distinguished by its brownish-
yellow color. In these and some other cases, a distinct organic
structure is left after the decalcification of the prismatic layer by
dilute acid; and this is most tenacious and substantial, where (as
in the Margaritacee) there is no proper periostracum ; as if the
horny matter which would have otherwise gone to form this in-
vestment, had been diffused as an intercellular substance between
the proper cell-walls. Generally speaking, a cellular layer may
be detected upon the external surface of bivalve shells, where
this has been protected by a periostracum, or has been prevented
in any other manner from undergoing abrasion; thus it is found
pretty generally in Chama, Trigonia, and Solen, and occasionally
in Anomia and Pecten.

338. In many other instances, however, although a cellular
arrangement is apparent in sections of the shell, no corresponding
structure can be distinctly seen in the delicate membrane left
after decalcification. In all such cases, the animal basis bears
but a very small proportion to the calcareous deposit, and the
shell is usually extremely hard. But there are numerous other
eases, in which no distinct traces of cellular structure can be de-
tected in the fully-formed shell; and in which it would seem as
if the consolidation of the animal basis by calcareous deposit had
taken place whilst the former was as yet in the condition of a
uniform gelatinous sarcode, before the commencement of any
differentiation into cell-wall and cell-contents. A very curious
appearance is presented by a section of the large hinge-tooth of
Mya arenaria (Fig. 255), in which the carbonate of lime seems to
be deposited in nodules, not dis-
tinctly separated from each other by
intervening membrane, and possess-
ing a crystalline structure resem-
bling that of the mineral termed
Wavellite. Approaches to this curi-
ous arrangement are seen in many
other shells. .

339. The internal layer of Bivalve
shells rarely presents any distinct
structure, when examined in a thin
section; and the residuum left after
decalcification is usually a structure- j
less “‘ basement-membrane.” This §
form of shell-substance may conse- oo 5
quently be distinguished as meM- — Section of hinge-tooth of Mya arenaria.
branous. In the Margaritacee and
many other families, this internal layer has a nacreous or iride-

510 MOLLUSCOUS ANIMALS GENERALLY.

scent lustre, which depends (as Sir D. Brewster has shown’) upon
the striation of its surface with a series of grooved lines, which

usually run nearly parallel to each other (Fig. 256). As these
lines are not obliterated

Fie. 256. by any amount of polish-
ing, it is obvious that
their presence depends
- upon something peculiar
in the texture of this
substance, and not upon
any mere superficial ar-
(q) rangement. When a
@ piece of nacre is carefully

“i examined, it becomes

“4 evident that the lines are
produced by the cropping
out of lamine of shell,
i situated more or less
pte sat We tiga obliquely to the plane of
oe ap ss <p aieean tir cae wie the Boe: The greater
Section inanimate, ae aka del margaritacea the dip of these lamine,

the closer will their edges

be; whilst the less the angle which they make with the surface,
the wider will be the interval between the lines. When the sec-
tion passes for any distance in the plane of a lamina, no lines
will present themselves on that space. And thus the appearance
of a section of nacre is such, as to have been aptly compared by
Sir J. Herschel? to the surface of a smoothed deal board, in which
the woody layers are cut perpendicularly to their surface in one
part, and nearly in their plane in another. Sir D. Brewster (loc.
cit.) appears to suppose that nacre consists of a multitude of
layers of carbonate of lime alternating with animal membrane ;
and that the presence of the grooved lines on the most highly
polished surface, is due’ to the wearing away of the edges of the
animal lamine, whilst those of the hard calcareous lamine stand
out. If each line upon the nacreous surface, however, indicates
a distinct layer of shell-substance, a very thin section of mother-
of-pearl ought to contain many thousand lamine, in accordance
with the number of lines upon its surface; these being frequently
no more than 1-7500th of an inch apart. But when the nacre is
treated with dilute acid, so as to dissolve its calcareous portion,
no such repetition of membranous layers is to be found; on the
contrary, if the piece of nacre be the product of one act of shell-
formation, there is but a single layer of membrane. The mem-
brane is usually found to present a more or less folded or platted
arrangement; but this has generally been obviously disturbed by
the disengagement of carbonic acid in the act of decalcification,
which tends to unfold the plaits. There is one shell, however,—

1% Philos, Transact,” 1814. 2 Edinb. Philos. Journal,” vol. ii.

STRUCTURE OF NACRE. 511

the well-known Haliotis splendens,—which affords us the oppor-
tunity of examining the plaits without any disturbance of their
arrangement, and thus presents a clear demonstration of the real
structure of nacre. This shell is for the most part made up of a
series of plates of animal matter, resembling tortoise-shell in its
aspect, alternating with thin layers of nacre; and if a piece of it
be submitted to the action of dilute acid, the calcareous portion
of the nacreous layers being dissolved away, the plates of animal
matter fall apart, each one carrying with it the membranous resi-
duum of the layer of nacre that was applied to its inner surface.
It will usually be found that the nacre-emembrane covering some
of these horny plates will remain in an undisturbed condition;
and their surfaces then exhibit their iridescent lustre, although all the
calcareous matter has been removed from their structure. On look-
ing at the surface with reflected light under a magnifying power
of 75 diameters, it is seen to present a series of folds or plaits
more or less regular; and the iridescent hues which these exhibit,
are often of the most gorgeous description. Ifthe membrane be
extended, however, with a pair of needles, these plaits are un-
folded, and it covers a much larger surface than before; but its
iridescence is then completely destroyed. This experiment,
then, demonstrates that the peculiar lineation of the surface of
nacre (on which its iridescence undoubtedly depends, as originally
shown by Sir D. Brewster) is due, not to the outcropping of alter-
nate layers of membranous and calcareous matter, but to the dis-
position of a single membranous layer in folds or plaits, which
lie more or less obliquely to the general surface. There are
several bivalve shells which present what may be termed a sub-
nacreous structure, their polished surfaces being covered with
lines indicative of folds in the basement-membrane; but these
folds are destitute of that regularity of arrangement, which is
necessary to produce the iridescent lustre. This is the case, for
example, with most of the Pectinide (or Scallop tribe), also with
some of the Mytilacee (or Mussel tribe), and with the common
Oyster. Where there is no indication of a regular corrugation of
the shell-membrane, there is not the least approach to the nacre-
ous aspect; and this is the case with the internal layer of by far
the greater number of shells, the presence of true nacre being
exceptional, save in a small number of families. It is of the
inner layer that those rounded concretions are usually formed,
which are often found in the interior of shells, and which, when
composed of nacreous substance resembling that of the lining of
the shell of Avicula, are known as pearls. Such concretions are
found in many other shells; but they are usually less remarkable
for their pearly lustre; and when formed at the edge of the
valves, they may be partly or even entirely made up of the pris-
matic substance of the external layer, and may be consequently
altogether destitute of the pearly aspect. The “membranous”
shell-substance, some form of which constitutes the internal layer

§12 MOLLUSCOUS ANIMALS GENERALLY.

of most bivalve shells, is occasionally traversed by tubes, which
seem to commence from the inner surface of the shell, and to
pass towards the exterior. These tubes vary in size from about
the 1-20,000th of an inch, or even less, to about the 1-2000th ;
but their general diameter, in the shells in which they most

abound, is about 1-4000th of an
ace inch. The direction and distri-
AOE bution of these tubes are ex-
tremely various in different ge-
nera: in Anomia ephippium they
are scantily distributed in the in-
ternal nacreous lamina, whilst in
| the yellow outer layer they are
very abundant, forming an irre-
gular network (Fig. 257), which
spreads out in a plane parallel

Tabular Shell-structure of Anoméia. to the surtace.

340. The ordinary account of the mode of growth of the shells
of Bivalve Mollusca,—that they are progressively enlarged by
the deposition of new lamins, each of which is in contact with
the internal surface of the preceding, and extends beyond it,—
does not express the whole truth; for it takes no account of the
fact that most shells are composed of two layers of very different
texture, and does not specify whether both these layers are thus
formed by the entire surface of the mantle whenever the shell
has to be extended, or whether only one is produced. An exami-
nation of Fig. 258 will clearly show the mode in which the

Fig. 258.

Vertical section of the lip of one of the valves of the shell of Una :—a, 6, c, successive formations
of the outer layer, a’ b/c’, the same of the inner layer.

operation is effected. This figure represents a section of one of the
valves of Unio oceidens, taken perpendicularly to its surface, and
passing from the margin or lip (at the left hand of the figure)
towards the hinge (which would be at some distance beyond the
right). This section brings into view the two substances of
which the shell is composed; traversing the outer or prismatic
layer in the direction of the length of its cells, and passing
through the nacreous lining, in such a manner as to bring into
view its numerous lamine, separated by the lines aa’, bb’, ce’,

SHELLS OF TEREBRATULE. 513

&c. ‘These lines evidently indicate the successive formations of
this layer; and it may be easily shown, by tracing them towards
the hinge on the one side, and towards the margin on the other,
that at every enlargement of the shell, its whole interior is lined
by a new nacreous lamina, in immediate contact with that which
preceded it. The number of such laminee, therefore, in the oldest
part of the shell, indicates the number of enlargements which it
has undergone. The outer or prismatic layer of the growing
shell, on the other hand, is only formed where the new structure
projects beyond the margin of the old; and thus we do not find
one layer of it overlapping another, except at the lines of junction
of two distinct formations. When the shell has attained its full
dimensions, however, new lamine of both layers still continue
to be added; and thus the lip becomes thickened by successive
formations of prismatic structure, each being applied to the inner
surface of the preceding, instead of to its free margin. A like
arrangement may be well seen in the Oyster ; with this difference,
that the successive layers have but a comparatively slight adhe-
sion to each other.

341. The shells of Terebratulw, and of several other genera of
Brachiopoda, are distinguished by peculiarities of structure, which
serve to distinguish them from all others. When thin sections
of them are microscopically examined, they exhibit the appear-
ance of long flattened prisms (Fig. 259, 6), which are arranged
with such obliquity, that their rounded extremities crop out upon
the inner surface of the shell in an imbricated (tile-like) manner
(a). All true Terebratulide, both recent and fossil, exhibit another
very remarkable peculiarity; namely, the presence of a large
number of perforations in the shell, generally passing nearly per-
pendicularly from one:surface to the other (as is shown in vertical
sections, Fig. 261), and terminating internally by open orifices

Fia. 259. Fig. 260,

EESC ICES & ee
Fig. 259. Internal surface (a), and oblique section (6), of Shell of Zerebratula (Waldheimia) australis.
Fig. 260. External surface of same.

(Fig. 259), whilst externally they are covered by the periostracum
(Fig. 260). Their diameter is greatest towards their external

surface, where they sometimes expand suddenly, so as to become
33

514

MOLLUSCOUS ANIMALS GENERALLY.

trumpet-shaped; and it is usually narrowed rather suddenly,

Fig. 261.

Vertical sections of Shell of Zerebratula (Wald-
heimia) australis:—showing at a the canals
opening by large trumpet-shaped orifices ou the
outer surface, and contracting at d, d, into nar-
row lubes; and presenting at B a bifurcation of
the canals,

when, as sometimes happens, a
new internal layer is formed as
a lining to the preceding (Fig.
261, 4,d d). Hence the diame-
ter of these canals, as shown in
different transverse sections of
one and the same shell, will
vary according to the part of its
thickness which the section hap-
pens to traverse. The different
species of Terebratulide, how-
ever, present very striking diver-
sities in the size and closeness
of the canals, as shown by sec-
tions taken in corresponding
parts of their shells; three ex-
amples of this kind are given
for the sake of comparison in
Figs. 262-264. These canals

are occupied, in the living state,
by tubular prolongations of the mantle, the interior of which is
filled with a fluid containing minute cells and granules, which,
from its corresponding in appearance with the fluid contained in
the great sinuses of the mantle, may be considered to be the
animal’s blood. Hence these cecal tubes may be inferred to

Fic. 264.
GANS

Fia. 262. Fie. 263,

EP selene
Abeer

Fig. 262. Horizontal section of Shell of Zererutula bullata (fossil, oolite).
Fig. 263. ae i “ of Megerlia lima (fossil, chalk).
Fig. 264. a “e «of Spiriferina rostrata (triassic).

possess a respiratory function ; and seem to be analogous to tubes
of a very similar nature, which extend into the “test” of many
Tunicata from their sinus system (§ 334). In the family Rhyneho-
nellide, which is represented by only two recent species (the RA.
psittacea and Rh. nigricans, both of which formerly ranked as
Terebratule), but which contains a very large proportion of fossil
Brachiopods, these canals are entirely absent; so that the unifor-
mity of their presence in the Terebratulide, and of their absence
in the Rhynchonellide, supplies a character of great value in the

{
STRUCTURE OF SHELL OF GASTEROPODA. 515

discrimination of the fossil shells belonging to these two groups
respectively. Great caution is necessary, however, in applying
this test; mere surface-markings cannot be relied on; and no
statement on this point is worthy of reliance, which is not based
on a microscopic examination of thin sections of the shell. In
the families Spiriferide and Strophonemide, on the other hand,
some species possess the perforations, whilst others are destitute
of them; so that their presence or absence there only serves to
mark out subordinate groups. This, however, is what holds
good in regard to characters of almost every description, in other
departments of Natural History, as well as in this; a character
which is of fundamental importance from its close relation to the
general plan of organization in one group, being, from its want
of constancy, of far less account in another.

342. There is not by any means the same amount of diversity
in the structure of the shell in the class of Gasteropoda, as that
which exists among the several tribes of Conchifera; a certain
typical plan of construction being common to by far the greater
number of them. The small proportion of animal matter con-
tained in most of these shells, is a very marked feature in their
character; and it serves to render other features indistinct, since
the residuum left after the removal of the calcareous matter is
usually so imperfect, as to give no clue whatever to the explana-
tion of the appearances shown by sections. Nevertheless, the
structure of these shells is by no means homogeneous, but
always exhibits indications, more or less clear, of an original
organic arrangement. The “porcellanous” shells are composed
of three layers, all presenting the same kind of structure, but
each differing from the others in the mode in which this is dis-
posed. For each layer is made up of an assemblage of thin
lamine placed side by side, which separate one from another,
apparently in the planes of rhomboidal cleavage, when the shell
is fractured; and, as was first pointed out by Mr. Bowerbank,
each of these lamin consists of a series of elongated spicules
(considered by him as prismatic cells filled with carbonate of
lime) lying side by side in close apposition; and these series are
disposed alternately in contrary directions, so as to intersect
each other nearly at right angles, though still lying in parallel
planes. The direction of the planes is different, however, in the
three layers of the shell, bearing the same relation to each other
as have those three sides of a cube which meet each other at the
same angle; and by this arrangement, which is better seen in
the fractured edge of Cyprea or any similar shell, than in thin
sections, the strength of the shell is greatly augmented. A
similar arrangement, obviously designed with the same purpose,
has been shown by Mr. Tomes to exist in the enamel of the

' For a particular account of the Author's researches on this group, see his memoir

on the subject, forming part of the Introduction of Mr Davidson's “ Monograph of the
British Fossil Brachiopoda,” published by the Palzontographical Society.

516 MOLLUSCOUS ANIMALS GENERALLY.

teeth of Rodentia. The principal departures from this plan of
structure are seen in Patella, Chiton, Haliotis, Turbo, and its
allies, and in the “naked” Gasteropods, many of which last,
both terrestrial and marine, have some rudiment of a shell.
Thus in the common Slug, Limax rufus, a thin oval plate, of
calcareous texture, is found imbedded in the shield-like fold of
the mantle covering the fore-part of its back; and if this be
examined in an early stage of its growth, it is found to consist
of an aggregation of cell-like bodies, generally somewhat hexa-
gonal in form, and consolidated by a deposit of calcareous
matter, which is sometimes so arranged as to be quite transpa-
rent, whilst in other instances it presents an appearance closely
resembling that delineated in Fig. 255. In the epidermis of the
mantle of some species of Dorzs, on the other hand, we find
long calcareous spicules, generally lying in parallel directions,
but not in contact with each other, giving firmness to the whole
of its dorsal portion; and these are sometimes covered with
small tubercles, like the spicules of Gorgonia (§ 809). They
may be separated from the soft tissue in which they are imbed-
ded, by means of caustic potash; and when treated with dilute
acid, whereby the calcareous matter is dissolved away, an organic
basis is left, retaining in some degree the form of the original
spicule. This basis cannot be said to be a true cell; but it
seems to be rather a cell in the earliest stage of its formation,
being an isolated particle of “sarcode” without wall or cavity ;
and the close correspondence between appearances presented by
thin sections of various “ univalye” shells, and the forms of the
spicules of Doris, seems to justify the conclusion, that even the
most compact shells of this group are constructed out of the like
elements, in a state of closer aggregation and more definite
arrangement, with the occasional occurrence of a layer of more
spheroidal bodies of the same kind, like those forming the rudi-
mentary shell of Limax.

343. The animals composing the class of Cephalopoda (Cuttle-
fish and Nautilus tribe), are for the most part unpossessed of
shells; and the structure of the few that we meet with in the
genera Nautilus, Argonauta (Paper-nautilus) and Spirula, does
not present any peculiarities that need here detain us. The
rudimentary shell or sepostaire of the common Cuttle-fish, how-
ever, which is frequently spoken of as the ‘“cuttle-fish bone,”
exhibits a very beautiful and remarkable structure, such as
causes sections of it to be very interesting microscopic objects.
The outer shelly portion of this body consists of horny layers,
alternating with calcified layers, in which last may be seen. an
hexagonal arrangement somewhat corresponding with that in
Fig. 255. The soft friable substance that occupies the hollow
of this boat-shaped shell, is formed of a number of delicate
plates, running across it from one side to the other in parallel
directions, but separated by intervals several times wider than

TONGUES OF GASTEROPODS. 517

the thickness of the plates; and these intervals are in great part
filled up by what. appear to be fibres or slender pillars, passing
from one plate or floor to another. A more careful examination
shows, however, that instead of a large number of detached
pillars, there exists a comparatively small number of very thin
sinuous laminee, which pass from one surface to the other, wind-
ing and doubling upon themselves, so that each lamina occupies
a considerable space. Their precise arrangement is best seen by
examining the parallel plates, after the sinuous lamine have
been detached from them; the lines of junction being distinctly
indicated upon these. By this arrangement, each layer is most
effectually supported by those with which it is connected above
and below; and the sinuosity of the thin intervening lamine,
answering exactly the same purpose as the “ corrugation” given
to iron plates for the sake of diminishing their flexibility, adds
greatly to the strength of this curious texture ; which is at the same
time lightened by the large amount of space between the paral-
lel plates that intervenes between the sinuosities of the lamine.
The best method of examining this structure, is to make sections
of it with a sharp knife in various directions, taking care that
the sections are no thicker than is requisite for holding together;
and these may be mounted on a black ground as opaque objects,
or in Canada balsam as transparent objects.

344, The structure of Shells generally is best examined by
making sections in different planes, as nearly parallel as may be
possible to the surfaces of the shell; and other sections at right
angles to these; the former may be designated as horizontal, the
latter as vertical. Nothing need here be added to the full direc-
tions for making such sections, which have already been given
(§§ 108-110). Much valuable information may also be derived,
however, from the examination of the surfaces presented by
fracture. The membranous residua left after the decalcification
of the shell by dilute acid, may be mounted in weak spirit or in
Goadby’s solution.

345. Tongue of Gasteropod Mollusks.—The organ which is
commonly known under this designation, is one of a very singu-
lar nature ; and we should be altogether wrong in conceiving of
it as having any likeness to that on which our ordinary ideas of
such an organ are founded. For instead of being a projecting
body, lying in the cavity of the mouth, it is a tube that passes
backwards and downwards beneath the mouth; its hinder end
being closed, whilst in front it opens obliquely upon the floor ot
the mouth, being (as it were) slit up and spread out, so as to
form a nearly flat surface. .On the interior of the tube, as
well as on the flat expansion of it, we find numerous transverse

! For fuller details on the minute structure of the shells of the Mollusca, see the
Author's memoirs on that subject in the “Reports of the British Association” for 1844
and 1847; also Mr. Bowerbank’s memoir on the same subject in “ Transact. of Micro-

scopical Society,” Ser. 1, vol.i; and Mr. Quekett’s “ Lectures on Histology,” vol, ii,
Chaps, xvi-xxii.

518 MOLLUSCOUS ANIMALS GENERALLY.

rows of minute teeth, which are set upon flattened plates ; each
principal tooth sometimes having a basal plate of its own, whilst
in other instances one plate carries several teeth. Of the for-
mer arrangement we have an example in the tongue of many

Fia. 265. Fra. 266.

RENN op ans '
IN AN MGAGUL7

,
y LV)
Ep
Sl Nyro”
i

‘| 4}
QW NBA
NR (" og ite
WW LW Age wy
RRR isa
f nee Os
( i j
H 1) Wy “iba

AWA

Fig. 265. Portion of the left half of the Palate of the Helix hortensis; the rows of teeth near the
edge separated from each other to show their forin.
Fig. 266, Palate of Zonites cellarius.

terrestrial Gasteropods, such as the Snail (Helix) and Slug (Lz-
max), in which the number of plates in each row is very con-
siderable (Figs. 265, 266), amounting to 180 in the large garden
Slug (Limaz maximus); whilst the latter prevails in many marine
Gasteropods, such as the common Whelk (Buecinum undatum),
the tongue of which has only three plates in each row, one bear-
ing the small central teeth, and the two others the large lateral
teeth (Fig. 269). The length of the tongue, and the number of
rows of teeth, vary greatly in different species. Generally speak-
ing, the tongue of the terrestrial Gasteropods is short, and is
contained entirely within the nearly globular head; but the
rows of teeth being closely set together, they are usually very
numerous, there being frequently more than 100, and in some
species as many as 160 or 170; so that the total number of
teeth may mount up, asin Helix pomatia, to 21,000, and in Limaz
maximus, to 26,800. The transverse rows are usually more or
less curved, as shown in Fig. 266, whilst the longitudinal rows
are quite straight; and the curvature takes its departure on each
side from a central longitudinal. row, the teeth of which are
symmetrical, whilst those of the lateral portions of each trans-
verse row present a modification of that symmetry, the pro-
minences on the inner side of each tooth being suppressed, whilst
those on the outer side are increased ; this modification being
observed to augment in degree, as we pass from the central line
towards the edges. The tongue of the marine Gasteropods is
generally longer, and its teeth larger; and in many instances it
extends far beyond the head, which may, indeed, contain but a
small part of it. Thus in the common Limpet (Patella), we find
the principal part of the tongue to lie folded up, but perfectly
free, in the abdominal cavity, between the intestines and the

TONGUES OF GASTEROPODS. 519

muscular foot; and in some species its length is twice or even
three times as great as that of the entire animal. In a large pro-
portion of cases, these tongues exhibit a very marked separation
between the central and the lateral portions (Figs. 267, 269); the
teeth of the central band being frequently small and smooth at
their edges, whilst those of the lateral are large and serrated.
The tongue of Trochus zizyphinus, represented in Fig. 267, is one
of the most beautiful examples of this form; not only the large
teeth of the lateral bands, but the delicate leaf-like teeth of the
central portion, having their edges minutely serrated. A yet
more complex type, however, is found in the tongue of Haliotis ;
in which there is a central band of teeth having nearly straight
edges instead of points; then, on each side, a lateral band con-
sisting of large teeth shaped like those of the shark ; and beyond
this, again, another lateral band on either side, composed of
several rows of smaller teeth. Very curious differences also
present themselves among the different species of the same
genus. Thus in Doris pilosa, the central band is almost entirely
wanting, and each lateral band is formed of a single row of very
large hooked teeth, set obliquely, like those of the lateral bands
in Fig. 267; whilst in Doris tuberculata, the central band is the

Fig. 267. Fia. 268.

Palate of Trochus zizyphinus. Palate of Doris tuberculata.

part most developed, and contains a number of rows of conical
teeth, standing almost perpendicularly, like those of a harrow
(Fig. 268). ; ;

346. Many other varieties might be described, did space per-
mit; but we must be content with adding, that the form and
arrangement of the teeth afford characters of great. value in
classification, as was first pointed out by Prof. Lovén (of Stock-
holm) in 1847, and has been since very strongly urged by Dr.
J. E. Gray, who considers that the structure of the tongue is one

520 MOLLUSCOUS ANIMALS GENERALLY.

of the best guides to the natural affinities of the species, genera,
and families of this group, since any important alteration in the
form or position of the teeth must be accompanied by some
corresponding peculiarity in the habits and manners of the ani-
mal! Hence a systematic examination and delineation of the
structure and arrangement of these organs, by the aid of the
Microscope and Camera Lucida, would be of the greatest service
to this department of Natural History. The short thick tube
of the Limaz and other terrestrial Gasteropods, appears adapted
for the trituration of the food previously to its passing into the
cesophagus ; for in these animals we find the roof of the mouth
farnished with a large strong horny plate, against which the flat
end of the tongue can work. On the other hand, the flattened
portion of the tongue of Buceinum and its allies is used hy these
animals as a file, with which they bore holes through the shells
of the mollusks that serve as their prey; this they are enabled
to effect, by everting that part of the proboscis-shaped mouth
whose floor is formed by the flattened part of the tongue, which
is thus brought to the exterior, and by giving a kind of sawing
motion to the organ, by means of the alternate action of two
pairs of muscles,—a protractor, and a retractor,—which put
forth and draw back a pair of cartilages whereon the tongue is
supported, and also elevate and depress its teeth. Of the use of
the long blind tubular part of the tongue in these Gasteropods,
however, scarcely any probable guess can be made; unless it be
a sort of “cavity of reserve,” from which a new toothed surface
may be continually supplied, as the old one is worn away, some-
what as the front teeth of the Rodents are constantly being regene-
rated from the surface of the pulps which occupy their hollow
conical bases, as fast as they are rubbed down at their edges.
347. The preparation of these tongues for the Microscope,
ean, of course, be only accomplished by carefully dissecting
them from their attachments within the head; and it will be
also necessary to remove the membrane that forms the sheath of
the tube, when this is thick enough to interfere with its transpa-
rency. The tube itself should be slit up with a pair of fine
scissors, through its entire length; and should be so opened out,
that its expanded surface may be a continuation of that which
forms the floor of the mouth. The mode of mounting it will
depend upon the manner in which it is to be viewed. For the
ordinary purposes of Microscopic examination, no method is so
good as mounting in fluid; either weak spirit or Goadby’s
solution answering very well. But many of these tongues,
especially those of the marine Gasteropods, become most beauti-

'« Annals of Natural History,” Ser. 2, vol. x, p. 413.

2 For additional details on the organization of the tongue and teeth of the Gasteropod
Mollusks, see Mr. W. Thomson, in “Cyclop. of Anat. and Physiol.” vol. iv, pp. 1142,
1143; and in “ Ann, of Nat. Hist.” Ser. 2, vol. vii, p. 86.

DEVELOPMENT OF GASTEROPODS. 521.

ful objects for the Polariscope, when they are mounted in Canada
balsam; the form and arrangement of

the teeth being very strongly brought Fie. 269.

out by it (Fig. 269), and a gorgeous
play of colors being exhibited when a
selenite plate is placed behind the ob-
ject, and the analyzing prism is made
to rotate. ;

348. The stomachs, also, of many
Gasteropod Mollusks are furnished
with teeth, which are implanted on
their walls for the further reduction of
the food; such teeth, very numerous
but of small size, and bearing a strong
resemblance to those of its tongue, are
found in the stomach of the common
Slug. In several marine Gasteropods,
however, especially Bulla, Seyllea, and
Aplysia, the gastric teeth are individu- — patate of Buccinum undatum, as
ally much larger, though less numerous, seen under polarized light.
and constitute a very efficient reducing
apparatus, especially when combined, as they frequently are,
with a horny or calcareous deposit in the walls of the stomach,
which converts it into a “ gizzard’ for the trituration of the
substances that have been divided by the teeth. ;

349. Development of Gasteropod Mollusks.—The history of em-
bryonic development may be studied with peculiar facility in
certain members of this class, and presents numerous pheno-
mena of great interest. The eggs (save among the terrestrial
species) are usually deposited in aggregate masses, each enclosed
in a common protective envelope. The nature of this envelope,
however, varies greatly: thus in the common Lymneus stagnalis,
or “ water-snail,” of our ponds and ditches, it is nothing else
than a mass of soft jelly, about the size of a sixpence, in which
‘from 50 to 60 eggs are imbedded, and which is attached to the
leaves or stems of aquatic plants; in the Buccinum undatum, or
common Whelk, it is a membranous case, connected with a con-
siderable number of similar cases by short stalks, so as to form
large globular masses, which may often be picked up on our
shores, especially between April and June; in the Purpura
lapillus, or Rock-whelp, it is a little flask-shaped capsule, having
a firm horny wall, which is attached by a sort of foot to the
surface of rocks between the tide-marks, great numbers being
often thus found standing erect side by side; whilst in_ the
Nudibranchiate order generally (consisting of the Doris, Hollis,
and other “sea-slugs’’) it forms a long tube with a membranous
wall, in which immense numbers of eggs (even half a million or
more) are packed closely together in the midst of a jelly-like
substance, this tube being disposed in coils of various forms,

522 MOLLUSCOUS ANIMALS GENERALLY.

which are usually attached to sea-weeds or zoophytes. The
course of development, in the first and last of these instances,
may be readily observed from the very earliest period, down to
that of the emersion of the embryo; owing to the extreme
transparency of the “nidamentum,” and of the egg-membranes
themselves. The first change which will be noticed by the ordi-
nary observer, is the “segmentation” of the yolk-mass, which
divides itself (after the manner of a cell undergoing duplicative
subdivision) into two parts, each of these two into two others,
and so on, until a mulberry-like mass of minute yolk segments
is evolved. Generally speaking, however, there may be noticed
at a very early stage of this process, as performed by Gasteropod
Mollusks, an inequality in the size of the segments (Fig. 271,
c); one set, derived from the larger of the two divisions (D) into
which the yolk-sphere first separates itself, being destined to
form the internal organs, whilst the other set of segments, of
much inferior dimensions, and formed by the subdivision of the
smaller half of the original sphere, furnishes the material for
the superficial parts. Soon after the “mulberry mass” has been
formed, it commonly begins to exhibit a very curious alternating
movement within the egg, two or three turns being made in one.
direction, and the same number in a reverse direction: this
movement, which is due to ciliary action, is often extremely
transitory in its duration; but in the Lymneus it continues
almost up to the escape of the embryo, and, when several ova
are brought into view at once under a low magnifying power,
the spectacle is a very curious one.

350. A separation is usually seen at an early period, between
the anterior or cephalic portion, and the posterior or visceral
portion, of the embryonic mass; and the development of the
former advances with the greater activity. One of the first
changes which is seen in it, consists in its extension into a sort
of fin-like membrane on either side, the edges of which are
fringed with long cilia (Fig. 270), whose movements may be
clearly distinguished whilst the embryo is still shut up within

the egg; at a very early

Fia. 270. period may also be discern-

ed the “auditory vesicles’
or rudimentary organs of
hearing (§ 853), which scarce-
ly attain any higher deve-
lopment in these creatures
: during the whole of life;
Uy and from the immediate
ee aes neighborhood of these is
Embryoes of Nudibranchiate Gasteropods. put forth a projection, which

is afterwards to be evolved

into the “foot” or muscular disk of the animal. While these
organs are making their appearance, the shell is being formed

PURPURA. 523

on the surface of the posterior portion, appearing first as a thin
covering over its hinder part, and gradually extending itself
until it becomes large enough to enclose the embryo com-
pletely, when this contracts itself. The ciliated lobes are best
seen in the embryoes of Nudibranchs, in which they are much
larger than in Lymneeus; and the fact of the universal presence
of a shell in the embryoes of the former group, is of peculiar
interest, as it is destined to be cast off very soon after they enter
upon active life. These embryoes may be seen to move about
as freely as the narrowness of their prison permits, for some time
previous to their emersion; and when set free by the rupture of
the egg-cases, they swim forth with great activity by the
action of their ciliated lobes,—these, like the wheels of Rotifera,
serving also to bring food to the mouth, which is at that time
unprovided with the reducing apparatus subsequently found in
it. The same is true of the embryo of Lymneus, save that its
swimming movements are less active, in consequence of the in-
ferior development of the ciliated lobes; and the currents pro-
duced by these seem to have reference chiefly to the provision of
supplies of food, and of aerated water for respiration. The
disappearance of the cilia has been observed by Mr. Hogg to be
coincident with the development of the teeth to a degree sufficient
to enable the young water-snail to crop its vegetable food ; and
he has further ascertained, that if the growing animal be kept
in fresh water alone for some time, with vegetable matter of any
kind, the gastric teeth are very imperfectly developed, and the
cilia are still retained.!

351. A very curious modification of the ordinary plan of deve-
lopment, is presented in the Pur-
pura lapillus ; and it is probable Fie. 271.
that something of the same kind
exists also in Buccinum, as also in
other Gasteropods of the same ex-
tensive Srder (Pectinibranchiata).
Each of the capsules already de-
scribed (§ 349) contains from 500
to 600 egg-like bodies (Fig. 271, a),
imbedded in a viscid gelatinous
substance; but only from 12 to 30
embryoes usually attain complete
development; and it is obvious .
from the large comparative size Early stages of embryonic development of
which these attain (Fig. 272, n), Pepwe lpia egte sme:
that each of them must include Fur Gherutes; p,1, 13, x, successive stages
an amount of substance equal to of development of early embryces.
that of a great number of the .
bodies originally found within the capsule. The explanation of
this fact (long since noticed by Dr. J. E. Gray in regard to Bucci-

1“ Transactions of Microscopical Society,” 2d Ser. vol. ii, p. 93.

524 MOLLUSCOUS ANIMALS GENERALLY.

num) seems to be as follows :—Of those 500 or 600 egg-like bodies,
only a small part are true ova, the remainder being merely yolk-
spherules, which are destined to serve for the nutrition of the
embryoes. The distinction between them manifests itself at a
very early period, even in the first segmentation; for while the
yolk-spherules divide into two equal hemispheres (Fig. 271, 8),
the real ova divide into a larger and a smaller segment (D); in
the cleft between these are seen the minute “ directive vesicles,”
which appear to be always double or even triple, although, from
being seen “end on,” only one may be visible; and near these
is generally to be seen a clear space in each segment. The dif-
ference is still more strongly marked in the subsequent divisions;
for whilst the cleavage of the yolk-spherules goes on irregularly,
so as to divide each into from 14 to 20 segments having no defi-
niteness of arrangement (c, 5, F, @), that of the ova takes place
in such a manner as to mark out the distinction already alluded
to between the cephalic and the visceral portions of the mass (H);
and the evolution of the former into distinct organs very speedily
commences. In the first instance, a narrow transparent border
is seen around the whole embryonic mass, which is broader at
the cephalic portion (1); next, this border is fringed with a short
cilia, and the cephalic extension into two lobes begins to show
itself; and then between the lobes a large mouth is formed,
opening through a short, wide cesophagus, the interior of which
is ciliated, into the visceral cavity, occupied as yet only by the
yolk particles originally belonging to the ovum (xk). Whilst
these developmental changes are taking place in the embryo, the
whole aggregate of segments formed by the subdivision of the
yolk-spherules coalesces into one mass, as shown at A, Fig. 272;
and the embryoes are often, in the first instance, so completely
buried within this, as only to be discoverable by tearing its por-
tions asunder; but’some of them may commonly be found upon
its exterior; and those contained in one capsule very commonly
exhibit the different stages of development represented in Fig.
271, u-x. After a short time, however, it becomes apparent
that the most advanced embryoes are beginning to swallow the
yolk-segments of the conglomerate mass; and capsules will
not unfrequently be met with, in which embryoes of various
sizes, as a, 6, ¢, d, e (Fig. 272, a), are projecting from their sur-
face, their difference in size not being accompanied by advance
in development, but merely depending upon the amount of this
“supplemental” yolk which the individuals have respectively
gulped down. For during the time in which they are engaged
in appropriating this additional supply of nutriment, although
they increase in size, yet they scarcely exhibit any other change;
so that the large embryo, Fig. 272, e, is not apparently more ad-
vanced as regards the formation of its organs, than the small
embryo, Fig. 271, kK. So soon as this operation has been com-
pleted, however, and the embryo has attained its full bulk, the

PURPURA. 525

evolution of its organs takes place very rapidly; the ciliated lobes
are much more highly de-

veloped, being extended Fig. 272.

in a long sinuous margin,
so as almost to remind the
observer of the “wheels”
of Rotifera (§ 277), and
being furnished with very
long cilia (Fig. 272, 3B);
the auditory vesicles, the
tentacula, the eyes, and
the foot, successively
make their appearance; a
curious rhythmically con-
tractile vesicle is seen, just
beneath the edge of the
shell in the region of the
neck, which may perhaps,
serve as a temporary Later stages of embryonic development of Purpura
heart; a little later, the lapillus :—a, conglomerate mass of vitelline segments, to

real heart may be seen fized embryo, inmore advanced stage of development.
pulsating beneath the dor-

sal part of the shell; and the mass of yolk-segments of which
the body is made up, gradually shapes itself into the various
organs of digestion, respiration, &c., during the evolution of
which (and while they are as yet far from complete) the capsule
thins away at its summit, and the embryoes make their escape
from it.

352. It happens not unfrequently, that one of the embryoes
which a capsule contains, does not acquire its supplemental
yolk in the manner now described, and can only proceed in its
development as far as its original yolk will afford it material;
and thus, at the time when the other embryoes have attained
their full size and maturity, a strange-looking creature, consist-
ing of two large ciliated lobes with scarcely the rudiment of a
body, may be seen in active motion among them. This may
happen, indeed, not only to one but to several embryoes within
the same capsule, especially if their number should be consider-
able; for it sometimes appears as if there were not food enough
for all, so that whilst some attain their full dimensions and com-
plete development, others remain of unusually small size, with-
out being deficient in any of their organs, and others again are
more or less completely abortive,—the supply of supplemental
yolk which they have obtained having been too small for the
development of their viscera, although it may have afforded
what was needed for that of the ciliated lobes, eyes, tentacles,
auditory vesicles, and even the foot,—or, on the other hand, no
additional supply whatever having been acquired by them, so
that their development has been arrested at a still earlier stage.

526 MOLLUSCOUS ANIMALS GENERALLY.

These phenomena are of so novel and remarkable a character, that
they furnish an abundant source of interest to any Microscopist
who may happen to be spending the months of August and Sep-
tember in a locality in which the Purpura abounds; since, by
opening a sufficient number of capsules, no difficulty need be
experienced in arriving at all the facts which have been noticed
in this brief summary.! It is much to be desired that such Mi-
croscopists as possess the requisite opportunity, would apply them-
selves to the study of the corresponding history in other Pectini-
branchiate Gasteropods, with a view of determining how far
the plan now described prevails through the order. And now
that these Mollusks have been brought not only to live, but to
breed, in artificial “‘vivaria,” it may be anticipated that a great
addition to our knowledge of this part of their life-history will
ere long be made.”

358. Ciliary Motion on Gills.—There is no object that is better
suited to exhibit the general phenomena of ciliary motion
(§ 276), than a portion of the gill of some “bivalve”? Mollusk.
The Oyster will answer the purpose sufficiently well; but the
cilia are much larger on the gills of the Mussel,’ as they are also
on those of the Anodon or common “fresh-water mussel” of our
ponds and streams. Nothing more is necessary, than to detach
a small portion of one of the riband-like bands, which will be
seen running parallel with the edge of each of the valves when
the shell is opened; and to place this, with a little ot the liquor
contained within the shell, upon a slip of glass,—taking care to
spread it out sufficiently with needles to separate the bars of
which it is composed, since it is on the edges of these, and
round their knobbed extremities, that the ciliary movement
presents itself,—and then covering it with a thin glass disk. Or
it will be convenient to place the object in the animalcule cage,
which will enable the observer to subject it to any degree of
pressure that he may find convenient. A magnifying power of
about 120 diameters is amply sufficient to afford a general view
of this spectacle; but a much greater amplification is needed, to
bring into view the peculiar mode in which the stroke of each
cilium is made. Few spectacles are more striking to the unpre-

1 Puller details on this subject will be found in the Author's account of his researches,
in the Second Series of the “Transactions of the Microscopical Society,” vol. iii, p. 17;
and he would refer such of his readers as may be desirous of knowing what has been
done by other observers in regard to the development of different species of Gastero-
pods, to the various Memoirs there cited.

2 The Author thinks it worth his while to mention the method which he has found
most convenient for exatnining the contents of the capsules of Purpura ; as he believes
that it may be advantageously adopted in many other cases. This consists in cutting
off the two ends of the capsule (taking care not to cut far into its cavity), and in
then forcing a jet of water through it, by inserting the end of a fine-pointed syringe
(§ 132) into one of the orifices thus made, so as to drive the contents of the capsule be-
fore it through the other. These should be received into a shallow cell, and first exa-
mined under a single microscope. A

5 This sbell-fish may be obtained, not merely at the sea-side, but likewise at the shops
of the Fishmongers who supply the humbler classes, even in midland towns.

TENTACLES OF PECTEN. 527

pared mind, than the exhibition of such wonderful activity as
will then become apparent, in a body which to all ordinary ob-
servation is so inert. This activity serves a double purpose; for
it not only drives a continual current of water over the sur-
face of the gills themselves, so as to effect the aeration of the
blood, but it also directs a portion of this current (as in the Tu-
nicata, § 338) to the mouth, so as to supply the digestive appara-
tus with the aliment afforded by the Diatomacee, Infusoria, &c.,
which it carries in with it.

854. Organs of Sense of Motlusks.—Some of the minuter and
more rudimentary forms of the special organs of sight, hearing,
and touch, which the Molluscous series presents, are very inte-
resting objects of Microscopic examination. Thus just within
the margin of each valve of Pecten, we see (when we observe
the animal in its living state, under water) a row of minute
circular points of great brilliancy, each surrounded by a dark
ring; these are the eyes, with which this creature is provided
for the purpose (it can scarcely be doubted) of directing its
peculiarly active movements. Each of them, when their struc-
ture is carefully examined, is found to be protected by a sclerotic
coat with a transparent cornea in front, and to possess a colored
iris (having a pupil) that is continuous with a layer of pigment
lining the sclerotic, a crystalline lens and vitreous body, and a
retinal expansion proceeding from an optic nerve which passes
to each eye from the trunk that runs along the margin of the
mantle. Eyes of still higher organization are borne upon the
head of most Gasteropod Mollusks, generally at the base of one
of the pairs of tentacles, but sometimes, as in the Snail and
Slug, at the points of these organs. In the latter case, the ten-
tacles are furnished with a very peculiar provision for the protec-
tion of the eyes; for when the extremity of either of them is
touched, it is drawn back into the basal part of the organ, much
as the finger of a glove may be pushed back into the palm. The
retraction of the tentacle is accomplished by a long muscular
slip, which arises within the head, and proceeds to the extremity
of the tentacle; whilst its protrusion 1s effected by the agency
of the circular bands with which the tubular wall of the tentacle
is itself furnished, the inverted portion being (as it were)
squeezed out by the contraction of the lower part into which it
has been drawn back. The structure of the eyes, and the curi-
ous provision just described, may easily be examined by snipping
off one of the eye-bearing tentacles with a pair of scissors.
None but the Cephalopod Mollusks have distinct organs of
hearing; but rudiments of such organs may be found in most
Gasteropods, attached to some part of the nervous collar that
surrounds the esophagus; and even in many Bivalves, in con-
nection with the nervous ganglion imbedded in the base of the
foot. These “auditory vesicles,” as they are termed, are minute
sacculi, each of which contains a fluid, wherein are suspended a

528 MOLLUSCOUS ANIMALS GENERALLY.

number of minute calcareous particles (named otolithes or ear-
stones), which are kept in a state of continual movement by the
action of cilia lining the vesicles. This “ wonderful spectacle,”
as it was truly designated by its discoverer Siebold, may be
brought into view without any dissection, by submitting the
head of any small and not very thick-skinned Gasteropod, or
the young of the larger forms, to gentle compression under the
Microscope, and transmitting a strong light through it. The
very early appearance of the auditory vesicles in the embryo Gaste-
ropod has been already alluded to (§ 350). Those who have the
opportunity of examining young specimens of the common Peeten,
will find it extremely interesting to watch the action of the very
delicate tentacles which they have the power of putting forth
from the margin of their mantle, the animal being confined in a
shallow cell, or in the zoophyte-trough; and if the observer
should be fortunate enough to obtain a specimen so young that
the valves are quite transparent, he will find the spectacle pre-
sented by the ciliary movement of the gills, as well as the active
play of the foot (of which the adult animal can make no such
use), to be worthy of more than a cursory glance.

855. Chromatophores of Cephalopods.—Almost any species of
Cuttle-fish (Sepia) or Squid (Loligo) will afford the opportunity of
examining the very curious provision which their skin contains
for changing its hue. This consists in the presence of numerous
large “pigment-cells,” containing coloring matter of various
tints; the prevailing color, however, being that of the fluid of
the ink-bag. These pigment-cells may present very different
forms, being sometimes nearly globular, whilst at other times
they are flattened and extended into radiating prolongations ;
and, by the peculiar contractility with which they are endowed,
they can pass from one to the other of these conditions, so as to
spread their colored contents over a comparatively large surface,
or to limit them within a comparatively small area. Very com-
monly there are different layers of these pigment-cells, their con-
tents having different hues in each layer; and thus a great variety
of coloration may be given, by the alteration of the form of the
cells of which one or another layer is made up. It is curious
that the changes in the hue of the skin appear to be influenced,
as in the case of the Chameleon, by the color of the surface with
which it may be in proximity. The alternate contractions and
extensions of these pigment-cells or “chromatophores” may be
easily observed in a piece of skin detached from the living animal,
and viewed as a transparent object; since they will continue for
some time, if the skin be placed in sea-water. And they may
also be well seen in the embryo Cuttle-fish, which will some-
times be found in a state of sufficient advancement, in the
grape-like eggs of these animals attached to sea-weeds, zoo-
phytes, &c.

CHAPTER XV.

ANNULOSA, OR WORMS.

356. Unper the general designation of “‘annulose” animals, or
Worms, may be grouped together all that lower portion of the
Articulated sub-kingdom, in which the division of the body into
longitudinally arranged segments is not distinctly marked out,
and in which there is an absence of those “articulated” or jointed
limbs, that constitute so distinct a feature of Insects and their
allies. This group includes the classes of Hntozoa or Intestinal
Worms, Rotifera or Wheel-Animalcules, Turbellaria, and Anne-
lida ; each of which furnishes many objects for Microscopic ex-
amination, that are of the highest scientific interest. As our
business, however, is less with the professed Physiologist, than
with the general inquirer into the minute wonders and beauties
of Nature, we shall pass over these classes (the Rotifera having
been already treated of in detail, Chap. IX), with only a notice
of such points as are likely to be specially deserving the attention
of observers of the latter order.

357. —Entozoa.—This class consists almost entirely of animals
of a very peculiar plan of organization, which are parasitic within
the bodies of other animals, and which obtain their nutriment by
the absorption of the juices of these,—thus bearing a striking
analogy to the parasitic Fungi (§§ 209-212). The most remarka-
ble feature in their structure, consists in the entire absence, or
the extremely low development, of their nutritive system, and
the extraordinary development of their reproductive apparatus.
Thus, in the common Tenia (tape-worm), which may be taken
as the type of the “cestoid” group, there is neither mouth nor:
stomach, the so-called “head” being merely an organ for attach-
ment, whilst the segments of the “body” contain repetitions of
a complex generative apparatus, the male and female sexual
organs being so united in each, as to enable it to fertilize and
bring to maturity its own very numerous eggs; and the chief
connection between these segments is established by two pairs
of longitudinal canals, which, though regarded by some as repre-
senting a digestive apparatus, and by others as a circulating
system, appear really to represent the “ water-vascular system,’
whose simplest condition has been noticed in the Wheel-animal-
cule (§ 278). Few among the recent results of microscopic in-
quiry have been more curious, a the elucidation of the real

3

5380 ANNULOSA, OR WORMS.

nature of the bodies formerly denominated cystic Entozoa, which
have always ranked until recently as a distinct group. These
are not found, like the preceding, in the cavity of the alimentary
canal of the animals they infest; but always occur in the sub-
stance of solid organs, such as the glands, muscles, &c. They
present themselves to the eye as bags or vesicles of various sizes,
sometimes occurring singly, sometimes in groups; but upon
careful examination,.each vesicle is found to bear upon some
part a “head” furnished with hooklets and suckers; and thus
may be either single, as in Cysticereus (the entozoon whose pre-
sence gives to pork what is known as the “ measly’’disorder), or
multiple, as in Cenurus, which is developed in the brain, chiefly
of sheep, giving rise to the disorder known as “the staggers.”
Now in none of these “cystic’’ forms has any generative appa-
ratus ever been discovered; and hence they are obviously to be
considered as imperfect animals. The close resemblance between
the “head” of certain Cysticerct and that of certain Teenie, first
suggested that the two might be different states of the same ani-
mal; and experiments recently made by those who have devoted
themselves to the working out of this curious subject, have led
to the assured conclusion, that the “ cystic’ Entozoa are nothing
else than ‘“cestoid” worms, whose development has been modi-
fied by the peculiarity of their position,—the large bag being
formed by a sort of dropsical accumulation of fluid when the
young are evolved in the midst of solid tissues, whilst the very
same bodies, conveyed into the alimentary canal of some carni-
vorous animal which has fed upon the flesh infested with them,
begin to bud forth the generative segments, the long succession
of which, united end to end, gives to the entire series a worm-
like aspect.

358. In the intestinal canal of Insects, Centipedes, &c., a very
curious kind of animal parasite is often to be met with, the sim-
plicity of whose structure seems to carry us back to the Protozoa
(Chap. TX). It is not yet by any means certain, however, that
we know the entire life-history of this parasite, the Gregarina ;
and it may be only a phase in the existence of some higher kind
of Entozoon. Each individual essentially consists of a single
cell, usually more or less ovate in form, and sometimes con-
siderably elongated; a sort of beak or proboscis frequently pro-
jects from one extremity ; and in some instances this is furnished
with a circular row of hooklets, closely resembling that which
is seen on the head of Tenia. Within the cavity of the cell,
whose contents are usually milk white and minutely granular,
there is generally seen a pellucid nucleus; and this becomes
first constricted and then cleft, when, as often happens, the cell
subdivides into two, by a process exactly analogous to that which
takes place in the simplest Protophytes (§ 150). The membrane
and its contents, except the nucleus, are soluble in acetic acid.
Cilia have been detected both upon the outer and the inner sur-

NEMATOID ENTOZOA. 531

face ; but these would seem destined, not so much to give motion
to the body, as to renew the stratum of fluid in contact with it ;
for such change of place as the animal does exhibit, is effected
by the contractions and extensions of the body generally, as in
the Ameeba (§ 261). A sort of “conjugation” has been seen to
take place between two individuals, whose bodies, coming into
contact with each other by corresponding points, first become
more globular in shape, and are then encysted by the formation
of a capsule around them both; and the partition walls between
their cavities disappear ; and the substance of the two bodies be-
comes completely fused together. As the product of this con-
jugation, there are first seen a number of globules or cell-like
bodies ; and these gradually assume a form so like that of Mavi-
cule (§ 184) as to have been mistaken for them; their walls,
however, are destitute of silex, and there is no further resem-
blance between the two kinds of bodies, than that of figure.
These “ pseudo-navicule” are set free, in time, by the bursting
of the capsule that encloses them ; and they develope themselves
into a new generation of Gregarine, first passing through an
Amebo-like form. It appears, however, thatthe “ pseudo-navi-
cule’’ or ‘“psorosperms’ may be also formed by the simple
division of the granular matter of a single Gregarina body, with-
out any conjugation.’

859. The higher forms of Entozoa, belonging to the “nema-
toid’”’ or thread-like order—of which the common Ascaris may
be taken ag a type, one species of it (the A. lumbricoides, or
“round worm”) being a common parasite in the small intestine
of man, while another (the A. vermicularis, or “thread worm’’)
is found rather in the lower bowel,—approach more closely to
the ordinary type of conformation of Worms; having a distinct
alimentary canal, which commences with a mouth at the anterior
extremity of the body, and which terminates by an anal orifice
near the other extremity ; and also Se a regular arrange-
ment of circular and longitudinal muscular fibres, by which the
body can be shortened, elongated, or bent in any direction. The
smaller species of Ascaris, by some or other of which almost
every Vertebrated animal is infested, are so transparent, that
every part of their internal organization may be made out,
especially with the assistance of the “‘ compressor,” without any
dissection; and the study of the structure and actions of their
generative apparatus has yielded many very interesting results,
especially in regard to the first formation of the ova, the mode
of their fertilization, and the history of their subsequent deve-
lopment. Some of the worms belonging to this group are not
parasitic in the bodies of other animals, but live in the midst of
dead or decomposing vegetable matter. The Gordius or hair-
worm, which is peculiar in not having any perceptible anal

' For the most recent information on this point, see a memoir by M. Nat, Lieberkihn,
in Mem. de l’Acad. Roy. de Belgique, tom. xvi.

532 ANNULOSA, OR WORMS.

orifice, seems to be properly a parasite in the intestines of water
insects; but it is frequently found in large knot-like masses
(whence its name) in the water or mud of the pools inhabited
by such insects, and may apparently be developed in these
situations. The Anguzllule are little eel-like worms, of which
one species, A. fluviatilis, is very often found in fresh water
amongst Desmidiew, Conferve, &c., also in wet moss and moist
earth, and sometimes also in the alimentary canal of snails,
frogs, fishes, insects, and larger worms; whilst another species,
A, tritici, is met with in the ears of wheat affected with the
blight termed the “cockle;” another, the A. glutinis, is found
in sour paste; and another, the A. acet’, was often found in
stale vinegar, until the more complete removal of mucilage and
the addition of sulphuric acid, in the course of the manufacture,
rendered this liquid a less favorable “‘habitat’’ for these little crea-
tures. A writhing mass of any of these species of “ eels,” is one
of the most curious spectacles which the Microscopist can exhibit
to the unscientific observer; and the capability which they all
possess (in common with the Rotifera and Tardigrada) of revival
after desiccation, at however remote an interval, enables him to
command this spectacle at any time. A grain of wheat within
which these worms (often called wbriones) are being developed,
gradually assumes the appearance of a black pepper corn; and
if it be divided in two, the interior will be found almost com-
pletely filled with a dense white cottony mass, occupying the
place of the flour, and leaving merely a small space for a little
glutinous matter. The cottony substance seems to the eye to
consist of bundles of fine fibres closely packed together ; but on
taking out a small portion, and putting it under the microscope,
with a little water under a thin glass cover, it will be found
after a short time (if not immediately) to be a wriggling mass of
life, the apparent fibres being really Anguillule, or the “eels”
of the Microscopist. If the seeds be soaked in water for a
couple of hours before they are laid open, the eels will be found
in a state of activity from the first; their movements, however,
are by no means so energetic as those of the A. glutinis or
‘“‘paste-eel.”” This last frequently makes its appearance spon-
taneously in the midst of paste that is turning sour; but the
best means of securing a supply for any occasion, consists in
allowing any portion of a mass of paste in which they may pre-
sent themselves, to dry up, and then, laying this by so long as it
may not be wanted, to introduce it into a mass of fresh paste,
which, if it be kept warm and moist, will be found after a few
days to swarm with these curious little creatures.

360. Besides the foregoing orders of Entozoa, the “trema-
tode” group must be named; of which the Distoma hepatiewm, or
“fluke,” found in the livers of sheep affected with the “rot,” isa
typical example. Into the details of the structure of this animal,
which has the general form of a sole, there is no occasion for us

TURBELLARIA. 533

here to enter: it is remarkable, however, for the branching form
of its digestive cavity, which extends throughout almost the
entire body, very much as in the Planarie (Fig. 273); and also
for the curious phenomena of its development, several distinct
forms being passed through between one sexual generation and
another. ‘These have been especially studied in the Distoma
which infests the Lymneus ; the ova of which are not developed
into the likeness of their parents, but into minute worm-like
bodies, which seem to be little else than masses of cells enclosed
in a contractile integument, no formed organs being found in
them; these cells, in their turn, are developed into independent
“zooids,” which escape from their containing cyst in the con-
dition of free ciliated animalcules; in this condition they remain
for some time, and then imbed themselves in the mucus that
covers the tail of the Mollusk, in which they undergo a gradual
development into true Distomata; and having thus acquired
their perfect, form, they penetrate the soft integument, and take
up their habitation in the interior of the body. Thus a consider-
able number of Distomata may be produced from a single ovum,
by a process of cell-multiplication in an early stage of its deve-
lopment. In some instances, the free ciliated larva possesses
distinct eyes; although they are wanting in the fully developed
Distoma, the peculiar “habitat” of which would render them
useless.

361. Turbellaria—This group of animals, which is distin-
guished by the presence of cilia over the entire surface of the
body, seems intermediate in some respects between the “trema-
tode’”’ Entozoa and the Leech-tribe among Annelida. It de-
serves special notice here, chiefly on account of the frequency
with which the worms of the Planarian tribe present themselves
among collections both of marine and fresh-water animals (par-
ticular species inhabiting either locality), and on account of
the curious organization which many of these present. Most of
the members of this tribe have elongated flattened bodies, and
move by a sort of gliding or crawling action over the surfaces of
aquatic plants and animals. Some of the smaller kinds are
sufficiently transparent to allow of their internal structure being
seen by transmitted light, especially when they are slightly com-
pressed; and the accompanying figure (Fig. 273) displays the
general conformation of their principal organs, as thus seen.
The body has the flattened sole-like shape of the “‘trematode”’
Entozoa; its mouth, which is situated at a considerable distance
from the anterior extremity of the body, is surrounded by a cir-
cular sucker, that is applied to the living surface from which the
animal draws its nutriment; and the buccal cavity (6) opens into
a short esophagus (¢), which leads at once to the cavity of the
stomach. In the true Planarie, the mouth is furnished with a
sort of long funnel-shaped proboscis; and this, even when de»
tached from the body, continues to swallow anything presented

534 ANNULOSA, OR WORMS.

to it. The cavity of the stomach does not give origin to any in-
testinal tube, nor is it provided with any second orifice; but a
large number of ramifying canals are prolonged from it, which
carry its contents into every part of the body. This seems to
render unnecessary any system of vessels for the circulation of
nutritive fluids; and the two principal trunks, with connecting
and ramifying branches, which may be observed in them, are
probably to be regarded in the light of a ‘“water-vascular’
system, the function of which is essentially respiratory. Both
sets of sexual organs are combined in the same individuals;
though the congress of two, each impregnating the ova of the
other, seems to be generally necessary. The ovaria, as in the
Entozoa, extend through a large
Fie. 273. part of their body, their ramifica-
tions proceeding from the two ovi-
ducts (%, k), which have a dilata-
tion (/) at their point of junction.
There is much obscurity about the
history of the embryonic develop-
ment of these animals; and the
facts observed by Siebold seem to
be best explained upon the hypo-
thesis, that what has been usually
considered as an egg is really an
egg-capsule containing several em-
bryoes with a store of supplemen-
tal yolk, as in Purpura (§ 351),.
which yolk is swallowed by the
embryoes at a very early period ot
their development within the cap-
sule. After their emersion from
the capsule, the embryoes bear so
strong a resemblance to certain
Infusoria, as to have led Prof.
Agassiz to the conclusion, that the
genera Paramecium and Kolpoda
are nothing else than Planarian
yy larvee (§ 266, note). This point,
Sid however, is still a matter for inves-
Structure of Polycelis levigatus (a Plana- tigation.! The Planaria, however,
tian worm) oo, mouth, paroanees by its do not multiply by eggs alone; for
circular sucker; b, buccal cuvity; ¢, ceso- .
phageal orifice; d@, stomach; e, ramifica- they occasionally undergo sponta-
tions of gasirie canals; f, cephalic gangtia NeoUs fission in a transverse di-
vesicula sewinali male gowral eunal, Tection, each segment becoming a
k, k, oviducts; J, dilatation at their point of perfect animal ; and an artificial
junction; m, female genital orifice. division into two or even more
parts may be practised with a like
result. In fact, the power of the Planarie to reproduce portions

'See § 129 of Siebold and Stannius’s “ Vergleichende Anatomie ;” also “ Muller’s
Archiv,” 1850, p. 485.

ANNELIDA. 5385
which have been removed, seems but little inferior to that of the
Hydra (§° 301); a circumstance which is peculiarly remarkable,
when the much higher character of their organization is borne
in mind. They possess a distinct pair of nervous ganglia (ff),
from which branches proceed to various parts of the body; and
in the neighborhood of these are usually to be observed a number
(varying from 2 to 40) of ocelli, or rudimentary eyes, each having
its refracting body or crystalline lens, its pigment layer, its

nerve-bulb, and its cornea-like bulging of the skin. The integu-
ment of many of these animals is fur-
nished with “thread-cells” or “filifer- Fia. 274.

ous capsules,” very much resembling
those of Zoophytes (§ 310).

862. Annelida.—This class includes
all the higher kinds of worm-like ani-
mals, the greater part of which are
marine, though there are several spe-
cies which inhabit fresh water, and
some which live on land. The body
in this class is usually very long, and
nearly always presents a well-marked
segmental digigion, the segments being
for the most part similar and equal to
each other, except at the two extremi-
ties; but in the lower forms, such as
the Leech and its allies, the segmental
division is very indistinctly seen, on
account of the general softness of the
integument. A large proportion ot
the marine Annelids have special re-
spiratory appendages, into which the
fluids of the body are sent for aeration ;
and these are situated upon the head
(Fig. 274), in those species which (like
the Serpula, Terebella, Sabellaria, &c.)
have their bodies enclosed by tubes,
either formed of a shelly substance

produced from their own surface, or
built up by the agglutination of grains
of sand, fragments of shell, &c.; whilst
they are distributed along the two
sides of the body, in such as swim
freely through the water, or crawl over
the surfaces of rocks, as is the case
with the Mereide, or simply bury
themselves in the sand, as the Areni-
cola or “lob-worm.” In these respi-

Circulating apparatus of Terebella
conchilega :—a, labial ring; 5, 6, tenta-
cula; ¢, first segment of the trunk;
d, skin of the back; e, pharynx; f, in-
testine; g, longitudinal muscles of the
inferior surface of the body; A, glan-
dular organ (liver ?); ¢. organs of gene-
ration ;j, feet; k, k, branchia; J, dorsal
vessel acting as a respiratory heart
m, dorso-intestinal vessel; 2, venous
sinus surrounding cesophagus; 1’, in-
ferior intestinal vessel; 0, 0, ventral
trunk; p, lateral vascular branches.

ratory appendages, the circulation of the fluids may be distinctly
seen by microscopic examination; and these fluids are of two

536 ANNULOSA, OR WORMS.

kinds,—first, a colorless fluid, containing numerous cell-like cor-
puscles, which can be seen in the smaller and more transparent
species to occupy the space that intervenes between the outer
surface of the alimentary canal and the inner wall of the body,
and to pass from this into canals which often ramify extensively
in the respiratory organs, but are never furnished with a return-
ing series of passages,—and second, a fluid which is usually red,
contains few floating particles, and is enclosed in a system of
proper vessels, that communicates with a central propelling
organ, and not only carries the fluid away from this, but also
brings it back again. In Terebella, we find a distinct provision
for the aeration of both fluids; for the first is transmitted to the
tendril-like tentacula which surround the mouth (Fig. 274, 6, 8),
whilst the second circulates through the beautiful arborescent bran-
chie(k, &) situated just behind the head. The former are covered
with cilia, the action of which continually renews the stratum of
water in contact with them, whilst the latter are destitute of these
organs; and thisseems to be the general fact as to the several appen-
dages to which these two fluids are respectively sent for aeration, the
nature of their distribution varying greatly in the different mem-
bers of the class. The red fluid is commonly considered as blood,
and the tubes through which it circulates as bloodvessels; but
the Author has elsewhere given his reasons! for coinciding in
the opinion of Mr. Huxley, that the colorless corpusculated fluid
which moves in the general cavity of the body and in its exten-
sions, is that which really represents the blood of other Articu-
lated Animals; and that the system of vessels carrying the red
fluid is to be likened on the one hand to the “ water-vascular
system” of the inferior Worms, and on the other to the tracheal
apparatus of Insects (§ 891).

363. In the observation of the beautiful spectacle presented by
the respiratory circulation of the various kinds of Annelids which
swarm on most of our shores, and in the examination of what is
going on in the interior of their bodies (where this is rendered
possible by their transparency), the Microscopist will find a most
fertile source of interesting occupation, and may easily, with care
and patience, make many valuable additions to our present stock
of knowledge on these points. There are many of these marine
Annelids, in which the appendages of various kinds put forth
from the sides of their bodies, furnish very beautiful microscopic
objects; as do also the different forms of teeth, jaws, &c., with
which the mouth is commonly armed in the free or non-tubicolar
species, these being eminently carnivorous. The early history of
their development, too, is extremely curious; for they come forth
from the egg in a condition very little more advanced than the
ciliated gemmules of polypes, consisting of a globular mass of
untransformed cells, certain parts of whose surface are covered
with cilia; in a few hours, however, this embryonic mass elon-

1 See his “ Principles of Comparative Physiology,” 4th Edit. §§ 218, 219, 292.

STRUCTURE AND DEVELOPMENT OF ANNELIDA. 6587

gates, and indications of a segmental division become apparent,
the head being (as it were) marked off in front, whilst behind
this is a large segment thickly covered with cilia, then a nar-
rower and non-ciliated segment, and lastly the caudal or tail-
segment which is furnished with cilia. A little later, a new seg-
ment is seen to be interposed in front of the caudal; and the
dark internal granular mass shapes itself into the outline of an
alimentary canal. The number of segments progressively in-
creases by the interposition of new ones between the caudal and
its preceding segments; the various -internal organs become
more and more distinct, eye-spots make their appearance, little
bristly appendages are put forth from the segments, and the
animal gradually assumes the likeness of its parent; a few days
being passed by the tubicolar kinds, however, in the actively
moving condition, before they settle down to the formation of a
tube. In places where Annelida abound, free swimming larvee
are often to be obtained at the same time and in the same man-
ner as those of the Echinoderms (§ 323); but to carry out any
systematic observations on their embryonic development, the
egos should be searched for in the situations which these animals
haunt. To one other phenomenon of the greatest interest, pre-
sented by various small marine Annelida, the attention of the
Microscopist should be specially directed ; this is their luminosity,
which is not a steady glow like that of the glow-worm or fire-fly,
but a series of vivid scintillations (strongly resembling those pro-
duced by an electric discharge through a tube spotted with tin
foil), that pass along a considerable number of segments, lasting
for an instant only, but capable of being repeatedly excited by
any irritation applied to the body of the animal. These scintil-
lations may be discerned under the microscope, even in separated
segments, when they are subjected to the irritation of a needle-
point or to a gentle pressure ; and it has been ascertained by the
careful observations of M. de Quatrefages, that they are given
out by the muscular fibres in the act of contraction.’

364. Among the fresh-water Annelida, those most interesting
to the Microscopist are the worms of the Nais tribe, which are
common in our rivers and ponds, living chiefly amidst the mud
at the bottom, and especially among the roots of aquatic plants.
Being blood-red in color, they give to the surface of the mud,
when they protrude themselves from it in large numbers and
keep the protruded portion of their bodies in constant undula-
tion, a very peculiar appearance ; but if disturbed, they withdraw
themselves suddenly and completely. These worms, from the
extreme transparence of their bodies, present peculiar facilities
for microscopic examination, and especially for the study of the
internal circulation of the red liquid commonly considered as
blood. There are here no external respiratory organs; and the

1 See his Memoirs on the Annelida of La Mancha, in “Ann, of Nat. Sci.” Sér. 2, tom.
xix, and Sér. 3, tom. xiv.

538 ANNULOSA, OR WORMS.

thinness of the general integument appears to supply all needful
facility for the aeration of the fluids. One large vascular trunk
(dorsal) may be seen lying above the intestinal canal, and another
(ventral) beneath it; and each of these enters a contractile dilata-
tion, or heart-like organ, situated just behind the head. The
fluid moves forwards in the dorsal trunk as far as the heart,
which it enters and dilates; and when this contracts, it propels
the fluid partly to the head, and partly to the ventral heart, which
is distended by it. The ventral heart, contracting in its turn,
sends the blood backwards along the ventral trunk to the tail,
whence it passes towards the head as before. In this circulation,
it branches off from each of the principal trunks into numerous
vessels proceeding to different parts of the body, which then
return into the other trunk; and there is a peculiar set of vascu-
lar coils, hanging down in the perigastric space that contains the
* corpusculated liquid representing the true blood, which seem
specially destined to convey to it the aerating influence received
by the red fluid in its circuit, thus acting (so to speak) like inter-
nal gills. The MNaid-worms have been observed to undergo
spontaneous division during the summer months, a new head
and its organs being formed for the posterior segment behind
the line of constriction, before its separation from the interior.
It has been generally believed that each segment continues to
live as an entire worm; but Dr. T. Williams has lately asserted,
that from the time when the division occurs, neither half takes
in any more food, and that the two segments only retain vitality
enough to enable them to be (as it were) the “nurses” of the
eggs which both include. In the Leech tribe, the apparatus of
teeth with which the mouth is furnished, is one of the most
curious among their points of minute structure ; and the common
“medicinal” leech affords one of the most interesting examples
of it. What is commonly termed the “bite” of the leech, is
really a saw cut, or rather a combination of three saw cuts,
radiating from acommon centre. If the mouth of the leech be
examined with a hand-magnifier, or even with the naked eye, it
will be seen to be a triangular aperture in the midst of a sucking
disk ; and on turning back the lips of that aperture, three little
white ridges are brought into view. Each of these is the convex
edge of a horny semicircle, which is bordered by a row of eighty
or ninety minute hard and sharp teeth; whilst the straight bor-
der of the semicircle is imbedded in the muscular substance of
the disk, by the action of which it is made to move backwards
and forwards in a saw-like manner, so that the teeth are enabled
to cut into the skin to which the suctorial disk has affixed itself.

CHAPTER XVI.

CRUSTACEA.

Passine from the lower division of the Articulated series to
the higher—that in which the body is furnished with distinctly
articulated or jointed limbs,—we come first to the class of Crus-
tacea, which includes (when used in its most comprehensive
sense) all those animals belonging to this group, which are fitted
for aquatic respiration. Jt thus comprehends a very extensive
range of forms; for although we are accustomed to think of the
Crab, Lobster, Cray-fish, and other well-known species of the
order Decapoda (ten-footed), as its typical examples, yet all these
belong to the highest of its many orders; and among the lower
are many of a far simpler structure, and not a few which would
not be recognized as belonging to the class at all, were it not for
the information derived from the study of their development as
to their real nature, which is far more apparent in their early
than it is in their adult condition. Many of the inferior kinds of
Crustacea are so minute and transparent, that their whole struc-
ture may be made out by the aid of the Microscope without any
preparation; this is the case, indeed, with nearly the whole group
of Entomostraca (§ 366), and with the larval forms even of the
Crab and its allies (§ 875); and we shall give our first attention
to these, afterwards noticing such points in the structure of the
larger kinds, as are likely to be of general interest.

365. One of the most curious examples of the reduction of an
elevated type to its very simplest form, which the Animal King-
dom affords, is presented by the group of Pycnogonide ; some
members of which may be found by attentive search in almost
every locality where sea-weeds abound, it being their habit to
crawl (or rather to sprawl) over the surfaces of these, and pro-
bably to imbibe as food the gelatinous substance with which they
are invested. The general form of their bodies (Fig. 275) usually
reminds us of that of some of the long-legged Crabs; the abdo-
men being almost or altogether deficient, whilst the head is very
small, and fused (as it were) into the thorax; so that the last
named region, with the members attached to it, constitutes nearly
the whole bulk of the animal. The head is extended in front
into a proboscis-like projection, at the extremity of which is the

540 CRUSTACEA.

narrow orifice of the mouth; which seems to be furnished with
vibratile cilia, that serve to draw into it the semi-fluid aliment.
Instead of being furnished (as in the higher Crustaceans) with
two pairs of antennee and numerous pairs of “ feet-jaws,” it has
but a single pair of either; it also bears four minute ocellz, or

Fie, 275.

Xo, | ll
SUSS Se
H\S
gO OM.
te 5,

Ammothea pycnogonoides :—a, narrow esophagus; b, stomach; ¢, intestine; d, digestive ceca of the
feet-jaws; e, €, digestive caca of the legs.

rudimentary eyes, set at a little distance from each other on a
sort of tubercle. From the thorax proceed four pairs of legs,
each composed of several joints, and terminated by a hooked
claw ; and by these members the animal drags itself slowly along,
instead of walking actively upon them like a crab. The mouth
leads to a very narrow esophagus (a), which passes back to the
central stomach (6), situated in the midst of the thorax, from the
hinder end of which a narrow intestine (c) passes off, to terminate
at the posterior extremity of the body. From the central stomach,
five pairs of cecal prolongations radiate; one pair (d) entering
the feet-jaws, the other four (e, e) penetrating the legs, and pass-
ing along them as far as the last joint but one; and these exten-
sions are covered with a layer of brownish-yellow granules, which
are probably to be regarded as a diffused and rudimentary con-
dition of the liver. The stomach and its ceecal prolongations are
continually executing peristaltic movements of a very curious
kind; for they contract and dilate with an irregular alternation,
so that a flux and reflux of their contents is constantly taking
place between the central portion and its radiating extensions,
and between one of these extensions and another. The space

ENTOMOSTRAGCA. 541

between the widely-extended stomach and the walls of the body
and limbs is occupied by a transparent liquid, in which are seen
floating a number of minute transparent corpuscles of irregular
size; and this fluid, which represents the blood, is kept in con-
tinual motion, not only by the general movements of the body
and limbs,*but also by the actions of the digestive apparatus;
since, whenever the ceecum of any one of the legs undergoes dila-
tation, a part of the cireumambient liquid will be pressed out
from the cavity of that limb, either into the thorax, or into some
other limb whose stomach is contracting. The fluid must obtain
its aeration through the general surface of the body, as there are
no special organs of respiration. The nervous system consists of
a single ganglion in the head (formed by the coalescence of a
pair), and of another in the thorax (formed by the coalescence of
four pairs), with which the cephalic ganglion is connected in the
usual mode, namely, by two nervous cords which diverge from
each other to embrace the esophagus. Of the reproduction of
this animal, nothing is yet known. In the study of the very
curious phenomena exhibited by the digestive apparatus, as well
as of the various points of internal conformation which have been
described, the achromatic condenser will be found useful, even
with the 1 inch, 2-3ds inch, or 4 inch objectives; for the imper-
fect transparence of the bodies of these animals renders it of im-
portance to drive a large quantity of light through them, and to
give to this light such a quality, as shall define the internal or-
gans as sharply as possible.
366. The Lntomostracous group of Crustaceans, nearly all the ’
existing members of which are of such minute size as to be only *
just visible to the naked eye, is distinguished by the enclosure
of the entire body within a horny or shelly casing, which some-
times closely resembles a bivalve shell in form and in the mode
of junction of its parts, whilst in other instances it is formed of
only a single piece, like the hard envelope of certain Rotifera
(§ 282, III). The segments into which the body is divided, are fre-
quently very numerous, and are for the most part similar to each
other; but there is a marked difference in regard to the appen-
dages which they bear, and to the mode in which these minister
to the locomotion of the animals. For in the Lophyropoda, or
bristly-footed tribe, the number of legs is small, not exceeding
five pairs, and their function is limited to locomotion, the respi-
ratory organs being attached to the parts in. the neighborhood of
the mouth; whilst in the Branchiopoda, or gill-footed tribe, the
same members serve both for locomotion and for respiration,
and the number of these is commonly large, being in Apus not
less than sixty pairs. The character of their movements differs
accordingly ; for whilst all the members of the first-named tribe
dart through the water in a succession of jerks, so as to have
acquired the common name of “ water-fleas,” those among the

542 CRUSTACEA.

latter which possess a great number of “ fin-feet,” swim with an
easy gliding movement, sometimes on their back alone (as is the
case with Branchipus), sometimes with equal facility on the back,
belly, or sides (as is done by Artemia salina, the “ brine shrimp’’).
Some of the most common forms of both tribes will now be
briefly noticed. ®

367. The tribe of Lophyropoda is divided into two orders; of
which the first, Ostracoda, is distinguished by the complete en-
closure of the body in a bivalve shell, by the small number of
legs, and by the absence of an external ovary. One of the best-
known examples is the little Cypris, which is a common inhabi-
tant of pools and streams; this may be recognized by its posses-
sion of two pairs of antenne, the first having numerous joints
with a pencil-like tuft of filaments, and projecting forwards
from the front of the head, whilst the second has more the shape
of legs, and is directed downwards; and by the limitation of its
legs to two pairs, of which the posterior does not make its ap-
pearance outside the shell, being bent upwards to give support
to the ovaries. The valves are generally opened sufficiently
wide, to allow the greater part of both pairs of antenne, and of
the front pair of legs, to pass out between them; but when the
animals are alarmed, they draw these members within the shell,
and close the valves firmly. They are very lively creatures,
being almost constantly seen in motion, either swimming by the
united action of their foot-like antenne and legs, or walking
upon plants and other solid bodies floating in the water. Nearly
allied to the preceding is the Cythere, whose body is furnished
with three pairs of legs, all projecting out of the shell, and
whose superior antenne are destitute of the filamentous brush ;
this genus is almost entirely marine, and some species of it may
almost invariably be met with in little pools among the rocks
between the tide-marks, creeping about (but not swimming)
amongst Conferve and Corallines. There is abundant evidence
of the former existence of Crustacea of this group, of larger size
than any now existing, to an enormous extent; for in certain
fresh-water strata, both of the Secondary and Tertiary series, we
find layers, sometimes of great extent and thickness, which are
almost entirely composed of the fossilized shells of Cyprides ;
whilst in certain parts of the Chalk, which was a marine de-
posit, the remains of bivalve shells resembling those of Cythere,
present themselves in such abundance as to form a considerable
part of its composition. Inthe order Copepoda, there is a jointed
shell forming a kind of buckler that almost entirely encloses the
head and thorax, an opening being left beneath, through which
the members project; and there are five pairs of legs, mostly
adapted for swimming, the fifth pair, however, being rudimentary
in the genus Cyclops, the commonest example of the group.
This genus receives its name from possessing only a single eye,

CYCLOPS, 543

or rather a single cluster of ocelli; which character, however, it
has in common with the two genera already named, as well as
with Daphnia (§ 368), and
with many other Entomos- Fig. 276.
traca. It contains numer-
ous species, some of which
belong to fresh water, whilst
others are marine. The
fresh-water species often
abound in the muddiest and
most stagnant pools, as well
as in the clearest springs;
the ordinary. water with
which London is supplied,
frequently contains large
numbers of them. Of the
marine species, some are to
be found in the localities in
which the Cythere is most
abundant, whilst others in-
habit the open ocean, and
must be collected by a fine
muslin net. The body of
the Cyclops is soft and ge-
latinous, and it is composed
of two distinct parts, & A; female of Cyclops quadricornis:—a, body; b,
thorax (Fig. 276, a) and an slisenmm4 sammie gor 4 meno
abdomen (0), of which the F, G, suoenane: weanes of a aecenee of ne
latter, being comparatively
slender, is commonly considered as a tail, though traversed by
the intestine which terminates near its extremity. The head,
which coalesces with the thorax, bears one very large pair of an-
tennee (c) possessing numerous articulations, and furnished with
bristly appendages, and another small pair (d); it is also furnished
with a pair of “mandibles” or true jaws, and with two pairs of
“ feet-jaws,” of which the hinder pair is the longer, and most
abundantly supplied with bristles. The legs (e) are all beset with
plumose tufts, as is also the tail (f, f) which is borne at the ex-
tremity of the abdomen. On either side of the abdomen of the
female, there is often to be seen an egg-capsule or external ova-
rium (B), within which the ova, after being fertilized, undergo
the earlier stages of their development. The Cyclops is a very
active creature, and strikes the water in swimming, not merely
with its legs and tail, but also with its antenne. The rapidly
repeated movements of its feet-jaws serve to create a whirlpool
in the surrounding water, by which minute animals of various
kinds, and even its own young, are brought to its mouth to be
devoured.

868. The tribe of Branchiopoda also is divided into two orders;

544 CRUSTACEA.

of which the Cladocera present the nearest approach to the pre-
ceding, having a bivalve carapace, no more than from four to
six pairs of legs, two pairs of antenne, of which one is large and
branched and adapted for swimming, and a single eye. The
commonest form of this is the Daphnia pulexr, sometimes called
the “arborescent water-flea” from the branching form of its an-
tenne. It is very abundant in many ponds and ditches, coming
to the surface in the mornings and evenings and in cloudy
weather, but seeking the depths of the water during the heat of
the day. It swims by taking short springs; and feeds on minute
particles of vegetable substances, not, however, rejecting animal
matter when offered. Some of the peculiar phenomena of its
reproduction will be presently described (§ 370). The order
Phyllopoda includes those Branchiopoda whose body is divided
into a great number of segments, nearly all of which are fur-
nished with leaf-like members, or ‘‘fin-feet.” The two families
which this order includes, however, differ considerably in their
conformation; for in that of which the genera Apus and Nebalia
are representatives, the body is enclosed in a shell, either shield-
like or bivalve, and the feet are generally very numerous; whilst
in that which contains Branchipus and Artemia, the body is en-
tirely unprotected, and the number of pairs of feet does not
exceed eleven. The Apus caneriformis, which is an animal of
comparatively large size, its entire length being about 2% inches,
is an inhabitant of stagnant waters; but although occasionally
very abundant in particular pools or ditches, it is not to be met
with nearly so commonly as the Entomostraca already noticed.
It is recognized by its large oval carapace, which covers the
head and body like a shield; by the nearly cylindrical form of
its body, which is composed of thirty articulations; and by the
multiplication of its legs, which amount to about sixty pairs.
The number of joints in these and in the other appendages is so
great, that in a single individual they may be safely estimated at
not less than two millions. These organs, however, are for the
most part small; and the instruments chiefly used by the animal
for locomotion are the first pair of feet, which are very much
elongated (bearing such a resemblance to the principal antenne
of other Entomostraca, as to be commonly ranked in the same
light), and are distinguished as rami or oars. With these they
can swim freely in any position; but when the “rami” are at
rest and the animal floats idly on the water, its fin-feet may be
seen to be in incessant motion, causing a sort of whirlpool in
the water, and bringing to the mouth the minute animals (chiefly
the smaller Entomostraca inhabiting the same localities) that
serve them as food. The Branchipus stagnalis has a slender,
cylindriform, and very transparent body of nearly an inch in
length, furnished with eleven pairs of fin-feet, but is destitute of
any protecting envelope; its head is furnished with a pair of
very curious prehensile organs (which are really modified an-

BRANCHIOPODS—TENACITY OF LIFE. 545

tenne), whence it has received the name of Ohetrocephalus; but
these are not used by it for the seizure of prey, the food of this
animal ae vegetable, and their function is to clasp the female
in the act of copulation. The Branchipus or Cheirocephalus is
certainly the most beautiful and elegant of all the Entomostraca,
being rendered extremely attractive to the view by the “unin-
terrupted undulatory wavy motion of its graceful branchial feet,
slightly tinged as they are with a light reddish hue, the brilliant
mixture of transparent bluish green and bright red of its pre-
hensile antenne, and its bright red tail with the beautiful plu-
mose sete springing from it:” unfortunately, however, it is a:
comparatively rare animal in this country. The Artemia salina
or ‘brine shrimp” is an animal of very similar organization, and
almost equally beautiful in its appearance and movements, but
of smaller size, its body being about half an inch in length. Its
“habitat” is very peculiar; for it is only found in the salt-pans
or brine-pits in which sea-water is undergoing concentration (as
at Lymington); and in these situations it is sometimes so abun-
dant, as to communicate a red tinge to the liquid.

369. Some of the most interesting points in the history of the
Entomostraca lie in the peculiar modes in which their Generative
function is performed, and in their tenacity of life when desic-
cated, in which last respect they correspond with many Rotifera
(§ 280). This provision is obviously intended to prevent them
from being completely exterminated, as they might otherwise
soon be, by the drying up of the pools, ditches, and other small
collections of water which constitute their usual “habitats.” It
does not appear, however, that the adult animals can beara
complete desiccation, although they will preserve their vitality in
mud that holds the smallest quantity of moisture; but their
eggs are more tenacious of life, and there is ample evidence that
these will become fertile on being moistened, after having con-
tinued for a long time in the condition of fine dust. Most
Entomostraca, too, are killed by severe cold, and thus the whole
race of adults perishes every winter; but their eggs seem
unaffected by the lowest temperature, and thus continue the
species which would otherwise be exterminated. Again, we
frequently meet in this group with that reproduction by gemma-
tion, which we have seen to prevail so extensively among the
lower Radiata and Mollusca. In many species there is a double
mode of multiplication, the sexual and the non-sexual. The
former takes place at certain seasons only, the males (which are
often so different in conformation from the females, that they
would not be supposed to belong to the same species, if they
were not seen in actual congress) disappearing entirely at other
times; whilst the latter continues at all periods of the year, so
long as warmth and food are supplied, and is repeated many
times (as in the Hydra), so as to give origin to as many succes-
sive “broods.” Further, a single act of impregnation serves to

35

546 CRUSTACEA.

fertilize not merely the ova which are then mature or nearly so,
but all those subsequently produced by the same female, which
are deposited at considerable intervals. In these two modes,
the multiplication of these little creatures is carried on with
great rapidity, the young animal speedily coming to maturity
and beginning to propagate; so that, according to the computa-
tion of Jurine, founded upon data ascertained by actual observa-
tion, a single fertilized female of the common Cyclops quadri-
cornis may be the progenitor in one year of 4,442,189,120 young.

370. The eggs of some Entomostraca are deposited freely in
the water, or are carefully attached in clusters to aquatic plants;
but they are more frequently carried for some time by the parent
in special receptacles developed from the posterior part of the
body; and in many cases they are retained there until the young
are ready to come forth, so that these animals may be said to be
ovo-viviparous. In the Daphnia, the eggs are received into a
large cavity between the back of the animal and its shell, and
there the young undergo almost their whole development, so as
to come forth in a form nearly resembling that of their parent.
Soon after their birth, a moult or exuviation of the shell takes
place; and the egg coverings are cast off with it. In a very
short time afterwards, another brood of eggs is seen in the
cavity, and the same process is repeated, the shell being again
exuviated after the young have been brought to maturity. At
certain times, however, the Daphnia may be seen with a dark
opaque substance within the back of the shell, which has been
called the ephippcum from its resemblance to a saddle. This,
when carefully examined, is found to be of dense texture, and
to be composed of a mass of hexagonal cells; and it contains
two oval bodies, each consisting of an ovum covered with a
horny casing, enveloped in a capsule which opens like a bivalve
shell. The first traces of the “‘ephippium” are seen after the
third moult, as a green matter in the ovaries, which differs both
in color and appearance from that of the eggs; after the fourth
moult, this green matter passes from the ovaries into the matrix
or open space on the back, and there becomes developed into
the ‘“ephippium ;” and at the fifth moult this is thrown off, and
the ephippium, with the two eggs enclosed, floats on the water
until the next spring, when the young are hatched with the
returning warmth of the season. This curious provision is ob-
viously destined to afford protection to the eggs which are to
endure the severity of winter cold; and some approach to it
may be seen in the remarkable firmness of the envelopes of the
“winter eggs’ of some of the Rotifera (§ 279). It has been
ascertained by Dr. Baird, that the young produced from the
ephippial eggs have the same power of continuing the race by
non-sexual reproduction, as the young developed under ordinary
circumstances.

371. In most Entomostraca, the young at the time of their

ENTOMOSTRACA, HISTORY OF DEVELOPMENT. 547

emersion from the egg differ considerably from the parent, espe-
cially in having only the thoracic portion of the body as yet
evolved, and in possessing but a small number of locomotive ap-
el ae the visual organs, too, are frequently wanting at first.
(See Fig. 276, c-c.) The process of development, however,
takes place with great rapidity; the animal at each successive
moult (which process is very commonly repeated at intervals of
a day or two) presenting some new parts, and becoming more
and more like its parent, which it very early resembles in its
power of multiplication, the female laying eggs before she has
attained her own full size. Even when the Entomostraca have
attained their full growth, they continue to exuviate their shell
at short intervals during the whole of life; and the purpose
which seems to be answered by this repeated moulting, is the
preventing the animal from being injured, or its movements ob-
structed, by the overgrowth of parasitic Animalcules and Con-
fervee; weal and sickly individuals being frequently seen to be
so covered with such parasites, that their motion and life are
soon arrested, apparently because they have not strength to cast
off and renew their envelopes. The process of development ap-
pears to depend in some degree upon the influence of light, being
retarded when the animals are secluded from it; but its rate is still
more influenced by heat; and this appears also to be the chief
agent that regulates the time which elapses between the moult-
ings of the adult, these, as in the Daphnia, taking place at inter-
vals of two days in warm summer weather, whilst several days
intervene between them when the weather is colder. The cast
shell carries with it the sheaths not only of the limbs and plumes,
but of the most delicate hairs and sete which are attached to
them. If the aninial have previously sustained the loss of a
member, it is generally renewed at the next moult, as in higher
Crustacea.'

372. Closely connected with the Entomostracous group is the
tribe of Suctorial Crustacea; which for the most part live as
parasites upon the exterior of other animals (especially Fish),
whose juices they imbibe by means of the peculiar proboscis-
like organ which takes in them the place of the jaws of other
Crustaceans; whilst other appendages, representing the feet-
jaws, are furnished with hooks, by which these parasites attach
themselves to the animals from whose juices they derive their
nutriment. Many of the Suctorial Crustacea bear a strong re-
semblance, even in their adult condition, to certain Entomo-
straca; but more commonly it is between the earlier forms of
the two groups that the resemblance is the closest, most of the
Suctoria undergoing such extraordinary changes in their progress
towards the adult condition, that if their complete forms were
alone attended to, they might be excluded from the class alto-

! For a complete and detailed account of this group, see Dr. Baird’s “ Natural History
of the British Entomostraca,” published by the Ray Society.

548 CRUSTACEA.

gether, as has (in fact) been done by many Zoologists. Among
those Suctorial Crustacea which present the nearest approach to
the ordinary Entomostracous type, may be specially mentioned
the Argulus foliaceus, which attaches itself to the surface of the
bodies of fresh-water fish, and is commonly known under the
name of the “fish-louse.” This animal has his body covered
with a large firm oval shield, which does not extend, however,
over the posterior part of the abdomen. The mouth is armed
with a pair of styliform mandibles; and on each side of the pro-
boscis there is a large short cylindrical appendage, terminated by
a curious sort of sucking disk, with another pair of longer jointed
members, terminated by prehensile hooks. These two pairs
of appendages, which are probably to be considered as repre-
senting the feet-jaws, are followed by four pairs of legs, which,
like those of the Branchiopoda, are chiefly adapted for swim-
ming; and the tail, also, is a kind of swimmeret. This little ani-
mal can leave the fish on which it feeds, and then swims freely
in the water, usually in a straight line, but frequently and sud-
denly changing its direction, and sometimes turning over and over
several times in succession. The stomach is remarkable for the
large cecal prolongations which it sends out on either side, im-
mediately beneath the shell; for these subdivide and ramify in-
such a manner, that they are distributed almost as minutely
as the cecal prolongations of the stomach of the Planaria (Fig.
273). The proper alimentary canal, however, is continued back-
wards from the central cavity of the stomach, as an intestinal
tube, which terminates in an anal orifice at the extremity of the
abdomen?

373. From the parasitic suctorial Crustacea, the transition is
not really so abrupt as it might at first sight appear, to the class
of Cirrhipeda, consisting of the Barnacles and their allies ; which,
like many of the Suctoria, are fixed to one spot during the adult
portion of their lives, but come into the world in a condition
that bears a strong resemblance to the early state of many of the
Crustacea. The departure from the ordinary Crustacean type in
the adult, is, in fact, so great, that it is not surprising that Zoo-
logists in general should have separated them; their superficial
resemblance to the Mollusca, indeed, having caused most syste-
matists to rank them in that series, until due weight was given
to those structural features which mark their Articulated charac-
ter. We must limit ourselves in our notice of this group, to that
very remarkable part of their history, the Microscopic study of
which has contributed most essentially to the elucidation of their
real nature. The observations of Mr. J. V. Thompson,? with the
extensions and rectifications which they have subsequently re-

' As this group is rather interesting to the professed Naturalist than to the amateur
Microscopist, even an outline view of it would be unsuitable to the present treatise;
andthe Anthor would refer such of his readers as may desire to study it, to the ad-

mirable treatise by Dr. Baird, already referred to.
2 « Zoological Researches,” No. III, 1830.

DECAPOD CRUSTACEA. 549

ceived from others, show that there is no essential difference be-
tween the early forms of the sessile (Balanide, or “ acorn-shells”’)
and of the peduneulated Cirrhipeds (Lepadide or “barnacles”);
for that both are active little animals (Fig. 277, a), possessing
three pairs of legs and a pair of compound eyes, and having the
body covered with an expanded shield, like that of many Ento-
mostracous Crustaceans, so as in no essential particular to differ
from the larva of Cyclops (Fig. 276, c). After going through a
series of metamorphoses, one stage of which is represented in
Fig. 277, 8, o, these larvee come to present a form D, which re-
minds us strongly of that of Daphnia; the body being enclosed

Fig. 277.

Development of Balanus balanoides :—aA, earliest form:—s, larva after second moult ;—¢, side view
of the same ;—p, stage immediately preceding the loss of activity; @, stomach (?); b, nucleus ot
future attachment (2).

in a shell composed of two valves, which are united along the
back, whilst they are free along their lower margin, where they
separate for the protrusion of a large and strong anterior pair of
prehensile limbs provided with an adhesive sucker:and hooks,
and of six pairs of posterior legs adapted for swimming. This
bivalve shell, with the members of both kinds, is subsequently
thrown off; the animal then attaches itself by its head, a portion
of which becomes excessively elongated into the “peduncle” of
the Barnacle, whilst in Balanus it expands into a broad disk ot
adhesion; the first thoracic segment sends backwards a prolonga-
tion, which arches over the rest of the body so as completely to
enclose it, and of which the exterior layer is consolidated into
the “multivalve” shell; whilst from the other thoracic segments
are evolved the six pairs of eirrhi,—which are long, slender,
many-jointed, tendril-like appendages, fringed with delicate fila-
ments covered with cilia, whose action serves both to bring food

550 CRUSTACEA.

to the mouth, and to maintain aerating currents in the water,—
from whose peculiar character the name of the group is derived.

374. The chief points of interest to the Microscopist in the
more highly organized forms of Crustacea, are furnished by the
structure of the shell, and by the metamorphosis of the larve,
both of which may be best studied in the commonest kinds.
The shell of the Decapods in its most complete form consists of
three strata; namely, 1, a horny structureless layer covering the
exterior; 2, a cellular stratum; and 3, a laminated tubular sub-
stance. The innermost and even the middle layers, however,
may be altogether wanting; thus in the Phyllosome or “ glass-
crabs,” the envelope is formed by the transparent horny layer
alone; and in many of the small Crabs belonging to the genus
Portuna, the whole substance of the carapace beneath the horny
investment is made up of hexagonal thick-walled cells. (It may
be here noticed, that the carapace of Daphnia, Branchipus, and
some other Entomostraca, exhibits the hexagonal division ; whilst
in many species this is not distinguishable.) It is in the large
thick-shelled Crabs that we find the three layers most differen-
tiated. Thus in the common Cancer pagurus, we may easily
separate the structureless horny covering after a short maceration
in dilute acid; the cellular layer, in which the pigmentary matter
of the colored parts of the shell is contained, may be easily
brought into view by grinding away as flat a piece as can be
selected, from the inner side, having first cemented the outer
surface to the glass slide, and by examining this with a magnify-
ing power of 250 diameters, driving a strong light through it
with the achromatic condenser; whilst the tubular structure ot
the thick inner layer may be readily demonstrated, by means of
sections parallel and perpendicular to its surface. This struc-
ture, which very strongly resembles that of dentine (§ 406), save
that the tubuli do not branch, but remain of the same size
through their whole course, may be particularly well seen in the
black extremity of the claw, which (apparently from some dif-
ference in the molecular arrangement of the mineral particles,
the organic structure being precisely the same) is much denser
than the rest of the shell, the former having almost the semi-
transparency of ivory, whilst the latter has a chalky opacity. In
a transverse section of the claw, the tubuli may be seen to radiate
from the central cavity towards the surface, so as very strongly
to resemble their arrangement in a tooth; and the resemblance
is still further increased by the presence, at tolerably regular
intervals, of minute sinuosities corresponding with the lamina-
tions of the shell, which seem, like the “secondary curvatures”’
of the dentinal tubuli, to indicate successive stages in the calcifi-
cation of the animal basis. This inner layer rises up through
the pigmentary layer of the Crab’s shell, in little papillary cleva-
tions; and it is from the deficiency of the pigmentary layer at
these parts, that the colored portion of the shell derives its

METAMORPHOSES OF DECAPODS. 551

minutely speckled appearance. Many departures from this type
are presented by the different species of Decapods; thus in the
Prawns there are large stellate pigment-cells (resembling those
of Fig. 827, ¢), the colors of which are often in remarkable con-
formity with those of the bottom of the rock-pools frequented by
these creatures; whilst in the Shrimps there is seldom any dis-
tinct trace of the cellular layer, and the calcareous portion of the
skeleton is disposed in the form of concentric rings, an approach
to which arrangement is seen in the papille of the surface of the
deepest layer of the Crab’s shell.

375. It is a very curious circumstance, that a strongly marked
difference exists between Crustaceans that are otherwise very
closely allied, in regard to the degree of change to which their
young are subject in their progress towards the adult condition.
For whilst the common Crab, Lobster, Spiny Lobster, Prawn, and
Shrimp, undergo a regular metamorphosis, the young of the
Land Crab and the Cray-fish come forth from the egg in a form
which corresponds in all essential particulars with that of their
parents. Generally speaking, a strong resemblance exists among
the young of all the species of Decapods which undergo a meta-
morphosis, whether they are afterwards to belong to the brachy-
ourous (short-tailed) or to the macrourous (long-tailed) division of
the group; and the forms of these larve are so peculiar, and so
entirely different from any of those into which they are ultimately
to be developed, that they were considered as belonging to a
distinct genus, Zoea, until their real nature was first ascertained
by Mr. J. V. Thompson. Thus in the earliest state of Carcinus
meenas (small edible crab), we see the head and thorax, which
form the principal bulk of the body, included within a large cara-
pace or shield (Fig. 278, a) furnished with a long projecting spine,
beneath which the fin-feet are put forth; whilst the abdominal

Fig. 278.

Metamorphosis of Carcinus menas :—a, first stage; B, Second stage; c, third stage, in which it
begins to assume the adult form; p, perfect torm.

segments, narrowed and prolonged, carry at the end a flattened
tail-fin, by the strokes of which upon the water, the propulsion
of the animal is chiefly effected. Its condition is hence compa-

552 CRUSTACEA.

rable, in almost all essential particulars, to that of Cyclops (§ 367).
In the case of the Lobster, Prawn, and other “macrourous”’
species, the metamorphosis chiefly consists in the separation of
the locomotive and respiratory functions, true legs being deve-
loped from the thoracic segments for the former, and true gills
(concealed within a special chamber formed by an extension of
the carapace beneath the body) for the latter; and the abdominal
segments increase in size, and become furnished with appen-
dages (false feet) of their own. In the Crabs, or “ brachyour-
ous” species, on the other hand, the alteration is much greater ;
for besides the change first noticed in the thoracic members and
respiratory organs, the thoracic region becomes much more
developed at the expense of the abdominal, the latter remaining
in an almost rudimentary condition, and being bent under the
body; the thoracic limbs are more completely adapted for walk-
ing, save the first pair, which are developed into chele or pincers;
and the little creature entirely loses the active swimming habits
which it originally possessed, and takes on the mode of life
peculiar to the adult. We have, in this history, a most charac-
teristic example of Von Bar’s great law of “progress from the
general to the special” in organic development; for the Ento-
mostracous form is thus seen to be common to the highest and
the lowest Crustaceans in the earliest phase of their lives; but
whilst the latter remain and go on to completion upon that type,
the former entirely diverge from it; and whilst diverging from
it, they also become differentiated from each other, the distinc-
tive characters of their families, genera, and species, evolving
themselves, as the individuals advance towards their mature
forms.

376. In collecting minute Crustacea, whether fresh-water or
marine, the use of the ring-net, as for -minute Acalephe or
Echinoderm larve, will be found the most efficient instrument;
and in favorable localities, the same “ gathering” will often con-
tain multitudes of various species of Entomostraca, accompanied,
perhaps, by the larve of higher Crustacea, by Echinoderm
larvee, by Annelid larve, and by the smaller Meduse. The
water containing these should be put into a large glass jar freely
exposed to the light; and after a little practice, the eye will -
become so far habituated to the general appearance and modes
of movement of these different forms of Animal life, as to be
able to distinguish them, one from the other. In selecting any
specimen for microscopic examination, the dipping tube (§ 71)
will be found invaluable. The study of the metamorphoses
of the larvee will be best prosecuted, by obtaining the fertilized
eggs which are carried about by the females, and watching the
history of their products.

CHAPTER XVII.

INSECTS AND ARACHNIDA.

THERE is no class in the whole Animal Kingdom which affords
to the Microscopist such a wonderful variety of interesting
objects, and such facilities for obtaining an almost endless suc-
cession of novelties, as that of Insects. For, in the first place,
the number of different kinds that may be brought together (at
the proper time) with extremely little trouble, far surpasses that
which any other group of Animals can supply to the most pains-
taking collector; then, again, each specimen will afford, to him
who knows how to employ his materials, a considerable number
of microscopic objects of very different kinds; and, thirdly,
although some of these objects require much care and dexterity
in their preparation, a large proportion may be got out, examined,
and mounted, with very little skill or trouble. Take, for exam-
ple, the common House-Fly :—its eyes may be easily mounted,
one as a transparent, the other as an opaque object (§ 383); its
antenne, although not such beautiful objects as those of many
other Diptera, are still well worth examination (§ 385); its
tongue or “proboscis” is a peculiarly interesting object (§ 386),
though requiring some care in its preparation; its spiracles,
which may be easily cut out from the sides of its body, have a
very curious structure (§ 392); its alimentary canal affords a
very good example of the minute distribution of the “tracher”
(§ 891); its wings, examined on a living specimen, newly come
forth from the pupa state, exhibit the circulation of the blood in
the “nervures” (§ 390); the wing of the insect when dead,
moreover, exhibits a most beautiful play of iridescent colors,
and shows a remarkable areolation of surface, when it is exa-
mined by light reflected from its surface at a particular angle
(§ 395) ; its foot has a very peculiar conformation, which is doubt-
less connected with its singular power of walking over smooth
surfaces in direct opposition to the force of gravity, although the
mode in which it serves this purpose is not yet certainly ascer-
tained (§ 897); and the structure and physiology of its sexual
apparatus, with the history of its development and metamor-
phoses, would of itself suffice to occupy the whole time of an

554 INSECTS AND ARACHNIDA.

observer who should desire thoroughly to work it out, not only
for months but for years. Hence in treating of this department
in such a work as the present, the author labors under the
embarras des richesses ; for to enter into such a description of the
parts of the structure of Insects most interesting to the Micro-
Scopist, as should be at all comparable in fulness with the
accounts which it has been thought desirable to give of other
classes, would swell out the volume to an inconvenient bulk;
and no course seems open, but to limit the treatment of the
subject to a notice of the kinds of objects which are likely to
prove most generally interesting, with a few illustrations that
may serve to make the descriptions more clear, and with an
enumeration of some of the sources whence a variety of speci-
mens of each class may be most readily obtained. And thus
limitation is the less to be regretted, since there already exist in
our language numerous elementary treatises on Entomology,
wherein the general structure of Insects is fully explained, and
the conformation of their minute parts as seen with the Micro-
scope is adequately illustrated.

377. A considerable number of the smaller Insects,—espe-
cially those belonging to the orders Coleoptera (beetles), Newrop-
tera (dragon fly, May fly, &c.), Hymenoptera (bee, wasp, &ec.), and
Diptera (two-winged flies), may be mounted entire as opaque
objects for low magnifying powers; care being taken to spread
out their legs, wings, &., so as adequately to display them,
which may be accomplished even after they have dried in other
positions, by softening them by steeping them in hot water, or,
where this is objectionable, by exposing them to steam. Full
directions on this point, applicable to small and large Insects
alike, will be found in all text-books of Entomology. There are
some, however, whose translucency allows them to be viewed as
transparent objects; and these are either to be mounted in
Canada balsam, or in weak spirit or glycerine, according to the
degree in which the horny opacity of their integument requires
the assistance of the former to facilitate the transmission of
light through it, or the softness and delicacy of their textures
renders a preservative liquid more desirable. Thus an ordinary
Flea or Bug will best be mounted in the former medium; but
the various parasites of the Louse kind, with some or other of
which almost every kind of animal is affected, should be set up
in the latter. Some of the aquatic larve of the Diptera and
Neuroptera, which are so transparent that their whole internal
organization can be made out without dissection, are very
beautiful and interesting objects, when examined in the living
state, especially because they allow the circulation of the blood
and the action, of the dorsal vessel to be discerned (§ 389).
Among these, there is none preferable to the larva of the
Ephemera marginata (day fly), which is distinguished by the pos-
session of a number of beautiful appendages on its body and

STRUCTURE OF THE INTEGUMENT OF INSECTS. 6555

tail, and is, moreover, an extremely common inhabitant of our
ponds and streams. This insect passes two or even three years
in its larva state, and during this time it repeatedly throws off its
skin; the cast-skin, when perfect, is an object of extreme
beauty, since, as it formed a complete sheath to the various
appendages of the body and tail, it continues to exhibit their
outlines with the utmost delicacy; arid by keeping these larvee
in a Vivarium, and by mounting the entire series of their cast
skins, a record is preserved of the successive changes they
undergo. Much care is necessary, however, to extend them
upon their slides, in consequence of their extreme fragility ; and
the best plan is to place the slip of glass under the skin whilst it
is floating on water, and to lift the object out upon the slide.
378. Structure of the Integument.—In treating of the separate
parts of the organization of Insects, which furnish the most in-
teresting objects of Microscopic study, we may most appropriately
commence with their integument and its appendages (scales,
hairs, &¢.) The body and members are closely invested by a
hardened skin, which acts as their skeleton, and affords points
of attachment to the muscles by which their several parts are
moved ; being soft and flexible, however, at the joints. The
skin is usually more or less horny in its texture, and is consoli-
dated by the animal substance termed chitine, as well as, in some
cases, by a small quantity of mineral matter. Itis in the Coleop-
tera that it attains its greatest development; the dermo-skeleton
of many beetles being so firm, as not only to confer upon them
an extraordinary power of passive resistance, but also to enable
them to put forth enormous force, by the action of the powerful
muscles which are attached to it. It may be stated as a general
rule, that the external layer of this dermo-skeleton is always
cellular, taking the place of an epidermis; and that the cells are
straight-sided and closely fitted together, so as to be polygonal
(usually hexagonal) in form. Of this we have a very good ex-
ample in the superficial layers (Fig. 286, 8) of the thin horny
lamelle or blades, which constitute the terminal portion of the
antenna of the Cockehaffer (Fig. 285); this layer being easily
distinguished from the intermediate portion of the lamina (a),
by careful focussing. In many beetles, the hexagonal areolation
of the surface is often distinguishable when the light is reflected
from it at a particular angle, even when not discernible in trans-
parent sections. The integument of the common Red Ant ex-
hibits the hexagonal cellular arrangement very distinctly through-
out; and the broad flat expansion on the leg of the Crabro (sand-
wasp) affords another beautiful example of a distinctly cellular
structure in the outer layer of the integument. The inner layer,
however, which constitutes the principal part of the thickness of
the horny casing of the Beetle tribe, seldom exhibits any distinct
organization; though it may be usually separated into several
lamine, which are sometimes traversed by tubes that pass into

556 INSECTS AND ARACHNIDA.

them from the inner surface, and extend towards the outer with-
out reaching it. Occasionally, however, even this exhibits very
clear indications of cellular structure ; of which a good example
is afforded by the middle layer of the lamelle of the antenna of
the Cockchaffer (Fig. 286, a), wherein is plainly to be seen an
assemblage of rounded cells with large nuclei, lying in the
midst of a homogeneous intercellular substance, and thus closely
resembling Cartilage (Fig. 324) in structure, though differing
from it in chemical composition.

379. Tegumentary Appendages.—The surface of many Insects
is beset, and is sometimes completely covered with appendages,
having sometimes the form of broad flat scales, sometimes that
of hairs more or less approaching the cylindrical shape, and
sometimes being intermediate between the two. The scaly in-
vestment is most complete among the Lepidoptera (butterfly and
moth tribe); the distinguishing character of the insects of this
order being derived from the presence of a regular layer of
scales, upon each side of their large membranous wings. It is
to the peculiar coloration of the scales, that the various hues and
figures are due, by which these wings are so commonly dis-
tinguished ; all the scales of one patch (for example) being green,
those of another red, and so on; forthe subjacent membrane re-
mains perfectly transparent and colorless, when the scales have
been brushed off from its surface. Hach scale seems to be com-
posed of two superficial colored laminez, enclosing a central
lamina of structureless membrane, the surface of which is highly
polished, and which acts as a “foil” to increase their brilliancy
by reflecting back the light that passes through them,—an ar-
rangement which may often be discerned in scales that have
lost a portion of their superficial layer by some accidental injury
(Fig. 281, c). The color of the superficial laminee seems to be
generally inherent in their substance, especially in the Lepidop-
tera; but it sometimes appears to be (like the prismatic hues of
a soap-bubble) a purely optical effect of their extreme thinness,
this being especially the case among those beetles, as the Cureulio
impertalis (diamond beetle), the scales of which have a metallic
lustre, and exhibit colors that vary with the mode in which the
light glances from them. Lach scale is furnished with a sort of
- handle at one end (Figs. 279-281), by which it is fitted into a
minute socket attached to the surface of the insect; and on the
wings of Lepidoptera these sockets are so arranged, that the
scales lie in very regular rows, each row overlapping a portion of
the next, so as to give to their surface, when sufficiently magni-
fied, very much the appearance of being tiled like the roof of a
house. Such an arrangement is said to be “imbricated.” The
forms of these scales are often very curious, and frequently differ
a good deal on the several parts of the wings and of the body of
the same individual; being usually more expanded on the for-
mer, and narrower and more hair-like on the latter. The

SCALES OF INSECTS. , 557

peculiar markings which many of these scales exhibit, very early
attracted the attention of those engaged in the improvement of
the Microscope by the application of the principle of achromatic
correction (p. 41); since these markings are entirely invisible,
however great may be the magnifying power employed, under
microscopes of ‘the older construction, owing to the necessary
limitation of their angular aperture; whilst, as they are brought
into view with a clearness and strength that are proportionate to
the extension of the angular aperture and the perfection with
which the aberrations are corrected, they serve as “test objects”
of the goodness of an achromatic combination. At first, the
scale of the Podura (Fig. 281) was the most difficult test known
for the highest powers; and a microscope which could only
exhibit an alternation of dark and light bands or striz upon its
surface, was considered a good one. But even the complete
“resolution” of these strie into their component markings, is
now considered as but a very ordinary “ test’ for the medium
powers of the Microscope; and tests of much greater difficulty,
and therefore more suitable for the higher, are afforded (as we
have seen, § 102, III) by the valves of the Diatomacer. Still,
the test scales of Insects have their use, in enabling us to ap-
preciate the performance of achromatics of medium power
(§ 102, IIT); and it’ will therefore be advantageous here to

Fic. 279. Fia. 280,

Scale of Morpho Menelaus. Battledoor Scale of Polyommatus argus
(azure blue),

notice a few of those which are most commonly employed for
this purpose.

880. Among the most beautiful of all these scales, both for
color and for regularity of marking, are those of the butterfly
termed Morpho Menelaus (Fig. 279). These are of a rich blue

558 INSECTS AND ARACHNIDA.

tint, and exhibit strong longitudinal strie, which seem due to
ribbed elevations of the superficial colored layer. There is also
an appearance of transverse striation, which cannot be seen at
all with an inferior objective, becomes very decided with a good
objective of medium focus, but is found, when submitted to the
test of a high power and achromatic condenser, to depend upon
a sort of beaded subdivision of the longitudinal ribs,—the trans-
verse strie that may be seen between these ribs, being apparently
produced by the beading of the ribs on the other surface of the
scale. The large scales of the Polyommatus argus (azure-blue
butterfly) resemble those of the Menelaus in form and structure,
but are more delicately marked. The same insect, however, fur-
nishes small scales, which are commonly termed the “battledoor”
scales, the resemblance which their form presents to that instru-
ment being usually much greater than in the specimen repre-
sented in He. 280; these scales, also, are marked by narrow
longitudinal ribbings, which at intervals expand into rounded or
oval elevations, that give to the scale a dotted appearance; at
the lower part of the scale, however, these dots are wanting; and
in the interval between the two portions, we observe a sort of
crescent, formed of minute pigment-granules, crossing the scale
transversely. The scales of the Pontia brassica (cabbage butterfly)
and of the Hinparchia janira (mea-
Fig. 281. dow-brown butterfly), have longitu-
dinal markings of a somewhat simi-
lar nature, but less sharply defined ;
these are further noticeable for the
brush-like appendage which each
scale bears at the end furthest from
its implantation. The Podura plum-
bea or “spring-tail” is a little wing-
less insect that is found amidst the
sawdust of many wine-cellars, espe-
cially such as are damp, leaping about
like a flea, by means of that peculiar
power of using its tail, from which
its name is derived. Its scales are
of different sizes and of different
degrees of strength of marking
(Fig. 281, a, B), and are therefore
by no means of uniform value as
tests. The general appearance of
Scales of Podura plumbea :—a, large their surface, under a power not suf-
strongly marked scale; B, small scale, ficient to resolve their marking, is
more faintly marked; c, portion of an that of watered silk, light and dark
injured scale, showing the nature of : ea lA B
the'markinigs: bands passing across with wavy ir-
regularity; but a well-corrected lens
of very moderate angular aperture, now suffices to resolve every
dark band into a row of short lines, each of these being thick at

Mi etanye
\ aN

it
iH

MODE OF VIEWING SURFACES OF INSECTS, 559

one end and coming to a point at the other, so that the impres-
sion conveyed is that of a set of spines projecting obliquely from
the flat surface of the scale, like the teeth of a.“‘hackle.” <A
more careful examination of scales, however, of which the super-
ficial layers have been partly removed (c), serves to show that
these dark lines are but the spaces between the minute wedge-
like particles, arranged side by side, and end to end, of which
those layers are made up; so that the structure of the scale does
not in reality differ essentially from the ordinary type Although
scarcely useful as a “ test-object,”’ since its structure is too easily
resolved, the scale of the Lepisma saccharina or “sugar-louse”
deserves notice; the longitudinal ribbings being so strongly
marked and so regular, as to give them an appearance resembling
that of many bivalve shells. The long narrow scale of the com-
mon Gnat, also, exhibits a few very prominent ribbings; and,
from its small size, it serves as a good test-object for the medium
powers.

381. The Hairs of many Insects, and still more of their larve,
are very interesting objects for the microscope, on account of
their branched or tufted conformation; this being particularly
remarkable in those with which the common hairy Caterpillars
are so abundantly beset. Some of these afford very good tests
for the perfect correction of objectives. Thus, the hair of the
Bee is pretty sure to exhibit strong prismatic colors, if the chro-
matic aberration should not have been exactly neutralized; and
that of the larva of the Dermestes, or “bacon-beetle,” was once
thought a very good test of defining power, and is still useful for
this purpose. It has a cylindrical shaft (Fig. 282, 8) with closely
set whorls of spiny protuberances, four or five in each whorl;
the highest of these whorls is composed of more knobby spines ;
and the hair is surmounted by a curious circle of six or seven
large filaments, attached by their pointed ends to its shaft, whilst
at their free extremities they dilate into knobs. An approach to
this structure is seen in the hairs of certain Myriapods (centi-
pedes, gally-worms, &c.), of which an example is shown in Fig.
282, A. ;

* 382. In examining the integument of Insects, and its appen-
dages, parts of the surface may be viewed either by reflected or
transmitted light, according to their degree of transparency and
the nature of their covering. The Beetle and Butterfly tribes
furnish the greater number of objects suitable to be viewed in

' Podure may be obtained by sprinkling a little oatmeal on a piece of black paper
near their haunts; and after leaving it there for a few hours, removing it carefully toa
large glazed basin, so that, when they leap from the paper (as they will when brought
to the light) they may fall into the basin, and may thus separate themselves from the
meal. The best way of obtaining their scales, is to confine several of them together
beneath a wine-glass inverted upon a piece of fine smooth paper; for the scales will be
detached by their leaps against the glass, and will fall upon the paper; and if they be
left thus confined for some time, they will be very likely, by treading npon some of the
scales, to bring them into the condition represented at c, Fig. 281, which best illustrates
their true nature.

560 INSECTS AND ARACHNIDA.

the former of these modes; and nothing is easier than to
mount portions of the elytra of the former (which are usually the
most showy portions of their bodies), or of the

Fig, 282. wings of the latter, in the manner described

* ij in § 123. The tribe of Oureulionide, in which

fi the surface of the body is beset with scales

having the most varied and lustrous hues, is
distinguished among all other Coleoptera for
the brillianey of the objects it affords; the
most remarkable in this respect being the
well-known Ourculio imperialis, or “diamond
beetle” of South America, parts of whose
elytra, when properly illuminated and looked
at with a low power, show like clusters of
jewels flashing against a dark velvet ground.
In many of the British Curculionide, which
are smaller and far less brilliant, the scales lie
at the bottom of little depressions of the sur-
face; and ifthe elytra of the “diamond beetle”
be carefully examined, it will be found that
. each of the clusters of scales which are arranged
upon it in rows, seems to rise out of a deep
pit which sinks in by its side. The transition
from scales to hairs 1s extremely well seen, by
comparing the different parts of the surface
of the “diamond beetle’ with each other.
The beauty and brilliancy of many objects of this kind are in-
creased by mounting them in cells in Canada balsam, even
though they are to be viewed with reflected light; other objects,
however, are rendered less attractive by this treatment; and in
order to ascertain, whether it is likely to improve or to deterio-
rate the specimen, it is a good plan first to test some other por-
tion of the body, having scales of the same kind, by touching it
with turpentine, and then to mount the part selected as an ob-
ject, either in balsam, or dry, according as the turpentine in-
creases or diminishes the brilliancy of the scales on the spot to
which it was applied. Portions of the wings of Lepidoptera are
best mounted as ,opaque objects, without any other preparation
than gumming them flat down to the card-board surface of the
slide (§ 123); care being taken to avoid disturbing the arrange-
ment of the scales, and to keep the objects, when mounted, as
secluded as possible from dust. In selecting such portions, it is
well to choose those which have the brightest and the most con-
trasted colors, foreign butterflies being in this respect usually
preferable to British ; and before attaching them to their slides,
care should be taken to ascertain in what position, with the
arrangement of light ordinarily used, they are seen to the best
advantage, and to fix them there accordingly. Whenever por-
tions of the integument of Insects are to be viewed as transparent

A, Hair of Myriapod.
B, Hair of Dermestes.

EYES OF INSECTS. 561

objects, for the display of their intimate structure, they should be
mounted in Canada balsam, after soaking for some time in tur-
pentine ; since this substance has a peculiar effect in increasing
the translucency. Not only the horny casings of perfect Insects of
various orders, but also those of their pupe, are worthy of this
kind of study; and objects of great beauty (such as the chrysalis
case of the Emperor-moth), as well as of scientific interest, are
sure to reward any who may prosecute it with any assiduity.
Further information may often be gained, by softening such
parts in potash, and viewing them in fluid. The scales of the
wings of Lepidoptera, &c., are best transferred to the slide, by
simply pressing a portion of the wing either upon the slip of
bee or upon the cover; if none should adhere, the glass may
rst be gently breathed on. Some of them are best seen when
examined “dry,” whilst others are more clear when mounted in
fluid; and for the determination of their exact structure, it is
well to have recourse to both these methods. If these scales are
to be used as ‘‘test-objects,” it is preferable to place them
between two pieces of thin glass, in the manner specified in
§ 122. Hairs, on the other hand, are best mounted in balsam.
383. Parts of the Head.—The Hyes of Insects, situated upon
the upper and outer part of the head, are usually very conspicu-
ous organs, and are frequently so large as to touch each other in
front (Fig. 288). We find in their structure a remarkable exam-
ple of that multiplication of similar parts, which seems to be
the predominating idea in the conformation of Articulated
animals; for each of the large protuberant bodies which we
designate as an eye, is really an aggregate of many hundred, or
even many thousand minute eyes, which are designated ocellt.
Approaches to this structure
are seen in the Annelida and Fig. 283.
Entomostraca; but the number
of ‘“ocelli” thus grouped toge-
ther is usually small. In the
higher Crustacea, however, the
ocelli are very numerous; their
compound eyes being construct-
ed upon the same general plan as
those of Insects, although their
shape and position are often very
peculiar (Fig. 843). The indi-
vidual ocelli are at once recog-
nized, when the composite eyes ' ‘
are examined under even a low ; Head and Compound Eyes of the Bee, shaw:
ps ing the ocelli in situ on one side (a), and dis-
magnifying power, by the . fa- placed on the other (B); @, a,a, stemmata; b, b,
cetted’’ appearance of the sur- antenna.
face (Fig. 283), which is marked
out by very regular divisions either into hexagons or into
squares: each facet is the cornea of a separate ocellus, and
36

562 INSECTS AND ARACHNIDA.

has a convexity of its own; hence by counting the facets,
we can ascertain the number of ocelli in each composite eye.
In the two eyes of the common Fly, there are as many as 4000;
in those of the Cabbage Butterfly, there are about 17,000; :in
the Dragon fly, 24,000; and in the Mordella beetle, 25,000. Be-
hind each “corneule” is a layer of dark pigment, which takes
the place, and serves the purpose, of the “iris” in the eyes
of Vertebrate animals; and this is perforated by a central aper-
ture or “pupil,” through which the rays of light that have
traversed the cornea gain access to the interior of the eye. The
further structure of these bodies is best examined by vertical
sections; and these show that the shape of each ocellus is coni-
cal, or rather pyramidal (Fig. 284), the cornea forming its base
(a), whilst its apex abuts upon a bulbous expansion of the optic

Fic. 284.

A, Section of the eye of Melolontha vulgaris (Cockvhafer):—s, a portion more highly magnified :—
a, facets of the cornea; }, transparent pyramids surrounded with pigment; c, fibres of the optic
nerve; @, trunk of the optic nerve.

nerve. Each ‘“corneule” acts as a distinct lens; as may be
shown by detaching the entire assemblage by maceration, and
then drying it (flattened out) upon a slip of glass; for when this
is placed under the microscope, if the point of a knife, scissors,
or any similar object, be interposed between the mirror and the
stage, the image of this point will be scen, by a proper adjust-
ment of the focus of the microscope, in every one of the lenses.
The focus of each “corneule” has been ascertained by experi-
ment to be equivalent to the length of the pyramid behind it;
so that the image which it produces will fall upon the extremity
of the filament of the optic nerve which passes to its point.
This pyramid consists of a transparent substance (B, 6), which
may be considered as representing the ‘vitreous humor;” and
the pyramids are separated from each other by a layer of dark
pigment, which completely encloses them, save at the pupillary
apertures which admit the rays that have passed through the
‘“corneules,”’ and at their smaller ends, where the pigment is
perforated by a set of apertures that give passage to the fibres of

EYES OF INSECTS. 563

the optic nerve (c), of which one proceeds to each ocellus. Thus
the rays which have passed through the several “ corneules” are
prevented from mixing with each other; and no rays save those
which pass in the axis of the pyramids, can reach the fibres of
the optic nerve. Hence it is evident that, as no two ocelli on
the same side have exactly the same axis, no two can receive
their rays from the same point of an object; and thus, as each
composite eye is immovably fixed upon the head, the combined
action of the entire aggregate will probably only afford but a
single image, resembling that which we obtain by means of our
single eyes. Although the foregoing may be considered as the
typical structure of the eyes of Insects, yet there are various
departures from it (most of them slight) in the different members
of the class. Thus in some cases the posterior surface of each
‘“‘corneule”’ is concave; and a space is left between it and the
iris-like diaphragm, which seems to be occupied by a watery
fluid or “aqueous humor;” in other instances, again, this space
is occupied by a double convex body, which seems to represent
the “crystalline lens ;’’ and this body is sometimes found behind
the iris, the number of ocelli being reduced, and each one being
larger, so that the cluster presents more resemblance to that of
Spiders, &. Besides their composite eyes, Insects usually pos-
sess a small number of rudimentary single eyes, resembling
those of the Arachnida; these are seated upon the top of the
head, and are termed stemmata (Fig. 288, a, a, a). It is remark-
able that the larve of Insects which undergo a complete meta-
morphosis, only possess single eyes; the composite eyes being
developed, at the same time with the wings and other parts
which are characteristic of the Imago state, during the latter
part of Pupal life.

384. Various modes of preparing and mounting the Eyes of
Insects may be adopted, according to the manner wherein they
are to be viewed. For the observation of their external facetted
surface by reflected light, it is better to lay down the entire
head, so as to present a front-face or a side-face, according to
the position of the eyes; the former giving a view of both eyes,
when they approach each other so as nearly or quite to meet (as
in Fig. 283); whilst the latter will best display one, when the
eyes are situated more at the sides of the head. For the
minuter examination of the “corneules,” however, these must
be separated from the hemispheroidal mass whose exterior they
form, by prolonged maceration ; and the pigment must be care-
fully washed away by means of a fine camel-hair brush, from their
inner or posterior surface. In flattening them out upon the glass
slide, one of two things must necessarily happen; either the
margin must tear when the central portion is pressed down to a
level; or, the margin remaining entire, the central portion must
be thrown into plaits, so that its corneules overlap one another.
As the latter condition interferes with the examination of the

564 INSECTS AND ARACHNIDA.

structure much more than the former does, it should be avoided
by making a number of slits in the margin of the convex mem-
brane before it is flattened out. Such preparations may be
mounted either in liquid, or in Canada balsam ; the latter being
preferable when (as sometimes happens) the membrane is so
horny as to be but imperfectly transparent. Vertical sections,
adapted to demonstrate the structure of the ocelli and their re-
lations to the optic nerve, can of course be only made when the
body of the insect is fresh; and these should be mounted in
fluid. The following are some of the Insects, whose eyes are
best adapted for Microscopic preparations :— Coleoptera, Cicindela,
Dytiscus, Melolontha (cockchafer), Lucanus (stag-beetle); Or-
thoptera, Acheta (house and field crickets), Locusta ; Hemiptera,
Notonecta (boat-fly); Mewroptera, Libellula (dragon-fly), Agrion ;
Hymenoptera, Vespide (wasps) and Apide (bees) of all kinds ;
Lepidoptera, Vanessa (various species of butterflies), Sphinx
ligustri (privet hawk-moth), Bombyx (silkworm-moth, and its
allies); Diptera, Tabanus (gad-fly), Asilus, Eristalis (drone-fly),
Tipula (crane-fly), Musca (house-fly), and many others.

885. The Antenne, which are the two jointed appendages
arising from the upper part of the head of Insects (Fig. 283, 8, 6),
present a most wonderful variety of conformation in the several
tribes of Insects; often ditfering considerably in the several
species of one genus, and even in the two sexes of the same
species. Hence the characters which they afford are extremely
useful in classification; especially since their structure must
almost necessarily be in some way related to the habits and
general economy of the creatures to which they belong (although
our imperfect acquaintance with their function prevents us from
clearly discerning this relation), so that their resemblances and
differences will generally be found to coincide with those re-
semblances and differences in general conformation, on which
every “natural” arrangement must be founded. Thus, in the
Coleopterous order, we tind one large family, including the glow-
worm, fire-fly, skip-jack, &c., distinguished by the toothed
or serrated form of the antenne, and hence called Serricornes ;
in another, of which the “burying-beetle” is the type, the
antennee are terminated by a club-shaped enlargement, so that
these beetles are termed Clavicornes ; in another, again, of which
the Hydrophilus or “large water-beetle”’ is an example, the
antenne are never longer and are commonly shorter than one
of the pairs of palpi, whence the name of Palpicornes is given
to this group; in the very large family that includes the Lucani
or “ stag-beetles,”’ with the Scarabeei of which the “ cockchafer’’
is the commonest example, the antenne terminate in a set of
leaf-like appendages, which are sometimes arranged like a fan
or the leaves of an open book (Fig. 285), are sometimes parallel
to each other like the teeth of a comb, and sometimes fold one
over the other, thence giving the name of Lamellicornes ; whilst
another large family is distinguished by the appellation Longi-

ANTENNZ OF INSECTS. 565

cornes, from the great length of the antenne, which are at least
as long as the body, and often longer.. Among the Lepidoptera,
again, the conformation of the

antennee frequently enables us ; Fig. 285.

at once to distinguish the group
to which any specimen belongs.
As every treatise on Entomo-
logy contains figures and de-
scriptions of the principal types
of conformation of these organs,
thereis no occasion here to dwell
upon them longer than to spe-
cify such as are most interesting
to the Microscopist; Coleoptera,
Brachinus, Calathus, Harpalus,
Dytiscus, Staphylinus, Philon-
thus, Elater, Lampyris, Silpha,
Hydrophilus, Aphodius, Melo-
lontha,Cetonia, Curculio; Orthop-
tera, Forficula (earwig), Blatta
(cockroach); Lepidoptera, Sphin-
ges (hawk-moths) and Nocturna
(moths) of various kinds, the
large “plumed” antenne of the
latter being peculiarly beautiful objects under a low magnifying
power; Diptera, Culicide (gnats of various kinds), Tipulide
(crane-flies and midges), Ta-

banus, Eristalis, and Mus- Fig. 286.

cidee (flies of various kinds). : e

All the larger antenne should
be put up in balsam, after
being soaked for some time
in turpentine; but the small
feathery antennex of gnatsand *
midges are so liable to dis-
tortion when thus mounted,
that it is better to set them
up in fluid, the head with its } ; , ,
pair of antennse being thus gienna of aastmina:n thei internal layers
preserved together when not their superficial layer.

too large.

886. The next point in the organization of Insects, to which
the attention of the Microscopist may be directed, is the struc-
ture of the Mouth. Here, again, we find almost infinite varieties
in the details of conformation; but these may be for the most
part reduced to a small number of types or plans, which are
characteristic of the different orders of Insects. It is among the
Coleoptera, or beetles, that we find the several parts of which the
mouth is composed, in their most distinct form; for although

Antenna of Delolontha (Cockchafer).

566 INSECTS AND ARACHNIDA.

some of these parts are much more highly developed in other
insects, other parts may be so much altered or so little developed,
as to be scarcely recognizable. The Coleoptera present the
typical conformation of the mandibulate mouth, which is adapted
for the prehension and division of solid substances; and this
consists of the following parts:—1. A pair of jaws, termed
mandibles, frequently furnished with powerful teeth, opening
laterally on either side of the mouth, and serving as the chief
instruments of manducation; 2. A second pair of jaws, termed
macille, smaller and weaker than the preceding, beneath which
they are placed, and serving to hold the food, and to convey it to
the back part of the mouth; 3, an upper lip, or labrum; 4, a
lower lip, or ladium; 5, one or two pairs of small jointed appen-
dages termed palpi, attached to the maxille, and hence called
maxillary palpi; 6, a pair of labial palpi. The labium is often
composed of several distinct parts; its basal portion being dis-
tinguished as the mentwm or chin, and its anterior portion being
sometimes considerably prolonged forwards, so as to form an
organ which is properly designated the ligula, but which is more
commonly known as the “tongue,” though not really entitled to

Fig. 287.

Tongue of common Fly :—a, lobes of ligula; }, portion enclosing the lancets formed by the
metamorphosis of the maxilla; ¢, maxillary palpi :—a, portion of one of the inetamorphosed trachese
enlarged.

that designation, the real tongue being a soft and projecting
organ that forms the floor of the mouth, and being only found
as a distinct part in a comparatively small number of insects, as

TRUNK OF BEE. 567

the Cricket. The ligula is extremely developed in the Fly kind,
in which it forms the chief part of what is commonly called the
“proboscis” (Fig. 287); and it also forms the “tongue” of the
Bee and its allies (Fig. 288). In the Diptera or two-winged flies
generally, the labrum, maxille,
mandibles, and the internal
tongue (where it exists) are
converted into delicate lancet-
shaped organs termed sete,
which, when closed together,
are received into a hollow on
the upper side of the labium
(Fig. 287, 6), but which are
capable of being used to make
punctures in the skin of ani-
mals or the epidermis of plants,
whence the juices may be drawn
forth by the proboscis. Fre-
quently, however, two or more
of these organs may be want-
ing, so that their number is re-
duced from six to four, three,
or two. In the Hymenoptera
(bee and wasp tribe), however, a
the Inbrum and the mandibles ,,%P# of mou fx main oy
(Fig. 288, b), much resemble d, labial alate e, ligula, or prolonged labium,
those of mandibulate insects, ae aan Sak at A ale aa
and are used for correspondin surface of the ligula, more highly magnified.
purposes; the maxillee (c) are greatly elongated, and form, when
closed, a tubular sheath for the ligula or “tongue,” through
which the honey is drawn up; the labial palpi (d) also are greatly
developed, and fold together like the maxille, so as to form an
inner sheath for the “tongue ;” while the “ligula” itself (e) is a
long tapering muscular organ, marked by an immense number
of short annular divisions, and densely covered over its whole
length with-long hairs (B). It is not tubular, as some have stated,
but is solid; when actively employed in taking food, it is ex-
tended to a great distance beyond the other parts of the mouth ;
but when at rest, it is closely packed up and concealed between
the maxille. “The manner,” says Mr. Newport, “in which the
honey is obtained when the organ is plunged into it at the bot-
tom of a flower, is by ‘lapping,’ or a constant succession of short
and quick extensions and contractions of the organ, which occa-
sion the fluid to-accumulate upon it and to ascend along its upper
surface, until it reaches the orifice of the tube formed by the
approximation of the maxille above, and of the labial palpi and
this part of the ligula below.”

387. By the plan of conformation just described, we are led to
that which prevails among the Lepidoptera or butterfly tribe,

568 INSECTS AND ARACHNIDA.

and which, being pre-eminently adapted for suction, is termed
the haustellate mouth. In these insects, the labrum and mandi-
bles are reduced to three minute triangular plates; whilst the
maxille are immensely elongated, and are united together along
the median line, to form the haustellium or proboscis, which con-
tains a tube formed by the junction of the two grooves that are
channelled out along their mutually applied surfaces, and which
serves to pump up the juices of deep cup-shaped flowers, into
which the size of their wings prevents these insects from enter-
ing. The length of this haustellium varies greatly ; thus in such
Lepidoptera as take no food in their perfect state, it is a very in-
significant organ; in some of the white Hawk-moths, which
hover over blossoms without alighting, it is nearly two inches in
length; and in most Butterflies and Moths it is about as long as
the body itself. This haustellium, which, when not in use, is
coiled up in a spiral beneath the mouth, is an extremely beautiful
microscopic object, owing to the peculiar banded arrangement it
exhibits (Fig. 289), which is probably due to the disposition of
its muscles. In many
instances, the two halves
may beseen to be locked
together by a set ot
hooked teeth, which are
inserted into little de-
pressions between the
teeth of the opposite
side. Each half, more-
over, may be ascertained
to contain a trachea or
air-tube (§ 391); and it
is probable, from the ob-
servations of Mr. New-
port,’ that the sucking
up of the juices of a
flower through the haus-
tellium (which is accomplished with great rapidity) is effected by
the agency of the respiratory apparatus. The proboscis of many
Butterflies is furnished, for some distance from its extremity,
with a double row of small projecting barrel-shaped bodies (shown
in Fig. 289), which are surmised by Mr. Newport to be organs
of taste. Numerous other modifications of the structure of the
mouth, existing in the different tribes of Insects, are well worthy
of the careful study of the Microscopist; but as detailed descrip-
tions of most of these will be found in every systematic treatise
on Entomology, the foregoing general account of the principal
types must sufiice.

388. Parts of the Body.—The conformation of the several
divisions of the Alimentary Canal presents such a multitude of

1 “Cyclopedia of Anatomy and Physiology,” vol. ii, p. 902.

Fra. 289.

proboscis) of Vanessa.

CIRCULATION OF BLOOD. 569

diversities, not only in different tribes of Insects, but in different
states of the same individual, that it would be utterly vain to
attempt here to give even a general idea of it; more especially
as it is a subject of far less interest to the ordinary Microscopist,
than it is to the professed Anatomist. Hence we shall only stop
to mention, that the muscular gizzard in which the esophagus
very commonly terminates, is often lined by several rows of
strong horny teeth for the reduction of the food, which furnish
very beautiful microscopic objects. These are particularly de-
veloped among the Grasshoppers, Crickets, and Locusts, the
nature of whose food causes them to require powerful instru-
ments for its reduction.

389. The Circulation of Blood may be distinctly watched in
many of the more transparent Larve, and may sometimes be ob-
served in the perfect Insect. It is kept up, not by an ordinary
heart, but by a “dorsal vessel,” which really consists of a suc-
cession of muscular hearts or contractile cavities, one for each
segment, opening one into another from behind forwards, so as
to form a continuous trunk, divided by valvular partitions. In
many larve, however, these partitions are very indistinct, and
the walls of the “ dorsal vessel” (so named from the position it
always occupies along the middle of the back) are so thin and
transparent that it can with difficulty be made out, a limitation
of the light by the diaphragm being often necessary. The blood
which moves through this trunk, and which is distributed by it
to the body, is a transparent and nearly colorless fluid, carrying |
with it a number of “oat-shaped”’ corpuscles, by the motion of
which its flow can be followed. The current enters the dorsal
vessel at its posterior extremity, and is propelled by the ‘con-
tractions of the successive chambers towards the head, being
prevented from moving in the opposite direction by the valves
between the chambers, which only open forwards. Arrived at
the anterior extremity of the dorsal vessel, the blood is distri-
buted into three principal channels; a central one, namely,
passing to the head, and a lateral one to eitherside, descending
so as to approach the lower surface of the body. It is from the
two lateral currents that the secondary streams diverge, which
pass into the legs and wings, and then return back to the main
stream; and it is from these also, that, in the larva of the Ephe-
mera marginata (day-fly), the extreme transparency of which
renders it one of the best of all subjects for the observation of
Insect circulation, the smaller currents diverge into the gill-like
appendages with which the body is furnished (§ 393). The
blood-currents seem rather to pass through channels excavated
among the tissues, than through vessels with distinct walls; but
it is not improbable that in the perfect Insect the case may be
different. In many aquatic larve, especially those of the Cul
cide (gnat tribe), the body is almost entirely occupied by the
visceral cavity; and the blood may be seen to move backwards

570 INSECTS AND ARACHNIDA.

in the space that surrounds the alimentary canal, which here
serves the purpose of the channels usually excavated through
the solid tissues, and which freely communicates at each end
with the dorsal vessel. This condition strongly resembles that
found in many Annelida. In some larve, whose development
is yet less advanced, even the dorsal vessel appears to be want-
ing, although the fluid of the visceral cavity (in which corpuscles
abound) is in a state of continual oscillatory movement.

390. The Circulation may be easily seen in the wings of many
insects in their Pupa state, especially in those of the Neurop-
terous order (such as dragon-flies and day-flies) which pass this
part of their lives in water, in a condition of activity; the pupa
of Agrion puella, one of the smaller dragon-flies, is a particularly
favorable subject for such observations. Each of the “nerves”
of the wings contains a “trachea” or air-tube (§ 891), which
branches off from the tracheal system of the body; and it is ina
space around the trachea that the blood may be seen to move,
when the hard framework of the nerve itself is not too opaque.
The same may be seen, however, in the wings of the pupe of Bees,
Butterflies, &e., which remain shut up motionless in their cases;
for this condition of apparent torpor is one of great activity of
their nutritive system, those organs, especially, which are pecu-
liar to the perfect insect, being then in a state of rapid growth,
and having a vigorous circulation of blood through them. In
certain Insects of nearly every order, a movement of fluid has
been seen in the wings for some little time after their last meta-
morphosis; but this movement soon ceases, and the wings dry up.
The common Fly is as good a subject for this observation, as can
be easily found; it must be caught within a few hours or days
of its first appearance; and the circulation may be most con-
veniently brought into view, by enclosing it (without water) in
the animalcule cage, and pressing down the cover sufficiently to
keep the body at rest, without doing it any injury.

391. The Respiratory Apparatus of Iusects attords a very in-
teresting series of microscopic objects; for, with great uniformity
in its general plan, there is almost infinite variety in its details.
The aeration of the blood in this class is provided for, not by the
transmission of the fluid to any special organ representing the
lung of a Vertebrated animal (§ 488) or the gill of a Mollusk
(§ 353), but by the introduction of air into every part of the body,
through a system of minutely distributed trachee or air-tubes,
which penetrate even the smallest and most delicate organs.
Thus, as we have seen, they pass into the haustellium or “ pro-
boscis” of the Butterfly (§ 386), and they are minutely distributed
in the elongated labiwm or “tongue” of the fly (Fig. 287). Their
general distribution is shown in Fig. 290; where we see two
long trunks (f) passing from one end of the body to the other,
and connected with each other by a transverse canal in every
segment; these trunks communicate, on the one hand, by

DISTRIBUTION OF TRACHEA, 571

short wide passages, with the “stigmata,” “spiracles,” or breath-
ing-pores (g), through
which the air enters and
is discharged; whilst
they give off branches to
the different segments,
which divide again and
again into ramifications
of extreme minuteness.
They usually communi-
cate also with a pair of air-
sacs (h) which are situated -
in the thorax; but the
size of these (which are
only found in the perfect
insect, no trace of them
existing in the larvee)
varies greatly in different
tribes, being usually
greatest in those insects
which (like the bee) can
sustain the longest and
most powerful flight, and
least in such as habitually
live upon the ground or
upon the surface of the
water. The structure of
the air-tubes reminds us
of that of the “ spiral ves-
sels” of Plants, which Tracheal system of Nepa (Water-scorpion):—a,
Mee ener Bert at fleas‘ ancond pair of wing; ton pte
nie 6 Dame tee st ened uailical age: g, one of the einer 9 Scant
the membrane that forms their
outer wall, an elastic fibre winds
round and round, so as to form
a spiral, closely resembling in
its position and functions the
spiral wire-spring of flexible
gas-pipes; within this again,
however, there is another mem-
branous wall to the air-tubes,
so that the spire winds between
their inner and outer coats. The
tongue of the Fly presents a
curious modification of this
structure, the purpose of which
is not apparent; for instead of
its trachee being kept pervious

Fia. 290.

Fig. 291.

Portion of a large Trachea of Dytiscus, with

after the usual fashion, by the some ofits principal branches.

572 INSECTS AND ARACHNIDA.

winding of a continuous spiral fibre through their interior, the
fibre is broken into rings, and these rings do not surround the
whole tube, but are terminated by a set of arches that pass from
one to another (Fig. 287, a). When a portion of one of the
great trunks with some of the principal branches of the tracheal
system has been dissected out, and so pressed in mounting that
the sides of the tubes are flattened against each other (as has
happened in the specimen represented in Fig. 291), the spire
forms two layers which are brought into close apposition; and a
. very beautiful appearance, resembling that of “watered silk,” is
produced by the crossing of the two sets of fibres, of which one
overlies the other. That this appearance, however, is altogether
an optical illusion, may be easily demonstrated by carefully
following the course of any one of the fibres, which will be
found to be perfectly regular.

392. The “stigmata” or “spiracles” through which the air
enters the tracheal system, are generally visible on the exterior
of the body of the Insect (especially on the abdominal segments)
as a series of pores along each margin of the under surface. In
most larvee, nearly every segment is provided with a pair; but
in the perfect insect, several of them remain closed, especially in
the thoracic region, so that their number is often considerably
reduced. The structure of the spiracles varies greatly in regard
to complexity in different Insects; and even where the general
plan is the same, the details of conformation are peculiar, so
that perhaps in scarcely any two species are they alike. Gene-
rally speaking, they are furnished with some kind of sieve at
their entrance, by which particles of dust, soot, &c., which would
otherwise enter the air-passages, are filtered out; and ‘this sieve
may be formed by the interlacement of the branches of minute
arborescent growths from the borders of the spiracle, as in the
common Fly (Fig. 292), or in the Dytiseus; or it may be a mem-
brane perforated with minute holes, and supported upon a frame-

Fia. 292, Fig, 293.

ou) SY Ri 4h wo

bY PONS ARENA \
WSAWel y
DAW) vo

i) ue

Spiracle of common Fly. Spiracle of Larva of Cockchafer.

work of bars that is prolonged in like manner from the thickened
margin of the aperture (Fig. 293), as in the larva of the Melo-

SPIRACLES. E 573

lontha (cockchafer). Not unfrequently, the centre of the aperture
is occupied by an impervious disk, from which radii proceed
to its margin, as is well seen in the spiracle of Zipula (crane-fly).
In those aquatic larvee which breathe air, we often find one of
the spiracles of the last segment of the abdomen prolonged into
a tube, the mouth of which remains at the surface, while the
body is immersed; the larvee of the Gnat tribe may frequently be
observed in this position.

393. There are many aquatic Larvee, however, which have an
entirely different provision for respiration ; being furnished with
external leaf-like or brush-like appendages, into which the trachez
are prolonged, so that, by absorbing air from the water that
bathes them, they may convey this into the interior of the body.
We cannot have a better example of this than is afforded by the
larva of the common Ephemera (day-fly), the body of which is
furnished with a set of branchial appendages resembling the “ fin-
feet”’ of Branchiopods (§ 368), whilst the three-pronged tail also
is fringed with clusters of delicate hairs which appear to minister
to the same function. In the larva of the Libdellula (dragon-fly),
the extension of the surface for aquatic respiration takes place
within the termination of the intestine; the lining membrane of
which is folded into an immense number of plaits, each contain-
ing a minutely ramified system of trachee; the water, slowly
drawn in through the anus for bathing this surface, is ejected
with such violence that the body is impelled in the opposite
direction ; and the air taken up by its trachee is carried, through
the system of air-tubes of which they form a part, into the
remotest organs. This apparatus is a peculiarly interesting
object for the Microscope, on account of the extraordinary co-
piousness of the distribution of the trachee in the intestinal
folds. :

394. The main trunks of the Tracheal system, with their prin-
cipal ramifications, may generally be got out with little difficulty,
by laying open the body of an insect or larva, under water, in a
dissecting-trough (§ 104), and removing the whole visceral mass,
taking care to leave as many as possible of the branches which
will be seen proceeding to this from the two great longitudinal
tracheee, to whose position these branches will serve as a guide.
Mr. Quekett recommends the following as the most simple
method of obtaining a perfect system of tracheal tubes from a
larva :—a small opening having been made in its body, this is to
be placed in strong acetic acid, which will soften or decompose
all the viscera; and the trachese may then be well washed with
the syringe, and removed from the body with the greatest facility,
by cutting away the connections of the main tubes with the
spiracles by means of fine-pointed scissors. In order to mount
them, they should be floated upon the slide, on which they should
then be laid out in the position best adapted for displaying them.
If they are to be mounted in Canada balsam, they should be

574 INSECTS AND ARACHNIDA.

allowed to dry upon the slide, and should then be treated in the
usual way; but their natural appearance is best preserved by
mounting them in fluid (weak spirit or Goadby’s solution), using
a shallow cell to prevent pressure. The finer ramifications of the
tracheal system may generally be seen particularly well in the
membranous wall of the stomach or intestine; and this, having
been laid out and dried upon the glass, may be mounted in
balsam so as to keep the trachez full of air (whereby they are
much better displayed), if care be taken to use balsam that has
been previously thickened, to drop this on the object without
liquefying it more than is absolutely necessary, and to heat the
slide and the cover (the heat may be advantageously applied
directly to the cover, after it has been put on, by turning over
the slide so that its upper face shall look downwards) only to
such a degree as to allow the balsam to spread and the cover to
be pressed down. The spiracles are easily dissected out by means
of a pointed knife or a pair of fine scissors; they should be
mounted in fluid, when their texture is soft; and in balsam,
when the integument is hard and horny.

395. Wings.—These organs are essentially composed of an
extension of the external membranous layer of the integument,
over a framework formed by prolongations of the inner horny
layer; within which prolongations, tracheze are nearly always to
be found, whilst they also contain channels through which blood
circulates during the growth of the wing and for a short time
after its completion. This is the simple structure presented to
us in the wings of Meuroptera (dragon-flies, &c.), Hymenoptera
(bees and wasps), Diptera (two-winged flies), and also of many
Homoptera (cicadee and aphides); and the principal interest of
these wings as microscopic objects, lies in the distribution of
their “veins’’ or “nerves” (for by both names are the ramifica-
tions of their skeleton known), and in certain points of acces-
sory structure. The venation of the wings is most beautiful in
the smaller Neuroptera; since it is the distinguishing feature of
this order, that the veins, after subdividing, reunite again, so as
to form a close network; whilst in the Hymenoptera and Dip-
tera such reunions are rare, especially towards the margin of
the wings, and the areole are much larger. Although the mem-
brane of which these wings are composed, appears perfectly
homogeneous when viewed by transmitted light, even with a
high magnifying power, yet, when viewed by light reflected
obliquely from their surfaces, an appearance of cellular areola-
tion is often discernible; this is well seen in the common Fly, in
which each of these areole has a hair in its centre. In order to
make this observation, as well as to bring out the very beautiful
iridescent hues which the wings of many minute insects (as the
Aphides) exhibit when thus viewed, it is convenient to hold the
wing in the stage-forceps, for the sake of giving it every variety
of inclination; and when that position has been found, which

WINGS AND ELYTRA OF INSECTS. 575

best displays its most interesting features, it should be set up as
nearly as possible in the same. For this purpose it should be
mounted on an opaque slide; but instead of being laid down
upon its surface, the wing should be raised a little above it, its
“stalk” being held in the proper position by a little cone of soft
wax, in the apex of which it may be imbedded. The wings of .
most Hymenoptera are remarkable for the peculiar apparatus by
which those of the same side are connected together, so as to
constitute in flight but one large wing ; this consists of a row ot
curved hooks on the anterior margin of the posterior wing,
which lay hold of the thickened and doubled-down posterior
edge of the anterior wing. These hooks are sufficiently appa-
rent in the wings of the common Bee, when examined with even
alow magnifying power; but they are seen better in the Wasp,
and better still in the Hornet. The peculiar scaly covering of the
wings of the Lepidoptera has already been noticed (§ 881); but
it may here be added that the entire wings of many of the
smaller and commoner insects of this order, such as the Tineide
or “ clothes’ moths,” form very beautiful opaque objects for low
powers; the most beautiful of all being the divided wings of the
Fissipennes or “plumed moths,” especially those of the genus
Pterophorus.

396. There are many Insects, however, in which the wings are
more or less consolidated by the interposition of a layer of horny
substance between the two layers of membrane. This plan of
structure is most fully carried out in the Coleoptera (beetles), in
which the anterior wings are so much thickened and are so little
extended, that they are useless in flight, and serve merely as
cases or covers for the posterior, which lie folded up beneath
them when not in use; hence these are distinguished as elytra.
These elytra, when the insect is at rest, meet along the median
line of the back, and cover nearly the whole upper surface of the
body; and it is upon them that the brilliant hues, by which the
integument of many of these insects is distinguished, are most
strikingly displayed. In the anterior wings of the Forficulide or
earwig tribe (which form the connecting link between this order
and the Orthoptera), the cellular structure may often be readily
distinguished when they are viewed by transmitted light, espe-
cially after having been mounted in Canada balsam. The ante-
rior wings of the Orthoptera (grasshoppers, crickets, &c.) although
not by any means so solidified as those of Coleoptera, contain a
great deal of horny matter; they are usually rendered sufficiently
transparent, however, by Canada balsam, to be viewed with
transmitted light; and many of them are so colored as to be very
showy objects (as are also the posterior fan-like wings) for the
solar or gas-microscope, although their large size, and the ab-
sence of any minute structure, prevent them from affording much
interest to the ordinary Microscopist. We must not omit to
mention, however, the curious sound-producing apparatus which

576 INSECTS AND ARACHNIDA.

is possessed by most insects of this order, and especially by the
common House-Cricket; this consists of the “tympanum” or
drum, which is a space on each of the upper wings, scarcely
crossed by veins, but bounded externally by a large dark vein
provided with three or four longitudinal ridges, and of the “file”
or “bow,” which is a transverse horny ridge in front of the tym-
panum, furnished with numerous teeth; and it is believed that
the sound is produced by the rubbing of the two bows across
each other, while its intensity is increased by the sounding-board
action of the tympanum. The wings of the Fulgoride (lantern-
flies) have much the same texture with those of the Orthoptera,
and possess about the same value as microscopic objects; differ-
ing considerably from the purely membranous wings of the Ci-
cadze and Aphides, which are associated with them in the order
Homoptera. In the order Hemiptera, to which belong various
kinds of land and water insects that have a suctorial mouth re-
sembling that of the common Bug, the wings of the anterior pair
are usually of parchmenty consistence, though membranous near
their tips, and are often so richly colored as to become very beau-
tiful objects, when mounted in balsam and viewed by transmitted
light; this is the case especially with the terrestrial vegetable-
feeding kinds, such as the Pentatoma and its allies, some of the
tropical forms of which rival the most brilliant of the Beetles.
The British species are by no means so interesting; and the
aquatic kinds, which, next to the bed-bugs, are the most com-
mon, always have a dull brown or almost black hue; even among
these last, however,—of which the Wotonecta (water-boatman) and
the Nepa (water-scorpion) are well-known forms,—the wings are
beautifully variegated by differences in the depth of that hue.
397. Feet.—Although the feet of Insects are formed pretty
much on one general plan, yet that plan is subject to considerable
modifications, in accordance with the habits of life of different
species. The entire limb usually consists of five divisions, namely,
the cora or hip, the trochanter, the femur or thigh, the tbia or
shank, and the tarsus or foot; and this last portion is made up
of several successive joints. The typical number of these joints
seems to be five; but that number is subject to reduction; and
the vast order Coleoptera is subdivided into primary groups, ac-
cording as the tarsus consists of five, four, or three segments.
The last joint of the tarsus is usually furnished with a pair of
strong hooks or claws (Figs. 294, 295); and these are often ser-
rated (that is, furnished with saw-like teeth), especially near the
base. The under surface of the other joints is frequently beset
with tufts of Hairs, which are arranged in various modes, some-
times forming a complete “sole ;” this is especially the case in
the family Cureulionide ; so that a pair of the feet of the “ dia-
mond-beetle,”’ mounted so that one shows the upper surface made
resplendent by its jewel-like scales, and the other the hairy
cushion beneath, is a very interesting object. In many Insects,

FEET OF INSECTS. 517

especially of the Fly kind, the foot is furnished. with a pair of
membranous expansions, termed pulvilli (Fig. 294); and these
are beset with numerous hairs, :

each of which has a minute Fig. 294.

disk at its extremity. This
structure is evidently connected
with the power which these in-
sects possess, of walking over
smooth surfaces in opposition
to the force of gravity; yet
there is still considerable un-
certainty as to the precise mode
in which it ministers to this
faculty. Some believe that the
“pulvilli” act as suckers, the
insect being held up by the
pressure of the air against their
upper surface, when a vacuum
is formed beneath; whilst Foot of Fly.

others maintain that the adhe-

sion is the result of the secretion of a viscid liquid from the
under side of the foot. The careful observations of Mr. Hep-
worth have led’ him to a conclusion which seems in harmony
with all the facts of the case; namely, that the minute disks at

Fie. 295,

a, Foot of Dytiscus, showing its apparatus of suckers; a, 6, large suckers; ¢ ordinary suckers :—
B, one of the ordinary suckers more highly magnified.

the extremity of.the individual hairs act as suckers, and that
each of them secretes a liquid, which, though not viscid, serves
to make its adhesion perfect. And this view of the case derives

1 See Mr. Hepworth’s communications to the “Quart. Journ. of Microsc. Science,”

vol, ii, p. 158, and vol. iii, p. 312,
37

578 INSECTS AND ARACHNIDA.

confirmation, from the presence of a similar apparatus, on a far
larger scale, on the foot of the Dytiscus (Fig. 295, a). The first
joints of the tarsus of this insect are widely expanded, so as to
form a nearly circular plate; and this is provided with a very
remarkable apparatus of suckers, of which one disk (a) is ex-
tremely large, and is furnished with strong radiating fibres, a
second Ss a smaller one formed on the same plan (a third, of
the like kind, being often present), whilst the greater number
are comparatively small tubular club-shaped bodies, each having
a very delicate membranous sucker at its extremity, as seen on a
larger scale at B. These last seem to resemble the hairs of the
Fly’s foot in every particular but dimension ; and an intermediate
size is presented by the hairs of many beetles, especially Curcu-
lionide. The feet of Caterpillars differ considerably from those
of perfect Insects. Those of the first three segments, which are
afterwards to be replaced by true legs, are furnished with strong
horny claws; but each of those of the other segments, which are
termed “ pro-legs,” is composed of a circular series of compara-
tively slender curved hooklets, by which the caterpillar is enabled
to cling to the minute roughnesses of the surface of the leaves,
&c., on which it feeds. This structure is well seen in the pro-
legs of the common Silk-worm.

398. Stings and Ovipositors.—The Insects of the order Hymen-
optera are all distinguished by the prolongation of the last seg-
ment of the abdomen into a peculiar organ, which, in one division
of the order, is a “sting,” and in the other is an “ ovipositor,”’
—an instrument for the deposition of the eggs, which is usually
also provided with the means of boring a hole for their reception.
The former group consists of the Bees, Wasps, Ants, &c.; the
latter of the Saw-flies, Gall-flies, Ichneumon-flies, &. These
two sets of instruments are not so unlike in structure, as they
are in function. The “sting” is usually formed of a pair of
darts, beset with barbed teeth at their points, and furnished at
their roots with powerful muscles whereby they can be caused
to project from their sheath, which is a horny case formed by the
prolongation of the integument of the last segment, slit into
two halves, which separate to allow the protrusion of the sting;
whilst the peculiar “venom” of the sting is due to the ejection,
by the same muscular action, of a poisonous liquid, from a bag
situated near the root of the sting, which passes down a canal
excavated between the darts, so as to be inserted into the punc-
ture which they make. The stings of the common Bee, Wasp,
and Hornet, may all be made to display this structure without
much difficulty in the dissection. The “ ovipositor” of such in-
sects as deposit their eggs in holes ready made, or in soft
animal or vegetable substances (as is the case with the Ichneu-
monide), is simply a long tube, which is enclosed, like the sting,
in a cleft sheath. In the Gall-flies (Cynipide), the extremity of
the ovipositor has a toothed edge, so as to act as a kind of saw,

STINGS AND OVIPOSITORS OF HYMENOPTERA. 579

whereby harder substances may be penetrated; and thus an
aperture is made in the leaf, stalk, or bud of the plant or tree
infested by the particular species, in which the egg is deposited,
together with a drop of fluid that has a peculiarly irritating effect
upon the vegetable tissues, occasioning the production of the
“ galls,” which are new growths that serve not only to protect
the larvee, but also to afford them nutriment. The Oak is in-
fested by several species of thesé insects, which deposit their
eggs in different parts of its fabric; and some of the small
“galls” which are often found upon the surface of oak leaves,
are extremely beautiful objects for the lower powers of the
Microscope. It is inthe Tenthredinide, or Saw-flies, and in their
allies the Stricide, that the ovipositor is furnished with the most
powerful apparatus for penetration ; and some of these insects can
bore by its means into hard timber. Their ‘saws’ are not un-
like the “stings” of Bees, &c., but are broader, are toothed for
a greater length, and are made to slide along a firm piece that
supports each blade, like the “back” of a carpenter’s “ tenon-
saw ;” they are worked alternately (one being protruded while
the other is drawn back) with great rapidity ; and when the per-
foration has been made, the two blades are separated enough to
allow the passage of the eggs between them. Many other In-
sects, especially of the order Diptera, have very prolonged ‘ovi-
positors, by means of which they can insert their eggs into the
integuments.of animals, or into other situations in which the
larvee will obtain appropriate nutriment; a remarkable example
of this is furnished by the Gad-fly ( Zabanus), whose ovipositor is
composed of several joints, capable of being drawn together or
extended like those of a telescope, and is terminated by boring
instruments; and the egg being conveyed by its means, not
only into but through the integument of the Ox, so as to be im-
bedded in the tissue beneath, a peculiar kind of inflammation is
set up there, which (as in the analogous case of the -gall-fly)
forms a nidus appropriate both to the protection and to the nutri-
tion of the larva. Other Insects which deposit their eggs in the
ground, such as the Locusts, have their ovipositors so shaped. as
to answer for digging holes for their reception. The preparations
which serve to display the foregoing parts, are best seen when
mounted in balsam; save in the case of the muscles and poison-
apparatus of the sting, which are better preserved in weak spirit
or Goadby’s solution.

399. The sexual organs of Insects furnish numerous objects of
extreme interest to the Anatomist and Physiologist; but as an
account, of them would be unsuitable to the present work, a re-
ference to a copious source of information respecting one of their
most curious features, and to a list of the species that afford good
illustrations, must here suffice.’ The Eggs of many Insects are

' See the Memoirs of M. Lacaze-Duthiers “Sur l'armure génitale des Insectes,” in
“ Ann. des Sci. Nat.” 3igme Sér. tom. xii, xiv, xvii, xviii, xix; and M. Ch. Robin's

580 INSECTS AND ARACHNIDA.

objects of great beauty, on account of the regularity of their
form, and the symmetry of the markings on their surface (Fig.
296). The most interesting belong for the most part to the
Lepidopterous order; and there are few among these that are not
worth examination, some of the commonest (such as those of the

Fia. 296.

Eggs of Insects magnified :—a, Pontia napi; B, Vanessa urtice ; c, Hipparchia tithous ;
v, Argynnis Lathonia.

Cabbage-butterfly, which are found covering large patches of the
leaves of that plant) being as remarkable as any. Those of the
puss-moth (Cerura vinula), the privet hawk-moth (Sphinx ligustrt),
the small tortoise-shell butterfly (Vanessa urtice), the meadow-
brown butterfly (Htpparchia janira), the brimstone-moth (Rumia
erategata), and the silk-worm (Bombyx mort), may be particularly
specified; and from other orders, those of the cockroach (Blatta
orientalis), field cricket (Acheta campestris), water scorpion (Nepa
ranatra), bug (Cimex lectulartus), cow-dung fly (Scatophaga ster-
coraria), and blow-fly (Musca vomitoria). In order to preserve
these eggs, they must be mounted in fluid in a cell; since they
will otherwise dry up and become misshapen. The remarkable
mode of reproduction that exists among the Aphides must not
pass unnoticed here, from its curious connection with the non-
sexual reproduction of Hntomostraca (§ 3869) and Rotzfera (§ 279),
as also of Hydra (§ 801) and Zoophytes generally, all of which
fall specially, most of them exclusively, under the observation of
the Microscopist. The wingless Aphides which may be seen in
the spring and early summer, may be considered as larvee or
pupee (the earlier states of this insect not being distinguishable
from its perfect form, except by their want of wings); and these
larvee, which, though commonly designated as females, are really
of no sex, give origin to a brood of similar wingless Aphides,
which come into the world alive, and which, before long, go
through a like process of multiplication. As many as from seven
to ten successive broods may thus be produced in the course of
a single season; so that from a single Aphis, it has been caleu-
lated that no fewer than ten thousand million millions may be
evolved within that period. In the latter part of the year, how-
ever, some of these larval Aphides attain their full development
into winged males and females, by which the true generative
process is performed, whose products are eggs, which, when
“ Mémoire sur les Objets qui peuvent étre conservés en Préparations Microscopiques”

(Paris, 1856), which is peculiarly full in the enumeration ot the objects of interest
afforded by the class of Insects,

PARASITIC ACARIDA. 581

hatched in the succeeding spring, give origin to a new brood of
larvee that repeat the curious life-history of their predecessors.’
The non-sexual multiplication of the larve is obviously a pro-
cess of gemmation, analogous to the multiplication of cells by
subdivision ; whilst the true Generative process, analogous to
the conjugation of cells, is only performed when perfect Aphides
of distinct sexes have been evolved.

400. Arachnida.—The general remarks which have been made
in regard to Insects, are equally applicablé to this class; which
includes, along with the Spiders and Scorpions, the tribe of
Acarida, which consists of the Mites and Ticks. Many of these
last are parasitic, and are popularly associated with the wingless
parasitic Insects, to which they bear a strong general resem-
blance, save in having eight legs instead of six. The true
“mites” (Acarine) generally have the legs adapted for walking,
and some of them are of active habits. The common cheese-
mite, as seen by the naked eye, is familiar to every one; yet few
who have not seen it under a microscope, have any idea of its
real conformation and movements; and a cluster of them, cut
out of the cheese they infest, and placed under a magnifying
power sufficiently low to enable a large number to be seen at
once, is one of the most amusing objects that can be shown to

_the young. There are many other species, which closely resem-
ble the cheese-mite in structure and habits, but which feed upon
different substances; and some of these are extremely destruc-
tive. To this group belongs a small species, the Sarcoptes scabiet,
whose presence appears to be the occasion of one of the most
disgusting diseases of the skin—the itch,—and which is hence
commonly termed the “itch insect.” It is not found in the
pustule itself, but in a burrow which passes off from one side of
it, and which is marked by a red line on the surface; and if this
burrow be carefully examined, the creature will very commonly,
but not always, be met with. It is scarcely visible to the naked
eye; but when examined under the microscope, it is found, to
have an oval body, a mouth of conical form, and eight feet, of
which the four anterior are terminated by small suckers, whilst
the four posterior end in very prolonged bristles. The male is
only about half the size of the female. The Riciniw or “ticks”
are usually destitute of eyes, but have the mouth provided with
lancets, that enable them to penetrate more readily the skins of
animals whose blood they suck. They are usually of a flattened,
round, or oval form; but they often acquire a very large size by
suction, and become distended like a blown bladder. Different
species are parasitic upon different animals; and they bury their
suckers (which are often furnished with minute recurved hooks)
so firmly in the skins of these, that they can hardly be detached
without pulling away the skin with them. It is probably the

! For a careful examination and philosophical appreciation of the real nature of this

process, see Dr. Waldo J. Burnett's Memoir in the “Transactions of the American
Academy of Arts and Sciences,” 1853.

582 INSECTS AND ARACHNIDA.

young of a species of this group, which is commonly known as
the “harvest bug,’ and which is usually designated as the
Acarus autumnalis; this is very common in the autumn upon
grass or other herbage, and insinuates itself into the skin at the
roots of the hair, producing a painful irritation; like other
Acarida, for some time after their emersion from the egg, it
possesses only six legs (the other pair being only acquired after
the first moult), so that its resemblance to parasitic insects
becomes still stronger. It is probable that to this group also
belongs the Demodex folliculorum, a creature which is very com-
monly found parasitic in the sebaceous follicles of the human
skin, especially in those of the nose. In order to obtain it,
pressure should be made upon any one of these that appears
enlarged and whitish, with a terminal black spot; the matter
forced out will consist principally of the accumulated sebaceous
secretion, having the parasites with their eggs and young min-
gled with it. These are to be separated by the addition of oil,
which will probably soften the sebaceous matter sufficiently to
set free the animals, which may be then removed with a pointed
brush; but if this mode should not be effectual, the fatty matter
may be dissolved away by digestion in a mixture of alcohol and
ether. The pustules in the skin of a dog affected with the
“mange” have been found by Mr. Topping to contain a Demo-
dex, which seems only to differ from that of the human sebaceous *
follicles in its somewhat smaller size; and M. Gruby is said to
have given to a dog a disease resembling the mange, if not
identical with it, by inoculating it with the human parasite.
The <Acarida are best preserved as microscopic objects, by
mounting in glycerine.

401. The number of objects of general interest, furnished to
the Microscopist by the Spider tribe, is by no means considera-
ble. Their eyes exhibit a condition intermediate between that
of Insects and Crustaceans, and that of Vertebrata; for they are
single like the ‘“stemmata” of the former, usually number from
six to eight, are sometimes clustered together in one mass, but
are sometimes disposed separately, while they present a decided
approach in internal structure to the type characteristic of the
visual organs of the latter. The structure of the Mouth is
always mandibulate, and is less complicated than that of the
mandibulate insects. The Respiratory apparatus, which, where
developed at all among the Acarida, is tracheary like that of
Insects, is here constructed upon a very different plan; for the
“stigmata,” which are usually four in number on each side,
open into a like number of respiratory sacculi, each of which
contains a series of leaf-like folds of its lining membrane, upon
which the blood is distributed so as to afford a large surface to
the air. In the structure of the limbs, the principal point
worthy of notice is the peculiar appendage with which they
usually terminate; for the strong claws, with a pair of which

SPINNING APPARATUS OF SPIDERS. 583

the last joint of the foot is furnished, have their edges cut into
comb-like teeth (Fig. 297),

which seem to be used by Fig, 297.

the animal as cleansing
instruments. One of the
most curious parts of the
organization of the Spiders
is the: “spinning appara-
tus,’ by means of which
they fabricate their elabo-
rately constructed webs.
This consists of the “spin-
Hein and of the glandu-
ar organs in which the ; eee
fluid ek Tenvelana gts the Foot, with comb-like be the common Spider
thread is elaborated. The

usual number of the spinnerets, which are situated at the poste-
rior extremity of the body, is six; they are little teat-like promi-
nences, beset with hairy appendages; and it is through a certain
set of these appendages, which are tubular and terminate in
fine-drawn points, that the glutinous secretion is forced out in a
multitude of streams of extreme minuteness. These streams.
harden into fibrils, immediately on coming into contact, with
the air; and the fibrils proceeding from all the
apertures ofeach spinneret, coalesce into asingle. Fie. 298.
thread. It is doubtful, however, whether all the 4 68
spinnerets are in action at once, or whether those. )

of different pairs may not have dissimilar functions;
for whilst the radiating threads of a spider's web
are simple (Wig. 298, a), those which lie across
these, forming its concentric circles or rather poly-
gons, are studded at intervals with viscid globules
(8), which appear to give to these threads their
peculiarly adhesive character; and it does not seem @
by any means unlikely, that each kind of thread
should be produced by its own pair of spinnerets.
The total number of spinning tubes varies greatly,
according to the species of the spider, and the sex
and age of the individual; being more than 1000
in some cases, and less than 100 in others. The
size and complexity of the secreting glandule vary

in like manner: thus in the Spiders which are most 9, 4:,ary thread
remarkable for the large dimensions and regular (), and giuti-:
construction. of their webs, they occupy a large — nousthread(s),
portion of the abdominal cavity, and are gomposed 75, “mmo
of slender branching tubes, whose length is in- ;
creased by numerous convolutions; whilst in those which have
only occasional use for their threads, the secreting organs are
either short and simple follicles, or are undivided tubes of mode-
rate length.

CHAPTER XVIII.

VERTEBRATED ANIMALS.

402. We are now arrived at that highest division of the Ani-
mal Kingdom, in which the bodily fabric attains its greatest
development, not only as to completeness, but also as to size;
and it is in most striking contrast with the class we have been
last considering. Since not only the entire bodies of Verte-
brated animals, but, generally speaking, the smallest of their
integral parts, are far too large to be viewed as Microscopic
objects, we can study their structure only by a separate exami-
nation of their component elements; and it seems, therefore, to
be a most appropriate course, to give, under this head, a sketch
of the microscopic characters of those primary tissues, of which
their fabric is made up, and which, although they may be traced
with more or less distinctness in the lower tribes of Animals,
attain their most complete development in this group. Since
the time when Schwann first made public the remarkable results
of his researches (p. 56), it has been very generally believed that
all the Animal tissues are formed, like those of Plants, by a
metamorphosis of Cells; an exception being taken, however, by
some Physiologists, in regard to the simple fibrous tissues (§ 417).
The tendency of many recent investigations, however, has been
to throw further doubt on the generality of this doctrine; since
they appear to indicate that many other tissues than the fibrous
may be formed (like these) by the consolidation of the plasma or
formative fluid, without passing through the intermediate condi-
tion of cells. Hence no attempt will here be made to do more
than describe the most important of those distinctive characters,
which the principal tissues present, when subjected to micro-
scopic examination ; and as it is of no essential consequence what
order is adopted, we may conveniently begin with the structure
of the skeleton,’ which gives support and protection to the softer
parts of the fabric. ,

403. Bone.—The Microscopic characters of osseous tissue may

' This term is used in its most general sense, as including not only the proper vertebral

or internal skeleton, but also the hard parts protecting the exterior of the body, which
forms the dermal skeleton.

STRUCTURE OF BONE. 585

sometimes be seen in very thin natural plates of bone, such as in
that forming the scapula A aesee eee of a Mouse; but they
are displayed more perfectly by artificial sections, the details of
the arrangement being dependent upon the nature of the speci-
men selected, and the direction in which the section is made.
Thus when the shaft of a “long’’ bone of a Bird or Mammal is
cut across in the middle of its length, we find it to consist of a
hollow cylinder of dense bone, surrounding a cavity which is
occupied by an oily marrow;. but if the section be made nearer
its extremity, we find the outside wall gradually becoming thinner,
whilst the interior, instead of forming one large cavity, is divided
into a vast number of small chambers or cancelli, which com-
municate with each other

and with the cavity of the Fig. 299,

shaft, and are filled, like it,
with marrow. In the bones
of Reptiles and Fishes, on
the other hand, this “ cancel-
lated” structure usually ex- .
tends throughout the shaft,
which is not so completely
differentiated into solid bone
and medullary cavity, as it
is in the higher Vertebrata.
In the most developed kinds
of “flat” bones, again, such
as those of the head, we find
the two surfaces to be com-
posed of dense plates of bone,
with a “cancellated” struc-
ture between them ; whilst Minute structure of Bone, as seen in transverse sec-
in the less perfect type pre- tion:—1. an ossicle surrounding an Haversian canal,
sented to us in the lower 3, showing the eae le oe
Vertebrata, the whole thick- tons orine lamelle pavalelwith the external surface
ness is usually more or less

“ cancellated,” that is, burrowed out by medullary cavities.
When we examine, under a low magnifying power, a longitu-
dinal section of a “long’’ bone, or a section of a ‘flat’’ bone
parallel to its surface, we find it traversed by numerous canals,
termed Haversian after their discoverer Havers, which are in
connection with the central cavity, and are filled, like it, with
marrow: in the shafts of long bones, these canals usually run in
the direction of their length, but are connected here and there
by cross branches; whilst in the flat bones, they form an irregu-
lar network. On applying a higher magnifying power to a thin
transverse section of a long bone, we observe that each of the
canals whose orifices present themselves in the field of view (Fig.
299), is the centre of a rod of bony tissue (1), usually more or less
circular in its form, which is arranged around it in concentric

586 VERTEBRATED ANIMALS.

rings, resembling those of an Exogenous Stem. These rings are
marked out and divided by circles of little dark spots; which,
when closely examined (2), are seen to be minute flattened
cavities excavated in the solid substance of the bone, from the
two flattened sides of which pass forth a number of extremely
minute tubules, one set extending inwards, or in the direction of
the centre of the system of rings, and the other outwards, or in
the direction of its cireumference ; and by the inosculation of the
tubules (which are termed canaliculi) of the different rings with
each other, a continuous communication is established between
the central Haversian canal and the outermost part of the bony
rod that surrounds it, which doubtless ministers to the nutrition
ot the texture. Bloodvessels are traceable into the Haversian
canals; but the “canaliculi,” being far too minute to carry
blood-corpuscles, can only convey a nutrient fluid that is sepa-
rated from the blood for the special service of the bone. ~
404, The minute cavities, or
lacune (sometimes, but erro-
neously termed ‘bone-corpus-
cles,’ as if they were solid
bodies), from which the canali-
culi proceed, are highly charac-
teristic of the true osseous struc-
ture; being never deficient in
the minutest parts of the bones
Potent pe al ora a eavity, of the higher Vertebrata, al-
een though those of Fishes are occa-
sionally destitute of them. The dark appearance which they
present is not due to opacity, but is simply an optical effect,
dependent (like the blackness of air-bubbles in liquids) upon the
dispersion of the rays by the highly-refracting substance that
surrounds them (§ 98). The size and form of the lacunee differ
considerably in the several Classes of Vertebrata, and even in
some instances in the Orders; so as to allow of the determination
of the tribe to which a bone belonged, by the microscopic exami-
nation of even a minute fragment of it (§ 453). The following
are the average dimensions of the lacune, in characteristic ex-
amples drawn from the four principal classes, expressed in
fractions of an inch :—

Fig, 300.

Long Diameter, Short Diameter.
Man, . ‘ : ‘ _ 1-1440 to 1-2400 1-4000 to 1-8000
Ostrich, . : : ‘ . 1-1333 to 1-2250 1-5425 to 1-9650
Turtle, . 5 . : 3 1-375 to 1-1150 1-4500 to 1-5840
Conger-eel, : : : 1-550 to 1-1135 1-4500 to 1-8000

The lacune of Birds are thus distinguished from those of Mam-
mals by their somewhat greater length and smaller breadth; but
they differ still more in the remarkable tortuosity of the canali-
culi, which wind backwards and forwards in a very irregular
manner. There is an extraordinary increase in length in the

STRUCTURE OF BONE, 587

lacunee of Reptiles, without a corresponding increase in breadth ;
and this is also seen in some Fishes, thowgh in general the lacunz
of the latter are remarkable for their angularity of form, and the
fewness of their radiations,—as shown in Fig. 301, which repre-
sents the lacune and ca-

naliculi in the bony scale Fra. 301.

of the Lepidosteus (“bony 7

pike” of the North Ame- a Uy
rican lakes and rivers), |<! ba AS
with which the bones of : ‘i ODA
its internal skeleton per- “|; 2/6
fectly agree in structure. f
The dimensions of the re BN
lacune in any bone do -

not bear any relation to en Reenet oe
: : ection of the bony scale of Lepidosteus :—a, showing the
the §1Ze of the animal to regular distribution of the lacunz and of the wonnectine

which it belonged; thus canaliculi; 6, small portion more highly magnified.

there is little or no per-

ceptible difference between their size in the enormous extinct
Iguanodon, and in the smallest Lizard now inhabiting the earth.
But they bear a close relation to the size of the blood-corpuscles
in the several classes; and this relation is particularly obvious
in the “perennibranchiate’” Batrachia, the extraordinary size of
whose blood-corpuscles will be presently noticed (§ 414):—

Long Diameter. Short Diameter.
Proteus, . 7 ‘ x : 1-570 to 1-980 1-885 to 1-1200
Siren, . . ‘ ‘ ‘ 1-290 to 1-480 1-540 to 1-975
‘Menopoma, . r : - 1-450 to 1-700 1-1300 to 1-2100
Lepidosiren, . : i , 1-375 to 1-494 1-980 to 1-2200
Pterodactyle, . . . : 1-445 to 1-1185 11-4000 to 1-5225!

405. In preparing sections of bone, it is important to avoid the
penetration of the Canada balsam into thé interior of the lacune
and canaliculi; since, when these are filled by it, they become
almost invisible. Hence it is preferable not to employ this ce-
ment at all, except, it may be, in the first instance; but to rub
down the section beneath the finger, guarding its surface with a
slice of cork or a slip of gutta percha (§ 111); and to give it such
a polish, that it may be seen to advantage even when mounted
dry. As the polishing, however, occupies much time, the benefit
which is derived from covering the surfaces of the specimen with
Canada balsam may be obtained, without the injury resulting
from the penetration of the balsam into its interior, by adopting
the following method. A quantity of balsam proportioned to the
size of the specimen is to be spread upon a glass slip, and to be

1 See Prof. J. Quekett’s Memoir on this subject, in the “ Transact. of the Microsc. Soc.”
Ser. 1, vol. ii; and bis more ample illustration of it in the “Illustrated Catalogue of the
Histological Collection in the Museum of the Roy. Coll. of Surgeons,” vol. ii.

588 VERTEBRATED ANIMALS.

rendered stiffer by boiling, until it becomes nearly solid when
cold; the same is to be done to the thin glass cover; next, the
specimen being placed on the balsamed surface of the slide, and
being overlaid by the balsamed cover, such a degree of warmth
is to be applied, as will suffice to liquefy the balsam, without
causing it to flow freely; and the glass cover is then to be quickly
pressed down, and the slide to be rapidly cooled, so as to give as
little time as possible for the penetration of the liquefied balsam
into the lacunar system. The same method may be employed in
making sections of Teeth. :

406. Teeth—The intimate structure of the Teeth in the
several classes and orders of Vertebrata presents differences
which are no less remarkable than those of their external form,
arrangement and succession. It will obviously be impossible
here to do more than sketch some of the most important of these
varieties. The principal part of the substance of all teeth is
made up of a solid tissue that has been appropriately termed
Dentine. In the Shark tribe, as in many other Fishes, the
general structure of this “dentine” is extremely analogous to
that of bone; the tooth being traversed by numerous canals,
which are continuous with the Haversian canals of the subjacent
bone, and receive bloodvessels from them (Fig. 302); and each
of these canals being surrounded by a system of tubuli (Fig.

Fia. 302. Fia. 303.

Fig. 302. Perpendicular section of tooth of Zamna, moderately enlarged, showing network of
medullary canals.

Fig. 803. Transverse section of portion of tooth of Pristis, more highly magnified, showing
orifices of medullary canals, with systems of radiating and inoseulating tubuli. |

303), which radiate into the surrounding solid substance. These
tubuli, however, do not enter lacune, nor is there any concentric
annular arrangement around the medullary canals; but each
system of tubuli is continued onwards through its own division

STRUCTURE OF TEETH. 589

of the tooth, the individual tubes sometimes giving off lateral
branches, whilst'in other in-

stances their trunks bifurcate. Fig. 304,

This arrangement is pecu-
liarly well displayed, when
sections of teeth constructed
upon this type are viewed as
opaque objects (Fig. 304). In
the teeth of the higher Ver-
tebrata, however, we usually
find the centre excavated into
a single cavity (Fig. 805), and
the. remainder destitute of
vascular canals; but there are
intermediate cases (as in the
teeth of the great fossil Sloths ;

in which ihe inner portion af picasso cena ho bese ei eal
the dentine is traversed by

prolongations of this cavity, conveying bloodvessels, which do not
pass into the exterior layers. The tubuli of the “non-vascular”’
dentine, which exists by itself in the teeth of nearly all Mammalia,
and which in the Elephant is known as “ivory,” all radiate from
the central cavity, and pass towards the surface of the tooth in a
nearly parallel course. Their diameter at their largest part
averages 1-10,000th of an inch; their smallest branches are im-
measurably fine. It is impossible that even the largest of them
can receive blood, as their diameter is far less than that of the
blood-dises; but it is probable that, like the canaliculi of bone,
they may absorb nutrient matter from the vascular surface upon
which theirinner extremities open. The tubuli in their course
present greater and lesser undulations; the former are few in
number; but the latter are numerous, and as they occur at the
same part of the course of several contiguous tubes, they give
rise to. the appearance of lines concentric with the centre ot
radiation. These secondary curvatures probably indicate, in
dentine, as in the crab’s shell (§ 374) successive stages of calcifi-
cation.

407. In the teeth of Man and most other Mammals, and in
those of many Reptiles and some Fishes, we find two other
substances, one of them harder, and the other softer, than den-
tine; the former is termed Hnamel ; and the latter Cementum or
Orusta Petrosa. The Enamel is composed of long prismatic cells,
closely resembling those of the prismatic shell-substance for-
merly described (§ 336), but on a far more minute scale; the
diameter of the cells not being more, in Man, than 1-5600th
of an inch. The length of the prisms corresponds with the
thickness of the layer of enamel; and the two surfaces of this
layer present the ends of the prisms, the form of which usually
approaches the hexagonal. The course of the enamel-prisms is

590 VERTEBRATED ANIMALS.

more or less wavy; and they are marked by numerous trans-
verse strie, resembling those of the pris-
Fia. 306. matic shell-substance, and probably origi-
nating in the same cause,—the coalescence
of a series of shorter cells, to form the
lengthened prism. In Man, and in Car-
nivorous animals, the enamel covers the
crown of the tooth only, with a simple cap
or superficial layer of tolerably uniform
thickness (Fig. 305, a), which follows the
surface of the dentine in all its inequalities ;
and its component prisms are directed at
right angles to that surface, their inner
extremities resting in slight but regular
depressions on the exterior of the dentine.
In the teeth of many of the Herbivorous
animals, however, the Enamel forms (with
: ; the Cementum) a series of vertical plates,
Molar Tathe 1 aamel;s, Which dip down into the substance of the
cementum or enacts: petrosa ; dentine, and present their edges alternately
&; dentine or ivory; & osse- with it, at the grinding surface of the tooth;
from hypertrophy of cemen- and there is in such teeth no continuous
tum; 5, pulp-cavity; 6 osse- Javer of enamel over the crown. The pur-
ous lacune at outer part of ‘ = .
dentine. pose of this arrangement is evidently to
provide, by the unequal wear of these
three substances,—of which the enamel is the hardest, and the
cementum the softest,—for the constant maintenance of a rough
surface, adapted to triturate the tough vegetable substances on
which these animals feed. The enamel is the least constant of
the dental tissues. It is more frequently absent than present
in the teeth of the class of Fishes; it is wanting in the entire
order of Ophidia (serpents) among existing Reptiles; and it
forms no part of the teeth of the Edentata (sloths, &c.) and
Cetacea (whales) amongst Mammals. The Cementum, or Crusta
Petrosa, has the characters of true bone ; possessing its distinctive’
stellate lacune and radiating canaliculi. Where it exists in
small amount, we do not find it traversed by medullary canals ;
but, like dentine, it is occasionally furnished with them, and
thus resembles bone in every particular. These medullary canals
enter its substance from the exterior of the tooth, and conse-
quently pass towards those which radiate from the central cavity
in the direction of the surface of the dentine, where this pos-
sesses a similar vascularity,—as was remarkably the case in the
teeth of the extinct Megatherium. In the Human tooth, how-
ever, the cementum has no such vascularity; but forms a thin
layer, which envelopes the root of the tooth, commencing near
the termination of the capping of enamel (Fig. 305, 4). In the
teeth of many Herbivorous Mammals, it dips down with the
enamel to form the vertical plates of the interior of the tooth;

SCALES OF FISHES. 591

and in the teeth of the Edentata, as well as of many Reptiles
and Fishes, it forms a thick continuous envelope over the whole
surface, until worn away at the crown.

408. Dermal Skeleton.—The skin of Fishes, of most Reptiles,
and of a few Mammals, is strengthened by plates of a horny,
cartilaginous, bony, or even enamel-like texture, which are some-
times fitted together at their edges, so as to form a continuous box-
like envelope, whilst more commonly they are so arranged as
partially to overlie one another, like the tiles on a roof; and it
is in this latter case that they are usually known as scales. Al-
though we are accustomed to associate in our minds the ‘“ scales”
of Fishes with those of Reptiles, yet they are essentially different
structures; the former -being developed in the substance of the
true skin, with a layer of which, in addition to the epidermis,
they are always covered; and bearing a resemblance to cartilage
and bone in their texture and composition; whilst the latter are
formed upon the surface of the true skin, and are to be con-
sidered as analogous to nails, hoofs, &c., and other “ epidermic
appendages.” In nearly all the existing Fishes, the scales are
flexible, being but little consolidated by calcareous deposit; and
in some species they are so thin and transparent, that, as they
do not project obliquely from the surface of the skin, they can
only be detected by raising the superficial layer of the skin, and
searching beneath it, or by tearing off the entire thickness of
the skin, and looking for'them near its under surface. This is
the case, for example, with the common el, and with the
Viviparous Blenny ; of either of which fish, the skin is a very
interesting object when dried and mounted in Canada balsam,
the scales being seen imbedded in its substance, whilst its outer
surface is studded with pigment-cells. Generally speaking, how-
ever, the posterior extremity of each scale projects obliquely
from the general surface, carrying before it the thin membrane
that encloses it, which is studded with pigment-cells ; and a por-
tion of the skin of almost any Fish, but especially of such as
have scales of the ctenoid kind (that is, furnished at their posterior
extremities with comb-like teeth, Fig. 307), when dried with its
scales in situ, is a very beautiful opaque object for the low
powers of the Microscope (Fig. 306). Care must be taken, how-
ever, that the light.is made to glance upon it in the most ad-
vantageous manner ; since the brilliancy with which it is reflected
from the comb-like projections, entirely depends upon the angle
at which it falls upon them. The only appearance of structure
exhibited by the thin flat scale of the Eel, when examined micro-
scopically, is the presence of a layer of isolated spheroidal trans-
parent bodies, imbedded in a plate of like transparency ; these,
from the researches of Prof. Williamson upon other scales, ap-
pear not to be cells (as they might readily be supposed to be),
but to be concretions of carbonate of lime. When the scale of
the Eel is examined by polarized light, its surface exhibits a

592 VERTEBRATED ANIMALS.

beautiful St. Andrew’s cross; and if a plate of selenite be placed
behind it, and the analyzing prism be made to revolve, a re-
markable play of colors is presented. ;

409. In studying the structure of the more highly-developed
scales, we may take as an illustration that of the Carp ; in which
two very distinct layers can be made out by a vertical section,
with a third but incomplete layer interposed between them.
The outer layer is composed of several
concentric lamine of a structureless trans-
parent substance, like that of cartilage;
the outermost of these lamine is the small-
est, and the size of the plates increases
progressively from without inwards, so

Fie. 307.

Fig. 306.

Portion of Skin of Sole, viewed as an opaque object. Scule of Sole, viewed asa
transparent object.

that their margins appear on the surface asa series of concentrie
lines; and their surfaces are thrown into ridges and furrows,
which commonly have a radiating direction. The inner layer is
composed of numerous lamine of a fibrous structure, the fibres
of each lamina being inclined at various angles to those of the
lamina above and below it. Between these two layers is inter-
posed a stratum of calcareous concretions, resembling those of
the scale of the Eel; these are sometimes globular or spheroidal,
but more commonly “lenticular,” that is, having the form of a
double convex lens. The scales which resemble those of the
Carp in having a form more or less circular, and in being desti-
tute of comb-like prolongations, are called eycloid; and such
are the characters of those of the salmon, herring, roach, &c.
The structure of the “ctenoid” scales (Fig. 307), which we find
in the sole, perch, pike, &c., does not differ essentially from that
of the ‘“‘cycloid,” save as to the projection of the comb-like teeth
from the posterior margin; and it does not appear that the
strongly-marked division which Prof. Agassiz has attempted to
establish between the ‘“‘cycloid” and the “ctenoid” orders of
fishes, on the basis of this difference, is in harmony with their
general organization. Scales of either kind may become con-
solidated to a considerable extent, by the calcification of their
soft substance; but still they never present any approach to the

SCALES OF FISHES. 593

true bony structure, such as is shown in the two orders to be
next adverted to. In the ganoid scales, on the other hand, the
whole substance of the scale is composed of a substance which
is essentially bony in its nature; its intimate structure being
almost always comparable to that of one or other of the varieties
which present themselves in the bones of the Vertebrate skele-
ton; and being very frequently identical with that of the bones
of the same fish, as is the case with the Lepidosteus (Fig. 301),
one of the few existing representatives of this order, which, in
former ages of the Harth’s history, comprehended a large num-
ber of important families. Their name (from yéoc splendor) is
bestowed on account of the smoothness, hardness, and high
polish of the outer surface of the scales; which is due to the
presence of a peculiar layer that has been likened (though erro-
neously) to the enamel of teeth, and is now distinguished as
ganoin. The scales of this order are for the most part angular
in their form; and are arranged in regular rows, the posterior
edges of each slightly overlapping the anterior ones of the next,
so as to form a very complete defensive armor to the body.
The scales of the placoid type, which characterizes the existing
Sharks and Rays, with their fossil analogues, are irregular in
their shape, and very commonly do not come into mutual con-
tact; but are separately imbedded in the skin, projecting from
its surface under various forms. In the Rays, each scale usually
consists of a flattened plate of a rounded shape, with a hard
spine projecting from its centre; in the Sharks (to which tribe
belongs the “ dog-fish” of our own coast) the scales have more
of the shape of teeth. This resemblance is not confined to
external form; for their intimate structure strongly resembles
that of dentine, their dense substance being traversed by tubuli,
which extend from their centre to their circumference in minute
ramifications, without any trace of osseous lacune. These
tooth-like scales are often so small, as to be invisible to the
naked eye; but they are well seen by drying a piece of the skin
to which they are attached, and mounting it in Canada balsam;
and they are most brilliantly shown by the assistance of polar-
ized light. A like structure is found to exist in the spiny rays
of the dorsal fin, which, also, are parts of the dermal skeleton ;
and these rays usually have a central cavity filled with medulla,
from which the tubuli radiate towards the circumference. This
structure is very well seen in thin sections of the fossil spiny
rays, which, with the teeth and scales, are often the sole relics of
the vast multitudes of Sharks that must have swarmed in the
ancient seas, their cartilaginous internal skeletons having entirely
decayed away. In making sections of bony scales, spiny rays,
&c., the method must be followed which has been already detailed
under the head of bone (§ 405).

410. The scales.of Reptiles, the feathers of Birds, and the hairs,

hoofs, nails, claws, and horns (when not bony) of Mammals, are
38

594. VERTEBRATED ANIMALS.

all Epidermie appendages; that is, they are produced upon the
surface, not within the substance, of the true skin, and are allied
in structure to the Epidermis (§ 419); being essentially com-
posed of aggregations of cells, filled with horny matter; and
frequently much altered in form. This structure may generally
be made out in horns, nails, &c., with little difficulty, by treating
thin sections of them with a dilute solution of soda; which after
a short time causes the cells that had been flattened into scales,
to resume their globular form. The most interesting modifica-
tions of this structure are presented to us in Hairs and in Fea-
thers; which forms of clothing are very similar to each other in
their essential structure, and are developed in the same manner,
—namely, by an increased production of epidermie cells at the
bottom of a flask-shaped follicle, which is formed in the substance
of the true skin, and which is supplied with abundance of blood
by a special distribution of vessels to its walls. When a hair is
pulled out “by its root,” its base exhibits a bulbous enlarge-
ment, of which the exterior is tolerably firm, whilst its interior
is occupied by a softer substance, which is known as the “pulp ;”
and it is to the continual augmentation of this pulp in the deeper
part of the follicle, and to its conversion into the peculiar sub-
stance of the hair when it has been pushed upwards to its narrow
neck, that the growth of the hair is due. The same is true of
feathers, the stems of which are but hairs on a larger scale; for
the “quill” is the part contained within the follicle, answering
to the “bulb” of the hair; and whilst the outer part of this is
converted into the peculiarly solid horny substance forming the
“barrel” of the quill, its interior is occupied, during the whole
‘period of the growth of the feather, with the soft pulp, only the
shrivelled remains of which, however, are found within it after
the quill has ceased to grow.

411. Although the Hairs of different Mammals differ greatly
in the appearances they present, we may generally distinguish
in them two elementary parts; namely, a cortical or investing
substance, of a dense horny texture, and a medullary or pith-like
substance, usually of a much softer texture, occupying the inte-
rior. The former can sometimes be distinctly made out to con-
sist of flattened scales arranged in an imbricated manner, as in
some of the hairs of the Sable (Fig. 808); whilst in the samie
hairs, the medullary substance is composed of large spheroidal
cells. In the Musk-deer, on the other hand, the cortical sub-
stance is nearly undistinguishable; and almost the entire hair
seems made up of thin-walled polygonal cells (Fig. 309). The
hair of the Reindeer, though much larger, has a very similar
structure; and its cells, except near the root, are occupied with
air alone, so as to seem black by transmitted light, except when
penetrated by the fluid in which they are mounted. In the hair
of the Mouse, Squirrel, and other small Rodents (Fig. 310, a, 8),
the cortical substance forms a tube, which we see crossed at

STRUCTURE OF HAIRS. 595

intervals by partitions that are sometimes complete, sometimes
only partial; these are the walls of the single or double line of
cells, of which the medullary

substance ismade up. Thehairs — Fi. 308. Fia. 309.

of the Bat tribe are commonly
distinguished by the projections
on their surface, which are affiil
formed by extensions of the ||}, j=
component scales of the cortical |
substance; these are particularly
well seen in the hairs of one of ff
the Indian species, which has a. \\
set of whorls of long narrow
leaflets (so to speak) arranged at
regular intervals on the stem
(c). In the hair of Pecari (Fig.
311), the cortical envelope sends
inwards a set of radial prolon-
gations, the interspaces of which
are occupied by the polygonal
cells of the medullary substance;
and this, on a larger scale, is the
structure of the “quills” of the
Porcupine; the radiating parti-
tions of which, when seen through
the more transparent parts of the
cortical sheath, give to the sur-
face of the latter a fluted appear-

. ; id — «
ance. The hair of the Ornitho- Fig. 808. Hair of Suble, showing large rounded"

rhyncus is a. very curious obj ect; ionising covered by imbricated scales
for whilst the lower part of it re- Fig. 309. Hair of Musk-deer, consisting almost
sembles the fine hair of the mouse &“titely of polygonal cells. i

. . ° Fig. 310. a, Small Hair of Squirrel; 3, Large
or squirrel, this thins away and pair of Squirrel ; c, Hair of Indian Bat.
then dilates again into a very
thick fibre, having a central portion composed of polygonal cells,
enclosed in a flattened sheath of a brown fibrous substance.
The structure of the Human hair is in certain respects peculiar.
When its outer surface is examined, it
is seén to be traversed by irregular lines Fig. 311.
(Fig. 312, a), which are most strongly
marked in foetal hairs; and these are
the indications of the imbricated ar-
rangement of the flattened cells or scales
which form the cortical layer. This
layer, as is shown by transverse sections

Transverse Section of Hair of

(c, D), is a very thin and transparent cy- Peeari,

linder; and it incloses the peculiar

fibrous substance, that constitutes the principal part of the shaft
of the hair. The constituent fibres of this substance, which

>

596 VERTEBRATED ANIMALES.

are marked out by the delicate striz that may be traced in Dn
tudinal sections of the hair (B), may be separated from each vi
by crushing the hair, especially after it has been cans :
some time in sulphuric acid; and each of them, when ee tad y
separated from its fellows, is found to be a long spindle-shape

Fig. 312.

Structure of Human Mair :—a, external surface of the shaft, showing the transverse strie and
jagged boundary caused by the imbrications of the cortical substance; B, longitudinal section of the
shafi, showing the fibrous character of the medullary substance, and the arrangement of the pig-
mentary matter; C, trausverse section, showing the distinction between the transparent envelope,
the cylinder of medullary substance, and the cellular centre; D, another transverse section showing
deficiency of central cellular substance.

cell. In the axis of this fibrous cylinder, there is very com-
monly a band which is formed of spheroidal cells; but this is
usually deficient in the fine hairs scattered over the general sur-
face of the body, and is not always present in those of the head.
The hue of the hair is due, partly to the presence of pigmentary
granules, either collected into patches, or diffused through its
substance; but partly also to the existence of a multitude of
minute air-spaces, which cause it to appear as dark by transmitted
and white by reflected light. The cells of the axis-band, in par-
ticular, are very commonly found to contain air, giving it the
black appearance shown at c. The difference between the black-
ness of pigment and that of air-spaces, may be readily determined
by attending to the characters of the latter as already laid down
(§§ 98, 99); and by watching the effects of the penetration of
oil of turpentine or other liquids, which do not alter the appear-
ance of pigment spots, but obliterate all the markings produced
by air-spaces, these returning again as the hair dries. In mount-
ing hairs as microscopic preparations, they should in the first
instance be cleansed of all their fatty matter by maceration in
ether; and they may then be put up, either in weak spirit or in

' Several writers regard this band of polygonal cells as the “medullary” substance,
and the fibrous structure which forms the principal body of the hair, as the “cortical”
substance; the transparent sheath receiving some separate designation. To the Author,
however, it appears perfectly clear that the transparent horny sheath, with its lines of
imbrication, is the representative of the cortical substance of other hairs; and that its

entire contents, whether polygonal cells or cells elongated into fusiform fibres, must be
considered as equivalent to their medullary substance.

STRUCTURE OF FEATHERS. 597

Canada balsam, as may be thought preferable, the former men-
struum being well adapted to display the characters of the finer
and more transparent hairs, while the latter allows the light to
penetrate more readily through the coarser and more opaque.
Transverse sections of hairs are best made by gluing or gumming
several together, and then putting them into the section-instru-
ment; those of human hair may be easily obtained, however, by
shaving a second time, very closely, a part of the surface over
which the razor has already passed more lightly, and by picking out
from the lather, and carefully washing, the sections thus taken off.

412. The stems of Feathers exhibit the same kind of structure
as hairs; their cortical portion being the horny sheath that en-
velopes the shaft, and their medullary portion being their pith-
like substance which that sheath includes. In small feathers,
this may usually be made very plain by mounting them in
Canada balsam ; in large feathers, however, the texture is some-
times so altered by the drying up of the pith (the cells of which
are always found to be occupied by air alone), that the cellular
structure cannot be demonstrated, save by boiling thin slices in
a dilute solution of potass, and not always even then. In small
feathers, especially such as have a downy character, the cellular
structure is very distinctly seen in the lamine or “‘barbs,”’ which
are sometimes found to be composed of single files or pear-
shaped cells, laid end to end; but in larger feathers, it is usually
necessary to increase the transparency of the barbs, especially
when these are thick and little pervious to light, either by soak-
ing them in turpentine, mounting them in Canada balsam, or
boiling them in a weak solution of potass. In the feathers
which are destined to strike-the air with great force in the act of
flight, we find the barbs fringed on each side with hair-like fila-
ments or pinne ;'on one side of each barb these filaments are
toothed on one edge, whilst on the other side they are furnished
with curved hooks; and as the two sets of pinne which spring
from two adjacent barbs, cross one another at an angle, and each
hooked pinna on one locks into the teeth of several of the
toothed pinne arising from the other, the barbs are connected
together very firmly by this apparatus of ‘“‘hooks ‘and eyes,”’
which reminds us of that already mentioned as to be observed
on the wings of Hymenopterous Insects (§ 895). Feathers or
portions of feathers of birds distinguished by the splendor of
their plumage, are very good objects for low magnifying powers,
when illuminated on an opaque ground; but care must be taken
that the light falls upon them at the angle necessary to produce
their most brilliant reflection into the axis of the microscope;
since feathers which exhibit the most brilliant metallic lustre to
an observer at one point, may seem very dull to the eye of
another in a different position. The small feathers of Humming
birds, portions of the feathers of the Peacock, and others of a
like kind, are well worthy of an examination; and the scientific

598 VERTEBRATED ANIMALS.

Microscopist who is but little attracted by mere gorgeousness,
may well apply himself to the discovery of the peculiar struc-
ture, which imparts to these objects their most remarkable cha-
racter.

413. Sections of Horns, Hoofs, Claws, and other like modifica-
tions of Epidermie structure,—which may be made by the
Section instrument (§ 107), the substance to be cut having been
softened, if necessary, by soaking in warm water,—do not in
general afford any very interesting features, when viewed in the
ordinary mode; but there are no objects on which Polarized
light produces more remarkable effects, or which display a more
beautiful variety of colors, when a plate of selenite is placed be-
hind them, and the analyzing prism is made to rotate. A
curious modification of the ordinary structure of horn, is pre-
sented in the appendage borne by the Rhinoceros upon its snout,
which in many points resembles a bundle of hairs, its substance
being arranged in minute cylinders around a number of separate
centres, which have probably been formed by independent
papille (Fig. 313). When transverse sections of these cylinders
are viewed by polarized light, each of them is seen to be marked
by a cross, somewhat resembling that of starch-grains; and the
lights and shadows of this cross are replaced by contrasted colors,
when the selenite-plate isinterposed. The substance commonly
but erroneously termed Whalebone, which is formed from the
surface of the membrane that lines the mouth of the whale, and
has no relation to its true bony skeleton, is almost identical in
structure with Rhinoceros-horn, and is similarly affected by
polarized light. The central portion of each of its component
fibres, like the medullary substance of hairs, contains cells that
have been so little altered as to be easily recognized; and the

outer or cortical portion also

Fra. 313. may be shown to have a like

structure, by macerating it in
a solution of potass, and then

in water. Sections of any of

the horny tissues are best
mounted in Canada balsam.

414. Blood.—Carrying our
Microscopic survey, now, to
the elementary parts of which
those softer tissues are made
up, that are subservient to
the active life of the body,
rather than to its merely me-
chanical requirements, we

Transverse Section of Horn of Rhinoceros, viewed shall in the first place notice
by Polarized Light. the isolated floating cells

contained in the Blood, and

known as the “blood-corpuscles.” These are of two kinds; the

RED CORPUSCLES OF BLOOD. 599

“red,” and the “white” or “colorless.” The former present, in
every instance, the form of a flattened disk, which is: circular in
Man and in most Mammalia (Fig. 315), but which is oval in
Birds, Reptiles (Fig. 314), and Fishes, and in a few Mammals
(all belonging to the Camel tribe); in the one form as in the
other, this disk is a flattened cell, whose walls are pellucid and
colorless, but whose contents are colored. They may be caused
to swell up and burst, however, by the imbibition of water; and
the perfect transparency and the homogeneous character of their
walls then become evident. The “red corpuscles” in the blood
of Oviparous Vertebrata are distinguished by the presence of a
distinct central spot or nucleus, which appears to be composed of
an aggregation of minute granules; this is most distinctly brought
into view by treating the blood-disks with acetic acid, which
renders the remaining portion extremely transparent, while it
increases the opacity of the nucleus (Fig. 314, d). It is remark-
able, however, that the “red corpuscles” of the blood of Mam-
mals should possess no obvious nucleus; the dark spot which is
seen in their centre (Fig. 315, 6), being merely an effect of refrac-

Fic. 314. Fia. 315.

Fig. 814. Red Corpuscles of Frog’s Blood:—1, 1, their flattened face; 2, particle turned nearly
edgeways; 3, colorless corpuscle; 4, red corpuscles altered by dilute acetic acid.

Fig. 315. Red Corpuscles of Human Blood; represented at a,as they are seen when rather
within the focus ofthe microscope, and at 6, as they appear when precisely in the focus.

tion, consequent upon the double coneave form of the disk. When
the corpuscles are treated with water, so that their form becomes
first flat, and then double convex, the dark spot disappears;
whilst, on the other hand, it is made more evident when the
concavity is increased by the partial emptying of the cell, which
may be accomplished by treating the blood-corpuscles with fluids
of greater density than their own contents. The size of the “red
corpuscles” is not altogether uniform in the same blood; thus it
varies in that of Man, from about 1-4000th to the 1-2800th of an
inch. But we generally find that there is an average size, which
is pretty constantly maintained among the different individuals
of the same species; that of Man may be stated at about 1-3200th
of an inch. The following Table' exhibits the average dimen-

1 These measurements are chiefly selected from those given by Mr. Gulliver in his
edition of Hewson’s Works, p. 236, et seq.

600 VERTEBRATED ANIMALS.

sions of some of the most interesting examples of the Red blood-
corpuscles, in the four classes of Vertebrated Animals, expressed
in fractions of an inch. Where two measurements are given,
they are the long and the short diameters of the same corpuscle.

MAMMALS.
Man, ..... . . . 13200|Camel, . . . . . 1-3254, 15921
Dog, . . . . . . « . 13542|Llama, . . . . . 1-3361, 1-6294
Whale,. . . . . . . . 1-83099|Java Musk-Deer, . . . .1-12325
Elephant, . . . . . . . 1-2745|Caucasian Goat, . . . . . 1-7045
Mousey... . . . . 1-3814!Two-toed Sloth, . .. . 1-2865
BIRDS.
Golden Eagle, . . 1-1812, 1-3832]Ostrich,. . . . . 1-1649, 1-3000
Owl,. . . . . « 41-1830, 1-3400|Cassowary,. . . . 1-1455, 1-2800
Crow, . . . . 11-1961, 1-4000|Heron, . . . . . 21-1913, 1-3491
Blue-Tit, . . . . 11-2313, 1-4128|/Fowl, . . . + - 1-2102, 1-3466
Parrot, . . . . . 1-1898, 1-4000/Gull, . . . . . 1-2097, 1-4000
REPTILES.
Turtle, . . . . . 1-1231, 1-1882|Frog, . . . . . 1-1108, 1-1821
Crocodile, . . . . 1-1231, 1-2286 | Water-Newt, . » 1-814, 1-1246
Green Lizard,. . . 1-1555, 1-2743) Siren, . . . . 1-420, 1-760
Slow-worm, . . . 1-1178, 1-2666)Proteus, . . . . 1-337
Viper, . . . . . 11-1274, 1-1800|Lepidosiren, . . . 1-570, 1-941
FISHES.
Perch, . . . . . 1-2099, 1-2824|Pike, . . . . . 1-2000, 1-3555
Carp, ¢ 5 » « » L242, 13909 |Bel, ya - . 4 4 161748, 12802
Gold-Fish,. . . . 1-1777, 1-2824|Gymnotus,. . . . 1-1745, 1-2599

Thus it appears that the smallest red corpuscles known are those
of the Musk-Deer ; whilst the largest are those of that curious
group of Batrachian (frog-like) Reptiles which retain their gills
through the whole of life; and the oval blood-disks of the Proteus,
being above 86 times as long as those of the Musk-Deer, and pro-
bably at least 20 times as broad, would cover no fewer than 720
of them.

415. The “colorless” corpuscles are more readily distinguished
in the blood of Reptiles, than in that of Man; being, in the
former case, of much smaller size, as well as having a circular
outline (Fig. 314, ce); whilst in the latter, their size and contour
are nearly the same, so that, as the red corpuscles themselves,
when seen in a single layer, have but a very pale hue, the de-
ficiency of color does not sensibly mark their difference of nature.
It is remarkable that, notwithstanding the great variations in the
sizes of the red corpuscles in different species of Vertebrated ani-
mals, the size of the “colorless” is extremely constant through-
out, their diameter being seldom much greater or less than
1-3000th of an inch in the warm-blooded classes, and 1-2500th in
Reptiles. Their ordinary form is globular; but their aspect is
subject to considerable variations, which seem to depend in great
part upon their phase of development. Thus in their early state,
in which they seem to be identical with the corpuscles found
floating in Chyle and Lymph, the cell-wall can seareely be dis-

COLORLESS CORPUSCLES OF BLOOD. 601

tinguished from the large nuclear mass which it incloses; by
treating the cell with water or acetic acid, however, the mem-
brane is distended, and the nucleus very commonly breaks up
into fragments in its interior. This last appearance seems natural
to the corpuscles in a more advanced condition ; and the isolated
particles are often to be seen executing an active molecular
movement within the cell, which continues when they are dis-
charged by the bursting of the cell, consequent upon the addition
of a solution of potass. These corpuscles are occasionally seen
to exhibit very curious changes of form, which remind us of those
of the Ameeba (§ 261); a protrusion taking place from the same
portion of the cell-wall, the form of which seems quite indetermi-
nate; and this being soon succeeded by another, from some dif-
ferent part of the cell, the first being either drawn in again, or
remaining as it was. These changes have been observed, not
only in the “ colorless corpuscles’ of the blood of various Verte-
brated animals, but also in the corpuscles floating in the circu-
lating fluid of the higher Invertebrata, such as the Crab, which
resemble the ‘“ colorless” corpuscles of Vertebrated blood rather
than its “red” corpuscles,—these last, in fact, being altogether
peculiar to the circulating fluid of Vertebrated animals.

416. In examining the Blood microscopically, it is, of course,
of importance to obtain as thin a stratum of it as possible, so
that the corpuscles may not overlie one another. This is best
accomplished by selecting a piece of thin glass of perfect flat-
ness, and then, having received a small drop of blood upon a
glass slide, to lay the thin glass, not upon this, but with its edge
just touching the edge of the drop; for the blood will then be
drawn in by capillary attraction, so as to spread in a uniformly
thin layer between the two glasses. The inexperienced observer
will be surprised at the very pale hue which the red corpuscles
exhibit beneath the microscope, when seen in a single stratum ;
but this surprise need no longer be felt, when it is borne in
mind that the thickness of the film of coloring fluid which they
contain, is probably not more than 1-20,000th of an inch; and if
a drop of ink, or of almost any colored liquid, however dark, be
pressed out between two glasses into an equally thin film, its hue
will be lightened in the same degree. The red hue of the
corpuscles, however, becomes obvious enough, when two or
more layers of them are seen through at once. The “colorless
corpuscles” in Human blood are usually not more than 1-350 of
the “red,” so that no more than one or two are likely to be in
the field at once; and these may generally be recognized most
readily, by their standing apart from the rest; for whilst the
“‘red” corpuscles have a tendency. to adhere to each other by
their discoidal surfaces, the “ colorless” show no such disposition.
Thin films of blood may be preserved in the liquid state, with
little change, by applying gold size or asphalte round the edge
of the thin glass cover before evaporation has had time to take

602 VERTEBRATED ANIMALS.

place; but it isin some respects preferable to dilute the liquid
with a small quantity of Goadby’s solution, its strength being so
adjusted as not to produce any endosmotic change of form in the
corpuscles. But itis farsimpler to allow such films to dry, with-
out any cover, and then merely to cover them for protection ;
and in this condition the general characters of the corpuscles can
be very well made out, notwithstanding that they have in some
degree shrivelled by the desiccation they have undergone. And
this method is particularly serviceable, as affording a fair means
of comparison, when the assistance of the Microscopist is sought
in determining, for Medico-legal purposes, the source of sus-
picious blood stains; the average dimensions of the dried blood-
corpuscles of the several domestic animals, being sufficiently
different from each other and from those of Man, to allow the
nature of any specimen to be pronounced upon with a high de-
gree of probability.

417. Simple Fibrous Tisswes.—A large proportion of every
animal fabric is made up of simple fibres, whose function is to
hold other parts together, or to serve as cords for the communi-
cation of movement. A very beautiful example of a fibrous
tissue of this kind, is furnished by the membrane of the com-
mon Fowl’s egg, which (as may be seen by examining an egg
whose shell remains soft for want of consolidation by calcareous
particles) consists of two principal layers, one serving as the
basis of the shell itself, and the other forming that lining to it,
which is known as the membrana putaminis. The latter may
be separated, by careful tearing with needles and forceps, after
prolonged maceration in water, into several matted lamell re-
sembling that represented in Fig. 816; and similar lamelle may
be readily obtained from the shell itself, by dissolving away its
lime by dilute acid. The simply fibrous structures of the body
generally, however, belong to one of two very definite kinds of
tissue ; the “white” and the “ yellow,” whose appearance, com-
position, and properties are very different. The white fibrous
tissue, though sometimes apparently composed of distinct fibres,
more commonly presents the aspect of bands, usually of a
flattened form, and attaining the breadth of 1-500th of an inch,
which are marked by numerous longitudinal streaks, but can
seldom be torn up into minute fibres of determinate size. The
fibres and bands are occasionally somewhat wavy in their direc-
tion; and they have a peculiar tendency to fall into undulations,
when it is attempted to tear them apart from each other (Fig.
317). This tissue is easily distinguished from the other, by the
effect of acetic acid, which swells it up and renders it transparent,
at the same time bringing into view certain oval nuclear cor-
puscles. It is perfectly inelastic; and we find it in such parts as
tendons, ordinary ligaments, fibrous capsules, &c., whose function
it is to resist tension without yielding to it. The yellow fibrous
tissue exists in the form of long, single, elastic, branching fila-

WHITE AND YELLOW FIBROUS TISSUE. 603

ments, with a dark decided border; which are disposed to curl
when not put on the stretch (Fig. 818). They are for the
most part between 1-5000th and 1-10,000th of an inch in
diameter; but they are often met with both larger and smaller.
They frequently anastomose, so as to form a network. This
tissue does not undergo any change, when treated with acetic

Fia. 316, Fie. 317.

NAN

Clio YL yh)

‘ous Tissue from Ligament.

Fibrous membrane from Egg-shell.

acid. It exists alone (that is, without any mixture of the white)
in parts which require a peculiar elasticity, such as the middle
coat of the Arteries, the Vocal Cords, the “ligamentum nuche”
of Quadrupeds, the elastic liga-

ment which holds together the Fig. 318.

valves of a Bivalve shell, and 5 SS]
that by which the claws of &
the Feline tribe are retracted ¥%
when not in use; and it enters
largely into the composition
of Areolar tissue. This con-
sists of a network of minute
fibres and bands, which are
interwoven in every direction,
so as to leave innumerable
areole or little spaces, which 5 murous Tissue from Ligamen
communicate freely with one ; of Call
another. Of these fibres, some

are of the yellow or elastic kind ; but the majority are composed
of the white fibrous tissue; and, as in that form of elementary
structure, they frequently present the form of broad flattened
bands, or membranous shreds, in which no distinct fibrous ar-
rangement is visible. The proportion of the two forms varies,
according to the amount of elasticity, or of simple resisting
power, which the endowments of the part may require. We
find this tissue in a very large proportion of the bodies of higher
Animals; thus it binds together the ultimate fibres of the
muscles and nerves into minute fasciculi, unites these fasciculi
into larger ones, these again into still larger ones which are

ip 3 rr \.. WX fe

ga Ga

= Ss
ee SS

604 VERTEBRATED ANIMALS.

obvious to the eye, and these into the entire muscle; whilst it
also forms the membranous divisions between distinct muscles.
In like manner it unites the elements of nerves, glands, &c.,
binds together the fat-cells into minute masses, these into larger
ones, and so on; and in this way it penetrates and forms part
of all the softer organs of the body. For the display of the
characters of these tissues, small and thin shreds may be cut
with the curved scissors from any part that affords them; and
these must be torn asunder with needles under the simple micro-
scope, until the fibres are separated to a degree sufficient to
enable them to be examined to advantage under a higher magnify-
ing power.

418. Skin, Mucous and Serous Membranes.—The Skin which
forms the external envelope of the body, is divisible into two
principal layers; the “true skin,” which usually makes up by
far the larger part of its thickness, and the “cuticle,” “scarf
skin,” or Epidermis, which covers it. At the mouth, nostrils,
and other orifices of the open cavities and canals of the body,
the skin passes into the membrane that lines these, which is
distinguished as the Mucous membrane, from the peculiar glairy
secretion of mucus by which its surface is protected. But the
great closed cavities of the body, which surround the heart,
lungs, intestines, &c., are lined by membranes of a different
kind; which, as they secrete only a thin serous fluid from their
surfaces, are known as Serous membranes. Both Mucous and
Serous membranes consist, like the skin, of a proper membra-
nous basis, and of a thin cuticular layer, which, as it differs in
many points from the epidermis, is distinguished as the Epithe-
lium (§ 421). The substance of the “true skin” and of the
“mucous” and “serous” membranes, is principally composed of
the fibrous tissues last described; but the skin and the mucous
membranes are very copiously supplied with bloodvessels and
with glandule of various kinds; and in the skin we also find
abundance of nerves and lymphatic vessels, as well as, in some
parts, of hair-follicles. The distribution of the vessels in the
skin and mucous membranes, which is one of the most interest-
ing features in their structure, and which will come under our
notice hereafter (Figs. 328, 829), is intimately connected with
their several functions. In serous membranes, on the other
hand, the supply of bloodvessels is more scanty, their function
being simply protective.

419. Epidermic and Epithelial Cell-layers—The Epidermis or
“cuticle” covers the exterior surfaces of the body, as a thin semi-
transparent pellicle, which is shown by microscopic examination
to consist of a series of layers of cells, which are continually
wearing off at the external surface, and are being renewed at
the surface of the true skin; so that the newest and deepest
layers gradually become the oldest and most superficial, and are
at last thrown off by slow desquamation. In their progress from

EPIDERMIS. 605

the internal to the external surface of the Epidermis, the cells
undergo a series of well-marked changes. When we examine
the innermost layer, we find it soft and granular; consisting of
nuclei, in various stages of development into cells, held together
by a tenacious semi-fluid substance. This was formerly con-
sidered as a distinct tissue, and was supposed to be the peculiar
seat of the color of the skin; it received the designation of rete
mucosum. Passing outwards, we find the cells more completely
formed; at first nearly spherical in shape, but becoming poly-
gonal where they are flattened one against another. As we
proceed further towards the surface, we perceive that the cells
are gradually more and more flattened, until they become mere
horny scales, their cavity being obliterated; their origin is indi-
cated, however, by the nucleus in the centre of each. This
change in form is accompanied by a change in the chemical
composition of the tissue, which seems to be due to the meta-
morphosis of the contents of the cells, into a horny substance
identical with that of which hair, horn, nails, hoofs, &c., are
- composed. Mingled with the epidermic cells, we find others
which secrete coloring-matter instead of horn; these are termed
“pigment-cells.” The most remarkable development of “ pig-
ment-cells” in the higher animals, is on the inner surface of the
Choroid coat of the eye, where they have a very regular arrange-
ment, and form several layers, known as the Pigmentum nigrum.
When examined separately, these cells are
found to have a polygonal form (Fig. 319, a), Fi. 319.
and to have a distinct nucleus (0) in their gg
interior. The black color is given by the
accumulation, within the cell, of a number
of flat, rounded, or oval granules, of extreme
minuteness, which exhibit an active move-
ment when set free from the cell, and even
whilst enclosed within it. The pigment-cells
are not always, however, of this simply- :
rounded or polygonal form; they sometimes Geils from Pigmentum
present remarkable stellate prolongations, Nigrum:—a, pigment-
under which form they are well seen in the 37 sranules concealing
skin of the Frog (Fig. 327, ¢,c). The gra- cies distinct.
dual formation of these prolongations may
be traced in the pigment-cells of the Tadpole during its meta-
morphosis (Fig. 820). Similar varieties of form are to be met
with in the pigmentary cells of Fishes and small Crustacea,
which also present a great variety of hues; and these seem to
have the power of likening their color to that of the bottom
over which the ‘animal may live, so as to serve for its conceal-
ment.

420. The structure of the Epidermis may be examined in a
variety of ways. If it be removed by maceration from the true
skin, the cellular nature of its under-surface is at once recognized,

606 VERTEBRATED ANIMALS.

when it is subjected to a magnifying power of 200 or 300 diame-
ters, by light transmitted through it, with this
Fig. 320. surface uppermost; and if the epidermis be that
¢ of a negro or any other dark-skinned race, the
pigment-cells will be very distinctly seen. This
under-surface of the epidermis is not flat, but is
excavated into pits and channels for the recep-
tion of the papillary elevations of the true skin ;
an arrangement which is shown on a large scale
in the thick cuticular covering of the Dog’s
foot, the subjacent papille being large enough
to be distinctly seen (when injected) with the
naked eye. The cellular nature of the newly-
formed layers is best seen, by examining a little
of the soft film that is found upon the surface of
the true skin, after the more consistent layers of
the cuticle have been raised by a blister. The
alteration which the cells of the external layers
have undergone, tends to obscure their character;
tah gees fom but if any fragment of epidermis be macerated
il of Tadpole :—a, a, ‘é 6 . 7
simple forms of rece for a little time in a weak solution of soda or
origin j D, b, more com potas, its dry scales become softened, and are
pte eae call filled out by imbibition into rounded or polygo-
nal cells. The same mode of treatment enables
us to make out the cellular structure in warts and corns, which
are epidermic growths from the surface of papille enlarged by
hypertrophy.

421. The Epithelium may be designated as a delicate cuticle,
covering all the free internal surfaces of the body, and thus lining
all its cavities, canals, &c. Save in the mouth and other parts in
which it approximates to the ordinary cuticle both in locality
and in nature, its cells usually form but a single layer; and are
so deficient in tenacity of mutual adhesion, that they cannot be
detached in the form of a continuous membrane. Their shape
varies greatly; for sometimes they are broad, flat, and scale-like,
and their edges approximate closely to each other, so as to form
what is termed a “ pavement” or “tessellated” epithelium ; such
cells are observable on the web of a frog’s foot, or on the tail of
the tadpole; for, though covering an external surface, the soft
moist cuticle of these parts has all the characters of an epithelium.
In other cases, the cells have more of the form of cylinders, stand-
ing erect side by side, one extremity of each cylinder forming
part of the free surface, whilst the other rests upon the membrane
to which it serves as a covering. If the cylinders be clgsely
pressed together, their form is changed into prisms; and such
epithelium is often known as “prismatic.” On the other hand,
if the surface on which it rests be convex, the bases or lower ends
of the cylinders become smaller than their free extremities; and
thus each has the form of a truncated cone rather than of a cylin-

EPITHELIUM—FAT-CELLS. 607

der, and such epithelium (of which that covering the villi of the
intestine, Fig. 328, is a peculiarly-good example) is termed
“conical.” But between these primary forms of epithelial cells,
there are several intermediate gradations; and one often passes
almost insensibly into the other. Any of these forms of Epi-
thelium may be furnished with cilia; but these appendages are
more commonly found attached to the elongated, than to the
flattened forms of epithelium-cells (Fig. 821). ‘Ciliated epi-
thelium” is found upon the lining

membrane of the air-passages in all Fig, 321.
air-breathing Vertebrata; and it also
presents itself in many other situa-
tions, in which a propulsive power
is needed to prevent an accumula-
tion of mucous or other secretions.
Owing to the very slight attachment _ “iialed Bpithelium,; a, nucleated cells,
that usually exists between the epi- pei
thelium and the membranous sur-

’ face whereon it lies, there is usually no difficulty whatever in
examining it; nothing more being necessary than to scrape the
surface of the membrane with a knife, and to add a little water
to what has been thus removed. The ciliary action will generally
be found to persist for some hours or even days after death, if
the animal has been previously in full vigor ;! and the cells that
bear the cilia, when detached from each other, will swim freely
about in water. If the thin fluid that is copiously discharged
from the nose in the first stage of an ordinary “cold in the head,”
be subjected to microscopic examination, 1t will commonly be
found to contain a great number of ciliated epithelium-cells that
have been thrown off from the lining membrane of the nasal
passages.

422. Fat.—One of the best examples which the bodies of
higher animals afford, of a tissue composed of an aggregation of
cells, is presented by the Adipose tissue; the cells of which are
distinguished by their power of drawing into themselves oleagi-
nous matter from the blood. Fat-cells are sometimes dispersed
in the interspaces of Areolar tissue; whilst in other cases they
are aggregated in distinct masses,—constituting the proper Adi-
pose tissue. The individual fat-cells always present a nearly
spherical or spheroidal form; sometimes, however, when they
are closely pressed together, they become somewhat polyhedral,
from the flattening of their walls against each other (Fig. 322).
Their intervals are traversed by a minute network of blood-
vessels, from which they derive their secretion; and it is proba-
bly by the constant moistening of their walls with a watery fluid,
that their contents are retained without the least transudation,

! Thus it has been observed in the lining of the windpipe of a decapitated criminal,
as much as seven days after death; and in that of the river-tortoise, it has been seén
fifteen days after death, even though putrefaction had already far advanced.

*

608 VERTEBRATED ANIMALS.

although these are quite fluid at the temperature of the living
body. Fat-cells, when filled with their characteristic contents,
have the peculiar appearance which has been
Fra. 322. already described as appertaining to oil-
globules (§ 99), being very bright in their
centre, and very dark towards their margin,
in consequence of their high refractive
power; but if, as often happens in prepara-
tions that have been long mounted, the oily
contents should have escaped, they then
look like any other cells of the same form.
Although the fatty matter which fills these
cells (consisting of a mixture of stearine or
of margarine with oleine) is liquid at the
ordinary temperature of the body of a warm-
blooded animal, yet its harder portion some-
moa times crystallizes on cooling; the crystals
eda and Adams tse: shooting from a centre, so as to form a star-
areolar tissue. shaped cluster. In examining the structure
of Adipose tissue, it is desirable, where
practicable, to have recourse to some specimen in which the fat-
cells lie in single layers, and in which they can be observed with-
out disturbing or laying them open; such a condition is found,
for example, in the mesentery of the mouse, and it is also occa-
sionally met with in the fat deposits which present themselves at
intervals in the connective tissues of the muscles, joints, &e.
Small collections of fat-cells are found in the deeper layers of the
true skin, and may be brought into view by vertical sections ot
it. And the structure of large masses of fat may be examined
by thin sections, these being placed under water in thin cells, so
as to take off the pressure of the thin glass from their surface,
which would cause the escape of the oil particles. No method
of mounting (so far as the Author is aware) is successful in
causing these cells permanently to retain their contents.

423. Cartilage-—In the ordinary forms of Cartilage, also, we
have an example of a tissue essentially composed of cells; but
these are commonly separated from each other by an intercel-
lular substance, the thickness of which differs greatly in different
kinds of cartilage, and even in different stages of the growth ot
any one. Thus in the cartilage of the external ear of a Bat or
Mouse (Fig. 323), the cells are packed as closely together as are
those of an ordinary vegetable parenchyma (Fig. 150, A); and
this seems to be the early condition of most cartilages that are
afterwards to present a different aspect. In the ordinary carti-
lages, however, that cover the extremities of the bones, so as to
form smooth surfaces for the working of the joints, the amount
of intercellular substance is usually considerable; and the carti-
lage-cells are commonly found imbedded in this, in clusters of
two, three, or four (Fig. 324), which are evidently formed by

STRUCTURE OF GLANDS. 609

a process of “duplicative subdivision” analogous to that by
which the multiplication of cells takes place in the Vegetable
Kingdom (Fig. 67). The substance of these cellular Cartilages
is entirely destitute of blood-

vessels; being nourished Fig. 324.

solely by imbibition from

WA
ey

“Hie 2 ss fu Ly 7
NG

Yj
IS a NANT RA

ie Goes Be
DMA TRIIUE if

“A
tal

Fig. 323. Cellular Curtilage of Mouse's ear.

Fig. 324. Section of the branchial Cartilage of Tadpole:—a, group of four cells, separating from
each other; b, pair of cells in apposition; c,c, nuclei of cartilage-cells; d, cavity contuining three
cells.

the blood brought to the membrane covering their surface.
Hence they may be compared, in regard to their grade of organi-
zation, with the larger Algee; which consist, like them, of aggre-
gations of cells held together by intercellular substance, without
vessels of any kind, and are nourished by imbibition through
their whole surface. There are many cases, however, in which
the structureless intercellular substance is replaced by bundles
of fibres, sometimes elastic, but more commonly non-elastic; such
combinations, which are termed fibro-cartilages, are interposed in
certain joints, wherein tension as well as pressure has to be re-
sisted, as, for example, between the vertebree of the spinal column,
and the bones of the pelvis. In examining the structure of Car-
tilage, nothing more is necessary than to make very thin sections
with a sharp razor or scalpel, or with a Valentin’s knife (§ 106),
or, if the specimen be large and dense (as the cartilage of the
ribs), with the section-instrument (§ 107). These sections may
be mounted in weak spirit, in Goadby’s solution, or in glycerine;
but in whatever way they are mounted, they undergo a gradual
change by the lapse of time, which renders them less fit to dis-
play the characteristic features of their structure.

424. Structure of Glands.—The various secretions of the body
(as the saliva, bile, urine, &c.) are formed by the instrumentality
of organs termed Glands; which are, for the most part, formed
on one fundamental type, whatever be the nature of their pro-
duct. The simplest idea of a gland is that which we gain from
an examination of the “follicles” or little bags imbedded in the
wall of the stomach; some of which secrete mucus for the pro-
tection of its surface, and others gastric juice. These little bags
are filled with cells of a spheroidal form, which may be consi-

39

610 VERTEBRATED ANIMALS.

dered as constituting their epithelial lining; these cells, in the
progress of their development, draw into themselves from the
blood the constituents of the particular product they are to
secrete; and they then seem to deliver it up, either by the burst-
ing or by the melting away of their walls, so that this product
may be poured forth from the mouth of the bag, into the cavity
in which it is wanted. The liver itself, in the lowest animals
wherein it is found, presents this condition. Some of the cells
that form the lining of the stomach in the Hydra and Actinia,
seem to be distinguished from the rest by their power of secreting
bile, which gives them a brownish-yellow tinge ; in many Polyzoa,
Compound Tunicata, and Annelida, these biliary cells can be
seen to occupy follicles in the walls of the stomach; in Insects,
these follicles are few in number, but are immensely elongated
so as to form biliary tubes, which lie loosely within the abdomi-
nal cavity, frequently making many convolutions within it, and
discharge their contents into the commencement of the intestinal
canal; whilst in the higher Mollusca, and in Crustacea, the folli-
cles are vastly multiplied in number, and are connected with the
ramifications of gland ducts, like grapes upon the stalks of their
bunch, so as to form a distinct mass, which now becomes known
as the liver. The examination of the biliary tubes of the Insect,
or of the biliary follicles of the Crab, which may be accomplished
with the utmost facility, is well adapted to give an idea of the
essential nature of glandular structure. Among Vertebrated
animals, the salivary glands, the pancreas (sweetbread), and the
mammary glands, are well adapted to display the follicular struc-
ture; nothing more being necessary than to make sections of’
these organs, thin enough to be viewed as transparent objects.
The liver of Vertebrata, however, presents certain peculiarities
of structure, which are not yet fully understood ; for although it
is essentially composed, like other glands, of secreting cells, yet
it has not yet been determined beyond doubt, whether these cells
are contained within any kind of membranous investment. The
kidneys of Vertebrated animals are made up of elongated tubes,
which are straight, and lined with a pavement-epithelium, in the
inner or “medullary” portion of the kidney, whilst they are con-
voluted, and filled with a spheroidal epithelium, in the outer or
“cortical.” Certain flask-shaped dilatations of these tubes in-
clude curious little knots of bloodvessels, which are known as the
“Malpighian bodies” of the kidney; these are well displayed in
injected preparations. For such a full and complete investiga-
tion of the structure of these organs as the Anatomist and Phy-
siologist require, various methods must be put in practice, which
this is not the place to detail. It is perfectly easy to demonstrate
the cellular nature of the substance of the liver, by simply scraping
a portion of its cut surface; since a number of its cells will be
then detached. The general arrangement of the cells in the
lobules, may be shown by means of sections thin enough to be

MUSCULAR FIBRE, 611

transparent; whilst the arrangement of the bloodvessels can only
be shown by means of injections (§ 433). Fragments of the
tubules of the kidney, sometimes. having the Malpighian cap-
sules in connection with them, may also be detached by scraping
its cut surface; but the true relations of these parts can only be
shown by thin transparent sections, and by injections of the
bloodvessels and tubuli. The simple follicles contained in the
walls of the stomach are brought into view by vertical sections;
but they may be still better examined by leaving small portions
of the lining membrane for a few days in dilute nitric acid (one
part to four of water), whereby the fibrous tissue will be so soft-
ened, that the clusters of glandular epithelium lining the cells
(which are but very little altered) will be readily separated.

425. Muscular Tissue—Although we are accustomed to speak
of this tissue as consisting of “fibres,” yet the ultimate struc-
ture of the “muscular fibre” is very different from that of the
simple fibrous tissues already described. When we examine an
ordinary Muscle (or piece of ‘“ flesh’) with the naked eye, we
observe that it is made up of a number of fasciculi or bundles of
fibres ; which are arranged side by side with great regularity, in
the direction in which the muscle is to act; and which are
united by areolar tissue. These fasciculi may be separated into
smaller parts, which appear like simple fibres; but when these
are examined by the microscope, they are found to be them-
selves fasciculi, composed of minuter fibres bound together by
delicate filaments of areolar tissue. By carefully separating
these, we may obtain the ultimate “muscular fibre.” This fibre
exists under two forms, the striated and the non-striated. The
former is chiefly distinguished by the transversely-striated ap-
pearance which it presents, and which is due to an alteration of
light and dark spaces along its whole extent; the breadth and
distance of those striw vary, however, in different fibres, and
even in different parts of the same fibre, according to its state
of contraction or relaxation. Longitudinal strie are also fre-
quently visible, which are due to a partial separation between
the component fibrille into which the fibre may be broken up.
When a fibre of this kind is more closely examined, it is seen to
consist of a delicate tubular sheath, quite distinct on the one
hand from the areolar tissue which binds the fibres into fasciculi,
and equally distinct from the internal substance of the fibre.
This membranous tube, which has been termed the myolemma,
is not perforated either by nerves or capillary vessels; and forms,
in fact, a complete barrier between the real elements of Muscular
structure, and the surrounding parts. These elements appear to
‘be very minute cylindrical particles with flattened faces of nearly
uniform size, and adherent to each other both by their flat sur-
faces and by their edges. The former adhesion is usually the
most powerful; and causes the substance of the fibre, when it is
broken up, to present itself in the form of delicate fibrille, each

612 VERTEBRATED ANIMALS.

of which is composed of a single row of the primitive particle.
(Fig. 825). The diameter of the fibres varies greatly in different
kinds of Vertebrated ani-
Fig, 325. mals. Its average is greater
in Reptiles and Fishes than
in Birds and Mammals, and
its extremes also are wider;
thus its dimensions vary in
the Frog from 1-100th to
1-1000th of an inch, and in
the Skate from 1-65th to
1-300th; whilst in the Hu-
Suriated Muscular fibre, separating into fibrilla. man subject, the average 18
about 1-400th of an inch,

and the extremes about 1-200th and 1-600th.
426. When the fibrille are separately examined, under a
magnifying power of from 250 to 400 diameters, they are seen
to present a cylindrical or slightly beaded form ;
Fig. 326. and their linearly aggregated particles then appear
to be minute cells. We observe the same alterna-
tion of light and dark spaces, as when the fibrille
are united into fibres or into small bundles; but
it may be distinctly seen, that each light space is
divided by a transverse line; and that there is a
pellucid border at the sides of the dark spaces, as
well as between their contiguous extremities (Fig.
326). This pellucid border seems to be the cell-
wall; the dark space enclosed by it (which is
usually bright in the centre) being the cavity of
the cell, which is filled with a highly refracting
substance. When the fibrilis in a state of relaxa-
tion, as seen at a, the diameter of the cells is
greatest in the longitudinal direction: but when
it is contracted, the fibril increases in diameter as
it diminishes in length; so that the transverse
diameter of each cell becomes equal to the longitu-
Surveture of the inal diameter, as seen at 6; or even exceeds it.
ulimae Fbrite Thus the act of Muscular contraction scems to
Coe consist in a change of form in the cells of the
fibrilin a state of Ultimate fibrillee, consequent upon a contraction
viens boled a between the walls of their two extremities; and it
a state of partiat 18 interesting to observe, how very closely it thus
contraction. corresponds with the contraction of certain Vege-
table tissues, of which the component cells are
capable of producing movements, when they are irritated, by’
means of a similar change of form. The diameter of the ulti-
mate fibrille will of course be subject to variations, in accord-
ance with their contracted or relaxed condition; but it seems to
be otherwise tolerably uniform in different animals, being for

sai (| ea) =

| ca |

MUSCULAR FIBRE. 613

the most part about 1-10,000th of an inch. It has been observed,
however, as high as 1-5000th of an inch, and as low as 1-20,000th,
even when the fibre was not put upon the stretch.

427. The “smooth” or non-striated form of Muscular fibre,
which is especially found in the walls of the stomach, intestines,
bladder, and other similar parts, is composed of flattened bands
whose diameter is usually between 2-2000th and 1-3000th of an
inch; and these bands are collected into fasciculi, which do not
lie parallel with each other, but which cross and interlace. By
macerating a portion of such muscular substance, however, in
dilute nitric acid (about one part of ordinary acid to three parts
of water) for two or three days, it is found that the bands just
mentioned may be easily separated into elongated fusiform cells,
not unlike woody fibre in shape; each distinguished for the most
part by the presence of a long staff-shaped nucleus, brought into
view by the action of acetic acid. These cells, in which the dis-
tinction between cell-wall and cell-contents can by no means be
clearly seen, are composed of a soft yellow substance, often con-
taining small pale granules, and sometimes yellow globules of
fatty matter. In the coats of the bloodvessels are found cells
having the same general characters, but shorter and wider in
form; and although some of these approach very closely in their
general appearance to epithelium-cells, yet they seem to have
quite a different nature, being distinguished by their contractile
endowments. :

428. In the examination of Muscular Tissue, a small portion
may be cut out with the curved scissors; and this should be torn
up into its component fibres, and these, if possible, should be
separated into their fibrille, by dissection with a pair of needles,
under the simple microscope. The general character of the
striated fibre are admirably shown in the large fibres of the
Frog; and by selecting a portion in which these fibres spread
themselves out to unite with an aponeurotic expansion, they
may often be found so well displayed in a single layer, as not
only to exhibit all their characters without any dissection, but
also to show their mode of connection with the simple fibrous
tissue of which the aponeurosis is formed. As the ordinary cha-
racters of the fibre are but little altered by boiling, this process
may be had recourse to for their more ready separation, espe-
cially in the case of the tongue. The separation of the fibres
into their fibrillz is only likely to be accomplished, in the higher
Vertebrata, by repeated attempts, of which the greater number
are likely to be unsuccessful; but it may be accomplished with
much greater facility in the Eel and other fish, the tenacity of
whose muscular tissue is much less. The characters of the
fibrillee are not nearly so well pronounced, however, in the Fish,
as in the warm-blooded Vertebrata; and among the latter, the
Pig has been found by Mr. Lealand (who has been peculiarly
successful in this class of preparations) to yield the best examples.

614 VERTEBRATED ANIMALS.

He lays great stress on the freshness of the specimen, which
should be taken from the body as soon as possible after death ;
and when a successful preparation has been made, it should be
preserved in Goadby’s solution. The shape of the fibres can
only be properly seen in cross sections; and these are best made
by drying a piece of muscle, so that very thin slices can be cut
with a sharp instrument, which on being moistened again, will
resume in great part their original characters. Striated muscu-
lar fibres are readily obtainable from the limbs of Crustacea and
of Insects ; and their presence is also readily distinguishable in
the bodies of Worms, even of very low organization; so that it
may be regarded as characteristic of the Articulated series gene-
rally. On the other hand, the Molluscous classes are for the
most part distinguished by the non-striation of their fibre ; there
are, however, two remarkable exceptions, strongly striated fibre
having been found in the Terebratula and other Brachiopods, and
also in many Polyzoa. Its presence seems always related to
energy and rapidity of movement; whilst the non-striated pre-
sents itself, where the movements are slower and feebler in their
character.

429. Nerve-substance.— Whenever a distinct Nervous system can
be made out, it is found to consist of two very different forms of
tissue ; namely, the vesicular, which are the essential components
of the ganglionic centres, and the tubular, of which the connect-
ing trunks consist. The -“ nerve-vesicles” or “ ganglion-glo-
bules” are cells, whose typical form may be regarded as globular ;
but they often present an extension into one or more long pro-
cesses, which give them a “caudate” or a “stellate” aspect.
These processes have been traced into continuity, in some in-
stances, with the axis-cylinders of nerve-tubes; whilst in other
cases they seem to inosculate with those of other vesicles. The
vesicles are filled with a finely-granular substance, which extends
into the prolongations; and they also usually contain pigment-
granules, which give them a reddish or yellowish. brown color ;
but these are commonly absent among the lower animals. It is
the presence of this pigment, however, which gives to collections
of ganglion-globules in the warm-blooded Vertebrata that pecu-
liar hue, which causes it to be known as the eineritious or gray
matter. Each of the nerve-tubes, on the other hand, of which
the trunks are composed, consists, in its most completely deve-
loped form, of a delicate membranous sheath, within which is a
hollow cylinder of a material known as the “white substance
of Schwann,” whose outer and inner boundaries are marked out
by two distinct lines, giving to each margin of the nerve-tube
what is described as a “double contour.” The centre or axis
of the tube is occupied by a transparent substance, which is
known as the “axis-cylinder;” and there is reason to believe
that this last is the essential component of the nervous fibre,
and that the hollow cylinder that surrounds it, serves, like the

MICROSCOPIC CHARACTERS OF NERVE-SUBSTANCE. 615

tubular sheath, for its complete isolation. The contents of the
membranous envelope are very soft, yielding to slight pressure ;
and they are so quickly altered by the contact of water or of any
liquids that are foreign to their nature, that their characters can
only be properly judged of when they are quite fresh. Besides
the proper tubular fibres, however, there are others, known as
“ gelatinous,’ which are considerably smaller than the preced-
ing, and do not exhibit any differentiation of parts. They are
flattened, soft, and homogeneous in their appearance, and con-
tain numerous nuclear particles, which are brought into view by
acetic acid. They can sometimes be seen to be continuous with
the axis-cylinders of the ordinary fibres, and also with the radiat-
ing prolongations of the vesicles; so that their nervous character,
which has been doubted by some anatomists, seems established
beyond doubt. The ultimate distribution of the nerve-fibres may
be readily traced in thin vertical sections of the skin, treated
with solution of soda. It was formerly supposed that all its
papille are furnished with nerve-fibres, and minister to sensa-
tion; but it is now known that a large proportion (at any rate)
of those furnished with loops of bloodvessels (Fig. 829, p), being
destitute of nerve-fibres, must have for their special office the
production of the epidermis; whilst those which, possessing
nerve-fibres, have sensory functions, are usually destitute of
bloodvessels. The greater part of the interior of each sensory
papilla of the skin, is occupied by a peculiar “axile body,”
which seems to be merely a bundle of ordinary fibrous tissue,
whereon the nerve-fibre appears to terminate. The nerve-fibres
are more readily seen, however, in the “fungiform”’ papille of
the tongue, to each of which several of them proceed; these
bodies, which are very transparent, may be well seen by snipping
off minute portions of the tongue of the Frog; or by snipping
off the papillee themselves from the surface of the living Human
tongue, which can be readily done by a dexterous use of the
curved scissors, with no more pain than the prick of a pin
would give. The transparency of any of these papille is in-
creased, by treating them with a solution of soda.

430. For the sake of obtaining a general acquaintance with
the microscopic characters of these principal forms of Nerve-
substance, it is best to have recourse to minute nerves and gan-
glia. The small nerves which are found between the skin and
the muscles of the back of the Frog, and which become appa-
rent when the former is being stripped off, are extremely suita-
ble for this purpose; and if-they be treated with strong acetic
acid,.a contraction of their tubes takes place, by which the axis
cylinder is forced out from their cut extremities, so as to be
made more apparent than it can be in any other way. The
“gelatinous” fibres are found in the greatest abundance in the
Sympathetic nerves ; and their characters may be best studied in
the smaller branches of that system. So, for the examination of

616 VERTEBRATED ANIMALS.

the ganglionic vesicles, and of their relation to the nerve-tubes,
it is better to take some minute ganglion as a whole (such as one
of the Sympathetic ganglia of the frog, mouse, or other small
animal), than to dissect the larger ganglionic masses, whose
structure can only be successfully studied by such as are profi-
cient in this kind of investigation. The nerves of the orbit of
the eye of Fish, with the ophthalmic ganglion and its branches,
which may be very readily got at in the Skate, and of which the
components may be separated without much difficulty, form one
of the most convenient objects for the demonstration of, the
principal forms of nerve-tissue, and especially for the connection
of nerve-fibres and ganglionic corpuscles. No method of pre-
serving the nerve-tissue has yet been devised, which makes it
worth while to attempt to mount preparations for the sake of
displaying its minute characters; but the general course of the
nerve-tubes, and the disposition of the ganglionic vesicles, may
be demonstrated in preparations preserved in weak spirit; and
when the skin has been injected, the passage of the nerve-fibres
to the papille can sometimes be traced in vertical sections,
mounted as opaque objects, and viewed by reflected light. The
following method, recommended by Mr. J. Lockhart Clarke, for
the examination of the structure of the Spinal Cord,' would be
equally applicable to that of other large ganglionic masses:—A
perfectly fresh cord is to be hardened in strong spirit, so that
extremely thin sections can be made with a very sharp knife;
and such sections, placed on slips of glass, are to be treated with
a mixture of one part of acetic acid and three of spirit, which
not only makes the fibrous portion more distinct, but also renders
the vesicular portion more transparent. If it be desired to
preserve such a section, it should be transferred, after maceration
for an hour or two in the mixture of acetic acid and spirit, into
pure spirit, in which it should be allowed to remain for about
the same space of time; from the spirit it should be transferred
to oil of turpentine, which soon expels the spirit, and renders
the section perfectly transparent, so that it can be examined with
high magnifying powers; and it may then be mounted in Canada
balsam in the usual manner.

431. Cireulation of the Blood.—One of the most interesting
spectacles that the microscopist can enjoy, is that which is fur-
nished by the circulation of the blood in the “ capillary” blood-
vessels, which distribute the fluid through the tissues it nourishes.
This, of course, can only be observed in such parts of animal
bodies, as are sufficiently thin and transparent to allow of the
transmission of light through them without any disturbance of
their ordinary structure; and the number of these is very
limited. The web of the Frog’s foot is perhaps the most suita-
ble for ordinary purposes, more especially since this animal is to
be easily obtained in almost every locality; and the following is

'See his Memoir on that subject, in “ Philos, Transact ,” 1851.

CIRCULATION OF BLOOD IN FROQ’S FOOT. 617

the arrangement which the author has found most convenient
for the purpose. A piece of thin cork is to be obtained, about
9 inches long and 8 inches wide (such pieces are prepared by the
cork-cutters, as soles), and a hole about 3-8ths of an inch in
diameter is to be cut.at about the middle of its length, in such a
position that, when the cork is secured upon the stage, this
aperture may correspond with the axis of the microscope. The
body of the frog is then to be folded in a piece of wet calico,
one leg being left free, in such a manner as to confine its move-
ments, but not to press too tightly upon its body; and being
then laid down near one end of the cork plate, the free leg is to
be extended, so that the foot can be laid over the central aper-
ture. The spreading out of the foot over the aperture is to be
accomplished, either by passing pins through the edge of the
web into the cork beneath, or by tying the ends of the toes by
threads to pins stuck into the cork at a small distance from the
aperture; the former method is by far the least troublesome, and
it may be doubted whether it is really the source of more suffer-
ing to the animal than the latter is, the confinement being
obviously that which is most felt. .A few turns of tape, carried
loosely around the calico bag, the projecting leg, and the cork,
serve to prevent any sudden start; and when all is secure, the
cork plate is to be laid down upon the stage of the microscope,
where a few more turns of the tape will serve to keep it in place.
The web being moistened with water (a precaution which should
be repeated as often as the membrane exhibits the least appear-
ance of dryness), and an adequate light being reflected through
the web from the mirror, this wonderful spectacle is brought
into view on the adjustment of the focus (a power of from 75 to
100 diameters being the most suitable for ordinary purposes),
provided that no obstacle to the movement of the blood be pro-
duced by undue pressure upon the body or leg of the animal.
It will not unfrequently be found, however, that the current of
blood is nearly or altogether stagnant for a time; this seems
occasionally due to the animal’s alarm at its new position, which
weakens or suspends the action of its heart, the movement
recommencing again after the lapse of a few minutes, although
no change has been made in any of the external conditions.
‘But if the movement should not renew itself, the tape which
passes over the body should be slackened; and if this does not
produce the désired effect, the calico envelope must also be
loosened. When everything has once been properly adjusted,
the animal will often lie for hours without moving, or will only
give an occasional twitch. The movement of the blood will be
distinctly seen by that of the corpuscles, which course after one
another through the network of capillaries that intervenes be-
tween the smallest arteries and the smallest veins; in those
tubes that pass most directly from the veins to the arteries, the
current is always in the same direction; but in those which pass

618 VERTEBRATED ANIMALS.

across between these, it may not unfrequently be seen that the
direction of the movement changes from time to time. The
larger vessels (Fig. 827), with which the capillaries are seen to

Fie, 327.

Capillary circulation in a portion of the web of a Frog's foot: 1, trunk of vein; 2,2, its branches:
3, 8, pigment-cells.

be connected, are almost always veins, as may be known from
the direction of the flow of blood in them from the branches
(2, 2) towards their trunks (1); the arteries, whose ultimate sub-
divisions discharge themselves into the capillary network, are
for the most part restricted to the immediate borders of the toes.
Whestggpwver of 200 or 250 diameters is employed, the visible
area is offcourse greatly reduced; but the individual vessels and

along thfé¢entre of cach tube, the colorless corpuscles which are
occasionally discernible, move slowly in the clear stream near
its margin.

432. The circulation may also be displayed in the tongue of the
Frog, by laying the animal down on its back, with its head close
to the hole in the cork-plate, and, after securing the body in this
position, drawing out the tongue with the forceps, and fixing it
on the other side of the hole with pins. This method, however,
is so much more distressing to the animal, that its employment
seems scarcely justifiable forthe mere purpose of display; and
nothing but some anticipate benefit to science, can justify the
laying open of the body of the living animal, for the purpose of

CIRCULATION IN TADPOLE AND FISH. 619

laa
examining the circylation of its lungs or mesentery. The tadpole
of the Frog, when gufficiently young, furnishes a good display of
the circulation in its tail; and the difficulty of keeping it quiet
during the obsexvation may be overcome, by gradually mixing
some lwt water with ‘that in which it is swimming, until it be-
comes motionless; this usually happens when it has been raised
to a temperature between 100 and 110°; and notwithstanding
that the muscles of the body are thrown into a state of spasmodic
rigidity by this treatment, the heart continues to pulsate, and the
circulation is maintained. The larva of the Water-Newt, when it
can be obtained, furnishes a most beautiful display of the circu-
lation, both in its external gills, and in its delicate feet. It may
be enclosed in a large aquatic box or in a shallow cell, gentle
pressure being made upon its body, so as to impede its moye-
ments, without stopping the heart’s action. The circulation may
also be seen in the tails of small fish, such as the Minnow or
-Stickle-back, by confining these animals in tubes, or in shallow
cells, or in a large aquatic box; but although the extreme trans-
parency of these parts adapts them well for this purpose in one
respect, yet the comparative scantiness of their bloodvessels pre-
vents them from being as suitable as the Frog’s web in another
not less important particular. One of the most beautiful of all
displays of the circulation, however, is that which may be seen
upon the yolk-bag of young Fish (such as the trout) soon after
they have been hatched; and as it is their habit to remain almost
entirely motionless at this stage of their existence, the observa-
tion can be made with the greatest facility by means of the zoo-
phyte-trough, provided that the subject of it can be obtained.
Now that the artificial breeding of these fish is largely practised
for the sake of stocking fish-ponds, there can seldom be much
difficulty in procuring specimens at the proper period. The store
of yolk which the yolk-bag supplies for the nutrition of the em-
bryo, not being exhausted in the Fish (as it is in the bird) pre-
viously to the hatching of the egg, this bag hangs down from the
belly of the little creature on its emersion; and continues to do
so until its contents have been absorbed into the body, which
does not happen for some little time afterwards. And the blood
is distributed over it in copious streams, partly that it may draw
into itself fresh nutritive material, and partly that it may be sub-
jected to the aerating influence of the surrounding water.

433. Injected Preparations.—Next to the circulation of the blood
in the living body, the varied distribution of the Capillaries in its
several organs, as shown by means of “injections” of coloring
matter thrown into their principal vessels, is one of the most in-
teresting subjects of microscopic examination. The art of making
successful preparations of this kind, is one in which perfection
can usually be attained only by long practice, and by attention
to a great number of minute particulars; and better specimens
may be obtained, therefore, from those who have made it a busi-
ness to prepare them, than are likely to be prepared by amateurs

620 VERTEBRATED ANIMALS.

for themselves. For this reason, no more than a general account
of the process will be here offered ; the minute details which need
to be attended to, in order to attain successful results, being
readily accessible elsewhere to such as desire to put it in practice.’
The coloring matter which is altogether most suitable when only
one set of vessels is to be injected, is Chinese vermilion. This,
however, as commonly sold, contains numerous particles of far
too large a size; and it is necessary first to reduce it to a greater
fineness by continued trituration in a mortar (an agate or a steel
mortar is the best) with a small quantity of water, and then to
get rid of the larger particles by a process of “levigation,” ex-
actly corresponding to that by which the particles of coarse sand,
&e., are separated from the Diatomacee (p. 305). The fine
powder thus obtained, ought not, when examined under a mag-
nifying power of 200 diameters, to exhibit particles of any appre-
ciable dimensions. The “size” or “gelatine” should be of a fine
and pure quality, and should be of sufficient strength to form a
tolerably firm jelly when cold, whilst quite limpid when warm.
It should be strained, whilst hot, through a piece of new flannel;
and great care should be taken to preserve it free from dust,
which may best be done by putting it into clean jars, covering
its surface with a thin layer of alcohol. The proportion of levi-
gated vermilion to be mixed with it for injection, is about 2 oz.
to a pint; and this is to be stirred in the melted size, until the
two are thoroughly incorporated, after which the mixture should
be strained through muslin. The injection is thrown into the
vessels by means of a brass syringe expressly constructed for the
purpose, which has several jet-pipes of different sizes, adapted
to the different dimensions of the vessels to be injected; and
these should either be furnished with a stop-eock to prevent the
return of the injection when the syringe is withdrawn, or a set
of small corks of different sizes should be kept in readiness,
with which they may be plugged. The pipe should be inserted
into the cut end of the trunk which is to be injected, and should
be tied therein by a silk thread. In injecting the vessels of fish,
mollusks, &c., the softness of the vessels renders them liable to
break in the attempt to tie them; and it is therefore better for
the operator to satisfy himself with introducing a pipe as large
as he can insert, and with passing it into the vessel as far as he
can without violence. All the vessels from which the injection
might escape, should be tied, and sometimes it is better to put
a ligature round a part of the organ or tissue itself; thus, for
example, when a portion of the intestinal tube is to be injected
through its branch of the mesenteric artery, not only should
ligatures be put round any divided vessels of the mesentery, but
the cut ends of the intestinal tube should be firmly tied. The
operation should either be performed when the body or organ is

' See especially the article “Injection,” in the “ Micrographic Dictionary ;” Dr. Beale’s

treatise on “ The Microscope, and its application to Clinical Medicine,” Chap. viii; and
M. Robin's work, “ Du Microscope et des Injections.” (Paris, 1849.) (See also Appendix.)

INJECTION OF BLOODVESSELS. 621

as fresh as possible, or after the expiry of sufficient time to allow
the rigor-mortis to pass off, the presence of this being ve
inimical to the success of the injection. The part should be
thoroughly warmed, by soaking in warm water for a time pro-
‘ portionate to its bulk; and the injection, the syringe, and the
pipes should also have been subjected to a temperature sufficiently
high to insure the free flow of the liquid. The force used in
pressing down the piston should be very moderate at first; but
should be gradually increased as the vessels become filled; and
it is better to keep up a steady pressure for some time, than to
attempt to distend them by a more powerful pressure, which
will be certain to cause extravasation. This pressure should be
maintained’ until the injection begins to flow from the large
veins, and the tissue is thoroughly reddened; and if one syringe-
ful of injection after another be required for this purpose, the
return of the injection should be prevented by stopping the
nozzle of the jet-pipe when the syringe is removed for refilling.
When the injection has been completed, any openings by which
it can escape should be secured, and the preparation should then
be placed for some hours in cold water, for the sake of causing
the size to “ set.’”

434, Although no injections look so well by reflected light,
as those which are made with vermilion, yet other coloring sub-
stances may be advantageously employed for particular purposes.
Thus the yellow chromate of lead, which is precipitated when a
solution of acetate of lead is mixed with a solution of chromate
of potass, is an extremely fine powder, which “runs” with great
facility in an injection, and has the advantage of being very
cheaply prepared. The best method of obtaining it, is to dis-
solve 200 grains of acetate of lead and 105 grains of chromate
of potass in separate quantities of water, to mix these, and then,
after the subsidence of the precipitate, to pour off the super-
natant fluid, so as to get rid of the acetate of potash which it
contains, since this is apt to corrode the walls of the vessels, if the
preparation be kept moist. The solutions should be mixed cold,
and the precipitate should not be allowed to dry before being in-
corporated with the size, four ounces of which will be the pro-
portion appropriate to the quantity of the coloring-substance pro-
duced by the above process. The same materials may be used
in such a manner that the decomposition takes places within the
vessels themselves, one of the solutions being thrown in first,
and then the other; and this process involves so little trouble or
expense, that it may be considered the best for those who are

! A simple mechanical arrangement for this purpose, by which the fatigue of main-
taining this pressure with his hand is saved to the operator, is described in the “ Micro-
graphic Dictionary,” p. 354.

2 The kidney of a sheep or pig is a very advantageous organ for the learner to practise
on; and he should first master the filling of the vessels from the arterial trunk alone,
and then, when he has succeeded in this, he shonld fill the tubuli _uriniferi with white
injection, before sending colored injection into the renal artery. The entire systemic

circulation of small animals, as mice, rats, frogs, &c., may be injected from the aorta;
and the pulmonary vessels from the pulmonary artery.

622 VERTEBRATED ANIMALS.

novices in the operation, and who are desirous of perfecting
themselves in the practice of the easier methods, before attempt-
ing the more costly. By M. Doyére, who first devised this
method, it was simply recommended to throw in saturated solu-
tions of the two salts, one after the other; but Dr. Goadby, who
has had much experience in the use of it, advises that gelatine
should be employed, in the proportion of 2 oz. dissolved in 8 oz.
of water, to 8 oz. of the saturated solutions of each salt. This
method answers very well for preparations that are to be mounted
dry ; but for such as are to be preserved in fluid, it is subject to
the disadvantage of retaining in the vessels the solution of
acetate of potash, which exerts a gradual corrosive action upon
them. Dr. Goadby has met this objection, however, by suggest-
ing the substitution of nitrate for acetate of lead; the resulting
nitrate of potash having rather a preservative than a corrosive
action on the vessels. When it is desired to inject two or more
sets of vessels (as the arteries, veins, and gland-ducts) of the
same preparation, different coloring substances should be em-
ployed. For a white injection, the carbonate of lead (prepared
by mixing solutions of acetate of lead and carbonate of soda,
and pouring off the supernatant liquid when the precipitate has
fallen) is the best material. No blue injections can be much recom-
mended, as they do not reflect light well, so that the vessels filled
with them seem almost black; the best is freshly-precipitated
Prussian blue (formed by mixing solutions of persulphate of
iron and ferroeyanide of potassium), which, to avoid the altera-
tion of its color by the free alkali of the blood, should be
triturated with its own weight of oxalic acid and a little water,
and the mixture should then be combined with size, in the pro-
portion of 146 grains of the former to 4 oz. of the latter.
435, Injeeted preparations may be preserved either dry or.in
fluid. The former method is well suited to sections of many
solid organs, in which the disposi-
Fia. 328. tion of the vessels does not sustain
much alteration by drying; for the
colors of the vessels are displayed
with greater brilliancy than by any
other method, when such slices,
after being well dried, are moist-
ened with turpentine and mounted
in Canada balsam. But for such
an injection as that shown in Fig.
328, in which the form and dispo-
sition of the intestinal villi would
be completely altered by drying, it
is indispensable that the prepara-
tion should be mounted in fluid, in
a cell deep enough to prevent any
pressure on its surface. Hither Goadby’s solution or weal spirit
answers the purpose very well.

Villi of Small Intestiue of Moukey.

DISTRIBUTION OF CAPILLARIES. 623

436, A well-injected preparation should have its vessels com-
pletely filled through every part; the particles of the coloring
matter should be so closely compacted together, that they should
not be distinguishable unless carefully looked for; and there
should be no patches of pale uninjected tissue. Still, although
the beauty of a specimen as a microscopic object is much im-
paired by a deficiency in the filling of its vessels, yet: to the ana-
tomist the disposition of the vessels will be as apparent when
they are only filled in part, as it is when they are fully distended;
and imperfectly injected capillaries are better seen, when thin
sections are mounted as transparent objects, than are such as
have been completely filled.

437. A relation may generally be traced between the disposi-
tion of the Capillary vessels, and the functions they are destined
to subserve ; but that relation is obviously (so to speak) of a me-
chanical kind; the arrangement of the vessels not in any way
determining the function, but merely administering to it, like
the arrangement of water or gas-pipes in a manufactory. Thus
in Fig. 829, a, we see that the capillaries of fatty tissue are dis-

Fie. 329.

Distribution of Capillaries Distribution of Capillary bloodvessels
in Mucous Membrane. in Skin of Finger.

posed in a network with rounded meshes, so as to distribute the
blood among the fat-cells (§ 422); whilst at B we see the meshes
enormously elongated, so as to permit muscular fibres to lie in
them. Again, at c we observe the disposition of the capillaries
around the orifices of the follicles of a mucous membrane; whilst
at D we see the looped arrangement which exists in the papillary
surface of the skin, and which is subservient to the nutrition of
the epidermis and to the activity of the sensory nerves.

624 VERTEBRATED ANIMALS.

438. In no part of the circulating apparatus, however, does
the disposition of the capillaries

Fig. 330. present more points of interest, than

it does in the Respiratory organs.
In Fishes, the respiratory surface is
formed by an outward extension
into fringes of gills, each of which
consists of an arch with straight
lamin hanging down from it ;:and
every one of these laminee (Fig. 330)
is furnished with a double row of
leaflets, which is most minutely
supplied with bloodvessels, their
network (as seen at A) being so close,
that its meshes (indicated by the
dots in the figure) cover less space
than the vessels themselves. The
gills of Fish are not ciliated on their
Yf, ““* ; surface like those of Mollusks and
a) SW of the larva of the Water-newt; the
necessity for such a mode of renew-
) ing the fluid in contact with them,
Two branchial processes of the Gill of the being superseded by the muscular
Eel, showing the branchial lamelle:—a. apparatus with which the gill-cham-
roton of ove of ese processes cunt ber is furnished. But in Reptiles,
mellee. the respiratory surface is formed by
the walls of an internal cavity, that

of the lungs: these organs, however, are constructed on a plan
very different from that which they present in higher Vertebrata,
the great extension of surface which is effected in the latter by
the minute subdivision of the cavity, not being here necessary.
In the Frog (for example) the cavity of each lung is undivided ;
its walls, which are thin and

Fia. 331. membranous at the lower part,

3 TO there present a simple smooth ex-

panse; and it is only at the upper
part, where the extensions of the
tracheal cartilage form a network
over the interior, that its surface
is depressed into sacculi, whose
lining is crowded with blood-
vessels (Fig. 331). In this man-
ner, a set of air-cells is formed
in the thickness of the upper
wall of the lung, which commu-
nicates with the general cavity,
and very much increases the sur-
face over which the blood comes into relation with the air; but
each air-cell has a capillary network of its own, which lies on

iN iE cme eee

WWMMLAE

Interior of apper part of Luny of Frog.

LUNGS OF BIRDS AND MAMMALS. 625

one side against its wall, so as only to be exposed to the air on
its free surface. In the elongated lung of the Snake, the same gene-
ral arrangement prevails; but the cartilaginous reticulation of its
upper part projects much further into the cavity, and encloses in
its meshes (which are usually square, or nearly so) several layers
of air-cells, which communicate, one through another, with the
general cavity. The structure of the lungs of Birds presents us
with an arrangement of a very different kind, the purpose of
which is to expose a very large amount of capillary surface to the
influence of the air. The entire mass of each may be considered
as subdivided into an immense number of “lobules” or “lung-
lets” (Fig. 832), each of which has its own bronchial tube (or

Fia. 332.

Interior structure of Lung of Fowl, as displayed by a section, a. passing in the direction of a
bronchial tube, and by another section, », cutting it across,

subdivision of the windpipe), and its own system of bloodvessels,
which have very little communication with those of other lobules.
Each lobule has a central cavity, which closely resembles that of
a Frog’s lung in miniature; having its walls strengthened by a
network of cartilage derived from the bronchial tube, in the in-
terstices of which are openings leading to sacculi in their sub-
stance. But each of these cavities is surrounded by a solid plexus
of bloodvessels, which does not seem to be covered by any limit-
ing membrane, but which admits air from the central cavity
freely between its meshes; and thus its capillaries are in imme-
diate relation with air on all sides, a provision that is obviously
very favorable to the complete and rapid aeration of the blood
they contain. In the lung of Man and Mammals, again, the plan
of structure differs from the foregoing, though the general effect
of it is the same. For the whole interior is divided up into
minute air-cells, which freely communicate with each other, and
with the ultimate ramifications of the air-tubes into which the
trachea (windpipe) subdivides; and the network of bloodvessels
(Fig. 833) is so disposed in the partitions between these cavities,
that the blood is exposed to the air on both sides. It has been

calculated that the number of these air-cells grouped around the
40

626 VERTEBRATED ANIMALS.

termination of each air-tube in man, is not less than 18,000;
and that the total number in the entire lungs is siz hundred
millions. .

439. The following list of the parts of the bodies of Verte-

brata, of which Injected pre-
Fra, 333 parations are most interesting
as Microscopic objects, may
be of service to those who
may be inclined to apply
themselves to their produc-
tion. Alimentary Canal;
Stomach, showing the orifices
of the gastric follicles, and
the rudimentary villi near the
pylorus; Small Intestine,
showing the villi and the
§ orifices of the follicles of
s ce La ee8J Tieberkiihn, and at its lower
Arrangement ge ea air-cells of part the Peyerian glands ;
Large Intestine, showing the
various glandular follicles:—Respiratory Organs; Lungs of
Mammals, Birds, and Reptiles; Gills and Swimming-bladder of
Fish:—Glandular Organs; Liver, Gall-bladder, Kidney, Paro-
tid:—Generative Organs ; Oviduct of Bird and Frog; Mamma-
lian Placenta; Uterine and Fetal Cotyledons of Ruminants:—
Organs of Sense; Iris, Choroid, and Ciliary processes of Eye,
Pupillary Membrane of fcetus; Papille of Tongue; Mucous
Membrane of Nose; Papille of Skin of finger:— Tegumentary
Organs ; Skin of different parts, hairy and smooth, with vertical
sections showing the vessels of the Hair-follicles, Sebaceous
glands, and Papille; Matrix of nails, hoofs, &c.:—Tissues ;
Fibrous, Muscular, Adipose, Sheath of Tendon.

440. Development.—The study of the Embryological develop-
ment of Vertebrated animals has been pursued of late years
with great zeal and success by the assistance of the Microscope;
but as this is a department of inquiry which needs for its suc-
cessful pursuit a thoroughly scientific culture, and is only likely
to be taken up by a professed Physiologist, no good purpose
seems likely to be served by here giving such an imperfect out-
line of the process, as could alone be introduced into a work
like the present; and the reader who may desire information
upon it, will find no difficulty in obtaining this through systema-
tic treatises on Physiology.’

1 The Author takes the liberty of referring to his “ Principles of Comparative Physio-
logy,” 4th Ed. chap. xi, as containing a general view of the whole subject, with refer-
ences to the principal sources of more detailed information.

CHAPTER XIX.
APPLICATIONS OF THE MICROSCOPE TO GEOLOGICAL INVESTIGATION.

441. Tux utility of the Microscope is by no means limited to
the determination of the structure and actions of the Organized
beings at present living on the surface of the earth; for a vast
amount of information is afforded by its means to the geological
inquirer, not only with regard to the minute characters of the .
many Vegetable and Animal remains that are entombed in the
successive strata of which its crust is composed, but also with
regard to the essential nature and composition of many of those
strata themselves. We cannot have a better example of its
value in both these respects, that that which is afforded by the
results of microscopic examination of lignite or fossilized wood,
and of ordinary coal, which there is every reason to regard as a
product of the decay of wood.

442. Specimens of Fossilized Wood, in a state of more or less
complete preservation, are found in numerous strata of very
different ages,—more frequently, of course, in those whose
materials were directly furnished by the dry land, and were
deposited in its immediate proximity, than in those which were
formed by the deposition of sediments at the bottom of a deep
ocean. Generally speaking, it is only when the wood is found
to have been penetrated by silex, that its organic structure is
well preserved; but instances occur every now and then, in
which penetration by carbonate of lime has proved equally favor-
able. In either case, transparent sections are needed for the
full display of the organization; but such sections, though made
with great facility when lime was the fossilizing material, require
much labor and skill when silex has to be dealt with. Occasion-
ally, however, it has happened that the infiltration has filled the
cavities of the cells and vessels, without consolidating their walls ;
and as the latter have undergone decay without being replaced
by any cementing material, the lignite, thus composed of the
internal “casts” of the woody tissues, is very friable, its fibres
separating from each other like those of asbestos; and their
lamine split asunder with a knife, or isolated fibres separated by
rubbing down between the fingers, exhibit the characters of the
woody structure extremely well, when mounted in Canada

628 MICROSCOPIC GEOLOGY.

balsam. Generally speaking, the lignites of the Tertiary strata
present a tolerably close resemblance to the wood of the existing
period; thus the ordinary structure of Dicotyledonous and Mono-
cotyledonous stems, may be discovered in such lignites in the
utmost perfection; and the peculiar modification presented by
Coniferous wood, is also most distinctly exhibited (Fig. 171).
As we descend, however, through the strata of the Secondary
period, we more and more rarely meet with the ordinary dicoty-
ledonous structure; and the lignites of the earliest deposits of
these series are, almost universally, either gymnosperms or
palms.? Descending into the Paleozoic series, we are presented
in the vast Coal formations of our own and other countries, with
an extraordinary proof of the prevalence of a most luxuriant
vegetation in a comparatively early period of the world’s history ;
and the microscope lends, the geologist essential assistance, not
only in determining the nature of much of that vegetation, but
also in demonstrating, what has been suspected on other grounds,
that Coal itself is nothing else than a mass of decomposed vege-
table matter, chiefly derived from the decay of Coniferous wood.
The determination of the characters of the Ferns, Sigillaria,
Lepidodendra, Calamites, and other kinds of vegetation whose
forms are preserved in the shales and sandstones that are inter-
posed between the strata of coal, must be chiefly based on their
external characters ; since it is very seldom that any of the speci-
mens present any such traces of minute internal structure, as
can be subjected to microscopic elucidation. But notwithstand-
ing the general absence of any definite form in the masses of de-
composed wood of which Coal itself consists (these having ap-
parently been reduced to a pulpy state by decay, before the
process of consolidation by pressure, aided perhaps by heat,
commenced), the traces of structure revealed by the Microscope,
are sufficient not only to determine its vegetable origin, but, in
some cases, to justify the Botanist in assigning the characters of
the vegetation from which it must have been derived. Different
specimens of Coal exhibit these structural characters in very
different degrees of*distinctness; but they uniformly indicate,
with a clearness proportionate to their distinctness, that such
vegetation must have been Coniferous in its nature, and that it
probably approximated most nearly to that group of existing
Coniferee, to which the Araucarie belong. These inferences
are based upon the fact, that the woody structure consists of
woody fibres without interposed vessels; upon the presence of
glandular dots on the woody fibres; and upon the peculiar
arrangement of these dots in two or more rows, alternating one
with another (§§ 231, 238).

443. In examining the structure of Coal, various methods may
be followed. Of those kinds which have sufficient tenacity, thin
sections may be made; but the opacity of the substance requires

1 Under this head are included the Cycadew, along with the ordinary Conifere or pine
an‘ fir tribe.

ROCKS FORMED OF MINUTE ORGANISMS. 629

that such sections should be ground extremely thin, before they
become transparent; and its friability renders this process one of
great difficulty. Any section must either cross the woody tissue
transversely, so that the appearance it presents will resemble that
of Fig. 170; or it must traverse it vertically, in which case the
fibrous structure will be brought into view, either as in Fig. 171, .
or as in Fig. 172; or it must pass in an intermediate direction.
The following method, which would seem not only to be more
simple, but also to give more satisfactory results, is reeommended
by the authors of the “Micrographic Dictionary” (p. 150) :—
“The coal is macerated for about a week in a solution of carbo-
nate of potass; at the end of that time, it is possible to cut tole-
rably thin slices with a razor. These slices are then placed in a
watch-glass with strong nitric acid, covered, and gently heated ;
they soon turn brownish, then yellow, when the process must be
arrested by dropping the whole into a saucer of cold water, or
else the coal would be dissolved. The slices thus treated appear
of a darkish amber color, very transparent, and exhibit the struc-
ture, when existing, most clearly. The specimens are best pre-
served in glycerine, in cells; we find that spirit renders them
opaque, and even Canada balsam has the same eftect.”” When
the coal is so friable, that no sections can be made of it by either
of these methods, it may be ground to fine powder, and the par-
ticles may then, after being mounted in Canada balsam, be sub-
jected to microscopic examination; the results which this method
affords, are by no means satisfactory in themselves; but they
will often enable the organic structure to be sufficiently deter-
mined, by the comparison of the appearances presented by such
fragments, with those which are more distinctly exhibited else-
where. Valuable information may often be obtained, too, by
treating the ash of an ordinary coal-fire in the same manner, or
(still better) by burning to a white ash a specimen of coal that
has been previously boiled in nitric acid, and then carefully
mounting the ash in Canada balsam; for mineral casts of vege-
table cells and fibres may often be distinctly recognized in such
‘ash; and such casts are not unfrequently best afforded by samples
of coal, in which the method of section is least successful in
bringing to light the traces of organic structure, as is the case,
for example, with the “anthracite” of Wales.

444, Passing on now to the Animal kingdom, we shall first
cite some parallel cases in which the essential nature of deposits
that form a very important part of the Earth’s crust, has been
determined by the assistance of the microscope; and shall then
select a few examples of the most important contributions which
it has afforded, to our acquaintance with types of Animal life
long since extinct. It is an admitted rule in Geological science,
that the past history of the Earth is to be interpreted, so far as
may be found possible, by the study of the changes which are

1 See Prof, Quekett's Memoir on the Minute Structure of the Torbane-hill Mineral, in
“ Transact. of the Microsc. Societ.” Ser. 2, vol. ii, p. 41, ef seq.

630 MICROSCOPIC GEOLOGY.

still going on. Thus, when we meet with an extensive stratum
of fossilized Diatomacee (§ 191) in what is now dry land, we can
entertain no doubt that this siliceous deposit originally accumu-
lated either at the bottom of a fresh-water lake, or beneath the
waters of the ocean; just as such deposits are formed at the pre-
sent time, by the production and death of successive genera-
tions of these bodies, whose indestructible casings accumulate
in the lapse of ages, so as to form layers whose thickness is only
limited by the time during which this process has been in action
(§ 190). In like manner, when we meet with a limestone-rock
entirely composed of the
Fig. 334. calcareous shells of Yora-
> minifera, some of them
entire, others broken up
into minute particles, we
interpret the phenomenon
by the fact, that the dredg-
ings obtained from certain
parts of the ocean-bottom
consists almost entirely of
remains of existing Fora-
minifera, in which entire
shells, the animals of
which may be yet alive,
are mingled with the
debris of others that
have been reduced by
theaction of the waves
to a fragmentary
state. Now in the
fine white mud which
is brought up from
almost every part of
the sea-bottom of the
Levant, where it forms
a stratum that is con-
tinually undergoing a
slow but steady in-
crease in thickness,
the microscopic re-
Microscopie Organisms in Levant Mud :—a, v, siliceous spi- searches of Prof. Wil-
ecules of Tedkyds B, H, spicules of Ceodia ‘ & Sponge-spicule liamson? have shown
(unknown); B, calcareous spicule of Grant; F,G, M, 0, por-
tions of calcareous skeleton of Echinodermata; H, I, calcareous that not only are there
atte see ere moltitedes of minute
remains of living or-

' Such a deposit, consisting chiefly of Orbilolites (§ 287) is at present in the act of -
formation on certain parts of the shores of Australia, as the Author is informed by Mr.
J. Beete Jukes; thus affording the exact parallel to the stratum of Orbitolites (belonging,
as the Author's investigations have led him to believe, to the very same species) that
forms part of the “ Caleaire Grossier” of the Paris basin.

?“ Memoirs of the Manchester Literary and Philosophical Society,” vol. viii,

COMPOSITION OF MARINE DEPOSITS. 631

ganisms, both animal and vegetable, but that it is entirely or
almost wholly composed of such remains. Among these were
about 26 species of Diatomacee (siliceous), 8 species of Foramini-
fera (calcareous), and a miscellaneous group of objects (Fig. 334),
consisting of calcareous and siliceous spicules of Sponges and
Gorgonie, and of fragments of the calcareous skeletons of Echi-
noderms and Mollusks.

445. Now almost exactly the same collection of forms, with
the exception of the siliceous Diatomacez, is found in many
parts of the “‘ Calcaire Grossier” of the Paris basin, as well as in
other extensive deposits of the same early tertiary period. And
there is little doubt that a large proportion of the great Creta-
ceous (chalk) formation has a like composition; for many parts

Fie 335,

Microscopic Organisms in Chalk from Gravesend; a, b, ve, d, Textularia globulosa; e, e, ¢,
Rotalia aspera; f, Textularia aculeata; g, Planularia hexas; h, Navicula.

of it consist in great part of the minuter kinds of Foraminifera,
whose shells are imbedded in a mass of apparently amorphous
particles, many of which, nevertheless, present indications of
being the worn fragments of similar shells, or of larger calcareous
organisms. In the Chalk of some localities, Foraminifera consti-
tute the principal part of the minute organisms which can be
recognized with the microscope (Figs. 835, 886); in other in-
stances, the disintegrated prisms of Pinna (§ 336) or other large
shells of the like structure (as Inoceramus) constitute the great
bulk; whilst in other cases, again, the chief part is made up of
the shells of Cytherina, a marine form of Entomostracous Crus-
tacean (§ 367). Different specimens of Chalk vary greatly in the

632 MICROSCOPIC GEOLOGY.

proportion which the distinctly organic remains bear to the
amorphous particles, and which the different kinds of the former
bear to each other; and this is quite what might be anticipated,
when we bear in mind the predominance of one or another tribe
of animals or plants in the several parts of a large area. True
Chalk seems to differ from the Levant Mud, in the small pro-
portion which the siliceous remains of Diatomacee bear, in the
former, to that which is mingled in the latter with the calcareous

Fig. 336,

Microscopic Organisms in Chalk frcm Meudon; partly seen as opaque, and partly as
transparent objects.

shells of Foraminifera, &c.; and it seems doubtful to what ex-
tent they were present in the seas of that epoch. Such remains
are found in abundance, however, forming marly strata which
alternate with those of a chalky nature, in the South of Europe
and the North of Africa (Fig. 101); and it is surmised by Prof.
Ehrenberg, that the layers of flint which the British Chalk con-
tains, have been derived by some metamorphic process from
similar layers of siliceous Diatomacew which have disappeared.
It is now certain, however, that the deposits referred to by Prof.
Ehrenberg are of an age later than that of the great Chalk for-
mation; so that little support is furnished by their phenomena
to his hypothesis. But whatever may have been the origin of
the siliceous material, it may lhe stated as a fact beyond all
question, that nodular flints and other analogous concretions
aoe as agates) may generally be considered as fossilized

ponges or Alcyonian Zoophytes; since not only are their
external forms and their superficial markings often highly cha-

ROCKS COMPOSED OF FORAMINIFERA. 633
racteristic of those organisms, but, when sections of them are
imade sufliciently thin to be transparent, a spongy texture may
be most distinctly recognized in their interior.’ It is curious
that many such sections contain well-preserved specimens of
Xanthidia, which are Desmidiacese whose divided body is covered
with long spinous projections, often cleft, and sometimes fur-
nished with hooks at their extremities; and we occasionally also
find upon their surface, or even imbedded in their substance,
Foraminiferous shells (especially Rotalie), in which not only the
substance of the shell has undergone silicification, but also that
of the soft animal body, the shrunken form of which may be re-
cognized in the dark carbonaceous hue imparted to the central
portion of the silex which fills each chamber.

446. In examining Chalk or other similar mixed aggregations,
whose component particles are easily separable from each other,
it is desirable to separate, with as little trouble as possible, the
larger and more definitely organized bodies, from the minute
amorphous particles; and the mode of doing this will depend
upon whether we are operating upon the large or upon the small
scale. If the former, a quantity of soft chalk should be rubbed
to powder with water, by means of a soft brush; and this water
should then be-proceeded with, according to the method of levi-
gation already directed for separating the Diatomacee (§ 192).
It will ustially be found that the first deposits contain the larger
Foraminifera, fragments of shell, &c., and that the smaller Fora-
minifera and Sponge spicules fall next; the fine amorphous
particles remaining diffused through the water after it has been
standing for some time, so that they may be poured away. The
organisms thus separated should be dried, and mounted in
Canada balsam. If the smaller scale of preparation be preferred,
as much chalk scraped fine as will lie on the point of a knife, is
to be laid on a drop of water on the glass slide, and allowed to
remain there for a few seconds; the water, with ariy particles
still floating on it, should then be removed; and the sediment
left on the glass should be dried and mounted in balsam. For
examining the structure of flints, such chips as may be obtained
with a hammer will commonly serve very well: a clear translu-
cent flint being first selected, and the chips that are obtained
being. soaked for a short time in turpentine (which increases
their transparency), those which show organic structure, whether
Sponge tissue or Xanthidia, are to be selected and mounted in
Canada balsam. The most perfect specimens of sponge-struc-
ture, however, are only to be obtained by slicing and polishing,
—a, process which is best performed by the lapidary.

447. There are various other deposits, of less extent and
importance than the great Chalk formation, which are, like it,
composed in great part of microscopic organisms, chiefly minute

1 See Mr. Bowerbank’s Memoirs in the “ Transact. of the Geolog. Societ.” 1840, and in
the “ Ann. of Nat. Hist.” 1st Ser. vols. vii, x.

634 MICROSCOPIC GEOLOGY.
a

Foraminifera; and the presence of animals of this group
may be recognized, by the assistance of this instrument, in sec-
tions of calcareous rocks of various dates, whose chief materials
seem to have been derived from Corals, Encrinite stems, or
Molluscous shells. Thus in the “Crag’’ formation (tertiary) of
the eastern coast of England, the greater portion of which is
perceived by the unassisted eye to be composed of fragments of
Shells, Corals (or rather Polyzoaria, § 325), and Echinodermata,
the microscope enables us to discover Foraminifera, minute
fragments of shells and corals, and spicules of Sponges; the
aggregate being such as is at present in process of formation on
many parts of our shores, and having been, therefore, in all
probability, a “littoral” formation, whilst the Chalk (with other
formations chiefly consisting of Foraminifera) was deposited at
the bottom of deeper waters. Many parts of the Oolitic (secon-
dary) formation have an almost identical character, save that the
forms, of organic life give evidence of a different age; and in
those portions which exhibit the “roé-stone”’ arrangement from
which the rock. derives its name (such as is beautifully displayed
in many specimens of Bath-stone and Portland-stone), it is found
by microscopic examination of transparent sections, that each
rounded concretion is composed of a series of concentric spheres
enclosing a central nucleus, which nucleus is often a Foramini-
ferous shell. In the Carboniferous (paleozoic) limestone, again,
well-preserved specimens of Foraminifera present themselves;
and there are certain bands of limestone of this epoch in Rus-
sia, varying in thickness from fifteen inches to five feet, and
frequently repeated through a vertical depth of two hundred
feet, which are almost entirely composed of Foraminiferous
shells belonging to a genus now extinct, the Fusulina.

448. It is not only, however, in the condition of organisms of
microscopic size, that the Foraminifera have contributed in an
important degree to the formation of the solid crust of the earth;
for the Nummiulitic limestone,'—which forms a band, often 1800
miles in breadth, and frequently of enormous thickness, that
may be traced from the Atlantic shores of Europe and Africa,
through Western Asia to Northern India and China, and over
vast areas of North America likewise,—is composed of an agere-
gation of larger bodies belonging to the same type ; the “ matrix,”
or rock-substance, in which these are imbedded, being itself
usually made up (as microscopic examination of their sections
demonstrates) of the comminuted particles of similar organisms,
and of smaller Foraminifera; although it is sometimes composed
(as in the British beds of London Clay which include Num-
mulites) of accumulations of clayey or other inorganic particles.
The structure of the Nummudlite itself, as elucidated by micro-
scopic examination, presents some extremely remarkable modi-
fications of the ordinary Foraminiferous type. It is composed

» The Pyramids of Egypt are made of this material.

STRUCTURE OF NUMMULITE. 635

of a series of chambers, symmetrically disposed in a spiral round
a centre, so that a section through its median plane would pre-
sent very much the appearance of Fig. 209; but each whorl in-
vests all the preceding whorls, so as to form a new layer over the
entire surface of the disk; and this layer is usually separated
from that which it covers, by an intervening space, which is
divided into smaller spaces of more or less regular form, by pro-
longations from the partitions that divide the chambers of the
central plane. These prolongations are very differently arranged
in different species; thus in some, as Nummulites distans, they
keep their own separate course, tending towards the centre;
whilst in others, as WV. levigata, they inosculate with each
other, so as to divide the space that intervenes between one
layer and another into an irregular network. Hence in a verti-
eal section, such as that of which a part is shown in Fig. 837, we

Fig. 337.

Vertical Section of portion of Nummulites levigata :—a, margin of external whorl; 6, one of the
outer row of chambers; c, c, whorl invested by a; d, one of the chambers of the fourth whorl from
the margin; e, e’, marginal portions of the enclosed whorls; /, investing portion of outer whorl; g, g,
spaces left between the investing portions of successive whorls; h, hk, sections of the partitions
dividing these.

see not only the succession of chambers along the central plane,
each of them having its own roof and floor, and its own lateral par-
titions dividing it Rott other chambers of the same whorl, but
we also see the superposition of layers over the inner whorls;
so that any chamber d in a whorl that is surrounded by three
otlers, is shut in above and below, not only by its proper shelly
covering, but by three additional layers formed by the pro-
longation of the shelly investments of the external whorls; and
in like manner, the innermost of the chambers here represented
(that nearest e) is enclosed by nine layers above and below, in
addition to that by which it is itself covered, these nine layers
being extensions of the covering of the nine whorls that surround
it. Notwithstanding that the inner chambers are thus so deeply
buried in the mass of investing whorls, yet there is evidence that
the segments of sarcode which they contained, were not cut off
from communication with the exterior; but that they may have
retained their vitality to the last. The shell itself is almost every-
where minutely porous, being penetrated by parallel tubuli,

636 MICROSCOPIC GEOLOGY.

which pass from one surface to the other like those of dentine.
These tubes are shown, as divided lengthways by a vertical sec-
tion, in Fig. 338 (a, a); whilst the appearance they present when

Fia. 338.

Portion of a thin section of Nummulites laevigata, taken in the direction of the preceding, highly
magnified to show the minute structure of the shell :—a. a, portions of the ordinary shell-substance
traversed by parallel tubuli; b, 6, portions forming the murginal wall, traversed by diverging and
larger tubuli; c, one of the chambers laid open; d, d,d, pillars of solid substance not perforated
by tubuli.

cut across in a horizontal section is shown in Fig. 339, the
transparent shell-substance, a, a, a, being closely dotted with
minute punctations which mark their orifices. In that portion
of the shell, however, which forms the margin of each whorl
(Fig. 338, 6, 6), the tubes are larger, and diverge from each
other at greater intervals; whilst at certain other points, d, ad, d,
the shell-substance is not perforated by tubes, but is peculiarly
dense in its texture, forming solid pillars which seem to strengthen
the other parts. In Nummulites whose surfaces have been much
exposed to attrition, it commonly happens that the pillars of the
superficial layer, being harder than the ordinary shell-substance,
and being consequently less worn down, are left as prominences;
the presence of which has often been accounted (but erroneously)
as a specific character. The successive chambers of the same
whorl communicate with each other by a passage left between
the inner edge of the partition that separates them, and the
margin of the preceding whorl that forms their inner boundary ;
this passage is sometimes a single large broad aperture, but is
more commonly formed by the more or less complete coalescence
of several separate perforations, as is seen in Fig. 337, 6. Such
marked differences in this respect are observable in the several
parts of one and the same specimen, that it is obvious that very
little account should be taken of differences in the form of aper-
ture, as affording specific or generic distinctions among Fora-
minifera of this type. But besides the foregoing means of com-
munication, by which the segments of sarcode included in the
inner chambers were enabled to continue receiving supplies of
nutriment, we meet in Nummulites with a remarkable develop-
ment of that system of “interseptal’”’ canals, one of the most
characteristic examples of which among recent Foraminifera is

ORBITOIDES. 637

presented in Fawjasina, as already described (§ 291). These
canals are frequently found to be filled up in Nummulites by the
fossilizing material; but a care- :
ful examination will generally Fic. 339.
disclose traces of them in the
middle of the partitions that
divide the chambers (Fig. 339,
b, 6), while from these may be
seen to proceed the lateral
branches (¢, ¢) which, after bur-
rowing (so to speak) in the walls
of the chambers, enter them by
large orifices (d). As the gene-
ral distribution of this system of
canals in the Nummulite 18 the Portion of Horizontal Section of Mum-
same as that shown in Faujasina mulite, showing the structure of the walls
(Fig. 209), and as the canals, and of the septa of the chambers:—a, Q, Uy
portion of the wall covering three chambers,
although smaller, are far more the punctations of which are the orifices of
numerous, it is obvious that tubuli; 6, », septa between these chambers,
through its means the segments ranches o entering the chambers, by
of sarcode occupying the cham- larger orifices, one of which is seen at d.
bers of the most internal walls
could send their pseudopodial. extensions at once to the exterior.
Of all Foraminifera, the Nummulite is undoubtedly one of the
most highly developed types; and its
extraordinary multiplication at the Fra. 340.
earliest part of the Tertiary period,
is a very curious feature in the Karth’s
history. It is commonly considered
that this type is now extinct; but the
Author, in common with Prof. Wil-
‘liamson, is disposed to question whe-
ther there is any essential difference
between Nummulites and the existing
genus Nonionina, which is very abun-
dant in certain localities; since in
many species of Nummulites, as in
Nonionina, the investing layers of the
successive whorls are in immediate
contact with those that have preceded
them, instead of being separated, as
in Fig. 337, by spaces prolonged from
the cavities of the chambers.
449. The same Nummulitic lime- = z
stone also contains, in certain locali- Scie inne nea es the super
ties (as the southwest of France, north- geiat tayer, and at b,b, the median layer.
eastern India, &c.) a vast abundance
of discoidal bodies termed Orbitoides, which are so similar to
Nummulites as to have been taken for them, but which, while

638 MICROSCOPIC GEOLOGY.

still Foraminiferous, are formed upon a plan of structure altoge-
ther different. On account of the minuteness of their parts, and
the completeness of their fossilization, their structure can only
be elucidated by sections thin enough to be examined by the
microscope with transmitted light; and it is consequently to the
assistance afforded by this instrument, that we are indebted for
our knowledge of the curious type of organization which it pre-
sents. When one of these disks (which vary in size, in different
species, from that of a four-penny piece to that of half a crown)
is rubbed down so as to display its internal organization, two
different kinds of structure are usually seen in it; one being
composed of chambers of very definite form, quadrangular in
some species, circular in others, arranged with a general but not
constant regularity in concentric circles (Figs. 340, 341, 6, 6); the
other, less transparent, being formed of minuter cells which have
no such constancy of form, but which might almost be taken for
the pieces of a dissected map (Figs. 840, 341, a, a). In the upper

Fig. 341.

Portions of the same section, more highly magnified :—a, superficial layer; 6, median layer.

and lower walls of these last, minute punctations may be ob-
served, which seem to be the orifices of connecting tubes whereby
they are perforated. The relations of these two kinds of struc-
ture to each other, are made evident by the examination of a
vertical section (Fig. 842); which shows that the portion a, Figs.

Fie. 342.

Vertical Section of Orbitoides Prattii, showing the large central cell at a, and the median layer
surrounding il, covered above and below by the superficial layers.

340, 341, forms the central plane, its concentric circles of cells
being arranged round a large central cell a, as in Orbitolite (Fig.
206); whilst the cells of the portion 6 are irregularly superposed
one upon the other, so as to form several layers, which are most
numerous towards the centre of the disk, and thin away gradu-
ally towards its margin. By the perforations in these layers, the
pseudopodia proceeding from the central plane of chambers may
have found their way direct to the surface, or at any rate would
have been brought into connection with the segments lying
nearer to it. No organisms precisely resembling the Orbitoides,

ORIGIN OF ROCK-FORMATIONS. 639

are known to exist at present; but there are some which differ
from it so little, that a knowledge of their structure helps mate-
rially to elucidate points, which would otherwise be rendered
obscure in it through the changes induced by fossilization.!

450.. The foregoing details, taken in addition to the facts of
like nature that have been mentioned in previous parts of this
work (as, for example, in § 294), will serve as examples of the
essential importance of microscopic investigation, in determin-
ing, on the one hand, the real character of various stratified
deposits, and, on the other, in elucidating the nature of the
organic remains which these may include. The former of these
lines of inquiry has not yet attracted the attention which it
deserves; since, as is very natural, the greater number of Micro-
scopists are more attracted by those definite forms which they
can distinctly recognize, than by the amorphous sediments which
present no definite structural characters. Yet it is a question of
extreme interest to the Geologist, to determine how far these
had their origin in the disintegration of organic structures; and
much light may often be thrown upon this question by careful
microscopic analysis.. Thus the author having been requested
by Mr. Chas. Darwin, about twelve years since, to examine into
the composition of the extensive calcareous deposit which covers
the surface of the Pampas region of South America, and to
compare it with that of the calcareous tufa still in process of
formation along the coast of Chili, was able to state that their
constituents were in all probability essentially the same, not-
withstanding the difference in their mode of aggregation. For
the Chilian tufa is obviously composed in great part of fragments
of shells, distinguishable by the naked eye; the dense matrix
in which these are imbedded is chiefly made up of minuter
fragments, only distinguishable as such by the microscope;
while through the midst of these is diffused an aggregation of
amorphous particles, that present every appearance of’ having
originated in the yet finer reduction of the same shells, either by
attrition or by decomposition. In the Pampas deposit, on the
other hand, the principal part was found to be composed of
amorphous particles, so similar in aspect to those of the Chilian
rock that their identity could scarcely be doubted; and scattered
at intervals through these were particles of shell, distinctly
recognizable by the microscope, though invisible to the naked
eye. Thus, although the evidence afforded by the larger frag-
ments of shell was altogether wanting in the Pampas deposit, it
could not.be doubted that the materials of both were the same,
those of the Pampean formation having been subject to greater
comminution than those of the Chilian; and this view served to

! See the Author’s Memoir on the Microscopic Structure of Nummulite, Orbitolite, and
Orbitoides, in the “ Quart. Journ. of the Geolog. Society,” for Feb., 1850; and the ad-
mirable “Description des Animaux Fossiles du Groupe Nummulitique de 1I'Inde,” by
MM. D’Archiac and Jules Haime.

640 MICROSCOPIC GEOLOGY.

confirm, whilst it was itself confirmed by, the idea thought most
probable on other grounds by Mr. Darwin, that the Pampean
formation was slowly accumulated at the mouth of the former
estuary of the Plata, and in the sea adjoining it. A similar line
of inquiry has been of late systematically pursued by Mr. R. C.
Sorby; who has applied himself to the microscopic study of the
composition of fresh-water marls and limestones, by ascertaining
the characters and appearances of the minute particles into
which shells resolve themselves by decay, and by estimating the
relative proportions of the organic and inorganic ingredients of
a rock, by delineating on paper (by means of the camera lucida)
the outlines of the particles visible in thin sections, then cutting
them out, and weighing the figures of each kind.’

451. It is obvious that, under ordinary circumstances, only
the hard parts of the bodies of animals that have been entombed
in the depths of the earth, are likely to be preserved; but from
these a vast amount of information may be drawn; and the
inspection of a microscopic fragment will often reveal, with the
utmost certainty, the entire nature of the organism of which it
formed part. In the examination of the minuter fossil Corals,
and of those Polyzoaries (§ 325) which are commonly ranked
with them, the assistance of the microscope is indispensable.
Minute fragments of the “test” or “spines” of Echinodermata,
and of all such Molluscous shells as present distinct appear-
ances of structure (this being especially the case with the Brachio-
poda, and with the families of Lamellibranchiate bivalves most
nearly allied to them), may be unerringly identified by its means,
when the external form of these fragments would give no assist-
ance whatever. In the study of the remarkable ancient group
of Trilobites, not only does a microscopic examination of the

casts which have been pre-

Fig, 343. served of the surface of their

eyes (Fig. 3438), serve to show
the entire conformity in the
structure of these organs to
the “composite” type which
is so remarkable a character-
istic of the higher Articu-
Bye of Trilobite. lata (§ 883), but it also brings

to light certain peculiarities

which help to determine the division of the great Crustacean series
with which this group has most alliance. It is in the case of
the Teeth, the Bones, and the Dermal skeleton of Vertebrated
animals, however, that the value of Microscopie inquiry becomes
most apparent; since the structure of these presents so many
characteristics that are subject to well-marked variations in their
several classes, orders, and families, that a knowledge of these

' See Mr. C. Darwin’s “ Geological Observations on South America,” p. 32.

2 See “ Quart. Journ. of Geolog. Science,” 1853, p. 344,

3 See Prof. Burmeister * On the Organization of the Trilobites,” published by the Ray
Society, p. 19.

FOSSIL TEETH. 641

characters frequently enables the Microscopist to determine the
nature of even the most fragmentary specimens, with a positive-
ness which must appear altogether misplaced to such as have
not studied the evidence.

452. It was in regard to Teeth, that the possibility of such de-
terminations was first made clear by the laborious researches of
Prof. Owen;' and the following may be given as examples of
their value:—A rock formation extends over many parts ot
Russia, whose mineral characters might justify its being likened
either to the Old or to the New Red Sandstone of this country,
and whose position relatively to other strata is such, that there is
great difficulty in obtaining evidence from the usual sources, as
to its place in the series. Hence the only hope of settling this
question (which was one of great practical importance, since, if
the formation were new red, Coal might be expected to underlie
it, whilst if old red, no reasonable hope of coal could be enter-
tained) lay in the determination of the Organic remains which
this stratum might yield; but unfortunately these were few and
fragmentary, consisting chiefly of teeth, which are seldom per-
fectly preserved. From the gigantic size of these teeth, together
with their form, it was at first inferred that they belonged to
Saurian Reptiles, in which case the sandstone must have been
considered as New Red; but microscopic examination of their
intimate structure unmistakably proved them to belong to a
genus of Fishes (Dendrodus) which is exclusively Paleozoic, and
thus decided that the formation must be Old Red. So again, the
microscopic examination of certain fragments of teeth found in
a Sandstone of Warwickshire, disclosed a most remarkable type
of tooth-structure (shown in Fig. 344), which was also ascertained
to exist in certain teeth
that had been discovered Fia. 344.
in the “keuper-sandstein” (~~~) Mae
of Wirtemberg; and the ions ls ,
identity or close resem- ER Oo
blance of the animals to | NY les
which these teeth belonged ff
having been thus establish-
ed, it became almost cer-
tain that the Warwickshire
and Wirtemberg sand-
stones were equivalent for-
mations, a point of much « |g.»
geological importance.
The next question arising
out of this discovery, was Wlbustul
the nature of the animal Section of Tooth of Labyrinthodon.
(provisionally termed La-
byrinthodon, a name expressive of the most peculiar feature in its

1 See his maguificent “ Odontography.”
Al

642 MICROSCOPIC GEOLOGY.

dental structure) to which these teeth belonged. They had been
referred, from external characters merely, to the order of Saurian
Reptiles; but these characters were by no means conclusive; and
as the nearest approaches to their peculiar internal structure are
presented by Fish-Lizards and Lizard-like Fish, it might be rea-
sonably expected that the Labyrinthodon would combine with
its reptilian characters an affinity to fish. This has been clearly
proved to be the case, by the subsequent discovery of parts of its
skeleton in which such characters are very obvious; and by a
very beautiful chain of reasoning, Prof. Owen succeeded in
establishing a strong probability, that the Labyrinthodon was a
gigantic Frog-like animal five or six feet long, with some pecu-
har affinities to Fishes, and a certain mixture also of Crocodilian
characters; and that it made the well-known foot-prints which
have been brought to light, after an entombment whose duration
can scarcely be conceived (much less estimated), in the Stourton
quarries of Cheshire.

458. The more recent researches of Prof. Quekett on the
minute structure of Bone,! promise to be scarcely less fruitful in
valuable results. From the average size and form of the “lacune, ”
their disposition in regard to each other and to the Haversian
canals, and the number and course of the canaliculi, he feels
assured that the nature of even a minute fragment of bone may
be determined with a considerable approach to certainty; and
the following examples, among many which might be cited, ap-
pear to justify such assurance. Dr. Falconer, the distinguished
investigator of the fossil remains of the Himalayan region, and
the discoverer of the gigantic fossil Tortoise of the Sivalik Hills,
having met with certain small bones about which he was doubt-
ful, placed them in the hands of Prof. Quekett for minute exami-
nation; and was informed, on microscopic evidence, that they
might certainly be pronounced Reptilian, and probably belonged
to an animal of the tortoise tribe; and this determination was
fully borne out by other evidence, which led Dr. Falconer to con-
clude that they were toe bones of his great tortoise. Some frag-
ments of bone were found, some years since, in a chalk-pit;
which were considered by Prof. Owen to have formed part of the
wing-bones of a long-winged sea-bird allied to the Albatross.
This determination, founded solely on considerations derived
from the very imperfectly preserved external forms of these frag-
ments, was called in question by some other paleontologists;
who thought it more probable that these bones belonged to a
large species of the extinct genus Pterodactylus, a flying-lizard,
whose wing was extended upon a single immensely prolonged
digit. No species of Pterodactyle, however, at all comparable
to this in dimensions, was at that time known; and the characters

' See his Memoir on the “ Comparative Structure of Bone,” in the “Transac. of the

Microsc, Societ,” Ser. 1, vol. ii; and the “Catalogue of the Histological Museum of the
Roy. Coll. of Surgeons,” vol. ii.

FOSSIL BONE. 643

furnished by the configuration of the bones, not being in any
degree decisive, the question would have remained unsettled, had
not an appeal been made to the Microscopic test. This appeal
* was so decisive, by showing that the minute structure of the bone
in question corresponded exactly with that of Pterodactyle bone,
and differed essentially from that of every known Bird, that no
one who placed the least reliance upon that evidence could enter-
tain the slightest doubt on the matter. By Prof. Owen, however,
the validity of that evidence was questioned, and the bone was
still maintained to be that of a bird; until the question was finally
set at rest, and the value of the microscopic test triumphantly
confirmed, by the discovery of undoubted Pterodactyle bones of
corresponding and even of greater dimensions, in the same and
other chalk quarries.’

! See Prof. Owen’s Monograph on the British Fossil Reptiles of the Chalk Formation,
p. 80, et seq. ‘

CHAPTER XX.
INORGANIC OR MINERAL KINGDOM.—POLARIZATION.

454. Aurnouen by far the most numerous and most important
applications of the Microscope, are those by which the structure
and actions of Organized beings are made known to us, yet there
are many Mineral substances which constitute both interesting
and beautiful objects; being remarkable either for the elegance
of their forms, or for the beauty of their colors, or for both com-
bined. The natural forms of inorganic substances, when in any
way symmetrical, are so in virtue of that peculiar arrangement
of their particles which is termed erystallization ; and each sub-
stance which crystallizes at all, does so after a certain type or
plan,—the identity or difference of these types furnishing cha-
racters of primary value to the Mineralogist. It does not follow,
however, that the form of the crystal shall be constantly the
same for each substance; on the contrary, the same plan of
crystallization may exhibit itself under a great variety of forms;
and the study of these, in such minute crystals as are appropriate
subjects for observation by the microscope, is not only a very
interesting application of its powers, but 1s capable of affording
some valuable hints to the designer. This is particularly the
ease with crystals of Snow, which belong to the “hexagonal
system,” the basis of every figure being a hexagon of six rays;
for these rays “become incrusted with an endless variety of
secondary formations of the same kind, some consisting of thin
lamine alone, others of solid but translucent prisms heaped one
upon another, and others gorgeously combining lamine and
prisms in the richest profusion ;’' the angles by which these
figures are bounded, being invariably 60° or 120°. Beautiful
arborescent forms are not unfrequently produced by the peculiar
mode of aggregation of individual crystals ; of this we have often
an example on a large scale on a frosted window; but micro-
scopic crystallizations sometimes present the same curious phe-
nomenon (Fig. 345). In the following list are enumerated some
of the most interesting natural specimens, which the Mineral
kingdom affords as microscopic objects; these should be viewed
by reflected light, under a very low power :—

'See Mr. Glaisher’s Memoir on “ Snow-Crystals in 1855,” with a number of beauti-
ful figures, in “ Quart. Journ. of Micros. Sci.” vol. iii, p. 179.

CRYSTALLIZATION OF SALTS, 645

Antimony, sulphuret. Tron, ilvaite or Elba-ore.
Asbestos. pyrites (sulphuret).
Aventurine. Lapis lazuli.
ditto, artificial. Lead, oxide (minium).
Copper, native, sulphuret (galena).
arseniate. Silver, crystallized.
malachite-ore. Tin, crystallized.
peacock-ore. oxide.
pyrites (sulphuret). sulphuret.
ruby-ore. Zine, crystallized,

455. The actual process of the Formation of Crystals may be
watched under the microscope with the greatest facility ; all that
is necessary being to lay on a slip
of glass, previously warmed, a Fia. 345.
saturated solution of the salt, and g
to incline the stage in a slight
degree, so that the drop shall be
thicker at its lower than at its
upper edge. The crystallization
will speedily begin at the upper
edge, where the proportion ot
liquid to solid is more speedily re-
duced by evaporation, and will
gradually extend downwards. If
it should go on too slowly, or
should cease altogether, whilst yet
a large proportion of the liquid
remains, the slide may be again
warmed, and the part already soli- Crystallized Silver.
dified may be redissolved; after
which the process will recommence with increased rapidity.
This interesting spectacle may be watched under any microscope;
and the works of Adams and others among the older observers,
testify to the great interest which it had for them. It becomes
far more striking, however, when the crystals, as they come into
being, are made to stand out bright upon a dark ground, by the
use of the spotted lens, the paraboloid, or any other form of
black-ground illumination; still more beautiful is the spectacle
when the Polarizing apparatus is employed, so as to invest the
crystals with the most gorgeous variety of hues. The following
list specifies the salts and other mineral substances, whose crys-
talline forms are most interesting. When these are viewed with
polarized light, some of them exhibit a beautiful variety of colors
of their own, whilst others require the interposition of the
selenite plate for the development of color.

Acetate of Copper. Arragonite (transparent sections).
of Manganese. Arseniate of Potass.
of Soda. Bicarbonate of Potass.

; of Zine. Bichromate of Potass.

Agate (transparent sections). Bichloride of Mercury.

Alum. Boracic acid.

646 INORGANIC OR MINERAL KINGDOM.

Borate of Ammonia. Nitrate of Uranium.

of Soda (borax). Oxalie acid.
Carbonate of Lime (from urine of | Oxalate of Ammonia.
horse). of Chromium.
of Potass. of Lime.
of Soda. of Potass.
Chlorate of Potass. of Soda.

Chloride of Barium. Oxalurate of Ammonia.

of Cobalt. Phosphate of Ammonia.
of Sodium. Ammoniaco-Magnesian (tri-
Cholesterine. ple, of urine).
Chromate of Potass. of Soda.
Citrie Acid. Prussiate of Potass (red).
Cyanide of Mercury. (yellow).

Salicine.
Sulphate of Ammonia.
of Cadmium.

Granite (transparent sections).
Hypermanganate of Potass.
Todide of Potassium.

of Quinine. of Copper.
Mannite. of Copper, ammoniated.
Murexide. of Iron.
Muriate of Ammonia. of Magnesia.
Nitrate of Ammonia. of Potassa.
of Barytes. of Soda.
of Bismuth. of Zinc.
of Copper. Tartaric Acid.
of Potass. Uric Acid.
of Soda. Urate of Ammonia.
of Strontian. of Soda.

456. It not unfrequently happens that a remarkably beautiful
specimen of crystallization developes itself, which the observer
desires to keep for display. In order to do this successfully, it
is necessary to exclude the air; and Mr. Warington recommends
castor-oil as the best preservative. A small quantity of this
should be poured on the crystallized surface, a gentle warmth
applied, and a thin glass cover then laid upon the drop, and
gradually pressed down; and after the superfluous oil has been
removed from the margin, a coat of marine glue or other varnish
is to be applied.

457. Although most of the objects furnished by Vegetable
and Animal structures, which are advantageously shown by-
Polarized light, have been already noticed in their appropriate
places, it will be useful here to recapitulate the principal, with
some additions.

Vegetable. Polypidoms of Hydrozoa (¢ 305).

Cuticles, Hairs, and Scales, from
Leaves (2% 220, 246).

Fibres of Cotton and Flax.

Raphides (¢ 230).

Spiral cells and vessels (¢2 228, 232).

Starch grains (2 229).

Wood, longitudinal sections of,
mounted in balsam (@ 239).
Animal.

Fibres and Spicules of Sponges (§
296).

Polyzoaries (2 330).
Spicules of Gorgonie (2 309).
Tongues (Palates) of Gasteropods
(3347).
Scales of Fishes (22 408, 409).
Sections of Hairs (@ 411).
of Quills (3 412).
of Horns (@ 413).
of Shells (3 336).
of Skin (2 418).
of Teeth (23 406, 407).
of Tendon, longitudinal.

APPENDIX.

THE MICROSCOPE AS A MEANS OF DIAGNOSIS.

APPENDIX BY THE EDITOR.

THE MICROSCOPE AS A MEANS OF DIAGNOSIS.

Value of the Microscope in the Diagnosis of Disease.—During the
past few years the Microscope, in the hands of the physician, has
become an indispensable auxiliary in the detection and diagnosis
of disease. The anatomist in his researches into the structure
and functions of various organs, and the physiologist in his at-
tempts to unveil the mysterious phenomena of life, alike find in
this instrument a valuable coadjutor. Indeed, the invention of
the microscope has added to the already extensive list of the
sciences another—Histology—full of importance and interest,
constituting as it necessarily does, the basis of pathology. The
results flowing from its application to medical inquiries are so
important, that it has, at length, been assigned a place in the
same category as the stethoscope, pleximeter, speculum, and
other well-tried instruments employed in physical exploration.
By its aid such an extensive acquaintance with the intimate
structure of the tissues of the animal economy, both in health
and disease, has been obtained, that the practitioner can now
pursue his difficult profession, with far more accurate and rational
views of the nature and pathology of the various affections which
he is called upon to treat, than were enjoyed by his predecessors.
Individual cases are constantly occurring where long-known and
well-attested methods of investigation have signally failed to
elicit the information necessary to a rational treatment. Upon
many such cases the microscope casts a flood of light. We have
but to. glance over the rapidly increasing literature of our profes-
sion, to discover many proofs of the obligations of practical and
scientific medicine to the invention and judicious application of
the microscope. By its aid the impositions so frequently prac-
tised upon the physician have been often detected. One of the
most common of these attempts at deception consists in mixing
various substances with urine, the patient pretending that he
voided them by the urethra. Some of these, such as starch,
flour, and sand, are readily detected by subjecting the fluid to

650 APPENDIX.

microscopic examination ; and even where milk has been added,
it can be distinguished by the presence of oil-globules, from the
so-called chylous urine, in which the fatty matter is found in a
molecular state. In the same way have been ascertained the
nature and origin of many strange and unusual substances dis-
charged from the bowels. Drs. Bennett, Todd, Quekett, and
others have placed upon record, numerous instances of the value
of the microscope, in detecting impositions and establishing a
certain diagnosis in obscure cases of disease. :

“Some years ago, I was summoned to see a Dispensary patient
laboring under bronchitis, who was spitting florid blood. On
examining the sputum with a microscope, I found that the
colored blood-corpuscles were those of a bird. On my telling
her that she had mixed a bird’s blood with the expectoration,
her astonishment was unbounded, and she confessed that she
had done so for the purpose of imposition.”

The malignant or non-malignant character of certain sus-
picious tumors has, on many occasions, been positively settled
by recourse to the microscope, as the following example will
show.

“ An eminent surgeon, in London, was treating a case of what
he considered to be pharyngeal abscess. Before opening it,
however, he scraped off a little of the matter on its surface with
his nail, and took it to Mr. Quekett, who told me that on examin-
ing it with a microscope, he found it to contain numerous can-
cer-cells. The tumor was allowed to progress uninterruptedly ;
and on the death of the individual, some months afterwards, the
bones at the base of the cranium were found to be enlarged,
from a cancerous growth.’”

That medico-legal science has been greatly enriched and ren-
dered far more certain in its results by the aid of the microscope,
few persons will deny. The ends of justice have sometimes de-
pended solely upon its power of detecting spermatozoa in cases
of rape, of distinguishing between the stains of blood and those
of colored fluids, or of pointing out the difference between human
hair and that of animals.

The microscope has afforded valuable assistance to the patho-
logist, in disclosing the obscure processes by which changes or
alterations in nutrition have gradually produced, in some of the
most complex tissues of the body, the peculiar morbid condition
known as fatty degeneration. In the hands of skilful observers,
this instrument has taught us that apoplexy is not always de-
pendent upon a plethoric or hyperemic state of the cerebral
vessels, but is, in many instances, the result of altered nutrition
affecting the structure of these vessels, impairing their strength
and elasticity, and otherwise altering their properties and func-
tions. A brief microscopic examination of the urine is not
unfrequently sufficient, as the laborious researches of Dr. John-

1 Bennett’s Introduction to Clinical Medicine. 2 Bennett, op. cit.
» Op

THE MICROSCOPE AS A MEANS OF DIAGNOSIS. 651

son have shown, to reveal, during life, the existence of this pecu-
liar pathological condition in the kidney.

But while, on the one hand, we urge upon the student the
importance of the study of microscopy, and direct his attention,
by way of proof, to the brilliant labors of the German School of
Histologists; on the other, we must caution him against its ex-
clusive cultivation, to the neglect of the other established and
reliable modes of investigation of which the intelligent physician
avails himself, in the daily routine of business. “ You must not
suppose,” writes Dr. Bennett,! “that an additional method of
gaining information implies abandonment of those, the utility
of which has stood the test of experience. Men must learn the
every-day use of their senses; must know how to feel, hear, and
see, in the same manner as they did before instruments were
invented. We don’t see the stars less clearly with our naked
sight, because the telescope is necessary for an astronomer.
Neither should a physician observe the symptoms of a disease
less accurately because he examines the chest with a stethoscope,
or a surgeon be less dexterous with the knife, because it is only
by means of the microscope he can determine with exactitude
the nature of a tumor.” ‘We should learn to distinguish be-
tween the mechanical means necessary for arriving at truths, and
those powers of observation and mental processes which enable
us to recognize, compare, and arrange the truths themselves. In
short, rather endeavor to observe carefully and reason correctly
on the facts presented to you, than waste your time in altering
the fashion and improving the physical properties of the means
by which facts are ascertained. At the same time, these are ab-
solutely necessary; and perhaps no kind of knowledge has been
so much advanced in modern times by the introduction of in-
struments and physical means of investigation, as that of medi-
cine. These enable the practitioner to extend the limits to
which otherwise his'senses would be limited. Ido not say em-
ploy one to the exclusion of the other, but be equally dexterous in
the use of all. Do not endeavor to gain a miserable reputation
as a microscopist, or as a stethoscopist; but by the appropriate
application of every instrument and means of research, seek to
arrive at the most exact diagnosis and knowledge of disease, so
as to earn for yourselves the title of enlightened medical
practitioners.”

As with all other mechanical aids to the senses, the microscope,
to be successfully applied in medicine, requires a degree of skill
in its manipulation not to be acquired at once, but by repeated
and persevering practice. Let the student, therefore, not be dis-
couraged by the many failures and uncertainties which, to a
greater or less extent, must necessarily accompany his early
efforts. Let him remember that exact and accurate habits of
observation are acquired slowly and almost insensibly, and that,
in attempting to obtain proficiency in any practical art or science,

1 Introduction to Clinical Medicine.

652 APPENDIX.

a methodical and systematic procedure is always requisite. So
many unknown objects, so many strange and unusual forms, so
many structural peculiarities are revealed to the eyes of the tyro
in microscopy, that he is at once plunged into profound con-
fusion, from which he can extricate himself only by adopting
the most laborious and rigid system of observation. He should
examine with the utmost care the physical appearance and cha-
racter of the ultimate structures; he should note the exact shape
of the object, whether round or oval, globular or flat, &c.; the
peculiarities of its edge or border, whether fine and brilliantly
illuminated, or dark and abrupt, whether smooth or rough, re-
gular or irregular, serrated or beaded, &c. -Peculiarities of color
produced by strong and faint, and by reflected and transmitted
light, should next claim his attention. The size of the object
should, in all cases, be obtained by actual measurement, and all
variations in diameter noted. The transparency must also be
observed,—whether the body be opaque or diaphanous. If
opaque, the degree of opacity must be stated, its causes, and the
effects upon the transmission of the luminous rays. The
superficial and deep-seated layers, and in the case of cellular and
tubular bodies, the contents should also be investigated ; and
lastly, the effects of various reagents upon these physical pro-
perties must be ascertained with the same care and patience.

It will thus be seen that the successful application of the micro-
scope to the diagnosis of disease, requires a very considerable
acquaintance with the healthy appearance and structure of both
the animal and vegetable tissues. Armed with this preliminary
knowledge, the student will be surprised at the facility with
which he will be enabled to distinguish from each other the
various animal solids and fluids, different morbid products, the
matters constituting food, &., whether these be unchanged, or
in a state of disintegration from the processes of mastication,
digestion, ulceration, &e.

In view, however, of the great difficulty experienced in demon-
strating accurately the histological character of the healthy
tissues, and the still greater difficulty of making out the charac-
teristics of morbid growths, the student should exercise great
caution and deliberation in pronouncing an opinion upon the
nature of any morbid tissues examined by him.

The student should early acquire the habit of recording all his
observations in a note-book kept expressly for the purpose. He
should exercise himself also in making drawings, as exact as
possible, of all the objects he examines. Such a practice, though
laborious, will leave upon his mind a more vivid and lasting im-
pression of the various objects of his research, and gradually
render him a very close and reliable observer.

EXAMINATION OF THE NERVOUS SYSTEM. 6538

EXAMINATION OF THE NERVOUS SYSTEM.

Brain.—As the nerve-fibres rapidly undergo change, the brain
should be examined very soon after death, by depositing minute
portions upon a perfectly clean

slip of glass, and moistening Fig. 346.

them with serum or a weak sac-

charine solution. If it is desired Ci B

to examine the distribution and O

arrangement of nerve-fibres, the
‘brain should be placed in a solu-
tion of chromic acid; by the
hardening thus produced it can
be easily cut into thin slices by
means of a Valentin’s knife.
The addition of water to a por-
tion of white cerebral matter
changes the natural appearance
of these fibres, by separating the be
oily and albuminous contents of C [Hak
the tubular sheath. The oily
matter collects into globules,
giving a beaded appearance to
the fibres. (Fig. 846, g, g’.) The
nerve-tubes may be rendered very
distinct by the addition ofa dilute
solution of caustic soda. ®@

Small portions of the meninges oie
of the brain may be examined in : Hebed
the same manner.

To examine the cerebral vessels, a thin section must be well
washed, and subjected to gentle pressure. The vessels are thus
deprived of their investing neurine, and may now be rendered
more distinct by the dilute caustic soda.

The corpora amylacea, or gritty particles found in the pineal
gland and other parts of the brain (Fig. 347), must be separated
from the nervous tissue for examination by repeated washing
in water.

Spinal Cord.—To examine the spinal cord with advantage, it
should first be hardened in a solution of chromic acid, or in
spirits of wine. The structure of thin sections is thus rendered
quite conspicuous. The following method was employed by Mr.
J. 8. Clarke.’

“A perfectly fresh cord was hardened in spirits of wine, so
that extremely thin sections, in various directions, could be made
by means of a very sharp knife. A section so made was placed
on a glass slide, and treated with a mixture composed of one part
of acetic acid and three of spirits of wine, which not only makes
the nerves and fibrous portion more distinct and conspicuous,

' Philosophical Transactions, 1851, Part ii.

ee we ae

654 APPENDIX.

but renders also the gray substance much more transparent.
The section was then covered with thin glass, and viewed first

Fig. 347.

The lower figure represents a choroid plexus with several small tumors at * * *, supposed at
first to have been tubercular; they proved to consist of aggregations of concentric corpuscles, chole-
sterine, and pure oil, united by areolar tissue; the concentric corpuscles which are shown above the
plexus are magnified 100 diameters.

by reflected light with low magnifying powers, and then by
transmitted light with higher ones.

“ According to the second method, the section is first mace-
rated for an hour or two in the mixture of acetic acid and spirit.
It is then removed into pure spirit, and allowed to remain there
for about the same space of time. From the spirit it is trans-
ferred to oil of turpentine, which expels the spirit in the form of
opaque globules, and shortly (sometimes immediately) renders
the section perfectly transparent. The preparation is then put
up in Canada balsam, and covered with
thin glass. By this means the nerve-
fibrils and vessels become so beautifully
distinct, that they may be clearly seen
with the highest powers of the micro-
scope. If the section be removed from
the turpentine when it is only semi-trans-
parent, we sometimes obtain a good view
of the arrangement of the bloodvessels.
This mode of preparation succeeds best in
cold weather; for in summer, the cord,
fresh when immersed in the spirit, re-
mains more or less spongy, instead of be-
coming firm and dense in the course of
five or six days. The spirit should be
diluted with an equal quantity of water
during the first day, after which it should
be used pure. Certain modifications of this mode of preparation

EXAMINATION OF THE MUSCULAR SYSTEM. 655

aoe be sometimes employed with advantage by a practised
and.”

Nerves.—The structure and arrangement of nerve-fibres are
best studied in the mesentery of small animals, as the newt;
though with a little care in manipulation they can be very well
displayed in any part of the nervous system. Their ultimate
distribution, however, presents greater difficulties. Phosphoric
acid, and solutions of caustic soda, and iodine of ditferent
strengths, are of great use in rendering these fibres more dis-
tinct. According to Dr. Waller, the tongue of the frog is best
adapted for examining the arrangement of nerve-fibres in papillee.
When the nerve-fibres are not quite fresh, or have been soaked
in water, and where they have been stretched or subjected
to pressure for some time, their structure will be found to have
undergone certain peculiar changes, as complete conversion into
fibrous tissue, fatty degeneration, &c. (Fig. 348.)

EXAMINATION OF THE MUSCULAR SYSTEM.

Muscular Fibre.—Sarcolemma.—Muscular fibre is of two kinds,
—the striated, voluntary, or muscular fibre of animal life; and
the unstriated, involuntary, or muscular fibre of organic life.

The voluntary muscles of man and the lower animals furnish
specimens of the striated fibre. They may be prepared for
examination by cutting out a small slice from a muscle, sepa-
rating the fibres with fine needles, and placing them upon a glass
slide, and adding a drop or two of water. Muscles which have
been boiled or hardened in chromic acid, corrosive sublimate, or
spirits of wine, yield excellent sections for examination. The
general anatomy of voluntary muscular fibre is well displayed
in the thin slips of muscle lying just beneath the skin of small
animals, as the frog; while the general arrangement and form
of the fibres is well shown, according to Beale, in a transverse
section of the pectoral muscle of a teal Ue a crecea),
which has been put upon the stretch, and allowed to become
perfectly dry.

The ultimate fibrille may be studied with advantage upon the
muscular tissue of the eel and pig. The fibrille are separated
and rendered distinct by maceration in chromic acid. From the
back of the throat, after a meal of meat, in the discharges of
cholera patients and in vomited matters, admirable specimens,
showing the transverse strie, may often be obtained. In
examining the arrangement of the nuclei, solutions of caustic
soda and acetic acid will be found very useful. :

In the tongue of the frog, as shown by Kolliker, and in the
upper lip of the rat, according to Huxley, peculiar fibres, known
as branched muscular fibres, may be found. To obtain specimens
of these fibres, the tongue of a frog is boiled for a short time in
water. A piece of the mucous membrane is then dissected away,

656 APPENDIX.

and a very small portion of the submucous tissue cut from the
edge of the tongue with a pair of sharp scissors. This is torn
into fragments with very fine needles, and then placed in the
field of a quarter-inch object-glass.. If the tongue is boiled
very long, the fibres become too brittle for separation and
examination. Agi th te

The crustacea, mollusca, and insecta present peculiarities in
the structure of their voluntary muscular fibre which separate
them in a marked manner from the higher divisions of the
vertebrata.

Fig. 349,

lt ff ge fale

aesgecmesnanOM er i
Mienueness Rint *

The involuntary, smooth, or nion-striated muscular fibres,
though appearing like flattened bands (Fig. 850), in reality, ac-
cording to Kélliker, consist of elongated cells. They are found
in various situations, as in the alimentary canal, the large and
small arteries, veins and lymphatics, the
trabecular tissue of the spleen, the uterus,
bladder, and urethra, &c.

“The contractile fibre-cells have been
arranged in three classes :—

1. Short rounded or flattened cells,
somewhat resembling epithelium.

2. Flattened bands, with fringed edges.

3. Long rounded or fusiform fibres,
slightly wavy, and terminating at each
end in a point.

Fra. 350.

Fic. 351.

eT

“The first two varieties are obtained from the bloodvessels.
The last form is met with in the intestinal canal, uterus, &c.
These cells may be readily isolated by macerating small pieces of
the muscular coat of the alimentary canal, &c., in dilute nitric
acid, containing about 20 per cent. of strong acid. By a little

EXAMINATION OF THE RESPIRATORY ORGANS. 657

tearing, with the aid of fine needles, separate cells may be readily
obtained.’” (Fig. 350.)

The sarcolemmais best seen in the long muscular fibres of
the fin of the skate, by tearing them apart with delicate needles
and spreading them out upon a piece of glass. In the heart
the sarcolemma is so thin that it can scarcely be detected. Some
observers doubt its existence (Fig. 351).

EXAMINATION OF THE RESPIRATORY ORGANS.

Healthy Lung.—The mucous membrane of the trachea and
bronchial tubes, and the
parenchymatous — struc- Fig. 352.
ture of the lung may be
readily examined by cut-
ting thin sections with
a very sharp knife,
moistening them with
water and _ spreading
them out upon slips of
glass in the ordinary
manner. To examine
the ciliated epithelium,
and the characteristic
movements of the cilia,
the air-passages should
be scraped and _ the
matters thus obtained
softened with serum in-
stead of water, and de-
posited upon glass. The
ciliary motion is well
displayed in the branchize ected ee eeogt a ree
of the mollusca, ae. te a, epithelium ; Lo seraisuainovic bo aay ranous wall,
oyster. The yellow elas-
tic tissue of the lung is rendered quite distinct by the addition
of acetic acid (Fig. 352).

To examine the vascular tissue, the lung should be injected
with a somewhat thick solution of transparent gelatine. This
oozing through the walls of the vessels, fills and expands the
air-cells so that their forms and arrangement can be easily de-
tected, while the vessels are seen in their natural position, and
apparently deprived of epithelium (Fig. 353).

An excellent idea of the characteristic appearance of the
tracheee of insects, may be obtained by separating with fine
needles the viscera of a fly, placing them on a glass slide, and
adding a few drops of water.

1 Beale. The Microscope, and its application to clinical medicine.
42

658 APPENDIX.

Morbid Lung.—Diseased lung is examined in the manner de-
seribed above. Emphysema-
tous, tuberculous and pneu-
monic lungs present points of
the highest interest to the stu-
dent of pathological histology.

“A small fragment of tole-
rably firm miliary tubercle,
squeezed between glasses with
a drop of water, and examined
under a magnifying power of
250 diameters linear, presents
a number of irregular shaped
bodies, approaching a round,
oval, or triangular form, vary-
ing in their longest diame-
ters from the 1-4000th to the
1-2000th of an inch. These are the so-called tuberele-corpusceles.
They are composed of a distinct wall, containing generally
three or more granules without any distinct nucleus, and are
mixed with numerous granules and molecules, varying in. size
from a point scarcely measurable to the 1-6000th of an inch in

diameter (Fig. 354, a). If we add to these bodies

Fra, 354, a drop of weak acetic acid, all the corpuscles

become more transparent, but are otherwise

unchanged, and many of the granules disap-
pear, as in Fig. 35-4. 6.”

Yellow Sn treated in the same manner
presents similar corpuscles imbedded in a mole-
cular and granular mass (Fig. 855). Sometimes
these corpuscles are observed to be larger and
rounder, resembling in this respect those of
scrofulous pus (Figs. 356, 357). Occasionally tuberculous matter
will be seen to consist almost entirely of granules, and at other
times of very minute molecules.

Arrangement of the Capillaries of the air-cells of
the Human Lung.

Fig. 355, Fie. 356. Fig. 357,

A thin section of the gray, semi-transparent granulation is
very different in appearance from ordinary tubercle. The con-
stituent elements, though more transparent, are less distinct
(Fig. 358). In the cretaceous and calcareous forms of tubercle

EXAMINATION OF THE RESPIRATORY ORGANS. 659

the corpuscles and granules are mixed with gritty saline parti-
cles of an irregular form and size. Crystals of cholesterine are
sometimes found in the cretaceous and cheesy varicties of tuber-
cle (Fig. 859). If no crystals can be detected, a small quantity

Fig. 358. Fig, 359,

Section of gray granulations after addition of acetic acid,
showing air-vesicles filled with tubercles.

of alcohol may be added to a portion of the tuberculous mass,
and then evaporated. As the evaporation proceeds, the crystals
will be formed.

’ Thin sections of calcareous lung present a granular appear-
ance, in consequence of the close aggregation of the minute
earthy particles. Fragments of the calcareous .mass may be
broken off, and examined with the low powers of the micro-
scope, as in the case of opaque objects generally. A drop of
acetic acid added to these fragments causes them to dissolve
with effervescence, showing the presence of carbonate. If this
solution be treated with excess of ammonia, phosphate of lime

Fig. 361. Fie. 362.

will be precipitated; solution of the oxalate of ammonia will
also detect the presence of lime. i

Irregular, black masses of pigmentary matter, consisting of
exceedingly minute molecules, are also frequently found, mixed
with tubercle (Fig. 860), giving the tissues a black or bluish

660 APPENDIX.

tinge. As the tubercle becomes older, the pigmentary matter
generally increases in quantity. It also varies in chemical com-
position according to its situation. That obtained from the
lungs and bronchial glands is pure charcoal and chemically
indestructible; that found in the peritoneum is destroyed by the
action of alcohol and the mineral acids.

Gulliver, Vogel, and Schroeder Van der Kolk affirm, that
nucleated cells may be observed in miliary tubercle; but both
Lebert and Bennett deny it. (Figs. 361, 362.)

It is oftentimes very difficult to distinguish tubercle from
fibrinous exudations and from cancerous growth. “If we are
asked,” writes Prof. Bennett, “to determine what is positively
tubercle, as distinguished from all other morbid products, we
must answer, that deposition which is composed of the peculiar
corpuscles and granules described and figured in the preceding
pages. From pus-corpuscles they are readily distinguished by
the action of acetic acid, which in them causes no granular
nucleus to appear. From plastic corpuscles they may be sepa-
rated by their irregular form, smaller size, and the absence of
primitive filaments. With the granular corpuscle they can
scarcely ever be confounded, on account of its large size, brown-
ish or blackish color, and nucleated or granular structure. The
cells of cancer are large, transparent, and distinctly nucleated,
and, consequently, easily distinguished from the small, non-
nucleated corpuscles of tubercle.” “The only other structure
likely to be confounded with tubercle is the reticulum of cancer,
which not only presents a yellowish appearance closely resem-
bling it, but is composed of nuclei and molecular matter result-
ing from the disintegration of cancer-cells. But, as this reticu-
lum is always associated with cancerous formation, it may at
once be distinguished by the cell-elements which accompany it.
It should further be noticed that every form of exudation, at a
certain period, presents a molecular and granular structure
throughout, and that then it becomes impossible to determine
its nature, unless it be associated with the more characteristic

Fia. 363. Fig. 364. Fia. 365, Fig. 366.
A B *
Ese
ae, ee).
Ws a OW
“089 (S15)

Fig. 363, a, Tubercle corpuscle from lung; 8, Pus corpuscles. Fig. 364. Plastic, or pyoid cor-
puseles. Fig.365. Granular corpuscles from cerebral softening. Fig 366, Corpuscles in reticulum
of cancer.

elements ‘distinctive of the simple, tubercular, or cancerous
exudations.” The accompanying figures will illustrate these
distinctions. (Figs. 363, 364, 865, 366.)

EXAMINATION OF THE RESPIRATORY ORGANS. 661

Where a cavity is found in the lung, separate examinations
should be made of its contents, the surface of the walls, and the
subjacent tissue.

In emphysema of the lungs, the investing membrane will be
often found full of very small holes; the vessels elongated, and
the interspaces much enlarged; and the yellow elastic fibres
stretched to such an extent as to be deprived of their elasticity.

In the first stage of pneumonia, the vesicular walls contain
here and there collections of minute granules. The epithelial
cells are separated from the basement membrane; and while the
nuclei are unaltered, the cell-
contents have become a little Fig, 367,
more granular. The minute
capillaries are very much
‘congested. As the engorge-
ment proceeds, granules col-
lect in greater quantities in
the air-cells; while in the
effused serum may be detect-
ed distinct blood-corpuscles,
small nucleated cells, and
exudation-corpuscles. These
changes are shown in Fig.
367.

In the second or stage of
red hepatization, the cavity
of the air-vesicle is filled with
cells about 0-018 of a milli-
metre in size, of very varied

Fic. 368, Fig. 369.

a

their contents. These are mixed with concrete albumen, oil-
granules, and free fat. (Figs. 368, 369.)

In the third stage—that of gray hepatization—large well-
marked cells may be seen, containing granules and oil. Most

662 APPENDIX.

of these cells are without nuclei. Occasionally they are found
associated with large masses of pus-cells. The epithelium is
wanting, and free fat-molecules and globules are abundant. (Fig.
370.) P

Fia, 370.

EXAMINATION OF THE GLANDULAR SYSTEM.

Liver.—The relation to each other of the constituent elements of
the liver, may be easily de-
Fia. 371. monstrated upon thin sections
eut out of the fresh liver of
a pig, with a Valentin’s
knife. The arrangement of
the minute vessels are best
seen in the injected liver of
a frog. The larger vessels
can be studied in thin sec-
tions, from which the cells
have been washed away by a
stream of water, and dilute
caustic soda afterwards ap-
plied. Excellent illustrative
specimens of the vessels may
be obtained, by injecting the
: y : ; liver of some of the lower
liver, highly magnified, and presenting to view . q
the reticulated structure of the biliary tubes. In animals, as the frog, with two
the centre of the figure is Sat aed nas vein different colors ; throwing one
cu eres and several anal banehes MIM into the portal vein, and the
run freely, it is seen standing in dots along the other into the hepaticartery or
course of the vessels. At the periphery are vein, so that the two shall meet
seen branches of the hepatic artery, vena por- . es : %
tarum, and hepatic duct.—After Leidy. in the capillaries. (Fig. 371.)
The hepatic cells lie in the

1 See a valuable paper by Dr. Da Costa, of Philadelphia, on the Pathological Anatomy
of Acute Pneumonia, in Amer. Journ. of Med. Sciences, Oct. 1855.

Transverse section of a lobule of the human

EXAMINATION OF THE GLANDULAR SYSTEM. 663

matrix or network formed by the union of the vascular and the
condensed cellular tissues. They are of different sizes, though
generally very small, and contain a few oil-globules. They may
be obtained by scraping a freshly-cut surface; placed upon a slip
of glass and moistened with a few drops of water, they are ready
for examination. These cells undergo various changes in disease.
Sometimes they are withered and shrunk; sometimes filled with
pale granules, as in diabetic cases, and at others, gorged with fat
to such an extent as to obliterate the cell-walls, and give to the
liver the appearance of ordinary adipose tissue. (Fig. 372.)

Fig. 372.

oe

Kidney.—The general arrangement of the straight and con-
voluted tubes, and the varying appearance of their epithelium,
may be well shown upon thin sec-
tions cut out of the cortical and Fig. 373,
medullary portions of the kidney,
by means of a Valentin’s knife.
By scraping the freshly-cut sur-
face, epithelial cells may be ob-
tained, mixed, however, with Mal-
pighian tufts and fragments of
tubes. (Fig. 873.) In the convo-
luted tubes the epithelium is thick
and glandular; in the straight
it presents a scaly appearance.
Care must be taken not to con-
found the tubes, as they bend
in and out through the matrix,
with circumscribed cysts. The §
kidney of the mouse and of many a, Portion of uriniferous tube lined by epithe-
of the other rodentia, are better lium. B, Epithelial cells, highly magnified. c,

. Portion of tube from medullary substance, de-
adapted for demonstrating the prived of epithelium.
matrix than the human kidney. '
Indeed, its existence in the latter has been doubted by some, not-

664 APPENDIX.

withstanding that Goodsir, Killiker, and Johnson have described
and figured it. “With care,” says Mr. Beale, “I believe it may
always be demonstrated in the healthy human kidney; and in
some specimens of fatty kidney, as well as in the small con-
tracted kidney of chronic nephritis, it may very readily be seen
by washing a thin section with a stream of water, in order to
remove the epithelium and remaining portion of the tubes. The
matrix appears to consist of very fine fibres, amongst which no
indications of the yellow element can be detected. By the ad-
dition of acetic acid it becomes more transparent, and a few
granules are developed, but no other change is produced.”

In the uriniferous tubes of the frog and newt, ciliary motion
is beautifully shown. The arrangement of the vessels of the
Malpighian tufts can be studied with facility and success in the
large tufts of the kidney of the horse.

Sections of kidney are best kept in large thin glass-cells con-
taining a solution of creasote or weak spirit and water. .

Morbid Kidney.—In disease the kidney oftentimes becomes
quite opaque. This condition may result from a variety of
causes; as, hypertrophy of the matrix, deposition of fatty matter,
and unusual accumulation of epithelium or oil-globules in the
tubes. To examine such a kidney, therefore, the sections should:
be exceedingly thin. The matrix and the vessels, which are often
much thickened in chronic nephritis, should be prepared for
examination by the addition of acetic acid, or dilute caustic
soda, and subsequent washing with clear water to remove the
epithelium and granular matter from the tubes.

Salivary Glands.—To examine the structure of the salivary
glands, thin sections of the fresh gland should be treated first
with acetic acid, and then with caustic soda in excess. The
epithelium of the ultimate lobules is rendered distinct by soaking
the section in acetic acid. In the ducts, large cells filled with
oil-globules may sometimes be detected.

Thymus and Thyroid Glands.—Sections of the recent glands
should, before being submitted to examination, be washed with
water to clean away the soft and pulpy portions, which are apt
to obscure the structure of the tissues. The relation of the lobules
and other constituents is best shown in sections hardened with
chromic acid; though it must be borne in mind that this process
alters the natural appearance of the cellular tissue. The mem-
branous thyroid gland of small animals is well adapted for micro-
scopic examination.

Adipose Tissue.-—To examine adipose tissue, small masses of
fat-cells may be taken from the subcutaneous areolar tissue, and
exposed to reflected light under a low power; or thin sections,
moistened with water, may be placed between two pieces of glass,
and examined by means of transmitted light. The arrangement
of vessels can only be demonstrated upon an injected prepara-
tion. Small acicular crystals, of margarie acid and margarine,

VASCULAR AND ABSORBENT SYSTEMS. 665

disposed in a stellate (Fig. 374, a) form, are sometimes observed,
especially in specimens obtained from

emaciated subjects." In disease, the fat- Fie. 374.

cells are sometimes found degenerated, E
and containing a serous fluid, in which
the nucleus is quite distinctly seen,
amidst numerous granules. Sometimes jf
the cell is shrivelled and irregular in
form; frequently it assumes an angular
shape.

Fatty degeneration consists in the con-
version of healthy structures into true
adipose tissue. The muscular system
seems to be most liable to this change.
Prior to the appearance of fatty degeneration in voluntary muscle,
the transverse strie disappear. According to Mr. Quekett, the
first trace of this disease is marked by a disturbance of the par-
ticles of myoline, which appear as so many very minute granules
scattered irregularly within the sarcolemma, leading one to sup-
pose that the delicate cell around each particle had given way,
thereby allowing the myoline to escape, and destroying all regu-
larity both of the transverse and longitudinal markings. As the
disease progresses, the myoline is replaced by minute highly-
oar globules of oil, until at last the whole sheath is full of
them.'

The muscular fibres of the heart, and especially those of the
musculi pectinati, afford frequent instances of the change in
question. Muscles which have been long disused, as in cases of
paralysis, club foot, &c., exhibit this species of degeneration in a
striking degree. ‘Fatty degeneration appears also to occur in
osseous tissues, and indeed the disease termed Mollities ossium is
of this nature. All bones so affected have thin walls, are always
more or less soft, and contain an abundance of oil. I have
examined the bones in several cases, and found that the disease
first commences in the bone-cells, the cell itself becoming larger
and larger, its canaliculi disappearing, and several of these cells
uniting to form a cavity, in which oil-globules soon make their
appearance, all the parts of the bone in the neighborhood of the
cells becoming at the same time thin and transparent from the
removal of the granules of earthy matter.” (Quekett.) In the
Lancet, for 1850, the student will find an interesting paper, by
Mr. Canton, on the Arcus Senilis, produced by fatty degenera-
tion of the cornea. In fatty degeneration of the kidney, the
epithelial cells become filled with numerous oil-globules, to such
an extent sometimes as to burst and be discharged in fragments,
leaving the surface of the tubules in some places almost bare.

' Lectures on Histology.

666 APPENDIX.

EXAMINATION OF THE VASCULAR AND ABSORBENT SYSTEMS.

Vessels.—The examination of the minute vessels requires but
little previous preparation. A piece of the pia mater, or the mesen-
tery of a young child, or a small artery from which the cerebral
neurine has been gently washed, may be placed for this purpose
under the microscope. The epithelial cells of the lining mem-
brane, and the contractile fibre-cells may be rendered distinct by
the addition of acetic acid. To demonstrate the fibre-cells of
the contractile coat, Dr. Beale recommends that an artery of
moderate size, and not quite fresh, be slit up, and its lining
membrane removed by careful scraping; the subjacent elastic
tissue is then to be removed and torn to pieces with fine needles,

and finally placed upon a glass slide and

Fig. 375. moistened with a few drops of water.

The spindle-shaped or muscular fibre-

cells are readily obtained from the renal
veins.

It is highly important that the student
should make himself well acquainted
with the healthy appearance of the mi-
nute arteries of the brain, since they suf-
fer remarkable changes in disease. In
white softening of the brain, they un-
dergo a sort of fatty degeneration, nu-
merous minute oil-globules being aggre-
. gated together at short intervals along

’ their walls. These oily masses are readily
detected by their high refracting power.
(Fig. 875.)

The vessels of the kidney are also,
from the changes they suffer in disease, worthy of especial inves-
tigation. To prepare them for examination it is only necessary
to wash out from a thin section the epithelium of the renal tubes,
and add a few drops of acetic acid to render them more distinct.
.The distinct arrangement of the nuclei of the circular and longi-
tudinal fibres, and the greater thickness of their walls, will serve
to distinguish the arteries from the veins. The coats of the
latter are very thin.

Thickening of the arterial coats of the corpora Malpighiana
is well seen, according to Dr. Johnson, in the small, contracted
drunkard’s kidney.’ The normal thickness of the Malpighian
artery is about one-fifth or one-sixth the diameter of the vessel ;
in this disease it is increased to one-third.

Some observers have thought that they detected epithelial cells
upon the external surface of the Malpighian vessels; but the
researches of Mr. Bowman negative this opinion.

' Diseases of the Kidneys.

SKIN, MUCOUS AND SEROUS MEMBRANES, 667

Plates and rings of bones, and atheromatous deposits, contain-
ing oil-globules, granules, and crystals of cholesterine, are all

Fie. 376, Fig. 377.

sometimes found in the larger ves-
sels. (Fig. 376, 377.)

Lymphaties.—It is very difficult to
examine the minute structure of the
lymphatic glands. The fluid which
exudes from a freshly cut surface
may be examined by mixing it with
water and placing it between two
pieces of glass. It is very important
to distinguish between lymphatic cells on the one hand, and pus-
globules and white corpuscles of the blood on the other ; not
only as regards their appearance, but also in relation to the dif-
ferent effects produced by reagents.

EXAMINATION OF THE SKIN, MUCOUS AND SEROUS
MEMBRANES, ETC.

Skin.—A good-view of all the structures composing the skin
may be obtained by making a vertical section. In this manner
the relation of the various layers, the arrangement of the hair-
bulbs and sebaceous follicles, and the position and course of the
sweat-ducts, may all be demonstrated.

The following method of procedure is recorded by Dr. Beale,
as quoted from Giraldis by Kolliker:

“The skin should be perfectly fresh, and a piece about two
inches square, or rather less, is to be stretched with the outer
surface downwards upon a thick deal board by means of numerous
pins. If the sudoriferous glands are to be included in the pre-
paration care must be taken to leave sufficient of the cellular
tissue adhering to the skin. The piece of skin is allowed to dry
by exposure to the air. Several small pieces taken from various
parts of the body may be pinned out on the same board, care
being taken to attach a label to each. Specimens may be taken
from the scalp, eyelids, chin, mamma, axilla, arm or leg, palm of
the hand, tips of the fingers, scrotum, and sole of the foot. With
these, the varying thickness of the epidermis and other peculiari-
ties in the different regions may be demonstrated.

668 APPENDIX.

“The portion of skin being quite dry, it is to be removed from
the board, and, after cutting off the edge, several thin sections
may be made by the aid of a very sharp knife through the whole
thickness. In order to obtain a good specimen of the spiral por-
tion of the sweat-ducts, the skin of the heel should be selected,
and the section should be made parallel with the furrows, and in
a slightly slanting direction, instead of at a right angle with the
surface.

“The sections may next be placed in a watch-glass, with a few
drops of clean water, and in the course of a short time it will be
found that they have again attained the original thickness of the
skin, in consequence of the absorption of water. They may now
be submitted to examination, and after selecting a satisfactory
specimen, it may be mounted in weak spirit and water, Goadby’s
solution, or other preservative fluid; or, the specimen may be
washed in water, placed upon a slide, and allowed to dry slowly
by spontaneous evaporation (when it will be found to have ad-
hered tightly to the glass), and mounted in Canada balsam, with
the usual precautions.”

Any opacity of the preparation may be removed by a weak
solution of potash or caustic soda. Soaking in ether will dis-
sipate the fat. The sweat-glands are made more distinct by
soaking the tissue in a mixture of one part of nitric acid and two
of water.

Large flakes of cuticle may be obtained for examination by ex-
posing a small piece of skin to a moist atmosphere for several
days. The superficial cells of the cuticle are brought into view
by scraping the surface of the skin with a knife. These cells are
flattened and adherent, and present a scaly appearance. The
deeper-seated epidermic cells are more or less round, and appear
to rest upon a layer of very minute granules mixed with coloring
matter. The deep cells are soluble in acetic acid ; the superficial
are not. On the under surface of the cuticle are found a number
of depressions, which receive the tactile papille of the cutis vera.

The papille may be studied either upon a vertical section
made in the manner above described, or upon a section of the
cutis itself, the cuticle having been first removed. From their
large size, the papille of the skin of the dog’s foot are well
adapted for examination. The papillary vessels are best seen in
an injected specimen, while the nerves and “axis-corpuscles”’ are
sometimes brought into view by the addition of acetic acid or a
weak solution of caustic soda.

The pigmentary cells are best seen in the skin of the negro, in
that of some of the lower animals, and also in freckled surfaces.

Cutaneous Eruptions, Growths, Ulcers, §-e.—Corns, callosities,
and condylomatous warts consist of condensed epidermic scales.
In Veruca achrocordon, the scales are collected around a central
canal supplied with bloodvessels. Small cutaneous tumors are
sometimes formed by the thickening of the subjacent areolar

SKIN, MUCOUS AND SEROUS MEMBRANES. 669

tissue. This appears to be the case in elephantiasis, where the
hypertrophy is increased by the effusion of plastic lymph into
the areole and its subsequent organization.

The squamous eruptions of the skin,—ichthyosis, pityriasis,
psoriasis,—all consist of collections of epidermic scales. In
pityriasis they.are placed loosely together ; in psoriasis they are
more aggregated ; and in ichthyosis very much condensed.

A number of epidermic scales,
arranged into the form of a capsule, Fig. 378.
constitute a favous crust. This cap-
sule is lined by a mass of very fine
granules, from which sprout crypto-
gamic plants in the greatest abun-
dance.

Upon healthy granulating sur-
faces may be seen pus-corpuscles,
fibre-cells in various stages of deve-
lopment, and newly-formed fibres.
(Fig. 378.) In scrofulous and un-
healthy sores, the broken-down pus
bears some resemblance to tubercle-corpuscles. The epithelial
ulcer or cancer, as it is commonly, but erro-
neously called, generally commences on the Eipe ote.
lip as a small induration or wart, which soon ———
softens in the centre, while the hardened
edges extend over the cheek and chin. This ;
softened matter consists of epithelial and fibre Fibrous tissue formed from
or fibro-plastic cells. (Fig. 381.) Sometimes any
the cells are large and flat, and contain numerous fat-molecules
and granules. (Fig. 880.) According to Bennett, the so-called

Fig. 381.

Fig. 380. Altered epithelial cells, from ulcer of lip. Fig. 881. Epithelial and fibre-cells, from
ulcer of lip.
chimney-sweeps’ cancer of the scrotum is essentially a similar
formation, consisting externally of flattened epithelial scales
passing into fibres; and, deeper-seated, either groups of younger

670 APPENDIX.

cells, or concentric layers of aggregated scales. The distinctions
between these growths and true cancer will be pointed out here-
after.

Mucous Membrane.—The submucous areolar tissue may be exa-
mined upon a small piece cut from the under surface of the mu-
cous membrane, and torn up with needles. Between the proper
muscular coat of the small intestine and the basement-membrane,
and in close apposition with the latter, Brucke has demonstrated a
thin layer of pale muscular fibres, which is known as the muscu-
lar layer of the mucous coat. The contractile fibre-cells of this
coat are disposed in circular and longitudinal directions. The
villi are best seen in a vertical section of the membrane. By
washing off the epithelium, and adding a solution of acetic and
nitric acid, eomposed of about one part of acid to four of water, the
muscular fibres of the villi will be brought into view. The villi
situated around intestinal ulcers are often found to be very much
elongated. In the examination of such ulcers it is important in
all cases to ascertain if the muscular coat has suffered from the
ulcerative action or not. The presence or absence of non-striated
fibres in the base of the ulcer will determine this point.

Serous and Synovial Membranes.—Serous membranes consist
mainly of condensed areolar tissue, containing an abundance of
yellow elastic fibres. At the surface this areolar tissue is very
dense; the deeper layers are less dense, and often contain fat-
cells. Portions of recent membrane are generally necessary to
demonstrate the delicate surface-cells. The fibres of the sub-
basement tissue, and often the vessels and nerves, are well seen
in the peritoneum of the mouse and other small animals. The
vessels of the synovial membranes should be injected before exa-
mination. In an injected specimen, the distribution of the vessels
in the fringe-like processes which dip down into the joint, is dis-
played to great advantage. In some cases of disease, as in ascites,
and pleurisy of long standing, great alterations take place in the
structure of the serous membrane, such as the deposition of a
thick cellular layer over the whole surface. Cells of a similar
character are also found in the fluid contained in the cavity.

Epithelium.—Kpithelium may be obtained for examination by
scraping a mucous or serous surface with a sharp knife. It
should then be placed upon a slip of glass, and moistened with
water. Very delicate cells should be treated with serum, syrup,
or a mixture of glycerine and water, in preference to pure water,
as the rapidity of endosmose is checked, and the liability to rup-
ture diminished. Acetic and nitric acids, tincture of iodine, and
solutions of potash and soda of different strengths, are the most
useful reagents in examining epithelium. Various kinds of .
epithelium are described by histologists.

Scaly epithelium may be procured from the vagina, the mouth,
&e.; a modified form exists in the epidermis, in nails, and in
hair. The vaginal epithelium consists of large, flat, ragged, and

EXAMINATION OF THE EYE. 671

very irregular cells, folded over each other, and perhaps creased
in different directions. The epithelial cells of the mouth have
very distinct nuclei, which are made to disappear under the
action of acetic acid.

Tessellated or pavement epithelium is beautifully shown in the
epidermis of the frog. It may be examined upon the choroid
coat of the eye, the lining membrane of the heart, arteries, veins,
and pelvis of the kidney, and upon serous surfaces generally.

Glandular or spheroidal epithelium consists of round cells,
which occasionally become polyhedral from mutual pressure.
The nucleus is usually well marked, and sometimes seems to be
surrounded with numerous minute granules and oil-globules.
This variety of epithelium is well shown in the sweat-glands, in
the convoluted tubes of the kidney, in the follicles of the sto-
mach, pancreas, liver, &c.

Columnar, prismatic, or cylindrical epithelium, may be obtained
from the gall-bladder, the ureters, the urethra, the intestinal
villi, and the follicles of Lieberkihn.

Ciliated epithelium is found in the human body in the follow-
ing situations:—On the surface of the ventricles of the brain,
and on the choroid plexuses; on the mucous membrane of the
nose and its sinuses; on the upper and posterior part of the soft
palate, and in the Eustachian tube; in the cavity of the tympa-
num ; on the membrane lining the frontal and sphenoidal sinuses;
on the inner surface of the lachrymal sac and lachrymal canal;
on the mucous membrane of the larynx, trachea, and bronchial
tubes; upon the os uteri; within the cavity of the uterus; through-
out the whole length of the Fallopian tubes, and upon their fim-
briated extremities (Beale).

For examination, this variety of epithelium may be obtained
from the back part of a frog’s mouth, or from the branchie of
an oyster or mussel.

EXAMINATION OF THE EYE.

The cornea is examined by dividing the ball transversely with
a sharp knife, washing the anterior half, and removing the ciliary
processes. Itis then pinned out flat and allowed to dry; thin
sections are next made with very fine scissors; these sections are
moistened with water, and finally treated with acetic acid, in
order to render the structures distinct.

The elements composing the retina are most satisfactorily
examined in microscopic sections made at right angles to the
surface of the membrane, after maceration in dilute solution of
chromic acid. Viewed in this manner, according to Prof. Good-
sir, it exhibits from the peripheral to the central margin of a
successful section a series of strata, which may be distinguished
‘as the bacillary, white cellular, gray cellular, filamentary, and
limitary layers.

672 7 APPENDIX.

There are several methods of preparing the crystalline lens for
examination. Minute portions of the recent lens may be mois-
tened with water and placed under the microscope. The lens
may be hardened in chromic acid, or soaked in oil for some time,
and thick sections then made. To examine the fibres of the
lens, the latter should be boiled, and the fibres torn off and sepa-
rated with needles. In cases of cataract, the soft, pulpy, exter-
nal portion of the lens will be seen to contain numerous oil-
globules, consisting, according to Beale, chiefly of cholesterine
dissolved in an oily fat. Larger globules of a different character
are also observed.

EXAMINATION OF THE HARD TISSUES.

Bone.—For the methods of cutting, grinding, and polishing
thin sections of the hard tissues, the student is referred to the
more elaborate works on the application of the microscope to
clinical medicine, and to the chapter on this subject, in the pre-
ceding pages, by the author.

A thin section of bone, viewed by transmitted light and with
a low power, presents numerous round or oval apertures. These
are the orifices of the Haversian canals. In the flat bones these
canals are radiating and parallel to the surfaces; in the long
bones, they are parallel to the axis. They communicate with
each other by transverse and oblique branches, and vary in size
from about 1-1000 to 1-200”.

Under a higher power (200) the lacune, bone-corpuscles, or
bone-cells, and the canaliculi or calcigerous canals, become visi-
ble, appearing like a number of dark spots with delicate lines
radiating from their sides. Their dark appearance,is due to the
contained air, which is readily dissipated by immersion in oil of
turpentine. They are oblong and flattened, and vary exceed-
ingly in size.

The laminated structure of the cartilage or osseous basis of
bone is best seen by previously digesting sections in hydrochloric
acid diluted with water (one part to twenty), in order to remove
the inorganic matter. The lamine have a fibrous appearance,
and are arranged either parallel to the surfaces of the bone, or in
concentric layers around the Haversian canals.

The nuclei of cartilage-cells may be rendered very distinct by
boiling the cartilage for two or three minutes in water or a solu-
tion of caustic soda.

The different steps in the development ot bone may be very
well studied upon the long bones of young animals, and also
upon the ossifying bones of the cranium.

Thin sections of bone may be preserved in the dry state ;
thick specimens should be mounted in thickened Canada bal-
sam. Sections of cartilage are best kept in weak spirits of wine,
or in weak solutions of creasote.

Teeth. Owing to the great hardness and brittleness of the

EXAMINATION OF THE HARD TISSUES. 673

enamel, and its tendency to chip off, considerable difficulty is
experienced in obtaining sections of teeth for examination. Sec-
tions having been obtained, they may be moistened with water,
turpentine, and Canada balsam, and examined by transmitted
light with low powers. A tooth that has been macerated in strong
acid for several days can be very readily cut in any direction.

The dentinal tubules are microscopic canals, pursuing a waving
and anastomosing course through the whole thickness of the
dentine, from the wall of the pulp-cavity to the cement and
enamel. According to Kélliker, each canal has a special wall,
rather less in thickness than its diameter, which can only be ob-
served in transverse sections, as a narrow yellowish ring sur-
rounding the cavity; in longitudinal sections, on the other hand,
it is almost entirely invisible. These tubules may be isolated
from each other by long maceration in acid, and subsequent
soaking in dilute caustic soda or potash.

The enamel consists of hexagonal or pentagonal prisms, one
extremity of which is attached to Nasmyth’s membrane, the
other to the dentine. These prisms are very closely united,
having no intervening substance between them.

The development of the teeth may be studied in the lower
animals, or in human embryos at different ages.

Nails.—By maceration in water the nail may be separated from
the skin and thin sections made by means of a sharp knife.

A nail consists of two layers, the upper or horny one forming
the true nail, and marked with ridges on its lower surface, while
the under soft one is continuous with the rete mucosum of the
skin, from whieh it differs by the cells being elongated and ar-
ranged perpendicularly. The horny layer is composed of flat-
tened epidermic cells aggregated into lamine. The addition of
caustic potash or soda in solution causes the nuclei to be de-
veloped.

Hair.—A. white hair is best adapted for demonstrating the
intimate structure of the shaft and other parts. For this purpose,
solutions of soda and potash and strong sulphuric and acetic
acids are found to be the most useful reagents.

The cortex, which constitutes a large part of the shaft, presents
upon its surface a great number of longitudinal striz or inter-
rupted dark lines and dots. Upon treating it with sulphuric
acid at a gentle heat, as recommended by Kolliker, it 1s first
changed into plates and fibres, varying in length and breadth,
and afterwards converted into elliptical or spindle-shaped cells,
which become flattened and angular from pressure. These cells
contain elongated, dark-looking nuclei and pigment-granules, to
which the color of the hair is due. The addition of caustic pot-
ash or soda will isolate these pigment-granules, and sometimes
cause them to exhibit molecular motion. The presence of small
spaces containing air, and the unequal refraction of light by dif-

43

674 APPENDIX.

ferent parts of the cells, give a striated or dotted appearance to
the shaft.

The medulla consists of numerous angular or rounded cells,
containing granules or globules of fat, and arranged in one or
more linear series.

The cells of the cuticular coat are somewhat flattened, and
quadrangular in form, the margins are black, and they are with-
out a nucleus.

The fibrous layer of the hair-follicle consists of an outer mem-
brane composed of areolar tissue, having longitudinal fibres, with
long, spindle-shaped nuclei, and an inner delicate membrane,
consisting of transverse fibres, with long and narrow nuclei. The
pulp of the hair consists of fibrous areolar tissue, containing
nuclei and granules of fat, but no cells.

EXAMINATION OF MORBID GROWTHS.

Morbid growths are of common occurrence, and are found
growing in different parts of the body; externally upon the
surface, and internally in the solid parenchyma of the viscera.

Sometimes these growths, as in the case of fatty and certain
fibrous tumors, bony exostoses, &c., consist of a simple hyper-
trophy or rapid development of the tissues of the part in which
they are located; very frequently, again, they are highly complex
in structure, and differ more or less from the surrounding tissues.
It is exceedingly difficult to classify them, even for the purposes
of study, since the microscopic characters of one run into and
blend almost imperceptibly with those of another. Thus the
so-called benign tumors present various shades of transition into
the malignant forms. It will be seen, therefore, that the varie-
ties of these growths are numerous.

Sometimes the cutaneous epithelium undergoes an unusual
development, constituting warts. The subcutaneous areolar tissue
of the foot, leg, scrotum, and other parts, may be hypertrophied
to such an extent as to occasion the most serious results.

In making an examination of morbid growths, ‘the secretion,
if such exists on the surface of the tumor, should be first sepa-
rately examined: secondly, the microscopical characters of the
juice which exudes from the freshly-cut surface should be ascer-
tained; and, lastly, a thin section ought to be made, in order to
determine the relation of the constituents of the tumor to each
other, and especially the proportions in which the different ele-
ments are present. Its connection with surrounding structures
may be seen by examining a thin section, which should include
a portion of the adjacent texture; and these observations should
be made first with low powers, and afterwards with a power of
about two hundred diameters.” (Beale.)

The arrangement and direction of fibres; the form, size, and
contents of cells; the presence or absence of nuclei, granules,

EXAMINATION OF MORBID GROWTHS. 675

&e., and the effects of different reagents, should be carefully
observed, and noted in a book kept for that purpose.

Cancer and Cancroid Growths.—“ Cancer, or carcinoma, is a
vascular, morbid production, characterized by a form of organic
cell, which is peculiar, and never enters as a constituent in any
normal tissue. It is usually deposited in the form of tumors,
but occasionally as an infiltration, in any of the organs of the
body, and the circumstances which give rise to its development
are yet unknown to us.

There are several varieties of cancer, and the physical ele-
ments which ordinarily enter into their composition are as
follow:

1. The characteristic cancer-cells, which are spherical, ovoid,
irregularly polyhedral, and frequently exhibit caudate prolonga-
tions. They average about the ‘02 mil. in diameter, and possess
finely granular contents, with a round or oval nucleolated nu-
cleus, as large or-larger than a pus-corpuscle. Sometimes can-
cer-cells are double the ordinary size, or more, and not unfre-
quently contain several nuclei, or even other cells, constituting
parent or endogenous cells.

2. Nuclei, which are spheroid or oval, and resemble those
within cancer-cells.

3. Granules, and amorphous liquid or semi-solid matter.

4, Fusiform or fibro-plastic cells. These are liable to be con-
founded with the characteristic cancer-cell, but usually may be
distinguished by the smaller nucleus, and the disposition to
elongate at opposite extremities, and pass from this condition
into the form of bands or fibres.

5. Fibrous tissue; most usually of the white variety, but not
unfrequently mingled with elastic fibres.

6. Black pigment, in granules, or contained within cells.

7. Fat, in granules, globules, and in the form of adipose cells.

8. Vessels.

The varieties of cancer are encephaloid, or medullary carci-
noma, scirrhus, colloid, melanosis, and fungus heematodes.

Encephaloid is that form in which the cancer-cell predominates
over every other constituent. Occasionally, the cancer-cells
exist in it to the exclusion of all other matters, except liquid,
granules, and vessels. ;

In scirrhus, fibrous matter predominates, and encloses the
cancer-cells within the areole.

Colloid is composed of a fibrous stroma, with loculi, filled with
a gelatinoid matter and cancer-cells.

Melanotic cancer consists of any of the preceding forms, com-
bined with black pigment.

Fungus hematodes is a term applied to an unusually vascular
form of cancer, or to any of the other varieties when they are
ulcerated and liable to bleed.’

1 Prof. J. Leidy, in Gluge’s Atlas of Histological Pathology, Amer. Ed. p. 69.

676 APPENDIX.

The cancer-cells may be demonstrated in the thick, opaque juice
which exudes from the freshly-cut surface of a cancerous tumor,
while the relation of the constituent elements of the mass are
best shown upon a thin section, made with a Valentin’s knife.
The fluid portions containing the cells will be found, in the are-
ole or interspaces formed by the crossing of the fibres. Both the
fibres and cells vary much in appearance in different specimens.
Sometimes the cells are round, sometimes elongated into fibres,
and occasionally they present very irregular forms. The nuclei
also differ considerably in numbers and size.

Dr. Walshe divides cancerous tumors into three varieties,
according as the viscous juice, fibrous, or cellular elements pre-
dominate.

Very great difficulty is often experienced in arriving at an
accurate opinion as to the cancerous or non-cancerous nature of
a tumor; because there is no single element which can be re-
garded as pathognomonic of true cancer. “ Neither the cha-
racter of the cells,” says Dr. Beale, “nor the nature of the
matrix, nor the arrangement of the elementary constituents, can
separately determine the point, and it is only by carefully noting
the collective appearances observed upon a microscopic exami-
nation that we shall be enabled to decide.”

Enchondroma, epithelioma, certain fibrous tumors containing
spindle-shaped cells, &c., resemble true cancer so strongly that
they have been called cancroid growths. For the peculiarities
of each of these varieties of tumor, the student is referred to
the works of Lebert, Bennett, Walshe, and other writers upon
this subject. In the following table, taken from Dr. Lionel
Beale’s work on the medical applications of the microscope, will
be found enumerated the most important characters which dis-
tinguish the true cancer-cells from those of cancroid tumors.

Cancerous. Caneroid.

Cells not connected with the matrix Cells connected with the matrix, often

in a regular manner, or forming lamine.

Cells differing much from each other
in size and form.

Cells readily separable from each other.

Cells not connected together at their
margins, their edges seldom forming
straicht lines.

Cells containing several smaller cells
in their interior often met with.

Nuclei varying much in size and num-
ber in different cells.

Juice scraped from the cut surface
containing many cells floating freely in
the fluid, and not connected with each
other.

forming distinct lamine.

Cells resembling each other in size
and general outline.

Cells often cohering by their edges,
which generally form straight lines, three
or four cells being frequently found
united together.

Cells usually containing one nucleus.

Nuclei not varying much in size in
different cells.

Juice scraped from the cut surface,
containing small collections of cells.
which are often connected with each
other.

Dr. Donaldson! asserts positively that true cancer can be dis-

} American Journal of Medical Sciences, January, 1853.

EXAMINATION OF MORBID GROWTHS. 6TT

tinguished from all other tissue, normal or pathological, by cer-
tain clear and well-defined elements. If we ‘compare the
physical characters of cancer with those of the simple tissues,
such as the muscular, areolar, dartoric, osseous, &c., or with
those of the compound, as the glandular, the synovial, the mu-
cous, &c., the difference will be very apparent. Its greater or
less firmness, its homogeneous fibrous aspect, with its lactescent
infiltrated juice, are very characteristic. The presence of this
peculiar fluid is, of itself, a point of differential diagnosis of great
value; the microscope always detecting in it, when found, the
presence of cancer-cells, &c. No matter what organ is the seat
of the disease, this fluid can generally be scraped from the cut
surface, or squeezed out by gentle pressure. It is particularly
abundant in encephaloid, and frequently
oozes out in drops, having a white cloudy Fig. 382.
appearance, of the consistence of cream,
and very much of its color, being slightly
tinged with yellow. It may sometimes,
on superficial inspection, be confounded
with light-colored pus, which has, how-
ever, with the yellow, a slightly greenish
tinge. If, from the conditions of its for-
mation, there can be any doubt, an appeal
to the microscope will at once settle it by
giving us the characteristic pus-globule”’
(Figs. 382, 383). Pus-Corpuscles.
“The element of cancer consists of three
parts, cell, nucleus, and nucleolus, all of which are peculiar to it.
“Tn all the varieties of cancerous tissue, nuclei are to be found
either enveloped by a cell, or floating free, generally more or less
of both; in some specimens there exist a large number of free
nuclei with only an occasional cell. The form and appearance
of these nuclei are the most constant and unvarying of all cancer
elements. They are (Fig. 384, a) ovoid, or more or less round ; the
latter are found more particularly when the eye or the lymphatic
glands are the organs diseased. Sometimes (as in 6) we find
little pieces of the wall of the nuclei apparently nicked out, but
evidently it is purely accidental, and the proper shape can easily
be recognized. They have, ordinarily, in width, a diameter ot
from 1-100th of a millimetre, or (a millimetre being equal to
039th of an inch) of -0039th of an inch to 1-66th of a millimetre ;
in one instance we met with one as wide as 1-38th of a milli-
metre; in length they measure from 1-133d to 1-100th of a milli-
metre. Their contour is dark and well defined, with the interior
containing very minute dark granulations; indeed, when the
specimen is perfectly fresh, they have a homogeneous aspect, the
granulations being so small as to give the appearance of a mere
shading (Fig. 384, ); if the specimen is kept a day or two we find

678 APPENDIX.

the interior filling up with large granulations (asin d). Within
these nuclei, when they have not been obscured by granular or
fatty degeneration, there is found, habitually, a small body, or
nucleolus, averaging in diameter about 1-500th of a millimetre.

Fig. 383. Fig. 384,

Pus-corpuscles after acetic acid. Free cancer nuclei.

These nucleoli have somewhat of a yellowish tinge, with a bril-
lant centre and dark borders, refracting light like the fat-vesicles.
We would call attention, particularly, to the peculiar brilliancy
of the centres of these nucleoli, which, we think, is characteristic;
it can almost invariably be noticed, if the focus is varied. Their
large size, in proportion to the nuclei, should also be noticed,
together with the great variableness of their position, sometimes
being near the centre, and again in close contact with the walls
(see Fig. 384, e). Ordinarily, in other elements, they are found
almost constantly in the centre. Very frequently two or three nu-
cleoli are found within the same nucleus. M. Robin! mentions
the action of acetic acid upon cancer-nuclei and their nucleoli as
differing from that on other elements, particularly epithelial; it
renders the nucleus gradually paler, together with the cell, de-
stroying neither, but the nucleolus is perfectly untouched by it;
whereas, in epithelial cells, where generally in those of the skin
the nucleoli are wanting, the action of acetic acid destroys the
cell, leaving the nucleus unaltered.”

The polygonal shape may be regarded as the typical form of
the cancer-cell. “In hard firm tumors, particularly those of the
breast and ovaries, the cells found are exceedingly irregular, some-
times nearly triangular. (Fig. 385, f.) The ovoid or spherical
are more frequently met with in soft or medullary cancer (Fig.
386, 9), Where there is but little pressure, although its juice appears
often to be but one mass of cells. It is rare, however, that per-
fectly round cells are met with, but very generally the angles are
well rounded in those which appear to be derived directly from

1 MS. notes of his Cours de Histologie, 1850.

EXAMINATION OF MORBID GROWTHS. ._ 679

the polygonal form, the diameter of which is very variable, ordi-
narily from 1-75th to 1-25th of a millimetre. One peculiarity of
this, as of the other forms of cancer-cell, is the presence of the
granulations of different sizes in their interior ; whereas, in epi-

Fig. 385. Fic. 386.

thelial cells, the interior is generally, when fresh, of course,
homogeneous. In cancer we find the three varieties of granula-
tions given by M. Robin.’ First, the very fine black dots, found
in all organic elements, and named by the French, very ap-
propriately, poussiére organique. Secondly, the gray granulations,
a form somewhat larger ; and, lastly, the fat granulations, distin-
guished by the refraction of the light. This first variety of cells
contains nuclei, having in their interior invariably one or more
nucleoli, both of which retain the characteristic points described
above. The large size of the nucleus, in proportion to the
diameter of its cell, will at once strike the eye of the careful ob-
server. The variable position,. also, of the nucleus within the
enclosure, appears to us to be peculiar to cancer ; in cells of other
structures, the rule is to find the nucleus very nearly in the centre,
except with fibro-plastic cells, where the nuclei appear to have a
peculiar affinity for the walls. All the varieties of cancer-cells
contain very frequently two or more nuclei; whereas, the epi-
thelial, more particularly those found on the surface of the body
(where there is most danger of confusion and doubt), but rarely
have more than one. Moreover, the cell of epithelium is much
larger than that of cancer, yet the cancer-nucleus is twice as large

! Tableaux d’Anatomie, &c. par Ch. Robin, Paris, 1851.

680 APPENDIX.

as that of epithelium, as is also the nucleolus, compared with that
found in epithelium.”
The caudated cells are of common occurrence in cancerous

Fic 387.

tumors; in cancer of the bladder they are invariably present.
(Fig. 887.) The fusiform cells are most frequently met with in
cancer of the bones. (Fig. 888.) The concentric cancer-cell is

Fic. 388,

best seen, according to Robin, in cancer of the uterus, breast, and
ovaries. (Fig. 889.) Examples of the compound or mother-cell

EXAMINATION OF ANIMAL FLUIDS. 681

of cancer and the agglomerated nuclei are shown in Figs. 390,
391 (after Donaldson}

Fie. 389, Fig. 390.

EXAMINATION OF ANIMAL FLUIDS.

Blood.—To examine blood microscopically it is only necessary
to press a small drop between two pieces of glass, until it is flat-
tened out into a thin layer. A number of yellow, round,
bi-concave disks will then be seen, varying in diameter from the
1-5000th to the 1-3000th of an inch, the average size being about
1-4000th of an inch. These disks have a bright margin, and a
dark centre; or a bright centre and a dark margin, according to

O © Fia. 393.
& e S
S mA ‘gee

o ® "Wg

the focus in which they are placed. (Fig. 892.) Exposure to
the atmosphere causes the edges of the corpuscles to lose their
smooth outline, and become irregularly notched or serrated,
and sometimes beaded. (Fig. 393 B.)

The corpuscles vary in size in different animals. Thus in
birds, fishes, and reptiles they are elliptical and flattened, and
exhibit a distinct nucleus, which is generally oval. In the camel
tribe they are elliptical and bi-convex.

682 APPENDIX.

The red globules are diminished to half their size by prolonged
maceration in serum. Water renders them spherical and de-
prives them of their color. In strong syrup they shrink very
much, from the rapid exosmosis which takes place.

Acetic acid renders the membrane of the corpuscle so trans-
parent, as to be almost invisible, while nitric acid causes the out-
line to become darker and thicker. Acid urine and the acid of
the gastric juice produces a similar effect, as is seen in cases of
hemorrhagic effusion into the stomach and bladder.

The colorless or lymph-corpuscles of the blood are spherical,
highly refractive, and vary in diameter from the 1-2500th to the
1-2000th of an inch. They have a granular appearance, which is
lost by immersion in water, and are specifically lighter than the
colored corpuscles. Within the cell-wall are numerous granules
and molecules of different sizes, and one or more nuclei. (Fig.
394.) These nuclei are rendered distinct by acetic acid, while

Fig. 394.

Colorless corpuscles. Blood in Leucocythemia.

the granules are dissolved. It has been estimated that the color-
less corpuscles constitute about 1-50th part of the corpuscular
element of healthy blood. In enlargement of the spleen and
lymphatic glands they increase in numbers, producing the con-
dition called by Bennett, Leucocythemia or “ white-cell blood.”
(Fig. 395.) In some dropsical and cancerous affections, a slight
increase of these white globules has been observed. In certain
extreme cases they equal the red corpuscles in number. Their
nuclei have occasionally been seen quite naked by Virchow and
Bennett. Dr. Beale speaks of finding in the blood of some
cholera cases, very large white cells, containing oil-globules col-
lected together in one part, while the remainder of the cell was
quite transparent.

Where the blood is thickened from an excess of fibrine the
colored corpuscles become caudate or flask-like in shape, and
aggregate themselves in irregular masses, instead of in the form
of rouleaux. (Fig. 396.)

According to Funke and Kolliker yellowish crystals are some-
times seen in the blood-corpuscles of the spleen of the dog,
perch, and other animals. Oil-granules have also been observed
in the blood, giving it a lactescent or creamy appearance. The

EXAMINATION OF ANIMAL FLUIDS. 683

microscopic changes which the blood undergoes in. plethora, fever,
and various other diseases, have yet to be accurately determined.

Milk.—A microscopic exa-
mination of milk reveals a Fig. 396.
number of spherical bodies,
having dark, smooth, and well-
defined margins, and a trans-
parent and highly refractive
centre, and varying from a
mere point up to the 1-4000th
or 1-3000th of an inch in dia-
meter. These bodies consist
of oil-globules invested with a
covering of albumen, which
prevents them from running
together and forming larger
globules when pressed between
two pieces of glass. If this
albuminous membrane be dis-
solved with a little acetic acid
or carbonate of soda, the oil is separated, and may be readily
collected. Under this treatment the smaller globules may be
made, by the slightest pressure, to run together and form larger
ones. ‘These globules collecting on the surface of milk, in virtue
of their lighter specific gravity, constitute cream. An excess
of ether effects the solution of the milk-globules, while water
causes them to swell out.

The colostrum or first milk
of the human female is yellow
in color, and contains many o00eoe® si
large cells filled with oil, and 28 OSG Gee.
mingled with a number of aes Seer
compound granular bodies, fo a O! :
which disappear about the fifth
or sixth day after delivery.
(Fig. 897.)

In fresh and healthy milk,
the globules are more or less
uniform in size, and move
freely in the surrounding fluid,
showing no tendency to aggre-
gate in masses. (Fig. 398.)

The microscope readily de-
tects. adulterations of milk.
The addition of water causes the globules to be separated far-
ther from each other. The presence of flour is determined by
large starch-corpuscles, which strike a blue color with iodine.
Gritty particles, soluble in the mineral acids, indicate the addition

Fig. 397.

684 APPENDIX.

of chalky matters. In milk to which sheep's

Fig. 398. brains have been added, fine nerve-tubes

9 2 ,% 6° will be seen in the field of the microscope
co geo” ” mingled with oil-globules. A tendency on
0 2229500 @ the part of the globules to collect in masses

8 8 080° oe is an indication of acidity. Pus and blood-
°8 See ae ae $ corpuscles are easily distinguished by their
2B rgree @ ° peculiar characteristics.

Oo) a

The richness of milk is dependent upon
the number of globules. In determining the quality of the milk
of different animals the greatest care in manipulation is ne-
cessary.

Saliva.—A drop of saliva placed upon a glass slide and covered
with a thin piece of glass, presents for examination epithelial
scales from the buccal mucous membrane, salivary corpuscles,
and numerous molecules and granules.

The epithelial scales are flat plates, varying in length from the
1-800th to the 1-500th of an inch. They are generally oblong in
shape, sometimes square, and occasionally very irregular. The
edges are curled up and often adherent to. those of other scales.
With a magnifying power of 250 diameters linear, a round or
oval nucleus may be seen in the substance of these scales, sur-
rounded with a great number of molecules and granules. The
addition of acetic acid renders the nucleus more distinct, at the
same time increasing the transparency of the scale. Water pro-
duces little or no effect.

“The salivary corpuscles are colorless, spherical bodies, with
smooth margins, varying in size from the 1-3000th to the 1-1800th
of an inch in diameter. They contain a round nucleus, varying
in size, but generally occupying a third of the cell; and between
this nucleus and the cell-wall are numerous molecules and
granules, which communicate to the entire corpuscle a finely
molecular aspect. The addition of water causes these bodies to
swell out and enlarge from endosmosis; while acetic acid some-
what dissolves the cell-wall, and it becomes more transparent;
while the nucleus appears more distinct as a single, double, or

¢ tripartite body. Both water and acetic

Fig. 399. acid also, produce coagulation of the

{oy albuminous matter contained in the

fluid of the saliva, which assumes the

form of molecular fibres, in which the

corpuscles and epithelial scales become

entangled, and present to the naked eye
a white film.” (Fig. 399.)

The salivary corpuscles are accom-
Ae panied with a quantity of molecular and
Savy oa "granular matter, which undergoes an

increase in ulceration of the mucous

1Dr. Bennett’s Introduction to Clinical Medicine.

EXAMINATION OF ANIMAL FLUIDS. 685

membrane of the mouth. The debris of’ various articles taken
as food are also often found in the saliva, rendering its study
more difficult to the unpractised eye.

Sputum.—To examine sputum it should first be placed in water,
in order that any dense cretaceous or tubercular portions may be
deposited at the bottom of the vessel, and thus separated from
the lighter portions, which, on account of the confined air, will
generally float upon the surface. The different constituent ele-
ments may then be isolated by breaking up small detached
masses with a glass rod, and spreading them out upon a glass
slide. Parts presenting any peculiar appearances, as dark spots,
fibrous tissue, &c., should be removed by means of broad-pointed
forceps and scissors, and examined separately and with much
care.

The various matters which enter into the camposition of
sputum, and which complicate its study, are thus enumerated by
Prof. Bennett.

“Ist. All the tissues which enter into the composition of the
lung, such as filamentous tissue, young and old epithelial cells,
blood-corpuscles, &. 2d. Mucus from the esophagus, fauces,
or mouth. 38d. Morbid growths, such as pus, pyoid and granular
cells, tubercle-corpuscles, granules and amorphous molecular
matter, pigmentary deposits of various forms, and parasitic vege-
tations, which are occasionally found in the lining membrane of
tubercular cavities. 4th. All the elements that enter into the
composition of the food, whether animal or vegetable, which
hang about the mouth or teeth, and which are often mingled
with the sputum, such as pieces of bone or cartilage, muscular
fasciculi, portions of esculent vegetables, as turnips, carrots, cab-
bages, &c. ; or of grain, as barley, tapioca, sago, &c.; or of bread
and cakes; or of fruit, as grapes, apples, oranges, &c.” It has
lately been asserted by Shroeder Van der Kolk, that fragments
of pulmonary tissue may be detected in the sputum before the
existence of ulceration can be revealed by physical exploration.
This, however, is doubted by Prof. Bennett.

A very common appearance in sputum under the microscope is
represented by small masses of molecular and granular matter.

In the sputum of phthisis small lumps of softened tubercle
may often be found, mingled with purulent mucus, at the bottom
of the vessel. They have a yellowish, cheesy appearance, and
consist of small and somewhat transparent cells, round, oval, or
triangular, in shape, and varying from the 1-120th to the 1-75th
of a millimetre in their longest diameter. They are known as
tubercle-corpuscles, contain a number of granules, and are sur-
rounded by free granular matter and oil-globules. (Fig. 400.)

In the sputum which accompanies the cretaceous or calcareous
transformation of tubercle in the lungs, small, hard or gritty,
and white masses will be found, consisting of amorphous aggre-
gations of phosphate and carbonate of lime mixed with some

686 APPENDIX.

animal matter. (Fig. 401.) Pus and blood-corpuscles are often
observed in the sputum, and occasionally crystals of choleste-
rine.

Fig. 400. Fic. 401.

Thesputum of acute pneumonia often contains minute fibrinous

casts of the bronchial tubes, together with large cells

Fic. 402. filled with oil-globules, and numerous finely granu-
lar cells, similar to pus-globules. (Fig. 402.)

The thickened sputum expectorated in the morn-
ing on first rising, consists of epithelial cells pressed
more or less closely together, and varying somewhat
both in shape and size. The dark color is due to
the numerous carbonaceous granules contained in the
cells.

Mucus.—The gelatinous material known 4s mucus,
presents ditlerent appearances, according to the pecu-
liar cell-structures and pigmentary matters which it
contains. It possesses no essential morphological
element, the so-called mucus-corpuscles being in all probability
merely pus-cells, or modifications of epithelium. According to
Prof. Bennett, irritation of a mucous surface causes the exuda-
tion which is poured out to be transformed into pus-corpuscles
by mixing with the gelatinous secretion. The thick white gela-
tinous mucus secreted by the lining-membrane of the os uteri
contains numerous epithelial cells, while gonorrhceal or catarrhal
mucus abounds in pus-cells. The viscid albuminous substance
in which these cells are contained manifests a marked tendency
to coagulate in the form of minute fibres, and constitutes the
most characteristic element of mucus. An increase of the cell-
elements, and a diminution of viscidity, are indications of disease;
while an increase of the albuminous matter, and a decrease in
the number of cells, are marks of a more healthy mucus.

Pus.—Normal pus, placed between two glasses and examined
with a magnifying power of two hundred diameters, exhibits
numerous granular corpuscles floating in a clear fluid, called
liquor puris. These corpuscles are larger than blood-globules,
have a smooth margin and a finely tuberculated surface, and
vary in diameter from the 1-1800th to the 1-1000th of an inch.
Many of them contain a round or oval nucleus, which is rendered
more distinct on the addition of water, and is liberated in the

EXAMINATION OF ANIMAL FLUIDS. 687

form of granules, having a central dark spot, by the addition ot
strong acetic acid, which dissolves the cell-wall. . (Fig. 403.) In

Fig. 403.

& 6 ) 6986

Dee ” @°
ss ve) oP

scrofulous pus and in various unhealthy discharges, these corpus-
cles lose their globular form, and are found surrounded with
numerous molecules and granules. (Fig. 404.) In gangrenous
and ichorous pus they are mixed with broken-down blood-glo-
bules, remains of tissue, &c.

Dr. Beale makes the following judicious remarks with regard
to these pus-corpuscles. ‘The cells above referred to have been
considered as characteristic of pus, and much trouble was taken,
in the earlier days of microscopical research, to assign definite
characters to them, by which they might be distinguished from
the so-called mucus-corpuscle, and other cells which they much
resemble. Such a distinction, however, cannot be made, for, in
the first place, cells may be obtained which present various
stages, apparently intermediate between an ordinary epithelial
cell, and a pus-globule; secondly, cells agreeing in their micro-
scopical characters with the pus-globule, are not unfrequently
formed on the surface of a mucous membrane, without its func-
tion being seriously impaired, and certainly without the occur-
rence of those preliminary changes which usually precede the
formation of pus; and, thirdly, cells are found in the lymph, in
the blood, in the lymphatic glands, in the serous fluid in the in-
terior of cysts, and in many other situations, which in their size,
form, and general appearance so much resemble the globules
found in true pus, that it is quite impossible to assign characters
by which they may be distinguished. The figures of these cells,
as they appear before and after treatment by acetic acid, often
could not be distinguished from the figures of pus-cells, treated
in a similar manner, given by the same authors.

“Cases occur in which it appears almost useless to attempt to
decide as to the presence or absence of pus, if only a few glo-
bules are to be found (nor do I think that if such were possible,
it would be of any advantage), because no characters by which
the globules can be distinguished individually have been laid
down.

“‘ At the same time it must not be supposed that the diagnosis
of pus is a matter of secondary importance; and all that is in-
tended in introducing these observations is to impress upon the
student the importance of not stating that pus has been found in

688 APPENDIX.

any particular locality, or in any particular fluid, merely because
a few cells having all the characters of a pus-globule have been
observed. To say that ‘pus had been found in the blood,’ or
that ‘the casts of the uriniferous tubes contained pus,’ would
ledd ‘to a very different inference from that derived from the
statement that ‘cells having all the characters of pus-globules
had been found in the blood,’ or that the ‘casts of the tubes con-
tained ‘cells resembling those of pus.’ The former will be true
in extremely few cases; the latter in a vast number that fall
under the observation of every practitioner. If, however, we
find a considerable number of globules under the field of the
microscope, of nearly uniform size, agreeing in general charac-
ters with the pus-globule, and upon the addition of acetic acid
exhibiting the characteristic reaction, we shall seldom be wrong
in inferring that they are really pus-cells.”

Feeces.—In the feces may be found, says Prof. Bennett, “ Ist.
All the parts which compose the structure of the walls of the
alimentary canal; 2d. All kinds of morbid products; and 8d.
All the elements which enter into the composition of food.”

In severe attacks of dysentery, epithelial scales, membranous
flakes, shreds of fibrous matter, pus-globules, and blood-corpus-
cles are all observed in the discharges, mingled sometimes with
crystals of the triple phosphate, and occasionally with numerous
torulee and sarcine. In ulceration of the intestines, pus-globules
may readily be detected upon the surface of the fecal masses.
Perfectly formed pus and blood-globules originate low down in
the rectum, near the anus; broken-down globules originate
higher up in the bowel. The white flocculi composing the stools
of cholera patients consist of epithelial cells imbedded in mucus.
Sometimes the sheaths of the villi are also found; together with
free nuclei.

In the stools of typhus and other fevers of a low type great
quantities of crystallized phosphates and carbonates are found.

Dr. Farre, Prof. Bennett, and others, have observed collections
of confervoid growths in the matters discharged from the bowels.

Urine.—The student should early accustom himself to the
examination of the various constituents of healthy urine. He
cannot be too familiar with the different appearances presented
by different specimens of this important secretion. Sometimes
the urine will appear utterly structureless or homogeneous,
offering absolutely nothing for examination. At other times,
even the well-educated eye, will with difficulty identify the
various and dissimilar objects crowded together in the field of
the microscope, and which have accidentally found their way
into the urine, or been introduced by the patient for purposes of
deception. Starch-granules, woody fibres, hair, fragments of
wool, cotton, feathers, &., have all in their turn, and very fre-
quently, been mistaken for some of the ordinary matters de-
posited by the urine. We take from Dr. Beale’s work on the

a

EXAMINATION OF ANIMAL FLUIDS. 689

Microscope, the following table of the most common extraneous
matters constantly met with in urinary deposits.

Fragments of human hair. Fragments of tea-leaves, or separated
Cats’ hair. spiral vessels and cellular tissue.
Hair from blankets. Fibres of coniferous or other wood
Portions of feathers. swept off the floor.

Fibres of worsted of various colors. Particles of sand.

Fibres of cotton of various colors. Oily matter in distinct globules, aris-
Fibres of flax. ing from the use of an oiled cathe-
Potato starch. ter, or from the accidental presence
Rice starch. of milk or butter.

Wheat starch, bread crumbs.

Great care, therefore, should be exercised in the collection and
preparation of urine for microscopic examination. It is a very
good practical rule to examine a portion of the urine an hour or
two after it is voided; and another portion after standing a day,
or in some instances two days. Occasionally it will be necessary
to institute the examination immediately upon the passage of
the secretion, as in those instances where there is a strong and
rapid tendency to decomposition upon exposure to the atmo-
sphere, or where this change has already taken place in the
bladder. Urine containing lithic acid or oxalate of lime should
be allowed to stand for some time in order that it may be de-
posited.

Perfectly healthy urine, after standing for about twelve hours,
exhibits a slight cloudy deposition, consisting of epithelial scales,
some crystals of the triple phosphate, and granular fragments of
the urate of ammonia.

Urinary deposits are best obtained for examination by pourin
the fluid into a tall wine-glass, or wide-mouthed bottle, capable
of containing several ounces, and allowing it to stand for a few
hours. The clear supernatant liquid should then be poured
off, and the thick turbid under-stratum of urine, containing the
deposit, emptied into a small test-tube. The sediment will thus
be obtained in a small bulk, and can readily be examined by
being deposited upon a glass slide after the liquid portions have
been removed by means of a pipette.

Large crystals of uric acid require an inch object-glass to be
seen distinctly; when very small a fourth of an inch glass is
necessary, as is the case also with the octohedral crystals of the
oxalate of lime, epithelium, casts of the uriniferous tubes, &c.
The eighth of an inch object-glass is best adapted for the exami-
nation of spermatozoa.

In examining the deposits small portions should be brought
into the field of the microscope at a time, and in this careful
manner the different constituents, and their relation to each
other, may first be studied to considerable advantage with the
lower magnifying powers. Afterwards the nature and structure
of each object may be more minutely investigated by subjecting

it to the higher glasses. Sometimes it will be found advisable
44

690 APPENDIX.

to examine the deposit in various fluids, such as water, mucilage,
spirit, Canada balsam, turpentine, &c. Occasionally it is neces-
sary to resort to certain chemical reagents, before the deposit can
be examined satisfactorily. Thus, in some amorphous sediments
containing lithic acid alone, or combined with alkaline bases, the
familiar rhomboidal crystals cannot be detected until the mass
be first dissolved with potash, and then treated with excess of
acetic acid.

ORGANIC CONSTITUENTS OF URINARY DEPOSITS.

In healthy urine the mucus settles towards the bottom, as a
flocculent, transparent, and somewhat bulky cloud. In this trans-
parent substance the microscope detects
merely a few granular cells, larger than
blood-corpuscles, of very delicate struc-
ture and surrounded by a few minute
granules. In disease the mucous de-
position often loses its transparency,
becoming viscid and thick from the
addition of various kinds of epithelium.
The peculiar appearance of the epithe-
lial cells will indicate the part of the-
genito-urinary mucous membrane from
which the mucus was secreted. (Fig.
405.) In some diseases of the bladder,
as cystitis, a thick, glairy, and gela-
tinous deposit will often appear, simulating inspissated mucus.
This is pus chemically changed by contact with the carbonate ot

ammonia generated in the de-
Fig. 406. composition of urea by the al-
kaline mucus. Very minute
octohedral crystals of oxalate
of lime are sometimes found
like dark square-shaped specks
imbedded in the mucus. A
power of two hundred is gene-
rally sufficient to distinguish
them. Fragments of cotton-
fibre, hair, &c., are sometimes
found incrusted with these crys-
tals.

The epithelium found in the
urine differs in different speci-
mens, according to the part of

a, Portion of a secreting canal from cortical the urinary apparatus from
Portion. B, Fpithelium gland cells, maguified 700 which itis derived. Inthe con-
times. n, Portion of a canal from medullary sub- : Z
tahoe OC kidney: voluted portion of the tubuli

uriniferi it is glandular, and
forms a thick layer upon the basement membrane. (Fig. 406.)

Mucous corpuscles and epithelium.

v

ORGANIC CONSTITUENTS OF URINARY DEPOSITS. 691

In the straight portion of the tubes it is flatter, and more like the
sealy variety. In the pelvis of the kidney, it is tessellated or
pavement-like, consisting of thin, flat scales united at their
edges. In the ureter it is columnar or cylindrical in shape, having
a large and distinct nucleus. In the fundus of the bladder colum-
nar epithelium is found mixed with large oval cells; flattened
cells having a distinct nucleus and nucleolus abound in the trigone.

Mucus, pus, blood, and epithelium from leucorrheea.

In the mucous follicles columnar epithelium is found; on the sur-
face between them, the scaly variety. The columnar variety pre-
vails in the posterior part of the urethra; anteriorly it becomes
sealy. The vaginal epithelium found in the urine of females, is
also of the scaly variety. (Fig. 407.)

Occasionally casts, consisting of moulds of the uriniferous
tubes, are observed in the urine. They furnish valuable aids in
arriving at a correct diagnosis
as to the pathological changes Fig. 408.
which may be going on in the
kidney. They consist mainly
of oily granules, or epithelial
cells abundantly supplied
with these granules. (Fig.
408 a.) Prof. Bennett divides
them into two distinct varie-
ties, namely,—‘ Ist. Fibrin-
ous or exudation casts, which
are most commonly found in
the urine at critical periods
of acute inflammations, especially in scarlatina, small-pox, pneu-
monia, &. 2d. Casts, with oily granules, indicative of chronic
. disease, and especially of Bright’s disease. (Fig. 409*.) At the

692 APPENDIX.

same time, it should be understood that they may be more or
less associated together, and that the rule is not invariable.”
Dr. Beale divides them into three classes according to their

diameter; namely, 1st. Casts of medium diameter, about the
1-700th of an inch. These

Fra. 409. contain granular matter with
epithelial debris, oil-globules,
and occasionally blood and
pus-corpuscles. In the urine
of a cholera patient, Dr.
Beale once detected dumb-
bell and octohedral crystals
of oxalate of lime in orte of
these casts. 2d. Casts of con-
siderable diameter, about the
1-500th of an inch. These
are transparent and have a
smooth, glistening, or waxy appearance. Sometimes they are
granular. 38d. Casts of small diameter about the 1-1000th of an
inch. According to Dr.
Johnson these originate in
cases in which there is no.
tendency on the part of the
epithelium to desquamate,
as in non-desquamative ne-
phritis.

Spermatozoa are some-
: times found in the urine
when examined soon after it has been passed. They can be seen
with a power of two hundred diameters, though in demonstrating
them it is better to employ a power of four hundred diameters. (Fig.

seBoe ©

2 ee

Fig. 410.

Tube containing an homogeneous cast.
Fig. 411.

if

411.) The presence of these bodies in the urine must not be regarded
as a sign of spermatorrhoa, unless accompanied with the symp-

3

ORGANIC CONSTITUENTS OF URINARY DEPOSITS. 693

toms of that disease. In urine, which has been allowed to stand
for some time, vibriones and certain forms of vegetable fungi or
torule are gradually developed. With a power of two hundred
diameters, vibriones, looking like minute lines, may be seen
writhing about in the mucus. They are always to be found in
decomposing urine, and are sometimes generated in the bladder.

The. species of-fungi vary in different specimens of urine, and
appear after different intervals of time. Dr. Hassall, however,
considers the different species to be merely the successive stages
of development of the same fungus; the stage of development
being dependent upon the degree of acidity of the urine, and the
length of time in which it has been exposed to the air. In acid
urine, containing nitrogenous matter, and exposed to the atmo-
sphere, a peculiar fungus is generated known as the penicilium
glaucum,—the same fungus which is developed in lactic acid
fermentation.

Dr. Hassall has shown that in urine containing even very
minute traces of sugar, a peculiar fungus is de-
veloped, which may be regarded as the charac- Fic. 412.
teristic test of the presence of sugar, since it is
found in no other condition of urine. In diabetic
urine torule are often very rapidly developed.
(Fig. 412.)

The fat-cells found in the urine are usually epi-
thelial cells loaded with oil. According to Dr.
Beale, fatty matter may occur in the urine in three
conditions. Ist. “‘ As distinct and separate globules,
resembling those which are produced by intimately
mixing oil with water by the aid of mucilage, &. (Fig. 413.)
When fatty matter occurs in this state only in urine, its presence
is usually accidental. 2d. In the form of globules enclosed
within a cell-wall, or in casts. 8d. In the so-called ‘ chylous
urine,’ the fatty matter is suspended in an exceedingly minute
state of division.”

Fie, 414.

ao

a4

Blood-globules generally form a brownish-red granular sedi-
ment at the bottom of the vessel. If the urine has been standing
long, the globules will appear very much changed in shape.
Acid urine containing blood has a smoky hue, the globules

694 APPENDIX.

appearing of a dark brown color. Where the liquid has a
neutral, or slightly alkaline reaction, the globules are red.
Pus-globulesare also occasionally found in the urine, more or less
changed in shape, according to the
Fra. 415. length of time they have remained
in the liquid. After long soaking
they completely disintegrate. De-
posits of pus are often accompanied
with crystals of the triple phosphate.
This is especially the case when the
pus is derived from the bladder.
Large and small organic globules,
exudation cells, spherical cells con-
taining nuclei and granular matter,
&c., are also foundin the urine. For
descriptions of these bodies, the stu-
dent is referred to the work of Dr.
Golding Bird, on Urinary Deposits.

INORGANIC CONSTITUENTS OF
URINARY DEPOSITS.

Lithie or Urie acid is one of
the most common urinary deposits.
In color it varies from a light fawn
to a deep orange-red, the usual hue
of the crystals being yellow. Some-
times they are almost colorless. They
assume a great variety of forms, the
most common and most characteris-
tic of which is the rhomboidal, Fig.
413,—the form usually generated
when the lithates are decomposed
by means of an acid. Fig. 414 re-
presents the peculiar forms of uric
acid found in the urine of patients
laboring under acute and scarla-
tinous dropsy. Sometimes the crys-
tals are square and lozenge-shaped.
Other varieties are seen to consist of adhering masses and

Fig. 416.

flat scales, with transverse and longitudinal markings. Some

INORGANIC CONSTITUENTS OF URINE, 695

times they are six-sided, resembling crystals of cystine, but dis-
tinguishable from the latter, by two of their sides being longer
than the others. Occasionally they appear as truncated or
rounded columns.

Cystine crystallizes in flat, hexagonal plates, with irregularly
hexagonal markings on their surface. Sometimes radiating
lines pass from an opaque centre to the margins. (Fig. 416.) A
deposit of cystine may be readily distinguished from that of
the pale urates, which it resembles in appearance, by not dis-
solving when heated.

Oxalate of Zime occurs in oc-
tohedral crystals, having one
axis shorter than the other two.
It is important to remember
that these crystals differ in ap-
pearance, according to the posi-
tion in which they are viewed, as
shown in Figs. 417, 418. When
large they may be seen with the

Fie, 418.

Various forms of oxalate of lime.

unassisted eye as minute glistening points imbedded in the sedi-
ment. Where crystals of the oxalate of lime are associated with
and obscured by the pale lithates, the addition of a drop or two
of solution of potash, by dissolving the latter, will render the
former more apparent.

Occasionally oxalate of lime assumes the form Fig. 419.
of dumb-bells. Dr. Golding Bird considers these a?
to consist of oxalurate of lime, on account of & ae
their polarizing influence upon light. (Fig. 419.) D &
The dumb-bell crystals are probably compound, ®
appearing to be formed of collections of minute © Ca)
acicular crystals. They are generally accom- e& >
panied by the octohedral form, and, according to — pumb-bell crystals.
Dr. Beale, their appearance is sometimes pre-
ceded and succeeded by the presence of the circular, oval, and
less regular forms of crystals. They are formed in the kidney,

696 APPENDIX.

having been met with in the uriniferous tubes after death, and
in fibrinous casts of those tubes. Phosphate of lime and lithic
acid also assume the dumb-bell form; but the solubility in pot-
ash, and the different refracting power of these latter crystals,
distinguish them from those of the oxalate.

Lithates constitute the so-called “‘lateritious deposits” in urine.
According to Heintz these buffcolored or deep red sediments
consist mainly of lithate of soda mixed with small portions of
the lithates of ammonia and lime, and a trace of the lithate of
magnesia. Under the microscope they appear as minute granules
in different states of aggregation. (Fig. 420.) The lithates of
ammonia and soda sometimes occur in spherical masses, adher-
ing to thin films of the phosphates. The ammoniacal lithate
occasionally assumes a stellate form; Prof. Bennett has seen it
arranged in such a manner as strongly to resemble in appearance
an organic membrane.

The triple phosphate, or ammonio-phosphate, of magnesia,
occurs in the form of triangular prisms, occasionally truncated,

Fia. 421. Fig. 422,

and sometimes with terminal facets. (Fig. 421.) If the urine be
very ammoniacal, they present a star-like or foliaceous appear-
ance (Fig. 422). Carbonate of lime is sometimes associated with
the earthy phosphates in human urine, but rarely in a crystalline
form. It generally appears in small round masses, or as an
amorphous powder.

INORGANIC CONSTITUENTS OF URINE. 697

Urinary deposits may be preserved either in the dry way, in
Canada balsam, turpentine, oil, and similar fluids, or in aqueous
solutions. Only large crystals of the oxalate of lime, lithic acid,
and some of the phosphates and lithates, can be preserved in the
dry way. Dr. Beale gives the following directions for the pre-
servation of urinary deposits: “After the crystals have been
allowed to collect at the bottom of a conical glass vessel, the
clear supernatant fluid is to be poured off, and the crystals are to
be washed with a little dilute alcohol, or with a very weak solu-
tion of acetic acid. When the process of washing has been re-
peated two or three times, a small quantity of the deposit is to
be transferred by means of a pipette to a glass slide, and the
greater part of the fluid soaked up with a small piece of blotting
paper. The crystals are next to be spread a little over the glass
with the aid of a fine needle, in order to separate the individual
crystals from each other; and the slide is to be placed in a warm
place, or in the sun, until quite dry; but care must be taken that
the drying is not carried on too rapidly, and that too great a
degree of heat is not employed. A narrow rim of paper, or card-
board, is next to be gummed on the slide so as to include the
erystals in a sort of shallow cell; and lastly, the glass cover is to
be put on and kept in its place either by anointing the edges with
a little gum-water, or by pasting it down with narrow strips of
paper, which may be variously arranged and ornamented accord-
ing to taste. ;

“Tf the crystals of lithic acid are to be mounted in Canada
balsam, they should be carefully dried first, as above directed,
and afterwards over sulphuric acid, and then moistened with a
small drop of spirits of turpentine. The slide is now to be
slightly warmed, in order to volatilize the greater part of the
turpentine, and a drop of Canada balsam is to be dropped upon
the preparation from the end of a wire, which may be readily
effected by holding the wire with the balsam over the lamp or
hot brass plate for a minute or two in order to soften it. The
slide is next to be held over a lamp, in order to keep the balsam
fluid until any air-bubbles which may be present have collected
into one spot on the surface of the liquid balsam, an operation
which is expedited by gently moving the slide from side to side.
The air-bubbles may now be removed by touching them with a
fine-pointed wire. Lastly, the glass cover is to be taken up with
a pair of forceps, slightly warmed over a lamp, and one edge is
allowed to touch the balsam. The surface is permitted to fall
gradually upon the balsam, so that it is wetted by it regularly,
and only by very slow degrees, for otherwise air-bubbles would
yet be included in the preparation. The glass slide with the pre-
paration may now be set aside to cool.”

There are many substances, however, which cannot be pre-
served to advantage in Canada balsam, or by the dry method.
Such are epithelium, casts, torule, confervee, fat-cells, pus, mucus,
&c. Such substances should be placed in shallow glass-cells,

698 APPENDIX.

and covered with aqueous solutions, varying in character and

strength to suit the specimen. The best preservative fluids are -
weak spirit, glycerine diluted with water, solutions of gelatine,

creasote, naphtha, &c. The gelatine solution answers very well

for the preservation of dumb-bell crystals of oxalate of lime,

while the creasote and naphtha solutions are better adapted for

the preservation of epithelium, tubular casts, &c. Crystals of the

triple phosphate are best kept in aqueous solutions of ammonia;

for cystine dilute acetic acid answers very well.

Vomited matters consist of articles of food variously altered
by the digestive processes, epithelium and mucus from the mouth,
fauces, pharynx, esophagus, and stomach, gastric juice, bile, and
the various matters generated in disease. As different portions
of vomit contain different ingredients, small portions taken from
points considerably separated, should successively be subjected
to examination. The various transitions which alimentary sub-
stances undergo in the stomach, must often necessarily render
the determination of the exact composition of the vomited matters
a point of extreme difficulty.

Starch-granules are often met with in abundance, but some-
times so changed as to require the addition of tincture of iodine
to detect them. Fig. 423 represents the appearance of starch

corpuscles after partial digestion in the
Fie, 423. stomach. The epithelium is also frequently
0% ge found to be more or less altered from en-
dosmosis, and partial digestion. Vibriones
and various species of torule are also ob-
served in vomit. The sarcina ventriculi, a pe-
culiar fungus discovered by Mr. Goodsir, in
matters ejected from the stomach, has also
been observed in the feces, in the urine,
and in an abscess of the lung. The fluid of
waterbrash consists mainly of epithelial
scales and small oil-globules. In the rice-water vomit of
cholera patients numerous flocculi of epithelial cells are found.
The coffee-ground vomit appears to consist mainly of the color-
ing matter of the blood reduced to a finely granular state
and mingled with disintegrated blood-corpuscles. The sedi-
ment deposited by the black-vomit of yellow fever upon stand-
ing, in all probability is chiefly composed of blood-globules in
various stages of disintegration. The epithelial cells of this
fluid “vary in respect to their abundance, size, and shape, and
while stated by some to have presented themselves in all the
specimens examined, they have, in some instances, been found
wanting. Of the six specimens reported upon by Dr. Leidy, two
were deficient in this particular. The size and shape of these
cells, as observed by Dr. Riddell, have already been referred to.
In the hands of Dr. Michel, the scaly, columnar, and spheroidal,
have, at different times, been plainly made out with their nuclei

SEROUS AND DROPSICAL FLUIDS. 699

and nucleoli, but in very different proportions—the scaly or la-
mellar cells being always most numerous.’

Uterine and Vaginal Discharges present quite different charac-
ters in different specimens. The examination should be insti-
tuted as soon after they are collected as possible, and without
the addition of water, as this may affect the natural appearance
of the constituent elements. Epithelial cells and blood-globules
in varying quantities compose the menstrual discharge. In leu-
corrheea many of the epithelial cells are
filled with oil-granules, and mingled to a Fig. 424.
greater or less extent with pus-corpuscles.
Blood-globules are also observed very
much altered in shape. (See Fig. 407.) In
cancer of the uterus the microscopic exa-
mination of the discharges, becomes
highly important in arriving at an accurate ;
diagnosis. Cancer-cells, in such cases, —
may often be detected in the discharges. ;
When they are broken down or considerably altered in form, not
a little difficulty will be experienced in assigning to them their
true value. The student should be careful, also, not to confound
the columnar epithelium of the ureter, with the spindle-shaped
cancer-cells. Fig. 424 represents the microscopic appearances of
some cancerous juice squeezed from the uterus; that to the left is
the natural appearance, the other after the addition of acetic acid.

SEROUS AND DROPSICAL FLUIDS.

The sedimentary matters should be collected from serous fluids,
and examined in the same way as urinary deposits.

An examination of the freshly effused fluid of ascites reveals
only a few cells floating in a
clear liquid. In chronic as- Fig. 425.
cites, however, numerous gra-
nular and spherical cells,
mostly non-nucleated and va-
rying in size, are observed.
The sediment consists of deli-
cate’ fibres, interlaced, and
having cells in the meshes
or interstices, together with
plates of cholesterine. Occa-
sionally blood and pus-cor-
puscles may also be detected.
The hydrocelic fluid consists of some delicate cells, and oil-
globules, and occasionally some spermatozoa and plates of chole-
sterine.

'Dr. R. La Roche on the Nature and Composition of Black Vomit. Amer. Jour. of,
Med. Sciences, April, 1854.

700 APPENDIX.

Cells, oil-globules, free granular matter, and occasionally blood-
corpuscles and crystals of cholesterine are the principal constitu-
ents of the deposit obtained from ovarian fluid. Sometimes
masses of gelatinous or colloid matter are mixed with these ele-
ments. Minute fibres are sometimes observed crossing each
other in various directions, and contain in their meshes thus
formed, a transparent jelly filled with round or oval corpuscles.
(See Fig. 424.) The cells are either small, transparent, granular,
and non-nucleated, or large, opaque, and filled with oil-globules.
Fig. 376 represents fatty granules, mixed with plates of choles-
terine from an ovarian tumor, after Prof. Bennett.

INJECTIONS.

In studying the vascularity of tissues, injected specimens are
of great utility. The student should give some attention, there-
fore, to the practice of injecting the different organized structures
which he may desire to examine. Dr. Beale, in his admirable
little work on the application of the microscope to clinical medi-
cine—a work of which we have availed ourselves freely in the
construction of this chapter—gives the following practical direc-
tions as to the time, mode, &c., of making injections.

“ Generally, it may be remarked that we should not attempt
to inject while the rigor mortis lasts. Many days may in some
cases with advantage be allowed to elapse, particularly if the
weather is cold, while in warm weather we are compelled to in-
ject soon after death. As a general rule, the more delicate
the tissue, and the thinner the vessels, the sooner should the

injection be performed. Many of the lower animals, annelids,

mollusea, &c., and fishes, should be injected soon after death.
In making minute injections of the brain, only a short time
should be allowed to elapse after the death of the animal, before
the injection is commenced. Injections of the alimentary canal
of the higher animals should be performed early—not more than
a day or two after.

“‘ Minute injections of the papillee of skin, particularly of the
fingers and toes, cannot be successfully made until the cuticle has
become somewhat softened by allowing the preparation to remain
-in a damp cloth, or to soak in water, for some days. In these
situations the vessels are strong, and in their ordinary state, the
injection will not traverse them, in consequence of the cuticle
preventing their gradual distension by the injecting fluid. A
similar plan must be followed in making injections of the tongue,
and other parts where the epithelial covering is unusually dense,
and firmly adherent to the vascular surface beneath.

“Tf the subject be a small animal, it is better to take out part
of the sternum, and fix the pipe in the aorta. If only part of an
animal is to be injected, the largest artery supplying the part
should be selected, and all the other open vessels may be tied or
stopped with the small forceps.

INJECTIONS OF VEINS, ETC. 701

“ A small portion of intestine can be injected by cutting out
the corresponding portion of mesentery attached to it; and after
searching for a large vessel, all the others may be tied, together
with the open ends of the alimentary tube.” “A pipe of some-
what smaller diameter than the vessel should be selected, and an
opening may then be made in the vessel of sufficient size to
admit the pipe, which can now be inserted. The needle, charged
with thread or silk, is then carefully passed round the vessel, the
thread seized with forceps, and the needle withdrawn over the
thread. This operation is sufficiently simple where the vessel is
large and strong; but where thin and easily torn, it requires great
care. The thread is now tied tightly round the vessel close to
the extremity of the pipe, and then attached to the two projecting
wires, to prevent the possibility of slipping.

“Tn injecting from veins a similar method is pursued, taking
care to choose a vein in which the valves are not numerous, or
in which they are altogether absent. The portal vein can be
reached by opening the abdominal cavity, care being taken not
to tear any of the branches below the point where the pipe is
inserted.

“Greater care is required to fix the pipe in the vessels of fish,
in consequence of their being so readily torn. Excellent injec-
tions of fish may frequently be made as follows: The tail is cut
off with a sharp knife at a short distance posterior to the anus,
and if the cut surface be examined the ventral artery may be
easily found situated immediately beneath the bodies of the ver-
tebre. A pipe is carefully introduced and pushed down some
distance, so as to prevent the injection from coming out, or the
end of the vessel may sometimes be separated from the surround-
ing parts and tied in the usual way. . By this simple proceeding
capital injections can often be made very easily.

‘“‘Minute injections of the branchie of some of the mollusca
may often be made by very carefully placing the pipe in the
largest vessel that can be found, and slowly injecting. The ex-
treme delicacy of the vessels prevents any attempt being made
to tie them to the pipe, and, of course, much injection will be
lost. From the large size of the vessels, however, much will run
into the capillaries. In this way I have easily succeeded in in-
jecting the branchie of the Pinna ingens, and fresh-water mussel
(Anodon), both of which form beautiful microscopical objects.

“Tn order to inject the smaller gasteropods (slugs, snails, &c.),
we must pursue a different method. In the muscular foot of
these are situated many large lacune, or cavities, which commu-
nicate with the vascular system, or, in fact, form the vessels
which are distributed to this organ. If the injection can be
forced into any of these lacune, it may be made to traverse the
whole vascular system. To introduce the pipe a small hole is
made obliquely in the foot, taking care not to force the instru-
ment too far. A small pipe is next inserted, and when the pre-

702 APPENDIX.

paration is warm enough the injection of size and vermilion 1s
very slowly and carefully forced in, and the progress which is
made can be seen by observing the vessels distributed to the
respiratory organs. When a sufficient quantity of injection has
been introduced, the pipe may be withdrawn, and the hole
plugged with a piece of wood cut to the proper size, to prevent
the injection again escaping before the size has had time to set.

“The vascular system of insects may sometimes be partially
injected by forcing the injection into the abdominal cavity, from
which it finds entrance into the dorsal vessel, and from thence is
distributed to various parts of the body. The injection in the
cavity of the abdomen is then allowed to escape. ;

“It is very important that the size and vermilion, or other in-
jection which is to be thrown into the vessels, should be
thoroughly mixed and well strained before being used. The
coloring matter, properly powdered, should be placed in a small
earthenware mortar, and the melted size or other fluid carefully
added by degrees, the whole being constantly stirred until well
mixed. When the proper color has been obtained, the whole
must be strained through muslin, or through a fine perforated
strainer, into another vessel, which should be kept warm. The
injection should be well stirred with a wooden stick previous to
filling the syringe.

“We can judge of the intensity of the color by removing a
drop of the solution with a stirring-rod, and allowing it to fall on
a white plate so as to form a thin stratum, which should have a
pretty deep color. It is always better to have too large a quan-
tity of the coloring matter rather than too little.

“Of vermilion, about two ounces will be sufficient for a pint
of size; but it is better in all cases to regulate the quantity by
examining the intensity of the color in the manner just men-
tioned.

‘“When the preparation is warmed through, the injection pro-
perly strained, and the pipe fixed in the vessel, we may proceed
carefully to inject, taking care that the injection is kept at a pro-
per temperature, by allowing it to remain in the warm water-
bath during the operation.

“The air should be first withdrawn from the upper part of the
vessel by means of the syringe, after which the stop-cock is
turned off and left attached to the pipe. The syringe is then
disconnected, and after being washed out once or twice with
warm water, is nearly filled with injection, which must be well
stirred up immediately before it is taken. The syringe should
not be quite filled, in order that the air in the pipe may be made
to rise into the syringe through the injection, by the ascent of the
piston, before any of the latter is forced into the vessel. The
end of the syringe is then to be pressed firmly into the’ upper

art of the stop-cock with a slightly screwing movement.

“The piston is now very gently forced down by the thumb,

INJECTIONS OF VEINS, ETC. 703

until the syringe has been nearly emptied, when the stop-cock
must be turned off, and the syringe refilled with warm injection
as before.

‘“‘Care must always be taken to keep the syringe in the inclined
position, so that any air which may be in it, may remain in the
upper part; and for the same reason, all the injection should not
be forced out, for fear of the enclosed air entering the vessels, in
which case all chance of obtaining a successful injection would
be destroyed.

“ After a certain quantity of fluid has been injected, it will be
necessary to use a greater amount of force, which, however, must
be increased very gradually, and should only be sufficient to de-
press the piston very slowly. If too great force be employed,
extravasation will be produced before the capillaries are. half
filled. Gentle and very gradually-increased pressure, kept up
for a considerable time, will cause the minute vessels to become
slowly distended without giving way to any great extent. At
the same time it must be borne in mind that extravasation fre-
quently occurs at various points in a successful injection ; but the
longer this event can be kept off, the more likely are we to
succeed.

“When the injection begins to flow from the large veins
mixed with the blood contained in these vessels, and the surface
of the injected preparation looks of a red color, and has a some-
what velvety appearance, we may infer that the injection has
been completed. This occurs at different periods. Sometimes
the first or second syringeful causes a general redness of surface,
while in other instances a considerable time will elapse before
more than a slight blush appears. As a general rule, it is better
to proceed slowly and cautiously, and to use as little force as pos-
sible, which should not be more than sufficient to produce an
observable depression on the piston. Many minute injections
will require an hour or more to complete. “

“When the injecting is completed, and all the openings by
which any of the injection could escape during cooling are closed,
the preparation should be placed in cold water, and allowed to
‘remain until the size has set, which will require twelve hours or
more in hot weather.”

In the Medical Examiner of Philadelphia, for December, 1849,
Dr. P. B. Goddard details the following method of making
minute ethereal injections, originally employed by him.

“For the purpose of making such an injection, the anatomist
must provide himself with a small and good syringe; some ver-
milion, very finely ground in oil; a glass-stoppered bottle, and some
sulphuric ether. The prepared vermilion paint must be putinto
the ground-stoppered bottle, and about twenty or thirty times its
bulk of sulphuric acid added; the stopper must then be put in
its place, and the whole well shaken. This forms the material
of the injection. Let the anatomist now procure the organ to be

704 APPENDIX,

injected (say a sheep’s kidney, which is very difficult to inject in
any other way, and forms an excellent criterion of success), and
fix his pipe in the artery, leaving the vein open. Having given
his material a good shake, let him pour it into a cup, and fill the
syringe. Now inject with a slow, gradual, and moderate pressure.
At first, the matter will return by the vein, colored, but in a few
moments this will cease, and nothing will appear except the clear
ether, which will distil freely from the patulous vein. This must
be watched, and when it ceases, the injection is complete. The
kidney is now to be placed in warm water of 120° Fahrenheit,
for a quarter of an hour, to drive off the ether, when it may be
sliced and dried, or preserved in alcohol, Goadby’s solution, or
any other antiseptic fluid. For glands, as the kidney, liver, &c.,
it is better to dry and mount the sections in Canada balsam, but
for membranous preparations, stomach, intestine, &c., the plan
of mounting in a cell filled with antiseptic solution is preferable.”

MICROSCOPES OF AMERICAN MANUFACTURE.

Microscopes of great excellence are manufactured in this
country. These, from their comparative cheapness, and the
facility with which they can be procured, offer inducements to
students and others to procure them at home, and thus save time
to themselves, atthe same time that they stimulate the manufac-
turers to make increased efforts to attain even greater excellence.
A brief description of some of the best will enable the reader to
form some comparative estimate of their value.

Mr. Cuarzes A. Spencer, of Canastota, New York, has manu-
factured a microscope of great excellence, the objectives of which
will bear comparison with the best of foreign construction. His
common angle of aperture for } inch objectives is 135°; for 4
inch, 170°, and for #y and 7g inch, 176°. This is believed to be
the largest angle ever given to an object-glass, and for sharpness
of definition and power of penetration, they are unexcelled by
any of foreign make.

‘To Mr. Spencer is due the credit of having first resolved, with
lenses of his own construction, the fine markings on the Navicula
Spencerii and Grammatophora Subtilissima: these minute shells
have since been adopted by microscopists as test-objects for the
highest powers. The Navicula Spencerii, will exhibit one set of
lines with Mr. Spencer’s }th-inch object-glass: both sets with
the 4th-inch. The Grammatophora Subtilissima is a good test
for a 7th or j;th.

Of several microscopes made by Mr. Spencer, two or three
only will be here noticed. His first-class or best instrument is
mounted on trunnions, and embraces all the acknowledged im-
provements, in form and stage, whereby the greatest steadiness
and freedom from tremor are secured. The price of this instru-

MICROSCOPES OF AMERICAN MAKE. 705

ment, with all the accessories and full sets of object-glasses, will
approach $850. (Fig. 426.)

Fig. 426,

Spencer’s Trunnion Microscope.

The second-class instruments, complete as to object-glasses and
accessories, but mounted less expensively, cost from $200 to $250.

A very efficient microscope, is one known as the ‘“ Pritchard
form:” this instrument has been somewhat modified by Mr.
Spencer, and where a less expensive instrument than either of
the others is desired, this one will be found a good working in-
strument, and available for all purposes of anatomical study. The
cost of this form, with object-glasses as high as the 4th, with the
usual accessories, is from $125 to $150.

Mr. Spencer also makes some simpler forms of instruments,
45 :

706 APPENDIX.

and yet very efficient working ones, with objectives as high as
th, the price of which does not exceed $75.1
Mr. Jas. W. Quuzen, of Philadelphia, has prepared one of the
most convenient and portable microscopes for the use of students
that has been made. It is all contained in a mahogany box, six
inches square and eleven inches high, with’a small drawer within
for objects, forceps, &c. The stand is of cast iron, with two up-
rights supporting the stage and body of the instrument; between
the uprights is an axis upon which the whole upper part of the
instrument turns, enabling it to take a horizontal or vertical
position, or any intermediate angle most convenient for observa-
tion. The movable part, consisting of the stage, the body, and
bar containing the adjustment, is fixed to the axis, on which it
readily turns. There is an inner tube for increasing power by
extending the distance between the eye and object-glass. Within
the quadrangular bar, to the top of which is attached the body of
the instrument, is the fine adjustment for foci; the milled head on
the top of the bar operates upon the spring within, and carries the
body and object-glass from, or to, the object being observed, with
the greatest facility. The
Fre. 427. stage upon which objects are
placed to be viewed is made
double, the upper portion be-
ing movable by a small lever
which produces rectilinear or
eccentric motion, thus giving
great facilities to the microsco-
pist for viewing any portion
of the object he may desire;
the slide containing the ob-
ject is kept in place by two
spring clips attached to the
stage ; the under portion ofthe
stage carries a revolving plate
to which the polarizing prism
is attached when in use; a
diaphragm with various aper-
tures is beneath the stage;
J. W. Queen’s Microscope. the mirror is made to slide
up and down on the tube
that supports it, and can be turned to any angle for light that
may be desired; a condensing lens for opaque objects, mounted
with a jointed arm, is attached to the collar through which the
body passes. ‘Two eye-pieces and two object-glasses are fur-
nished with the instrument, also the polarizing prisms. The
lowest power is about 50 diameters, and that can be increased to
400 or 500. A drawing-prism can also be furnished when de-
sired. (Fig. 427. )
Messrs. J. & W. Grunow, of New Haven, Connecticut, have in-

' See Hassall’s Microscopic Anatomy, edited by H. Vanarsdale, M.D,

MICROSCOPES OF AMERICAN MAKE. 707

vented an admirable Student’s Microscope, which commends
itself to all who desire efficiency, cheapness, and portability.
The accompanying cut explains its appearance and mode of action.
It is mounted on a tripod base, with uprights of japanned cast
iron. It has a quick and a slow movement, with draw-tube and
a stage 3 by 4 inches, movable by a lever. This movement the
Messrs. G. have nearly perfected, and at the suggestion of Dr.
Goddard, of this city, an eminent microscopist, they have so
arranged it that the stage follows the hand instead of taking the
opposite direction, as is usually the case in other instruments
having the lever stage. (Fig. 428.)

Fig. 428,

\ / m
pth 2 i

J. & W. Grunow’s Student's Microscope.

Messrs. Grunow have also improved their stand in the mode
of adaptation of accessory apparatus, especially of that which is
attached below the stage; this is held in place by a bayonet

708 APPENDIX.

catch, and when once centred it may be detached and reattached
with the greatest facility, without requiring a readjustment.
Fig. 429 represents a smaller and less expensive form of stu-
dent’s microscope, made by the Messrs. Grunow, and possessing
the same objectives as that represented in Fig. 428, but with a non-

Fia, 429.

movable stage. Messrs. Grunow also manufacture a first class
microscope, with brass mountings and all the accessories. (Fig.
430.) Their instruments have given great satisfaction wherever
they have been used.

THE INVERTED MICROSCOPE OF DR. J. LAWRENCE SMITH.

This instrument was invented and brought to the notice of
the Société de Biologie of Paris, in 1850, by Dr. Smith, for whom

SMITH’S INVERTED MICROSCOPE. 709

the first one was constructed by Nachet, of Paris. Its design is
to enable the chemist to carry on observations under the micro-
scope without the risk of injuring his objectives, or at least having
his view obscured, by the fumes arising from liquids experi-
mented upon. This has always been a serious difficulty in

Fie. 430.

by

micro-chemical research, and, together with the difficulty of
manipulating in the limited space between the object-glass and
the stage, has hitherto prevented this branch of scientific inquiry
from being fully illustrated. “The only way,” says Dr. Smith,
“by which these difficulties can be surmounted, is by putting
the object-glass beneath the stage and the object above it, with
an optical arrangement of such a nature as to permit observa-
tion.” It was with this view that M. Chevalier made a chemical

710 APPENDIX.

support, to go with his general instrument, and so constructed
it, that it could be inverted so as to have the stage above, and
the objective below the object; but every one who has used it
knows how awkward it is for manipulation, although exceed-
ingly ingenious. Dr. Smith, impressed with these difficulties,
was led to the construction of the instrument, which, in this
country, bears his name.

It was important for the arrangement in question, so to have
the relative position of the stage and eye-piece, that the eye,
while on a level with the latter, could readily see the former, and
guide the required manipulation.

The most important part of the instrument is a four-sided prism,
Fig. 430, with the angles a8, be,
cd, and da, respectively 55°, Fig, 431.
1074°, 524°, 145°, the angles

being of such dimensions that
a ray of light passing into the D
prism in the direction Ha,and

perpendicular to the upper sur- *

faceofthe prism, afterundergo- 7=e=y—————

ing total reflection from the in- eC

ner surfaces (on both of which

the light strikes at an angle

much less than forty-five de-
grees), will pass out perpendi-
cular to the surface connected a

with the body of the instru- ao L,

ment. A

It will be readily seen how é
a ray of light, entering the
object-glass, descends into the prism, and passes out of it up-
wards, through the eye-glass, the tube of which is inclined to the
perpendicular 35°. The other parts of the instrument will be
understood by looking at the figure. (Fig. 431.) The illumina-
tion of the object is effected by a prism, instead of a mirror.

In examining an object with this microscope, the object is
arranged in the ordinary way; when liquid, it is placed in a
watch-glass, or such glass cells as are convenient to use. In
employing reagents, they can be added and watched immediately,
for it is readily seen how the eye guides the manipulation on the
stage and looks into the instrument almost at one and the same
time.

In observing with high powers, as the object-glass is beneath
the glass supporting the object, and as the glass is usually of a
certain thickness, the method of observation must be changed.
For all powers resorted to in chemical examination this difficulty
never occurs, and in using high powers it is easily obviated.
When the object is already mounted and dry, the thin glass can
be readily turned downwards; but where it is moist, as for in-

SMITH’S INVERTED MICROSCOPE. 711

stance, in examining fresh Desmidie and Diatomacee, the following
plan is resorted to, namely: to use a cell, made of a thin piece
of brass or glass, perforated with a hole, about a half an inch in
diameter; it is best to give the hole a considerable bevel in one
direction, as it facilitates the cleaning of it. Over the small end

Fig. 432.

of the hole a piece of thin glass is stuck, with balsam or other
cement. When used, the object to be examined is placed within,
and a cover of thin glass placed above. When brass is used to
make the cell, it may be as thin as the twentieth of an inch.
Dr. Smith remarks that for all observation with high powers,
the Inverted Microscope is decidedly superior to the ordinary
forms of mounting, for in the latter case, when an object-glass
of a 72th or ¢sth inch focus is used, the focus is too short to admit
of the use of cells; whereas, in the inverted form, as the object
is looked at from beneath, the cell may be as thick as one pleases.
Another thing connected with this class of observations, is that
the Diatomaces and Desmidie can be observed to much greater
advantage from beneath than from above, for reasons that will
be obvious to persons accustomed to observe these classes of
objects.

Another advantage possessed by this instrument calculated to
extend its use for general purposes, is its great capacity for every
variety of illumination, without sacrificing the ease and freedom

712 APPENDIX.

from fatigue belonging to the use of this form of miscroscope ;
for when placed ona table, rather higher than the one commonly
used, and a foot or two from the edge, the observer can recline
on his arms, and observe for hours without the slightest sensa-
tion of fatigue.t Messrs. J. & W. Grunow, New Haven, Conn.,
are the manufacturers of this instrument.

DR. J. LAWRENCE SMITH’S GONIOMETER AND MICROMETER.

Professor Smith has also invented a Goniometer for measur-
ing the angles of crystals under the microscope. It is also com-
bined with a Micrometer. The following is a description of the
instrument with the method of using. (Figs. 433-4.)

His the upper end of the draw-tube of the microscope, with
the ring & soldered to it. Over this ring &, screws another ring
F, which serves as a support and asa centre to the graduated circle
D, which freely, but without shaking, revolves upon the same.
Into the bore of the ring F, fits by its lower conical end A, the
tube G, which is held in it bya screw-ring y, that preventsits being
taken out. Into the tube G, which also has a free revolving
movement, fits the positive eye-piece a, d being the field-lens,
s the eye-lens.

The slide 6 6, on opposite sides of G, admits of the micrometer
with its mounting B, B being introduced into G, and the gradua-
tion being brought into the field of the eye-piece.

Fig. 433.

ro Ca _T f
E \ tl
i
C is an index, attached to @ by the screw e; it may be taken
off, when the apparatus is not used as a goniometer.

1See American Journal of Science and Arts, for September, 1852, in which the
entire paper of Prof. Smith will be found,

USE OF THE GONIOMETER. 713

USE OF THE’ GONIOMETER.

Bring the object into focus near the centre of the field of the
micrometer, apply your finger to the knob K, and revolve the
micrometer, till the lines of its graduation are parallel to one

Fig. 434,

side of the angle to be measured. Revolve then separately the
graduated circle, till zero is brought to agree with the point of the
index @. Then revolve again the micrometer by the knob K,
until the graduation lines are parallel to the other side of the
angle to be measured, when the index C’ will show the value of
this angle. (The references are the same in both cuts.)

The graduated lines of the micrometer are generally ,}, of the
American inch apart. But their relative value as micrometer,
with the different object-glasses and eye-pieces, must be ascer-
tained by a glass stage-micrometer, and recorded in a table.

INDEX.

Aberration, chromatic, 73, 74.
spherical, 71, 72.

Acalephs, see Medusa.

Acarida, 581, 582.

Achyla prolifera, 315, 316.

Acineta-form of Vorticella, 419, 420,

Achnanthes, 297.

Achromatic Condenser, 131-133, 136; use
ol, 172, 193.

Achromatic correction, 41 ; principle of, 73,
74; application of, 74-76.

Actiniform Zoophytes, 474-476.

Actinocyclus, 289, 290.

Actinophrys, 407-469,

Adipose tissue, 607, 608, 664.

Adjustment of Focus, 86, 87; uses of, 162-

165.

of Object-glass, for thickness
of cover, 76, 77; mode of
making, 165-168.

Agates, sponge-remains in, 633.

Air-bubbles, microscopic appearances of,
184,

Alcyonian Zoophytes, 472-474.

Alcyonidium, 496, 497.

Atex, higher, microscopic structure of,
328-333 (see Protophyta).

Amaroucium, structure of, 501, 502.

Amici’s Prism for oblique illumination, 137.

Ameba, 405-407.

Anachoris alsinastrum, rotation in, 364,

65

Anagallis, petal of, spiral vessels in, 396.

Angular aperture of object- glasses, 71-3,
76; real value of, 188-192.

Animalcule-Cage, 148, 168.

ANIMALCULES, early researches on, 38;
Ehrenberg’s observations on, 47-49, 411—
424; Dujardin’s researches on, 49; see
Infusoria, Rhizopoda, and Rotifera.

Animals, Distinction of, from Plants, 247,
248, 409, 410.

ANNELIDA, 535; marine, circulation in, 535,
536 ; metamorphoses of, 536, 537; lumi-
nosity of, 537; fresh-water, 537, 538.

Annular Condenser, Shadbolt’s, 139, 140.

ANNULOSA, 529; see Entozoa, Turbellaria,
and Annelida.

Anomia, structure of shell of, 512.

Antenne of Insects, 564, 565.

Anthers, structure of, 396, 397.

Antheridia of Cryptogamia, discovery of,
45, 46; see Antherozoids.

Antherozoids, of Vaucheria, 314 ; of Sphe-

roplea, 318; of Characew, 325, 326; of
Fuci, 330; of Floridew, 331; of Mar-
chantia, 347; of Mosses, 349; of Ferns,
355, 356.

Aphides, non-sexual reproduction of, 580,
581.

Anthozoa, 457, 472-476.

Apple, cuticle ‘of, 389, 390.

Apus, 544.

Aquatic Box, 148, 169.

ARACHNIDA, microscopic forms of, 581, 582 ;
eyes of, 582; respiratory organs of, 582,
583 5 feet of, 583 ; spinning apparatus of,
583.

Arachnoidiscus, 290, 291.

Archegonia, of Marchantia, 344-347; of
Mosses, 349; of Ferns, 356-358.

Arcus Senilis, 665.

Areolar tissue, 603,

Argulus, 547, 548.

Artemia, 545,

Ascaris, 531, 532.

Asci of Lichens, 334; of Fungi, 335.

Ascidians, compound, 50,500; social, 502-
505.

Asphalte, use of, 207.

Aspidium, fructification of, 353-355.

Aspidisca-form of ‘Trichoda, 421.

Asteriada, skeleton of, 482, 483 ; metamor-
phoses of, 486-488.

Asteroida, 472-474.

Auditory vesicles of Mollusks, 527, 528 ;
st ogee of, 525.

Avicularia of Polyzoa, 498, 499.

Azure blue butterfly, scales of, 195, 558.

Bacillaria paradoza, 296; movements of,
287, 288.

Bailey, Prof., his diatomaceous tests, 199.

Balani, metamorphoses of, 548-550.

Bark, structure of, 384, 385.

Barnacles, metamorphoses of, 548-550.

Bat, hair of, 195, 595, 596.

Battledoor scale ‘of Polyommatus, 195, 558,

Batrachospermea, 321, 322.

Bee, eyes of, 561; proboscis of, 567;
wings of, 574; sting of, 578.

Berg- mehl, 303, 304.

Beroe, 470, 471.

Biddulphia, 299; markings on, 281; self-
division of, 284,

Binocular Microscopes, 114-117.

Bird, Dr. Golding, on preparation of Zoo-
phytes, 474.

716

Birps, bone of, 587 ; feathers of, 597, 598;
blood of, 599, 600; lungs of, 624-626.

Bird’s-head processes of Polyzoa, 498, 499.

Black-Japan varnish, 219.

Black-Ground Illuminators, 138-140, 174,
175.

Blenny, viviparous, scales of, 591.

Blood-Disks of Vertebrata, 183, 598-601;
mode of examining and preserving, 601,
602; circulation of, mode of examining,
616-619, 691.

Bloodvessels, injected preparations of,
619-623 ; disposition of, in different parts,
623-626; morbid, 666.

Bone, structure of, 183, 584-587 ; mode of
making sections of, 207-211, 587.

Bones, Fossil, examination of, 207-643.

Botrytis bassiana, 336.

Botryllians, 502.

Bowerbankia, 50, 496, 500.

Brachionus, 427, 429, 434.

Brachiopoda, structure of shell of, 513-515.

Branchwpoda, 542-545.

Branchipus, 545.

Brooke, Mr., his Object-glass holder, 127.

Brunswick-black, use of, 218.

Buccinum, tongue of, 521; egg-capsules
of, 522; development of, 523.

Bugs and their allies, 648 ; wings of, 676.

Bugula avicularia, 498, 499.

Bull’s-Eye Condenser, 143 ; use of, 178.

Busk, Mr. G , on Volvox, 260, 265.

Butterflies, see Lepidoptera.

Cabinets for microscopic objects, 243.

Cactus, raphides of, 371.

Calycanthus, stem of, 385.

Camera Lucida, 125, 126; use of, in Mi-
crometry, 126.

Campanularide, 463-465.

Campylodiscus, 292.

Canada balsam, use of, as cement, 208, 209,
219, 220; mounting of objects in, 224-232.

Canal-system of Foraminifera, 446, 447.

Canaliculi of bone, 585-587.

Cancer cells, 675.

Capillaries, circulation in, 616-619; injec-
tion of, 619-622; distribution of, 623-626.

Carp, scales of, 592.

Cartilage, structure of, 608, 609.

Cells for mounting objects, of cement, 235;
of thin glass, 236; of plate-glass, 237 ;
shallow, 237; deep and built up, 238-240;
mounting objects in, 240-242.

Cells, Animal, nature of, 404, 405,

Cells, Vegetable, 42; nature of, 249;
rotation in, 363-367 ; thickening deposits
in, 367, 368; spiral deposits in, 369;
starch-grains in, 370 371; raphides in, 37).

Cellular ‘Tissue, ordinary form of, 360-362 ;
stellate, 362; cubical, 363; dimensions
of, 363; component cells of, 363.

Cement-Cells, mode of making, 235, 236.

Cementum of Teeth, 589-591.

Cepuaxopops, shell of, 516, 517; chromato-
phores of, 528.

Ceramiacee, 331.

Chetophoracee, 321, 322.

Chalk, Foraminifera, &c., of, 631-633.

Characee, 322, 323; rotation of fluid in, 47,

INDEX.

324; multiplication of, by zoospores, 324;
sexual apparatus of, 325, 326.

Cherry-stone, cells of, 368. ; ;

Chemical Reagents, use of, in Microscopic
research, 211-213. a

Chilodon, teeth of, 415; self-division of,
418.

Chirodota, calcareous skeleton of, 486. |

Chloride of Calcium, as mounting medium,
233.

Choroid, pigment of, 605.

Chromatic Aberration, 71,72; means of re
ducing and correcting, 73, 74.

Chromatophores of Cephalopods, 527.

Cidaris, spines of, 481. :

Ciliary action, nature of, 424, 425; on gills
of Mollusks, 527.

Ciliated epithelium, 606, 607.

Circulation of Blood in Vertebrata, 616-
619; in Insects, 569, 570; alternating, in
Tunicata, 504, 505.

Cirrhipeds, metamorphoses of, 548-550.

Clavellinide, 503.

Clarke, Mr. J. L., his mode of preparing
sections of Spinal Cord, 616.

Cleanliness, importance of, to Microscope,
158-160; in mounting objects, 242.

Closterium, movement of fluid in, 267, 268;
duplicative subdivision of, 268, 269; mul-
tiplication of, by gonidia, 275; conjuga-
tion of, 274.

Clypeaster, spines of, 481.

Coal, nature of, 627-629.

Coarse-adjustment, 86-88 ; uses of, 162, 163.

Cockchaffer, cellular integument of, 556;
eyes of, 562; antenna of, 565; spiracle of
larva of, 572.

Cockle of wheat, 531, 532.

Coddingtgn lens. 80.

Cohn, Dr., his account of various states of
Protococcus. 953-259; his researches on
Infusoria, 425, vote; on reproduction of
Rotifera, 430, 431.

Coleoptera, mouth of, 565-567.

Collection of objects, general directions for,
243-245,

Collomia, spiral fibres of, 368-370,

Colostrum, 653.

Columella of Mosses, 35].

Comatula, metamorphosis of, 490.

Compound Microscope, principle of, 81-85 ;
various forms of, 06-117.

Compressorium, 150-152; use of, 168.

Concave lenses, refraction by, 69.

Conceptacles of Marchantia, 345, 346.

Condenser, Achromatic, 131-133, 136; use

of, 128, 173.

Annular, 139,

for Opaque Objects. ordinary,
144; bull’s-eye, 144; mode
of using, 177-179.

Confervacee, 317; self-division of, 318;
zoospores of, 318; sexual reproduction of,
318, 319.

Conifere, peculiar woody fibre of, 372; ab-
sence of ducts in, 375, 382; fossil, 382,
628, 629,

Conjugation of Palmoglea, 252; of Des-
midiacee, 274-276 ; of Diatomace#, 284-
286 ; of Conjugates, 319, 320 ; (supposed)
of Actinophrys, 408.

INDEX.

Contractile vesicle of Volvox, 260; of Ame-
ba, 405; of Actinophrys, 407; of Infuso-
ria, 417, 418.

Convex lenses, refraction by, 65-69; for-
mation of images by, 69.

Coquilla nut, cells of, 368.

Coral, red, 473; stony, 473, 474.

Corallines (zoophytic), 38,49 ; true, 331, 332.

Cordylophora, 461, 462.

Cork, 380.

Corpuscles of Blood, 598-601.

Corti, Abbé, on rotation in Chara, 47.

Corynida, 461, 462.

Coscinodiscus, 289, 290.

Cosmarium, self-division of, 269; conjuga-
tion of, 274.

Crab, shell-structure of, 550, 551; meta-
morphoses of, 551, 552.

Cricket, gastric teeth of, 569; sounds pro-
duced by, 575.

Crinoidea, skeleton of, 482.

Crusta petrosa of Teeth, 589-591.

Crustacea, 539; lower forms of, 539-541;
entomostracous, 541-546; suctorial, 547,
548; cirrhiped, 548-550; decapod, shell
of, 550, 551; metamorphoses of, 551, 552.

Cryprocamia, microscopic study of, 43-46 ;
movements of, 44; sexuality of, 45, 46,
359. (See Protophyta, Algew, Mosses, &c.)

Crystals of snow, 644.

Crystallization, Microscopic, 645.

Ctenoid scales of Fish, 594,

Curculionide, 556-559.

Cutaneous eruptions, 668,

Cuticle of Equisetacex, 358; of Flowering
Plants, 388-391.

Cuttle-fish, shell of, 516, 517.

Cycloid scales of Fish, 592.

Cyclops, 542, 543 ; fertility of, 546.

Cydippe, 470, 471.

Cypris, 541, 542.

Cyprea, structure of shell of, 515.

Cystic Entozoa. 530.

Cysticercus, 530.

Cythere, 542,

Dalrymple, Mr , on Notommata, 429.

Dalyell, Sir J. G.,on development of Me-
dusz, 468-470.

Daphnia, 544; ephippial eggs of, 546, 547.

Darwin, Mr., on Pampean formation, 639,
640.

Deane’s Gelatine, 232-234.

Decapod Crustacea, shell of, 550, 551; me-
tamorphoses of, 551, 552.

Defining power of object-glasses, 187, 188.

Demodex folliculorum, 582.

Dentine of Teeth, 588, 589.

Dendrodus, teeth of, 641.

Dermestes, hair of, 195, 559.

Desmidiacee, general structure of, 265-267 ;
movement of fluid in, 267, 268; duplica-
tive subdivision of, 268-270; formation of

_gonidia by, 270-273; organization and
multiplication of varieties in, 273, 274;
conjugation of, 274-276; collection of,
276, 277.

Deutzia, stellate hairs of, 390, 391.

Development, Von Baer’s law of, 52.

Animal, application of Mi-
croscope 10, 50-57,

T17

Development, Vegetable, application of Mi-
croscope to, 42-47,

Diamond-beetle, 556-560 ; foot of, 576.

Diaphragm-Plate, 130, 131,

Diatoma, 298.

Diatomaceae, vegetable nature of, 277; co-
hesion of frustules of, 278, 279; siliceous
envelope of, 277-280; markings of, 280-
283 ; self-division of, 283, 284; gonidia
of, 284; conjugation of, 284-286; limits
of species of, 286, 287, 301; movements
of, 287, 288; classification of, 288-301 ;
general habits of, 301-303; fossilized de-
posits of, 303, 304, 629-633 ; collection of,
304-306 ; mounting of, 306, 307; their
value as tests, 195-199.

Dicotyledonous Stems, structure of, 378-
386

Dictyochaliz, 453.

Didymoprium, self-division of, 269; conju-
gation of, 274, 275.

Diffraction of Light, errors arising from,
181, 182.

Dipping-Tubes, 152.

Dissecting Microscope, Quekett’s, 94-96.

Smith and Beck’s,
103-105.

Dissection, microscopic, 201-203.

Distoma, 532, 533.

,Dog, foot of, epidermis of, 606.

Doris, spicular skeleton of, 516.

Dotted Ducts, 374.

Doublet, microscopic, 79.

Draw-Tube, 118, 119.

Dropsical fluids, examination of, 699.

Dry-mounting of objects, 221-225,

Ducts of Plants, 374, 375.

Dujardin, M., on Rotifera, 432-435.

Duplicative subdivision, of Palmoglea, 252;
of Protococcus, 255; of Desmidiacee,
268-270; of Diatomacez, 283, 284; of
Confervacez, 318, 3193; of Protozoa, 407—
409 ; of Infusoria, 418.

Dusideia, skeleton of, 455.

Dytiscus, foot of, 577, 578.

Eagle Ray, teeth of, 589.

Echinida, shell of, 477, 478; ambulacral
disks of, 479; spines of, 479, 480; pedi-
cellarie of, 481,482; teeth of, 482; me-
tamorphosis of, 488-491.

Ecuinopermata, skeleton of, 477-486;
metamorphoses of, 486-491.

Educational Microscopes, 93-97, 104, note.

Educational Value of Microscope, 57-64.

Eel, scales of, 591, 592.

Eels, of Paste and Vinegar, 531.

Eggs of Insects, 579, 580.

Egg-shell, fibrous structure of, 602.

Ehrenberg, Prot., his researches on Ani-
malcules, 47-49, 411-424, 428-435; on
Polycystina, 449-452.

Elaters of Marchantia, 349.

Elementary Tissues: see Tissues.

Elytra, of Beetles, 575. ’

Embryo, vegetable, development of, 400,

Enamel of ‘Teeth, 589-591.

Encrinites, 482.

Encysting process of Infusoria, 419-422.

Endochrome of vegetable cell, 249.

718

Enterobryus, 338-340.

Entomostracous Crustacea, 541; their clas-
sification, 541-545; reproduction of, 545-
547.

Entozoa, 529; simplest form of, 530, 531;
cystic, 530; nematoid, 531, 532; trema-
tode, 532, 533.

Ephemera, larva of, 555-569, 573.

Epidermis of Animals, structure of, 604,

605.
of Plants, nature of, 391.

Epithelium, 606, 607; ciliated, 607, 608.

Equisetacee, 358; cuticle of, 358; spores
of, 359.

Erector, 119, 120.

Ether injection, 703.

Euryale, skeleton of, 482.

Eye, examination of, 67].

Eyes, care of, 158.

Eyes, of Mollusks, 526, 527; of Insects,
561-564.

Eye. piece, 82; Huyghenian, 83, 84 ; Rams-
den’s, 84, 85; Achromatic, 85; Menis-
cus, 85; Micrometric, 122-124, 713.

Fallacies of Microscopists, 39-41, 180-186.

Falconer, Dr., on bones of fossil Tortoise,
642.

Fat-cells, 607, 608; capillaries of, 623, 624.

Fatty degeneration, 665.

Faujasina, 439; canal-system of, 446, 447.

Feathers, structure of, 597, 598.

Feet of Insects, 576, 578.

Ferns, 352, 253; tructification of, 353, 354;
spores of, 354, 355; prothallium of, 355;
antheridia of, 355, 3563 archegonia of,
356, 357; generation and development
of, 357, 358.

Fertilization of ovule, in flowering plants,
399-401,

Fibre-cells of anthers, 396, 397.

Fibres, Muscular, 611-614.

Nervous, 614-616.

Fibrilla of Muscle, structure of, 612, 613.

Fibrous tissues, 602-604.

Field’s Compound Microscope, 97-99.
Simple Microscope, 93, 94.
Filiferous capsules of Zoophytes, 474-476.

Finder, 129, 130.

Fine Adjustment, 86, 87; uses of, 163,
164

Fisues, bone of, 587; teeth of. 588; scales
of, 591-593; blood of, 598-600; circula-
tion in, 619; gills of, 624.

Fishing-Tubes, 132.

Flatness of field of object-glasses, 189.

Flint, organic structure in, 633; examina-
tion of, 624,

Floridee, 33).

Floscularians, 432, 433.

Flowers, small, as microscopic objects, 394,
395,

Fluid, mounting objects in, 234-242.

Fluke, 532, 533,

Flustra, 49, 492-497,

Fly, number of objects furnished by, 553 ;
tongue of, 566, 567; spiracle of, 572;
wing of, 571; foot of, 576, 577. :

Focal Adjustment, 86, 87; precautions in
making, 162-165 ; errors arising trom im-
perfection of, 183, 184.

Foraminifera, 48, 436; their relation to

INDEX.

Rhizopoda, 437; their general structure,
437-440; peculiar forms of, 440-445; re-
lation of, to Sponges, 446; canal-system
of, 446, 447; collection and mounting of,
446-449 ; fossil deposits of, 629-634,

Forceps, 153; stage, 146.

Fossil Bone, 642.

Diatomacee, 303, 304, 629-633.

Fossil Foraminifera, 629-639.

Polycystina, 451, 452.
Sponges, 632.
Teeth, 641.

Wood, 388, 627-629.

Fowl, lung of, 625.

Frog, blood of, 599, 600; circulation in web
of, 616-618; in tongue of, 618, 619; lung
of, 624. :

Fucacee, 328, 325; sexual apparatus of,
328-331; development of, 331.

Fungi, simplest forms of, 334, 335; in
bodies of living animals, 335-340 ; in sub-
stance, or on surface of plants, 340-343 ;
higher forms of, 343, 344.

Fusulina, 634.

Furze, Mr., his arrangement for illumina
tion, 143,

Gad-flies, ovipositor of, 579.

Gaillonella, 299.

Gairdner’s Simple Microscope, 92, 93.

Gall-flies, ovipositor of, 579.

Ganoid scales of Fish, 593.

Gasteroropa, structure of shell of, 515,
516; tongues of, 517-521 ; development
of, 521-525; organs of sense of, 526-528.

Gastric teeth of Mollusks, 521; of Insects,

Gelatine, Deane’s, 232-234.

Gelatinous nerve-fibres, 614, 615.

Geology, applications of Microscope to,
627.

Geranium-petal, peculiar cells of, 395.

Gills. of Mollusks, ciliary motion on, 526;
of Fishes, distribution of vessels in, 624;
of Water-newt, circulation in, 629; ciliary
movement in, 624.

Gillett’s Condenser, 132.

Glands. structure of, 609-611.

Glass Slides, 214,

Thin, 214-217.
Glue, liquid, use of, 218.
marine, use of, 219-221,

Glycerine, use of, in mounting objects, 232.

Gnats, larve of, 569, 570.

Goadby’s Solution, 233.

Gold-size, use of, 218.

Goniometer, 124.

Gomphonema, 294, 295,

Gonidia, multiplication by, in. Desmidiacer,
270-272; in Diatomacee, 284 ; in Hydro-
dictyon, 300; in Chara, 325; in Floridee,
3315 in Lichens, 333.

Gorgonia, spicules of, 474.

Gosse, Mr., on Melicerta, 433; on thread-
cells of Zoophytes, 474-476.

Grammatophora, 298; its use as test, 199.

Grantia, structure of, 309-317.

Grasses, silicified cuticle of, 390, 391.

Gregarina, 530, 531.

eee and Polishing of Sections, 207-

1;

INDEX.

Gromia, 437, 438.

Growing-Slide, 147. : Shs

Grubb’s Prism for oblique illumination,
137.

Guano, Diatomacee of, 304-306.

Hairs, of Mammals, 183; structure of, 593-
596; mode of mounting, 597; of Insects,
559-561.

Hairs, of vegetable cuticles, 390; rotation
of fluid in, 365, 366,

Halichondria, spicules of, 454.

Harvest-bug 582.

Haversian Canals of bone, 585.

fleliopelta, 290, 291.

Haustellate Mouth, 567, 568,

Henfrey, Mr., on development of pollen-
grains, 396,

Hepatice, 344; see Marchantia.

Herapathite, 140.

Hepworth, Mr., on feet of Insects, 577.

Highley’s Hospital Microscope, 99, 100.

Hippocrepian Polyzoa, 497-500.

Histology, 54.

Hematococcus, its relations to Protococcus,

254

sanguineus, 308.
Hogg, Mr., on development of Lymneus,
523.

Holland, Mr., his triplet, 80.

Holethurida, skeletons of, 485, 486.

Hoofs, structure of, 598.

Hooker, Dr. Jas.,on Antarctic Diatomacee,
301, 302.

Horns, structure of, 598.

Huxley, Mr., on Rotifera, 430, 431, 435;
on Noctiluca, 472; on blood of Annelida,
536.

Huyghenian eye-piece, 82-84.

Hydatina, 434; reproduction of, 431.

Hydra, discovery of, 37; structure of, 457-
461

Hydrodict yon, 316, 317.

Hydrozoa, 461-470.

Hymenoptera, proboscis of, 566, 567 ; wings
of, 574; stings and ovipositors of, 578-
579,

Jackson, Mr., his eye-piece micrometer,
122, 123.
Jelly-fish, development of, 467-470.

Ice-plant, cuticle of, 390.
Ichneumonide, ovipositor of, 578.
Illumination of opaque objects, 176-180;
of transparent objects, 172-175.
Illuminators, Black-ground, 138-140, 174,
175.
Oblique, 135-138, 173, 174.
White Cloud, 134, 173.
Images, formation of, by convex lenses,
69.

Indicator, 124.

Indusium of Ferns, 352-354.

Inflection of Light, errors arising from,
181, 182.

Infundibulate Polyzoa, 497-500.

Infusorial Earths, 303-306, 629.

Inrusorra, 48, 411, 412; structure of, 413-
417; movements of, 415, 416; repro-

719

duction of, 418-423; peculiar forms of,
423, 424,

Injections of bloodvessels, mode of making,
619-622; mode of mounting, 622, 623, 700.

Inorganic substances as objects, 644,

Insects, great number of objects furnished
by, 553, 554; microscopic forms of, 554,
555; antenne of, 564, 565; circulation of
blood in, 569, 570; eggs of, 579-581;
eyes of, 561-564; feet af 576-578 ; gastric
teeth of, 569; hairs of, 559-561 ; integu-
ment of, 555, 556; mouth of, 565-568;
ovipositors of, 578, 579; scales of, 556-
561; spiracles of, 572-574; stings of,
578, 579; trachez of, 570-574; wings of,
574-576.

Tris, structure of leaf of, 392-394.

Isthmia, 298; markings on, 280, 281; self-
division of, 283, :

lteh- Acarus, 587.

Integument of Insects, structure of, 555,
556.

Kidneys, structure of, 610; morbid, 664.

Labelling of objects, 242, 243,

Labyrinthodon, tooth of, 641.

Lacune of bone, 585-588.

Laguncula, 492-495, 500.

Lamps, microscope, 154~157.

Lealand, Mr., his preparations of muscular
fibre, 195, 614.

Leaves, structure of, 392-394; mode of
examining, 394.

Leech, 538; teeth of, 538,

Legg, Mr., on collection of Foraminifera,
447-149.

Lepidoptera, scales of, 556-561; proboscis
of, 567, 568; wings of, 574, 575; eggs
of, 564.

Lepidosteus, bony scales of, 586, 587, 593.

Lepisma, scales of, 559.

Lepralia, 492-497.

Lever of Contact, 216.

Levant Mud, microscopic organisms of,
630-633.

Lever-Stage, 128, 707.

Lichens, 333, 334.

Licmophora, 295, 296.

Lieberkiihn, speculum of, 146; mode of
using. 179, 180.

Light, suitable for Microscope, 154-157;
position of, 157; arrangement of, for
transparent objects, 169-176; for opaque
objects, 177-180.

Liquid Glue, use of, 218.

Lister, Mr., his improvements in Achro-
matic lenses, 75, 76.

Liver, structure of, 609; morbid, 663.

Lungs of Reptiles, 624; of Birds, 624, 625;
of Mammals, 626; morbid, 658,

Lymneus, development of, 521, 522.

Magnetic Stage, 130.

Magnifying power, mode of determining,
199, 200; augmentation of, 161; of dil-
ferent objectives, 192~196.

Mahogany, section of, 383.

Mamma .s, bone of, 587; teeth of, 589-591 ;
hairs, &c., of, 593-598; blood of, 598-
602; lungs of, 625.

720

Man, hair of, 595, 596.

Mandibulate mouth of Insects, 565-567.

Marchantia, general structure, of, 344, 345;
stomata of, 345, 346; conceptacles of,
346; sexual apparatus of, 347, 348.

Margaritacee, shells of, 506-508, 509,

Marine Glue, uses of, 219-221.

Mastogloia, 299-301,

Medullary Rays, 381-384.

Meduse, development of, from Zoophytes,
52, 53, 467-470,

Megatherium, teeth of, 590.

Melicertians, 432-434.

Meloseira, 299; self-division of, 284; con-
jugation of, 286.

Menelaus, scale of, 557.

Meniscus eye-piece, 85.

Meridion, 296, 297.

Metamorphoses of Animals, 50; of Cirrhi-
peds, 50, 548-550; of Crustacea, 52, 551,
552; of Echinoderms, 52, 486-491; of
Infusoria, 419-422 ; of Mollusks, 51, 504,
505; of Annelids, 52, 536, 537.

Micrometer, Cobweb, 120-122; eye-piece,
122-124.

Micrometry, by Micrometer, 120-124; by
Camera Lucida, 126.

Microscope, early history of, 35-41; later

history of, 41-57; educa-
tional uses of, 57-64.

optical principles of construc-
tion of, 77-85 ; mechanical
principles of construction
of, 86-90.

Compound, 81-85, 96, 97.

Field’s, 97-99.

Highley’s, 99, 100.

Nachet’s, 100-102.

Ditto, binocular, 114-117.

Powell and Lealand’s, 110-
112.

Ross’s, 108-110.

Smith and Beck’s large, 112-
114,

Ditto dissecting, 103-105.

Ditto student’s, 102, 103.

Ditto educational, 104, note.

Warington’s universal, 105-
108.

Simple, 77-81, 90.

Field’s, 93, 94.

Gairdner’s, 92, 93.

Grunow’s, 706.

Queen’s, 706.

Quekett’s, 94-96.

Ross’s, 90-92,

Spencer's, 704.

support required for, 154;
care of, 158-160; general
arrangement of, 160; for
transparent objects, 168-
172; for opaque objects,
175-177.

Microscopic Dissections, 201-203,
Microscopiats, fallacies of, 39-41.
Microtome, 203, 204. :

Mildew, fungous vegetation of, 340, 341.

Milk, 683.

Millon’s test for albuminous substances, 213.

Mineral Objects, 645.

Minnow, circulation in, 619.

we . igi hy Eee ain

INDEX.

Molecular movement, 185, 186.

Motuusca, shells of, 506-517; tongues of
517-521; development of, 521-525;
ciliary motion on gills of, 526; organs of
sense of, 527, 528.

Monocotyledonous Stems,
376-378.

Morbid growths, examination of, 674.

Morpho Menelaus, scale of, 194, 557.

Mossss, structure of, 348, 349; sexual ap-
paratus of, 347-350; urns of, 350, 351 ;
peristome of, 351: development of spores
of, 352.

Moths ; see Lepidoptera.

Mould, fangous vegetation of, 340, 341.

Mounting of objects ; see Objects.

Mounting- Plate, 219.

Mouse, Ear of, cartilage of, 608.

Mouth of Insects, 565-568.

Mucous Membranes, structure of, 604;
capillaries of, 623; ulcers of, 670.

Miiller, O. F., his researches on Animal-
cules, 38.

Miiller, Prof., his researches on Fchino-
derm-larvee, 486-491.

Muscardine, or silk-worm disease, 44, 45,

structure of,

336.

Muscular fibre, structure of, 611-613; value
of, as test-object, 195; mode of examining
and preparing, 613, 614, 655; capillaries
of, 623, 624.

Musk-deer, hair of, 595.

Mussel, ciliary action on gills of, 526.

Mya, structure of hinge-tooth of, 509.

Mycelium of Fungi, 340-343.

Myliobates, teeth of, 589.

Nachet’s Microscope, 100-102; his Bino-
cular Microscope, 114-117; his prism for
oblique illumination, 136, 137.

Nacre, structure of, 509-511.

Nais, 537, 538.

Nassula, teeth of, 415.

Navicule, 293, 294; movements of, 287.

Needles for dissection, mode of mounting,
203.

Nematoid Entozea, 531, 532.

Nepenthes, spiral vessels of, 374.

Nervous Tissue, structure of, 614, 615,
653; mode of examining, 615, 616, 653.

Newt, circulation in larva of, 619.

Nicol-Prism, 140.

Nobert’s Test, 196, 197.

Noctiluca, 471, 472.

Nostochucee, 312, 313.

Notommata, 429-435.

Nucleus of Vegetable cells, 251, 365; of
Infusoria, 418.

Nudibranchs, development of, 521, 522.

Nummulite, structure of, 446, 634-637.

Nuphar lutea, parenchyma of, 362.

Object-Finder, 129, 130.

Object-glasses, achromatic, principle of, 73,
74; construction of, 74-76; adjustment
of, for covering of object, 76, 77, 165-
168; defining power of, 187, 188; pene-
trating power of, 188; resolving power
of, 188, 189; flatness of field of, 189;
comparative value of, 188-192; different
powers of, 193-198; tests for, 193-199;

INDEX.

determination of magnifying power of,

199, 200,

Object-glass holder, Mr. Brooke's, 127.

Otlecl: Marker, 127, 128.

Objects, mode of mounting, dry, 221-224;
in Canada balsam, 224-232; in preserva-
tive fluids, 232-242; see Opaque and
Transparent Objects.

Oblique Illuminators, 135-138, 173, 174.

Ocelli of compound eyes of Insects, 561.

Gidogonium, zoospore of, 318; sexual re-
production of, 319. :

Oil-globules, microscopic appearances of,
184,

Oleander, cuticle of, 389.

Oncidium, spiral cells of, 368,

Onion, raphides of, 371.

Oolite, structure of, 634,

Opaque Objects, arrangement of Micro-
scope for, 175-177; various modes of illu-
minating, 177-180; modes of mounting,
121-124.

Opercula of Mosses, 350.

Ophiocoma, 482.

Ophiurida, skeleton of, 482, 483.

Ophryding, 423.

Orbitoides, structure of, 637-639.

Orbitolite, structure and development of,
440-445.

Ornithorhyncus, hair of, 595.

Oscillatoriacee, 311-313.

Ovipositors, 578, 579.

Ovules of Phanerogamia, 399; fertilization
of, 48, 399, 400; mode of studying, 400,
401.

Owen, Prof., on Fossil Teeth, 641, 642; on
Fossil Bone, 642, 643.

Oxytricha-form of Trichoda, 421, 422.

Palm, stem of, 377, 378.

Palmellacee, 307-309.

Palmoglea macrococca, life-history of, 251-
253.

Pampean deposit, organic composition of,
639

Papille of skin, structure of, 605-615; of
tongue, 615,

Parabolic Illuminator, 139, 140.

Paramecium, 413, 414; contractile vesicle
of, 417; multiplication of, 418.

Parasitic fungi, 335-443.

Pearls, structure of, 509-511,

Pecari, hair of, 595.

Pecten, eyes of, 527; tentacles of, 528.

Pediastrum, multiplication and develop-
ment of, 270-273.

Pedicellarie of Echinoderms, 481, 482.

Penetrating power of object-glasses, 188.

Pentacrinus, skeleton of, 482; larval, 491.

Peristome of Mosses, 350, 351.

Perophora, 502-505.

Petals of Flowers, structure of, 395, 396.

Pettenkofer’s test, 212.

PHANEROGAMIA, elementary tissues of, 360-
376 (see Tissues of Plants); stems and
roots of, 376-388; cuticle and leaves of,
388-394 ; flowers of, 394-401; seeds of,
401-403.

Phytelephas, cells of, 368.

Phyllopoda, 544.

721

Pigment-cells. 605,

Pith, structure of, 378, 379.

Pinna, structure of shell of, 506-508.

Pinnularia, 294.

Placoid scales of Fish, 593,

Planaria, 533-535,

Plants, distinction of from Animals, 247,
248, 409, 410.

Plantago, rotation in hairs of, 366.

Pleurosigma, 294; nature of markings on,
281, 282 ; value of, as tests, 195-198,

Pluteus-larva of Echinus, 488-490.

Pneumonia, pathological condition in, 661.

Podura, scale of, 195, 556, 557.

Polarization, objects suitable for, 645.

Polarizing Apparatus, 140-143,

Pollen-grains, development of, 397; struc-
ture and markings of, 194, 397-399,

Polycystina, nature of, 449, 450; distribu-
tion of, 450-452.

Polygastrica ; see Infusoria.

Polyommatus argus, scale of, 557, 558.

Polypes ; see Hydra and Zoophytes.

Polypodium, fructification of, 353.

Potyzoa, 49, 492; general structure of, 492-
496; molluscan nature of, 496; classifi-
cation of, 497-500.

Potato-disease, 342.

Powell and Lealand’s Microscope, 110-112;
their Achromatic Condenser, 133.

Preservative Liquids, 232-234.

Primordial utricle, 248.

Prismatic shell-substance, 506-508.

Prisms, Dujardin’s, 133, 134,173; Nachet’s,
136; Amici’s, 137; Grubb’s, 137; pola-
rizing, 140, 141.

Proboscis of Bee, 566, 567; of Batterfly,
567, 568; of Fly, 566, 567.

Proteus, 405.

Protococcus pluvialis, life-history of, 253-
257; various forms of, 257, 258; con-
ditions influencing changes of, 258, 259.

Protoplasm of vegetable cell, 248.

Protopuyta, general characters of, 247-

49

Protozoa, 404-409 ; their relations to Pro-
tophyta, 247, 248, 409, 410.

Pseudopodia, of Rhizopods, 407-411.

Pterodactyle, bone of, 642.

Puccinia, 341.

Purpura, development of, 521-525.

Pycnogonide, 539-541.

Quekett, Mr., his Dissecting Microscope,
94-96 ; his Indicator, 124; on Structure of
Bone, 642, 643.

Querquedula crecca, 655.

Rainey, Mr., his moderator, 156,

Ramsden’s eye-piece, 84, 85.

Raphides, vegetable, 371, 372.

Reade, Rev. J. B., on black-ground illumi-
nation, 138.

Reagents, Chemical, use of, in Microscopic
research, 211-213.

Red Corpuscles of Blood, 599, 600.

Red Snow, 307.

Refraction, laws of, 65, 66; by convex
lenses, 65-69; by concave and meniscus
lenses, 69.

46

722

Reindeer, hair of, 595.

Rertites, bone of, 587; teeth of, 591;
scales of, 593; blood of, 598-600; lungs
of, 624.

Resolving power of object-glasses, 187-189.

Rete Mucosum, 604.

Reticulated Ducts, 374.

Rhinoceros, horn of, 598.

Ruizoropa, 47, 410, 411.

Rhubarb, raphides of, 371.

Rhynconellida, structure of shell of, 513-515.

Rice- Paper, 362.

Rochea falcata, 390.

Rocks, structure of, 639.

Roots, structure of, 386; mode of making
sections of, 386-388.

Rosalina, 439.

Ross, Mr., on adjustment of object-glass,

his Compound Microscope, 108-
110; his Achromatic Con-
denser, 131-133; his Simple
Microscope, 90-92; his lever
of contact, 216; his side re-
flector, 145; his eye-piece
Micrometer, 122.

Rotation of fluid in Chara, 324; in cells of
Phanerogamia, 363-367.

Rotifer, anatomy of, 428-130 ; reproduction
ot, 431; desiccation of, 432; occurrence
of, in leaf-cells of Sphagnum, 426.

Rorirera, 57, 412; general structure of,
426-430 ; reproduction of, 430-432 ; desic-
cation of, 432; classification of, 432-434.

Rush, stellate parenchyma of, 362.

Rust, of Corn, 341.

Sable, hair of, 595.

Saliva, 684.

Sarcode, 405-409,

Sarcolemma, 655,

Saw-flies, ovipositor of, 578.

Scalariform duc's of Ferns, 352, 353, 374.

Scales, of cuticle of Plants, 390.

of Fish, 591-593.

of Insects, 556-561; their use as
test-objects, 194.

of Reptiles and Mammals, 594.

Schacht on fertilization of ovule, 399-401.

Schleiden, Prof., his researches, 42; on
fertilization of ovule, 399-401.

Schultz, Prof., his experiments on develop-
ment of Infusoria, 422, 423.

Schultz’s solution, 212.

Schwann, doctrines of, 56.

Scissors for microscopic dissection, 201-203 ;
for cutting thin sections, 204.

Sclerogen, deposit of, on walls of cells, 367.

Sea- Anemone, 474-476.

Sealing-wax varnish, 219.

Section-Instrument, 205-207.

Sections, thin, mode of making, of soft sub-
stances, 204, 205; of substances of me-
dium hardness, 205-207; of hard sub-
stances, 207-211; of Wood, 386-388 ; of
Echinus-spines, 483, 484; of Bones and
Teeth, 587; of Hairs, 597.

Seeds, microscopic characters of, 401-403.

Segmentation of Yolk-mass, 521.

Seleuite- Plate, 142,

INDEX.

Self-division of cells; see Duplicative Sub-
division.

Serous membranes, structure of, 604.

Sertularide. 463-465.

Shadbolt, Mr., on Arachnoidiscus, 290.

his Annular condenser, 139; his
Turn-table, 236.

Shark, teeth of, 588, 589; scales, &c., of,

593

Shell, of Crustacea, 550, 551; of Echinida,
477, 478; of Mollusca, 506-517.

Side- Reflector, Ross's, 145.

Siliceous Cuticles, 358, 391.

Silk- worm disease, 336.

Simple Microscope. principle of, 77-81;
various forms of, 90-96.

Siphonacee, 313-317. .

Skin, structure of, 604,605 ; papilla of, 605-
615,

Slider-forceps, 226.

Slides, glass, 214.

wooden, 221, 222.

Slug, rudimentary shell of, 516.
Smith’s, Prof. J. L., inverted microscope,
710; goniometer and micrometer, 712.
Smith, Prof. W.,on Diatomacee, 301, 302.
Smith and Beck’s Dissecting Microscope,
103-105; their Large Compound Micro-
scope, 112-114; their Achromatic Con-
denser, 133; their Student’s Microscope,
102, 103; their Educational Microscopes,
89.

Snake, lung of, 624.

Snow-crystals, 644.

Sole, skin and scales of, 591, 592.

Sollitt’s Achromatic Condenser, 136.

Sorby, Mr., his microscopic examination of
rocks, 640.

Spatangus, spines of, 481.

Speculum-disk for drawing, 125.

Spencer, Mr., his object-glass, 51, note; his
microscopes, 704,

Spermatia of Lichens, 334; of Fungi, 344.

Spermogonia of Lichens, 333; of Fungi,
344

Sphacelaria, 328.

Sphagnum, peculiar cells of, 348, 349; oc-
currence of Rotifer in leaf-cells of, 426,
Spheria, development of, within animals,

338.

Spheroplea, sexual reproduction of, 318.

Spherosira volvor, 264.

Spherical Aberration, 70; means of re-
ducing and correcting, 71, 72.

Spicules of Sponges, 453-455 ; of Alcyonian
Zoophytes, 472-474; of Tunicated Mol-
lusks, 500; of Doris, 516.

Spiders, eyes of, 582; respiratory organs of,
aa feet of, 583; spinning apparatus of,

abies! Cord, mode of preparing sections of,

Spines of Echinus, &c., 479, 480; mode of
making sections of, 482-484.

Spinning-apparatus of Spiders, 583.

Spiracles of Insects, 571-573.

Spiral Vessels, 373, 374.

Sponges, their structure, 452, 453; ciliary
action in, 453; skeleton of, 453-455; re-
production of, 455 ; examination of, 455 ;
fossil, 633.

INDEX.

Sporangia, of Desmidiacer, 274, 275; of
Diatomacew, 284-286; of Fuci, 330.

Spores of Hepatice, 347; of Mosses, 351,
352; of Ferns, 355; of Equisetaces, 358.

Spotted Lens, 138.

Spring-press, 227.

Spirogyra, 241,

Sputum, 685.

Squirrel, hair of, 594, 595.

Stage, lever, 128, 129; magnetic, 130.

movements of, 109, 110.

Stage-Forceps, 146.

Stage-Plate, glass, 147.

Stanhope lens, 80, 8).

Star- Anise, cells of seed-coat of, 367, 368.

Starch Granules in cells, 370, 371; appear-
ance of, by polarized light, 370, 371.

Staurastrum, prominences of, 265, 266;
self-division of, 269; varieties of, 273.

Stein, Dr., his researches on Infusoria, 419,
420.

Stellate cells of Rush, 362; of water-lily,

62

Stemmata of Insects, 563.
Stems, Endogenous, structure of, 376-378.
Fixogenous, structure and develop-
ment of, 378-386.
Mode of making sections of, 386-
388.
Stentor, 423.
Stephanoceros, Eichornii, 433.
Stickleback, circulation in, 619.
Stigmata of Insects, 571-573.
Stings, structure of, 578, 579.
Stomata of Marchantia, 345, 346; of Flow-
ering Plants, 391, 392.
Suctorial Crustacea, 547, 548.
Suminski, Count, on development of Ferns,
46.
Surirella, 293; conjugation in, 284.
Swarming, of Desmidiacez, 270.
Synapta, calcareous skeleton of, 485, 486.

Tadpole, pigment-cells of, 604, 605; mode

of viewing circulation in, 619.

Tenia, 529, 530

Tardigrada, 435; desiccation of, 432.

Teeth, of Echinida, 482; of Mollusks, 517—
521; of Leech. 538; of Vertebrata, struc-
ture of, 588-591; fossil, 641, 642; mode
of making sections of, 207-211, 587.

Terebella, circulation and respiration in,
35, 536.

Terebratula, structure of shell of,.513-515,

Test-Bottles, 212.

Test-Liquids, 212, 213.

Test-Objccts, 192-199.

Tetraspores of Floridew, 331, 332.

Thalassicolla, 445.

Thaumantias, 467.

Thece of Fungi, 334, 335; of Ferns, 352,

353.
Thin Glass, 214-216,
Thompson, Mr. J. V., on Polyzoa, 492; on
metamorphosis of Cirrhipeds, 548-550;
on metamorphoses of Crustacea, 551,

552.
Thread-cells of Zoophytes, 474-476.
Thread, glutinous, of spider’s web, 582, 583.
Thrush, fungous vegetation of, 340,
Thwaites’s fluid for Alga, 232.

728

Thymus and thyroid gland, 664.

Ticks, 581.

Tinea favosa, fungous vegetation of, 340.

Tissues, Elementary, of Animals, micro-
scopic study of, 53-55, 584; independent
life of, 56, 57; see Blood, Bone, Capilla-
ries, Cartilage, Epidermis, Epithelium,
Fat, Feathers, Fibrous Tissues, Glands,
Hair, Horn, Mucous Membranes, Muscle,
Nervous Tissues, Pigment-cells, Scales,
Serous Membranes, ‘l'eeth.

Tissues, Elementary, of Plants, 360; cel-
lular, 360-363; varieties of, 367-371;
woody, 372; fibro-vascular, 372; vascu-
lar, 373, 374; vasilform, 374, 375; dis-
section of, 375, 376,

Tongues of Gasteropods, 517-520; of In-
secis, 565-567.

Torula cerevisie, 334, 335.

Trachez of Insects, 570-572 ; mode of pre-
paring, 573, 574.

Tradescantia, rotation in hairs of, 365, 366.

Transparent Objects, arrangement of Mi-
croscope for, 168-172; various modes of
illuminating, 172-175.

Trematode Entozoa, 532, 533.

Trembley, his researches on the Hydra, 37.

Triceratium, 292; markings on, 281,

Trychoda lynceus, bristles of, 415; meta-
morphoses of, 420-422.

Trilobite, eye of, 640,

Triplet, Microscopic, 80.

Trout, circulation in young, 619.

Tubercle, microscopic appearance of, 658,

Tubularide, 462, 463, 465.

Tubules, nervous, 614, 615.

Tunicata, Compound, general organiza-
tion of. 500-502; different types of, 502-
504; alternating circulation in, 504, 505 ;
development of, 505.

Turbellaria, 533-535,

Turn-table, Shadbolt’s, 236,

Ulvacee, 309-311.

Unionide, shells of, 508-512.
Uredo, 342.

Urinary deposits, 688.

Urns of Mosses, 350, 351.

Vacuoles, microscopic appearances of, 185,

Valentin’s knife, 205,

Vallisneria spiralis, rotation in,°363, 364.

Varnishes useful to Microscopists, 216-219.

Vasiform Tissue, 374, 375.

Vaucher, his researches on Conferve, 38.

Vaucheria, 313; zoospores of, 314, 315;
sexual reproduction of, 315, 316.

Vegetable Organization, general nature of,
248; see Plants.

Vegetable Cell, nature of, 248, 249.

Vegetable Ivory, 368.

VERTEBRATA, elementary structure af, 585—
616 (see Tissues); blood of, 598-601 ;
circulation in, 616-619; development of,
626.

Vesicles of Nervous tissue, 614, 615.

Vibracula of Polyzoa, 498, 499,

Villi of intestine, injections of, 622,

Vine disease, 342.

Volvox, structure of, 259, 260; develop-
ment of, 261-265,

724

Vomited matters, 698,

Vomit, black, 648.

Von Baer’s law of development, 52.

Vorticella, 416-423; encysting process in,
419, 420.

‘Warington's Universal Microscope, 105-
0

Water-vascular system, of Rotifera, 429,
430; of Entozoa, 530.
Wenham, Mr., his Parabolic Speculum,
139

his observations on rotation,
364-367.

Whalebone, structure of, 598.
Wheel- Animalcules; see Rotifera.
White-Cloud Illuminator, 134, 173.
White Corpuscles of blood, 598-601.
White Fibrous tissue, 603.
Williamson, Prof., on Volvox, 261-265.
Wings of Insects, 574-576.
Winter-eges of Rotifera, 431; of Hydra,

61; 8f Entomostraca, 546.

THE

INDEX.

Wood, of Exogenous stems, 378-38:. _
Woody Fibre, 372; glandular, of Conifere,
373.

Xanthidia of Flints, 633.

Yeast, a vegetable substance, 45; produc-
tion of, 45, 334, 335,

Yellow fibrous tissue, 603, 604,

Yellow Water-lily, parenchyma of, 362.

Yucca, stomata of, 391, 392.

Zoophyte- Trough, 149, 150.

Zoopuytes, 457; Hydraform, 461-465;
preparation of, for microscope, 465-467 ;
development of Medusa from, 52, 53,
467-470; Alcyonian, 472-474; Actini-
form, 474-476.

Zoospores, formation of, by Ulvacee, 310,
311; by Vaucheria, 314, 315; by Achlya,
315, 316; by Confervaceew, 318, 319; by
Chetophoracee, 321; by Fucacez, 330,
331.

END.

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ASHTON (T. J.),
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4 BLANCHARD & LEA’S MEDICAL

BUDD (GEORGE), M.D., F.R.S.,

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ON DISEASES OF THE LIVER.

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| with the progress of modern science.

pp. 500. $3 00.
ig not perceptibly changed, the history of liver dis-

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We have no hesitation in recommending this bock
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BUMSTEAD (FREEMAN J.) M.D.,
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THE PATHOLOGY AND TREATMENT OF VENEREAL DISEASES,

including the results of recent investigations upon the subject. With illustrations on wood. In
one very handsome octavo volume, of nearly 700 pages, extra cloth; $3 75. (Now Ready.)

By far the most valuable contribution to this par-
ticular branch of practice that has seen the light
within the last score of years. His clear and accu-
rate descriptions of the various forms of venereal
disease, and especially the methods of treatment he
proposes, are worthy of the highest encomium. In
these respects it is better adapted for the assistance
of the every-day practitioner than any other with
which we are acquainted. In variety of methods
proposed, in minuteness of direction, guided by care-
sul discrimination of varying forms and eomplica-
tions, we write down the book as uasurpassed. It
is a work which should be in the possessivn of every
practitioner.— Chicago Med. Journal. Nov. 1861.

The foregoing admirable volume comes to us, em-
bracing the whole subject of syphilology, resolving
many a doubt, correcting and confirming many an
entertained opinion, and in our estimation the best,
completest, fullest monogiaph on thia subject in our
language. As far as the author’s labors themselves
‘are concerned, we feel it u duty to say that he has
not only exhausted his subject, but he has presented
to us, without the slightest hyperbole, the best di-
Sadia treatise on these diseases in our Janguage.

e has carried its literature duwn to the present
moment, and has achieved his task in a manner
which eannot but redound to his ciedit.—British
American Journal, Oct. 1861. a

We believe this treatise will come to be regarded
as high authority in this branch of medical practice,
and we cordially commend it to the favorable notice
of our brethren in the profession. For our own part,
we candidly confess that we have received many
‘new ideas from ita perusal, as well as modified many
‘views which we have long, and, as we now think,
erroneously entertained on the subject of syphilis.

Tosum up allina few words, this book isone which
no practising physician or medical student can very
well afford: to do without.—American Med. Times,
Nov. 2, 1861.

The whole work presents a complete history of
venereal diseases, comprising much interesting and
valuable material that has been spread through med-
ical journals within the last twenty years—the pe-
tiod of many experiments and investigations on the
subject—the whole carefully digested by the aid of
the author’s extensive personal experience, and
offered to the profession in an admirable furm. Its
completeness is secured by guod plates, which are
especially full in the anatomy of the genital organs.
We have examined it with great satisfaction, and
congratulate the medical profession in America on
the nationality of a work that may fairly be called
original —Berkshire Med. Journal, Dee. 1861.

One thing, however, we are impelled to say, that
we have met with no other book on syphilis, in the
Engtish language, which gave so full, clear, and
impartial views of the important subj-cts on whieh
it treata. We cannot, however, refrain from ex-
pressing our satisfaction with the full and pers pica-
ous manner in which the subject has been presented,
and the careful attentiva to minute details, so use-
ful—not to say indispensab!e—in a practical treatise.
In conclusion, if we may be pardoned the use of a
phrase now become stereotyped, but which we here
employ in all seriousness and sincerity, we do not
hesitate to express the opinion that Dr. Bumstead’s
Treatise on Venereal Diseases is a ‘* work without
which no medical library will hereafter be consi-
dered complete.’’—Boston Med, and Surg. Journal,
Sept. 5, 1861.

BARCLAY (A. W.), M.D.,;
Assistant Physician to St. George’s Hospital, &c.

A MANUAL OF MEDICAL DIAGNOSIS; being an Analysis of the Signs

and Symptoms of Disease. Second American from the second and revised London edition. In
one neat octavo volume, extra cloth, of 451 pages. $225. (INVow ready.)

The demand for a seond edition of this work shows that the vacancy which it attempts to sup-
ly has beeu recognized by the profession, and that the efforts of the author to meet the want have
fen successful, The revision which it has enjoyed will render it better adapted than before to
afford assistance to the learner in the prosecution of his studies, and to the practitioner who requires

a convenient and accessible manual for speedy reference in the exigencies of his daily duties.

For

this latier purpose its complete and extensive Index renders it especially valuable, offering facilities
for immediately turning to any class of symptoms, or any variety of disease.

The task of composing such a work is neither an
easy nor a light one; but Dr, Barclay has performed
it in a manner which meets our most unqualified
approbation. He is no mere theorist; he knows his
work thoroughly, and in attempting to perform it,
has not exceeded his powers.— British Med. Journal,

We venture to predict that the work will be de-
servedly popular, and soon become, like Watson’s
Practice, an indispensable necessity to the practi-
tioner.— NV. A. Med. Journal,

An inestimable work of reference for the youn,
practitioner and student.—Nashville Med. Journal.

We hope the volume will have an extensive cir-
culation, not among students of medicine only, but
practitioners also. They will never regret a faith-
ful study of its pages.— Cincinnati Lancet.

An important acquisition to medical literature.
It isa work of high merit, both from the vast im-
portance of the subject upon which it treats, and
also from the real apility displayed in ‘te elabora-
tion. In conclusion, let us bespeak for this volume
that attention of every student of our art which it
so richly deserves — that place in every medical
library which it cun so well adora.--Peninsular
Medical Journal.

BARTLETT (ELISHA), M.D.
THE HISTORY, DIAGNOSIS, AND TREATMENT OF THE FEVERS

OF THE UNITED STATES. A new and revised edition.

By Atonzo Ciarg , M.D., Prof.

of Pathology and Practical Medicine in the N. Y. College of Physicians and Surgeons, &c. In
one octavo volume, of six hundred pages, extracloth. Price $3 00.

It is a work of great practical value and Interest
containing much that is new relative to the several
diseases of which it treats, and, with the additions
of the editor, is fully up to the times. The distinct-
ive features of the different forma of fever are plainly
and forcibly portrayed, and the lines of demarcation
carefully and accurately drawn, and to the Ameri-
can practitioner isa more valuable and safe guide
than any work on fever extant.—Ohio Med. and
Surg Journal, ~

This excellent monograph on febrile disease, has

stood deservedly high since its first publication. It
will be seen that it has now reached its fourth edi-
tion under the supervision of Prof. A. Clark, a gen-
tleman who, from the nature of his studies and pur-
suits, is well calculated to appreciate and discuss
the many intricate and difficult questions in patho-
logy. His annotations add much to the interest of

)the work, and have brought it well up. to the condi-
tion of the science as it exists at the present day

in regard to this class of diseases.—Southern Med.
and Surg. Journal.

a

BLANCHARD & LEA’S MEDICAL

BARWELL (RICHARD,) F-R.C.S.,
Assistant Surgeon Charing Cross Hospital, &c.

A TREATISE ON DISEASES OF THE JOINTS. Illustrated with engrav-

ings on wood.
(Now Ready.)

In one very handsome octavo volume, of about 500 pages, extra cloth; $35 00.

‘“A treatise on Diseases of the Joints equal to, or rather beyond the current knowledge of the
day, has long been required—my professional brethren must judge whether the ensuing pages may
supply the deficiency No author is fit to estimate his own work at the moment of its completion,
but it may be permitted me to say that the study of joint diseases has very much occupied my atten-

tion, even from my studentship,
has been almost unremitting, . . . .

and that for the last six or eight years my devotion to that subject
The real weight of my work has been at the bedside,

and the greatest labor devoted to interpreting symptoms and remedying their cause.””—AvuTHOR’s

PREFACE.

At the outset we may state that the work is
worthy of much praise, and bears evidence of much
thoughtful and careful mquiry, and here and there
of no slight originality. We have already carried
this notice further than we intended to do, but nut
to the extent the work deserves. We can only add,
that the perusal of it has afforded us great pleasure.
The author has evidently worked very hard at his
subject, and his investigations into the Physiology
und Pathology of Joints have been carried on in a
manner which entitles him to be listened to with
attention and respect. We must not omit to men-
tion the very admirable plates with which the vo-
lumeisenriched. We seldom meet with such strik-
ing and faithful delineations of disease.—London
Med. Times and Gazette, Feb. 9, 1861.

We cannot take Jeave, however, of Mr. Barwell,
without congratulating him on the interesting
amount of information which he has compressed

to be of much use to the practising surgeon who
may bein wunt of a treatise on diseases of the Joints,
and at the same time one which contains the latest
information on artizular affections and the opera-
tions for cheir cure.—Dublin Med. Press, Feb. 27,
1861.

This volume will be welcomed, both by the pa-
thologist and the surgeon, as being the record of
much honest research and careful investigation into
the nature and treatment of a most important class
of disorders. We cannot conclude this notice of a
valuable and useful book withvuat calling attention
to the amount of bond fide work 1t contains. Inthe
present day of universu! book- making, it is no slight
matter for a volume to show luburious inveatiga~-
tiou, and at the same tine original thought, on the
part of its auchor, whom we mav congratulate on
the saccesstul completion of his arduous task.—
London Lancet, March 9, 1&61.

into his book. The work appears to us calculated

CARPENTER (WILLIAM 8.), M.O., F.R.S., &e.,

f£xaminer in Physiology and Comparative Anatumy in the University of London.

PRINCIPLES OF HUMAN PHYSIOLOGY; with their chief applications to
Psychology, Pathology, Therapeutics, Hygiene, and Forensic Medicine. A new American, from
the last and revised London edition. With nearly three hundred illustrations. Edited, with addi-
tions, by Francis Gurney Situ, M. D., Professor of the Institutes of Medicine in the Pennsyl-
vania Medical College, é&c. In one very large and beautiful octavo volume, of about nine hundred
large pages, handsomely printed and strongly bound in leather, with raised bands. $4 25.

In the preparation of this new edition, the author hax spared no labor to render it, as heretofore,
a complete and lucid exposition of the most advanced condition of its important subject. The
amount of the additions required to effect this object thoroughly, joined to the former large size of
the volume, presenting objections arising from the unwieldy bulk of the work, he has omitted all
those portions not beuring directly upon Human PuysioLoey, designing to incorporate them in
his forthcoming Treatise on GenzRAL Puystotocy. As a full and accurate text-book on the Phy-
siology of Man, the work in its present condition therefore presents even greater claims upon
the student and physician than those which have heretofore won for it the very wide and distin-
guished favor which it has so long enjoyed. The additions of Prof. Smith will be found to supply
avhatever may have been wanting to the American student, while the introduction of many new
iiustrations, and the most careful mechanical execution, render the volume one of the most at-

tractive as yet issued.

For upwards of thirteen years Dr. Carpenter’s
work has been considered by the profession gene-
rally, both in this country and England, as the most
valuable compendium on the subject of physiology
mourlanguage. This distinction it owes to the high
attainments and unwearied industry of its accom-
plished author. The present edition (which, like the
last American one, was prepared by the author him-
self), is the result of such extensive revision, that it
may almost be considered a new work. We need
hardly say, in concluding this brief notice, that while
the work is indispensable to every student of medi-
cine in this country, it will amply repay the practi-
tioner for its perusal by the interest and value of its
contents.—Boston Med. and Surg. Jowrnal.

This is a standard work—the text-book used by all
medical students who read the English language.
{thas passed through several editions in order to
keep pace with the rapidly growing science of Phy-
siology. Nuthing need be said im its praise, for its
merits are universally known; we have nothing to
say of its defects, for they only appear where the
science of which. it treats is incomplete.— Western
Lancet.

The most complete exposition of physiology which
any language can at present give.—Brit, and For.
Med.-Chirurg. Review.

The greatest, the most reliable, and the best book
on the subject which we know of in the English
language.—Stethoscope.

To eulogize this great work would be superfluons.
We should observe, however, that in this edition
the author has remodelled a large portion of the
furmer, and the editor has added much matter of in-
terest, especially in the Corm of illustrations. We
may confidently recommend it as the must complete
work on Human Physivlogy in our language—
Southern Med. and Surg. Journal.

The most complete work on the science in our
language.—Am. Med. Journal.

The most complete work now extant in our lan-
guage.—N. O. Med. Register.

The best text-book in the language on this ex-
tensive subject.—London Med. Times.

A complete cyclopsdia of this branch of science.
—N. Y. Med. Times. ee

The profersion of this country, and perhaps also
of Europe, havea txiously and for sometime awaited
the announcement of this new edition of Carpenter's
Human Pisnlvays His former editions have for
many years been almost the only text-book on Phy-
siology in all our medical schvols, and its circula-
tion among the profession hus been unsurpassed by
a work in any department of medical science.

t ls quite unnecessary for us to speak of this
work as its merits would justify. The mere an-
nouncement of itsappeurance will afford the highest
pleasure to every student of Physiology, while ita
perusal will be of infinite service in advancing
physiological science.—Ohio Med. and Surg. Journ,

AND SCIENTIFIC PUBLICATIONS. 7

CARPENTER (WILLIAM B.), M.D., F.R.S.,

Examiner in Physiology and Comparative Anatomy in the University of London.

THE MICROSCOPE AND ITS REVELATIONS. With an Appendix con-

taining the Applications of the Microscope to Clinical Medicine, &c. By F.G. Smiru, M. D.
ilustrated by four hundred and thirty-four beautiful engravings on wood. In one large and very
handsome octavo volume, of 724 pages, extra cloth, $4 00; leather, $4 50.

Dr. Carpenter’s position as a microscopist and physiologist, and his great experience as a teacher,
eminently qualify him to produce what has long been wanted—a good text-book on the practical
use of the microscope. In the present volume his object has been, as stated in his Preface, “to
combine, within a moderate compass, that information with regard to the use of his ‘tools,’ which
is most essential to the working microscopist, with such an account of the objects best fitted for
his study, as might qualify him to comprehend what he observes, and might thus prepare him to
benefit science, whilst expanding and refreshing his ownmind ’’? That he has succeeded in accom-
plishing this, no one acquainted with his previous labors can doubt.

The great importance of the microscope as a means of diagnosis, and the number of microsco-
pists who are also physicians, have induced the American publishers, with the author’s approval, to
add an Appendix, carefully prepared by Professor Smith, on the applications of the instrument to
clinical medicine, together with an account of American Microscopes, their modifications and

accessories.

This portion of the work is illustrated with nearly one hundred wood-cuts, and, it is

hoped, will adapt the volume more particularly to the use of the American student.

Those who are acquainted with Dr. Carpenter’s
revious writings on Animal and Vegetable Physio-
ogy, will fully understand how vasta store of know-

ledge he is able to bring to bear upon so comprehen-
sive a subject as the revelations of the microscope;
and even those who have no previous acquaintance
with the construction or uses of this instrument,
will find abundance of information conveyed in clear
and simple language.—Med. Times and Gazette.

Although originally not intended as a strictly

medical work, the additions by Prof. Smith give it
a positive claim upon the profession, for which we
doubt not he will receive their sincere thanks. In-
deed, we know not where the student of medicine
will find such a complete and satisfactory collection
of microscopic facts bearing upon physiology and
practical medicine as is contained in Prof. Smith’s
appendix; and this of itself, it seems to us, is fully
worth the cost of the volume.—Lowisville Medical
Review.

BY THE SAME AUTHOR.

ELEMENTS (OR MANUAL) OF PHYSIOLOGY, INCLUDING PHYSIO-

LOGICAL ANATOMY. Second American, from a new and revised London edition.
In one very handsome octavo volume, leather.

one hundred and ninety illustrations.
$3 00.

With
pp. 566.

In publishing the first edition of this work, its title was altered from that of the London volume,
by the substitution of the word “ Elements’’ for that of ‘ Manual,” and with the author’s sanction
the title of ‘‘Elements”’ is still retained as being more expressive of the scope of the treatise.

To say that it is the best manual of Physiology

Those who have occasion for an elementary trea-

now before the public, would not do sufficient justice | tise on Physiology, cannot do better than to possesa

to the author —Buffalo Medical Journal.

themselves of the manualof Dr, Carpenter.— Medical

In his former works it would seem that he had| #xaminer.

exhausted the subject of Physiology. In the present,

The best and most complete exposé of modern

he gives theessence, as it were, of the whole—N. Y.| Physiology, in one volume, extant in the English

Journal of Medicine.

language.—St. Lowis Medical Journal.

BY THE SAME AUTHOR.

PRINCIPLES OF COMPARATIVE PHYSIOLOGY. New American, from

the Fourth and Revised London edition.
three hundred beautiful illustrations. pp. 752.

This book should not only be read but thoroughly
studied by every member of the profession. None
are too wise or old, to be benefited thereby. But
especially to the younger class would we cordiall
commend it as best fitted of any work in the Englis
L uage to quality them for the reception and com-
preheuiaiint of those truths which are daily being de-
veloped in physiology.—Medical Counsellor.

Without pretending to it, it is an encyclopedia of
the subject, accurate and complete in all respects—
a truthful reflection of the advanced state at which
the science has now arrived.—Dublin Quarterly
Journal of Medical Science.

A truly magnificent work—in itself a perfect phy-
siological study.—Ranking’s Abstract.

This work stands without its fellow. It is one
few men in Europecould have undertaken; it is one

In one large and handsome octavo volume, with over

Extra cloth, $4 80; leather, raised bands, $5 25.

no man, we believe, could have brought to so suc-
cessful an issue as Dr. Carpenter. It required for
its production a physiologist at once deeply read in
the labors of others, capable of taking a general

critical, and unprejudiced view of those labors, an

of combining the varied, heterogeneous materials at
his disposal, so as to form an harmonious whole.
We feel that this abstract can give the reader a very
imperfect idea of the fulness of this work, and no
idea of its unity, of the admirable marner in whieh
material has been brought, from the most various
sources, to conduce to its conipleteness, of the lucid-
ity of the reasoning it contains, or of the clearness
oF emmunae in which the whole is clothed. Notthe
profession only, but the scientific world at large,
must feel deeply indebted to Dr. Carpenter for this
great work. It must, indeed, add largely even to
his high reputation.—Medical Times.

BY THE SAME AUTHOR. (Preparing.)

PRINCIPLES OF GENERAL PHYSIOLOGY, INCLUDING ORGANIC
CHEMISTRY AND HISTOLOGY. With a General Sketch of the Vegetable and Animal
Kingdom. In one large and very handsome octavo volume, with several hundred illustrations.

BY THE SAME AUTHOR.

A PRIZE ESSAY ON THE USE OF ALCOHOLIC LIQUORS IN HEALTH
AND DISEASE. New edition, with a Preface by D. F. Conpiz, M. D., and explanations of

scientific words.

In one neat 12mo. volume, extra cloth. pp. 178. 50 cents.

BLANCHARD & LEA’S MEDICAL

CONDIE (D.F.), M.D., &c.

A PRACTICAL TREATISE ON THE DISEASES OF CHILDREN. Fifth
edition, revised and augmented. In one large volume, 8vo., leather, of over 750 pages. $3 25.
(Just Issued, 1859.)

In presenting a new and revised edition of this favorite work, the publishers have only to state
that the author has endeavored to render it in every respect “a complete and faithful exposition of
the pathology and therapeutics of the maladies incident to the earlier stages of existence—a full
and exact account of the diseases of infancy and childhood.” To accomplish this he has subjected
the whole work to a careful and thorough revision, rewriting a considerable portion, and adding
several new chapters. In this manner it is hoped that any deficiencies which may have previously
existed’ have been supplied, that the recent labors of practitioners and observers have been tho-
roughly incorporated, and that in every point the work will be found to maintain the high reputation
it has enjoyed as a complete and thoroughly practical book of reterence in infantile affections.

A few notices of previous editions are subjoined.

Dr. Condie’s scholarship, acumen, industry, and
practical sense are manifested in this, as in all his
numerous contributions to science.—Dr. Holmes’s
Report to the American Medical Association.

We pronounced the first edition to be the beat
work on the diseases of children in the English
language, and, bieeeiistat all that has been
published, we still regard it in that light —Medical

Taken asa whole, in our judgment, Dr. Condie’s
Treatise is the one from the perusal of which the
practitioner in this country will rise with the great-
eat satisfaction.— Western Journal of Medicine and
Surgery.

One of the best works upon the Diseases of Chil-
dren in the English language.— Western Lancet.

We feel assured from actual experience that nc
physician’s library can be complete without a copy
of this work.—N. Y. Journal of Medicine.

A veritable pediatric encyclopedia, and an honoi
to American medical literature.--Ohio Medical and
Surgical Journal,

Wefeel persuaded that the American medica! pro-
fession will soon regard it not only as a very good,
but as the veRyY BEsT ‘‘ Practical Treatise on the
Diseases of Children.””—American Medical Journal

In the department of infantile therapeutics, the
work of Dr. Condie is considered one of the best
which hus been published in the English language.
—The Stethoscope.

Examiner.

The value of works by native authors on the dis-
eases which the physician is called upon to combat,
will be appreciated by all; and the work of Dr. Con-
die has gained for itself the character of a sate guide
tur students, and a useful work for consultation by
those engaged in practice.—N. Y. Med. Times.

This is the fourth edition of this deservedly popu-
lar treatise. During the interval since the last edi-
tion, it has been subjected to a thorough revision
by the author; and all new observations in the
pathulogy and therapeuties of children have been
included in the present volume. As we said bi fore,
we do not know of a better book on diseases of chit-
dren, and to a large part of its recommendations we
yield un unhesituting concurrence.—Buffalo Med.
Journal.

Perhaps the most full and complete work now be-
‘ore the profession of the United States; indeed, we

may say in the English language. It is vastly supe-
cior to must of .ts predecessors.—Tvansylvania Med,

Journal

CHRISTISON (ROBERT), M.D., V.P.R.S.E., &c.

A DISPENSATORY; or, Commentary

on the Pharmacopeias of Great Britain

and the United States; comprising the Natural History, Description, Chemistry, Pharmacy, Ac-

tions, Uses, and Doses of the Articles of the Materia Medica. c
proved, with a Supplement containing the most important New Remedies.
tions, and two hundred and thirteen large wood-engravings.

Second edition, revised and im-
With copious Addi-
By R. EGLesFeLp Grirrita, M.D.

In one very large and handsome octavo volume, leather, raised bands, of over 1000 pages. $3 50.

COOPER (BRANSBY 8B.), F. R.S.
LECTURES ON THE PRINCIPLES AND PRACTICH OF SURGERY.

in one very large octavo volume, extra cloth, of 750 pages. $3 00.

COOPER ON DISLOCATIONS AND FRAC-
TURES OF THE JOINTS.—Edited by BRansBy
B. Cooprr, F.R.8., &e. With additional Ob-
servations by Prof. J.C. WaRREN. A new Ame-
rican edition. In one handsome octavo volume,
extra cloth, of about 500 pages, with numerous
illustrations on wood. $3 25.

COOPER ON THE ANATOMY AND DISEASES
OF THE BREAST, with pa tiie Miscellane-
ous and Surgical Papers. One large volume, im-
perial 8vo., extra cloth, with 252 figures, on 36
plates. $2 50.

COOPER ON THE STRUCTURE AND DIS-
EASES OF THE TESTIS, AND ON THE
THYMUS GLAND. One vol. imperial 8vo., ex-
tra cloth, with 177 figures on 29 plates. $2 00.

COPLAND ON THE CAUSES, NATURE, AND
TREATMENT OF PALSY AND APOPLEXY.
an one volume, royal 12mo., extra cloth. pp. 326.

cents.

CLYMER ON FEVERS; THEIR DIAGNOSIS,
PATHOLOGY, AND TREATMENT In one
octavo volume, leather, of 600 pages. $1 50.

COLOMBAT DE LYISERE ON THE DISEASES
OF FEMALES, and on the special Hygiene of
their Sex. Translated, with many Notes and Ad-
ditions, by C. D. Mzigs,M.D. Second edition,
Tevised and improved In one large volume, oe-
>) aaa with numerous wood-cuts. pp. 720,

3.50.

CARSON (JOSEPH), M. D.,
Professor of Materia Medica and Pharmacy in the University of Pennsylvania.
SYNOPSIS OF THE COURSE OF LECTURES ON MATERIA MEDICA

AND PHARMACY, delivered in the University of Pennsylvania. Second and revised edi-
tion. In one very neat octavo volume, extra cloth, of 208 piges, $1 50.

CURLING (T. B.), F.R. 8.,
Surgeon to the London Hospital, President of the Hunterian Society, &c,
A PRACTICAL TREATISE ON DISEASES OF THE TESTIS, SPERMA-

TIC CORD, AND SCROTUM. Second American, from the second and enlarged English edi-
tion. In one handsome octavo volume, extra cloth, with numerous illustrations. pp. 420. $2 00.

AND SCIENTIFIC PUBLICATIONS. 9

CHURCHILL (FLEETWOOD), M.D., M. RI. A.
ON THE THEORY AND PRACTICE OF MIDWIFERY. A new American

from the fourth revised and enlarged London edition. With Notes and Additions, by D. Francis
Connie, M. D., author of a ‘‘Practical Treatise on the Diseases of Children,’ ée. With 194
illustrations. In one very handsome octavo volume, leather, of nearly 700 large pages. $3 50.
(Just Issued.)

This work has been so'long an established favorite, both as a text-book for the learner and as a
reliable aid in consultation (or the practitioner, that in presenting a new edition it is only necessary
to call attention to the yery extended improvements which 11 has received. Having had the benefit
of two revisions by the author since the last American reprint, it has been materially enlarged, and
Dr. Churehill’s well-known conscientious industry is a guarantee that every portion has been tho-
roughly brought up with the latest results of European investigation in all departments of the sci-
ence and art of obstetrics. The recent date of the last Dublin edition has not left much of novelty
for the American editor to introduce, but he has endeavored to insert whatever. has since appeared,
together with such matters a~ his experience has shown him would be desirable for the American
student, including a large number of illustrations With the sanction of the author he has added
in the form of an appendix, some chapters from a little ‘Manual for Midwives and Nurses,’’ re-
cently issued by Dr. Churchill, believing that the details there presented can hardly fail to prove of
advantage to the junior practitioner. Tne result of all these additions is that the work now con-
tains fully one-half more matter than the last American edition, with nearly one-half more illus-
trations, so that notwithstanding the use of a smaller type, the volume contains almost two hundred
pages more than before,

No effort has been spared to secure an improvement in the mechanical execution of the work
equal to that which the text has received, and the volume is confidently presented as one of the
handsomest that has thus far been luid before the American profession; while the very low price

at which it is offered should secure for it a place in every lecture-room and on every office table.

A better book in which to learn these important
points we have not met than Dr. Churchill’s. Every
page of it is full of instruction; the opinion of all
writers of authority is given on questions of diffi-
culty, as well as the directions and advice of the
learned autnor himself, to which he adds the result
of statistical inquiry, putting statistics in their pro-
per place and giving them their due weight, and no
more. We have never read a book more free from
professional jealousy than Dr. Churchill’s. It ap-
pears to be written with the true design of a book on
Medicine, viz: to give all that is known on the sub-
ject of which he treats, both theoretically and prac-
tically, and to advance such opinions of his own as
he believes will benefit medical science, and insure
the safety of the patient. We have said enough to
convey to the profession that this book of Dr. Chur-
chill’s is admirably suited for a book of reference
fur the practitioner, as well asa text-book for the
student, and we hope it may be extensively pur-
chased amongst our readers. To them we most
strongly recommend it.— Dublin Medical Press,
June 20, 1860.

To bestow praise ona book that has received such
marked approbation would be superfluous. Weneed
only say, therefore, that if the first edition was
thought worthy of a favorable reception by the
medical public, we can confidently affirm that this
will be found much more so. The lecturer, the
practitioner, and the student, may all have recourse
to its pages, and derive from their perusal much in-
terest and instruction in everything relating to theo-
retical and practical midwifery.—Dublin Quarterly
Journal of Medical Science.

A work of very great merit, and such as we can
confidently recommend to the study of every obste-
tric practitioner.—London Medical Gazette.

This is certainly the most perfect system extant.
It is the best adapted for the purposes of a text-
book, and that which he whose necessities confine
him to one book, should select in preference to all
others.—Southern Medical and Surgical Journal,

The most popular work on midwifery ever issued
‘rom the American press.—Charleston Med. Journal,

Were we reduced to the necessity of having but
gne work on midwifery, and permitted to choose,
we would unhesitatingly take Churchill.— Western
Med. and Surg. Journal,

It is impossible to conceive a more useful and
slegant manual than Dr. Churchill’s Practice of
Midwifery.—Provincial Medical Journal.

Certainly, in our opinion, the very best work on
he subject which exists.—N, Y. Annalist.

No work holds a higher position, or is more de-
serving of being placed in the hands of the tyro
the advanced student, or the practitioner.— Medica
Examiner.

Previous editions, under the editorial supervision
of Prof R. M. Huston, have been received with
marked favor, and they deserved it; but this, re-
printed from a very late Dublin edition, carefully
revised and brought up by the author to the present
time, does present an unusually accurate and able
exposition of every important particular embraced
in the department of midwifery. * * The clearness,
directness, and precision of its teachings, together
with the great amount of statistical research which
its text exhibits, have served to place it already in
the foremost rank of works in this department of re
medial science.—lV. 0. Med. and Surg. Journal.

In our opinion, it forms one of the best if not th
very best text-book and epitome of obstetric science
which we at present possess in the English lan-
guage.— Monthly Journal of Medical Science.

The clearness and precision of style in whichit is
written, and the greatamount of statistical researeh
which it contains, have served to placeit inthe firat
rank of works in this departmentof medical science.
—wN. Y. Journal of Medicine.

Few treatises will be found better adapted as a
text-book for the student, or as a manual for the
frequent consultation of the young practitioner,--
American Medical Journal.

BY THE SAME AUTHOR. (Lately Published.)

ON THE DISEASES OF INFANTS AND CHILDREN. Second American
Edition, revised and enlarged by the author. Edited, with Notes, by W. V. Keatine, M.D. In
one large and handsome volume, extra cloth, of over 700 pages. $3 00, or in leather, $3 25.

In preparing this work a second time for the American profession, the author has spared no
labor in giving it a very thorough revision, introducing several new chapters, and rewriting others,
while every portion of the volume has been subjected to a severe scrutiny. The efforts of the
American editor have been directed to supplying such information relative to matters peculiar
to this country as might have escaped the attention of the author, and the whole may, there-
fore, be safely pronounced one of the most complete works on the subject accessible to the Ame-
rican Profession. By an alteration in the size of the page, these very extensive additions have
been accommodated without unduly increasing the size of the work.

; BY THE SAME AUTHOR.
ESSAYS ON THE PUERPERAL FEVER, AND OTHER DISEASES PE-
CULIAR TO WOMEN. Selected from the writings of British Authors previous to the close of
the Eighteenth Century. In one neatactavo volume, extra cloth, of about 450 pages. $2 50.

10 BLANCHARD & LEA’S MEDICAL

CHURCHILL (FLEETWOOD), M.D.,M.R.1,A., &c.

ON THE DISEASES OF WOMEN; including those of Pregnancy and Child-
bed. A new American edition, revised by the Author. With Notes and Additions, by D. FRaN-
crs ConpIE, M. D., author of “A Practical Treatise on the Disea-es of Children.” ith nume-
rous illustrations. In one large and handsome octavo volume, leather, of 768 pages. $3 00.

This edition of Dr. Churchill’s very popular treatise may almost be termed a new work, 80
thoroughly has he revised it in every portion. It will be found greatly enlarged, and completely
brought up to the most recent condition of the subject, while the very handsome series of illustra-
tions introduced, representing such pathological conditions as can be accurately portrayed, present
a novel feature, and afford valuable assistance to the young practitioner. Such additions as ap-
peared desirable for the American student have been made by the editor, Dr. Condie, while a
marked improvement in the mechanical execution keeps pace with the advance in all other respects
which the volume has undergone, while the price has been kept at the former very moderate rate.

It comprises, unquestionably, one of the most ex-
act and comprehensive expositions of the present
state of medical knowledge in respect to the diseases
of women that has yet been published.—Am. Journ.
Med. Sciences.

This work is the most reliable which we possess
on this subject; and is deservedly popular with the
profession.—CAarleston Med. Journal, July, 1857.

extent that Dr. Churchill does. His, indeed, is the
only thorough treatise we know of on the subject;
and it may be commended to practitioners and stu-
dents as a masterpiece in its particular department.
—The Western Journal of Medicineand Surgery.
As a comprehensive manual! for students, or a
work of reference for practitioners, it surpasses any
uther that has ever issued on the same subject from

We know of no author who deserves that uppro- | the British press.—Dudlin Quart. Journal.

bation, on ‘the diseases of females,”’ to the same

DICKSON (S. H.),;

M.D.,
Professor of Practice of Medicine in the Jefferson Medical College, Philadelphia.

ELEMENTS OF MEDICINE; a Compendious View of Pathology and Thera

peutics, or the History and Treatment of Diseases. Second edition, revised. In one large and
handsome octavo volume, of 750 pages, leather. $3 75. (Just Issued.)

The steady demand which has so soon exhausted the first edition of this work, sufficiently shows
that the author was wot mistaken in supposing that a volume of this character was needed—an
elementary manual of practice, which should present the leading principles of medicine with the
practical results, in a condensed and perspicuous manner. Disencumbered of unnecessary detail
and fruitless speculations, it embodies what is most requisite for the student to learn, and at the
game time what the active practitioner wants when obliged, in the daily calls of his profession, to
refresh his memory on special points. The clear and attractive style of the author renders the
whole ea+y of comprehension, while his long experience gives to his teachings an authority every-
where acknowledged. Few physicians, indeed, have had wider opportunities for observation and
experience, and few, perhaps, have used them to better purpose As the result of a long life de-
voted to stndy and practice, the present edition, revised and brought up to the date of publication,
will doubtless maintain the reputation already acquired as a condensed and convenient American
text-book on the Practice of Medicine.

DRUITT (ROBERT), M.R.C.S., &c.
THE PRINCIPLES AND PRACTICE OF MODERN SURGERY. A new

and revised American from the eighth enlarged and improved London edition. Lllustrated with
four hundred and thirty-two wood-engravings. In one very handsomely printed octavo volume,
leather. of nearly 700 large pages. $350. (Just Isswed.)

A work which like Druitt’s SurGery has for so many years maintained the position of a lead-
ing favorite with all classes of the profession, needs no special recommendation to attract attention
to a revised edition. Itis only necessary to state that the author hus spared no paius to keep the
work up to its well earned reputation of presenting in a small and convenient compass the Tarest
condition of every department of surgery, considered both as a science and as an art; and that the
services of a competent American editur have been employed to intruduce whatever novelties may
have escaped the author’s attention, or may prove of service to the American practitioner. As
several editions have appeared in London since the issue of the last American reprint, the volume
has had the benefit of repeated revisions by the author, resulting in a very thorough alteration and
improvement. ‘The extent of these additions may be estimated from the fact that it now contains
about one-third more matter than the previous American edition, and that notwithstanding the
adoption of a smalier type, the pages have been increased by about one hundred, while nearly two
hundred and fifty wood-cuts have been added to the former list of illustrahons.

A marked inprovement will also be perceived in the mechanical aud artistical execution of the
work, which, printed in the best style, on new type, and fine paper, leaves little to be desired as
regards external finish; while at the very low price affixed it will be found one of the cheapest
voluines accessible 10 the profession.

Thir popular volume, now a most comprehensive
work on suigery, has undergone many currections,
improvements, and additions, and the principles and
the practice of the art have been brought down to
the latest recoruand observation. Of the operations
in surgery itis impossible toepeak toohighiy, The
descriptions ure so Clear and concise, and the illus-
trations so avcurate and numerous, that the student
can have no dif.culty, with inatrument in hand, and
book by his side, over the dead body, in obtaining
a proper knowledge and sufficient tact in this much
neglected department of medical education.—British
and Foreign Medico-Chirurg, Review, Jan. 1960.

In the present edition the author has entirely re-
written many of the chapters, and bas ineurpurated
the various improvements and additions in modern
surgery. On carefuliy going over it, we find that

nothing of real practical importance has been omit-
ted; it presents a faithful epitome of everything re-
lating t> surgery up Lo the present hour. It is de-
servedly a popular munual, both with the student
and practitioner.—London Lancet, Nov. 19, 1859.

In closing this brief notice, we recommend as cor-
dially as ever this most useful and comprehensive
hand-bouk. It must prove a vast assistance, not
only to the student of surgery, but also to the busy
practitioner whe may not have the leisure to devote

imself to the study of more lengthy volumes.—
London Med. Times and Gazette, Oct. 22, 1859.

In a word, this eighth edition of Dr. Druitt’a
Manual! of Surgery is all that the surgical student
or practitioner could desire. — Dublin Quarterly
Journal of Med. Sciences, Nov. 1859,

AND SCIENTIFIC PUBLICATIONS. 11

DALTON, JR. (J. ©.); M. D.
Professor of Physiology in the College of Physicians, New York.

A TREATISE ON HUMAN PHYSIOLOGY, designed for the use of Students

and Practitioners of Medicine. Second edition, revised and enlarged, with two hundred and
seventy-one illustrations on wood. In one very beautiful octavo volume, of 700 pages, extra
cloth, $4 00; leather, raised bands, $4 50. (Jzst Isswed, 1861.)

The general favor which has so soon exhausted an edition of this work has afforded the author
an opportunity in its revision of supplying the deficiencies which existed in the former volume.
This has caused the insertion of two new chapters—one on the Special Senses, the other on Im-
bibition, Exnalation, and the Functions of the Lymphatic System—besides numerous additions of
smaller amount scattered through the work, and a general revision designed to bring it thoroughly
up to the present condition of the science with regard to all points which may be considered ax
definitely settled. A number of new illustrations has been introduced, and the work, it is hoped,

in its improved form, may continue to command the confidence of those for whose use it is in-

tended

It will be seen, therefore, that Dr. Dalton’s best
efforts have been directed towards perfecting his
work, The additions are marked by the same fea-
tures which characterize the remainder of the vol-
ume, and render it by far the most desirable text-
book on physiology to place in the hands of the
stuvent which, su far as we are aware, exists in
the Engiish language, or perhaps in any other. We
therefure have no hesitation in recommending Dr.
Dalton’s book for the classes for which it is intend-
ed, satisfied as we are that it is better adapted to
their use than any other work of the kind to which
they have access.—American Journal of the Med.
Sctences, April, 1861.

It is, therefore, no disparagement to the many
books upon physiology, most excellent in their day,
to say that Daltun’s is the only one that gives us the
science as it was known to the best philosophers
throughout the world, at the beginning of the cur-
rent year. It states in comprehensive but concise
diction, the facts established by experiment, or
other method of demonstration, and details, in an
understandable manner, how it is done, but abstains
from the discussion of unsettled or theoretical points,
Herein it is unique; and these characteristics ren:
ger ita text-book without a rival, for those who
desire to study physiological science as it is knuwn
to its most successful cultivators, And it is physi-
ology thus presented that lies at the foundation of
correct pathological knowledge; and this in turn is
the basis of rational therapeutics; so that patholo-
gy, in fact, becomes of prime importance in the
proper discharge of our every-day practical duties.
—Cincinnati Lancet, May, 1861.

Dr. Dalton needs no word of praise fromus. He
is universally recognizea as among the first, if not
the very first, of American physiologists now living.
The first edition of his admirable work appeared but
two years since, and the advance of science, his

own original views and experiments, together with
a desire to supply what he considered some deficien-
cies in the first edition, have already made the pre-
sent one a necessity, and it will no doubt be even
more Sen sought for than the first. That it ia
not merely a reprint, will be seen from the author’s
statement of the following principal additions and
alterations which he has made. The present, like
the first edition, is printed in the highest style of the
printer’s art, and the illustrations are truly admira-
ble tor their clearness in expressing exactly what
their author intended.—Boston Medical and Surgi-
eal Journal, March 28, 1861.

It is unnecessary to give a detail of the additions;
suffice it tosay, that they are numerous and import-
ant, and such as will render the work still more
valuable and acceptable to the profession as a learn-
ed and original treatise on this all-important branch
of medicine. All that was said in commendation
of the getting up of the first edition, and the superior
style of the illustrations, apply with equal force to
this. No better work on physiology can be placed
in the hand of the student.—St. Louis Medical and
Surgical Journal, May, 1861.

These additious, while tes:ifying to the learning
and industry of the author, render the book exceed-
ingly useful, as the most complete exposé of a sci-
ence, of which Dr. Dalton is doubtless the ablest
tepresentative on this side of the Atlantic. —New
Orleans Med. Times, May, 1861.

A second edition of this deservedly popular work
having been called for in the short space of two
years, the author has supylied deficiencies, which
existed in the former volume, and has thus more
completely fulfilled his design of presenting to the
profession a reliable and precise text book, and one
which we consider the best outline on the subject
of which it treats, in any language.—N. American

Medico-Chirurg. Review, May, 1861.

DUNGLISON, FORBES, TWEEDIE, AND CONOLLY.
THE CYCLOPAIDIA OF PRACTICAL MEDICINE: comprising Treatises on

the Nature and Treatment of Diseases, Materia Medica, and Therapeutics, Diseases of Women

and Children, Medical Jurisprudence, &c. &c.

{In four large super-royal octavo volumes, of

3254 double-columned pages, strongly and handsomely bound, with raised bands. $12 00.
*,* This work contains no less than four hundred and eighteen distinct treatises, contributed by

sixty-eight distinguished physicians, rendering it
practitioner.

The most complete work on Practical Medicine
extant; or, at least, in our language.—Buffalo
Medical and Surgical Journal.

For reference, it is above all price to every prac-
titioner.— Western Lancet.

One of the most valuable medical publications of
the day—as a work of reference it is invaluable.—
Western Journal of Medicine and Surgery.

It has been to us, both as learner and teacher, a
work for ready and frequent reference, une in which
modern English medicine is exhibited in the most
advantageous light.—Medical Examiner.

DEWEES’S COMPREHENSIVE SYSTEM OF
MIDWIFERY. Illustrated by occasional cases
and many engravings. Twelfth edition, with the
author’s last improvements and corrections In
one octavo volume, extra cloth, of 600 pages. $3 20.

DEWEES’S TREATISE ON THE PHYSICAL

a complete library of reference for the country

The editors are practitioners of established repu-
tation, and the lis: of contributors embraces many
of the most eminent professors and teachers of Lon-
don, Edinburgh, Dublin, and Glasgow. It is, in-
deed, the great merit o} this work that the principal
articles have been furnished by practitioners who
have not only devoted especial attention to the dis-
eases about which they have written, but have
also enjoyed opportunities for an extensive practi-
cal acquaintance with them and whose reputation
carries the assurance of their competency justly to
appreciate the opinions 0! others, while it stamps
their own doctrines wit! high and just authority.—
American Medical Journal.

AND MEDICAL TREATMENT OF CHILD
REN. The last edition. In one volume, octavo,
extra cloth, 48 pages. $2 80

DEWEES’S TREATISE ON THE DISEASES
OF FEMALES. Tenth edition. In one volume.

octavo extra cloth, 532 pages, with plates. $3 o6

12 BLANCHARD & LEA’S MEDICAL

DUNGLISON (ROBLEY), M.D.,

Professor of Institutes of Medicine in the Jefferson Medical College, Philadelphia.

NEW AND ENLARGED EDITION.
MEDICAL LEXICON; a Dictionary of Medical Science, containing a concise

Explanation of the various Subjects and Terms of Anatomy, Physiology, Pathology, Hygiene,
Therapeutics. Pharmacology, Pharmacy, Surgery, Obstetrics, Medical Jurisprudence, Dentistry,
&c. Notices of Climate and of Mineral Waters; Formule for Officinal, Empirical, and Dietetic
Preparations, &c. With French and other Synonymes. Revised and very greatly enlarged.
Jn one very large and handsome octavo volume, of 992 double-columned pages, in small type ;
strongly bound in leather, with raised bands. Price $4 00.

Especial care has been devoted in the preparation of this edition to render it in every respect
worthy a continuance of the very remarkable favor which it has hitherto enjoyed. The rapid
sale of FrrrEen large editions, and the constantly increasing demand, show that it is regarded by
the profession as the standard authority. Stimulated by this fact, the author has endeavored in the
present revision to introduce whatever might be necessary ‘to make it a satisfactory and desira-
ble—if not indispensable—lexicon, in which the student may search without disappointment for
every term that has been legitimated in the nomenclature of the science.’”? To accomplish this,
large additious have been found requisite, and the extent of the author’s labors may be estimated
from the fact that about Six Tuousanp subjects and terms have been introduced throughout, ren-
dering the whole number of definitions about Sixty THousanp, to accommodate which, the num-
ber of pages has been increased by nearly a hundred, notwithstanding an enlargement in the size
of the page. The medical press, both in this country and in England, has prononnced the work in-
dispensable to all medical students and practitioners, and the present improved edition will not lose
that enviable reputation.

The publishers have endeavored to render the mechanical execution worthy of a volume of such
universul use in daily reference. The greatest care has been exercised to obtain the typographical
accuracy so necessary in a work of the kind. By the small but exceedingly clear type employed,
an immense amount of matter is condensed in its thousand ample pages, while the binding will be
found strong and durable. With all these improvements and enlargements, the price has been kept
at the former very moderate rate, placing it within the reach of all.

This work. the appearance of the fifteenth edition | tells us in his preface that he has added about six
of which, it has become vur duty and pleasure to | thousand terms and subjects to this edition, which,
announce, is perhaps the most stupendous monument | before, was considered universally as the best work
of labor and erudition in medical literature. One! of the kind in any language.—Silliman’s Journal,
would hardly suppose after constant use of the pre- | March, 1:58.
ceding editions, where we have never failed to find) He has razed his gigantic structure to the founda-
a sufficiently full explanation of every medical term, | tions, and remodelled and reconstructed the entire
that in this edition aban sir thousand subjects pile. No less than siz thousand additional subjects
and terms have been added,’’ with a careful revision | and terms are illustrated and analyzed in this new
and correction of the entire work. It is only neces- | edition, swelling the grand aggregate to beyond
sary to announce the advent of this edition to make! sixty thousand! Thus is placed’ before the profes-
it occupy the place of the preceding one on the table | sion'a complete and thorough exponent of medical
of every medical man, as it is wit hout doubt the best terminology, without rival or posstbility of rivalry.
and most comprehensive work of the kind which has | _ Nashville Journ of Med. and Surg., Jan. 1858

ared.— 2 . . 1858. ee ; : apeeiiaete
ever appeared.—_ buffalo Med. Journ., Jan. 1853 It is universally acknowledged, we believe, that

The work is a monument of patient research, | this work is incomparably the best and most com-
skilful judgment, and vast physical labor, that will | plete Medical Lexicon in the English language.
perpetuate the name of the author more effectually | The amount of labor which the distinguished author
than any possible device of stone or metal. Dr. | has bestowed upon it is truly wonderful, and the
Dunglison deserves the thanks not only of the Ame- lesining and research displayed in its preparation
rican profession, but of the whole medical world.— | re equally remarkable Comment and commenda-
North Am. Medico-Chir. Review, Jan. 1555. tion are unnecessary, as no one at the present day

A Medical Dictionary better adapted for the wants | thinks of purchasing any other Medical Dictionary
of the profession than any other with which we are : tian this —St. Lowis Med. and Surg. Journ., Jan.
acquainted, and of a character which places it far 58.
above comparison and competition.—dm. Journ. It is the foundation stone of a good medical libra-
Med. Sciences, Jan. 1858. ry, and should always be ipeluded in the first list of

We need only say, that the addition of 6,000 new | books purchased by the medical student.—Am. Med.
terms, with their accompanying definitions, may be Monthly, Jan. 1858.
suid to constitute a new work, by itself. We have A very perfeet work of the kind, undoubtedly the
examined the Dictionary attentively, and are most) Most perfect in the English langnage.—2icd. aad
happy to pronounce it unrivalled of its kind. The | Surg. Aeporter, Jan 1558.
erudition displayed, and the extraordinary industry It is now emphatically the Medical Dictionary of
whirh must have been demanded, in its preparation | the English language, and for it there is no substi-
and perfection, redound to the lasting credit of its) tute —N. H Med Journ. Jan. 1858
author, and have furnished usa with a volume tad is- Iti : . 2 ¢ :
pensable at the present day, to all who would find 1 is scarcely necessary to remark that any medi-
themselves au niveau with the highest standards of | C® library wanting a copy of Dunglison’s Lexicon
medical information.—Bostor Medical and Surgical , ust be imperfect —Cra Lancet, Jan, 1858.
Journal, Dec. 31, 1857. _ We have ever considered it the best authority pub-

Good lexicons and encyelopedie works generally, | lished, and the present edition we may safely say has
ate the most labor-saving contrivances which lite- qa equal in the world.—Peninsular Med. Journal,
Tary men enjoy; and the labor which is required to | “®"- 1858.
produce them in the perfect manner of this example The most complete authority on the subject to be
ls something appalling to contemplate. The author | foundin any language.—Va. Med. Journal, Feb. 58.

BY THE SAME AUTHOR.

THE PRACTICE OF MEDICINE. A Treatise on Special Pathology and The-

rapeutics. Third Edition. In two large octavo volumes, leather, of 1,500 pages. $6 25.

AND SCIENTIFIC PUBLICATIONS. 13

DUNGLISON (ROBLEY), M.D.,

Professor of Institutes of Medicine in the Jefferson Medical College, Philadelphia.

HUMAN PHYSIOLOGY. LHighth edition. Thoroughly revised and exten-

sively modified and enlarged, with five hundred and thirty-two illuxtrations. In two large and
handsomely printed octavo volumes, leather, of about 1500 pages. $7 00.

In revising this work for its eighth appearance, the author has spared no labor to render it worthy
a continuance of the very great favor which has been extended to it by the profession. The whole
contents have been rearranged, aid to a great extent remodelled; the investigations which of late
years have been so numerous and so important, have been carefully examined and incorporated,
and the work in every respect has been brought up to a level with the present state of the subject.
The object of the author has been to render it a concise but comprehensive treatise, containing the
whole body of physiological science, to which the student and man of science can at all times refer
with the certainty of finding whatever they are in search of, fully presented in all its aspects; and

on no former edition has the author bestowed more labor to secure this result.

We believe that it can truly be said, no more com-
plete repertory of facts upon the subject treated,
éan anywhere befound. The author has, moreover,
that enviable tact at description and that facility
and ease of expression which render him peculiarly
acceptable to the casuul, or the studious reader.
This faculty, so requisite in setting furth many
graver and less attractive subjects, lends additional
charms to one always fascinating. —Boston Med.
and Surg. Journal.

The most complete and satisfactory system of
Physiology in the English language.—Amer. Med.
Journal,

BY THE SAME AUTHOR.

The best work of the kind in the English lan-
guage.—Szlliman’s Journal,

The present edition the author has made a peifect
mirror of the science as it is at the present hour.
As a work upon physiology proper, the science of
the functions performed by the body, the student will
find it all he wishes.—Nashville Journ. of Med.

That he has succeeded, most admirably succeeded
in his purpose, is en from the appearance of
aneighth edition. It is now the greatencyclopedia
on the subject, and worthy of a place in every phy-
sician’s library.— Western Lancet,

(A new edition.)

GENERAL THERAPEUTICS AND MATERIA MEDICA; adapted for a

Medical Text-book. With Indexes of Remedies and of Diseases and their Remedies.
Epition, revised and improved. With one hundred and ninety-three illustrations.
and handsomely printed octavo vols., leather, of about 1100 pages. $6 00.

Tn announcing a new edition of Dr. Dunglison’s
General Therapeutics and Materia Medica, we have
no words of commendation tou bestow upon a wurk
whose merits have been heretofore so often and so
justly extolled. Lt must not be supposed, however,
that the present is a mere reprint of the previous
edition; the character of the author for laborious
research, judicious analysis, and clearness of ex-
pression, is fully sustuined by the numerous addi-
tions he has made to the work, and the careful re-
vision tu which he has subjected the whole.—N. A.
Medico-Chir. Review, Jan. 1853.

BY THE SAME AUTHOR.

SIxTH
In two large

The work will, we have little doubt, be bought
and read by the majority of medical students; ica
size, arrangement, and reliability recommend it to
all; no one, we venture tu predict, will study it
without profit. and there are few to whom it will
not be in sume measure useful as a work of refer-
ence. The young practitioner, more especially, will
find the copious indexes appended to this edizsion of
great ussistance in the selection and preparation of
suitable formule.—Charleston Med. Journ.and Re-
view, Jan. 1858.

(A new Edition.)

NEW REMEDIES, WITH FORMULA FOR THEIR PREPARATION AND

ADMINISTRATION. Seventh edition, with extensive Additions.

volume, leather, of 770 pages. $3 75.

In one very large octavo

Another edition of the ““New Remedies’’ having been called for, the author has endeavored to
add everything of moment that has appeared since the publication of the last edition.
The articles treated of in the former editions wikl be found to have undergone considerable ex-

pansion in this, in order that the author might be enabled to introduce, as far as practicable, the
results of the subsequent experience of others, as well as of his own observation and reflection ;
and to make the work still more deserving of the extended circulation with which the preceding
editions have been favored by the profession. By an enlargement of the page, the numerous addi-

tions have been incorporated without greatly increasing the bulk of the volume.—Preface.

One of the most useful of the author’s works.—
Southern Medical and Surgical Journal.

This elaborate and useful volume should be
found in every medical library, for as a book of re-
ference, for physicians, it is unsurpassed by any
other work in existence, and the double index for
digcases and for remedies, will be found greatly to

The great learning of the author, and his remark-
able industry in pushing his researches into every
source whence information is derivable, have enabled
him to throw together an extensive mass of facts
and statements, accompanied by full reference to
authorities; which last feature renders the work
practically valuable to investigators who desire te
examine the original papers.—The American Journal

enhance its value.—New York Med. Gazette, | of Pharmacy

ELLIS (BENJAMIN), M.D.
THE MEDICAL FORMULARY: being a Collection of Prescriptions, derived

from the writings and practice of many of the most eminent physicians of America and Europe.
Together with the usual Dietetic Preparations and Antidotes for Poisons. To which is added
an Appendix, on the Endermic use of Medicines, and on the use of Ether and Chloroform. The
whole accompanied with a few brief Pharmaceutic and Medical Observations. Eleventh edition,
revised and much extended by Rogert P. Tuomas, M. D., Professor ot Materia Medica in the
Philadelphia College of Pharmacy. (Preparing.)

14 BLANCHARD & LEA’S MEDICAL

ERICHSEN (JOHN),
Professor of Surgery in University College, London, &c.

THE SCIENCE AND ART OF SURGERY; Berne a TREATISE ON SURGICAL
Inturies, Diszasts, AND OpErations. New and improved American, from the second enlarged
and carefully revised London edition. Illustrated with over four hundred engravings on wood.
Tn one large and handsome octave volume, of one thousand closely printed pages, leather,
raised bands. $4 50. (Just Issued.)

The very distinguished favor with which this work has been received on both sides of the Atlan-
tic has stimulated the author to render it even more worthy of the position which it has so rapidly
atiained asa standard authority. Every portion has been carefully revised, numerous additions
have been made, and the most watchful care hax been exercised to render it a complete exponent
of the most advanced condition of surgical seience. In this manner the work has been enlarged b
abont a hundred pages, while the series of engravings has been increased by more than a hundred,
rendering it one of the most thoroughly illustrated volumes before the profession. The additions of
the author having rendered unnecessary most of the notes of the former American editor, but litthe
has been added in this country; some few notes and occasional illustrations have, however, been

introduced to elucidate American modes of practice.

{tis,in our humble judgment. decidedly the best
book «f the kind in the English language. Strange
that jost such books are notofiener produced by pub-
ie teachers of surgery in this country and Great
Mritam Indeed. itis a matter of creat astonishment
bnt no less true than astonishing, that of the mauy
works on surgery republished in this country within
the Jast fifteen or twenty years as text-books for
medical students, this is the only one that even ap-
proximates to the fulfilment of the peculiar wants of
young men tstentering upon the study of this branch
ofthe profession.— Western Jour .of Med. and Surgery.

Its value is greatly enhanced by a very copious
well-arrangedindex. We regard this as one of the
most valuable contributionsto modern surgery. To
one entering his novitiate of practice, we regard 11
the most serviceable guide which hecancorsult. He
will find a fulness cftetalllondingtins throcgh every

step of the operajion, and not deserting him until the
final issue of the case is decided —Sethoscope.

Embracing, as wil! be perceived, the whole sargi-
eal domain, and each division of itself almost com-
plete and perfect, cach chapter full and explicit, each
subject faithfully exhibited, we can only express ow
estimate of it in the aggregate. We consider itan
excellent contribution 10 surgery, as probably the
best single volume now extant on the subject, and
with great pleasure we add it to our text-books.—
Nashville Journal of Medicine ard Surgery

Prof. Erichsen’s work, for its size, has not been
surpaszed; his nine hundred and vcight pages, pro-
fusely illustrated, are rich in physiological, patholo-
gical, and operative suggestions, doctrines, detaile,
and processes; and will prove a reliable resaurce
for information, both to physician and surgeon, tn the
hour of peril.—NV. 0. Med. and Surg. Journal. ~

FLINT (AUSTIN), M. D.,

Professor of the Theory and Practice of Medicine in the University of Louisville, &c.

PHYSICAL EXPLORATION AND DIAGNOSIS OF DISHEASES AFFECT.

ING THE RESPIRATORY ORGANS.

cloth, 636 pages. $3 00.

We regard it, in point both of arrangement and of
the marked ability of its treatment of the subjects,
us destined to take the first rank in works of this
elass So faras our information extends, it has at
present no equal. To the practitioner, as well as
the student, it will be invaluable in clearing up the
diagnosis of doubtful eases, and in shedding light
upon difficult phenomena.— Buffalo Med. Journal.

BY THE SAME AUTHOR,

In one large and handsome octavo volume, extra

A work of original observation of the highest ment.
Werecommend the treatise to every one who wishes
to become a correct auscultator. Based to a very
large extent upon cases numerically examined, it
carries the evidence of enreful study and diserimina-
tion upon every page. It does eredit to the author,
and, through hima, to the profession in this country.
It is, what we cannot ea!l every book upon auscul-
tation, a readable book.— Am. Jour. Med. Sciences.

(Now Ready.)

A PRACTICAL TREATISE ON THE DIAGNOSIS, PATHOLOGY, AND

TREATMENT OF DISEASES OF THE HEART.

500 pages, extra cloth. $275.

We do not know that Dr. Flint has written any-
thing which is not first rate; but this, his latest con-
tribution to medical literature, in Gur opinion, sur-
passes all the others. The work is most comprehen-
sive in its scope, and mest sound in the views it evun-
ciates, The descriptions are clear und methodical;
the statements ure substantiated by facts, and are
made with snch simplicity and sincerity, that with-
out them they would earry conviction. The style
ig admirably clear, direct, and free from dryness
With Dr. Walshe’s excellent treatise before us, we
have no hesitation in saying that Dr. Flint’s book is
the best work on the heart in the English language.
—Boston Med. and Surg. Journal.

We have thus endeavored to present our readers
with a fair analysis of this remarkable work. Pre-
ferring toemploy the very words of the distinguished
author, wherever it was possible, we have essayed
ty condense into the briefest spacea general view of
his observations and suggestions, and to direet the
attention of onr brethren to the abounding rtores of
vaJuable matter here collected and arranged for their
use and instruction. No medica! library will here
after be considered complete without this volume;
and we tens! it will promptly find its way into the
hands of every Ame’ ienp student and physician.—
N Am, Med. Chir. Review

This last work of Prof. Flint will add much to
hig previous well-earneu celebrity, as a wrier of

In one neat octavo volume, of about

great force and beauty, and, with his previous work,
Places him at the head of Amencan writers upon
diseases of the chest. We nave adopted his work
upon the heart ag a text-book, believing it to be
more valuable for that purpose than any work of the
kind that has yet appeared.— Nashville Med. Journ.

With more than pleasure do we hail the advent of
this work, for it fills a wide gap on the list of text-
beoks for our schuols, and is, tor the practitioner,
the n.ost valuable practical work of its kind —N. 0.
Med. News.

In regard to the merits of the work, we have no
hesitation in pronouncing it full, accurate, and ju-
dicious. Considering the pres'nt state of science,
such a work was much needed. {ft should ve in the
hands of every practitioner —Chicngo Med Journal.

But these are very trivial spots, and in no wise
prevent us from declaring our most hearty approval
of the author’s ability, industry, and conscientious-
ness.— Dublin Quarterly Tournal of Med. Sciences.

He has labored on wi'h the same industry and care,
and his place among the first authors of our countr
is becoming fully established. To this end, the work
whose title is given above, coniributes in no small
degree, Our spa‘e will not admit of an extended
analysis, and we will close this orief notice by
commending it without reserve to every class of
readers in the profession.— Peninsular Med. Journ.

MEME ENTIFIC PUBLICATIONS. 15

FOWNES (GEORGE), PH.D., &c.
A MANUAL OF ELEMENTARY CHEMISTRY; Theoretical and Practical.

From the seventh revised and corrected London edition. With one hundred and ninety-seven
illustrations Edited by Roperr Bripers, M.D. In one large royal 12mo volume, of 600
pages. In leather, $1 65; extra cloth, $1 50. (Jast Issued.)

The death of the author having placed the editorial care of this work in the practised hands of
Drs. Bence Jones and A. W. Hoffman, everything has been done in its revision which experience
could suggest to keep it on a level with the rapid advance of chemical science. The additions
requisite to this purpose have neces: itated an enlargement of the page, notwithstanding which the
work has been increased by about fifty pages. At the same time every care has been used to
maintain its distinclive character as a condensed manual for the student, divested of all unnecessary
detail or mere theoretical speculation. The additions have, of course, been mainly in the depart-
ment of Organic Chemistry, which has made such rapid progress within the last few years, but
te equal attention has been bestowed on the other branches of the subject—Chemical Physics and

norganic Chemistry—to present all investigations and discoveries of importance, and to keep up
the reputation of the volume as a complete manual of the whole science, admirably adapted for the

learner.

By the use of a small but exceedingly clear type the matter of a large octavo is compressed

within the convenient and portable limits of a moderate sized duodecimo, and at the very low price
affixed, 1t is offered as one of the cheapest volumes before the profession.

Dr. Fownes’ excellent work has heen universally
recognized everywhere in lis own and this country,
as the best elementary treatise on chemistry in the
English tongue, and is very geuerally adopted, we
believe, asthe standard text book in all¢ urcolleges,
both literary and scientific —Charleston Med. Journ.
and Review.

A standard manual, which has long enjoyed the
reputation of embodying much knowledge in a small
space. The author hasachieved the difficult task of
condensation with musterly tact. His book is con-
cise without being dry, and brief without being too
dogmatical or general.— Virginia Med.and Surgical
Journal,

FISKE FUND PRIZE ESSAYS — THE EF-
FECTS OF CLIMATE ON TUBERCULOUS
DISEASE. By Fowin Lez,M.R.C S , London,
and THE INFLUENCE JF PREGNANCY ON
THE DEVELOPMENT OF TUBERUCLES By

The work of Dr. Fownes has long been before
the public, and its merits have been fully appreci-
ated as the best text-book on chemistry now in
existence. We do not, of course, place it in a rank
superior to the works of Brande, Graham, Turner,
Gregory, or Gmelin, but we say that, as a work
for students, it is preferable to any of them.—Lon-
don Journal of Medicine.

A work well adapted to the wants of the student
It is an excellent exposition of the chief doctrines
and facts of modern chemistry. The sizeof the work,
and still more the condensed yet perspicuous style
in which it is written, absolve it from the charges
very properly urged against most manuals termed
popular.—Edinburgh Journal of Medical Science.

Epwarp Warren, M.D , of Edenton, N.C. To-
gether inoneneat 8vo volume, extra cloth, ®I 00.
FRICK ON RENALAFFECTIONS; their Diag-
nosis and Pathology. With illustrations. One
volume, royal 12mo0., extra cloth. 75 cents.

FERGUSSON (WILLIAM), F.R.S.,

Professor of Surgery in King’s College, London, &c.

A SYSTEM OF PRACTICAL SURGERY. Fourth American, from the third

and enlarged London edition.

In one large and beautifully printed octavo volume, of about 700

pages, with 393 handsome illustrations, leather. $3 00.

GRAHAM (THOMAS), F.R.S.
THE ELEMENTS OF INORGANIC CHEMISTRY, including the Applica-

tions of the Science in the Arts. New and much enlarged edition, by Henry Watts and RoBert
Bripces, M.D. Complete in one large and handsome octavo volume, of over 800 very large
pages, with two hundred and thirty-two wood-cuts, extra cloth. $4 00.

Part II., completing the work from p. 431 to end, with Index, Title Matter, &c., may be

*y
had separate, cloth backs and paper sides.
From Prof. E. N. Horsford, Harvard College.

Price $2 50.

afford to be without this edition of Prof. Graham’s

It has, mn its earlier and less perfect editions, been | Elements.—Silliman’s Journal, March, (858.

familiar to me, and the excellence of its plan and
the clearness and completeness of its discussions,
have long been my admiration.

From Prof. Wolcott Gibbs, N. Y. Free Academy.

The work is an admirable one in all respects, and
its republication here cannot fail to exert a positive

No reader of English works on this science can | influence upon the progress of science in this country.

GRIFFITH (ROBERT E.), M.D., &c.
A UNIVERSAL FORMULARY, containing the methods of Preparing and Ad-

ministering Officinal and other Medicines. The whole adapted to Physicians and Pharmacen-

tists.

Second Enition, thoroughly revised, with numerous additions, by Ropert P. Tuomas,

M. D., Professor of Materia Medica in the Philadelphia College of Pharmacy. In one large and

handsome octavo volume, extra cloth, of 650 pages, double columns.

It was a work requiring much perseverance, and
when published was looked upon as by far the best
work ofits kind that had tssued from the American
press. Prof Thomas has certainly “improved.” as
well as added tothis Formulary, and has rendered it
additionally deserving of the confidence of pharma-
ceutists and physicians.—Am. Journal of Pharmacy.

We are happy to announce a new and improved
edition of this, one of the most valuable and useful
works thathave emanated from an American pen.
It would do eredit to any coumtry, and will be found
of daily usefulness to practitioners of medicine; it is
better adapted to their purposes than the dispensato-
ries.—Southern Med. and Surg. Journal.

Itis one of the most useful books a country practi-

tioner can possibly have.—Medical Chronicle.

$3 00; or in sheep, $3 25.

This is a work of six hundred and fifty one pages,
ambracing allan the subjeet of preparing and admi-
nistering medicines that can be desired by the physi-
sian and pharmaceutist.— Western Lancet.

The amountof useful, every-day matter.for a prae-
licing physician, is really immense.—Boston Med.
and Surg. Journal.

This edition has been greatly improved by the re-
vision and ample additions of Dr Thomas, and is
now, we believe, one of the mosi complete works
of its kind in any language. The additions amount
10 aboulseventy pages, and no effort has been spared
to include in them all the recent improvements. 4
work of this kind appears to us indispensable to the
physician, and there is none we can more cordially
recommend. WN Y Journalof Medicine.

BLANCHARD & LEA’S“MEDICAL

GROSS (SAMUEL D.), M.D.,
Professor of Surgery in the Jefferson Medical College of Philadelphia, &c.

Enlarged Edition—Now Ready, January, 1862.
A SYSTEM OF SURGERY: Pathological, Diagnostic, Therapeutic, and Opera-

tive. Illustrated by Twerve Honprrp and TwenTy-sEvVEN Eneravines. Second edition,

much enlarged and carefully revived. In two large and beautifully printed octavo_volumes, of

about twenty-two hundred pages; strongly bound in leather, with raised bands. Price $12.

The exhanstion in little more than two years of a large edition of so elaborate and comprehen-
sive a work as this is che best evidence that the author was not mistaken in his estimate of the
want which existed of a complete American System of Surgery, presenting the science in all its
necessary details and in all its branches. That he has xueceeded in the attempt to supply this want
1s shown not only by the rapid sale of the work, but also by the very favorable manner in which it
has bern received by the organs of the profession in this conntry and in Europe, and by the fact that
a translation is now preparing in Holland—a mark of appreciatioa not often bestowed on any scien-
tific work so extended in size

The author has not been msensible to the kindness thus bestowed upon his labors, and in revising
the work for a new edition he has ~pared no pains to render it worthy of the favor with which it
has been received. Every portion bas been subjected to close examination and revision; any defi-
ciencies apparent have been supplied, and the results of recent progress in the science and art of
surgery have been everywhere introduced; while the series of illustrations has been enlarged by
the addition of nearly three hundred wood-cuts, rendering it one of the most thoroughly illustrated
works ever laid before the profession. To accommodate these very extensive additions, the work
has been printed upon a smaller type, so that notwithstanding the very large increase tn the matter
and value of the book, ils size is more convenient and less cumbrous than belore. Every care has
heen taken in the printing to render the typographical execution unexcep'ionable, and it is confi-
dently presented as a work in every way worthy of a place in even the most limited library of the

Pp actitioner or student.

A few testimonials of the value of the former edition are appended.

Has Dr. Gross satisfactorily fulfilled this object ?
A carelut perusal of his volumes enubles us to give
an answer in theaffirmative. Notonly has he given
to the reader an elaborate and well-written account
of his own vast experience, but he has not failed to
embody in hia pages the opinions and practice of
surgeons in this and other countries of Europe. The
result has been a work of such completeness, that it
has no superior in the systematic treatises on sur-
gery which have emanated from English or Conti-
vental authors. It has been justly objected that
these have been far from complete in many essential
particulars, many of them having been deficient in
some of the most important points which should
characterize such works Some of them have been
elaborate—too elaborate—with respect to certain
diseases, while they have merely glanced at, or
given an unsatisfactory account of, others equally
important to the surgeon. Dr. Gross hus avoided
this error, and has produced the most complete work
that has yet issued from the press on the science and
practice of surgery. Itis not, strictly speaking, w
Dictionary of Surgery, but it gives to the reader all
the information that he may require for his treat nent
of surgical diseases, Jlaving said so much, it might
apneur superfluous to add another word; but it is
only due to Dr. Gross to state that he has embraced
the opportunily of transferring to his pages a vast
number of engravings from English and other au-
thors, iustrative of the pathology and treatment of
surgical diseuses. To these ure adiled several hun-
dred original woed-ents. The work altogether eom-
mends itself to the attention of British surgeons,
from whom it cannot fail to mret with extensive
patronage.—London Lancet, Sept. 1, 1800.

Of Dr. Gross’s treatise on Surgery we can say
no more than that it is the most elaborate and com-
plete work on this branch of the | paling art which
has ever been published in any country. A sys-
tematic work, it admits of no analytical review;
but, did our space permit, we should gladly give
some extracts from tt, to enable our readers to judge
of the c'assical style of the author, and the exhaust-
ing way in which each subject is treated.— Dublin
Quarterly Journal of Med. Science.

The work is so superior to its predecessors in
matter and extent, as well as in illustrations and
style of publication, that we ean honestly recom-
mend it as the best work of the kind to be taken
home hy the ypung practitioner.—Am. Med. Touran.

With pleasure we reeurd the completion of this
long-anticipsted work. The reputation which the
author has for many years sustained, both as a eur-
geon and asa writer, had prepared us to expect a
treatise of great excellence and originality; but we
confess we were by no means prepared for the work
which is before us—the most complete treatise upon
surgery ever published, either in this or any other
country, and we might, perhaps, safelv say, the
most original. There is ne subject belonging pro-
perly to surgery which hus not received from the
authota due share of attention. Dr. Grogs has sup-
pled a wantin surgical literature which has long
been felt by practitioners; he has furnished us with
a complete practical trentise upon surgery in all its
departments As Americins, we are proud of the
achievement; as surgeons, we are most sincerely
thankful to him for his extraord nary labors in our
behalf —N. Y. Monthly Keview and Buffalo Med.
Journal,

BY THE SAME AUTHOR.
ELEMENTS OF PATHOLOGICAL ANATOMY. Third edition, thoroughly

revised and greatly improved. In one large and very handsome octavo volume, with about three
hundred and fifty beautiful illustrations, of which a large number are from original drawings.

Price in extra cloth, #4 75; leather, raised bands, $5 28.

(Lately Published.)

The very rapid advances in the Science of Pathological Anatomy during the last few years have

rendered essential a thorough modification of this work, with a view of making it a correct expo-
nent of the present state of the subject. ‘The very careful manner in which this task has been
executed, and the amount of alteration which it has undergone, have enabled the author to say that
“Cwith the many changes and improvements now introduced, the work may be regarded almost as
a new treatise,’’ while the eflorts of the author have been seconded as regards the mechanical
execution of the volume, rendering it one of the handsomest productions of the American press.

We most sincerely congratulate the author on the We have been favorably impressed with the gene-
successful manner in which he has accomplished his | ral manner in which Dr, Gross has executed his task
proposed object. His book is most adm OLY cal- | of affording a comprehensive digest of the present
culated to fill up a blank which has long been felt to | state of the literature of Pathological Anatomy, and
exist in this department of medical literature, and | have much pleasure in recommending his work to
as such must become very widely circulated amongst | our reuders, as we believe one well deserving of
all classes of the profession.— Dublin Quarterly | dilivent perusal and careful study.—Montreal Mea.
Journ. of Med. Science, Nov. 1857. Chron., Sept. 1857.

BY THE SAME AUTHOR.
A PRACTICAL TREATISE ON FOREIGN BODIES IN THE AIR-PAS.

SAGES. Jn one handsome octavo volume, extra cloth, with illustrations. pp. 468. $2 75,

AND SCIENTIFIC PUBLICATIONS, 17

GROSS (SAMUEL D.), M.D.,
Professor of Surgery in the Jefferson Medical College of Philadelphia, &c.

A PRACTICAL TREATISE ON THE DISEASES, INJURIES, AND
MALFORMATIONS OF THE URINARY BLADDER, THE PROSTATE GLAND, AND
THE URETHRA. Second Edition, revised and much enlarged, with one hundred and eighty-
four illustrations. In one large and very handsome octavo volume, of over nine hundred pages.
In leather, raised bands, $5 25; extra cloth, $4 75.

Philosophical in its design, methodical in its ar- | agree with us, that there is no work in the English
tangement, ample and sound in its practical details, | language which can make any just pretensions to
it may in truth be said to leave scarcely anything to | be its equal.—N. Y. Journal of Medicine.
be pa On’ se, portant a subject.—Boston Med.| 4 volume replete with truths and principles of the
oad OERE dourna. ; utmost value intheinvestigation of these diseases.—

Whoever will peruse the vast amount of valuable| American Medical Journal,
practical information it contains, will, we think,

GRAY (HENRY), F.R.S.,

Lecturer on Anatoiny at St. George’s Hospital, London, &e.

ANATOMY, DESCRIPTIVE AND SURGICAL. The Drawings by H. V.

Carter, M. D., late Demonstrator on Anatomy at St. George’s Hospital; the Dissections jointly
by the AurHor and Dr. Carrer. Second American, from the second revised and improved
London edition. In one magnificent imperial octavo volume, of over 800 pages, with 398 large
and elaborate engravings on wood. Price in extra cloth, $6 25; leather, raised bands, $7 00.
(Now Ready, 1862.)

The speedy exhaustion of a large edition of this work is sufficient evidence that its plan and exe-
cution have been found to present superior practical advantages in facilitating the study of Anato-
my. In presenting it to the profession a second time, the author has availed him-elf of the oppor-
tunity to supply any deficiencies which experience in its use had shown to exist, and to correct
any errors of detail, 10 which the first edition of a scientific work on so extensive and complicated
a science is liable. These improvements have resulted in some increase in the size of the volume,
while Lwenty-six new wood-cuts have been added to the beautiful series of illustrations which
form so distinctive a feature of the work. The American edition has been passed through the press
under the supervision of a competent professional man, who has taken every care to render it in
all respects accurate, and it is now presented, without any increase of price, as fitted to maintain

and extend the popularity which it bas everywhere acquired

With little trouble, the busy practitioner whose
knowledge ofanatomy may have become obscured by
want of practice, may now resuscitate his former
anatomical lore, and be ready for any emergency.
It is to this class of individuals, and not to the stu-
dent alone, that this work will ultimately tend to
be of most incalculable advantage, and we feel sat-
isfied that the library of the medical man will soon
be considered incomplete in which a copy of this
work does not exist.— Madras Quarterly Journal
of Med. Science, July, 1861.

This edition is much improved and enlarged, and
contains several] new illustrations by Dr. Westma-
eott. The volume is a complete companion to the
dissecting-room, and saves the necessity of the stu
dent possessing a variety of ‘‘ Manuals.??—The Lon-
don Lancet, Feb. 9, 1861.

The work before us is one entitled to the highest
praise, and we accordingly welcome it as a valu-
able addition to medical literature. Intermediate
in fulness of detail between the treatises of Siar
pey and of Wilson, its characteristic merit lies in
the number and excellence of the engravings 1t
contains. Most of these are original, of much
larger than ordinary size, and admirably executed.
The various parts are also lettered after the plan
adopted in Holden’s Osteology. It would be diffi-
cult to over-estimate the noventance offered by this
mode of pictorial iNustration. ones, ligaments,
muscles, bloodvessels, and nerves are each in turn
figured, and marked with their appropriate names;
thus enabling thestudent to ecmprehend, ata glance,
what would otherwise often be ignored, or at any
rate, acquired only by prolonged and irksome ap-
plication. In conclusion, we heartily commend the
work of Mr. Gray to the attention of the medical
profession, feeling certain that it should be regarded
as one of the must valuable contributions ever made
to educational literature —N. Y. Monthly Review.
Dec. 1859.

In this view, we regard the work of Mr. Gray as
far better adapted to the wants of the profession,
and especially of the student, than any treatise on
anatomy yet published in thiscountry. It is destined.
we believe, to supersede ill others, both as a manual
of dissections, and a standard of reference to the
student of general or relative anatomy.—WN. Y.
Journal of Medicine, Nov, 1859.

For this truly admirable work the profession is
indebted to the distinguished author of ‘Gray on
the Spleen.’? The vacancy it fills has been long felt

to exist in this country. Mr. Gray writes through-
out with both branches of his subject in view. is
description of each particular part is followed by a
notice of its relations to the parts with which it is
connected, and this, too, sufficiently ample for all
the purposes of the operative surgeon. After de-
seribing the bones and muscles, he gives a concise
statement of the fractures to which the bones of
the extremities are most liable, together with the
amount and direction of the displacement to which
the fragments are subjected by muscular action.
The section on arteries is remarkably full and ac-
curate, Not only is the surgical anatomy given to
every important vessel, with directions for its liga-
tion, but at the end of the description of each arte-
rial trunk we have a useful summary of the irregu-
larities which may occur in its origin, course, and
termination —N. A. Med. Chir. Review, Mar. 1359.

Mr. Gray’s book, in excellency of arrangement
and completeness of execution, exceeds any work
on anatomy hitherto published in the English lan-
guage, affording a complete view of the structure of
the human body, with especial reference to practical
surgery. Thus the volume constitutes a perfect book
of reference for the practitioner, demanding a place
in even the most limited library of the physician or
surgeon, and a work of necessity for the student. to
fix in his mind what he has learned hy the dissecting
knife from the book of nature.—The Dublin Quar-
terly Journal of Med. Sciences, Nov. 1858.

In our judgment, the mode of illustration adopted
in the present volume cannot but present many ad-
vantages to the studentof anatomy. To the zealous
disciple of Vesalius, earnestly desirous of real i1m-
provement, the book will certainly be of immense
value; but, at the same time, we must also confess
that to those simply desirous of ‘¢eramming?? it
will be an undoubted godsend. The peculiar value
of Mr. Gray’s mode of illustration is nuwhere more
markedly evident than in the chapter on osteology,
and especially in those portions which treat of the
bones of the head and of th2ir development. The
study of these parts is thus made one of comparative
ease, if notof positive pleasure; and those bugbears
of the student, the temporal and sphenoid bones, are
shorn of half their terrors. It is, in our estimation,
an admirable and complete text-book for the student,
and a useful work of reference for the practitioner;
its pictorial character forming a novel element, to
which we have already sufficiently alluded.—Am,
Journ, Med. Sei., July, 1859.

18

BLANCHARD & LEA’S MEDICAL

GIBSON’S INSTITUTES AND PRACTICE OF
SURGERY. Eighth edition, improved and al-
tered. With thirty-four plates. In twohandsome
octavo volumes, containing about 1,000 pages,
leather, raised band1. $6 50.

GARDNER’S MEDICAL CHEMISTRY, for the
use of Students and the Profession. In one royal
12mo. vol., cloth, pp. 896, with wood.cuts. $1.

GLUGE’S ATLAS OF PATHOLOGICAL HIS-
TOLOGY. Translated, with Notes and Addi-

tions by JoszpH Letpy, M.D. In one volume,
very large imperial! quarto, extra cloth, with 320
copper- plate figures, plain and eolored, $5 00.

HUGHES? INTRODUCTION TO THE PRAC-
TICE OF AUSCULTAVION AND OTHER
MODES OF PHYSICAL DIAGNOSIS. IN DIS-
EASES OF THE LUNGS AND HEART. Be-
cond edition 1 vol. royal 12mo., ex. cloth, pp.
304. $1 00.

HAMILTON (FRANK H.), M. D.,
Professor of Surgery in the Long Island College Hospital.

A PRACTICAL TREATISE ON FRACTURES AND DISLOCATIONS. Ia

one large and handsome octavo volume, of over 750 pages, with 289 illustrations. $425. (Vow

Ready, January, 1860.)

Among the many good workers at surgery of whom
America may now boast rot the leastis Frank Hast-
ings Hamilton; and the volume before us is (we say
it with w pang of wounded patriotism) the best and
handiest book on the subject in the Erglish lan-
guage. Jt is in vain to attempt a review of it;
nearly as vain to seek for any sins, either of com-
mission or omission. We have seen no work on
practical surgery which we would sooner recom-
mend to our brother surgeons, especially those of
‘ the services,’? cr those whose practice lies in dis-
tricts where a man has necessarily to rely on his
own unaided reeources. The practitioner will find
in it directions for nearly every possible actiaent,
easily found and comprehended; and mueh pleasant
reading for him to muse over in the after considera-
tion of his cases.— Edinburgh Med. Journ Feb 1661.

This is x valuable contribution to the surgery of
most important affections, and is the more welcome,
inasmuch as at the present time we do not possess
a single complete treatise on Fractures and Dislo-
cations in the Knglish language. [t has remained for
our Amevican brother to produce a complete treatise
upon the subject, and bring together in a cunvenient
form those alterations and improvements that have
been made from time totime in the treatment of these
affections, One great and valuable feature in the
work befure us is the fact that it comprises all the
improvemen's introduced into the practice of both
Engtish and American surgery, and though far from
omitting mention of our continental neighbors, the
author by no means encourages the notion—but too
prevalent in some quarters—that nothing is good
unless imported fram France or Germany. The
latter half of the work is devoted to the considera-
tion of the various dislocations and their appropri-
ate treatment. and its merit is fully equal to that of
bet a portion.—The London Lancet, May 5,

It is emphatically the book upon the subjects of
which it treats, and we cannot doubt that it will
continue so to be for an indefinite period of time.
When we say, however, that we believe it will at
unce take ils place as the best book for consultation
by the practitioner; and that it will form the most
complete, available, and reliable ced in emergen-
cies of every nature connected with its subjects; and
also that the student of surgery may make it his text-
book with entire confidence, and with pleasure also,
from its agreeable and easy style—we think our own

opinion may be gathered as to its value.—Roston
Medical and Surgical Journal, March 1, 1860.

The work ts concise, judiciuus, and accurate, and
adapted to the wants of the student, practiticner,
and investigator, honorable to the author and to the
profession.—Chicago Med. Journal, March, 1860.

We regard this work as an honor not only to its
author, but to the profession of ourcountry, Were
we to review it choroughly, we could not convey to
the mind of the reader more foreibly our honest
opinion expressed in the few words—we think it the
best bouk of its kind extant. Every man interested
in surgery will scon have this work on his desk,
He who does not, will be the loser—New Orleans
Medical News, March, 1860.

Now that it is before us, we feel bound to say that
much as was expected from it, and onerous As was
the undertaking, it has surpassed expectation, and
achieved more than was pledged in its behalf; for
its title does not express in full the richness of ita
contents. On the whole, we are prouder of this
work than of any which has for years emanated
from the American medical press; its sale will cer-
tainly be very large in this country, and we antici-
pate its eliciting much attention in Europe.—Nash-
ville Medical Record, Mar. 1860.

Every surgeon, young and old, should possess
himeelf of it, and give it a careful perusal, in doing
which he will be richly repaid.—St. Louis Med.
and Surg. Journal, March, 1860.

Dr. HamiJton is fortunate in having succeeded in
filling the void, so long felt, with what cannot fail
to be at onceaccepted as a model monograph ia some
respects, and a work of classical authority. We
sincerely congratulate the profession of the United
States on the appearance of such a publication from
one of their number. We have reason to be proud
of it as an original work, both in a literary and ari-
entific point of view, and to esteem 1t as a valuable
guide ina most difficult and important branch of
study and practice. On every account, therefore
we hope that it may svon be widely known abroad
as an evideare of genuine progress on this side of
the Atlantic, and further, that 1t may be still more
widely known at home as un authoritative teacher
from which every one muy profitably learn, and as
affording an example of honest, well-directed, and
untiring jndustry in authorship which every surgeon
May emulate. Am. Med. Journal, April, 1860,

HOBLYN (RICHARD D.), M, D.
A DICTIONARY OF THE TERMS USED IN MEDICINE AND THE

COLLATERAL SCIENCES. A new American edition.

Revised, with numerous Additions,

by Isaac Hays, M. D., editor of the American Journal of the Medical Sciences.”’ In one large
royal 12mo, volume, leather, of over 500 double columned pages. $1 50.

To both practitioner and student, we recommend use ; embracing every department of medical science

this dictionary as being convenient in size, accurate
in definition, and sufficiently full and complete for
ordinary consultation.—Charleston Med. Journ.
We know of no dictionary better arranged and
adapted. It isnotencumbered with the obsoleteterms
of a bygone age, but it contains all that are now in

HOLLAND’S MEDICAL NOTES AND RE-
FLECT(UNS. From the third London edition.
In one handsome octavo volume, extra cloth, $3.

HORNER’S SPECIAL ANATOMY AND HiS-

down to the very latest date.—Western Lancet.

Hoblyn’s Dictionary has long been a favorite with
us. Itis the best bovk of definitions we have, and
ought always to be upon the student’s table.—
Southern Med, and Surg. Journal,

TOLOGY. Eighth edition. Extensiv-ly revised
and modified. {n two large octavo volumes, ex-
tra cluth, of more than 1000 pages, with over 300
illustrutions. $6 00.

AND SCIENTIFIC PUBLICATIONS. 19

HODGE (HUGH L.), M.D.,

Professor of Midwifery and the Diseases of Women and Children in the University of Pennsylvania, &c.

ON DISEASES PECULIAR TO WOMEN, including Displacements of the

Uterus. With original illustrations. In one
pages, extra cloth. $325. (Now Ready.)

We will say at once that. the work fulfils its object
eapitally well; and we will moreover venture the
assertion that it will inaugurate an improved prac-
tice throughout this whole country. The secrets of
the authors success ure 80 clearly revealed that the
attentive student cannot fail to insure a goodly por-
tion of similar success in his own practice. Itisa
credit to all medical literature; and we add, that
the physician who does not place it in his library,
and who does not faithfully com its pages, will lose
a vase deal of knowledge that would be most useful
to himself and beneficial to his patients. Iz 7s @
practiral work of the highest order of merit; and it
will take rank as such immediately.— Maryland and
Virginia Medical Journal, Feb. 1861.

This contribution towards the elucidation of the
pathology and treatment of some of the diseases
peculiar to women, cannot fail to meet with a favor
able reception from the medical profession, The
eharacter of the particular maladies of which the
work before us treats; their frequency, variety, and
obscurity ; the amount of malaiseand even of actual
suffering by which they are invariably attended;
their obstinacy, the difficulty with which they are
overcome, and ul eir disposition again and again to
1ecur—these, taken in connection with the entire
competency of the author to render a correct ac-
gount of their nature, their causes, and their appro-

beautifully printed octavo volume, of nearly 500

priate management—his ample experience, his ma-
tured judgment, and his perfect conscientiousness—
inves this publication with an interest and value to
whieh few of the medical treatises of a recent date
ean lay a stronger, if, perchance, »n equal claim.—
Am. Journ. Med Sciences, Jan. 1861

Indeed, although no part of the volume is not emi-
nently deserving of perusal and study, we think that
the nine chapters devoted to this subject, are espe-
cially so, and we know of no more valuable mono-
graph upon the symptoms, prognosis, and manage-
ment of these annoying maladtes than is conetituted
by this part of the work. We cannot but regard it
ag one of the most originul and m >st practical works
of the day ; one which every accoucheur and physi-
ciaa should most carefully reid; for we are per-
suaded that he will arise from its perusal with new
ideas, which will induct him into a more rational
practice in regard to many a suffering femile, who
may have placed her health in his hands.—British
American Journal, Feb. 1€61.

Of the many excellences of the work we will not
speak at length. Weadvise ail who would acquire
a krowledge of the proper management of the mala-
dies of which it treats, to study it with care. The
second part is of itself a most valuable contribution
to the practice of our arc.—Am. Med. Monthly and
New York Review, Feb. 1861.

The illustrations, which are all original, are drawn to a uniform scale of one-half the natural size.

HABERSHON (S. O.), M.D.,

Assistant Physician to and Lecturer on Materia Medica and Therapeutics at Guy’s Hospital, &c.

PATHOLOGICAL AND PRACTICAL OBSERVATIONS ON DISEASES
OF THE ALIMENTARY CANAL, CESOPHAGUS, STOMACH, C/ECUM, AND INTES-

TINES. With illustrations on wood.
eloth $1175. (iVow Ready.)

In one handsome octavo volume of 312 pagey, extra

JONES (T. WHARTON), F.R.S.,

Professor of Ophthalmic Medicine and Surgery in University College, London, &c.

THE PRINCIPLES AND PRACTICE OF OPHTHALMIC
AND SURGERY. With one hundred and ten illustrations.

MEDICINE

Second American from the second

and revised London edition, with additions by Epwarp HartsHorne, M.D., Surgeon to Wills’
Hospital, &e. In one large, handsome royal 12mo. volume, extra cloth, of 50U pages. $1 50.

JONES (C. HANDFIELD), F.R.S., & EDWARD H. SIEVEKING, M.D.,

Assistant Physicians and Lecturers in St. Mary’s Hospital, London.

A MANUAL OF PATHOLOGICAL ANATOMY. First American Edition,

Revised. With three hundred and ninety-seven handsome wood engravings.
beautiful octavo volume of nearly 750 pages, leather.

As a concise text-book, containing, in a condensed
form, a comp?ete outline of what is known in the
domain of Pathological Anatomy, it is perhaps the
best work in the English language. Its great merit
consists in its completeness and brevity, and in this
Tespect it supplies a great desideratum in our lite-
rature. Heretofore the student of pathology was

KIRKES (WILLIAM

In one large and
$3 75.

obliged to glean from a great number of monographs,
and the field was so extensive that but few cultivated
it with any degree of success. As a simple work
of reference, therefore, it is of great value to the
student of pathological anatomy, and should be in
every physician’s library.— Western Lancet.

SENHOUSE), M.D.,

Demonstrator of Murbid Anatomy at St. Bartholomew’s Hospital, &c.

A MANUAL OF PHYSIOLOGY.

A new American, from the third and

improved London edition. With two hundred illustrations. In one large and handsome royal

12mo. volume, leather. pp. 586. $2 00.

This is a new and very much improved edition of
Dr. Kirkes’ well-known Handbook of Physiology.
It combines conciseness with completeness, and is,
therefore, admirably adapted for consultation by the
busy practitioner.—Dwublin Quarterly Journal.

One of the very best handbooks of Physiology we
possess—presenting just such an outline of the sci-
ence 28 the student requires during his attendance
upon a course of lectures, or for reference whilst
preparing for examination.—Am. Medical Journal.

{ts excellence is in its compactness, its clearness,

(Lately Published.)

and its carefully cited authorities. It is the most
convenient of text-books. These gentlemen, Messrs.
Kirkes and Paget, have the gift of telling us what
we want to know, without thinking it necessary
to tell us all they know.—Boston Med and Surg.
Journal.

For the student beginning this study, and the
practitiuner who has but leisure to refresh his
memory, this book is invaluable, as it contains al]
that it is important to know.—Charleston Med.
Journal,

20

BLANCHARD & LEA’S MEDICAL

KNAPP’S TECHNOLOGY; or, Chemistry applied

to the Arts and to Manufactures. Edited by Dr.
Ronatps, Dr. RicHarpson, and Prof. W. R.

Jounson. In two handsome 8vo. vols., withabout |

500 wood-engravings. $6 00.

LAYCOCK’S LECTURES ON THE PRINCI-
PLES AND METHODS OF MEDICAL OB-
SERVATION AND RESEARCH. For the Use
of Advanced Students and Junior Practitioners.
In one royal 12mo. volume, extra cloth. Price $1.

LALLEMAND AND WILSON,
A PRACTICAL TREATISE ON THE CAUSES, SYMPTOMS, AND

TREATMENT OF SPERMATORRHGA.
Henry J McDouveau.

Third American edition.
OF THE VESICULAD SEMINALES; anp THEIR ASSOCIATED ORGANS.
ence to the Morbid Secretions of the Prostatic and Urethral! Mucous Membrane.

Translated and edited b
ON DISEASE
With special refer-
By Marzis

By M. LaLiemanp.
To which is added

Wirson, M.D. In one neat octavo volume, of about 400 pp., extra cloth. $2 00. (Just Issued.)

LA ROCHE (R.), M.D., &c. : :
YELLOW FEVER, considered in its Historical, Pathological, Etiological, and
Therapeutical Relations. Including a Sketch of the Disease as it has occurred in Philadelphia
from 1699 to 1854, with an examination of the connections between it and the fevers known under
the same name in other parts of temperate as well as in tropical regions. In two large and
handsome octavo volumes of nearly 1500 pages, extra cloth. $7 00.

From Professor S. H. Dickson, Charleston, S.C.,
September 18, 1855.

A monument of intelligent and well applied re-
search, almost without example. It is, indeed, in
itself, a large library, and is destined to constitute
the special resort as a book of reference, in the
subject of which it treats, to all future time.

We have not time at present, engaged as we are,
by et and by night, in the work of combating this
very disease, now prevailing in our city, to do more
than give this cursory notice of what we consider
as undoubtedly the most able and erudite medical
publication our country has yet produced But in
view of the startling fact, that this, the most malig-

nant and unmanageable disease of modern times,
has for several years been prevailing in our country
toa greater extent than ever before; that it is no
longer confined to either large or small cities, but
penetrates country villages, plantations, and farm-
houses; that it is treated with scarcely better suc-
cess now than thirty or forty years ago; that there
is vast mischief done by ignorant pretenders to know-
ledge in regard to the disease, and in view of the pro-
bability that a majority of southern physicians will
be called upon to treat the disease, we trust that this
able and comprehensive treatise will he very gene-
tally read in the south.—Memphis Med. Recorder.

BY THE SAME AUTHOR.

PNEUMONIA ; its Supposed Connection, Pathological and Etiological, with Au-
tumnal Fevers, including an Inquiry into the Existence and Morbid Agency of Malaria. In one
handsome octavo volume, extra cloth, of 500 pages. $3 00.

LAWRENCE (W.), F.R.S., &c.

A TREATISE ON DISEASES OF

THE EYE. A new edition, edited,

with numerous additions, and 243 illustrations, by Isaac Hays, M. D., Surgeon to Will’s Hospi-

tal, &e.

with raised bands. $5 00.

In one very large and handsome octavo volume, of 950 pages, strongly bound in leather

LUDLOW (J. L.), M.D.
A MANUAL OF EXAMINATIONS upon Anatomy, Physiology, Surgery,

Practice of Medicine, Obstetrics, Materia Medica, Chemistry, Pharmacy, aud Therapeutics.

To

which is added a Medical Formulary. Third edition, thoroughly revised and greatly extended

and enlarged. With 370 illustrations.

large pages $2 50.

We know of no better companion for the student
during the hours spent in the lecture room, or to re-
fresh, at a glance, his memory of the various topics

In one handsome royal 12mo. volume, leather, of 816

crammed into his head by the various professors to
whom he is compelled to listen.— Western Lancet,
May, 1857.

LEHMANN (C. G.)

PHYSIOLOGICAL CHEMISTRY.

Translated from the second edition by

Grores E. Day, M. D., F.R.S., &c., edited by R. E. Rocers, M. D., Professor of Chemistry
in the Medical Department of the University of Pennsylvania, with illustrations selected from

Funke’s Atlas of Physiological Seay and an Appendix of plates.
: |

and handsome octavo volumes, extra clot

trations. $6 00.

The work of Lehmann stands unrivalled as the
most comprehensive book of reference and informa-
tion extant on every branch of the subject on which
it treats.—Edinburgh Journal of Medicai Science.

Complete in two large

containing 1200 pages, with nearly two hundred illus-

The most important contribution as yet made to
Physivlogical Chemistry.—Am. Journal Med, Sci-
ences, Jan. 1856.

BY THE SAME AUTHOR. (Lately Published.)

MANUAL OF CHEMICAL PHYSIOLOGY. Translated from the German,

with Notes and Additions, by J. Cuesron Morris, M.D., with an latroductory Essay on Vital

Force, by Professor SamurL Jackson, M. D., of the University of Pemsylvania. With illus-

trations on wood. In one very handsome octavo volume, extra cloth, of 336 pages. $2 25.

From Prof. Jackson's Introductory Essay.

In adopting the handbook of Dr. Lehmann as a manual of Organic Chemistry for the use of the
students of the University, aud in recommending his original work of PuystoLocicaL CHEMISTRY
for their more mature studies, the high value of his researches, and the great weight of his autho-
rity in that important department of medical science are fully recognized.

AND SCIENTIFIC PUBLICATIONS. 21

LYONS (ROBERT D.), K. ©. C.,
Late Pathologist in-chief to the British Army in the Crimea, &c.

A TREATISE ON FEVER; or, selections from a course of Lectures on Fever.

- Being part of a course of Theory and Practice of Medicine. In one neat octavo volume, of 362
pages, extra cloth; $200. (ow Ready.)

From the Author’s Preface.

“Tam induced to publish this work on Fever with a view to bring within the reach of the
student and junior practitioner, in a convenient form, the more recent results of inquiries into the
Pathology and Therapeutics of this formidable class of diseases.

“ The works of the great writers on Fever are so numerous, and in the present day are scattered
in so many languages, that they are difficult of access, not only to students but also to practitioners.
T shall deem myself fortunate if I can in any measure supply the want which is felt in this respect.

We have great pleasure in recommending Dr.| cine. We consider the work a most valuable addi-

Lyons’ work on Fever to the attention of the pro-
fession. It isa work which cannot fail to enhance
the author’s previous well-earned reputation, asa
diligent, careful, and accurate observer.—British
Med, Journal, March 2, 1861.

Taken as a whole we cun reeommend it in the
highest terms as well worthy the careful perusal
and study of every student and practitioner of medi-

tion to medical literature, and one destined to wield
no little influence over the mind of the profession.—
Med and Surg. Reportr, May 4, 1861.

This is an admirable work upon the most remark-
able and most important class of diseases to which
mankind are liable.—Med. Journ. of N. Carolina,
May, 1861.

MEIGS (CHARLES D.), M.D.,
Professor of Obstetrics, &c. in the Jefferson Medical College, Philadelphia.

OBSTETRICS: THE SCIENCE AND THE ART. Third edition, revised

and improved. With one hundred and twenty-nine illustrations. In one beautifully printed octavo

volume, leather, of seven hundred and fifty-two large pages.

Though the work has received only five pages of
enlargement, its chapters throughout wear the im-
pressof carefulrevision. Expunging and rewriting,
remodelling its sentences, with occasional new ma-
terial, all evince a lively desire that it shall deserve
to be regarded as improved in manner as well as
matter. In the matter, every stroke of the pen has
increased the value of the book, both in expungings
and additions —Western Lancet, Jan. 1857.

BY THE SAME AUTHOR.

$3 75, :

The best American work on Midwifery that is
accessible to the student and practitioner—N. W.
Med. and Surg. Journal, Jan. 1857.

This is a stundard work by a great American Ob-
stetrician. Jt 1s the third and last edition, and, in
the language of the preface, the author has ‘‘brought
the subject up to the latest dates of real improve-
ment in our art and Science.’’—Nashville Journ. of
Med. and Surg., May, 1857.

(Just Issued.)

WOMAN: HER DISEASES AND THEIR REMEDIES. A Series of Leo-

tures to his Class.
volume, leather, of over 700 pages. $3 60.

In other respects, in our estimation, too much ean-
not be said in praise of this work. It abounds with
beautiful passages, and fur conciseness, fur origin-
ality, and for aj] that is commendable in a work on
the diseases of females, it 1s not excelled, and pro-
bably not equalled in the English language. On the
whole, we know of no work ou the diseases of wo-
men which we can so cordially commend to the
student ond practitioneras the one befure us.—Ohio
Med. and Surg. Journal.

The body of the book is worthy of attentive con-
sideration, and is evidently the production of a
clever, thoughtful, and sagacivus physician. Dr.
Meigs’s letters on the diseases of the external or-
gans, contain many interesting and rare cases, and
many instructive observations. We tuke our leave
of Dr. Meigs, with a high opinion of his talents and
originality.— The British and Foreign Medico-Chi-
rurgical Review.

Every chapter is replete with practical instruc-
tion, and bears the iiapress of being the composition
of an acute and experienced mind. There isa terse-
ness, and at the same time an accuracy in his de-
scription of symptoms, and in the rules fur diagnosis,

Fourth and Improved edition.

Tn one large and beautifully printed octave

which cannot fail to recommend the volume to the
attention of the reader.—Ranking’s Abstract.

It contains a vast amount of practical knowledge
ody one who has accurately observed and retaine
the experience of many years.—Dubsin Quarterly
Journal,

Full of important matter, conveyed ina ready and
agreeable manuer.—St.Lowis Med. and Surg. Jour.

There is an off-hand fervor, a glow, and a warm-
aeartedness infecting the effort of Dr. Meigs, which
ig entirely captivating, and which absolutely hur-
ties the reader diecoueh from beginning toend. Be-
sides, the book teems with solid instruction, and
it shows the very highest evidence of ability, viz.,
the clearness with which the information is pre-
sented. We know of no better test of one’s under-
3tanding a subject than the evidence of the power
of lucidly explaining it. The most elementary, as
well as the obscurest subjects, under the pencil of
Prof. Meigs, are isolated and made to stand out in
such bold relief, a8 tu produce distinct impressions
upon the mind and memory of the reader. — The
Charleston Med. Journal.

BY THE SAME AUTHOR.

ON THE NATURE, SIGNS, AND TREATMENT OF CHILDBED

FEVER. In a Series of Letters addressed to the Students of his Class.
50.

octavo volume, extra cloth, of 365 pages. $2

The instructive and interesting author of this
work, whose previous labors have placed his coun-
trymen under deep and abiding oblizations, again
challenges their admiration in the fresh and vigor.
ous, attractive and racy pages before us. It isa de-

BY THE SAME AUTHOR;

In one handsome

lectable book. * * * This treatise upon child-
bed fevers will have an extensive sale, being des-
tined, as it deserves, to finda place in the library
of every practitioner who scorns tolag in the rear.—
Nashvrlle Journal of Medicine and Surgery.

WITH COLORED PLATES.

A TREATISE ON ACUTE AND CHRONIC DISEASES OF THE NECK

OF THE UTERUS. With numerous plates, drawn and colored from nature in the highest
style of art. In one handsome octavo volume, extra cloth. $4 50.

22 BLANCHARD & LEA’S MEDICAL

MACLISE (JOSEPH), SURGEON.
SURGICAL ANATOMY. Forming one volume, very large imperial quarto.

With sixty-eight large and splendid Plates, drawn in the best style and beautifully colored. Con-

taining one hundred and ninety Figures, many of them the size of life.

Together with copious

and explanatory letter-press. Strongly and handsomely bound in extra cloth, being one of the

cheapest and best executed Surgical works as yet issued in this country. $11 00.

*,* The size of this work prevents its transmission through the post-office as a whole, but those
who desire to have copies forwarded by mail, can receive them in five parts, done up in stout

wrappers. Price $9 00.

_ One of the greatest artisthe triumpha of the age
in Bureisal Anatomy.—British American Medical
Journal,

No practitioner whose means will admit should
fail to possess 1t.—Ranking’s Abstract.

Too much cannot be said in its praise; indeed,
we have not language to do it justice Ohio Medi-
eal and Surgical Journal.

The most accurately engraved and beautifully
colored plates we have ever seen in an American
bonk—one of the best and cheapest surgical works
ever published. Buffalo Medical Journal,

It is very rare that so elegantly printed, 30 well
illustrated, and so useful a work, ia offered at so
moderate a price.—Charleston Medical Journal.

Its plates can boast a superiority which places
them almost beyond the reach of competition.— Medi-
cal Examiner.

Country practitioners will find these plates of im-
mense value.—N. Y. Medical Gazette.

A work which has no parallel in point of aceu-
racy and cheapness in the English language.—WN. Y.
Journal of Medicine.

We are extremely gratified to announce to the
profession the completion of this truly magnificent
work, which, as a whole, certainly stands unri-
valled, both for accuracy of drawing, beauty of
coloring, and all the requisite explanations of the
subject in hand.-The New Orleans Medical and
Surgical Journal,

This is by far the ablest work on Surgical Ana-
tomy that has come under our observation. We
know of no other work that would justify a stu-
dent, in any degree, for neglect of actual dissec-
tion. In those sudden emergencies that so often
arise, and which require the instantaneous command
of minute anatomical knowledge, a work of this kind
keeps the details of the dissecting-room perpetual)
fresh in the memory.—The Western Journal of Medi-
cine and Surgery.

MILLER (HENRY), M.D.,
Professor of Obstetrics and Diseases of Women and Children in the University of Louisville.

PRINCIPLES AND PRACTICE OF OBSTETRICS, &c.; including the Treat-

ment of Chronic Inflammation of the Cervix and Body of the Uterus considered as a frequent

cause of Abortion,
tavo volume, of over 600 pages.

We congratulate the author that the task 1s done.
We congratulate him that he hasgiven to the medi-
eal public a work which wil! secure for hima high
and permanent position among the standard autho-
Tities on the principles and practice of obstetrics.
Congratulations are not less due to the medical pro-
fession of this country, on the acquisition of a trea-
tise embodying the results of the studies, reflections,
and experience of Prof. Miller. Few men, if any,
in this country, are more competent thun he to write
on thisdepartment of medicine. Engaged for thirty-
five years in an extended practice of ubstetrics, for
many years a teacher of this branch of instruction
in one of the largest of our institutions, a diligent
student as well asa careful observer, an original and
independent thinker, wedded to no hobbies, ever
ready to consider without prejudice new views, and
to adopt innovations if they are really improvements
and withal a clear, agreeable writer, a practica:
treatise from his pen could not fail to possess great
value.—Buffalo Med Journal,

In fact, this volume must take its place among the
Stundard systematic treatises on obstetrics; a posi-

With about one hundred illustrations on wood.
(Lately Published.) $3 75.

In one very handsome oc-

tion to which its merits justly entitleit. The style
is such that the descriptionsare clear, and each sub-
ject is discussed and elucidated with due regard to
its practical benrings, which cannot fail to make it
acceptable and valuable to buth students and prac-
titioners. We cannot, however, close this brief
notice without congratulating the author and the
profession on the production of such an excellent
treatise. The author is a western man of whom we
feel proud, and we cannot but think that his book
will find many readers und warm admirers wherever
obstetrics is taught and studied asa science and an
art.—The Cincinnat: Lancetand Observer.

A most respectuble and valuable addition to our
home medical literature, and one reflecting credit
alike on the author and the institution to which he
is attached. The student will find in this work a
most useful guide to his studies; the cuuntry prae-
titioner, rusty in his reading, can obtain from ite
pages a fair resumé of the modern literature of the
science; and we hupe tosee this American produc-
tion generally consulted by the profession.—Va.
Med. Journal.

MACKENZIE (W.), M.D.,
Surgeon Oculist in Scotland in ordinary to Her Majesty, &c. &c.

A PRACTICAL TREATISE ON DISKASES AND INJURIES OF THE
EYE. To which is prefixed an Anatomica! Introduction explanatory of a Horizontal Section of
the Human Eyeball, by Tuomas Wuarton Jonzs, F.R.S. From the Fourth Revised and En-
larged London Edition. With Notes and Additions by AppinELL Hewson, M. D., Surgeon to
Wills Hospital, &e. 8c. In one very largeand handsome octavo volume, leather, raised bands, with

plates and numerous wood-cuts. $5 25.

The treatise of Dr. Mackenzie indisputably holds
the first place, and forms, in respect of learning and
research, an Encyclopedia unequalled in extent by
any other work of the kind, either English or foreign.
a on Diseases of the Eye.

Few modern books on any department of medicine
or surgery have met with such extended circulation,
or have procured for their authors a like amount of
European celebrity. The immense research which
it displayed, the thorough acquaintance with the
eubject, practically as well as theoretically,aund the

BMAYNE’S DISPENSATORY AND THERA-
PEUTICAL REMEMBRANCER. With ever
Practical Formula euntained in the three Britis
Phurmacopeias. Edited, with the addition of the
Formule of the U.S. Pharmacopa@ia, by R. E.
GairritH,M.D 1 12mo. vol.ex.cl.,300 pp. 75 ¢.

able manner in which the author’s storesof learnin

and experience were rendered availablefor genera
use, at once procured for the first edition, as well
the continent as in this country, that high position
as a standard work which each successive edition
has more firmly established. We consider it the
duty of every one who has the love of his profession
and the welfare of his patient at heart, to make him-
self familiar with this the most complete work in
the English language upon the diseases of the eye.
——Med. Times and Gazette.

MALGAIGNE’S OPERATIVE SURGERY, based
on Normal and Pathological Anatomy. rans-
lated from the French by FREDERICK BRITTAN,
A.B.,M.D. Withnumerous i)lustrutionson wood.
In one handsome octavo vulume, extra eloth, of
nearly six hundred pages. #2 25.

AND SCIENTIFIC

PUBLICATIONS. 23

MILLER (JAMES), F.A.S.E.,
Professor of Surgery in the University of Edinburgh, &c.

PRINCIPLES OF SURGERY. Fourth American, from the third and revised

Edinburgh edition. In one large and very beautiful volume, leather, of 700 pages, with two

hundred and forty illustrations on wood. $3 75

The work of Mr. Miller is too well and too favor-
ably known among us, as one of our best text-books,
to render any further notice of it necessary than the
announcement of a new edition, the fowrth in our
country, a proof of its extensive circulation among
us. Asa concise and reliable exposition of the sci-
ence of modern surgery, it stands deservedly high—
we know not its superior.—Boston Med. and Surg.
Journal,

BY THE SAME AUTHOR.

THE PRACTICE OF SURGERY.

burgh edition.
engravings on wood.

No encomium of ours could add to the popularity
of Miller’s Surgery. Its reputation in this country
is unsurpassed by that of any other work, and, when
taken in connection with the author’s Principles of
Surgery, constitutes a whole, without reference to
which noconscientious surgeon would be willing to
practice his art.— Southern Med.and Surg. Journal,

itis seldom that two volumes have ever made so
profound an impression in so short a time as the
‘Principles”’ and the ‘‘ Practice” of Surgery by
Mr. Miller—or so richly merited the reputation they
have acquired. The author is an eminently sensi-
ble, practical, and well-informed man, who knows
exactly what he is talking about and exactly how to
talk it —Kentucky Medical Recorder.

By the almost unanimous voice of the profession,

Revised by the American editor.
In one large octavo volume, leather, of nearly 700 pages.

The work takes rank with Watson’s Practice of
Physic; it certainly does not fall behind that great
work in soundness of principle or depth of reason-
ing and research No physician who values hia re-
putation, or seeks the interests uf his clients, can
acquit himself before his God and the world without
making himself familiar with the sound and philo-
sophical views developed in the foregoing book.—
New Orleans Med.and Surg. Journal,

(Just Issued.)

Fourth American from the last Hdin-
Illustrated by three hundred and sixty-four
$3 75.

his works, both on the principles and practice of
surgery have been assigned thehighest rank. If we
were limited to but one work on surgery, that one
should be Miller’s, as we regard it as superior to all
others.—St. Louis Med. and Surg. Journal.

The author has in this and his ‘* Principles,” pre-
sented to the profession one of the most complete and
reliable systems of Surgery extant. His style of
writing 1s original, impressive, and engaging, ener-
getic, concise, and lucid. Few have the faculty of
condensing so much in small space, and at the same
time so persistently holding theattention. Whether
asa text-book for students or a book of reference
for practitioners, it cannot be too strongly recom-
mended.—Southern Journal of Med.and Physical
Sciences,

MORLAND (W. W.), M. D.,

Fellow of the Massachusetts Medical Society, &e.

DISEASES OF THE URINARY ORGANS; a Compendium of their Diagnosis,

Pathology, and Treatment. With illustrations.
about 600 pages, extra cloth.

Taken asa whole, we can recommend Dr. Mor-
land’s compendium asa very desirable addition to
the library of every medical or surgical practi-
tioner —Brit and For. Med.-Chir. Rev., April, 1859

Every medical practitioner whose attention has
been to any extent attracted towards the class of
diseases to which this treatise relutes, must have
often and sorely experienced the want of some full,
yet concise recent compendium to whiclv he could

In one large and handsome octavo volume, of

(Just Issued.) $3 50.

refer. This desideratum has been supplied by Dr.
Morland, and it lias been ably done. He has placed
before us a full, judicious, and reliable digest.
Bach subject is treated with sufficient minuteness,
yetina suceinct, narrational style, such as tu render
the work one of great interest, and one which will
prove in the highest degree useful to the general
practitioner.—N. Y. Journ. of Medicine,

BY THE SAME AUTHOR —(NVow Ready.)

THE MORBID EFFECTS OF THE

RETENTION IN THE BLOOD OF

THE ELEMENTS OF THE URINARY SECRETION. Being the Dissertation to which the

Fiske Fund Prize was awarded, July 11, 1861.

cloth. 75 cents.

In one small octavo volume, 83 pages, extra

MONTGOMERY (W.F.), M.D., M.R.1.A., &c.,

Professor of Midwifery in the King and Queen’s College of Physicians in Ireland, &c.

AN EXPOSITION OF THE SIGNS AND SYMPTOMS OF PREGNANCY.

With some other Papers on Subjects connected with Midwifery. From the second and enlarged

English edition. With two exquisite colored

handsome octavo volume, extra cloth, of nearly 600 pages.

A book unusually rich in practical suggestions.—
Am Journal Med. Sciences, Jan. 1857.

These several subjects so interesting in them-
selves, and su important, every one of them, to the
most delicate and precious of social relations, con-
trolling often the honur and domestic peace of a
family, the Jena of offspring, or the life of ite
parent, are all treated with an elegance of diction,
fulness of illustrations, acuteness and justice of rea-
soning, unparalleled in obstetrics, and unsurpassed in
medicine. The reader’s interest can never flag, so

plates, and numerous wocd-cuts. In one very
(Lately Published.) $3 75.

fresh, and vigorous, and classical is our author’s
style; and one forgets, in the renewed charm of
avery page, that it, and every line, and every word
has been weighed and reweighed through years of
preparation; that this is of all others the book of
Obstetric Law, on each of its several topics; on all
points connected with pregnancy, to be every where
received as a manual of special jurisprudence, at
once announcing fact, afording argument, establish-
ing precedent, and governing alike the juryman, ad-
vocate, and judge. — N. A. Med.-Chir. Review.

MOHR (FRANCIS), PH. D., AND REDWOOD (THEOPHILUS),
PRACTICAL PHARMACY. Comprising the Arrangements, Apparatus, and

Manipulations of the Pharmaceutical Shop and Laboratory. Edited, with extensive Additions,
by Prof. Wittram Procter, of the Philadelphia College of Pharmacy. In one handsomely
printed octavo volume, extra cloth, of 570 pages, with over 500 engravings on wood. $2 79.

24 BLANCHARD & LEA’S MEDICAL

NEILL (JOHN), M. D.,
Surgeon to the Pennsylvania Hospital, &c.; and

FRANCIS GURNEY SMITH, M.D.,

Professor of Institutes of Medicine in the Pennsylvania Medical College.

AN ANALYTICAL COMPENDIUM OF THE VARIOUS BRANCHES
OF MEDICAL SCIENCE; for the Use and Examination of Students. A new edition, revised
and improved. In one very large and handsomely printed royal 12mo. volume, of about one
thousand pages, with 374 wood-cuts. Strongly bound in leather, with raised bands. $3 00.

The very flattering reception which has been accorded to this work, and the high estimate placed
upon it by the profession, as evinced by the constant and increasing demand which has rapidly ex-
hausted two large editions, have stimulated the authors to render the volume in its present revision
more worthy of the success which has attended it. It has accordingly been thoroughly examined,
and such errors as had on former occasions escaped observation have been corrected, and whatever
additions were necessary 1o maintain it on a level with the advance of science have been introduced.
The extended series of illustrations has been still further increased and much improved, while, by
a slight enlargement of the page, these various additions have been incorporated without increasing
the bulk of the volume. a 4

The work is, therefore, again presented as eminently worthy of the favor with which it has hitherto
been received. As a book for daily reference by the student requiring a guide to his more elaborate
text-books, as a manual for precepiors desiring to stimulate their students by frequent and accurate
examination, or as a source from which the practitioners of older date may easily and cheaply acquire
a knowledge of the changes and improvement in professional science, its reputation is permanently
established.

The best work of the kind with which we are
acquainted. — Med. Examiner.

Having made free use of this volume in our ex-
aminations of pupils, we can epeak from experi-
ence in recommending it as an admirable compend
for students, and as especially useful to preceptora
who examine their pupils. It will save the teacher
much labor by enabling him readily to recall all of
the points upon which his pupils should be ex-
amined. A work of this sort should be in the nands
of every one who takes pupils into his office with a
view of examining them; and this is unquestionably
the best of its class.—Transylvania Med. Journal,

In the rapid course of lectures, where work for

the students is heavy, and review necessary for an
examination, a compend is not only valuable, but
itis almost a sine gua non. The one before us is,
in most of the divisions, the most unexceptionable
of all books of the Kind that we know of. The
newest and soundest doctrines and the latest im-
provements and discoveries are explicitly, though
eoncisely, laid before the student. There isa class
to whom we very sincerely commend this cheap book
as worth its weight in silver—that class is the gradu-
ates in medicine of more than ten years’ standing
who have not studied medicine since. They will
perhaps find out from it that the science isnot exactly
now what it was when they left it off —The Stetho-
Scope,

NELIGAN (J. MOORE), M.D., M.R.1.A., &c,
ATLAS OF CUTANEOUS DISEASES. In one beautiful quarto volume, extra

cloth, with splendid colored plates, presenting nearly one hundred elaborate representations of

dixease. $4 50.

This beautiful volume is intended as a complete and accurate representation of all the varieties
of Dixeases of the Skin. While it can be consulted in conjunetion with any work on Practice, it bas
especial reference to the author’s ‘¢ Treatise on Diseases of the Skin,” so favorably received by the
profession some years since. The publishers feel justified in saying that few more beautifully exe-

cuted plates have ever been presented to the profession of this country.

Neligan’s Atlas of Cutaneons Diseases supplies a
long existent desideratum much felt by the largest
class of our profession. It presents, in quarto size.
16 plates, each containing from 8 to 6 figures, and
forming in alla total of 90 distinet representations
of the different species of skin affections, grouped
together in genera or families. The illustrations
have been taken from nature, and have leen copied
with such fidelity that they present a striking picture
of life; in which the reduced scale aptly serves to

give, ata coup deil, the remarkable peculiarities
of each individual variety. And while thus the dis
ease is rendered more definable. there is yet no loss
of proportion incurred by the necessary concentra-
tion. Each figure is highly colored, and so truthful
has the artist been that the most fastid ous observer
could not justly take exception to the correctness of
the execution of the pictures under his scrutiny.—
Montreal Med. Chronicle.

BY THE SAME AUTHOR.

A PRACTICAL TREATISE ON DISEASES OF THE SKIN.

Third

American edition. In one neat roya! 12mo. volume, extra cloth, of 334 pages. $1 00.

ga@x~ The two volumes will be sent by mail on receipt of Five Dollars.

OWEN ON THE DIFFERENT FORMS OF
THE SKELETON, AND OF THE TEETH.

One vol. royal 12mo., extra cloth with numerous
illustrations. $1 25

PIRRIE (WILLIAM), F.R.S.E.,

Professor of Surgery in the University of Aberdeen.

THE PRINCIPLES AND PRACTICE OF SURGERY. Rdited by Jonn

Neiut, M. D., Professor of Surgery in the Penna. Medical College, Surgeon tothe Pennsylvania

Hospital, &c, In one very handsome octavo volume, leather,

$3 75,

We know of no other surgical work of a reason-
able size, wherein there is so much theory and prac-
tice, or where subjects are more soundly or clearly
taught.—The Stethoscope.

Prof. Pirrie, in the work before us, hae elabo-

of 780 pages, with 316 illustrations.

rately discussed.the principles of surgery, and a
safe and effectual practice predicated upon them.
Perhaps no work upon this subject heretofore issued
is so full upon the science of the art of surgery.—
Nashville Journal of Medicine and Surgery.

AND SCIENTIFIC PUBLICATIONS. 25

PARRISH (EDWARD),

Lecturer on Practical Pharmacy and Materia Medica in the Pennsylvania Academy of Medicine, &c.

AN INTRODUCTION TO PRACTICAL PHARMACY. Designed as a Text-

Book tor the Student, and as a Guide for the Physician and Pharmaceutist. With many For-

mulze and Prescriptions. Second edition, greatly enlarged and improved, In one handsome

octavo volume of 720 pages, with several hundred Illustrations, extra cloth. $3 50. (Just

Issued.)

During the short time in which this work has been before the profession, it has been received
with very great favor, and sn assuming the position of a standard authority, it has filled a vacancy
which had been severely felt. Stimulated by this encouragement, the author, in availing himself
of the opportunity of revision, has spared no pains to render it more worthy of the confidence be-
stowed upon it, and his assiduous labors have made it rather a new book than a new edition, many
portions having been rewritten, and much new and important matter added. These alterations and
Improvements have been rendered necessary by the rapid progress made by pharmaceutical science
during the last few years, and by the additional experience obtained in the practical use of the
volume us a text-book and work of reference. To accommodate these improvements, the size of
the page has been materially enlarged, and the number of pages considerably increased, presenting
in all nearly one-half more matter than the last edition, The work is therefore now presented asa
complete exponent of the subject in its most advanced condition. From the most ordinary matters
in the dispensing office, to the most complicated details of the vegetable alkaloids, it is hoped that
everything requisite to the practising physician, and to the apothecary, will be found fully and
clearly set forth, and that the new matter alone will be worth more than the very moderate cost of

the work to those who have been consulting the previous edition.

That Edward Parrish, in writing a book upon
practical Pharmacy some few years ago—one emi-
nently original and unique—did the medical and
pharmaceutical professious a great and valuable ser-
yice, no one, we think, who has had access to its
pages will deny; doubly welcome, then, is this new
edition, containing the added results of his recent
and rich experience as an observer, teacher, and
practic x] operator in the pharmaceutical Jaboratory.
The excellent plan of the first is more thoroughly,
and in detail, carried outin this edition.— Peninsular
Med. Journal, Jan. 1860.

Of course, all apothecaries who have not already
a copy of the first edition will procure one of this;
itis, therefore, to physicians residing in the country
and in small towns, who cannot avail themselves of
the skill of an educated pharmaceutist, that we
would especially commend this work. In it they

will find all that they desire to know, and should
know, but very little of which they do really know
in reference to this important collateral branch of
their profession; for it is a well established fact,
that, in the ecueation of physicians, while the sci-
ence of medicine is generally well taught, very
lictle attention is paid to the art of preparing them
for use, and we know not how this defect can be so
well remedied as by prucuring and consulting Dr.
Partrish’s excellent work.—St. Louis Med. Journal.
Jan. 1860.

We know of no work on the subject which would
be more indispensable to the physician or student
desiring information on the subject of which it treats.
With Grifith’s ‘‘ Medical Formulary’? and this, the
practising physician would be supplied with nearly
or quite all the most useful information on the sub-
ject, Charleston Med, Jour.and Review, Jan. 1860

PEASLEE (E. R.),; M.D.,
Professor of Physiology and General Pathology in the New York Medical College.

HUMAN HISTOLOGY, in its relations to Anatomy, Physiology, and Pathology;

for the use of Medical Students.
some octavo volume, of over 600 pages.

It embraces a library upon the topics discussed
within itself, and is just what the teacherand learner
need. Another advantage, by nv means to be over-
looked, everything of real value in the wide range
which it embraces, is with great skill compressed
ito an octavo volume of but little more than s1x
hundred pages. We have not only the whole sub-
ject of Histulogy, interesting in itself, ably and fully
discussed, but what is of infinitely greater interest
to the student, because of greater practical value,
are its relations to Anatumy, Physiology, and Pa-
thology, which are here fully and satisfactorily set
forth.— Nashville Journ. of Med. and Surgery.

With four hundred and thirty-four illustrations,
(Lately Published.) $3 75.

In one hand-

We would recommend it to the medical student
and practitioner, as containing a summary of all that
is known of the important subjects which it treats;
of all that is contained in the great works of Simon
and Lehmann, and the organic chemists in general.
Master this one volume, we would say tu the medical
student and practitioner—master this book and you
know all that is known of the great fundamental
ptinciples of medicine, and we have xo hesitation
in saying that it isaa honor to the American medi-
eal profession that one of its members should have
produced it.—St. Lowis Med.and Surg. Journal.

PEREIRA (JONATHAN), M.D., F.R.S., ANDL.S,.

THE ELEMENTS OF MATERIA

MEDICA AND THERAPEUTICS.

Third American edition, enlarged and improved by the author; including Notices of most of the
Medicinal Substances in use in the civilized world, and forming an Encyclopedia of Materia
Medica. Edited, with Additions, by Josepu Carson, M. D., Professor of Materia Medica and

Pharmacy in the University of Pennsylvania.

In two very large octavo volumes of 2100 pages,

on small type, with about 500 illustrations on stone and wood, strongly bound in leather, with

raised bands. $Y 00.
«* Vol. IL. will no longer be sold separate.

PARKER (LANGSTON),

Surgeon to the Queen’s Hospital, Birmingham.

THE MODERN TREATMENT OF SYPHILITIC DISHASES, BOTH PRI-
MARY AND SECONDARY; comprising the Treatment of Constitutional and Confirmed Syphi-
lis, by a safe and successful method. With numerous Cases, Formule, and Clinical Observa-
tions. From the Third and entirely rewritten London edition. In one neat octavo volume,
extra cloth, of 316 pages. $1 75.

ROYLE’S MATERIA MEDICA AND THERAPEUTICS; including the
Preparations of the Pharmacopeias of London, Edinburgh, Dublin, and of the United States.
With many new medicines. Edited by Joseru Carson, M.D. With ninety-eight illustrations
In one large octavo volume, extra cloth, of about 700 pages. $3 00.

26

BLANCHARD & LEA’S MEDICAL

RAMSBOTHAM (FRANCIS H.), M.D.
THE PRINCIPLES AND PRACTICE OF OBSTETRIC MEDICINE AND

SURGERY, in reference to the Process of Parturition. A new and enlarged edition, thoroughly
revised by the Author. With Additions by W. V. Kratine, M. D., Professor of Obstetrics, &c., in
the Jefferson Medical College, Philadelphia. In one large and handsome imperial octavo volume,
of 650 pages, strongly bound in leather, with raised bands; with sixty-four beautiful Plates, and
numerous Wood-cuts in the text, containing in al} nearly 200 large and beautiful figures. $5 00.
From Prof. Hodge, of the Unwersity of Pa.
To the American public, it is most valuable, from its itrinsie undoubted excellence, and as being
the best authorized exponent of British Midwifery. Its circulation will, I trust, be extensive throughout

our country.

It is mnupeeneary to say anything in regard to the
utility of this work. It is already appreciated in our
country for the value of the matter, the clearness of
its style, and the fulness of its illustrations. To the
physician’s library it is indispensable, while to the
student as a text-book, from which to extract the
material for laying the foundation of an education on
obstetrical science, it hus no superior.—Ohio Med
and Surg. Journal,

The publishers have secured its suceess by the

truly elegant style in which they have brought it
out, excelling themselves in its production, espe-
cially in ita plates. It is dedicated to Prof. Meigs,
and has the emphatic endorsement of Prof. Hodge,
as the best exponent of British Midwifery. We
kniw of no text-book which deserves in all respects
to be more highly recommended to students, and we
could wish to see it in the hands of every practitioner,
for they will find it invaluable for reference.— Med.
Gazette.

RICORD (P.), M.D.
A TREATISE ON THE VENEREAL DISEASKH. By Jonn Hunter, F.R.8.
With copious Additions, by Pu. Ricorp, M.D. Translated and Edited, with Notes, by FREEMAN

J. Bumsteap. M.D

, Lecturer on Venereal at the College of Physicians and Surgeons, New York.
Second edition, revised, containing a résumé of Ricorp’s Recent LecTuRES ON CHANCRE.

In

one handsome octavo volunie, extra cloth, of 550 pages, witheight plates. $3 25. (Just Issued.)
In revising this work, the editor has endeavored to introduce whatever matter of interest the re-

cent investigations of syphilographers have added to our knowledge of the subject.

The principal

source from which this has been derived is the volume of “ Lectures on Chancre,’’ published a few
months since by M. Ricord, which affords a large amount of new and instructive material on many

controverted points.

In the previous edition, M. Ricord’s additions amounted to nearly one-third

of the whule, and with the matter now introduced, the work may be considered to present his views
and experience more thoroughly and completely than any other.

Every one will recognize the atiractiveness and
value which this work derives from thus presenting
the opinions of these two masters side by side. But,
it must be admitted, whai has made the fortune of
the book, is the fact that it contains the ‘‘most com-
plete embodiment of the veritable doctrines of the
Hépital du Midi,” which has ever been made public.
The doctrinal ideas of M. Ricord, ideas which, if not
universally adopted,are incontestabiy dominant. have
heretofore only been interpreted by moreorlessskilful

secretaries, sometimes accredited and sometimes not,

In the notes to Hunter, the master subsututes him-
selfforhis interpreters, and gives hisoriginal thoughts
to the world in a lucid and perfectly intelligible man-
ner. In conclusion we can say that this is incon-
testably the besttreatise on syphilis with which we
are acquainted, and, as we do not often employ the
phrase, we may be excused for expressing the hope
that it may find a place in the library of every phy-
sician.— Virginia Med. and Surg. Journal.

BY THE SAME AUTHOR.

RICORD’S LETTERS ON SYPHILIS. Translated by W. P. Larrimors, M.D.

In one neat octavo volume, of 270 pages, extra cloth. $200.

ROKITANSKY (CARL), M.D.,

Curator of the Imperial] Pathological Museum, and Professor at the University of Vienna, &c.

A MANUAL OF PATHOLOGICAL ANATOMY. Four volumes, octavo,

bound in two, extra cloth, of about 1200 pages.

wine, C. H. Moore, andG, E. Day. $5 50.

The profession is too well acquainted with the re-
putation of Rokitansky’s work to need our assur-
ance that thie is one of the most profound, thorough
and valuable books ever issued from the medica
press. It is svi generis, und has no standard of com-

arison. It is only necessary to announce that it is
issued in a form as cheap as is compatible with ite
size and preservation, and its sale follows as a
matter of course. No library can be called com-
plete without it—_Buffalo Med. Journal.

An attempt to give our readers any adequate idea
of the vast amount of instruction aceumulated in
these volumes, would be feeble und hopeless. The
effort of the distinguished author to concentrate
in asmall space his great fund of knowledge, has

Translated by W. E. Swain, Epwarp Sigvg-

80 charged his text with valuable truths, that any
attempt of a reviewer to epitomize is at once para-
lyzed, and must end in a failure.— Western Lancet.

As this is the highest source of knowledge upon
the important subject of which it treats, no real
student can afford to be withuat it. The American
publishers have entitled themselves to the thanks of
the profession of their country, for this timeous and
beautiful edition. Nashville Journal of Medicine.

Asa book of reference, therefore, this work must
prove of inestimable value, and we cannot toohighly
recommend it to the profession.—CAarleston Med.
Journaland Review.

This book is a necessity to every practitioner. —
Am. Med. Monthly. ee

RIGBY (EDWARD), M, D.,
Senior Physician to the General Lying-in Hospital, &c.

A SYSTEM OF MIDWIFERY. With Notes and Additional Llustrations.

Second American Edition. One volume octavo, extra cloth, 422 pages. $2 50.
BY THE SAME AUTHOR. (Lately Published.)

ON THE CONSTITUTIONAL TREATMENT OF FEMALE DISEASES.

In one neat royal 12mo. volume, exira cloth, of about 250 pages. $1 00.

AND SCIENTIFIC PUBLICATIONS. 27

STILLE (ALFRED), M.D.
THERAPEUTICS AND MATERIA MEDICA; a Systematic Treatise on the

Action and Uses of Medicinal Agents, including their Description and History. In two large

and tiandsome octavo volumes, of 1789 pages. (Just Issued.) $800.

This work is designed especially for the student and practitioner of medicine, and treats the various
articles of the Materia Medica from the point of view of the bedside, and not of the shop or of the
feeiure-room While thus endeavoring to give all practical information likely to be useful with
respect (o the employment of special remedies in special affections, and the results to be anticipated
trom their administration, a copious Iudex of Diseases and their Remedies renders the work emi-
nently fitted for reference by showing at a glance the different means which have been employed,
and enabling the practitioner to extend his resources in difficult ca-es with all that the expe: ience

of the protession has suggested.

Rarely, indeed, have we had submitted to us a
work on medicine so ponderous in its dimensious
aa that now before ue, and yet so fascinating in its
contents. It is, therefore. with a peeuliar gratifi-
cation that we recognize in Dr. Siillé the posses-
8100 Of many of those more distinguished qualifica-
tions which entitle him to approbation, and which
justify himin coming before his medical brethren
as an instructor, A comprehensive Knowledge,
tested by a sound and penetrating judgment, jomed
to a love uf progress - which a discriminating spirit
of inquiry has tempered so as to uccept nothing new
because it is new, and abandon nothing old because
it is old, but which estimates either accorcing to its
relations ‘oa just logic and experience—manifests
itself everywhere, and gives tu the guidance of the
author all ‘he assurance of safety which the diffi
eulties of his sub ectcanallow. In conclusion, we
earnestly advise our readers to ascertaio fur them-
selves, by astudy of Dr Srillé’s volumes, the great
value and iutercst of the stores of knowledge they
present. We have plearure in referring ruther to
the ample treasury of undoubted truths, the real and
assured Conquest of medicine, accumulated by Dr.
Stille in his pages; and commend the sum of his la-
bors to the attention of our readers, as alike honor-
uble to our science, and creditable to the zeal, the
eandor, and the jadgment of him who has garnered
the whole so carefully.—Edinburgh Med. Journal.

Our expectations of the value of this work were
based on the well-kuown reputation and character
of the author as a man of scholarly attainments, an
elegant writer, a candid inquirer after truth, anda
appa anae thinker; we knew that che task would

6 conscientiously performed, and that few, if any,
among tne distinguished medical teachers in this
country are better qualified than Le to prepare a
systenatic treatise on therapeutics in arcordance |
with the present requirements of medical science.
Our preliminary examination of the work has saus-

fied us that we were not mistaken in our anticipa-
tions.—New Orleans Medical News, March, 1960.
The most recent authority is the one last men-
tioned, Shllé. His great work on ‘+ Materia Medi-
ea and Therapeuties,’’ published last year, in two
octavo volumes, of some sixteen hundred pages,
while it embodies the results of the labor of others
up to the time of publication, is enriched witha
reat amount of original observation and research.
Ve would draw attention, by the way, to the very
convenient mode in which the Indez is arranged in
this work. There is firstan ‘* Index of Remedies ;”?
next an ‘Index of Diseases and their Remedies.”
Such an arrangement of the Indices, in our opinion,
greatly enhances the practical value of books of this
kind, In tedious, obstinate cases of disease, where
we have to try one remedy after another until our
stock is pretty nearly exhausted, and we are almost
driven to our wit’s end, such an index as the second
of the two just mentioned, is precisely what we
want.—London Med. Times and Gazette, April, 1861.

We think this work will do much to obviate the
reluctance toa thurough investigation of this branch
of scientifie study, for in the wide range of medical
literature treasured in the English tongue, we shall
hardly find a work written in a style more elear and
simple, conveying forcibly the facts taught, and yet
free from curgidity and redundancy. There isa tas-
cination in its pages that will insure to ita wide
popularity and attentive perusal, and a degree of
us2fulness not often attained theough the influence
of asingle work. The author has much enhanced

the practical utility of his bouk by passing briefly

over the physical, botani val, and commercial history
of medicines, and directing attention chiefly to their
physiological action, and their application for the
amelioration or cure of disease. He izn res hypothe-
sie and theory which are sv alluring to many medical
writers, and sv liable to lead thei astray, and con-
fines him:elf to such facts 2s have been tried in the
crucible of experience.—Caicago Medical Journal.

SMITH (HENRY H.), M.D. AND HORNER (WILLIAM E.), M.D.
AN ANATOMICAL ATLAS, illustrative of the Structure of the Human Body.

In one volume, large imperial octavo, extra cloth, with about six hundred and fifty beautiful

figures. $3 00.

These figures are well selected, and present a
complete and accurate representation of that won-
derful fabric, the human body. The plan of this
Atlas, which renders it sv peculiarly convenient
for the student, und its superb artistical execution,
have been ulready pointed out. We must congratu-

late the student upon the completion of this Atlas
as it is the most convenient work of the kind that
has yet appeared; and we must add, the very beau-
tiful manner in which it is ‘‘ got up” isso creditable
to the country as to be flattering to our national
pride.—American Medical Journal.

SHARPEY (WILLIAM), M.D., JONES QUAIN, M.D., AND
RICHARD QUAIN, F.R.S., &c.

HUMAN ANATOMY. Revised, with Notes and Additions, by JosepH Lery,

M.D., Professor of Anatomy in the University

volumes, leather, of about thirteen hundred pages.

engravings on wood. $6 00.

o Nyy Meds

SIMPSON (J

of Pennsylvania. Complete in two large octavo
Beautifully illustrated with over five hundred

Professor of Midwifery, &c., in the University of Edinburgh, &c.

CLINICAL LECTURES ON THE DISEASES OF FEMALES. With nume-

rous illustrations,

This valuable series of practical Lectures is now appearing in the “‘Mepican News anp

Lrprary”’ for 1860, 1861, and 1862,

and can thus be had without cost by subscribers to tbe

“ Amarican JOURNAL OF THE MEDICAL Scignces.” See p. 2.

SOLLY ON THE HUMAN BRAIN; its Structure
Phystology, and Disenses. From the Second and
much enlarged London edition.
volume, extra cloth, of 500 pages, with 120 wood-
cuts. $2 00.

SKEY’S UPERATIVE SURGERY. In one very

in one vctave | gIMON's

handsome octavo volume, extra cloth, of over 659
pages, with about one hundred wood-cuts. $3 25.
GENERAL PATHOLOGY, as condue-
ive to the Estabiishment of Rational Principles
for the prevention ano Cure of Disease In one
octavo volume, extra cloth, of 212 pages. $1 26.

28 BLANCHARD & LEA’S MEDICAL

SARGENT (F. W.), M.D.
ON BANDAGING AND OTHER OPERATIONS OF MINOR SURGERY.

New edition, with an additional chapter on Military Surgery. One handsome royal 12mo. vol.,

ofnearly 400 pages, with 184 wood cuts. Leather, $1 50. (Now Ready.)

The value of this work as a handy and convenient manual for surgeons engaged in active duty in
the field and hospital, has induced the publishers 10 render it more complete for those purposes by
the addition of a chapter on gun-shot wounds and other matters peculiar to military surgery. In
its present form, therefore, with no increare in price, it will be found a very cheap and convenient

vade-mecum for consultation and reterence in the daily exigencies of military as well as civil

practice. ;

‘We have read Bourgerie’s Minor Surgery with
pleasure and profit, but in many respects the volume
now betore us immeasurably transcends it. We
consider that no better book could be placed in the
hands of an hospital dresser, or the young surgeon,
whose education in this respect has not been per-
fected We most eurdially commend this volume
as one which the medical student should most close
ly study, to perfect himself in these minor surgical
operations in which neatness and dexterity are 20
much required, and on which a great portion of his
reputation as a future surgeon must evidently rest
And to the surgeon in practice it must prove itself
a valuable vulame, as instructive on many pints
which he may have furgotten.—Brit'sh American
Journal, May, 1862.

The instruction given upon the subject of Ban-
daging, is alone of great value, and while the author
modestly proposes to instruct the students of medi-
cine, and the younger physicians, we will say that
experienced physicians will obtain many exceed-
ingly valuable suggestions by its perusal. Wutn-
out attempting to particularize further, we will
conclude our brief notice by saying, that it will be
found one ot the most satisfactory manuals for refer-
ence io the field, or hospital yet published; thor-
oughly adapted to the wants of Military surgeons,
and at the same time equally useful fur reauy and
convenient reference by surgeons every where.—
Buffalo Med. and Surg. Journal, June, 1262,

SMITH (W. TYLER), M.D.,
Physician Accoucheur to St. Mary’s Hospital, &c.

ON PARTURITION, AND THE PRINCIPLES AND PRACTICE OF

OBSTETRICS. In one royal 12mo. volume, extra cloth, of 400 pages.

$1 25.

BY THE SAME AUTHOR.
A PRACTICAL TREATISE ON THE PATHOLOGY AND TREATMENT

OF LEUCORRHGA. With numerous illustrations. In one very handsome octavo volume,

extra cloth, of about 250 pages. $150, 4

TANNER (T. H.), M.D.,
Physician to the Hospital for Women, &e.

A MANUAL OF CLINICAL MEDICINE AND PHYSICAL DIAGNOSIS.

To which is added The Code of Ethics of the American Medical Association.
In one neat volume, small 12mo., extra cloth, 874 cents.

American Edition.

Second

TAYLOR (ALFRED S.), M.D., F.R.S.,
Lecturer on Medical Jurisprudence and Chemistry in Guy’s Hospital.

MEDICAL JURISPRUDENCE. Fifth American, from the seventh improved
and enlarged London edition. With Notes and References to American Decisions, by Epwarp
HarrsHornE, M.D. In one large 8vo. volume, leather, of over 700 pages. (Now Ready.) $3 25.
This standard work having had the advantage of two revisions at the hands of the author since

the appearance of the Jast American edition, will be found thoroughly revised and brought up com-

pletely to the present state of the science.

Asa work of authority, it must therefore inaimtain its

position, both as a text-book for the student, and a compendious treatise to which tne practitioner
ean at all times refer in cases of doubt or difficulty.

No work upon the subject can be put into the
hands of students either of law or medicine which
will engage them more closely or profitably; and
none could be offered to the busy practitioner of
either calling, for the purpose of casual or hasty
reference, that would be more likely toufford the aid
desired. We thereforerecommend it as the best and
safest manual for daily use.—American Journal of
Medical Sciences.

It is not excess of praise to say that the volume
before us is the very best treatise extant on Medical
Jurisprudence. In saying this, we do not wish to
be understood as detracting from the merits of the
excellent works of Beck, Ryan, Traill, Guy, and
others; but in interest and value we think it must
be conceded that Taylor is superior to anything that
has preceded it.— NV. W. Medicaland Surg. Journal

It is at once comprehensive and eminently prac-

American and British legal medicine. It should be
in the possession of every physician, as the subject
is one of great and increasing importance to the
public as well as to the professron.—St. Lous Med.
and Surg. Journal,

This work of Dr. Taylor’s is generally acknow-
ledged to be one of the ablest extant on the subject
of medical jurisprudence. 1t is certainly one of the
Most attractive books that we have met with; sup-
plying so much both to interest and instruct, that
we do not hesitate to affirm that after having once
commenced its perusal, few could be prevailed upon
to desist before completing it. In the Jast Lonaon
edition, all the newly observed and accurately re-
corded facts have been inserted, including much
that is recent of Chemical, Microscopical, and Pa-
thological research, besides papers on numerous
subjects never before published.—Charleston Med.

tical, and by universal consent stands at the head of | Journal and Review.

BY THE SAME AUTHOR.

ON POISONS, IN RELATION TO MEDICAL JURISPRUDENCE AND

MEDICINE. Second American, from a second and revised London edition. in one large
octavo volume, of 755 pages, leather. $3 50.

Mr. Taylor’s position as the leading medical jurist of England, has conferred on him extraordi-
nary advantages in acquiring experience on these subjects, nearly all cases of moment being
referred to him for exumination, as an expert whose testimony 1s generally accepted as final.
The results of his labors, therefore, ax gathered together in this volume, carefully weighed and
sifted, and presented in the clear and intelligible style for which he is noted, may be received
as an acknowle !ged authority, and as a guide to be followed with implicit confidence.

AND SCIENTIFIC PUBLICATIONS. 29

TODD (ROBERT BENTLEY), M.D., F.R.S.,
Professor of Physiology in King’s College, London; and
WILLIAM BOWMAN, F.R.S.,

Demonstrator of Anatomy in King’s College, London.

THE PHYSIOLOGICAL ANATOMY AND PHYSIOLOGY OF MAN. With

about three hundred large and beautiful illustrations on wood. Complete in one large octavo
volume, of 950 pages, leather. Price $4 50.

(e Gentlemen who have received portions of this work, as published in the ‘¢* Mepicat News

AND Liprary,’” can now complete their copies, if immediate application be made.

Tt will be fur-

nished as follows, free by mail, in paper covers, with cloth backs.

Parts L., IIL., IT1. (pp. 25 to 552), $2 50.

Part IV. (pp. 553 to end, with Title, Preface, Contents, &c.), $2 00.

Or, Part

A magnificent contribution to British medicine,
and the American physician who shall fail to peruse
it, wil: have failed to read one of the most instruc-
tive books of the nineteenth century.—N. O. Med
and Surg. Journal,

Itis more concise than Carpenter’s Principles, and
more modern than the accessible edition of Maller’s
Elements; its details are brief, but sufficient; ite
descriptions vivid; its illustrations exact and copi-
ous; and its language terse and perspicuous. —
Charleston Med. Journal.

We know of no work on the subject of physiology

TODD (R. B.)

M.

V., Section II. (pp. 725 to end, with Title, Preface, Contents, &c.), $1 25.

so well adapted to the wants of the medical student.
Its completion has been thus long delayed, that the
authors might secure accuracy by personal observa-
tion.—St. Louis Med. and Surg. Journal.

Our notice, though it conveys but a very feeble
and imperfect ideo of the magnitude and importance
of the work now under consideration, already tran-
scends our limits; and, with the indulgence of our
teaders, and the hope that they will peruse the book
for themselves, as we feel we can with confidence
recommend it, we leave it in their hands. — The
Northwestern Med. and Surg. Journal.

D., F.R.S., &e,

CLINICAL LECTURES ON CERTAIN DISEASES OF THE URINARY

ORGANS AND ON DROPSIES.

BY THE SAME AUTHOR.

CLINICAL LECTURES ON CERTAIN ACUTH DISEASES.

In one octavo volume, 284 pages.

$1 50.
(Now Ready.)
In one neat

octavo volume, of 320 pages, extra cloth. $175.

TOYNBEE (JOSEPH), F.R.S.,

Aural Surgeon to, and Lecturer on Surgery at, St. Mary’s Hospital.

A PRACTICAL TREATISE ON DISEASES OF THE EAR; their Diag-

nosis, Pathology, and Treatment.

The work, as was stated at the outset of our no-
tice, is a model of its kind, and every page and para-

raph of it are worthy of the most thorough study.
Cousidered all in all—as an original work, well
written, philosuphically elaborated, and happily il-
lustrated with cases and drawings—it is by far the
ablest monograph that has ever appeared on the
anatomy and diseases of the ear, and one of the must
valuable contributions to theart and science of sur-
gery in the nineteenth century. Amer. Medico-
Chirurg Review, Sept. 1860.

To recommend such a work, even after the mere
hint we have given of its original excellence and
value, would be a work of supererogation. We ate
speaking Within the limits of modest acknowledg-

Illustrated with one hundred engravings on wood.
very handsome octavo volume, extra cloth, $3 00.

In one
(Just Issued.)

ment, and with a sincere and unhiassed judgment,
when we affirm that asa treatise on Aural Surgery,
it is without a rivel in our language or any other.—
Charleston Med. Journ and Review, Sept. 1860.

The work of Mr. Toynber is undoubtedly, upon
the whole the must valuable production of tne kind
in any language. The author has long veen known
by his numerous monographs upon subjects con-
nected with diseases of the ear, and is now regarded
as the highest authority on most points in his de-
partment of science. Mr Toynbee’s work, as we
have already said, is undoubteuly the most reliable
guide for the study of the diseases of the ear in any
language, and should be in the library of every phy-
sician.— Chicago Med. Journal, July, 1860.

WILLIAMS (C. J. B.), M.D., F-R.S.,

Professor of Clinical Medicine in University College, London, &e.

PRINCIPLES OF MEDICINE. An Elementary View of the Causes, Nature,

Treatment, Diagnosis, and Prognosis of Disease; with brief remarks on Hygienics, or the pre-

servation of health. A new American, from the third and revised London edition.
(Just Issued.)

volume, leather, of about 500 pages. $2 50.

We find that the deeply-interesting matter and
style of this book have so far fascinated us, that we
have unconsciously hung upon its pages, not too
long, indeed, for our own profit, but longer than re-
viewers can be permitted to indulge. e leave the
further analysis to the student and practitioner. Our
judgment of the work has already been sufficiently

in one octavo

expressed. Itisa judgment of almost unqualified
praise.—London Lancet.

A text-book to which no other in our language is
comparable.—CaAarleston Medical Journal.

No work has ever achieved or maintained a more
deserved reputation.—Va, Med. and Surg. Journal,

WHAT TO OBSERVE
AT THE BEDSIDE AND AFTER DEATH, IN MEDICAL CASES.

Published under theauthority of the London Society for Medical Observation.

Anew American,

from the second and revised London edition. In one very handsome volume, royal 12mo., extra

cloth. $1 00.

To the observer who prefers accuracy to blunders
and precision to carelessness, this little book is ja-
valuable.—N. Hf. Journal of Medicine,

One of the finest aids toa young practitioner we
have ever seen.— Peninsular Journal of Medicine.

BLANCHARD & LEA’S MEDICAL

New and much enlarged edition—(Just Issued.)

WATSON (THOMAS), M.0O., &c.,
Late Physician to the Middlesex Hospital, &c.

LECTURES ON THE PRINCIPLES AND PRACTICE OF PHYSIC.

Delivered at King’s College, London. A new American, from the last revised and enlarged
English edition, with Additions, by D, Francis Conpig, M. D., author of A Practical Treatise
on the Diseases of Children,” &e.” With one hundred and eighty.five illustrations on wood. In
one very large and handsome volume, imperial octavo, of over 1200 clu-ely printed pages in
small type; the whole strongly bound in leather, with raised bands. Price $4 20.

That the high reputation of this work might be fully maintained, the author has subjected it to a
thorough revision; every portion has been examined with the aid of the most recent researches
in pathology, and the results of modern investigations in both theoretical and practical rubjects
have been carefully weighed and embudied throughout its pages. The watchtul scrutiny of the
editor has likewise introduced whatever possesses immediate importance to the American physician
in relation to diseases incident to our climate which are little known in England, as well as those
points in which experience here has Jed to different modes of practice ; and he has al-o added largely
to the series of illustrations, believing that in this manner valuable asvistance may be conveyed to
the student in elucidating the text. The work will, therefore, be found thoroughly on a level with
the most advanced state of medical science on both sides of the Atlante.

The additions which the work has received are shown by the tact that notwithstanding an en-
largement in the size of the page, more than two hundred additional pages have been necessary
to accommodate the two large volumes of the London edition (which sells at ten dollars), within
the compass of a single volume, and in its present form it contains the matter of at least three
ordinary octavos. Believing it to be a work which should lie on the table of every physician, and
be in the hauds of every student, the publishers have put it at a price within the reach of all, making
it oue of the cheapest books as yet presented to the American profession, while at the same time
the beauty of its mechanical execution renders it an exceedingly attractive volume.

The fourth edition now appeats, so carefully re-
vised, as to add considerably to the value of a book
already ucknowledged, wherever the English lan-
guage is read, tu be beyond all comparison the best
aj stemutic work on the Principles and Practice of
Physic in the whole range of medical literature.
Every lecture contains proof of the extreme anxiety
of the author to keep pace wich he advancing know-
ledge of the day, and to bring the results of the
labors, not only of physicians, but of chemists and
histol« gists, before his readers, wherever they can
be turued to useful account. One searcely knows
whether to admire most the pure, simple, forcible
English—the vast amount of useful practical in-
formation condensed inro the Leetures—or the man-
ly, kind-hearted, unussuming character of the lec-
turer shining through his work.—Lond. Med. Times.

Thus these admirable volumes come before the
profession in their fourth edition, abounding in those
distinguished attributes of moderation, Judgment,
erudite cultivation, clearness, and eloquence, wilh"
which they were from the first invested, but yet
richer than before in the results of more prolonged
observation, and in the able appreciation of the
latest advances tn pathology and medicine by one
of the must profuund medical thinkers of the day.—

London Lancet.

Tue lecturer’s skill, his wisdum, his learning, are
equalled by the ease of his graceful diction, hia elo-
quence, and the far higher qualities of candor, of
cvurtesy, of modesty, and of generous appreciation
of meritin others —N. A. Med -Chir Review.

Watson’s unrivalled, perhaps unapproachable
work on Practice—the copious addirions made to
which (the fourth edition) have given it all the no-
velty and much of the interest of a new book.—
Charleston Med. Journal,

Lecturers, practitioners, and students of medicine
will] equally hail the reappearance of the work of
Dr. Watson in the form of a new—a fourth—edition.
We merely do justice to our own feelings, and, we
are sure, of the whule profession, if we thank him
for having, in the trouble and turinuil of a large
practice, made leisure Lo supply the hiatus caused
by the exhaustion of the publisher’s stock of the
third edition, which has been severely felt for the
last three years. For Dr. Watson has not merely
caused the lectures to be reprinted, but sealtered
through the whole work we find additions or altera-
tions Which prove that the author hus in every way
sought to bring up his teaching to the level uf -he
mol recent ucquisitions in science.— Brit. and For,
Medico-Chir. Review.

WALSHE (W. H.), M.D.,

Professor of the Principles and Practice of Medicine in University College, London, &c.

A PRACTICAL TREATISH ON DI3EASES OF THE LUNGS; iucludiog
the Principles of Physical Diagnosis. A new American, from the third revised aud much en-
farged Loncon edition, In one vol. octavo, of 468 pages $2 25,

The present edition has been carelully revised and much enlarged, and may be said in the main
to be rewritten. Descriptions of several diseases, previously omitied, are now introduced; the
causes and mode of production of the more important affectious, so fac as they possess direct prac-
ueal significance, are succinctly inquired into; an effort has been made to bring tne description of
anatumical characters to the Jevel of the wants of the practical physician; and the diagnosis and
progtiosis of each complaiut are more completely considered. Tne seciions on TrearmMent and
ihe Appendix (concerning the influence of climate on pulmonary disorders), have, e: pecially, been
largely extended.—Author’s Preface.

BY THE SAME AUTHOR.

A PRACTICAL TREATISE ON THE DISEASES OF THE HEART AND
GREAT VESSELS, including the Principles of Physical Diagnosis Third American, from the
third revised and much enla ged Londuu edition. In une handsome octave vulume of 420 pages,
extra cloth. $225. (Just Ready.)

From the Author's Preface.

The present edition has been carefully revired; much new matter has been added, and the entire
work in a measure remodelled. Numerous facts and discussions, mure or lesx completely novel,
will be found in the dexcripuon of tae prinesples of physical diagnosis; but the chief additions bave
been made in the practical portions of the buok. Several aflecttons, of which little or uv account
bad heen given in the previous editions, are now treated of ju detail. Fanctional disurders of the
heart, the flequoney uf which is almost rivaled by the inisery they inflict, have been clorely recom
sidered; more especially an attempt has been miue to render their essential nature clearer, apd
consequently their treatment more succeestul, by au analysis of their dynamic e.ements.

AND SCIENTIFIC PUBLICATIONS

31

New and much enlarged edition—(Just Issued. )
WILSON (ERASMUS), F.R.S.

A SYSTEM OF HUMAN ANATOMY, General and Special.

A new and re-

vised American, from the last and enlarged English Edition. Edited by W. H.Gosrecurt, M. D.,

Professor of Anatomy in the Pennsylvania Medical College, &e. Illustrated with three hundred

and ning yeoven engravings on wood. In one large and exquisitely printed octavo volume, of
a

over 600 large pages; leather. $3 25.

The publishers trust that the well earned reputation so long enjoyed by this work will be more

than maintained by the present edition.

Besides a very thorough revision by the author, it has been

most carefully examined by the editor, and the efforts of both have been directed to introducing
precyning which increased experience in its use has suggested as desirable to render ita complete

text-

ook for those seeking to obtain or to renew an acquaintance with Human Anatomy. The

amount of additions which it has thus received may be estimated from the fact that the present
edition contains over one-fourth more matter than the last, rendering a smaller type and an enlarged
page requisite to keep the volume within a convenient size. The editor has exercised the utmost
caution to obtain entire accuracy in the text, and has largely increased the number of illustra-
tions, of which there are about one hundred and fifty more in this edition than in the last, thus

bringing distinctly before the eye of the student everything of interest or importance.

it may be recommended to the student as no less
distinguished by its accuracy and clearness of de-
scription than by its typographical elegance. The
wood-cuts are exquisite.—Brit.and For. Medical
Review.

An elegant edition of one of the most useful and
accurate systems of anatumical science which has
been issued from the press The illustrations are
really beautiful. In its style the work is extremely
concise and intelligible. No one can possibly take
up this volume without being struck with the great

BY THE SAME AUTHOR.

beauty of its mechanical execution, and the clear-

nese of the descriptions which it contains is equally

evident. Let students, by all means examine tue

claims of this work on their notice, before they pur-

chase a text-book of the vitally important science

aes this volume so fully and easily unfolds.—
ancet,

We regard it as the best system now extant fur
students.— Western Lancet.

lt therefore receives our highest commendation.—
Southern Med. and Surg. Journal,

(Just Issued.)

ON DISEASES OF THE SKIN. Fourth and enlarged American, from the last

and improved London edition.

The writings of Wilson, upon diseases of the skin,
are by far the most scientific and practical that
have ever been presented to the medical world on
this subject. The present edition isa great improve-
ment on all its predecessors. To dwell upon all the
great merits and high claims of the work before us,
seriatim, would indeed be an agreeable service; it
would bea mental homage which we could freely
offer, but we should thus occupy an undue amount
of space in this Journal. We will, however, look

In one large octavo volume, of 650 pages, extra cloth, $2 75.

at some of the more salient points with which it
abounds, and which make itincompara uty superior in
excellence to all other treatises on the subjeetof der-
matology. No mere speculative views are allowed
a place in this volume, which, without a doubt, will,
for a very long period, be acknowledged as the chief
standard work on dermatology. The principles of
an enlightened and rational therapeia are introduced
on every appropriate occasion.—Am. Jour. Med.
Science, Oct. 1857.

ALSO, NOW READY,

A SERIES OF PLATES ILLUSTRATING WILSON ON DISEASES OF

THE SKIN; consisting of nineteen beautifully executed plates, of which twelve are exquisitely
colored, presenting the Norma! Anatomy and Pathology of the Skin, and containing accurate re-

presentations of about one hundred varieties of disease, most of them the size of nature.

in cloth $4 25.

Price

In beauty of drawing and accuracy and finish of coloring these plates will be found equal to
anything of the kind as yet issued in this country. ©

The plates by which this edition is accompanied
leave nothing to be desired, so far as excellence of
delineation and perfect aceuracy of illustration are
eoncerned.— Medico-Chirurgical Review. 7

Ot these plates it is impossible to speak too highly
The representations uf the various forms of cutane-
ous disease are singularly acenrate, and the cvlor-
ing exceeds almust anything we have met with in
point of delicacy and finish.— British and Foreign
Medical Review.

We have already expressed our high appreciation
of Mr. Wilson’s treatise on Diseases of the Skm.
The plates are comprised in a separate volume,
which we counsel al! those who possess the text to
purchase. It is beautiful specimen of color print-
ing, and the representations of the various forms of
skin disease are us faithful as is possible in plates
of the size.— Boston Med.and Surg. Journal, April
8, 1868.

BY THE SAME AUTHOR.

ON CONSTITUTIONAL AND HEREDITARY SYPHILIS, AND ON
SYPHILITIC ERUPTIONS. In one small octavo volume, extra cloth, beautifully printed, with
four exquisite colored plates, presenting more than thirty varieties of syphilitic eruptions. $2 25.

BY THE SAME AUTHOR,

HEALTHY SKIN; A Popular Treatise on the Skin and Hair, their Preserva-

tion and Management. Second American, from the fourth London edition. One neat volume,
royal 12mo., extra cloth, of about 300 pages, with numerous illustrations. $1 00; paper cover,

75 cents.

BY THE SAME AUTHOR.

THE DISSECTOR’S MANUAL; or, Practical and Surgical Anatomy. Third

American, trom the last revised and eularged English edition. Modified and rearranged, by

Wiuuiam Hunt, M. D., Demonstrator of Anatomy in the University ot Pennsylvania,

In one

large and handsome royal 12:nv. volume, leather, of 582 pages, with 154 illustrations. $2 00.

32

BLANCHARD & LEA’S MEDICAL PUBLICATIONS.

WINSLOW (FORBES), M.D., D.C.L., &c.
ON OBSCURE DISEASES OF THE BRAIN AND DISORDERS OF THE

MIND; their incipient Symptoms, Pathology,

handsome octavo volume, of nearly 600 pages.

We close this brief and necessarily very imperfect
notice of Dr. Winslow’s great und classical work,
by expressing our conviction that it is long since so
lumportant and beautifully written a volume has is-
sued from the British medical! press —Dublin Med.
Press, July 25, (860.

We honestly believe this to be the best book of the
season.— Aanking’s Abstract, July, 1860.

It ear: cd us back to our old days of novel reading,
it kept us from our dirner, from our business, and
frou. our slumbers; in short, we laid it down only
wen we had got to the end of the last paragraph
and even then turned back to the repe!usal of severa
passages which we had inarked as requiring fur:her
study We have failed entirely in the above notice
to give an adequate acknowledgment of the profit
and pleasure with which we have perused the above
work, We can only say to our readers, study it

Diagnosis, Treatment, and Prophylaxis. In one

(Just Issued.) $300.

yourselves; and we extend the invitation to unpro-
fessional as well as professional men, believing that
it contains matter deeply interesting not to physi-
cians alone, but toall who appreciate the truth that:
‘¢ The propec study of mankind 1s man.?’—. Vashville
Medical Record, July, 160.

The latter portion of Dr. Winslow’s work is ex-
clusively devoted to the consideration of Cerebral
Pathology. It completely exhausts the subject, in
the sume manner as the previous seventeen chapters
relating to morbid psychical phenomena left nothing
unnoticed in reference tu the mental symptoms pre-
monitory of cerebral disease It is impossible to
overrate the benefits likely to result from a general
perusal of Dr. Winslow’s valuavle and deeply in-
teresting work —London Lancet, June 23, 1860.

It contains an immense mags of information.—
Brit. and For. Med.-Chir. Review, Oct. 1€60.

WEST (CHARLES), M.D.,

Accoucheur to and Lecturer on Midwifery at St. Bartholomew’s Hospital, Physician to the Hospital for

Sick Children, &c.

LECTURES ON THE DISEASES OF WOMEN. Sceond American, from the
second London edition. In one handsome octavo volume, extra cloth, of about 500 pages ;
price $250. (Mow Ready, July, 1861.)

*,* Gentieu.n who received the first portion, as issued in the ‘‘ Medical News and Library,”’ can

now complete their cupies by procuring Part IL, being page 309 to end, with Index, Title matter,

, &ce., 8vo., cloth, price $1.

*& We must now conclude this hastily written sketch
.th the confident assurance to our readers that the

work will well repay perusal. The conscientivus,

painstaking, practical physician 1sapparent on every

page. —N. Y. Journal of Medicine, March, 1858.
We know of no treatise of the kind so complete

and yet so compact.—Chicago Med. Jour. Jan. 1858.

A fairer, more honest, mure earnest, and more re-
liable investigator of the many diseases of women
and children is not to be found in any country.—
Southern Med. and Surg. Journal, January 1858.

We gladly recommend his Lectures as in the high-
est degree instructive to all who are interested in
obstetric practice.—London Lancet.

We have to say of it, briefly and decidedly, that
it is the best work on the subject in any language ;
and that it stamps Dr. West asthe facile princeps
vf British obstetric authors.— Edinb, Med, Journ.

Asa writer, Dr. West stunds, in our opinion, sec-
ond only to Watson, the ** Macaulay of Medicine ;”’
he possesses that happy faculty of clothing instrue-

BY THE SAME AUTHOR.

LECTURES ON THE DISEASES

Third American, from the fourth enlarged and improved Loudon edition.
octavo volume, extra cloth, of about six hundred and fitty pages.

The three former editions of the work now before
us have placed the author in tne foremost rank of
those physicians who have cevoted special attention
to the diseases of early life We uttempt no ana-
lysis of thisedition, but may refer the reader togsome
of the chapters to which the largest aduitions have
been made—those on Diphtheria, Disorders of the
Mind, and (diucy, for instance—asg a provi that the
work 18 reully a new edition; not uw mere reprint.
Jn its pretent shape it will be tound of the greatest
pusstble service in the every-day practice uf nine-
tenths of the profession.—Med, Times and Gazette,
London, Dec. 10, 1859.

All things consid: red. this book of Dr. West is
by far the best treatise in our language upon such
modificutions of morbid action and disease us ure
witnessed when we have to deal with itaney and
ebildhuud. lt is true that it confines itself to such
disorders as come wichin the proviace of the phy-
sicean, and even with respect tu tuese it 1s unequal

aa regards minutencas of consideration, and some

tion in easy garments; combining pleasure with
profit, he leuds his pupils, in spite of the ancient
proverb, along a royal road to learning. His work
is one whieh wiJl not satisfy the extreme on either
side, butitis one that wilt please the great majority
why are seeking truth, and one that will convince
the student that he has committed himself to a can-
did, sate, and valuable guide.—V. A. Med.-Chirurg.
Review, July, 1858.

Happy in his simplicity of manner, and moderate
in his expression of opinion, the author is a sound
reasoner and a good practitioner, and his book 1s
worthy of the hunusume garb in which it has ap-
peured.— Virginia Med. Journal.

We must take leuve of Dr. Weat’s very useful
work, with our commendation or the clearness of
its style, and the incustry and sobriety of Judgment
of which 1t gives evidence.—London Med Times.

Sound judgment and goud sense pervade every
chapter ui the vouk. From its perusal we have de-
rived unmixed satisfuction.—Uublin Quart. Juurn.

(Just Issued.)
OF INFANCY AND CHILDHOOD.

In one handsome

$275.

diseases it omits to notice altogether. But those
who know anything of the present condition of
pediatrics will readily admit chat it would be next
to nnpossible to effect more, or effect it better, than
the accoucheur of St. Bartholomew’s has done ina
single volume. The leeture (X VI.) upon Disorders
of the Mind in chiloren is an admirabie specimen of
the vulue of the later information conveyed in the
Lectures of Dr, Charles West.—London Lancet,
Uet. 22, 1859.

Since the appearance of the first edition, about
eleven years ago, the experience of the author has
doubled; su that, whereus the lectures at first were
founded on six hundred observations, and one hun-
dred and eiguty dissections nade amung neatly four-
teen thousand children, they now embody the results
of nine hundred observations, and two hundred and
eighty-eigbt post-mortem examinations made among
nearly thirty thousand children, who, during the
past twenty yeurs, have been under his cure, —
British Med. Journal, Oct. 1, 1859.

BY THE SAME AUTHOR.

AN ENQUIRY INTO THE PATHOLOGICAL IMPORTANCE OF ULCER.

ATION OF THE OS UTERI. In one neat

WHITEHEAD ON THE CAUSES AND TREAT-
MENT OF ABORTION AND STERILITY.

octavo volume, extra cloth. $1 00.

Second American Edition. In one volume, octa-
vo extracloth, pp. 308. $1 75.