THE MICKOSCOPE

BIOLOGY
LIBRARY

^ s, V

POLARISCOPK OliJKCTS.

15S ItiD

I'LATK VJJI.

Edmund Evans.

THE MICROSCOPE:

HISTOKY, CONSTRUCTION, AND APPLICATION

BEING

•

A FAMILIAR INTRODUCTION TO THE USE OF THE INSTRUMENT,
AND THE STUDY OF MICROSCOPICAL SCIENCE.

BY JABEZ HOGG, F.L.S., F.RM.S.
\\

SECRETARY, ROYAL MICROSCOPICAL SOCIETY ;

MEMBER OF THE

aOYAL COLLEGE OF SURGEONS OF ENGLAND; AUTHOR OF "ELEMENTS OF NATURAL PHILOSOPHY,
" A MANUAL OF OPHTHALMOSCOPIC SURGERY," ETC.

WITH UPWARDS OF FIFE HUNDRED ENGRA VINGS, AND
COLOURED ILLUSTRATIONS BY TUFFEN WEST.

LONDON :
GEORGE ROUTLEDGE AND SONS,

NEW YORK : 416, BROOME STREET,
1869.

Wo

fllOLOGY
LIBRARY

LONDON :

R. CLAY, SONS, AND TAYLOR, PRINTERS,
BREAD STREET HILL.

PREFACE TO THE SIXTH EDITION.

issuing the SIXTH Edition of this Work on
the MICROSCOPE, we may state that it has
been thoroughly revised and for the most part
re-written. Eight carefully and beautifully
executed Plates are added, which were drawn
by Tuffen West from natural objects, engraved
and printed by Edmund Evans in the first style of colour-
printing.

The Author cannot but express his grateful surprise at
the extraordinarily popular reception which his 'book has
met with : a sale of fifty thousand is an unprecedented
event for a work of the kind. This circumstance is
extremely gratifying to him, because it affords reasonable
grounds for believing that his work has been useful, and
encourages renewed effort to make the volume still more
acceptable. It has been his endeavour to bring the
information contained in its pages up to the most recent
discoveries ; although, in a daily progressing field of
science, it is almost impossible to keep pace with the
advance of knowledge in all its ramifications.

The passing remarks the Author has seen occasion to
make upon the various objects that have fallen under his
notice are intended to serve, as would a finger-post or

VI PREFACE.

guide in a country abounding in treasures. It was
impossible to have attempted a more detailed descrip-
tion than has been given in dealing with the vast expanse
of natural objects presented to his contemplation. If,
however, the notices have been sufficiently ample and
precise to assist the study of the reader, the Author will
have accomplished the most cherished object he had in
view in presenting the work to the public.

1, BEDFORD SQXTAKK,

October, 13t>7,

PREFACE TO THE FIRST EDITION.

HE Author of this Publication entered upon
his task with some hesitation and diffidence ;
but the reasons which influenced him to
undertake it may be briefly told, and they
at once explain his motives, and plead his
justification, for the work which he now
ventures to submit to the indulgent con-
sideration of his readers.

It had been to him for some time a sub-
ject of regret, that one of the most useful
and fascinating studies — that which belongs to the do-
main of microscopic observation — should be, if not wholly
neglected, at best but coldly and indifferently appreciated
by the great mass of the general public ; and he formed
a strong opinion, that this apathy and inattention were
mainly attributable to the want of some concise, yet suffi-
ciently comprehensive, popular account of the Microscope,
both as regards the management and manipulation of the
instrument, and the varied wonders and hidden realms of
beauty that are disclosed and developed by its aid. He
saw around him valuable, erudite, and splendid volumes ;
which, however, being chiefly designed for circulation
amongst a special class of readers, were necessarily pub-

Vlll PREFACE.

lished at a price that renders them practically unattainable
by the great bulk of the public. They are careful and
beautiful contributions to the objects of science, but they
cannot adequately bring the value and charm of micro-
scopic studies home, so to speak, to the firesides of the
people. Day after day, new and interesting discoveries,
and amplifications of truth already discerned, have been
made, but they have been either sacrificed in serials, or,
more usually, devoted to the pages of class publications ;
and thus this most important and attractive study has
teen, in a great measure, the province of the few only,
who have derived from it a rich store of enlightenment
and gratification : the many not having, however, parti-
cipated, to any great extent, in the instruction and enter-
tainment which always follow in the train of microscopical
studies.1

The manifold uses and advantages of the Microscope
crowd upon us in such profusion, that we can only attempt
to enumerate them in the briefest and most rapid manner
in these prefatory pages.

It is not many years since this invaluable instrument
was regarded in the light of a costly toy ; it is now the
inseparable companion of the man of science. In the
medical world, its utility and necessity are fully appre-
ciated, even by those who formerly were slow to perceive
its benefits ; now, knowledge which could not be obtained
even by the minutest dissection is acquired readily by its
assistance, which has become as essential to the anatomist
and pathologist as are the scalpel and bedside observation.
The smallest portion of a» diseased structure, placed under
a Microscope, will tell more in one minute to the ex-
perienced eye, than could be ascertained by long examina-

(1) At the time this work was written, scarcely a book of the kind had been
published at a price within the reach of the working classes

PREFACE. ix

tion of the mass of disease in the ordinary method.
Microscopic agency, in thus assisting the medical man,
contributes much to the alleviation of those multiplied
" ills which flesh is heir to." So fully impressed were the
Council of the Eoyal College of Surgeons with the import-
ance of the facts brought to light in a short space of time,
that, in 1841, they determined to establish a Professorship
of Histology, and to form a collection of preparations of
the elementary tissues of both animals and vegetables,
healthy and morbid, which should illustrate the value of
microscopical investigations in physiology and medical
science. From that time, histological anatomy deservedly
became an important branch of the education of the
medical student.

In the study of Vegetable Physiology, the Microscope
is an indispensable instrument ; it enables the student to
trace the earliest forms of vegetable life, and the functions
of the different tissues and vessels in plants. Valuable
assistance is derived from its agency in the detection of
adulterations. In the examination of flour, an article of
so much importance to all, the Microscope enables us
to judge of the size and shape of the starch-grains, their
markings, their isolation and agglomeration, and thus to
distinguish the starch-grains of one meal from those of
another. It detects these and other ingredients, invisible
to the naked eye, whether precipitated in atoms or aggre-
gated in crystals, which adulterate our food, our drink,
and our medicines. It discloses the lurking poison in
the minute crystallisations which its solutions precipitate.
" It tells the murderer that the blood which stains him is
that of his brother, and not of the other life which he
pretends to have taken; and as a witness against the
criminal, it on one occasion appealed to the very sand on
which he trod at midnight."

x PREFACE:

The zoologist finds in the Microscope a necessary co-
operator. To the geologist it reveals, among a multiplicity
of other facts, " that our large coal-beds are the ruins of a
gigantic vegetation ; and the vast limestone rocks, which
are so abundant on the earth's surface, are the catacombs
of myriads of animal tribes, too minute to be perceived by
the unaided vision."

Ey " conducting the eye to the confines of the visible
form," the Microscope proves an effective auxiliary in
denning the geometric properties of bodies. Its influence
as an instrument of research upon the structure of bodies
has been compared to that of the galvanic battery, in the
hands of Davy, upon Chemistry. It detects the smallest
structural difference, heretofore inappreciable, and, as an
ally of Chemistry, enables us to discover the very small
changes of form and colour effected by test-fluids upon
solids ; and dissects for us, so to speak, the most multiplex
compounds. It opens out to the mind an extended and
vast tract, opulent in wonders, rich in beauties, and bound-
less in extent.

The Microscope not only assists studies, and develops
objects of profound interest, but also opens up innumer-
able sources of entertainment and amusement, in the
ordinary conventional acceptation of these terms; — dis-
closing to us peculiarities and attractions in abundance ; —
impressing us with the wonderful and beautifully-skilful
adaptation of all parts of creation, and filling our minds
with additional reverence and admiration for the beneficent
and Almighty Creator.

The Author will conclude these prefatory observations
with a few words in explanation of his arrangements,
and by way of acknowledgment to those to whom he is
indebted. He has sought, in the volume that he now lays
before the public, to point out and elucidate at once in a

PREFACE.

practical manner and in a popular style, the vast fund of
utility and amusement which the Microscope affords, and
has endeavoured to touch upon most of the interesting
subjects for microscopic observation as fully as the restric-
tions of a limited space, and the nature of the succinct
summary, would permit. To have dwelt upon each in
complete detail would have necessitated the issue of many
expensive volumes — and this would have entirely frustrated
the aim which the writer had in view j he has, therefore, con-
tented himself with the humble, but, he trusts, not useless,
task of setting up a finger-post, so to say, to direct the
inquirer into the wider road. In the section of the work
devoted to the minuter portion of creation, he has ventured
to dwell somewhat longer, in the belief that that depart-
ment is more especially the province of the microscopist.
He has arranged his topics under special headings, and in
separate chapters, for the sake of perspicuity and precision ;
and has brought the ever-welcome aid of illustrations to
convey his explanatory remarks more vividly to the minds
of his readers. He is peculiarly indebted to Professor
Quekett, whose valuable lectures, delivered annually in
the Eoyal College of Surgeons, and whose multifarious and
successful researches, have pre-eminently distinguished him
as the microscopist of the day. From notes made during
the lectures spoken of, and from the many admirable
papers which this gentleman has published, much sound
information has been gleaned ; and the Author has to thank
him, in the most sincere and cordial manner, for placing
at his disposal the mass of contributions with which he
has enriched microscopical science. A free use has been
made of the researches of scientific investigators generally
— Leeuwenhoek, Ehrenberg, Carpenter, Johnston, Ealfs,
Busk, Gosse, Huxley, Hassall, Lobb, Davies, and other
members of the Microscopical Society of London. His

Xil PREFACE.

acknowledgments are likewise due to Mr. George Pearson,
for the great care he has bestowed upon the engravings
which illustrate these pages.

Finally, it is the Author's hope that, by the instru-
mentality of this volume, he may possibly assist in bring-
ing the Microscope, and its most valuable and delightful
studies, before the general public in a more familiar, com-
pendious, and economical form than has hitherto been
attempted ; and that he may thus, in these days of a
diffused f taste for reading and the spread of cheap pub-
lications, supply further exercise for the intellectual
faculties, — contribute to the additional amusement and
instruction of the family circle, — and aid the student of
nature in investigating the wonderful and exquisite works
of the Almighty. If it shall be the good fortune of this
work, which is now confided with great diffidence to the
consideration of the public, to succeed in however slight a
degree, in furthering this design, the Author will feel
sincerely happy, and will be fully repaid for the attention,
time, and labour that he has expended.

LONDON, May, 1854.

PAKT I.

HISTORY OF THE INVENTION AND IMPROVEMENTS
OF THE MICROSCOPE.

CHAPTER 1.

3

HISTORY OP THE INVENTION AND IMPROVEMENTS OF THE
MICROSCOPE

CHAPTER II.

MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IN THE
CONSTRUCTION OF THE MICROSCOPE — LENSES— MODE OF
ESTIMATING THEIR POWER — MICROMETERS — POLARISED
LIGHT — CAMERA LUCIDA — BINOCULAR INSTRUMENT —
PHOTOGRAPHIC-DRAWING — M1CROSPECTROSCOPY — ACHRO-
MATIC LENSES — MAGNIFYING POWER — WOLLASTON'S
DOUBLET — CODDINGTON'S LENS — SIMPLE AND COMPOUND
MICROSCOPES — QUEKETT'S, ROSS'S, POWELL AND LEA-
LAND'S, BAKER'S, PILLISCHER'S, LADDS', MURRAY'S, HIGH-
LEY'S, COLLINS'S, AND OTHER MICROSCOPES 15

XIV CONTENTS.

CHAPTER III.

PAGE

PRELIMINARY DIRECTIONS — ILLUMINATION — ACCESSORY APPA-
RATUS—ACHROMATIC ILLUMINATOR — GILLETT'S, ROSS'S,

WEBSTER'S, AND ot-HER CONDENSERS — OBLIQUE ILLUMI-
NATION— DOUBLE PRISM ILLUMINATION — LIEBERKUHN
— SIDE-REFLECTOR—OBJECT-FINDERS — SECTION CUTTERS

— COLLECTING OBJECTS— MODE OF INJECTING PREPARING

AND MOUNTING OBJECTS, ETC 159

PART II.

CHAPTER I.

VEGETABLE KINGDOM — VITAL AND CHEMICAL CHARACTERISTICS
OF CELLS — MICROSCOPIC FORMS OF VEGETABLE CELLS-
FUNGI— FUNGOID DISEASES — ALG2B —CONFERVA — DESMI-
DIACE.E — MOSSES — FERNS — STRUCTURE OF PLANTS —
ADULTERATION OF ARTICLES USED FOR FOOD — PREPARA-
TION AND MOUNTING— FOSSIL PLANTS . ..... 255

CHAPTER II.

PROTOZOA GREGARINJ3— RHIZOPOD A — POLYCYSTINA — DIA-

TOMACE-S! — FOSSIL INFUSORIA — SPONGES — VORTICELLA —
ACTINIZO A — ROTIFERA— POLYPIFER A — ACALEPH A — ECHI-
NODERMATA 366

CONTENTS. XV

CHAPTER III.

PAGB

POLYZOA — MOLLUSCA — GASTEROPODA — BRAOHIOPODA — CONCHI-
FERA — CEPHALOPODA — PTEROPODA — TUNICATA — CRUS-
TACEA— ENTOMOSTR AC A — CIRRI PEDA — ENTOZO A — ANNU-
LOSA — ANNELIDA 9 511

CHAPTER IV.

SUB-KINGDOM ARTICULATA — INSECTA — ARACHNIDA .... 579

CHAPTER V.

rA — PHYSIOLOGY — HISTOLOGY — BOUNDARY BE-
TWEEN THE TWO KINGDOMS— CELL THEORY— GROWTH OF
TISSUES— SPECIAL TISSUES— SKIN, NERVES, CARTILAGE,
TEETH, BONE, ETC .............. 654

CHAPTER VI.

INORGANIC OR MINERAL KINGDOM — FORMATION OF CRYSTALS

— POLARISATION — SPECTRUM ANALYSIS, ETC ..... 728

DESCRIPTION OF COLOUEED PLATES.
PLATE I.— Page 255.

PROTOPHYTA.

Fig. 1. Pezizabicolor — 2. Truffle — 3. Sphseiiaherbarum : a. piece of dead plant, with

5. herbarum natural size ; b. section of same, slightly magnified ; d. Ascus with
spores, and paraphyses more magnified — 4. Peziza pygmsea — 5. Proliferous
form -of same— 6. P. corpulasis; Ascus with spores and paraphyses,
merely given as a further illustration of structure in Peziza — 7. Yeast,
good — 8. Yeast, exhausted— 9. Phyllactinia guttata — 10. Yeast with fayus
spores and mycelium— 11. Favus ferment, with torulse and bacteria-like
bodies— 12. Puccinia-like-form in ditto, growing from saccharine solution —
13. Aerozoa — 14. Sporules, <fec. from eczema produced by yeast — 15. Volvox
globator— 16. Amoeboid condition of portion of volvox— 17. Puccinia buxi—
18. Ditto, more enlarged— <17 to 20 illustrate Coniomycetes)—lQ. JBcidium
grossularise, transverse section of leaf of currant affected by : a. spermo-
gones on upper surface ; ft. perithecia with spores — 20. Phragmidium bul-
bosum, development of — 21. Parmelia parietina, trans, section through a
spermogone, showing green gonidia and spermatia escaping — 22. .tEcidium
berberidis, from leaf of berberry- 23. Vaucheria sessilis— 24. Stephano-
sphsera pluvialis : a. Full-grown example, germ-cells spindle-shaped, with
protoplasmic elongations, ft. Resting-cell. c. division into four. d. Free
swimming ciliated young specimen, e. Amoeboid condition— 25. a, 6, c, d, e,
f and g, Development of Lichen gonidia — 26. Parmelia stellaris (Lichen),
vertical section through apothecium, showing asci, spores, and paraphyses,
with gonidia and filamentous medulla, a. Spermatophore with spermatia
— 27. Moss gonidia assuming amoeboid form.

The intention of this plate has been, first to show illustrations of
various forms of Protophytes, as the lowest types of vegetable
structure ; (from 7 to 14), supposed modes of development or rudi-
mentary conditions ; and Confervoideee illustrated by Vaucheria in
the Siphonacese, f. 23, Stephanosphsera 24, and Volvox 15, in the
Volvocinese ; and their remarkable amoeboid conditions illustrated
by 16, 24 e, and 27. The protean forms assumed in development
by 7 to 14 ; 24 a to e ; 25 a to g, and 27.

PLATE II.— Page 274.

PROTOPHYTA. AIGM.

Fig. 27. Ceramium acanthonotum — 28. Triploceras gracile— 29. Cosmanum
radiatum— 30. Micrasterias denticulata — 31. Docidium pristidse — 32. Calli-
thamnion plumula — 33. Diatomacese, living : a. Licmophora splendida ;

6. Achnanthes longipes ; c. Grammatophora marina. These figures are in-
tended to show the general character of the endochrome and growth of
frustule — 34. Callithamnion refractum — 35, Jungermannia albicans. b. re-
presents elater and spores— 36. Leaf with antheridia, or male elements, which
are represented more magnified at a to the left of the figure — 37. Ceramium-
echinotum — 38. Pleurosigma angulatum, side view— 39. Delesseria hypo-
glossum— 40. Pleurosigma angulatum, front view, endochrome not repre-
sented— 41. Ceramium flabelligerum.

The intention of this plate is chiefly to show various forms of
Algse. The figures of Desmids, 28 to 33, illustrate the appearance
6

XV111 DESCRIPTION OP COLOURED PLATES.

of the endochrome, and introduce some new forms, described by
E. G. Lobb and W. Archer, Quar. Jour. Micro. Sci. vol. v. 1865,
p. 255 : and 38, 40 to illustrate diatom circulation.

PLATE III.— Page 376.

PKOTOZOA — EHIZOPODA.

Figs. 43, 44, 45, 46, 47, 48, 49, 50, 51, 52. These figures are from diagrams by
Major Owen, to illustrate a paper given in Jour. Linn. Soc. vol. viii. p. 202.
They illustrate forms of living Polycystina, sketched from life by Major
Owen, and show the richly coloured appearance of the sarcode ; figs. 48 to 52
— 53. Monocystis lumbricorum, round form — 54. Monocystis lumbricorum,
the usual elongated shape — 55. Monocystis serpulae — 56. Gregarina Sie-
boldii ; illustration of septate form, with reflexed hook-like processes—
57. Monocystis lumbricorum, encysted — 58. Monocystis lumbricorum,
more advanced and pseudo-naviceUae forming —59. Monocystis lumbricorum,
free pseudo-navicella of— 60, 61. Monocystis lumbricorum, amoeboid forms
of— 62. Cruciate sponge-spicule— 63. Asteromma Humboldtii— 64. Ed'zoon
Canadense, represents appearance of a portion of the natural size— 65. Eo-
zoon Canadense, magnified, showing portions of cell-walls left uncoloured,
the animal sarcode inhabiting it coloured dark green as in nature, and
converted by fossilization into a siliceous mineral : the narrow bands pass-
ing between these are processes (stolons) of the same substance — 66. Acti-
nophrys Sol, budding— 67. Euglena viridis ; a. contracted, b. elongated form
— 68. Acineta tuberosa — 69. OBcistes longicornis (Davis). — 70. Oxytricha
gibba (side view)— 71. Oxytricha pellionella —72. Limnias (? n. sp.)— 73.
Cyclidium glaucoma— 74. Glaucoma scintillans— 75 to 79, 80 to 85, illustrate
forms of Foraminifera found by Major Owen, living— 75. Globigerina (Or-
bulina) acerosa, n. sp., broken open to show interior— 76. Globigerina
(OrbuHna) continens, n. sp. broken open to show interior— 77. Globigerina
hirsuta — 78. Globigerina (Orbulina) universa — 79. Globigerina bulloides —
80. Conochilus vorticella— 81. Globigerina bulloides— 82. Globigerina in-
flata, sinistral shell— 83. Pulvinulina Micheliniana— 84. Pulvinulina Canari-
ensis— 85. P. Menardii.

The figures of recent Polycystina illustrate the surface-fauna of
mid-ocean ; the original drawings were made from living specimens,
as were those of the . Foraminifera ; they well represent in their
natural state these elegant and interesting objects. 53 to 61 give
some idea of the state of our knowledge of forms and life-history
of the Gregarinse. Figures of Infusoria 67, 68, 70, 71, 73, 74 :
69, 72, new forms of Eotifera.

PLATE IV.— Page $11.

POLTZOA.

Fig. 86. Hartea elegans— 87. Side view of Synaptaspicula— 88. Ophiocomarosola
(very immature specimen), a. Claw hooks, b. Palmate spicula. The develop-
ment of this creature has been described by G. Hodge, in Transactions of
Tyneside Naturalists' Field-Club — 89. Spine of a star-fish, particularly
interesting as showing the reticular calcareous network obtaining in this
as in all other hard parts of the Echinodermata — 90. Very minute Spa-
tangus, obtained from stomach of a bream : many of the spines are gone,
but the structure of the shell is intact and forms a beautiful object, interest-
ing in connexion with the source whence obtained— 91. Ophiocoma neglecta ;
wriggling or brittle Starfish. The plate does not admit of a figure on a

scafe sufficient to show the. full beauty of this object — 92. Tubularia Du-
dibulata from Uraster glacialis— 94. Pedi-

mortierii — 93. Pedicellaria mandibulat

DESCRIPTION OF COLOURED PLATES. XIX

cellaria forcepiforma, from the same — 95. Cristatella mucedo, statoblast —
96. Cristatella mucedo, statoblast, edge-view— 97. Early stage of develop-
ment of same — 98. Lophopus crystallinus — 99. PlumateUa repens and ova,
on a piece of submerged stem— 100. Tsenia echinococcus— 101. Hydatids in
human liver ^-102. Bilharzia haematobia — 103. Amphistoma conicum — 104.
Trichina spiralis from Hambro' pork— 105. Trichina spiralia extracted—
106, 107. Fasciola gigantea, after Cobbold.

PLATE y.—Page 538.

MOLLT7SCA.

Fig. 108. Velutina Isevigata, portion of lingual membrane — 109. Velutina Isevi-
gata, part of mandible— 110. Hybocystis blennius, portion of palate— 111.
Sepia officinalis, portion of palate— 112. Aplysia hybrida, part of man-
dible— 113. Loligo vulgaris, part of palate — 114. Haliotis tuberculatus, part
of palate— 115. Cistula catenata, part of palate— 116. Patella radiata, part
of palate — 117. Acmecea virginea, part of palate — 118. Cymba olla, part of
palate — 119. Scapander ligniarius— 120. Oncidoris bilamellata, part of
palate— 121. Testacella Maugei, part of palate— 122. Pleurobranchus plu-
mula, part of mandible — 123. Turbo marmoratus, part of palate.

Figs. 108 to 123, Lingual membranes of Molluscs ; the drawings
made by Mrs. Maples from specimens in the late S. P. Wood-
ward's collection, now the property of F. E. Edwards, Esq.

Chosen without any special order, and simply as showing good
examples of the wonderful forms met with in the mouth-armature
of Gasteropod and Cephalopod Mollusca ; viewed by polarised light
and selenite stage.

PLATE VI.— Page 576.

INSECTA.

Fig. 124. Egg of Caradina Morpheus, Mottled Rustic Moth— 125. Egg of Tortoise-
shell Butterfly, Vanessa Urtica — 126. Egg of Common Footman, Lithosia
complanula — 127. Egg of Shark Moth, Cucullia Umbratica — 128. Maple-
aphis — 129. Egg-shell of Acarus, empty— • 130. Egg of House-Fly — 131.
Mouth of Tsetse- Fly, Glossina morsitans— 132. Vapourer Moth, Orgyia
antiqua : antenna of male— 133. Vapourer Moth, antenna of female ; a.
branch more magnified to show rudimentary condition of the parts —
134. Tortoise-shell Butterfly; head in profile, showing large compound
eye, one of the palpi, and spiral tongue— 135. Tortoise-beetle, Cassida
viridis ; under surface of left fore-foot, to show the bifurcate tenent ap-
pendages, one of which is given at a. more magnified. This form of
appendage is characteristic of the family. See West on Feet of Insects,
Linn. Trans, vol. xxiii. tab. 43 — 136. Egg of Blue Argus Butterfly,
Polyommatus Argus — 137. Egg of Mottled Umber, Erannis Defolaria—
138. Egg of Ennomos erosaria, Thorn-Moth— 139. Egg of Aspilates Qilvaria,
Straw Belle — 140. Blow-fly, Musca Voniitoria; left fore-foot, under-
surface, to show teuent hairs; a b more magnified; a from below, 6
from the side— 141. House-fly larva — 142. Amara communis, left fore-foot,
under-surface, to show form of tenent appendages, of which one is given
more magnified at a. These, in the ground beetles, are met with only in
the males, and seem to be used for sexual purposes. The way in which
they are protected when not in use is shown by T. West— 143. Ephydra
riparia : left fore-foot, under-surface. This fly is met with sometimes in
immense numbers on the water in salt-marshes ; it has no power of climb-
ing on glass, which is explained by the structure of the tenent hairs ;
the central tactile organ also is very peculiar, the whole acting as a float,
one to each foot, to enable the fly to rest on the surface of the water ; a. one

XX DESCRIPTION OF COLOURED PLATES.

of the external hairs— 144. Egg of Bot-Fly ; the larva just escaping— 145.
Egg of parasite of Pheasant— 146. Egg of Scatophaga— 147. Egg of parasite
of magpie— 148. Egg of Jodisvernaria (Small Emerald Butterfly).

PLATE VII.— Page 654.

VERTEBRATA.

Fig. 149. Toe of mouse, integuments, bone of foot, and vessels— 150. Tongue of
mouse, showing erectile papillae, muscular layer, &c.— 151. Brain of rat,
showing its vascular supply — 152. Tongue of cat, showing fungi-form papillae,
with capillary loops passing into them, vessels, <fec.; perpendicular section
—153. Kidney of cat, showing Malpighian turfts and arteries— 154. Small
Intestine of rat, showing villi and layer of mucous membrane — 155. Nose of
mouse, showing vascular supply to roots of whiskers— 156. Vascular supply
to internal gill of tadpole, during one phase of its development— 157. Sec-
tion through sclerotic and retina of cat's-eye, showing vascular supply of
choroid and other coats— 158. Internal gill of tadpole, fully developed, exhi-
biting crests and vascular system, after Whitney.

This plate is designed to show the value of injected preparations
in the delineation of animal structures. By thus artificially re-
storing the blood and distending the tissue, a much better idea is
obtained of the relative condition of parts during life, while we
receive much assistance in the elucidation of complicated and deli-
cate membranes, the appearance of erectile tissues, papillae, &c.

PLATE VIII.— To face Title.

POLARISCOPE OBJECTS.

Fig. 158. New Red Sandstone— 159. Quartz— 160. Granite— 161. Sulph. Copper
- 162. Saliginine — 163. Sulph. Iron and Cobalt, crystallized in the way
described by Thomas— 164. Borax — 165. Sulph. Nickel and Potash— 166.
Kreatine — 167. Starch granules — 168. Aspartie Acid — 169. Fibre-Cells,
Orchid.— 170. Equisetum cuticle— 171. Spicula Holothuria, Australia— 172.
Spicula Holothuria, Port Essington — 173. Deutzia Scabra ; upper and under
surface — 174. Cat's tongue, process— 175. Prawn shell, exuvia with crystals
of lime— 176. Grayling scale — 177. Scyllium oaniculum scale — 178. Rhi-
noceros horn, transverse section — 179. Horse hoof— 180. Dytiscus, elytra
with crystals of lime.

This plate is especially intended to illustrate the beautiful and
gorgeous spectacle produced by polarised light on the various
objects here grouped together. It will be seen that all structures
belonging either to the animal, vegetable, or mineral kingdoms in
which the power of unequal or double refraction is suspected to be
present, are those which may be submitted to this mode of miwo-
ohemical investigation.

PLATE IX.— Woodcut.— Page 498.

ASTEROIDEA— ECHINID^I— CRUSTACEA, &c.

THE MICROSCOPE.

PART I.

HISTORY OF THE INVENTION AND IMPROVEMENTS OF
THE MICROSCOPE.

CHAPTER I.

HISTORY OF THE MICBOSCCPE.

HE instrument known as the Mi-
croscope derives its name from
two Greek words, /UK/OOS, small)
and or/coTreo), to mew; that is, to
see or view such minute objects
as without its aid would be in-
visible.

The honour of the invention
is claimed by the Italians and the
Dutch; the name of the inventor,
however, is lost. Probably the
discovery did not at first appear
sufficiently important to engage
the attention of those men who,
by their reputation in science, were able to establish an
opinion of its merit, and to hand down the name of its
inventor to succeeding ages.

If we consider the microscope as an instrument con-
sisting of one lens only, it is not at all improbable that it
was known at a very early period, nay even in a degree to

2 HISTORY OP THE MICROSCOPE.

the Greeks and Romans ; at any rate, it is tolerably certain
that spectacles were used as early as the thirteenth century.
Now as the glasses of these were made of different con-
vexities, and consequently of different magnifying powers,
it is natural to suppose that smaller and more convex
lenses were made, and applied to the examination of
minute objects. Many among the learned refuse to the
ancients a knowledge of magnifying lenses, and & fortiori
that of refracting tebscopes, since, according to them, the
Greeks and Romans had only very imperfect notions with
respect to the fabrication of glass.

From a passage in Aristophanes it is plain that globules
of glass were sold at the shops of the grocers of Athens, in
the time of that comic author. He speaks of them as
" burning spheres."

Pliny states that the immense theatre (it was capable of
containing eighty thousand persons) erected at Rome by
Scaurus, son-in-law of Sylla, was three stories in height,
and that the second of these stories was entirely inlaid
with a mosaic of glass. *

Ptolemy, in his " Optics," has inserted a table of the
refractions which light experiences under different angles
of incidence, in passing from air into glass. The values
of these angles, which differ only in a slight degree from
those obtained in the present day by means of similar ex-
periments, prove that the glass of the ancients differed
very little from that manufactured in our own times.

There is in the French Cabinet of Medals a seal, said to
have belonged to Michael Angelo, the fabrication of which,
it is believed, ascends to a very remote epoch, and upon
which fifteen figures have been engraven in a circular
space of fourteen millimetres in diameter. These figures
are not all visible to the naked eye.

Cicero makes mention of an Iliad of Homer written
upon parchment, which was comprised in a nutshell.

Pliny relates that Myrrnecides, a Milesian, executed in
ivory a square figure which a fly covered with its wings.

Unless it be maintained that the powers of vision of our
ancestors surpassed those of the most skilful modern
artists, these facts establish that the magnifying property
of lenses was known to the Greeks and Romans nearly

HISTORY OF THE MICROSCOPE. 3

two thousand years ago. We may besides advance a step
further, and borrow from Seneca a passage whence the
same truth will emerge in a manner still more direct and
decisive. In the " Natural Questions " we read : " How-
ever small and obscure the writing may be, it appears
larger and clearer when viewed through a globule of glass
filled with water."

Dutens has seen in the Museum of Portici ancient
lenses which had a focal length of only nine millimetres.
He actually possessed one of these lenses, but of a longer
focus, which was extracted from the ruins of Hercu-
laneuin.

At the meeting of the British Association, held at
Belfast in the year 1852, Sir David Brewster showed a
plate of rock-crystal worked into the form of a lens, which
was recently found among the ruins of Nineveh. Sir
David Brewster, so competent a j udge in a question of this
kind, maintained that this lens had been destined for
optical purposes, and that it never was an article of dress.

It is not difficult to fix the period when the microscope
first began to be generally known, and to be used for the
purpose of examining minute objects ; for though we are
ignorant of the name of the first inventor, we are acquainted
with the names of those who introduced it to public view.
Zacharias Jansens and his son are said to have made micro-
scopes before the year 1590 : about that time the ingenious
Cornelius Drebell brought one made by them with him
to England, and showed it to William Borrell and others.
It is possible this instrument of Dreb ell's was not strictly
what is now called a microscope, but was rather a kind
of microscopic telescope, something similar in principle
to that lately described by M. Aepinus in a letter to the
Academy of Sciences at St. Petersburg. It was formed of
a copper tube six feet long and one inch in diameter,
supported by three brass pillars in the shape of dolphins ;
these were fixed to a base of ebony, on which the objects
to be viewed by the. microscope were placed. Fontana, in
a work which he published in 1646, says that he had made
microscopes in the year 1618 : this may be perfectly true,
without derogating from the merit of the Jansens; for
we have many instances in our own times of more than
B 2

4 HISTORY OP THE MICROSCOPE.

one person having made the same invention nearly simul-
taneously, without any communication from one to the
other. In 1685 Stelluti published a description of the
parts of a bee, which he had examined with a microscope.

The history of the microscope, like that of nations and
arts, has had its brilliant periods, in which it shone with
uncommon splendour, and was cultivated with extraordi-
nary ardour ; and these have been succeeded by intervals
marked with no discovery, and in which the science seemed
to fade away, or at least to lie dormant, till some favour-
able circumstance — the discovery of a new object, or some
new improvement in the instruments of observation —
awakened the attention of the curious, and reanimated
their researches. Thus, soon after the invention of the
microscope, the field it presented to observation was culti-
vated by men of the first rank in science, who enriched
almost every branch of natural history by the discoveries
they made by means of this instrument.

The Single, or Simple Microscope. — We shall first speak of
the single microscope, that having been invented and used
long before the double or compound microscope. When
the lenses of the single microscope are very convex, and
consequently the magnifying power great, the field of view
is small ; and it is so difficult to adjust with accuracy their
focal distance, that it requires some practice to render the
use of them familiar. It was with an instrument of this
kind that Leeuwenhoek and Swammerdam, Lyonet and
Ellis, examined the invisible forms of nature, and by their
example stimulated others to the same pursuit.

About the year 1665, small glass globules began to be
occasionally applied to the single microscope, instead of
convex lenses ; and by these globules an immense magni-
fying power was obtained. Their invention has been
generally attributed to M. Hartsoeker ; though it appears
that we are really indebted to the celebrated Dr. Hooke
for this discovery, for he described the manner of making
them in the preface to his Micrographia Illustrata, pub-
lished in the year 1656.

Mr. Stephen Gray1 having observed some irregular
particles within a glass globule, and finding that they

(1) Philosophical Transactions, 1696.

HISTORY OP THE MICROSCOPE. 5

appeared distinct and prodigiously magnified when held
close to his eye, concluded, that if he placed a globule of
water in which there were any particles more opaque than
the water near his eye, he should see those particles dis-
tinctly and highly magnified. The result of this idea far
exceeded his expectation. His method was, to take on a
pin a small portion of water which he knew contained
gome minute animalcules ; this he laid on the end of a
small piece of brass wire, till there was formed somewhat
more than a hemisphere of water ; on applying it then to
the eye, he found the animalcules enormously magnified ;
for those which were scarcely discernible with his glass
globules, with this appeared as large as ordinary-sized
peas.

Dr. Hooke thus describes the method of using this
water-microscope : " If you are desirous," he says, " of
.obtaining a microscope with one single refraction, and
consequently capable of procuring the greatest clearness
and brightness any one kind of microscope is susceptible
of, spread a little of the fluid you intend to examine on
a glass plate ; bring this under one of your globules, then
move it gently upwards till the fluid touches the globule,
to which it will soon adhere, and that so firmly as to bear
being moved a little backwards or forwards. By looking
through the globule, you will then have a perfect view of
the animalcules in the drop."

The construction of the single microscope is so simple,
that it is susceptible of but little improvement, and has
therefore undergone few alterations ; and these have been
chiefly confined to the mode of mounting it, or to addi-
tions to its apparatus. The greatest improvement this
instrument has received was made by Lieberkuhn,1 about
the year 1740 : it consists in placing the small lens in the
centre of a highly-polished concave speculum of silver, by
which means a strong light is reflected upon the upper
surface of an object, which is thus examined with great
ease and pleasure. Before this contrivance, it was almost
impossible to examine small opaque objects with any
degree of exactness ; for the dark side of the object being
next the eye, and also overshadowed by the proximity of

(1) Dr. Nathaniel Lieberkuhn of Berlin.

HISTORY OF THE MICKOSCOPE.

the instrument, its appearance was necessarily obscure and
indistinct. Lieberkuhn adapted a separate microscope to
every object : but all this labour was
not bestowed on trifling objects ; his
were generally the most curious ana-
tomical preparations, twelve of which,
with their microscopes, are deposited in
the Museum of the Eoyal College of
Surgeons.

Lieberkuhn's instrument, fig. 1, is
thus described by Professor Quekett r1 a b
represents a piece of brass tube, about an
inch long and an inch in diameter, which
is provided with a cap at each extremity ;
the one at a carries a small double -con vex
lens of half an inch in focal length, whilst
the one at b carries a condensing lens three-
quarters of an inch in diameter.

A vertical section of one of these instru-
ments is seen in fig. 2 : a represents the mag-
nifier, which is lodged in a cavity formed
partly by the cap a, and by the silver cup
or speculum I. In front of the lens is the
speculum I, which is a quarter of an inch
thick at. its edge, and whose focus is about
half an inch j in front of this again there is
a disk of metal c, three-eighths of an inch in
diameter, connected by a wire with the small
Fis- h knob d • upon this disk the injected object
is fastened, and is covered over with some
kind of varnish which has dried of a hemispherical figure.
Between this knob and the inside and
outside of the tube there are two slips of
thin brass, which act as springs to keep
the wire and disk steady. When the
knob is moved, the injected object is
carried to or from the lens, so as to be in
its focus, and to be seen distinctly, whilst
the condensing lens b serves to concen-
trate the light on the speculum. To the

(1) Practical Treatise on the Microscope, p. 16.

Fig. 2.

Lieberkuhn's Micro-
scope.

HISTORY OF THE MICROSCOPE. 7

lower part of the tube a handle of eboiry, about three
inches in length, is attached by a brass ferrule and two
screws. The use of this instrument is obvious : it is
held in the hand in such a position that the rays of light
from a lamp or white cloud may fall on the condenser b,
by which they are concentrated on the speculum I ; this,
again, further condenses them on the object and the
disk c, which object, when so illuminated, can readily be
adjusted by the little knob d, so as to be in the focus of
the small magnifier at a.

We must not omit in this place some account of Leeu-
wenhoek's microscopes, which were rendered famous
throughout all Europe, on account of the numerous dis-
coveries he had made with them. At his death he be-
queathed a part of them to the Royal Society.

The microscopes he used were all single, and fitted up in
a convenient and simple manner : each consisted of a very
small double- con vex lens, let into a socket between two
plates riveted together, and pierced with a small hole ; the
object was placed on a silver point or needle, which, by
means of screws adapted for that purpose, might be turned
about, raised or depressed at pleasure, and thus be brought
nearer to, or be removed farther from the glass, as the eye
of the observer, the nature of the object, and the conve-
nient examination of its parts required.

Leeuwenhoek fixed his objects, if they were solid, to these
points with glue ; if they were fluid, he fitted them on a
little plate of talc, or thin-blown glass, which he afterwards
glued to the needle in the same manner as his other
objects. The glasses were all exceedingly clear, and of
different magnifying powers, proportioned to the nature of
the object and the parts designed to be examined. He
observed, in his letter to the Royal Society, that "from
upwards of forty years' experience, he had found the most
considerable discoveries were to be made with glasses of
moderate magnifying power, which exhibited the object
with the most perfect brightness and distinctness." Each
instrument was devoted to one or two objects j hence he
had always some hundreds by him.

The three first compound microscopes that attract our
notice are those of Dr. Hooke, Eustachio Divini, and Philip

8 HISTORY OF THE MICROSCOPE,

Bonnani. Dr. Hooke gives us an account of his in the
preface to his Micrographia, published in the year 1667 :
it was about three inches in diameter, seven inches long,
and furnished with four draw-out tubes, by which it might
be lengthened as occasion required ; it had three glasses —
a small object-glass, a middle glass, and a deep eye-glass.
Dr. Hooke used all the glasses when he wanted to take in
a considerable part of an object at once, as by the middle
glass a number of radiating pencils were conveyed to the
eye which would otherwise have been lost ; but when he
wanted to examine with accuracy the small parts of any
substance, he took out the middle glass, and only made
use of the eye and object lenses ; " for," he writes, " the
fewer the refractions are, the clearer and brighter the
object appears."

Dr. Hooke also gave us the first and most simple method
of finding how much any compound microscope magnifies
an object. He placed an accurate scale, divided into very
minute parts of an inch, on the stage of the microscope ;
adjusted the microscope till the divisions appeared distinct,
and then observed with the other eye how many divisions
of a rule similarly divided and laid on the stage were
included in one of the magnified divisions ; " for if one
division, as seen with one eye through the microscope,
extends to thirty divisions on the rule, which is seen by
the naked eye, it is evident that the diameter of the object
is increased or magnified thirty times."

An account of Eustachio Divini's microscope was read
at the Royal Society in 1668. It consisted of an object-
lens, a middle glass, and two eye-glasses, which were plano-
convex lenses, and were placed so that they touched each
other in the centre of their convex surfaces. The tube in
which the glasses were enclosed was as large as a man's
leg, and the eye-glasses as broad as the palm 'of the hand.
It had four several lengths : when shut up was 1 6 inches
long, and magnified the diameter of an object 41 times,
at the second length 90, at the third length 111, and at
the fourth length 143 times. It does not appear that
Divini varied the object-glasses.

Philip Bonnani published an account of his two micro-
scopes in 1698. Both were compound. The first waa

HISTORY OF THE MICROSCOPE. 9

similar to that which Mr. Martin published as new, in his
Micrographia Nova, in 1712. His second was like the
former, composed of three glasses, one for the eye, a
middle glass, and an object lens; they were mounted in a
cylindrical tube, which was placed in a horizontal position ;
behind the stage was a small tube with a convex lens at
each end ; beyond this was a lamp ; the whole capable of
various adjustments, and regulated by a pinion and rack.
The small tube was used to condense the light on to the
object.

A short time before this, Sir Isaac Newton having dis-
covered his celebrated theory of light and colours, was led
to improve the telescope, and apply his principles most
successfully to the construction of a compound reflecting
microscope. On the 6th of February, 1 672, he communi-
cated to the Eoyal Society his " design of a microscope by
reflection." It consisted of a concave spherical speculum
of metal, and an eye-glass which magnified the reflected
image of any object placed between them in the conjugate
focus of the speculum. He also pointed out the proper
mode of illuminating objects by artificial light, as he
describes it, "of any convenient colour not too much
compounded," mo?zo-chromatic. We find other two plans
of this kind ; the first that of Dr. Robert Barker, and the
second that of Dr. Smith. In the latter there were two
reflecting mirrors, one concave, and the other convex : the
image was viewed by a lens. This microscope, though far
from being executed in the best manner, performed, says
Dr. Smith, very well, so that he did not doubt it would
have excelled others, had it been properly finished.

In 1738, Lieberkuhn's invention of the solar microscope
was communicated to the public. The vast magnifying
power obtained by this instrument, the colossal grandeur
with which it exhibited the " minutiae of nature/' the plea-
sure which arose from being able to display the same object
to a number of observers at the same time, by affording a
new source of rational amusement, increased the number
of microscopic observers, who were further stimulated to
the same pursuits by Mr. Trembley's famous discovery of
the polype. The discovery of the wonderful properties of
this little animal, together with the works of Mr. Trembley;

10 HISTORY OF THE MICROSCOPE.

Mr. Baker, and Mr. Adams, combined to spread the repu-
tation of the instrument.

In 1742, Mr. Henry Baker, F.R.S., published an ad-
mirable treatise on the microscope. He also read several
papers before the Royal Society on the subject of his
microscopic discoveries. In the wood-cut (fig. 3) at the
end of this chapter we have represented an elegant scroll
" pocket microscope with a speculum," described by him
as a new invention.

In 1770, Dr. Hill published a treatise, in which he
endeavours by means of the microscope to explain the
construction of timber, and to show the number, the
nature, and office of its several parts, their various
arrangements and proportions in the different kinds ; and
he points out a way of judging, from the structure of
trees, the uses they will best serve in the affairs of life.

M. L. F. Delabarre published an account of his micro-
scope in 1777. It does not appear that it was superior in
any respect to those that were then made in England. It
was inferior to some; for those made by Mr. Adams, in
1771, possessed all the advantages of Delabarre's in a
higher degree, except that of changing the eye-glasses.

In 1774, Mr. George Adams, the son of the above, im-
proved his father's invention, and rendered it useful for
viewing opaque as well as transparent objects. This in-
strument, made and described by him,1 continued in use
up to the time of the invention of the achromatic im-
provement, proposed and made in 1815 for Amici, who
subsequently gave so much time to the investigation of
polarised light, and the adaptation of a polarising apparatus
to the microscope.

In 1812, Dr. Wollaston proposed a doublet in which
the glasses were in contact, under the name of a " Periscopic
Microscope." And he says, "with this doublet I have
seen the finest striee and serratures on the scales of the
lepisma and podura, and the scales on a gnat's wing."

In the year 1816, Frauenhofer, a celebrated optician of
Munich, constructed object-glasses for the microscope of a
single achromatic lens, in which the two glasses, although
in juxtaposition, were not cemented together: these glasses

(1) Microscopical Essays, 1787.

HISTORY OF THE MICROSCOPE. 11

were very thick, and of long focus. Although such con-
siderable improvements had taken place in the making of
achromatic object-glasses since their first discovery by
Euler in 1776, we find, even at so late a period as 1821,
M. Biot writing, "that opticians regarded as impossible
the construction of a good achromatic microscope." Dr.
Wollaston also was of the same opinion, " that the com-
pound instrument would never rival the single."

In 1823, experiments were commenced in France by
M. Selligues, which were followed up by Frauenhofer in
Munich, by Amici in Modena, by M. Chevalier in Paris,
and by the late Dr. Goring and Mr. Tulley in London. To
M. Selligues we are indebted for the first plan of making
an object-glass composed of four achromatic compound
lenses, each consisting of two lenses. The focal length of
each object-glass was eighteen lines, its diameter six lines,
and its thickness in the centre six lines, the aperture only
one line. They could be used combined or separated.

A microscope constructed on this principle, by M. Che-
valier, was presented by M. Selligues to the Academic des
/Sciences on the 5th of April, 1824. In the same year, and
without a knowledge of what had been done on the Con-
tinent, the late Mr. Tulley, at the suggestion of Dr. Goring,
constructed an achromatic object-glass for a compound
microscope of nine-tenths of an inch focal length, com-
posed of three lenses, and transmitting a pencil of
eighteen degrees ; this was the first that had been made in
England.

Sir David Brewster first pointed out in 1813, the value
of precious stones, the diamond, ruby, garnet, &c., for the
construction of microscopes. " The durability," he says,
" of lenses made of precious stones is one of their greatest
recommendations. Lenses of glass undergo decomposition,
and lose their polish in course of time. Mr. Baker found
the glass lenses of Leeuwenhoek utterly useless after they
became the property of the .Royal Society. The glass
articles found in Nimroud were decomposed, while the
rock crystal lens was uninjured." Mr. Pritchard at one
time made two plano-convex lenses from a very perfect
diamond, one the twentieth of an inch focus, which waa

12 HISTORY OF THE MICROSCOPE.

purchased by the late Duke of Buckingham, and another
the thirtieth of an inch focus.

In March 1825, M. Chevalier presented to the Society
for the Encouragement of the Sciences, an achromatic
lens of four lines focus, two lines in diameter, and one line
in thickness in the centre. This lens was greatly superior
to the one before noticed, which had been made by him
for M. Selligues.

In 1826, Professor Amici, of Modena, who from the
year 1815 to 1824 had abandoned his experiments on the
achromatic object-glass, was induced, after the report of
Fresnel to the Academy of Science, to resume them ; and
in 1827 he brought to this country and to Paris a hori-
zontal microscope, in which the object-glass was composed
of three lenses superposed, each having a focus of six lines
and a large aperture. This microscope had also extra eye-
pieces, by which the magnifying power could be increased.
A microscope constructed on Amici's plan by Chevalier,
during the stay of that physician in Paris, was exhibited
at the Louvre, and a silver medal was awarded to its
maker.1

" While these practical investigations were in progress,"
says Mr. Ross, "the subject of achromatism engaged the
attention of some of the most profound mathematicians in
England. Sir John Herschel, Professors Airy and Barlow,
Mr. Coddington, and others, contributed largely to the
theoretical examination of the subject; and though the
results of their labours were not immediately applicable
to the microscope, they essentially promoted its im-
provement."

Mr. Jackson Lister, in 1829, succeeded in forming a
combination of lenses upon the theory propounded by
these gentlemen, and effected one of the greatest improve-
ments in the manufacture of object-glasses, by joining
together a plano-concave flint lens and a convex, by means
of a transparent cement, Canada balsam. This is desirable

(1) In 1855, when the Jury on Microscopes at the Paris Exposition were com-
paring the rival instruments, Professor Amici brought a compound achromatic
microscope, comparatively of small dimensions, which exhibited certain striae
in test objects better than any of the instruments under examination. This
superiority was produced by the introduction of a drop of water between the
object and the object-glass.

HISTORY OF THE MICROSCOPE. 13

to be taken as a basis for the microscopic object-glass : it
diminishes very nearly half the loss of light from reflec-
tion, which is considerable at the numerous surfaces of a
combination ; the clearness of the field and brightness of
the picture is evidently increased by doing this ; and it
prevents any dewiness or vegetation from forming on the
inner surfaces. Since this time, Mr. Ross has been con-
stantly employed in bringing the manufacture of object-
glasses to their greatest perfection, and at length they
have attained to their present improved manufacture.
Having applied Mr. Lister's principles with a degree of
success never anticipated, so perfect were the corrections
given to the achromatic object-glass, so completely were
the errors of sphericity and dispersion balanced or de-
stroyed, that the circumstance of covering the object
with a plate of the thinnest glass or talc disturbed the
corrections, if they had been adapted to an uncovered
object, and rendered an object-glass which was perfect
under one condition sensibly defective under the other.
Here was another and unexpected difficulty to be over-
come, but which was finally accomplished; for in a com-
munication made to the Society of Arts in 1837, Mr. Ross
stated, that by separating the anterior lens in the combi-
nation from the other two, he had been completely suc-
cessful. The construction of this object-glass will be
illustrated and explained in a future chapter.

The rapid improvement in the manufacture of the
achromatic compound microscope in this country has been
greatly furthered by the spirit of liberality evinced by Sir
David Brewster, the late Dr. Goring, Mr. R. H. Solly,
and Mr. Bowerbank. To the patronage of Dr. Goring
we owe the construction of the first triplet achromatic
object-glass, of the diamond lens, and of the improved
reflecting instrument of Amici by Cuthbert.

The achromatic microscopes now manufactured by our
London makers, Mr. Ross, Messrs. Powell and Lealand,
and Messrs. Smith and Beck, are unequalled in any part
of the world. This opinion is confirmed by the reports of
the juries on the Exhibition of Works of Industry of all
Nations, 1851; at that time the instruments exhibited by
Mr. Ross and Messrs. Smith and Beck, by far excelled

14 HISTORY OF THE MICROSCOPE.

those of all other countries. Messrs. Powell and Lealand's
microscope, with object-glasses, was selected by the Royal
Society as the best against all competitors. See Juries'
Reports for much interesting matter on this subject;
article "Microscope" Penny Cyclopaedia, by Mr. Ross;
Practical Treatise on the Microscope, by Professor Quekett ;
Sir David Brewster's Treatise on the Microscope; Dujardin's
Observateur; Maudl, Traite pratique du Microscope; Dr
Robin> Du Microscope, &c.

Pig. S.— Baker's Scroll or Pocket Microscope, and the Modern Compound
Microscope of W. Ladd's manufacture.

CHAPTER II.

MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IN THE CONSTRUCTION
OF THE MICROSCOPE— LENSES— MODE OF ESTIMATING THEIP. POWBB,
ETC. — ACHROMATIC LENSES — MAGNIFYING FOWEE —
WOLLASTON'S DOUBLET — CODDINGTON'S LENS — EOSS'S
SIMPLE AND COMPOUND MICROSCOPES — MICROMETERS,
ETC.

the construction of the modern mi-
croscope, optical and mechanical prin-
ciples of some importance are involved.
These principles we shall briefly ex-
plain, together with the more recent
improvements effected in the instru-
ment generally.1

The microscope depends for its
utility and operation upon concave
and convex lenses, and the course of
the rays of light passing through them.
Lenses are usually denned as pieces of
glass, or other transparent substances,
having their two surfaces so formed
that the rays of light, in passing
through them, have their direction
changed, and are made to converge or diverge from their
original parallelism, or to become parallel after converging
or diverging. When a ray of light passes in an oblique
direction from one transparent medium to another of a
different density, the direction of the ray is changed both
on entering and leaving ; this influence is the result of the
well-known law of refraction, — that a ray of light passing
from a rare into a dense medium is refracted towards the
perpendicular, and vice versd.

(1) For a full explanation of the laws of optics, and their application to the
construction of lenses, the reader is referred to Dr. Bird and Mr. Brooke's
"Manual of Natural Philosophy," Professor Potter's "Elementary Treatise on
Optics," Sir David firewater's "Optics," &c.

16

CONSTRUCTION OF THE MICROSCOPE.

Dr. Arnott remarks : " But for this fact, which to many
persons might at first appear a subject of regret, as pre-
venting the distinct vision of objects through all trans-
parent media, light could have been of little utility to
man. There could have been neither lenses, as now ; nor
any optical instruments, as telescopes and microscopes, of
which lenses form a part ; nor even the eye itself." Bays
of light falling perpendicularly upon a surface of glass or
other transparent substance, pass through without being
bent from the original line of their direction. Thus, if a

ray pass from k perpendicularly to the surface of the piece
of glass at e (fig. 4), it will go on to h in the right line
k e o g h. But if the same ray be directed to the surface e
obliquely, as from a, instead of passing through in a direct
line to 6 in the direction aemb, it will be refracted to d,
in a direction approaching nearer to the perpendicular
line k h. The ray a e is termed the ray of incidence, or
the incident ray ; and the angle a e k which it makes with
the perpendicular k h is called the angle of incidence.
That part of the ray from e to d passing through the
transparent medium is called the ray of refraction, or the
refracted ray ; and the angle deg which it makes with the

CONSTRUCTION OF THE MICROSCOPE. 17

perpendicular is called the angle of refraction. The ray
projected from a to e and refracted to d, in passing out of
the transparent medium as at d, is as much bent from the
line of the retracted ray e d as that was from the line of
the original ray a e b • the ray then passes from d to c,
parallel to the line of the original ray a e b. It follows,
then, that any ray passing through a transparent medium,
whose two surfaces, the one at which the ray enters, and
the one at which it passes out, are parallel planes, is first
refracted from its original course ; but in passing out is
bent into a line parallel to, and running in the same direc-
tion as the original line, the only difference being, that its
course at this stage is shifted a little to one side of that of
the original. If from the centre e a circle be described
with any radius, as d e, the arc a a' measures the angle of
incidence a e k, and the arc g' d the angle of refraction
g e d. A line a k drawn from the point a perpendicular
to k h is called the sine of the angle of incidence; and the
line d g drawn from the point d perpendicular to Tc h i&
called the sine of the angle of refraction. From the con-
clusions drawn from the principles of geometry, it has
been found, that in any particular transparent substance
the sine of the angle of incidence a k has always the same
ratio to the sine dg of the angle of refraction, no matter
what be the degree of obliquity with which the ray of inci-
dence a e is projected to the surface of the transparent
medium. If the ray of incidence passes from air obliquely
into water, the sine of incidence is to that of refraction as
4 to 3 ; if it passes from air into glass, the proportion is as
3 to 2 ; and if from air into diamond, it is as 5 to 2.

By the help of glasses of certain forms, we unite in the
same sensible point a great number of rays proceeding
from one point of an object ; and as each ray carries with
it the image of the point from whence it proceeded, and
all the rays united must form an image of the object from
whence they were emitted, this image is brighter in pro-
portion as there are more rays united, and more distinct
in proportion as the order in which they proceeded is
better preserved in their union. The point at which
parallel rays meet after converging through a lens is called
the principal focus, and its distance from the middle of

18

CONSTRUCTION OF THE MICROSCOPE.

the lens the focal length. The radiant point and its image
after refraction are called conjugate foci. These foci vary
according to the distance of the radiant points. In. every
lens the right line perpendicular to the two surfaces is
called the axis of the lens, and is seen in the annexed
figure ; the point where the axis cuts the surface is called
the vertex of the lens.

Fig. 5 is intended to represent the different forms of
lenses in use ; a is a plane glass of equal thickness

throughout; b, a meniscus, concave on one side, convex on
the other ; c, a double-concave ; d, a plano-concave ; c, a
double-convex ; /, a plano-convex.

The lenses employed in the construction of microscopes
are chiefly convex; concave lenses being only used to make
certain modifications in the course of the rays passing
through those of a convex form, whereby their perform-
ance is rendered more exact. In accordance with the laws
of refraction, when a pencil of parallel rays, passing-
through the air, impinges upon a convex surface of glass,
the rays are made to converge; for they will be bent
towards the centre of the circle, the radius being perpen-
dicular to each point of curvature. Parallel rays, falling
on a plano-convex lens, are brought to a focus at the dis-
tance of its diameter ; and conversely, rays diverging from
that point are rendered parallel. Plano-convex lenses pos-
sess properties which render them valuable in the con-
struction of microscopes.

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

CONSTRUCTION OF THE MICROSCOPE. 19

diverging from that point are rendered parallel. Hence
the focus of a double-convex lens will be at just half the
distance, or half the length, of the focus of a plano-convex
lens having the same curvature on one side. The distance
of the focus from the lens will depend as much on the
degree of curvature as upon the refracting power (called
the index of refraction) of the glass of which it may be
formed. A lens of crown-glass will have a longer focus
than a similar one of flint-glass ; since the latter has a
greater refracting power than the former. For all ordinary-
practical purposes, we may consider the principal focus —
as the focus for parallel rays is termed — of a double-convex
lens to be at the distance of its radius, that is, in its centre
of curvature ; 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. The converse of all
this occurs when divergent rays are made to fall on a
convex lens. Rays already converging are brought together
at a point nearer than the principal focus : whereas rays
diverging from a point within the principal focus are ren-
dered still more diverging, though in a diminished degree.
Rays diverging from points more distant than the prin-
cipal focus on either side, are brought to a focus beyond
it ; if the point of divergence be within the circle of curva-
ture, the focus of convergence will be beyond it ; and vice
versa. 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 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 pro-
duct by half the sum of the radii.

The refracting influence of concave lenses will be pre-
cisely 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. If
a lens be convex on one side and concave on the other,
c 2

20

CONSTKUCTION OF THE MICROSCOPE.

forming what is termed a meniscus, its effect will depend
upon the proportion between the two curvatures.

The rules by which the foci of all lenses may be found,
will be more advantageously studied in works on Optics.

As each ray carries with it the image of the object from
whence it proceeded, it follows, that if those rays, after
intersecting each other, and having formed an image at
their intersection, are again united by refraction or re-
flection, they will form a new image, and that repeatedly,
so long as their order is not disturbed. It follows, also,
that when the course of the luminous ray through several
lenses is under* consideration, we may look on the image
first produced as an object in reference to the second lens,
and may consider the second image as produced by this
object, and so on successively. This is, indeed, a principle
involved in the adaptation of lenses t^ magnifying objects ;
and in fig. 6, it is seen that if the point of light be situated

Fig. 6.

above the line of the axis, the focus will then be below it,
and vice versd; but the surface of every luminous body may
be regarded as comprehending an infinite number of such
points, from all of which a pencil of light-rays proceeds,
and is refracted according to the general law; 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. If any object be placed at twice the

CONSTRUCTION OF THE MICROSCOPE.

21

distance of the principal focus, the image being formed at
an equal distance on the other side of the lens, will be of
the same dimensions with the object, as in fig. 7; but if

Fig. 7.

the object be placed nearer to the lens, the image will be
farther from it, and of larger dimensions, as in fig. 8 ; and,

Fig. 8.

on the other hand, if the object be farther from the lens,
the image will be nearer to it, and smaller than itself.
But it is to be observed, that the larger the image is in
proportion to the object, the less bright it will be, because
the same amount of light has to be spread over a greater
surface ; whilst a smaller image will be much more
brilliant.

Aberration of Lenses. — Although the image of an object
produced by the convex lens, fig. 8, appears at first view
to be an exact reproduction of the object, it is found,
when siibmitted to rigorous examination, to be more or less
confused and indistinct : which is augmented when viewed
in a microscope. This indistinctness and confusion arises
from two causes, one depending on form, and the other on
the material of the lens. That which depends on the
form of the lens we shall now proceed to explain.

4* CONSTRUCTION OP THE MICROSCOPE.

In optical instruments the curvature of the lenses,
employed is spherical, that being the only form which
can be given by grinding with the requisite degree of
truth. But convergent lenses, with spherical curvatures,
have the defect of not bringing all the rays of light which
pass through them to one and the same focus. Each
circle of rays from the axis of the lens to its circumference
has a different focus, as shown in fig. 9. The rays a a,

Fig. 9.

which pass through the lens near its circumference, it is
seen to be more refracted, or come to a focus at a shorter
distance behind it than the rays b 6, which pass through
near its centre or axis, and are less refracted. The conse-
quence of this defect of lenses with spherical curvatures,
which is called spherical aberration, is that a well denned
image or picture is not formed by them, for when the
object is focused, for the circumferential rays, the picture
projected to the eye is rendered indistinct by a halo or
confusion produced by the central rays falling in a circle
of dissipation, before they have come to a focus. On the
other hand, when placed in the focus of the central rays,
the picture formed by them is rendered indistinct by the
halo produced by the circumferential rays, which have
already come to a focus and crossed, now fall in a state of
divergence, forming a circle of dissipation. The grosser
effects of this spherical aberration are corrected by cutting
off the passage of the rays a a, through the circumferences
of the lens, by means of a stop diaphragm, so that the
central rays, b b, only are concerned in the formation of
the picture. This defect is reduced to a minimum, by

CONSTRUCTION OF THE MICROSCOPE.

23

using the meniscus form of lens, which is the segment of
an ellipsoid instead of a sphere.

The ellipse and the hyperbola are curves of this kind,
in which the curvature diminishes from the central ray, or
axis, to the circumference b • and mathematicians have
shown how spherical aberration may be entirely removed
by lenses whose sections are ellipses or hyperbolas. For
this curious discovery we are indebted to Descartes.

If a I, a I', for example, fig. 10, be part of an ellipse

Fig. 10.

whose greater axis is to the distance between its foci // as
the index of refraction is to unity, then parallel rays
r I', r" I incident upon the elliptical surface I' a I, will be
refracted by the single action of that surface into lines
which would meet exactly in the farther focus /, if there
were no second surface intervening between I a I' and/
But as every useful lens must have two surfaces, we have
only to describe a circle I a I' round /as a centre, for 'the
second surface of the lens I ' I.

As all the rays refracted at the surface I a I' converge
accurately to / and as the circular surface I a I' is perpen-
dicular to every one of the refracted rays, all these rays
will go on to/ without suffering any refraction at the circular
surface. Hence it should follow, that a meniscus whose
convex surface is part of an ellipsoid, and whose convex
surface is part of any spherical surface whose centre is in
the farther focus, will have no appreciable spherical
aberration, and will refract parallel rays incident on its
convex surface to the farther focus.

2l CONSTRUCTION OP THE MICROSCOPE.

In like manner, a concavo-convex lens, fig. 11,11', whose
wncave surface I a' I' is a circle described round the farther

Fig. 11.

focus of the ellipse, will cause parallel rays b I, br I , to
diverge in directions I r, I'r", which, when continued back-
wards, will meet exactly in the focus/, which will be its
virtual focus.

If a plano-convex lens, fig. 12, has its convex surface
I a I' part of a hyperboloid, formed by the revolution of a

hyperbola whose greater axis is to the distance between
the foci as unity is to the index of refraction, then parallel
rays rl, r" I' falling perpendicularly on the plane surface,
will be refracted without aberration to the further focus
of the hyperboloid. The same property belongs to a
plano-concave lens having a similar hyperbolic surface, and
receiving parallel rays on its plane surface.1

(1) It must be borne in mind, that in none of those lenses would the object
be correctly eeen in focus, except at the one point known as the mathematical
or geometrical axis of the lens.

CONSTRUCTION OF THE MICROSCOPE. 25

When the convex side, of a plano-convex lens is exposed
to parallel rays, the distance of the focus from the plane
side will be equal to twice the radius of its convex surface
diminished by two-thirds of the thickness of the lens ;
but when the plane is exposed to parallel rays, the distance
of the focus from the convex side will be equal to twice
the radius.

A meniscus with spherical surfaces, fig. 13, has the
property of refracting all converging rays to its focus, if

Fig. 13.

its first surface be convex, provided the distance of the
point of convergence or divergence from the centre of the
first surface is to the radius of the first surface as the index
of refraction is to unity. Thus, if m I I' n be a meni-
scus, and r I, re I' rays converging to the point e, whose
distance e c from the centre of the first surface I a I' of the
meniscus is to the radius c a, or c I, as the index of refrac-
tion is to unity, that is as 1'500 to 1 in glass ; then if/ is
the focus of the first surface, describe, with any radius less
than / a, a circle m a' n for the second surface of the lens.
Now it will be found by projection, that the rays r I, r I',
whether near the axis a e or remote from it, will be re-
fracted accurately to the focus /; and as all these rays fall
perpendicularly on the second surface m n, they will still
pass on, without refraction, to the focus/. In like man-
ner, it is obvious that rays /£,/£', diverging from /will

2G

CONSTRUCTION OP THE MICROSCOPE.

be refracted into r l,r' I', which diverge accurately from
the virtual focus.1

Spherical aberration is not so much connected with the
focal length of the lens as depending on the relative con~
vexity of its surfaces, and is much reduced by observing
a certain ratio between the radii of its anterior and pos-
terior surfaces; thus the spherical aberration of a lens,
the radius of one surface of which is six or seven times
greater than that of the other, as in fig. 14, is very much

Fig. 14.

less when its more convex surface is turned forward to
receive parallel rays, than when its less convex surface is
turned forwards.

This is still better effected, or even got rid of altogether,
by using combinations of lenses, so disposed that their
opposite aberrations shall correct each other, whilst mag-
nifying power is gained. For it is seen that, as the aber-
ration of a concave lens is just the opposite of that of a
convex lens, the aberration of a convex lens
placed in its most favourable position may be
corrected by a concave lens of much less
power in its most favourable position. This
is the principle of a combination proposed by
Sir John F. W. Herschel, fig. 15, an " aplanatic
doublet," consisting of a double-convex lens
and a meniscus ; a doublet of this kind is
found extremely useful and available for micro-
scopic purposes : it affords a large field, like
the Coddington lens.

Chromatic aberration. — Another and serious difficulty
arises, in the unequal refrangibility of the different

(1) Brewster's "Treatise on Optics."

Fig. 15.

CONSTRUCTION OF THE MICROSCOPE.

27

coloured rays which together make up white light, so that
they are not all brought to the same focus, even by a lens
free from spherical aberration. It is, indeed, this differ-
ence in their refrangibility which causes their complete
separation by the prism into a spectrum.

The correction of chromatic with spherical aberration is
effected in a most ingenious manner, by combining a con-
vex lens made of crown-glass, and a concave lens of flint-
glass. If we examine closely the image projected on the
table of a camera obscura provided with a common lens,
we see that it is bordered with the colours of the rainbow 3
or if we look through a common magnifying-glass at the
letters on the title-page of a book, we see them slightly
coloured at their edges in the same manner. The cause
of this iridescent border is that the primitive rays — red,
yellow, and blue, — of which a colourless ray of light is com-
posed, are not all equally refrangible. Hence they are
not all brought to one point or focus, but the blue rays
being the most refrangible, come to a focus nearer the lens
than the yellow ones, which are less refrangible, and the
yellow rays than the red, which are the least refrangible.
Thus, in fig. 16, chromatic aberration proves still more

Fig. 16.

detrimental to the distinct definition of images formed by
a lens, than spherical aberration. This arises more from
the size of the circles of dissipation, than from the iri-
descent border, and it may still exist, although the spherical
aberration of the lens be altogether corrected. Chromatic
aberration is, as before stated, corrected by combining, in
the construction of lenses, two media of opposite form, and
differing from each other in the proportion in which they

28

CONSTRUCTION OF THE MICROSCOPE.

respectively refract and disperse the rays of light ; so that
the one medium may, by equal and contrary dispersion,
neutralize the dispersion caused by the other, without, at
the same time, wholly neutralizing its refraction. Remark-
able enough, the media found the most valuable for such
a purpose should be the combination of pieces of crown
and flint glass, of crown-glass whose index of refraction is
1'519, and dispersive power 0'036, and of flint-glass whose
index of refraction is 1-589, and dispersive power O0393.
The focal length of the convex crown-glass lens must be
4J inches, and that of the concave flint-glass lens 7f
inches, the combined focal length of which is 10 inches.
The following tig. 17 will serve us to explain how rays
of liglit are brought to a single focus, free from colour.

Fig. 17.

In this diagram, L L is a convex lens of crown-glass, and
1 1 a concave one of flint-glass. A convex lens will refract
a ray of light (s) falling at P on it exactly in the same
manner as the prism ABC, whose faces touch the two
surfaces of the lens at the points where the ray enters, and
quits. The ray s F, thus refracted by the lens L L, or
prism ABC, would have formed a spectrum (P T) on a
screen or wall, had there been no other lens, the violet ray
(F v) crossing the axis of the lens at v, and going to the
upper end (P) of the spectrum ; and the red ray (F R)
going to the lower end (T). But, as the flint-glass lens (I I)
or the prism A a c, which receives the rays F v, PR, at the
same points, is interposed, these rays will be united at /,
and form a small circle of white light, the ray (s F) being
now refracted without colour from its primitive direction

CONSTRUCTION OF THE MICROSCOFE, 29

(a FI) into the new direction (F/). In like manner, the
corresponding ray (s' F') will be refracted to f, and a white
and colourless image there formed by the two lenses.

The Magnifying Power of Lenses. — To assist us in gain-
ing a clearer notion of the mode in which a single lens
serves to magnify minute objects, it is necessary to take a
passing glance at the ordinary phenomena of vision. The
human eye is so constituted, that it can only have distinct
vision when the rays falling upon it are parallel or slightly
divergent ; because the retina, on which the image im-
pinges, requires the intervention of the crystalline lens to
bring the rays to an accurate focus upon its surface. The
limit of distinct vision is generally estimated at from six
to ten inches; objects viewed nearer, to most persons,
become indistinct, although they may be larger. The
apparent size of an object
is, indeed, the angle it sub-
tends to the eye, or the
angle formed by two lines
drawn from the centre of
the eye to the extremity of
the object. This will be
understood upon reference
to fig. 1 8. The lines drawn
from the eye to A and R form
an angle, which, when the
distance is small, is nearly
twice as great as the angle
from the eye to o w, formed by lines drawn at twice the
distance. The arrow at A R will therefore appear nearly
twice as long as o w, being seen under twice the angle ;
and in the same proportion for any greater or less differ-
ence in distance. This, then, is called the angle of vision^
or the visual angle. Now the utility of a convex lens
interposed between a near object and the eye consists in
its reducing the divergence of the rays forming the several
pencils issuing from it ; so that they enter the eye in a
state of moderate divergence, as if they had issued from
an object beyond the nearest limit of distinct vision ; and
a well-defined image is consequently formed upon the
retina. In fig. 19, a double-convex lens is placed before

30

CONSTRUCTION OF THE MICROSCOPE.

the eye, near which is a small arrow, to represent the
object uiider examination ; and the cones drawn from it

Fig. 19.

are portions of the rays of light diverging from those
points and falling upon the lens. These rays, if permitted
to fall at once upon the pupil, would be too divergent to
allow of their being brought to a focus upon the retina by
the dioptric media of the eye. But being first passed
through the lens, they are bent into nearly parallel lines,
or into lines diverging from some points within the limits
of distinct vision. Thus altered, the eye receives them
precisely as if they had emanated directly from a larger
arrow placed at ten inches from the eye. The difference
between the real and the imaginary arrow is called the
magnifying power of the lens. The object, when thus
seen, appears to be magnified nearly in the proportion
which the focal distance of the lens bears to the distance
of the object when viewed by the unassisted eye ; and is
entirely owing to the object being distinctly viewed so
much nearer to the eye than it could be without the lens. l
With these preliminary remarks as to the medium by
which microscopic power is obtained, we shall proceed te
apply them, to the construction of a perfect instrument

lrhe Microscope. — A microscope, as we have before ax-
plained, may be either a single, or simple^ or a compound

(1) " The Magnifying Power of Short Spaces " has been most ably elucidated by
John Gorham, Esq. M.ll.C.S. See Journal of Microscopical Society, October.
1854.

CONSTRUCTION OP THE MICROSCOPE. 31

instrument. The simple microscope may consist of one,
as seen in fig. 19, or of two or three lenses; but these
latter are so arranged as to have the effect only of a single
lens. In the compound microscope, not less than two
lenses must be employed : one to form an inverted image
of the object, which, being the nearest to the object, is
called the object-glass; and the other to magnify this
image, and from being next the eye of the observer, called
the eye-glass. Both these may be formed out of a com-
bination of lenses, as will be hereafter seen.

We have hitherto considered a lens only in reference to
its enlargement of the object, or the increase of the angle
under which the object is seen. A further and equally
important consideration is that of the number of rays or
quantity of light by which every point of the object is
rendered visible ; and much may be accomplished, as we
have before pointed out, by the combination of two or
more lenses instead of one, thus reducing the angles of
incidence and refraction. The first satisfactory arrange-
ment for this purpose was the invention of the celebrated
Dr. Wollastou. His doublet (fig. 20) consisted of two
plano-convex lenses having their focal lengths in the pro-
portion of one to three, or nearly so, and placed at a
distance which can be ascertained best by actual expe-
riment. Their plane sides are placed towards the object,
and the lens of shortest focal length next the object.

It appears that Dr. Wollaston was led to this invention
by considering that the achromatic Huyghenian eye-
piece, which will be presently described, would, if reversed,
possess similar good properties as a simple microscope.
But it will be evident, when the eye-piece is understood,
that the circumstances which render it achromatic are
very imperfectly applicable to the simple microscope, and
that the doublet, without a nice adjustment of the stop,
would be valueless. ' Dr. Wollaston makes no allusion to
a stop, nor is it certain that he contemplated its intro-
duction ; although his illness, which terminated fatally
soon after the presentation of his paper to the Royal
Society, may account for the omission.

The nature of the corrections which take place in the
doublet is explained in the annexed diagram, where I o I' is

32

CONSTRUCTION OF THE MICROSCOPE.

the object, p a portion of the cornea of the eye, and d d
the stop, or limiting aperture.

Fig. 20.

Now it will be observed that each of the pencils of light
from the extremities 1 11 of the object is rendered excentri-
cal by the stop ; consequently, each passes through the two
lenses on opposite sides of their common axis o p; thus
each becomes affected by opposite errors, which to some ex-
tent balance and correct each other. To take the pencil I,
for instance, which enters the eye at r 6, r b : it is bent to
the right at the first lens, and to the left at the second ;
and as each bending alters the direction of the blue rays
more than the red, and moreovef^as the blue rays fall

CONSTRUCTION OP THE MICROSCOPE. 33

nearer the margin of the second lens, where the refraction,
being more powerful than near the centre, compensates in
some degree for the greater focal length of the second
lens, the blue rays will emerge very nearly parallel, and
of consequence colourless to the eye. At the same time,
the spherical aberration has been diminished by the
circumstance that the side of the pencil which passes
one lens nearest the axis passes the other nearest the
margin.

This explanation applies only to the pencils near the
extremities of the object. The central pencils, it is obvious,
would pass both lenses symmetrically, the same portions
of light occupying nearly the same relative places on both
lenses. The blue light would enter the second lens nearer
to its axis than the red ; and being thus less refracted than
the red by the second lens, a small amount of compensa-
tion would take place, quite different in principle, and
inferior in degree, to that which is produced in the excen-
trical pencils. In the intermediate spaces the corrections
are still more imperfect and uncertain ; and this explains
the cause of the aberrations which must of necessity exist
even in the best-made doublet. It is, however, infinitely
superior to a single lens, and will transmit a pencil of an
angle of from 35° to 50° without any very sensible errors.
It exhibits, therefore, many of the usual test-objects in a
very beautiful manner.

The next step in the improvement of the simple micro-
scope bears more relation to the eye-piece ; this was
effected by Mr. Holland : it consists in substituting two
lenses for the first in the doublet, and retaining the stop
between them and the third. The first bending being
thus effected by two lenses instead of one, is accompanied
by smaller aberrations, which are, therefore, more com-
pletely balanced or corrected at the second bending, in the
opposite direction, by the third lens.

Hand Magnifiers, — Before we proceed further, it will
be as well to bestow a passing notice on the simple hand
magnifier, so often employed by microscopists in the pre-
liminary examinations of objects.

A very good form of lens was proposed by Dr. Wollaston,
and called by him the Periscopic lens : which consisted of

34 CONSTRUCTION OF THE MICROSCOPE.

two hemispherical lenses cemented together by their plane
faces, having a stop between them to limit the aperture.
A similar proposal was made by Sir David Brewster in
1820, who, however, executed the project in a better man-
ner, by cutting a groove in a whole sphere, and filling the
groove with opaque matter. His lens, which is better
known as the Coddington lens,1 is shown at fig. 21 : it
gives a large field of view, which is equally good in all
directions, as it is evident that the pencils a 6 and b a pass

Fig. 21.

through under precisely the same circumstances. Its
spherical form has the further advantage of rendering the
position in which it is held of comparatively little conse-
quence. It is therefore very convenient as a hand magni-
fier ; but its definition is, of course, not so good as that of
a well-made doublet or achromatic lens. It is generally
set in a folding case, as represented in the figure, and so
contrived that it is admirably adapted for the waistcoat-
pocket ; which, together with the small holder, fig. 22, for

(1) The late Mr. Coddington, of Cambridge, who had a high opinion of the
value of this lens, had one of these grooved spheres executed by Mr. Carey,
who gave it the name of the Coddington Lens, supposing that it was invented
by the person who employed him, whereas Mr. Coddington never laid claim to
it, and the circumstance of his having one made was not until nine years after
it was described by Sir David Brewster in the " Edinburgh Journal."

CONSTRUCTION OF THE MICROSCOPE. 36

securing small objects and holding them during examina-
tion, are all that is required for afield instrument during
a day's ramble. This useful little holder may be purchased
in a case at Mr. Weedon's, 41, Hart-street, Bloomsbury.
The Stanhope lens is similarly constructed, although not
so good and convenient as the former, and is but seldom
to be purchased properly made.

When the magnifying power of a lens is considerable,
or when its focal length is short, and its proper distance
from the object equally short, it then becomes necessary
to be placed at a proper distance with great precision ; it
cannot therefore be held with sufficient accuracy and
steadiness by the unassisted hand, but must be mounted
in a frame, having a rack or screw to move it towards or
from another frame or stage which holds the object. It
is then called a microscope; and it is furnished, accord-
ing to circumstances, with lenses and mirrors to collect
and reflect the light upon the object, with other conve-
niences.

Fig. 23. — Ross's Simple Microscope.

The best of the kind was that contrived by Mr. Ross,
represented in fig. 23 ; and consists of a circular foot e,
from which rises a short tubular stem d, into which

36 CONSTRUCTION OF THE MICROSCOPE.

slides another short tube c, carrying at its top a joint /;
to this joint is fixed a square tube a, through which a rod
b slides; this rod has at one end another but smaller
joint g, to which is attached a collar h, for receiving the
lens i. By means of the joint at/, the square rod can be
moved up or down, so as to bring the lens close to the
object; and by the rod sliding through the square tube a,
the distance between the stand and the lens may be either
increased or diminished : the joint g, at the end of the
rod, is for the purpose of allowing the lens to be brought
either horizontally or at an angle to the subject to be
investigated. By means of the sliding arm the distance
between the table and the jointed arm can be increased
or diminished. This microscope is provided with lenses
of one-inch and half-inch focal length, and is thereby
most useful for the examination and dissection of objects.
It is readily unscrewed and taken to pieces, and may be
packed in a small case for the pocket.

Another highly-useful and more complete simple micro-
scope was contrived by Mr. W. Valentine, and made for
him by Mr. Ross in 1831. It is thus described by the
latter gentleman, and is represented in fig. 24. It is sup-
ported on a firm tripod, made of bell-metal, the feet of
which, a a a. are made to close up for the purpose of pack-
ing it in a box. The firm pillar b rises from the tripod,
and carries the stage e; this is further strengthened by the
two supports rr. From the pillar a triangular bar d, and
a triangular tube c, is moved up and down by a screw,
having fifty threads in the inch, and turned by a large
milled head v, which is situated at the base of the pillar :
this is the fine adjustment. The small triangular bar d
is moved up and down within the triangular tube c, by
turning the milled head t, forming the coarse adjustment :
this bar carries the lens-holder mnop. The stage e con-
sists of three plates ; the lowest one is firmly attached to
the pillar, and upon this the other two work. The upper
one carries a small elevated stage g, on which the objects
are placed; this stage is mounted on a tube/ and has a
spring clip h, for holding, if necessary, the objects under
examination. By means of two screws placed diagonally,
one of which is seen at #, this elevated stage can be moved

CONSTRUCTION OF THE MICROSCOPE.

37

in two directions, at right angles to one another; and thus
different parts of objects can be brought successively into

Fig. 24.— Valentine's Microscope.

the field of view. The arm n p, for carrying the lenses,
is attached to the triangular bar d by a conical pin, on
which it is made to turn horizontally, and the arm itself
can be lengthened or shortened by means of the rack and
pinion m o ; hence the lens q can be applied t^ every part
of an object without moving the stage.

The mirror / is fitted into the largest of the three legs,
and consists of a concave and plane glass reflector. To
the under side of the stage is fitted a Wollaston's condenser
Ic ; and the lens is made to slide up and down by means
of two small handles projecting from the cell in which the
lens is set. Two small tubes i, with either a condensing
lens for opaque objects, or a pair of forceps, may be
attached to this side of the stage. The magnifiers are

38 CONSTRUCTION OP THE MICROSCOPE.

either simple lenses or doublets ; or it could be easily con-
verted into a compound microscope by inserting a com-
pound body, supported on a bent arm, in the place of the
one carrying the single lenses.

An arrangement devised by the late Mr. Quekett, for a
dissecting microscope, represented in fig. 25, is one of value

Fig. 25.— Quekett's Simple Microscope.

and convenience. The instrument is made by Mr. Ladd
of Beck Street, and is furnished by him with three mag-
nifiers, namely, an inch, and half-inch, ordinary lenses,
and a quarter-inch Coddington ; these will be found to be
the powers most useful for the purposes to which this
instrument is specially adapted. The lenses, mirror, con-
denser, vertical stem, &c., all fit into hollows cut for their
reception on the under side of the stage, and are then
covered an$ kept in place by the side flaps : so that, when
packed together, and the flaps kept secure by an India
rubber band, the instrument is very conveniently portable.
The size and firmness of the stage afford great facilities
for dissection, and other scientific investigations-

THE COMPOUND MICROSCOPE. — The compound microscope
may, as before stated, consist of only two lenses, while a
simple microscope has been shown to contain sometimes
three. In the triplet for the simple microscope, however,
it was explained that the object of the first two lenses was

CONSTRUCTION OP THE MICROSCOPE.

39

to do what might have been accomplished, though not so
well, by one ; and the third merely effected certain modi-
fications in the light before it en-
tered the eye. But in the com-
pound microscope the two lenses
have totally different functions : the
first receives the rays from the ob-
ject, and bringing them to new foci,
forms an image, which the second
lens treats as an original object, and
magnifies it just as the single mi-
croscope magnified the object itself.
Fig. 26 shows the earliest form of
the compound microscope, with the
magnified image of a fly, as given
by Adams, which he describes as
consisting of an object-glass, In, a
field glass de, and an eye-glass, /#;
the object, 6' o, being placed a little
further from the lens than its prin-
cipal focal distance, the pencil of
rays from which converge to a focus,
and form an inverted image of the
object at p q, which image is viewed
by the eye placed at a through
the eye-glass /#. The rays remain
parallel after passing out until they
reach the eye, when they will con-
verge by the refractive powers of
this organ, and be collected on the
retina. But the image differs from
the real object in a very essential
particular. The light being emitted
from the object in every direc-
tion, renders it visible to an eye
placed in any position; but the points of the image formed
by a lens emitting no more than a small conical body of
rays, which it receives from the glass, can be visible only
to the eye situate within its range. Thus the pencil of
rays emanating from the object at o, unless converged by
the field-lens to /, would cross each other, and diverge

Fig 26.

4.0 CONSTRUCTION OF THE MICROSCOPE.

towards h, and therefore would never arrive at the lens/*?,
without the interposition of the plano-convex lens at de,
placed at a smaller distance from the object ; and by this
means the pencil d n, which would have proceeded to h,
is refracted or bent towards the lens/^r, having a radial
point at p q. The object is magnified upon two accounts :
first, because if we view the image with the naked eye, it
would appear as much longer than the object as the image
is really longer than it, or as the distance/ 6 is greater
than the distance from the real object to/' ; and secondly,
because this picture is again magnified by the eye-glass.
The compound microscope, then, consists of an object-lens,
I n, by which the image is formed, enlarged, and inverted ;
an amplifying lens, d e, by which the field of view is en-
larged, and is consequently called the field-glass ; and an
eye-glass or lens/*?, by which the eye is permitted to ap-
proach very near, and consequently enabled to view the
image under a large angle of apparent magnitude. The
two, when combined, are termed the eye-piece.

Mr. Lister's investigations in the year 1829, made for
the purpose of improving and correcting the imperfections
of the object-glasses of the compound microscope, led to
the most important results. Mr. Ross also presented to
the Society of Arts, in 1837, a paper on the subject, this
was published in the 51st volume of their Transactions:
he thus writes : —

"In the course of a practical investigation, with the
view of constructing a combination of lenses for the object-
glass of a compound microscope which should be free from
the effects of aberration, both for central and oblique
pencils of great angle, I obtained the greatest possible
distance between the object and object-glass; for in
object-glasses of short focal length, their closeness to the
object has been an obstacle in many cases to the use of
high magnifying powers, and is a constant source of
inconvenience.

" In the improved combination the diameter is only suf-
ficient to admit the proper pencil ; the convex lenses are
wrought to an edge, and the concave have only sufficient
thickness to support their figure : consequently the com-
bination is the thinnest possible, and it follows that there

CONSTRUCTION OF THE MICROSCOPE. 41

will be the greatest distance between the object and the
object-glass. The focal length is -| of an inch, having an
angular aperture of 60°, with a distance of -^ of an inch,
and a magnifying power of 970 times linear, with perfect
definition on the most difficult Podura scales. I have
made object-glasses -^ of an inch focal length ; but as the
angular aperture cannot be advantageously increased if
the greatest distance between the object and object-glass is
preserved, their use will be very limited.

"The quality of the definition produced by an achro-
matic compound microscope will depend upon the accuracy
with which the aberrations, both chromatic and spherical,
are balanced, together with the general perfection of the
workmanship. Now in Wollaston's doublets and Holland's
triplets there are no means of producing a balance of the
aberrations, as they are composed of convex lenses only ;
therefore the best thing that can be done is to make the
aberrations a minimum. The remaining positive aberra-
tion in these forms produces its peculiar effect upon
objects (particularly the detail of the thin transparent
class), which may lead to misapprehension of their true
structure ; but with the achromatic object-glass, where
the aberrations are correctly balanced, the most minute
parts of an object are accurately displayed, so that a satis-
factory judgment of their character maybe formed. When
an object has its aberrations balanced for viewing an
opaque object, and it is required to examine that object
by transmitted light, the correction will remain ; but if it
is necessary to immerse the object in a fluid, or to cover it
with glass, an aberration arises from these circumstances
which will disturb the previous correction, and conse-
quently deteriorate the definition ; and this defect will be
more obvious from the increase of distance between the
object and object-glass.

" If an object-glass is constructed as represented in
fig. 27, where the posterior combination p and the middle
m have together an excess of negative aberration, and if
this be corrected by the anterior combination a having an
excess of positive aberration, then this latter combination,
can be made to act more or less powerfully upon p and m.,
by making it approach to or recede from them ; for when

42 CONSTRUCTION OF THE MICROSCOPE.

the three act in close contact, the distance of the object
from the object-glass is greatest, and consequently the
rays from the object are diverging
from a point at a greater distance
than when the combinations are
separated; and as a lens bends
the rays more, or acts with greater
effect, the more distant the object
is from which the rays diverge, the
effect of the anterior combination
a upon the other two, p and ra,
will vary with its distance from
thence.

" When, therefore, the correction
of the whole is effected for an
opaque object, with a certain dis-
tance between the anterior and middle combination, if they
are then put in contact, the distance between the object
and object-glass will be increased ; consequently, the ante-
rior combination will act more powerfully, and the whole
will have an excess of positive aberration. Now the effect
of the aberration produced by a piece of flat and parallel
glass being of the negative character, it is obvious that the
above considerations suggest the means of correction, by
moving the lenses nearer together, till the positive aberra-
tion thereby produced balances the negative aberration
caused by the medium.

" The preceding refers only to the spherical aberration ;
but the effect of the chromatic is also seen when an object
is covered with a piece of glass : for in the course of my
experiments I observed that it produced a chromatic
thickening of the outline of the Podura and other delicate
scales; and if diverging rays near the axis and at the
margin are projected through a piece of flat parallel glass,
with the various indices of refraction for the different
colours, it will be seen that each ray will emerge, sepa-
rated, into a beam consisting of the component colours of
the ray, and that each beam is widely different in form.
This difference, being magnified by the power of the
microscope, readily accounts for the chromatic thickening
of the outline just mentioned. Therefore, to obtain the

CONSTRUCTION OP THE MICROSCOPE.

43

finest definition of extremely delicate and minute objects,
they should be viewed without a covering; if it be
desirable to immerse them in a fluid, they should be
covered with the thinnest possible film of talc, as, from the
character of the chromatic aberration, it will be seen that
varying the distances of the combinations will not sensibly
affect the correction ; though object-lenses may be made
to include a given fluid, or solid medium, in their correc-
tion for colour.

" The mechanism for applying these principles to the
correction of an object-glass under the various circum-
stances, is represented in fig. 28,
where the anterior lens is set in
the end of a tube a, which slides
on the cylinder 6, containing the
remainder of the combination;
the tube a, holding the lens nearest
the object, may then be moved
upon the cylinder 6, for the pur-
pose of varying the distance, ac-
cording to the thickness of the
glass covering the object, by
turning the screwed ring c, or
more simply by sliding the one on
the other, and clamping them to-
gether when adjusted. An aper-
ture is made in the tube a, within
which is seen a mark engraved on

the cylinder ; and on the edge of which are two marks, a
longer and a shorter, engraved upon the tube. When the
mark on the cylinder coincides with the longer mark on
the tube, the adjustment is perfect for an uncovered
object; and when the coincidence is with the short mark,
the proper distance is obtained to balance the aberrations
produced by glass the hundredth of an inch thick, and
such glass can be readily supplied. This adjustment should
be tested experimentally by moving the milled edge, so as
to separate or close together the combinations, and then
bringing the object to distinct vision by the screw adjust-
ment of the microscope. In this process the milled edge
of the object-glass will be employed to adjust for character

Fig. 28.

44 CONSTRUCTION OF THE MICROSCOPE.

of definition, and the fine screw movement of the micro-
scope for correct focus.

" It is hardly necessary to observe, that the necessity
for this correction is wholly independent of any particular
construction of the object-glass, as in all cases where the
object-glass is corrected for an object uncovered, any
covering of glass will create a different value of aberra-
tion to the first lens, which previously balanced the aber-
ration resulting from the rest of the lenses ; and as this
disturbance is effected at the first refraction, it is inde-
pendent of the other part of the combination. The visibi-
lity of the effect depends on the distance of the object from
the object-glass, the angle of the pencil transmitted, the
focal length of the combination, the thickness of the glass
covering the object, and the general perfection of the cor-
rections of chromatism and the oblique pencils.

"With this adjusting object-glass, therefore, we can
have the requisites of the greatest possible distance
between the object and object-glass, an intense and
sharply-defined image throughout the field, from the
large pencil transmitted, and the accurate correction of
the aberrations ; also, by the adjustment, the means of
preserving that correction under all the varied circum-
stances in which it may be necessary to place an object for
the purpose of observation."

Angle of Aperture. — The definition of an object-glass
much depends upon the in-
creased " angle of aperture."
The angle of aperture is that
angle, which the most ex-
treme rays that are capable
of being transmitted through
the object-glass make at the
point of focus : b a b, in
figs. 29 and 30, is the angle
of aperture ; but it will be
seen that the angle of aper-
ture is much greater in fig.
29 than in fig. 30, which re-
presents an uncorrected lens;
consequently, a much larger quantity of light is trans-

CONSTRUCTION OF THE MICROSCOPE. 45

mitted by the former than by the latter, when any
object is subjected to examination. In order to see an
object distinctly with an uncorrected lens, it is ne-
cessary to diminish the aperture so much, by the aid of
stops, as to interfere with the transmission of the amount
of light required to see the object perfectly. The greatest
angle of aperture of which a given lens is capable, will be
found by determining the greatest obliquity with which it
is possible for rays to fall upon the object-glass, so as to be
refracted to the eye-glass. Dr. Goring and Mr. Pritchard
contrived an instrument for ascertaining this, for any
given object-glass ; which instrument is fully described in
Dr. Lardner's useful little work on the microscope.

A very perfect instrument for measuring the angle of
aperture, designed by Mr. Gillett, consists of two micro-
scopes, the optical axes of which may be adjusted to
coincidence. One of these is attached horizontally to the
traversing arm of a horizontal graduated circle, and is
adjusted so that the point of a needle, made to coincide
with the axis of motion of the movable arm, may be in
focus and in the centre of the field of view. The other
microscope, to which the object-glass to be examined is
attached, is fixed, and so adjusted that the point of the
same needle may be in focus in the centre of its field. The
eye-piece of the latter is then removed, and a cap with a
very small aperture is substituted, close to which a lamp
is placed. It is evident that the rays transmitted by the
aperture will pursue the same course in reaching the point
of the needle as the visual rays from that point to the
eye, but in a contrary direction ; and being transmitted
through the movable microscope, the eye will perceive an
image of the bright spot of light throughout that angular
space that represents the true aperture of the object-glass
examined. The applications of this instrument in the
construction of object-glasses are too numerous to be here
detailed: amongst the most obvious of which may be
mentioned the ready means it presents of determining the
nature, and measuring the amount of aberration in any
given optical combination.

There is yet another source of inaccuracy which is more
mechanical than optical. All the lenses composing the

46

CONSTRUCTION OP THE MICROSCOPE.

microscope require to be set in their respective tubes, so*
that their several axes shall be directed in the same
straight line with the greatest mathematical precision.
This is what is called centering the lenses, and it is a
process which, in the case of microscopes, demands
great skill on the part of the manufacturer. The slightest
deviation from true centering would
cause the images produced by the
lenses to be laterally displaced, one
being thrown more or less to the right,
and the other to the left, or one up-
a, wards and the other downwards; and
even though the aberrations should be
perfectly effaced, the superposition of
B such displaced images would effectually
destroy the efficiency of the instru-
ment. 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 its field, notwithstanding
the great alteration in focus.

Fig. 31 represents the body of one
of Mr. Ross's compound microscopes
with the triple object-glass, where o is
an object ; and above it is seen the
triple achromatic object-glass, in con-
nection with the eye-piece e e, ff the
plano-convex lens ; e e being the eye-
glass, and // the field-glass, and be-
tween them, at 66, a dark spot or dia-
phragm. The course of the light is
shown by three rays- drawn from the
centre, and three from each end of the
object o; these rays, if not prevented by the lens //, or
the diaphragm at 6 6, would form an image at a a; but as
they meet with the lens // in their passage, they are

Fig. 31.

CONSTRUCTION OP THE MICROSCOPE. 47

"converged by it and meet at b b, where the diaphragm is
placed to intercept all the light except that required for
the formation of a perfect image ; the image at b b is
farther magnified by the lens e e, as if it were an original
object. The triple achromatic combination constructed
on Mr. Lister's improved plan,, although capable of trans-
mitting large angular pencils, and corrected as to its own
errors of spherical and chromatic aberration, would, in
some instances, be less effective without an eye-piece of
peculiar construction.

The eye-piece, which up to this time is considered to be
the best to employ with achromatic object-glasses, to the
performance of which it is desired to give the greatest
possible effect, is described by Mr. Cornelius Varley, in the
fifty -first volume of the Transactions of the Society of Arts.
The eye-piece in question was invented by Huyghens for
telescopes, with no other view than that of diminishing the
spherical aberration by producing the refractions at two
glasses instead of one, and of increasing the field of view.
It consists of two plano-convex lenses, with their plane
sides towards the eye, and placed at a distance apart equal
to half the sum of their focal lengths, with a stop or
diaphragm placed midway between the lenses. Huyghens
was not aware of the value of his eye-piece ; it was
reserved for Boscovich to point out that he had, by this
important arrangement, accidentally corrected a great part
of the chromatic aberration. Let lig. 32 represent the
Huygheniau eye-piece of a microscope, // being the field-
glass, and e e the eye-glass, and I m n the two extreme
rays of each of the three pencils emanating from the
centre and ends of the object, of which, but for the field-
glass, a series of coloured images would be formed from r r
to b b ; those near r r being red, those near b b blue, and
the intermediate ones green, yellow, and so on, corres-
ponding with the colours of the prismatic spectrum. This
order of colours is the reverse of that of the common com-
pound microscope, in which the single object-glass projects
the red image beyond the blue.

The effect just described, of projecting the blue image
beyond the red, is purposely produced for reasons presently
to be given, and is called over-correcting the object-glass

48

CONSTRUCTION OF THE MICROSCOPE.

as to colour. It is to be observed also, that the images'
b b and r r are curved in the wrong direction to be dis-
tinctly seen by a convex eye-lens, and this is a further
defect of the compound microscope of two lenses. But

Fig. 32.

the field-glass, at the same time that it bends the rays and
converges them to foci at b' b' and / r', also reverses the
curvature of the images as there shown, and gives them
the form best adapted for distinct vision by the eye-glass e e.
The field- glass has at the same time brought the blue and
red images closer together, so that they are adapted to

CONSTRUCTION OF THE MICROSCOPE. 49

•pass uiicoloured through the eye-glass. To render this
important point more intelligible, let it be supposed that
the object-glass had not been over-corrected, that it had
been perfectly achromatic ; the rays would then have
become coloured as soon as they had passed the field-glass ;
the blue rays, to -take the central pencil, for example,
would converge at b", and the red rays at r", which is just
the reverse of what the eye-lens requires ; for as its blue
focus is also shorter than its red, it would demand rather
that the blue image should be at r, and the red at b".
This effect we have shown to be produced by the over-
correction of the object-glass, which protrudes the blue
foci b b as much beyond the red foci r r as the sum of
the distances between the red and the blue foci of the
field-lens and eye-lens ; so that the separation b r is
exactly taken up in passing through those two lenses, and
the whole of the colours coincide as to focal distance as
soon as the rays have passed the eye-lens. But while they
coincide as to distance, they differ in another respect, —
the blue images are rendered smaller than the red by the
superior refractive power of the field-glass upon the blue
rays. In tracing the pencil I, for instance, it will be
noticed that, after passing the field-glass, two sets of lines
are drawn, one whole and one dotted, the former repre-
senting the red, and the latter the blue rays. This is the
accidental effect in the Huyghenian eye-piece pointed out
by Boscovich. The separation into colours of the field-
glass is like the over-correction of the object-glass, — it
leads to a subsequent complete correction. For if the
differently coloured rays were kept together till they
reached the eye-glass, they would then become coloured,
and present coloured images to the eye ; but fortunately,
and most beautifully, the separation effected by the field-
glass causes the blue rays to fall so much nearer the centre
of the eye-glass, where, owing to the spherical figure, the
refractive power is less than at the margin, that that
spherical error of the eye-lens constitutes a nearly perfect
balance to the chromatic dispersion of the field-lens,
and the blue and red rays I' and I" emerge sensibly
parallel, presenting, in consequence, the p'erfect defini-
tion of a single point to the eye. The same reasoning

50

CONSTRUCTION OP THE MICKOSCOPE.

Fig. 33.

is true of the intermediate colours and of the other
pencils. The eye-glass e, e not only brings together the
images &' b', r r, but it likewise has the most important
effect of rendering them flat, thus at once correcting both
the chromatic and spherical aberration.

The Huyghenian eye-piece, which we- have described, is
the best for merely optical purposes ; but when it is
required to measure the magnified image,
we use the eye-piece invented by Mr.
Ramsden, and called by him the micrometer
eye-piece. The arrangement may be readily
understood upon reference to fig. 33. The
field-glass has now its plane face turned
towards the object j the rays from the ob-
ject are made to converge immediately in
front of the field-glass ; and here is placed a plane-glass,
on which are engraved divisions of l-100th of an inch or

less. The markings of these
divisions come into focus,
therefore, at the same time
as the image of the object,
and both are distinctly seen
together. The glass with its
divisions is shown in fig. 34,
on which, at A, are seen some
magnified grains of starch.
Thus the measure of the
magnified image is given by
mere inspection ; and the
value of such measurements,
in reference to the real object, when once obtained, is con-
stant for the same object-glass.

It is affirmed by Mr. Ross, that if the achromatic prin-
ciple 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 produc-
tive of valuable results, appears from Mr. Brooke's state-
ment, that he has employed as an eye-piece, a triplet
objective of ^one inch focus, the definition obtained by it
being superior to that afforded by the ordinary Huyghe-
uian eye-piece. Some of the lo \vest French achromatic

CONSTRUCTION OF THE MICROSCOPE. 51

object-glasses answer extremely well for this purpose ; and
as the sets are usually made removable, the front pair can
be readily separated for the experiment.

Mr. Lister places on the stage of his microscope a
divided scale, the value of which is known ; and viewing
the scale as the microscopic object, observes how many of
the divisions on the scale attached to the eye-piece corre-
spond with one of those in the magnified image. If, for
instance, ten of those in the eye-piece correspond with one
of those in the image, and if the divisions are known to be
equal, then the image is ten times larger than the object,
and the dimensions of the object are ten times less than
indicated by the micrometer. If the divisions on the
micrometer and on the magnified scale are not equal, it
becomes a mere rule- of- three sum ; but in general this
trouble is taken by the maker of the instrument, who
furnishes a table showing the value of each division of the
micrometer for every object-glass with which it may be
used.

Mr. Jackson invented the simple and cheap form of
micrometer, represented in fig. 35, which he described
in the Microscopical Society's Transactions, 1840. It
consists of a slip of glass placed in the focus of the eye-
glass, with the divisions sufficiently fine to have the value
of the ten-thousandth of an inch with the quarter-inch
object-glass, and the twenty- thousandth with the eighth ;
at the same time the half, or even the quarter of a
division may be estimated, thus affording the means of
attaining all the accuracy that is really available. It
may therefore entirely supersede the more complicated
and expensive screw-micrometer, being much handier
to use, and not liable to derangement in inexperienced
hands.

The positive eye-piece gives the best view of the micro-
meter, the negative of the object. The former is quite
free from distortion, even to the edges of the field j but
the object is slightly coloured. The latter is free from
colour, but is slightly distorted at the edges. In the
centre of the field, however, to the extent of half its
diameter, there is no perceptible distortion ; and the
clearness of the definition gives a precision to the measure-
E 2

O2 CONSTRUCTION OF THE MICROSCOPE.

ment which is very satisfactory. For this reason Mr.
Jackson gives it the preference.

Fig. 35. — Mr. Jackson's Micrometer eye-piece.

Short bold lines are ruled on a piece of glass, a, fig. 35 ;
and to facilitate counting, the fifth is drawn longer, and
the tenth still longer, as in the common rule. Very finely
levigated plumbago is rubbed into the lines, to render
them visible ; and they are covered with a piece of thin
glass, cemented by Canada balsam, to secure the plumbago
from being wiped out. The slip of glass thus prepared is
placed in a thin brass frame, so that it may slide freely ;
and is acted on at one end by a pushing-screw, and at the
other by a slight spring.

Slips are cut in the negative eye-piece on each side, b,
so that the brass frame may be pressed across the field in
the focus of the eye-glass, as at m; the cell of which
should have a longer screw than usual, to admit of adjust-

CONSTRUCTION OP THE MICROSCOPE. 53

ment for different eyes. The brass frame is retained in its
place by a spring within the tube of the eye-piece ; and
in using it the object is brought to the centre of the field
by the stage movements • and the coincidence between
one side of it and one of the long lines is made with great
accuracy by means of the small pushing-screw that moves
the slip of glass. The divisions are then read off as easily
as the inches and tenths on a common rule. The operation,
indeed, is nothing more than the laying a rule across the
body to be measured; and it matters not whether the
object be transparent or opaque, mounted or not mounted,
if its edges can be distinctly seen, its diameter can be
taken.

Previously, however, to using the micrometer, the value
of the divisions should be ascertained with each object-
glass; the mode of doing which is best performed as
follows : —

" Lay a slip of ruled glass on the stage ; and having
turned the eye-piece so that the lines on the two glasses
are parallel, read off the number of divisions in the eye-
piece which cover one on the stage. Repeat this process
with different portions of the stage-micrometer, and if
there be any difference, take the mean. Suppose the
hundredth of an inch on the stage requires eighteen divi-
sions in the eye-piece to cover it ; it is quite plain that an
inch would require eighteen hundred, and an object which
occupied nine of these divisions would measure the two-
hundredth of an inch. This is the common mode of
expressing microscopical measurements ; but I am of
opinion that a decimal notation would be preferable, if
universally adopted.

" Take the instance supposed, and let the microscope be
furnished with a draw- tube, marked on the side with
inches and tenths. By drawing this out a short distance,
the image of the stage micrometer may be expanded until
one division is covered by twenty in the eye-piece. These
will then have the value of two-thousandths of an inch,
and the object which before measured nine will then mea-
sure ten ; which, divided by 2,000, gives the decimal
fraction -005.

" Enter in a table the length to which the tube is drawn

54 CONSTRUCTION OF THE MICROSCOPE.

out, and the number of divisions on the eye-piece micro-
meter equivalent to an inch on the stage ; and any
measurements afterwards taken with that micrometer and
object-glass may, by a short process of mental arithmetic,
be reduced to the decimal parts of an inch, if not actually
observed in them.

" In ascertaining the value of the micrometer with a
deep object-glass, the hundredth of an inch on the stage
will occupy too much of the field ; the two-hundredth or
five-hundredth should then be used, and the number of
divisions corresponding to that quantity be multiplied by
two hundred or five hundred, as the case may be.

" The micrometer shomd not be fitted into too deep an
eye-piece, for it is essential to preserve clear definition.
The middle eye-piece is for most purposes the best, pro-
vided the object-glass be of the first quality ; otherwise,
use the eye-piece of lowest power. The lens above the
micrometer should not be of shorter focus than three-
quarters of an inch, even with the best object-glasses; and
the slit cut in the tube can be closed at any time by a
small sliding bar, as at I, fig. 35."

We subjoin the following comparative micrometrical
measures given by Dr. Hannover, as a reference-table.

Millemetre.

Paris lines.

Vienna lines.

Rhenish lines.

English inch.

1

0-443296

0-4555550

0-458813

0-0393708

2-255829

1

1 027643

1-035003

0-0888138

2-195149

0-973101

1

1-0071625

0-0864248

2-179538

0-966181

0-992888

1

0-0858101

25-39954

11-25952

11-57076

11-65364

1

The wonderful tracing on glass executed by M. Nobert,
of Earth, in Prussia, deserves attention. The plan adopted
by him is, to trace on glass ten separate bands at equal
distances from each other, each band being composed of
parallel lines of some fraction of a Prussian inch apart ; in
some they are l-1000th, and in others only l-4000th of A
Prussian inch separated. The distance of these parallel
lines forms part of a geometric series : —

CONSTRUCTION OF THE MICROSCOPE.

55

0-001000 lines.
0-000857 .,
0-000735 '„:
0-000630 „
0-000540 ,,

0-000463 lines.
0-000397 ,,
0-000340 „
0-000292 „
0-000225 .,

To see these lines at all, it is requisite to use a micro-
scope with a magnifying power of 100 diameters; the
bands containing the fewest number of lines will then be
visible. To distinguish the finer lines, it will be necessary
to use a magnifying power of 300, and then the lines which
are only l-4700th of an inch (Prussian) apart will be
seen perfectly traced. Of all the tests yet found for
object-glasses of high power, these would seem the most
valuable. These tracings have tended to confirm the
undulating theory of light, the different colours of the
spectrum being exhibited in the ruled spaces according to
the separation of the lines ; and in those cases where the
distances between the lines are smaller than the length of
the violet-coloured waves, no colour is perceived ; and it
is stated, that if inequalities amounting to '000002 line
occur in some of the systems, stripes of another colour
would appear in them.

Achromatic object-glasses for microscopes are of various
foci, differing from 2 inches to l-50th of an inch.

Magnifying Poiver of Mr. Ross's Olject-Glai
various Eye-Pieces.

with his

EYE GLASSES,
or

OBJECT GLASSES.

EYE-PIECES.

2-inch.

1-inch.

£-inch.

i-inch.

-|-inch.

Tyinch.

A

20

60

100

220

420

600

B

30

80

130

350

670

8V 0

C

40

100

180

500

900

1200

Value of each

space in the Mi-
crometer eye-

too

riv

T5oo

TsVs

•Gtto

TsToo"

glass, with the
various object-

•0025

•001031

•0005263

•0002325

•0001111

•000074

glasses.

56

CONSTRUCTION OF THE MICROSCOPE.

Magnifying Power of Messrs. Powell and LealancCs
Achromatic Object-Glasses.

Object
Glasses.

Angular
Aperture.

Magnifying Power with the various
Eye-Pieces.

Price.

Inches.
2

|

I

Deg.

14
28
70
95
125
145
175

No. 1.

25
50
100
200
400
fiOO
800

No. 2.

No. 3.

No. 4.

No. 5.

£ 8.

2 15
3 0

5 0
5 5
8 8
10 10
16 16

37
74
148
296
592
888
1184

50
100
200
400
800
1200
1600

100
200
400
800
160C
2400
3200

150
300
600
1200
2400
3600
4800

Schmidt's goniometer positive eye-piece, for measuring
the angles of crystals, is so arranged as to be easily rotated
within a large and accurately graduated circle. In the
focus of the eye-piece a single cobweb is drawn across, and
to the upper part is attached a vernier. The crystals
being placed in the field of the microscope, and care being
taken that they lie perfectly flat, the vernier is brought to
zero, and then the whole apparatus turned until the line
is parallel with one face of the crystal ; the frame-work
bearing the cobweb, with the vernier, is now rotated until
the cobweb becomes parallel with the next face of the
crystal, and the number of degrees which it has traversed
may then be accurately read off.

To the most complete instruments a set of eye-pieces,
consisting of not less than three, is usually made. These
differ in power ; the longest is always the lowest power,
and is marked A. Its angular aperture, which determines
the size of the field of view, is generally less than that of
the others (if constructed on the Huyghenean plan), being
limited by the diameter of the bod}'. It is usually about
20 degrees. The next eye- piece, or middle power, marked
s, and the deepest, c, have more than 30 degrees of angular
aperture.

For viewing thin sections of recent or fossil woods,
coal, the fructification of ferns and mosses ; fossil-shells,
seeds, small insects, or parts of larger ones ; molluscs or

DEFINING AND PENETRATING POWER. 57

the circulation in the frog, &c., the eye-piece A is best
adapted.

For examining the details of any of the above objects,
it will be advisable to substitute the eye-piece B, which
also should be used in the observation of crystals when
illuminated by polarised light, the pollen of flowers, minute
dissection of insects, the vascular and cellular tissues of
plants, the Haversian canals and lacunae of bone, and the
serrated laminse of the crystalline lens in the eyes of birds
and fishes.

The eye-piece c is of use when it is requisite to investi-
gate the intimate structure of delicate tissues ; and also in
observations upon fossil infusoria, volvox, scales from
moths' wings, raphides, &c. The employment of this eye-
piece, when a higher power is required, obviates the neces-
sity of using a deeper object-glass, which always occasions
a fresh arrangement of the illumination and focus. It
must be borne in mind, that the more powerful the eye-
piece, the more apparent will the imperfections of the
object-glass become ; hence less confidence should be
placed in the observations made under a powerful eye-
piece than when a similar degree of amplification is
obtained with a shallow one and a deeper object-glass.

The degree of perfection in the construction of the
optical part of a microscope is judged of by the distinct-
ness and comfort with which it exhibits certain objects,
the details of which can only be made visible by combi-
nations of lenses of high magnifying power, and a near
approach to correctness. Such are termed by the micro-
scopist test-objects. Mr. C. Brooke, F.R.S., whose labours
have been devoted to the correction of errors which have
crept into this part of philosophical research, says: — In
order to arrive at any satisfactory conclusions regarding
the action of any transparent medium on light, it is neces-
sary to form some definite conceptions regarding the ex-
ternal form and internal structure of the medium. This
observation appears to apply in full force to microscopic
test-objects; and for the purposes of the present inquiry,
it will suffice to limit our observations to the structure of
two well-known test-objects, — the scales of Podura plumbea,
and the siliceous loricse, or valves of the genus Pleurosigma,

58 CONSTRUCTION OF THE MICROSCOPE.

freed from organic matter : the former of these is com-
monly adopted as the test of the defining power of an
achromatic object-glass, and the several species of the
latter as the tests of the penetrating or separating power,
as it has been termed. The denning power depends only
on the due correction of chromatic and spherical aberra-
tions, so that the image of any point of an object formed
on the retina may not overlap and confuse the images of
adjacent points. This correction is never theoretically
perfect, since there will always be residual terms in the
general expression for the aberration, whatever practicable
number of surfaces we may introduce as arbitrary con-
stants; but it is practically perfect when the residual
error is a quantity less than that which the eye can appre-
ciate. The separation of the markings of the Pleurosig-
mata and other analogous objects is found to depend on
good defining power associated with large angle of
aperture.

The Podura scale appears to be a compound structure,
consisting of a very delicate transparent lamina or mem-
brane, covered with an imbricated arrangement of epi-
thelial plates, the length of which is six or eight times
their breadth, somewhat resembling the tiles on a roof, or
the long pile of some kinds of plush. This structure may
be readily shown by putting a live Podura into a small
test-tube, and inverting it on a glass-slide ; the insect
should then be allowed for some time to leap and run
about in the confined space. By this means the scales
will be freely deposited on the glass ; and being subse-
quently trodden on by the insect, several will be found
from which the epithelial plates have been partially rubbed
off, and at the margin of the undisturbed portion the form
and position of the plates may be readily recognised.
This structure appears to be rendered most evident by
mounting the scales thus obtained in Canada balsam, and
illuminating them by means of Wenham's parabolic re-
flector. The structure may also be very clearly recognised
when the scale is seen as an opaque object under a Ross's
-J^-th (specially adjusted for uncovered objects), illuminated
by a combination of the parabola and a flat Lieberkuhn.
The under-side of the scale thus appears as a smooth

DEFINING AND PENETRATING POWER. 59

glistening surface, with very slight markings, correspond-
ing, probably, to the points of insertion of the plates on
the contrary side. The minuteness and close proximity
of the epithelial plates will readily account for their being
a good test of definition, while their prominence renders
them independent of the separating power due to large
angle of aperture.

The structure of the second class of test-objects above
mentioned differs entirely from that above described ; it
will suffice for the present purpose to notice the valves of
three species only of the genus Pleurosigma ; which, as
arranged in the order of easy visibility, are, P. formosum,
P. hippocampus, P. angulatum. These appear to consist
of a lamina of homogeneous transparent silex, studded
with rounded knobs of protuberances, which, in P. formosum
and P. angulatum, are arranged like a tier of round shot,
in a triangular pile, and in hippocampus like a similar tier
in a quadrangular pile, as has frequently been described ;
and the visibility of these projections is probably propro-
tional to their convexity. The " dots" have by some been
supposed to be depressions ; this, however, is clearly not
the case, as fracture is invariably observed to take place
between the rows of dots, and not through them, as would
naturally occur if the dots were depressions, and conse-
quently the substance is thinner there than elsewhere.

This, in fact, is always observed to take place in the
siliceous loricse of some of the border tribes that occupy a
sort of neutral, and yet not undisputed, ground between
the confines of the animal and vegetable kingdoms; as,
for example, the Isthmia, which possesses a reticulated
structure, with depressions between the meshes, somewhat
analogous to that which would result from pasting together
bobbin-net and tissue-paper. The valves of P. angulatum,
and similar other objects, have been by some writers sup-
posed to be made up of two substances possessing different
degrees of refractive power; but this hypothesis is purely gra-
tuitous, since the observed phenomena will naturally result
from a series of rounded or lenticular protuberances of one
homogeneous substance. Moreover, if the centres of the
markings were centres of greatest density, if, in fact, the
structure were at all analogous to that of the crystalline

60 CONSTRUCTION OF THE MICROSCOPE.

lens, it is difficult to conceive why the oblique rays only
should be visibly affected. When P. hippocampus or P.for-
mosum is illuminated by a Gillett's condenser, with a cen-
tral stop placed under the lenses, and viewed by a quarter-
inch object-glass of 70° aperture, both being accurately
adjusted, we may observe in succession, as the object-glass
approaches the object, first a series of well-defined bright
dots ; secondly, a series of dark dots replacing these ; and
thirdly, the latter are again replaced by bright dots, not,
however, as well defined, as the first series. A similar
succession of bright and dark points may be observed in
the centre of the markings of some species of Coscinodiscus
from Bermuda.

These appearances would result if a thin plate of glass
were studded with minute, equal, and equidistant plano-
convex lenses, the foci of which would necessarily lie in
the game plane. If the focal surface, or plane of vision, of
the object-glass be made to coincide with this plane, a
series of bright points would result from the accumulation
of the light falling on each lens. If the plane of vision be
next made to coincide with the surfaces of the lenses, these
points would appear dark, in consequence of the rays being
refracted towards points now out of focus. Lastly, if the
plane of vision be made to coincide with the plane beneath
the lenses that contain their several foci, so that each lens
may be, as it were, combined with the object-glass, then a
second series of bright points will result from the accumu-
lation of the rays transmitted at those points. Moreover,
as all rays capable of entering the object-glass are concerned
in the formation of the second series of bright focal points,
whereas the first series are formed by the rays of a conical
shell of light only, it is evident that the circle of least
confusion must be much less, and therefore the bright
points better defined in the first than in the last series.

If the supposed lenses were of small convexity, it is
evident that the course of the more oblique rays only
would be sensibly influenced ; hence probably the structure
of P. angulatum is recognised only by object-glasses of
large angular apertures, which are capable of admitting
very oblique rays,

It does not appear to be desirable that objects should be

MECHANICAL ARRANGEMENTS. 61

illuminated by an entire, or, as it may be termed, a solid
cone of light of much larger angle than that of the object-
glass. The extinction of an object by excess of illumina-
tion may be well illustrated by viewing with a one-incH
object-glass the Isthmia, illuminated by Gillett's condenser.
When this is in focus, and its full aperture open, the
markings above described are wholly invisible ; but as the
aperture is successively diminished by the revolving dia-
phragm, the object becomes more and more distinct, and
is perfectly denned when the aperture of the illuminating
pencil is reduced to about 20°. The same point may be
attained, although with much sacrifice of definition, by
gradually depressing the condenser, so that the rays may
diverge before they reach the object; and it may be
remarked, generally, that the definition of objects is
always most perfect when an illuminating pencil of suit-
able form is accurately adjusted to focus, that is, so that
the source of light and the plane of vision may be conju-
gate foci of the illuminator. If a condenser of 120°
aperture, or upwards, be used as an illuminator, the mark-
ings of Diatomacese will be scarcely distinguishable with
the best object-glass, the glare of the central rays over-
powering the structure of those that are more oblique.

There are indeed almost as many methods employed
for bringing out the markings on test-objects, as there are
skilled and efficient microscopists, each one preferring his
own, simply because he has been at great pains in work-
ing it out with the utmost nicety. The late Professor
Quekett, in his treatise on the microscope, recommends
" oblique light with the mirror and lamp, removing all
appliances under the stage ; then, after much patience and
perseverance, Grammatophora subtilissima and the Amician
test may be resolved." Another plan is to use the flat
mirror, the achromatic condenser, and a paraffin lamp, day-
light not being so easily managed, or even so good for the
•Jth or higher objectives.

Mr. Lobb's method is seen in Fig. 36 : — "The microscope
is placed in the horizontal position, and a small camphine
lamp so adjusted that its reservoir may be close against
the end of the rack-tube ; having the A eye-piece, the
one-inch objective, and the achromatic condenser of 170°

62

THE MICROSCOPE.

aperture, place No. 1 aperture of the wheel of dia-
phragms in tlie field, then, looking through the eye-piece,
centre the aperture accurately; then bring No. 11 aper-
ture in the field, and again centre the lamp flame, and be
careful that it corresponds with the axis of the pupil of
the eye.

" Should we wish to examine hairs, scales, or morbid
structures, use "No. 3, 4, or 5 apertures of the wheel of
diaphragms without a stop, the |th, iVth, to^h, ^fth, or
object-glasses, and the A, B, or C eye-piece as

Fig. 36. — Powell ami Lealand's Microscope arranged for LoWs illumination.
A. Secondary Stage carrying Achromatic Condenser.

thought proper ; now bring the object into focus, and by
racking up the condenser for the best light, very clear
and satisfactory definition will be obtained. Nothing
more is required when examining these objects than the
selection of the most suitable aperture, and focussing the
condenser for the illumination which defines the best ; too
much and too little light being equally bad.

" If we wish to examine objects such as Pleurosigma

EXAMINATION OF TEST-OBJECTS. 63

formosum, P. quadratum, P. angulalum, and their allies,
bring No. 11 aperture in the field, rack up the con-
denser until the field is very bright, then put on No. 1
stop, and rack up the condenser until the stop disappears :
if the desired effect be not obtained, try No. 2 stop ; the
condenser will then require to be racked up still higher,
and the dots will come out easily. To examine Navicula
cuspidatum, N. rhomboides, Pleu-rosigma fasciola, Pluero-
sigma macrum, &c., still use No. 11 aperture, and stop
No. 2, which will require a slight alteration in position
only, when the checks will appear distinctly.

" For the Amician test use the slots instead of No. 2
stop j and for very difficult lines, such as those of the
Acus", the condenser must be so arranged (when focussed
up till the field becomes exceedingly bright) that a shadow
is thrown on the object from the left hand, and No. 1
and No. 2 stop used, so as to darken a little the right
hand side of the field. The -g-th and ^-th object-glasses
are generally found the best suited for the Acus with the
B eye-piece ; in fact, the B eye-piece is mostly to be pre-
ferred with high powers."

In short, the whole requires perfect centering as well
as careful illumination, and the condenser used must
have a wide aperture : we have found Collins's answer
exceedingly well, and with it we have brought out the
markings on the P. fasciola, JV. Acus, &c.

When employing high powers for viewing test, or
indeed any objects, only that part which is exactly in
focus can be perfectly seen at one time ; and even a very
slight turn of the ./me adjustment, or " slow motion," often
causes a totally different set of appearances to present
themselves. It is desirable during our examination to
keep the finger on the slow motion, and thus bring into
view different parts or thicknesses of an object, so that in
the most careful manner layers or sets of vessels may be
seen and continuously traced. A clearer idea of the
nature of a doubtful structure is in this way obtained,
while we are in the act, as it were, of changing the focus.
When different structural features present themselves on
different planes, it is often a most difficult task to deter-
mine which of them is the nearer. This may be regarded

64 THE MICROSCOPE.

as a result inherent in our mode of viewing objects by
transmitted light; nevertheless it is often productive of
serious embarrassment when we are dealing with the
almost inappreciable markings on the siliceous diatoms, &c.
The following general rule is given by Mr. Wenham
(Quart. Journ. Micros. Scien. 1854, p. 138) for securing
the most efficient performance of an object-glass with any
ordinary object : — " Select any dark speck or opaque por-
tion of the object, and bring the outline into perfect
focus j then lay the finger on the milled head of the fine
adjustment, 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 ex-
pansion, or coma, be when the object is without the focus,
or farther from the objective, the lenses must be placed
further asunder, or towards the mark ' uncovered.' If
the greater coma be when the object is within the focus,
or nearer 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, the
Diatoms, &c.) a set of distinct dots or other markings.
Tor if the dots have a tendency to run into lines when the
object is 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 glasses must be
further separated." Mr. Wenham remarks upon the dif-
ficulty of accurately making this adjustment even in the
best made objectives.

Mr. E. Beck, in a paper contributed to the proceedings
of the Eoyal Microscopical Society, directs particular
attention to avoidance of errors of interpretation. Viewing
objects by transmitted light, he observes, is a method
peculiar to the microscopist ; it is, however, one to which
our vision, applied in the ordinary way, is so much un-
accustomed, that in many instances it not only conveys
imperfect notions of an object, but produces appearances
which bear little or no resemblance to the true structure

ERRORS OP INTERPRETATION.

65

of the object. An instance of this is furnished in an
examination of the scales of Lepisma saccharina.

" Upon the more abundant scales the most prominent
markings appear as a series of double lines, which run
parallel and at considerable intervals from end to end of
the scale, whilst other lines, generally much fainter,
radiate from the quill, and take the same direction as the
outline of the scale when near the fixed or quill end ;
but there is, in addition, an interrupted appearance at the
sides of the scale which is very different from the mere
union, or ' cross-hatchings,' of the two sets of lines."
(Fig. 37, Nos. 1 and 2, the upper portions.)

Fig. 37.— Portions of Scales of Lepisma, after Beck.

The scales themselves are formed of some truly trans-
parent substance, for water instantly and almost entirely
obliterates their markings, but they reappear unaltered as
the moisture leaves them ; therefore the fact of their being
visible at all, under any circumstances, is due to the refrac-
tion of light by superficial irregularities, and the following
experiment establishes this fact, whilst it determines at
the same time the structure of each side of the scale, a

66 THE MICROSCOPE.

matter which, it is impossible to do from the appearance of
the markings in their unaltered state : —

"Bemove some of the scales by pressing a clean and dry
slide against the body of the insect, and cover them with
a piece of thin glass, which may be prevented from moving
by a little paste at each corner. No. 3 may then be taken
as an exaggerated section of the various parts. AB is the
glass slide, with a scale, (7, closely adherent to it, and D
the thin glass cover. If a very small drop of water be
placed at the edge of the thin glass, it will run under by
capillary attraction ; but when it reaches the scale, C, it
will run first between it and the glass slide A B, because
the attraction there will be greater, and consequently the
markings on that side of the scale which is in contact with
the slide will be obliterated, while those on the other side
will, for some time at least, remain unaltered : when such
is the case, the strongly marked vertical lines disappear,
and the radiating ones become continuous. (See No. 1,
the lower left hand portion.) To try the same experiment
with the other, or inner surface of the scales, it is only
requisite to transfer them, by pressing the first piece of
glass, by which they were taken from the insect, upon
another piece, and then the same process as before may be
repeated with the scales that have adhered to the second
slide ; the radiating lines will now disappear, and the ver-
tical ones become continuous. (See No. 2, left portion.)
These results, therefore, show that the interrupted appear-
ance is produced by two sets of uninterrupted lines on
different surfaces, the lines in each instance being caused
by corrugations or folds on the external surfaces of the
scales. Nos. 1 and 2 are parts of a camera lucida drawing
of a scale which happened to have the opposite surfaces
obliterated in different parts. No. 4 shows parts of a
small scale in a dry and natural state ; at the upper part
the interrupted appearance is not much unlike that seen
at the sides of the larger scales, but lower down, where
lines of equal strength cross nearly at right angles, the
lines are entirely lost in a series of dots, and exactly the
same appearance is shown in No. 5 to be produced by two
scales at a part where they overlie each other, although
p.ach one separately shows only parallel vertical lines."

ERRORS OF INTERPRETATION. 67

Another very characteristic fallacy resulting from con-
figuration is furnished in the supposed tubular structure
of human hair. When we view this object by transmitted
light, it presents the appearance of a darkish flattened
band down the centre ; this, however, is entirely due to
the convergence of the rays of light produced by the
convexity of the surface of the hair. That it is a solid
structure is proved by making a transverse section of the
hair-shaft, when it is seen filled up with medullary sub-
sjance, with the centre somewhat darker than the other
part. It is, in fact, a spiral outgrowth of epithelial scales,
overlapping each other like tiles on a house-top, and this
gives a striated appearance to the surface. A cylindrical
thread of glass in balsam appears as a flattened, band-like
streak, of little brilliancy. Another instance of fallacy
arising from diversity in the refractive power of the in-
ternal parts of an object, is furnished by the mistakes for-
merly made with regard to the true character of the lacunae
and canaliculi of bone-structure, which were long mis-
taken for solid corpuscles, with radiating opaque filaments
proceeding from a dense centre j we now know them to
be minute chambers, with diverging passages, excavated in
the solid osseous substance. That such is truly the case,
is shown by the effects of Canada balsam : as this infil-
trates the osseous substance, and fills up the excavations,
it quite obliterates the bone corpuscles.

The molecular movements of finely divided particles,
seen in nearly all cases when certain objects are first
suspended in water, or other fluids, is often a source of
embarrassment to beginners. If a minute portion of
indigo or carmine be rubbed up with a little water, and
a drop placed on a glass slide under the microscope, it will
at once exhibit this peculiar perpetual motion appearance.
This movement was first observed in the granular particles
seen among the pollen grains of plants, known as fovilla,
which are set free when the pollen is crushed. Important
vital endowments were formerly attributed to these par-
ticles, but Dr. Eobert Brown showed such granules were
common enough both in organic and inorganic substances,
and therefore they were in no way particularly "indicative
of life." We must especially notice another point which

68 THE MICROSCOPE.

is a common cause of annoyance, as well as a source of
embarrassment, to the microscopist, the disturbance pro-
duced by the passage of light through transparent bodies ;
this greatly impairs the sharpness of outline, and is caused
by what is called the inflection or diffraction of light.

If a divergent pencil of light fall upon any opaque
object placed between the light and a screen, it is evident
that a shadow will be cast upon the screen : from our
previous observation that light always moves in straight
lines, we should expect to find that the image would be
clear,' sharp, and well-defined ; but we know from experi-
ment that this is not so, and that there will be no exact
margin between the strongly illuminated part outside, and
that part of the screen which is covered by the object, but
there will be more or less of a shading off at the edges of
the image.

From this it is inferred that the rays of light which
pass the edges of the opaque object do not proceed in the
same straight lines in which they would have proceeded if
the object had not been present. This effect is called in-
flection or diffraction, and is a consequence of the general
property of undulation. When any system of waves meets
with an obstacle, subsidiary systems of undulation will be
formed round the extremities of the obstacle, and will be
propagated from those points independently of, and simul-
taneously with, the original system of waves. And for a
certain space around the lines in which the rays, grazing
the edge of the opaque body, would have proceeded, the
two systems of undulation will intersect and produce the
phenomena of interference.

If the opaque body be very small, and the distance
from the luminous point very large in proportion, the two
pencils formed by inflection will intersect, and all the
phenomena of interference will ensue. Thus, if the light
be homogeneous, a bright line of light will be formed
under the centre of the opaque object, outside of which
will be dark lines, and then bright and dark lines alter-
nately. If the light be compound solar light, a series of
coloured fringes will be formed. The following is a very
good illustration of how errors of interpretation may
easily arise. If a small sphere formed of any opaque sub-

DIFFRACTION SHADOW. 69

stance be suspended in a dark room, and a pencil of homo-
geneous light be allowed to fall upon it, so that its shadow
may be received on a screen, it will be found that a bright
spot will appear in the middle of the shadow, outside of
which will be a dark circle, and beyond this a bright
circle, and so on, the circles corresponding successively
to the interference of the rays, by which their brilliancy
is either doubled or extinguished ; the colour of the bright
circles corresponds to that of the light. If common com-
pound light be used, the central spot will be white, and
will be surrounded by a series of coloured fringes.

No rule can be laid down for the avoidance of errors
such as we have been dwelling upon, but the practised
microscopist will, however, in time learn, almost as it were
instinctively, to overcome the difficulties of diffraction, as
well as those due to oblique illumination at certain angles,
particularly in that which results in the production of a
double image or overlying shadow, which we have seen
nearly as strongly marked as the real image. This kind
of shadow is sometimes called the "diffraction spectrum"
although it must be evident to anyone who will be at the
trouble to study the subject, that it is due to a different
cause. It cannot be denied that errors of interpretation
are not unfrequently due, as Mr. Brooke has shown, to
the increasing desire there is to produce object-glasses with
large angles of aperture. Mr. Brooke observes : — " The
superiority in resolving power possessed by objectives of
large angular aperture is obtained at the expense of other
advantages." And Messrs. Sullivant and Wormley, in their
paper on " Robert's Test-Plate and the Striae of Diatoms,"
American Journal of Science, 1861, are convinced "that
when the resolving power of an objective is near its limit,
' spectral ' or spurious lines are to be seen, and these are
only to be distinguished from the true by a practised eye.'
Hence they think " that the mere exhibition of lines is
not always conclusive evidence of their ultimate resolu-
tion." ' For the same reason we have not the amount
of confidence in the higher powers that some observers
seem to have ; we know, indeed, with every increase in
this direction, how liable we are to encounter unforeseen
errors and exaggerations, and we still prefer the £th or

70 THE MICROSCOPE.

J-inch of Eoss, because we know its precise working and
defining power, and that most of the great achievements and
discoveries of the microscope have been made with powers
in no way superior to the last-mentioned J objective. The
many important contributions to microscopy by Owen,
Carpenter, Quekett, Ealfs, &c. have been made with
powers of limited capacity.

MECHANICAL ARRANGEMENTS.

Having explained the more important optical principles
of the achromatic compound microscope, it remains for
us to notice the mechanical and accessory arrangements
for giving these principles their full effect. In few philo-
sophical instruments is theoretical perfection so nearly
reached as in the microscope: in it the highest optical
skill is combined with the most consummate mechanical
contrivance, and the mechanism of the instrument is of
much more importance than might be imagined by those
who have not studied the subject. In the first place, steadi-
ness, or freedom from vibrations not equally communicated
to the object under examination, and to the object-glass or
lenses by which it is viewed, is a point of the utmost im-
portance. The various improvements which of late years
have combined to make the microscope the superior instru-
ment it is, may be classed under eight heads : —

1. The circular rack, which is placed immediately under
the stage, and which is capable of carrying it round, in
some instruments, the entire revolution of a circle, is a
very convenient movement for altering the angle at which
an object is viewed, without putting it out of field or focus;
it may also be used as a goniometer, for measuring crystals.

2. The clamping arc, peculiar to Eoss's microscopes, fixes
the microscope at any inclination, even after the suspension
joint has become supple by long use.

3. The advantage of the sub-stage for holding and ad-
justing, by universal motions, all the illuminating and
polarising apparatus placed beneath the object, can hardly
be overrated.

4. The dark-ground illuminator is an excellent contri-
vance by which a bright light is apparently thrown on
semi-opaque objects, though really coming beneath them,

OPTICAL IMPROVEMENTS. 71

but so obliquely, that none of it enters the object-glass
but that which is interrupted by the object.

5. Mr. Brooke's double nose-piece, or Baker's treble, is
a useful piece of mechanism attached to the end of the
microscope body, by which two or three object-glasses
can be screwed on to it at once, and rapidly changed.

6. The double arm to the mirror allows it to be ex-
tended so as to cast a very oblique light on objects, as
well as to be raised near them without any preparatory
movement.

7. The separation of the outer and inner lenses of object-
glasses is an arrangement by which the greatest possible
flatness of field and penetration are secured.

8. The great and manifold advantages of the binocular
arrangement are very obvious ; objects stand out with
stereoscopic effect, and the ease to the eyes of the observer
is very great. When high powers are required, the prism
can be drawn aside, and the microscope used as a mon-
ocular instrument.

As regards recent optical improvements, Mr. Ross (the
elder), as we have already explained (page 40), was the
first to notice that however perfect the correction of an
object-glass might be, " the circumstance of covering the
object with a piece of the thinnest glass or talc, disturbed
the corrections if they had been adapted to an uncovered
object, and rendered an object-glass which was perfect
under one condition, seriously defective under the other."
To remedy this defect, he devised the well-known contri-
vance called the adjustment of object-glasses, by which
they are rendered equally correct for covered or uncovered
objects.

The following diagrams (fig. 38) of the different object-
glasses will help to explain the complex structure, and
consequent costliness, of an achromatic combination. The
double-convex and plano-convex lenses are of crown glass,
and the piano- and double-concave, and meniscus lenses,
of flint glass.

It will be seen, therefore, that each of the object-glasses
from the J to the gV, is made up of as many as eight dis-
tinct lenses, the back combination being a triplet composed
of two double-convex lenses of crown, with a double-

72

THE MICROSCOPE.

concave lens of flint glass between them, the intermediate
combination being a doublet composed of a double-convex
lens of crown glass with a doiible-concave of flint glass ;
and the front combination being another triplet composed
of two plano-convex lenses of crown, and a plano-concave
lens of flint glass between them. This will also explain
the composition of the shallower object-glasses ; the dis-
tance between the different combinations throughout all
the objectives, and their size, depending on the amount of
magnifying power required. It may be briefly stated that
the principal qualities to be looked for in an object-glass

Fig. 38. —

A, Double-convex lens ; B, Plano-concave ; C, Bi-oonvex and plano-concave,
united : shown in their various combinations, as at D, form the 3-in. 2-in. or
IJ-in. ; at E, 1-in. and f-in. ; and at F, the |-in. /0-in. J-in. and ^-in. ob-
jectives.

are, 1st, Resolution, or the power of showing clearly mir
details, which is chiefly effected by increase of light

minute
ad-
mitted through the objective, by what is termed angular
aperture; 2d, Penetration, or that power which enables
the observer to see deep into the structure of objects with-
out any alteration of focus ; 3d, Definition, or the capa-
bilities of an objective for showing the various details of
an object, especially its boundaries, with the most perfect
and exquisite sharpness ; 4th, Flatness of field, or marginal
and central definition, which denotes the exact capability

OPTICAL IMPROVEMENTS. 73

of the objective to show the peripheral or marginal por-
tions of the field with the same sharpness as the central.1

A considerable accession of available power has been
effected by both Foreign and English manufacturers since
the appearance of the third edition of our book, 1859. In
those by continental makers, this has been achieved by
the intervention of a third medium between the external
surface of the objective, and the covering glass of the
object. We may particularize those of M. Hartnack
Oberhauser's successor, as being most conspicuous ; but
the objective, which is said to be superior to all yet manu-
factured, is the -g^th of an inch of Powell and Lealand,
who, some time before, produced good objectives of ^g-th
and ^¥th of an inc;h focus. In these object-glasses, exces-
sive angular aperture has been judiciously sacrificed to a
more comprehensive and practical utility. It should be
stated, however, that the priority of construction of an
effective ^th objective is due to Mr. Wenham, to whom
the microscope was largely indebted before he made this
glass in 1856. It was constructed on a principle differing
from that usually adopted in the high powers, in having a
single front lens. A single anterior lens transmits more
light, gives clearer definition, with any required extent of
aperture; from its simplicity, it is comparatively freer
from errors of workmanship, and the chromatic and
spherical aberrations can be more perfectly corrected.
Mr. Wenham says, "that such object-glasses will chal-
lenge comparison with the best made and more expensive
forms."

Dr. Beale's account of the performance of the ^jth is,
that it is even better than the ^th inch. Plenty of light
for illuminating the objects to be examined is obtained by
the use of a condenser provided with a thin cap, having an
opening of not more than ^j^h inch in diameter. The
objects should be covered with the thinnest glass, or with
mica, and then there is room to focus to the lower surface
of very thin specimens, which can alone be examined by
such high powers. Particular attention is drawn to these
very high powers, because the statements recently made in

(1) See an excellent paper by J. Plumer, Esq. " On the Choice of a Micro-
scope." Micros. Journ. vol. iii. p. 153.

74 THE MICROSCOPE.

favour of the spontaneous generation theory, may pro-
bably be studied with some advantage. Not only are the
minuter atoms too small to be studied by the -^tk or •£$ th,
but particles too transparent to be observed by the ^th
are, according to Dr. Beale, distinctly demonstrated by
the -g^th ; he observes, " I feel sure that further careful
study, by the aid of these high powers, of the develop-
ment and increase of some of the lowest organisms, and
the movements which have been seen to occur in certain
forms of living matter (amo3ba, white blood-corpuscles,
young epithelial cells, &c.), will lead to most valuable
results, bearing upon the much debated question of vital
actions.

" The most delicate constituent of the nerve-fibres of
the plexus in the summit of the papilla (see Phil. Trans.
for 1864) can be readily traced by the aid of this power.
The finest nerve-fibres thus rendered visible, are so thin,
that in a drawing they would be represented by fine
single lines. Near the summit of the papilla there is a
very intricate interlacement of nerve-fibres, which, although
scarcely brought out by the ^th, is very clearly demon-
strated by this power. In this object, the separation of
the fibres, as they ramify in various places, one behind
another, is remarkable, and the flat appearance of the
specimen as seen by the g^th gives place to that of con-
siderable depth of tissue and perspective. The finest
nerve-fibres, ramifying in the cornea of the eye, and in
certain forms of connective tissue, are beautifully brought
out ; and their relation to the delicate processes from the
connective-tissue corpuscles can be more satisfactorily
demonstrated than by the ^th. The advantage of the
•g'jjth in such investigations seems mainly due to its re-
markable power of penetration."

The one great drawback to the use of this objective,
and a very serious one to most microscopists, is its costli-
ness. The price of this power alone is almost more than
many can afford to give for a complete instrument.

In flatness of field, and in perfection of definition, both
at the centre and margin of the field of view, few objec-
tives have equalled the recent xV^n OI" -Mr- Ross, who
appears to have inherited his late father's well-known skill

PENETRATING POWER. 75

in all that appertains to the microscope. Mr. Baker has
also made considerable advances in the same direction:
his objectives have been made with a greater angle of
aperture than formerly, and with more penetration. Much
misconception, however, exists with regard to the available
angle of aperture for optical requirements ; it will be as
well to remark that an admirable method of determining
this was proposed by Professor Govin, of Turin, which
consists in placing the microscope perpendicularly to any
plane dark non-reflecting surface (as a table covered with
a green cloth), and having converted the instrument into
a telescope, by placing above the eye-piece a suitable com-
bination of two lenses (such as the Examining-Glass of
Mr. Eoss), and then examining and marking the greatest
lateral distance on either side at which a clear image of
some distinct object, such as a narrow strip of white card-
board or paper, laid on the table can be perceived. " Half
the distance between these two points, divided by the ver-
tical distance of the focal point of the objective from the
surface of the table, will, by reference to a table of natural
tangents, give half the required angle of aperture. This
will, in many cases, be found to be considerably less than
what may be termed the angle of admission of diffused
light. To illustrate this, supposing the focal point to be
at a distance of O'Ol inch from the surface of the objective,
a reference to a table of natural tangents will show that an
angular aperture of 17° will necessitate a linear aperture of
0-22 inch : an aperture of 170° will require 0'28 inch, and
one of 174°, of 0'38 inch, in order to admit the extreme
rays, which, for objectives of ^th inch focus, is manifestly
impossible."

In regard to angle of aperture, it may be stated once
and for all, that large angle of aperture is necessarily
incompatible with that far more generally useful quality
of penetration. Penetrating power l is synonymous with

(1) Penetrating Power. " The origin of this term will be found in the Phil,
frans. for 1800, in an article by Sir Wm. Herschel, entitled ' On the Power of
Penetration into space possessed by Telescopes.' In that article, we are told
that when, owing to the darkness, a distant church steeple was invisible, a certain
telescope described, clearly showed the time upon the clock. This, adds Sir
William, was not owing to magnifying power alone, for the steeple could not be
discerned by the naked eye. And he has shown in the same article, that the

76 THE MICROSCOPE.

depth of focus, that is, extreme distance of two planes, the
points of which are at the same time sufficiently in focus
for the purpose of distinct vision. This distance will
manifestly increase as the angle of aperture diminishes,
just as in a landscape camera the fore and back grounds
can be brought into sensible focus simultaneously only by
the use of a small diaphragm, which greatly diminishes
the angular aperture of the incident pencils. But, at the
same time, it must be borne in mind, that illumination,
cceteris paribus, increases or diminishes with angle of
aperture, and the best working glass will be that in which
a compromise is effected between these two conflicting
requisites.

We entirely agree with Mr. Brooke, that "for all practical
purposes, except developing the markings of diatoms, an
objective of moderate aperture will be found most available.
It may reasonably be doubted whether the development of
the dottings of difficult diatoms is not an object rather of
curiosity than of utility, and whether it is worth the labour
that has been bestowed upon the production of glasses for
that especial purpose ; the labour of construction being
immensely augmented by the difficulty of duly balancing
the aberrations of the more oblique pencils. So much is
this the case, that in the best constructed objectives of the

words 'penetrating power' have a definite meaning, and that the amount of
this power possessed by a telescope, can be obtained by calculation. And of
course, this must also be true of a microscope. This power, says Mr. Ryland,
in a very interesting paper, must not be confused with angular aperture, which
has reference to the objective alone ; neither has it any connexion with either
definition or thickness of field. In a word, as magnifying power expresses the
angle subtended by an object or image at the eye of the observer, so penetrative
power is the measure of the angle subtended by the eye at the object, or the
equivalent of that angle in the case of telescopic or microscopic vision. The
one is the measure of size, the other of brightness. The latter, however, must
not be confused with -' illumination.' The one power is neither less important
nor less essential to distinct vision than the other. There required little mag-
nifying power, and there was no illumination, in the case o'f the church steeple,
still the hour could be read on the dial"

The third power, — the visual power of microscopes,— is one which has rarely
been recognised as distinct.

For an object to be magnified 100 times, that is seen at 100th part of the
distance, it is necessary not only that the angle subtended by it at the eye — the
magnifying power — but also the angle subtended by the eye at the object — the
penetrating power— shall be increased one hundred-fold. When this is the case,
the visual power will be 100 also.

If we approach an object bodily, these angles naturally increase in the same
proportion, but it is not so where optical instruments are employed — R. G.
Ryland " On the Optical Powers of the Microscope." — Micros. Jour. Scienc^
vol. vii. p. 27.

MAGNIFYING POWER. 77

largest angles, the visual effect is sensibly impaired when
the rays are transmitted through any other thickness of
covering-glass than that for which they have been specially
corrected."

The value of penetrating power is especially felt when
the binocular arrangement is employed, since the assistance
which it is able to give in the estimation of the solid
forms of objects, is altogether neutralized by the employ-
ment of objectives of such wide angular aperture as not to
show any part of the object, save what is precisely in
focus; and, therefore, there cannot be a doubt of the supe-
rior value of objectives of a moderate angle of aperture
for ordinary working purposes.

" Successful observation, with very high power, is
mainly dependent upon illumination. Indeed, by ordinary
means, it is not possible to obtain a light sufficiently in-
tense to illustrate an object magnified 3,000 diameters.
I have tried various plans, and have come to the conclu-
sion, that the most satisfactory results are obtained by the
use of Kelner's eye-piece as a condenser. By this means I
can obtain a light sufficient for a magnifying power of
10,000 linear.

" My method of increasing the size of the image, with-
out altering the object-glass, is as follows : —

" Supposing the limits of magnifying power of the
object-glass to have been reached, I then increase the
distance between it and the eye-piece, by lengthening the
body by the aid of a draw-tube. The 2*5 th objective
being applied when the tube is increased in length, so
that from the lowest glass of the object-glass to the eye-
glass of eye-piece, the distance measures 24 inches, the
magnifying power corresponds to upwards of 10,000 dia-
meters, 20 inches about 6,000, 15 inches about 2,600, 11
inches about 1,800.

" If there is any reflection from the interior of the tube
which renders the image indistinct, let the tube be lined
with black velvet ; of course the practical utility of in-
creasing the magnifying power entirely depends upon the
character of the specimen, and the preparations best
suited for examination by very high powers must be im-
mersed in the strongest glycerine that can be procured

78 THE MICROSCOPE.

In this way, I have been able to see points which I have
failed to bring out in any other way." J

Magnifying power, as we have already explained, has to
do with size only, and only expresses the magnitude of the
angle subtended by the enlarged image, at the eye, as com-
pared with that subtended by the object itself under the
circumstances of ordinary standard vision; namely, at a
distance of ten inches from the eye.

The Kelner eye-piece, while it increases the magnifica-
tion, detracts from the definition ; on this account, it is
only used when desirous to show the whole of an object
at once, as an insect, or in viewing the series of rings
formed by different crystals with polarized light. This
differs from the ordinary Huyghenian eye-piece in having
a double-convex field-glass, and an achromatic meniscus

COMPOUND MICROSCOPES.

It should be understood that the descriptions we are
about to give of Compound Microscopes cannot embrace
that of every manufacturer. Want of space forbids this,
and therefore we particularly wish to disclaim any inten-
tion of instituting invidious comparisons ; our desire is
solely that of giving, as concisely as possible, a description
of those instruments that have more immediately fallen
under our notice, or have been the companions of our
microscopical pursuits. At the head of our list stands —

Eoss's microscope, an instrument of which the aim is
not simplicity, but perfection — not the production of the
best effect compatible with limited means, but the attain-
ment of everything that the microscope can accomplish,
without regard to cost or complexity. Without any un-
due preference, the first place may fairly be assigned to
this large Compound Microscope of Mr. Eoss, as the one
which was earliest brought (in all essential features, at
least) to its present form. The general plan of Mr. Eoss's
microscope will be seen to be essentially that which has
been adopted in a simpler form by many other makers ;
but it is carried out with the greatest attention to solidity

(1) Beale, " How to Work with the Microscope."

BOSS'S MICROSCOPE.

79

of construction, in those parts especially which are most
liable to tremor, and to the due balancing of the weight
of the different parts upon the horizontal axis. The
" coarse " adjustment is made by the large milled-head

Fig. 39. — Ross's No. la Large Microscope, with Binocular arrangement and

Object-glass. Scale &.
B. Sub-stage of ditto, with new Achromatic Condenser. Scale $.

situated just behind the summit of the uprights, which
turns a pinion working into a rack 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 con-

80 THE MICROSCOPE.

cealed by the stage-fittings) is attached to the other end of
the axis of the pinion (as in fig. 39), 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 pro-
jecting 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
traversing 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 coincidence of the axis of the body with
the centre of the stage, and with the axis of the illu-
minating 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 laid, 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
microscope, its perfect adjustment being then obtained
by traversing movements. 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
two- thirds of a revolution, without in the least disturbing
the place of the object, or removing it from the field of
the microscope. This rotatory movement is useful for two
purposes — first, in the examination of very delicate objects

POWELL AND LEALAND'S MICROSCOPE. 81

by oblique ligbt, in order that, without disturbing the
illuminating apparatus, the effect of the light and shadow
may be seen in every direction, whereby important addi-
tional information is often gained ; and, 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 rota-
tion of either of the prisms themselves. The graduation
of the circular rack, moreover, enables it to be used as
a goniometer. In the improved form of this instrument
here represented, the whole stage-apparatus is made so
thin, and the opening beneath so large, as to permit the
employment of light of extreme obliquity ; and to enable
the mirror to afford this, it is mounted upon an extending
arm, the socket of which slides upon a cylindrical stem.
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. Eoss the " secondary
stage " (shown separately at B), which consists of a cylin-
drical tube for the reception of the achromatic condenser,
the polarizing prisms and other fittings as in Messrs. Powell
and Lealand's arrangement; it is here shown as fitted with
a condenser specially devised by Mr. T. Ross for the illu-
mination of a large field under low magnifying powers.
To this secondary stage, also, a rotatory motion is com-
municated by the turning of a milled-head ; and' a tra-
versing 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
that its axis may be brought into perfect coincidence with
the axis of the " body."

The mechanical movements and general finish of the
instrument is all that can be desired by the practised
observer, and tends towards that saving of time and
labour as essential in microscopical pursuits as in other
branches of science. Although our description is confined
to Mr. Ross's first-class microscope, other instruments
without the accessory arrangements described may be had
equally well made and suited to the means of the student,
ranging in prices from 121. 12s. upwards.

G

THE MICROSCOPE.

The general plan of Powell and Lealand's Compound
Microscope is represented in fig. 40. The tripod-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

Fig. 40.— Powell and Lealand's Microscope, with Amid prism arrange^
for oblique illumination.

action by the double-milled head, whereby the coarse au-
justment of the focus is obtained. To the upper part of
the triangular bar a broad arm is fixed, bearing the com-
pound body ; this arm is hollow, and contains the mechanism
for the fine adjustment, which is effected by turning the
small milled-head. The arm is connected with the tri-
angular bar by a strong conical pin, on which it turns, so
that the compound body may be moved aside from the
stage when necessary ; by a mechanical arrangement it

LADD'S MICROSCOPE. 83

stops when central. The stage is of an entirely new con-
struction, having vertical, horizontal, and circular move-
ments, and graduated for the purpose of registering objects
so as to be found at pleasure; and in order to do this
effectually a clamping piece is provided against which the
object slide rests, and the circular motion of the stage is
stopped. It is an exceedingly effectual method of finding
a favourite object. The stage is remarkably strong, and
at the same time so thin, that the utmost obliquity of
illumination is attainable, the under portion being entirely
turned out : it has a dove-tailed sliding bar moveable
by rack and pinion ; into this bar slides the under stage,
having vertical and horizontal motions for centering, and
also a circular motion ; into the stage are affixed the
various appliances for underneath illumination, removed
in our woodcut. Their achromatic condenser is of 170°
aperture, with nine openings and five central stops. The
openings and stops having independent movements, the
manipulator can regulate these at will, which is admitted
to be an improvement. There is an especial appliance
provided for the use of a set of dark- wells, with or with-
out the condenser. The mirror is attached to a quadrant
of brass and two arms, in order to obtain greater obliquity
of illumination ; the whole fits into a short piece of tube
made to slide either up or down the long tube attached
to the bottom of the stage by which the mirror is con-
nected with the other part of the stand ; the reflectors
are both plane and concave, as in other instruments.

Powell and Lealand have another pattern, somewhat
resembling the instrument just described, but larger and
more massive in its general arrangements. The construc-
tion of the stage and sub-stage differ entirely : both of
these rest on a large solid brass ring, firmly attached to
the stem of the instrument. The upper side of this ring
bears a sort of carriage that supports the stage, and to
this carriage a rotatory motion is given by a milled-head,
the amount of the movement which may be carried through
an entire revolution being exactly measured by the gradua-
tion of a circle of gun-metal, which is borne on the upper
surface of the ring. The rotatory action of the stage being
thus effected beneath the traversing movement, the center-

G2

84 THE MICROSCOPE.

ing of an object "brought into the axis of the microscope
is not disturbed by it ; and the workmanship is so accurate
that the stage may be driven through its whole revolution
without throwing out of the field an object viewed with
the ^th objective. The stage withal is made thin enough
to admit of the most oblique light being thrown on the
object, such as that obtained by the use of the Amici
prism, as shown arranged in the preceding figure. The
sub-stage is also provided with rotatory, rectangular, and
vertical movements, and is made in such a manner as to
admit of the simultaneous use of the polarising prism and
of the achromatic condenser. This instrument combines
remarkable steadiness with great solidity, and is so well
balanced on its horizontal axis that it requires no clamping
in whatever position it may be placed.

• Cheaper instruments are furnished by Powell and Lea-
land, such as a student's microscope, with f -inch stage
movement, coarse and fine adjustments to body, plane and
concave mirrors, revolving diaphragm, Lister's dark-wells,
and two eye-pieces, for the price of SI.

An improved form of microscope (fig. 41) is manu-
factured by Mr. Ladd, of Beak Street, Eegent Street ;
having a stand so simple and light in its construction as
to render it very portable and useful. It is fitted with a
magnetic stage, which facilitates the moving of the objects
when placed on it by the unaided fingers; a point of some
importance to such microscopists as desire to retain and
cultivate delicacy of touch in preference to that growing
dependence upcm mechanical movements. The main
features of this form of microscope are, that the bear-
ings for the compound body, stage, and sub-stage are all
fitted, while connected together into the dovetailed brass
bar running from top to bottom of the instrument. The
magnet is attached to the under part of the stage, and a
gilt iron bar, ledge, or keeper, serves for an object-rest.
The sub-stage is constructed -of three thin plates having
rectangular movements, the top one having a tube attached,
into which is fitted the Polariscope, spotted lens, &c., the
focussing of which is by a rack placed below. The mirror,
being provided with a double-jointed arm, can be used
with any amount of obliquity. The stand forms a tripod

BAKER'S MICROSCOPE. 85

strengthened by cross bars ; the beauty of the chain move-
ment (with which all Mr. Ladd's microscopes are furnished)
is made apparent by a simple and effective fine adjustment

Fig. 41.— Ladd's Students Microscope.

attached to the milled head, thus making the one adjust-
ment subsidiary to both purposes. The general appearance
of the instrument is one of elegance, stability, lightness,
and compactness.

Mr. Baker (Holborn) has kept pace with our leading
manufacturers, and his first-class microscopes fairly entitle
him to take his place among the makers of superior in-
struments. One of his best forms, shown in fig. 42,
combines good workmanship with remarkable solidity and
completeness in all its details.

In this instrument, two uprights are strengthened by
two internal buttresses mounted on a solid tripod. At
the upper part, and between the uprights, is an axis upon
which the whole of the upper part of the instrument
turns, so as to enable it to take a horizontal, vertical, or

86

THE MICROSCOPE.

any intermediate position — such, for instance, as that
shown in the drawing. This moveable part is fixed to
the axis near the centre of gravity, and consists of the
stage and the arm screwed into the square bar which

t'ig. 42. — Maker's ho. 1 (Jon^o and, Microscope.

carries the tube or body, with object-glass screwed into
its place. The upper or table-stage has rectangular rack-
and-pinion movements, working one inch in each direction.
A circular and sliding motion is also given to the top plate.

BAKERS STUDENT'S.

87

The square bar, together with the arm and microscope-
tube, is moved by the larger milled-heads, and a more

Fig. 43.— Baker's No. 2 Compound Microscope.

delicate adjustment of this optical part is effected by the
smaller milled-head seen behind the body. This milled-
head is graduated, affording a means of measuring the

88

THE MICROSCOPE.

thickness of an object or the thin covering-glass. The
other milled-head fixes the arm to the square bar. Below
the table-stage is the secondary or sub-stage, into which is
fitted the diaphragm, polariscope, achromatic condenser,
and other illuminating apparatus. It is supplied with
centering screws, circular and focussing rack-work, giving
perfect and accurate adjustments. Sliding upon the lower
end of the instrument is a large double mirror, with
double-jointed arm, and above this a full-size Amici prism
for oblique illumination. The microscope is furnished with
a draw-tube, divided into tenths of an inch, and is thus
rendered as perfect as is necessary for all purposes.

Fig. 43 represents Mr. Baker's smaller Compound
Microscope, differing in some respects from that just

Fig. 44.— Maker's Educational Microscope.

BAKER'S BINOCULAR.

described. It is not fitted with sub-stage, but such an
appliance may be readily attached, dovetailed grooves being
left for the purpose. The motions to stage and body, and
general finish, are similar to those of the best instruments,
and it is altogether such a microscope as can be well re-
commended for medical or other purposes where a good
stand is required, and to which it is intended that further
additions shall be hereafter made.

A smaller compound achromatic microscope, called the
" Educational," fig. 44, is made by Mr. Baker. This is
peculiarly adapted for students, and is supplied in a neat
mahogany case, with the necessary apparatus and excellent
object-glasses, for the small price of 4£ 4s. If with iron
stand and in portable case, 31. 3s.

Mr. Baker, in his binocular instrument, fig. 46, has
succeeded in reducing some of the difficulties to a mini-
mum. The setting of the prism, with its necessary stops,
is so contrived that it is contained
in one piece or fitting, so that
when the monocular body is re-
quired to be used, this piece can
be removed, and an uninterrupted
field obtained, the light enter-
ing the tube at the utmost obli-
quity for high powers. At fig. 45,
the body and nose-piece is seen de-
tached. It has this advantage,
that the prism remains in perma-
nent adjustment when the brass
nose-piece B is screwed home.

Another feature in connexion
with the use of the binocular,
and not the least important, is
that of illumination ; we have
been much pleased with the aim-

pie arrangement Of a cheap COn- A. Bodies detached Jrom Stand.

denser by the same optician. It *• Nose-piece conning Prism.
consists of two plano-convex lenses, the lower one being
hemispherical ; the upper lens (of a somewhat smaller
diameter) is placed just within its focus; the two are
fitted into a sliding-tube which admits of easy adjustment.

THE MICROSCOPE.

This condenser has the property of throwing a soft
white- cloud with low powers, adding greatly to the defini-
tion and stereoscopic effect of the binocular ; it is moreover
useful in giving a full, clear field with the higher powers.

Fig. 46. — Baker's Studenfs Binocular Microscope.

"We can also refer with some confidence to the Student's
Binocular Microscope produced by Mr. Baker; it pos-
sesses remarkable excellence for the small sum charged
for it. This instrument is rather larger than the Educa-
tional by the same maker, and is fitted with sliding-stage.
It has the usual coarse and fine movements, and is supplied

PILLISCHEB'S MICEOSCOPE. 91

with a double mirror and one pair of eye-pieces, the latter
having rack and pinion adjustment. It is seen in fig. 46,
and sold as there represented for 61. — a less sum than is
charged for altering the larger microscopes.

Fiy. 4.7,—PiUischer's No. 1 Binocular Microioopt.

92 THE MICROSCOPE.

Mr. Pillischer (New Bond Street) is favourably known
for the excellency of his instruments. His No. 1 Micro-
scope (fig. 47) is of good workmanship, and somewhat
novel in design. It is constructed on a plan which may
be described as intermediate between that of Smith and
Beck and Ross's well-known pattern, and in point of
finish is quite equal to the microscopes of the first-
mentioned manufacturers. The bent form given to the
arm carrying the body gives increased strength and soli-
dity to the instrument, although it is doubtful whether
it adds to its steadiness when placed in the horizontal
position. The straight body rests for a great part of its
length upon a straight bar of solid brass, ploughed into
a groove for the reception of the rack which is attached
to the body, the groove being of such a form that the rack
is held firmly while it glides smoothly through it. This
is so firm, and gi'/es such a steady uniform motion, as
almost to render the fine adjustment unnecessary. The
tine adjustment screw is removed from the usual position
and placed in front of the body, just above and in front
of the Wenham prism. The binocular bodies are inclined
at a smaller angle to one another than in most makers,
which, with the range of motion given to the eye-pieces
Vy the rack and pinion, enables observers whose eyes
differ greatly in separation to use the instrument with
equal facility. The prism is so well set that it illuminates
both fields with equal intensity. The stage is provided
with rectangular traversing movements to the extent of
an inch and a quarter in each direction. The milled-heads
which effect these are placed on the same axis, instead of
side by side, one of them — the vertical one — being re-
peated on the left of the stage, so that the movements
may be communicated either by the right hand alone or
by both hands acting in concert. The stage-plate has the
ordinary vertical and rotatory motions, but to a much
greater extent than usual ; and the platform which carries
the object is provided with a spring clip to secure the
object when the stage is placed in the vertical position.
A regularly fitted sub-stage with centering screws is made
in the usual way to carry an achromatic condenser, dia-
phragm, polarising, and other apparatus — in short, no

PILLISCHER'S STUDENT'S.

93

instrument can be better adapted than this to all the
ordinary wants of the pathologist or skilled microscopist.
The object-glasses furnished with this instrument are
thoroughly good working powers.

i''ig. 4S. — PMischer's larger Student's Microscope.

Fig. 48 is a compound microscope, made by Mr. Pilli-
scher for the use of students. In every respect it is
a compact, handy instrument, and well finished in its
mechanical details. The body is furnished with a draw-
tube, .by which its length can be increased about six

94 THE MICROSCOPE.

inches ; coarse and fine adjustments ; moveable mecha-
nical stage as in the larger instrument; two eye-pieces;
superior objectives of 1 inch and ^-inch focus, of 15° and
80° angular aperture ; condenser, polarising apparatus and
selenite, parabolic reflector, diaphragm, &c., packed in a
mahogany case, for the price of 151. 15s. This instru-
ment takes its place among the best of its class.

Fig. W.—Pillischefs 52. Prize Medal Microscope.

The instrument fig. 49 Mr. Pillischer designates his
51. Prize Medal Microscope, is an excellent student's in-
strument, simple and novel in its construction, and well
adapted to almost any description of work. The body is
furnished with a draw- tube and fine adjustment ; the arm
which supports this derives additional steadiness from the
square solid form given to the box in which the rack and
pinion move. A convenient and simple lever-stage, with
a double joint, enables the right hand to move the object

95

in any direction with great facility. This can be readily
detached when it is desired to clear the stage for a frog-
plate, &c. The instrument is furnished with a dividing
set of powers, working with a tolerably flat-field j dia-
phragm, condenser for opaque objects, live box, &c. The
whole packs in a neat case, measuring only 8x6 inches ;
forming one of the most portable microscopes for the use
of the student we have seen.

The Binocular manufactured by Mr. Collins (Great Titch-
field Street, Portland Place), is constructed on the model
suggested by Dr. Harley, and contains all the recent im-
provements for combining rapidity of application with
simplicity in manipulation. Indeed, so far as the saving
of time is concerned, we scarcely know how a change for
the better could be devised. The whole of the appliances
of the instrument, prism, polariscope, stage condenser,
objectives of both high and low powers, &c. are attached
to the microscope itself, and that, too, in such a manner
as to enable the observer to place them in exact position
without the turn of a single screw or a moment's delay.

Collins's Binocular, represented in fig. 50, is fitted into
the bottom of a mahogany box, which forms at the same
time the stand ; round it a groove is run to receive the
lip of a glass shade. The instrument itself is made of
polished brass, and is eighteen inches high. The eye-
pieces are supplied with shades (a a) to protect the eyes.

At the end of the transverse arm (/) is the box which
contains both Wenham's binocular prism and the analyser
of the polariscope ; and by merely drawing it a little out,
or pushing it further in, the instrument can be instantly
changed from a binocular to a monocular, and still further
to a polarising microscope.

Immediately beneath (/) are the two objectives, a
quarter and an inch ; so that, in order to change the
power, all that is necessary is to slide them backwards or
forwards. Moreover, these are fitted with the universal
screw, so that either of them may be detached, as in an
ordinary instrument, and a quarter, or one-eighth, or other
power put in its place, at the option of the observer. The
instrument is fitted with a coarse and fine adjustment, and
has the additional advantage of a magnetic stage, in the

96

THE MICROSCOPE.

cross-bar (h) of which is a groove, in order that the ob-
server may enjoy the luxury of applying a Maltwood's
finder, as in larger instruments possessing moveable stages.

Fig. 50.- Collins' s Binocular Microscope.

Beneath the stage is seen the polariser (p), fitted into the
circular diaphragm. The double mirror (m) possesses a
triple joint, so that it can be applied obliquely in all
directions.

Collins's Student five-guinea Binocular Microscope con-
sists of two eye-pieces, rack-adjustment, top-sliding stage,
wheel of diaphragms, concave mirrors with adjustments,
axes for inclining to any angle, tweezers and glass plate,
1 in. and J in. achromatic objectives, C series. Packed

COLLINS'S STUDENT'S. 97

in polished mahogany cabinet complete (fig. 51): an ex-
ceedingly cheap instrument.

Fig. 51. — Collins' c Student's Binocular Microscope.

Collinses Lawson Binocular Dissecting Microscope. —
This instrument is intended to supply a want, often felt
in anatomical and botanical investigations, when only a
moderate magnifying power is required.

In consequence of using both eyes it can be worked with
for a length of time with great comfort. A large range of
field is obtained, and plenty of room for working. It
consists of a neat oblong French-polished mahogany box,
measuring, when closed, 6J in. by 4 in., fig. 52. The top
and front let down by hinges, and on the inside of them
are fitted the scissors, needles, and knives necessary for
dissecting. The two sides draw out about six inches,
and are hollowed out so as to serve as rests for the hands.
The magnification is obtained by two lenses mounted in
the eye-pieces, as represented in the diagram, and may be
adjusted to the focus by a sliding bar. These show the
object beautifully in relief. Beneath is a gutta-percha
trough or stage, to pin the object down to, which can be

n

98

THE MICROSCOPE.

filled with water if required. Under this is the mirror
for transparent illumination, and the light from it is passed
through a circle of glass in the centre of the trough. The

Fig. 52. — Laivson's Dissecting Microscope.

instrument is admirably adapted for the wants of students
in the preparation and dissection of microscopic objects,
and also answers well for botanical investigations.

A cheap form of Dissect-
ing Microscope, represented
in the annexed woodcut
(fig. 53), has been con-
structed by Mr. Baker.
The instrument consists of
a solid circular foot of brass,
from the border of which
arises a firm pillar support-
ing the stage — which is of
ample dimensions — and a
firm horizontal bar, into
which the lenses are
screwed. The latter is ele-
vated and depressed by a
rack and pinion movement.
Fig. 53.- Baker's Dissecting Microscope the milled-h ead being situate

HIGHLEY*S MICROSCOPE.

99

at a level a little below tliat of the stage. In the centre
of the foot is placed the mirror, which moves in an arc
of brass ; that, in its turn, works upon a pivot in the foot
of the instrument. This handy microscope, with three
powers and mahogany case, is sold at thirty-five shillings.

Fig. 5i.—HigJiley's Professional Microscope.

Highley's Professional Microscope, shown in fig. 54, is
a useful and well-made instrument, mounted on a tripod,
with coarse and fine adjustment, mechanical stage, &c.
The mode in which the body is supported is very good
in principle, and the milled-heads for the coarse adjust-
ment are in a position which is easily reached by the left-
hand when the elbow is resting on the table, whilst the
right-hand finds the milled-heads of the traversing stage,
&c. It is arranged for a secondary stage, and all the
necessary apparatus to make a complete instrument. Al-
though the tripod is a very good form for a microscope,
it requires all the solidity and metal of a Powell and
Lealand, or it will not remain (without clamping) perfectly
steady and well balanced when placed in the horizontal

H2

100 THE MICROSCOPE.

position. The new form of tripod by this manufacturer
is, however, well constructed, and, in our opinion, possesses
advantages both in weight and steadiness.

Fig. 55.—Highley's Complete Studenfs Microscope.

Highley's Complete Microscope, of which the general
plan is shown in the accompanying fig. 55, may be classed
among the cheapest form of instruments manufactured for
the use of the student. The stand is made in the tripod
form, and the coarse adjustment given by the usual rack
and pinion motion, whilst the fine adjustment, or slow
motion, is given by a milled-head acting on the ob-
jective. The roominess, flatness, and thinness of the stage

HOW'S MICROSCOPE.

101

especially adapt it for the examination of anatomical and
pathological specimens. The usual diaphragm-plate admits
the application of illuminating apparatus, such as the
Webster condenser, polarising prism, &c. The cost of
the instrument, fitted with two good ordinary object-
lasses of 1 inch and inch focus, is 61. 16s. Qd.

Fig. 56.— How's Students Microscope.

Mr. How (Poster Lane) is the manufacturer of the im-
posing-looking instrument fig. 56. It is of fair workman-

102 , THE MICROSCOPE.

ship, suitable for all ordinary investigations, well deserving
a place among cheap microscopes for the student. The
stand is of brass, firm and well finished ; the body is
fitted with coarse and fine adjustments for focussing ; and
a draw-tube for increasing the magnifying power of the
eye-piece. The stage has an arrangement, simple but
novel in construction, by which a near approach to a
universal movement is obtained. The moveable, or upper
plate, is held to the fixed lower plate with springs, and,
although offering a convenient resistance, allows of a
smoothness of motion quite remarkable. It resembles
the magnetic stage, but is far more reliable, and can be
moved upwards, downwards, laterally, or in a slanting direc-
tion, thus enabling the microscopist to follow living objects
with great facility, superseding to some extent the more
expensive mechanical stage. A dividing set of object-
glasses is supplied with the B eye-piece, thus giving a
range of power varying from 40 to about 200 diameters.
His powers are of English workmanship, but differ from
the higher-priced objectives in having smaller angular
apertures, which is, perhaps, a legitimate mode of lessening
the cost. The instrument being made with the universal
screw, other objectives of a better class can be added at
any time. There is also a condenser mounted on a brass
stand for the illumination of opaque objects. The whole
is fitted in a mahogany case, with drawer for objects, and
sold at 51. bs.

Murray and Heath's (Jermyn Street) Student's Micro-
scope (fig. 57) is a good solid form of instrument with a
bent tripod-stand. The great object of furnishing a stand
at a low price which shall be capable, if desired, of being
adapted to the use of the higher objectives, and fitted for
the addition of all accessory apparatus, has been very
satisfactorily carried out and obtained in this microscope.
The stand is remarkably firm, and, being bronzed over, is
well adapted for daily use in the class-room or laboratory.
The adjustment is effected by a chain-movement, which
gives sufficient delicacy for powers up to the J inch. The
stage is perfectly flat, and the slide-rest moves smoothly
and freely over it. If the instrument is intended for use
in the laboratory, a glass stage is made to replace the brass

MURRAY AND HEATH'S MICROSCOPE. 103

one. The objectives furnished with this microscope are a
i inch of 75° angular aperture, and a 1 inch of 15°, both
of excellent quality. A binocular body, with fine adjust-

Fig. 57.— Murray and Heath's 51 5s. Studenfs Microscope.

ment, is added for a small additional sum, and the instru-
ment then becomes all the student can desire.

Murray and Heath's Class Microscope, represented in
fig. 58, is especially intended for the use of teachers in
the demonstration of objects to a class of students. It is
but too well known to those who are engaged in teaching
how liable the objects exhibited, and sometimes even the
object-glass itself, are to be injured in the hands of those

104

THE MICROSCOPE.

unaccustomed to use the microscope. In order to avoid
this risk, Messrs. Murray and Heath have constructed an
instrument intended to combine an ordinary with a de-
monstrating or class microscope. It consists of the usual
microscope body (A), which can be inclined at any angle,
with a mirror (c) on a ball-and-socket joint ; and a stage-
plate with universal movement. When about to be used as
a class microscope, the slide is placed in a shallow box
into which it is locked by means of a key. The same
key locks this box firmly on the stage-plate. When the
object has been found, this latter can be secured firmly
on the stage in the same manner. After focussing, the

Fig. 58.— Murray and Heath's Class Microscope.

body is also locked in its place with the same key, which
is seen at D, the final adjustment being made with the
eye-piece. The body is then placed in the horizontal posi-
tion, and fastened with a screw. The instrument can now
be passed round a class-room without possibility of injury
either to object or object-glass. The illumination is ob-
tained either by directing the instrument towards the
window, or by means of a small lamp (B), similar to that
employed by Dr. Beale, and which can be so adjusted as
to be used either for opaque or transparent objects.

This instrument appears to be particularly well adapted
to the purposes for which it is intended, and, at the same
time, if without the contrivance for locking, to be a useful
portable form for general, professional, or sea-side pur-
poses.

BEALE'S CLASS MICROSCOPE. 105

It should be added, that a novel and efficient form of
achromatic condenser is supplied with the instrument;
a series of small stops of various sizes are made to drop
into a minute hole drilled in the centre of the anterior
plano-convex lens, which convert it into a spot-glass, or
dark-ground illuminator. The whole is packed in a
mahogany case, and sold for 51. 5s.

Fig. 59.— Beetle's Clinical Microscope.

Dr. Beale devised an exceedingly simple and con-
venient form of microscope, for the purposes of clinical
instruction and of class demonstration (fig. 59). Over the
body of the microscope, which is of small dimensions, a
tube is fitted with a Ttell-shaped mouth at the end. This
tube slides freely over the body, but is capable of being
fixed at will by means of a clamping-screw. The slide con-
taining the object is placed across the bell-mouth, and held
there by a spring pressing against the back of it, and is
thus maintained perpendicularly to the axis of the instru-
ment. "When the focus is adjusted the clamping-screw is
fixed, and the fine adjustment necessary for the differ-
ences of vision in different individuals is effected by
drawing out or pressing in the eye-piece. The object and
object-glass are thus protected from mutual injury, an
accident of by no means unfrequent occurrence in careless
or unpractised hands. In this form the instrument is
adapted to the clinical examination of secretions, &c. and
must be directed by the hand towards day or artificial
light. For demonstration to a class, this instrument is
attached horizontally to a small wooden stand by means
of a clamp, supported by two legs. To the stand a small

1 06 THE MICROSCOPE.

oil-lamp is likewise attached ; and a stem proceeding from
the lower edge of the bell-mouth carries any desired form
of condensing or illuminating apparatus. This stand is
capable of being freely handed round a large class without
the focus becoming at all deranged, even when a very deep
objective is employed. This instrument is manufactured
by Mr. S. Highley.1

Fig. 60.— Warington's Universal Microscope.

While alluding to cheap microscopes, we would men-
tion Warington's Travelling Microscope, made by Salmon,
100, Fenchurch Street. It has a simple, firm, wooden
stand, whereby the cost is greatly diminished ; and an
arrangement of its parts which enables it to be used for

(1) A very simple instrument, contrived by Mr. T. C. Archer for the purpose
of being used either as a lecture-room or as an ordinary table microscope, is
manufactured by Messrs. Parkes of Birmingham, and sold, with a set of achro-
matic powers, for 21. 5s. in case complete.

SEA-SIDE MICROSCOPES.

107

viewing objects in aquaria, and under other circumstances
where any ordinary form of instrument could not be made
available. It is altogether a useful student's microscope,
having the recommendation of folding up into a small com-
pass, and not liable to much injury either from chemical
or marine investigations. For 31. this microscope is furnished

ivig. Oi. — h' a/ring ton's Mt,cruscope packed.

complete, with one eye-piece, quite sufficient for all ordi-
nary investigations.

Fig. 60 is a representation of Warington's microscope,
as it appears when put together, and ready for use ; and
fig. 61 for packing in a small wood case. The draw-tube
itself is the coarse adjustment ; whilst a finer is secured by
a well-made union-joint, into which the object-glass is made
to screw. With an additional arm for the reception of a
single lens, it can be converted into a dissecting microscope.

Fig. 62.— -Murray and Heath's Sea-side Pocket Microscope.

108

THE MICROSCOPE*

Fig. 62 represents a small portable instrument by Murray
and Heath, designated " The Sea-side Pocket Microscope,"
the chief recommendation of which is its simplicity of
construction and its small compact form ; the whole packs
into a case six inches long, and may be carried without
incumbrance in the pocket of the field-naturalist.

The body of the instrument is seen at c, supported on
a tripod, which is removed and folded up at B. If desired,
it can be used in the upright position, as at A, when a
pair of short legs placed near the mirror must be turned
down, and forms a tolerably steady support to the body.
The adjustment is made by sliding the body through the
outer tube, which carries a triple combination of achromatic
objectives. A live-box, &c. is added ; and, when packed
in a morocco case, is sold for 21. 5*.

mA Fig. 63.— Baker's Travels Microscope.

An instrument somewhat similar in appearance to the
foregoing, but differing so materially in detail as almost to

BAKER'S TRAVELLER'S MICROSCOPE. 109

claim to be a new invention (fig. 63), has been introduced
by Baker, and not inappropriately called "The Travel-
ler's Microscope," from its obvious capabilities. The aim
has been to combine steadiness with extreme portability.
The compound body is permanently affixed to the fore-leg
of the tripod-stand ; the two other legs are supported on
capstan-bar joints, which can be tightened at pleasure, or
folded up parallel with the former when not in use. The
difficulty of using high powers with an instrument the
body of which slides in cloth is well known ; the tube
becomes tarnished by continued use, and a firm adjust-
ment, which shall be easy of access, is almost indispen-
sable. To obtain an approximate focus, the inner tube is
drawn out until the combined length of the tubes is eight
inches; the body is then returned to its "jacket," and
placed at a proper distance from the stage to suit the
object-glass employed. The fine adjustment is effected by
means of a tangent-screw (fifty threads to the inch) placed
conveniently behind the body, and worked by a milled-
head acting on a spring contained in the upright which
supports the body.

This part of the instrument is very satisfactory ; it is
steady and works efficiently. A mechanical stage is not
generally applied, but caii be if required. Sufficient
movement is obtained by a plain stage, with two springs
to hold the live-box or glass slip.

This microscope is carried in a leathern case 10 inches
by 3, seen in the woodcut (similar to that made for deer-
stalking telescopes), and fitted with object-glass, eye-piece,
live-box, &c. ; the weight of the whole not exceeding two
pounds in weight, and it therefore especially recommends
itself to the field-naturalist.

The whole merit of this invention is due to Mr. Moginie,
of Mr. Baker's establishment, Holborn, who has devoted
much time and thoughtfulness towards bringing it to its
present state of perfection.

Highley's Pocket Microscope (fig. 64), for botanical or
field uses, consists of a short tube furnished with a sliding
eye-tube, fitting into an outer tube. The coarse adjustment
is made by sliding the body through the outer tube, which
carries the object ; the fine adjustment by sliding the eye-

110 THE MICROSCOPE.

tube in or out. The object, if transparent, is illuminated
either by holding up the microscope towards a white cloud,
or other source of light, or by directing it towards a mirror
laid upon the table at such an angle as to reflect the light.

Fig. 64.—Highley's Pocket Microscope.

If opaque, it is allowed to receive direct light through an
aperture in the outer tube. The extreme simplicity and
portability of the instrument — which is only six inches
long — constitutes its chief recommendation.

Norman's (178, City Eoad) Universal Educational
Microscope consists of a well-finished stand with tripod
foot and two uprights, with axis for giving inclination to
the optical part. The body has quick and slow motions,
one Huyghenian eye-piece, three achromatic object-glasses,
viz. a J-inch dividing into ^ and 1 inch, all of fair de-
nning power and English made. The stage has a large
sliding-piece, and a revolving Awheel of diaphragms ; the
mirror has sliding and oblique motions for the better illu-
mination of the object under examination. The following
apparatus is also supplied with the instrument : — a stand
condenser with adjustment, stage and hand forceps, live-
box or animalculse cage, a frog-plate for viewing the circu-
lation of the blood in the web of a frog's foot ; also three
good objects to test the different object-glasses, one hol-
lowed and two plain slips, some thin glass. The whole is
packed in a mahogany or walnut cabinet, with a drawer
for objects, lock and key, and sold for the small price of
31. 5«.

24 first-class objects, suited for the object-glasses, are
supplied with this instrument for U. Is.

Mr. E. Wheeler's (Holloway) well-made instruments de-
serve commendation and notice ; they are carefully finished
and quite up to the modern standard. The full assorted
sets of objects which Mr. Wheeler supplies in a very neat

SIMPLE MICROSCOPES. Ill

book-folding case, the names on which can be read off at
a glance, are particularly well selected. Many of the cases
are so arranged as to form complete sets of certain classes
of specimens admirably suited for educational purposes, and
also for the elucidation of general and particular principles ;
as, for instance, the various parts of an insect, to show
peculiarities of structure for the illustration of entomo-
logical lectures, the same for botanical, anatomical, &c.
Many of our drawings have been made from Mr. Wheeler's
excellent specimens.

Mr. Piper, of the Old Change Microscopical Society,
devised a convenient, cheap, and portable object-case. It
is a compact oblong paste-board box, made to contain six,
twelve, or twenty-four shallow trays, with six or twelve
divisions just the size of the ordinary glass slides. The
objects lie flat in these trays, which pack one above the
other. For handiness, neat packing, facility of finding
and reading off names of objects, this case cannot be
surpassed. It is but right to add, that it is adapted to
the use of those whose aim is the economically useful
cabinet for storing and classifying objects. This "uni-
versal" object-case is sold by Baker, Holborn.

Several forms of simple microscopes have been devised
for field use under various designations, such as " Diatom
Finders," &c. One of the most useful little instruments
of the class is that described by Mr. J. 1ST. Tomkins, in
the Trans. Micros. Soc. vol. vii. p. 57, 1859. Another
was invented by Dr. W. Gairdner of Edinburgh, and made
by Mr. Bryson of that city, neatly packed in a case for the
waistcoat-pocket. Want of space will not permit us to
enter further into this department, nor can we go- into
a critical examination of the productions of numerous
well-known makers of microscopes ; as, for instance, the
Educational Microscopes of Messrs. Smith and Beck, of
Cheapside; Mr. Browning, 111, Minories; Mr. Matthews
of Portugal Street ; Mr. Dancer of Manchester ; Messrs.
Abraham of Liverpool ; Mr. King of Bristol, &c. — all of
whom have obtained a deservedly high reputation for
their convenient forms of educational and other well-
manufactured instruments.

112 THE MICROSCOPE.

APPLICATION OP BINOCULARITY TO THE MICROSCOPE.

The application -of this principle to microscopic pur-
poses seems to have been tried as early as 1677, by a
French philosopher, le P£re Cherubin, of Orleans, a Capu-
chin friar. The following is an extract from the description
given by him of his instrument : " Some years ago I
resolved to effect what I had long before premeditated, to
make a microscope to see the smallest objects with the
two eyes conjointly; and this project has succeeded even
beyond my expectation, with advantages above the single
instrument so extraordinary and so surprising, that every
intelligent person to whom I have shown the effect, has
assured me that inquiring philosophers will be highly
pleased with the communication."

This communication long slumbered and was forgotten,
and nothing more was heard of the subject until Professor
Wheatstone's very surprising invention of the stereoscope,
which he evidently expected to apply to the microscope,
for he applied to both Eoss and Powell to make him
a binocular microscope. But this was not done; and
during the year 1853 a notice appeared in Sillimaris
American Journal of a binocular instrument constructed
by Professor Riddel of America, who contrived a binocular
microscope in 1851, with the view " of rendering both eyes
serviceable in microscopic observations." " Behind the ob-
jective," he says, " and as near thereto as possible, the light
is equally divided and bent at right angles, and made to
travel in opposite directions, by means of two rectangular
prisms, which are in contact by their edges somewhat
ground away, the reflected rays are received, at a proper
distance for binocular vision, upon two other rectangular
prisms, and again bent at right angles, being thus either
completely inverted for an inverted microscope/ or restored
to their first direction for the direct microscope." M.
Nachet also constructed a binocular microscope, upon the
same principle as his double microscope, with the tubes
placed vertically and 2 J inches distant. This had many
disadvantages and inconveniences, which Mr. F. H. Wenham
ingeniously succeeded in modifying and improving.

THE BINOCULAR MICROSCOPE. ]J3

In describing his improvements, he observes : " That in
obtaining binocularity with the compound achromatic mi-
croscope, in its complete acting state, there are far greater
practical difficulties to contend against, and which it is
highly important to overcome, in order to correct some of
the false appearances arising from what is considered the
very perfection of the instrument.

" All the object-glasses, from the one-inch upwards, are
possessed of considerable angular aperture ; consequently,
images of the object are obtained from a different point of
view, with the two opposite extremes of the margin of the
cone of rays; and the resulting effect is, that there are a
number of dissimilar perspectives of the object all blended
together upon the single retina at once. For this reason,
if the object has any considerable bulk, we shall have a
more accurate notion of its form by reducing the aperture
of the object-glass.

" Select any object lying in an inclined position, and
place it in the centre of the field of view of the micro-
scope; then, with a card held close to the object-glass,
stop off alternately the right or left hand portion of the
front lens : it will be seen that during each alternate
change certain parts of the object will alter in their rela-
tive position.

" To illustrate this, fig. 65 <*, I
are enlarged drawings of a portion
of the egg of the common bed-bug
(Cimex lecticularis), the operculum
•which covers the orifice having
been forced off at the time the
young was hatched. The figures
exactly represent the two positions
that the inclined orifice will oc-
cupy when the right and left hand

portions of the object-glass are stopped off. It was illumi-
nated as an opaque object, and drawn under a two-thirds
object-glass of about 28° of aperture. If this experiment
is repeated, by holding the card over the eye-piece, and
stopping off alternately the right and left half of the
ultimate emergent pencil, exactly the same changes and
appearances will be observed in the object under view,
i

114

THE MICROSCOPE

The two different images just produced are such as are
required for obtaining stereoscopic vision. It is therefore
evident that if, instead of bringing them confusedly toge-
ther into one eye, we can separate them so as to bring fig.
96 a b into the left and right eye, in the combined effect
of the two projections, we shall obtain all that is necessary
to enable us to form a correct judgment of the solidity
and distances of the various parts of the object.

" Diagram 3, fig. 66, represents the methods that I have
contrived for obtaining the effect of bringing the two eyes

Fig. 66.

sufficiently close to each other to enable them both to see
through the same eye-piece together, a a a are rays con-
verging from the field lens of the eye-piece ; after passing
the eye-lens b, if not intercepted, they would come to a
focus at c ; but they are arrested by the inclined surfaces,
d d, of two solid glass prisms. From the refraction of the
under incident surface of the prisms, the focus of the eye-
piece becomes elongated, and falls within the substance of
the glass at e. The rays then diverge, and after being
reflected by the second inclined surface /, emerge from the
upper side of the prism, when their course is rendered
still more divergent, as shown by the figure. The reflecting
angle that I have given to the prisms is 47|-°. I also find
it is requisite to grind away the contact edges of the
prisms, as represented, as it prevents the extreme margins

THE BINOCULAR MICROSCOPE. 115

of the reflecting surfaces from coming into operation^
which can seldom be made very perfect.

" The definition with these prisms is good ; but they
are liable to objection on account of the extremely small
portion of the field of view that they take in, and which
arises from the distance that the eyes are of necessity
placed beyond the focus of the eye-piece, where, the rays
being divergent, the pupil of the eye is incapable of taking
them all in ; also there is great nicety required in the
length of the prisms, which must differ for nearly every
different observer."

The great disadvantages of the first arrangement of the
binocular microscope were the expensive alterations
required in their adaptation : to most persons, the view
that it gave of the object was pseudoscopic, and not that
of solidity and roundness ; and the two bodies being
united at a fixed angle of convergence, the distance be-
tween their axes could not be adapted to the varying
distances between the eyes of different individuals. At
length, these, as well as other defects, have been com-
pletely overcome by the improvements the instrument
has recently received at the hands of the inventor; and
we have no hesitation in saying that Wenham's prism is
the most valuable addition the microscope has received
since the perfection of the object-glasses. The adaptation
does not at all interfere with the use of the instrument
as a monocjular microscope, and such additions as the
microspectroscope can be as easily used with it as in the
old form ; it also affords a ready comparison between
the object as seen singly, and by natural double vision,
and thus may be obtained an ever ready test, or sight
analysis of the structure under examination. Besides,
the relief afforded to the eyes is, to our sensation,
something quite marvellous, arid we believe, therefore,
much less risk is run of doing injury to vision. Objects
become easily distinguishable, more especially all opaque
or semi-opaque ones ; and for the more transparent ones
all that is required is to use care in their illumination —
diffuse the light by placing a piece of ordinary tracing or
tissue paper, or ground glass, between the light and the
object ; or even polarised light for peculiar substances will

116 THE MICKOSCOPE.

enable us to bring them out in greater perfection and
beauty. Another advantage gained by the last improvement
is, that the ordinary single-bodied microscope can be con-
verted into a binocular instrument by simply fixing an-
other tube at the proper angle, and adding a small prism
mounted in a brass box. The latter is made to slide into
the lower part of the body immediately over the objective.
By its aid the rays of light proceeding from the object
are reflected in two directions, which, by means of the
double body, are conveyed to both eyes, and thereby a
stereoscopic view of the object under observation is ob-
tained. The most important point to be observed, when
using the binocular, is that each eye has a clear view of
the object. This is readily ascertained by closing the eyes
alternately without moving the head away from the in-
strument, when, if it be found that the two images do not
quite coincide, it must be corrected by racking out or in
the draw-tubes, which should form a part of the bodies
of all binoculars. If both fields be not equally illuminated,
the object is not rendered stereoscopic.

Mr. Wenham's most important improvement consists in
splitting up and dividing the pencil of rays proceeding from
the objective by the interposition of a prism of the form
shown in fig. 67. This is so placed in the body or tube
of the microscope (fig. 68, a) as only to interrupt one-half
(a c) of the pencil, the other half (a b) going on con-
tinuously to the field-glass, eye-piece, of the principal
body. The interrupted half of the pencil, on its entrance
into the prism, is subjected to very slight refraction, since
its axial ray is perpendicular to the surface it meets.
Within the prism it is subjected to two reflections at
6 and c, which send it forth again obliquely on the line
6 towards the eye-piece of the secondary body, to the left-
hand side of the figure ; and since at its emergence its
axial ray is again perpendicular to the surface of the glass,
it suffers no more refraction on passing out of the prism
than on entering it. By this arrangement, the image re-
ceived by the right eye is formed by the rays which have
passed through the left half of the objective ; whilst the
image received by the left eye is formed by the rays which
have passed through the right half, and which have been

WENHAM'S BINOCULAR.

117

subjective to two reflections within the prism, passing
through only two surfaces of glass. The prism is held
by the ends only on the sides of a small brass drawer,
so that all the four polished surfaces are accessible, and
should slide in so far that its edge may just reach the

Fig. 67.

Fig. 68.

central line of the objective, and oe drawn back against
a stop, so as to clear the aperture of the same. In this
case the straight tube acts as a single microscope.

" Both the transmitting and reflecting surfaces of the
prism should be accessible, for the purpose of wiping off
particles of dust or mildew — particles of any kind ad-
hering to the prism will prevent total reflection at the
point of contact. If the prism is well made and polished,
and of the smallest size possible for admitting the pencil,
the difference between the direct and reflected image is
^scarcely appreciable.

" The binocular constructed as we have described performs
satisfactorily up to the £th inch; but for powers above

118 THE MICROSCOPE.

this a special arrangement is needed for the prism, -which
must be set close behind the lens of the £th or
TVth inch, in order to obtain an entire field of view in
each eye. This it is found to accomplish perfectly when
placed in that position ; but still, for very delicate test-
objects, requiring the utmost extent of aperture for their
definition, it will not resolve them as clearly as with a
single body, from the fact that the aperture is divided
and half only effective in each eye. This difficulty has
at length been nearly overcome by Messrs. Powell and
Lealand, by means of an inclined disc of glass with
parallel sides, the partial reflection from the under surface
of which is again reflected into the second eye, by means
of a rectangular prism. As the disc is made thinner, so
do the images approximate and the distance between them
diminish. Therefore, if the glass is made as thin as pos-
sible, and a very slight angle givea to the two sides, it
may be so arranged that both images are ultimately com-
bined at the eye-piece. There would be no difficulty in
working the glass to a mean thickness of 5^5 th of an
inch. In this form the angle between the sides would be
so exceedingly small that - the chromatic effect, considered
as a prism, would be inappreciable in the direct eye-tube.1
" A strong light should be avoided for the illumination
of objects observed with the binocular microscope, as
direct rays tend to destroy the stereoscopic effect. The
illuminator that has been found to give an excellent effect
consists of three plano-convex lenses, so combined as to
give a very large area of light, as well as great intensity.
The final emergent pencil should have, if possible, an
angular aperture of 170°. Just above the top lens should
be .placed a sliding-cap, the crown of which is covered
with a diffusing film. For this, the best material is the
beautiful snow-white powder obtained from turning glass
with a diamond turning-tool. This may be obtained from
the opticians, and should be well washed to free it from
the larger particles. A thin film of this impalpable
powder should be compressed between two discs of thin
glass, and fixed in the top of the sliding-cap, which is to
be raised or lowered till the most intense light is obtained

(1) Quarterly Journal of Mwroscopieal Science, vol. i. 1861, and vol. vi. 1866

SPECTRO-MIOROSCOPT. 119

on the film. This illuminator is employed in the position
of the achromatic condenser, and a disc of slightly coloured
neutral tint-glass placed below the bottom lens increases
the purity of the light, and gives greater distinctness to
objects. The effect of this diffusing film is sometimes
enhanced by condensing light down on the object from
above as well as from below."

An important improvement has been effected in Nachet's
binocular by Professor Smith, of Kenyon College, U.S.
It consists in the adaptation of Nachet's set of prisms for
use as eye-pieces, with any monocular instrument. The
prisms being mounted in a light material, vulcanite, are
made to fit into the microscope body and take the place
of the ordinary eye-piece. The image transmitted by the
objective is brought to a focus on the face of the first
equilateral triangular prism by the intervention of an
erector eye-piece placed beneath it. The second set of
prisms are by a rack-and-pinion movement adjusted to
suit any visual angle; while the illumination of both
fields is quite perfect, even with high powers.

SPECTRO-MICBOSCOPT.

The application of the spectroscope to the microscope is
one of the most beautiful additions the instrument has lately
received. The honour of the invention appears to belong
to H. C. Sorby, F.E.S., whose first experiments were made
with a simple triangular prism, arranged and fixed below
the stage, so that a minute spectrum of any transparent
object might be readily examined, when placed in position
immediately before the slit. Shortly after the publication
of Mr. Sorby's paper, Mr. Huggins proposed to adapt a
direct vision spectroscope to the eye-piece, and so enable
us to view the spectra of opaque as well as transparent
objects. The exact form of prism finally adopted, and
now in general use, is that known as the Sorby-Browning
Spectroscope.

The first spectroscope made by Mr. Browning (Minories)
is represented in fig. 69. A prism is placed at P, which is
enclosed in a box, so as to give a black field, by excluding

120

THE MICROSCOPE.

extraneous light. The rays of light, after passing between
the knife-edges at K, are rendered parallel by means of
the lens at L. Then passing through the prism and con-
denser (c), they reach the object at o. The light is placed
at w, and if it be proposed to examine a liquid, it can be
placed in a small tube (T), closed at one end ; or a trans-
parent object may be placed on the stage in the usual

Fig. 69.— Sectional view of the Browning Spectroscope.

manner. By the addition of a small telescope, instead of
a condenser, this contrivance can be applied to a micro-
scope in place of the eye-piece, and it can then be used for
the examination of opaque objects.

The great objection to this form is its limited range,
and the constant shifting of parts it requires for finding
and focussing the object, and the awkward position of the
microscope, whether it be used under the stage or as an
eye-piece.

Fig. 70.— The Browning Hiiggin^ Micro-tpectroscope.

The apparatus used by Mr. Huggins (fig. 70) was a star

SPECTRO-MICROSCOPY. 121

spectroscope, of which the collimative-tube was inserted
in the body of the microscope, instead of an eye-piece.
With this apparatus he has succeeded in obtaining a
spectrum showing the absorption-bands from a mere frag-
ment of single blood- disc, when mounted as a transparent
object. In fig. 70, K represents the knife-edges, o the tube
containing the collimating-lens, p the prisms, T the teles-
cope, and M the micrometer ; the object is placed on the
stages at o, and must be illuminated from below if trans-
parent, or, if opaque, from above by any kind of con-
denser.

Mr. Sorby suggested that a prism might be made of
dense flint-glass, of such a form that it could be used in
two different positions, and that in one it should give
twice the dispersion that it would in the other, but that
the angle made by the incident and emergent rays should
be the same in "both positions.

Fig- 71. Fig. 72.

Figs. 71 and 72 represent prisms of the kind made by
Mr. Browning, used in two different positions, i and i'
being the same angle as i and i'.

For most absorption-bands, particularly if faint, the
prism would be used in the first position, in which it
gives the least dispersion ; but when greater dispersion
is required, so as to separate some particular lines more
widely, or to show the spectra of the metals, or Fraun-
hofer's lines in the solar spectrum, then the prism must
be used as in fig. 72. This answers well for liquids or
transparent objects, but it is, of course, not applicable to
opaque objects.

122

THE MICROSCOPE.

To combine both, purposes, some form of direct vision-
prisms which can bo applied to the body of the micro-
scope is required. Fig. 73 represents the arrangement of
direct vision-prisms, invented by A. Herschel. The line
R R' shows the path of a ray of light through the prisms,
where it would be seen that the emergent ray R' is parallel
and coincident with the incident ray R.

Fig. 73.

Fig. 74.

Another very compact combination is shown in fig. 74.
Any number of these prisms (p P P.) may be used, accord-
ing to the amount of dispersion required. They are
mounted in a similar way to a Mcols' prism, and are
applied directly over the eye-piece of the microscope.
The slit s s is placed in the focus of the first glass (F) if
a negative, or below the second glass if a positive eye-
piece be employed. One edge of the slit is moveable,
and, in using the instrument, the slit is first opened wide,
so that a clear view of the object is obtained. The part
of the object of which the spectrum is to be examined
is then made to coincide with the fixed edge of the slit,
and the moveable edge is screwed up, until a brilliant
coloured spectrum is produced. The absorption-bands
will then be readily found by slightly altering the focus.
This contrivance answers perfectly for opaque objects

SPECTEO-MICROSCOPY. 123

without any preparation ; and, when desirable, the same
prism can be placed below the stage, and a micrometer
used in the eye-piece of the microscope, thus avoiding a
multiplication of apparatus.

The latest improvement is that shown in fig. 75, also
effected, by Mr. Browning, who deserves great credit for
the skill displayed in the invention and construction of
this new and elegant micro-spectroscope.

Fig. 75.— The Sorby-Browning Micro-spectroscope.

The prism is contained in a small tube, which can be
removed at pleasure. Below the prism is an achromatic
eye-piece, having an adjustable slit between the two
lenses, the upper lens being furnished with a screw
motion to focus the slit. A side slit, capable of adjust-
ment, admits, when required, a second beam of light from
any object whose spectrum it is desired to compare with
that of the object placed on the stage of the microscope.
This second beam of light strikes against a very small
prism, suitably placed inside the apparatus, and is reflected
up through the compound prism, forming a spectrum in
the same field with that obtained from the object on the
stage.

A is a brass tube, carrying the compound direct vision
prism. B, a milled head, with screw motion to adjust the
focus of the achromatic eye lens, c, milled head, with
screw motion to open or shut the slit vertically. Another

124 THE MICROSCOPE.

screw at right angles to c, but which from its position
could not be shown in the cut, regulates the slit hori-
zontally. This screw has a larger head, and when once
recognised cannot be mistaken for the other. D D is an appa-
ratus for holding a small tube, that the spectrum given
by its contents may be compared with that from an object
on the stage. E is a square-headed screw, opening and shut-
ting a slit to admit the quantity of light required to form
the second spectrum. A light entering the round hole
near E, strikes against the right-angled prism, which we
have mentioned as being placed inside the apparatus, and
is reflected up through the slit belonging to the compound
prism. If any incandescent object be placed in a suitable
position with reference to the round hole, its spectrum
will be obtained, p shows the position of the field lens of
the eye-piece. G is a tube made to fit the microscope to
which the instrument is applied. To use this instrument
insert G, like an eye-piece in the microscope tube, taking
care that the slit at the top of the eye-piece is in the same
direction as the slit below the prism. Screw on to the
microscope the object-glass required, and place the object
whose spectrum is to be viewed on the stage. Illuminate
with the stage mirror if it be transparent; with mirror,
Lieberkiihn, and dark well, by side reflector, or bull's-eye
condenser if opaque. Remove A, and open the slit by
means of the milled-head, not shown in cut, but which is
at right angles to D D. When the slit is sufficiently open
the rest of the apparatus acts like an ordinary eye-piece,
and any object can be focussed in the usual way. Having
focussed the object, replace A, and gradually close the slit
till a good spectrum is obtained. The spectrum will be
much improved by throwing the object a little out of
focus.

Every part of the spectrum differs a little from adjacent
parts in refrangibility, and delicate bands or lines can only
be brought out by accurately focussing that particular part
of the spectrum. This can be done by the milled head B.
Disappointment will occur in any attempt at delicate in-
vestigation if this direction be not carefully attended to.

At E a small mirror is attached, which is omitted in the
diagram to prevent confusion. It is like the mirror belo^

SPECTRO- MICROSCOPY. 125

the stage of a microscope, and is mounted in a similar
manner. By means of this mirror light may, be*reflected
into the eye-piece, and in this way two spectra may be
procured from one lamp.

For observing the spectra of liquids in cells or tubes
of considerable diameter, say not less than i\yth of an
inch, powers from 2 inch to 1 inch will be the most
suitable, and of course low powers only can be used to
investigate the spectra of opaque objects ; but when the
spectra of very minute objects are to be viewed, powers of
from half an inch to one-twentieth, or even higher, may
be employed.

Blood, madder, aniline red, permanganate of potash, in
crystals or solution, are convenient substances to begin
experiments with. Solutions when made too strong pro-
duce dark clouds instead of absorption bands. Professor
Church has recently pointed out that zircon, an almost
colourless stone, gives well-defined absorption-bands.

Mr. Sorby says of the correct performance of a spectrum
adaptation, " The best tests are, first, that the absorption-
bands in blood can be seen when they are very faint ;
second, to well divide the bands in permanganate of
potash; and, third, to see distinctly the very fine line
given in the red by a solution of chloride of cobalt dis-
solved in a concentrated cold solution of chloride of calcium :
there is a line so fine that it looks like a Fraunhofer's
line. An instrument that shows all these well is all that
can be desired.

" The objects most easily obtained, and which furnish
us with the greatest variety of spectra, are coloured
crystals, coloured solutions, and coloured glasses. The
spectrum microscope enables us to examine the spectra ol
very minute crystals, of very small quantities of material
in solution, and of small blow-pipe beads. As previously
named, the thickness of the object makes a very great
difference in the spectrum. For example, an extremely
thin crystal of ferricyanide of potassium cuts off all the
blue rays, and leaves merely red, orange, yellow, and more
or less green ; but on increasing the thickness, the green
and yellow disappear ; and when very much thicker, little
else but a bright red light is transmitted. In all such

126 THE MICROSCOPE.

cases, the, apparent magnitude of the effect of an increase
in thickness is far greater when the object is thin than
when thick, and past a certain thickness the change is
comparatively very slight. If only small crystals can be
obtained, it is well to mount a number of different thick-
nesses ; but when it is possible to obtain crystals of suf-
ficient size, it is far better to make them into wedge-
shaped objects, since then the effect of gradual change in
thickness can easily be observed. Different kinds of
crystals require different treatment, but, as a general rule,
I find that it is best to grind them on moderately soft
Water-of-Ayr stone with a small quantity of water, which
soon becomes a saturated solution, and then to polish
them with a little rouge spread on paper laid over a flat
surface ; or else, in some cases, to dissolve off a thin layer
by carefully rubbing the crystal on moist blotting-paper
until the scratches are removed. Then, whenever it is
admissible, I mount the crystal on a glass, and also cover
it with a piece of thin glass with Canada balsam. Strongly
coloured solutions may be examined in test-tubes, or may
be kept sealed up in small bottles made out of glass tubes,
the light then examined being that which passes through
the centre of the tube from side to side. (Most of these
solutions require the addition of a little gum Arabic to
make them keep.) Such tubes may be laid on the ordinary
stage, or laid on the stage attached to the eye-piece.
Smaller quantities may be examined in cells cut out of
thick glass tubes, one side being fixed on the ordinary
glass with Canada balsam, like a microscopic object, and
the other covered with thin glass, which readily holds on
by capillary attraction, or may be cemented fast with gold
size or Canada balsam, if it be desirable to keep it as a
permanent object. Such tubes may be made of any length
that may be required for very slightly-coloured solutions.
Cells made out of spirit thermometer tubes, so as to be
about j\yth of an inch in diameter, and \ an inch long,
are very suitable for the examination of very small quan-
tities ; but where plenty of material can be obtained, it
is far better to use cells cut out of strong tubes, having
an interior diameter of about f ths of an inch, cut wedge-
shape, so that the thickness of the solution may be £th

SPECTRO-MICRO8COPY. 127

of an inch, or more, on one side, and not above 3l0th on
the other ; and then the effect of different thicknesses can
easily be ascertained.

" Fortunately, the various modifications of the colouring
matter of blood yield such well-marked and characteristic
spectra, that there are few subjects to which the spectrum-
microscope can be applied with greater advantage than the
detection of blood-stains, even when perfectly dry. For
this purpose condensed light may be used, provided a
sufficiently bright light be thrown on the object by means
of a parabolic reflector or bull's-eye condenser. A speck
of blood on white paper shows the spectrum very well,
provided it be fresh, and the colour be neither too dark
nor too light, and the thickness of the colouring matter
neither too great nor too little. A mere atom, invisible to
the naked eye, which would not weigh above the icoioooth
of a grain, is then sufficient to show the characteristic
absorption-bands. They are, however, far better seen in
solution. About yo^th of a grain of liquid blood, in a cell
of ^th of an inch in diameter, and J an inch long, gives
a spectrum as well marked as could be desired. In
exhibiting the instrument to a number of persons at a
meeting, I have found that no object is more convenient,
or excites more attention, than one in which a number of
cells are fixed in a line, side by side, containing a solution
of various red-colouring matters. In one I mount blood,
which gives two well-marked absorption-bands in the
green ; in another magenta, which gives only one distinct
band in the green; and in another I place the juice of
some red-coloured fruit, which shows no well-defined
absorption-band. Keeping a larger cell containing blood
on the stage attached to the eye-piece, these three objects
can be passed one after another in front of the object-glass,
and the total difference between the spectrum of blood and
that of either fruit-juice or magenta, and the perfect iden-
tity of the spectra when both are blood, can be seen at
a glance. By holding coloured glasses, which cut off the
red, but allow the green rays to pass, we can readily. show
how the presence of any foreign colouring-matter, which
entirely alters the general colour, might not in any degree
disguise the characteristic part of the spectrum ; and by

128

THE MICROSCOPE.

changing the cell held on the eye-piece for a tube con-
taining an ammoniacal solution of cochineal, it is easy to
show that, though it yields a spectrum with two absorp-
tion-bands, more like those due to blood than I have seen
in any other substance, they differ so much in relation,
size, and position, that there is no chance of their being
confounded when compared together side by side." l

We have been usually taught that the red-blood corpuscles consisted of two
substances, haematin and globulin; but later researches lead to the belief
that they consist of one crystalline substance, termed globulin or hcemato-globu-
lin. A solution of this substance, as well as of certain products of its decom-
position, produces the absorption-bands referred to. Hoppe was the first to
demonstrate this fact : he found that a very dilute solution of blood was suffi-
cient for the purpose. Professor Stokes proved that this colouring-matter is

capable of existing in two
statesofoxidation,andthat
a very different spectrum
is produced according as
the substance, which hrf
has termed cruorine, is in
a more or less oxidised
condition. 2 Proto-sulphate
of iron, or proto-chloride
of tin, causes the reduction
of the colouring-matter,
and, by exposure to air,
oxygen is absorbed, and
the solution again exhibits
the spectrum character-
istic of the more oxidised
state. The different sub-
stances obtained from
blood colouring - matter
_ _ produce different bands.

I 111 9B'] IIBH1 HHilHHH Thus, hmnatin gives rise
• to a band in the red spec-
• tram ; hcemato - globulin
I produces two bands, the
• second twice the breadth
of the first in the yellow
portion of the spectrum
between the lines D and E,
No. 1. The absorption-
bands differ according to
the strength of the solu-
tion employed, and the
medium in which the blood-
salt is dissolved ; but an
exceedingly minute pro-
portion dissolved in water
is sufficient to bring out
very distinct bands.

No. 1. Arterial Blood, Scarlet Cruorine.

No. 2. Venous Blood, Purple Cruorine.

No. 3. Blood treated with Acetic Acid.

II

No. 4. Solution of Hcematin.

ABSORPTION-BANDS, AFTER STOKES.

(1) Popular Science Review, January, 1866.

(2) Professor Stokes, " On the Reduction and Oxidation of the Colouring-
matter of the Blood" (Proceed. Royal Soc. vol. xiii. p. 355). The oxidising
solution is made as follows : — To a solution of proto-sulphate of iron, enough
tartaric acid is added to prevent precipitation by alkalies. A small quantity of
this solution, made slightly alkaline by ammonia or carbonate of soda, is to be
added to the weak solution of blood in water.

THE CAMERA LUCIDA.

THE CAMERA LUCIDA.

The Camera Lucida, fig. 79, invented by Dr. Wollaston,
in 1807, is a valuable addition to the microscope,
for making drawings of structures, or for obtaining,
with a micrometer, measurements of objects. It consists

Fig. 79.

of a four-sided prism of glass, set in a brass frame or case,
as represented in the figure annexed ; and by means of a
short tube it is slipped over the front part of either of the
eye-pieces, its cap having been previously removed.
Mr. Ross attaches the prism, by two short supports, to
a circular piece of brass at the end of the tube ; on this it
can be slightly rotated, whilst the prism itself can also be
turned up or down, by means of two screws with milled

K

130 THE MICROSCOPE.

heads. So arranged, the camera may be adapted to the
eye-piece, the microscope having been previously placed
in a horizontal position ; if the light be then reflected up
through the compound body, an eye placed over the
square hole in the frame of the prism will see the image of
any object on the stage upon a sheet of white paper
placed on the table immediately below it. But should it
happen that the whole of the field of view is not well
illuminated, then, either by revolving the circular plate or
turning the prism upon the screws, the desired object will
be effected. The chief difficulty in the use of this instru-
ment is for the artist to be able to see, at one and the
same time, the pencil and the image. To facilitate this in
some measure, the one or two lenses below the prism will
cause the rays from the paper and pencil to diverge at the
same angle as those received from the prism, whereby
both object and pencil may be seen with the same degree
of distinctness.

The following is the method for employing the Camera
Lucida with the microscope. The first step to be taken,
after the object about to be drawn has been properly
illuminated, adjusted, and brought into the centre of the
field of view, is to place the compound body of the micro-
scope in a horizontal position, and to fix it there. The
cap of the eye-piece having been removed, the camera is
to be slid on in its stead : if the prism be properly
adjusted, a circle of white light, with the object within it,
will be seen on a piece of white paper placed on the table
immediately under the camera, when the eye of the
observer is placed over the uncovered edge of the prism,
and its axis directed towards the paper on the table.
Should, however, the field of view be only in part illumi-
nated, the prism must either be turned round on the eye-
piece, or revolved on its axis, by the screws affixed to its
frame-work, until the entire field is illuminated. The
next step is to procure a hard, sharp-pointed pencil, which,
in order to be well seen, may be blackened with ink round
the point ; the observer is then to bring his eye so near
the edge of the prism that he may be able to see on the
paper, at one and the same time, the pencil-point and the
image of the object. When he has accomplished this, the

THE CAMERA LUCIDA. 131

pencil may be moved along the outline of the image, so
as to trace it on the paper. However easy this may
appear in description, it will be found very difficult in
practice ; and the observer must not be foiled in his first
attempts, but must persevere until he accomplishes his
purpose. Sometimes he will find that he can see the
pencil-point, and all at once it disappears : this happens
from the movement of the axis of the eye. The plan then
is to keep the pencil upon the paper, and to move about
the eye until the pencil is again seen, when the eye is to
be kept steadfastly fixed on the same position until the
entire outline is traced. It will be found the best plan for
the beginner to employ at first an inch object-glass, and
some object, such as a piece of moss, that has a well-
defined outline, and to make many tracings, and examine
how nearly they agree with each other ; and when he has
succeeded to his liking, he may then take a more compli-
cated subject. If the operation is conducted by lamp-
light, it will be found very advantageous not to illuminate
the object too much, but rather to illuminate the paper
on which the sketch is to be made, either by means of the
lamp with the condensing lens, or a small taper placed
near it. When the object is so complicated that too much
time would be required for it to be completed at one
sitting, the paper should be fixed to the table by a weight,
or on a board by drawing-pins, An excellent plan to
adopt is to fix the microscope on a piece of deal about two
feet in length and one foot in breadth, and to pin the
paper to the same; there will then be no risk of the shift-
ing of the paper, as, when the wood is moved, both micro-
scope and paper will move with it. In all sketches made
by the camera, certain things must be borne in mind ; the
eye, when once applied to it, should be kept steadily fixed
in one position; and if the sketches are to be reserved for
comparison with others, the distance between the paper
and the camera should be always the same. A short rule
or a piece of wood may be placed between the paper and
the under-surface either of the compound body or the arm
Rupporting it, in order to regulate the distance, as the size
of the drawing made by the camera will depend upon the
distance between it and the paper. It is also very desirable,
K 2

132 THE MICROSCOPE.

before the camera is removed, to make a tracing in some
part of the paper of two or more of the divisions of the
stage micrometer, in order that they may form a guide to
the measurement of all parts of the object. Some persons
cover the whole of the drawing over with squares, to facili-
tate, not only the measurement, but in order that a larger
or smaller drawing may be made from it than that given
by the camera. It must be recollected, that an accurate
outline is the only thing the camera will give : the finishing
of the picture must depend entirely upon the skill of the
artist himself.

ON THE POLARISATION OF LIGHT AS APPLIED TO THE
MICROSCOPE.

Common light moves in two planes at right angles to
each other, polarised light moves only in one plane.
Common light may be turned into polarised light either
by transmission or reflection ; in the first instance, one of
the planes of common light is got rid of by reflection, in
the other, by absorption. Huyghens was among the first
to notice that a ray of light has not the same properties
in every part of its circumference, and he compared it to
a magnet or a collection of magnets ; and supposed that
the minute particles of which it was said to be composed
had different poles, which, when acted on in certain ways,
arranged themselves in particular positions ; and thence
the term polarisation, a term having neither reference to
cause nor effect. It is to Malus, however, who, in 1808,
discovered polarisation by reflection, that we are indebted
for the series of splendid phenomena which have since that
period been developed ; phenomena of such surpassing
oeauty as far to exceed all ordinary objects presented
to our eyes under the microscope. It has been truly
observed by Sir David Brewster, that " the application of
the principles of double refraction to the examination of
stnictures is of the highest value. The chemist may per-
form the most dexterous analysis ; the crystallographer
may examine crystals by the nicest determination of their
forms and cleavage ; the anatomist or botanist may use
the dissecting knife and microscope with the most exqui-
site skill; but there are still structures in the mineral,

POLARISED LIGHT. 133

vegetable, and animal kingdoms, which defy all such modes
of examination, and which will yield only to the magical
analysis of polarised light. A body which is quite trans-
parent to the eye, and which might be judged as mono-
tonous in structure as it is in aspect, will yet exhibit,
under polarised light, the most exquisite organisation, and
will display the result of new laws of combination which
the imagination even could scarcely have conceived. In
evidence of the utility of this agent in exploring mineral,
vegetable, and animal structures, the extraordinary organi-
sation of Apophyllite and Analcime may be referred to ;
also the symmetrical and figurate depositions of siliceous
crystals in the epidermis of equisetaceous plants, and the
wonderful variations of density in the crystalline lenses of
the eyes of animals.

Fitf. 80.

If we transmit a beam of the sun's light through a cir-
cular aperture into a darkened room, and if we reflect it
from any crystallised or uncrystallised body, or transmit
it through a thin plate of either of them, it will be reflcted
and transmitted in the very same manner, and with the
same intensity, whether the surface of the body is held
above or below the beam, or on the right side or left, pro-
vided that in all cases it falls upon the surface in the same
manner; or, what amounts to the same thing, the beam of
solar light has the same properties on all its sides: and
this is true, whether it is white light as directly emitted
from the sun, or from a candle or any burning or self-
luminous body; and all such light is called common light.
A section of such a beam of light will be a circle, like a b
c d, fig. 80 ; and we shall distinguish the section of a beam

134 THE MICROSCOPE.

of common light by a circle with two diameters a b, c d, at
right angles to each other.

If we now allow the same beam of light to fall upon a
rhomb of Iceland spar, and examine the two circular
beams, 0 o E e, formed by double refraction, we shall find,
1st, that the beams 0 o E e have different properties on
different sides, so that each of them differs in this respect
from the beam of common light.

2d. That the beam 0 o differs from E e in nothing ex^
cepting that the former has the same properties at the
sides a b' that the latter has at the sides c' and d' • or in
general that the diameters of the beam, at the extremities
of which the beam has similar properties, are at right
angles to each other, as a b' and c' d' for example.

Theso two beams, 0 o, E e, are therefore said to be
polarised, or to be beams of polarised light, because they
have sides or poles of different properties and planes passing-
through the lines a b, c d ; or a' b', c' d', are said to be the
planes of polarisation of each beam, because they have the
same property, and one which no other plane passing
through the beam possesses.

Now it is a curious fact, that if we cause the two
polarised beams 0 o, E e to be united into one, or if we
produce them by a thin plate of Iceland spar, which is not
capable of separating them, we obtain a beam which has
exactly the same properties as the beam abed of common
light. Hence we infer that a beam of common light, a b
c d, consists of two beams of polarised light, whose plane
of polarisation, or whose diameters of similar properties,
are at right angles to one another. If 0 o be laid above
E e, it will produce a figure like a b c d', and we shall
therefore represent polarised light by such figures. If we
were to place 0 o above E e, so that the planes of polarisa-
tion a' b' and c d' coincide, then we should have a beam of
polarised light twice as luminous as either 0 o or E e, and
possessing exactly the same properties; for the lines of
similar property in the one beam coincide with the lines of
similar property in the other. Hence it follows that there
are three ways of converting a beam of common light, a b
c d, into a beam or beams of polarised light.

1st. We may separate the beam of common light, abed,

POLARISED LIGHT. 135

component parts 0 o and E e. 2d. We may turn round
the planes of polarisation, abed, till they coincide or are
parallel to each other. 3d. We may absorb or stop one of
the beams, and leave the other, which will consequently
be in a state of polarisation."1

The first of these methods of producing polarised light
is that in which we employ a doubly refracting crystal,
and was first discovered to exist in a transparent mineral
substance called Iceland spar, calcareous spar, or carbonate
of lime. This substance is admirably adapted for exhibit-
ing this phenomenon, and is the one generally used by
microscopists. Iceland spar is composed of fifty-six parts
of lime and forty-four parts of carbonic acid ; it is found
in various shapes in almost all
countries; but whether found in
crystals or in masses, we can always
cleave it or split it into shapes re-
presented by fig. 81, which is called
a rhomb of Iceland spar, a solid
bounded by six equal and similar
rhomboidal surfaces, whose sides
are parallel, and whose angles b a c>
a c d, are 101° 55' and 78° 6'. The
line a x, called the axis of the rhomb, or of the crystal, is
equally inclined to each of the six faces at an angle of
45° 23.' It is very transparent, and generally colourless. Its
natural faces when it is split are commonly even and per-
fectly polished ; but when they are not so, we may, by a
new clevage, replace the imperfect face by a better one,
or we may grind and polish an imperfect face.

It is found that in all bodies where there seems to be
an irregularity of structure, as salts, crystallised minerals,
&c., on light passing through them, it is divided into two
distinct pencils. If we take a crystal of Iceland spar, and
look at a black line or dot on a sheet of paper, there will
appear to be two lines or dots ; and on turning the spar
round, these objects will seem to turn round also; and
twice in the revolution they will fall upon each other,
which occurs when the two positions of the spar are exactly
opposite, that is, when turned one-half from the position

(1) Brewster's "Optics."

136 1HB MICROSCOPE.

where it is first observed. In the accompanying diagram,
fig. 82, the line appears double, as a & and c d, or the dot,

Fig. 82.

as e and/. Or allow a ray of light, g h, to fall thus on the
crystal, it will in its passage through be separated into two
rays, kf, he; and on coming to the opposite surface of the
crystal, they will pass out at ef in the direction of i k,
parallel to g h. The plane I m n o is designated the prin-
cipal section of the crystal, and the line drawn from the
solid angle I to the angle o is where the axis of the crystal
is contained; it is also the optic axis of the mineral. Now
when a ray of light passes along this axis, it is undivided,
and there is only one image ; but in all other directions
there are two.

If two crystals of Iceland spar be u?ed, the only differ-
ence will be, that the objects seem farther apart, from the
increased thickness. But if two crystals be placed with
their principal sections at right angles to each other, the
ordinary ray refracted in the first will be the extraordinary
in the second, and so on vice versd. At the intermediate
position of the two crystals there is a subdivision of each
ray, and therefore four images are seen ; when the crystals
are at an angle of 45° to each other, then the images are
all seen of equal intensity.

Mr. Nicol first succeeded in making rhombs of Iceland
spar into single-image prisms, by dividing one into two
equal portions. His mode of proceeding is thus described
in the Edinburgh Philosophical Journal (vol. vi. p. 83) :

POLARISED LIGfiT. 137

"A rhomb of Iceland spar of one-fourth of an inch in
length, and about four-eighths of an inch in breadth and
thickness, is divided into two equal portions in a plane,
passing through the acute lateral angle, and nearly touching
the obtuse solid angle. The sectional plane of each of
these halves must be carefully polished, and the portions
cemented firmly with Canada balsam, so as to form a
rhomb similar to what it was before its division ; by this
management the ordinary and extraordinary rays are so
separated that only one of them is transmitted : the cause
of this great divergence of the rays is considered to be
owing to the action of the Canada balsam, the refractive
index of which (1-549) is that between the ordinary
(1-6543) and the extraordinary (1-4833) refraction of
calcareous spar, arid which will change the direction of
both rays in an opposite manner before they enter the
posterior half of the combination." The direction of rays

Fig. 83.

passing through such a prism is indicated by the arrow,
fig. 83, and the combination is shown mounted, one for

Fig. 85.

use under the stage of the microscope, fig. 84, termed the
polariser; another, fig. 85, screwed on to and above the

138

THE MICROSCOPE.

object -glasses, is called the analyser. The definition is
better if the analyser be placed at top of the A eye-piece,
and it is more easily rotated than the polariser.

Method of using the polarising Prism, fig. 84. — After
having adapted it to slide into a groove on the under-surface
of the stage, it is held in its place by turning the small
milled-head screw at one end : the other prism, fig. 85, is
screwed on above the object-glasses, and made to pass into
the body of the microscope itself. The light having been
reflected through them by the mirror, it becomes necessary
to make the axes of the two prisms coincide; this is done
by regulating the milled-head screw, until by revolving the
polarising prism, the field of view is entirely darkened twice
during one revolution. This should be
ascertained, and carefully corrected by
the maker and adapter of the apparatus.
If very minute salts or crystals are to be
viewed, it is preferable to place the ana-
lyser above the eye-piece; it will then
require to be mounted as in fig. 86. Thus
the polariscope consists of two parts ; one
for polarising, the other for analysing
or testing the light. There is no essen-
tial difference between the two parts,
except what convenience or economy may
lead us to adopt ; and either part, there-
fore, may be used as polariser or analyser •
but whichever we use as the polariser, the
other becomes the analyser.
The tourmaline, a precious stone of a neutral or bluish
tint, forms an excellent analyser ; it should be cut about
•gLjth of an inch thick, and parallel to its axis. The great
objection to it is, that the transmitted polarised beam is
more or less coloured. The best tourmaline to choose is
the one that stops the most light when its axis is at right
angles to that of the polariser, and yet admits the most
when in the same plane. It is necessary to choose the
stone as perfect as possible, the size is of no importance
when used with the microscope.

In the illumination of objects by polarised light, when
tinder view with high powers, for the purpose of obtaining

Fig. 86.

POLARISED LIGHT.

139

the maximum effect, it is also requisite that the angle of
aperture of the polariser should be the same as the object-
glass, each ray of which should be directly opposed by a
ray of polarised light. The Polarising Condenser is merely
an ordinary achromatic condenser of large aperture, close
under the bottom lens of which is placed a plate of tour-
maline, used in combination with a superposed film of
selenite or not, as required . The effect of this arrangement
on some objects is very remarkable, bringing out strongly
colours which are almost invisible by the usual mode.

The production of colour by polarised light has been
thus most clearly and comprehensively explained by Mr.
Woodward, in his " Introduction to the Study of Polarised
Light."1

Fig. 87 A.

? :s::

abed represent the rectangular vibrations by which
a ray of common light is supposed to be propagated.

e, a plate of tourmaline, called in this situation the
polariser, and so turned that a b may vibrate in the plane
of its crystallographical axis.

(1) Mr. Woodward constructed a very available form of polari scope for most
purposes ; the instrument is described in Elements of Natural Philosophy, by
Jabez Hopg.

140 THE MICROSCOPE.

/, light polarised by e, by stopping the vibrations c d,
and transmitting those of a b.

g, a piece of selenite of such a thickness as to produce
red light, and its complementary colour green.

h, the polarised light / bifurcated, or divided into ordi-
nary and extraordinary rays, and thus said to be de-
polarised by the double refractor g, and forming two planes
of polarised light, o and e, vibrating at right angles to
each other.

?', a second plate of tourmaline, here called the analyser,
with its axis in the same direction as that of e, through
which the several systems of waves of the ordinary and
extraordinary rays A, not being inclined at a greater
angle to the axis of the analyser than that of 45 degrees,
are transmitted and brought together under conditions
that may produce interferences.

k, the waves R o and R e, for red light of the ordinary
and extraordinary systems meeting in the same state of
vibration, occasioned by a difference of an even number
of half undulations, and thus forming a wave of doubled
intensity for red light.

I m, the waves Y o and T e and B o and B e for yellow and
blue of the ordinary and extraordinary systems respec-
tively meeting together, with a difference of an odd
number of half undulations, and thus neutralising each
other by interferences.

n, red light, the result of the coincidence of the waves
for red light, and the neutralisation by interferences of
those for yellow and blue respectively.

h, fig. 87 B, depolarised light, as fig. 87 A.

i, the analyser turned one quarter of a circle, its axis
being at right angles to that of i in fig. 87 A.

k, the waves R o R e, for red light of the ordinary and
extraordinary systems meeting together with a difference
of an odd number of half undulations, and thus neutral-
ising each other by interference.

I m, the waves Y o Y e and B o B e, for yellow and blue of
the two systems severally meeting together in the same
state of vibration, occasioned by the difference of an even
number of half undulations, and forming by their coin-
cidences waves of doubled intensity for yellow and blue
light.

POLARISED LIGHT. 141

n, green light, the result of the coincidences of the
waves for yellow and blue light respectively, and the
neutralisation by interference of those for red light.

By substituting Nicol's prisms for the two plates of
tourmaline, and by the addition of the object-glass and
eye-piece, the diagrams would then represent the passage
of polarised light through a microscope.

For showing objects by polarised light under the micro-
scope that are not in themselves doubly refractive, put
upon the stage a film of selenite, which exhibits, under
ordinary circumstances, the red ray in one position of the
polarising prism, and the green ray in another, using a
double-image prism over the eye-piece ; each arc will
assume one of these complementary colours, whilst the
centre of the field will remain colourless. Into this field
introduce any microscopic object which in the usual
arrangement of the polariscope undergoes no change in
colour, when it will immediately display the most brilliant
effects. Sections of wood, feathers, algse, and scales, are
among the objects best suited for this kind of exhibition.
The power suited for the purpose is a two-inch object-
glass, the intensity of colour, as well as the separating
power of the prism, being impaired under much higher
amplification; although in some few instances, such as in
viewing animalcules, the one-inch object-glass is perhaps
to be preferred.

Selenite is the native crystallised hydrated sulphate of
lime. A beautiful fibrous variety called satin gypsum is
found in Derbyshire. It is found also at Shotover Hill,
near Oxford, where the labourers call it quarry-glass. Very
large crystals of it are found at Montmartre, near Paris.
The form of the crystal most frequently met with is that
of an oblique rectangular prism, with ten rhomboidal
faces, two of which are much larger than the rest. It is
usually slit into thin laminae parallel to these large
lateral faces; the film having a thickness of from one-
twentieth to the one-sixtieth of an inch. In the two rec-
tangular directions they allow perpendicular rays of pola-
rised light to traverse them unchanged; these directions
are called the neutral axes. In two other directions,
however, which form respectively angles of 45° with the

142 THE MICROSCOPE.

neutral axes, these films have the property of double
refraction. These directions are known as the depolarising
axes.

The thickness of the film of selenite determines the
particular tint. If, therefore, we use a film of irregular
thickness, different colours are presented by the different
thicknesses. These facts admit of very curious and beau-
tiful illustration, when used under the object placed on the
stage of the microscope. The films employed should be
mounted between two glasses for protection. Some persons
employ a large film mounted in this way between plates of
glass, with a raised edge, to act as a stage for supporting
the object, it is then called the " selenite stage." The best
film for the microscope is that which gives blue, and its
complementary colour yellow. Mr. Darker has constructed
a very neat stage of brass for this purpose, producing a
mixture of all the colours by superimposing three films,
one on the other ; by a slight variation in their positions,
produced by means of an endless-screw motion, all the
colours of the spectrum are shown. When objects are
thus exhibited, we must bear in mind that all the negative
tints, as we term them, are diminished, and all the
positive ones increased ; the effect of this plate is to mask
the true character of the phenomena. Polarised structures
should therefore never be drawn and coloured under such
conditions.

Dr. Herapath, of Bristol, described a salt of quinine,
which is remarkable for its polarising properties. The salt
was first accidentally observed by Mr. Phelps, a pupil of
Dr. Herapath's, in a bottle which contained a solution of
disulphate of quinine: the salt is formed by dissolving
disulphate of quinine in concentrated acetic acid, then
warming the solution, and dropping into it carefully, and
by small quantities at a time, a spirituous solution of
iodine. On placing this mixture aside for some hours,
brilliant plates of the new salt will be formed. The crystals
of this salt, when examined by reflected light, have a
brilliant emerald-green colour, with almost a metallic
lustre ; they appear like portions of the elytree of cantha-
rides, and are also very similar to murexide in appearance.
When examined by transmitted light, they scarcely possess

POLARISED LIGHT. 143

any colour, there is only a slightly olive-green tinge ; but
if two crystals, crossing at right angles, be examined, the
spot where they intersect appears perfectly black, even if
the crystals are not one five-hundredth of an inch in thick-
ness. If the light be in the slightest degree polarised — as
by reflection from a cloud, or by the blue sky, or from the
glass surface of the mirror of the microscope placed at the
polarising angle 56° 45' — these little prisms immediately
assume complementary colours: one appears green, and
the other pink, and the part at which they cross is a
chocolate or deep chestnut-brown, instead of black. Aa
the result of a series of very elaborate experiments, Dr.
Herapath finds that this salt possesses the properties of
tourmaline in a very exalted degree, as well as of a plate
of selenite ; so that it combines the properties of polarising
a ray and of depolarising it. Dr. Herapath has succeeded
in making artificial tourmalines large enough to surmount
the eye-piece of the microscope; so that all experiments
with those crystals upon polarised light may be made
without the tourmaline or Nicol's prism. The brilliancy
of the colours is much more intense with the artificial
crystal than when employing the natural tourmaline. As
an analyser above the eye-piece, it offers some advantages
over the Kicol's prism in the same position, as it gives a
perfectly uniform tint of colour over a much more exten-
sive field than can be had with the prism.1 As these
crystals are liable to be injured by damp, and thus lose
their polarising property, when out of use they should be
kept in a dark dry place.

" The following experiments, if carefully performed, will
illustrate the most striking phenomena of double refraction,
and form a useful introduction to the practical application
of this principle.

(1) Dr. Herapath has given a later and better process for the manufacture of
these artificial tourmalines in the Quarterly Journal of Microscopical Science for

January, 1854. " These beautiful rosette crystals are best made as follows :

Take a moderately strong solution of Cinchonidine in Herapath's test-fluid (as
already described). A little of this is dropped on the centre of a slide and laid
down for a time, until the first crystals are observed to be formed near the
margin. The slide should now be placed upon the stage of the microscope and
the progress of formation of the crystals closely watched. When these are'seen
to be large enough, and it is deemed necessary to stop their further development,
the slide must be quickly transferred to the palm of the hand, the warmth of
which will be found sufficient to stop further crystallization."

144 THE MICROSCOPE.

"A plate of brass, fig. 88, three inches by one, perforated
with a series of holes from about one-sixteenth to one-

Fig. 88. — Red is represented by perpendicular lines ; Green by oblique.

fourth of an inch in diameter; the size of the smallest
should be in accordance with the power of the object-glass,
and the separating power of the double refraction.

" Experiment 1. — Place the brass plate so that the smallest
hole shall be in the centre of the stage of the instrument;
employ a low power (1J or 2 inch) object-glass, and adjust
the focus as for an ordinary microscopic object; place the
double image prism over the eye-piece, and there will
appear two distinct images; then, by revolving the prism,
these will describe a circle, the circumference of which
cuts the centre of the field of view; the one is called the
ordinary, the other the extraordinary ray. By passing the
slide along, that the larger orifices may appear in the field,
the images will not be completely separated, but will
overlap, as represented in the figure.

" Experiment 2. — Screw the Nicol's prism into its place
under the stage, still retaining the double image prism
over the eye-piece ; then, by examining the object, there
will appear in some positions two, but in others only one
image; and it will be observed, that at 90° from the latter
position this ray will be cut off, and that which was first
observed will become visible; at 180°, or one-half the
circle, an alternate change will take place ; at 270°, another
change; and at 360°, or the completion of the circle, the
original appearance.

" Before proceeding to the next experiment, it will be as
well to observe the position of the Nicol's prism, which
should be adjusted with its angles parallel to the square
parts of the stage. In order to secure the greatest
brilliancy in the experiment, the proper relative position
of the selenite may be determined bv noticing the natural

POLARISED LIGHT. ] 45

flaws in the film, which will be observed to run parallel
with each other; these flaws should be adjusted at about
46° from the square parts of the stage, to obtain the
greatest amount of depolarisation.

"Experiment 3. — If we now take the plate of seleuite thus
prepared, and place it under the piece of brass on the
stage, we shall see, instead of the alternate black and
white images, two coloured images composed of the con-
stituents of white light, which will alternately change by
revolving the eye- piece at every quarter of the circle ; then,
by passing along the brass, the images will overlap ; and
at the point at which they do so, white light will be pro-
duced. If, by accident, the prism be placed at an angle of
45° from the square part of the stage, no particular colour
will be perceived; and it will then illustrate the phenomena
of the neutral axis of the selenite, because when placed in
that relative position no depolarisation takes place. The
phenomena of polarised light may be further illustrated
by the addition of a second double image prism, and a
film of selenite adapted between the two. The systems
of coloured rings in crystals cut perpendicularly to the
principal axis of the crystal are best seen by employing the
lowest object-glass."

To show the phenomena of the rings reund the optic
axes of the crystals, Mr. Lobb adopts the following plan,
which is by far the best, and the rings are exhibited in the
greatest perfection : —

1. The B eye-piece without a diaphragm, and the lenses
so adjusted that the field-lens may be brought nearer to,
or farther from the eye-lens as occasion may require ; thus
giving different powers, and different fields, and when
adjusted for the largest field it will be full 15 inches, and
take in the widest separation of the axis of the aragonite.

2. A crystal stage to receive the crystals, and to be
placed over the eye-piece, so constructed as to receive a
tourmaline, and that to turn round.

3. A tourmaline of a blue tint.

4. A large Nicol's prism as a polariser.

5. A common two-inch lens, not achromatic; which
must be set in a brass tube long enough when screwed into

L

146 THE MICROSCOPE.

the microscope to reach the polariser, that all extraneous
light may be excluded.

The concave mirror should be used with a bull's-eye
condenser by lamplight. The condenser may be dispensed
with by daylight. The above apparatus is furnished by
Messrs. Powell and Lealand.

The crystals best adapted to show the phenomena of
rings round the optic axes, are : —

Quartz. — A uniaxial crystal, one system of rings, no
entire cross of black, only the ends of it, the centre being
coloured, and as the tourmaline is revolved, the colour
gradually changing into all the colours of the spectrum,
one colour only displayed at once.

Quartz. — Cut so as to exhibit right-handed polarisation.

Quartz. — Cut so as to exhibit left-handed polarisation ;
that is, the one shows the same phenomena when the
tourmaline is turned to the right, as the other does when
turned to the left.

Quartz. — Cut so as to exhibit straight lines.

Cole Spar. — A uniaxial crystal, one system of rings, and
a black cross, which changes into a white cro^s on revolving
the tourmaline, and the colours of the rings into their
complementary colours,

Topaz. — A biaxial crystal, although it has two axes, only
exhibits one system of rings with one fringe, owing to the
wide separation of the axes. The fringe and colours
change on revolving the tourmaline ; this is the case in all
the crystals.

Borax. — A biaxial crystal; the colours more intense
than in topaz, but the rings not so complete, — only one
set of rings taken in, from the same cause as topaz.

Rochelle Salt. — A biaxial crystal; the colours more
widely spread. Very beautiful. Only one set of rings
taken in.

Carbonate of Lead. — A biaxial crystal, axes not much
separated, both systems of rings exhibited, far more widely
spread than those of nitre.

Aragonite. — A biaxial crystal, axes widely separated ; but
both systems of rings exhibited, and decidedly the best
crystal for displaying the phenomena of biaxial crystals.

The field-lens of the eye-piece requires to be brought as

POLARISED LIGHT. 147

close as possible to the eye-lens, to see properly the pheno-
mena in quartz and aragonite ; it must be placed at an
intermediate distance for viewing topaz, borax, Rochelle
salt, and carbonate of lead ; it must be drawn out to its
full extent to view nitre and calc spar.

The powers of the micro-polariscope cannot be better
displayed than in the exhibition of the foregoing pheno-
mena; there is nothing more beautiful, and few studies
more interesting and enlarging to the mind than that of
light, whether common or polarised, which must be entered
upon if the phenomena are to be understood.

The crystal eye-piece, with an artificial tourmaline as an
analyser, will be found very useful for polariscope objects
generally; there is some spherical aberration, but the
largeness of the field far more than compensates for the
same; it does best for those objects that require the two-
inch object glass.

Mr. Darker of Lambeth, Messrs. Elliott of the Strand,
Messrs. Home and- Co., Newgate St., and M. Soliel of
Paris, supply properly cut crystals.

It was long believed that all crystals had only one axis
of double refraction; but Brewster found that the great
body of crystals, which are either formed by art, or which
occur in the mineral kingdom, have two axes of double re-
fraction, or rather axes around which the double refraction
takes place; in the axes themselves there is no double
refraction.

Nitre crystallises in six-sided prisms with angles of about
120.° It has two axes of double refraction, along which
a ray of light is not divided into two. These axes are each
inclined about 2^° to the axes of the prism, and 5° to each
other. If, therefore, we cut off a piece from a prism of
nitre with a knife driven by a smart blow of a hammer,
and polish the two surfaces perpendicular to the axes of
the prism, so as to leave the thickness of the sixth or
eighth of an inch, and then transmit a ray of polarised
light along the axes of the prism, we shall see the double
system of rings shown in figs. 89 and 90.

When the line connecting the two axes of the crystal is
inclined 45° to the plane of primitive polarisation, a cross
is seen as at fig. 89, on revolving the nitre, it gradually

L2

148

THE MICROSCOPE.

assumes the form of the two hyperbolic curves, fig. 90. But.
if the tourmaline be revolved, the black crossed lines will

Fig. 90.

be replaced by white spaces, and the red rings by green,
the yellow by indigo, and so on. These systems of rings
have, generally speaking, the same colours as those of
thin plates, or as those of a system of rings round one
axis. The orders of the colours commence at the centres
of each system; but at a certain distance, which corre-
sponds to the sixth ring, the rings, instead of returning
and encircling each pole, encircle the two poles as an
ellipse does its two foci. When we diminish or increase
the thickness of the plate of nitre, the rings are diminished
or increased accordingly.

Small specimens of salts may also be crystallised and
mounted in Canada balsam for viewing under the stage of
the microscope ; by arresting the crystallisation at certain
stages, a greater variety of forms and colours will be
obtained : we may enumerate salicine, asparagine, acetate
of copper, phospho-borate of soda, sugar, carbonate of
lime, chlorate of potassa, oxalic acid, and all the oxalates
found in urine, with the other salts from the same fluid, a
few of which are shown at fig 91.

Dr. W. B. Herapath contributed an interesting addi-
tion to the uses of polarised light, by applying it to discover
the salts of alkaloids, quinine, &c. in the urine of patients.

POLARISED LIGHT. 149

*

lie says : " It has long been a favourite subject of inquiry
with the professional man to trace the course of remedies

TT-.&

^^m 6fg^

^» ^t* s&S^ fi&yi BR

0

A

'6,

aa+V
Q VZa

•2o«

+**z*

Fijj. 91.— Urinary Salts.

a, Uric acid; b, Oxalate of lime, octahedral crystals of; c, Oxalate of lime
allowed to dry, forming a black cube; d, Oxalate of lime, as it occasionally
appears, termed the dumb-bell crystal.

in the system of the patient under his care, aiid to know
what has become of the various substances which he might
have administered during the treatment of the disease.

" Having been struck with the facility of application,
and the extreme delicacy of the reaction of polarised light,
when going through the series of experiments upon the
sulphate of iodo-quinine, I determined upon attempting
to bring this method practically into use for the detection
of minute quantities of quinine in organic fluids ; and after
more or less success by different methods of experimenting,
I have at length discovered a process by which it is possible
to obtain demonstrative evidence of the presence of quinine,
even if in quantities not exceeding the one-millionth part
of a grain; in fact, in quantities so exceedingly minute, that
all other methods would fail in recognising its existence.
Take for test-fluid a mixture of three drachms of pure
acetic acid, with one fluid-drachm of rectified spirits-of-
wine, to which add six drops of diluted sulphuric acid.

" One drop of this test-fluid placed on a glass-slide,
and the merest atom of the alkaloid added, in a short time

150

THE MICROSCOPE.

solution will take place ; then, upon the tip of a very fine
glass-rod let an extremely minute drop of the alcoholic
solution of iodine be added. The first effect is the produc-
tion of the yellow or cinnamon-coloured compound of iodine
and quinine, which forms as a small circular spot j the
alcohol separates in little drops, which by a sort of repul-
sive movement, drive the fluid away ; after a time, the acid
liquid again flows over the spot, and the polarising crystals
of sulphate of iodo-quinine are slowly produced in beautiful
rosettes. This succeeds best without the aid of heat.

" To render these crystals evident, it merely remains to
bring the glass-slide upon the field of the microscope, with
the selenite stage and single tourmaline, or Nicol's prism,
beneath it ; instantly the crystals assume the two comple-
mentary colours of the stage ; red and green, supposing
that the pink stage is employed, or blue and yellow, pro-
vided the blue selenite is made use of. All those crystals
at right angles to the plane of the tourmaline, producing

Pig. 92. — In this figure heraldic lines are adopted to denote colour. The
dotted parts indicate yellow, the straight lines red, the horizontal lines bine,
and the diagonal, -or oblique lines, green. The arrows show the plane of the
tourmaline, a, blue stage ; b, red stage of selenite employed.

that tint which an analysing-plate of tourmaline would
produce when at right angles to the polarising-plate ;

POLARISED LIGHT.

151

whilst those at 90° to these educe the complementary tint,
as the analysing-plate would also have done if revolved
through an arc of 90°.

" This test is so ready of application, and so delicate,
that it must become, the test, par excellence, for quinine:
fig. 92, a and b. Not only do these peculiar crystals act
in the way just related, but they may be easily proved to
possess the whole of the optical properties of that remark-
able salt of quinine, the sulphate of iodo-quinine.

" To test for quinidine, it is merely necessary to allow
the drop of acid solution to evaporate to dryness upon the
slide, and to examine the crystalline mass by two tourma-
lines, crossed at right angles, and without the stage.
Immediately little circular discs of white, with a well-
defined black cross very vividly shown, start into existence,
should quinidine be present even in very minute traces.
These crystals are represented in fig. 93.

**

93.

" If we employ the selenite stage in the examination of
this object, we obtain one of the most gorgeous appear-
ances in the whole domain of the polarising-microscope :
the black cross at once disappears, and is replaced by one
which consists of two colours, being divided into a cross

THE Ull'llOSCOPH.

i

Fig. 94.— S»ow Crystal*.

SNOW CRVSTALS. 153

having a red and green fringe, whilst the four intermediate
sectors are of a gorgeous orange-yellow. These appear-
ances alter upon the revolution of the analysing-plate of
tourmaline ; when the blue stage is employed, the cross
will assume a blue or yellow tint, according to the position
of the analysing-plate. These phenomena are analogous
to those exhibited by certain circular crystals of boracic
acid, and to those circular discs of salicine (prepared by
fusion) ; the difference being, that the salts of quinidinc
have more intense depolarising powers than either of the
other substances ; besides which, the mode of preparation
effectually excludes these from consideration. Quinine
prepared in the same manner as quinidine has a very
different mode of crystallisation ; but it occasionally pre-
sents circular corneous plates, also exhibiting the black
cross and white sectors, but not with one-tenth part of the
brilliancy, which of course enables us readily to discrimi-
nate the two."

Ice doubly refracts, while water singly refracts. Ice
takes the rhomboidic form ; and snow in its crystalline
form may be regarded as the skeleton crystals of thivs
system. A sheet of clear ice, of about one inch thick, and
slowly formed in still weather, will show the circular rings
and cross if viewed by polarised light.

It is probable that the conditions of snow formation are
more complex than might be imagined, familiar as we are
with the conditions relating to the crystallisation of water
on the earth's surface. Dr. Smallwood, of Isle Jesus,
Canada East, has traced an apparent connection between
the form of the compound varieties of snow crystals and
the electrical condition of the atmosphere, whether nega-
tive or positive ; and is instituting experiments for his
better information on the subject.

A great variety of animal, vegetable, and other sub-
stances possess a doubly refracting or depolarising struc-
ture, as : a quill cut and laid out flat on glass ; the cornea
of a sheep's eye ; skin, hair, a thin section of a finger-nail ;
sections of bone, teeth, horn, silk, cotton, whalebone ;
stems of plants containing silica or flint ; barley, wheat, &c.
The larger-grained starches form splendid objects; tous-
les-mois, being the largest, may be taken as a type of all

154 THE MICROSCOPE.

the others. It presents a black cross, the arms of which
meet at the hilum. On rotating the analyser, the

black cross disappears, and
at 90° is replaced by a white
cross ; another, but much
fainter black cross being per-
ceived between the arms of
the white cross. Hitherto,
however, no colour is percep-
tible. But if a thin plate of
selenite be interposed between
the starch-grains and the po-

Fotat ' Starch, seen under polarised , I J'J J

light. lariser, most splendid and

delicate colours appear. All

the colours change by revolving the analyser, and become
complementary at every quadrant of the circle. West and
East India arrow-root, sago, tapioca, and many other
starch-grains, present a similar appearance ; but in pro-
portion as the grains are smaller, so are their markings
and colourings less distinct.

" The application of this modification of light to the
illumination of very minute structures has not yet been
fully carried out ; but still there is no test of differences
in density between any two or more parts of the same
substance that can at all approach it in delicacy. All
structures, therefore, belonging either to the animal, vege-
table, or mineral kingdom, in which the power of unequal
or double refraction is suspected to be present, are those
that should especially be investigated by polarized light.
Some of the most delicate of the elementary tissues of
animal, such as the tubes of nerves, the ultimate fibrilke
of muscles, &c., are amongst the most striking subjects that
may be studied with advantage under this method of illu-
mination. Every structure that the microscopist is
investigating should be examined by this light, as well
as by that either transmitted or reflected. Objects
mounted in Canada balsam, that are far too delicate to
exhibit any structure under transmitted, will often be
well seen under polarised light ; its uses, therefore, are
manifold."1

(1) Quekett's Practical Treatise on the Use of the Microscope.

APPLICATION OP PHOTOGRAPHY. 155

A fine effect may be obtained by using Furze's spotted
lens, with a Herapathite polariser; see Mic. Soc. Trans.
2d series, vol. iii. p. 63.

APPLICATION OP PHOTOGRAPHY TO THE MICROSCOPE.

At the time this book was projected, it was thought that
if the objects so beautifully exhibited under the microscope
could be drawn by light on the page of the book, or on
the wood-blocks, so that the engraver might work directly
from the drawings thus made, truthfulness would be in-
sured, and we should present to the reader a valuable
record of microscopic research never before seen or
attempted. But in this we were doomed to disappoint-
ment by the existence of a patent, which presented ob-
stacles too great to be surmounted ; and the idea was
abandoned, with the exception of a few drawings then
prepared, and ready to hand : the patent restrictions having
been since removed, we have embodied them in our pages.
The eye and feet of fly, antenna of moth, paddles of whirli-
gig, with a few others, were first taken on a film of collo-
dion, then floated off the glass on to the surface of a block
of wood, the wood having been previously and lightly
inked with printer's ink or amber-varnish, and the film
gently rubbed or smoothed down to an even surface, at
the same time carefully pressing out all bubbles of air or
fluid.

For the purposes of photography the only necessary
addition to the ordinary microscope is that of a dark
chamber ; it should indeed form a camera obscura, having
at one end an aperture for the insertion of the eye-piece
end of the microscopic tube, and at the other a groove for
carrying the crown-glass for focussing. This dark chamber
must not exceed eighteen inches in length; for if longer,
the pencil of light transmitted by the object-glass is dif-
fused over too large a surface, and a faint and unsatis-
factory picture results therefrom. Another advantage is,
that pictures at this distance are in size very nearly equal
to the object seen in the microscope. In some instances,
bettor pictures are produced by taking away the eye-piece

156 THE MICROSCOPE.

of the microscope altogether. The time of producing the
picture varies from five to twenty seconds, with the strength
of the daylight. A camphine lamp, light Cannel coal-gas,
or the lime-light, will enable a good manipulator to pro-
duce pictures nearly equal to those produced by sun-light.
Collodion offers the best medium, as a strong negative can
be made to produce any number of printed positives.

The light is transmitted from the mirror through the
object and lenses, and brought to a focus on the ground-
glass, or prepared surface of collodion, in the usual manner.
Care must be taken not to use the burning focus of the
lenses. The gas microscope may be used to make an
enlarged copy of an object, it is only necessary to pin up
against the screen a piece of prepared calotype paper to
receive the reflected image. Mr. Wenham gives direc-
tions for improving " microscopic photography " in the
Quarterly Journal of Microscopical Science for January,
1855. In this paper be has shovm how to insure quick
and accurate focussing ; or, in other words, the making of
the actinic and visual foci of the objective coincident. The
simplest and cheapest way of producing coincidence is to
screw a biconvex lens into the place of the back-stop of
the object-glass, which thus acts as part of its optical com-
bination. An ordinary spectacle lens, carefully centred
and turned down to the required size, answers the purpose
exceedingly well.

An excellent method has been proposed and adopted by
Mr. Wenham, for exhibiting the form of certain very
minute markings upon objects. A negative photographic
impression of the object is first taken on collodion, in the
ordinary way, with the highest power of the microscope
that can be used. After this has been properly fixed, it is
placed in the sliding frame of an ordinary camera, and the
frame end of the latter adjusted into an opening cut in
the shutter of a perfectly dark room. Parallel rays of
sunlight are then thrown through the picture by means
of a flat piece of looking-glass fixed outside the shutter at
such an angle as to catch and reflect the rays through the
camera. A screen standing in the room, opposite the lens
of the camera, will now receive an image, exactly as from
a magic lantern, and the size of the image will be proper-

APPLICATION OF PHOTOGRAPHY. 157:

tionate to the distance. On. this screen is placed a sheet
of photogenic paper intended to receive the magnified
picture. We ought to add. however, that it requires con-
siderable practice to avoid the distortion and error of
definition occasioned by a want of coincidence in the
chemical and visual foci. Imperfections are much in-
creased when the highest powers of the microscope are
employed ; false notions of structure are also given,
which is the case in Mr. Wenham's photograph of P. An
gulatum.

Mr. S. Highley has a mode of adapting an object-glass to
the ordinary camera, for the purpose of taking microscopic
objects on collodion and other surfaces, fig. 96; a sec-
tional view of his arrangement is here given, which is

Fig. 9d. — Hiyhley't Camera.

very compact, steady, and ever ready for immediate use.
The tube A screws into the flange of a camera which has
a range of twenty-four inches; the front of this tube is
closed, and into it screws the object-glass B. Over A slides
another tube c; this is closed by a plate, D, which extends
beyond the upper and lower circumference of o, and carries
a small tube, E, on which the mirror F is adjusted. To the
upper part of D the fine adjustment G is attached ; this
consists of a spring-wire coil acting on an inner tube, to
which the stage-plate H is fixed, and is regulated by a gra-
duated head, K, acting on a fine screw, likewise attached to

158 THE MICROSCOPE.

the stage-plate, after the manner of Oberhauser's micro-
scopes. An index L is affixed opposite the graduated head
K. The stage and clamp slides vertically on H ; and by
sliding this up or down, and the glass object-slide hori-
zontally, the requisite amount of movement is obtained to
bring the object into the field. The object being brought
into view, the image is roughly adjusted on the focussing-
glass by sliding c on A ; the focussing is completed by aid
of the fine adjustments G K, and allowance then made for
the amount of non-coincidence between the chemical and
visual foci of the object-glass. The difference in each glass
employed should be ascertained by experiment in the first
instance, and then noted. By employing a finely-ground
focussing-glass greased with oil, this arrangement forms an
agreeable method of viewing microscopical objects with
both eyes, and is less fatiguing. As a very large field is
presented to the observer, this arrangement might be
advantageously employed for class demonstration.

Fig. 97. — Highley's Photo-micrographic Arrangement. *

This arrangement combines the most recent improve-
ments of Dr. Maddox, and consists of a lens-carrier with
ordinary adjustments; stage with gymbal motions so as
to bring any object parallel to the surface of the object-
glass ; bright ground illuminator, graduating diaphragm ;
and a speculum reflector for giving the light from a
single surface.

CHAPTER III.

PRELIMINARY DIRECTIONS — ILLUMINATION — ACCESSORV APPARATUS —
GILLETT'S, ROSS'S, WEBSTER'S, AND OTHER CONDENSERS — OBLIQUE
ILLUMINATION— DOUBLE PRISM ILLUMINATION— THE LIEBERKUHN — SIDB
REFLECTOR — GAS-LAMPS — OBJECT FINDERS — COLLECTING STICKS — ANI-
MALCULE CAGES — SECTION CUTTERS — PREPARING AND MOUNTING OB-
JECTS, ETC.

AVING selected an apartment
with a northern aspect, and, if
possible, with only one window,
and that not overshadowed by
trees or buildings : in such a
room, on a firm, steady table,
keep your instruments and ap-
paratus open, and at all times
ready for observation. A large
bell-glass will be found most
convenient for keeping dust from
the microscope when set up for
use. In winter it will be proper
to slightly warm the instrument
before it is used, otherwise the
perspiration from the eye will
condense on the eye-glass, and
greatly impede vision. When
you clean the eye-glasses, do not remove more than one at
a time, and replace it before you touch another ; by so
doing you will preserve the component glasses in their
proper places : recollect that if intermingled they are
useless. Keep a piece of well-dusted and very dry
chamois leather, slightly impregnated with the finest
tripoli or rotten-stone powder, in a small box, to wipe
the glasses.

160 THE MICROSCOPE.

When you look through the instrument, be sure to
place your eye quite close to the eye-piece, otherwise the
whole field of view will not be visible ; and observe, more-
over, if you see a round disc of light, at least when the
object is not on the slider-holder : if you do not, it is a
sign that something is wrong; perhaps the body is not
placed directly before the stage aperture, or may not be
properly directed towards the light. Use the smallest
amount of light possible, if you work for any length ot
time. Choose a steady light, with a shade to protect the
eyes, one of the old-fashioned fan-shades will be found
useful for this purpose : use the eyes alternately. Sit in a
comfortable position, and bring the instrument to the
proper angle, which will prevent congestion of the eyes ;
this is indicated if the microscopist is annoyed with little
moving objects apparently floating before them : if the
eye-lashes are reflected from the eye-glass, you are looking
upon the eye-glass instead of through it. Take care that
the mirror is properly arranged.

The following are Sir David Brewster's excellent direc-
tions for viewing objects : —

" First. Protect the eye from all surrounding light, let-
ting only the rays which proceed from the illuminated
centre of the object fall upon it.

" Secondly. Delicate observations should not be made
when the fluid which lubricates the cornea is in a viscid
state, or there is any irritation or inflammation about any
part of the eye.

" Thirdly. The best position for microscopic observations
is with the microscope bent to such an angle with the
body, that the head may always remain in a natural and
easy attitude ; consequently, the worst position would be
that which compels us to look downwards vertically.

" Fourthly. If we lie horizontally on the back, parallel
markings and lines on objects will be seen more perfectly
when their direction is vertical, or in a contrary direction
to that in which the lubricating fluid descends over the
cornea of the eye.

" Fifthly. Only a portion of the object should be viewed
at one time, and every other part excluded. The light
which illuminates that part should be admitted through a

ILLUMINATING THE OBJECTS. 161

small diaphragm : at night, from the concentrated light of
a sperm-oil or gas lamp, having a faint blue-tinted chim-
ney-glass, to correct the yellow colour which predominates
in all our artificial illumination. If in the day-time, close
a portion of the window-shutters.

" Sixthly. In all cases when high powers are used, the
intensity of the illumination should be increased by optical
contrivances below the object and stage : this is generally
effected by using achromatic condensers beneath the stage.
The apparatus for illumination should be as perfect as the
magnifying power."

If these directions are strictly followed, no injury to the
eyes from using a microscope need be feared.

Mr. Ross very properly remarks, that the manner in
which an object is lighted is second in importance only to
the excellence of the glass through which it is seen. When
investigating any new or unknown specimen, it should be
viewed in turns by every description of light, direct and
oblique, as a transparent object and as an opaque object,
with strong and with faint light, with large angular pencils
thrown in all possible directions. Every change will pro-
bably develope some new fact in reference to the structure
of the object, which should itself be varied in the mode of
mounting in every possible way.

It should be seen both wet and dry, and immersed in
fluids of various qualities and densities ; such as water,
alcohol, oil, and Canada balsam ; the last having a refrac-
tive power nearly equal to that of glass.

If the object be a delicate vegetable tissue, it will be, in
some respects, rendered more visible by gently heating or
scorching before a clear fire, between two plates of glass.
In this way the spiral vessels of asparagus and other
similar vegetables will be beautifully displayed. Dyeing
the objects in tincture of iodine, or some one of the dye-
woods, will, in some cases, answer the purpose better.

But the principal question in regard to illumination is
the magnitude of the illuminating pencil, particularly in
reference to transparent objects. Generally speaking, the
illuminating pencil should be not quite so large as can
be received by the lens : any light beyond this produces
indistinctness and glare. The superfluous light from the

M

162 THE MICROSCOPE.

mirror may be cut off by a screen, having various-sized
apertures placed below the stage.

The Diaphragm, fig. 98, is the instrument used for
effecting this purpose. It consists of two plates of brass,
one of which is perforated with four or five holes of dit-

Fig. 98.— The Diaphragm.

ferent sizes ; this plate is of a circular figure, and is made
to revolve upon another plate by a central pin or axis ;
this last plate is also provided with a hole as large as the
largest in the diaphragm-plate, and corresponds in situa-
tion to the axis of the compound body. To ascertain
when either of the holes in the diaphragm-plate is in the
centre, a bent spring is fitted into the second plate, and
rubs against the edge of the diaphragm-plate, which is
provided with notches. The space between the smallest
and largest is great enough to use for the purpose of shut-
ting off all the light from the mirror.

GILLETT'S ILLUMINATOR, OR CONDENSER. — The advan-
tages of employing an achromatic condenser were first
pointed out by Dujardin, since which time an object-glass
has been frequently but inconveniently employed ; and
more recently achromatic illuminators have been con-
structed by most of our instrument makers. Some years
since, Mr. Gillett was led by observation to appreciate the
importance of controlling not merely the quantity of light
which may be effected by a diaphragm placed anywhere
between the source of light and the object, but the angle
of aperture of the illuminating pencil, which can be effected
only by a diaphragm placed immediately behind the
achromatic illuminating combination. Such a diaphragm
is represented in fig. 99, manufactured by Mr. Ross : it
consists of an achromatic illuminating lens c, which is

GILLETT'S ILLUMINATOR.

163

about equal to an object-glass of one-quarter of an inch
focal length, having an angular aperture of 80°. This
lens is placed on the top of a brass tube, intersecting

Fig. 9i). — Gilletfs Condenser.

which, at an angle of about 25°, is a circular rotating
brass plate a b, provided with a conical diaphragm, having
a series of circular apertures of different sizes h g, each of
which in succession, as the diaphragm is rotated, propor-
tionally limits the light transmitted through the illumi-
nating lens. The circular plate in which the conical dia-
phragm is fixed is provided with a spring and catch efy
the latter indicating when an aperture is central with the
illuminating lens, also the number of the aperture as
marked on the graduated circular plate. Three of these
apertures have central discs, for circularly oblique illumi-
nation, allowing only the passage of a hollow cone of light
to illuminate the object. The illuminator above described
is placed in the secondary stage i i, which is situated below
the general stage of the microscope, and consists of a
cylindrical tube having a rotatory motion, also a rect-
angular adjustment, which is effected by means of two
screws I m, one in front, and the other on the left side of
its frame. This tube receives and supports all the various

164? THE MICROSCOPE.

illuminating and polarising apparatus, or other auxiliaries
which are placed underneath the object. The tube and its
frame are affixed to a dovetailed sliding bar Tc, which can
be easily moved up or down, or taken off for conveniently
attaching the various apparatus. This sliding bar fits into
a second sliding bar, which, by means of a milled-head
screw, moving a rack and pinion, regulates the distance of
the apparatus from the stage.

Directions for Use by Day or Lamplight. — In the adjust-
ment of the compound body of the microscope with the
illuminator above described, two important results are to
be sought — first, their centricity, and secondly, the fittest
condensation of the light to be employed. With regard to
the first, place the illuminator in the cylindrical tube, and
press upwards 'the sliding bar in its place, until checked
by the stop ; move the microscope body either vertically
or inclined for convenient use; and with the rack and
pinion which regulates the sliding bar, bring the illu-
minating lens to a level with the upper surface of the
object-stage ; then move the arm which holds the micro-
scope body to the right, until it meets the stop, whereby
its central position is attained ; adjust the reflecting mirror
so as to throw light up the illuminator, and place upon
the mirror a piece of clean white paper to obtain a uniform
disc of light. Then put on the low eye-piece, and a low
power (the half-inch), as more convenient for the mere
adjustment of the instrument ; place a transparent object
on the stage, adjust the microscope-tube, until vision is
obtained of the object ; then remove the object, and take
off the cap of the eye-piece, and in its place fix on the eye-
glass called the " centering eye-glass," described below,
which will be found greatly to facilitate the adjustmenl
now under consideration, namely, the centering of the
compound body of the microscope with the illuminating
apparatus of whatever description.1 The centering-glass,
being thus affixed to the top of the eye-piece, is then to

(1) This centering-glass consists of a tubular cap containing two plano-convex
lenses, which are applied and adjusted so that the image of the aperture in the
object-glass, and the images of the apertures at the lenses and in the diaphragms
contained in the tube which holds the illuminating combination, may all be in
focus at the same time, as with the same adjustment they may be brought suffi-
ciently near in focus to recognise their centricity.

GILLETT'S ILLUMINATOK. 165

be adjusted by its sliding- tube (without disturbing the
microscope-tube) until the images of the diaphragms in
the object-glass and centering lens are distinctly seen.
The illuminator should now be moved by means of the
left-hand screw on the secondary stage, while looking
through the microscope, to enable the observer to recog-
nise the diaphragm belonging to the illuminator, and by
means of the two adjusting screws, to place this diaphragm
central with the others ; thus, the first condition, that of
centricity, will be accomplished. Remove the white paper
from the mirror, and also the centering-glass, and replace
the cap on the eye-piece, also the object on the stage, of
which distinct vision should then be obtained by the rack
and pinion, or fine screw adjustment, should it have
become deranged.

The second process is to ascertain that the fittest con-
centration of light is obtained. For this purpose the
mirror should now be so inclined that the image of some
intercepting distant object, such as a house-top, or chim-
ney, tree, window-frame, or (if lamp-light be employed)
the lamp's flame may be brought into the field of view ;
these, though not distinctly seen, may be recognised by
partially darkening or otherwise occupying the field; then
distinct vision of such object must be obtained by means
of the rack and pinion moving the secondary stage to and
from the object. Excepting the case of the lamp's flame,
the above objects are considered as the representatives of
the source of light ; for when daylight is employed — as, for
example, a white cloud — its motion prevents the image
being easily produced : then it is convenient to employ a
distant object, such as the above, — the difference of the
focal length of the illuminating lens for such an object,
and for the white cloud, being almost insensible. This
last adjustment being effected by the movement of the
secondary stage alone, the microscope tube remaining un-
disturbed, also the object on the object-stage uninterrupted
in focus, the source of the illuminating light and the
object to be examined will both be distinctly seen at the
same time. These adjustments, whether for daylight or
lamplight, being completed, the mirror may be turned so
as wholly to reflect the light either of the sky or of the

166 THE MICROSCOPE. ,

lamp; and the eye-piece and object-glass suitable for
examining the object may be employed, and the focus
adjusted accordingly. The conical diaphragm with its
various apertures may now be rotated, until that quality
of illumination is obtained which gives a cool, distinct,
and definite view of the object. Upon changing the
object-glass, the centering eye-glass should always be
employed to ascertain that the centricity of the illumi-
nating condenser and microscope body has not been
deranged.

It has been stated that the image of a white cloud oppo-
site the sun is the best for illuminating transparent objects
when viewed by transmitted light. Mr. Gillett has success-
fully imitated this natural surface by an apparatus, consist-
ing of a large parabolic reflector, with a small camphine
lamp on an adjustable stand, having its flame nearly in
the focus; also of two other reflectors of hyperbolic figure,
which are employed according to the object-glasses used on
the microscope. The parabolic mirror and one of these are
attached opposite to each other on the bent arm by which
they are supported, having their axes coincident, and the
enamel disc placed between them. The small hyperbolic
reflector receives the light reflected from the large paro-
bolic reflector, and concentrates the rays on the small
enamel disc. The surface of this disc is roughened, so that
the forms of all the incident pencils are broken up, and
the effect of a white cloud produced.

Several important modifications and valuable improve-
ments in condensers have been introduced by makers, and,
therefore, deserve especial notice. Two things should be
required of achromatic condensers intended for general use
and for research : First, that the optical combination em-
ployed should be adapted to a considerable range of power
— say, from an inch, or §ds upwards to the highest ; and,
secondly, that they should be capable of working with a
large aperture through the ordinary glass slides. When
low powers are employed, a pleasantly lit field can be
obtained by using a condenser a little out of focus, so that
the rays cross before reaching the object ; but a condenser
for general use should send a sufficient quantity, and no
more, of oblique rays, when in focus, through an object

ROSS'S CONDENSER. 167

seen with very moderate magnification, and should be
capable of giving a dark-ground illumination with a J
inch or §ds object glass.

In Mr. Ross's j^ths condenser, represented at A,
fig. 39, these desiderata are well provided for. The
optical combination is exactly the same as in his large
angled -f^ths objectives, and the front lens has a diarMeter
of. £th of an inch. In all good condensers the diaphragm
should be brought close to the lower lens ; that is the
oase with this instrument, which is provided with two
revolving wheels of diaphragms. The upper one is pierced
with eight circular apertures ; one of which is filled in
with a polarizing slice of tourmaline ; another is made
with a little rim, so as to receive any experimental stops
the microscopist may wish to try. Omitting this last-
mentioned stop, we have seven others, marked respec-
tively 109°, 95°, 82°, 70°, 59°, 49°, and 40°. These stops
allow the lenses to work with the angles of aperture
named. In the wheel of diaphragms, below them, is
arranged another set of stops, for combination with the
preceding.

A single slot stop keeps out the central rays, and
allows a radial beam, including its proportion of marginal
rays, to illuminate the object. This can be used with the
larger of the open stops. The two-slot stop gives passages
to two such pencils of light, one at right angles to the
other, a plan very effective with certain diatoms and other
objects. The three-slot stop allows the transmission of
three pencils, equidistant from each other. This gives the
three readings of the P. angulatum. The arrangement
for working the diaphragms in the condenser is very con-
venient, and the whole apparatus rotates with the sub-stage.
The lenses are also capable of adjustment to suit different
thicknesses of glass.

The proportion which, from the size of the front lens,
the marginal and central rays bear to each other, is such
that, when the stop allowing 40° of aperture is employed,
the two sets of lines, on Pleurosigma hippocampus and P.
angulatum, are distinctly shown with a one-fiftn objective
and an A eye-piece. A slight change in the position of
the flat mirror makes this stop work excellently with the

168 THE MICROSCOPE.

Podura scale. Thus, this arrangement enables an experi-
menter viewing a new object to see surface markings, and
to obtain penetration with one and the same stop; an
important gain in original investigation. The slot stops
have been found very useful in investigating unknown
objects, as well as in displaying those that are known;
andnvith the whole aperture and the two-slot stop, many
diatoms with double sets of lines are well brought out.
The microscopist will find that from 40° to 59° angle of
aperture will, in many cases, give the best results, when a
J or £ objective is employed.

An excellent condenser of very large angular aperture
is made by Messrs. Powell and Lealand, in which every
requisite modification of the illuminating pencil may be
produced by two revolving discs, one containing apertures
of various sizes, and the other various diaphragms for
excluding the • central portion, or for admitting only
angular portions, of the pencil of light. These discs are
placed immediately below the posterior lens of the illumi-
nator. This method of modifying the illuminating pencil
was first applied in Gillett's condenser, as constructed
by Mr. Eoss. The improved hemispherical condenser
lately introduced by the Rev. J. B. Eeade, answers
its purpose remarkably well. The plane surface of the
hemisphere is placed upwards, and is covered by a dia-
phragm, in which are marginal apertures, capable of adjust-
ment either to an interval of 90° with each other, when
the arrangement of the dots to be developed is quad-
rangular, as in P. rhomboides, or P. hippocampus? or to
one of 60° and 120°, when they are arranged in equilateral
triangles, as in P. anyulatum, &c. An ingenious plan of
illuminating minute objects, mounted in Canada balsam,
by reflected light, has been devised by Mr. Wenhant:
this consists of a small truncated glass paraboloid, which
is temporarily attached to the under side of the slide
containing the object, by a little gum, oil, or fluid Canada
balsam. The rays internally reflected from the convex
surface of the paraboloid, impinge very obliquely on the
under-surface of the slide, are transmitted in consequence
of the fluid-uniting medium, and then internally reflected
from the upper surface of the covering glass on to the

169

object* Very minute variations of surface contour may
by these means be rendered evident.

Collins's Webster's Universal Achromatic Condenser
(fig. 100), a superior mechanical contrivance, is provided
with a diaphragm which so gradually shuts off all excess
of light, that any amount of illumination can be admitted

Fig. 100.— Collins's Webster's Universal Condenser. Shutter Diaphragm seen separately

with the greatest nicety. This valuable addition to the
microscope can be fitted to any instrument with or without
a sub-stage arrangement. Its chief advantages are that,
while its performing qualities take rank with much more
expensive forms, it is moderately cheap, and is at once an
achromatic condenser, parabolic illuminator, and graduating
diaphragm, with polariser added. By means of a lever, the
central aperture can be gradually closed, without losing
sight of the object, and at the same time the alteration is
effected with a great amount of delicacy. Provided an
object-glass has sufficient "resolving power," its capa-
bilities are greatly increased by this condenser, in bringing
out the markings on the difficult test-objects; when in
connexion with the Polariscope, a great increase of light
is obtained — so much so that, by using a polarising prism
with the "spot lens stop" the object appears brilliantly
illumined on a dark ground, with fine coloured effects.
When high powers are used in connexion with the polari-
scope, the advantage derived by such an addition to the
ordinary mode of illumination will be at once apparent to
every microscopist.

170 THE MICROSCOPE.

Professor Smith, of Kenyon College, America, invented
a condenser for the illumination of opaque objects under
high powers. It has been felt that it would be of im-
mense advantage to the physiologist if he could illuminate
small bodies, such as blood-globules, and view them as
opaque objects with the Jth or -j^th ; hitherto there have
been great difficulties in the way of accomplishing this,
but Professor Smith has hit upon a contrivance which
promises to be useful.

In this instrument a pencil of light is admitted above
the objective and thrown down through it on to the object,
by means of a small silver mirror placed on one side, and
cutting off a portion of the aperture. Powell and Lealand
devised what they considered to be an improvement, and
substituted for the small silver mirror, to which Professor
Smith gave a preference, a flat piece of glass placed at an
angle of 45° across the tube, interposed like an adapter
between the objective and the microscope body. A pencil
of light entering by a side aperture striking against this
flat glass is partly reflected down through the objective
and. on to the object, the magnified image of which is
viewed through the glass. If the flat glass be ground so
as to have parallel surfaces, no great amount of error can
be detected.

Smith and Beck place a disc of thin covering glass, at
an angle of about 45°, in the optic axis of the microscope
body, close behind the setting of the object-glass in a special
adapter, leaving a suitable aperture for admitting light from
a lamp, rays from which are reflected downwards upon the
object. The object-glass is thus made its own achromatic
condenser.

But the idea of employing the object-glass as its own
condenser was suggested by Mr. Hewitt five years ago,
and then Mr. Wenham was induced to give the plan a
trial. A concave speculum was fitted at an angle into the
body of the microscope, having a central hole sufficiently
large to admit the full pencil from the objective, through
the back of which the rays from a lamp (the light from
which was admitted through a hole in the side of the
body) were reflected downwards. The object was strongly
illuminated, but there was so much glare from the internal

OBLIQUE ILLUMINATION. 171

fittings, and a reflection from the back of the object-
glass-lenses, that an unfavourable opinion was formed of
its practicability. It has since been demonstrated that
the light was too intense ; and the most useful, the central
portion of rays, were wanting. A simple disc of thin
glass and its partial reflection meets these objections. If
such a disc be used with a little care, it is found to be
quite as accurate as the other plan, and the natural surface
of the glass is a better reflector than any artificial one. It
has, however, the disadvantage of extreme fragility. By
making the object-glass its own condenser, and examining
diatoms as opaque objects under high powers, we may
now hope to solve the much vexed question as to the true
nature of their markings. Mr. Browning has employed
the apparatus in a form much more nearly resembling that
of the original inventor, only substituting a small glass
reflecting-prism for the metallic reflector. Some advan-
tages are gained by the adoption of this latter arrangement.
Such modes of illumination bid fair to correct many errors
of interpretation resulting from an exclusive use of trans
parent illumination.

Oblique Illumination is of the greatest importance in
the demonstration of structure, especially that of test-
objects ; and much greater obliquity is often required
than can be obtained by throwing the mirror out of the
axis of the microscope. Various methods are described ih
the "Transactions " of the Microscopical Society of London,
for almost every microscopist has devoted some attention
to the subject in his attempts to resolve the more diffi-
cult lined or dotted objects, as diatoms ; therefore, to
give a full description of all is quite uncalled for, if
not impossible, in our pages ; it is nevertheless most
advisable, in doubtful cases, to have recourse to every
method which shall present the object under a different
aspect. One of the earliest methods devised for obtaining
oblique light, was the eccentric prism of Nachet, which
occupied the place of the present achromatic condenser,
and, like it, received its light from the mirror ; by simply
turning it in its socket, oblique rays were thrown upon the
object from every side. This had, however, defects which
Mr. Sollitt proposed to remedy, by employing an achro-

172 THE MICROSCOPE.

matic condenser of a very long focus and large aperture,
mounted in such a way as to enable its axis to be inclined
to that of the microscope through a wide angular range ;
a condenser of this construction, he says, is also suitable
for all ordinary purposes.1 A combination of the reflect-
ing and refracting powers of a prism is much preferred by
some ; such, for instance, as that known as Amici's prism,
which causes the rays to be reflected by a plane surface,
and made to converge by a lenticular one, so that the
prism answers the double purpose of mirror and condenser
at the same time. "Abraham's Achromatic Lenticular
Prism " is an excellent substitute for the achromatic con-
denser, and answers the double purpose of mirror and con
denser. This prism, represented half- size in fig. 101, is made

Fig. 101. — Abraham's Achromatic Lenticular Prism. Half-size.

up of two kinds of glass, set in a frame of brass ; the part
employed as the reflector (A) is of flint glass, hollowed out at
its upper surface, and into this is accurately fitted a double
convex lens of crown glass (B), so contrived as to have a
focus of about four inches. By the tube (G), the prism can
be applied to the ordinary support of the mirror ; and by
means of the flat semicircle (B), and a joint in the connect-
ing piece (tf), it can be turned in every possible direction,
the semicircle sliding through a spring clip at E. By this

(1) Quart. Journal Micros. Science, vol. iii. p. 87.

OBLIQUE ILLUMINATION. 173

instrument, achromatic condensed light may be thrown
upon any object on the stage. The prism has the usual
swinging motion, accomplished by the frame turning on
two screws, one of which is seen at c, at the end of the
semicircle.

A thin stage is of importance when a very oblique
pencil is used, and, to a certain extent, the larger its lower
aperture, the more oblique will be the rays we are enabled
to transmit to the object. For this reason the thin stage
introduced by such makers a% Powell and Lealand, is in
every way an improvement on the thicker stage of the
older instruments. A revolving stage also possesses ad-
vantages : it enables the observer to keep the object in
the centre of the field of view, and while its various parts
are thus presented in succession to rays of greater or less
obliquity, an insight into the structure is often afforded
which could not otherwise have been obtained. " Thus,
suppose that an object be marked by longitudinal striae,
too faint to be seen by ordinary direct light, the oblique
light most useful for bringing them into view will be that
proceeding in either of the directions c and D ; that which
falls upon it in the directions A and B
tending to obscure the striae rather than
to disclose them. But if the striae 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 D, but will be shown best by that
which makes the strongest shadow; B

hence, if there be a projecting ridge,
with an abrupt side looking towards c, it will be bast seen
by light from D ; whilst, if there be a furrow with a steep
bank on the side of c, it will be by light from that side that
it will be best displayed. But it is not at all unfrequent
for the longitudinal striae to be crossed by others j and
these transverse striae will usually be best seen by the light
that is least favourable for the longitudinal, so that, in
order to bring them into distinct view, either the illumi-
nating pencil or the object must be moved a quarter
round."

If 4 THE MICROSCOPE.

For those who desire to obtain a very oblique illumi-
nating pencil, with objectives of lower powers, but large
angular aperture, and with an inexpensive arrangement,
the Hemispherical Condenser (Kettledrum) of the Rev.
J. B. Eeade will be found serviceable.1 This gentleman
now, however, uses a double hemispherical condenser for
the examination of the most difficult tests ; and the great
obliquity of the illuminating pencils gives every facility
for dealing with the close fine lines of the Amician test
and the Macrum. Diaphragms of tinfoil are placed
between the two hemispheres. By looking down the
body of the microscope when the eye-piece is removed,
and examining the dimensions of the little discs of light,
it is seen at a glance whether one or other of the aper-
tures require to be more or less deeply cut. In the one
case, the little lappet of tinfoil can be so doubled as to
shorten the aperture, and, in the other, it may be cut
deeper and thrown further back. To obtain these very
slight but not unimportant variations, and in a moment,
is an advantage which observers will readily recognise.
Mr. Eeade also uses more durable diaphragms of thin
brass, and, by a new arrangement, the precise amount of
light is obtained at once. A fixed diaphragm, with aper-
tures at right angles to each other, and cut nearly to the
centre, is placed on the lower hemisphere ; and another
diaphragm, of which the outline is a right angle upon a
semicircle, is placed in a slit of the tube between the
condensers, so that the vertex of the right angle divides
the space between the long V apertures of the lower
diaphragm. When pushed home, it nearly shuts up these
apertures of the fixed diaphragm ; but by gently drawing
it out,«and moving it a little sideways, if necessary, we
can obtain, with the utmost nicety, just that length of
either aperture which the test-lines under examination
require.

The very perfection of oblique illumination for resolving
the markings on test-objects, is the double prism made
use of by Mr. J. Newton Tomkins. The method of employ-
ing the two prisms we give in our friend's words : —

(1) Rev. J. B. Reade, F.R.S. on a New Hemispherical Condenser. Trans.
Micros. Soc. 1861, p. 59, and vol. vii. page 3, 1867.

SOLLITT'S ILLUMINATION. 175

" My first attempts at oblique prism-illumination were
made, many years ago, with Abraham's (of Liverpool)
Achromatic Lenticular Prism ; the high character given
of the performance of this instrument by the late Professor
Quekett and by Mr. Sollitt, of Hull, led me to believe
that it would entirely supersede the necessity of using a
condenser during the examination of the highest class
test-objects. In my hands, however, it failed to do this ;
the pencil of light transmitted proved to be too diffused,
and the shadows too faint to enable me to bring out the
markings of single-lined tests satisfactorily. I subjoin Mr.
Sollitt's directions for using this prism, as communicated

Fig. 102 —Sollitt's Single-Prism Illumination.

to Mr. Abraham : — ' When I require the prism for defi-
nition and direct light, I use it in place of the mirror
under the stage ; but when required for oblique light, that
is, for illuminating lined objects, or for black-ground
illumination, I use it on a separate stand, as sliown in
fig. 102, the object being illuminated by the very oblique
ray, c u. Let A B be a supposed ray of direct light, coin-
cident with the axis of the microscope, then so long as the
angle o B A is less than half the angle of aperture of the
object lenses, the field will remain illuminated by oblique
light, and the lined objects (if placed in their proper
position) will be brought out in the most beautiful manner.
I place the prism about five inches in front of the object,
and by this method, with my widest apertures, I bring

176 THE MICROSCOPE.

out the lines on Navicula Angulata, Ceratoneis Fasciola,
Amician Test, Grommatophora Subtilissima, and even on
the Navicula Acus, with, the greatest ease. In viewing
these delicate objects, the lines must be at right angles
with the direction of the light. If the angle c B A be
greater than half the angle of aperture of the object lenses,
then you have the object beautifully illuminated on a
black ground ; and when the light is properly managed,
the result is very superior to that obtained by the parabolic
reflector — the objects on the black-ground appear as though
they were in full sunlight, bringing out the fine markings
on delicate tissues most satisfactorily.'

"My next trial was made with a small rectangular
achromatic prism with a focus of two inches and a half —
not of four or five inches, as in Mr. Sollitt's case — fur-
nished by Messrs. Powell and Lealand ; and I then found
it easy to resolve the markings of all test -objects which
were disposed at right angles with the source of illumina-
tion. With a view of resolving the crossed-lines of P.
Formosum, N. Angulata, and the like, I employed the
usual microscope mirror, so disposed by means of a double-
jointed arm that the light from the lamp might be reflected
as nearly as possible at right angles with the second set of
lines, but met with but moderate success, since the double
reflection, due to the primary reflection from the silvered
surface of the mirror, and the secondary reflection from
the glass of 'the mirror itself, caused a haze that militated
materially against true definition of the markings which
characterise such delicate tests as N. Rhomboides, P. Ma-
crum, &c.

"The next step was to substitute for the mirror a second
lamp and a second prism, also mounted on a separate stand,
with rack- work adjustment, and provided with a universal-
joint arm. The Success of this plan was undoubted ; I
was now enabled to resolve the crossed lines of N. Rkom-
boides (the Amician Test of the. London, although, per-
haps, not of the American microscopists) with a sharpness
which was hitherto unattainable ; and even the difficult
object P. Macrum came out in well-defined squares. The
advantage of the universal-joint fitted to the second prism
consists in the fact that the diagonal lines of such tests as

DOUBLE PRISM ILLUMINATION,

177

P. Rigidum may be brought out with ease by simply
inclining the prism to the angle necessary to cause the
shadows of this series of lines to fall directly opposite to
the source of light.

" The method of using this combination will be readily
understood by referring to fig. 103.

"The microscope (A) is placed at the usual angle of
inclination ; a valve — say, of N. Rhomboides — is selected
which lies vertically on the stage ; the front lamp (c) is
adjusted so that the centre of the flame shall be eleven
inches above the table, and ten inches from the object ;
an object glass of moderate angle, such as a Ross's old
J inch, with 60° of aperture, will be found convenient
for this first step in the process ; the front prism (D), with
its convex surface turned towards the lamp (c), is placed
1J — 2 inches from the stage, and so adjusted that the
pencil of transmitted light shall fall with the utmost
obliquity on the object ; now (referring to the former
lig. 102), the angle c B A being about 40°, or greater than

Fig. 103. — Mr. Newton Tonkins' Double Prisvi Illumination.

half the angle of aperture of the lens, the valve under
examination will be brightly illuminated on a black-

N

178 THE MICROSCOPE.

ground. An Jth, ^th, or a ^gth, is then substituted for
the J inch lens ; and since the angle of aperture of either
of these lenses exceeds 140°, the whole field will be illu-
minated with a very oblique pencil of light. By careful
manipulation of the prism, and the closest attention to the
due adjustment of the object-glass itself, the transverse
markings on the valve (which are by far the most difficult
to resolve) should now come out with great clearness.

"The reason for using the \ inch lens in the first
instance, is to find, by 'Maltwood,' or otherwise, the
particular object desired, and to determine the exact
position of lamp and prism ; by commencing to work with
the ^jth or ^th these would be impracticable. The light
of the lamp is now to be shut off, and a side prism/ (B)
inclined parallel to the plane of the stage-plate, and
brought as near to the under-side of the object as the
form of the fixed stage will admit, placed in position.
The light of a second lamp (E) is then caused, as before,
to fall very obliquely on the object, and the longitudinal
markings will be readily shown. On restoring the light
of the front lamp (c), and paying particular attention that
neither light shall be in excess, the valve will be brought
out in squares, with a sharpness and a delicacy of tracing
which I venture to assert will bear comparison with the
best results obtained by use of the expensive modern
condenser. I would by no means undervalue the advan-
tages to be derived from the employment of the condensers
now furnished by our eminent makers ; but, seeing that
these are manifestly articles of luxury, I incline to the
opinion, that to those microscopists who are economically
disposed, and already possess one rectangular prism, the
trifling addition of a second prism and a second lamp will
enable them to do good service to the cause of resolving
many difficult test-objects hitherto insurmountable, amongst
which I would place in the foremost rank Amphipleura
pellucida (N. Acus), the markings on which I do not
yet despair of seeing ' crossed ' by some enthusiastic
observer."

We have witnessed with surprise the ease with which
difficult markings are brought out by this mode of illumi-
nation.

THE PARABOLIC REFLECTOR.

179

The Parabolic Reflector.— Mr. F. H. Wenham (Micros.
Trans. 1851) proposed a parabolic illuminator, for the pur-
pose of obtaining perfect definition under high powers.
Those who have experimented on the subject, may have ob-
served that there is something in the nature of oblique light
reflected from a metallic surface particularly favourable for
the purpose of bringing out minute markings, which may,
in some measure, be attributed to the circumstance of light
so reflected being purely achromatic. In order to render
this property available, Mr. Wenham contrived a very in-
genious metallic reflector, by which the condensation of
lateral light may be effected.1

Fig. 104.— Wenham' s Parabolic Reflector.

" The apparatus is shown in section in fig. 104 ; a, a is
a parabolic reflector, of a tenth of an inch focus, with a

(1) Mr. Shadbolt contrived a modification of Wenham's Reflector, and called
it a <f Sphero- Annular Condenser;" which consists of a ring of glass whose
surface was so shaped as to present a prismatic section, the inclination of the
outer side being such as to produce a total reflection 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 combination
of both methods is adopted in the parabolic illuminator now very generally
used. This consists of a paraboloid of glass resembling a cast of the interior
of Weuham's Parabolic Speculum, but reflecting the rays which fall upon the
surface of the glass like Shadbolt's Annular Condenser.
N 2

180 THE MICROSCOPE.

polished silver surface, having the apex so far cut away as
to bring the focal point at such a distance above the top
of the apparatus (which is closed with a screw-cap when
not in use) as may allow the rays to pass through the
thickest glass commonly used for mounting objects upon
before coming to a focus.

" At the base of the parabola is placed a disc of thin
glass 6 6, in the centre of which is cemented a dark well,
with a flange equal in diameter to the aperture at the top
of the reflector, for the purpose of preventing the direct
rays from the source of light passing through the
apparatus.

"The reflector is moved to and from the object by
means of the rack and pinion c, and has similar adjust-
ments for centering, and is fixed under the stage of the
microscope in the same way as the ordinary achromatic
condenser: in addition, there is a revolving diaphragm d,
made to slide on the bottom tube of the apparatus ; it has
two apertures e e, placed diametrically, for the purpose of
obtaining two pencils of oblique light in opposite direc-
tions. The effects of the chromatic and spherical aber-
rations, in the shape of fog and colour about the objects,
caused by the glass slides upon which they are mounted,
frequently require compensation; for as the parabola has
the property of throwing parallel rays uncoloured to a
point, when used alone, it is most suitable for objects
without glass underneath.

" By the addition of a meniscus, this compensation is
obtained, and also greater purity and intensity of illumina-
tion is procured ; and as the silver reflector is now closed
with glass, it is hermetically sealed, and permanently pro-
tected from dust and damp, and will therefore retain its
polish. The light most suitable for this method of illumi-
nation is lamp or candle light, the rays of which must in
all cases be rendered parallel by means of a large plano-
convex lens, or condenser; the light may then be used
direct, or reflected from the plane mirror. The object
having been adjusted, the illuminator is moved to and fro
till the best effect is produced. For the purpose of viewing
some objects,, such as naviculsD, the circular diaphragm
should be slid on the extremity of the apparatus, and

THE LIEBERKUHN.

181

revolved till the two pencils of light are thrown most
suitably across the object."

The Lieberkuhn, — The concave speculum termed a
" Lieberkuhn," from its celebrated inventor, was formerly
much in use as a reflector, but is now almost abandoned,
or rather replaced by other and better contrivances. The
Lieberkuhn is generally attached to the object-glass, in
the manner represented at fig. 105, where a exhibits the
lower part of the compound body, b, the object-glass, over
which is slid a tube and the
Lieberkuhn, c, attached to it ;
the rays of light reflected from
the mirror are brought to a focus
upon an object d, placed between
it and the mirror. The object
may either be mounted on a slip
of glass, or else held in the for-
ceps, / ; and when too small to
fill up the entire field of view,
or when transparent, it is neces-
sary to place behind it the dark
well, e.

Each Lieberkuhn being
mounted on a short piece of

tube, can be slid up and down ,on the outside of the
object-glass, so that the maximum of illumination may be
readily obtained. In the higher powers the end of the
object-glass is turned small enough to pass through the
aperture in the centre of the Lieberkuhn ; but in the
lower powers, where a great amount of reflecting surface
would be lost on account of the large size of the glasses
employed if this plan were adopted, the aperture in the
centre of the Lieberkuhn is made to admit as many rays
as will fill the field of view, and no more.

As the flood of light thrown back by the Lieberkuhn is
sometimes so great as to obliterate much of the beauty and
delicacy of structure of certain objects, it was proposed by
Mr. Bridgeman, of Norwich, to cover up a portion of its
reflecting surface by gumming a piece of dull-black paper
over one half of the reflector ; then, by rotating the
Lieberkuhn upon the object-glass, any proportion of oblique

182 THE MICROSCOPE.

light may be thrown upon the object, and in any particular
direction. In this way points of structure have been
brought out which were lost under the full illumination of
the Lieberkiihn. Mr. Beck sought to effect an improve-
ment upon the proposal of Mr. Bridgeman, and, by
employing the segment of a Lieberkiihn, produced what he
terms a "Parabolic reflector." This is made to slide in the
ordinary way over the object-glass, and admits of being
turned in any direction towards the source of light. The
parabolic reflector can also be employed with high powers.
Mr. Sorby discovered, while experimenting with a reflector
of the kind, the value of studying the peculiarities of
objects under every kind of illumination ; for, on viewing
specimens of iron and steel with this reflector, he found
that, owing to the obliquity of illumination, the more
brilliantly polished parts reflected the light beyond the
aperture of the objective, and he could not therefore
distinguish them from those parts which merely absorbed
the light. To throw the illumination more perpendicularly
upon the specimen, he was obliged to place a small flat
mirror immediately in front of the objective, and cover half
its aperture, and at the same time stop-off, by means of a
semi-cylindrical tube, the light from the parabolic reflector.
By such an arrangement, Mr. Sorby found it produce the
reverse appearances of the former mode of illumination,
and it proved to be a valuable aid in ascertaining the true
condition of the object. Mr. Baker has produced a cheaper
and simpler form of this parabolic reflector, which answers
its purpose remarkably well, giving increased facilities for
the illumination of opaque objects with the microscope
set in that direction most convenient for working. The
brilliancy of the illumination is very much increased by
placing a condensing-lens before the light, or by employing
the Bockett lamp. It is, however, only just to Mr. Ross
that we should add, that this " parabolic reflector " io
but a slight modification of his Side-reflector, contrived
several years ago, for the purpose of superseding the
Lieberkiihn.

The Bull's-eye Condenser. — All opaque objects require to
be illuminated by rays \vhich, being thrown upon their sur-
face, shall be reflected back into the microscope. The samR

BULL-6-ETE CONDENSER.

183

mode of viewing objects is often applied to semi-opaque,
or even some transparent ones, to demonstrate peculiarities
of structure. A condensing lens is used for converging
rays from a lamp upon the
mirror ; or for reducing the
diverging rays of the lamp
to parallelism, for use either
with the parabolic illumi-
nator, or Eoss's side-reflector.
A plano-convex lens (fig.
106), of about three inches
focal length, is the form ge-
nerally adopted ; it is borne
upon a swivel-joint, which
allows of its being turned
in any direction, and placed
at any angle; the tube is
double, and thus admits of
being lengthened or short-
ened. When used by day-
light, its plane side should
be turned towards the ob-
ject, and the same position
should be given when used
for converging the rays from
a lamp ; but when used
with the parabolic or side-
reflector, the plane side
must be turned towards the
lamp. Sometimes a smaller,

double convex lens is made use of in addition; this is
then often fixed into the stage of the microscope.

In fig. 107 the bull's-eye lens, c, slides up and down
a brass rod, screwed into a solid foot ; and made to con-
centrate the light upon the object from the table- gas-
lamp, d. Mr. Brooke's method of viewing opaque objects
under the highest powers of the microscope (the & and -a\
inch object-glass) is effected by two reflections. The rays
from a lamp rendered parallel by a condensing lens are
received on an elliptic reflector, the end of which is cut
off a little beyond the focus; the rays of light converging

Fig. 106.— The Condensing Lens.

184

THE MICROSCOPE.

from this surface are reflected down on the object by a
plane mirror attached to the object-glass, and on a level

Fig. 107. — Condenser and Table Gas-lamp.

with the outer surface. By such means the structure of
the scale of the Podura, and the different characters of its
inner and outer surfaces, are rendered distinctly visible.

Lamps. — It is of the utmost importance, both on account
of the injury often done to the eyes, as well as for the per-
fection of illumination when artificial light is employed, that
its quality should be of the whitest and purest kind. The
most useful and economical lamp is Collins' Bockett lamp ;
it consists of a good paraffin lamp, reflector, and a 2^
condenser, mounted together on a brass-rod stand, which
admits of being raised from 9 to 1 6 inches. The pale -blue
chimney supplied with it gives whiteness to the flame,
and for all the requirements of the microscopist it is de-

MICROSCOPE LAMPS.

185

Fig. 108. — Collins' Bockett Lamp.

cidedly the most convenient lamp we have seen. Those

Fig. IW.—HigMey's Gas-lamp, with Steam-bath aftacfocL

186

THE MICROSCOPE.

among us who have gas at command will, no doubt, give
it the preference on account of its convenience, and
freedom from all kind of trouble. An excellent form of
gas-lamp is Highley's (fig. 109).

The mono-chromatic gas-lamp, fig. 1 10, is very useful and
most economical. Gas, as a source of light, presents great
advantages over oil and spirit, on account of cleanliness,
being ever ready for use, and affording a perfect control
over the flame ; but when the ordinary gas-lamps are used

Fig. 110. — Gas-lamp arranged for iise.

for the purpose of illuminating the field of the micro
scope, a yellow glaring light is given, alike injurious to
the eye and the definition of the object under examina-
tion. To correct these evils, this lamp was arranged, which

FINDERS AND INDICATORS. 18?

is also otherwise useful to the microscopist. It consists
of a stage A, supported by a tube and socket, sliding on
an upright rod rising from the stand. This carries an
argand burner B ; a metal cone c rises to the level of the
burner, and is about one-eighth of an inch from its outer
margin.

This arrangement gives a bright cylindrical flame. The
bottom of the stage A is covered with wire-gauze, to cut
off irregular currents of air, and thus secures a steady
flame. Over the burner is placed a Leblond's blue glass
chimney D. This corrects the colour of the flame to a
certain extent ; but it is still further rectified by a disc of
bluish-black neutral-tint glass E, fitted in a tube F, attached
obliquely to the shield G. Q is a half- cylinder of metal,
which serves to shield the eyes from all extraneous light,
but may be rotated on the stage A by aid of the ivory
knot H, when the full light from the flame is desired. A
metallic reflector I, fixed on its supports, so as to be
parallel to E, concentrates the light. By the combination
of the two glasses D and E, the yellow rays of the flame
are absorbed, and the arrangement affords a soft white
light, which may be still further improved by receiving
the rays on a concave mirror, backed with plaster-of- Paris
L j and where a very strong light is required, a condensing
lens should be interposed, as shown in the cut, between
the lamp and the mirror of the microscope. By removing
the shield o, and bringing the shade M over the burner, it
may be used as a reading-lamp. A retort ring N supports
a water-bath o, or a wrought- iron plate P, 6 inches by 2|
inches, both used in mounting objects. The stop-cock Q
gives the means of regulating the flame. The screw R
clamps the lamp-head at any height desired. The lamp
may be attached to any gas-supply by vulcanised India-
rubber tubing.

Finders and Indicators. — A finder, as applied to the
microscope, is the means of registering the position of any
particular object in a slide : as, for instance, some particu-
larly good specimen of a diatom, so that it may be referred
to at a future time. The subject has been fully discussed
in the pages of the Quarterly Journal of Microscopical
Science. The traversing stage admits of such finders aa

188 THE MICROSCOPE.

those of Mr. Okeden, Mr. Tyrrell, Mr. Amyot, &c.,
being used. The first named (Mr. Okeden' s) 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

Fig. 111.— Amyot's Object Finder.

relation to the fixed plate, while the second gives him the
like power of setting the horizontally-sliding plate by the
intermediate. The finder the author has been in the
habit of using for some years is a very ingenious and
effective instrument described by Mr. Amyot. It consists
of a box-wood plate, with a circular hole -y^ths of an inch
in diameter cut out of its centre, into which a disc of
ivory, pierced in the exact centre with a very fine needle,
fits; this disc can be readily removed by seizing a little
brass peg, attached to it, with the forceps. The box-wood
is ruled with two axes, vertical and horizontal, which are
graduated to 50ths or lOOths of an inch. The diagram
(fig. Ill) represents the finder with bone centre-piece in
situ. The dotted ring shows the rabbet on which the
centre-piece rests ; a, brass pin attached to centre-piece ;
bf 6, two brass pins for steadying the instrument against the

OBJECT FINDERS. 189

left side of the microscope stage. The scales may be ruled
in brass or bronze and inlaid, and horizontal lines might
be ruled on the surface of the stage as a guide for placing
the slide. This form of instrument possesses the advantage
of not requiring the common object slides to be ruled, or
in any way prepared.

It is thus used : — 1st. Put the finder on the stage and
find the central needle hole with the microscope. 2d. Ke-
rnove the centre-piece with a small pair of forceps.
3d. Place the slide on the wood, taking care that the stage
screws be not used to move the object after the finder has
once been centred.

The position of any object then occupying the centre of
the field will be shown by the sides and ends of the slide
on the scales of the finder, and can be registered at sight.
To find the object again : — Find the centre hole, remove
the disk as before, then place the slide according to the
letter and number marked upon it, when the object sought
will occupy the centre of the field.

For those microscopists whose instruments are without
a traversing stage " Maltwood's finder " will be found an
efficient substitute for the one just described. This consists
of a glass slide, 3x1^ inches, on which is photographed a
scale occupying a square inch ; this is divided by horizontal
and vertical lines into 2,500 squares, each of which con-
tains two numbers marking its "latitude," or place in
the vertical series, and its "longitude," or place in the
horizontal series. The scale is in each instance an exact
distance from the bottom and left-hand end of the glass
slide ; and the slide when in use should rest upon the
ledge of the stage of the microscope, and be made to abut
against a stop, a simple pin, about an inch and a half from
the centre of the stage. To use this finder, the object-
slide must be placed under the microscope with the same
care as the finder ; and when some especial object, whose
place it is desired to record, has been brought into the
field of view, the object-slide being removed, the finder
laid down in its place, the numbers of the square then in
the field of view are to be read off and recorded. This
should also be recorded upon the object-slide ; and at any
future time, when it is wished to refer to the same object,

190 THE MICROSCOPE.

the process will have to be reversed, by first finding this
particular square on the finder, and then replacing it by
the object-slide.

A simple form of finder, suggested by Mr. W. K. Bridge-
man, of Norwich, and sold by Baker, Holborn, is, from
its ingenuity and comparative accuracy, worthy of notice.

Fig. 112.— Bridgeman's Finder,

This finder (fig. 112) consists of a curved pin of steel,
which is attached to the stand by means of a circular
fitting of brass. It is so contrived that when the mechanical
stage is brought into the rectangular position, and an
object laid thereon, it can be pressed down upon the slide.
If the latter be covered with paper, the point of the pin
leaves a slight puncture : all that is necessary, when we
wish to examine the object in future, is to move the stage
till the puncture on the slide comes under the point of
the finder.

Forceps. — For holding minute objects, such as parts of
plants or insects, to be examined either as transparent or
opaque objects, the most useful is represented by fig.113,

Fig. 113.

and consists of a piece of steel wire, about three inches
long, which slides through a small tube, connected to a
stout pin by means of a cradle-joint ; to one end of the
wire is attached a pair of blades, fitting closely together
by their own elasticity, but which, for the reception of any

DIPPING TUBES,

191

object, may be separated by pressing the two projecting
studs ; to the opposite end of the wire is adapted a small
brass cup, filled with cork, into which pins, passed through
discs of cork, card-board, or other material, having objects
mounted on them, may be stuck.

Dipping-tubes are tubes of glass, fig. 114, about nine inches
in length, open at both ends, and from one-eighth to one-

rig. 114.— Dipping Tubes.

Fig. 115.

fourth of an inch in diameter. The ends must be nicely
rounded off in the flame of a blow-pipe ; some of them may
be made perfectly straight, while others should be drawn out
to a fine point, and made of either of the shapes a, b, c, d, e.
The method of using them is as follows : — Supposing the
animalcules are contained in a phial or glass jar (fig. 115),
and having observed where they are most numerous, —
either with the naked eye, or with a pocket-magnifier, — -

192 THE MICROSCOPE.

either of the glass-tubes, having one end previously closed
by the thumb or fore-finger, wetted for the purpose, is
introduced into the phial in the manner represented by
the figure : this prevents the water from entering the
tube ; and when the end is near to the object which it is
wished to obtain, the finger is to be quickly removed and
as quickly replaced. The moment the finger is taken off,
the atmospheric pressure will force the water, and with it,
in all probability, the desired objects, up the tube. "When
the finger has been replaced, the tube containing the fluid
should be withdrawn from the phial ; and as the tube is
almost certain to contain much more fluid than is requisite,
the entire quantity must be dropped into a watch-glass,
and the particular insect can be caught by putting the
tube over it, when a small quantity of fluid is sure to run
up by capillary attraction. This small quantity is to be
placed upon a glass-slide for examination. It is necessary
to add a small quantity of vegetable matter to animalcules,
if we wish to keep them alive for many days ; and as
many species are found on conferva? and duck-weed, some
instrument is required to take small portions of such plants

Fig. 116.

out of the jar in which they are growing. For this pur-
pose it will be necessary to make use of the forceps,
fig. 116, made of brass; the points are a little curved, to
keep them accurately together, and the blades are provided
with a hole and a steadying-pin. This instrument is also
useful for picking up any minute object.

Fig. 117, at B, is represented a convenient, cheap, and
portable "Collecting-bottle and Stick;" simply an ordinary
walking-cane divided by a screw, or socket-joint, into two
parts for the convenience of packing, and terminated by a
brass ring, which is either a fixture or made to screw on
and off. This ring is adapted to receive the male-screw of
the well-known wide-mouthed bottle, used by perfumers

COLLECTING BOTTLE AND NET.

193

and chemists for pomade ; this is exactly adapted
to fit into the screw of the brass ring. The facilities

Fig. 117.

A. Trough for showing circulation in fish-tail.

B. Collecting bottle and stick.

afforded "by such an arrangement are obvious enough ;
broken bottles can be readily replaced at a small cost,
and each bottle when filled corked up and replaced by
another. A small fine-gauze net and a hook is made to
screw into the same stock ; the whole packs into a very-
small compass.

Fig. 118.— Collecting Net.

Collecting Animalcules. — For collecting fresh water or
marine animals, the small net, made similar to a landing-
net, fig. 118, will be found useful : this should be securely
fastened to the brass ring a, and fitted firmly into the
socket 6 ; when not in use, the socket may be carried in
the pocket ; and the net, by contracting the diameter of
the ring (which the construction admits of) may be carried
inside the hat.

For collecting desmids, diatoms, and other small crea-
tures, Mr. Williamson has a cheap and simple contrivance
for converting the end of a walking-stick or umbrella into
what he terms a "collecting-stick." In fig. 119, a repre-

o

194

THE MICROSCOPE.

sents a piece of whalebone, about 18 inches long, bent

round the end of the stick or umbrella, b, and made fast
in that position by one or two rings,
c, of gutta-percha, india-rubber, or
of brass, d. A small wide-mouthed
bottle, having a rim which will
prevent its falling through, is
now inserted in the loop thus
formed, and is held tightly there
by the ends of the whalebone
being drawn further through the
ring, and thus diminishing the
size of the loop. The bottle thus
fixed may be used for dipping out
the animalcules. Whalebone can
be moulded to any form by plac-
ing it for a short time near the
fire.

Fig. 120 is a box containing
six bottles for holding the speci-
mens when caught. These bottles
should be filled up to the cork
with water when and where col-
lected, and care must be taken
not to mix the specimens from
one brook with those from another,

otherwise serious damage may take place, and on reaching

home we may find the greater part of our stock either

dead or dying. Always separate

the various species as speedily

as possible. This can be done

easily, by emptying each bottle

in its turn into a soup-plate ;

then with the feather of a pen

first lift out the smaller ones,

and with the quill-end cut like

a scoop lift out the larger,

classifying and allotting each

to its separate bottle.

Live-Box. — Mr. Varley im- Fis- 120-

proved the form of this instrument by making a channel

Fig. 119.

ANIMALCULE-CAGE.

195

all round the object- plate, so that the fluid and animalcules
in it were retained at the top of the object-plate by capil-
lary attraction. The cover is made in the usual way to
slide up and down over the object-plate. The plate of
brass to which the tube supporting the tablet and cover
is attached, is of a circular form, slightly flattened on its
two opposite sides for convenience of package. The in-

Fig. 121. — Varley's Animalcule-cage.

strunient is seen in elevation and in section in fig. 121
A, B, in both figures, is a flat- plate of brass to which the
short tube carrying the object-plate or tablet is fixed ;
d, the piece of brass into which the tablet c is fastened ;
b, the, tubular part of the cover, into the rim of which
the thin plate of glass a is cemented.

Compressorium. — The purpose of this instrument is to
apply a gradual pressure to objects whose structure can
only be made out when they are pressed or thinned out
by extension. The general plan of the Compressorium is
shown in fig 122

Ross's Compressorium consists of a stout plate of brass
A, about three inches long, halving in its centre a piece of
glass like the bottom of a live-box. This piece of glass
is set in a frame JB, which slides in and out so that it can
be removed for the convenience of preparing any object
upon it, under water if desirable. The upper moveable
part D is attached to a screw-motion at G; and at one end
of the brass-plate J., which forms the bed of the instru-
ment, is an upright piece of brass C, grooved so as to
o2

196

THE MICROSCOPE.

receive a vertical plate, to which a downward motion is
given by a single fine screw, surrounded by a spiral spring,
which elevates the plate as soon as the screw-pressure is
removed. ' The vertical plate carries an arm at right angles
to its own plane, terminating in a square frame Dy capable
of receiving very thin, or somewhat thicker glass. The
arm has likewise a horizontal motion, so that the upper

Fig. 122.— Boss's Compressorium.

plate D can be turned completely off the lower one B.
Should the thin upper glass be broken, it can be instantly
replaced, as no cement is required ; it is merely needful to
remove the fragments and slip a fresh glass in. It often
happens that on account of the trouble attendant upon
the use of all ordinary Compressoriums, the microscopist
simply uses a slide and a piece of covering-glass ; but if
he wishes an exact means of regulating the pressure,
some such compressorium as Ross's should always be
employed.

CHARA AND POLYPE TROUGHS. 197

Smith and Beck's trough for chara and polypes, a sec-
tional view of which is shown at fig. 123, is made of three
pieces of glass, the bottom being a thick strip,
and the front a of thinner glass than the back
b ; the whole is cemented together with Jeffery's
marine-glue. The method adopted for confining
objects near to the front glass varies according
to circumstances. One of the most convenient
plans is to place in the trough a piece of glass
that will stand across it diagonally, as at c ; then
if the object be heavier than water, it will sink,
until stopped by this plate of glass. At other \c\\
times, when used to view chara, the diagonal
plate may be made to press it close to the front
by means of thin strips of glass, a wedge of glass
or cork, or even a folded spring. When using &
the trough, it is necessary that the microscope Fl?-128-
should be in a position nearly horizontal.

Mr. Walker's trough for exhibiting the circulation ot
the blood in a fish's tail, &c. (fig. 117 A) consists of a piece
of plate-glass about 6 inches long, and 2 inches wide ;
upon this, three other pieces of plate-glass, about J
inch wide, are cemented with marine-glue. Three pieces
of strong covering glass, about a ^ inch wide, are
also cemented on to the plate, and a piece of mode-
rately strong covering glass on to the top of these thin
slips ; a piece of plate-glass is then cemented to the top
of the thin glass, abutting on the ends of the slips ; the
whole forming an open trough, terminating in a thin cell,
which is closed at all parts, except where it communicates
with the bottom of the trough.

The fish, wrapped in a little wet linen, is placed in the
trough, and the tail is thrust flat into the thin cell ; a
small quantity of water is placed in the large trough, and
the fish kept in its place by one or two elastic bands or
strips of thin sheet-lead passed round the glass and over
the body of the fish.

The advantages of this arrangement are :— 1st. The
fish cannot throw up its tail and splash the object-glass
with water. 2d. In consequence of the tail being kept
flat in the cell, the view is perfect, and there is little risk

198 THE MICROSCOPE.

of the object getting out of focus. 3d. If the tail "be not
pushed too far into the cell, the vessels at its root are not
compressed, and the circulation goes on very freely.
4th. The fish may be kept on the stage of the microscope
for two or three hours without injury. Mr. Macaulay has
suggested, as an improvement, that the three sides of the
cell should be made of a single strip of plate-glass, bent to
the shape represented in our wood-cut.

Growing-cells. — Considerable attention has been given
to various forms of growing-cells for maintaining a con-
tinuous supply of fresh water to objects under constant
observation, f ^r the purpose of sustaining vital growth for
a long period. The employment of such cells is strongly
commended to microscopists, as there is yet much to
be discovered concerning the metamorphoses which some
of the lowci microscopic forms of plant and animal life
pass through ; a patient investigation will probably show
that many which are now classed as distinct species
are merely different phases of the same type, which alter-
nate in a higher or lower scale of development accord-
ing to the varied conditions of temperature and nutrition
under which they are grown.

Professor Smith, of Kenyon College, furnished us with
what he has called a growing slide, or trough. It con-
sists of two pieces of thinnish glass cemented together ;
in one corner of the upper cover a small hole is bored,
and through this a fresh supply of water is introduced
without in any way disturbing the desmid, or living object
under inspection. Mr. Beck has contrived an improved
form of cell ; but, whilst the first-mentioned may be con-
structed for a few pence, the latter cannot be had for a
less price than ten shillings.

Dissecting Knives, &c. — Knives and needles of various
kinds and sizes are required for microscopic dissection ; the
best for the purpose are represented in tigs. 124, 125, and
126, being, in fact, the very delicately made knives used
by surgeons in operations upon the eye. Dissecting needles
may be either straight or curved. They may be fixed, or
made to take in and out of their handles. The most con-
venient are shown in fig. 125; those made of Palladium
by Mr. Weedon, Hart Street, are very much the best.

Fig. 124.

FK125

Fig. 126.

The mode of using a pair of needles in breaking up
tissues into very small pieces is represented in fig. 127.

Fig. 127.— Teasing-out Membrane.

With a pair of the small needles held firmly hetween the
fore-finger and thumb, the structure must be teased out ;

200

THE MICROSCOPE.

an operation which requires care and perseverance, as most
of the animal tissues are very difficult of separation. All
substances should be carefully separated from dust and
other impurities which renders their structure indistinct
or confusing. With very delicate membranes, and with
those of the nervous system of the smaller animals, in-
sects, &c., it becomes necessary that the investigation
should be carried on under water, or in fluid of some sort,
in a glass cell, and having a strong light thrown down
upon it by the aid of the condensing lens, as represented
in fig. 128. A certain amount of change of structure must
be expected and allowed for; as nearly all membranes
imbibe some portion of the fluid. Delicate structures are
often advantageously wetted with dilute solutions of sugar
or common salt, to prevent the changes from endosmosia,
which result from the use of pure water. The contents of
bodies are frequently rendered more distinct by the addi-

Fig. 128.— Dissecting under water.

tion of re-agents. If the object be a portion of an in-
jected animal, it is better to pin it out on a leaded-cork,

VALENTIN S KNIFE.

201

covered with white wax, and then immerse it in the water-
trough ; the more delicate the structure, the sooner after
death should it be examined, especially animal tissues.
With some vegetable structures, the dissection should be
carried on under water. The sepa-
ration of the woody and vascular
tissues, and the spiral vessels, is best
effected by maceration and tearing
with fine needles.

Valentin's Knife. — For making fine
sections of large substances, or those
soft in structure, such as the liver,
spleen, kidney, &c., the double-bladed
knife, the invention of Professor
Valentin, may be used with advan-
tage. An improved construction of
this knife, by the late Mr. John
Quekett, is represented in fig. 129.1
It consists of two blades, one of
which is prolonged by a flat piece of
steel to form a handle, and having
two pieces of wood riveted to it, for
the purpose of its being held more
steadily ; to this blade another one
is attached by a screw ; this last is
also lengthened by a shorter piece of
steel, and both it and the preceding
have slots cut out in them exactly
opposite to each other, up and down
which slot a rivet with two heads is
made to slide, for the purpose either
of allowing the blades to be widely
separated or brought so closely to-
gether as to touch. One head of this
rivet, being smaller than the hole in
the end of the slot, can be drawn Fis- 129.

through it ; so that the blade seen in the front of the figure
may be turned away from the other in order to be sharpened,

(1) Another fcim of this instrument is constructed by Mr. Matthews the
blades being made with a convex instead of a straight edge, 'their distances from
each other being regulated by a milled-head screw, and their separation for
cleaning being more readily accomplished.

1 1

202

THE MICROSCOPE.

or allow of the section made by it being taKen away from
between the blades. The blades are so constructed that
their opposed surfaces are either flat or very slightly concave,
that they may fit accurately to each other, which is effected
more completely by a steadying pin, seen at the base of the
front blade. When the instrument is required to be used,
the thickness of the section about to be made will depend
upon the distance the blades are apart ; and this is regu-
lated by sliding up and down the rivet, as the blades, by
their own elasticity, will always spring open and keep the
rivet in place ; a cut is then to be made by it, as with
an ordinary knife, ax\d the part cut will be found between
the blades, from which it may be separated either by open-
ing them as wide as possible by the rivet, or by turning
them apart in the manner before described, and floating
the section out in water.

Dissecting Scissors. — In addition to the forceps and
knives, scissors will be necessary for the purposes of dissec-
tion: of these the most useful are shown in fig. 130. They

Fig. 130.— Dissecting Scissors.

are made both straight and curved ; of the first kind, two
pairs will be required, one having the extremities broad,
and the other sharp-pointed ; if large dissections be under-
taken, a still stronger pair, with the extremities broad,
and made rough like a file, will be necessary. In dis-
secting under the microscope, the curved-pointed pair
shown at / are the most convenient. In all of these
instruments the points should fit accurately together :
sometimes those that are very sharp are apt to cross ; this

SMITHES SECTION INSTKUMENT.

203

may in a great measure be prevented by having the
branches wide at the base where they are riveted. The
points can be sharpened on a hone, and a magnifier em-
ployed to examine if they fit closely together.

Section-cutting Instruments. — There are a numerous class
of substances much too hard to admit of being cut either
by scissors or a Valentin's knife, more especially if we re-
quire very thin and perfect sections. As most important
information is to be gained respecting the structure of
various substances, such as stems and roots of plants,
horns, hoofs, cartilages, and other firm parts of animals,
by cutting very thin sections for mounting as transparent
objects, it would be quite impossible for the microscopist
to get on without a section-cutting instrument. Among
the many mechanical contrivances which have been de-
vised for the purpose, the ingenious little machine in-
vented by Mr. James Smith1 will be found to do its work
with neatness and precision.

Vertical or top view. Side view.

Fig. 131. — Smitli's Section Instrument.

Smith's Section Instrument (fig. 131) consists of an outer
tube A, A, the upper part of which screws into the lower,
and has at the top a flat circular plate B, E, which
forms the cutting-table. .Firmly fixed to the lower part
of the tube A, and extending throughout its whole length,
is the inner tube B, B, which forms, with the moveable
bar D, a holding for the specimen to be cut, while, at the
same time, it supports the upper part of the tube A, A, and
gives it greater firmness in screwing up and down. The

(1) " On a Section Instrument, by James Smith." (Micros. Soc. Trans.
vol. viii. page 1, 1860.)

204 THE MICROSCOPE.

bar D moving backwards and forwards in the tube by
means of the screws c, c, serves, in conjunction with the
points F, F, to fix the specimen to be cut, which is effected
as follows : —

The cutting surface E, B, being slightly screwed up, as
shown in the drawing, and the bar D being drawn back
a sufficient distance, the specimen to be cut is placed in
the instrument, and firmly fixed by turning the screws
c, c ; it is then cut level with the surface by a proper
knife or chisel, and the table being screwed down one or
more divisions (as shown in the left-hand diagram), a
section is cut, and if found of sufficient thinness, a number
may be cut by continuing to turn the table down a similar
number of divisions, until it will screw no further, when
the table must be again screwed up, and the specimen
loosened and raised if more sections be required. The
principal points of the instrument are : —

1st. Its portability — the tube being about two and a
half inches long by one inch in diameter. 2d. The
specimen to be cut is fixed once for all, and the cutting-
surface screwed down to it, a feature that will render it
peculiarly applicable to the cutting of soft substances.
3d. The ease with which a number of sections may be
cut without disturbing the specimen when once properly
fixed, while the size of the tube, and the facility with
which it can be adapted to objects of various diameters,
enable the operator to get sections of stems of plants, &c.
whole. In cutting sections of hard woods, which require
considerable purchase, the instrument may be placed in a
semicircular opening in the edge of the working-table, so
that the flat plate or cutting-surface may rest upon it, and
the strain thrown on the table. When used for cutting
soft substances, it can be held in the hand.

Fig. 130 represents Mr. Gibbon's "Section-cutting Ma-
chine." It consists of a stout brass frame, A A, having
an opening in the top plate, for a tube B, half an inch in
diameter, and in depth one and a half inches. In this
tube a loose piston, c, works freely, and is steadied by the
slot seen in it. To a female screw D, motion is given by
the toothed wheel ; and the teeth of which, /?, answer
the triple purposes of thumb-milling, ratchet-stop, and

SECTION CUTTING.

205

graduation. This is screwed to a block of wood, F, having
a rabbet cut in for the purpose of securing it to the table.

Fig. 132. —Gibbon's Section Cutting Muckku.

The machine is self-regulating, and is capable of being
worked as rapidly as the skill of the operator may dictate.
Sections of woods, when cut from hard woods containing
gum, resin, &c., should be soaked in essential oil, alcohol,
or ether, before they are mounted as transparent objects.
A razor may be fixed to the bench for the purpose of
cutting these fine sections, or a fine plane will answer very
well. The instrument used by Mr. Topping, fig. 133, con-
sists of a 6, a flat piece of mahogany, seven inches long
and four wide, to the under surface of which is attached,
at right angles, a piece g of same size as a b. d is a flat
plate of brass, four inches long and three wide, screwed to
the upper surface of a b ; to the middle of this plate is
attached a tube of the same metal e i, three inches long
and half an inch in diameter, and provided at its lower
end with a screw /, working in a nut, and having a disk k
exactly adapted to the bore of the tube j this disk is con-
nected with the upper end of the screw, and is moved up
or down by it. c is another screw connected with a curved
piece of brass h, which is capable of being carried to the
opposite side of the tube by it. The piece of wood about

THE MICROSCOPE.

to be cut is put into the tube e, and is raised or depressed
by the screw/; whilst, before cutting, the curved piece of

Fig. 133,— Topping's Section Cutting Machine.

metal h should be firmly pressed against it by the screw c.
This instrument, if fastened to the edge of a bench or
table, is always ready for use. The knife employed may
be one constructed for the purpose ; or a razor ground flat
on one side.

Method of making Sections. — If the wood be green, it
should be cut to the required length, and be immersed for
a few days in strong alcohol, to get rid of all resinous
matters. When this is accomplished, it may be soaked in
water for a week or ten days ; it will then be ready for
cutting. If the wood be dry, it should be first soaked in
water and afterwards immersed in spirit, and before cutting
placed in water again, as in the case of the green wood.
The wood, if too large, should be cut so as to fit tightly
into the square hole, and be driven into it by a wooden
mallet; if, on the contrary, it be round, and at the same
time too small for the hole, wedges of deal or other soft
wood may be employed to fix it firmly : these will have
the advantage of affording support, and if necessary, may
be cut with the specimen, from which they may afterwards
be easily separated. The process of cutting consists in
raising the wood by the micrometer screw, so that the

SECTION-CUTTING.

207

thinnest possible slice may be taken off by the knife ; after
a few thick slices have been removed to make the surface
level, a small quantity of water or spirit may be placed
upon it; the screw is then to be turned one or more
divisions, and the knife passed over the wood until a slice
is removed; this, if well wetted, will not curl up, but will
adhere to the knife, from which it may be removed by
pressing blotting-paper upon it, or by sliding it off upon
a piece of glass by means of a wetted finger. The plan
generally adopted is to have a vessel of water by the side of
the machine, and to place every section in it : those that
are thin can then be easily separated from the thick by
their floating more readily in the water ; and all that are
good, and not immediately wanted, may be put away in
bottles with spirit and water, and preserved for future
examination. If the entire structure of any exogenous
wood is required to be examined, the sections must be
made in at least three different ways; these may be
termed the transverse, the longitudinal, and the oblique,
or, as they are sometimes called, the horizontal, ver-
tical, and tangental : each of these will exhibit different

Fig. loi.— Sections of Wood.

appearances, as may be seen upon reference to fig. 134 :
6 is a vertical section through the pith of a coniferous
plant: this exhibits the medullary rays, which are known

208 THE MICROSCOPE.

to the cabinet-maker as the silver grain; and at e is a
magnified view of a part of the same: the woody fibres
are seen with their dots I, and the horizontal lines k indi-
cating the medullary rays cut lengthwise ; whilst at c is a
tangental section, and /a portion of the same magnified:
the openings of the medullary rays m m, and the woody
fibres with vertical slices of the dots, are seen. Very
instructive preparations may be made by cutting oblique
sections of the stem, especially when large vessels are
present, as then the internal structure of the walls of some
of them may oftentimes be examined. The diagram above
given refers only to sections of a pine ; all exogenous stems,
however, will exhibit three different appearances, according
to the direction in which the cut is made ; but in order to
arrive at a true understanding of the arrangement of the
woody and vascular bundles in endogens, horizontal and
vertical sections only will be required. Many specimens
of wood that are very hard and brittle may be much
softened by boiling in water ; and as the cutting-machine
will answer for other structures besides wood, it should
be stated, that all horny tissues will also be softened by
boiling, and can then be cut very readily.

Preparation of Hard Tissues. — All sections of recent and
greasy bones should be soaked in ether for some time, and
afterwards dried in the air, before they are fit for the saw,
file, and hone ; by dissolving out the grease, the lacunae
and canaliculi show up very much "better. When it is
wished to examine the bone-cells of fossil bone, chippings
only are required; these may be procured by striking the
bone with the sharp edge of a small mineralogical-hammer:
carefully select the thinnest of the chips, and mount them
at once, without grinding, in Canada balsam. If desirable
to compare bone structures, it must be borne in mind that
the specimens for comparison should be cut in one and the
same direction ; as the bone-cells, on which we rely for our
determination, are always longest in the direction of the
shaft of the bone, it follows that if one section were trans-
verse, and the other longitudinal, there must be a vast
difference in the measurement of the bone-cells, in conse-
quence of their long diameter being seen in the one case,

SECTIONS OF TEETH.

209

and their short diameter in the other. In all doubtful
cases, the better plan is to examine a number of fragments,
both transverse and longitudinal, taken from the same
bone, and to form an opinion from the shape of bone-cell
which most commonly prevails.

The Teeth. — The best mode of examining teeth is by
making fine sections. Specimens should be token, both
from young and old teeth, to note
the changes. A longitudinal or
transverse slice should be first
taken off; a circular saw, fitted to
the lathe, fig. 135, cuts sections
very quickly — then rub down, first
by the aid of the corundum- wheel,
— which should also be fitted to
the bead-stock of the lathe, — then
finish them off between two
pieces of water-of-Ayr stone, and
finally clean and polish between
plates of glass, or on a polishing
strap with putty powder. The
section requires to be washed in
ether, to remove all dirt and im-
purities ; when well polished and
dried, it may be preserved under
thin glass, and cemented down
with gold-size or varnish.

Such polished sections are preferable to many others
which, on account of their irregular surface, require to be
covered with fluids, as Canada-balsam, turpentine. &c., in
order to fit them for examination with high powers. It
almost always happens, that some portion of these fluids
enters the dentine, which then becomes indistinct, artd
almost invisible in its ramifications.

Two sections made perpendicularly to one another
through the middle of the crown and fang of a tooth,
from before backwards, and from right to left, are suffi-
cient to exhibit the more important features of the teeth ;
but sections ought also to be prepared, showing the surface
of the pulp cavity and that of the enamel; and likewise
various oblique and transverse sections through the dentine

Fig. 135 —Small Latke for
polishing.

210 THE MICKOSCOPE.

in the fangs, to exhibit the anastomoses of their branches.
The dental cartilage is easily shown by maceration in
hydrochloric-acid, a process which requires a longer or
shorter time, according to the concentration of the acid.
It is very instructive also to macerate thin sections in
acid, and to examine them upon a slip of glass, at
intervals, until they entirely break up. The enamel
prisms are readily isolated in developing enamel in this
way, and the transverse lines readily seen when the section
is moistened with hydrochloric acid. The early develop-
ment may be studied in embryos of two, three, or four
months with the simple microscope ; and in transverse
sections of parts hardened in spirits of wine. The pulp of
mature teeth is obtained by breaking them in a vice, and
the nerves can be made out without difficulty on the addi-
tion of a dilute solution of caustic soda,

To cut through the enamel of the tooth, it will be
necessary to lessen the friction, by dropping water upon
the saw as it is made to revolve. The section is after-
wards very quickly ground down by holding it against
the flat side of the corundum- wheel.1 A small handle,
mounted with shell-lac, to fix the section in, forms a ready
holder : polish, as before directed, between two pieces of
the water-of-Ayr stone, or on a hone of Turkey-stone kept
wet with water. As the flatness of the polished surface is
a matter of the first importance, that of the stones them-
selves should be tested from time to time ; and whenever
they are found to have been rubbed down on one part
more than another, they should be flattened on a paving
stone with fine sand, or on a lead plate with emery. When
this has been sufficiently accomplished, the section is to be
secured, with Canada balsam, to a slip of thick well-
atfnealed glass, in the following manner : — Some Canada
balsam, previously rendered somewhat stiff by 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 size 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

Ip

(1) Corundum is a species of emery composition ; alumina, red oxide of iron,
and lime ; it is much used by dentists as a polishing material.

PREPARING SECTIONS. 211

hardness should be tested with the edge of the thumb-
nail, for it should be with difficulty indented by pressure,
and yet should not be 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 of the right consistence, the section
should be laid upon its surface, with the polished side
downwards ; the slip of glass is next to be gradually
warmed until the balsam is softened, care being taken to
avoid the formation of bubbles, and the section is then to
be gently pressed down upon the liquefied balsam in a sort
of wave towards the side, and an equable pressure being
finally made over the whole. When the section has been
thus secured to the glass, it may be readily reduced in
thickness by grinding. 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 section
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 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 is not carried too far ; and frequent
recourse should be had to the microscope to examine it.
The final polish must be given upon a leathern strap, or
upon the surface of a board covered with buff-leather,
sprinkled with putty-powder and water, until all marks
and scratches have been rubbed out of the section.

In mounting sections of bone, or teeth, it is important
to avoid the penetration of the Canada balsam into the
interior of the lacunce and canaliculi; since, when these
are filled by it, they become almost invisible. 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
p2

212 THE MICROSCOPE.

into its interior, by adopting the following method : —
A small quantity of balsam, proportioned to the size of
the specimen, is to be spread upon a slip of glass, and to
be rendered stifier 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, 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.

Circular Disc. — For the purpose of cutting glass covers
or mating shallow cells with japanners' gold-size for mount-
ing objects,1 fig. 136 will be found useful; it is made

Fig. 136.— Circular Disc Machine.

of two circular wheels of wood, these being let into a
solid block of wood, and secured there by central screws.
A handle of wood is fixed into the upper part of one, for
the purpose of turning it round, the motion being com-
municated to the other by an endless band of catgut
running in the grooved edge of each. On the upper sur-
face of the wheel, under the right hand, are fixed, by
means of screws, two strips of brass, which serve as springs

(I) Mr. Shadbolt's little turn -table, invented for the same purpose, is in every
way superior to this, and is now in very general nse.

GLASS CELL CUTTING. 213

for securing the glass slip; a camel's-hair pencil, previously
dipped in japanners' gold-size, is then taken between the
finger and thumb, and held as represented in the woodcut,
when the wheel is put in motion, and a perfect circle is
rapidly formed ; the cell is then removed and put aside to
dry. In the same way, by securing a sheet of thin glass
under the brass springs, and substituting for the pencil
a cutting diamond, a circular cover may be readily cut
out. A cutting diamond is not only useful to the micro-
scopist for the above purpose, but also for writing the
names of mounted objects on the ends of the glass slides.
A glazier's diamond for cutting glass slides is both conve-
nient and economical : the mode of using it may be acquired
in any glazier's shop.

Cutting glass cells. — Mr. H. H. Brown has also con-
trived a brass plate for cutting out the centres of pieces of
thin glass, to form very shallow cells. It consists of a thin
plate of brass, perforated with holes corresponding to the
diameter of the cell required, and counter-sunk to a suit-
able thickness. To use it, it must be heated, and a little
sealing-wax or shellac melted into the counter-sunk parts ;
on this, while hot, the disc of thin glass is to be firmly
pressed. When cold, the centres may be easily removed
with a common rat's-tail file, the edges being afterwards
smoothed over by a fine watch-maker's file. The plate
must once more be heated and the glass rings removed,
and finally be cleansed from, adhesive wax by a little ether.
Mr. Brooke has long made use of a small brass press for
the purpose of cutting out thin circles of glass and con-
verting the same into shallow cells.

Cells for mounting objects may be made of vulcanite
by slicing-tubing made of this material. Glycerine does
not act upon it. Mr. Henry Lee uses cells cut from tubes
of cardboard; these he finds very useful for mounting dry
and opaque objects. Both have the great advantage of
cheapness — the former are sold for about 3d. a dozen and
the latter Is. a gross. Mr. Suffolk devised a cheap tin-cdl,
which must partially supersede the more expensive glass-
cell; it appears to answer equally well for fluid or dry
mounting. The metallic rings for making these cells
are manufactured in various sizes and thicknesses by

THE MICROSCOPE.

Collins, of Great Titchfield Street, and sold at 3d. per
dozen.

Dr. Guy brought under the notice of microscopists, a
plan for preserving metallic sublimations, crystals, &c. in
small round, or oval tubes, hermetically sealed at both
ends. This plan may be made available for the display of
insects, parts of flowers, as stamens, pollen, &c. See his
paper in the Micros. Journal, New Series, vol. ii. p. 77.

Fig. 137, full size. — Spring-clip for mounting.

B". Maddox describes a Wire Spring-clip for mounting
purposes, Micros. Soc. Trans. 1865, p. 84. To make the
clip, take a straight piece of brass wire four and three-
quarter inches in length, turn one end at six-eighths of an
inch with a pair of wire-pliers at right angles ; this second
portion, at half an inch, again bend at right angles in the
same plane ; now, at three-quarters of an inch, turn the
wire over on itself, leaving at the bend space sufficient to
admit a thick slide. At one inch and five-eighths twist
the wire completely on itself, and bring the now short
ends at right angles to the longest part ; file this end quit*
Hat. Give the first portion of the wire a slight curvature,
so that the point and bend may act as a stiff spring
against the under surface of the slide when applied. This,
although a very simple and inexpensive^ clip to make, has
been very much improved upon, as will be admitted by
those who have used the little handy spring-clip shown
full size in fig. 137. The Universal Clip, as it deserves to
be called, may be purchased for Is. 6d. per doz. of Baker,
Holborn, so that objects of great delicacy can be mounted
and left to dry and harden for any necessary length of
time. The little nipple which is seen to press upon the
glass cover in fig. 138, is made of a piece of cork or thick
leather. The clip simply requires pinching together be-
tween the thumb and finger; as soon as it is released the

MOUNTING OBJECTS. 215

little cork nipple comes down with considerable force upon
the glass cover. In mounting algae, &c. with a gelatine
medium, the specimen should
be placed on the glass slide
with a small quantity of water,
and when properly arranged,
the thin glass cover must be
carefully put on, and a suffi-
cient quantity of gelatine me-
dium placed by its side ; gentle
heat should be applied to &*
out the water, when the gela-
tine flows under to take its place ; then put the object
aside to dry and harden.

General Directions for the Preparation and Mounting
of Objects. — The objects exhibited by the microscope are
either opaque or transparent. The former, in the majority
of instances, require little or no preparation beyond placing
them in such a position as to show their external surface
by reflected or condensed light, and covering with thin glass to
exclude dust. Those objects, however, which it is intended
to examine by transmitted light require, in most cases, to
be prepared previously to mounting them, in whatevei
vehicle may be found most suitable for exhibiting theii
structure. The medium most used for mounting trans
parent objects is Canada balsam. The pure balsam is,
however, too thick for use, and it requires to be diluted
with spirit of turpentine to render it sufficiently fluid to
permeate the structure to be exhibited. As a general rule,
it should be just fluid enough to drop readily from the
point of a needle. Those who desire to avoid the trouble
of mixing their own mounting medium, can procure it
ready for use from any of the microscope makers. There
are some few objects whose structure is so transparent
that they must be mounted dry. Scales from the wings
of butterflies and moths, of the podura and lepisma sac-
charina, and some of the diatomaceae are of this class. All
that is necessary in preparing objects for dry mounting,
is to take care that they are free from extraneous matter,
and to fix them permanently in that position in which
their structure will show to the best advantage. Care

216 THE MICROSCOPE.

should "be taken to have no draught of air through the
room while handling very delicate objects ; many a beauti-
ful object has been wafted from under the hand of the
microscopist in this way, sometimes, even by his own
breath.

The preparation of very minute objects which require
particular chemical treatment before mounting, will be
more fully described hereafter. To this class belong the
diatomacese, whose delicate structure forms one of the most
beautiful objects which can be exhibited. In mounting
entomological specimens, the first thing, of course, is the
dissection of the insect. This is best accomplished by
the aid of Collins's Dissecting Microscope, a pair of small
brass forceps, and very finely-pointed scissors ; the parts
to be prepared and mounted should first be carefully
detached from the insect with the scissors, then immersed
in a solution of caustic alkali (Liquor Potassse) for a few
days, to soften and dissolve out the fat and soft parts : the
length of time it is necessary to immerse them can only be
ascertained by experience, but, as a general rule, the objects
assume a certain amount of transparency when they have
been long enough in the alkali ; when this is ascertained
to be the case, the object is to be placed in a flat receptacle
(a shallow pomatum pot is as good a thing as can be used),
and put to soak for two or three hours in soft or distilled
water. It is then to be placed between two slips of glass,
and gently pressed till the softer parts, &c. are removed.
These will frequently adhere to the edge of the object ; it
will, therefore, be necessary to wash the latter carefully
in water to get rid of the superfluous matter, a process
which will be much aided by delicate touches of a camel's-
hair brush. Place the object now and then under the
microscope to see that all extraneous matter is removed,
and when this is accomplished take the specimen up care-
fully with the camel's-hair brush, and lay it on a piece of
very smooth paper (thick ivory note is very good for
the purpose), arrange it, if necessary, to its natural appear-
ance with the brush and a finely-pointed needle, place a
second piece of paper over it, and press it flat between
two slips of glass, and compress it by one of the American
clips which may be bought for a few pence per dozen.

PREPARING AND MOUNTING. 217

When thoroughly dry (which it will probably be in about
twenty-four hours, if in a warm room), separate the
glasses, and gently unfold the paper ; then, with a little
careful manipulation, the object may be readily detached,
and should be at once placed in a little spirit of turpentine,
where it should remain for a few days till it is rendered
transparent and fit for mounting. The time during which
it should remain in this liquid will depend on the struc-
ture ; some objects, such as wings of flies, will be quickly
permeated, while horny and dense objects require an
immersion of a fortnight or even longer. A pomatum pot
with a concave bottom and well-fitting lid will be found
to answer admirably for the soaking process, and it is
well, in preparing several specimens at a time, to have two
pots, one for large and medium, the other for very small
objects, or the smaller ones will be found often to adhere
to the larger.

The glasses on which objects are mounted are usually
slips of flatted crown or sheet glass cut to a size of three
inches by one, and ground at the edges. The mode ol
mounting the object is as follows : — Having chosen a glass
slide, clean and polish it with a piece of chamois leather,
ascertain the centre of the slide by means of a piece of
paper or card of exactly the same size as itself, and in
which a hole has been cut exactly in the centre,
place the piece of paper under the slide, and, having
removed the object to be mounted from the turpentine in

Fig. 139. — Showing the mode of placing Glass Cover on the Object.

which it has been soaked, lay it on the slide on the spot
corresponding to the hole in the card underneath ; then
take up a small quantity of the prepared Canada balsam
on the point of a large needle or pointed pen-knife, and

213 THE MICROSCOPE.

drop it immediately over the object, slightly warm the
under part of the slide over a spirit-lamp to diffuse the
balsam and cause it thoroughly to penetrate the object,
and immediately cover the latter with one of the small
circles of thin glass, sold by opticians for the purpose.
In laying the glass cover on the object, care should be
taken to bring the edge of the circle down first, and let
the other fall slowly on the object (see fig. 139), to prevent
the formation of bubbles from the sudden displacement of
the air. It requires some little practice to keep the object
in the centre of the circle.

Sometimes, notwithstanding all the care of the operator,
bubbles will appear. These may generally be got rid of
by gently warming the under part of the slide over the
spirit-lamp, when the bubbles will usually leave the
object, and travel towards the edge of the circle. In most
cases they will entirely disappear as the balsam becomes
lirmer and drier. If it be desired to dry the balsam
quickly, the slide may be placed in some warm situation
where the heat does not much exceed 100°, and it must
be maintained in a perfectly horizontal position, to prevent
displacement, until the balsam has become dry. When
this has been ascertained to be the case, the superfluous
balsam which surrounds the edge of the circle may be
scraped off by the point of a penknife; and when the
major part has been removed in this way, the remainder
may be got rid of, and the edges of balsam rendered smooth
by rubbing gently with an old silk handkerchief moistened
with spirit of turpentine. The edge of the circle of balsam
will probably appear white and dull, but it may be rendered
transparent by gently warming the under part of the slide
over a spirit-lamp, and again placing the object in a warm
room till the balsam has a second time become hard and
dry ; after which the name of the object should be written
with a small writing diamond at one end of the slide.
Some microscopists prefer to cover the slide with orna-
mental paper, which may be procured very cheaply.

In covering the slides with paper, their edges need not
be ground, but may be rubbed with a fine file, which will
prevent the sharp glass from damaging the paper cover,
and cutting the fingers of the operator. The foregoing is

PREPARING AND MOUNTING. 219

the method by which objects are mounted in balsam ;
there are, however, some specimens, the mounting of
which, in balsam, would render them almost invisible, in
which case — if not suitable for dry-mounting — they should
be placed in fluid in cells, the size and depth of which
must be regulated by the proportions of the object. If
it be the scale of a fish, or the pollen of a flower, a very
shallow cell will suffice, and it may be formed of " Bruns-
wick black" in the manner already described. When the
cell is quite dry, take the object (which should have been
some time previously soaked in the fluid in which it is to
be mounted to dispel the air from its substance), place it in
the middle of the circle, fill the space quite full of the
mounting fluid, and cover it with a glass circle ; place the
edge down first, and bring the whole surface of the circle
very gradually upon the cell as pointed out in the former
case. Some of the fluid will immediately escape under the
edge ; this may be absorbed by a piece of filtering paper.
Should too much escape, a bubble will make its appearance
in the cell ; in this case the process must be repeated.
"When this has been performed successfully, secure the glass
circle in its place with a small spring-clip j then take a
cameFs-hair brush, charged with varnish, and carry it
round, and slightly over the edge of the cover. Allow the
first layer to dry before another is added, and continue to
add more gradually until the cell is made perfectly air-tight.
Glass or metal cells must be employed for those objects
whose bulk renders the method just described inadmissible.
Glass-cells may be fastened to the glass-slide either by
Canada balsam, by Jefferey's marine glue, or Brunswick
black ; the latter will be rendered very durable by mixing
it with a small quantity of India-rubber varnish (made by
dissolving small strips of caoutchouc in gas-tar). The pro-
cess of mounting in glass-cells is similar to that employed
in making varnish-cells, except that a somewhat larger
quantity of cementing medium is required on account of
the greater weight of the cell. Objects mounted in this
way should always be kept in the horizontal position, and
a little fresh varnish applied now and then, if the cement
show any tendency to crack.

In mounting objects in balsam, great care should be

220 THE MICROSCOPE.

taken to have the specimens quite dry before soaking them
in turpentine. Objects mounted in cells, on the contrary
should have become perfectly saturated with the mounting
fluid before being finally secured.

It is preferable to mount and preserve specimens of anhnal
tissues in shallow cells, to avoid undue pressure on the
preparation. Cells intended to contain preparations im-
mersed in fluid must be made of a substance impervious
to the fluid used; on the whole, the
most useful are those made with
circles of thin glass, cemented to
the glass-slide with marine glue,
such as we have here represented
(fig. 140). The surface of the glass

Fig" 14° f°r should be sliSh% roughened before

applying the cement.

Different modes of mounting may be employed with
advantage, to show different structures ; entomological
specimens, such as legs, wings, spiracles, tracheae, ovi-
positors, stings, tongues, palates, corneae, &c. show best
in balsam : the trachea of the house-cricket, however,
should be mounted dry. Sections of bone show best,
when mounted dry, or in a cell with fluid. Scales of
butterflies, moths, &c. should be mounted dry. Other
objects, as sections of wood and stones of fruit, exhibit
their structure best in a cell with fluid.

There are some objects much more difficult to prepare
than others, and which tax the patience of the beginner
in a manner which can hardly be imagined by any one
who has never made the attempt. The structure of many
creatures is so delicate, as to require the very greatest care to
prevent mutilation, and consequent spoliation of the spe-
cimen. The beginner, therefore, must not be discouraged
by a few failures in commencing, but should persevere
in his attempts, and constant practice will soon teach him
the best way of managing intricate and difficult objects.
The room in which he operates should be free from dust,
smoke, and intrusion, and everything used should be kept
scrupulously clean, since a very small speck of dirt, which
may be almost invisible by the naked eye, will assume
unpleasant proportions under the microscope, and not only

PREPARING AND MOUNTING. 221

mar the beauty, but possibly interrupt a clear view of a
very splendid and delicate object. Then, again, if the
microscopist prefers to cut and grind his own glass slips,
he should be very careful that there are no sand-specks or
air-bubbles in the centre of the slide, or of the glass-
cover : many a good object has been spoiled from neglect
of this precaution. A good light by which to work is
also highly important. In using the ordinary microscope,
the microscopist should keep both eyes open, the practice of
closing the eye not in use being injurious to the sight
of both. The beginner who is about to purchase a micro-
scope, will do well to procure a binocular, the price of
which has been reduced so much as to bring it within
the reach of those of even moderate means.

The preservation of objects is a matter of much im-
portance. They ought to be kept in a cool and dry
place. Sections of bone, the pollen of plants, and the
scales of the podura and butterflies, become spoiled if
kept in a damp atmosphere. Objects -mounted dry should
be carefully protected from dust, which will find its way
into crevices and corners where one might hardly suppose
it could possibly enter.

Some opaque objects require dry mounting; others
show best in fluid ; the elytra of some beetles are mag-
nificent objects when mounted in balsam. Cells punched
out of thick mill-board, or turned in some hard wood, or
Mr. Suffolk's metal-rings, are much lighter and more con-
venient than glass for such objects, and also for those
mounted dry. In mounting objects in fluid, the glass-cover
should come nearly, but not quite, to the edge of the cell ;
a slight margin must be left for the cement, which ought
to project slightly over the edge of the cover, in order to
unite it securely to the cell. In cells, however, that con-
tain balsam, there is no necessity for cement, and the
appearance of the slide will be improved by choosing a
cover of exactly the same size as the cell.

There are some objects which require considerable dex-
terity and patience to prepare them for mounting. The
petal of the pelargonium is one of these. It is necessary
to split it in order to show its structure to perfection.
This is effected by dividing the base of the petal with a

222 THE MICROSCOPE.

sharp penknife, and then, with two small pairs of forceps,
tearing asunder the two parts ; the upper surface, which
is the part to be mounted, must then be dried and placed
for a short time in spirit of turpentine, previously to
being mounted in balsam. If well prepared, the colour
of the petal will be almost as fresh as in its natural state.

In mounting diatomacese, to show them as nearly as
possible in their natural condition, they should be first
well washed in distilled water and mounted in a medium
composed of one part of spirits of wine to seven parts of
distilled water. The siliceous coverings of the diatoms,
however, which show such beautiful forms under the
higher powers of the microscope, require considerable
preparation. The guano, or infusorial earth containing
them, should first be washed several times in water till
the water is colourless, allowing sufficient time for pre-
cipitation between each washing. The deposit must then
be put into nitro-hydrochloric acid (equal parts of nitric
and hydrochloric acids). A violent effervescence takes
place, and when this has subsided, the whole should be
subjected to heat, nearly but not quite up to the boiling-
point, for six or eight hours. The acid must now be care-
fully poured off, and the precipitate washed in a large
quantity of water, allowing some three or four hours
between each washing, for the subsidence of some of the
lighter forms ; the sediment must be examined under
the microscope with an inch object-glass, and the siliceous
valves of the diatoms picked out with a coarse hair or
bristle.

When it is desired to exhibit one of the larger forms,
it can be placed separately in the middle of a glass-slide,
and mounted in Canada balsam ; or when it is wished to
mount several forms at once, the fluid containing the
skeletons should be gently shaken, and a drop spread over
the centre of a slide, the glass being held over a spirit-
lamp till the fluid has all evaporated, when the object may
be either dry-covered or mounted in balsam in the usual
way, according as its structure may require the one or the
other treatment. Diatoms may be kept in distilled water
in a small corked phial for any length of time.

For vegetable preparations, distilled water in which

GLYCERINE JELLY. 223

camphor has been kept is a good mounting medium ; some
preparers, however, add spirits of wine in the proportion
of one draehm to eleven drachms of water ; others add to
these saltpetre, two grains to the ounce of fluid. The
mounting-fluid should be prepared and allowed to settle,
when the major part can be poured off clear — a much
better mode than filtering, as particles of the paper are
apt to get mixed with the liquid.

F. M. Rimmington's Glycerine Jelly has become an
established preparation, and one found to possess many
advantages over Canada balsam, and some other media
used for the same purpose, in the facility with which
objects can be mounted, and efficiently preserved, and the
transparency it gives to many animal and vegetable struc-
tures. Its antiseptic powers are sufficient to prevent
changes in any object immersed in it, if not too bulky.
It is especially adapted for mounting algse, fungi, vegetable
and animal tissues, urinary deposits (as casts, epithelium,
crystals), also anatomical specimens, starch granules, des-
midiacese, diatomaceae, &e. Objects to be mounted in this
medium only require to be soaked in weak alcohol for a
time, greater or less, as may be necessary, for the purpose
of dissolving out any soluble matter, or for driving out
air entangled in the cellular meshes. When it is thought
that this has been accomplished, the object is laid on a
slide and freed from superfluous moisture, the slide gently
warmed, and a quantity of the jelly, deemed sufficient for
the purpose, laid by the side of it, and made to touch it.
It will thus be immersed; the cover, previously warmed, is
to be laid upon it, and gently pressed. The slide may now
be laid aside and finished by running it round with varnish.

The jelly should be liquefied by holding the bottle at
some distance above a lamp, or by dipping it into hot
water. No more than what is necessary need be liquefied,
and it should never be made hot.

For certain delicate organisms, as the desmidiacese and
diatomacese, whose plasma may be affected by too dense
a medium, the jelly may be diluted one-quarter or one-
third with camphor-water.

For mounting pathological or injected preparations, the
following medium will be found to answer very well : —

224 THE MICROSCOPE.

Bichloride of mercury, one grain ; chloride of sodium,
ninety grains; distilled water, one pint: set aside, and, when
perfectly clear, decant and preserve in a stoppered bottle.
All preparations used in mounting, and objects themselves,
should be carefully preserved from dust. Balsam should
be kept in a wide-mouthed bottle, over which a small
tumbler or cupping-glass must be inverted. It is ad-
visable to avoid the use of a cork, as it will be broken
in attempting to withdraw it, and portions will not only
adhere to the neck of the bottle, but are apt to get into
the balsam. Objects, and parts of objects, already prepared
and dry, may be kept neatly folded up in ivory-paper, as
it is not well to have too many objects in the turpentine
at the same time, in order to avoid confusion. Glass-
slides which are soiled with balsam can be cleaned witli
turpentine and a piece of rag — the glass circles will require
to be soaked in turpentine to get rid of any balsam they
may happen to contract. When a greasy appearance is
present, it may be removed by a piece of rag moistened
with rectified spirit. Some remove it by rubbing the
glass with caustic alkali ; but as this liquid acts on flint-
glass, and sometimes makes it partially opaque or milky,
its use should be entirely discarded — a weak solution of
ammonia, or cyanide of potassium, answers the purpose best.
In order to demonstrate the internal structure of animal
tissues under very high magnifying powers, Dr. Beale1 says
the specimen must be placed in a viscid medium, and sub-
jected to considerable pressure to make it sufficiently thin.
Price's glycerine, having a specific gravity of 1,21-0, and
a strong syrup, are the best adapted for preserving all soft
tissues. In practice, the specimen is first immersed in a
solution of weak glycerine or syrup, and the density ol
the fluid is gradually increased. In this way, and in the
course of • two or three days, the softest and most delicate
tissues swell out, and become more transparent; but no
chemical change is produced in the specimens. The one
thing to be observed is, that the strength of these fluids
should be increased very gradually until the whole of the
tissues are thoroughly penetrated and saturated by the
strongest that can be obtained. Cerebral tissues, delicate

(1) Beale, " How to Work with the Microscope."

STAINING ANIMAL TISSUES. 225

nervous textures, like the retina, may be permeated by
the strongest glycerine, and, when fully saturated with it,
dissected with a /degree of minuteness unattainable in any
other way. " The smallest animalcules, entozoa, polyps,
molluscs, insects, Crustacea, fungi, algae, and the delicate
parts of vegetable tissues, are equally well preserved by
it." All the various colouring-solutions, as carmine, aniline,
&c., should be always prepared for use with glycerine or
syrup as a basis.

The staining or colouring fluid employed by Dr. Beale
is made as follows : — Carmine, 10 grains ; strong liquid
ammonia, J drachm. ; Price's glycerine, 2 ounces ; dis-
tilled water, 2 ounces ; alcohol, |- ounce. The carmine
is >to be placed in a test-tube, and the ammonia added to
it. Upon applying the gentle heat of a spirit-lamp, it is
dissolved. Boil it up for a few seconds, and allow it to
cool before adding the glycerine and rest of the ingredients.
Lastly, pass it through a filter, or allow it to stand by and
decant off the clear solution. The solution should neither
be too alkaline, nor perfectly neutral ; if the former, the
colouring becomes too intense, and thus much of the soft
or imperfectly formed tissue is destroyed; and, if the
latter, the uniform staining of tissue and germinal matter
equally mars the result. The permeating power of the
solution may be increased by the addition of a little more
water and alcohol.

After the specimen has been properly stained, it should
be washed in a solution, consisting of strong glycerine two
parts, water one part ; and then transferred to the following
acid fluid: — Strong glycerine, one ounce; strong acetic acid,
five drops; where it must remain three or four days to
regain the volume it occupied when fresh. To mount
specimens so prepared, take a small portion and spread it
out on the glass-slide ; add a drop of fresh glycerine, and
cover with thin glass ; warm it gently, and press it down,
with a needle-point.

Examine the specimen with a quarter power, and, if a
good deal of granular matter appears to be mixed in with
it, remove the glass cover, and wash it by adding drop
after drop of the glycerine and acid solution. The slide
fcliould be inclined, and, at the same time, gently warmed

Q

226 THE MICROSCOPE.

over the lamp. When a few drops of pure glycerine have
been allowed to flow over it, the thin glass cover must be
re-applied and pressed tightly down. If the preparation
looks clear under an eighth or twelfth, the glass cover may
be cemented on, and the specimen left to dry. The success
of Dr. Beale's process, it appears, much depends upon the
care and patience with which each stage of the soaking,
washing, warming, and pressure is carried out. Each point
of structural difference is gradually brought out by sub-
jecting the specimen to a little firmer pressure, or by
soaking it in a little fresh glycerine in a watch-glass, and
then applying gentle heat. By the aid of needles, and
a little careful manipulation, tissues may be laid out per-
fectly smooth and flat.

A word about making and preparing Transparent In-
jections.— The great desideratum of a transparent injecting
fluid is, that it shall not, by the action of osmosis, dye the
tissue meant to be injected. This at once bars the use of
soluble colours, and necessitates the use of insoluble colour-
ing matter in an exceedingly fine state of subdivision.
The following composition is stated to succeed admirably,
showing vessels of ^rJWth of an inch diameter, with a
clear outline even under a £th objective, without a grain
of extravasation of the colouring matter: — Take 180 grains
best carmine j J fluid ounce of ammonia, common strength,
sp. gr. 0-92 ; 3 to 4 ounces distilled water. Put these
ingredients into a small flask, and allow them to digest
without heat for 24 or 36 hours, or until the carmine
is dissolved. Then take a "Winchester quart-bottle, and
mark upon it the line to which 16 ounces of water
extend. The coloured solution must then be filtered
into the bottle, and pure water must be added until
the whole is equal to 16 ounces. Next dissolve 600
grains of potash-alum in about 10 fluid ounces of water,
and add to this, under constant boiling, a solution of
carbonate of soda, until a slight permanent precipitate
is produced. Filter and add water up to 16 fluid ounces.
Boil, and add this solution, while boiling, to the cold
amnioniacal solution of carmine in the Winchester quart,
and shake vigorously for a few minutes. A drop now
placed upon white filter-paper should show no coloured

MOUNTING POLYZOA. 227

ring; if it do, the whole must be rejected. Supposing
the precipitation to be complete, or nearly so, shake
vigorously for half an hour, and allow to stand till quite
cold ; the shaking must then "be renewed, and the bottle
filled up with cold water. After allowing the precipitate
to settle for a day, draw off the clear supernatant fluid
with a syphon. Eepeat the washing until the clear fluid
gives no precipitate with chloride of barium. So much
water must be left with the fluid that at last it may
measure 40 fluid ounces. For the injection-fluid, take 24
ounces of the above coloured fluid, and 3 ounces of good
gelatine; allow these to remain together all night, then
dissolve by the aid of a water-bath, and strain through
fine muslin. On injecting, the ordinary precautions for a
gelatine injection are alone necessary.

Mounting Polyzoa. — Mr. Morris, of Bath, has succeeded
in obtaining beautiful specimens of polyzoa and hydroid
zoophytes, with expanded tentacles, by adding spirit of
wine, drop by drop, to the salt-water cell in which they
have been confined. The polypidoms should be thus
treated as soon as possible after capture.

A plan of mounting objects in a mixture of balsam and
chloroform is described by Mr. Wm. Henry Heys in the
Microscopical Journal thus : — Take a quantity of the oldest
balsam procurable, and place it in an open glass cup, and
mix with it as much chloroform as will make the whole
quite fluid, so that a very small quantity will drop from
the lip of the containing vessel. Then put this prepared
balsam into long thin half-ounce vials, and cork and set
them aside for at least a month. The advantage of having
it ready-made is, that there is no waste, and none of the
usual and troublesome preparation required for putting up
objects in Canada balsam; and if it has stood for some
time, it loses- the yellow tinge which is observable in most
samples when first mixed, and, moreover, air-bubbles escape
more readily.

Mr. Goadby's fluids are cheap and most effectual for
preserving and mounting animal structures in. The fol-
lowing are his formulae : —

Take for ]N"o. 1 solution, biy salt, 4 oz. ; alum, 2 oz. ;
corrosive sublimate, 2 grains; boiling water, 1 quart: mix.

228 THE MICROSCOPE.

For No. 2 solution, bay salt, 4 oz. ; alum, 2 oz. ; corrosive,
sublimate, 4 grs. ; boiling-water, 2 quarts : mix.

The No. 1 is too strong for most -purposes, and should
only be employed where great astringency is needed to
give form and support to very delicate structures. No. 2
is best adapted for permanent preparation ; but neither
should be used in the preservation of animals containing
carbonate of lime (all the mollusca), as the alum becomes
decomposed, sulphate of lime is precipitated, and the pre-
paration spoiled. For such use the following : —

Bay salt, 8 oz. ; corrosive sublimate, 2 grs.; water,
1 quart : mix.

The corrosive sublimate is used to prevent the growth
of vegetation in the fluid ; but as this salt possesses the
property of coagulating albumen, these solutions cannot be
used in the preservation of ova, or when it is desired to
maintain the transparency of certain tissues, such as the
cellular tissue, the white corpuscles of the blood, &c.

Mr. Goadby's method of making marine-glue for cement-
ing cells is as follows : dissolve separately equal parts of
shell-lac and India-rubber in coal or mineral naphtha, and
afterwards mix the solutions carefully by the application
of heat. It may be rendered thinner by the addition of
more naphtha, and is always readily dissolved by naphtha,
ether, or solution of potash, when it becomes hard or dry
in our stock-pots.

Preparation and Preservation of Algce, <kc. — Mr. Ralfs
gives excellent directions for making preparations of algse
for microscopic investigations : — " The fluid found to
answer best is ma<C>3 in the following way : to sixteen
parts of distilled water add one part of rectified spirits
of wine, and a few drops of creosote, sufficient to saturate
it ; stir in a small quantity of prepared chalk, and then
filter ; with this fluid mix an equal measure, of camphor-
water (water saturated with camphor); and before using,
strain off through a piece of fine linen.

" This fluid I do not find to alter the appearance of
the endochrome of algse more than distilled water alone
does after some time ; there is certainly less probability of
confervoid filaments making their appearance in the pre-
parations ; and there would seem to be nothing to prevent

PRESERVATION OF ALGJB. 229

such a growth from taking place, when the object is
mounted in water only, provided a germ of one of these
minute plants happen to be present, as well as a small
quantity of free carbonic acid.

" My method of making cells in which to mount pre-
parations of algJB is as follows : some objects require very
shallow, and others somewhat deeper cells. The former
may be made with a mixture of japanners' gold-size and
litharge, to which (if a dark colour is preferred) a small
quantity of lamp-black can be added. These materials
should be rubbed up together with a painter's muller, and
the mixture laid on the slips of glass with a camel-hair
pencil as expeditiously as possible, since it quickly becomes
hard ; so that it is expedient to make but a small quantity
at a time. For the deeper cells marine-glue answers ex-
tremely well, provided it is not too soft. It must be
melted and dropped upon the slip of glass : then flattened,
whilst warm, with a piece of wet glass, and what is super-
fluous cut away with a knife, so as to leave only the walls
of the cell ; these, if they have become loosened, may be
made firm again by warming the under surface of the slip
of glass. The surface of the cells must be made quite flat ;
which can be easily done by rubbing them upon a wet
piece of smooth marble, covered with the finest emery-
powder.

" When about to mount a preparation, a very thin
layer of gold-size must be put upon the wall of the cell,
as well as on the edge of the piece of thin glass which is
to cover it ; before this is quite dry, the fluid with the
cbject is to be put into the cell, and the cover of thin glass
slowly laid upon it, beginning at one end ; gentle pressure
must then be used to squeeze out the superfluous fluid ;
and, after carefully wiping the slide dry, a thin coat of
gold-size should be applied round the edge of the cell, and
a second coat so soon as the first is dry; a thin coat or
two of black sealing-wax varnish may then be put on with
advantage, in order to prevent effectually the admission
of air into the cell, or the escape of fluid out of it.

" I would remark, that the gold-size employed should
be of the consistence of treacle ; when purchased, it is
usually too fluid, and should be exposed for some time m

230 THE MICROSCOPE.

an open vessel ; a process which renders it fit for use. In
mounting the Desmidacece, great attention is necessary to
exclude air-bubbles, which cannot be avoided unless the
fluid completely fills the cells ; and also not to use too
much fluid, as in this case the smaller species will often be
washed away on the escape of the superfluous portion. As
the cells cannot be sealed whilst any moisture remains on
their edge, it should be removed by blotting-paper, in
preference to any other mode. A thin description of glass
is manufactured expressly for the purpose of covering
specimens when mounted.

" The rare species of Desmidacece are frequently scattered
amongst decayed vegetable matter, so that it is difficult to
procure good specimens for mounting. In such cases, a
small portion of the mass should be mixed with a little of
the creosote fluid, and stirred briskly with a needle.
After this has been done, the Desmidacece will sink to the
bottom, when the refuse should be carefully removed.
Successive portions having been thus treated, specimens
will at length be procured sufficiently free from foreign
matter. Even in ordinary circumstances, if a small extra
quantity of fluid be placed in the cell, and the slide gently
inclined, most of the dirt may be removed by a needle
before the cell is closed ; which process will materially
increase the beauty of the preparation.

" If the cells are insufficiently baked, the japan occa-
sionally peels off the glass after the specimen has been
mounted for some time. To obviate this inconvenience,
Mr. Jenner previously heats the cell, with much caution,
over a rushlight, until the japan becomes of a dark colour,
and vapour ceases to arise from it. When gold-size is used
for closing the cell, the intrusion of some of it frequently
destroys valuable specimens, whatever care may be taken.
Mr. Jenner has therefore relinquished it, and now employs
a varnish made of coarsely comminuted purified shell-lac
or translucent sealing-wax, to which is added rectified
spirits of wine, in sufficient quantity to cover it. This
varnish will be ready for use in about twelve hours : when
it is too thick, a little more spirit should be added. Mr.
Jenner applies three coats of this varnish, and about a week
afterwards a fourth, composed of japan varnish or gold-

INJECTING ANIMAL BODIES. 231

size.1 To preserve the brush in a fit state, it should
always be cleaned with spirits of wine whenever it has
been used."

Mr. Topping's fluid for mounting consists of one ounce
of rectified spirits to five ounces of distilled water ; this he
thinks superior to any other combination. To preserve
delicate colours, however, he prefers to use a solution of
acetate of alumina, one ounce of the acetate to four ounces
of distilled water : of other solutions he says, that they
tend to destroy the colouring matter of delicate objects,
and ultimately spoil them by rendering them opaque.

Injecting Animal Bodies. — For minute injections, the
most essential instrument is a proper syringe. This is
usually made of brass, of such a size
that the top of the thumb may press on
the button at the top of the piston-rod
when drawn out, while the body is sup-
ported between the two fingers. Fig.
141 represents the syringe : a is a cylin-
drical brass body, with a screw at the
top for the purpose of firmly screwing
down the cover 6, after the piston c is
introduced into it ; this is rendered
air-tight with leather; the bottom of
the syringe d also unscrews for the con-
venience of cleaning ; e is a stop-cock,
on the end of which another stop-cock
/ fits accurately ; and on the end of
this either of the small pipes g, which
are of different sizes, may be fixed. The
transverse wires across the pipes are in-
tended to secure them more tightly to the
vessels, into which they may be inserted with thread, so
that they may not slip out. In addition to the syringe,
a large tin vessel, to contain hot water, with two or three
smaller ones fixed in it, for the injections, will be found
useful.

To prepare the material for injecting : — Take of the
finest and most transparent glue one pound, break it into
small pieces, put it into an earthen pot, and pour on it

(1) " Coachmaker's Black" is an excellent varnish.

Fig. 141.

232 THE MICROSOOPIS,

three pints of cold water ; let it stand twenty-four hours,
stirring it now and then with a stick; then set it over
a slow fire for half an hour, or until all the pieces are per-
fectly dissolved ; skim off the froth from the surface, and
strain through a flannel for use. Isinglass and cuttings of
parchment make an excellent size, and are preferable for
very particular injections. If gelatine be employed it must
be soaked for some hours in cold water before it is warmed.
About an ounce of gelatine to a pint of water will be suf-
ficiently strong, but in very hot weather it is necessary to
add a little more gelatine. It must be soaked in part of
the cold water until it swells up and becomes soft, when the
rest of the water, made hot, is to be added. Good gelatine
for injecting purposes may be obtained for two shillings a
pound.

The size thus prepared may be coloured with any of the
following : —

For Red. To a pint of size, add 2 oz. of Chinese vermilion.
,, Yellow. ,, ,, 2J oz. of chrome-yellow.

„ White. „ „ 3|oz. of flake-white.

„ Blue. ,, ,, 6 oz. of fine blue smalts.

It is necessary to remember, that whatever colouring
matter is employed must be very finely levigated before it is
mixed with the injection. This is a matter of great im-
portance: for a small lump or mass of colour, dirt, &c.
will clog the minute vessels, so that the injection will not
pass into them, and the object will be defeated. The mix-
ture of size and colour should be frequently stirred, or the
colouring matter will sink to the bottom. Respecting the
choice of a proper subject for injecting, it may be remarked,
that the injection will usually go furthest in young subjects ;
and the more the fluids have been exhausted during life,
the greater will be the success of the injection.

To prepare the subject, the principal points to be aimed
at are, to dissolve the fluids, empty the vessels of them,
relax the solids, and prevent the injection from coagulating
too soon. For this purpose it is necessary to place the
animal, or part to be injected, in warm water, as hot as
the operator's hand will bear. This should be kept at
nearly the same temperature for some time by occasionally
adding hot water. The length of time required is in pro-
portion to the size of the part and the amount of its

INJECTING ANIMAL BODIES.

233

rigidity. Ruysch (from whom the art of injecting has
been called the Ruyschian art.) recommends a previous
maceration for a day or two in cold water.

The size must always be kept hot with the aid of warm
water ; for if a naked fire be used, there is danger of
burning it. The size may be placed in a vessel which can
be heated by standing it in a common tin saucepan of hot
water. A convenient form of apparatus for melting the
size, and afterwards keeping it at a proper temperature, is

Fig. 142.— Melting Vessel.

shown in fig. 142. It consists merely of a water-bath, in
which the cans containing the injecting fluid can be kept
hot, and their contents protected from dust by means of
their covers. A small apparatus of this kind could be
made by any tin-worker, and fitted over a gas jet to stand
on the table.

The operator should be provided with several pairs of
strong forceps, for seizing the vessel or stopping the escape

Fig. 143.

of injection. A small needle, fig. 143, will be found useful
for passing the thread round the vessel into which the

234 THE MICROSCOPE.

injecting pipe is to be inserted. Where the vessels ara
large, a needle commonly known as an aneurism needle
answers the purpose very well. The thickness of thread
must vary according to the size of the vessel. The silk
used by surgeons will be found the best adapted for th«
purpose, and not too thin, or it may cut through the
vessel.

When the size and the subject have both been properly
prepared, have the injection as hot as the fingers can well
bear. One of the pipes g, fig. 141, must then be placed in
the largest artery of the part, and made secure by tying.
Put the stop-cock / into the open end of the pipe e, and
it is then ready to receive the injection from successive
applications to the syringe a, leaving sufficient space only
for the piston c. The injection should be thrown in by a
very steady and gentle pressure on the end of the piston-
rod. The resistance of the vessels, when nearly full, is often
considerable; but it must not be overcome by violent
pressure with the syringe. When as much injection is
passed as may be thought advisable, the preparation may
be left (with the stop-cock closed in the pipe) for twenty-
four hours, when more material may be thrown in.

As the method of injecting the minute capillaries with
coloured size is often attended with doubtful success,
various other plans have been proposed. Euysch's method,
according to Rigerius, was to employ melted tallow coloured
with vermilion, to which in the summer a little white wax
was added. Monro recommended coloured oil of turpen-
tine for the small vessels ; after the use of which, he threw
in the common coarse injection. This is made of tallow
and red lead, well mixed and heated before it is used.
The cold paint injection succeeds well if thrown carefully
into the minute arteries; but its tendency to become
brown by age is an objection to its use.

Professor Breschet frequently employed with success milk,
isinglass, the alcoholic solution of gum-lac, spirit varnish,
and spirit of turpentine ; but he highly recommends the
colouring matter extracted from Campeachy, Fernambone,
or Sandal woods. He says : " The colouring matter of
Campeachy wood easily dissolves in water and in alcohol ;
it is so penetrating that it becomes rapidly spread through

INJECTING ANIMAL BODIES. 235

the vascular net-works. The sole inconvenience of this
kind of injection is, that it cannot be made to distend any
except most delicate vessels, and that its ready penetra-
tion does not admit of distinguishing between arteries,
veins, and lymphatics." He also recommends a solution
of caoutchouc.

Another process, which may be termed the chemical
process, was published in the Comptes Rendus, 1841, as
the invention of M. Doyers. According to this, an aqueous
solution of bichromate of potass, 1,048 grains to two pints
of water, is thrown into the vessels; and after a short
time, in the same manner and in the same vessels, an
aqueous solution of acetate of lead, 2,000 grains to a pint
of water, is injected. This is an excellent method, as the
material is quite fluid, and the precipitation of the chromate
of lead which takes place in the vessels themselves gives a
fine sulphur-yellow colour. Mr. Topping prepares many
fine injections in this way.

Mr. Goadby has improved upon the process last named
by uniting to the chemical solutions a portion of gelatine,
as follows :

Saturated solution of bichromate of potash, 8 fluid
ounces; water, 8 ounces; gelatine, 2 ounces.

Saturated solution of acetate of lead, 8 fluid ounces;
water, 8 ounces; gelatine, 2 ounces.

The majority of preparations thus injected require to be
dried and mounted in Canada balsam. Each preparation,
when placed on a slip of glass, will necessarily possess
more or less of the coloured infiltrated gelatine, (by this is
meant the gelatine coloured by the blood, which, together
with the acetate of potash resulting from the chemical
decomposition, may have transuded through the coats of
the vessel,) which, when dry, forms, together with the
different shades of the chromate of lead, beautiful objects,
possessing depth and richness of colour. The gelatine also
separates and defines the different layers of vessels: the
arteries are always readily distinguishable by the purity
and brightness of the chromate of lead within them, while
the veins are detected by the altered colour imparted by
the blood.

Those preparations which require to be kept wet can be

236 TUB MICROSCOPE.

preserved perfectly in Mr. Goadby's No. 2 fluid, specific
gravity 1*100; the No. 1 fluid destroys them.

" I would recommend that the slips of glass employed
for the dry preparation be instantly inscribed with the
name of the preparation, written with a diamond ; for,
when dry, it is difficult to recognise one preparation from
the other, until the operator's eye be educated to the
effects of this chemico-gelatinous injection. Where so
much wet abounds, gummed paper is apt to come off.
When dry, it is sufficient, for the purpose of brief exami-
nation by the microscope, to wet the surface of a prepara-
tion with clean oil of turpentine ; immediately after
examination, it should be put away carefully in a box, to
keep it from the dust, until it can be mounted in Canada
balsam.

" The bichromate of potash is greatly superior in colour
to the chromate, which yields too pale a yellow; and sub-
sequent experience has proved that the acetate of potash
frequently effects its liberation by destruction of the
capillaries, and this even long after the preparations have
been mounted in Canada balsam; perhaps this may be
owing to some chemical action of the acetate of potash
upon them. I would suggest the substitution of the
nitrate for the acetate of lead, as we should then have, in
the liberated nitrate of potash, a valuable auxiliary in the
process of preservation. Although highly desirable, as
the demonstrator of the capillaries of normal tissues, I do
not think this kind of injection fitted for morbid prepara-
tions ; the infiltrated gelatine producing appearances of a
.puzzling kind, and calculated to mislead the pathologist.
In preparing portions of dried well-injected skin for
examination by the microscope, I have tried the effect of
dilute nitric acid as a corroder with very good results.
But, probabty, liquor potassa would have answered this
purpose better.

" When size-injection is to be employed, coloured either
with vermilion or the chromate of lead, the animal should
be previously prepared by bleeding, to empty the vessels ;
for if they be filled with coagulated blood, it is quite im-
possible to transmit even size, to say nothing of the colour-
ing matter. Hence the difficulty of procuring good

TRANSPARENT INJECTIONS. 23T

injections of the human subject. But with the chemico-
gelatinous injections no such preparation is necessary; and
success should always be certain, for the potash liquefies
the blood, while constant and long-continued pressure by
the syringe drives it through the parietes of the vessel
into the cellular tissue."

Transparent Injections. — " Much more strongly," writes
Dr. Beale, "can I recommend to you the use of transparent
fluids for making injections. It is true, that these are not
likely to be so much admired by general observers as
opaque injections. Indeed, it is not easy to find any
object which will rival in beauty many tissues that have
been freely injected with vermilion or chromate of lead ;
although it must be confessed that from such preparations
we learn but little save the general arrangement of the
capillary vessels of the part, their capacity, and the mag-
nitude of the meshes of the network. Of the relations
which these vessels bear to the elementary structures
which give to the texture under examination its peculiar
properties, such preparations tell us nothing. Opaque
injections are for the most part only adapted for examina-
tion with low powers, while the tissues to which the vessels
are distributed can only be seen with the help of very high
magnifying powers. Transparent injections, on the other
hand, though they fail to excite the wonder of the un-
initiated, show us not only the general arrangement of
the capillary network, but the precise relation which
each little tube bears to the tissue with which it is in
contact.

" In order to make injected preparations for examination
by transmitted light, several different substances may be
used as injecting fluids.

" Injection with Plain Size. — A tissue which has been in-
jected with plain size, when cold is of a good consistence
for obtaining thin sections, and many important points
may be learned from a specimen prepared in this manner
which would not be detected by other modes of prepara-
tion. A mixture of equal parts of gelatine and glycerino
is, however, much to be preferred for this purpose, and
the specimen thus prepared is sure to keep well.

"Colour ing Matters for Transparent Injections. — The chief

238 THE MICROSCOPE.

colouring matters used for making transparent injections
are carmine and Prussian Hue. The former is prepared
by adding a little solution of ammonia (liquor ammonife)
to the carmine, and diluting the mixture until the proper
colour is obtained, or it may be diluted with size.

" The Prussian Blue consists of an insoluble precipitate,
so minutely divided, that it appears like a solution to the
eye. The particles of freshly prepared Prussian blue are
very much smaller than those of any of the colouring
matters employed for making opaque injections.

"Advantages of Employing Prussian Blue. — I have lately
been employing Prussian blue very much, and according
to my experience it possesses advantages over every other
colouring matter. It is inexpensive, — may be injected
cold, — the preparation does not require to be warmed, —
no size is required — it penetrates the capillaries without
the necessity of applying much force, — it does not run out
when a section is made for examination, — neither do any
particles which may escape from the larger vessels divided
in making the section, adhere to it and thus render the
section obscure, — a structure may be well injected with it
in the course of a few minutes. Specimens prepared in
this manner may be preserved in any of the ordinary pre-
servative solutions, or may be dried and mounted in Canada
balsam, (but I give the preference to glycerine, or glycerine
jelly,) and they may be examined with the highest magni-
fying powers. After having tried very many methods of
making this preparation I have found the following one to
succeed best.

" Composition of the Prussian Blue Fluid for Making
Transparent Injections : —

Glycerine 1 oz.

Wood, naphtha, or pyroacetic spirit . , . l£ drachms.

Spirits of wine 1 oz.

Ferrocyanide of potassium 12 grs.

Tincture of sesquichloride of iron ... 1 drachm.
Water 4 ozs.

" The ferrocyanide of potassium is to be dissolved in one
ounce of the water, and the tincture of sesquichloride of
iron added to another ounce. These solutions should be
mixed together very gradually, and well shaken in a bottle.

INJECTING TISSUES. 2S9

i

The iron being added to the solution of the ferrocyanide of
potassium. When thoroughly mixed, these solutions should
produce a dark blue mixture, in which no precipitate or
flocculi are observable. Next, the naphtha is to be mixed
with the spirit, and the glycerine and the remaining two
ounces of the water added. This colourless fluid is, lastly,
to be slowly mixed with the Prussian blue, the whole being
well shaken in a large bottle during the admixture. The
tincture of sesquichloride of iron is recommended because
it can always be obtained of uniform strength. It is
generally called the muriated tincture of iron, and may
always be purchased of druggists.

" Permit me, then, most earnestly to recommend all who
are fond of injecting, to employ transparent injections, and
to endeavour, by trying various transparent colouring
matters, to discover several which may be employed for
the purpose ; for I feel sure that by the use of carefully
prepared transparent injections, many new points in the
anatomy of tissues will be made out.

" Of Injecting Different Systems of Vessels with Different
Colours. — It is often desirable to inject different systems
of vessels distributed to a part with different colours, in
order to ascertain the arrangement of each set of vessels
and their relation to each other. A portion of the gall-
bladder in which the veins have been injected with white
lead, and the arteries with vermilion forms a beautiful
preparation. Each artery, even to its smallest branches,
is seen to be accompanied by two small veins, one lying
on either side of it.

" In this injection of the liver, four sets of tubes have
been injected as follows : — The artery with vermilion, the
portal vein with white lead, the duct with Prussian blue,
and the hepatic vein with lake. There are many opaque
colouring matters which may be employed for double
injections, but I am acquainted with very few transparent
ones, the employment of which affords very satisfactory
results.

" Mercurial Injections are not much used for micro-
scopical purposes, although mercury was much employed
formerly for injecting lymphatic vessels and the ducts of
glandular organs. The pressure of the column of mercury

240 THE MICROSCOPE.

supersedes the necessity of any other kind of force for
driving it into the vessels. The mercurial injecting
apparatus consists of a glass tube, about half an inch in
diameter and twelve inches in length, to one end of which
has been fitted a steel screw to which a steel injecting pipe
may be attached. The pipes and stopcocks must be made
of steel, for otherwise they would be destroyed by the
action of the mercury.

" Injecting the Lower Animals. — The vessels of fishes are
exceedingly tender, and require great caution in filling
them. It is often difficult or quite impossible to tie the
pipe in the vessel of a fish, and it will generally be found
a much easier process to cut off the tail of the fish, and
put the pipe into the divided vessel which lies imme-
diately beneath the spinal column. In this simple manner
beautiful injections of fish may be made.

"Mollusca. — (Slug, snail, oyster, &c.) The tenuity of the
vessels of the mollusca often renders it impossible to tie
the pipe in the usual manner. The capillaries are, how-
ever, usually very large, so that the injection runs very
readily. In different parts of the bodies of these animals
are numerous lacunae or spaces, which communicate
directly with the vessels. Now, if an opening be made
through the integument of the muscular foot of the
animal, a pipe may be inserted, and thus the vessels may
be injected from these lacunae with comparative facility.

"Insects. — Injections of insects may be made by forcing
the injection into the general abdominal cavity, when it
passes into the dorsal vessel and is afterwards distributed
to the system. The superfluous injection is then washed
away, and such parts of the body as may be required,
removed for examination.

" Of the Practical Operation of Injecting. — I propose now
to inject a frog and the eye of an ox, in order that you
may see the several steps of the process. We must bear
in mind that a successful injection cannot be made until
the muscular rigidity which comes on shortly after death,
and which affects the muscular fibres of the arteries as
well as those of the muscles themselves, has passed off.
In some few instances in which the fluid does not neces-
sarily pass through arterial trunks before it reaches the

INJECTING TISSUES. 241

capillaries (as in the liver), the injection may be effected
satisfactorily immediately after the death of the animal.

" The steps of the process are very similar in making the
opaque injections, except that when size is employed, the
specimen must be placed in warm water until warm
through, otherwise the size will solidify in the smaller
vessels, and the further flow of the injecting fluid will be
prevented. Soaking for many hours is sometimes neces-
sary for warming a large preparation thoroughly, and it is
desirable to change the water frequently. The size must
also be kept warm, strained immediately before use, and
well stirred up each time the syringe is filled.

" In the first place, the following instruments must be
conveniently arranged : —

" The syringe thoroughly clean and in working order,
with pipes, stopcock, and corks.

" One or two scalpels.

" Two or three pair of sharp scissors.

"Dissecting forceps.

" Bull's-nose forceps, for stopping up any vessel through
which the injection may escape accidentally.

" Curved needle, threaded with silk or thread, the thick-
ness of the latter depending upon the size of the vessel to
be tied.

" Wash-bottle. Injecting fluid in a small vessel.

" I will commence with the frog. An incision is made
through the skin, and the sternum divided in the middle
line with a pair of strong scissors ; the two sides may
easily be separated, and the heart is exposed. Next the
sac in which the heart is contained (pericardium) is opened
with scissors and the fleshy part of the heart seized with
the forceps ; a small opening is made near its lower part,
and a considerable quantity of blood escapes from the
wound — this is washed away carefully by the wash-bottle.
Into the opening — the tip of the heart being still held
firmly by the forceps, a pipe is inserted and directed
upwards towards the base of the heart to the point where
the artery is seen to be connected with the muscular sub-
stance. Before I insert the pipe, however, I draw up
a little of the injecting fluid so as to fill it, for if this were
not done, when I began to inject, the air contained in tlie

242 THE MICROSCOPE.

pipe would necessarily be forced into the vessels, and the
injection would fail.

" The point of the pipe can with very little trouble be
made to enter the artery. The needle with the thread is
next carried round the vessel and the thread seized with
forceps, the needle unthreaded and withdrawn, or one end
of the thread may be held firmly, while the needle is with-
drawn over it in the opposite direction. The thread is
new tied over the vessel, so as to include the tip of the
pipe only, for if the pipe be tied too far up, there is greater
danger of its point passing through the delicate coats of
the vessel.

" The nozzle of the syringe, which has been well washed
in warm water, is now plunged beneath the surface of the
fluid, the piston moved up and down two or three times,
so as to force out the air completely, and the syringe
filled with fluid. It is then connected with the pipe, which
is firmly held by the finger and thumb of the left hand,
with a screwing movement, a little of the injection being
first forced into the wide part of the pipe so as to prevent
the possibility of any air being included.

" The pipe and syringe being still held with the left hand,
the piston is slowly and gently forced down with a slightly
screwing movement with the right, care being taken not
to distend the vessel so as to endanger rupture of its
coats. The handle of the syringe is to be kept uppermost,
and the syringe should never be completely emptied, in
case of a little air remaining, which would thus be
forced into the vessels. The injection is now observed
running into the smaller vessels in different parts of the
organism.

" I will now proceed to inject the ox-eye in the same
manner. The pipe is inserted into this branch of artery
close to the nerve. Two minutes will probably be suffi-
cient to ensure a complete injection. In making an
injection of the eye, if the globe becomes very much
distended by the entrance of the injecting fluid, an opening
may be made in the cornea to allow the escape of the
aqueous fluid which will leave room for the entrance of
the injection, and permit the complete distension of the
vessels.

INJECTING TISSUES. 243

" We will now examine these injections. A portion of
the intestine of the frog may be removed with scissors,
opened, and the mucous surface washed with the aid of
the wash-bottle. It may be allowed to soak in glycerine
for a short time, and then examined.

" This portion of the delicate choroidal membrane which
has been carefully removed in the same manner shows the
vessels perfectly injected, and in this preparation of the
ciliary processes you will not fail to observe that all the
capillary vessels are fully distended with fluid, although
the injection was made so quickly.

" Of Injecting the Ducts of Glands. — The modes of inject-
ing which we have just considered, although applicable to
the injection of vessels, are not adapted for injecting the
ducts and glandular structure of glands ; for as these
ducts usually contain a certain quantity of the secretion,
and are always lined with epithelium, it follows that when
we attempt to force fluid into the duct, the epithelium
and secretion must be driven towards the secreting struc-
ture of the gland, which is thus effectually plugged up
with a colourless material, and there is no possibility of
making out the arrangement of the parts. In such a case
it is obviously useless to introduce an injecting fluid, for
the greatest force which could be employed would be insuf-
ficient to drive the contents through the basement mem-
brane, and the only possible result of the attempt would
be rupture of the thin walls of the secreting structure and
extravasation of the contents. As I have before mentioned,
partial success has been obtained by employing mercury,
but the preparations thus made are not adapted for micro-
scopical observation.

" After death the minute ducts of the liver always contain
a little bile. No force which can be employed is sufficient
to force this bile through the basement membrane, for it
will not permeate it in this direction. When any attempt
is made to inject the ducts, the epithelium and mucus, in
their interior, and the bile, form an insurmountable barrier
to the onward course of the injection. Hence it was ob-
viously necessary to remove the bile from the ducts before
one could hope to make a successful injection. It occurred
to me, that any accumulation of fluid in the smallest

R2

244 THE MICROSCOPE.

branches of the portal vein or in the capillaries, must ne-
cessarily compress the ducts and the secreting structure of
the liver which fill up the intervals between them. The
result of such a pressure would be to drive the bile towards
the large ducts and to promote its escape. Tepid water
was, therefore, injected into the portal vein. The liver
became greatly distended, and bile with much ductal
epithelium flowed by drops from the divided extremity of
the duct. The bile soon became thinner, owing to its
dilution with water, which permeated the intervening mem-
brane, and entered the ducts. These long, narrow, highly-
tortuous channels were thus effectually washed out from
the point where they commenced as tubes not more than
1 -300th of an inch in diameter, to their termination in the
common duct, and much of the thick layer of epithelium
lining their interior was washed out at the same time.
The water was removed by placing the liver in cloths with
sponges under pressure for twenty-four hours or longer.
All the vessels and the duct were then perfectly empty
and in a very favourable state for receiving injection. The
duct was first injected with a coloured material. Freshly
precipitated chromate of lead, white lead, vermilion, or
other colouring matter may be used, but for many reasons
to which I have alluded, the Prussian blue injection is the
one best adapted for this purpose. It is the only material
which furnishes good results when the injected prepara-
tions are required to be submitted to high magnifying
powers. Preparations injected in this manner should be
examined as transparent objects." 1

Of Preparing Portions of Injected Preparations for Mi-
croscopical Examination. — When thin tissues, such as the
mucous membrane of the intestines or other parts, have
been injected, it is necessary to lay them perfectly flat,
and wash the mucus and epithelium from the free sur-
face, either by forcing a current of water from the wash-
bottle, or by placing them in water and brushing the
surface gently with a camel's hair brush. Pieces of a
convenient size may then be removed and mounted in
a solution of naphtha and creosote, in dilute alcohol, in

(1) Dr. L. Beale, "On the Anatomy of the Liver of Man and Vertebrate
Ammals."

CHEMICAL RE- AGENTS. 245

glycerine, or in gelatine and glycerine. The most im-
portant points in any such injections are shown if the
preparation be dried and mounted in Canada balsam. The
specimen must, in the first place, be well washed and
floated upon a glass slide \vith a considerable quantity of
water, which must be allowed to flow off the slide very
gradually. The specimen may then be allowed to dry
under a glass shade, in order that it may be protected
from dust. The drying should be effected at the ordinary
temperature of the air, but it is much expedited if a
shallow basin filled with sulphuric acid be placed with it
under a bell-jar."

Chemical Re-agents. — The following chemical re-agents
and preservative fluids are recommended for microscopic
uses i1

1. Alcohol, principally for the removal of air from
sections of wood and other preparations ; also as a solvent
for certain colouring matters.

2. JEther, chiefly as a solvent for resins, fatty and other
essential oils, &c. ; also useful for the removal of air.

3. Solution of Caustic Potass, as a solvent for fatty
matters; also of use occasionally in consequence of its
action upon the rest of the cell-contents and thickening
layers. This solution acts best upon being heated.

4. Solution of Iodine (iodine one grain, iodide of potas-
sium three grains, distilled, water one ounce) for the
coloration of the cell-membrane and of the cell-contents.

5. Concentrated Sulphuric Acid, employed chiefly in the
examination of pollen and spores.

6. Diluted Sulphuric Acid (three parts acid, one part
water), for the coloration of cells previously immersed in
the iodine solution. The preparation is first moistened
with the iodine solution, which is afterwards removed with
a hair pencil, and a drop of sulphuric acid added by means
of a glass rod ; the preparation is then immediately covered
with a piece of glass. The action of the sulphuric acid
and iodine, as well as that of the iodised chloride of zinc
solution, is not always uniform throughout the whole

(1) A set of 12 test-bottles, packed in a small box, is supplied by Mr.
Matthews of Portugal Street, Lincoln's Inn Fields, the price of which is only a
few shillings.

246 THE MICROSCOPE.

surface of the preparation. The colour is more intense
•where the mixture is more concentrated; it frequently
happens that many spots remain uncoloured. The colour
changes after some time, the blue being frequently changed
into red after twenty-four hours.

7. A Solution of Chloride of Zinc, Iodine, and Iodide of
Potassium. A drop of this compound solution, added to
a preparation placed in a little water, produces the same
colour as iodine and sulphuric acid. This solution, which
was first proposed and employed by Professor Schultz, is
more convenient in its application than iodine and sulphuric
acid, and performs nearly the same services, while it does
not, like the sulphuric acid, destroy the tissues to which it
is applied. It is prepared by dissolving zinc in hydro-
chloric acid ; the solution is then saturated with iodide of
potassium : more iodine is to be added if necessary, and
the solution diluted with water.

8. Nitric Acid, or what is better, chlorate of potass and
nitric acid, as an agent to effect the isolation of cells. The
mode of employing this agent, also discovered by Professor
Schultz, is as follows : —

The object, a thin section of wood, for instance, is intro-
duced, with an equal bulk of chloride, or chlorate of potass,
into a long and moderately wide tube, and as much nitric
acid as will at least cover the whole.

The tube is then warmed over a spirit-lamp ; a copious
evolution of gas takes place, upon which the tube is re-
moved from the flame, and the action of the oxidising agent
allowed to continue for two or three minutes. The con-
tents of the tube are then poured into a watch glass with
water, from which the slightly cohering particles are col-
lected and placed in a tube, and again boiled in alcohol as
long as any colour is communicated.

They are again boiled in a little water. The cells may
now be isolated under the simple microscope by means of
needles. The boiling with nitric acid and chlorate of
potass should never be carried on in the same room with
the microscope, the glasses of which may suffer injury
from the vapours. The same remark applies to all chemical
vapours.

Thin sections of vegetable tissue are warmed for half a

CHEMICAL RE-AGENTS. 247

minute, or a minute, in a watch-glass : boiling is here un-
necessary. The section is taken out, and treated with
water in another watch-glass.

9. Oil of Lemons, or any other essential oil, a drop of
which will be found of value in the investigation of pollen
and spores.

Lastly may be enumerated a pretty strong solution of
Carbonate of Soda and also of Acetic Acid; which latter,
however, is more especially useful in the investigation of
animal tissues.

To the above may be added a test for protein compounds.
This test is composed of sugar and sulphuric acid, and is
thus employed : — A thin section or portion of the tissue to
be examined is placed in a drop of simple syrup, this is
tfien removed by means of a hair pencil, and a drop of the
diluted sulphuric acid added ; the red colour usually does
not appear until after the lapse of about ten minutes.

In making thin sections of tissues, it is recommended
that, in those objects the consistence of which differs in
different parts, the section should be carried from the
harder into the softer portion; also, in making a thin
section of a very minute yielding substance, to enclose it
between two pieces of cork, and to slice the whole together.
It is also useful sometimes to saturate the object with
mucilage, which is to be allowed to dry slowly; in this
way very delicate tissues may be sliced, or otherwise ,
divided without injury, and with great facility.

Some of the above re-agents must be used with caution, as
it is not unusual for them to assume crystalline forms while
under the microscope. Without a knowledge of this fact, and
a perfect recognition of crystalline forms, errors in micro-
chemical research must occur. For example, if a drop of
liquor potassee be allowed to evaporate on a slip of glass,
crystals appear, chiefly of six-sided tables, precisely like
cystine ; when in quantity, they are often crowded together
as the cystine plates are, and sometimes exhibit a similar
nucleus-like body in their centres. This peculiarity of
crystallization does not arise from the presence of impurities ;
perfectly pure potash often exhibits the same phenomenon.

The form of the crystals of acetate of potash varies
according to the strength of the acid out of which it

248 THE MICROSCOPE.

crystallizes, and if formed out of strong acid, very much
resembles that of the crystals of uric acid ; when mixed
up with other forms, long dagger-like or lancet-shaped
crystals are seen, which might well deceive.

We may also notice in this place what Majendie pointed
out, that in certain albuminous mixtures, iodine loses the
property of colouring starch blue. This difficulty must be
got rid of before iodine can be said to be an infallible test
in micro-chemistry.

Collecting Objects. — Mr. G. Shadbolt contributes the fol-
lowing useful hints for collecting objects for microscopical
examination : —

"Rivers, brooks, springs, fountains, ponds, marshes,
bogs, and rocks by the sea-side, are all localities that may
-be expected to be productive; some being more prolific
ihan others, and the species obtained differing, of course,
in general, to a certain extent, according to the habitat.
On considering the nature of some of the places indicated,
it will be apparent that, in order to spend a day in col-
lecting with any comfort, it will be necessary to make
some provision for keeping the feet dry, for which a pair
of India-rubber goloshes will answer, or better still, a pair
of waterproof fishing-boots ; but without one or other the
work is by no means pleasant.

" A dozen or two of small bottles made of glass-tubing,
f about half an inch in diameter, and without necks, and
from one to two inches in length, are the most convenient
depositories for the specimens, if intended ultimately foi
mounting; and it is advisable also to take two or three
wide-mouthed bottles of a larger size, holding from one to
two fluid-ounces, an old iron spoon, a tin box, some pieces
of line'n or calico, two or three inches square, a piece of.
string, a slip or two of glass, with the edges ground, such
as are used for mounting objects; and lastly, a good and
pretty powerful hand-magnifier. Two Coddington lenses,
mounted in one frame of about half an inch, and one-tenth
of an inch in focal power, are specially convenient.

" Swanscombe Salt-marsh will be found well worth a
visit; and it can be reached by steam-boat or railway
from London-bridge to Northfleet. On quitting the rail-
way station, make towards the almshouses on the top of

COLLECTING OBJECTS. 24.9

the hill; and arriving at the road, turn to the left, descend
the hill, and cross a sort of bridge over a somewhat insig-
nificant stream. Continue along the main-road a little
farther, to a point where it begins to ascend again, and
diverges to the left towards the railway; here quit it,
taking your course along an obscure road, nearly in a
direct line with the main one ; passing a windmill on the
right hand, and continuing until you arrive at another
still more obscure road, turning off to the right; which
road appears as if made of the mud dredged from the
bottom of the river, and partially hardened. This is
Swanscombe Salt-marsh; and the road just described
leads towards Broad Ness Beacon. On either side is a
sort of ditch ; one containing salt or very brackish water,
the other filled with a sort of black mud, about the con-
sistence of cream, the surface being in parts of a slaty
grey, with little patches here and there of a most brilliant
brown colour, glistening in the sunshine, and presenting a
striking contrast to the sombre shade. By carefully in-
sinuating the end of one of the slips of glass under this
brilliant brown substance, and raising it gently, it can be
examined with the Coddington; and it will probably be
found to consist of myriads of specimens of Pleurosigma
(navicula of Ehrenberg) angulatum, or balticum, or some
other species of this genus. The iron spoon is now useful,
as by its aid the brown stratum, with little or no mud, can
be skimmed off and bottled for future examination. On
the surface of the water in the other ditch may be noticed
a floating mass of a dark olive colour, which to the touch
feels not unlike a lump of the curd of milk, and consists
of Cyclotella menighiniana, and a surirella or two em-
bedded in a mass of Spirulina hutchinsia; and another
mass of floating weed, which feels harsh to the touch, pro-
ceeding from a quantity of a synedra, closely investing a
filamentous alga; and elsewhere Melosira nummuloides
(gallionella of Ehrenberg).

" In a trench by the sea-wall, as it is termed, is a mass
of brown matter of a shade somewhat different to any
hitherto observed, adhering to some of the parts of the
trench, being partially submerged, and having a some-
what tremulous motion on agitating the water. This is a

250 THE MICROSCOPE.

species of Schizonema; and it consists of a quantity of
gelatinous hollow filaments filled with an immense number
of bright-brown shuttle-shaped bodies, like very minute
naviculce.

" It is not necessary to be particular about collecting
the specimen free from mud, as the filaments are so tough
that the mud can be readily washed away by shaking the
whole violently in a bottle of water, and pouring off the
mud, without at all injuring the specimen. The Amphi-
porium alatum communicates a somewhat frothy appear-
ance to the otherwise clear water, and to get any quantity
of this requires a little management ; but by skimming
the surface with the spoon, and using one of the larger
bottles, an abundance may readily be obtained. Between
the sea-wall and the river the marsh is intersected in every
direction with a number of meandering creeks, being in
some places eight to ten feet deep, though in others quite
shallow; but it is exceedingly difficult to make one's way
amongst them, and I have never found them so prolific
any where, on the few occasions of my visiting the place,
as in the parts more away from the influence of the tide.
It will be observed, that the brilliant brown colour, of a
deep but bright cinnamon tint, is one of the best indica-
tions of the presence of diatomacece; and though this is by
no means universal, the variation is most frequently de-
pendent upon the presence of something which qualifies
the tint. The peculiarity of the colour is due to the
endochrome contained in the frustule; and this must in
general be got rid of before the beautiful and delicate
marking can be made out. But it is highly advantageous
and instructive to view them in a living state ; and this
should be done as soon as possible after reaching home
with all specimens procured from salt-water localities, as
they rapidly putrefy in confinement, and emit a most
disgusting odour, not unlike that arising from a box of
inferior congreve-matches.

" Washing in fresh water, and then immersing in creo-
sote water, preserves many of the species in a very natural-
looking manner; but they are killed by the fresh water,
and the endochrome becomes much condensed in the
Pleurosigmata and some other species. The addition of

COLLECTING OBJECTS. 251

spirits quite spoils the appearance of the frustules, as it
dissolves the endochrome.

" There is another salt-marsh a little farther down the
same railway, at Higham, which it would be well to
explore. The most favourable months for procuring dia-
tomacece, are April, May, September, and October; but
some species are found in perfection as early as February,
and many as late as November, and a few at all times of
the year. There is a piece of boggy ground near Keston,
beyond Bromley, in Kent, where the river Ravensbourne
takes its rise, where many interesting species of desmi-
dacece and other fresh-water algae may be procured. From
Bromley, walk on towards Keston, passing near Hayes
Common and Bromley Common on the right. Continue
for about another half-mile along the road, and then turu
to the right hand; pass the reservoirs, and approach an
open space where there is a bog of about a quarter of a
mile in extent ; and tending towards the right, make your
way amongst heaths, ferns, mosses, and the beautiful
Drosera rotundifolia (sun-dew), to the lower part of the
little stream rippling through a sort of narrow trench in
the Sphagnum, &c. By working your way up the stream,
you avoid the inconvenience which would otherwise be
experienced of the water being rendered turbid, in con-
sequence of having to tread in the boggy ground. In the
centre of the little stream may be observed something of a
pale pea-green colour flickering about in the current,
which, on your attempting to grasp, most likely eludes
you, and slips through the fingers, from being of a gelatin-
ous nature. It consists of a hyaline substance, with a
comparatively small quantity of a bright green endo-
chrome, disposed in little branches, and this is the Dra-
parnaldia glomerata. Another object is a mass of green
filaments, rather harsh to the touch, and very slippery.
When viewed with a lens of moderate power, each filament
is seen to be surrounded with several bands of green dots,
looking like a ribbon twisted spirally, and may be recog-
nised as a species of Zygnema. In various parts there
are other Zygnemacece, as spirogyra, mougeotia, mesocarpus,
and many more.

" Keeping up the stream, and occasionally diverging a

252 THE MICROSCOPE.

little on either side of it, amongst the miniature Days and
pools formed by the sphagnum, on looking straight down
into the water we shall probably see at the bottom a little
mass of jelly of a bright green, studded with numerous
brilliant bubbles of oxygen-gas. This is the general
appearance of most of the desmidacece, as Micrasterias,
JKuastrum, Closterium, Cosmarium, &c. The spoon is also
a handy tool in this case, though, by practice, the finger
will do nearly as well ; the chief difficulty arises when
the specimen is brought to the surface of the water, it not
being easy to get it out without losing a considerable por-
tion of it. Little pools in the bog, made by the footsteps
of cattle, are particularly good spots to find desmidiece,
many species being in a very contracted space. The most
prolific bog is at Tunbridge Wells, near a house known as
Fisher's Castle, not far from Hurst Wood. There is also a
good one at Esher, at a spot called West-End. It must
not be imagined that nothing can be obtained in this
department of botany without going some distance from
town ; but assuredly only commoner and fewer species can
be met with nearer home. At the West India Docks are
Synedra fasciculata, Gomphonema curvata, Diatoma elonga-
tnm, Diatoma vulgare, Surirella ovata, &c. ; and at this
same place a few objects, not of the botanical class, as
Spongilla fluviatilis, Cordylophora lacustris, Alcyonella,
stagnorum, <fec., are obtainable in abundance in the autumn.
In the ornamental water in St. James's Park may be found
Cocconema lanceolatum, and other species of this genus,
Gomphonema cristatum, &c. Epping Forest, about the
neighbourhood of Leytonstone, Snaresbrook, Wanstead,
and Woodford Bridge, are also capital localities for the
filamentous algse, especially the last-named, where Nitella,
translucens and Chara mdgaris abound." 1

On the north side of the Serpentine, Hyde Park, espe-
cially near the bridge, may be found : —

Cymbella maculata.
Gomphonema cristatum.
Scenedesmus quadricauda.

,, obliquus.

Ankistrodesmus falcatus.
Pediastrum Heptactys.
Cocconema lanceolatum.
Amphora ovalis.

Cocconeis placentula.

Uvella hyalina.

Gallionella nummuloides.

Euastrum elegans.

Pixidula operculata.

Cladophora glomerata and Sphjero-

plea crispa, with many other

algae.

(1) "Quarterly Journal of Microscopical Science.'

LIST OF OBJECTS.

253

Mr. Wheeler, of Tollington Road, Hollo way, N"., has
furnished us with the following list of 100 interesting
and popular objects, in book-case complete : —

Tests :

Pieurosigma angulata,
„ strigosa.

,, formosum.

Scales of Podura.

,, Lepisma.
Hair of Indian bat.
„ mouse.
,, Larva of Dermestes.

Triceratium from Thames mud.
Arachnoidiscus.

*"os. infusoria from Guano.
Fos. infusoria, Barbadoes.

,, Upper Bann, Ireland

„ Island of Mail.

„ Tuscany.

Infusoria from Thames mud.
Spicules of Gor^onia.
,, sponge.

,, ,, fresh water.

Gemmules of sponge.

Section of shell— Pinna.
,, ,, crab.

Haliotis.

, , spine of Echin u s .

,, ,, Cidaris.

Xanthidia in flint.
Moss agate.
Limestone.

Fossil tooth of shark

fish.

Fossil bone of whale.
„ reptile.

elk.

Fossil wood (Exogen).

,, (Endogen).
Sections of coal.
Simple cellular tissue.
Stellate tissue.
Fibro-cellular tissue.
Spiral vessels.
Hairs from leaf of Deutzia.
Seeds of a fern.
Sections of fir.

„ oak.

,, mahogany.

,, clematis.

Petal of geranium.

Leaf insect.

Flea.

Parasite of peacock.

Skin of caterpillar.

Wing of a butterfly.

Scales of ditto,
t'roboscis of blow-fly.
Stomach of ditto.
Foot of ditto.
Spiracles of Dytiscus.
Foot of Ophion.
Proboscis of moth.

Tran. sects, of human hairs.

„ hairs of elephant.

,, whalebone.

Feather of bird.
Trans, sects, of human bone.

„ bone of bird.

„ ,. fish.

„ ,, reptile.

Blood of bird.
„ fish.
„ reptile.
,, human.

Opaque : —
Gold dust.
Fossil shells.
Pollens.
Fern spores.
Needle antimony.
Avanturine.

Polariscope : —
Selenite.
Starch.

Hairs from leaf.
Embryo oysters.
Rhinoceros horn.
Hoof of horse.
Agate.
Sandstone.

Sulphate of Cadmium.
Salicine.
Tartaric acid.
Carbonate of lime.

Anatomical : —
Section of cartilage, showing tLe

formation of the bone-cells.
Muscle of mammalia.
„ reptile,
bird,
fish.

Injections of : —
Human lung.
„ intestine.
„ skin.
,, kidney.
,, stomach.
i, muscle.
,, section of finger.

254

THE MICROSCOPE.

Mr. Collins has introduced a very complete Mounting-
Case, which will prove useful to microscopists, especially
so to those who devote a good deal of attention to the
preparation of specimens. A place is here found for
everything : the little box contains : — Shadbolt's turn-
table, brass table, spirit-lamp, pipettes, spring clips,
wooden clips, tweezers, tin cells, balsam, marine glue,
asphalte, turps, gold size, thin glass covers, glass slips, and
five extra bottles. The price of this neat and convenient
case is 30s. Another box, more particularly adapted for
anatomical purposes, includes a neat injecting apparatus.

Fig. 143.— Cottinf Mounting Cabinet.

A modification of Dr. Beale's neutral-tint glass for
drawing is made by Mr. Collins, who supplies three glasses
of different shades, which drop into a dovetail, so that
they can be more easily cleaned and efficiently adapted
to the power used ; with his more complete instruments a
prism is also supplied.

FUNGI, ALGA;, LICHENS, ETC.

; I "

- ~ @

o<3

t&

«*1

Tufi'cn West, del.

Pl.ATK

PAKT II.

THE VEGETABLE KINGDOM — VITAL CHARACTERISTICS OF CELLS — THE PRO-
TOCOCCUS PLUVIALIS — OSCILLATOR!.^ — FtJNGI — ALG^E — DESMIBACE^E —
MOSSES — FERNS — STRUCTURE OF PLANTS— STARCH— ADULTERATION OF
ARTICLES USED FOR FOOD— PREPARATION OF VEGETABLE STRUCTURES,
ETC.

^

the introduction of the achro-
matic microscope, we have obtained
nearly the whole of the valuable
information we possess of the mi-
nute structure of plants. Indeed
in no department of nature has
microscopic investigation been more
fertile of results than in that of
the vegetable kingdom. The hum-
blest tribes of plants have had
for microscopists an attraction, —
unequalled by that of any other
department of nature, — from the
time of our countryman Eobert
Brown, down to the present day.
Although Brown had observed and
recorded certain facts in the phy-
siology of vegetable life, it was
Professor Schleiden's labours that
brought to light the great truth,
" that t/ie life-history of the individual cell is the first
important and indispensable basis whereon to found a
true physiology of the life-history of plants, as well as
that of the higher orders of creation." The first problem

256 THE MICROSCOPE.

which this observer set himself to solve, was, How is the
cell originated ? It is not here desirable to go deeply into
this most interesting inquiry; the object proposed is to
give a slight sketch of the formative processes of plant
life, chiefly in its relation to the earliest, or cell condition.

Almost every day brings forth a new discovery by
which old land-marks established with a view to the separa-
tion, arrangement, and classification of the vegetable and
animal kingdoms become unsettled; the lowest forms of
life, vegetable and animal, approach so near to each other,
that we cannot with certainty always discriminate them.,
and say where the one ends and the other begins. The
boundary assigned to the vegetable kingdom is, perhaps,
too limited, and our definition of a vegetable organism
requires to be enlarged : of this any one who will be at
the trouble to study the microscopic forms of life must
feel perfectly convinced. At the present day, the only
generally applicable rule that can be applied to distinguish
animals from vegetables is the dependence of the animal
for nutriment upon organic compounds already formed,
which it takes into the interior of its body; this at
once distinguishes it from the plant, which only possesses
the power of obtaining its alimentary matter, by absorp-
tion, from the inorganic elements by which it is surrounded.
Although there appear to be certain exceptions to this
rule, yet it almost universally prevails.

Kiitzing maintains, that every organic being is con-
stituted of vegetable and animal elements, and according
as the one or the other prevails, the being becomes an
animal or a vegetable : in the first stages of the develop-
ment of superior beings, and permanently in those of
inferior rank, the two elements are equally balanced. " If
nature," writes Humboldt, " had endowed us with micro-
scopic powers of sight, and if the integuments of plants
were transparent, the vegetable kingdom would by no
means present that aspect of immobility and repose under
which it appears to our senses." And so with regard to
the instruments of motion in the higher classes of crea-
tion, the muscles of animals very soon disappear as we
descend in the scale to the simplest forms of life ; never-
theless, we cannot deny animality to those minute crea-

CHAEACTERISTIOS OF CELLS. 257

tures — as the Amoeba — in which, we are quite unable
to distinguish either muscles or any other distinct organs.
Hence there is always some danger of believing that to be
simple which in reality only seems to be so? and which
the minuteness or transparency of organization may only
conceal from our limited power of vision.

Plants and animals, if seen at the earliest stage of
existence, present themselves to our eyes as an aggregation
of transparent cells. Everything prior to the appearance
of the cell may, in the actual state of our microscopical
knowledge, be considered as not fully and certainly demon-
strated; and therefore it is incumbent upon us to take our
starting-point from the simple cell, which is the same, in re-
spect to its principal characters, in animals and vegetables.
The external coating of a cell is nearly or quite solid and
transparent, and with no indication of structure; while
in its interior is found a liquid or solid substance, with a
nucleus either adhering to its wall or within its cavity.
A nucleolus can sometimes be demonstrated within the
nucleus ; and (a state common to all living cells) an in-
cessant mutual interchange of materials is going on between
the fluid contents and matter external to the cell, by
a process termed osmose, or diffusion, which causes a per-
petual variation in its relative condition. Chemical reagents
give a manifestly different result in the animal and vege-
table cell, hence we may conclude that there is an important
difference in their chemical composition. The vegetable
cell has an extremely fine delicate membrane lining the
inner wall, to perceive which we must have recourse
to reagents, and then we find the apparently simple cell-
wall made up of two layers, each differing in composition
and properties. The inner layer has received the name of
primordial utricle, and its composition has been shown
to be albuminous ; agreeing in this respect with the/orm-
ative substance of animal tissues. The external layer is
regarded as the cell-wall, although it takes no part, essen-
tially, in the formation of the cell ; it is composed of cellu-
lin, a material allied to the cellulose of vegetable tissues.
The contents are more or less coloured : the internal
colouring substance is termed endochrome ; when green it
is called chlorophyll.

258 THE MICROSCOPE.

The successive changes in the cell contents furnish
other very important characteristics, such as the dis-
appearance and re-absorption of the nucleus ; this occurs
in every cell at some period of its existence ; in the cells
of the higher plants, the inner membrane, or primordial
utricle, entirely disappears. The Algse, and some few
unicellular plants, form an exception to the rule. In the
animal, the enlargement of the cell-wall takes place in a
uniform manner, whereas in the plant this is eifected by
a deposition of successive layers on its inner surface, in the
shape of continuous rings, spiral bands, or other inter-
mediate forms. Then the wall not only increases in size,
but appears to possess a power of separating and appro-
priating certain substances, as lime, silica, lignine, &c.,
which form the so-called cuticle. In animals as well as
in plants, new cells are formed within the old cells ; but
in the former, this process of a new formation begins in
the extracellular fluid, while in the latter it is mostly
endogenous. Multiplication of vegetable cells is effected
by three different modes : 1st, Many nuclei appear in the
maternal cell floating together with granular matter;
around each collects a minute vesicle, this gradually
increasing fills the maternal cell, which is eventually
absorbed. 2d, The internal substance of the cell divides
into two or more portions, each being furnished with a
nucleus. 3d, In the third mode of multiplication, the
, wall itself of the maternal cell becomes gradually con-
stricted, and divides into two portions.*

* "In most cells, especially when young, a minute, rounded, colourless
body may be seen, either in the middle or on one side, called the nucleus. This is
very distinct in a cell of the pulp of an apple : and within this nucleus is often
to be seen another smaller body, frequently appearing as a mere dot, called the
nucleolus.

" The nucleus is imbedded in a soft substance, which fills up the entire cell ;
this is the protoplasm (protos, first, plasma, formative substance). As it is very
transparent, it is readily overlooked ; but it may usually be shown distinctly
liy adding a little glycerine to the edge of the cover with a glass rod, when it
contracts and separates from the cell-walls. The protoplasm in some cells is
semi-solid, and of uniform consistence, while in others it is liquid in the centre,
the outer portion being somewhat firmer, and immediately in contact with the
cell-wall. In the latter case it forms an inner cell to the cell-wall, and is called
the primordial utricle. The terms ' protoplasm ' and ' primordial utricle ' are
however used by some authors synonymously.

"The protoplasm is the essential portion of the cell, and it forms or secretes
the cell-wall upon its outer surface in the process of formation of the cell, con-
sidered as a whole. It is also of different chemical composition, from the cell-
wrall being allied in this respect to animal matter."— Griffiths.

CELL-DEVELOPMENT. 259

Taking for our examination the more simple organisms
among vegetables, we shall find numbers which present, in
their earliest as well as in their permanent state, the cell
in its simplest condition, and its reproduction a bare re-
petition of the same thing. Unicellular plants, then, in
the strictest sense, are represented only by those in which
the whole cycle of life is completely shut up in the one
cell ; the first reconstruction or division being at once the
commencement of a new cycle, in which, consequently,
the whole vegetative life is run through in the same cell
where the propagation also appears.

Fig. 144.— Cell Development. (Protococcus pluvialis.)

Proiococcus pluvialis, Riitzing. Hcematococcus^ pluvialis, Flotow. CKlamido-
coccus versatilis, A Braun. Chlamidococcus pluvialis. Flotow and Braun.

A, division of a simple cell into two, each primordial vesicle having developed a
cellulin envelope around itself; B, Zoospores, after their escape from the
cells ; c, division of an encysted cell into segments ; D, division of another
cell, with vibratile filaments projecting from cell- wall; E, an encysted cell ;
F, division of an encysted cell into four, with vibratile filaments projecting ;
o, division of a young cell into two.

The most widely distributed of these single-cell plants
is the Palmoglcea macrococca, of Kiitzing, which spreads
itself as a green slime over damp stones, walls, &c. If a
small portion be scraped off and placed on a slip of glass,
and examined with a half or quarter-inch power, it will be
seen to consist of a number of ovoid cells, having a trans-
parent structureless envelope, nearly filled by a granular
matter of a greenish colour. • At certain periods this mass
divides into two parts, and ultimately the coll becomes two.
Sometimes the cells are united end to end, just as we see
s2

260 THE MICROSCOPE.

them united in the actively-growing yeast plant ; but in
this case the growth is accelerated, apparently, by cold and
damp. Another plant belonging to the same species, the
Protococcus pluvialis, is found in every pool of water, the
spores of which must be always floating in the air, since
it appears after every shower of rain.

Unicellular plants occur in the series of Fungi and
Algce, which' have many and very varied correspondence in
morphological respects. The unicellular Algae — that is to
say, Algae, the contents of which, containing already
organized particles, are inclosed in a single, semifluid
envelope, and this again in a cell-membrane, often
consisting of several layers of different kinds ; and many,
moreover, possess the power of dividing into several
secondary cells, for the most part equivalent to the primary
cell. To this species of unicellular plant belongs Protococcus
pluvialis. That this is the case is clearly seen in the still
form of this plant, which is most distinctly characterised
by its cell-membrane, a more or less thick though always
colourless envelope. It never, however, secretes true
thickening layers on the surface. Although this cell-
membrane exhibits all the optical characters of one com-
posed of cellulose, it is impossible to demonstrate the
presence of that principle by means of iodine and sulphuric
acid ; it is not coloured by those reagents even after the
contents of the cell have been expressed.

The contents vary much in consistence, colour, solid
and fluid constituents ; the red and green portions of
which appear to be of equal physiological importance.
The green colour is removed by ether, on the evaporation
of which solvent there remain green as well as colourless
drops. Dilute sulphuric acid at first renders the colour
paler; but its prolonged action produces a bright green
hue, which gradually becomes more and more intense, and
often almost a blue-green. Hydrochloric acid has a simi-
lar effect j a tinge of brown is produced by nitric acid.
Carbonate of potash scarcely affects the green colour ; it
is gradually but totally destroyed by caustic potash, the
contents at the same time swelling and becoming
transparent.

The change of colour from green to red in Euglena

UNICELLULAR PLANTS. 261

appears to be a process very nearly allied to that which
takes place in Protococcus, if it be not identical with it.
The red substance of Prot. pluvialis is not always of an
oily aspect ; it only becomes so in more advanced age.
And according to Cohn's researches, this oily material is
much more generally distributed than has been supposed,
among the lower Algae; occurring in many true brown
spores, such as of (Edogonium, Spirogyra, Vaucheria, &c.

When still or motile cells of Protococcus are brought in
contact with a very weak solution of iodine, they become
internally, in most parts, of an intense violet or blue colour.
With respect to the solid constituents of the Protococcus
cell contents, they may be distinguished into chlorophyll
vesicles, colourless or green particles, amylaceous granules,
and nucleus. The motile form of Protococcus consists,
as it were, of two cells, one within the other, both of which,
however, differ essentially from the common vegetable cell :
the external having a true cell-membrane and fluid con-
tents j the other, or internal one, with denser, muco-gela-
tinous coloured contents, but without a true cell-wall.
Cohn called the external transparent vesicle the " enve-
loping " cell," and the internal coloured one the " primor-
dial cell." The term "primordial sac, or utricle, " can
only be applied to its peripheral layer, and not to that
together with the contents.

The form of Protococcus (fig. 144) presents a perfect
analogy between the primordial cell and the nucleus of
the common plant-cell. The filaments which proceed
from the central mass to the peripheric cell-wall, are
tubular, giving passage to the red molecules from the
central mass. These filaments, however, which proceed
from the outer wall of the primordial cell towards the
inner surface of the enveloping cell, correspond morpho-
logically to the so-termed mucous filaments by which the
cytoblasts are commonly retained in the centre of their
cells. That they also correspond chemically with these,
is proved by the fact that they are rendered more distinct
by iodine, and that they can be made to retract by means
of reagents ; and in fact they exhibit, in the course
of development, peculiarities which characterise them as
consisting of protoplasm.

262 THE MICROSCOPE.

The existence of delicate threads passing from the
central mass to the enveloping cells, and the appearance
occasionally of little particles having molecular motion,
serve to show that the contents of the enveloping cell are
less of a gelatinous consistence, than of a fluid nature.
And the continuity of the primordial cell- wall with the
filaments proves it is surrounded only with a layer of
protoplasm, and is not inclosed in a dense membrane
of cellulose. The most distinctive characteristic of the
primordial cell, and what appears to constitute its most
essential importance in the life of the cell in general, but
particularly in that of the zoospore, consists in its being
the contractile element of the vegetable organism — that
is to say, that from an intrinsic activity it possesses the
faculty of altering its figure, without any corresponding
change in volume.

The Protococcus pluvialis has true motile organs,
namely, two long vibratile cilia arising from the primordial
cell (fig. 144, B, a), which, passing through two openings in
the enveloping cell, move about in the water. These organs,
during the life of the cell, move so rapidly, that it is
then difficult to perceive them ; they are only recognisable
by the currents they produce in the water. But when
the motion is slackened they are evident enough. They
are also rendered very distinct by iodine. They are always
placed upon the extreme point of the conical elongation,
on the anterior end of the primordial cell, and in such a
manner as to appear to be immediate continuations of its
substance ; and as that process itself consists of protoplasm,
it is evident that the cilia must be regarded also as com-
posed of the same substance. They resemble, in some
respects, the so-called proboscis of certain Infusoria, such
as Euglena and Monads, and do not differ very materially
from the non-vibratile, retractile filaments of Acineta and

It is only that portion of the vibratile filaments beyond
the enveloping cell that exhibits any motion, the portion
within the outer cell being always motionless, and in that
part of their course the filaments appear to be surrounded
with a sheath. This seems to be the case, not only from
the greater thickness at that part, but also from the cir-

UNICELLULAR PLANTS. 263

cumstance that when, passing from the cell form into the
still condition, the cilia disappear, the Y-shaped, or forked
internal portions remain visible. And it is then, also, that
the openings through the enveloping cell-wall become, for
the first time, visible.

Perhaps the most remarkable of all the numerous
aspects presented by Protococcus pluvialis, is the form of
naked zoospores named byFlotow Hcematococcus porphyro-
cephalus. These are extraordinarily minute globules, con-
sisting of a green, red, and colourless substance in unequal
proportions. The colourless protoplasm in them, as in all
primordial cells, constitutes the outermost delicate boun-
dary; the red substance is for the most part collected
towards the anterior end in minute spherules ; the granular
green substance occupies more the under part, while the
middle is usually colourless.

Propagation depends upon a division of the cell
contents, particularly of the colourless or coloured proto-
plasm, or of the primordial sac. This body, without any
demonstrable influence of a nucleus, is capable of sub-
dividing into a determinate number of portions. Each of
these acquires a globular figure, and in the next place
surrounds itself with an envelope of protoplasm, and then
represents a visible organism, which after the reabsorption
of the parent cell-membrane, is capable of existence as an
independent reproductive individual. Besides these, which
are the most usual modes of propagation — viz. that of the
still- cells into two, and of the motile into four, secondary
cells — there are a number of others which may be con-
sidered as irregular, and in which forms are produced
which do not re-enter the usual cycle until they have
gone through a series of generations. Sometimes, under
certain circumstances, the cell-contents of the still form
separate into eight or more portions, which become naked
zoospores t of small size (fig. 144 B.) It is not quite
clear what becomes of this form of motile zoospores, but
there seems reason for believing that they occasionally
develop an enveloping cyst, and thus become encysted
zoospores, and at other times secrete a cellulin tissue,
and become still-colls ; but most of them probably perish
without any further change. They would thus correspond

264 THE MICROSCOPE.

with the smaller motile spores observed by Thuret and
A. Braun in other Algae (the Fucoid, &c.), associated with
the larger germinating spores, themselves deprived of the
germinative faculty.

It appears that both longitudinal and transverse division
of the primordial cell may take place; but that the
vibratile cilia of the parent cell retain almost to the last
moment their function and their motion after the primor-
dial cell inclosed by it has long been detached as a whole,
and become transformed into the independent secondary
cells (fig. 144, G).

The most striking of the vital phenomena presented by
this organism is that of periodicity. Certain forms — for
instance, encysted zoospores, of a certain colour, appear in
a given infusion, at first exclusively, then they gradually
diminish, become more and more rare, and finally dis-
appear altogether. After some time their number again
increases, and reaches as before to an incredible extent ;
and this proceeding may be repeated several times.
Thus, a glass which at one time presented only still
forms, contained at another nothing but motile ones. The
same thing may be observed with respect to segmen-
tation. If a number of motile cells be transferred
from a larger glass into a small vessel, it will be found,
after the lapse of a few hours, that most of them have
subsided to the bottom, and in the course of the day they
will all be observed to be on the point of subdivision. On
the following morning the divisional generation will have
become free ; on the next, the bottom of the vessel
will be found covered with a new generation of self-
dividing cells, which again ^proceed to the formation of a
new generation, and so on. This regularity, however, is
not always observed. The influence of every change in
the external conditions of life upon the propagation is
very remarkable. It is only necessary to pour water
from a smaller into a larger and shallower vessel? or one of
a different kind, to at once induce the commencement of
segmentation in numerous cells. The same thing occurs
in other Algae ; thus the Vaucheria almost always develop
zoospores, at whatever time of year they may be brought
from their natural habitat into a room. Light is conducive

FRESH-WATER ALOE. 265

to the manifestation of vital action in the motile zoospores,
and they always seek it, collecting themselves at the
surface of the water, and at the edges of the vessel.

But in the act of propagation, on the contrary, and when
about to pass into the still condition, the motile Pro-
tococcus cell seems to shun the light; at all events it
then seeks the bottom of the vessel, or that part of the
drop of water in which it may be placed, furthest from
the light. Too strong sunlight, as when it is concentrated
by a lens, at once kills the zoospores.. A temperature of
undue elevation is injurious to the development of the
more vigorous vital activity, that is to say, for the forma-
tion of the zoospores ; whilst a more moderate warmth,
particularly that of the vernal sun, is singularly favour-
able to it. Frost destroys the motile, but not the still
zoospores.*

Stephanosplwera pluvialis is another variety of fresh-
water algae, first observed by Cohn. It consists of a
hyaline globe, containing eight green primordial cells,
arranged in a circle (see Plate 1, No. 24 d). The globe
rotates, somewhat in the same manner as the volvox, by
the aid of projecting cilise, two of which are seen to proceed
from each cell and pierce the transparent envelope. Every
cell divides first into two, then four, and lastly eight
young cells, each of which divides into a great number of
microgonidia, and are seen to have a motion within the
globe, and ultimately escape from it, Under certain cir-
cumstances each of the eight cells is observed to move
about in the interior of the mother-cell ; eventually they
escape, lose their cilia, form a thicker membrane as at 6,
for a time become motionless, and sink to the bottom of
the vessel. If the vessel be permitted to become thoroughly
dry, and again water is poured into it, motile Stephano-
spheera reappear : from which circumstances it is probable
that the green globes are the resting spores of the plant.
When in its condition of greatest activity its division into
eight is perfected during the night, and early in the
morning the young family escapes from the cell, soon to
pass through similar changes. It is calculated that in

* On the "Natural History of Protococcus pluvialis." by F. Cohn. translated
by G. Busk, F.R.S. for the Ray Society

266 THE MICROSCOPE.

eight days, under favourable circumstances, 16,777,216
families may be formed from one resting-cell of Stephano-
sphaera. In certain of the cells, and at particular periods,
the remarkable amaboid bodies (Plate 1, No. 24 c), have
been noticed. There is a marked difference between
Stephanosphaera and Chlamydococcus, " for, while in the
latter the individual portions of a primordial cell separate
entirely from one another, each developing its own enve-
loping membrane, and ultimately escaping as a unicellular
individual ; in the former, on the other hand, the eight
portions remain for a time united as a family." *

The simplest forms of vegetable life are met with in the
Confervoids, which are as interesting as they are in-
structive to the microscopist. The confervas consist of
unbranched filaments composed of cylindrical cells, placed
end to end; their reproductive process is carried on by
zoospores produced from the cell contents. The fresh-
water genera are principally of a yellowish green colour ;
sometimes presenting a striated appearance, which has
given rise to a supposition that their filaments are spiral.
They are indeed plentifully distributed both in fresh and
salt-water.

Oscillatoriacece. — The study of the structure of the Oscil-
latorice is particularly interesting, from the fact that we
may not unreasonably expect to find in it a key to the
singular motion from which they received their generic
name, and which now, for more than a century, has
formed an object of curiosity and interest to the micro-
scopist, without having received, as yet, a satisfactory
explanation.

The following different tissues are observable in the true
Oscillatorice : — 1, An outer inclosing sheath ; 2, A special
cell-membrane, with its contents ; and 3, The axis, or pith,
of the filament.

" The filaments of certain species are inclosed in sheaths
or continuous tubes, never showing any cross-markings
corresponding to the striae of the filament ; they are clearly
composed of a kind of cellulose, although they remain
unaffected by iodine. In other species, these tubes are

* See an interesting paper by F. Currey, F.R.S. Journal of Microscopical
Science, vol. vi. 1858, p. 131 ; also by Mr. Wm. Archer, vol. v. 1865, p. 116

OONFERVOID ALOE.

absent, or have not yet been observed; when present,
they will be found projecting on one or both sides of

Fig. 145.— Confervce.

1, Volwx globator. 2, A section of volypx, showing the ciliated margin of the
cell. 3, A portion more highly magnified, to show the young volvocina, with
their nuclei and thread-like attachments. 4, Spirogyra, near which are spores
in different stages of development. 5, Conferva floceosa. 6, Stigeoclonium
protensum, jointed filaments and single zoospores. 7, Staurocarpus gracilis,
conjugating filaments and spores.

the filament, being somewhat longer than the latter.
Filaments inclosed in sheaths never, or but slightly, ex-
hibit their peculiar motion, although they may be seen
sliding in them, backwards and forwards, or leaving them
altogether.

The filaments themselves have been supposed to consist
wholly of protoplasm; this view, however, is scarcely
correct, since the protoplasm is enclosed in a cell-mem-
brane. The cellulin coat always shows cross-markings
corresponding to the striae when such are observable

268

MICROSCOPE.

in the filament, and which, divide it into distinct joints
or cells.

The presence of this cell-membrane may be best de-
monstrated by breaking up the filaments, either by moving
the thin glass cover, or by cutting through a mass of them
in all directions with a fine dissecting knife. On now
examining the slide, in most in-
stances many detached empty
pieces of this cell-membrane, with
its striae, will be found, as well
as filaments partly deprived of
the protoplasm, showing in those
places the empty, striated cel-
lulin coat. On the application
of iodine all these appearances
become unmistakably evident ;
the greater portions of the fila-
ment turning brown or red, while
the empty cells, with their striae,
remain either unaffected, or at

Fig. 146.— Mesogiwvermwuiaris, most present a slight yellowish
tint> as is frequently the case
with cellulose when old.
With regard to the contents of the cell, the protoplasm
(or endochrome) is coloured in the Oscillatorice, and is de-
posited within it in the form of circular bands or rings
around the axis of the cylindrical filament ; iodine turns
them brown or red, and syrup and dilute sulphuric acid
produce a beautiful rose colour. As to their mode of pro-
pagation, nothing positive is known. If kept for some
time they gradually lose their green colour — those exposed
to the sun, much sooner than others less exposed; the
stratum eventually becoming brown, sinks to the bottom
of the vessel, and presents a granular layer, embodying
great numbers of filaments in all stages of decay.*

The movements oi the Oscillatorice are indeed very sin-
gular, so much so that it is in vain to attempt to explain
them as altogether dependent on physical causes, and
equally so to show that they are due to a sarcode or animal

* Dr. F. d'Alquen, "On the Structure of the Osclllatoriae," Journal of
Microtcopical Science, voL iv. p. 245. 1856.

MARINE ALG^l.

269

membrane. Their motion is not less lively than that of
the Eacterice, which Dujardin and Ehrenberg placed among
infusional animalcules. To observe the movements of the
filaments, the very uppermost surface ought to be brought
into focus, leaving the margins rather undefined, bearing in
mind that the filament is not a flat but a cylindrical body.
Certainly, with regard to its moyement, or the mechanism
by which it is effected, nothing positive is known.

The Badllaria paradoxa is by far the most interesting
specimen of the genus ; the movements of which are very
remarkable, and so little understood that it is rightly
called paradoxical.

The Marine Confervoid Alga3 present a general appear-
ance which might at first sight be mistaken for plants
very much higher in the scale of organization. In the
Ulvacea3, the frond has no longer the form of a filament,
but assumes that of a membranous expansion of the cell.
These cells, in which zoospores are found, have an in_
creased quantity of green protoplasm
accumulated towards one point of the
cell-wall; and the zoospores are ob-
served to converge with their apices
towards the same point. Insv>some
genera, which seem to be closely re-
lated in form.' and structure to the
Bryopsidece, we notice this important
difference, that the zoospores are de-
veloped in an organ specially destined
to this purpose, which presents pecu-
liarities of form, distinguishing it from
every other part of the branching
tubular frond. In the genus Derbesia,
distinct spore cases are seen, a young
branch of which, when destined to be- Fig
come a sporecase, instead of elongating
indefinitely, begins, after having arrived
at a certain length, to swell out into
an ovoid -vesicle, in the cavity of which a rapid accumu-
lation of protoplasma takes place. This is then separated
from the rest of the plant, and becomes an opaque mass,
surrounded by a distinct membrane. After a time a

147. — Sphacelaria
cirrhosa, with spore*
borne at the sides of t/w;
branchlets.

270 THE MICROSCOPE.

division of the mass takes place, arid a number of pyriform
zoospores, each of which is furnished with a crown of ciliae,
are set free.

In many families of the olive-coloured Algae, reproduc-
tion by zoospores is the general rule ; they differ, however,
in the arrangement of their cilia. These organs, which
are always two in number, are usually of unequal length,
and emanate not from the beak, but from a reddish-
coloured point in its neighbourhood. The shortest is
directed backwards, and seems to serve during the motion
of the spo_'e as a rudder. The longest, directed forwards, is
closely applied to the colourless beak. Ectocarpus is one
of the simplest forms of olive-coloured Algae, consisting
of branching filaments, the extremity of any of which is
liable to become converted into a sporangium, by the ab-
sorption of the septa of the terminal cells. The zoospores
are arranged in regular horizontal layers. In many genera
a peculiarity exists, the signification of which is not yet
completely understood — namely, that of a double fructifi-
cation. The ovoidal sporangia contain numerous zoospores.
In the genus Cutleria (fig. 150), there is seen another feature
of interest : the appearance of two kinds of organs, which
seem to be opposed to each other as regards their repro-
ductive functions. The sporangia not only differ from
those of other genera, but the frond consists of olive-
coloured irregularly-divided flabelli, on each side of which
tufts (sori) consisting of the reproductive organs, inter-
mixed with hair-like bodies, are scattered. The zoospores
are divided by transverse partitions into four cavities, each
of which is again bisected by a longitudinal median
septum. When first thrown off they are in appearance so
much like the spores of Puccinia, that they may be mis-
taken for them ; they are, however, about three times larger
than those of the other olive-coloured algae.

The fruit of most olive-green Sea-weeds is enclosed
in spherical cavities under the epidermis of the frond,
termed conceptacles, and may be either male or female.
The zoids are bottle-shaped, each possessing a pair of cilia ;
the transparent vesicle in which they are contained is
itself inclosed in a second of similar form, and we have
no certain evidence of the function performed by the

MARINE ALGJE.

271

antheridia. In monoecious and -dioecious Fuci, the female
conceptacles are distinguished from the male by their olive
colour. The spores are developed in each in the interior of
a perispore, which is borne on a pedicle emanating from the
inner wall of the conceptacle. They rupture the perispore
at the apex ; at first the spore appears simple, but soon after
a series of changes take
place, consisting in a
splitting of the endo-
chrome into six or eight
masses, which become
spheroidal sporules. A
budding-out occurs in a
few hours' time, and ulti-
mately elongates into a
cylindrical tube. The
VaucJierice present a dou-
ble mode of reproduction,
and their fronds consist
of branched tubes, much
resembling in general
character that of the
Hryopsidece, from which
indeed they differ only in respect of the arrangement of
their contents, chlorophyll. In that most remarkable
plant Saprolegnia ferox, which is structually so closely
allied to Vaucherice, though separated from them by the
absence of green colouring matter, we find a correspond-
ing analogy in the processes of its development. In the
process of the formation of its zoospores, we have an
intermediate step between that of the Alga3 and a class of
plants usually placed among Fungi. Cohn has shown us
that Pilobolus is structually more closely allied to the
former class than to that of the latter. Pilobolus has
a somewhat remarkable ephemeral existence; the spore
germinates about mid-day, the plant grows till evening,
re-opens during the night, and in the morning the spore-case
bursts and the whole disappears, leaving behind scarcely
a trace of its former existence.

Eed Sea-weeds, Floridece, present great varieties of struc-
ture, although comparatively little is known of their re-

Fig. US.— Development of Viva,.

A, isolated cells of spores. B and c, clus-
tering of the same. D, cells in the fila-
mentous stage.

272

THE MICROSCOPE.

productive processes ; it will, however, be sufficient for our
purpose to notice the three leading forms. The first form,
to which the term polyspore has been applied, is that of
a gelatinous or membranous pericarp or conceptacle, in
which an indefinite number of sporidia are contained.
This organ may be either at the summit or base of a
branch, or it may be concealed in or below the cortical
layer of the stem. In some cases a number of sporidium-
bearing filaments emanate from a kind of membrane
at the base of a spheroidal cellular perisporangium, by
the rupture of which the sporidia formed from the
endochrome of the filaments make their escape. Other
changes have been observed ; however, they all agree in
one particular, namely, — that the sporidium is developed
in the interior of a cell, the wall of which forms its
perispore, and the internal protoplasmic membrane en-
dochrome, the sporidium itself, for
the escape of which the perispore rup-
tures at its apex.

The second form is more simple,
and consists of a globular or ovoid
cell, containing a central granular
mass, which ultimately divides into
four quadrate-shaped spores, which
when at maturity escape by rupture
of the cell-wall. This organ, called
a tetraspore, takes its origin in the
cortical layer. The tetraspores are
arranged either in an isolated manner
along the branches, or in numbers to-
gether ; in some instances the branches
which contain them are so modified in
form that they look like special or-
gans, and have been called stichidia ;
as, for example, in Dasya (fig. 149).
Of the third kind of reproductive or-
and two rows of tetra- gan a difference of opinion exists as to

spores. Magnified 50 7i • •/? .• j> ^i • JT • T

diameters. the signification of their antheridia;

although always produced in precisely

the same situations as the tetraspores and polyspores,

they are "agglomerations of little colourless cells, either

MARINE ALOE.

273

united in a bunch as in Griffithsia, or enclosed in a trans-
parent cylinder, as in Polysiphonia, or covering a kind of ex-
panded disc of peculiar form, as in Laurencia" According
to competent observers, these cellules contain spermatozoids.
Nageli describes the spermatozoid as a spiral fibre, which, as
it escapes, lengthens itself in the form of a screw. Thuret
does not coincide in this view ; on the contrary, he says
that the contents are granular, and offer no trace of a
spiral filament, but are expelled from the cells by a slow
motion. The antheridia appear in their most simple form
in Calliihamnio^ being reduced to a mass of cells com-
posed of numerous little bunches which are sessile on the
bifurcations of the terminal branches. Are not these spiral
filaments closely allied to Oscillatoriacece ? The spores are
simpler structures than the tetraspores, and mostly occupy
a more important posi-
tion. They are not scat-
tered through the frond,
but grouped in definite
masses, and generally
enclosed in a special
capsule or conceptacle,
which may be mistaken
for a tetraspore case.
The simplest form of
the spore fruit consists
of spherical masses of
spores attached to the
wall of the frond, or
imbedded in its sub-
stance, without a prope^'
conceptacle ; such a fruit
is called a favellidium,
and occurs in Haly-
menia ; the same name
is applied to the fruits
of similar structures not
perfectly immersed,, as
those of Gfigartina, Gelidium, &c., where they form tuber-
cular swellings on the lobes. In some, the tubercles pre-
sent a pore at the summit, through which the spores find

Fig. 150. — Cutleria diclwtoma. Section of a
lacinia of a frond, showing the stalked eight
chambered oosporanges growing on tufts
with intercalated hairs Magnified 50 dia-
meters.

274 THE MICKOSCOPB.

exit; when such a fruit is wholly external, as in Cera-
mium (see Plate II. Nos. 27 and 37) and Callithamnion,
it is called a favella. The characteristic of Delesseria,
No. 39, the coccidium, either occurs on lateral branches, or
is sessile on the face of the frond, and consists of a case
of angular spores attached to a central wall. The cera-
midium is the most complete form of the conceptacular
fruit : this is enclosed in an rvate case, with an apical
spore, containing a tuft of pear-shaped spores arising from
the base of the cavity.

The general external appearance of the Eed Sea- weeds
is very varied. They are exquisite objects for the Micro-
scope ; we have figured several interesting varieties in
Plate II., each showing peculiarities of fructification. Their
beautiful leaf-like fronds are either simple, lobed, or
curiously pinnate or feathered. The Floridese of warmer
climates exhibit most elegantly formed reticulated fronds,
as may be seen on reference to the late Dr. Harvey's last
great work, " Phycologia Australica"

In the plant which results from the germination of the
aggregate zoospores of Vaucheria, a genus of Siphonacea3
(Plate I. fig. 23), Kaisten has observed that on those
filaments which come in contact with the atmosphere,
are formed organs of a peculiar structure, which have
the appearance of nipple or egg-shaped buddings-out
of the cell-wall, distributed in pairs along the whole
course of the older filaments ; one elongates and curves
round to meet its fellow, which is seen to swell out
into a globular form; finally conjugation takes place,
preceded, however, by the conversion of the green con-
tents of the tubular organ into oil globules. If the fila-
ments be gathered at a favourable period, and cultivated
in a vessel of water well exposed to the light, the blind
ends, or ramifications of the filaments, are found densely
filled with green contents, appearing to be almost black ;
if these ends be watched early in the morning, a remark-
able series of changes is seen to occur in them when
about to produce gonidia, and, ultimately, they escape
in a peculiar way from the filament. The admirable essays
of linger, Kageli, and Pringsheim on the process of their
reproduction might be consulted with advantage.

DKSMIDIACEJ<:, DIATOMACE^:, AI.G.K.

Tu (Ten West, dpi.

Edmund Evans.

I'l.ATK JI.

VOLVOX GLOBATOR.

275

A fresli- water alga of singular "beauty and interest to
tlie microscopist is the Volvox globator. This little cell
so well known to the older observers as the globe-
animalcule, or revolving-cell, is represented in fig. 145,
Nos. 1, 2, 3, and Plate I. No. 15. These revolving globular
bodies were for a very long time classed with the lower
forms of animal life, and there remained for the micro-
chemical investigator of the present time to settle the per-
plexing question, and assign to them a place among plants.
Leeuwenhoek first perceived the motion of what he
termed globes, "not more than the 30th of an inch in

diameter, rolling through
water ; and judged them to
be animated." These globes
are studded with innumerable
minute green spots, each of
which is seen to be a perfect
cell, about the 3,500th part of
an inch in size, with a nucleus
and two active cilia attached.
The whole are bound together
by threads forming a beautiful
net-work. Within the globe
busy active nature is at work
carefully providing a continu-
ance of the species; and from
six to twenty little bright-
green spheres have been found
enclosed in the larger trans-
parent case. As each little
cell arrives at maturity, the
parent cell enlarges, and
, just before the young burst ultimately bursts asunder,
nlthpeJeeSt,rorhcS: lurching torth its offspring
. 3, Docidium ciavatum. 4, to seek an independent exis-
astrum gradiis. ^ence. Both older and

younger spheres possess openings through which the water
freely flows, affording food and air to the wonderfully
constructed little being.

Dr. Carpenter believes, "The Volvodnece, whose vegetable
nature has been made known to us by observation of cer-
T2

Fig. 151.

276 THE MICROSCOPE.

tain stages in the history of their lives, are but the motile
forms (Zoospores) of some other plants, whose relation to
them is at present unknown." Professor Williamson,
having carefully examined the Volvox globato?*, says : —
" That the increase of its internal cells is carried on in a
manner precisely analogous to that of the algee; that
between the outer integument and the primordial cell- wall
of each cell, a hyaline membrane is secreted, causing the
outer integument to expand; and as the primordial cell-
wall is attached to it at various points, it causes the inter-
nal colouring-matter, or endochrome, to assume a stellate
form (see Plate I. No. 15), the points of one cell being in
contact with those of the neighbouring cell, these points
forming at a subsequent period the lines of communication
between the green spots generally seen within the full-
grown Volvox." Cilia can be distinctly seen on the outer
edge of the adult Volvox ; by compressing and rupturing
one, they may even be counted. Professor Busk has been
able to satisfy himself, by the addition of the chemical
test iodine, of the presence of a very minute quantity of
starch in the interior of the Volvox, which he considers
as conclusive of their vegetable character. A singular
provision is made in the structure of the gemmules, con-
sisting of a slender elastic filament, by which each is at-
tached to the parent cell- wall : at times it appears to thrust
itself out, as if in search of food ; it is then seen quickly to
recover its former nestling-place by contracting the tether.
It is impossible not to recognize the great similarity
between the structure of Volvox, and that of the motile
cell of Protococcus pluvialis. The influence of re-agents
will sometimes cause the connecting processes of the young
cells as in Protococcus, to be drawn back into the central
mass, and the connecting threads are sometimes seen as
double lines, which seem like tubular prolongations of a
consistent membrane. At other times they appear to be con-
nected by star-like prolongations to the parent cell, Plate I.
No. 15, presenting an almost identical appearance with
Pediastrum pertusum. Mr. Busk says that the body
designated by Ehrenberg Splwerosira volvox is an ordinary
volvox in a different phase of development; its only
marked feature of dissimilarity being that a large propor-

VOLVOCINE-ffi. 277

tion of the green cells, instead of being single, are very
commonly double or quadruple ; and the groups of ciliated
cells thus produced, form by their aggregation discoid
bodies, each furnished with a single cilium. These clusters
separate themselves from the primary sphere, and swim
forth freely under the forms which have been designated
Uvella and Syncrypta by Ehrenberg. According to Mr.
Carter, however, Splwerosira is the male or spermatic
form of Volvox globator. Dr. Braxton Hicks believes that
he has seen the young volvox pass into an amoeboid state ;
he observes : — "Towards the end of autumn the endochrome
mass of the volvox increases to nearly double its ordinary
size, but instead of undergoing the usual subdivision, so
as to produce a macro-gonidium, it loses its colour and
regularity of form, and becomes an irregular mass of
colourless protoplasum, containing a number of brownish
granules." (Plate I. K"o. 16.)

The final change and ultimate destination of these
curious amoeboid bodies have not as yet been made out ;
but from Dr. Hick's previous observation, made on similar
bodies developed from the protoplasmic contents of the
cells of the roots of mosses, " which in the course of two
hours become changed into ciliated bodies," he thinks it
very probable that this is designedly the way in which
these fragile structures are enabled to retain life, and to
resist all the varied external conditions, such as damp,
dryness, and rapid alternations of heat and cold.1

(1) We have had volvox under the microscope for several months, towards the
end of summer and throughout the autumn, and made more than a hundred
examinations, without having once seen the remarkable change described by
Dr. Hicks in the Quarterly Jour. Micros. Science, vol. viii. p. 96, 1862. Never-
theless, as Mr. Archer observes: — "If this reasoning be correct, then contrac-
tility, amoeboid contractility — for I can find no more comprehensive and expressive
single adjective — must be accepted as an inherent quality or characteristic,
occasionally more or less vividly evinced, of the vegetable cell-contents, and
this in common with the animal ; in other words, that the nature of the proto-
plasm in each is similar, as has indeed, as is well known, been urged before on
grounds not so strong; thus reserving Siebold's doctrine, that this very con-
tractility formed the strongest distinction between animals and plants, as he
assumed it to be present in the former and absent in the latter of the two
kingdoms of the organic world. Therefore, an organism whose known structural
affinities, and whose mode of growth and of ultimate fructification point it out
as truly a plant, but of which, however, certain cells may for a time assume a
contractile, even a locomotive, quasi-rhizopodous state, must not by any means
on this latter account alone be assumed as even temporarily belonging to the
animal kingdom, or as tending towards a mutation of its vegetable nature.
And from this it of course follows that an organism whose structural affinities
and reproduction are unknown, but which may possibly present an actively

278 THE MICROSCOPE.

Desmidiacece. — A remarkably beautiful family of confer-
void algae, the most distinctive characteristics of the species
being their bilateral symmetry. Each frastule is, however,
a perfect unicellular plant, with a homogeneous structureless
membrane, enclosing a cellular skeleton filled with chloro-
phyll. Four modes of reproduction have been observed in
the desmids, and many points still remain to be cleared
up. Braun remarks of the products of conjugation, " that
they do not pass, like the swarming-cells of the Palmellacece
and the reproductive cells of the Diatomacese, directly and
by uninterrupted growth into the primary generation of
the new vegetative series, but persist for a long time in a
condition of rest, during which, excepting as regards im-
perceptible internal processes, they remain wholly un-
changed. To distinguish these from the germ-cell (gonidia)
I shall call them seed-cells (spores). Certain early condi-
tions observed in Closterium and JEuastrum, namely, families
of unusually small individuals, enclosed in transparent,
colourless vesicles, render it even probable that in certain
genera of this family a number of individuals are produced
from one spore, by a formation of transitory generations
occurring already within the spore." *

contractile, even locomotive power, need not on this latter account be assumed
as therefore necessarily an animal. In the former category fall the Volvocinacese
and Rhisidium ; in the latter category Euglena and its allies, the so-called
Astasisean Infusoria, suggest themselves ; and these must of course wait until
their reproduction and history are better known before we can feel satisfied as
to their true position ; yet it seems highly probable that these will presently, if
they do not even now, take their place amongst admitted plants.

" Several writers have, indeed, from time to time, put forward the (now, I
think, generally accepted) view that the protoplasm of the vegatable and the
sarcode of the animal cell are identical in nature ; and, in seeking for analogies
as regards contractility in the vegetable protoplasm as compared with the
animal, and as demonstrative thereof, special attention has been directed to
several of the now familiar phenomena displayed by certain vegetable cells.
Such are the vibratory movements of cilise, and drawing in of these, the circula-
tory movements of the cell contents, as in the hairs of the Tradescantia, &c., the
contractile vacuole in Gonium, Volvox, &c., and so forth. But while these are,
I think, unquestionably to a considerable, but more limited extent, manifesta-
tions of the same phenomenon, it seems to me that none of these cases present
so exact an analogy, strongly as they may indicate it, with the rhizopodous con-
tractility as do the amoeboid bodies of Stephanosphaera, of Volvox, of the
Moss-radicles, and of Rhisidium. The amoeboid bodies of Stephanosphsera seem
to display this rhizopodous contractility in greatly the most marked or ex-
aggerated degree, as their vigorous and energetic power of locomotion indicate :
in them, and indeed in those of Volvox, the Moss, and Rhisidium, the pseudo-
podal processes and their mode of protrusion and withdrawal, the flow of the
granules', and the locomotion of the whole body, were in all respects analogous
to the similar phenomena evinced by a true amoeba."— Wm. Archer, Quarterly
Journ. Micros. Science, vol. v. p. 185.

(1) " The Phenomenon of Rejuvenescence in Nature."

DESMIDIACEJJ. 279

Reproduction both by conjugation and subdivision
variously modified, is common to all the families of
Desmidiaceae ; and in the Zygnemaceee, which have a
close relation to them, the phenomena of conjugation are
very well known. In Staurocarpus we have those re-
markable quadrate spores formed in the cross branch,
produced by conjugation. In Spirogyra the union of two
cells belonging to the opposite filaments takes place by the
expansion of one side of each, so as to form a papilla or
short rounded-off tube (see fig. 145). The ends of the two
projections then come into contact, become slightly flattened,
then pressed together, and finally united. The double wall
formed by their union dissolves, or is broken through, so
that a free passage is established between the two cells.
Upon this, the whole of the chlorophyll, previously
arranged round the inside of each of the cells, becomes a
confused mass, which soon forms itself either in the cavity
of one of them, or in the connecting canal, into a globular
or oval spore invested with the colourless cellulose mem-
brane shown in one of our drawings of Penium (Fig. 155).
In Glosterium conjugation takes place in a somewhat
similar manner, represented at No. 25, although it is
quite clear that if the formation of germs by conjugation
were the only provision for the reproduction of a species,
all must disappear, inasmuch as the conjugation and
consequent destruction of a pair of Closteria for the
formation of one new plant will ultimately destroy the
species.1 Another mode, however, that of subdivision,
appears to be designed as an effectual safeguard against
such a possible extinction. Mr. Lobb has observed this
process take place in Micrasterias denticulata (Plate II.
fig. 30), in the course of three hours and a half. The small
hyaline hemisphere, put forth in the first instance from each
frustule, enlarges with the flowing in of the endochrome ; it
then undergoes progressive subdivision at its edges, first
into three lobes, then into five, then into seven, then into
thirteen, and finally at the time of its separation, acquires
the characteristic notched outline of its type, being only
distinguishable from the older half by its smaller size.2

(1) In certain species of Closterium the act of conjugation gives origin to two
sporangise. (2) E. G. Lobb, Trans. Micros. Soc. N.S. vol. i., 1861.

280

THE MICROSCOPE.

Desmidiacece. — The once disputed question relating to
the vegetable nature of these cells received much valuable
elucidation from Mr. Ealfs, who gave to the world the

Fig. 152.

1, Euattrum oblongum. 2, Micra^terias rolata. 3, Desmidium quadrangulatum.
4, Didymoprium Grevillii.

results of his laborious researches in his excellent work on
The British Desmidiece, published in 1848; and the con-
clusions arrived at by this painstaking author have been
generally accepted by men of science. The interest which
has so long attached to this topic will warrant us in
devoting some space to its consideration ; and we avail our-
selves for that purpose of Mr. Ralfs' labours, with a
recommendation to those of our readers who would
wish to familiarise themselves more completely with this
peculiar species, to consult the pages of the book above
referred to.

Desmidiacece are grass-green in colour, surrounded by a
transparent structureless membrane, a few only having
their integuments coloured; they are all inhabitants of
fresh water. Their most obvious peculiarities are the
beauty and variety of their forms and their external mark-
ings and appendages ; but their most distinctive character
is their evident division into two or more segments. Each
cell or joint in the Desmidiacece generally consist of two
symmetrical valves or segments ; and the suture or line of
junction is in general well marked. The multiplication of
the cells by repeated transverse division is full of interest,

DESMIDIACEJE.

281

both on account of the remarkable manner in which it
takes place, and because it unfolds the nature of the pro-
cess in other families, and furnishes a valuable addition to
our knowledge of their structure and physiology.

Kg. 153.

5, Micrasterias, sporangium of. 6, Didymoprium Borreri. 7, Cosmarium Ral/sii.
8, Staurastrum hvrsutum.

The compressed and deeply-constricted cells of Euastrum
offer most favourable opportunities for ascertaining the
manner of their division ; for although the frond is really
a single cell, yet this cell in all its stages appears like two,
the segments being always distinct, even from the com-
mencement. As the connecting portion is so small, and
necessarily produces the new segments, which cannot arise
from a broader base than its opening, these are at first
very minute ; though they rapidly increase in size. The
segments are separated by the elongation of the connecting
tube, which is converted into two roundish hyaline lobules.
These lobules increase in size, acquire colour, and gradually
put on the appearance of the old portions. Of course, as
they increase, the original segments are pushed further
asunder, and at length are disconnected, each taking with
it a new segment to supply the place of that from which
it has separated.

It is curious to trace the progressive development of
the new portions. At first they are devoid of colour, and

282 THE MICROSCOPE.

have much the appearance of condensed gelatine ; but as
they increase in size, the internal fluid acquires a green
tint, which is at first very faint, but soon becomes darker ;

Fig. 154.

7, Sphcerozosma vertebratum. 8, 9, XantMdice. 10, X. armatum. 11, Cosma-
rium crenatum. 13, IV, Sporangia of Cosmarium. 14, X. fasiculutum. 19,
Arthrodesmus convergens. 15, Staurastrum tumidum. 16, Staurastrum dilitatum.

Sit leugt.h it assumes a granular state. At the same time
the new segments increase in size, and obtain their normal
figure ; the covering in some species shows the presence
of puncta or granules. In Xanthidium and Staurastrum
the spines and processes make their appearance last,
beginning as mere tubercles, and then lengthening until
they attain their perfect form and size, armed with setae ;
but complete separation frequently occurs before the whole
process is completed. This singular process is repeated
again and again, so that the older segments are united
successively, as it were, with many generations. When
the cells approach maturity, molecular movements may
be at times noticed in their contents, precisely similar to
what has been described by Agardh and others as occurring
in Confervas. This movement has been aptly termed a
swarming. All the Desmidiacece are semi-gelatinous. In
some the mucus is condensed into a distinct and well-defined

DESMIDIACE.E.

283

hyaline sheath or covering, as in Didymoprium Grevillii
and Staurastrum, tumidum ; in others it is more attenu-
ated, and the fact that it forms a covering is discerned

Fig. 155.

21, Penium. 24, Pediastrum Itiradiatum. 25, Closterium, showing conjugation
or self-division. 27, Penium Jenneri. 28, Aplogonum desmidium, 29, Pedias-
trum pecticum. 30, Ankistrodesmus falcatus. 33, Conjugation of Penium
margaritaceum. 34. Spirotcemia. 35, Closteriiim.

only by its preventing the contact of the coloured cells.
In general its quantity is merely sufficient to hold the
fronds together in a kind of filmy cloud, which is dispersed
by the slightest touch. When they are left exposed by
the evaporation of the water, this mucus becomes denser,
and is apparently secreted in larger quantities, to protect
them from the effects of drought. Meyen states, " that the
large and small granules contain starch, and were some-
times even entirely composed of it ; " and " in the month
of May he observed many specimens of Closterium in
which the whole interior was granulated ; these grains gave
with iodine the beautiful blue colour, indicative of the
presence of starch."1

(1) The test for starch can be easily applied, and so remove any doubt that,
may exist. It is only necessary to bear in mind that unless granular matter

284: THE MICROSCOPE.

" Did we trust solely to the eye, we should indeed be
very liable to pronounce these variable and beautiful forms
as belonging to animals rather than vegetables. All
favours this supposition. Their symmetrical division into
parts; the exquisite disc-form, finely cut and toothed
Micrasterias ; the lobed Euastrum; the Cosmarium, glit-
tering as it were with gems ; the XantMdium, armed with
spines ; the scimitar-shaped Closterium, embellished with
striae ; the Desmidium, resembling a tape- worm ; and the
strangely insect-like Staurastrum, sometimes furnished
with arms, as if for the purpose of seizing its prey ; — all
these characteristics appear to a superficial observer to
belong rather to the lowest forms of animal, than vege-
table life." Another indication Dr. Bailey .adduced, by
rendering apparent their power of motion; taking a por-
tion of mud covered with Closteria, and placing it in
water exposed to light ; after a time, it will be seen that
if the Closteria are buried in the mud, they work their
way to the surface, and cover it with a green stratum :
this is no doubt owing to the stimulus light exerts upon
all matter, although at first appearing very like a volun-
tary effort. Another is afforded by their retiring beneath
the surface when the pools dry up. Mr. Ealfs states that
he has tak;en advantage of this circumstance to obtain
specimens less mingled with foreign matter than they
would otherwise have been.

During the summmer of 1854 the Rev. Lord S. G.
Osborne drew our attention to the economy of an interest-
ing specimen of this family, the Closterium Lunula; after
many careful investigations he came to the conclusion
that the membrane of the endochrome, both on its inner
and outer surface, is ciliated.

In the Closterium Lunula, we have ascertained that the
best view of its circulation is obtained by the use of
strong daylight, or sunlight transmitted through coloured
glass, or such a combination of tinted glass as that

be seen in the interior of the cell, starch cannot be present. A small quantity of
diluted tincture of iodine may be applied, removing the free iodine by the aid of
heat, occasionally adding a little water to facilitate its removal. This also will
assist in the removal of the brownish stain which at first obscures the charac-
teristic purple tint; and then, by applying the highest power of the microscope,
the peculiar colour of the purple iodide of starch will in general be perceived.

DESMIDIACEJ].

285

proposed by Mr. Rainey, and adapted to a l-4th achro-
matic condenser ; with which must be used a l-8th ob-
ject-glass. The Gillett's condenser, or parabolic reflector,
will do equally well if used with a l-8th objective. In
diagram A, fig. 156, a specimen of the C. Lunula, as seen

Fig. 156. — Closteria Lunula.

with the above arrangement of microscopic power, and a
deep eye-piece, the cilia are in full action along the edge of
the membrane which encloses the endochrome ; and also,
but not so distinctly, along the inside of the edges of the
frond itself. Their action is precisely the same as that
in the branchiae of the mussel : there is the same wavy
motion; and as the water dries up between the glasses
in which the specimen is enclosed, the circulation becomes
fainter, and the cilia are seen with more distinctness.

In diagram A, a line is drawn at I to a small oval mark;
these exist at intervals, and more or less in number over
the surface of the endochrome itself, beneath the mem-
brane which invests it. These seem to be attached by
small pedicles, and are usually seen in motion on the spot
to which they are thus fastened ; from time to time they

286 THE MICROSCOPE.

break away, and are carried by the circulation of the fluid,
which works all over the endochrome, to the chambers at
the extremities ; there they join a crowd of similar bodies,
each in action within those chambers, when the specimen
is a healthy one.

The circulation, when made out over the centre of the
frond, for instance at a, is in appearance of a wholly
different nature from that seen at the edges. In the
latter, the matter circulated is in globules, passing each
other, in distinct lines, in opposite directions ; in the cir-
culation as seen at a, the streams are broad, tortuous, of
far greater body, and passing with much less rapidity. To
see the centre circulation, use a Gillett's illuminator and
the l-8th power ; work the fine adjustment so as to bring
the centre of the frond into focus, then almost lose it by
raising the objective ; after this, with great care, work the
milled head till the dark body of the endochrome is made
out ; a hair's-breadth more adjustment gives this circula-
tion with the utmost distinctness, if it is a good specimen.
It will be clearly seen, by the same means, at all the
points where the spaces are put ; and from them may be
traced, with care, down to both extremities.

The endochrome itself is evidently so constructed as to
admit of contraction and expansion in every direction. At
times the edges are in semi-lunar curves, leaving uninter-
rupted clear spaces visible between the green matter and
the investing membrane ; at other times, the endochrome
is seen with a straight margin, but so contracted as to
leave a well-defined transparent space along its whole edge,
between itself and the exterior case. It is interesting to
keep changing the focus, that at one moment we may see
the globular circulation between the outer and inner case,
and again the mere sluggish movement between the inner
case and the endochrome.

At B is given an enlarged sketch of one extremity of
a 0. Lunula. The arrows within the chamber pointing to
b, denote the direction of a very strong current of fluid,
which can be detected, and occasionally traced, most dis-
tinctly ; it is acted upon by cilia at the edges of the
chamber, but its chief force appears to come from some
impulse given from the very centre of the endochrome.

DESMIDIACE^. 287

The fluid is here acting in positive jets, that is, with an
almost arterial action ; and according to the strength with
which it is acting at the time, the loose floating bodies are
propelled to a greater or less distance from the end of the
endochrome ; the fluid thus impelled from a centre, and
kept in activity by the lateral cilia, causes strong eddies,
which give a twisting motion to the free bodies. The
line — a, in this diagram, denotes the outline of the mem-
brane which encloses the endochrome ; on both sides of
this cilia may be detected. The circulation exterior to it
passes and repasses it in opposite directions, in three or
four distinct courses of globules ; these, when they arrive
at — c, seem to encounter the fluid jetted through an
aperture at the apex of the chamber ; which disperses them
so much, that they appear to be driven, for the most part,
back again on the precise course by which they had
arrived. Some, however, do enter the chamber ; occasion-
ally, but very rarely, one of the loose bodies may be seen
to escape from within, and get into the outer current, it is
then carried about until it becomes adherent to the side of
the frond.

With regard to the propagation of the 0. Lunula, we
have never seen anything like conjugation; but we have
repeatedly seen what the reverend gentleman has so well
described — increase by self- division.

Observe the diagram D ; but for the moment suppose
the two halves of the frond, represented as separate,
to just overlap each other. Having watched for some
time, the one half may be seen to remain passive ; the
other has a motion from side to side, as if moving on an
axis at the point of juncture : the separation then becomes
more and more evident, the motion more active, until at
last with a jerk one segment leaves the other, and they
are seen as drawn. It will be observed, that in each
segment the endochrome has already a waist ; but there
is only one chamber, which is the one belonging to the
one extremity of the original entire frond. The globular
circulation, for some hours previous to subdivision^and for
some few hours afterwards, runs quite round the obtuse
end of the endochrome — a, by almost imperceptible
degrees; from the end of the endochrome symptoms of

288 THE MICROSCOPE.

an elongation of the membranous sac appear, giving a
semi-lunar sort of chamber ; this, as the endochrome
elongates, becomes more denned, until it has the form and
outline of the chamber at the perfect extremity. The
obtuse end — 6 of the frond is at the same time elongat-
ing and contracting ; these processes go on ; in about five
hours from the division of the one segment from the other,
the appearance of each half is that of a nearly perfect
specimen, the chamber at the new end is complete, the
globular circulation exterior to it becomes affected by the cir-
culation from within the said chamber; and, in a few hours
more, some of the free bodies descend, become exposed to,
and tossed about in the eddies of the chamber, and the
frond, under a l-6th power, shows itself in all its beau-
tiful construction. E is a diagram of one end of a C. didy-
motocum, in which the same process was noticed.

The Euastrum Didelta is well worthy
of attention, as well as many other species,
the Xanthidium Penium, Docidium, &c.

The Arthrodesmus Incus has a very
beautiful hyaline membrane stretching
from point to point, cut at the edges,
something like the Micrasterias. This is
represented at fig. 157.

The Mode of Finding and Taking Desmidiacece. — As
the difficulty of obtaining specimens is very great, it will
materially assist the efforts of the microscopist to know
the method adopted by Mr. Ealfs, Mr. Jenner, and Mr.
Thwaites. " In the water the filamentous species resemble
the Zygnemata ; but their green colour is generally paler
and more opaque. When they are much diffused in the
water, take a piece of linen, about the size of a pocket
handkerchief, lay it on the ground in the form of a bag,
and then, by the aid of a tin box, scoop up the water
and strain it through the bag, repeating the process as
often as may be required. The larger species, Euastrum,
Micrasterias, Closterium, &c., are generally situated at the
bottom of the pool, either spread out as a thin gelatinous
stratum, or collected into finger-like tufts. If the finger
be gently passed beneath them, they will rise to the sur-
face in little masses, and with care may be removed and

DESMIDIACEJE. 289

strained through the linen as above described. At first
nothing appears on the linen except a mere stain or a little
dirt ; but by repeated fillings-up and strainings a consi-
derable quantity will be obtained. If not very gelatinous,
the water passes freely through the linen, from which the
specimen can be scraped with a knife, and transferred to a
smaller piece ; but in many species the fluid at length
does not admit of being strained off without the employ-
ment of such force as would cause the fronds also to pass
through, and in this case it should be poured into bottles
until they are quite full. But many species of Stauras-
trum, Pediastrum, &c., usually form a greenish or dirty
cloud upon the stems and leaves of the filiform aquatic
plants ; and to collect them requires more care than is
necessary in the former instances. In this state the
slightest touch will break up the whole mass, and disperse
it through the water : for securing them, let the hand be
passed very gently into the water and beneath the cloud,
the palm upwards and the fingers apart, so that the leaves
or stem of the inverted plant may lie between them, and
as near the palm as possible ; then close the fingers, and
keeping the hand in the same position, but concave, draw
it cautiously towards the surface ; when, if the plant has
been allowed to slip easily and equably through the fingers,
the Desmidiacece, in this way brushed off, will be found
lying in the palm. The greatest difficulty is in withdraw-
ing the hand from the surface of the water, and probably
but little will be retained at first ; practice, however, will
soon render the operation easy and successful. The con-
tents of the hand should be at once transferred either to a
bottle, or, in case much water has been taken up, into the
box, which must be close at hand ; and when this is full,
it can be emptied on the linen as before. But in this case
the linen should be pressed gently, and a portion only of
the water expelled, the remainder being poured into the
bottle, and the process repeated as often as necessary."

When carried home, the bottles will apparently contain
only foul water ; but if it remain undisturbed for a few
hours, the Desmidiacece will sink to the bottom, and most
of the water may then be poured off. If a little filtered
rain-water be added occasionally, to replace what has been

•

290 THE MICROSCOPE.

drawn off, and the bottle be exposed to the light of the sun,
the Desmidiacece will remain unaltered for a long time.

Fungi.— '-This interesting class of cellular flowerless
plants are chiefly microscopic, many requiring a high magni-
fying power to determine their peculiarities of structure.
They abound in damp places, among decaying and decayed
vegetable and animal matters, everywhere, and in almost
every place. The structure of all Fungi exhibits a well de-
fined separation into two parts, a mycelium (thallus) jointed
and branched, forming a kind of cottony filamentous mass,
and a reproductive spore or fruit, which, although exceed-
ingly minute, differs somewhat in appearance under the
microscope. The "spawn" used for planting mushroom
beds is composed of mycelium, and may be readily obtained
for examination (fig. 188, No. 19). The dust- like powder
of any of the moulds or mildew when sprinkled on a slip
of glass and kept under a bell glass over water, will soon
throw out filaments and spores in all directions.

De Bary's observations show that resting-spores are not
peculiar to the algae ; for he found them in two genera of
fungi, and Tulasne ascertained their production in Perono-
sporce, many of which are parasitic, as P. parasitica, a
species found on the cabbage and turnip leaf, as well as
on the shepherd's-purse, Gapsella bursapastoris. For the
growth of P. infestans, the potato mould, the exclusion
of light seems to be needful, and it is easy to conceive
how the spores, washed down to the tuber during heavy
rains, throw out germinating threads, which easily pene-
trate the thick cuticle of the potato, and quickly produce a
murrain.

The Rev. M. J. Berkeley, our English authority on
Fungi, says : — " The genus Gystopus comprises those para-
sitic fungi amongst the Uredines which are remarkable for
their white spores. Till the resting-spores of the different
species were ascertained, it was almost impossible to find
good distinctive characters : one species at least, Cystopus
candidws, is to be found everywhere on the common
shepherd's-purse, and often accompanied by Peronospora
parasitica. It is also frequent on the cruciferse : the aero-
spores, or gonidia, which spring from the swollen threads
of the mycelium, form necklaces, as in oidium, the joints

PARASITIC FUNGI. 291

of which give rise to zoospores, as first observed by Pre-
vost, in 1807. Like those of Peronospora, they move
about in water by means of two lash-like appendages, and
there germinate. When resting on the leaves of a plant,
they make their way by means of a germinating thread
into its subjacent tissues, and throw out little suckers.
The branched mycelium gives off 'sporangia and antheridia,
exactly as in Peronospora ; when ripe, the sporangia are
strongly warted. They fall, doubtless, with the leaves to
the ground, where they remain till a fitting season arrives
for their development. The provision made for the rapid
development of these parasites and for the preservation of
their species is truly marvellous, and sufficiently accounts
for the difficulty of extermination and their apparently
sudden dispersion, especially in wet weather."

De Bary's observations on the germination of Uromyces
appendiculatus are interesting, inasmuch as they show that
the sporidia produce a mycelium, from which springs in
succession — 1st, spermogonia; 2dly, peridia, producing
chains of orange-coloured fruit, or, in other words, an
JEcidium; and 3dly, the original fruit of Uromyces, ac-
companied by the more simple fruit commonly called
uredo, and now called wedo-stylospores. The germination
of the fruit produced 'by the peridia, as well as that of
the uredo-stylospoies, produces, according to De Bary,
1st, Uredo-stylospoies, and 2d, the original Uromyces-
spores. Thus we see the Uromyces-spoies passing through
the generations of promyceliuin, sporidia, and mycelium —
the latter producing successively the two different products,
spermogonia and aBcidia, and ultimately the original fruit
of Uromyces, accompanied by the Uredo. The spermatia,
or contents of the spermogonia, never germinate ; but we
find the fruit of the secidia, and also of the Uredo, repro-
ducing first the Uredo itself, and subsequently the original
fruit of Uromyces. Other interesting points, noticed by
the same author, are, " that not only has each species of
parasite a certain special nutrient plant, but that in certain
Uredines with multiple fruit and alternate generations
each sort of reproductive organ buries its germ in a dif-
ierent nutrient plant ; and that the vegetation of the para-
site is the cause of the disease."
u2

292 THE MICROSCOPE.

De Bary has also carried out a series of experiments
which go far to satisfy him that the sporidia of Puccinia
qraminis germinate on the leaves of Rerberis, and that the
^Ecidium of the JBerberis (Plate I. No. 22) is a stage in the
cycle of development of Puccinia. Thus, whilst in most
Uredines the entire development is carried out upon one
and the same nutrient plant, the alternate generations in
Puccinia graminis require a change of host. This is a
state of things well understood now in the animal kingdom
in the TaBniae and Trematoda, but Puccinia graminis is,
we believe, the first of the parasitic fungi in which it has
been particularly ascertained. Another point of interest
is a confirmation of the supposed injurious effect of the
proximity of Berberis to corn, which has been denied.
De Bary further shows that Mucor mucedo (the common
mould) has three, if not four, different forms of fruit ; and
that the mould called Thamnidium by Link, or Ascophora
degans by Corda, and the mould described by Berkeley as
Botrytis Jonesii, and made into a new genus by Fresenius,
under the name of Chcetocladium, are only varieties of the
fruit of Mucor mucedo. Also that yeast, Achyla, Sapro-
legnia, and Entomophthora or JEmpusa, are identically the
same as Mucor mucedo, consequently that a large reduction
is needed in the genera of the mucorini.

The main interest, however, of De Bary's paper on the
fructification of the Ascomycetes, consists in observations
on Erysiphe Gichoracearum, &c., in which the author
traces the origin of the perithecium, from its earliest state
up to the formation of the single ascus and spores. He
notices two cells as being always present and visible from
the earliest period, one of which he conjectures may be
the female, and the other the antheridium or male organ.
He says that the cell, by the division of which the ascus
and its coating are formed, only develops itself when it
has been in contact with the antheridium ; and he con-
eiders it very probab'le that impregration is effected "by
such contact, and that the perithecium of Erysiphe (ex-
cepting the outer wall) is the product of such impreg
nation.

De Bary's paper or parasitic fungi was, it appears,
undertaken with a view to contribute to the solution of

PARASITIC FUNGI. 29 J

the question as to their origin ; and he concludes that
endophytes are not produced from the metamorphosed
substance of diseased plants, but that they originate from
germs which penetrate healthy plants and develop a
mycelium. In the course of his investigations he notices
the occurrence in the genus Cystopus of organs similar to
t'lose long since discovered by Tulasne in Peronospora,
which have been called Oogonia. He observes that rami-
fications perform the functions of antheridia, or male
organs ; and he proceeds to describe the production by the
oospores (or impregnated contents of the oogonia) of active
zoospores, similar to those produced by the ordinary spores
of Cystopus. Dr. De Bary states that these zoospores, after
remaining active for three or four hours, lose their cilia and
power of motion, assume a cellulose covering, and ger-
minate. He adds that the germ-filaments enter readily
by the stomates and leaves of the nutrient plant, but that
those filaments only become developed which enter the
stomates of cotyledons. In Peronospora the development
of the antheridia, oogonia, and oospores is said by De Bary
to be the same as in Cystopus ; and he gives particulars of
the mode of germination of the conidia, and remarks on
the growth of the parasite, which will be more profitably
studied in the paper itself.

Parasitic fungi, vegetable blights as they are commonly
called, have of late years become objects of earnest atten-
tion, on account both of the enormous damage done to our
growing crops, and also of the many curious facts in their
history which have been brought to light. Corn-blights
consist chiefly of mildew, Puccinia, smut, bunt, rust, or
red-robin, Uredo. Oidium is a common mildew ; J3o-
trytis another; jEcidium forms a kind of rust infecting
pear-trees, the peridia of which form a very pretty object
for the microscope. (Plate I. 'No. 22, jEcidium Berberidis.)
In the full-grown condition they appear as 'little cups filled
with reddish-brown powder (spores), and may be detected in
their earliest stages by the deformities they produce in the,
structure of the plants infested, or by pale or reddish spots
on the green surface, arising from the presence of the
fungus beneath. They are common on the coltsfoot, the
berberry, gooseberry, buckthorn, nettle, &c. Plate I. No. 19,

294 THE MICROSCOPE.

represents a vertical section of a leaf of black-currant, in-
fested with. JEcidium grossularice ; its spermogonia are
seen on the surface, and the perithecia below. The family
Sphceriacei (No. 3, Plate I.), common enough on most
herbaceous stems, first seem to be little black spots, a;
when examined more closely are found to resemble little
brownish bottles, b, filled with rolls of spores. Other in-
structive specimens are —

Cystopus candidus (Uredo olim), Crucifer White-rust;
conidia equal, globose ; membrane equal, ochraceous ;
oospores sub-globose, epispore yellowish-brown, with irre-
gular obtuse warts : warts solid. On shepherd's purse,
cabbage, and other Cruciferse : receptacle consisting of
thick branched threads ; conidia concatenate, at length
separating ; oospores deeply seated on the mycelium. —
Phyllactinia guttata (Olim Erysiphe). Plate I. No. 9.
Hazel Blight ; amphigenous ; mycelium web-like, often
evanescent; conceptacles large, scattered, hemispherical,
at length depressed; appendages hyaline, rigid, simple;
sporangia 4-20, containing 2-4 spores. On leaves of haw-
thorn, hazel, ash, elm, -&c. — Aregma (Phragmidium) bul-
bosum. Plate I. No. 20. Bramble Brand; hypogynous,
with a dull red stain on the upper surface; spores in
large tufts, 4-septate, terminal joint apiculate; peduncles
incrassated, and bulbous at the base. — Puccinia variabilis,
Variable Brand ; sori amphigenous, minute, roundish, sur-
rounded by the ruptured epidermis, nearly black ; spores
variable, obtuse, cells often subdivided ; peduncle very
short. On leaves of dandelion. — Puccinia buxi, Box Brand.
Plate I. No. 17. Sori sub-rotund, convex, and scattered;
spores brown, oblong, rather strongly constricted, lower
cell slightly attenuated; peduncle very long. On both
surfaces of box leaves : spores uniseptate, supported on a
distinct peduncle. Plate I. No. 18. — Trichobasis (Uredo
olim) senecionis, Groundsel- rust ; spots obliterated ; sori
solitary or regularly crowded ; sub-rotund and oval, on the
under surface, surrounded by the ruptured epidermis;
spores sub-globose, orange. On various species of groundsel :
spores free ; attached at first to a short peduncle, which
at length falls away.

It appears that at particular periods of the year the

PARASITIC FUNGI. 295

atmosphere is, so to speak, more fully charged with, the
various spores of fungi than it is at others. The spores of
the moulds aspergillus, penicillium, and puccinia are per-
haps the most widely distributed bodies, and towards the
end of the hot weather, or about autumn time, they are
very abundant. Among those who have taken them at this
period of the year, we must ever associate the name of the
Eev. Lord Godolphin Osborne, who first experimented in
this direction during the cholera visitation of 1854. He
exposed prepared slips of glass, slightly moistened with
glycerine, over cesspools, gully-holes, &c., near the dwell-
ings of those where the disease appeared, and caught
what he termed aerozoa — chiefly minute germs and spores
of fungi. A drawing made from one of these glasses
(Plate I. No. 13), exhibits spores almost identical with
those found on the human skin, &c.

From the year 1854 to the present time we have amused
ourselves by catching these floating atoms, and, so far as
we can judge, they are found everywhere, and in and on
every conceivable thing, if we only look close enough for
them. Even the open mouth is an excellent trap ; of
this there is ample evidence, since we find on the delicate
membrane lining the mouth of the sucking, crying infant,
and on the diphtheritic sore throat of the adult, the de-
structive plant Oidium albicans. The human or animal
stomach is invaded, and in a certain deranged condition we
find the Sarcina ventriculi, with its remarkable-looking
quaternate spores, its torulse, &c., seriously interfering with
the functions of this organ.1 Torula diabetica is another
of these destructive products found in the human bladder.

Fig. 158.— Sarcina ventriculi.

(1) What part do the fungi, or bacteria, play in the production of that fearful
scourge of the human race, cancer? is a question not unfrequently asked since

296 THE MICROSCOPE.

It is now more than a quarter of a century since Pro-
fessor Owen first pointed out the vegetable nature of a
diseased growth found in the lungs of a Flamingo he
was dissecting. Soon after, Bassi discovered the vege-
table character of a disease which caused great devas-
tation among silkworms ; and, about the same time.
Schonlein, of Berlin, was led to the detection of certain
cryptogamic vegetable formations in connexion with skin
diseases.

The Favus fungus is perhaps best known from its
having been the first to attract the attention of Schonlein.
It is commonly called cupped ringworm, or honeycomb
scall, but it is very rarely seen in this metropolis. The
crust is of a dingy yellow colour, and almost entirely
composed of the Acliorion, mixed with epithelial scales
and broken hairs. When the fungus once establishes
itself, so fearful are its ravages, that in a very short space
of time the whole of the cutaneous surface, with the ex-
ception of the palms of the hands and soles of the feet,
becomes covered with it. As the spores penetrate the
hair-follicles they destroy the sheaths of the hairs, which
shrivel up and lose their colouring matter, and then break
off, leaving the surface bald.

Upon comparing the fermentation of the achorion
fungus with that of good healthy yeast, it will be seen to
be almost identical. In the first place, it is as actively

in the first edition of this bookJ1854) we expressed a belief in "the fungoid
origin of cancer." Subsequent examinations of diseased structure more or less
tend to confirm this view ; it appears that in this disease we have superadded to
a fungoid growth " degraded germinal matter" — which, by its entrance into the
circulation, produces a ferment and blood poisoning. The circular animal cell
degenerates, is converted into the ovoid or elongated vegetable cell, and ulti-
mately the structure, or some organ it may be, is changed into that remarkable-
looking caudate body, the typical cancer cell. This in some respects bears the
most perfect resemblance to certain spores of fungi, and to the yeast torulse.
As might be expected, its form is modified and its character more or less
changed by the peculiar kind of nourishment and condensed tissue in which it
is deposited and grows ; its powers of growth are, so to speak, perverted and
degraded, and then, as we see in other instances, it soon obtains a power of in-
definite multiplication, and destroys, not only the vitality of the organ, but the
individual. M. Davaine believes he has traced splenic disease in sheep to the
entrance into the blood of bacterium-like bodies, and fungi ; a zymotic disease
is caused by the ferment, and by the rapid growth of the fungi the life of the
animal is quickly sacrificed to the destroyer.

To mount specimens of fungi, separate them, and add a drop or two of spirit:
when this lias evaporated, add a drop of glycerine solution, or balsam dissolved
in chloroform, and put on a glass cover. If the balsam renders the asci too
transparent, use gelatine : no cells are required.

YEAST DEVELOPMENT. 297

carried on by the former as by the latter. There is, how-
ever, just a slight difference in the size of the spores • or
cells (Plate I. Noa. 7, 8, 11), those from yeast being the
larger and more clearly spherical, with a greater number
of reproductive spores, — that is, cells with a single, clear,
nucleated cell in their interior, — while others are filled
with a darker granular matter, having only a slight ten-
dency to coalesce or become filamentous ; those from
achorion are for the most part ovoid, and very prone to
coalesce and produce elongated cells or torulas. With re-
ference to the slight difference in size, we must look upon
this as a matter of very little importance ; for to the pre-
sence of light in the one case, and its almost total exclu-
sion in the other, this difference, no doubt, is almost en-
tirely due. It would be more trustworthy if comparisons
of this kind could be made at the same stage of develop-
ment ; for be it remembered that yeast obtained from a
brewery is in a more favourable state, inasmuch as it is
stopped at a certain stage of growth or development, and
then set to begin its fermentation over again in fresh sup-
plies of a new pabulum, which give increased health and
vigour to the plant ; while, on the other hand, the
achorion, or Favus fungus, is obtained and used in an ex-
hausted state from an already ill-nourished or starved-out
soil. Neither can we attach much importance to differ-
ences in size and form of the spores, for even this occurs
in yeast ferment ; and although the ovoid is most fre-
quently seen in achorion, it is equally common to yeast
when exhausted. This is strikingly exhibited in Plate
I. No. 8, a drawing made from a drop of exhausted yeast
taken from porter • here we have oval and elongated cells
with torulaa. To ensure success in these and similar ex-
periments., the fungus or yeast should be left floating on
the surface of liquids ; the process is either carried on very
slowly, or is entirely arrested by submersion.

Turpin and others, in their experiments on yeast, noticed
that the cells become oval and bud out in about an hour after
being added to the wort (fig. 159) ; but this change depends
as much upon temperature and density of the solution as
upon the quality of the yeast. It is a well-ascertained
fact that when yeast is added to distillery wash, which is

298 THE MICROSCOPE.

worked at a higher temperature than brewers' wort, fer-
mentation commences earlier, and the yeast-cell grows to a
much larger size. It is, indeed, forced in this way much
as a plant in a hothouse is, and then obtains to greater
perfection in a shorter time. It will, however, be seen
that it sooner becomes exhausted ; and now, if we take a
portion of this yeast and add it to barley wort, and at the
same time keep it in a temperature of from 60° to 65°
Fahr., it ferments languidly, and small yeast-cells are the
product. If the yeast is allowed to stand in a warm
place for a few days, it partially recovers its activity, but
never quite. With such a yeast there is always a good
deal of torulae mixed up with the degenerated cells, and
sometimes a filamentous mass, which falls to the bottom of
the vessel ; from this stage it readily passes to that of
must and mildew, and then becomes a wasteful feeder or
destroyer.

With yeast already in a state of exhaustion, we have
seen a crop of fungus produced in the head of a strumous
boy, seven years of age, who was much out of health, and
had suffered from eczema of the eyelids, with impetigo.
On placing portions of the broken hairs on a glass slip,
and moistening with a drop of liquor potassse, spores and
torulas were seen in abundance; represented in Plate I.
No. 14.

In another experiment we took portions of penicillium
and aspergillus moulds, and added these to sweetwort,
and stood them by in a warm room. On the second
day afterwards in one of the solutions, and the third in
the other, fermentation had fairly set in ; the surface of
the solution was covered with a film, which proved to be
well-developed ovoid spores, filled with smaller granular
spores (conidia) : Plate I. No. 8. On the sixth day the
cells changed in form and were more spherical. Again
removing these to another supply of fresh wort, the results
obtained were quite characteristic of exhausted yeast
ferment.

Extreme simplicity of structure characterises all moulds
or mildews. Their reproductive organs are somewhat
more complex, and both in penicillium and aspergillus the
mycelium terminates in a club-shaped head, bearing upon

YEAST PLANT.

it smaller filaments with, small bead-like bodies upon the
apex, piled one npon the other, or, more properly speak-
ing, strung together; these, again, are surmounted by
larger spores of a discoid shape filled with, granular
matter, and others which are quite empty. Those of the
aspergillus are apparently without granular matter or
nuclei, and are more highly refractive. The puccinia are
club-shaped, the very rapid growth of the spores and
spawn of which appears to exert a specific and peculiarly
exhaustive action over the tissues of the plant on which it
feeds. Plate I. No. 12, represents a portion of the mould
taken from a saccharine solution.

The yeast plant, in its most perfect condition, is chiefly
made up of globular vesicles, measuring, when fully

grown, about the

of an inch in diameter. The

older cells are filled with granular or nucleated matter ;
the nucleus rapidly increases, and nearly fills up the parent
cell, which then becomes ovoid, and ultimately the young
cell buds out and is separated from the parent. Some-

Fig. 159.— A diagrammatic representation of the development of the Yeast Plant.

No 1 Fresh Yeast; No. 2, one hour after adding it to wort; No. 3, three
hours ; No. 4, eight hours ; No. 5, third day, after which jointed filaments
are produced.

times other and smaller ceils are formed within the young
one before it leaves the parent globule. This process goes

300

THE MICROSCOPE.

on most rapidly until the supply of food becomes ex-
hausted ; the vesicles, it would appear, derive their
nourishment by the process of osmose, sucking in, as it
were, certain portions of the organic fluid and chemically
decomposing it, appropriating a part of its nitrogen and
throwing off' the carbonic acid. If, however, it be placed

Fig. 160. — Fungoid growths.

1, Section from a Tomata, showing sporangise growing from cuticle. 2, A por-
tion of same, detached, to show the mode of budding out from the upper part
of a branch. 3, Vertical and lateral views of spores with oospores turned out.
6, 7, and 8, Different stages of growth of Mycoderma cerevlsice. 9, Torula
diabetica.

in any adverse condition, it becomes surrounded by layers
of condensed material, resulting from the death of the

MOULDS, ETC.

301

germinal matter ; ultimately a mere trace of life remains,
which, taking the form of an impalpable powder, is free to
be driven hither and thither with every breath of air.

From these facts we may conclude that it matters little
whether we take yeast, achorion, or penicillium spores;
the resultant is the same, and depends much more on the
food or nourishment supplied, whether the pabulum con-
tains more or less of a saccharine, albuminous, or nitro-
genous material, lactic acid, &c., together with light and
temperature ; whether we have a mould (green or blue),
an achorion, or yeast fungus produced. Diversity of form
in the cells, as well as quality and quantity of their
material contents, are certainly due to, and in a manner
regulated and controlled by that beautiful law of diffusion,
which admits, separates, sifts, and refines the coarser from

Fig. 161.— Fungi. (Magnified 200 diameters.)

1, Brachydadlum penicillatum, growing on the stem of a plant. 2, Asyergillus
glauciLs, growing on cheese, /fee. 3, Botrytis ; the common form of mould on
decaying vegetable substances. 4, Sphceria, fungi caught over a sewer (foul
air). 5, Fungi growing on a pumpkin. 6, Fungi caught in the air at the
time of the cholera visitation, 1854.

the finer, the lighter from the denser particles, through
the porous structure of the cell-wall.

302 THE MICROSCOPE.

We cannot conclude this brief notice of the fungi with-
out adding a few words upon that curious group of subter-
ranean plants, which instead of producing their spores at
the summit of a basidium, or extremity of a simple filament,
produces them in the interior of a vesicle or pouch, called
a theca or ascus. Of this species the best known example
is the truffle (Tuber tibarium).

It is, perhaps, not very generally known that the
curiously formed, irregular mass, so much esteemed for its
delicious taste, and sought after as a luxury, the truffle, is
in truth a species of mushroom ; more properly speaking, a
subterranean puff-ball, or fungus. Its existence, entirely
removed from the action of light, is an anomaly even
among plants of the fungus kind ; for light, although not
in a large degree necessary to the fungus, is almost
always indispensable to its full development. It would,
therefore, be most difficult to discover, if it were not for
a peculiar and penetrating odour, which dogs are taught
to recognise ; and by the aid of these useful animals its
presence is detected hidden beneath the soil.

Tulasne and others have pointed out that these fungi
present two essentially different types. In the one, Hy-
menogastrece, the internal fleshy mass presents a number of
irregular cavities, lined by a membrane analogous to that
which clothes the gills of the Agaric, and the superficial
cells produce at their free extremities three or four spores,
or seeds, which become detached, and eventually fill up
the cavities. The other type, Elaphemycce, Tuberacece,
comprising those of the truffle kind, and as may be sur-
mised by the scientific name assigned to them — Tuber
cibarium, — are plants characterised from the underground
root presenting a fleshy mass, the outer surface of which
constitutes the common envelope, peridium, while the
numerous narrow sinuous cavities are lined and in part
filled up by filamentous tissue, mingled with cells of a
peculiar form, and terminating in spores.

A section from, the fleshy-looking mass cut very thin
(Plate I. No. 2), and viewed under a power of 250
diameters, is found to be chiefly composed of cellular
substance, the interspaces of which are filled up by
jointed filaments, homologous to the mycelium or spawn

TRUFFLES. 303

of other fungi, — in the mushroom, as an example, it is the
mushroom spawn, — while the veins, the reproductive
parts, contain in their cellular tissue minute ovoid capsules,
with two or more globular yellowish seeds ; this curious
structure having all the parts of nutrition and reproduction
enclosed internally, instead of externally, as in other fungi.

Truffles are produced in this way : the mycelium quickly
decays and allows the fungoid body to grow on in an
isolated condition. About September the ground becomes
covered with numerous white cylindrical articulated fila-
ments, not visible singly to the unassisted eye, but by
their immense numbers and rapid growth readily seen,
and found traversing the soil in every direction. These
white flaxen threads are continuous with other flocculent
filaments of the same nature. In the young truffles the
external layer is gradually consolidated, and in a short
time the destruction of the flocculent filaments are com-
plete and lost in the young plant, which is soon isolated
in the soil, and then the outer or cortical coat hardens,
and ultimately has the appearance of a small nut. Thus,
like other fungi, truffles are reproduced by spores, which
give origin to filamentous mycelium and seed-vessels, the
source of numerous offspring. Groups of spores are pretty
objects ; their stellate appearance reminds one of the
Xanthidia3 ; the mass of the full-grown plant at particular
seasons is almost wholly made up of these bodies, which
are of a yellowish-brown colour.

In these plants we have a double system of laminated
filaments ; one set arising from the cortical tissue absorb-
ing the surrounding moisture and serving to transmit this
to the cells in which the spores are formed, being there-
fore the organs of nutrition ; the others white and opaque,
terminating externally also, but conveying air to all parts
of the body, and bringing the whole into contact with
sporigenous cells.

The spores are developed freely in the vesicular cells
destined to produce them. They are limited in number
in each vesicle; less than two is never seen in one vesicle;
the hexagonal basket-work arrangement of each seed ap-
pears to close with a lid, and ten or twelve short spines
project out from every point.

304: THE MICROSCOPE.

Beneath the external dark-coloured reticulated mem-
brane is a second integument, smooth and transparent,
easily separated by maceration, although it resists the
action of chemical agents, and is not coloured by iodine.
The simple cavity of the internal spore is filled with
minute granular particles and fatty globules, suspended
in a fluid probably albuminous, as well as the various
chemical salts found by Kiegel, and upon which its peculiar
flavour depends.

" Two new British fungi" are figured and described by
the Kev. M. J. Berkeley, in vol. xxv. p. 431, Linnean
Soc. Trans. Peziza pygmoea, Plate I. No. 4, is a remark-
ably interesting specimen of a genus which presents much
variety in form. The description given of it is, " that it is
about J inch high, the stem often splitting or branching
out into several divisions, each of which is terminated by
a minute cup, giving the plant the appearance of a Ditiola,
or a Tympanis. Each cup produces other smaller cups on
its surface ; the branched and young cups resemble the
genus Solenia: in a specimen found at Wimbledon, the
mass of secondary cups gave the plant almost the ap-
pearance of a small Gyromitra." The proliferous form is
shown at Plate I. No. 5. The colour of the mature plant
is a bright apricot, whitish and tormentose at the base of
the stem. Found in swampy places, rotten gorse, &c. at
Ascot, Wimbledon, &c. Peziza belongs to the Ascomycetous
fungi ; the genus contains numerous species, and many of
them are brightly coloured, as in the very pretty P. bicolor,
Plate I. No. 1. Tulasne says that some of them have a
secondary fructification, consisting of stylospores. They
are mostly found growing on trunks of trees, dead
wood, &c.

We now pass to the examination of Lichens ; in these
plants, as in the Fungi, the germination of the spore
consists in the emission of a hollow filament from some
part of its surface. This filament, which is simply an
extension of the spore-membrane, branches repeatedly,
and spreads over the surface on which the spore has beeu
sown ; at the same time it divides by numerous septa
•which occur at irregular intervals. By the intertwining
of the resultant ramifications, a stroma is formed, to which

LICHEXS. 305

the term hypothallus is applied, and which, constitutes the
vegetative system of the future lichen. So far the develop-
ment is the same as that of the fungi ; but at a longer or
shorter period after the formation of the hypothallus, we
may observe upon its surface a whitish layer of spheroidal
cellules, intimately united with each other as well as with
the filaments from which they take their origin. This
layer is the groundwork for a second formation of globular
cells, and these are only to be distinguished from the
first by the chlorophyll which they contain. They are
called gonidia, and are peculiar to Lichens. Such is the
formation of the most simply organized of the class, as the
Verrucarice, the receptacles (apothecia) of which closely
resemble those of a SpJweria, and are found upon the sur-
face of the hypothallus. In the more complicated foliaceous
Lichens, as Parmelia, the mature thallus is made up of two
kinds of tissues, the medullary and the cortical. The cor-
ticular portion forms ths layers, an inferior and superior,
and consists of thick-walled cells, closely adherent to
each other ; from the surface of the inferior layer are given
off numerous root-like appendages, on either side of which,
or rather embedded in its cortical substance, are the gonidia,
which form a green tissue. Of the spore-like organs,
spermatia and stylospores, there are three varieties, to
which the terms apothecia, spermogonia, and pyenides
have been applied. The most common form of the apo-
thecium is that of the disc, which may bo plane, convex,
or cup-shaped. This form is that which characterises the
Gymnocarpous Lichens. In the Angiocarpece the organ is
closed upwards, its superior surface becoming internal, so-
as to form a conceptacle like that of the Pyrenomy-
cetes; the form, however, of which is subject to much
variation.

The reproductive organs of Lichens, as in Fungi, are of
five kinds .— 1, Sporules, which are formed by the con-
struction and subsequent separation of the extremity of a
simple cylindrical filament ; 2, Spermatia with their sup-
porting pedicles ; 3, Stylospores with their styles ; 4,
Theca3 or asci ; 5, Basidia with their basidiospores. As
regards the complexity of their form and structure they
may be taken in the order in which they are here placed ;

30 b THE MICROSCOPE.

but, of the last-mentioned, it should be stated that they are
almost solely found in Fungi, which have really no other
reproductive organ. The spores present many points of dif-
ference, both in number and character, in different genera
and species, and for this reason are most interesting micro-
scopic objects. We would direct the reader's attention to
an interesting and valuable paper, from the pen of Dr.
Lauder Lindsay, in the Linnean Soc. Trans., vol. xxv.
p. 493, " On the Lichens of New Zealand" (the country
par excellence of certain Lichens). The paper is very
beautifully illustrated, showing chiefly the minute or
microscopic anatomy of the reproductive organs of the
species examined, especially the character of their spores
and spermatia.

A vertical section of Parmelia stellata is given in
Plate I. No. 26: it belongs to an extensive genus of
Gyninocarpous open-fruited Lichens, found growing upon
trees, palings, stones, walls, &c. The emission of the ripe
spores of the Lichens is a curious process, and not unlike
that which is seen to take place in some of the Fungi, as
in Pezizce, Sphcerice, &c. If a portion of the thallus be
moistened and placed in a common phial, with the apothecia
turned toward one side, in a few hours the opposite sur-
face of the glass will be found covered with patches of
spores, easily perceptible by their colour ; or if placed on
a moistened surface, and one of the usual glass slips laid
over it, the latter will be covered in a short time. As to
the powers of dissemination of these lowly organized
plants, Dr. Hicks's observations lead to the conclusion
that the gonidia of Lichens have greater powers in this
direction than has been generally supposed. He found
by placing a clean sheet of glass in the open air during a
fall of snow, and receiving the melting water in a tube or
bottle, that he obtained large quantities of what has been
looked upon as a "unicellular plant, commonly called
' Chlorococcus,' the cells of which may remain in a dor-
mant condition for a long time during cold weather,
but upon the return of warmth and moisture they begin
to increase by a process of subdivision, into two, four,
or eight portions, which soon assume a rounded form and
burst the parent cell-wall open; these secondary cells

LICHENS. 307

soon begin to divide and subdivide again, and tiis process
may go on without much variation even for years. The
phenomena described may also be watched by taking a
portion of the bark of a tree on which the Chlorococcus
has been deposited, and placing it under a glass to keep it
in a moderately moist atmosphere ; the only difference
being a change in colour, which is caused by the growth of
the fibres, as may be seen on microscopical examination.
And this," Dr. Hicks says, "is an instructive point, be-
cause it will be found that the colour varies notably accord-
ing to the Lichen prevalent in its neighbourhood." x He
thinks there can be no doubt that what has been
called Chlorococcus, is nothing more than the gonidia of
some Lichen ; and that under suitable conditions, chiefly
drought and warmth, the gonidium often throws out from
its external envelope, a small fibre, which, adhering and
branching, ultimately encases it and forms a " soridium."
' The soridia also remain dormant for a very long time,
and do not develop into thalli unless in a favourable
situation ; in some cases it may be for years. It will be
easily perceived that the soridium contains all the elements
of a thallus in miniature j in fact, a thallus does frequently
arise from one alone, yet, generally, the fibres of neigh-
bouring soridia interlace, and thus a thallus is matured
more rapidly. This is one of -the causes of the variation
of appearance, so common in many species of Lichens, and
is more readily seen towards the centre of the parent
thallus. "When the gonidia remain attached to the parent
thallus, the circumstances are, of course, generally very
favourable, and then they develop into secondary thalli,
attached more or less to the older one, which, in many
instances, decays beneath them. This process being con-
tinued year after year, gives an apparent thickness and
spongy appearance to the Lichen, and is the principal
cause of the various modifications in the external aspect
of the Lichens which caused them formerly to be mis-
classified." 2

(1) "For instance, where the yellow Parmelia is found, the Chlorococcus will
assume a yellow tinge in its soridial stage. Viewed by transmitted ligbt, they
are also opaque balls, with irregular outline."

(2) " Contributions to the Knowledge of the Development of the Gonidia of
Lichens." By J. Braxton Hicks, M.D. &c., Quarterly Journal of Microscopical
Science, vol. viii. 860, p. 239. j

x2

308

THE MICROSCOPE.

The little group of Hepaticce or Liverworts, which is
intermediate between Lichens and Mosses, presents nume-
rous objects of interest for the microscopist. These
plants are produced by dust-like grains called spores, and
minute cellular nodules called gemmce or buds. The
gemmse of Marchantia polymorphia are produced in
elegant membranous cups, with a toothed margin growing
on the upper surface of the frond, especially in very damp
court yards between the stones, or near running water,
where its lobed fronds are found covering extensive
surfaces of moist soil. At the period of fructification,
these fronds send up stalks, which carry at their summit
round shield-like or radiating discs. Besides which, it
generally bears upon its surface a number of little open
basket-shaped " conceptacles " which are borne upon the
surface of the frond, as in fig. 162, and may be found

in all stages of develop-
ment. When mature
it contains a number of
little green round or ob-
long discs, each com-
posed of two or more
layers of cells; the wall
is surmounted by a glis-
tening fringe of teeth,
whose edges are them-
selves regularly fringed
with minute outgrowths.
The cup seems to be
formed by a develop-
ment of the superior

epidermis, which is raised up and finally bursts and
spreads out, laying bare the seeds. The development of
this structure presents much analogy to that of the sori of
Ferns.

Mwcacece, Mosses, are an interesting form of vegetable
life, Linnaeus called them servi, — servants, or w®rkmen, —
as they seem to labour to produce vegetation in newly-
formed countries, where soil is not yet formed. They also
fill and consolidate bogs, and form rich mould for the
growth of larger plants, which they protect from the

Fig. 162,—Gemmiparous Conceptacle of Mar-
chantia polymorphia, expanding and rising
from the surface of a frond.

MOSSES. 309

winter's cold. The common, or Wall Screw-moss, fig.
U3, growing almost every where on old walls and other
brick-work, if examined closely, will be found to have
springing from its base numerous very slender stems, each

Fig. 163. — Screw Moss.

of which terminates in a dark brown case, which encloses

its fruit. If a patch of the moss is gathered when in

this state, and the green part of the base is put into water,

the threads of the fringe will uncoil and disentangle them-

selves in a most curious and beautiful manner ; from

this circumstance the plant takes its popular name of

Screw-moss. The leaf usually consists of either a single or

a double layer of cells, having flattened sides, by which

they adhere one to anotner. The

leaf-cells of the Sphagnum bog-

moss, fig. 179, exhibit a very curi-

ous departure from the ordinary

type ; for instead of being small and

polygonal, they are large and elon-

gated, and contain spiral fibres

loosely coiled in their interior. Mr.

Huxley pointed out, that the young

leaf does not differ from the older,

and that both are evolved by a

gradual process vt" differentiation"

Mosses, like liverworts, possess

bothantheridiaand pistillida, which

j • .1 P r.

are engaged in the process of fruc-
tification. The fertilized cell be-
comes gradually developed into a

]£- 164.— Mouth of Capsule of

Funaria, showing p£risiome.

conical body elevated

310

THE MICROSCOPE.

upon a foot stalk ; and this at length tears across the
walls of the flask-shaped body, carrying the higher
part upwards as a calyptra or hood upon its summit,
while the lower part remains to form a kind of collar
round the base. These spore-capsules are closed on their
summit by opercula or lids, and their mouths when
laid open are surrounded by a beautiful toothed fringe,
termed the peristome. This fringe is shown in fig. 164-
in mouth* of capsule of Funaria, with its peristome
in situ. The fringes of teeth are variously constructed,
and are of great service in discrimi-
nating the genera. In Neckera anti-
pyretica. fig. 165, the peristome is
double, the inner being composed of
teeth united by cross bars, forming
a very pretty trellis. The seed spores
are contained in the upper part of
the capsule, where they are clus-
tered round a central pillar, which
Fig. 165.— Double Peristome of is termed the columella : and at the

Neckera Aniipyretica. ,. c , , , . '

time of maturity, the interior of the
capsule is almost entirely occupied by spores.

It may here be mentioned, that all mosses and lichens
are more easily detached from the rocks and walls on
which they grow in frosty weather than at any other

season, and consequently
they are best studied in
winter. One of the com-
monest, Scale-moss, fig.
166 (Jungermannia biden-
fata), grows in patches,
in moist, shady situa-
tions, near the roots of
trees: see Plate II. Nos.

35 an(J 36< The see(J.

Fig. iM.-Scaie.Mo,,.

vessels are little oval bodies, which if gathered when
unexpanded, and brought into a warm room, burst
under the eye with violence the moment a drop of
water is applied to them, the valves of the vessel taking
the shape of a cross, and the seeds distending in a cloud
of brown dust. If this dust be examined with the

EQUISETACE^E.

311

microscope, a number of curious little chains, looking
something like the spring of a watch, will be found
among it, their use being to scatter the seeds j and if the
seed-vessel be examined while in
the act of bursting, these little
springs will be found twisting
and writhing about like a nest
of serpents. The undulating
Hair-moss (Polytriclium undu-
latum), fig. 167, is found on
moist shady banks, and in
woods and thickets. The seed-
vessel has a curious shaggy cap ;
but in its construction it is very
similar to that of the Screw-
moss, except that the fringe
around its opening is not twisted.

Eguisetacece. — The history of
the development of the Equise-
taceae (horse-tails) corresponds in
some respects with that of Ferns.
The spore-case of this solitary
genus is a most interesting object
under the microscope ; they have
apparently only one coat, for the
outer coat splits up into four
thread-like processes (elaters),
clubbed at their free ends.
"While the spore remains on the
sporange, these fibres are rolled round the spore, as seen
in fig. 170, G; but by gently shaking the fruit spike, the
spores are discharged, the coiled fibres immediately unroll,
as at P, their elasticity causing them to spring about in a
most curious manner. In a few minutes this motion appa-
rently ceases, but if breathed upon they again unroll and
dart about with wonderful elasticity.

Ferns. — In the Ferns we have an intermediate state,
somewhat between mosses and flowering plants; this
worJd not apply to the reproductive apparatus, which is
formed upon the same type as that of Mosses ; and,
furthermore, it is to be observed, that Ferns do not form

Fig. 167. — Hair-Moss in Fruit.

312

THE MICROSCOPE.

buds like other plants, but that their leaves, or fronds as
they are properly called, when they first appear, are rolled
up in a circinate form, and gradually unfold, as in fig. 168.

Fig. l6S.—Male Fern. A portion ol leaf with sorL

Ferns have no visible flowers; and their seeds are produced
in clusters, called sor.i, on the backs of the leaves. Ench
sorus contains numerous thecse, and each theca encloses
almost innumerable sporanges, with spores or seeds.
There are numerous kinds of ferns, all remarkable for some
interesting peculiarity; but it is their spores which are
chiefly sought for by the microscopist.

The first account of the true mode of development of
Ferns from their spores was published in 1844, by Nageli,
in a memoir entitled Moving Spiral Filaments (spermatic
filaments) in Ferns, wherein he announced the existence of
the bodies now called antheridia; but, mistaking the
archegonia for modified forms of the antheridia, he was
led away from a minute investigation of them. If he had
followed the development of the prothallia further, he
would have detected the relations of the nascent embryo,
which would probably have put him on the right track.
As it was, the remarkable discovery of the moving spiral
filaments occupied all his attention, and caused him to fall

FERNS. 313

into an error in certain important respects ; for example,
he has represented what is undoubtedly an archcgonium
filled with cellules, sperm-cells, which, he states, " emerged
from it as from the antheridia" This description is not
quite correct.

The reproduction of ferns had, until within the last few
years, been a vexed question among botanists. The riddle
was at length solved by the labours of Count Suminski,
who discovered that it is in the structures developed from
the spores in germination that the pistillidia and antheridia
of ferns are to be sought. The nature of the phenomena
by which the propagation of ferns is effected, is as follows.
In all the different species of ferns, the spores are contained
in brown dots, on lines collected on the under surfaces, or
along the edges of the fronds. Each of the spore-cases
is surrounded by an elastic
ring, which when the time
arrives for the spores to be
set free, makes an effort
to straighten itself, and in
so doing causes the spore-
case to which it is attached
to split open, and the spore
dust to be dispersed. Very
soon after these spores
have begun to germinate,
a flat plate-like expansion. v.

K , ,r, . ' Fig- 169.— Sorus of Deparia prolifcra.

somewhat resembling a

heart in form, shows itself. This expansion gradually
thickens, the tube from which it had sprung withering
away. So far, observes Mr. Henfrey, there is nothing very
remarkable in the development of these plants from their
spores, but the succeeding phenomena are exceedingly
curious. The main particulars are thus described by him :
" At an early period of the expanding growth of the leaf-
like product of the spore, termed the prothallium or
germ-frond, a number of little cellular bodies are found
projecting from the lower surface, which, if placed in
water when ripe, burst and discharge a quantity of micro-
scopic filaments, curled like a corkscrew, and furnished
with vibrating hair-like appendages, by the motion of

314 THE MICROSCOPE.

which they are rapidly propelled through the water. The
cellular bodies from which these are discharged are termed
the antheridia of the ferns, and are in their physiological
nature the representatives of the pollen of the flowering
plants. At a somewhat later period other cellular bodies
of larger size and more complex structure are found in
small numbers about the central part of the lower surface
of the prothallium on the thickened portion, situated
between the notch and the part where the radical filaments
arise. These, the pistillidia or archegonia of the ferns, are
analogous to the ovules or nascent seeds of flowering
plants, and contain, like them, a germinal vesicle, which
becomes fertilized through the agency of the spiral fila-
ments mentioned above, and is then gradually developed
into an embryo plant possessing a terminal bud. This
bud begins at once to. unfold and push out leaves with a
circulate vernation, which are of a very simple form at
first, and rise up to view beneath the prothallium, coming
out at the notch ; single fibrous roots are at the same
time sent down into the earth, the delicate expanded pro-
thallium withers away, and the foundation of the perfect
fern plant is laid. As the bud unfolds new leaves, the
root stock gradually acquires size and strength, and the
leaves become larger and more developed ; but it is a long
time before they assume the complete form characteristic
of the species."

These observations on Ferns have acquired vastly-
increased interest from the subsequent investigations of
Hoffmeister, Mettenius, and Suminski, on the allied Cryp-
togams, and, above all, from Hoffmeister's observations on
the processes occurring in the impregnation of the Coni-
fers. Not only have these investigations given us a satis-
factory interpretation of the archegonia and antheridia of
the Mosses and Liverworts, but they have made known
and co-ordinated the existence of analogous phenomena
in the Equisetacece, Lycopodiacece, and JRhizocctrpece, and
shown, moreover, that the bodies described by Mr. Brown
in the Conifers, under the name of " corpuscles," are
analogous to the archegonia of the Cryptogams ; so that a
link is hereby formed between these groups and the higher
flowering plants.

CHAEA. 015

The fruits, cr sori, of Ferns afford a very beautiful
variety of objects for the microscopist, and they possess an
advantage in requiring little or no preparation — nothing
more being necessary than that of taking a portion of a
frond, place it on a glass-slip under the microscope, and
throwing a condensed light upon it by the aid of the side
reflector. Even germination may be watched by simply
employing gentle heat and moisture. Take, as Hoff-
meister directs, a frond of a Fern whose fructification is
mature, lay it upon a piece of glass covered with fine
paper, and place the spore-bearing surface downwards
upon this j in the course of a day or two this paper will
be found to be covered with a fine brownish dust, which
consists of the liberated spores. These must be carefully
collected, and spread out upon the surface of a smooth
fragment of porous sandstone, and then- placed in a saucer,
the bottom of which is before covered with water ; a glass
tumbler being inverted over it to ensure the requisite supply
of moisture, and prevent rapid evaporization. Some of the
prothallia soon germinate ; if the cup be kept only slightly
moist for some time, and then suddenly watered, a large
number of antheridia and archegonia quickly open, and in a
few hours the surface of the larger prothallia will be covered
with moving antherozoids. If sections of these be made,
that is, the canals laid open, with a power of 200 or 300
diameters we may occasionally see antherozoids in motion,

CHAEAOEJ:. — Char a vulgar is is the plant in which the
important fact of vegetable circulation was discovered ;
Fig. 170, No. 1, is a portion of the plant of the natural
size. Every knot or joint may produce roots ; but it is
somewhat remarkable, that they always proceed from the
upper surface of the knot, atid then turn downwards ; so
that it is not peculiar that the first roots also should rise
upwards with the plant, come out of the "base of the
branch, and then turn downwards.

Mr. Varley noticed : — " The ripe globules spontaneously
open; the filaments expand and separate into clusters."
" These tube-like filaments are divided into numerous
compartments, in which are produced the most extra-
ordinary objects ever observed of vegetable origin, Fig.
170 A. At first they are seen agitating and moving in their

316

THE MICROSCOPE.

cells, where they are coiled up in their confined spaces,
every cell holding one. They gradually escape from their

Fig. 170.

1, Branch of Chara vulgaris. 2, Magnified view : the arrows indicate the course
taken by the granules in the tubes. 3, A limb of ditto, with buds at joints.
4, Portion of a leaf of Vallisneria spiralis, with cells and granules.

CHARA. 317

cells, and the whole field soon appears filled with life.
They are generally spirals of two or three coils, and
never become straight, though their agitated motion alters
their shape in some degree. At their foremost end is a
filament so fine as only to be seen by its motion, which is
very rapid and vibratory, running along it in waves : and
of a globule be forcibly opened before it is ripe, the fila-
ments will give little or no indication of life."

They swim about freely for a time, but gradually getting
slower and slower ; in about an hour they become quite
motionless. linger described these moving filaments in
Sphagnum (bog-moss) as Infusoria, under the name of

Fig. m.—AntkeridiaofC/iarafragilis, $c.

A, Portion of filament dividing into Phytozoa, " antkeroids." B, A valve, with
its group of antheridial filaments, composed of a series of cells, within each of
which an aniherozoid is formed, c, The escape of the mature antherozoids is
shown. D, Anther idium, or globule, developed at the base of nucule. E, ^M-
cule enlarged, and globule laid open by the separation of its valves. F, Spores
and elaters of Equisetum. G, Spores surrounded by elaters of Equisetum.

Spirillum ; and consequently they have been the cause of
much controversy. Schleiden, very properly denying their
animal nature, says : — " They are nothing more than fibre

318 THE MICROSCOPE.

in an early stage of development." The Characeae are all
aquatic plants of filamentous structure. Some authors
have divided the species into two genera, Nitella (simple
tubes) and Chara (cortical tubes). The circulation in
the ordinary tubes or cells consists in the movement
of the gelatinous protoplasmic sac, seen, as one mass, slowly
passing up one side, across the ends, and down the
opposite side, not perpendicularly, but in an oblique or
spiral course, as indicated in the figure. The Characcce
multiply by gemma3, produced at the articulations of
their stems.

Mr. H. J. Carter, in a paper of great interest, published
January, 1857, on the "Development of the Root-cell and
its Nucleus, in Chara Verticillata," describes a structureless
cell-wall, and a protoplasm composed of many organs.
" This," he says, " is surrounded by a cell, the ' proto-
plasmic sac/ which is divided into a fixed and rotatory
portion ; these again respectively enclose the nucleus
' granules,' and axial fluid ; while small portions of irre-
gular shaped granular bodies are common to both. If
we take the simple root-cell about the eighteenth hour
after germination, when it will be about half-an-inch long,
and 1 -600th of an inch broad, and place it in water between
two slips of glass for microscopic observation, under a
magnifying power of about four hundred diameters, we
shall find, if the circulation be active and the cell-wall
strong and healthy, that the nucleus, which is globular,
gradually becomes somewhat flattened, having several
hyaline vacuoles of different sizes ; the change goes on
gradually until it appears of more elongated form, growing
fainter on its outline, and then entirely disappears, leaving
a white space corresponding to its capsule or cell-wall,
with a faint remnant of some structure on the centre.
Subsequently, this space becomes filled up with the fixed
protoplasm, and after an hour or two the nucleus re-
appears a little behind its former situation, but now
reduced in size, and with its nucleolus double, instead of
single as before ; each nucleolus being about one-fourth
part as large as the old nucleolus, and hardly perceptible.
Meanwhile a faint septum is seen obliquely extending
across the fixed protoplasm, a little beyond the nucleus ;

DEVELOPMENT OP CHARA. 319

and if iodine be applied at this time, the division is seen
to be confined to the protoplasm, as the latter, from ccn-
traction, withdraws itself from each side of the line
where the septum appeared, and leaves a free space which
is bounded laterally by an uninterrupted continuation of
the protoplasmic sac. In this way changes go on until its
shape is altered and it becomes converted into a bunch
of rootlets. Thus the new cells are never entirely with-
out a nucleus, which would appear to exert some influ-
ence upon their development, for as soon as the only two
new cells which the root-cell gives off are formed, the old
nucleus becomes effete.

" Now as to the office of the nucleus, nothing more is
revealed to us in the development of the roots of Chara,
than that, so long as new cells are to be budded forth,
the nucleus continues in active operation, but when this
ceases it becomes effete ; while the rotation of the pro-
toplasm and subsequent enlargement of the cell, &c.,
which are much better exemplified in the plant-stem than
in the root-cell, go on after the nucleus ceases to exist.
Hence the development of the root-cells of Chara affords us
nothing positive respecting the functions of this organ ;
and therefore, if we wish to assign to it any uses in par-
ticular, they must be derived from analogy with some
organism in which there is a similar nucleus whose office is
known. If for this purpose we may be allowed to
compare the nucleus of Chara with that of the rhizo-
podous cell, which inhabits its protoplasm, we shall
find the two identical in elementary composition ; that
is, both consist at first of a ' nuclear utricle,' respec-
tively enclosing a structureless homogeneous nucleolus ; .
the latter, too, in both, is endowed with a low degree of
movement.

" After this, however, the nucleolus of the Rhizopod cell
becomes granular and opaque ; and when, under circum-
stances favourable for propagation, a new cell-wall is
formed around the nuclear utricle, — or this may be an
enlargement of the nuclear utricle itself, — I do not know
which j the granular substance of the nucleolus becomes
circumscribed, and shows that it is surrounded by a sphe-
rical, capsular cell ; the granules enlarge, separate, pass

320 THE MICROSCOPE.

through the spherical capsule into the cavity of the
nuclear utricle ; a mass of protoplasm makes its appearance,
and this divides up into monads, or, as I first called them,
' gonidia.' ]

"The movement of the rotating protoplasm in the
Characece is also very slow ; for, when it is viewed in the
long internodes of Nitella with a very low power, or even
with the naked eye, it seems hardly to move faster than
the foot of a Gasteropod; still there is no positive evidence
that it moves round the cell after the manner of the latter,
although it would appear to possess the power of move-
ment per sc. Hence the question remains undecided, viz.
whether it moves round the cell by itself, or by the aid of
cilia disposed on the inner surface of the protoplasmic sac,
in like manner to those which appear to exist in the
abdominal cavity of Vaginicola crystalline!,, and which have
been seen in Closterium lunula."2

The stems and arms of Chara are tubular, and entirely
covered with smaller tubes, the circulation can mostly be
observed in these, as shown at Fig. 170. Any ordinary cut-
ting to obtain sections would squeeze the tube flat, and spoil
it and the lining ; it is, therefore, better to avoid this, by
laying the Chara on smooth wood, just covered with
water; then, with a sharp knife, make suddenly a num-
ber of quick cuts across it, and so obtain the various
sections required. Wet a slip of glass, and turn the wood
over so as just to touch the water, and the sections
will fall from the wood on to the glass, ready for the
microscope.

"The Chara tribe is most abundant in still waters or
• ponds that never become quite dry ; if found in running
water, it is mostly met with out of the current, in holes or
side bays, where the stream has little effect, and never on
any prominence exposed to the current. If the Chara
could bear a current, its fruit would mostly be carried on
and be deposited in whorls ; but it sends out from its
variouo joints very long roots into the water, and these
would by agitation be destroyed, and then the plant

(1) Ann. and Mag. Nat. Hist. vol. xvii. 1856.

(2) In Plate I. No. 27, is represented the Moss gonida, assuming the amoeboid
form as described by Dr. Hieics in the Linnean Trans. 1862.

CHARA. 32 1

decays ; for although it may grow long before roots are
formed, yet when they are produced their destruction
involves the death of the plant. In order, therefore, to
preserve Chara, every care must be taken to imitate the
stillness of the water by never shaking or suddenly turning
the vessel. It is also important that the Chara should be
disturbed as little as possible ; and if requisite, it must
be done in the most gentle manner, as, for instance, in
cutting off a specimen, or causing it to descend in order
to keep the summit of the plant below the surface of the
water.

Similar care is requisite for Vallisneria; but the warmest
and most equal temperature is better suited to this plant.
It should be planted in the middle of the jar in about
two inches deep of mould, which has been closely
pressed ; over this place two or three handfuls of leaves,
then gently fill the jar with water. When the water
requires to be changed, a small portion is sufficient to
change at a time. It appears to thrive in proportion to
the frequency of the changing of the water, taking care
that the water added rather increases the temperature
than lowers it.

The natural habitat of the Frog-bit, another water-
plant of great interest, is on the surface of ponds and
ditches ; in the autumn its seeds fall, and become buried
in the mud at the bottom during the winter; in the
spring these plants rise to the surface, produce flowers,
and grow to their full size during summer. Chara may be
found in many places around London, the Isle of Dogs,
and in ditches near the Thames bank.

Anacharis alsinastrum. — This remarkable plant is so
unlike any other .water-plant, that it may be at once
recognised by its leaves growing in threes round a slender
stringy stem. The watermen on the river have already
named it " Water-thyme," from a faint general resemblance
which it bears to that plant. In 1851 the Anacharis
was noticed by Mr. Marshall and others in the river
at Ely, but not in great quantities. Next year it had
increased so much, that the river might be said to be full
of it.

The colour of the plant is deep green ; the leaves are
Y

322 THE MICROSCOPE.

nearly half an inch long, by an eighth wide, egg-shaped at
the point, and beset with minute teeth, which cause them to
cling. The stems are very brittle, so that whenever the
plant is disturbed, fragments are broken off. Its powers
of increase are prodigious, as every fragment is capable of
becoming an independent plant, producing roots and
stems, and extending itself indefinitely in every direction.
Most of our water-plants require, in order to their increase,
to be rooted in the bottom or sides of the river or drain
in which they are found; but this is independent altogether
of that condition, and actually grows as it travels slowly
down the stream after being cut. The specific gravity of
it is so nearly that of water, that it is more disposed to sink
than float. A small branch of the plant is represented,
with a Hydra attached to it, in a subsequent chapter.

Mr. Lawson pointed out the particular cells in which
the current or circulation will be most readily seen —
viz. the elongated cells around the margin of the leaf
and those of the midrib. On examining the leaf with
polarised light, these cells, and these alone, are found to
contain a large proportion of silica, and present a very
interesting appearance. A bright band of light encircles
the leaf, and traverses its centre. In fact, the leaf is set,
as it were, in a framework of silica. By boiling the leaf
for a short time in equal parts of nitric acid and water,
a portion of the vegetable tissue is destroyed, and the
silica rendered more distinct, without changing the form
of the leaf.1

It is necessary to make a thin section or strip from the
leaf of Vattisneria, for the purpose of exhibiting the circu-
lation in the cells, as shown in fig. 170, No. 4. Among the
cells granules, a few of a more transparent character than
the rest, may be seen, having a nucleolus within.

The phenomenon of cell rotation is seen in other plants
besides those growing in water. The leaf of the common
plantain or dock, Plantago, furnishes a good example; the
movement being seen both in the cells of the plant, and
hairs of the cuticle torn from the midribs. The Spider-
wort will be noticed further on.

(1) See also a paper in Vol. IV. Microscopical Journal of Science, on tl«> Ci-
eulatiou. in the Leaf of Anacharis, by Mr. F. H. Wenham.

STRUCTURE OF PLANTS, 323

Structure of Plants. — The development of cells in plants
takes place in all cases in essentially the same way,
but the form of the result is subject to a number of im-
portant modifications. Most elementary works on Botany
enter so fully into this interesting question, that it is quite
unnecessary to do more than refer very briefly to the
more important structural peculiarities of plants. Cell-
division, as we have seen, is the universal formative pro-
cess by which vegetative growth is effected, and free-cell-
formation occurs only in the production of cells connected
with reproduction. In the lower classes of plants, espe-
cially in aquatic genera, we can observe the process of cell-
division in all its details ; but in the higher, knowledge
of this kind is only accessible by dissection.

As long as the cell retains its primordial utricle, it is
capable of producing new cells, and organized forms of
assimilated matter, like starch, chlorophyll, &c. in its con-
tents. This is the case in all nascent tissues, but it ceases
to be so at various periods in different parts of the vege-
table organization. In all woody tissues, in all pitted and
spiral-fibrous cells it disappears early ; the secondary de-
posits of the ligneous character being formed apparently
from the watery cell-sap. In herbaceous organs, such as
leaves, in the cells of the cellular plants generally, the
primordial utricle remains. "This explains why the
power to form adventitious buds exists not only in the
cambrium layer of the higher plants, but, under certain
conditions, even in the leaves, and why germination or
propagation by little cellular bulbels, or isolated cells
detached from the vegetative organs, is so common among
the cellular plants, and in the Mosses and Liverworts,
where parenchymatous tissues so greatly predominate." —
(Henfrey.)

The tissues of plants, properly so called, consist of col-
lections of cells of uniform character, permanently combined
together by more or less complete union of their outer sur-
faces. Tissues are of many kinds, according to the form
of the cells, the character of the cell-membrane, and the
manner in which the cells are connected together. The
milk-vessels found in connexion with certain cells appear
to be formed out of the intercellular passages, and not by

Y2

324 . THE MICROSCOPE.

fusion of cells ; hence they do not constitute a true cellular
tissue.

Vascular tissue is formed by the fusion of perpendicular
rows of cells ; by the absorption of their contiguous walls
they become converted into continuous tubes of more or
less considerable length. Then we have a combination of
tissues destined for particular purposes in the economy of
the plant, divided into three primary systems — the Cellular,
the Fibro-vascular, and Cortical. The 1st, Cellular, forms
the great mass of the living structure of plants ; and it is
in this system that the vital processes of vegetation are
chiefly carried on. The 2d, Fibro-vascular, forms all the
woody structures, which in all cases are composed of a
quantity of conjoined portions of cellular and vascular
tissue arranged in a peculiar manner ; differing in their
modes of growth in different classes of plants, and which
in consequence present considerable differences in the
structure of their mature sterns. The 3d, Cortical, also
termed the epidermal, exists in the form of a simple flat
layer of cells united firmly together by their sides, and
forming a continuous coat over the surface of a plant.
Such a layer clothes all the organs of plants above the
Mosses, and, as stems grow older, the epidermal layer
gives place to the bark or rind. Stomata are orifices
between the meeting angles of the epidermal cells ; most
abundant usually on the lower surface of leaves, often
wanting on the upper surface. On the leaves of aquatic
plants they are only found on the upper surface, and are
absent where the leaf touches the water.

Hairs and scales of all kind depend on the development
of the epidermal cells. Simple hairs are merely single
epidermal cells produced in a tubular filament, and when
cell-multiplication occurs in them they present a number
of joints ; see hairs of nettle, fig. 188, No. 2. Thorns, such
as those of the rose, are aborted branches, in which the
cells become thickened by woody secondary deposits. In
leathery or hard leaves, and in the thick tough leaves of
succulent plants, such as the aloes, the secondary layers
acquire great thickness. The aerial roots of the Orchi-
daceaa exhibit a curious structure, the growing extremities
beiug clothed by a whitish cellular tissue composed of several

FORMATION OF WOODY FIBRE. 325

layers of cells with a delicate spiral fibrous deposit on
their walls. This layer forms a kind of coat over the real
epidermis of the root, and is known by the name of the
Velamen radicum. The young shoots of Dicotyledonous
trees and shrubs are clothed with epidermis-like herbaceous
plants ; but, before the close of the past season of growth,
in most cases the green colour gives place to brown, which
is owing to the formation of a layer of cork from the outer
layers of cortical parenchyma. Cork is composed of
tubular thin-walled cells containing only air ; and some-
times these intercellular passages occupy a considerable
space, and communicate in all directions, forming a system
of air-spaces in the tissue. In addition there is the secre-
tory system, consisting of glands, simple and compound,,
milk-vessels, and canals filled with resins, oils, &c.

Much of the physiological history of plant life has yet
to be made out : the mode in which the circulation and
the formation of wood are carried on is by no means a
settled question. Mr. Herbert Spencer observes i1 — " That
the supposition that certain vessels and strings of partially
united cells, lined with spiral, annular, reticulated, or
other frameworks, are carriers of the plant juices, is
objected to on the ground that they often contain air;
as the pressure of air arrests the movements of blood
through arteries and veins, its presence on the ducts of
stems and patioles is assumed to unfit them as channels
for sap. On the other hand, that these structures have
a respiratory office, as some have thought, is certainly
not more tenable, since the presence of air in them
negatives the belief that their function is to distribute-
liquid. The presence of liquid in them equally nega-
tives the belief that their function is to distribute air.
!N"or can any better defence be made for the hypothesis
which I find propounded, that these parts serve 'to
give strength to the parenchyma.' In the absence of any
feasible alternative, the hypothesis that these vessels are
distributors of sap claims reconsideration." To obtain data
for an opinion on this vexed question, Mr. Spencer insti-
tuted a series of experiments on the absorption of dyes by
plants. His first experiments were failures, and it was only

(1) Linnean Soc. Trans, vol. xxv. paf « 405.

326. THE MICROSCOPE.

after trying experiments with leaves of different ages and
different characters, and with undeveloped axes, as well as
with axes of special kinds, that it became manifest that
the appearances presented by ordinary stems, when thus
tested, are in a great degree misleading. " If an adult shoot
of a tree or shrub be cut off, and have its lower end placed
in an alumed decoction of logwood, or a dilute solution
of magenta,1 the dye will, in the course of a few hours,
ascend to a distance, varying according to the rate of eva-
poration from the leaves. On making longitudinal
sections of the part traversed by it, the dye is found to
have penetrated extensive tracts of the woody tissue ; and,
on making transverse sections, the openings of the ducts
appear as empty spaces in the midst of a deeply-coloured
prosenchyma. It would thus seem that the liquid is carried
up the denser parts of the vascular bundles, neglecting the
cambium layer, the central pith, and the spiral vessels of
the medullary sheath." This, however, is found to be only
partially true. " There are indications that while the layer
of pitted cells next the cambium has served as a channel
for part of the liquid, the rest has ascended the pitted
ducts, and oozed out of these into the prosenchyma around.
This is seen, if, instead of allowing the dye time for oozing
through the prosenchyma, the end of the shoot be just
dipped into the dye and taken out again, we find that,
although it has become diffused to some distance round
the ducts, it has left tracts of wood between the ducts
mentioned. Again, if we use one dye after another, a
shoot that has absorbed magenta for an hour and then
placed for five minutes in the logwood decoction, transverse
sections taken at a short distance from the end of the shoot,
show the mouths of the ducts surrounded by dark stains
in the midst of the much wider red stains. The behaviour
of these corresponds perfectly with the expectation that a
liquid will ascend capillary tubes in preference to simple
cellular tissue, or tissue not differentiated into continuous

(1) "These two dyes have affinities fbr different components of the tissues, and
may be advantageously used in different cases. Magenta is rapidly taken up by
woody matter and secondary deposits, while logwood colours the cell-membranes,
and takes but reluctantly to the substances seized by magenta. By trying both
of them on the same structure, we may guard ourselves against any error arising
from relative combination."

STRUCTURE OF PLANTS.

327

canals. Experiments with leaves bring out parallel facts ;
and this, then, is confirmed, that in ordinary stems the
staining of the wood by an ascending coloured liquid is
due, not to the passage of the coloured liquid up the sub-

Fig. 172.— Termination of Vascular System (after Spencer).

1. Absorbent organ from the leaf of Euphorbia neriifolia. The cluster of
fibrous cells forming one of the terminations of the vascular system is here
embedded in a solid parenchyma.

2. A structure of analogous kind from the leaf of Ficus elastica. Here the
expanded terminations of the vessels are embedded in the network paren-
chyma, the cells of which unite to form envelopes for them.

3. End view of an absorbent organ from the root of a turnip. It is taken
from the outermost layer of vessels. Its funnel-shaped interior is drawn as it
presents itself when looked at from the outside of this la»yer, its narrow end
being directed towards the centre of the turnip.

4. Shows on a larger scale one of these absorbents from the leaf of Panax
Lessonii. In this figure is clearly seen the way in which the cells of the net-
work parenchyma unite into a closely-fitting case for the spiral cells.

5. A less-developed absorbent, showing its approximate connexion with a
duct. In their simplest forms, these structures consist of only two fenestratod
cells, with their ends bent round so as to meet. Such types occur in the ceil-

'328 THE MICROSCOPE.

tral mass of the turnip, where the vascular system is relatively imperfect
Besides the comparatively regular forms of these absorbents, there are forms
composed of amorphous masses of fenestrated cells. It should be added that
both the regular and irregular kinds are very variable in their numbers : in
some turnips they are abundant, and in others scarcely to be found. Possibly
their presence depends on the age of the turnip.

6. Represents a much more massive absorbent from the same leaf, the sur-
rounding tissues being omitted.

7. Similarly represents, without its sheath, an absorbent from the leaf of
Clusia flava.

8. A longitudinal section through the axis of another such organ, showing its
annuli of reticulated cells when cut through. The cellular tissue which fills
the interior is supposed to be removed.

stance of the wood, but to the permeability of its ducts
and such of its pitted cells as are united into regular
canals ; and the facts showing this at the same time in-
dicate with tolerable clearness the process by which wood
is formed, for what in these cases is seen to take place
with dye may be fairly presumed to take place with sap."

Taking it, then, as a fact that the vessels and ducts are
the channels through which the sap is distributed, the
varying permeability of their walls, and consequent for-
mation of wood, is due to the exposure of the plant
to intermittent mechanical strains, actual or potential, or
both, in this way. "If a trunk, a bough, shoot, or a
petule is bent by a gust of wind, the substance of its
convex side is subject to longitudinal tension, the substance
of its concave side being at the same time compressed.
This is the primary mechanical effect. The secondary is
when the tissues of the convex side are stretched, they
also produce lateral compression of them. In short, that
" the formation of wood is due to intermittent transverse
strains, such as are produced in the aerial parts of upright
plants by the action of the wind." Thus the subject is
most ingeniously worked out, and the results of many
very interesting and instructive experiments are recorded
by the author of the paper.

"In the course of experiments on the absorption of
dyes by leaves, it happened that, in making sections
parallel to the plane of a leaf, with the view of separating
its middle layer, containing the vessels, I came upon some
structures that were new to me. These structures, where
they are present, form the terminations of the vascular
system. They are masses of irregular and imperfectly
united fibrous cells, such as those out of which vessels

STRUCTURE OF PLANTS. 329

are developed ; and they are sometimes slender, sometimes
bulky — usually, however, being more or less club-shaped.
In transverse sections of leaves, their distinctive characters
are not shown ; they are taken for the smaller veins. It
is only by carefully slicing away the surface of a leaf,
until we come down to that part which contains them,
that we get any idea of their nature. Fig. 172, No. 1, repre-
sents a specimen taken from a leaf of. Euphorbia neriifolia.
Occupying one of the interspaces of the ultimate venous
network, it consists of a spirally-lined duct or set of
ducts, which connects with the neighbouring vein a
cluster of half-reticulated, half-scalariform cells. These
cells have projections, many of them tapering, which insert
themselves into the adjacent intercellular spaces, thus
producing an extensive surface of contact between the
organ and the embedding tissues. A further trait is, that
the ensheathing prosenchyma is either but little developed
or wholly absent ; and consequently this expanded vascular
structure, especially at its end, comes immediately in con-
tact with the tissues concerned in assimilation. The leaf
of Euphorbia neriifolia is a very fleshy one ; and in it
these organs are distributed through a compact, though
watery, cellular mass. But in any leaf, of the ordinary
type, which possesses them, they lie in the network of
parenchyma, composing its lower layer ; and wherever they
occur in this layer its cells unite to enclose them. This
arrangement is shown in No. 2, representing a sample
from the Caoutchouc-leaf as seen with the upper part of
its envelope removed ; and it is shown still more clearly
in a sample from the leaf of Panax Lessonii, No, 4.
Nos. 6 and 7 represent, without their sheaths, other such
organs from the leaves of Panax Lessonii and Clusia
jlava. Some relation seems to exist between their forms
and the thicknesses of the layers in which they lie.
Certain very thick leaves, such as those of Clusia Jlava,
have them less abundantly distributed than is usual, but
more massive. When the parenchyma is developed not
to so great an extreme, though still largely, as in the
leaves of Holly, Aucuba, Camellia, they are not so bulky ;
and in thinner leaves, like those of Privet, Elder, &c.,
they become longer and less conspicuously club-shaped.

330 THE MICROSCOPE.

" Some adaptations to their respective positions seem
implied by these modifications ; and we may naturally
expect that in many thin leaves these free ends, becoming
still narrower, lose the distinctive and suggestive characters
possessed by those shown in the drawings. Relations of
this kind are not regular, however. In various other
genera, members of which 1 have examined, as Rhus,
Viburnum, Griselinia, Brexia, Botryodendron, Pereskia,
the variations in the bulk and form of these structures are
not directly determined by the spaces which the leaves
allow; obviously there are other modifying causes. It
should be added that while these expanded free extre-
mities graduate into tapering free extremities, not differing
from ordinary vessels, they also pass insensibly into the
ordinary inosculations. Occasionally, along with numerous
free endings, there occur loops ; and from such loops there
are transitions to the ultimate meshes of the veins.

" These organs are by no means common to all leaves.
In many that afford ample spaces for them they are not to
be found. So far as I have observed, they are absent from
the thick leaves of plants which form very little wood.
In Sempervivum, in Echeveria, in Bryophyllum they do not
appear to exist ; and I have been unable to discern them
in Kalanchoe rotundifolia, in Kleinia ante-euphorbium, and
ficoides, in the several species of Crassula, and in other suc-
culent plants. It may be added that they are not absolutely
confined to leaves, but occur in stems that have assumed
the functions of leaves. At least I have found, in the
green parenchyma of Opuntia, organs that are analogous,
though much more rudely and irregularly formed. In
other parts, too, that have usurped the leaf-function, they
occur, as in the phyllodes of the Australian acacias.
These have them abundantly developed ; and it is interest-
ing to observe that here, where the two vertically-placed
surfaces of the flattened-out petiole are equally adapted to
the assimilative function, there exist two layers of. these
expanded vascular terminations, one applied to the inner
surface of each layer of parenchyma.

"Considering the structures and positions of these organs,
as well as the natures of the plants possessing them, may
we not form a shrewd suspicion respecting their function 1

STRUCTURE OF PLANTS. 331

la-it not probable that they facilitate absorption of the juices
carried back from the leaf for the nutrition of the stem
and roots ? They are admirably adapted for performing
this office. Their component fibrous cells, having angles
insinuated between the cells of the parenchyma, are shaped
just as they should be for taking up its contents, and the
absence of sheathing tissue between them and the paren-
chyma facilitates the passage of the elaborated liquids.
Moreover, there is the fact that they are allied to organs
which obviously have absorbent functions. I am indebted
to Dr. Hooker for pointing out the figures of two such
organs in the Icones Anatomicce of Link. One of them
is from the end of a dicotyledonous root-fibre, and the other
is from the prothallus of a young fern. In each case a
cluster of fibrous cells, seated at a place from which liquid
has to be drawn, is connected by vessels with the parts to
which liquid has been carried. I have met with another
such organ, more elaborately constructed, evidently adapted
to the same office, in the common turnip-root. As shown by
the end view and longitudinal section in Nos. 3, 5, and 8,
this organ consists of rings of fenestrated cells, arranged
with varying degrees of regularity into a funnel, ordinarily
having its apex directed towards the central mass of the
turnip, with which it has, in some cases at least, a traceable
connexion by a canal. Presenting as it does an external
porous surface terminating one of the branches of the vas-
cular system, each of these organs is well fitted for taking
up with rapidity the nutriment laid by in the turnip-root,
and used by the plant when it sends up its flower-stalk.
The cotyledons of young beans furnish other examples
of such structures, exactly in the places where, if they be
absorbents, we may expect to find them. Amid the
branchings and inosculations of the vascular layer running
through the mass of nutriment deposited in each coty-
ledon, there are found conspicuous free terminations that
are club-shaped, and which prove to be composed, like
those in leaves, of irregularly-formed and clustered fibrous
cells, some of them diverging from the plane of the vascular
layer, dipping down into the mass of starch and albumen
which the young plant has to utilize, and which these
structures can have no other function but to take up."

332

THE MICROSCOPE.

To return to cell- development ; we found the cell chang-
ing in its outward form, the transparent membranous cell
wall becoming thickened, and spontaneous fissure taking
place; and thus is formed a series of connected cells
variously modified and arranged, according to the conditions
under which they are developed and the functions which
they are destined to exercise. The typical form, as we have

b

Fig. 173. — o, elementary cells ; 6, branched cellular tissue.

before observed, of the vegetable cell is spheroidal ; but
when developed under pressure within walls, or denser
tissues, it takes other shapes ;
as the oblong, lobed, square,
prismatical, cylindrical, fusi-
form, muriform, stellate, fila-
mentous, &c. : and is then
termed Parenchyma, and the
cells woven together are called
cellular tissue. In pulpy fruits
the cells may be easily separated
one from the other : a thin trans-
verse section of a strawberry is
represented at fig. 188, No. 15 :
within the cells are smaller
cells, commonly known as the
pulp. Fig. 173, a, is the ele-
mentary form of oval cells or
„ ;h°ef £Sg£ Asides, passing on to the for-
nai shape of cells. ~ 2, A vertical mation of branched cellular

section of elongated cell. , . 7 -r> 111

tissue, b. Kemarkable speci-
mens of the filamentous tissue may be seen in fig. 188,
No. 19, the circular elongated cells from the Mushroom •
only another and more closely connected growth of muce-
dinous fungi, commonly called mushroom spawn.

Fig. 174.

CELLULAR TISSUE?.

333

Fig. 175.— Stellate tissue, from stem
of a Rush.

Fig. 175, in the stellate tissue cut from the stem of a
rush, we have the forma-
tive network dividing into
ducts for the purpose of
giving strength and light-
ness to the stem of the plant.
These ducts may undergo
other transformations; the
cell itself become gra-
dually changed into a
spiral continuous tube or
duct, as seen in fig. 198 ;
these are sometimes formed by the breaking down of the
partitions ; in the centre of which we may have a com-
pound spiral duct, resembling portions of tracheae from
the silkworm.

Another important change occurs in the original cell, —
it is that of its conversion into woody fibre. Common
woody fibre (Pleurenchyma)
has its sides free from de-
finite markings. In the
coniferous plants, the tubes
are furnished with circular
discs ; these discs are
thought to be contrivances
to enable the tubules of

the WOOdy tissues tO dis- Fig. 176.— A section of stem of Clematis,

charge their contents- from
one to the other, or into the
cellular spaces. Plants having aromatic secretions are
furnished with glands ; these form a series of interesting
objects, and such as the sage-leaf should be mounted as
opaque specimens. A large central gland is seen in a section
of a leaf from Ficus elastica, India-rubber-tree, fig. 177, No. 2.
Professor Quekett observes, " The nature of the pores, or
discs, in conifers, has long been a subject for controversy;
it is now certain that the bordered pores are not peculiar to
one fibre, but are formed between two contiguous to each
other, and always exist in greatest numbers on those sides
of the woody fibres parallel to the medullary rays. They
are hollow ; their shape biconvex ; and in their centre is

ivilh -pores, highly magnified, to show
the line which passes round them.

334

THE MICROSCOPE.

a small circular or oval spot, fig. 176 : the latter may
occur singly, or be crossed by another at right angle?,

2

J

Fig. 177.

1, Vertical section of root of Alder, with outer wall. 2, A vertical section of a
leaf of the India-rubber tree, exhibiting a central gland.

which gives the appearance of a cross, as in fig. 204, Nos. 3,
4, a vertical section of fossil wood, remarkable for having
three or four rows of woody tissue occupied by large pores
without central markings."

We now pass to the milk, lacticiferous ducts or tissue, —

the proper vessels of the old
writers. These ducts con-
vey a peculiar fluid, some-
times called latex, usually
turbid, and coloured red,
white, or yellow ; often,
however, colourless. It is
supposed they carry latex
to all the newly-formed
organs, which are nourished
by it. The fluid becomes
darker after being mounted for specimens to be viewed
under the microscope. This tissue is remarkable from its
resemblance to the earliest aggregation of cells, the yeast-
plant, and therefore has some claim to being considered
the stage of development preceding that of the reticu-

Fig. 178. —Lacticiferous tissue.

CELLULAR TISSUES.

335

lated ducts seen in fig. 178. In a section from tho
India-rubber-tree, fig. 177, No. 2, a network of these lac-
tiferous tubes •will be found filled with a brownish or

Fig. 179.

1, A portion of the leaf of Sphagnum, showing ducts, vascular tissue, and spiral
fibre in the interior of its cells. 2, Porous cells, from the testa of Gourd-
seed, communicating with each other, and resembling ducts.

granular matter ; that in fig. 178 is an enlarged view of
this tissue from the wood of an exogen, taken near the
root.

1, Eeticulated ducts.

Fig. 180.
2, A vertical section of Fern-root.

In many plants external to the cuticle, there exists a
very delicate transparent pellicle, without any decided
traces of organisation, though occasionally somewhat gra-
nular in appearance, and marked by lines that seem to
be impressions of the junction of the cells in contact with
each other. In nearly all plants, the cuticle is perforated

336

THE MICROSCOPE.

by minute openings termed Stomata, which are bordered by
cells of a peculiar form, distinct from those of the cuticle.
In Iris germanica, fig. 181, each surface has nearly 12,000

Fig. 181.

2.

1, Portion of a vertical section of the Leaf of the Iris: a, a, elongated cells of
the epidermis ; b, stomata cut through longitudinally ; c, c, cells of the
parenchyma; d,d, colourless tissue of the interior of the leaf. 2, Portion of
leaf of Iris germanica, torn from its surface ; a, elongated cells of the cuticle ;
b, cells of the stomata; c, cells of the parenchyma • d, impressions on the epi-
dermic cells ; e, lacunae in the parenchyma.

stomata in every square inch ; and in 'Yucca each surface
has about 40,000.

The structure of the leaf of the common Iris shows
a central portion, formed by thick- walled colourless tissue,
very different from ordinary leaf-cells or from woody fibre.

Fig. 182. —A portion of the epidermis of the Sugar-cane, showing Ihe two kinds oj
cells of which it is composed. (Magnified 200 diameters.)

CELLULAR TISSUE. 337

Variously-cut sections of leaves should be made, and slices
taken parallel to the surfaces at different distances, for the
purpose of microscopic examination.

Among the cell-contents of some plants, are beautiful
crystals called Raphides : the term is derived from pcu^is,
a needle, from the resemblance of the crystal to a needle.
They are composed of the phosphate and oxalate of lime ;
there is a difference of opinion as to their use in the
economy of the plant.

Mr. Gulliver has insisted upon the value of Eaphides
as characteristic points in many families of plants.

He observes that doubts as to the value of raphides as
natural characters and as to their importance in the vege-
table economy at all will be entertained by those who do
not clearly distinguish between raphides and sphaBraphides.
Schleiden asserts that the "needle-formed crystals, in
bundles of from twenty to thirty in a cell, are present in
almost all plants," and "that inorganic crystals are rarely
met with in cells in a full state of vitality."

He further states that so really practical is the presence
or absence of raphides, that by noticing them he has been
able to pick out pots of seedling Onagraceas, which had
been accidentally mixed with pots of other seedlings of
the same age, and at that period of growth when no
botanical character before in use would have been so
readily sufficient for the diagnosis.

If we examine a portion of the layers of an onion, fig.
183, No. 1, or a thin section of the stem or root of the
garden rhubarb, fig. 183, No. 4, we shall find many cells
in which, either bundles of needle-shaped crystals, or
masses of a stellate form occur, not strictly raphides.

Raphides were first noticed by Malpighi in Opuntia.
and subsequently described by Jurine and Raspail.
According to the latter observer, the needle-shape or
acicular are composed of phosphate, and the stellate of
oxalate of lime. There are others having lime as a basis,
in combination with tartaric, malic, or citric acid. These
are easily destroyed by acetic acid, and are also very soluble
in many of the fluids employed in the conservation of ob-
jects; some of them are as large as the l-40th of an inch,
others are as small as the l-1000th. They occur in all

338

THE MICROSCOPE.

parts of the plant ; in the stem, bark, leaves, stipules,
petals, fruit, root, and even in the pollen, with some
exceptions. They are always situated in the interior
of cells, and not, as stated by Raspail and others, in the

rig. IBS.

1, A section from the outer layer of the bulb of an Onion, showing crystals of
carbonate of lime. 3, Cells of the Pear, showing Sclerogen, or gritty tissue.
4, Cells of garden Rhubarb, filled with raphides. 5, Cells from same, filled
with starch-grains.

intercellular passages.1 Some of the containing cells be-
come much elongated ; but still the cell- wall can be readily
traced. In some species of Aloe, as, for instance, Aloe
verrucosa, with the naked eye we are able to discern small
silky filaments: when magnified, they are found to be
bundles of the acicular form of raphides, which no doubt
act the part of a stay or prop to the internal soft pulp.

In portions of the cuticle of the medicinal squill —
Scilla maritima — several large cells may be observed, full
of bundles of needle-shaped crystal. These cells, however,
do not lie in the same plane as the smaller ones belonging
to the cuticle. In the cuticle of an onion every cell is oc-
cupied either by an octahedral or a prismatic crystal of
oxalate of lime : in some specimens the octahedral form
predominates ; but in others from the same plant the

(1) "As an exception, many years ago they were discovered in the interior of
the spiral vessels in the stem of the grape-vine ; but with some botanists this
vould not be considered as an exceptional case, the vessels being regarded as
'jlongated cells."— Quekett.

CRYSTALS IN PLANTS.

339

crystals will be principally prismatic, and are arranged as
if they were beginning to assume a stellate form. Some
plants, as many of the cactus
tribe, are made up almost
entirely of raphides. In
some instances every cell of
the cuticle contains a stel-
late mass of crystals ; in
others the whole interior is
full of them, rendering the
plant so exceedingly brittle,
that the least touch will
occasion a fracture; so much
so, that some specimens of
Cactus senilis, said to be a
thousand years old, which
were sent a few years since
to Kew from South America,
were obliged to be packed

, , • ,1 11 j.i5 Fig. 184 — Siliceous cuticle from under

in COtton, With all the Care surface of leaf of Deutzia scabra.

of the most delicate jewel-
lery, to preserve them during transport.

Raphides, of peculiar figure, are common in the bark of
many trees. In the Hiccory
(Carya alba) may be ob-
served masses of flattened
prisms having both extre-
mities pointed. In vertical
sections from the stem of
Elceagnus angustifolia, nu-
merous raphides of large size
are embedded in the pith.
Raphides are also found in
the bark of the apple-tree,
and in the testa of the seeds
of the elm ; every cell con-
tains two or more very
minute crystals.

In figs. 184 and 185 we

have other representations We.i95.-suiceotu cvtici* of Grau
of the crystalline structure

z 2

340

THE MICROSCOPE.

of plants, in sections taken from grass, and the leaf of
Deutzia scdbra. This insoluble material is called silica,
and is abundantly distributed throughout certain orders
of plants, leaving a skeleton after the soft vegetable
matters have been destroyed : masses of it, having the
appearance of irregularly-formed blackened glass, will
always be found after the burning of hay or straw ; which
is caused by the fusion of the silica contained in the
cuticle combining with the potash in the vegetable tissue,
thus forming a silicate of potash (glass). To display this
siliceous structure, it is necessary to cut very thin slices
from the cuticle, and mount them in fluid or Canada

In the Grammacece, especially the canes ; in the Equi-
setum hyemale, or Dutch rush ; in the husk of the rice,

wheat, and other grains, —
silica is abundantly found.
In the Pharus cristatus,
an exotic grass, fig. 185,
we hare beautifully-ar-
ranged masses of silica with
raphides. The leaves of
Deutzia, fig. 184 are re-
markable for their stel-
late hairs developed from
the cuticle, of both their
upper and under surfaces ;
forming most interesting
arid attractive objects when
examined under the micro-
scope with polarised light.
See Plate VIII. No. 173.

Silica is found in all Ru-
biacece; both in the stern
and leaves, and if present in sufficient thickness, depolarises
light. This is especially the case in the prickles, which
all these plants have on the margin of the leaves and the
angles of the stem. One of the order Composite, a plant
popularly known as the "sneeze wort," (Archillce ptarmica)
has a large amount of silica in the hairs found on the
double serratures of its leaves ; commonly said to be the

Fig. 186. -Portion of the huslc of Wheat,
showing siliceous crystals.

CELL-CONTENTS. — STARCH.

341

cause of its errhine properties when powdered and used as
snuff. It is in the underlying or true epidermis, that the
silica occurs. This membrane is permeable by fluids, not
by means of pores, but by endosmotic force.

The most generally-distributed and conspicuous of the
cell-contents is Starch; at
the same time it is one of
great value and interest, per-
forming a similar office in
the economy of plants as that
of fat in animals. It occurs
in all plants at some period of
their existence, and is the
chief and great mark of dis-
tinction between the vege-
table and animal kingdoms.
Its presence is detected by
testing with a solution of.
iodine, which changes it to
a characteristic blue or violet
colour.1 Being insoluble in

COld Water, it Can be readily Fig. IS?.— Section of a Cane : with cell-

washed away and separated SdfcjSSattSST1'""'
from other matters contained

in the cellular parts of full-grown plants. It is often
found in small granular masses in the interior of cells,
shown in fig. 183 from the garden-rhubarb. Starch-grains
are variable in size: the tous-les-mois, fig. 188, No. 5, are
very large ; in the potato, No. 14, they are smaller ; and
in rice, No. 6, they are very small indeed. Nearly all pre-
sent the appearance of concentric irregular circles ; and most
of the granules have a circular spot, termed the hilum,
around which a large number of curved lines arrange them-
selves : better seen under polarised light. Plate VIII. No. 167.
Leeuwenhoek, to whom we are indebted for the earliest
notice of starch-granules, enters with considerable minute-
ness into a description of those of several plants — such as
wheat, barley, rye, oats, peas, beans, kidney-beans, buck-
wheat, maize, and rice ; and veiy carefully describes
experiments made by him ia order to investigate the
structure of starch-granules. Dr. Reissek regards the

(1) This is not a test for starch when coml-ined with albuminous matters.

342 THE MICROSCOPE.

granule as a perfect cell, from the phenomena presented
during its decay or dissolution, when left for some time in
water. Schleiden and others, after examining its expan-
sion and alteration under the influence of heat and of
sulphuric acid, considered it to be a solid homogeneous
structure.

Professor Busk agrees with M. Martin in believing the
primary form of the starch-granule to be " a spherical or
ovate vesicle, the appearance of which under the micro-
scope, when submitted to the action of strong sulphuric
acid, conveys the idea of an unfolding of plaits or rugae,
which have, as it were, been tucked in towards the centre
of the starch-grain." 1 The mode of applying the concen-
trated sulphuric acid is thus described by Mr. Busk : — " A
small quantity of the starch to be examined is placed
upon a slip of glass, and covered with five or six drops of
water, in which it is well stirred about ; then with the
point of a slender glass-rod the smallest possible quantity
of solution of iodine is applied, which requires to be
quickly and well mixed with the starch and water; as
much of the latter as will must be allowed to drain off,
leaving the moistened starch behind, or a portion of it
may be removed by an inclination of the glass, before it is
covered with a piece of thin glass. The object must be
placed on the field of the microscope, and the J-inch
object-glass brought to a focus close to the upper edge of
the thin glass. With a slender glass-rod a small drop of
strong sulphuric acid must be carefully placed immediately
upon, or rather above the edge of the cover, great care
being necessary to prevent its running over. The acid
quickly insinuates itself between the glasses, and its course
may be traced by the rapid change in the appearance of
the starch-granules as it comes in contact with them.
The course of the acid is to be followed by moving the
object gently upwards ; and when, from its diffusion, the
re-agent begins to act slowly, the peculiar changes in the
starch- granules can be more readily witnessed. In pressing
or moving the glasses, the starch disc becomes torn, and
is then distinctly seen, especially in those coloured blue, to

(1) Professor G. Busk, F.R.S., on the Structure of the Starch-granule; Quar-
terly Journal of Microscopical Science, April, 1853.

CELL-CONTENTS STARCH.

343

consist of two layers, an upper and a lower one ; and the
collapsed vesicular bodies of an extremely fine but strong
and elastic membrane." Mr. Busk believes the hilum
to be a central opening into the interior of the ovate
vesicle.

16

1, Nucleated Cells. 2, Stinging-nettle Hairs, Urtica Dioica. 3, Ciliated spores
of Confervce. 4, Starch grains, broken by the application of heat. 5, Starch
from Tous-les-mois. 6. Starch from Bice. 7, Starch from Sago. 8, Imita-
tion Sago-starch. 9, Wheat-starch. 10, Rhubarb-starch, in isolated
cells. 11, Maize-starch. 12, Oat-starch. 13, Barley-starch. 14, Potato-
starch. 15, Section of Strawberry, cells ovoid, containing granular matter.
16, Section of Potato, with starch destroyed by fungoid disease. 17, Potato,
with nearly all starch-grains absent. 18, Section of Potato, cells filled with
healthy starch. (These starches are grouped for comparison.) 19, Mushroom
spawn, elongated cells.

Nitric acid communicates to wheat-starch a fine orange-
yellow colour; and recently-prepared tincture of guaiacum
gives a blue colour to the starch of good wheat-flour.

344 THE MICROSCOPE.

Pure wheat-flour is almost entirely dissolved in a strong
solution of potash, containing twelve per cent, of the alkali ;
but mineral substances used for the purpose of adultera-
tion remain undissolved.

Wheat-flour is frequently adulterated with various sub-
stances ; and in the detection of these adulterations, the
microscope, together with a slight knowledge of the action
of chemical re-agents, lends important assistance. It
enables us to judge of the size, shape, and markings on the
starch grains, and thereby to distinguish the granules of

Fig. 189. — Wheat-Flour Starch granuli-s, with a small portion of its cellulose.
(Magnified 420 diameters.)

one meal from that of another. In some cases the micro-
scopic examination is aided by an application of a solu-
tion of potash. Thus we may readily detect the mixture
of wheat-flour with either potato-starch, meal of the
pea or bean, by the addition of a little water to a small
quantity of the flour, then, by adding a few drops of
a solution of potash (made of the strength one part liquid
potash to three parts of water), the granules of the potato-

ADULTERATION OF WHEAT-FLOUR.

345

starch will immediately swell up, and acquire three or four
times their natural size ; while those of the wheat -starch
are scarcely affected by it ; if adulterated with pea or bean
meal, the hexagonal tissue of the seed is at the same time
rendered very obvious under the microscope. Polarised
light will be of use as an additional aid ; wheat-starch
presents a faint black cross proceeding from the central
hilum, whereas the starch of the oat shows nothing of
the kind.

Fig. 190.— Potato Starch-granules, sold under the name of British Arrow-root,
used to adulterate flour and bread. (Magnified 240 diameters.)

»

The diseases of wheat and corn are readily detected
under the microscope ; some of which will be seen to be
produced by a parasitic fungus, and by an animalcule re-
presented iii another place : all are more or less dangerous
when mixed with articles of food.

Adulteration of bread with boiled and mashed potatoes,
next to that by alum, is, perhaps, the one which is most
commonly resorted to. The great objection to the use of
potatoes in bread, is, that they are made to take the place

346 THE MICROSCOPE.

of an article very much more nutritious. This adulteration
can be instantly detected by means of the microscope.
The cells which contain the starch- corpuscles are, in the
potato, very large, fig. 190 ; in the raw potato they are
adherent to each other, and form a reticulated structure,
in the meshes of which the well-defined starch-granules
are clearly seen ; in the boiled potato, however, the cells
separate readily from each other, each forming a distinct
article : the starch-corpuscles are less distinct and of an
altered form.

Fig. 191.— Adulterated Cocoa, sold under the name of Homoeopathic Cocca.
(After H assail.)

aaa, granules and cells of cocoa; bbb, granules of Canna-starch, or Tous-lea-
mois ; c, granules of Tapioca-starch.

Adulteration with alum and "stuff." — This adulteration
is practised with a twofold object : first to render flour of
a bad colour and inferior quality white and equal, in
appearance only, to flour of superior quality ; and secondly
to enable the flour to retain a larger proportion of water,

ADULTERATION OP FOOD.

347

by which the loaf is made to -weigh heavier. By dissolving
out the alum in water and then re-crystallising it under
the microscope, this adulteration is readily detected.

Before leaving the subject of starch, allusion may be
made to the prevalent and destructive epidemic amongst
potatoes, which is a disease of the tuber, not of the haulm
or leaves. " Examined in an early stage, such potatoes
are found to be composed of cells of the usual size ; but
they contain little or no starch : this will be seen upon
reference to Nos. 16 and 17, fig. 188. Hence it may ba

Fig. 192. — Structure and Character of genuine Ground Coffee. (After Hassall.)

inferred, that the natural nutriment of the plant being
deficient, the haulm dies, the cells of the tuber soon turn
black and decompose ; and fungi developed as in most
other decaying vegetable substances.

" This will undoubtedly explain the most prominent
symptom of the potato-disease, the tendency to decom-
position ; and is a point in which the microscope confirms
the result of chemical experiment : for it has been found

348 THE MICROSCOPE.

that the diseased potatoes contain a larger proportion of
water than those that are healthy. A want of organizing
power is evidently the cause of this deficiency of starch ;
but we fear the microscope will never tell us in what the
want of this organising force consists." l

The adulteration of articles of food and drink has long
been a matter of uneasy interest, and of strong, though
vague, misgiving. Accum's Death in the Pot, between
thirty and forty years ago, awoke attention to the subject;
which has since been more or less accurately explored by

Fig. 193.— Sample of Coffee, adulterated with both Chicory and Roasted
Wheat. (AfterHassall.)

a a a, small fragments of coffee ; b b b, portions of chicory ; ccc, starch-granules
of wheat.

Mitchell, Normandy, Chevalier, Jules Gamier, and Harel;
and has at length derived a singularly lucid exposi-
tion from Dr. Hassall's researches, whose report of these
inquiries fills between 600 and 700 closely printed pages

(1) Professor Quekett's Histology of Vegetablts. We would refer the reader
to a curious work on Fungi, by Arimini, an Italian botanist, 1759.

ADULTERATION OF FOOD. 349

of a large octavo, replete with details of the fraudulent
contaminations commonly practised by the people's pur-
veyors, at the people's expense of health and pocket.1

" In nearly all articles," said Dr. Hassall, before a com-
mittee appointed by the House of Commons to inquire
into these adulterations, " whether food, drink, or drugs,
my opinion is that adulteration prevails. And many of
the substances employed in the adulterating process were
not only injurious to health, but even poisonous." The-
microscope was the effective instrument in the work of

Fig. 194.— Tea adulterated with foreign leaves. (After Hassall.)

a, upper surface of leaf ; b, lower surface, showing cells; c, chlorophyll cells;
rf, elongated cells found on the upper surface of the leaf in the course of the
veins ; e, spiral vessel; /, cell of turmeric ; g, fragment of Prussian blue; h
particles of white powder, probably China clay.

detection. Less than five years ago, it would, we are told,
have been impossible to detect the presence of chicory in
coffee : in fact, the opinion of three distinguished chemists
was actually quoted in the House of Commons to that effect ;

(1) Food and its Adulterations; comprising the Reports of the Analytical Sani-
tary Commission of the Lancet, for the years 1851 to 1854 inclusive. By Arthur
Hill Hassall, M.D.

350 THE MICROSCOPE.

whereas by the use of the microscope the differences of
structure in these two substances, as in many other cases,
can be promptly discerned. Out of thirty-four samples of
coffee purchased, chicory was discovered in thirty-one ;
chicory itself being also adulterated with all manner of
compounds. There is no falling back either upon tea or
chocolate ; for these seem rather worse used than coffee.
Tea is adulterated, not only here, but still more in China ;
while as to chocolate, the processes employed in corrupting
the manufacture are described as " diabolical." " It is

Fig. 195.

1, Radiating cells from the outer shell of the Ivory Nut. 2, Section of a Nut,
showing cells with small radiating pores.

often mixed with brick-dust to the amount of ten per
cent., ochre twelve per cent., and peroxide of iron twenty-
two per cent., and animal fats of the worst description. In
this country, cocoa is sold under the names of flake, rock,
granulated, soluble, dietetic, homoeopathic cocoa, &c., fig.
191. Such names are evidently employed to disguise the
fact that they are compounded of sugar, starch, and other
substances.

To return to the subject more immediately before us —
Some of the plants belonging to the Orchidese — Com-
melinece — particularly Tradescantia virginica (Spiderwort),
portions of the epidermis, and the jointed hairs of
the filament, form interesting microscopic objects. The
surface of the latter is marked with extremely fine longi-
tudinal parallel equidistant lines or striae, whose intervals
are equal, from about 15^00 to 2oj*0(y of an inch. It
might therefore in some cases be used as a micrometer or
test object. The nucleus of the joint or cell is very dis-
tinct as well as regular in form ; and by gentle pressure

CIRCULATION OF SAP IN PLANTS. 351

is easily separated entire from the joint. It then appears
to be exactly round, nearly lenticular, and its granular
matter is either held together by a coagulated pulp not
visibly granular, or, which may be considered equally pro-
bable, by an enveloping membrane. The analogy of this
nucleus to that existing in the various stages of develop-
ment of the colls in which the grains of pollen are formed
in the same species, is sufficiently obvious.

In the joint of the same, when immersed in water,
being at the same time freed from air, and consequently
made more transparent, a circulation of very minute
granular matter is visible. This requires at least a J power
to show it well. The motion of the granular fluid is
seldom in one uniform circle, but in several apparently
independent currents : and these again, though often
exactly longitudinal, and consequently in the direction of
the striae of the membrane, are not unfrequently observed
forming various angles with these striae. The smallest of
the currents appear to consist of a single series of granules.
The course of these currents seems often in some degree
affected by the nucleus, towards or from which many of
them occasionally tend or appear to proceed. They can
hardly, however, be said to be impeded by the nucleus,
for they are occasionally observed passing between its
surface and that of the cell ; a proof that this body does
not adhere to both sides of the cavity, and also that the
number and various directions of the currents cannot be
owing to partial obstructions arising from the unequal
compression of the cell.

Flower-buds. — "In the very early stage of the flower-
bud, while the anthera are yet colourless, their loculi
are filled with minute lenticular grains, having a trans-
parent flat limb, with a slightly convex and minutely
granular semi-opaque disc. This disc is the nucleus of
the cell, which probably loses its membrane or limb, and,
gradually enlarging, forms in the next stage a grain also
lenticular, and which is marked either with only one
transparent line dividing it into two equal parts, or with
two lines crossing at right angles, and dividing it into four
equal parts. In each of the quadratures a small nucleus
is visible ; and, even where one transparent line is only dis-

352 THE MICROSCOPE.

tinguishable, two nuclei may frequently be found in each
semicircular division. These nuclei may be readily ex-
tracted from the containing grain by pressure, and after
separation retain their original form. In the next stage,
the greater number of grains consist of the semicircular
divisions, naturally separated, but now containing only
one nucleus, which has gradually increased in size. In
the succeeding stage the grain apparently consists of the
nucleus of the former stage, but considerably enlarged,
and having an oval form, and a somewhat granular surface.
This oval grain, continuing to increase in size, and in the
thickening of its membrane, acquires a pale yellow colour;
and is now the perfect grain pollen."

In the whole tribe of Orchidefe an abundance of raphides
may be found in almost every part of the cellular tissue.
The crystals are usually cylindrical in form, and so arranged
as to disguise their true character, often causing them to
be overlooked : by making use of a dark-ground illumina-
tor, or polarised light, this is not likely to occur. The
cause of the disease known as " spot " in Orchids, of
which several kinds have been noticed by cultivators, has
been traced by Mr. Berkeley, in one instance, to the oc-
currence of a minute parasitic fungus, belonging to the
genus Leptothyrium. A description of the disease, with
illustrations, giving the general appearance of the diseased
leaves, and a magnified figure of the parasite, appears in
the 1st part of the new series of the Journal of the Horti-
cultural Society.

The Colouring matter of Flowers. — M. F. Hildebrands,
having carefully investigated the colouring matters of
flowers, has arrived at the following conclusion respecting
them, and their distribution in the tissue of the several
organs.

1. That the colour of flowers is in constant connexion
with the cell contents, never with the walls of cells.

2. Blue, violet, rose, and (if there be no yellow in the
flower) deep red are due, with little exception, to a cell-
fluid of corresponding colour.

3. Yellow, orange, and green, are usually associated
with solid, granular, or vesicular substances in the
cells.

WOODY TISSUE.

353

4. Brown or gray, and in many cases bright red and
orange (apparently uniform to the naked eye), are found
to be compounded of other colours, as yellow, green, or
orange with violet, or green and red; bright red and orange
in like manner of blue-red with yellow or orange.

5. Black, excepting in the bean, is due to a very deeply-
coloured cell-fluid.

6. All the cells of an organ are rarely uniformly
coloured.

7. The colour usually resides in one or in a few of the
outer layers of cells.

8. The coloured cells are but exceptionally covered by
a layer of uncoloured ones.

9. Combinations of colour are occasioned by diversely-
coloured matters in the same or in adjacent cells.

The Woody tissue of plants is not without its interest,
it consists of elongated transparent tubes of considerable
strength : some are almost entirely made up of this
tissue. It is by far the most useful, and supplies
material for our linen, cordage, paper, and many
other important articles in every
branch of art. This tissue, re-
markable for its toughness, is
termed fibre, the outer membrane
of which is usually structureless.
In Flax and Hemp, in which the
fibres are of great length, there
are traces of transverse markings,
and tubercles at short intervals.
In the rough condition, in which
it is imported into this country,
the fibres have been separated, to
a certain extent, by a process
termed hackling. It is once
more subjected to a repetition of
hackling, maceration, and bleach-
ing, before it can be reduced to the
white silky condition required by the spinner and weaver,
when it has the appearance of structureless tubes, fig. 197 B.
China-grass, New Zealand flax, and some other plants, pro-
duce a similar material, but are not so strong, in conse
A A

Pig. 196.

Fibres of Silk. B, Fibres
of Cotton.

354

THE MICROSCOPE.

quence of the outer membrane containing more lignine.
It is important to the manufacturer that he should be
able to determine the true character of some of the textures
of articles of clothing, and this he may readily do with the
microscope. In linen we find each component thread made
up of the longitudinal, rounded, unmarked fibres of flax ; but
if cotton has been mixed, we recognise a flattened, more or
!ess twisted band, as in fig. 1966, having a very striking
resemblance to hair, which, in
reality, it is ; since, in the condi-
tion of elongated cells, it lines the
inner surface of the pod. These,
again, should be contrasted with
the filaments of silk, fig. 196 A, and
also of wool, fig. 197 A. The latter
may be at once recognised by the
zigzag transverse markings on its
fibres. The surface of wool is
covered with these furrowed and
twisted fine cross lines, of which
there are from 2,000 to 4,000 in
an inch. On this structure de-
pends its felting property. In
judging of fleeces, attention should
be paid to the fineness and elasti-
city of the fibre, — the furrowed and scaly surface, as shown
by the microscope, — the quantity of fibre in a given surface,
the purity of the fleece, upon which depend the success of
the scouring and subsequent operations.

In the mummy-cloths of the Egyptians, flax only was
used, whereas the Peruvians used cotton alone. By recent
improvements introduced into the manufacturing pro-
cesses, flax has been reduced to the fineness and texture of
silk, and made to resemble other materials.

Silk is secreted from a pair of long tubes ending in
a pore of the under-lip of the silkworm. Each thread is
made of two filaments coming from these, and they are
glued together by a secretion from a small gland near.
The quality of the silk depends on the character and
difference of the two secretions.

All woody fibre is made up of elongated cells, generally

Fig. 197.

A., Wool of Sheep. B, Fila-
ments of Flax.

VASCULAR TISSUE.

355

more or less pointed at both extremities, and having their
walls strengthened by internal deposits. Occasionally,
however, the fibre is short, as in the Clematis, Elder, &c. ;
it is marked with pores or dots, from a deficiency of the
internal deposits at these points.
Vascular tissue consists of
(jells, more or less elongated,
joined end to end, or over-
lapping each other, in which
either a spiral fibre, or a mo-
dification of the same, has
been deposited ; hence, if the
spiral be perfect, it is called
a true spiral vessel ; if inter-
rupted, or the fibre breaks up
into rings, it is termed annu-
lar; if the rings are connected
together by branching fibres,
so that a network is pro-
duced, the vessel is called
reticulated; if the vertical
fibres are short, and equidis-
tant, the vessel is said to be
scalariform, from its resemblance to a ladder. Spiral
vessels have been also termed trachece, from their resem-
blance to the air-tubes of insects, as in fig. 198.

Under this head other membranaceous tubes are included,
in which the arrangement of the fibre has been consider-
ably modified in its deposition. Elongated tubes or ducts,
with porous walls, come under the head of vascular tissue ;
they somewhat differ from the spiral varieties, inasmuch
as they cannot be unrolled without breaking. It is a
curious fact, that mostly the spiral coils from right to
left ; and it has been suggested that the direction of the
fibre may determine that in which the plant coils round
an upright pole. The Hop has left-handed spirals, and is
a left-handed climber, which would therefore appear to
support this theory. The nature of the fibre, and the
development of the tissue, have been frequently the subject
of dispu-te between botanists.
The late Mr. Edwin Quekett gave much attention to this

AA2

Fig. 188.— Simple and compound
amral vessels.

356

THE MICROSCOPE.

subject ; and published an excellent paper in the Micro-
scopical Society's Transactions, 1840, which contains the
results of his observations.

1 Fig. 1&9.

I, Interior cast of the siliceous portion of spiral tubes of the Opuntia. 2, Vertical
section of Elm, showing spiral fibre.

In order to watch the development of the membranous
tubes of plants, no better example can be chosen than the

Fig. 200.

,j A transverse section of Taxus baccata (Yew), showing the woody fibre
2, Vertical section of the Yew, exhibiting pores and spira] fibres.

VASCULAK TISSUE. 357

young flower-stalk of the long-leek (Allium porrum), in
the state in which this vegetable is usually sent to market;
it is then most frequently found to be about an inch or

Fig. 201.

1 , Portion ol transverse section of stem of Cedar, showing pith, wood, and bark.
2. Portion of transverse section of stem of Clematis, showing medullary rays.

more in length, and from a quarter to half an inch in
diameter. This membrane occurs very low down amidst the
sheathing bases of the leaves; and from having to lengthen
to two or three feet, and containing large vessels, it forms
a very fit subject for ascertaining the early appearances of
the vascular tissue.

To examine the development of vessels, it is necessary
to be very careful in making dissections of the recent
plant; and it will be found useful to macerate the specimen
for a time in boiling water, which will render the tissues
more easily separable. When the examination is directed
in search of the larger vessels, it will be found that at this
early stage they present merely the form of very elongated
cells, arranged in distinct lines; amongst which some
vessels, especially the annular, will be found matured,
even before the cytoblasts have disappeared from the cells
of the surrounding tissue.

As development proceeds, the vessels rapidly increase
in length, till they arrive at perfection. No increase in
diameter is perceptible after their first formation. At
this period, in the living plant the young vessels appear
full of fluid, which is apparently, as remarked by Schleiden,
of a thick character, and which he has designated vege-
table jelly ; by boiling which, or by the addition of alcohol,
the contents, or at least the albuminous portion, become
coagulated. From this circumstance, every cell appears

358

THE MICROSCOPE.

to enclose another in a shrivelled condition ; this state is

sometimes so far extended, that a thick granular cord is

all that can be seen of the contents.

" The period of growth at which the laying down of

fibre commences, determines the distance between the
several coils; for instance, when it is
first formed, the coils are quite close,
scarcely any perceptible trace of mem-
brane existing between them. In the
annular vessel, the development of
the cell and the adherence of the
granules to each other are conducted
in the same manner ; the deposit
showing a tendency towards the spiral
direction, by the presence of a spire
connecting two rings, or by a ring
being developed in the middle of a
spiral fibre. The annular vessel is
the first observed in the youngest
parts of plants, and when found alone

Fig. 202. _,* section from indicates a low degree of organisation;
the stem of a coniferous as shown by its occurrence in Spha-
ffi&£5&5^ 9™*> Equuetum, and Lycopodmm,
the zones of annual which plants, in the ascending scale of

growth, annual rings. f. , . , , X ,

vegetation, are almost the first that
possess vascular tissue.

" It will be found that spiral fibre occurring with rings
marks a higher step in the scale of organising power; the
true spiral more so; and the reticulated and dotted mark
the highest ; this being the order in which these several
vessels are placed in herbaceous exogens proceeding from
within outwards, the differences of structure of the several
vessels being indices of the vital energy of the plant at
the several periods of its development. In those vessels
in which the annular or spiral character of the fibre is
departed from, some curious modifications of the above
process are to be observed, as in the reticulated vessels
met with in the common balsam (Salsamina hortensis).
The primary formation of fibre in these vessels :s marked
by the tendency of the granules to take a spiral course,
when it happens that some one of the granules becomes

VASCULAR TISSUE. 359

enlarged by the deposition of new matter around it. This
becomes a point originating another fibre or branch, which
becomes developed by the successive attraction of granules
into bead-like strings, taking a contrary direction to the
original fibre, forming a cross-bar, or ramifying, thereby
causing the appearance by which the vessel is recognised.

" In the exogenic vessel, the development of fibre proceeds
in the same manner as in the last example ; but the vessels
will be seen to be dotted with a central mark, usually of a
red colour, which, when viewed under high power, may be
thought to resemble a minute garnet set in the centre of
each dot. This red colour is owing to the dot being
somewhat hollowed or cupped, and the centre only thin
membrane. These vessels are best seen in the young
shoots of the Willow. In the endogenic vessel the con-
necting branches are given off beneath each other, so that
the dots, which are rounded, are arranged in longitudinal
rows ; but in the acrogenic, or scalariform, in which the
vessels are generally angular, and present distinct facets,
the branches come off in the same line, corresponding
generally to the angles of the vessel; the spaces left
between are linear instead of round."

Mr. E. Quekett affirms, in opposition to the views enter-
tained by Mirbel, Richard, and Bischoff, "that the dots
left in these several vessels are not holes, neither do they
consist of broken-up fibre, but are the membranous tubes,
unsupported by internal deposit ; and on account of the
extreme tenuity of the tissue, and the minute space between
the fibres, the light in its transmission becomes decomposed,
and appears of a greenish-red hue. The structure of the
dot is best seen by examining the broken edge of any such
vessels, when it will be found that the fracture has been
caused by the vessel giving way from one dot to another,
so that the torn edge of the membrane can be observed in
each dot."

PREPARATION OF VEGETABLE TISSUES.

The proper mode of preparing and preserving vegetable
tissues is a matter of some importance to the microscopist;
we therefore propose to add a few general directions for
the student's guidance.

360 THE MICROSCOPE.

Vegetable tissues are best prepared for the microscope
by making thin sections, either by maceration, by tearing be-
tween the thumb and the blade of a knife, or by dissection.

The spiral and other vessels of plants require to be
dissected out under a simple magnifying-glass. Take, for
instance, a piece of asparagus, and separate with the
needle-points the vessels, which require to be finished
under a magnifying-glass, in a single drop of distilled
water. When properly done, keep in spirits of wine and
water until mounted.

Vascular tissue requires both maceration and dissection
for its separation. The cuticle or external covering of
plants is a highly interesting structure ; it is best seen in the
pelargonium, oleander, &c. ; and may be mounted dry or
in Canada balsam.

Cellular tissue is best seen in fine sections from the pith
of elder, pulp of peach, pear, &c. The petals of flowers
are mostly composed of cellular tissue, and their brilliant
colours arise from the fluid contained within the cells. In
the petal of the anagallis, or scarlet chickweed, the spiral
vessels diverging from the base, and the singular cellules
which fringe the edge, are very interesting. 'The petal of
the geranium is one of the most beautiful, objects for
microscopic examination. The usual way of preparing it
is by immersing the leaf in sulphuric ether for a few
seconds, allowing the fluid to evaporate, and then putting-
it up dry. Dr. Inman of Liverpool suggests the following
method : " First peel off the epidermis from the petal, which
may be readily done by making an incision through it at
the end of the leaf, and then tearing it forwards by the
forceps. This is then arranged on a slip of glass, and
allowed to dry ; when dry, it adheres to the glass. Place
on it a little Canada balsam diluted with turpentine, and
boil it for an instant over the spirit-lamp ; this blisters it,
but does not remove the colour ; then cover it with a thin
slip of glass, to preserve it. Many cells will be found
showing the mamilla very distinctly, and the hairs sur-
rounding its base, each being slightly curved and pointed
towards the apex of the mamilla. It is these hairs and the
mamilla which give the velvety appearance to the petal."

Fibro-cellular tissue is found readily in Sphagnum or

PREPARATION OP TISSUES.

361

bog-moss, and in the elegant creeper Cobcea scandens. In
some orchidaceous plants the leaves are almost entirely
composed of it. A modification of this form of tissue is
found in the testa of some seeds, as in those of Salvia,
Collomia grandiflora, &c.

The curious and interesting sporules of ferns, when
•ripe, burst, and are dispersed to a distance; so that they
should be gathered before they come to maturity, and
mounted as opaque objects. The development of ferns
may be observed by placing the seeds in moistened flannel,
and keeping them at a warm temperature. At first a
single cellule is produced, then a second ; after this the
first divides into two, and then others follow ; by which a
lateral increase takes place.

Pollen-grains from most flowers are very interesting
objects; the darker kinds show best when mounted in
dark cells, and viewed as opaque ; objects more trans-

Fig. 203. —Pollen grains and seeds.

A, Seed of Clove-pink. B, Poppy seed. c. Pollen of Passion
cfcrulen). D, Pollen of Cobtsa sraitdcns.

)wer (Passiflora

parent should be mounted in fluid, to show internal
structure. The prettiest and most delicate forms are found
in Amarantacece, Cucurbitacece, Malvaceae, and Passiftorece ;
others are furnished from the Convolvulus, Geranium,
Campanula, Hollyhock, and some other plants. Tho
curious peculiarities of a few are shown in fig. 203.

362 THE MICROSCOPE.

Many of the smaller kinds of seeds will reward the
microscopist ; use only a low power ; that of Caryo-
phyllum (clove-pink), is regularly covered with curiously-
jagged divisions; every one of which has a small bright,
black hemispherical knob in its middle, represented in
fig. 160, A.

The seeds of the carrot are remarkably formed,'
having some resemblance to a star-fish, with its long
radiating processes. The seeds of umbelliferous plants
have peculiar receptacles for essential oil, in their coats,
termed vittce; various points of interest may be noted
as occurring in the iestce, envelopes of seeds, such as
the fibre-cells of Cobcea, and the stellate cells of the
Star-anise.

All plants are provided with hairs ; and a few, like
insects, with hairs of a defensive character. Those in
the Urtica dioica, commonly called the Stinging-nettle, are
elongated hairs, developed from the cuticle, usually of a
conical figure, and containing an irritating fluid ; in some
of them a circulation is visible : when examined under the
microscope, with a power of 100 diameters, they present
the appearance seen at fig. 188, No. 2. At No. 3, same
figure, are represented a few interesting ciliated spores
from Confervce.

The circulation of the fluid-contents of vegetable cells
may be examined at the same time with the Chlorophyll
globules, by selecting for the purpose the transparent
water-plants Char a, Nitella, Anacharis, and Vallisneria,
or the hairs of Groundsel and Tradescantia. The circula-
tion of the sap in plants growing in water is termed by
botanists Cydosis.

Fossil plants. — We detect in some of the primordial
fossils a noticeable likeness to families familiar to the
modern algaeologist. The cord-like plant, Chorda filium,
known as ' dead men's ropes,' from its proving fatal at
times to the too adventurous swimmer who gets entangled
in its thick wreaths, had a Lower Silurian representative,
known to the palaeontologist as the Palceochorda, or
ancient chorda, which existed, apparently, in two species, —
a larger and a smaller. The still better known Chondrus
crispus, the Irish moss, or Carrageen moss, has, likewise,

FOSSIL PLANTS.

363

The fucoids, or kelp-

its apparent, though more distant representative, in Chon-
dritis, a Lower Silurian alga, of which there seems to
exist at least three species,
weeds, appear to have also
their representatives in such
plants as Fucoides gracilis,
of the Lower Silurians of
the Malverns ; in short, the
Thallogens of the first ages
of vegetable life, seem to
have resembled, in the group,
and in at least their more
prominent features, iheAlgce
of the existing time. And
with the first indications of
land we pass direct from the
Thallogens to the Acrogens,
— from the sea-weeds to the
fern - allies. The Lycopo-
diacece, or club-mosses, bear
in the axils of their leaves
minute circular cases, which
form the receptacles of their
spore-like seeds. And when,
high in the Upper Silurian
system, and just when pre-
paring to quit it for the
Lower Old Red Sandstone,
we detect our earliest ter-
restrial organisms, we find that they are composed exclu-
sively of those little spore-receptacles.

" The existing plants whence we derive our analogies in
dealing with the vegetation of this early period, contribute
but little, if at all, to the support of animal life. The
ferns and their allies remain untouched by the grazing
animals. Our native club-mosses, though once used in
medicine, are positively deleterious ; horsetails (Equise-
tacece), though harmless, so abound in silex, which wrap
them round with a cuticle of stone, that they are rarely
cropped by cattle ; while the thickets of fern which cover
our hill and dell, and seem so temptingly rich and green

Fig. 204.

Woody fibre from the root of the
Elder, exhibiting small pores. 2,
"Woody fibre of fossil wood, showing
large pores. 3, Woody fibre of fossil
wood, bordered with pores and spiral
fibres. 4, Fossil wood taken from coal.

364

THE MICROSCOPE.

in their season, scarce support the existence of a single
creature; and remain untouched, in stem and leaf, from
their first appearance in spring, until they droop and
wither under the frosts of early winter.

" It is not until we enter into the earlier Tertiaries that
we succeed in detecting a true dicotyledonous tree ; on such
an amount of observation is this order determined, that
when Dr. John Wilson, the Parsee Missionary, submitted
to me specimens of fossil woods which he had picked up
in the Egyptian Desert, in order that, if possible, I might
determine their age, I told him that if they exhibited the
coniferous structure, they might belong to any geologic
period from the times of the Lower Old Ked Sandstone
downwards; but if they manifested in their tissue the
dicotyledonous character, they could not be older than the
times of the Tertiary. On submitting them in thin slices
to the microscope, they were found to exhibit the peculiar
dicotyledonous structure as strongly as the oak or chest-
nut. And Lieutenant Newbold's researches in the deposit
in which they occur has since demonstrated, on strati-
graphical evidence, that it belongs to the comparatively
modern formations of the Tertiary.

" The flora of the coal measures was the richest and most
luxuriant, in at least individual productions, with which
the fossil botanist has formed any acquaintance. Never
before or since did our planet bear so rank a vegetation as
that of which the numerous coal seams and inflammable
shales of the carboniferous period form but a portion of
the remains, — the portion spared, in the first instance, by
dissipation and decay, and in the second by the denuding
agencies. Almost all our coal, — the stored-up fuel of a
world, — forms but a comparatively small part of the pro-
duce of this wonderful flora. Yet, with all this singularly
profuse vegetation of the coal measures, it was a flora un-
fitted, apparently, for the support of either graminiverous
bird or herbivorous quadruped. Nor does the flora of the
Oolite seem to have been in the least suited for the pur-
poses of the shepherd or herdsman. Not until we enter
on the Tertiary periods do we find floras amid which man
might have profitably laboured : nay, there are whole orders
and families of plants, of the very first importance to man,

FOSSIL PLANTS. 365

which do not appear until late in even the Tertiary ages.
The true grasses scarce appear in the fossil state at all.
For the first time, amid the remains of a flora that seems
to have had its few flowers,— the Oolitic ages, — do we
detect, in a few broken fragments of the wings of butter-
flies, decided traces of the flower-sucking insects. Not,
however, until we enter into the great Tertiary division do
these become numerous. The first bee makes its appear-
ance in the amber of the Eocene, locked up hermetically
in its gem-like tomb, — an embalmed corpse in a crystal
coffin, — along with fragments of flower-bearing herbs and
trees. Her tomb remains to testify to the gradual fitting
up of our earth as a place of habitation for a creature
destined to seek delight for the mind and eye, as certainly
as for the proper senses, and in especial marks the intro-
duction of the stately forest trees, and the arrival of thf
delicious flowers." l

11 Sweet flowers ! what living eye hath viewed
Their myriads? endlessly renewed ;
Wherever strikes the sun's glad ray,
Where'er the subtile waters stray,
Wherever sportive zephyrs bend
Their course, or genial showers descend."

(1) Hugh Miller's Testimony of the Rock*.

CHAPTER II.

DIVISION OF ANIMAL KINGDOM.

PBOTOZOA— GfiEGABIN^I— EHIZOPODA— POLYCYSTINA— DIATOMACE^E— FOSSIL
INFUSORIA, SPONGID.E, HYDROZOA, VOBTICELL.E,
AOTINOZOA, BOTIFEE^E, POLYZOA. &c.

'INCE our very limited space forbade
more than a cursory glance at
the many and varied points of
beauty and arrangement dis-
played in every part of the vege-
table kingdom; so in the pre-
sent division is it necessary
to be equally brief in noticing
the wonders displayed by the
help of the microscope, in the
world of animal life. In the
course of remarks made upon
the early condition of vegetable

life, we drew attention to the difficulties presented in all
attempts to mark out the boundary line between vege-
tables and animals, and to define where the one ends,
and the other begins.

Upon reviewing the different characters by which
it has been attempted to distinguish the special subjects
of the botanist and zoologist, we find that animals and
plants are not two natural divisions, but are specialised
members of one and the same group of organised beings.
When a certain number of characters concur in the same
organism, its title to be regarded as a "plant," or an
" animal," may be readily recognised ; but there are very
numerous living beings, especially those that retain the

DIVISION OP ANIMAL KINGDOM. 367

form of nucleated cells, which manifest the common or-
ganic characters, but are without the true distinctive
superadditions of either kingdom.

The animal kingdom is conveniently arranged under the
following primary groups, sub-kingdoms, or departments :
— PROTOZOA, CCELENTERATA, ANNULOSA, MOLLUSCA, and
VERTEBRATA. These are again divided into classes, classes
into orders, orders into families, families into genera, and
genera into species. In the first-named department, the
Protozoa, is included a vast number of creatures of the
simplest organisation, classified as follows: — 1. Gregarinidse,
2. Rhizopoda, 3. Polycystina, 4. Thalassicollidse, 5. Spongidae,
6. Infusoria. It is not unusual to place Ehizopoda and
its typical form, Amoeba, in the front rank; and as the
presence of a mouth characterises the Infusoria, the re-
maining part of the Protozoa are frequently designated by
a collective name, Astomata.

The first-named, Gregarinidce, form a group of the very
simplest structural character, and any one of them, setting
minor modifications aside, may be said to consist of a sac,
composed of a more or less structureless membrane, con-
taining a soft semi-fluid substance, in the midst of which
is a circular vacuole or vesicle, having in its centre a more
solid particle or nucleus. Professor Huxley appends to
this description the obvious, but highly important re-
flection, that its statements are all true concerning the ova
of any of the animals much higher in the scale.1 The
Gregarinidce inhabit the bodies of other animals, and they
multiply by becoming encysted, and dividing into a multi-
tude of minute objects, called pseudo-navicellce, from their
resemblance in shape to the ship-like diatoms (naviculce).
When a young pseudo-navicella escapes, it behaves some-
what like an amoeba, and, if it chance to get swallowed
by an appropriate host, it grows into the parent form.
The whole life-history of these creatures is not known, as
they have not been traced into the exhibition of sexual
properties ; and it is therefore possible that their position
in the scale may not be exactly defined.

In the course of the numerous investigations made of
the flesh of animals dying during the year 1866 from the
cattle-plague, it was noticed that large quantities of pecu-
liar bodies infested the muscular structures, more especially

(1) Huxley's "Lectures on the Elements of Comparative Anatomy."

368 THE MICROSCOPE.

that of the heart, and it was supposed that these had
some share in the production of the disease ; but upon
making further investigations this has been found not to
be so, and since the same bodies are known to be gene-
rally distributed throughout the ultimate fibres of animals
dying from other diseases, the only interest that can
attach to the discovery is, that it promises to add some
valuable facts to our knowledge of the remarkable group
of Protozoa, the Gregarince. The Gregarines observed
in the flesh of oxen, and described by Dr. Beale,
have elongated spindle-shaped sacs, containing granular
reniform bodies arranged horizontally, and apparently
capable of multiplying by division. The investing
sac is covered with minute, motionless, hair-like bodies.
No nucleus is present in the sac; but the reniform
granular masses are stated by Dr. Cobbold to possess
nucleoli. The structure thus presented is not far removed
from that of many Gregarince, particularly of the larger
individuals occurring in the earthworm, though the hair
like processes sometimes observable on these are con-
sidered as extraneous by Dr. Leiberkiihn. The compacted
reniform masses may be considered as the results of a pro-
cess of segmentation, similar to that by which the pseudo-
naviculse are formed. The bodies thus described are by
no means peculiar to diseased cattle ; they are met
with in the healthy muscles of the ox, sheep, pig, deer,
rat, mouse, mole, and perhaps other animals. Gregarince,
in various stages, are represented in Plate III. figs. 53,
54, 55, and 56. Miescher, in 1843, described such bodies,
taken from the muscles of a mouse, and a very good
account of them, obtained from the muscles of a pig, is
given by Mr. Eainey, in the " Philosophical Transactions,"
for 1857, though he erroneously regarded them as the
young stage of cestoid entozoa. They have been described
under a variety of titles, such as worm-nodules, egg-sacs,
eggs of the fluke, young measles, " corpuscles produced by
muscular degeneration,' &c. When considered in con-
nexion with the minute cysts described by Gabler, Virchow,
and Dressier, from the human liver, they have an especial
interest ; and the observations of Lindernann on the psoro-
spermial sacs obtained from the hair of a peasant at

GREGARINA OF EARTHWORM. 369

Mschney-Nbvgorod, and in the kidneys of a patient who
died from Bright's disease, bear very strongly on the nature
of these bodies. The people of Novgorod are believed to
get these parasites from washing in water in which Grega-
rince abound.1 The most interesting inquiry which is
placed before us by these various facts is whether, as
Professor Leuckart has observed, "the psorospermiae "
(and we may add the " spurious entozoa " of cattle, and
even many so-called Gregarince) are to be considered as
the result of a special animal development, or whether
they are the final products of pathological metamor-
phosis.

It appears, from the reseaches of M. Clapar&de and
others, that some of the unilocular forms do present very
curious, elongated, and active forms, which, from their
movements and general appearance, might be mistaken for
nematodes. Dr. Joseph Leidy has, in the " Transactions
of the Philadelphia Society, 1853," denied the fact that
the Gregarince are unicellular animals, on the following
grounds : — In the examinations of some new species of
Gregarince which he has described, and also in the
G. Blotharum of Siehold, he discovered that the membrane
enclosing the granular mass of the posterior sac was
double. He observes : " Within the parietal tunic of the
posterior sac is a second membrane, which is transparent,
colourless, and marked by a most beautiful set of exceed-
ingly regular parallel longitudinal lines."

M. Leiberkiihn contributed a very elaborate paper
on the Gregarina of the earthworm. He does not express
any very decided opinion upon the two questions which
have been discussed by Leidy and Bruch, but devotes the
principal part of his memoir to the development and re-
production of the Gregarinse. With regard to the develop-
ment of Gregarinae into a filaria-like worm, which Bruch
thought probable, M. Leiberkiihn says but little, but,
nevertheless, has proved beyond doubt that the nematodes

(1) Many vague and improbable statements appeared at one time on a sup-
posed discovery of Gregarinss in the human hair. Upon a more careful exami-
nation being made by competent persons, the foreign body proved to be a well-
known vegetable fungus, often found associated with a disease, or dirty
neglect'ed state of the skin. It is very well known that Gregarines are never
found on free or exposed surfaces.

B B

370 THE MICROSCOPE,

of the earthworm are developed fro n eggs, whence they
emerge, not as Gregarinse, but as true nematodes. The
transformation of two Gregarinse, after a process of encysta-
tion, into navicula-like bodies, has been fully described by
Bruch ; but Leiberkiihn has more carefully illustrated the
changes that go on, and has endeavoured to trace the ex-
istence of the pseudo-naviculee after they have been
expelled from the cyst. In the perivisceral cavity of the
earthworm he found large numbers of small corpuscles,
exhibiting amceba-like movements, and likewise pseudo-
naviculse, containing granules, formed from encysted Gre-
garine. He imagines that these latter bodies burst, and
that their contained granules develope into the amoebiform
bodies which subsequently become Gregarinse. M. Lei-
berkiihn shortly afterwards published another paper, > in
which he adopts the same view, that the amcebiform
corpuscles of the' blood of fish are Gregarines. But few
physiologists will feel disposed to agree with him, in
considering these bodies as parasites.

Mr. E. Eay Lankester has contributed a valuable
and exhaustive paper on this subject ; l he observes : " I
have made careful examination of more than a hundred
worms, for the purpose of studying these questions, but
have succeeded in arriving at no other conclusion than
that certain forms of these may be the products of encysted
Gregarinse. The G. Lumbrici is one of those forms which
are unilocular, and are met with most frequently among
Annelids. It consists of a transparent contractile sac
(which has not hitherto been demonstrated to be formed
by more than a single membrane), enclosing the charac-
teristic granules and vesicle. The vesicle is not always very
distinct, and is sometimes altogether absent ; occasionally
it contains no granules, sometimes several, one of which
is generally nucleated. In some of these cysts a number
of nucleated cells may be seen, developing together from
the enclosed Gregarina, which gradually become fused
together and broken up, until the entire mass is converted
into these nucleated bodies, which are then evident in
different stages of development, assuming the form of a

(1) B. Ray Lankester, " On the Gregarinid® found in the common Earth-
worm."— Micros. Trans. voL iii. p. 83.

PROTOZOA. — GREGARIN^E. 371

double cone, like that presented by some species of
Diatomacese, whence their name pseudo-naviculae. At
length the cyst contains nothing but pseudo-naviculae,
sometimes enclosing granules, which gradually disappear,
and finally the cyst bursts. Encystation seems to take
place much more rarely among the bilocular forms of
Gregarinae than in the unilocular species found in the
earthworm and other Annelids."

In the Gregarince the food is taken in indiscriminately
at every point of the surface of the body by imbibition.
The food most likely is in the fluid state. In Spongilla,
also, this is probably the case. But it is generally agreed
that in Amoeba, Actinophrys, and agastric Infusoria, only
solid alimentary particles are taken as food. The simplest
animal is indeed far more complex than is implied in the
word unicellular, and it can be clearly proved that there
are few points in common between a simple cell and a so-
called unicellular protozoon. The system of contractile
vesicles and dependent sinuses, so general in the least
organized protozoon, is unknown in the history of cells.
Fluid absoption by the surface is the normal method of
feeding in these low types of animal life. This absorptive
faculty is an inherent property of the substance of which
they are composed. It attracts certain aliments, as gela-
tine attracts water. Tissue, distinguished by the same
character, prevails throughout the entire class of the Pro-
tozoa. Although the Gregarince mostly inhabit the intes-
tines of invertebrate animals, they are often found in the
alimentary canal of the Vertebrata. In this class they
appear to be represented, however, by very closely allied
organisms, the Psorospermice. Mu'ller gave this last-
mentioned name to some very singular minute bodies he
discovered within sacs upon the skin and gills, and in the
internal organs, of many fishes. These animals are gene-
rally of a cylindrical or somewhat elliptical form, although
sometimes a sort of head appears to be produced by the
constriction of the anterior extremity of the body, and
this head-like portion is occasionally furnished with a
curious soft process and lobes. They are very sluggish in
their movements, although a few possess true cilia. Their
curious mode of development, with other points in the

BB 2

372

THE MICROSCOPE.

history of these minute parasites, are well worthy of
investigation.

The Rhizopoda appear as creatures of a low type of
organization, and are considered, with the former, to hold
a medium state between animals and vegetables. Almost
all of them live in water ; it would be a fruitless search
to look for distinct internal organs, as the small bladder-
looking spaces enclosed within their substance, — believed
by Ehrenberg to be stomachs, — present only the appear-
ance of transparent gelatinous cells, or rather moving
spaces, within the sarcode envelope, and may be regarded
as the earliest dawn of a circulatory system.

The term Rhizopoda is derived from the Greek, and

Fig. 205.— Simple Rhizopods.

A, Difflugia proteiformis. B, Difflugia oUonga. c, D, Arcella acuminata and
dentata.

means " root-footed,"— the body is composed entirely of
gelatinous matter, sarcode, — motion being effected by the
extension of portions of the substance into processes,
which, as in fig. 205, is seen to partake of various forms.

Lobosa. — In the deposit formed at the bottom of fresh-
water ponds, we may often meet with a singular minute
gelatinous body, which constantly changes its form even
under our eyes ; and moves about by means of finger-like
processes, called pseudopodia, which it appears to have the
power of shooting out from any part of its substance.

PROTOZOA. — AMCEBA.

373

This shapeless mass is well known to microscopic observers
under the name of the Proteus (Amoeba diffiuens, fig. 206),
which, from the continual changes of shape it presents, is

Fig. 206.— Amaiba dij/luens, or Proteiis, in different forms.

honoured with the name of a fabled god, who could be
either animal, vegetable, or mineral in his nature. This
curious animal presents us with the essential characters of
the large class Rhizopoda, in their simplest form. It ap-
pears to be of an exceedingly voracious disposition, seizing
upon any minute aquatic animals or plants that may come
in its way, and appropriating them to the nutrition of its
own gelatinous body. The mode in which this tender
and apparently helpless creature effects this object is very
remarkable. The gelatinous matter of which it is com-
posed is capable, as we have seen, of extension in every
direction ; accordingly, when the A moeba meets with any-
thing that it regards as suitable for its support, the sub-
stance of the creature, as it were, grows round the object
until it is completely enclosed within its body. The sub-
stances swallowed (if such a term be admissible) by this
hungry mass of jelly are often so large, that the creature
itself only seems to form a sort of gelatinous coat enclosing
its prey.

Professor Ecker believes in an exact similarity of con-
tractile substance between that of the lower animal forms,
such as the Rhizopoda, and that observed in the Hydra.
He says : " The properties of this substance, in its simplest
form, are seen in the Amoeba, the body of which, as is
known, consists of a perfectly transparent albumen-like
homogeneous substance, in which nothing but a few
granules are imbedded, and which presents no trace of

374 THE MICROSCOPE.

further organization. This substance is in the highest
degree extensible and contractile ; and from the main mass
are given out, now in one part and now in another, per-
fectly transparent rounded processes, which glide over the
glass like oil, and are then again merged in a central mass.
There is no external membrane. In the body of the
Am&ba there occur, besides the granules, clear spaces with
fluid contents, which are sometimes unchangeable in
form, and sometimes exhibit rhythmical contractions."

Belonging to the family is the very curious Acineta of
Ehrenberg, Actinophrys sol, " sun-animalcule." This
creature consists of a jelly-like contractile substance, or
sarcode, with tentacular filaments radiating from the
central mass, in such a manner as to have suggested the
name for the species. It abounds in pools where Desmi-
diacece are found in many parts around London; they
are ravenous feeders, not only upon the Desmidiacece, but
also upon all kinds of minute spores and animalcules.
(Plate III. fig. 66.) It was on examining some beautiful
Desmidiacece that my attention was arrested by the
curious appearance of two or three very small Actinophrys
floating very lightly upon the surface of the water, in the
form of a ball, with their delicate tentacular filaments
perfectly erect all over their bodies ; in fact, they seemed
to be floating upon these delicate filaments.1

The most beautiful forms of the Rhizopoda are found
among those possessing a calcareous covering, as the
Polythalamia, Itosalina, Faujasina, &c. ; their systematic
arrangement is founded upon their shells, which exhibit
a very great diversity in form. Out of these forms, it
would appear that the labours of various naturalists in the
last hundred years have made us acquainted with nearly
2,000 recent and fossil Foraminifera ; and although the
observations of Dr. Carpenter2 tend to show the pro-
bability that very many of these supposed species are
merely varieties, still the number is sufficiently great
to prove the importance and interesting nature of the
inquiry.

(1) Western, Juurn. Micros. Science, vol. iv. New series, p. 11C; Clapa-
rede, Ann. Nat. His. Second series, vol. xv. p. 211.

(2) Carpenter's "Introduction to the Study of the For«uninifera," published
by the Ray Soc. 1862.

FORAMINIFERA. 375

Dr. Schultze acknowledges the difficulties attending the
study of the Rhizopoda, and insists, very properly, upon
the necessity of viewing them in all positions, and under
different modes of illumination and of preparation, in
order to arrive at a due conception of their astonishing
conformation. When the shells of Foraminifera are dis-
solved in dilute acid, an organic basis is always left after
the removal of the calcareous matter, accurately retaining
the form of the shell with all its openings and pores.
The earthy constituent is mainly carbonate of lime ; but
Dr. Schultze has satisfied himself of the presence of a
minute amount of phosphate of lime in the shells of
recent Orbiculina adunca from the Antilles and of Poly-
tfomdla strigilata from the Adriatic.

Fig. 207.

1, Separated prisms from outer layer of Tinna shell. .?.^6keletons4of Forami-
nifera from limestone. 3, Recent shell of Polystomella crispa ; viewed with
dark-ground illuminator.

The solitary JRhizopoda, furnished with a horny shell or
capsule, forming a case for the animal, is nearly the only
representative of the Arcellidce. In the Arcella, from
which the family derives its name, the shell is somewhat
of a bell-shape, with a very large round opening, In

376 THE MICROSCOPE.

EnglypJia it is of an oval or flask-like form, with the
opening at the smaller end, and the shell appears as
though formed of a sort of mosaic of small horny pieces.
In Difflugia, Fig. 205, A B, the shell is often globular.
Ehizopods which never develop more than one chamber
or loculus are classed as Monothalamia.1

The Polyihalamia, or Multilocular Ehizopods, in their
earliest state, are -unilocular ; but, as the animal increases,
successive chambers are added in a definite pattern for
each family of the order. They all inhabit the sea, and
frequently occur in such great numbers, that the fine
calcareous sand which constitutes the sea-shore in many
places consists almost entirely of their microscopic coats.
At former periods of the earth's history, they existed in
even greater profusion than at present ; and their fragile
shells form the principal constituent of several very
important geological formations. Thus the chalk appears
to consist almost entirely of the shells of these animals,
either in a perfect state, or worn and broken by the action
of the waves ; they occur again in great quantities in the
rnarly and sandy strata of the Tertiary epoch.

In the Stichostegidoe the chambers are placed end to
end in a row, so as form a straight or but slightly curved
shell. In the second family, the Enallostegidce, the
chambers are arranged alternately in two or three parallel
lines ; and as the construction of the shell is always
commenced with a single small chamber, the whole neces-
sarily acquires a more or less pyramidal form. The third
family, the Helicostegidce, presents us with some of the most
beautiful forms that it is possible to meet with in shells.
They commence by a small central chamber ; and each of
the subsequent chambers, which are arranged in a spiral
form so as to give the entire shell much the aspect of a
minute flattened snail, is larger than the one preceding it.
It is in this family that we find the nearest approach, in
external form, to the large chambered shells of the cepha-
lopodous mollusca, of which the Nautilus pompilius is an
example. The fourth family, the JSntomostegidce, stand in the
same relation to the preceding as the Enallostegidce to the

(1) Dlffiugia and Ancella form a connecting link between the naked forms,
Amceba, Actinophrys, &c. and the shell-bearing Rhizopods, Lagena striata, &c.

(iRKGARTNTDA, PoLYCYSTINA, FORAMINIFERA, RoTIFERA, ETC.

--.;

Tuflfen West, del.

Edmund Evans.

FORAMINIFERA. 377

Stichostegidce ; that is to say, the chambers are also arranged
in a spiral form, but in a double series. A fifth family
includes those shells in which the chambers are arranged
round a common perpendicular axis in such a manner that
each chamber occupies the entire length of the shell. The
orifices of the chambers are placed alternately at each end
of the shell, and are furnished with a curious tooth-like
process. The Miliola serve as an example of this family.
Every handful of sea-sand, every shaking of a dried sponge,
and the contents of the stomachs of most Lamellibranch
molluscs, oyster and mussel, are pretty sure to exhibit a
considerable admixture of these minute calcareous, or
occasionally silicious, Foraminifera.

It is considered that the fossil shells, termed Num-
mulites, found in great quantities in the chalk and lower
tertiary strata, are also to be regarded as members of this
class ; in a fossilized state, whole mountains consist almost
entirely of their shells. The late Professor Quekett had an
opportunity of examining a few living specimens, which, he
says, " are composed of a sarcode element, built up into a
series of chambers with calcareous material."

The great Pyramid of Egypt, covering eleven acres of
ground, is based on blocks of limestone consisting of
Foraminifera, Nummulites, or stone coin, and other fossil
animalcules. Nummulites vary in size from a very minute
object to that of a crown-piece, and many appear like a
snake coiled up in a round form. A chain of moun-
tains in the United States, 300 feet high, seems wholly
formed of one kind of these fossil-shells. The crystalline
marble of the Pyrenees, and the limestone ranges at
the head of the Adriatic gulf, are composed of small
Nummulites. Vast deposits of Foraminifera have been
traced in Egypt and the Holy Land, on the shores of
the Red Sea, Arabia, and Hindostan, and, in fact, may be
said to spread over thousands of square miles from the
Pyrenees to the Himalayas.

The fossilized Foraminifera in the Poorbaudar lime-
stone, although occasionally reaching the twenty-fifth, do
not average more than the hundredth part of an inch in
diameter ; so that more than a million of them may be
computed to exist in a cubic inch of the stone. They may

378 THE MICROSCOPE.

be separated into two divisions — those in which the cells
are large, the regularity of their arrangement visible, and
their bond of union consisting of a single constructed por-
tion between each; and those in which the cells are
minute, not averaging more than the 900th part of an
inch in diameter, the regularity of their arrangement not
distinctly seen, and their bond of union consisting of many
thread-like filaments. To ascertain the mineral composi-
tion of the amber- coloured particles or casts, after having
found that it was mostly carbonate of lime with which
they were surrounded, they were placed for a few mo-
ments in the reducing flame of a blow-pipe, and it was
observed that on subsequently exposing them to the influ-
ence of a magnet, they were all attracted by it. Hence, in
a rough way, this rock may be said to be composed of
carbonate of lime and oxide of iron.

By far the greater number of Foraminifera are marine.
They are found in most seas, and in those of the tropics
they increase both in size and variety, forming extensive
deposits.

During the Canadian Geological Survey large masses
of what appeared to be a fossil organism, the Eozoon
Canadense, were discovered in rocks situated near the
base of the Laurentian series of North America. Dr.
Dawson, of Montreal, referred these remains to an animal
of the foraminiferal type j and specimens were sent by
Sir W. Logan to Dr. Carpenter, requesting him to subject
them to a careful examination. As far back as 1858 Sir
"W. Logan had suspected the existence of organic remains
in specimens from the Grand Calumet limestone, oh the
Ottawa river, but a microscopic examination of one of
these specimens was not successful. Similar forms being
seen by Sir William in blocks from the Grenville bed of
the Laurentian limestone were in their turn tried, and
ultimately revealed their true structure to Dr. Dawson
and Dr. Sterry Hunt.

The masses oi which these fossils consist are composed
of layers of serpentine alternating with calc-spar. It
was found by these observers that the calcareous layers
represented the original shell ; and the siliceous layers
the flesh, or sarcode, of the once living creature. These

EOZOON CANADENSE. • 379

results were arrived at through comparison of the appear-
ance presented by the Eozoon with the microscopic struc-
ture which Dr. Carpenter had previously shown to
characterise certain members of the foraminifera. The
Eozoon not only exceeded other known foraminifera in
size, to an extent that might have easily led observers
astray, but, from its apparently very irregular mode of
growth, its general external form afforded no help in its
identification, and it was only by careful examination of
its minute structure that its true character could be
ascertained. Dr. Carpenter says : — " The minute struc-
ture of Eozoon may be determined by the microscopic
examination either of thin transparent sections, or of
portions which have been subjected to the action of
dilute acids, so as to remove the calcareous shell, leaving
only the internal casts, or models, in silex, of the chambers
and other cavities, originally occupied by the substance of
one animal."

Dr. Carpenter found the preservation of minute struc-
ture so complete that he was able to detect " delicate
pseudopodial threads, which were put forth through pores
in the shell wall, of less than ]0^00th of an inch in
diameter " (see Plate III. figs. 64, 65) ; and in a paper
read at the meeting of the Geological Society he stated
that he had detected Eozoon in a specimen of ophicalcite
from Cesha Lipa in Bohemia, in a specimen of gneiss from
near Moldau, and in a specimen of serpentine limestone
sent to Sir C. Lyell by Dr. Giimbel, of Bavaria, all these
being parts of the great formation of " fundamental "
gneiss, which is considered by Sir Roderick Murchison
as the equivalent of the Laurentian rocks of Canada.
There can be little doubt that a rich field of research is
now opened to those who will undertake the examination
of rocks of various ages, which present the appearance
of analogous structure ; as it is, the microscope has been
the means of demonstrating the existence of animal life
at a very ancient geological date ; and, in the words of
Sir W. Logan, " we are carried back to a period so far
remote that the appearance of the so-called Primordial
Fauna may be considered a comparatively modern event."

Recent Foraminifera present symmetrical shells, of

380 ' THE MICROSCOPE.

minute size for the most part, and consisting, as we
have already seen, either of one, two, or more con-
nected chambers. A jelly-like mass, or " sarcode," occu-
pies the chambers and their connecting passages ; and,
protruding itself both from the external aperture of

i 2

Fib'. 208.

1, Section of Faujasina: a a, radiating interseptal canals; 6, their internal
bifurcations ; c, a transverse branch ; d, tubular wall of the chambers. 2,
Eosalina ornata, with its pseudopodia protraded.

the last chamber, and in many cases from the sometimes
numerous perforations in the shell: walls, extends itself not
only over the surface of the shell, but also into radiating
contractile threads or pseudopodia, and into gemmule-like
masses, which latter become coated over with calcareous
matter, and thus form additional segments of the animal.1
" Foraminifera, indeed, are to be compared with the
other lowest orders of animals and of plants in the study
of their specific relations. In these several low forms of
creatures we have comparatively few species, but ex-
tremely numerous individuals, with an enormous range of

(1) Among the more important works on Foraminifera, reference may be
made to D'Orbigny's Foraminiferes fossiles du Bassin Tertiaire de Viennc.
(Autriehe) ; Schultze, Ueber den Organismus der Polylhalamien, 1854 ; Car-
penter's and Williamson's Researches on the Foraminifera, Phil. Trans. 1856.
Also an excellent paper by Mr. W. B. Parker, in the Annals of Natural History,
April, 1857. Specimens of Foraminifera may be obtained for examination from
the shaking of dried Sponges; but if required alive, they must be dredged for, or
picked off the fronds of living seaweeds, over the surface of which they are
seen to move by the aid of a Ions.

FORAMINIFERA.

381

variety. In the higher orders of plants and animals the
specific forms are more definite, there being a more com-
plex organization, harmonizing with the special habits of
each creature ; and the individuals of each species are less

Fig. 2u'J. — Foraminifera taken in Deep-sea Soundings. (Atlantic.)

numerous than is the case in the Protozoans and Proto-
phytes."

These lowly organized Furaminifera, having great
simplicity of structure, more easily adapt themselves to
varying external conditions than the more complex and
specialized higher animals.

382

THE MICROSCOPE.

In the deep-sea soundings, portions of many beau-
tiful Diatoms, figured and described by Professor W.
Smith, in gatherings from the Bay of Biscay, near Biar-
ritz, are Melosira cribrosa, marine, orbicular, cellulate,

Pig. 210. — Foraminifera taken in Deep-sea Soundings. (Atlantic.)

cellules, all equal and hexagonal. He writes : " In De-
cember, 1853, I received isolated frustules of this species,
collected on the coast of Normandy, under the above
name, from M. de Brebisson ; and I have since detected
the same in a gathering from the Black Sea. In no case
have I seen the frustules in a recent state, and do not know

FORAMINIFERA. 383

whether they ever form a lengthened filament. As this is
the only circumstance that would justify their separation
from Coscinodiscus, to which the separated valve would
otherwise seem to belong (Synop. British Diatomacece,
vol. i. p. 22), their position in Melosira must rest upon the
authority of my accurate correspondent."

In figs. 209 and 210 are represented many of the beau-
tiful forms brought up with soundings made in 1856, for
the purpose of ascertaining the depth of the Atlantic,
prior to the laying down of the electric telegraph wire
from England to America ; these specimens were taken
from a depth of 2,070 fathoms.

Major S. E. J. Owen, while dredging the surface ol
mid-ocean — Indian and Atlantic oceans — found attached to
his nets a few interesting forms of Rhizopods, belonging to
the two genera GloUgerina and Pulvinulina, which always
make their appearance on the surface of the ocean after
sunset.1

"Many of the forms," writes this observer, "have
hitherto been claimed by the geologist, but I have found
them enjoying life in this their true home, the siliceous
shells filled with coloured sarcode, and sometimes this
sarcode in a state of distension somewhat similar to that
found projecting from the Foraminifera, but not in such
slender threads. There are no objects in nature more
brilliant in their colouring or more exquisitely delicate in
their forms and structure. Some are of but one colour,
crimson, yellow, or blue ; sometimes two colours are found
on the same individual, but always separate, and rarely if
ever mixed to form green or purple. In a globular
species, whose shell is made up of the most delicate fret-
work, the brilliant colours of the sarcode shine through the
little perforations very prettily. In two specimens of the
triangular and square forms (Plate III. figs. 44, 45, and
46), the respective tints of yellow and crimson are vivid
and delicately shaded. In one the pink lines are concen-
tric ; while another is of a stellate form (fig. 43), the
points and uncoloured parts being bright clear crystal,
while a beautiful crimson ring surrounds the central por-

(1) Journ. Linn. Soc. vol. viii. p. 202; vol. ix. p. 147, 1866, and January,
1867.

384 THE MICROSCOPE.

tion. One globular species appears like a specimen of the
Chinese ball-cutting — one sphere within another ; but it
is of a marked and distinct kind.

"The shells of some of the globular forms of these
Polycystina, whose conjugation I believe I have witnessed,
are composed of a fine fretwork, with one or more large"
circular holes ; and I suspect the junction to take place
by the union of two such apertures. That the figures of
these shells become elongated, lose their globular form
after death, and present a disturbed surface is seen in
some of the figures represented near the bottom part of
Plate III." Major Owen proposes to make Orbulina a
subgenus of Globigerina. The internal chambers of the
former are in form remarkably like those of the latter,
and like them also they present themselves with varying
surfaces, some free from, while others are covered with,
spines. Those without internal chambers have been
known as Orbulina universa^ fig. 78, Plate III. while
figs. 75 and 76, although members of the same family,
have been separated ; but he wishes to see all united under
the name of " Globigerina universa"

The minute siliceous shells of Polycystina present won-
derful- beauty and variety of form ; all are more or less
perforated, and often prolonged into spines or other pro-
jections, through which the sarcode body extends itself
into pseudopodial prblongations resembling those of Acti-
nophrys. When seen besporting themselves in all their
living splendour, their brilliancy of colouring, says Major
Owen, "renders them objects of unusual attraction." We
have endeavoured to give some idea of the colour of the
living forms in Plate III. Nos. 43 to 52. The same ob-
server believes that they wish to avoid the light, " as they
are rarely found on the surface of the sea in the day time j
it is after sunset, and during the first part of the night
especially, that they make their appearance."

The Polycystina appear to have most affinity with the
fioraminifera. Thirty four genera and about two hundred
and ninety species have been described. They are most
abundant in the fossil state ; and are very plentiful in the
rocks of Bermuda, in the tripoli of Eichmond, Virginia, in
the marls of Sicily, and other places. Their minute shells

SPONGES. 385

form beautiful microscopic objects for the binocular ; they
must be mounted dry, and viewed either with the dark
ground illuminator, or by condensed light.

SPONGIADJE. SPONGES.

The term Porifera, or Canal-bearing Zoophyte, was
applied by Professor Grant to designate the remarkable
class of organized beings known as sponges, which are met
with in every sea, growing in great abundance on the
surface of rocks.

Ellis, in the course of his investigations, was astounded
by discovering that sponges possessed a system of pores
and vessels, through which sea-water passed, with all the
appearance of the regular circulation of fluids in animal
bodies, and for the seeming purpose of conveying ani-
malcules to the animals for food.

The description given of sponges by Dr. Johnston is,
that they are " organized bodies growing in a variety of
forms, permanently rooted, unmoving and irritable, fleshy,
fibro-reticular, or irregularly cellular ; elastic and bibulous,
composed of a fibro-corneous axis or skeleton, often inter-
woven with siliceous or calcareous spicula, and containing
an organic gelatine in the interstices and interior canals ;
and are reproduced by gelatinous granules called gem-
mules, which are generated in the interior, but in no
special organ. All are aquatic, and with few exceptions
marine."1 Our author continues : — " Mr. John Hogg, in a
letter to me dated June 25, states that the green colour
of the fresh-water sponge (Spongilla fluviatilis] depends
upon the action of light, as he has proved by experi-
ments which showed that pale-coloured specimens became
green when they were exposed for a few days to the
light and full rays of the sun ; while, on the contrary,
green specimens were blanched by being made to grow
in darkness or shade."

The living sponge, when highly magnified, exhibits a
reticulated structure, permeated by pores, which united
into cells or tubes, ramify through the mass in every
direction, and terminate in larger openings. In most

(1) See Dr. Johnston's History of British Sponges, and Mr. TJowerbank's revi-
sion of the class, in the publications of the Ray Society.
C C

386

THE MICROSCOPE.

sponges the tissue is strengthened and supported by
spines, spicula, of various forms; and which, in some
species, are siliceous, and in others calcareous. The
minute pores, through which the water is imbibed, have
a fine transverse gelatinous network and projecting spicula,
for the purpose of excluding large animals cr noxious par-
ticles ; water incessantly enters into these pores, traverses
the cells or tubes, and is finally ejected from the larger

Fig. 211.

1, A portion of Sponge, Halichondria simulans, showing siliceous spicula
imbedded in the sarcode matrix. 2, Spicula divested of its matrix.

vents. But the pores of the sponge have not the power of
contracting and expanding, as Ellis supposed ; the water
is attracted to these openings by the action of instruments
of a very extraordinary nature (cilia), by which currents
are produced in the fluid, and propelled in the direction
required by the economy of the animal.

Mr. Bowerbank, in a paper on the "Structure and
Vitality of Spongiadce" states that sponges consist princi-
pally of sarcode, strengthened sometimes by a siliceous or
calcareous skeleton, having remarkable reparative and
digestive powers, and consequently a most tenacious
vitality j so much so, that having cut a living sponge into
three segments, and reversed the position of the centre
piece, after the lapse of a moderate interval, a complete
junction of the parts became effected, so as to render the
previous separation indistinguishable.

Professor Grant's careful and laborious researches, have
finally classed sponges in the animal series of the creation.

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388 THE MICROSCOPE.

He ascertained that the water was perpetually sucked into
the substance of the sponge, through the minute pores that
cover its surface, and again expelled through the larger
orifices. His own account is so very interesting, that we
cannot resist giving, in his own words, the results arrived
at in these investigations : — " Having placed a portion of
live- sponge (Sponyia coalita, fig. 1, No. 213) in a watch-

Fig. 213.
1. Spwu'ta a>alita. 2, Spongia panicta.

glass with some sea-water, I beheld for the first time the
splendid spectacle of this living fountain, better repre-
sented in No. 2, vomiting forth from a circular cavity an
impetuous torrent of liquid matter, and hurling along in
rapid succession opaque masses, which it strewed every-
where around. The beauty and novelty of such a scene
in the animal kingdom long arrested my attention ; but
after twenty-five minutes of constant observation, I was
obliged to withdraw my eye from fatigue, without having
seen the torrent for one instant change its direction, or
diminish the rapidity of its course. In observing another
species (Spongia paniced), I placed two entire portions of
this together ' in a glass of sea- water, with their orifices
opposite to each other at the distance of two inches ; they
appeared to the naked eye like two living batteries, and
soon covered each other with the materials they ejected.
I placed one of them in a shallow vessel, and just covered

SPONGES. 389

its surface and highest orifice with water. On strewing
some powdered chalk on the surface of the water, the
currents were visible to a great distance ; and on placing
some pieces of cork or of dry paper over the apertures, I
could perceive them moving, by the force of the currents,
at the distance of ten feet from the table on which the
specimen rested."

Dr. K. Lieberkiihn, in his valuable contributions to
the History of the Development of the Spongillce, observes
that with regard to the skeleton of S. fluviatilis, the
spicules are not united at the base by a siliceous material,
as stated by Meyen, but by a substance destructible by
heat. The spicules are usually arranged in aggregate
bundles, which meet point to point at an obtuse arfgle, and
project slightly above the surface of the sponge. Minute
portions of the gelatinous substance exhibit under the
microscope amoeba-like movements, respecting which it is
unknown whether they are vital phenomena, as supposed
by Dujardin, or referable to a process of decomposition.1

The living spongillas are often seated, not immediately
upon the wood, stone, &c. upon which they may be
growing, but separated from it by a peculiar dark-brown
substance often several inches thick. This mass is com-
posed chiefly of the remains of the dead sponge, empty
gemmule-cases with their amphidiscs, various forms of
siliceous spicules, &c. ; and occasionally there may be

(1) The motile phenomena hitherto observed in sponges are connected with
larger or smaller portions of the external integument, and of the exhalent
tubules, or with isolated cells. When the exhalent tubules of Spongilla con-
tract, their walls become shortened and thickened, and the previously smooth
surface uneven, from the presence of the spherical contracted cells, whose
outlines at the same time are rendered very distinct, whilst they were before
invisible, or at most here and there perceptible. Other motile phenomena are
witnessed when a Spongilla with external membrane and exhalent canals is
produced from a cut-off portion. The fragment thus cut off may be so thin as
to consist of only a single layer of reticular parenchymatous fibres. The inter-
stitial rounded, oval,' or irregular spaces, under these circumstances, become for
the most part closed, owing to the gradual increase in breadth of the trape-
culse, or cavities may be left when their membranes are stretched over them
only from the upper and under sides of the trabeculae, which enclose a space
between them, and may become portions of the outer membrane with exhalent
canals. It cannot be determined with certainty to what extent this change of
form is connected with any multiplication of cells. Lastly, movements in the
individual cells have been noticed, the globular cells becoming stellate, and the
stellate ones globular in turn, but without any locomotion. This phenomenon
occurs, not only in the cells of the uninjured substance, but also in those which
have been detached.— N. Leiberkiihn, " On the Motile Phenomena in Sponges,"
Micros. Journ. vol. iv. 1864, p. 189, and Journ. Micros. Science, vol. v. 1857, p.
212, "On the Development of the Spongillaa."

390

THE MICROSCOPE.

found in it gemmules still retaining their brown colour
and contents capable of development.

Fig. 214.— Geodia Barretti (Bowerbank;.

A section at right angles to the surface, exhibiting the radial disposition of the
fasciculi of the skeleton, and a portion of the dermal crust of the sponge,
magnified 50 diameters, a, intermarginal cavities ; 6, .the basal diaphragms of
the intermarginal cavities ; c, imbedded ovaria forming the dermal crust of
the sponge ; d, the large patento tern ate spicula, the heads of which form the
areas, for the valvular bases of the intermarginal cavities ; e, recurvo-ternate
defensive and aggressive spicula within the summits of the intercellular
spaces of the sponge ; /, portions of the interstitial membranes of the
sponge, crowded with minute stellate spicula ; g, portions of the secondary
system of external defensive spicula. (1)

The usual contents of the gemmules have been described
by Meyen (Muller's Archiv. 1839, p. 83). In many in-

(1) See Bowerbank's Monograph of the British Spo-ngiadce, Eay Soc. ?• 1®.

SPONGES. 391

stances Lieberkiihn found that the globular arrangement
no longer existed, the globules being replaced by granules
exhibiting an active molecular motion. That the gem-
mules are formed from agglomerations of sponge-cells may
be readily proved in the branched sponge containing
smooth gemmules. Lieberkiihn notices four kinds of
gemmules characterised respectively by their cases or
shells.

1. Those with smooth cases.

2. Those with stellate amphidiscs.

3. Those with amphidiscs, in which the discoid ex-
tremities are entire, and not stellate.

4. Gemmules whose case, instead of amphidiscs, is fur-
nished with minute, usually slightly curved siliceous
spicules.

It would appear, therefore, that the " globules " of
Meyen are nothing more than altered sponge-cells. The
autumn is the most favourable season for observing the
process of their formation.

In the journal of the Bombay branch of the Eoyal
Asiatic Society for 1849, Surgeon EL J. Carter gives a very
accurate account of fresh-water sponges found in the
water tanks of Bombay. Of five species that he disco-
vered, one was the Spongilla friabilis, the others he named
Sp. cinerea, Sp. alba, Sp. Meyeni, Sp. plumosa.

Spongilla cinerea is stated to present on its surface a
dark rusty, copper colour, lighter towards the interior, and
purplish under water. It throws up no processes, but
extends horizontally in circular patches, over surfaces two
or three feet in circumference, or accumulates on small
objects ; and is seldom more than half an inch in thick-
ness. It is found on the sides of fresh -water tanks, on
rocks, stones, or gravel. The ova are spheroidal, about
l-63d of an inch in diameter, presenting rough points ex-
ternally. Spicula of two kinds, large and small ; large
spicula, slightly curved, smooth, pointed at both ends,
about l-67th of an inch in length ; small spicula, slightly
curved, thickly spiniferous, about l-380th of an inch in
length.

Spongilla friabilis. — Growing in circumscribed masses,
on fixed bodies, or enveloping floating objects ; seldom

392

THE MICROSCOPE.

attaining more than two inches in thickness. From the
other sponges it is distinguished by the smooth spicula
which surround its seed-like bodies, and the matted
structure.

Spongilla alba. — Its texture is coarse and open ; struc-
ture reticulated. The investing membrane abounds in
minute spicula; has seed-like spheroidal bodies about
l-30th of an inch in diameter, with rough points exter-
nally. The large spicula are slightly curved, smooth,
pointed at each end, about l-54th of an inch in length ;
the small spicula are slightly curved, thickly spiniferous,
or pointed at both ends; the former, pertaining to the
seed-like bodies, are about 1 -200th of an inch in length ;
the latter, pertaining to the investing membrane, are more
slender, and a little less in length; these last numerous
small fcpiniferous spicula when dry present a white- lace
appearance, from which Mr. Carter gives them the name
of alba.

Spongilla meyeni is massive, having large lobes, mam-
millary eminences, or pyramidal, compressed, obtuse, or
sharp-pointed projections, of an inch or more in height ;
also low wavy ridges. Its seed-like bodies are spheroidal,
about l-47th of an inch in diameter, studded with little
toothed discs.

Mr. Carter enters very minutely into the structure of
" fresh- water sponge, which " — he believes — " is composed
of a fleshy mass, supported on a fibrous, reticulated, horny
skeleton. The fleshy mass containing a great number
of seed-like bodies in all stages of development, and
the horny skeleton permeated throughout with siliceous
spicula. When the fleshy mass is examined by the aid of
the microscope, it is found to be composed of a number of
cells, imbedded in and held together by an intercellular
substance.

" In the development of the sponge-cell of Spongilla, a
set of large granules make their appearance at a very early
period, and increase in number and size until they form
a remarkable feature. At this time they are about
1-1 0,000th of an inch in diameter, of an elliptical shape,
and of a light amber colour by transmitted light ; they
are the colour bearing granules or cells, arid give the

SPONGES. 393

colour of chlorophyll to this organism when it becomes
green. The transparent intercellular substance of Spon-
gilla has a polymorphism equally great with the fully
developed cells. This, however, can only be satisfactorily
seen when the new sponge is growing out from the seed-
like body, at which time it spreads itself over the glass in
a transparent film, charged with contracting vesicles of dif-
ferent sizes, and in various degrees of dilatation and con-
traction. How this substance is produced so early, it is
difficult to conceive, since it seems to come into existence
independently of the development of the sponge-ovules,
which are seen imbedded in it, and there undergoing
their transformation into sponge-cells. The spicula., too,
are developed synchronously with the advancing trans-
parent border, from little glairy globules about the size of
the largest ovules, which send out a linear process on
each side, and thus gradually grow into their ultimate
forms. The only way of accounting for the early appear-
ance of this intercellular-substance is to consider that it is
a development from some remnants of the original proto-
plasm ; and perhaps possesses also the power of producing
new sponge-cells, as we see the protoplasm in Vwticella
and the roots of Chara producing new buds, independently
of the cell-nucleus.

" The cells of the investing membrane are characterised
by their uniformly granular composition and colourless
appearance. They are nucleated, possess the contracting
vesicle singly or in plurality, and are spread over the
membrane in such numbers, that it seems to be almost
entirely composed of them ; while they are of such
extreme thinness, and drawn out into such long digitated
forms, that they present a foliated arrangement, not unlike
a compressed layer of multifidous leaves, ever moving and
changing their shapes. The apertures are circular or
elliptical holes in the investing membrane in the cells.
Through these apertures the particles of food are admitted
into the cavity of the investing membrane. The Paren-
chyma consists of a mass of gelatinous substance, in which
are embedded the smooth spicules and ovi-bearing cells,
and through which pass the afferent and efferent canals.
The ovi-bearing cells do not burst and allow their con-

394 THE MICROSCOPE.

tents to become indiscriminately scattered through the
gelatinous mass in which they are imbedded, but each
becomes developed separately in the following way : — the
ovules and granules of the ovi- bearing cells subside into a
granular mass by the former losing their defined shape
and passing into small mono-ciliated and unciliated sponge
cells ; this mass then becomes spread over the interior
surface of the ovi-bearing cell, leaving a cavity in the
centre, into which the cilia of the monociliated sponge-
cells dip and keep up an undulating motion ; meanwhile,
an aperture becomes developed in one part of the cell
which communicates with the adjoining afferent canal, and
thus the ovi-bearing cell passes into an ampullaceous
spherical sac. The cilia may now be seen undulating in
the interior ; and if the Spongilla be fed with carmine, this
colouring matter will not only be observed to be entirely
confined to the ampullaceous sacs, but when the Spongilla
is torn to pieces and placed under a microscope, particles
of the carmine will be found in the interior of the mono-
ciliated and unciliated sponge cells, proving that of such
cells the ampullaceous sac is partly composed. This sac
then must be regarded as the animal of Spongilla, as
much as the Polype- cell is regarded as the animal of the
Polype, and the whole mass of Spongilla as analogous to
a Polypidom.

" The united efforts of all the ciliated sponge- cells in
the ampullaceous sac are quite sufficient to produce a con-
siderable current, and thus catch the particles of food as
they pass through the afferent canals. Thus we find
Spongilla composed of a number of stomachal sacs im-
bedded in a gelatinous substance permeated with spicules
for its support, and an apparatus for bringing them food, as
well as one for conveying away the refuse, while the nourish-
ment abstracted by the process of digestion common to
Rhizopodous cells (e.g. Amoeba), no doubt passes through the
intercellular gelatinous substance into the general develop-
ment of the mass ; and if right in comparing the ampul-
laceous sacs to the stomachal cavities of the simplest
polypes, are we not further justified in drawing a resem-
blance between the ciliated sponge-cells and those which
line the stomach of Cordylophora, of Otostoma, and many

DEVELOPMENT OF SPONGES. 395

of Ehrenberg's Allotreta, together with those in the stomach
of the Rotifera, and Planaria ?

"The 'swarm-spore,' described by M. N". Lieberkiihn,
appears to be a ciliated form of the seed-like body, and
the same as the * gemmule ' described by Grant ; but this
I have not yet been able to see. The formation of the
seed-like body, however, now that we know the struc-
ture of the ampullaceous sacs, seems very intelligible,
for we have only to conceive an enlargement of the small
sponge-cells lining the interior, with the addition of
ovules to them respectively, and the spicule-bearing
sponge-cells of the cortical substance supplying the
spicular crust to the exterior, to have a globular capsule
thus composed, with a hilum precisely like the seed-like
body — a conjecture which seems to derive support from
the fact, that in some instances, when Spongilla is begin-
ning to experience the want of nourishment, these sacs,
small as they are, assume a defined, rigid, spherical form,
from their pellicle becoming hardened and encrusted with
extremely minute spicules." *

Clionce. — Not the least wonderful circumstance con-
nected with the history of sponges, is the power possessed
by certain species of boring into substances, the hardness
of which might be considered as a sufficient protection
against such apparently contemptible foes. Shells (both
living and dead), coral, and even solid rocks, are attacked
by these humble destroyers, gradually broken up, and, no
doubt, finally reduced to such a state as to render sub-
stances which would otherwise remain dead and useless in
the economy of nature available for the supply of the
necessities of other living creatures.

These boring sponges constitute the genus Cliona of
Dr. Grant. They are branched in their form, or consist of
lobes united by delicate stems ; they all bury themselves
in shells or other calcareous objects, preserving their com-
munication with the water by means of perforations in the
outer wall of the shell. The mechanism by which a crea-
ture of so low a type of organisation contrives to produce
such remarkable effects is still doubtful, from the great
difficulties which lie in the way of coming to any satis-

(1) Ar.n. of Nat, Hist., July, ISA?.

386

THE MICROSCOPE.

factory conclusions upon the habits of an animal that
works so completely in the dark as the Cliona celata — it
will probably long remain so. Mr. Hancock, to whom we
are indebted for a valuable memoir upon the boring
sponges, published in the Annals and Magazine of Natural
History, attributes their excavating power to the presence
of a multitude of minute siliceous crystalline particles
adhering to the surface of the sponge ; these he supposes
to be set in motion by some means analogous to ciliary
action. In whatever way this action may be produced,
however, there can be no doubt that these sponges are
constantly and silently effecting the disintegration of sub-
marine calcareous bodies — the shelly coverings, it may be,
of animals far higher in organisation than they ; nay, in
many instances they prove themselves formidable enemies
even to living mollusca, by boring completely through the
shell. In this case the animal whose domicile is so unce-
remoniously invaded, has no alternative but to raise a wall
of new shelly matter between himself and his unwelcome
guest ; and in this mariner generally succeeds at last in
barring him out.

Skeletons of Sponges. — The skeletons of sponges, which
give shape and substance to the mass of sarcode that con-
stitutes the living animal, is best made out by cutting thin
slices of sponge submitted to firm compression, and view-
ing these slices mounted upon a dark ground, or backed up
with black paper.

The skeletons of sponges are composed principally of
two materials, the one animal, the other mineral ; the first
of a fibrous horny nature, the second either siliceous or
calcareous. The fibrous portion consist of a network of
smooth, and more or less cylindrical, threads of a light-
yellow colour, and, with few exceptions, always solid ;
they frequently anastamose, and vary considerably in size ;
when developed to a great extent, needle-shaped siliceous
bodies termed spicula (little spines) are formed in their in-
terior ; in a few cases only one of these spicula is met
with, but most commonly they occur in bundles. In some
sponges, as those belonging to the genus Halichondria, the
same horny kind of material is present in greater or less
abundance ; but its fibrous structure has become obscure :

SPONGES.

397

the fibres, however, in these cases are represented ly sili-
ceous needle-shaped spicula, and the horny matter serves
the important office of binding them firmly together, as

Fig. 216.

1. Transverse section of a branch of Myriapore. 2, A section of the stem of

Virgularia mirabilis. 3, A spiculum from the outer surface of a Sea-pen. 4,

Spicula from crust of Isis hippuris. 5, Spicula from Gorgonct elongata. 6,
Spicula from Alcyonium. 7, Spicula from Gorgonict, umbraculum.

shown in fig. 213, ~No. 1. There are, however, some re-
markable exceptions to this rule, one, Dictyochalix pumi-
ceus, described by Mr. S. Stutchbury, in which the fibrous
skeleton is composed of threads of silex quite as trans-
parent as glass ; another, the Hyalonema, Glass-rope.

The mineral portion, as before stated, consists of spicula
composed either of silica or carbonate of lime ; the first
kind is the most common and likewise most variable in
shape, and presents every gradation in form, from the
acuate or needle-shaped to that of a star. The calcareous
spicula, on the contrary, are more simple in their form,

THE MICROSCOPE.

being principally acicular, but not unfrequently branched
or even tri- or quad-radiate ; the two kinds, the sili-
ceous and calcareous, according to Dr. Johnston, not
having hitherto been detected co- existent in any native
sponges.

The spicula exhibit a more or less distinct trace of a
central cavity or canal, the extremities of which are closed,
or hermetically sealed ; in their natural situation they are
invested by an animal membrane, sarcode, which is not
confined to their external surface ; but in many of the
large kinds, as pointed out by Mr. Bowerbank, its "presence
may be detected in their central cavity, by exposing them
for a short time to a red heat, when the animal matter
will become carbonised, and appear as a black line in their
interior.

Many authors have described the spicula as being crys-
talline, and of an angular figure, and have considered them
analogous to the raphides in plants ; but it requires no
great magnifying power to prove that they are always
round, and, according to their size, are made up of one or
more concentric layers, as shown in fig. 212, No. 2. The
spicula occupy certain definite situations in sponges ;
some are peculiar to the crust, others to the sarcode,
others to the margins of the large canals, others to the
fibrous network of the skeleton, and others belong exclu-
sively to the gemmules. Thus, for instance, in Pachyma-
tisma Johnstonia, according to Mr. Bowerbank, the spicules
of 'the crust are simple, minute, and fusiform, having their
surfaces irregularly tuberculated, and their terminations
very obtuse ; whilst those of the sarcode are of a stellate
form, the rays varying in number from three to ten or
twelve.

Silica, however, may be found in one or more species of
sponge of the genus Dysidea, not only in the form of
spicula, but as grains of sand of irregular shape and size,
evidently of extraneous origin, but so firmly surrounded
by horny matter as to form, with a few short and slightly-
curved spicula, the fibrous skeleton of the animal. In these
sponges the spicula are of large size, and are disposed in
lines parallel with the masses of sand.

Most of the sponges of the earlier geological periods had

SPONGES. 399

tubular fibres ; but in all existing species, with one or two
exceptions, they are solid. These tubular fibres are very
commonly filled with portions of iron, which accounts for
the colour of many of the remains in flint.

The Moss-agates, found among the pebbles at Brighton
and elsewhere, are flints containing the fossilised remains of
sponges. The coloured fibres seen in the Green-jaspers of
the East are of the same character. There is reason to
believe that most flints were originally sponges ; those
from chalk even retain their original form. Recent
sponges from the Sussex coast present forms precisely
similar to some chalk flints, but it is from sections made
sufficiently thin to be transparent, for examination under
the microscope, that we learn their true nature and
origin.

Every horny sponge, whilst living, is invested with a
coating of jelly-like substance, which can only be preserved
by placing the sponge in spirit and water immediately
after its removal from its place of growth. Spicula are
not exclusively confined to the body of sponges, but occa-
sionally form the skeleton of the gemmules, and are situated
either on the external or internal surface of these bodies.
A good example of the former kind occurs in the common
fresh-water sponge (Spongilla fluviatilis), represented in
fig. 216, No. 1, and No. 3. The spicula are very minute
in size, and are disposed in lines radiating from the
centre to the circumference, the markings on the outer
surface of the gemmules being the ends of spicula. In all
the young gemmules the spicula project from the outer
margin as so many spines ; but in process of growth the
spines become more and more blunt, until at last they
appear as so many angular tubercles. Turkey sponge
(Sponyia officinalis) is brought from the Mediterranean,
has a horny network skeleton rather fine in the fibres,
solid, small in size, and light in colour. In some larger
specimens there is a single large fibre, or a bundle of
smaller ones. In Halichondria simulans the skeleton is a
framework of siliceous needle-shaped spicula, arranged in
bundles kept together by a thick coat of horny matter.
Other species of Halichondria have siliceous spicula
pointed at both extremities — acerate (fig. 212, No. 2) j

400 THE MICROSCOPE.

while the spicula of some are round at one end, and
pointed at the other — acuate j some have spicula round at
one end, the former being dilated into a knob — spinulate.

1, Gemmule of Spongilla fluviatilis, enclosed in spicula. 2, Biro tulate, spicula,
from Fluviatilis. 3, Gemmules of Spongilla fluviatilis, after having been im-
mersed in acid, to show coatiug of birotulate spicula.

Among the genus Grantia, Geodia, and Levant sponge,
are found spicula of a large size, radiating in three direc-
tions— triradiate. In the Levant specimen, a central
communicating cavity can be distinctly seen. Some
Smyrna sponges, and species of Geodia, have four rays —
quadriradiate. Some spicula in P. Johnstonia and Geodia
have as many as ten rays — multiradiate. In some species
of Tethya and Geodia the spicula consist of a central sphe-
rical body, from which short conical spines proceed —
stellate spicula. (Fig. 212, Nos. 4 and 5.) Spicula
having both extremities bent alike — bicurvate — have been
obtained from Trieste sponge. Some South Sea sponges
have spicula twice bent, and have extremities like the
nukes of an anchor — bicurvate anchorate ; 'sometimes the
flukes have three pointed ends. (Fig. 212, No. 6.) The
gemmules in fresh-water sponges are generally found in
the oldest portions near the base, and each one is protected
by a framework of bundles of acerate spicula of the flesh,
as shown in fig. 212, No. 9 ; but in many marine species,
Geodia and Pachymatisma, they are principally confined to
the crust. In the fresh- water sponges, the amount of
unimal matter in the gemmules is considerable ; but in

SPICULA FROM SPONGES. 401

Pachymatisma, Geodia, and many other marine species, a
very small quantity only is ever to be found, the substance
of each gemmule being almost entirely composed of
minute siliceous spicula ; if they be viewed when taken
fresh from the sponge, and also after removing the animal
matter by boiling in acid, a slight increase in trans-
parency is. the only perceptible difference of appearance
noticed.

HYALONEMA, " GLASS-KOPE " SPONGE. — A bundle of from
200 to 300 threads of transparent silica, glistening with a
satiny lustre like the most brilliant spun glass ; each
thread is about eighteen inches long, in the middle the
thickness of a knitting needle, and gradually tapering
towards either end to a fine point ; the whole bundle
coiled like a strand of rope into a lengthened spiral, the
threads of the middle and lower portions remaining com-
pactly coiled by a permanent twist of the individual
threads ; the upper portions of the coil frayed out, so
that the glassy threads stand separate from each other.
The spicules on the outside of the coil stretch its entire
length, each taking about two and a half turns of the
spiral. One of these long needles is about one-third of a
line in diameter in the centre, gradually tapering towards
either end. The spirally twisted portion of the needle
occupies rather more than the middle half of its entire
length. In the lower portion of the coil, which is em-
bedded in the sponge, the spicule becomes straight, and
tapers down to an extreme tenuity, ultimately becoming
so fine that it is scarcely possible to trace it to its termi-
nation.

"Many spicules of the awl-shaped and simple cross
types, especially short spicules, are met with within the
siliceous coil to its very centre, and, in cases where the
coil has been brought home without the sponge, such
needles can be shaken out from the interstices of the
threads. The spicules of Hyalonema are marked in their
character, and all the forms are found in all specimens of
the sponge imbedding the characteristic bundle of enor-
mous spicules j so that there can be no reasonable doubt
of the specific identity of the sponge in all cases.

" Within the round apertures on the surface of the

D D

402 . THE MICROSCOPE.

sponge there is usually a brownish orange-coloured mem-
brane, which Schultze found presented the marked ch&
racters of a minute parasitic polyp, probably alcyonarian,
which inhabited the oscula and their passages during the
life of the sponge.

" The glassy wisp of Hyalonema is certainly very re-
markable, but it is not entirely without analogy. Hyalo-
nema seems to represent the extreme form of a little group
of sponges, including, with probably a few other forms,
Euplectella (Alcyonellum) speciosa (Quoi and Gaimard), and
E. cucumer (Owen). The last-named is an oval sponge
with siliceous spicules, in form and character somewhat
like the spicules of Hyalonema. From one end of the
sponge a tuft of long siliceous threads, resembling in
structure those of the Japan sponge, twine round a stone
or other foreign body. Dr. Bowerbank isolated one of
the spines of Euplectella, three inches long." See Intel-
lectual Observer, March, 1867.

INFUSORIA.

The term Infusoria is applied to a certain class of
animals because they were first discovered in water where
vegetable matter was decomposing, the infusion was con-
sidered necessary for their production. Now, however, it
is an established fact, that they are in a healthier state of
existence when taken from pure streams and clear ponds
than from putrid and stagnant waters. A little bundle of
hay, or sage leaves, left for about ten days in a mug con-
taining some pure rain-water, caught before entering a
butt, produces the common wheel-animalcules, which are
found adhering to the sides of the mug near to the surface
of the water. The only use of the vegetable matter seems
to be to facilitate in some way the development of the ova
of animalcules which find their way into the water. It
was at one time thought an indispensable condition that
air be admitted to the infusion : but even this element is
not absolutely needed in the case of infusorial life ; and
the appearance of living organisms at all under the circum-
stances, has been regarded as important evidence in favour
of the doctrine of spontaneous generation.

INFUSOBIA. 403

The astronomer turns his telescope from the earth, and
ranges over the vast vault of heaven, to detect and delineate
the beautiful objects of his pursuit. The naturalist turns
his microscope to the earth, and in a drop of water finds a
wondrous world of animated beings, more numerous than
the stars of the milky way ; and these he classifies into
genera and families, and catalogues in his history of the
invisible world.

The Infusoria are a mighty family, as they frequently,
in countless myriads, cover leagues of the ocean, and give
to it a beautiful tinge from their vivid hue. They are
discovered in all climes, have been found alive sixty feet
below the surface of the earth, and in the mud brought up
from a depth of sixteen hundred feet of the ocean. They
exist at the poles and the equator, in the fluids of the
animal body, and plants, and in the most powerful acids.
A brotherhood will be found in a little transparent shell,
to which a drop of water is a world ; and within these are
sometimes other communities, performing all the functions
granted them by their Creator, and eagerly pursuing the
chase of others less than themselves.

The forms of the Infusoria are endless ; some changing
their shape at pleasure, others resembling globes, eels,
trumpets, serpents, boats, stars, pitchers, wheels, flasks,
cups, funnels, fans, and fruits.

The multiplication of the species is effected in some by
spontaneous division or fissuration, in others by gemma-
tion or budding, as well as a true sexual process. The
first step in the process by which infusorial animals are
eliminated, is the formation of globular corpuscles or cells,
which, by their aggregation in some cases, and individual
evolutions in others, give birth to organisms which sub-
sequently appear.

The Infusoria have no night in their existence ; they
issue into life in a state of activity, and continue the
duration of their being in one ceaseless state of motion ;
their term is short, they have no time for rest, and there-
fore have but one day, which ends only with their death
and decomposition. Nevertheless, they appear to love
that which promotes life, — the light of heaven • but
others, born in the bowels of the earth, and who never

404 THE MICKOSCOPE.

partook of the blessing, like the ignorant among man-
kind, have their own contracted round of unenlightened
joys, perform their mechanical duties, and expire hidden
an i unknown.

On examining the structure of infusorial animalcules,
some are found to have a soft yielding skin, so elastic as
to stretch when food or other circumstances render it
necessary, returning again to its previous condition as the
cause of distension ceases ; these are designated illoricated,
which signifies shell-less. Others are termed loricated,
from being covered with a shell, which is beautifully
transparent, and flexible like horn. When the delicate
and soft substance in which the functions of life perforrr.
their allotted duties perishes, the coat that protected it
from injury during its hours of existence remains as a
token of the past labours of nature ; this covering con-
sists mostly of siliceous material or of lime united with
oxide of iron, destructible in some instances either by
chemical agents or by fire.

Some of these minute beings have apportioned to them
setce, or bristles ; these stiff hairs, attached to the surface
of their bodies, do not rotate, but are movable, and appear
to be a means for the support of their bodies, as aids in
climbing over obstacles that present themselves, or as
feelers. Others are possessed of unci, or hooks, projecting
from the under part of the body, which are capable of
motion ; and by their means the animalcule can attach
itself to anything that lies in its way. Some, again,
have styles, which are a kind of thick bristle, jointed
at the base, possessing a movement, but not rotary ; they
are in the shape of a cone, large at their base, and delicate at
their summit. Many, also, can extend and withdraw their
bodies at pleasure, in a similar manner to the snail or
leech.

One of the most interesting and important organs pos-
sessed by infusorial animalcules is scientifically known by
the term cilium, which is the Latin word for eyelash, the
plural being cilia. Its appearance is that of a minute
delicate hair.

The cilium is not only useful in the act of progression,
but also as an assistance in procuring food ; the two duti«j#

INFUSORIA — CILIA. 405

being performed at the same time, the motion of the
organs that propels it forward causing a current to set
towards the mouth, which carries with it the prey on
which the animal feeds. From the cilia being found in
the sills of the young tadpole, the oyster, and mussel, it
would appear that they are serviceable as organs of respi-
ration, by imbibing oxygen, and emitting the carbonic acid
generated in the blood during its circulation through the
body; they are also believed to be the medium of taste
and touch. It is not only at the mouth, but over the
whole body that cilia are discovered ; and it is now satis-
factorily shown that cilia exist also in .the internal organs
of man and other vertebrated animals ; and are agents
by which many of the most important functions of the
animal economy are performed. They vary in size from
the 1000th to the 10,000th of an inch in length. These
minute organs would often be invisible, were it not from
the water being coloured when placed under a microscope ;
then the little currents made by the action of the cilia are
easily perceived; and when the water is evaporated, the
delicate tracing of their formation may be observed on the
glass. They are differently placed, and vary in quantity
in the numerous species of Infusoria. In some they are
in rows the whole length of the body, in others on the
base ; many have them over the whole of the body ; some-
times they fringe the mouth, form bands around projec-
tions on the body ; and many have but two projecting
from, the mouth, as long as the body of the creature.
Ehrenberg says they are fixed at their base by the bulb
moving in a socket, in a similar manner to a man's out-
stretched arm; and by their moving round in a circle,
they form a cone, of which the apex is the bulb. Poison,
galvanism applied to the animal, even death, will not im-
mediately stop the motion of the cilia ; they continue
moving some hours afterwards, even longer than nervous
or muscular action can be sustained, until the fluids dry
up, and they stiffen.

Very little is known of the muscular attachment of cilia
in Infusoria ; but the motive power must be derived from
muscular structure in all. Now in the wheel-animalcules
the cilia are in circular rows ; and each revolves around

406 THE MICROSCOPE.

its bulb, giving a singular appearance, seeming to move
together like a wheel upon its axle, whence their name
Rotifer ; in a few of these muscles can be traced. The
cilia must not be mistaken by the young microscopist for
the stiff hairs and bristles found on some, and serving, as
before stated, for the purpose of locomotion in crawling or
climbing.

If the roof of the mouth of a living frog be scraped
with the end of a scalpel, and the detached mucous mem-
brane placed on a glass slide, and examined with a power
of 300 diameters, the ciliated epithelium-cells will be well
seen. When a number of these are collected together, the
movement is effected with apparent regularity; but in
detached scales it is often so violent, that the scale itself is
whirled about in a similar manner to an animalcule pro-
vided with a locomotive apparatus of the same description,
and has frequently been mistaken for such. The animals
commonly employed for the examination of the cilia are
the oyster and the mussel; but the latter are generally
preferred.

To exhibit the movement to the best advantage, the
following method must be adopted : — open carefully
the shells of one of those molluscs, spilling as little as
possible of the contained fluid; then with a pair of fine
scissors remove a portion of one of the gills (branchiae) ;
lay this on a slide, or the tablet of an animalcule cage, and
add to it a drop or two of the fluid from the shell ; by
means of the needle-points separate the filaments one-from
the other, cover it lightly with a thin piece of glass, and
it is ready for examination. The cilia may then be seen
in several rows beating and lashing the water, and pro-
ducing an infinity of currents in it. If fresh water instead
of that from the shell be added, the movement will speedily
stop ; hence the necessity of the caution of preserving the
liquid contained in the shell. To observe the action of any
one of the cilia, and its form and structure, some hours
should be allowed to elapse after the preparation of the
filaments as above given, their movements then will have
become sluggish. If a power of 400 diameters be used,
and that part of the cilia attached to the epithelium scale
oarefully watched, each one will be found to revolve a

INFUSORIA. 407

quarter of a circle, whereby a " feathering movement " is
effected, and a current in one direction constantly pro-
duced. In the higher animals, the action of the cilia can
only be observed a very short time after death. In a polypus
of the nose, when situated at the upper and back part of
the Schneiderian membrane, the cilia may be beautifully
seen in rapid action some few hours after its removal ; but
in the respiratory and other tracts, where ciliated epi-
thelium, is found, it would be almost impossible ever to
see it in action, unless the body were opened immediately
after death. In some animals it may be seen in the in-
terior of the kidney, as first made known by Professor
Bowman in the expanding extremity of the small tube
surrounding the network of blood-vessels forming the so-
called Malpighian body. In order to exhibit the ciliary
action, the kidney should have a very thin slice cut from
it; and this is to be moistened with the serum of the
blood of the same animal. The vascular and secreting
portions of the organ may then be seen with a power of
250 diameters, and also the cilia in the expanded extremity
of each tube, as it passes over to surround the vessels ; the
epithelium of the tubes themselves is of the spheroidal or
glandular character.

The infusorial and invisible atoms of life have various
periods allotted to them for the enjoyments of existence ;
some accomplish their destiny in a few hours, others in a
few weeks. The watchful devotee in this branch of science
has traced an animalcule through a course of existence
extending to the old age of twenty-three days. The vital
spark flies instantaneously in general ; but in those of a
higher organisation there is a spasmodic convulsion, as if the
delicate and intricate machinery rendered life so exquisite,
that the parting with the " heavenly flame " was reluctant
and painful. The most surprising circumstance attendant
on the nature of some of the Infusoria is that of apparent
death. When the water or mud in which they have sported
in the fulness of buoyant health becomes dried up, they lie
an inanimate speck of matter ; but after months, nay, years,
a drop of water being applied, their bodies will be resusci-
tated, and in a short time their frames become active with
life. Leeuwenhoek kept some in a hard and dry condition,

408 THE MICROSCOPE.

and restored them to life after a sleep of more than
twenty-one months. Professor Owen saw an animalcule
that had been entombed in a grave of dry sand four years
reborn to all the activity of life. Spallanzani tried the
experiment of alternate life and death, and accomplished
it in some instances on the same object fifteen times ; after
which nature was exhausted, and refused further aid in
this miraculous care of those minute objects of her won-
derful works.

Naturalists consider the phosphoric light of the marine
animalcule to be the effect of vital action. The sparks
are intermittem: like the fire-fly; they measure from the
12,000th to the 100th of an inch in size. Captain Scoresby
found that the broad expanse of waters at Greenland was
nearly all discoloured by animalcules, and computed that
of some species one hundred and fifty millions would find
ample room in a tumbler of water. The phosphorescence
of the sea is eloquently portrayed by Darwin, in his
Voyage of the Beagle. Mr. Gosse thus describes the
luminous appearances presented by a closer inspection of
these minute animalcules : " Some weeks afterwards I had
an opportunity of becoming .acquainted with the minute
animals, to which a great portion of the luminousness of
the sea is attributed. One of my large glass vases of sea-
water I had observed to become suddenly at night, when
tapped with the finger, studded with minute but brilliant
sparks at various points on the surface of the water. I set
the jar in the window, and was not long in discovering,
without the aid of a lens, a goodly number of the tiny
jelly-like globules of Noctiluca miliaris swimming about
in various directions. They swam with an even gliding
motion, much resembling that of the Volvox globator of
our fresh-water pools. They congregated in little groups,
and a shake of the vessel sent them darting down from
the surface. It was not easy to keep them in view when
seen, owing rather to their extreme delicacy and colourless
transparency than to their minuteness. They were, in
fact, distinctly appreciable by the naked eye, measuring
from l-50th to l-30th of an inch in diameter." Nocti-
luca miliaris belongs to the highest class of the Protozoa,
and with a power of about 200 diameters they are seen

INFUSORIA. 409

of various forms and stages of growth, represented in
fig. 217.1

Ehrenberg included in his family of Infusoria, Rhizop-
oda, Unicellular, and other Algse, embryonic forms, and
Rotifers. Most naturalists, however, now admit that the

Fig. 217. — Noctiluca miliaris.

organization of the Rotiferse is of a far higher nature than
had been suspected by Ehrenberg • and some assert that
their proper place in the classification of animals is the
annulose sub-kingdom ; the true nature of many of the In-
fusoria is still a disputed question. In outward form they
may be said to vary almost indefinitely ; but anatomically
their bodies should be regarded as consisting of three dis-
tinct structures. The cuticle or integument (" pellicula " of
Carter), on which are borne the cilia and other locomotive
apparatus ; the cortical layer or parenchyma of the body
(" diaphane " of Carter) ; and the chyme mass, occupying
the abdominal cavity, or interior of the body (sarcode or
" abdominal mucus " of Carter), within which the par-
ticles of food rotate. The term "ventral" is usually ap-
plied to that side of the body on which the mouth is
placed.

In the well-known Parameecium we have the true and
most widely distributed type of the Infusoria. The
general structural character of this minute animal is
common to the species ; indeed, its structural features may
be accepted as a fair definition of the whole group. The
Parameecium is surrounded on its external covering by
cilia, wbich are constantly in action, and enable it to move
about in its watery element in a most remarkably active
manner. At one point the body appears to be slightly

(1) See Gosse's Naturalises Rambles .- Huxley, Micro. Journal, 1S55.

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412 THE MICROSCOPE.

Monads vary in their colours, some are red, green, or
yellow, others nearly colourless. In shape they are round
or oval (5 and 6, fig. 226), and possessed of immense
activity, having one or more cilia devoted to the purpose
of locomotion. Monads have been claimed by the bota-
nist, and accordingly placed among the Volvocinece, confer-
void Algce. Ehrenberg described them as Infusoria. He
says : " All true Infusoria — even the smallest monads, are
organised animal bodies."

VIBRIO. — Vibriones. — In this family Ehrenberg wrongly
includes the well-known eels in paste and vinegar.

Vibrio spirilla, Trembling animalcules, when motionless
are seen as very minute bodies ; but when exerting the
powers of locomotion they take a spiral form, like the
threads of a fine screw, and by undulations wind them-
selves through the water with rapidity. Each apparent
hair is a collection of animals bound together by a pliant
band; thus, as they are individually so small, little is
known of their structure. Still they form very interesting
objects to view ; their very minuteness claiming attention,
while their activity and motions excite surprise. The
species are numerous, as represented in fig. 218. They are
almost invariably the first organisms found in decaying
acetous and putrefying organic matters. When treated
with iodine and then sulphuric acid, their jointed structure
is rendered visible to the higest powers of the microscope,
but not otherwise.

ASTASI.EA. — Astasia, signifying without a station, in con-
tradistinction to those living in groups, is the term given
to a kind of crimson-coloured animalcule, the 350th of an
inch in length, that exist in enormous numbers, and give
the waters in which they live the appearance of their
bodies. Ehrenberg describes several varieties of them.

The family Euglenoe of Dujardin in many particulars
corresponds with that of the AstasicE of Ehrenberg ; while
Mr. Carter would refer Euglence to the vegetable and
Astasice to the animal kingdom. "The power, however,
to vary the figure can be no adequate character, for this is
partaken by the gonidia of various algae; the tapering,
hairlike prolongation, the existence of one, two, or more-
ciliary filaments, and the red speck, are also the well-

INFUSORIA. 413

known characteristics of some zoospores." The individuals
are all free, and furnished with a hairlike appendage ; ova
are perceptible in Astasia hcematodes, and probably exist in
other species. From their varying colour, their apparent
changes of form, and the rapidity of their motions, they
are most interesting objects under the microscope. The
immense number in which these Infusoria are sometimes
developed in a few days, and the blood-red colour they
impart, have frequently been the cause of alarm and
anxiety to persons residing in the vicinity of ponds which
have become coloured by their swarming. Ehrenberg de-
scribes a species of Euglena, E. sanguinea, and he con-
jectures that the miracle in Egypt, recorded by Moses, of
turning the water into blood, might have been effected by
the agency of these creatures. Very lately, Mr. Shep-
pard l met with another specimen, probably belonging
to this family, adhering to the submerged stones in a
clear spring, between Ashford and Maids tone. His
specimens were taken home in a piece of glazed paper,
and upon opening them he found the paper " stained
with hues of red, blue, and purple;" and the whole " re-
sembling clots of red jelly, or recently coagulated blood."
Upon placing a small quantity on a glass side for viewing
under the Microscope, " the colour appeared to be opaque-
red, looking like a small quantity of vermilion mixed with
the water ; but when held up to the light the red disap-
peared, and a pale transparent blue took its place."

Believing this colour to depend upon the presence of
albumen mixed with the animal organisms, Mr. Sheppard
placed a small quantity of the jelly-like substance in con-
tact with some white of egg diluted with water ; and " soon
the whole became converted into magenta dye," the
solution exhibiting the same colouring properties, namely,
that of reflecting from its surface all the red and yellow
rays, and transmitting the blue and violet/' Mr. Brown-
ing, upon submitting specimens to the micro-spectroscope,
found that it gave a very marked band in the red-ray. The
whole spectrum is, indeed, very remarkable, and, writes

(1) "An example of the production of a coloured fluid possessing remarkable
qualities by the action of monads (or some other znicroscopic organism) upon
organized substances." By J. B. Sheppard, M.R.C.S.— Trans. Micros. Soc. July,
1367, p. 64.

414 THE 1IICROSCOPE.

Mr. Sorby, "it is the only blue solution in class C (of
which blood is the type) that gives this particular spec-
trum." The fluid emits a most pungent and disagreeable
odour when the bottle in which it is kept is uncorked.

The common form of the Euglence is represented in
Plate III. No. 67, a contracted, b elongated. Oxytricha
are larger and the body more elongated ; their movements
are more impulsive, alternately creeping, running, and
climbing. In all the species digestive vacuoles are evi-
dent ; and they multiply by self-division, as well as ova.
Ehrenberg counted ten cilia anteriorly, and four or five
setae posteriorly. The species is found both in fresh and
brackish water. Plate III. No. 70, represents a side view
of 0. gibba, No. 71, 0. Pellionella. In the genus Glau-
coma, Nos. 73 and 74, Ehrenberg saw "indications of an
alimentary canal." Dujardin places Glaucoma among
ParamaBcia ; the body is oval and covered with cilia ;
mouth large, with vibratory valves ; increase takes place
by self-division. A re- examination of all the enumerated
species of Infusoria is quite necessary before we can come
to any safe conclusion as to their true affinities, especially
as many appear to be only larval forms of life.

" The question of how far individuals belonging to the
same species may vary is one more intimately connected
with that department of Zoology which treats of the dis-
tribution of animals than their development. For it can
be readily shown that animals are capable of becoming
modified to an indefinite extent by the physical conditions
under which they are placed, and, indeed, that one species
may be, so to speak, made to pass into that of another ; so
that many of the apparently dissimilar animal forms found
on the earth may be more correctly viewed as varieties of
the same species, the differences between them being due
to the external agencies to which each has respectively
been subjected."

The remarkable manner in which the Infusoria make
their appearance in fluids, and the seeming inexplicable
phases in their existence, led some early observers to start
a " spontaneous generation " theory of life ; but the re-
searches of M. Pasteur and others have completely exploded
this view of the formation of living organisms. The order

INFUSORIA. 415

in which these minute creatures appear in vegetable in-
fusions has been made the subject of careful inquiry. Mr.
Samuelson, whose researches on this point were carried on
in conjunction with Dr. Balbiani of Paris, and confirmed
by him, tells us that when a carefully prepared infusion of
vegetable matter in distilled water is exposed to the air,
the Protozoa which first appear in it are Amoebae : these in
a few days disappear, and are succeded by ciliated infusoria,
such as Kolpoda, Cyclidium glaucoma, and sometimes Vor-
ticella, and these in their turn by what we have looked
upon as higher forms, Oxytrichum, Euplotes, Kerona, &c.
Mr. Samuelson thinks that Monads are but the larval con-
dition of the ciliated infusoria, and he noticed the constant
occurrence of Monads belonging to the species Circomonas
fiisi/ormis, or acuminata of Dujardin, &c., in pure distilled
water after a certain exposure to the air, and this without
the previous admixture of vegetable matter of any kind in
the water. The same results were obtained upon shaking
rags, from various and distant parts of the world, over the
distilled water; in all cases in about three weeks he
invariably obtained forms of ciliated infusoria. " The fusi-
form body of the Circomonas bears a long whip-like cilium
at its anterior end, and a short seta at its caudal extremity :
this finally drops off, and when exposed to excessive heat
and light, the animal is transformed into an Amosba."

Mr. Samuelson's results do not very materially differ
from our own, save in one or two particulars. The suc-
cession of generations do not take quite the same course,
and the animal and vegetable bodies generally appear
simultaneously, or so soon after each other that it is at
times difficult to decide the priority of appearance ; but
our experiments have been chiefly confined to collections
of rain and distilled water, without the addition of vege-
table matter of any kind. We are, however, quite agreed
as to the very extensive distribution of these infusorial
germs, and their great tenacity of life. With regard to the
supposed purity of rain-water, at no time can it be taken
without the numerous matters floating in the air being
brought down with it ; and, consequently, within a few hours
after it is caught, Protococcus pluvialis, Amoeba, and Girco-
monas may always be found in vast numbers. It is somewhat

416

THE MICROSCOPE.

remarkable that the purest snow-water, caught in a clear
glass vessel, and allowed to remain well corked, will, in
the course of two or three weeks, be found to contain
Amoeba and Circomonas, but it rarely presents other forms
of animal life ; the vegetable matter then completes its
growth very slowly, gradually passes to Confervse, and for a
time no other change is seen to take place ; so that it is
painfully apparent that the atmosphere in which we live and
move and have our being is something more than a mixture
of gases, as apparently determined by chemical analysis.

Fig. 219.

1, Achnunthidiwm coarotatuni, 2, A. litieare. 3, TryUiondla gracillis. 4,
Amphitetras antediluviana. 5, 6, and 7, Orthosira spinosa. Front view, with
globular and oval forms. (Fossil Infusoria from Springfield, Barbadoes.)

Ehrenberg's " Poly gastric Infusoria" have indeed under-
gone a complete revision : some have been degraded to the
vegetable kingdom, as the Desmidiaceve, Volvocinece, &c.,
whilst others have been advanced a step higher in the
animal series ; none having received so much attention from
microscopists, or excited so much controversy, as the Desmi-^
diacece and Diatomacece. The first of these we have already
disposed of in our remarks on the vegetable kingdom,
where we must be content to leave them for the present ;

DIATOMACE^!. 417

not so the Diatomacem, which offer many interesting struc-
tural characteristics of sufficient importance to warrant our
keeping them in the animal division. They are most
striking objects under the microscope, from the very pecu-
liar beauty and variety of their forms, and from their
bilateral symmetry, external markings, and indestructible
siliceous skeletons ; so that we believe they would be more
correctly placed in a median, or Molluscian sub-kingdom.
Appearing everywhere with the first-born of life, and
wherever matter is found in a condition fit for their deve-
lopment and nourishment, these marvellous indestructible
creatures have been preserved and brought down to us, in
forms unchanged, from the remotest periods of our globe's
history; and supplying, as they do to the microscopist,
some of the most valuable test-objects, — the Gyrosigma,
Grrammatophora, Fragilaria, fiipidopJiora, Pleurosigma
angulatum, with many others, — it cannot be a matter of
surprise that considerable attention should have been di-
rected to them, and an earnest inquiry instituted into their
nature and structure.

"Comparing," says Kiitzing, "the arguments which
seem to indicate the vegetable nature of Diatomacece with
those which favour their animal nature, we are of ne.ces-
sity led to the latter opinion. If we suppose them to be
plants, we must admit every frustule, every Navicula to be
a cell. We must suppose this cell with walls penetrated
by silica, developed within another cell of a different
nature, at least in every case where there is a distinct
peduncle, or investing tube. In this siliceous wall we
must recognise a complication certainly unequalled in the
vegetable kingdom. It would still remain to be proved
that the eminently nitrogenous internal substance corre-
sponded with the generic substance, and that the oil
globules could take the place of starch. The multipli-
cation would be a simple cellular reduplication ; but it
would remain to be proved that it takes place, as in other
vegetable cells, either by the formation of two distinct
primitive utricles, or by the introflection or constriction of
the wall itself. Finally, there would still remain un-
explained the external motions and the internal changes ;
and we must prove the accumulated observations on the
E E

418

THE MICROSCOPE.

exterior organs of motion to be false, by a clearer line of
argument than has hitherto been adopted by those who
are opposed to this view. But again, admitting their
animal nature, much would remain to be investigated,
both in their organic structure and their vital functions ;
excepting this, so far as we know, we have only one diffi-
culty to overcome, that of the probably ternary non-
azotised composition of the external gelatinous substance
of the peduncles and investing tubes. But as the presence
of nitrogen is not a positive character of animal nature,

Fig. 220.

1, Cymbella Ehreribergii. 2, Side view of the same, showing an arrangement of
the sarcode and pseudopodia. 3, Pleurosigmata lanceolatum. 4, Lateral view
of a portion of the same. 5, 6, and 7, Pinnularia. 8, Diatoma vulgare. 9,
Nitzschia varvula.

so the absence of it is not a proof of vegetable. And, in
order that the objection should really have some weight,
it would be well to demonstrate that this substance is
isomeric with starch. For then, supposing all the argu-
ments in favour of the animal nature of Diatomacece were
proved by new and more circumstantial observations, this
peculiarity, if it deserve the name of objection, might still
be regarded as an important discovery. We should then
have in the animal, as well as in the vegetable kingdom, a
ternary substance similar to that forming the bases of the
vegetable tissue."

DIATOMACE^:.

419

Diatomacece, brittleworts, siliceous £acilla?'ia, are organ-
isms composed of two symmetrical plates or valves, narrow
or wand-like, navicular — as a miniature boat or "little
ship ; " hence their name, Navicula. A rectangular or
prismatic figure is, however, the typical form of this
family, and the angles of junction of the valves are as a
rule, acute. Deeply notched frustules, such as we see in
the Desmids, Micrasterias denticulata, Docidium pristidce,
Plate II. Xos. 30 and 31, do not occur, and the produc-
tion of spines and tubercles is rare among the Diatoms.
Each individual Diatom is enclosed by a soft organic
matter (sarcode) ; the internal portion is yellowish or
orange-brown in colour. In the discoid forms two por-
tions are commonly distinguishable, viz. the disc and
margin — or rim, and these present different markings, with
an occasional central prominence, called an umbo or boss.
Great variety of outline may prevail in a genus, so much
so, that no accurate definition can be safely
laid down : thus in the genera Navicula,
Pinnularia, the frustules are in one aspect
boat-shaped, and in another oblong with
truncated ends, prismatic. Mr. Brightwell
thus describes and explains the transitions
of form produced by a change in position
of the frustules of the genus Triceratium.1
" The normal view of the frustule may be
represented by a vertical section of a tri-
angular prism. If the frustule be placed
upon one of its flat sides, we look down
upon its ridge and obtain a front view of
its two other sloping sides. If it be placed
upon one of its ridges, we have a front'
view of one of its flat sides, generally
broader than long, and of its smooth or

,. Fig. 221.— Gompho-

trausparent suture or connecting mem- nema eiongatum
brane. If the frustule be progressing •** wpitatum.
towards self-division, it is then often considerably longer
than broad, and when nearly matured for separation, pre-
sents the appearance of a double frustule." So with re-

1) Journ. Micros. Soc. vol. I. p. 248.
EE2

420 THE MICROSCOPE.

gard to the beautiful Surirella cvnstricta, the side view is
no longer bacillar, but the breadth of the valve is very
considerable, and when about to undergo subdivision it
becomes square-shaped. The distinctive character, how-
ever, of this genus, in addition to the presence of canaliculi,
is derived from the longitudinal line down the centre of
each valve, and the prolongation of the margins into
" alae." The sudden change in appearance presented to
the eye as the frustule is seen to roll over, is very remark-
able. As a rule, therefore, we must examine all specimens
in every aspect, to accomplish which very shallow cells
should be selected, say of 1-1 00th of an inch deep, and
covered with glass l-250th of an inch thick. A good
penetrating objective must be used, and careful illumina-
tion obtained. The examination of living specimens
should be conducted during very bright weather, the
mirror directed towards a white cloud, or even sunlight :
with coloured glasses to protect the eyes from injury.
The Diatomaceae are perhaps more widely distributed than
any other class of infusorial life ; they inhabit fresh, salt,
and brackish water ; many grow attached to other bodies
by a stalk (Plate II. No. 33), Licmophora and Achnanthes;
while others, as the Pleurosigma, No. 40, swim about
perfectly free in the water.

There are a considerable number of Diatomaceae which,
while in the young state, are enclosed in a muco-gelatinous
sheath ; while others are attached by a stipes or stalk to
Algae. Ehrenberg recognised a tribe of compound Dia-
toms, with a double lorica, and introduced them into his
great family of JBacillaria, under the name of Lacernata or
Navicula. Silex enters largely into the composition of
their valves, but, being in combination with organic sub-
stances, it does not depolarize light. In several genera
silex is very deficient, and the wall of the frustule of
great delicacy. Mr. Brightwell, speaking of the lorica or
siliceous covering of the Triceratium, states " that the
valves are resolvable into several distinct layers of silex,
dividing like thin divisions of talc, and frequently of such
exquisite delicacy as to be difficult of detection." Na'geli
speaks of a mucilaginous pellicle on the inside of the
organic layer as a sort of third tunic ; and, as Meneghini

DIATOMACKffi.

421

truly observes, " An organic membrane ought to exist, for
the silica could not become solid except by crystallizing or
depositing itself on some pre-existing substance." The
surface of the frustules is generally very beautifully
sculptured, and the markings assume the appearance of
dots (puncta), stripes (strise), ribs (costae), pinnules
(pinnae), of furrows and fine lines j longitudinal, trans-
verse, and radiating bands ; canals or canaliculi ; and of
cells or areolse ; whilst all present striking varieties and
modifications in their form, character, and degree of deve-
lopment. Again, the fine lines or striae of many frustules
are resolvable into rows of minute dots, such as occur in
Pleurosigma, &c.

The nature of the markings on the Diatom valves is one
of considerable in-
terest, and has ex-
cited much atten-
tion, and attempts
have been made to
produce them arti-
ficially. On the ad-
dition of sulphuric
acid to a mixture of
powdered fluor spar
and sand, an imme-
diate evolution of
fluoride of silicon
takes place, as is
shown by the white
fumes. This white-
ness is due to the
presence of minute
particles of silex
arising out of the
decomposition of the
fluoride by the mois-
ture contained in the
atmosphere ; and il
a solid body be ex-
posed to these vapours, a portion of the silex will be
deposited on it, in the form of a fine white powder, con-

Fig. 222.

1, Pleurosigma attmuatum. 2, Pleurosigma an
gulatum, magnified 250 diameters. 3 , Pleuro-
sigma Spencerii, magnified 350 diameters.

422 THE MICROSCOPE.

sisting of thin walled vesicles filled with air. If some of
the deposit be crushed between two pieces of glass, and
examined with a power of about 300 diameters, a marking
will be perceived on the outer or convex surface of many of
these vesicles, similar to that of many Diatomacese, such
as Pleurosigma, Coscinodiscus, &c. Hounded elevations,
more or less hexagonal at the base, and more or less
regularly arranged, cover the surface of the siliceous
pellicle, and not unfrequently this kind of marking is so
regular as to give the fragments exactly the appearance of
portions of diatomaceous valves.

This remarkable circumstance attracted the attention of
Professor Max Schultze, who devoted a great deal of time
to the investigation of the subject, and has recorded in a
voluminous paper1 the results of his observations. He
says, " The appearances presented under the microscope by
the siliceous pellicles were such as to suggest that they
were due possibly to crystallisation. The minute eleva-
tions on the surface, when viewed on the side, often appear
sharply acuminate, so as readily to convey the impression
that they are formed by minute crystals of silex ; and this
impression is strengthened at first sight by their sharply
detined hexagonal basis, when viewed vertically. The
circumstance, again, that these elevations are sometimes
rounded at the summit and circular at the base, might be
attributed to the accidental interference of free hydrofluo-
silicic acid, &c. But experiments to eleminate the action
of this agent showed that it had nothing to do with the
variety of appearance in the elevations.

" Most of the species of the diatomaceae are characterised
by the presence on their outer surface of certain differences
of relief, referable either to elevations or to depressions
disposed in rows. The opinions of microscopists with re-
spect to the nature of this marking are divided. Whilst
in the larger forms, and those distinguished by their coarser
dots, the appearance is manifestly due to the existence of
thinner spots in the valve, we can not so easily explain the
cause of the striation or punctation in Pleurosigtna
angulatum and similar finely-marked forms. In these it

(1) " Verhandl. d. Natur Hist. Vereinsder Preussiscli. Rheinland, u. West-
r>h.il." Jahr xx. p. 1. Micros. Jour. Science, vol. iii. p. 120.

DIATOMxVCE^E. 423

often seems as if the appearance- were due to pyramidal
elevations, with hexagonal bases, standing in regnlar rows,
exactly like those observed in the siliceous vesicles above
mentioned.

" In any case, it seemed likely, since the marking just
noticed is essentially alike in many different species of
diatoms, that its ultimate causes were to be sought, less,
perhaps, in any organic formative process, than in the
deposition of silex under the same laws as those by which
its deposition in the other case is regulated. Were this ulti-
mate cause shown to be crystallisation the question would
be solved. But that the secretion of amorphous silex in
diatoms, as in these pellicles, is undeniable, on account of
their specific gravity being about 2 '2, the specific gravity
of crystallised silex being 2-6."

But further investigation rendered the correctness of
this assumption (that the markings are due to crystallisa-
tion) doubtful in the highest degree, and it soon became
quite certain that neither in the artificial siliceous pellicles
nor in the diatom valves are the peculiar forms essentially
due to a crystalline structure.

Mr. Charles Stodder, of Boston, says, " I have reasons
for thinking that neither party has the true explanation
of the structure. My opinion is that the exterior of the
shell is smooth, or nearly so, and that the borders of the
hexagons, or other shaped areolse, and costse of the Cos-
tate forms, are internal projections from the outer plate,
as on the under side of the leaf of the Victoria Regia, in-
tended to give strength to the cell with the smallest
quantity of material. This will explain the trace of the
hexagons seen on the inner plate of Neliopelta, as only
the projecting wall of the areolse would come in contact
with the inner plate. Dr. Griffiths reasoned that the
areolse were depressions, because they were the thinnest
parts of the shell ; the facts are correct, but the inference
may not be, as there is another explanation of the pheno-
mena." See directions for the illumination of test-objects,
page 174.

Movements of Diatoms. — The researches of Professor
Max Schultze, of Bonn, published 1865, appear to throw
some light on the vexed question of the movements of the

424 THE MICROSCOPE.

Diatomacece. This author is of opinion that a sa.rcod«
substance envelopes the external surface of the diatom,
and its movement is due to this agent exclusively. He
prefers the P. angulatum, Plate II. JSo. 38, for examination
to the larger P. balticum, because the transverse markings
on its frustule do not impede to so great an extent the
observation of what is going on within. When you have
a living specimen of P. angulatum under the microscope,
it always has its broad side turned to view, with one long
curved "raphe" uppermost, and the other in contact with
the glass on which it is placed ; at the central part is seen
the thickened " umbilicus," Plate 2, No. 40. Within the
siliceous frustule is the yellow colouring matter, or "endo-
chrome," which fills the cavity more or less completely,
and is arranged in two longitudinal masses, to the right
and left of the raphe. In the broader part of the frus-
tule these bands of endochrome describe one or two com-
plicated windings. It is only possible in those specimens
in which the bands are narrow properly to trace their
foldings, and ascertain that only two exist, since an
examination of frustules richer in endochrome has led to
the impression that there are three or four of these bands.
"The next objects which strike the eye on examining
a living Pleurosigma are highly refractive oil-globules.
These are four in number ; one pair near either end of the
the Diatom. They are not, however, all in the same place,
one globule of each pair being nearer the observer than
the other ; their relative position is best seen when a view
of the narrow side of the frustule can be obtained, so that
one raphe is to the left and the other to the right. The
blue-black colour, which is assumed by these globules
after the Diatom has been treated with hyperosmic acid,
demonstrates that they consist of oleaginous matter. The
middle of the cavity of the frustule is occupied by a
colourless finely granular mass, whose position in the body
is not so clearly seen in the fla.t view as in the side view.
Besides the central mass, the conical cavities at either end
of the siliceous shell are seen to be filled with a similar
granular substance, and two linear extensions from each of
the three masses are developed, closely underlying that
part of the shell which is beneath the raphas; so that

DIATOMACEJfc. 425

in the side view they appear attached to the right and left
edges of the interior of the frustule. This colourless
granular substance carries in its centre, near the middle
part of the Diatom, an imperfectly developed nucleus
which it is not very easy to see, but may be easily de-
monstrated by the application of acid. The colourless
substance is what, in other Diatoms, Schultze shows to be
Protoplasm, or vegetable sarcode, and which contains
numerous small refractive particles. On adding a drop of
hyperosmic acid, these are coloured blue-black, and prove
to be fat. It is, however, exceedingly difficult to deter-
mine the exact limitations of the protoplasm, on ac-
count of the highly refractive character of the siliceous
shell, and the obstruction presented by the bands of
endochrome.

After a short distance, the protoplasm reappears, and
is contracted into a considerable mass within the conical
terminations of the frustule. Schultze observed in this
part of the protoplasm a rapid molecular movement such
as is known to occur in the Closterium, and further, a
current of the granules of the protoplasm along the raphe.
Pleurosigma angulatum " crawls" as do all Diatoms pos-
sessing a raphe, along this line of suture. To crawl along,
it must have a fixed support. He believes free swimming
movements are never to be observed in this or in any
other Diatom. Accordingly, Schultze invariably found
that the raphe is in contact with either the glass slip or
the glass cover, between which the Diatom is placed, or is
in apposition with some foreign body of considerable size.
Schultze repeated the experiments of Siebold, and ob-
served, as he and also Wenham had done long before,
that particles of foreign matter stick to the raphe as
though it were covered with some glutinous material,
and are carried slowly along by the action of a current.
This he observed in many Diatomacese, and found in-
variably that foreign particles adhered only to the raphe,
or what corresponded to it. "There is obviously," says
Schultze, " but one explanation ; it is clear that there must
be a band of protoplasm lying along the raphe, which
causes- the particles of colouring matter to adhere, and
gives rise to a gliding movement. For there is but one phe-

426 THE MICROSCOPE.

nomenon which can be compared with the gliding motion
of foreign bodies on the Diatomaceae, and that is, the
taking up and casting off of particles by the pseudopodia
of the rhizopoda, as observed, for instance, on placing a
living Gromia or Miliolina in still water along with
powdered carmine. The nature of the adhesion and of
the motion is in both cases the same in all respects. And
since, with Diatoms as unicellular organisms, protoplasm
forms the principal part of the cell body (in many cases
two distinctly moving protoplasms), everything suggests
that the external movements are referable to the move-
ments of this protoplasm." It is quite evident to those
who have studied the movements of the Diatoms that
they are surrounded by a sarcode structure far more deli-
cate in its character than that of the Amoeba. Six years
before Schultze's observations were piiblished, the fact
appeared in a third edition of this work, page 307 ; therein
it is stated that "The act of progression rather favours
the notion of contractile tentacular filaments, — pseudo-
podia, — as the organs of locomotion and prehension. The
hyaline or sarcode covering is of so transparant a nature
that as yet no microscopic power has enabled us to assign
its precise boundary and attachments.1 Some observers
would deny a membranaceous (hyaline) covering of any
kind to Diatoms, which we have certainly seen." Pro-
fessor Smith, of America, has satisfactorily traced a sar-
code covering in Pinnularia. The denning power, pene-
tration of the objective, and mode of illumination, is
everything in such investigations.

It was in 1841 Messrs. Harrison and Sollitt, of Hull,
discovered the beautiful longitudinal and transverse stria?
(groovings) on the Pleurosigma hippocampus. A curved
graceful line runs done the shell, in the centre of which is
an expanded oval opening. Near to the central opening

(1) Referring to the strength and vigour of the movements of the Diato-
macese, Dr. Donkin (Quart. Jour. Mic. Sci. vol. VI. new series, p. 26), observed
a species Bacillaria cursoria, discovered by himself, push away "A. arenaria,
a species at least six times their own size ; " and Mr. Barkas states that he has
seen them " push away particles of foreign matter, and that with the greatest
apparent ease, at least one hundred times larger than all the frustules coin-
bmed ; and what is more remarkable still, is that they not only push the accu-
mulated particles away when they are in their direct line of motion, but, if
they merely touch them in passing, they drag them after them as though the.>
were literally hold by some magnetic attraction, or strong cement."

DIATOMAO&E.

427

the dots elongate crossways, presenting the appearance of
small short bands. The Pleurosigma angulatum (fig. 223),
was first discovered in the Humber ; the lines upon its
surface resemble the most elegant tracery, which are
resolvable into raised minute dots. The markings are
seen to be longitudinal, transverse, and oblique.

In the vicinity of Hull many very interesting varieties
of DiatomacecB have been found, the beauty of the varied
forms of which are such as to delight the microscopist ;'

1, PUuroeigma angulatum. •!, Portion of the same, magnified 1200 diameters.
3, Portion of P. formosum, magnified 5500 diameters.

at the same time some of them are highly useful, as form-
ing that class of test objects which are best calculated above
all others for determining the excellence and powers of
object-glasses. It has been shown by Mr. Sollitt that
the markings on some of the shells are so fine as to range
between the 30,000th and 130,000th of an inch; the
Pleurosigma strigilis having the strongest markings, and
the Pleurosigma acus the finest.

As to the value of the Diatomacece as test-objects, it is
generally admitted, and since Mr. J. D. Sollitt first pro-
posed the use of their shells for this purpose, we append
his measurements of the lines : —

Amphiplenra Pellucida, or Acus, 130,000 in the inch, cross lines.

Bigmoidea, 70,000 in the inch.
Navicula Rhomboides, 111,000 in the inch, cross lines.

428 THE MICROSCOPE.

Pleurosigraa Fasciola, fine shell, 86,000 in the inch, cross lines.
„ ,, strong shell, 64,000 in the inch, cross lines.

„ Strigosum, 72,000 in the inch, diagonal lines.

,, Angulatum, 51,000 in the inch, diagonal lines.

„ Quadratum, 50,000 in the inch, diagonal lines.

Spencerii, 50,000 in the inch, cross lines.

Attenuatum, 42,000 in the inch, cross lines.

Balticum, 40,000 in the inch, cross lines.

Formosum, 32,000 in the inch, diagonal lines.

Strigilis, 30,000 in the inch, cross lines.

Mr. Norman, of Hull, has favoured us with the follow-
ing : —

HINTS FOR COLLECTING DIATOMACE^.

These minute forms are found in all waters, but the
most interesting species are those found in salt water,
especially shallow lagoons, salt water marshes, estuaries of
rivers, pools left by the tide, &c.

Their presence in any quantity is always shown by the
colour they impart to the aquatic plants and sea-weeds
they are found attached to, and if found on the mud,
which is very frequently the case, they impart to it also a
yellowish brown colour approaching to black brown, if in
great numbers. This brownish pellicle, if carefully re-
moved with a spoon (without disturbing the mud) will be
found very pure. Capital gatherings of Diatomaceae
might be obtained by carefully scraping the brown coloured
layer from mooring posts, and piles of wharfs and jetties.

In clear running ditches the plants and stones have
often long streamers of yellowish brown slimy matter
attached to them, which is generally entirely Diato-
maceous.

When found in large quantities on the mud the layer
is often covered with bead-like bubbles of oxygen. This
often detaches them from the bottom and buoys them to
the surface, where they form a dense brown scum, which
is blown to leeward in large quantities, and presents the
general appearance of dark-coloured yeast. In this form
it may be collected in abundance, often quite free from
particles of sand and other impurities. Good and rare
species have been obtained from the stomachs of oysters,
scallops, and other shell-fish inhabiting deep water. The
sea-cucumbers (Holothuridse) found so frequently in
southern latitudes contain many species. These animals

DIATOMACE2E. 429

might be simply dried and preserved just as found, and
the contents of the stomach afterwards obtained by
dissection.

Noctilucae, which are the cause of phosphorescence in
the sea, are Diatom feeders, and might be caught in large
quantities in a fine gauze towing-net, and preserved. The
Ascidians found attached to oyster shells and stones from
deep water have yielded excellent gatherings. The Salpse
often noticed in warm latitudes floating on the surface of
the sea, and assuming chain and other like forms, should
be bottled up for examination. These Salpae are well
known Diatom feeders. Deep-sea soundings ought to be
preserved, especially from great depths, and are often
exclusively Diatomaceous. Sea-weed from rocks ought to
be preserved, especially the smaller species, and if covered
with a brown furriness, so much the better. Very rare
species have been found in immense quantities in the
ARCTIC and ANTARCTIC regions, by melting the "pancake
ice," often found discoloured by these minute beings. The
sea is often observed to be covered by brownish patches.
The discoloured water (or " spawn" as it is called) should
be collected, filtered through cotton wool, and the
brown residue preserved. When a fine impalpable dust
is observed to be falling at sea, it ought to be collected
from the folded sails and other places where it lodges.
This may yield Diatornacese, which from the method of
collecting would be highly interesting to examine. The
roots of the various species of Mangrove (Rhizaphora),
which form impenetrable barriers along the salt water
rivers and estuaries in the tropical parts of Africa,
Australia, the Eastern Archipelago, &c., are found fre-
quently covered with a brown mucous slime very rich in
Diatomacese. When the Diatomacese are collected from
any of the above-mentioned sources, they may be at once
transferred to small bottles, or the deposit may be partially
dried and wrapped up in pieces of paper or tinfoil.
When placed in bottles, a few drops of spirits added will
keep them nice and sweet. In all cases it is essential to
keep the gatherings separate and distinct, and that the
locality whence obtained be written on each package.

The collector will probably find that, notwithstanding

430 THE MICROSCOPE.

every care, his specimens are mixed with much foreign
matter, in the form of minute particles of mud or sand,
which impair their value, and interfere with observation,
especially with the higher powers of his instrument.
These substances the student may remove in various
ways : by repeated washings in pure water, and at the
same time, profiting by the various specific gravities of the
Diatoms and the intermixed substances, to secure their
separation ; but, more particularly, by availing himself of
the tendency which the Diatomacece generally have to
make their way towards the light. This affords an easy
mode of separating and procuring them in a tolerably clean
state ; all that is necessary being to place the gathering
which contains them in a shallow vessel, and leave them
undisturbed for a sufficient length of time in the sunlight,
and then carefully remove them from the surface of the
mud or water. The simplest method of preserving the
specimens, and the one most generally useful to the scien-
tific observer, is simply to dry them upon small portions of
talc, which can at any time be placed under the micro-
scope, and examined without further preparation; and
this mode possesses one great advantage, — that is, that the
specimens can be submitted without further preparation to
a heat sufficient to remove all the cell-contents and softer
parts, leaving the siliceous epiderm' in a transparent
state.

ON CLEANING DIATOMACEOUS DEPOSITS. — "The first
point to be ascertained is the nature of the material which
binds the mass together. In the generality of deposits,
this seems to be aluminous or earthy matter, often mixed
with some siliceous material which renders the action of
acids of little avail. When the bulk of the deposit is
clayey matter, the best plan is to place the lumps broken
quite small into a vessel and pour on a few ounces of hot
water, rendered thoroughly alkaline with common washing
soda. This plan frequently answers, causing the lumps to
swell, gradually separating into layers, and finally falling
asunder into a pulpy mass. The strong soda ley must
now be removed by repeated washing, and afterwards
boiling in a flask with pure nitric acid ; the whole must
afterwards be transferred to a large stoppered vessel and

FOSSIL INFUSORIA. 431

violently shaken, in order to break up the minute frag-
ments of dirt, and set free the siliceous Diatoms. After
shaking, allow the vessel to stand for half an hour or
more according to the size and density of the valves : the
Diatoms having subdivided, the dirty water is drawn off
by a syphon, arid fresh water added, and the shaking re-
peated. The whole secret depends upon getting rid of
the impurities by this violent shaking and washing ; when
quite free from all impurities the material may be trans-
ferred to a test tube, washed in distilled water, and finally
mounted."1

Fossil Infusoria. — Startling and almost incredible as the
assertion may appear to some, it is none the less a fact,
established beyond all question by the aid of the micro-
scope, that some of our most gigantic mountain-ranges,
such as the mighty Andes, towering into space 25,250 feet
above the level of the sea, their base occupying so vast an
area of land ; as als"6 our massive limestone rocks, the sand
that covers our boundless deserts, and the soil of many of
our wide-extended plains ; are principally composed of
portions of invisible animalcules. And, as Dr. Buckland
truly observes : " The remains of such minute animals
have added much more to the mass of materials which
compose the exterior crust of the globe than the bones of
elephants, hippopotami, and whales."

The stratum of slate, fourteen feet thick, found at Bilin,
in Austria, was the first that was discovered to consist almost
entirely of minute flinty shells. A cubic inch does not
weigh quite half an ounce ; and in this bulk it is estimated
there are not less than forty thousand millions of indi-
vidual organic remains ! This slate, as well as the Tripoli,
found in Africa, is ground to a powder, and sold for
polishing. The similarity of the formation of each is
proved by the microscope ; and their properties being the
same, in commerce they both pass under the name of
Tripoli : one merchant alone in Berlin disposes annually of
many hundred tons weight. The thickness of a single shell
is about the sixth of a human hair, and its weight the hun-

(1) G. Norman, Esq. Micros. Journ. vol. iv. p. 238. For other methods of
cleaning and preparing Diatoms, see Smith's Synopsis of the British Diatn-
macete; also Quar. Journ. Micros. Science, vol. vii. p. 167, and vol. i. N. 8. 1861,
p. 143.

432

THE MICROSCOPE.

dred-and-eighty-seven-millionth part of a grain. The
well-known Turkey stone, so much used for the purpose of
sharpening razors and tools ; the Rotten-stone of com-
merce, a polishing material ; and the pavement of the
quadrangle of the Royal Exchange, are all composed of
infusorial remains.

Fig. 224.

1, Shell of Araehnoidiscus. 2, Actinocyclus (Bermuda). 3, Cocconeis (Algoa Bay).
4, Coscinodiscus (Bermuda.) 5, Isthmia enervis. 6. Zygoceros rhombus.

The bergh-mekl, mountain-meal, in Nor way and Lapland,
has been found thirty feet in thickness ; in Saxony, twenty-
eight feet thick ; and it has also been discovered in Tus-
cany, Bohemia, Africa, Asia, the South Sea Islands, and
South America ; of this, almost the entire mass is com-
posed of flinty skeletons of Diatomaceas. That in Tuscany
and Bohemia resembles pure magnesia, and consists
entirely of a shell called campilodiscus, about the 200th
of an inch in size.

FOSSIL INFUSORIA. 433

Darwin, writing of Patagonia, says : " Here along the
coast, for hundreds of miles, we have our great tertiary for-
mation, including many tertiary shells, all apparently
extinct. The most common shell is a massive gigantic
oyster, sometimes a foot or more in diameter. The beds
composing this formation are covered by others of a
peculiar soft white stone, including much gypsum, and
resembling chalk ; but really of the nature of pumice-
stone. It is highly remarkable, from its being composed,
to at least one-tenth of its bulk, of Infusoria; and Pro-
fessor Ehrenberg has already recognized in it thirty
marine forms. This bed, which extends for five hundred
miles along the coast, and probably runs to a considerably
greater distance, is more than eight hundred feet in thick-
ness at Port St. Julian." Ehrenberg discovered in the
rock of the volcanic island of Ascension many siliceous
shells of fresh- water Infusoria; and the same indefatigable
investigator found that the immense oceans of sandy
deserts in Africa were in great part composed of the shells
of animalcules. The mighty Deltas, and other deposits of
rivers, are also found to be filled with the remains of this
vast family of minute organization. At Richmond in
Virginia, United States, there is a flinty marl many miles
in extent, and from twelve to twenty-five feet in thickness,
almost wholly composed of the shells of marine animal-
cules j for in the slightest particles of it they are discover-
able. On these myriads of skeletons are built the towns
of Richmond and Petersburg. The species in these earths
are chiefly Namculce; but the most attractive, from the
beauty of its form, is the Coscinodiscus, or sieve -like disc,
found alike near Cuxhaven, at the mouth of the Elbe, in
the Baltic, near Wismar, in the guano, and the stomachs
of our oysters, scallops, and other shell-fish. Another
large deposit is found at Andover, Connecticut ; and
Ehrenberg states "that similar beds occur by the river
Amazon, and in great extent from Virginia to Labrador."
The chalk and flints of our sea-coasts are found to be
principally shells and animal remains. Ehrenberg com-
putes, that in a cubic inch of chalk there are the remains
of a million distinct organic beings. The Paris basin, one
hundred and eighty miles long, and averaging ninety in

FF

434 THE MICROSCOPE.

breadth, abounds in Infusoria and other siliceous remains.
Ehrenberg, on examining the immense deposit of mud
at the harbour of Wismar, Mecklenburg-Schwerin, found
one-tenth to consist of the shells of Infusoria ; giving a
mass of animal remains amounting to 22,885 cubic feet
in bulk, and weighing forty tons, as the quantity annually
deposited there. How vast, how utterly incomprehen-
sible, then, must be the number of once living beings,
whose remains have in the lapse of time accumulated !
In the frigid regions of the North Pole no less than sixty-
eight species of the fossil Infusoria have been found.
The guano of the island of Ichaboe abounds with fossil
Infusoria, which must have first entered the stomachs of
fish, then those of the sea-fowl, and became ultimately
deposited on the islands, incrustating its surface ; whence
they are transported, after the lapse of centuries, to aid
the fruition of the earth, for the benefit of the present race
of civilized man. The hazy and injurious atmosphere met
with off Cape Verd Islands, and hundreds of miles distant
from the coast of Africa, is caused entirely by a brown
dust, which upon being examined microscopically by
Ehrenberg, was found chiefly to consist of the flinty sheila
of Infusoria, and the siliceous tissue of plants : of these
Infusoria, sixty-four proved to belong to fresh-watei
species, and two were denizens of the ocean. From the
direction of the periodical winds, this dust is reasonably
supposed to be the finer portions of the sands of the desert
of the interior of Africa.

The deposit of the beneficent Nile, that fertilises so
large a tract of country, has undergone the keen scientific
scrutiny of Ehrenberg ; and he found the nutritive prin-
ciple to consist of fossil Infusoria. So profusely were they
diffused, that he could not detect the smallest particle of
the deposit that did not contain the remains of one or
more of the extensive but diminutive family that once
revelled in all the enjoyment of animal existence. It is
very remarkable that at Holderness, in digging out a sub-
merged forest on the coast, numbers of fresh-water fossil
DiatomacecB have been discovered, although the sea flows
over the place at every tide.

Mode of Preparing Fossil Infusoria. — Before entering

PREPARATION OP FOSSIL INFUSORIA. 435

on further details of the fossil Infusoria, we would first
state how they may be prepared for microscopic examina-
tion. A great many of the infusorial earths may be
mounted as objects without any previous washing or pre-
paration : some, such as chalk, however, must be repeat-
edly washed, to deprive the Infusoria of all impurities ;
whilst others, by far the most numerous class, require
either to be digested for a long time, or even boiled in
strong nitric or hydro-chloric acid, for the same purpose.
Place a small portion of the earth to be prepared in a test-
tube, or other convenient vessel, capable of bearing the
heat of a lamp ; then pour upon it enough diluted hydro-
chloric acid to about half fill the tube. Brisk effervescence
will now take place, which may be assisted by the applica-
tion of a small amount of heat, either from a sand-bath or
from a lamp : as soon as the action of the acid has ceased,
another supply may be added, and the same continued
until no further effect is produced. Strong nitric acid
should now be substituted for the hydro-chloric, when a
further effervescence will take place, which may be greatly
aided by heat ; after two or three fresh supplies of this
acid, distilled water may be employed to neutralise all the
remains of the acid in the tube ; and this repeated until
the water comes away perfectly clear, and without any
trace of acidity. The residuum of the earth, which con-
sists of silica, will contain all the infusorial forms ; and
some of this may be taken up by a dipping-tube, laid on
a slide, and examined in the usual manner. Should per-
fect specimens of the Cosdnodiscus, Gallionella, or Nawr
cula be present, they may be mounted in Canada balsam ;
if not, the slide may be wiped clean, and another portion
of the sediment taken, and dealt with in the same way,
which, if good, after being dried, may be mounted in Canada
balsam.

Dr. Redfern adopts an excellent mode of isolating Navi-
culoe and other test-objects. He says : " Having found
the methods ordinarily employed very tedious, and fre-
quently destructive of the specimens, I adopted the follow-
ing plan. Select a fine hair which has been split at its
free extremity into from three to five or six parts, and
having fixed it in a common needle-holder by passing it

FF2

436 THE MICROSCOPE.

through a slit in a piece of cork, use it as a forceps under
a two-thirds of an inch objective, with an erecting eye-
piece. When the split extremity of the hair touches the
glass-slide, its parts separate from each other to an amount
proportionate to the pressure, and on beii.g brought up to
the object, are easily made to seize it, when it can be
transferred as a single specimen to another slide without
injury. The object is most easily seized when pushed to
the edge of the fluid on the slide. Hairs split at the ex-
tremity may always be found in a shaving-brush which has
been in use for some time. Those should be selected which
have thin split portions so closely in contact that they
appear single until touched at their ends. I have also
found entire hairs very useful, when set in needle-holders,
in a similar manner ; any amount of flexibility being given
to them by regulating the length of the part of the hair
in use." Professor Smith, of Kenyon, U.S. contrived a
very ingenious " Mechanical finger " for picking up and
arranging diatoms and other minute objects.

Professor J. W. Bailey, of New York, has enriched the
Museum of the College of Surgeons with several valuable
specimens of the skeletons of Infusoria; among them is a
fresh-water JBacillaria, named Meridion circulare, which
Professor Quekett, in the Historical Catalogue, describes
as " consisting of a series of wedge-shaped bivalve siliceous
loricse, arranged in spiral coils ; when perfect, and in cer-
tain positions, they resemble circles ; each lorica is articu-
lated by two lateral surfaces." It is asserted that they
creep about when free from the stalk-plate. (Fig. 225, No.
1 6.) Cocconema lanceolata have two lanceolate flinty, cases
that taper towards their ends, one of which is attached to
a little foot. Each lorica has a line marked in its centre,
and transverse rows of dots on both sides : Ehrenberg says
there are twenty-six rows in the one-hundredth of a line.
(Fig, 225, No. 14.) Achnanthes Longipes have at the
margins two coarse convex pieces roughly dotted, and two
inner pieces firmly grooved ; the inside seems filled with
green matter. At one corner they are affixed to a jointed
pedicle, which in many specimens contains green granules.
In a specimen of a fossil Eimotia, found in some Bermuda
earth, the flinty case is /a four parts; it is of a half-

FOSSIL INFUSORIA.

437

lanceolate shape, and a little indented on both margins ;
two of them have curved rows of dots, and the other two
are partly grooved with finer rows. Ehrenberg says they
have four openings, all on one side (fig. 225, No. 13),

Fig. 225.

7, Campilodiscus clypeiis. 8, Mddlllphia. 9, GaUionelia snlcata. 10, Trice-
r>itium, found in Thames mud. 11, Gomphonema geminatum, with their stalk-
like attachments. 12, Dictyocha fibula. 13, Eunotia. 14, Cocconema. 15, Fra-
gilaria pectinalis. 16, Meridian circular e. 17, Diatoma flocculosum.

presenting a row of dots varying very much in number ;
minute striae in some cases extend from each dot towards
the middle of the lorica ; and on the circumference there
are two of these dots. The spirals and the individual
lorica are very fragile, and therefore easily separated from
each other. Of a glistening whiteness is the ribbon-like
flinty case of Frayilaria pectinalis, which consists of
many bivalve segments : on the articulating surface there
are small grooves, represented in fig. 225, No. 15. A sin-

438 THE MICROSCOPE.

gular class of objects are Diatoma flocculosum, being rather
oblong-looking, and joined -to each other at opposite cor-
ners : they are sometimes grooved on each side. (Fig. 225,
No. 17.) The "Swollen Eunotia" is generally about
from the llth to the 200th of an inch in length: a
groove, widest in the centre, and tapering off to the ends,
passes along its centre on both sides ; it has curved lines
proceeding from it. So wonderfully close are these lines
or ribs, that as many as eight of them have been
counted in the space of the 1200th of an inch. They are
usually found when alive adhering to a branch of some
weed that forms the green coating over stagnant waters.
They propagate by self-division ; a slight line running
down the centre marks where the separation will occur,
on each becoming perfectly developed as a distinct crea-
ture ; and thus they grow and separate, filling the earth
with their flinty shells.

Gallionella sulcata is found in many parts of North
America ; it somewhat resembles the cylindrical box for
spices, which was at one time so common among good
housewives; scientifically, it is described as consisting of
chains of cylindrical bivalve loricse, having their outer
surfaces marked or furrowed with longitudinal striae ; short
joints may occasionally be seen, having their ends upper-
most, the depth of the furrows being shown on the margin ;
within the margin is a thin transparent rim having ra-
diating striae. Sometimes as many as forty will be found
joined together. (Fig. 225, No. 9.) The Gallionella received
its designation from a celebrated French naturalist named
Gaillon, it is often termed the Box-chain Animalcule, and
when the flinty case is seen lying on its face, it much re-
sembles a coin. These living infusoria are found in almost
all waters, and are stated to be so rapid in their growth,
that one hundred and forty millions will by self-division
be produced in twenty-four hours. A species named the
Striped Gallionella was discovered by Dr. Mantell near
London ; the same species is also found in the ocean.
Sometimes the chains are three inches long; their size is
from the 14th to the 400th part of an inch.

Professor Quekett, in the catalogue we have referred to,
describes an '•' earth from Bohemia, particularly rich in

FOSSIL INFUSORIA. 439

fossil specimens of Navicula viridis, which consists of four
prismatic loricee, two ventral and two lateral ; the former
having round, the latter truncate extremities ; and both
provided with two rows of transverse markings and dots,
longer and more marked on the ventral than on the lateral
surfaces. The specimens having their ventral surfaces
uppermost, exhibit a longitudinal marking in the centre,
with a slight dilatation or knob at each extremity ; this
marking is interrupted in the middle of the lorica, and a
diamond-shaped spot is left ; if one of the lateral loricse be
examined, two of the same spots will be seen, one on each
side ; they are of triangular figure, and appear to be thicker
parts of the shell, described as holes by Ehrenberg." Four
smaller triangular spots may be observed in the same
lorica, one being situated at each corner ; these also have
been considered as openings by Ehrenberg : their length
varies considerably; some exceed the 100th, whilst others
are even smaller than the 1000th of an inch. Isthmia ener-
ms (fig. 224, No. 5) is usually found attached to sea-weed ; it
is in three parts; and of a trapezoid shape, the centre part
appears like a band passing over, and is bounded by broad
straight lines : its outer surface is covered with a network
of rounded reticulations, arranged in parallel lines. Among
the most remarkable is Amphitetras antediluviana ; this
is of a cubical or box-like figure, and consists of three
portions, the one in the centre being in the form of a band.
as shown at fig. 225, No. 8, and the two lateral ones having
four slightly projecting angles, with an opening into each.
When viewed in detached pieces, the central one is like
a box, and the two lateral portions resemble the cover and
bottom. The former may be readily known, as consisting
merely of a square frame-work with striated sides ; but
both the latter are marked with radiating reticulations.
When recent, they are found in zigzag chains, from their
cohering only by alternate angles. In some instances, as
in Biddulphia, and Isthmia, two young specimens may be
found within an old one. Cocconeis is marked with eight
or ten lines proceeding from the inner margin to the
centre ; between which are dotted furrows, with the earlier
spot in the centre of each. (Fig. 224, No. 3.)

Campilodiscus clyptuz is oval, and curved in opposite

440 THE MICROSCOPE,

ways at the long and short diameters. On the margin
there are two series of dots, sometimes joined ; and on the
oval centre there are also dots about the margin, while the
middle is nearly plain. (Fig. 225, No. 7.) Actinocyclus has
a round bivalve flinty case, with numerous cells formed by
radiating partitions; very often every alternate cell only
is on the same plane. The specimen in the Museum of
the College of Surgeons is exquisite in its markings ; it
was found in some Bermuda earth, and has a beautifully-
raised margin, and a five-rayed star in the centre ; the
number of cells is ten, five being on one plane and five on
another. One set has the usual hexagonal reticulations
crossed with diagonal lines, the other has the same lines,
with a much smaller series of triangular reticulations, so
disposed that they appear to form with each other parts
of very small circles. One valve from this specimen is
represented in fig. 224, No. 2.

As well as the beautiful shell of the Coscinodiscus, found
both in a fossil and recent state, there is one of exquisite
elegance and richness, of the genus Arachnoidiscus, so
named from the resemblance of the markings of the shell
to the slender fibres of a spider's web. (Fig. 224, No. 1.) This
is found in the guano of Ichaboe, and also in earth from
the United States, as well as among sea-weed from Japan,
and the Cape of Good Hope. Mr. Shadbolt believes :
" These shells are not, strictly speaking, bivalves, although
capable of being separated into two corresponding por-
tions ; but are more properly multivalves, each shell con-
sisting of two discoid portions, and two annular valves
exactly similar respectively to one another." (See Micro-
scopical Society's Transactions, for an excellent paper on
these shells by Mr. Shadbolt.)

Artists who design for art-manufacturers might derive
many useful hints from the revelations of the microscope,
as evidenced in the arrangement of the shell last noticed,
and in that of the genus Coscinodiscus; a very handsome ob-
ject, the shells of which are marked with a network of cells
in a hexagonal form, arranged in radiating lines or circles,
and varying from l-200th to l-800th of an inch in diameter.
A specimen found in Bermuda earth has on one of its valves
two parallel rows of oval cells that form a kind of cross ;

XANTHIDIA. 441

which gradually enlarge from the centre to the margin ;
the angles of the cross are filled up with hexagonal cella
as previously noticed. (Fig. 224, No. 4.)

The unskilled manipulator may for some time endeavour
to adjust a slide, having a piece of glass exposed not larger
in size than a pea, on which he is informed an invisible
object worthy his attention is fixed, before he is rewarded
by a sight of Triceratium favus, extracted from the mud of
the too-muddy Thames. The hexagonal markings, cells,
are beautiful, and at each corner there is a curved pro-
jecting horn or foot. (Fig. 225, No. 10.) In Bermuda earth
there is a small species found, which has its three margins
curved ; and also a curious species, which resembles the
triradiate spiculum of a sponge.

It is remarkable how, in these minute and obscure
organisms, we find ourselves met by the same difficulties
concerning any positive laws governing the formation
of generic types, as in larger and more complex forms of
animal and vegetable life. It appears as if we could
carry our real knowledge little beyond that of species ; and
when we attempt to define kinds and groups, we are en-
countered on every side by forms, which set at nought our
definitions.

Man even uses infusorial remains as food ; for the berg-
mehl, or mountain-meal found in Swedish Lapland, and
which, in periods of scarcity, the poor are driven to mix
with their flour, is principally composed of the flinty shells
of the Gallionella sulcata, Namcula viridis, and Gompho-
nema geminatum. Dr. Trail, on analysing it, found it
to consist of 22 per cent of organic matter, 72 of silica,
o-85 of alumina, and O15 of oxide of iron. This woiild
seem to be the same substance described by M. Laribe the
missionary, and put to a similar use in China : " This
earth," he says, "is only used in seasons of extreme
dearth."

XANTHIDIA. — In conjunction with the skeletons of the
former species it will be as well to offer a few remarks upon
animals long classed with Infusoria, and but rarely found
except in the fossil state. There is every reason to believe
that the Xanthidia, double-bar animalcules, are sporangia
of Desmidiacece. In proof of this it can be shown that

442

THE MICROSCOPE.

their skeletons are composed of a horny substance, and not
of silica, as was once supposed.

The name Xanthidia is derived from a Greek word sig-
nifying yellow, that being their prevailing hue. They are
found plenteously in a fossil state, imbedded in flint, as
many as twenty being detected in a piece the twelfth of
an inch in diameter ; in fact, it is rare to find a gun-flint
without them. When living they may be described as
having a round transparent shell, from which proceed
spikes varying in size and shape. One kind, found by Dr.
Bailey in the United States, was of an oval form, the 288th
of an inch in length ; and another species circular, found
by the late Dr. Mautell, at Clapham : both were of a
beautiful green colour. Specimens of Branched Xanthi-
dium, found in flint by Dr. Mantell, were from the 300th
to the 500th of an inch in diameter. Mr. Ralfs says:
" That the orbicular spinous bodies so frequent in flint,
are fossil sporangia of Desmidiacece, cannot, I think, be
doubted, when they are compared with figures of the
more recent forms. Indeed, the late Dr. G. Mantell, who,
in his Medals of Creation, without any misgiving, had
adopted Ehrenberg's ideas concerning them, changed his
opinion ; and in his last work regards them as having been
reproductive bodies, although he is still uncertain whether
they are of vegetable origin."

The fossil forms vary as much as recent Sporangia, in
being smooth, bristly, or furnished with spines, some
are simple, and others branched at the extremity. Some-
times, a membrane may be traced, even more distinctly
than in recent specimens, either covering the spines, or
entangled with them. Writers have described the fossil
forms as having been siliceous in the living state ; but
Mr. Williamson informs us that he possesses specimens
which exhibit bent spines and torn margins ; and this
wholly contradicts the idea that they were siliceous be-
fore they were embedded in the flint. In the present
state of our knowledge, it would be somewhat premature
to identify the fossil with recent species ; it is better,
therefore, at least for the present, to retain the names
bestowed on the former by those observers who have de-
scribed them.

XANTHIDIA. 443

Near to Sydden Spoint, and the Round Down Cliff, on
the Dover beach, Mr. H. Deane cut out a piece of pyrites
with the adherent chalk, which, on examination, " exposed
to view bodies similar to, if not identical with, Xan-
thidia in flints ; he clearly recognised X. spinosum, ramo-
sum, tubiferum, simplex, tubiferum recurvum, malleoferum,
and pyxidiculum, together with casts of Polythalamia, and
other bodies frequently found in flints. In shape they are
somewhat flattened spheres, the greater part of them
having a remarkable resemblance to gemmules of sponge,
with a circular opening in the centre of one of the
flattened sides. The arms or spines of all appear to be
perfectly closed at the ends, even including those which
have been considered in the flint, specimens decidedly
tubiferous ; showing that if the arms are tubes, they could
afford no egress to a ciliated apparatus similar to those
existing among Zoophytes. On submitting them to pres-
sure in water between two pieces of glass, they were torn
asunder laterally, like a horny or tough cartilaginous sub-
stance ; and the arms in immediate contact with the glass
were bent. Some specimens, put up after several weeks'
maceration in water, were so flaccid, that, as the water in
which they were suspended evaporated away, the spines or
arms fell inclined to the glass. These circumstances alone
seem clearly to disprove the idea of their being purely
siliceous. The casts of the Polythalamia, portions of
minute crustaceans, &c. appeared also to be, like the Xan-
thidia, some modification of organic matter ; and in the case
of the Polythalamia, the bodies are so perfectly preserved,
that in some the lining membranes of the shells are readily
distinguishable."

Mr. Wilkinson, who examined recent Xanthidia found in
the Thames mud, and slime, on piles and stones at Green-
hithe, said that, in his opinion, they are not siliceous,
but of a horny nature, similar to the wiry sponges, which
Mr. Bowerbank describes as being very difficult to destroy
without the action of fire. He also met with a peculiarity
in a X. spinosum, which he has never seen in any other
species ; it was in a piece of a gun-flint. There appeared,
as it were, a groove or division round the circum-
ference, similar to that formed by two cups when placed

444 THE MICROSCOPE.

on each other, so as to make their rims or upper edges
meet.

The other fossil Infusoria, found most abundantly in the
chalk and flint of England, are the Rotalia, or wheel- shaped,
and the Teoctularia or woven-work animalcules ; the latter
having the appearance of a cluster of eggs in a pyramidical
form, the largest being at the base, and lessening towards
the apex.

We must here bring to a close this short notice of
some of the marvellous creations in the invisible world ;
every glimpse inspiring awe, from the immensity, variety,
beauty, and minuteness of its organised habitants. Immen-
sity, in its common impression on the mind, hardly conveys
the idea of the myriads upon myriads of Infusoria that
have lived and died to produce the tripoli, the opal, the
flints, the bog-iron> the ochres, and limestones of the world.

Professor Owen beautifully explains the uses of this vast
amount of animalcule life: — "Consider their incredible
numbers, their universal distribution, their insatiable
voracity ; and that it is the particles of decaying vegetable
and animal bodies which they are appointed to devour
and assimilate. Surely we must, in some degree, be in-
debted to these ever-active, invisible scavengers, for the
salubrity of the atmosphere and the purity of water. Nor
is this all ; they perform a still more important office in
preventing the gradual diminution of the present amount
of organised matter upon the earth. For when this matter
is dissolved or suspended in water, in that state of com-
minution and decay which immediately precedes its final
decomposition into the elementary gases, and its con-
sequent return from the organic to the inorganic world,
thesB wakeful members of nature's invisible police are
everywhere ready to arrest the fugitive organised particles,
and turn them back into the ascending stream of animal
life. Having converted the dead and decomposing par-
ticles into their own living tissues, they themselves become
the food of larger Infusoria, and of numerous other small
animals, which in their turn are devoured by larger ani-
mals ; and thus a food, fit for the nourishment of the
highest organised beings, is brought back, by a short route,
from the extremity of the realms of organised matter.

VORTICELLID.fi. 445

These invisible animalcules may be compared, in the great
organic world, to the minute capillaries in the microcosm
of the animal body ; receiving organic matter in its state
of minutest subdivision, and when in full career to escape
from the organic system, turning it back, by a new route,
towards the central and highest point of that system."

Such, then, seem to be some of the purposes for which
are created the wonderful invisible myriads of infusorial
animalcules. In the words of Holy Writ : " All these
things live and remain for ever for all uses ; and they are
all obedient. All things are double one against another ;
and He hath made nothing imperfect. One thing estab-
lisheth the good of another ; and who shall be filled with
beholding His glory ? "

VORTICELLID^;. — We now come to a family, which includes
some of the most beautiful of living infusorial animalcules,
and in which we meet with phenomena more curious than
any yet witnessed, and perhaps as wonderful as any that
will be presented to our notice, in the natural history of
the higher classes of animals. The family of Vorticellidce,
bell-animalcules, are characterised by the possession of a
fringe of rather long cilia, surrounding the anterior ex-
tremity, which can be exerted and drawn in at the pleasure
of the creatures. Some are furnished with a horny case
for the protection of their delicate bedies, 'whilst others
are quite naked.

The genus Vorticella, from which the name given to
the family is derived, consists of little creatures placed at
the top of a long flexible stalk, the other extremity of
which is attached to some object, such as the stem or leaves
of an aquatic plant. This stem, slender as it is, is never-
theless a hollow tube, through the entire length of which
runs a muscular thread of still more minute diameter.
When in activity, and secure from danger, the little Vor-
ticella stretches its stalk to the utmost, whilst its fringe of
cilia is constantly drawing to its mouth any luckless
animalcule that may come within the influence of the
vortex it creates ; but at the least alarm the cilia vanish,
and the stalk, with the rapidity of lightning, draws itself
up into a little spiral coil. But the Vorticella is not
wholly condemned to pass a sort of vegetable existence.

446

THE MICROSCOPE.

rooted, as it were, to a single spot by its slender stalk ; its
Creator has foreseen the probable arrival of a period in its
existence when the power of locomotion would become

Fig. 226.

1, 2y 3, Hydros in various stages of development. 4, A group of Stentor poly-
morphus, many-shaped Stentor. 5, EngletM. 6, Monads.

necessary, and this necessity is provided for in a manner
calculated to excite our highest admiration. At the lower
extremity of the body of the animal, at the point of its
junction with the stalk, a new fringe of cilia is deve-
loped ; and when this is fully formed, the Vorticella quits
its stalk, and casts itself freely upon its world of waters.
The development of this locomotive fringe of cilia, and
the subsequent acquisition of the power of swimming by
the Vorticella, is generally connected with the propagation
of the species, which, in this and some of the allied genera,
presents a series of most curious and complicated phe-
nomena.

VORTICELLID^;. 447

The Vorticella possess means of propagation which is
denied to other Infusoria, with the exception of a few,
although we meet with the same in other forms of animal
life. The mode of reproduction referred to is called
gemmation; it consists in the production of a sort of
bud, which gradually acquires the form and structure
of the perfect animal. In the Vorticellce, these buds,
when mature, quit the parent stem after developing a
circlet of cilia at the lower extremity, and fix themselves
in a new habitation in exactly the same manner as those
individuals produced by the fissuration of the bell.

At an earlier or later period of their existence, the
Vorticelloe withdraw the discs surrounded by cilia which
forms the anterior portion of their bodies, and con-
tracting themselves into a ball, secrete a gelatinous cover-
ing, which gradually solidifies, and forms a sort of capsule,
within which the animal is completely inclosed. By this
process the little animal is said to become encysted; and
at this point of its history it is seen to be more compli-
cated. Sometimes its further progress commences by the
breaking up of the nucleus into a number of minute oval
discs, which swim about in the thin gelatinous mass ink
which the substance of a parent has become dissolved.
The body of the parent animal, inclosed within the cyst,
now becomes apparently divided into separate little sacs
or bags, some of which gradually acquire a considerable
increase in size, and at length break through the walls of
the cyst. After a time one of these projections of the
internal substance bursts at the apex; and through the
opening thus formed the gelatinous contents of the cyst,
enclosed embryos, are suddenly shot out into the water,
there to become diffused, giving rise to new generations.
From the name Acineta given to them by Ehrenberg, who
described them as a new genus, they are denominated
Acineta-forms.

But the final object of this singular metamorphosis
still remains to be described. The nucleus, which at the
change of the encysted animalcule into the Acineta-form
was still distinctly observable, becomes entirely and alto-
gether converted into an active young Vorticella, acquiring
an ovate form, with a circlet of cilia round its narrower

448 THE MICROSCOPE.

extremity, and presenting at the opposite end a distinct
mouth. Within this young animal, whilst still inclosed in
the body of its parent, we see a distinct nucleus, and the
usual contractile space of the full-grown creature. When
mature, the offspring tears its way through the membranes
inclosing the Acineta, which, however, immediately close
again. The latter continues protruding and retracting ita
filaments, and soon produces in its interior a new nucleus,
which in its turn becomes metamorphosed into a young
Vorticella.

The same faculty of enclosing themselves in a cyst is
said to be made use of by the Vor-
ticella, as a means of self-preservation
if the water in which they have been
living dries up. When the animal is
thus encased, the mud at the bottom
of the pool may be baked quite hard
in the sun without doing it the least
injury ; and in this state the creatures
are often taken up by the wind with
the dust which it raises from the sur-
face of the parched ground, and borne
ig. 227. along to great distances, so as to cause

Vorticdla microstoma. , , . ° &

their appearance in most unexpected
loocalities (they are frequently found in roof gutters), where
the first shower of rain calls them back to active life.

Conochilus vorticella,1 belonging to the family ^Ecistina,
Plate III. No. 80, is one of the most remarkable and in-
teresting Rotifers met with. It is found in compound
groups of a whitish globular form in shallow ponds about
London. On Hampstead Heath a good supply is often
obtained throughout the summer months. The group
consists of from twenty to thirty, or more, animals, of about
twice the size of the full-grown volvox, and, like the
latter, can be readily seen actively rolling about when the
collecting-bottle is held up to the light. The colony is
attached to a centre disc, resembling a wheel with its
naves and spokes. The foot-stalk is three or four times
the length of the body, and has a somewhat spiral form,
which it contracts at pleasure, drawing the body down in
an instant close to the axis, although it does not appear to

(1) Commonly called volvox, but this is an error, as it clearly does not belong
to the Volvocinse.

UOTIFRf^E. 449

have the power of retracting itself perfectly within the
hyaline membrane. The hyaline membrane is at certain
periods of the year so very translucent that it cannot be
made out ; later in the season it is found studded with para-
sitic desmids, when its gelatinous form is readily seen. The
body is ovoid or cup-shaped, and the mouth is surrounded
by long cilia, which are always in rapid motion. When
the animal becomes alarmed it instantly retracts, and then
has the appearance of a small round ball. On the frontal
plane four thickish conical erect papillae are placed, each fur-
nished with one or more spines or seke ; very near their
base, rather behind, and between the division of the
ciliary band, are the very minute visual organs. The
jaws, it is said, are furnished with teeth, but these we
have not been able to make out, chiefly owing to their
disposition to break up in a short time after being placed
in confinement. The stomach is oval, and two ovoid
bodies are observed near the termination of the oesophagus ;
below these the ova-sack encloses a single ovum of a dark
colour. The ovum is surrounded by spinous processes, or
cilia, and when first thrown off it lodges for a time in the
hyaline membrane ; but, when set free, moves slowly
about. A few minutes after being placed in the glass-cell
the colony become uneasy, break themselves off one after
the other, and swim away to die. They were formerly
classed among Volvocinece, but bear no resemblance to
them, except in their roll through the water j and are
more properly placed among the Eotifers.

Acineta tuberosa, Plate 111. No. 68. — The researches of
Stein are said to prove that the several members of this
family are simply a developmental phase of Vorticellina;
this view, however, is controverted by Lachmann, Cla-
parede, and others who have witnessed the reproduction of
Acinetce from parent forms. A . tuberosa has a triangular-
shaped body and three obtuse tubercles or horns, each
furnished with tentacula. Many other forms of this
genus are well known ; but, notwithstanding the diversity
in construction, Stein, declares their tubular ramified pro-
cesses to be morphologically and physiologically identical
with ordinary tentacula. Vaginicola crystallina he puts
forward as one of the best illustrations to be obtained of

G G

450 THE MICROSCOPE.

the conversion of an encysted Vorticellina into an Acineta.
He also considers Actinophrys Sol and Podophrya fixa
(Ehr.) to be the acinetiform representatives of Vorticella
microstoma.

Stentors, Trichodina, and a few others are included by
some authors in the Vorticellina. Stentors (fig. 226, No. 4)
are exclusively found in fresh water, between or upon
water plants in still running waters. Some are colourless,
others green, black, or clear blue. " It is," says M. Du-
jardin, " in the Stentors where we can view the several
supposed internal organs isolately, and that new observa-
tions will make known their real nature."

Rotiferce comprise animals which were placed by
Ehrenberg in nine genera ; named Ptygura, ^Ecistes, Cono-
chilus, Megalotiocha, Lacinularia, Tubicolaria, Limnias,
Melicerta, and Cephalosiphon. As, however, each of these
genera contain but a single species, Mr. Gosse proposes to
reduce the nine to two ; thus, Ptygura, jfflcistes, Tubico-
laria, Limnias, Melicerta, and Cephalosiphon, as they seem
to be only so many species of one genus, might constitute
one, and Megalotrocha, Lacinularia, and Conochilus, an-
other. Mr. Gosse also wishes to construct a family to be
called Melicertodce; in this he would include two genera,
Melicerta and Megalotrocha, degrading some of the present
genera to form species of Melicerta, and others, to constitute
three species of Megalotrocha. Each group will be readily
distinguished — the former by the circumstance that the
individuals are solitary ; in the latter they are, in adult
life, aggregated in a common envelope — spherical masses,
composed of many animals radiating from a central point.
These compound masses are either free or fixed. In the
genus Melicerta, or tube-dwellers proper, the front 01
upper part of the body is capable of being turned in
upon itself, concealed with purse-like folds, and of being
expanded, at the will of the animal, into a disc form, which
is usually much wider than the diameter of the body ;
this again is either flat or in the form of a shallow funnel.
Its outline will form either a simple circle, as in M. pty-
gura and M. cecistes, two circles united at one point, as in
Limnias (Plate III. No. 72), or four sinuous lobes, more or
less developed, as in M . cephalosiphon, M. tubicolaria, and

BOTIFERffi. 451

M. ringens, in each of which there is, according to Pro-
fessor Huxley, a double edge to the disc, of which the
subordinate one is placed on the under-side, and a little
within the line of the principle one. The former is fringed
with minute cilia, whose vibratile waves form well-marked
movements, which run evenly along the margin. The
eggs are usually laid within the case.

To the genus Melicerta Mr. H. Davis 1 adds one, if not
two, new species, which he has named, provisionally, M.
longicornis and M. intermedia^. The two peculiarities of
these new forms are the remarkable length of the antennae,
and the construction of tube-dwellings for the purpose of
concealing themselves and their eggs. (Plate III. No.
69.) jEcistes longicornis : each animal lives in a separate
semi-transparent cylindrical sheath (urceolus), into which
it entirely withdraws on the approach of danger. The foot-
stalk is long, and firmly attached to the bottom of the tube.
Two or three ova are concealed in the lower part of the urce-
olus. The trochal disc is large, and completely surrounded
by a ciliary wreath. The antennae, two, are very long, well
placed below the disc, and terminating in a small brush of
setae. The tube, Mr. Davis believes, is built up in the same
way as that of Melicerta.

Mr. Slack describes, in the " Intellectual Observer,"
a tubicolous Rotifer, discovered in the stems of the Ana-
charis, which shows an affinity with JZcistes, Limnias. and
Melicerta, but differs in some points, especially in the an-
tennae; this, named by Mr. Gosse Cephalosiphon, displays
a single antenna of extraordinary length and versatile
power. Like Melicerta and Limnias, it shows no visible
construction below the disc, whereas in jEcistes this is a
conspicuous feature.

" The animal inhabits a case slightly trumpet-shaped,
generally of greater length and slenderness compared with
those of its allies, standing erect on the pond-weed. It is
irregular and floccose in outline, very opaque, and of a
deep umber brown by transmitted light, but of a much
lighter hue by reflected light. It is composed, doubtless,
of an excretion from the skin as the foundation layer,

(1) "On two new species of the genus .fficistes," by Henry Davis, F.R.M.S,
Micros. Soc. Trans. April 1807.

452 THE MICROSCOPE.

thickened and rendered opaque by the addition of the
dark material, which I conjecture to be the fsecal pellets
sucessively discharged in process of growth. Contrary to
the rule in the allied genera, the petaloid disc is made to
open by the bending forward of the head towards the
ventral aspect, and its widest margin is the dorsal one.
Immediately behind the disc are two minute lateral horn-
like points, which project from the head, and curve to-
wards each other. These are sometimes visible both in a
frontal and a lateral view, and with the disc closed or
open ; but at other times the closest scrutiny fails in dis-
cerning them. Behind these, in the median line, there
is an organ which is never concealed : it is the single
antenna, which stands up perpendicularly from, the occiput
to a great height (being almost half as long as the body,
exclusive of the foot), and generally arches over the front,
but is capable of vigorous and sudden movements to and
fro, and from side to side. It is evidently tubular through-
out ; either a simple tube with thick walls, or else, if the
walls are thin, furnished with a slender piston which runs
through its length.

" The Cfphalosiphon is very lively and active in its
motions. It is very ready to protrude from its case, and
not at all prone to retire upon ordinary alarms, such as a
jar upon the instrument, that would send the Floscularia
or the Steplianoceros into its retreat in an instant. It is
very curious to see it protruding : the long antenna is first
thrust out, and jerked to and fro as a feeler, exploring the
surrounding water for safety. The entire height of an
average specimen, in its ordinary state of extension, is
l-33d of an inch ; of which the foot is l-50th, the body
l-200th, and the antennae 1 -400th of an inch.

The rotating or wheel-animalcules occupy the most
conspicuous place among infusorial animals. They re-
quire water for their development, although they are
indwellers occasionally of the cells of mosses and damp
weeds. They do not possess many stomachs, but one,
and generally have teeth and jaws to supply its wants.
They can elongate and contract their bodies, and some
species have their extremity prolonged to a tail, or rather
a foot, or a forked process, by means of which they

ROTIFERS.

453

fix themselves to extraneous substances ; while the cilia
is in rapid motion, this prevents the anterior portion of
the body being drawn in by the force of the rotatory

Fig. 228.

1, The common Wheel-Animalcule, Rotifer vulgaris, with its cilia or rotators
b, protruded ; c, its horn ; d, oesophagus ; e, gut ; /, outer case ; g, eggs. 2, The
same in a contracted state, and at rest : at g is seen the development of the
young. 3, Pitcher-shaped Brack/onus: a, its jaws; b, shell; c, cilia, or rota-
tors : d. tail 4. Bakers Brachionus : a, the jaws and teeth ; b, the shell ; c,
the cilia ; e, the stomach.

action. They multiply by eggs ; a few have been seen to
bring forth their young alive. In the atmosphere the eggs
have been discovered whirling along by the force of the
wind to some resting-place, where, when circumstances
admit, they spring into active life, and fulfil their appointed
destiny. The eggs are of an oval form, and some ten,
twenty, or thirty may be seen in an animal, of a brown
colour, others are of a delicate pink and deep golden yel-
lo\r. In those of a light colour, the young are sometimes

154 THE MICROSCOPE.

seen with their cilia in active vibration. Ehrenberg
accurately described the upper part of a common wheel-ani-
malcule, with the cilia, jaws, teeth, eyes, &c., as seen under
a magnifying power of 200 diameters, and represented in
fig. 228, No. 1. The small arrows indicate the direction of
the currents produced by the cilia b, turning on their base.
At the will of the animal a change is made in the direction
in which the wheels appear to revolve, these it has the
power of withdrawing, with the quickness of thought; a
cluster of hairs appears at the extremity, that do not
revolve, and certainly differ from the cilia: as they are
usually protruded when the creature is moving from place
to place, their function has been imagined to be that of
feelers.

The red spots, very generally believed to be the eyes of
the Rotifer ve> are mostly of a bright red colour ; and the
number and arrangement of these organs vary. In some
species there have been discovered as many as eight, often
placed on either side of the head, in a row, circle,
or cluster, and in some they take a triangular shape.
The Rotiferoe delight in the sunshine; and when the
bright luminary is hidden behind clouds, the animals
sink to the bottom of the water, and there remain.
When the water of their haunts is becoming much evapo-
rated, they rise to the top, and give a bright-red tint to
it ; but when caught and placed in a jar, their beautiful
colour fades in a few days. Locomotion is performed by
swimnJmg, the rotatory action of the crowns of cilia im-
pelling it forward; in other instances it bends its body,
then moves its tail up towards the head, with the two
processes that serve as feet near the tail; it then jerks its
head to a further distance, again draws up its tail, and so
proceeds on its journey. Another peculiarity is that
of drawing in the head and tail until nearly globular,
and remaining in this condition fixed by the sucker; at
other times they become a complete ball, and are rolled
about by every agitation of the water.

The body of the wheel-animalcule is of a whitish colour;
its form is indicated in the engraving. The tube for
respiration appears to allow of water passing to the inside.
On the food being drawn by the currents to the cup part

TIOTIFER2E.

455

of the wheels, it passes through a funnel as it were to tho
mouth, which is situated rather lower down, and where
the food is crushed by teeth placed on the plates of the
jaw, with a hammer-like action ; from this point it passes
through the alimentary canal for the sustenance of the
animal.

BRACHION^A. — Ehrenberg's genus Brachionus, " Spine-
bearing animalcules," belonging to the Rotifer ce, are truly
interesting, from their very perfect and complex orga-
nisation. Some are entirely enclosed in a horny covering,
others only partially covered. Their structure, so beau-
tiful and symmetrical, has always made them favourites
with those who delight in microscopical studies. — Bra-
chionus striatus, " Striped shell animalcule " (No. 3, fig.
228), of an elegant, jug-like form, has tho transparent
coat or carapace, striated and scalloped out at the upper
part ; through which the citron-
coloured inhabitant protrudes itself.
Two hornlike processes are appended
to its under-side. As occasions re-
quire, it sinks firmly and securely
within its crystal home, which is suffi-
ciently transparent to permit a view
of its organisation. Its progress is
effected by means of ciliary processes.
— Brachionus Paid, or Anurce Cervi-
cornis, "Bent horn animalcule," is
possessed of double rotatory organs,
and four long processes, which project
above the external coat. It measures
the 9 Oth part of an inch. — Brachionus
Ovalis, " Egg-shaped brachionus," is
remarkable for the strength -of its
transparent coat, which is beyond
that of other horny creatures. Its
projecting tail, as well as head, is at
pleasure withdrawn into its very Fig 229

strong case. — Brachionus Dentatus, lf BmcUonw omiis closed
" Toothed brachionus." This active, 2' Cilia displayed,
bright pink- eyed little creature, the 90th part of an inch
in size, is apparently enclosed in a two-valved shell, having

458 THE MICROSCOPE.

each end indented so as to form two pair of teeth. Mr.
Pritchard says:— "In addition to the rotatory organa
for supplying it with food, I have observed it attached
to a stem of confervce, and abrading it with its teeth
fixed in the bulbous oesophagus, which, during the opera-
tion, oscillates quickly; the rotatory cilia at the same
time move rapidly, which makes it highly probable that
they perform some office connected with the organs of
respiration, as their motion seems altogether unnecessary
while the creature is feeding in this manner." — Brachionus
Bdkeri, "Baker's brachionus," (fig. 228, No. 4), is a curious
and beautifully-formed animal. At the points of a half-
circle are situated the rotatory organs and cilia, between
which rise some long spines, each side of the shell pro-
ceeding to a point in the lower part, while a square seems
taken out of its body, forming thus two spines ; from the
central part of the body projects a long tail. The eggs are
sometimes attached to these spines, and in other instances
are seen in the ovisac.

Notommata Aurita, the " Eared notommata." — The ana-
tomy of this animal, a genus of Rotiferce, family Hyda-
tincea, has been most lucidly explained and illustrated by
Mr. P. H. Gosse, in the Microscopical Society's Transactions.

Mr. Gosse states, that his specimens were found in a jar
of water obtained in the autumn from a pond near Wai-
thamstow, the jar having stood in his study-window
through the winter; and from a swarm in the succeeding
February he selected one the 70th of an inch in length
when extended, but its contractions and elongations
rendered its size variable.

" Its form, viewed dorsally, is somewhat cylindrical, but
it frequently becomes pyriform by the repletion of the
abdominal viscera. Viewed laterally, the back is arched
gibbous posteriorly, with the head somewhat obliquely
truncate, the belly nearly straight. The posterior ex-
tremity is produced into a retractile foot, terminating in
two pointed toes ; this, both in function and structure, is
certainly analogous to a limb, and must not be mistaken
for the tail, which is a minute projection higher up the
body. When not swimming or rotating, the head assumes
a rounded outline, displaying through the transparent

ROTIFERS. 457

integument an oval mark on each side, within which a
tremulous motion is perceived ; but at the pleasure of the
animal a semi-globular lobe is suddenly projected from
each of these spots by evolution of the integument.
These projections have suggested the trivial name of
aurita. Each lobe is crowned with a wheel of cilia, the
rapid rotation of whose waves forms the principal source
of swift progression in swimming. The protrusions of
these lobes are evidently eversions of the skin, ordinarily
concealed in two lateral cavities. They may be protruded
by pressure, and are then seen to be covered with long
but firm and close-set cilia, which are bent backward, and
move more languidly, as death approaches. The whole
front is also fringed with short vibratile cilia, which extend
all along the face, as far as the constriction of the neck.
The whole body is clear and nearly colourless ; but its
transparency is much hindered by the net-work of dim
lines and corrugations that are everywhere seen, particu-
larly all about the head."

Mr. Gosse, throwing a little carmine into the water, saw the
jaws working slightly, the points opening a little way, and
then closing ; the rods of the hammers were drawn towards
the bottom for opening, and upwards for closing. A little
mass of pigment, was soon accumulated beneath the tips
of the jaws, which spread itself over a rounded surface,
but did not pass farther; nor did an atom at this time go
into the stomach.

After entering into further minute details of the little
animal, he observes: "They possess organs that many
others do not, and want some that others possess. They
prove that the minuteness of the animals of this class
does not prevent them from having an organisation most
elaborate and complex, and therefore it justifies the belief
that the Rotiferce should occupy a place in the scale of
animal life much higher than that which has been commonly
assigned to them."

Like most of the class, this Notommata is predatory.
Mr. Gosse once saw one eagerly nibbling at the contracted
body of a sluggish Rotifer vulgaris; the mouth was drawn
obliquely forward, and the jaws were protruded to the food,
80 as to touch it. It did not appear, however, to do the

458 THE MICROSCOPE.

rotifer much damage. It appeared chiefly to feed on
monads.

FLOSOULARI^A. — The Stephanoceros, " Crowned animal-
cule." This beautiful little creature is about the 36th
of an inch in length; and is enclosed in a transparent
cylindrical flexible case, ovei which it protrudes five long
arms in a graceful manner, which, touching at their points,
give a form from which it derives its name. These
arms are furnished with several rows of short cilia, and
retain the prey brought within their grasp until it can be
swallowed. The case is attached to the animal on the
part we may term the shoulders; so that when it shrinks
down in its transparent home, the case is drawn inwards.
To the bottom of its home it is secured by an elongation
of the body; and this part, as well as the body, contracts
instantly on the approach of danger, the arms coming
close together are also withdrawn. Its mouth differs
a little from the common wheel-animalcule ; it has two
distinct sets of teeth, with which it tears and crushes its
food. The eggs of the Stephanoceros, after leaving the ani-
mal's body, remain in their crystal-like shell until hatched ;
and Dr. Mantell from close observation found, that about
eighty hours elapsed before their organs were all developed
and fitted for use.

Limnias Ceratophylli, " Water-nymph," is of this family,
bsing about the 20th of an inch in size, and is enclosed in
a white transparent cylindrical case, one-half the length of
the animal ; which, being glutinous, becomes of a brownish
colour, from the adhesion of extraneous matter. Its rota-
tory apparatus is divided into two lobes, possessing vibra-
ting cilia, as well as a singular projecting angular chin. In
the rows of little eggs in the body of the parent, may
clearly be distinguished most of the young organs in a
state of activity. From its fondness for hornwort, it is
often called by the name of that plant. (Plate III. No. 72.)

Floscularia Ornata, " Elegant floscularia," is a beautiful
type of the family, and has its rotatory organs divided
into several parts; when it contracts itself into a small
compass, its transparent covering becomes wrinkled. This
creature is an interesting object, as its internal structure
can be seen through the translucent sheath that constitutes

KOTIFEKJB. 4:59

its dwelling. The little beings are very rapacious, although
but the 108th part of an inch in size. Floscularia Pro-
boscidea, " Horned floscularia," has six lobes, fringed with
cilia shorter than in the preceding species. Its name is de-
rived from a peculiar kind of horn or proboscis, also having
cilia placed in the centre of the lobes. The eggs cast off
by the parent enclosed in a sheath, are very pretty objects
for microscopic observation. In fact, the tinted case, the
light ethereal frame of the tiny animal, the variously
coloured food, &c., in the stomach, combine in rendering it
singularly interesting.

Melicerta Ringens, " Beaded melicerta." — Of all the Me-
licerta, or " Honey floscularia," this is the most beautiful.
Its crystalline body is first enclosed in a pellucid covering,
wider at the top than the bottom, of a dark yellow or
reddish-brown colour, which gradually becomes encrusted
with zones of a variety of shapes, glued together by some
peculiar exudation that hardens in water : it is these little
pellets, appearing as rows of beads, give the name to
the animal. Mr. Gosse furnishes an excellent account of
the " architectural instincts of Melicerta ringens" which is
not only truly surprising, but full of interest. He writes : —
" This is an animalcule so minute as to be with difficulty
appreciable by the naked eye, inhabiting a tube composed of
pellets, which it forms and lays one by one. It is a mason
who not only builds up his mansion brick by brick, but
makes his bricks as he goes on, from substances which he
collects around him, shaping them in a mould which he
carries upon his body.

" The animal, as it slowly protrudes itself from its inge-
niously-formed mansion, appears a complicated mass of
transparent flesh, involved in many folds, displaying at
one side a pair of hooked spines, and at the other two
slender, short blunt processes projecting horizontally. As
it exposes itself more and more, suddenly two large rounded
discs are expanded, around which, at the same instant,
a wreath of cilia is seen performing its surprising motions.
Often the animal contents itself with this degree of ex-
posure ; but sometimes it protrudes farther, and displays
two other smaller leaflets opposite to the former, but in
the same plane, margined with cilia in like manner. T!IP

460 THE MICROSCOPE.

appearance is not unlike that of a flower of four unequal
petals; from which circumstance Linnsous gave it the
name ringens, by which it is still known."

Below the large petals on the ventral aspect, and just
above the level of the projecting respiratory tubes, is a
small circular disc or aperture, within the margin of which
a rapid rotation goes on. This little organ, which seems
to have hitherto escaped observation, Mr. Gosse can com-
pare to nothing so well as to one of those little circular
ventilators which we sometimes see in one of the upper
panes of a kitchen-window, running round and round, for
the cure of smoky chimneys. The gizzard, or muscular
bulb of the gullet, is always very distinct, and its structure
is readily demonstrated. It consists of two sub-hemisphe-
rical portions, or jaws, each of which is crossed by three
developed teeth, which are succeeded by three or four
parallel lines, as if new teeth might grow from thence.
The teeth are straight, slender, swelling towards their
extremity, and pointed. These armed hemispheres work
on each other, and on a V-shaped or tabuliform apparatus
beneath, common to most of the Rotifers, but in this genus
very small.

The pellets composing the case are very regular in form
and position : in a fine specimen, about the 1-2 8th of an
inch in length when fully expanded, of which the tube was
the l-36th of an inch, Mr. Gosse counted about fifteen
longitudinal rows of pellets at one view, which might
give about thirty-two or thirty-four rows in all.

In November, 1850, Mr. Gosse found a fine specimen
attached to a submerged moss from a pond at Hackney;
this he saw engaged in building its case, and at the same
time discovered the use of the curious little rotatory organ
on the neck, When fully expanded, the head is bent back
at nearly a right angle to the body, so that the disc is
placed nearly perpendicularly, instead of horizontally ; the
larger petals, which are the frontal ones, being above the
smaller pair. Now, below the large petals (that is, on the
ventral side) there is a projecting angular chin, which is
ciliated ; and immediately below this is the little organ in
question. It appears to form a small hemispherical cup,
and is capable of some degree of projection, as if on a short

MOTIPER2E. 461

pcdicla. On mixing carmine with the water, the course of
the ciliary current is readily traced, and forms a fine
spectacle. The particles are hurled round the margin of
the disc, until they pass off in front through the great
sinus, between the larger petals. If the pigment be abun-
dant, the cloudy torrent for the most part rushes off, and
prevents our seeing what takes place ; but if the atoms be
few, we see them swiftly glide along the facial surface, fol-
lowing the irregularities of outline with beautiful precision,
dash round the projecting chin like a fleet of boats doubling
a bold headland, and lodge themselves, one after another,
in the little cup-like receptacle beneath. Mr. Gosse, be-
lieving that the pellets of the case might be prepared in
the cup-like receptacle, watched the animal, and presently
had the satisfaction of seeing it bend its head forward, as
anticipated, and after a second or two raise it again ; the
little cup having in the meantime lost its contents. It
immediately began to fill again ; and when it was full, and
the contents were consolidated by rotation, aided probably
by the admixture of a salivary secretion, it was again bent
down to the margin of the case, and emptied of its pellet.
This process he saw repeated many times in succession,
until a goodly array of dark-red pellets were laid upon the
yellowish-brown ones, but very irregularly. After a certain
number were deposited in one part, the animal would
suddenly turn itself round in its case, and deposit some
in another part. It took from two and a half to three and
a half miautes to make and deposit a pellet.

Melicerta may be found in clear ponds, niill-ponds, and
other places through which a current of water gently
flows. It a portion of water-weed be brought home and
placed in a small glass zoophyte-trough, and carefully exa-
mined with a magnifying power of about fifty diameters,
a few delicate looking projections of a reddish brown
colour will probably be seen adhering to the plant ; these
are the tubular cases of melicerta, which, after a short
period of rest, will throw out little animals of one-twelfth
of an'inch in length.1

(1) For further information, see Gosse, Trans. Micros. Soc. vol. iii. 1852,
p. 58 ; Slack's Marvels of Pond Life. 1861 ; and Pritchard's History of Infusoria,
4th Edition. 1S61.

462

THE MICROSCOPE.

POLJPIFERA. — The chief characteristic of this vast race
of animals is, that their mouths are surrounded by
radiating tentacula, arranged some-
what like the ray of a flower; and hence
the term Zoophyte. So plant-like,
indeed, are their forms, that the early
observers regarded them as vegetating
stones, and invented many theories to
explain their growth.

They belong to a sub-kingdom
termed Ccelenterata, now divided and
subdivided by Professor Huxley into
the following : —

Septa, 4o., x 5 or 6. Septa, &c., x 4.

Simple soft-bodied.

1. ACTINIDJE. 1. BEROID;E.

Actinea, Minyas. Cydippe, Cesium.

Compound — Skeleton spicular.

2. ZOANTHIDJE. 2. ALCYONID.E.

Zoanthus. Alcyonium.

Compound — Skeleton sclerobasic.
3. ANTIPATHIDJE. 3. GORGONIDA.

Antipathes. Gorgonia, Itis,

Corallium,

Compound and Simple — Skeleton thecal — continuous.

4. PERFORATA.

Porites, Madrepora.

5. TABULATA.

Millepora, Seriatopora.

. 6. APOROSA.
Cifdthina, Ocultna.
Aalraea, Fungia.

4. TUJBIPORIDJE.
Tubipora,
5. RUGOSA.
Stauria, Cyathanonib.
Cynthophyllum.
Cystiphyllum.

Opposed to all our common ideas
of animal life is this singular portion
of creation. If we cut a limb off a tree,
or sever that of an animal, these parts
will wither and decompose, bv passing

Fi0'. I2b0.— Asteroid * . .» - /» VT X ?

Zoophytes. into other forms of matte*'. Cut a tree
across its middle, and its natural symmetry is irrepa-
rably disfigured ; slit it down its centre, and it -is de-
stroyed : all animals so treated suffer instant death, with
the exception of the polype tribe ; for they will put forth
new limbs, form a new head or tail, and if slit, become
two separate perfect creatures.

POLTPIFERA. 463

The seas which wash our shores swarm with beautiful
forms of minute Polypes, having nearly the same organisa-
tion as the Hydra, but which are protected by an external
horny integument. This peculiar covering sends forth
shoots or buds, which are developed into new polypes, thus
producing a compound animal; but the exercise of this
gemmiparous faculty is prevented by a horny defence
from effecting any other change than that of adding to the
general size, and to the number of tentacles, prehensile
fingers, and digestive sacs ; yet the pattern according to
which new polypes, and branches of polypes, are developed,
is fixed and determinate in each species, and there conse-
quently results a particular form of the whole compound
animal, by which the species can be readily recognized.

Cordylophora, a fresh water group of zoophytes, has
been made the subject of an admirable memoir by Pro-
fessor Allman. (See Phil. Trans. 1853, "On the
Anatomy and Physiology of Cordylophora.") In the inte-
resting and pretty group, Corynidce, the tentacles are
not arranged in a single transverse series, as in Hydra,
but are usually scattered more or less irregularly over
the surface of the polype • while in Tubularia there are
two transverse rows of tentacles, an upper shorter, and
a lower longer. The reproductive organs, which in Hydra
are extremely simple, attain, in many of the Corynidce and
Tubular iadas, to the condition of zooids, sometimes be-
coming detached, and swimming about freely before dis-
charging their products. These free zooids have always
the form of a bell or disc, from whose centre a pyriform
or oval body — either a closed sac or an open-mouthed
polype — is suspended; and they have been regarded as
distinct animals, and grouped together with other forms of
Hydrozoa, under the head of Medusas. The bell possesses
considerable contractility, and at each contraction the
water which fills its cavity is forced out, and the bell itself
is thereby propelled in the opposite direction. In Tubu-
laria a more completely medusiform body is developed,
but is never detached.

In the Sertulariadce, the numerous digestive zooids, or
polypes, developed from the original germ, remain always
attached; but their most remarkable feature is the posses-

464 THE MICROSCOPE.

sion of a " cell," surrounding the base of each polype, and
usually capable of receiving it when retracted. The de-
velopment of this cell at once distinguishes it from the
not altogether dissimilar group, the Diphydce and Physo-
phoridce. In some Sertulariadce (Sertularia dynamena),
the margins of the cells are converted into membranous
valves; and in the genus Plumularia, we find special
organs of offence.

The Diphydce are among the most remarkable and
beautiful inhabitants of the ocean, to whose warmer
regions, they, like the Physophoridce, are principally con-
fined. They are free swimmers in the adult state, and
probably, at all times of their existence ; but while actively
locomotive by means of the contractions of the natatorial
organs with which they are provided, they possess no
special supporting apparatus, or " float," such as that de-
veloped in the Physophoridce. The tentacle of the Diphydce
is a long filiform process of the peduncle, capable of great
elongation and contraction ; the terminal filament of
which is closely beset with minute thread-cells, so that the
whole must constitute a very efficient weapon of offence.
Three genera of the Physophoridce are particularly worthy
of notice : the Physalia, whose air-vesicle may attain the
length of eight or nine inches, while its formidable ten-
tacles hang down for as many feet, inflicting instantaneous
death upon the smaller animals, and giving rise to no small
amount of pain and irritation, even in man ; and the
Velella and Porpita, in which the texture of the air-vesicle
is so exceedingly firm, as to give it the appearance of an
internal shell, while its cavity is subdivided into numerous
chambers. Originally, however, the " shell " of the Velella
is a perfectly simple air-vesicle, like that of any other
Physophorid. In the very peculiar genus Lucernaria, —
lovely " Lamp-polype," with little knobbed tentacles — we
have a Hydrozoon, in which the polype occupies the centre
of an expanded disc, the two presenting essentially the same
structure and relations as in the Medusiform zooids of
other divisions. In fact, a Lucernaria is in all essential
respects comparable to an Aurelia, or other Medusa fixed
by the middle of the upper surface of its disc.

Mr. Huxley prefers the term Lucernariadce to that of

POLYPIPERA. 465

Medusae; and he does so " from the fact that the Medusidcz
of authors consists of two groups, the Naked-eyed (Gym-
nopht/ialmata) and the Covered-eyed (Stegnnophthalmatd).
Some of which, the Aurelia, is but a derivative zooid form
of an animal, essentially resembling Lucernaria; while so
far as regards the Naked-eyed Medusae, we have no evidence
that any genus except jEginopsis, is other than the repro-
ductive zooid of one of the Hydridoe or Sertulariadce. It
seems better, therefore, to avoid the term Medusae, as the
denomination of an ascertained group, reserving it merely
to denote the medusiform creatures of whose origin we
are ignorant, but whose structure entitles them to a pro-
visional place among the Lucernariadce. As our know-
ledge increases, we shall be able to .arrange those Medusae
which are the zooids of Hydridae, Sertulariadce } Diphydce,
or Physophoridae, under their respective groups, while the
rest will form the sub-sections of the Lucernariadce; the
first consisting of such forms as A urelia and Rhizostoma,
zooids developed by fission from fixed Lucernariadce; the
second consisting of such forms as JZginopsis, free Lucer-
nariadce, developed at once from the ovum, without any
fixed state."

The Actinozoa are those Ccelenterata in which the
stomach is a sac suspended within and entirely distinct
from the body, from whose parietes it is separated by
a portion of the general cavity of the body, which may
receive the special denomination of " perivisceral cavity.''
The stomach communicates freely by an inferior aperture
with the general cavity. A rough conception of the rela-
tions between the Actinozoa and the Hydrozoa may b^
obtained by supposing the walls of the natatorial disc of a
Lucernaria to become united with those of its central
polype ; it would then become, to all intents and purposes,
an Actizozoon. As the Hydra is the type of the Hydro-
zoa, so the "Sea-anemone" (A ztinia) is considered to be the
type of the Actinozoa. As in the Hydrozoa, the body of
the Actinia is essentially composed of two layers, a super-
ficial layer, composed of polygonal cells, frequently de-
tached and renewed again, beneath which lies a granular
layer ; whilst in the deep dermal layer two sets of mus-
cular fibres are found,- -a superficial circular, and a deep
H H

466 THE MICROSCOPE.

longitudinal set : both are flattened, and exhibit no trans-
verse striation. In some Actiniae, such as A. mesembryan-
theyium, bright blue sacs are placed at the edges of the oral

Fig. 231. — Hydra, with tentacles displayed and magnified, adhering to a stalk of-
Anacharis alsinastrwni.

disc, while in A.gemmacea, A. sessilis, &c. clear spots are
scattered over the integument, which have been regarded
as apertures or tubercles ; M. Hollard, however, states, that
these are imperforate Ampullce, possessing a kind of bila-
biate mouth, surrounded by a sphincter- like arrangement of
muscular fibres. Any foreign body introduced into these
ampullae is seized and forcibly held; or if the finger be
placed within reach, it gives the sensation of a very fine
rasp passing over it. The margins of the radiate tentacles
of the young animal are surrounded by cilia ; the gastric
epithelium is likewise ciliated, and doubtless secretes a
powerfully solvent fluid. The majority of the Actinice
are oviparous, the young being developed from ova within,
and evacuated by the mouth : they are also capable of
multiplication by budding, and occasionally by fission
while their power of restoring themselves after muti

POLYPIFERA. 467

lation appears to be as great as that possessed by the
Hydra,1

The great majority of the Actinozoa exhibit a structure
closely corresponding with that of the Actimince ; but from
the manner in which they grow up into compound masses
of associated Zooids, produced by gemmation or by fission,
they stand in nearly the same relation to Actinia, as the
compound Hydrozoa to Hydra.

Sir John Dayell believes that Actinias conquer their prey
by mere strength ; this is doubtless the case, as from
experience we find nothing like a stinging property be-
longing to the tentacles ; nor are there any poison vesicles
attached thereunto. The tentacles appear to be armed
with rows of spines, which give a clinging and slight
rasping sensation when the finger is thrust against them ;
and by the same means they are able to obtain a firm
hold of any smaller animal that falls within their reach.
Animals with a hard case or shell seem to escape from
their clutches without having sustained the smallest in-
jury. The same remarks apply to the Hydra; they have
neither the power to sting or benumb their prey, as
asserted by many authorities. It has been said that
certain minute organs found in polypes, and variously
styled thread capsules, filiferous capsules, or urticating
cells, are stinging organs. This thread Agassiz likens te
a lasso thrown by the polype to secure its prey. Mr.
Lewes writes : — " On a survey of the places where these
'urticating cells' are present, I stumbled upon an unlucky
fact, and one likely to excite our suspicion. They are
present in a few jelly-fish which urticate, in Actiniae which
urticate, and in all polypes, which, if they do not urticate,

(l)The Author's aquarium affords at this time (1856) a curious illustration of
increase both by budding and fissuration, in a beautiful A. dianthus. In the first
case an offset was seen to protrude ; it resembled a small bud near the foot; this
increased until it attained to a perfect animal of a considerable size, when it be-
came detached. In another, the animal, after having remained for several weeks
lirmly adherent to the side of the glass, with a part of its disc out of the water, by a
great effort tore itself away, leaving six small pieces behind, attached to the glass.
.For some days these pieces served only to mark so many spots, but in about &
week rudimentary tentacles were observed to be sprouting out from each piece,
which went on rapidly increasing, and ultimately six perfect animals resulted
therefrom. The repair of the marginal portion of the disc of the parent animal
was completed in a few days, and it suffered no injury whatever from its self-
mutilation. This furnishes a proof, if one were wanting, of the hydrozoid cha-
racter of this class of animals.

H H 2

i68 THE MICROSCOPE.

are popularly supposed to do so, and at any rate possess
some peculiar power of adhesion. In all these cases, organ
and function may be said to go together ; but the cells are
also present in the majority of jelly-fish which do not
urticate, in Solids which do not urticate, and in Planarioe
which do not urticate. Here, then, we have the organ
without any corresponding function; urticating cells,
but no urtication. It thus appears that animals having
the cells, have none of the power attributed to the
cells ; and that even in those animals which have the
power, it is only present in the tentacles, where the cells
are much less abundant than in parts not manifesting the
power ; the conclusion, therefore, presses on us, that the
power does not depend upon these cells. When at rest,
and in an ordinary natural state, the animal is never seen
to dart out these threads, nor upon capturing his prey ; it
is only when some force is used to dislodge him from some
spot to which he has securely attached himself, that he
presses or squeezes out these threads ; more for the pur-
pose of compressing himself into a closer and smaller
mass, to add to the difficulty of detaching him.

"Actinice do not effect their preparation of nutriment by
chemical means ; that is, they do not, in the strict sense of
the term, digest, but simply derive nourishment by mecha-
nical pressure, exerted upon any particle of food that they
may draw into their stomachs. This has been proved by
experiments made after the manner of Reaumur. A small
piece of meat having been put into a quill, and ajlowed to
remain in the stomach of the Actinia sufficiently long, and
then withdrawn, no solvent fluid is found to have acted
upon it. When placed under the microscope the muscle
fibres are not at all disintegrated, and the striae are as
perfect as before the experiment, with the exception of a
pulpiness and loss of colour, as in any ordinary mechanical
maceration.

" Light has been thrown upon the reproductive system
of the Actinice by M. Jules Haime, in the Annales des
Sciences Naturelles, 1854, 4ieme s6rie, torn, i.; which con-
tains accurate and detailed descriptions and plates of the
disposition of ova and spermatozoa in the Actiniae. Tc
find the ovaries it is only necessary to take a live animal,

POLYIIPERA. 469

and with a rapid, but not $eep incision, lay open the
envelope from the outside ; a series of convoluted bands
will bulge through the opening, but if these are quickly
brushed aside, certain lobular or grape-like masses will be
perceived, darker in colour, and almost entirely hidden by
these bands, but growing from the wall of the envelope.
They do not appear to have a fixed locality, as they may
be found near the base, about the centre, or close to the
disc ; it is, therefore, sometimes necessary to make three
or four incisions before detecting them; once seen, they
will be easily distinguished from the convoluted bands,
although very difficult to remove them without removing
some of the bands."

The manner in which the aggregation of zooids, consti-
tuting a compound coral, is developed from the primarily
solitary Actinozoic embryo, exercises an all-important
influence upon the form of the Corallum. Sometimes, as
in most Turbinolidce, neither gemmation nor fission ever
take place. In the Oculinidce, gemmation alone occurs,
and in these and other Actinozoa, the development of buds
takes place either from the base or from the sides of a
corallite, cr from the coenosarc. Certain of the extinct
Rugosa, however, exhibit calicular gemmation, the buds
being developed from the oral disc or cup, which can
hardly have retained any active vitality. The massive
coralla of some Cyathophyllidce} thus standing like inverted
pyramids, all the buds supported upon the narrow surface
of the primary zooid, have a very singular and striking
aspect. The Beroidce appear at first to differ very widely
from the type of structure which prevails among the
other Actinozoa, but a close examination of any of their
forms suffices to demonstrate the justice of the conclusion
advocated by Frey and Leuckart, as to their essential
identity with Actinia. The Cydippe, which abounds upon
our own coasts, affords, from its small size and extreme
transparency, an excellent subject for the student of Be-
roidce. It is impossible here to enter into the varieties
of form presented by the Beroidce, and which chiefly arise
from the development of lateral lobes, a process which is
carried to so great a length in Cesium that the body
becomes ribbon-like. The Beroidce and the Actinidce

470 THE MICROSCOPE.

inhabit the shallower and .even ofeeper parts of all seas ;
Alcyonidoe and Gorgonidos are found at considerable
depths; Oorallium and Gorgonia abound both in cold
and warm latitudes. The Perforata and Tdbulata almost
exclusively haunt the shallower parts of warm seas, but
the Turbinolidce extend into very cold regions. The whole
group of the Rugosa, is now extinct, only one genus,
Holocystis, having survived even the palaeozoic period. Not
only heat, but light, and probably rapid and effectual
aeration, are essential conditions for the activity of the
reef -building Actinozoa. Different species of corals exhibit
great differences as to the rapidity of growth, and the
depth at which they nourish best ; and no one must be
taken as evidence for another in these respects. Certain
species of Perforata, Madreporidce, and Poritidce, appear
to be at once the fastest growers, and those which delight
in the shallowest waters. The Astrceidce among the
Aporosa, and Seriatopora among the Tdbulata, live at
greater depths, and are probably slower of increase. The
most careful accounts of the structure of corals extant, are
from the pens of M. M. Milne Edwards and Haime, pub-
lished at various times in the Annales des Sciences Natu-
relles, in the Memoires du Museum, and in the publications
of the Palseontographical Society ; and by Mr. Darwin,
whose beautiful work on Coral Reefs will amply repay
perusal.

With these brief introductory observations, the principal
part of which have been derived from Professor Huxley's
lectures, we proceed to direct the reader's attention to
some of the more interesting generic forms.

HYDRA, FRESH- WATER POLYPE. — In polypes of this
family the body generally consists of a homogeneous
aggregation of vesicular granules, held together by a sort
of glairy intercellular substance, and capable of great
extension and contraction; so that the creature can at
pleasure assume a great variety of forms, extending its
body and tentacles until the latter become so fine as to be
almost invisible, and again retracting itself until it acquires
the appearance of a small gelatinous mass. The tentacles
which surround the anterior extremity are irregular in
number; they are capable of extension to a very great

HYDRA. 47 1

length when seeking for prey; and on corning in contact
with any object floating through the water, they imme-
diately twine round it, and convey it to the mouth. In
some genera the tentacles appear to be tubular, the inter-
nal cavity being continuous with that of the stomach.
The mouth is situated in the centre of the circle of ten-
tacles, and leads directly into a simple digestive cavity.

Hydrce are found in ponds and rivulets, adhering to the
leaves of aquatic plants, or twigs and sticks that have
fallen into the water. When stretched out, they resemble
pieces of hair, from a quarter to three-quarters of an inch
in length. Some are of a light-green colour, and others
brown or yellow; that is, the five varieties found in
England. It received its name from its several long arms
being supposed to resemble the fifty-headed water-serpent
called Hydra, which was destroyed by Hercules in the
lake of Lerna, as we are informed in fabulous history.
Leeuwenhoek, in 1703, first drew attention to the Hydra;
and in 1739, M. Trembley from the Hague, more accu-
rately described its habits.

Polypes are not vegetarians ; M. Trembley fed Hydrce
on minced fish, beef, mutton, and veal; they are voracious
and active in seizing worms and larvae much larger than
themselves, which they devour with avidity. They care-
fully and adroitly bring their food towards their mouth;
and when near, pounce upon it with eagerness. To make
up for the want of teeth, the mouth enlarges to receive
the food brought to it by the arms that have twined around
the sacrifice. The red worm that tinges the mud of the
Thames appears to be the dainty dish they like best to
have set before them. Dr. Mantell saw the lasso of a
polype thrown over two worms at the same time; yet
they could not escape, and lost all power of motion.

Dr. Johnston states : " Sometimes it happens that two
polypes will seize upon the same worm, when a struggle for
the prey ensues, in which the strongest gains, of course,
the victory; or each polype begins quietly to swallow his
portion, and continues to gulp down his half, until the
mouths of the pair near, and come at length into actual
contact. The rest that now ensues, appears to prove that
they are sensible of their untoward position, from whicb

472 TUB MICROSCOPE.

they are frequently liberated by the opportune break of
the worm, when each obtains his share ; but should the
prey prove too tough, woe to the unready! the more
resolute dilates the mouth to the requisite extent, and
deliberately swallows his opponent; sometimes partially,
so as, however, to compel the discharge of the bait ; while
at other times the entire polype is engulfed ! But a polype
is no fitting food for a polype, and his capacity of endurance
saves him from this living tomb ; for, after a time, when
the worm is sucked out of him, the sufferer is disgorged
with no other loss than his dinner."

The organ of prehension, which is called the hasta, con-
sists of a sac opening at the surface of the tentacle, within
which, at the lower portion, is placed a saucer- shaped
vesicle, supporting a minute ovate body, which again bears
a sharp calcareous piece called the sagitta, arrow. This
can be pushed out at the pleasure of the animal, serving
to roughen the surface of the tentacle, and afford a much
firmer hold of its living prey. The polype increases
rapidly : a portion of the body swells, a young one puts
forth its head from the part, its arms begin to grow, it
then is industrious in catching food ; its body, communi-
cating with that of its parent and participating in the
fears and actions of its progenitor, is finally cast off to
wander the world of waters. Sometimes, ere yet free from
parental attachment, it has two generations on its own
body. Four or five offspring are thus produced weekly.
But the most extraordinary circumstance in respect to this
creature is thus described by M. Trembley : " If one of
them be cut in two, the fore part, which contains the head
and mouth and arms, lengthens itself, creeps, and eats on
the same day. The tail part forms a head and mouth at
the wounded end, and shoots forth arms more or less
speedily, as the heat is favourable. If the polype be cut
the long way through the head, stomach, and body, each
part is half a pipe, with half a head, half a mouth, and
some of the arms at one of its ends. The edges of these
half pipes gradually round themselves and unite, beginning
at the tail end ; and the half mouth and half stomach of
each becomes complete. A polype has been cut lengthways
at seven in the morning, and in eight hours afterwards

TUBULARIAD.E, 473

each part has devoured a worm as long as itself." Still
more wonderful is the fact, that if turned inside out,
the parts at once accommodate themselves to their new
condition, and carry on all their functions as before
the accident. Indeed, this animal seems so peculiarly
endowed with the germs of vitality in every part of its
body, that it may be cut into ten pieces, and everyone
will become a new, perfect, living animal. This seems
bordering on the vegetable kingdom, in which it is
common to propagate by means of slips from the mature
shrub.

The best known of the British species are Hydra vul-
garis, Common polype, H. viridis, Green polype, ff. Fusea,
Brown polype, //. verrucosa, and H. lutea.

Every reflecting person who reads even the slight
sketch we have given of this polype must be struck \vitl
astonishment at a creature so primitive in structure, pos-
sessing the actions, sensations, and powers of higher
organised beings. The stomach is but one simple struc-
tureless membrane or cell, the external surface-cells form-
ing a kind of double skin, the inside a mere wall of cells
running crosswise, possessed of a velvet-like surface, and
red or brown coloured grains held together by a glutinous
substance. This singular formation, with some of the
functions of animal life, has led to many learned surmises
and discussions tending to the most important results in
the science of physiology.

TUBULARIAD^:. — The Tubular or Vaginated Polypes are
of an arborescent appearance ; the animals live near the
ends of branches, and are found attached to stones, sea-
weeds, and shells.1 The Tubularia indivisa, " Individed
tubes," are found on shells, with a living head resembling
a fine scarlet cluster of blossoms. Ellis says, " they seem
part of an oat-straw with the joints cut off." At the summit
protrudes the scarlet- coloured polypes, well furnished with
tentacula, and connected with a pinkish fluid that fills tlu
tubes. It was in these that Dr. Roget discovered the
singular peculiarity of a circulation, similar to that seen
in many pknts. He says, " In a specimen of the Tubu-

(1) These are grouped with Hydroida, and at the head of the family stand
Van Beneclen's Hydractinia ; and Gaertner's Coryne.

£- THE SIICROSCOPE.

laria indivisa, when magnified one hundred times, a
current of particles was seen within the tubular stem of
the polype, strikingly resembling, in steadiness and
continuity of its stream, the vegetable circulation in
the chara. Its general course was parallel to the slightly
spiral lines of irregular spots on the surface of the tube,
ascending on the one side, and descending on the other ;
each of the opposite currents occupying one-half of the
circumference of the cylindric cavity. At the knots, or
contracted parts of the tube, slight eddies were noticed
in the currents ; and at each end of the tube the par-
ticles were seen to turn round, and pass over to the other
side.

" The particles carried by it present an analogy to those
of the blood in the higher animals of one side, and of the
sap of vegetables on the other. Some of them appear to be
derived from the digested food, and others from the
melting down of parts absorbed ; but it would be highly
interesting to ascertain distinctly how they are produced,
and what is the office they perform, as well as the true
character of their remarkable activity and seemingly
spontaneous motions ; for the hypothesis of their indi-
vidual vitality is too startling to be adopted without good
evidence."

Respecting the singular property of the head dropping
off, Tubularia indivisa, Sir J. G. Dalyell observes, " The
head is deciduous, falling in general soon after recovery
from the sea. It is regenerated at intervals of from ten
days to several weeks, but with the number of external
organs successively diminishing, though the stem is always
elongated. It seerns to rise within this tubular stem from
below, and to be dependent on the presence of the internal
tenacious matter with which the tube is occupied. A head
springs from the remaining stem, cut off very near the
root ; and a redundance of heads may be obtained from
artificial sections. Thus, twenty-two heads were produced
through the course of 150 days from three sections of a
single stem."

Included in this family are the T. ramous, T. ramea, the
branched pipe-coralline, with its dark brown stem termi-
nating in clusters of red and yellow polyps ; and the

TUBULARIAD.E.

475

Hermia Glandulosa of Dr. Johnston, who says — " I found
the name in Shakspeare :

' What wicked and dissembling glass of mine,
Made me compare with Hermia's sphery eyne ?' "

The fancy that the glands which surround the head*
were the guardians of the animal, its " sphery eyne/' sug-
gested the name here adopted.
These polypes are adherent by
a tubular fibre, and creep along
the surface of the obj ect on which
they grow ; they are seldom
an inch in height, irregularly
branched; the stem filiform,
tubular, horny, sub-pellucid,
wrinkled, and sometimes ringed
at intervals, especially at the
origin of the branches, each of
^Yhich is terminated with an
oval or club-shaped head of a
reddish colour, and armed with
short scattered tentacula,tipped
with a globular apex. The ends
of the branches are not perfo-
rated, but completely covered
with a continuation of the horny
sheath of the stem. The animal
can bend its armed hands at
will, or give to any separate ten-
taculum a distinct motion and
direction ; but all its move-
ments are very slow.

The beautiful little Coryne Cor'yne."' "2," A "tubercle ' detached!

stauridia, " Slender coryne," and masnitied 20° diameter*,
(fig. 232, No. 1), is thus described by Mr. Gosse : " It via*
found by me adhering to the footstalk of a Rhodymenia,
about which it creeps in the form of a white thread ; by
placing both beneath the microscope, this thread appeared
cylindrical and tubular, perfectly transparent, without
wrinkles, but permeated by a central core, apparently cel-
lular in texture, and hollow ; within which a rather slow

Fig. 232.
1, Coryne Stauridia, Slender

476 THE MICROSCOPE.

circulation of globules, few in number, and remote, is per-
ceived. It sends off numerous branches ; the terminal
head of which is oblong, cylindrical, rounded at the end.
At the extreme point are fixed four tentacula of the usual
form, long, slender, and furnished with globular heads ;
one of which is shown at No. 2, detached, and more highly
magnified. It is much infested with parasites : a vorticella
grows on it, and a sort of vibrio ; the latter in immense
numbers, forming aggregated clusters here and there ;
the individuals adhering to each other, and projecting in
bristling points in every direction. These animalcules
vary in length ; some being as long as l-80th of an inch,
with a diameter of l-7000th of an inch. They are straight,
equal in thickness throughout, and marked with distinct
transverse lines ; they bend themselves about with consi-
derable activity, and frequently adhere to the polype by
one extremity, while the remainder projects freely."

Some of this family attain a considerable size ; the
Corymorpha, nutans, one of the most beautiful of the
group, attains a length of four inches and a half. Of
the beauty of its appearance, Forbes, who discovered it in
the British seas, speaks in the following terms : " When
placed in a vessel of sea- water, it presented the appearance
of a beautiful flower. Its head gracefully nodded (whence
the appropriate specific appellation given it by Sars), bend-
ing the upper part of its stem. It waved its long tentacula
to and fro at pleasure, but seemed to have no power of
contracting them. It could not be regarded as by any
means an apathetic animal, and its beauty excited the
admiration of all who saw it." The general colour of the
creature is a delicate pink, with longitudinal lines of
brownish or red dots. The tentacles are very numerous
and long, and of a white colour ; and the ovaries, which
are situated immediately above the circle of tentacles,
are orange. Most of the Tubulariadce inhabit the sea ;
one species, the Cordylophora lacustris, is found in the
dock of the Grand Canal, Dublin, in water which is per-
fectly fresh.

SERTULARIADJS. — This interesting and beautiful family
of polypes derive their name from their plant-like appear-
ance, and are readily attainable on our own sea-shores.

SERTULARIAD.E.

177

Linnseus made a large genus of them ; but Lamarck con-
Biderably reduced his classification. There are seventeen
British species, which Dr. Fleming proposes to divide into
two groups, with stems simple or compound.

The tentacles of Sertularia
are abundantly supplied with
cilia ; the cells are pitcher-
shaped, arranged alternately,
or in pairs obliquely, not
exactly opposite, on the stem
and branches of the poly-
pidom, which is horny. La-
mouroux classed with this
family Thoa; of which there
have been several kinds found
ii* Great Britain. The name
is supposed to be derived from
the Greek word for sharp;
but we think, with Dr. John-
ston, that it more probably FJg> 23S.-Sickle-CoraUine. Sertu-

is a mis-spelling of Thoe, one *«"«. Poiypidom of.

of the Nereids, nymphs of the sea. They are generally
of a brown and yellow colour, branched, and from an inch
and a half to six inches in height.

Sertularia pumila. — This is parasitic, and spreads its
brown-coloured shoots over various fuci and sea-shells;
but rarely attains more than half an inch in height.
Stewart says : — " This species, and probably many others,
in some particular states of the atmosphere, emits a phos-
phorescent light in the dark. If a leaf of the fucus
serratus, with Sertularia upon it, receives a smart stroke
in the dark, the whole is most beautifully illuminated,
every denticle seeming to be on fire."

On the south-eastern coast of England the most common
kind found is the Sertularia setacea, or operculata, Seahair-
Coralline : it reaches from six inches and upwards in
height, and grows in tufts, like bunches of hair. The
stem and branches seem composed of separate pieces,
fitting accurately into each other, and terminate in a
star-like head, from which radiate the tentacles. Mr.
Lister was observing a living specimen, when a little

•HO THE MICROSCOPE.

globular animalcule swam rapidly by one of the expanded
polypes; the latter immediately contracted, seized the
globule, and brought it to the mouth or central opening
by its tentacula ; these gradually opened Ggr.in, with

the exception of one, which
remained folded, with its ex-
tremity on the animalcule.
The month instantly seemed
filled with cilia, which, closing;
over the prey, was carried
slowly down its stomach ;
here it was imperfectly seen,
and soon disappeared.

Appertaining to this family
are Dr. Fleming's Thuiarea,
so named by him from their
resemblance to a cedar-tree;
some kinds look more like a
knobbed thornstick with a
bottle-clearer at the top ;
others resemble a fir-tree.
Antennularia are so called
from, their resemblance to a
lobster's antenna. They are
plentiful on the north-eastern
coast of England and the
coast of Ireland, brown in
Fig. 234. colour, and covered with

i, piumuiaria pinnata, Feather poiypc, hair-like little branches; and
2, Doris tubercuiata, Sea slug. as the hairy process is con-
tinued up its jointed stem, it is sometimes denominated
Sea-beard. Dr. HassaU's Coppinia is another very interest-
ing species.

The Plumularia, so named from their shoots and
otfsets being plumose, are an extensive and beautiful,
family. Professor Grant thus describes the Plumularia
falcata : " The Sickle Coralline is common in the deepei
parts of the Frith of Forth ; its vesicles are very numerous,
and its ova are in full maturity at the beginning of May.
The ova are large, of a light-brown colour, semi-opaque,
nearly spherical, composed of minute transparent granules,

8ERTULARIADJ5. 479

ciliated on the surface, and distinctly irritable. There
are only two ova in each vesicle ; so that they do not
require any external capsules, like those of the Campanu-
laria, to allow them sufficient space to come to maturity.
On placing an entire vesicle, with its two ova, under the
microscope, we perceive through the transparent sides the
cilia vibrating on the surface of the contained ova, and the
currents produced in the fluid within by their motion.
When we open the vesicles with two needles, in a drop of
sea- water, the ova glide to and fro through the water, at
first slowly, but afterwards more quickly, and their cilia
propel them with the same part always forward. They
are highly irritable, and frequently contract their bodies
so as to exhibit those singular changes of form spoken of
by Cavolini. These contractions are particularly observed
when they come in contact with a hair, a filament of
conferva, a grain of sand, or any minute object ; and they
are likewise frequent and remarkable at the time when
the ovum is busied in attaching its body permanently to
the surface of the glass. After fixing themselves, they
become flat and circular, and the more opaque parts of
the ova assume a radiated appearance ; so that they now
appear, even to the naked eye, like so many minute grey-
coloured stars, having the interstices between the rays
filled with a colourless transparent matter, which seems to
harden into horn. The grey matter swells in the centre,
where the rays meet, and rises perpendicularly upwards
surrounded by the transparent horny matter, so as to form
the trunk of the future zoophyte. The rays first formed
are obviously the fleshy central substance of the roots ;
and the portion of that substance which grows perpen-
dicularly upwards, forms the fleshy central part of the
stem. As early as I could observe the stem, it was open
at the top ; and when it bifurcated to form two branches,
both were open at their extremities ; but the fleshy central
matter had nowhere developed itself as yet into the form
of a polype. Polypes, therefore, are not the first formed of
this zoophyte, but appear long after the formation of the
root and stem, as the leaves and flowers of a plant."

Attached tofucus and shells in abundance on the southern
coast of England, may be found the Plumularia cristata. It

480 THE MICROSCOPE.

is affixed by a horny, branching, interlacing, tubular fibre
to the object on which it grows. At different parts there
nre plumose shoots, usually about an inch in height. The
cells are of a yellow colour, set in the stalk, of a bell-
shape, and are compared to the flower of the lily of the
valley ; the rim is cut into eight equal teeth ; the polype
minute and delicate, tentacles ten and annulate, with a
mouth infundibuliform in shape.

" Each plume," says Mr. Lister, in reference to a speci-
men of this species, "might comprise from 400 to 500
polypes ;" " and a specimen," writes Dr. Johnston, " of no
unusual size, before me, has twelve plumes, with certainly
not fewer cells on each than the larger number mentioned :
thus giving 6000 polypes as the tenantry of a single poly-
pidom ! Now, many such specimens, all united too by a
common fibre, and all the offshoots of one common parent,
are often located on one sea-weed, the site then of a popu-
lation which nor London nor Pekin can rival."

Plumularia pinnata, " Feather polyp," (represented mag-
nified in fig. 234, No. 1,) is as remarkable for the ele-
gance of its form, as its likeness to the feather of a pen.
It serves not among the denizens of the deep the same
purpose as its earthly prototype ; nature writes her
works in hieroglyphics formed by the objects themselves.
It is plumous, and the cells in a close row, cup-like,
and supported on the under side by a lengthened spinous
process.

An interest pervades the valuable work of Dr. Johnston,
arising from the circumstance that the plates and wood-
cuts which adorn the volume are, with few exceptions,
engraved from drawings made for it by Mrs. Johnston,
who also engraved several of them ; and the Doctor states,
he could not have undertaken the history without such
assistance. From this devotion too, and understanding of
the subject, it was natural, when an opportunity presented
itself, to write in the catalogue of Zoophytes a lasting
memorial of his " colleague :" and thus is written the
graceful compliment of the beautiful Plumularia Catha-
rina : " Catharine's Feather," whose stem is plumous, pinnae
opposite, bent inwards; cells distant, campanulate, with
an even margin ; vesicles scattered, pear-shaped, smooth.

SERTULABIADJS. 481

Found in old shells, corallines, &c., in deep water; in
Frith of Forth and in Berwick Bay, by Dr. Coldstream.

The sub-families, Campanularia and Laomedea, are also
frequently found on our shores ; they possess a simple
circle of cilia on their feelers or arms, with pitcher-
shaped cells on stalks that branch, twist, or climb on an
axis.

Campanularia volubilis, tl Twining polype," is the com-
monest of the family : it is parasitical, and infests the an-
tennae of crabs ; its stem is filiform, and at the end of
its slender branches are situated the cells containing the
polypes. The polype itself is slender when protruded,
somewhat like Plumularia pinnata, and becomes dilated
at the base into a sort of foot which spreads over the dia-
phragm ; widening again at the top, where it fills the
mouth of the cell, and gives origin to about twenty slender
tentacula, set in two or three series. From the central
space, which is surrounded by tentacles, a large fleshy
mouth protrudes, somewhat funnel-shaped, with lips, en-
dowed with the power of protrusion and contraction;
these appear to be very sensitive. Mr. Gosse found the
species in great abundance round Small-mouth Caves.

The Campanularia gelatinosa and its beautiful bell-
shaped cells, out of which the animals protrude, giving the
semblance of a green flower on a delicate pink stalk. It
is indeed an interesting object, and currents may be
seen in its tubes. Dr. Johnston says, " On Saturday, May
29th, 1837, a specimen of Campanularia gelatinosa was
procured from the shore ; and after having ascertained
that the polypes were active and entire, it was placed
in a saucer of sea-water. Here it remained undisturbed
until Monday afternoon, when all the polypes had dis-
appeared. Some cells were empty, or nearly so ; others
were half-filled with the wasted body of the polype,
which had lost, however, every vestige of their tentacula.
The water had become putrid, and the specimen was
therefore removed to another vessel with pure water, and
again set aside. On examining it on the Thursday, June
1st, the cells were evidently filling again, although no
tentacula were visibly protruded ; but on the afternoon of
Friday, June 2d, every cell had its polype, complete, and

r i

482 THE MICROSCOPE.

displayed in the greatest perfection. Had these singular
facts been known to Linnaeus, how eagerly and effectively
would he have impressed them into the support of his
favourite theory ! Like the flowers of the field, the heads,
or 'flores,' of these polypidoms expand their petaloid
arms, which after a time fall, like blighted blossoms off a
tree ; they do become ' old in their youth,' and, rendered
hebetous and unfit for duty or ornament by age or acci-
dent, the common trunk throws them off, and supplies its
wants by ever-young and vigorous growths. The pheno-
mena are of those which justly challenge admiration, and
excuse a sober scepticism, so alien are they to all we are
accustomed to observe in more familiar organisms. Faithful
observation renders the fact undeniable ; but besides that,
a reflection on the history of the Hydra might almost
have led us to anticipate such events in the life of these
Zoophytes. ' Verily, for mine own part/ observes Baker,
'the more I look into Nature's works, the sooner am
I induced to believe of her even those things that seem
incredible.' "

ACTINIAD^. — All persons accustomed to wander by the
sea-shore must have admired the livid green, dark little
jelly-masses adhering to the rocks, — called Actinia, from a
Greek word signifying a ray, — and left in some little pool
by the ebbing tide, living as they do principally within
high and low water mark, and expanding their broad sur-
faces and fringing feelers to the finger of inquisitive youth,
so often thrust into the centre, to feel the effect of the
suction and rasping, as the poor animal draws itself up in
the form of a little fleshy hillock.

Some few years ago it might have been necessary to
explain what we meant by an Actinia, or " Sea-anemone ;"
thanks to the universal distribution of aquaria, this
beautiful class of animals is no longer unfamiliar to the
world. Nevertheless, much as people read, and hear, and
write, and observe in the matter, we do not hesitate to say
that the natural arrangement of these animals is as little
known in the world of naturalists, as their very existence
was a short time ago to the world at large. A familiar
instance of this position may be given in a few words.
Dr. Johnston (Hist. Brit. Zooph.) describes three distinct

483

Actinice, under the names of A. troglodytes (the Cave-
dweller), A. viduata, and A. Anguicoma (the Snaky-
locked). Mr. Gosse, in his Devonshire Coast, makes A.
viduata synonymous with A. anguicoma ; and gives a
drawing and a description of an anemone which he calls
anguicoma^ and which closely resembles undoubted
specimens of Johnston's A. troglodytes. Many objections
might be taken to Mr. Gosse's description of species, which
he makes out from the number of their tentacles, although
found in company with each other, and, as he justly re-
marks^ are of " the same size and form."

Of the voracity of the actinia many remarkable state-
ments have been made known; it may nevertheless be
kept in the aquarium for many months, if supplied with

1, Actinia rubra Sea marigold, near which is one shown retracted. 2, Actinia
bellis, Daisy sea-aiiemone (side view).

water containing particles of organic matter. Although
the several structures of actinia admit of being resolved
into two foundation membranes, an ectoderm and an en-
doderm, yet each of these, more especially the former,
manifests a tendency to differentiate into secondary layers,
so that several apparently distinct tissiies are recognisable
in the body of the fully-formed animal. Both membrane?
have their free surfaces more or less covered with cilia
ii 2

484 THE MICROSCOPE.

and the margin of the disc is furnished with a series of
white or bright blue specks, which some observers believe
to be rudimentary organs of vision ; but they are rather
to be regarded as sac-shaped prolongations of the outer
layer. A transverse section of the
body of the actinia exhibits two
concentric tubes, the outer being
constituted by the body-wall, and
the inner by the digestive sac.
The wide space which intervenes
between these tubes is divided by
a number of radiating partitions, or
"mesenteries," arriving at definite
intervals from the inner surface of
Fig. M6.-Actinia uiiis, seen the body wall. To the face of the
from above with its crown of mesenteries are attached the repro-

tentacles fully expanded. , ,. , . ,

ductive organs, which occur as

thickened bands of a reddish tint, at certain periods
filled with ova. The animal has the power of effecting
considerable alterations of form, as well as of locomo-
tion ; although if well supplied with food it attaches
itself so firmly as not to be removed without laceration
of its base.

Allied to the family Actinice are those laminated, in-
verted pyramidal looking bodies, Fungia, commonly called
"Sea-mushrooms," often found in great variety. The
colour of the polypidom is white, of a flattened round
shape, made up of thin plates or scales, embedded in a
translucent jelly-like substance, and within which is a
large polype ; the foot-stalk, by means of which the
animal is attached to the rock whereon it lives, is of a
calcareous nature. Ellis says : "The more elevated folds
or plaits have borders like the denticulated edge of
needlework-lace. These are covered with innumerable
oblong vesicles, formed of a gelatinous substance, which
appear alive under water, and may be observed to move
like an insect. I have observed these radiating folds of
the animal, which secrete the lamellaB, and which shrink
between them when the animal contracts itself on being
disturbed. They are constantly moving in tremulous un-
dulations ; but the vesicles appeared to me to be air-

ACTINIJL

485

vessels placed along the edges of the folds, and the vesi-
cles disappeared when the animal was touched."

Fig. 237.— Actinozoa.

1, Fungia agariciformis. 2, Alcyonium, Cydonium Mulleri. 3, Cydoniuin,
polypes protruding and tentacles expanded, others closed. 4, Zoantharia,
viewed from above. 5, Madrepore Abrotanoide. 6, Madrepore, cell slightly
magnified, showing internal structure. 7, Corallido} ; Coral, 8, Coral, polypes
protruding from the cells. 9, Gorgonia nobilfe, polypes expanded. 10, Tubi-
pora musica. 11, a tube of same, with polype expanded, and one cut longi-
tudinally to show internal structure. 12, Sertularia, polypes protruded ; and
others withdrawn into polypidoms

486 THE MICROSCOPE.

MADREPORID^J. — Madrepores, Mother-pores, "tree
corals," differ from other corals in not having a small
skeleton, but one inducted by numbers of small cells for
the residence of the living animal : these are very visible
in the Madrepore muricata, when the polype is dead and
decomposed ; but most distinct in the Oculina ramea, as
they are situated at the apparently broken stumps that
branch from the trunk of the skeleton (fig. 237, No. 5).
Every branch is seen to be covered with multitudes of
small pits or dots, scarcely visible to the unassisted vision ;
but, when viewed under the microscope, are found to be
cells of th$ most beautiful construction, remarkable alike
for their mathematical regularity and the exquisite fineness
of the materials employed in their composition. A mag-
nified drawing of a cell is given at No. 6. The living
polypes are exquisite objects for a low power ; their vary-
ing colours adding to the richness of the hues covering the
bed of the ocean.

ASTEROIDE.&. — A group of Zoophytes received the name
of Asteroida from the polypes presenting the form of a
star. The fleshy mass is supported by hard calcareous
spicula ; some having thick branching processes, perform-
ing the part of the skeleton in the human frame. This
central internal support is usually denominated the axis.
The fleshy mass, or covering, is possessed of sensation, and
is ramified by vascular tubes and canals for the sustenance
of the animal, and carrying on its vital functions. In-
cluded in this genera are Gorgoniadce, Pennatulidoe, Alcy-
onidce, Isidce, and Tubiporidce.

The term coral, or corallum, is restricted to the hard
structures deposited in the tissues or by the tissues of the
Actinozoa. The whole of this class, however, which are
thought to possess a framework called a " coral," are not
coralligenous. The Ctenophora, and several species, as the
soft-bodied non-adherent Zoantharia, deposit no corallum.
There are two kinds of such structure, one called the
" sclerobasic " corallum, a true tegumentary excretion,
formed by the successive growths from the outer surface of
the ocderon ; and another, the " sclerodermic " corallum,
deposited within the tissues of the animal. Two prin-
cipal modifications of form distinguish the sclerobasis : in

ASTEROIDE^. . 487

some it constitutes a free axis, virgate or primately divided
and varying in thickness ; in others it is attached, simple
or branched, and plant-like, as in Gorgonidce, from which
circumstance the name of " Sea-shrubs " has been applied
to them. In the Gorgonia we have, in addition to the
basal corallum, a deposition of tissue secretions, sclero-
dermic spicules appear within the substance of the in-
vesting membrane, and when the animal is dried, and the
soft parts washed away, a thin layer of calcareous spicules
is seen adhering to the horny sclerobasis. M. Valen-
ciennes made out five kinds of spicules, or sclerites, which
he severally designates capitate, fusiform, massive, stellate,
and squamous. These spicules form interesting objects
for the microscope, mounted dry or in balsam. " The
parts of a typical coralite are these : first, an outer wall, or
- theca,' somewhat cylindrical in form, terminating distally
in a cup-like excavation, or ' calice,' and having its central
axis traversed by a columella. The space between this
and the theca is divided into loculi, or chambers, by a
number of radiating vertical partitions, the septa. These
do not, in certain instances, quite reach the columella, but
are broken up into upright pillars or pali, arranged in one,
two, or more circulai rows termed ' coronets \ ' all of
which are best brought into view by transverse section."
Longitudinal division of a corallite shows certain modifi-
cations and changes in the partitions, or dissepiments ; and
the septa are seen to be covered with " styliform or echi-
nulate processes," which meet to form " synapticulse 01
transverse props, extending across the loculi like the bars
of a grate." Nevertheless, there is no difficulty in recog-
nising the close resemblance that such an organism pre-
sents to the typical Actinia, and they have accordingly
been classed with the Actinozoa.

The Gorgonidcb are permanently fixed, as are many other
corallitic actinozoa, and multiply by continuous gemma-
tion. As to their muscular system, most of them appear
to be well endowed in this particular. Pennatulidce pos-
sess so much muscular contractibility, that Mr. Darwin
relates, that on the south coast of America he observed
" a Sea-pen which, on being touched, forcibly drew back
into the sand some inches of its compound, polypi-covered

488 . THE MICROSCOPE.

mass." The muscular fibre, however, is wanting in those
distinct transverse striae, so fully developed in the muscle
of the higher orders of animals.

The ova of the compound Actinias are of a rounded
form, often brilliantly coloured, and their embryos, by a
series, of gradual changes, finally assume the appearance
and condition of the parent. Milne Edwards, to whom
we are indebted for most of our knowledge of the repro-
ductive processes of actinozoa, insists on the necessity of
distinguishing between that of gemmation and fissura-
tion, the polype-bud at first being no more than a pro-
tuberance from the parent "enclosing a csecal diverticulum
of the somatic cavity." Both simple and composite Fun-
gidce occur, and multiply by lateral gemmation.

The Gorgonidce differ from all other Alcyonaria in
having an erect branching caenosarc so firmly rooted that
they are reputed to rival oaks in size ; but it is doubtful
whether they ever attain to a height of more than five or
six feet.

Pennatulidce. — This family derives its name from
penna, a quill, and the spicula closely resemble a pen, one
of which is represented in fig. 239, No. 1. The polypes
are fleshy white, provided with eight rather long retractile
tentacula, beautifully ciliated on the inner aspect with two
series of short processes, and strengthened moreover with
crystalline spicula, there being a row of these up the
stalk : the series of smaller processes are ciliated. The
mouth, in the centre of the tentacula, is somewhat
angular, and bounded by a white ligament, a process from
which encircles the base of each tentaculum, and thus
seems to issue from an aperture. The ova lie between the
membraneous part of the pinnae ; they are globular, of a
yellowish colour, and by a little pressure can be made to
pass through the mouth.

Dr. Grant writes : "A more singular and beautiful
spectacle could scarcely be conceived than that of a deep
purple Pennatula phosphorea, with all its delicate trans-
parent polypes expanded and emitting their usual brilliant
phosphorescent light, sailing through the still and dark
abyss, by the regular and synchronous pulsations of the
minute fringed arms of the polypes." The power of

TUBIPORID^!. 489

locomotion is doubted by other writers, and the pale blue
light is said only to be emitted when under the influence
of some degree of irritation.

Alcyonaria. — Actinozoa, in which each polype is fur-
nished with eight primately fringed tentacles. Corallum
sclerobasic or spicular.

Alcyonium digitatum, " Fingered Alcyonium " (Fig.
237, No. 2).— The French call it Main de Mer, "sea-
hand," the Germans Diebshand, "thief's hand." Some-
times they are very small ; but when larger are named by
the fishermen Cows' -paps, and Dead Meris Hands. The
mass, at first repulsive, when placed in sea-water gradually
expands into delicately pellucid polypes, with crowns of
beautiful tentacula. The cells occupied by the polypes are
placed at the terminations of canals which run through
the polypidom, and which, by their union with each
other, serve to maintain a communication between the in-
dividual polypes constituting the mass. The rest of the
polypidom is made up of a transparent gelatinous sub-
stance, containing calcareous spicula, and pervaded by
numerous small fibres, which form a sort of irregular net-
work. Alcyonidce aife always attached to submarine
bodies. The species already mentioned is exceedingly
common round our coasts ; so much so that, as Dr. .John-
ston says, " scarce a shell or stone can be dredged from
the deep that does not serve as a support to one or more
specimens."

The ova, as Professor Grant remarks, placed under the
microscope, and viewed by transmitted light, appear as
opaque spheres surrounded by a thin transparent margin,
which increase in thickness as the ova begin to grow,
and such of the ova as lie in contact unite and grow as
one ovum. A rapid current in the water immediately
around each ovum, drawing along with it all the loose
particles and floating animalcules, is distinctly seen moving
with an equal velocity as in other ciliated ova ; and a
zone of very minute vibrating cilia is quite perceptible,
surrounding the transparent margin of all the ova.

TUBIPORID^:. — To this family belongs the handsome
Tuliporamusica, "Organ-pipe Coral" (fig. 237, No. 10), the
polypidom of which is composed of parallel tubes, united by

490 THE MICROSCOPE.

lateral plates, or transverse partitions, placed at regular dis-
tances; in this manner large masses, consisting of a congeries
of pipes or tubes, are formed. When, the animals are
alive, each tube contains a polype of a beautiful bright-
green colour, and the upper part of the surface is covered
with a gelatinous mass, formed by a confluence of the
polypes. This species occurs in great abundance on the
coasts of New South Wales, of the Eed Sea, and of the
Molucca Islands, varying in colour from a bright red to a
deep orange. It grows in large hemispherical masses, from
one to two feet in circumstance, which first appear as
small specks adhering to a shell or rock ; as they increase,
the tubes resemble a group of diverging rays, and at length
other tubes are produced on the transverse plates, thus
filling up the intervals, and constituting one uniform
tubular mass ; the surface being covered with a green
fleshy substance beset with stellate polypes.

Mr. Dana, who devoted much time to the examination
of the corals of the Pacific, thus writes of their diversities
of form and character : — " Trees of coral are well known ;
and, although not emulating in size the oaks of our forests
— for they do not exceed six or eight feet in height— they
are gracefully branched, and the whole surface blooms with
coral polypes in place of leaves and flowers. Shrubbery,
turfts of rushes, beds of pinks, and feathery mosses, are
most exactly imitated. Many species spread out in broad
leaves or folia, and resemble some large-leaved plant just
unfolding ; when alive, the surface of each leaf is covered
with polype flowers. The cactus, the lichen, clinging to
the rock, and the fungus in all its varieties, have their
numerous representatives. Besides these forms imitating
vegetation, there are gracefully-modelled vases, some of
which are three or four feet in diameter, made up of a
network of branches and branchlets and sprigs of flowers.
There are also solid coral hemispheres like domes among
the vases and shrubbery, occasionally ten or even twent}r
feet in diameter, whose symmetrical surface is gorgeously
decked, with polype-stars of purple and emerald green."

Nothing can be more impressive than the manner in
which these diminutive creatures carry out their stupen-
dous undertakings, which we denominate instinct, intelli-

ACALEPttffi. 491

gence, or design. Commencing betimes from a depth of a
thousand or fifteen hundred feet, they work upwards in a
perpendicular direction ; and on arriving at the surface
form a crescent, presenting the back of the arch in that
direction from which the storms and winds generally pro-
ceed : by which means the wall protects the busy millions
at work beneath and within. These breakwaters will re-
sist more powerful seas than if formed of granite ; rising
as they do in a mighty expanse of water, exposed to the
utmost powers of the heavy and tumultuous billows that
eternally lash against them.

As we glance at the map of the world, and think of the
profusion of fragrant vegetation and delicious food almost
spontaneously produced on the lovely sunny islands of the
broad Pacific, how startling does it seem, when we are
told that these islands, bearing on their bosoms gardens of
Eden, are entirely formed by the slow-growing corals,
which, rising up in beautiful and delicate forms, displace
the mighty ocean, defy its gigantic strength, and display a
shelly bosom to the expanse of day ! The vegetation of
the sea, cast on its surface, undergoes a chemical change ;
the deposit from rains aids in filling up the little gaping
catacomb, the fowls of the air and the ocean find a resting
place, and assist in clothing the rocks ; mosses carpet the
surface, seed brought by birds, plants carried by the
oceanic currents, animalcules floating in the atmosphere,
live, propagate, and die, and are succeeded, by the assist-
ance their remains bestow, by more advanced vegetable and
animal life : and thus generation after generation exist and
perish, until at length the coral island becomes a paradise
filled with the choicest exotics, the most beautiful birds
and delicious fruits, among which man may indolently
revel to the utmost desire of his heart.

ACALEPELE. — In great variety of form and colour,
swimming freely about the waters of the ocean, are found
in abundance the beautiful Acalephce. Some of them
have a remarkable stinging property, from which circum-
stance they derive their name of Sea-nettles ; others, from
their gelatinous nature, are known as Sea-jelly, or Jelly-
fish.

These interesting animals were first arranged in three

4:92 THE MICROSCOPE.

orders : A. stabiles (fixed), A. liber ce (free), and A. Tiydro-
staticce (hydrostatic). Cuvier classed them in two orders :
A. simplices and A. hydrostaticce. They
are now, however, divided differently,
and arranged in groups according to the
peculiar mode by which they effect their
locomotion. A very interesting point of
connexion between this class and the
preceding is the interchange of form.
Some of the Zoophyta, as the Tubula-
riadce and the Campanulariadce, • give
birth to a progeny which are in every
respect Naked-eyed Medusae ; while, on
the other hand, the young of the Medusae
are in their earlier stages stationary

The Medusae spread on the surface of the water a beau-
ful jelly-like mass, in form resembling an umbrella ; and,
by a continual contraction and opening out of this, they
swim freely about (Plate IX. c, d, e, h). They are all
more or less' phosphorescent. The Beroe, one of the family
Ctenophora, propel themselves with active ciliated arms.
The Physalidce have an organ common to fishes, — swim-
ming bladders, — by filling or emptying which they rise or
sink, and move along in their watery home.

The Medusoid family, Lucernaridce, has, from a mis-
taken view of its organization, been referred to the class
Actinozoa : Milne-Edwards has, however, placed it in a
sub-class, under the name of Podactinaria. In the
Lucernaridce the body is cup-shaped, about an inch in
height, terminating in a short foot-stalk. Eound the
distal margin of the cup arise a number of short tentacles,
which are disposed in eight or nine turfts ; in Carduella
they form one continuous series. Their free extremities
appear sucker-like, and the whole organism is semi-trans-
parent, of a gelatinous consistence, and variously coloured.
The cup, viewed from above, presents in its centre a four-
lobed mouth, which is seen to form the free extremity of
a distinct polypite, occupying the axis of the entire
hydrosoma. Its gastric region exhibits a number of
tubular filaments, arranged in vertical rows dipping into

LUCERNARIDj;. 493

the digestive cavity. The space between the polypite-wall
and the inner surface of the cup is equally divided. A
circular sinus has its course beneath the insertion of the
tentacles. By means of a band of muscular fibres which
transverse its margin, and another set which radiate
towards the polypite, the distal extremity of the cup can
be folded or drawn inwards. It has been observed to
detach itself, and swim in an inverted position by the
slowly repeated movements of its cup-like umbrella, thus
resembling Pelagia, a more active and permanently free
member of the same order.

Three families of the beautiful Lucernaridae, all of
which are at once distinguishable by' their umbrella, may
be denned as follows : —

Family 1, Lucernaridae. Eeproductive elements de-
veloped in the primitive hydrosoma, without the inter-
vention of free zooids. Umbrella with short marginal
tentacles and a proximal hydrorhiza. Polypite single.
Family 2, Pelagidae. Eeproductive elements developed in
a free umbrella, which either constitutes the primitative
hydrosoma, or is produced by fission from an attached
Lucernaroid. Umbrella with marginal tentacles. Poly-
pite single. Family 3, Ehizostomidse. Eeproductive ele-
ments developed in free zooids produced by fission from
attached Lucernaroids. Umbrella without marginal ten-
tacles. Polypites numerous, modified, forming with the
genitalia a dendriform mass depending from the umbrella.

For a further description of this interesting species see
Professor Muller's paper, Journal of Microscopical Science,
vol. iii. p. 265 ; or, Professor Greene's Manual of the
Ccelenterata.

The flat circular horny disc forming the skeleton of
Propita gigantea, to the naked eye exhibits both radiating
and concentric markings ; and, when examined with a
power of 40 diameters, its upper surface is found to be
furrowed, and two rows of small projecting spines occui
upon the ridges between the furrows, the ridges being the
radiating fibres above noticed. The under-surface, or that
to which the greater portion of the soft parts of the
animal are attached, is more deeply furrowed j and plicae
or folds of the mantle fit accurately into the furrows, from

494 THE MICROSCOPE.

which they can easily be removed by the application of a
gentle force. The concentric markings have in all cases
small scalloped edges ; they occur at certain regular inter-
vals, and are so many indications of the lines of growth.
In the centre there is a circular depression ; and between
its circumference and that of the first concentric marking
there are eight flattened radii. If the under-surface be
examined with a power of 100 linear, the ridges will all
be found to have small jointed tubular processes like hairs
projecting from them. In no part of this horny tissue is
there a trace of a cellular or a reticular structure.

Wonderfully beautiful as are these creatures in form and
colour, the amount ' of solid matter contained in their
tissues is incredibly small. The greater part of their sub-
stance appears to consist of a fluid, differing little, if at
all, from the sea-water in which the animal swims ; and
when this is drained away, so extreme is the tenuity of
the membranes which contained it, that the dried residue
of a jelly-fish, weighing two pounds, which was exa-
mined by Professor Owen, weighed only thirty grains.
The transparency of the tissues render the whole of the
Acalephoe delightful objects for the microscope.1

The Echiiiodermata belong to the division Annuloida, the
most familiar of examples of which are star-fishes and
sea-urchins. The labours of that distinguished comparative
anatomist and physiologist of Berlin, Johannes Miiller,
have made us better acquainted with the structure and
development of these remarkable animals than with those
of most classes of the animal kingdom. The series of feet
which protrude along certain fixed lines from the body of
an Echinoderm have received the name of " ambulacra ; "
and hence, says Mr. Huxley, " we may distinguish their
system of vessels as the ambulacral vascular system. The
existence of an ambulacral vascular system has as yet been
demonstrated only in the following orders : — Echinidea,
Ophiuridea, Crinoidea, Asteridea, and ffolothuridea, with
which the fossil Cystidea and Blastoirfm are inseparably
connected. I therefore limit the Ecliinodermata to the

(1) See an excellent paper in the Transactions of the Microscopical Society,
" On the Anatomy of Two Species of Naked-eyed Medusae," by G. Busk, Esq. ;
also Professor Forbes' works on this family.

ASTERIDEA. 495

very natural group formed by these orders. A more or
less complete calcareous skeleton is always developed
within the Echinoderms, resembling that of the Actinozoa,
not only in this respect, but also in consisting of detached
spicula. In this form the skeleton remains in the Holo-
thuridea, but in the other Uchinoderms, the spicula coalesce
into networks, which may become consolidated into dense
plates by additional deposits. It is by the different shape
and arrangement of these plates that the diversity ex-
hibited by the skeletons of different Echinodemata is
produced."

Asteridea. — Star-fishes have been divided according to
the mode of locomotion into Spinigrades, moving by
means of spines ; Cirrhigrades, by suckers ; and Pinni-
grades, by fins or pinnae. Of the last-named division we
have only one British genus, Comatula. At the very
extremity of each ray is an organ like an eye, having
spinous appendages, which are termed the eyelids. It is
doubtful, however, whether these parts have really any
visual endowment ; no proof of their possessing the
faculty of sight has ever been advanced, and, from what
we know of the nature of this sense generally in the
lowe'st forms of animal life, we should be disposed to con-
sider that the organs in question must serve some other as
yet unknown purpose.

The species Ophiura and Ophiocoma, Plate IV. Nos. 88
and 91, may be easily recognised by the great length and
tenuity of their rays, and their excessive fragility. The
whole surface, both of disc and rays, is covered by scales,
which are so closely approximated as to give an almost
perfectly smooth surface. These scales are arranged in
definite and often in very beautiful patterns, and in some
species the primary scales are edged or encircled by series
of circular bosses or tubercles, giving a reticulated appear-
ance to the disc and rays. Ophicoma rosula has its spines
tipped with curious anchor-shaped processes, which are
supposed to facilitate the motion of the creature. In
Ophiura they are very short, and not apparent without
careful inspection ; while in Ophiocoma they are so long
as to give quite a bristly, sinous appearance to the animal,
being sometimes, ' in fact, very much longer than the

496 THE MICROSCOPE.

breadth of the rays. A striking species is the Palmipes
membranaceus, the " Bird's-foot Sea-star," which is almost
as thin as parchment, and might, as Professor Forbes says,
be readily mistaken for the torn-off skin of some bulkier
species. Its surface is covered with a number of raised
tubercles, and very closely-set fasciculi of short and sharp
spines. Asterias aurantiaca and Luidia fragilissima
present a surface-structure very different from any of the
species previously noticed, their tuberculated epidermis
being so closely set with upright spines as to be almost
wholly invisible. These spines are arranged in a radiated
or rosette-shaped manner, and have a roughened surface.
A portion of the ray of Luidia forms a microscopic object
of exquisite beauty. A single spine is given in Plate IV.
No. 89.

The cirrhigrade star-fishes are furnished with certain
curious appendages, the use of which is at present very
imperfectly understood. These are the " pedicellarice" and
" madreporiform tubercle." The latter is a rounded,
cushion-like eminence of considerable size, situated on the
disc, mostly very much out of the centre. It is irregularly
fissured in a radiate manner, and is not at all unlike the
animal from which it derives its name. Various conjec-
tures have been made as to the use of this tubercle.
Forbes looks upon it as being merely the analogue of the
stalk which exists in the young condition of the crinoid
star-fishes. The pedicellarice (Plate IV. Nos. 93 and 94)
are pincer-like organs irregularly scattered over the surface
of the animal, and which have distinct characters in the
different species. They were supposed to be parasitic
creatures, but are now generally admitted to be true epider-
mic appendages. They are in a constantly active motion
during the life of the star-fish, and grasp firmly anything
which is brought between their blades. Their nearest
analogues are the birds' -head processes which occur in
certain zoophytes. The Pedicellarice of Echinus are par-
tially covered with ciliated epithelium : they are also
placed upon a stalk, the lower portion of which encloses
a calcareous nucleus, whilst the other portions are soft, and
spirally retractile.

The Feather-star (Comatula rosacea) is perhaps the most

ASTERIDEA. 497

interesting of the British star-fishes, and quite unique in
the gracefulness of its form and the exquisite beauty of its
colouring ; its life-history is not only remarkable, but it
possesses the additional interest of being the only living
representative in our seas of the group of organisms so
familiar to us in the fossil state as Encrinites. The deli-
cate structure of this species renders it impossible to ex-
hibit it satisfactorily in a dry or mounted state. The cen-
tral cup-shaped body gives off five rays, which divide so
near the base as to appear like ten. These are furnished
throughout their length with membranaceous pinnae.
Tubularia Dumortierii, Plate IV. IsTo. 92, appears rather
to belong to Comatula than Tubularia. A description of
this interesting polype will be found in Johnston's Brit.
Zoophytes , p. 53.

Professor Wyville Thompson, in a paper on " Sea-
Lilies " (see Intellectual Observer, August, 1864), says: —
" Comatula rosacea, the most common British species, is
found abundantly in Lamlash Bay, in Arran and Strang-
ford Loughs, in Dulkey Sound, in Kirkwall Bay, and
generally distributed in deep water all round the British
and Irish coasts. In general structure it resembles very
closely the head of Neocrinus decorus ; it has, however, no
stem, but in the position of the stem, and forming the
base of the cup, there is a hemispherical plate covered
with rows of cirrhi, exactly like the stem-cirrhi on the
stalked forms. When at rest it holds on to a stone or
weed, and spreads out its beautiful feathery crimson
arms, like the petals of a flower. At other times it swims
rapidly through the water by graceful impulses of its arms.
In spring, the hundreds of ovaries dotted over its pinnules
are turgid with eggs, and if at this time it is captured, and
placed with some sea-weed in a tank, bunches of bright
orange-coloured eggs hang in clusters around, giving the
delicate pinnatic arms the appearance of the fronds of
some wonderfully graceful fern in rich fructification.

" The phases passed through by the young before they
come to resemble their parents in form and mode of life
are of extraordinary beauty, and most instructive in deter-
mining the true zoological relation which the free crinoids
bear to their fixed ancestors. At first a minute, almost
K K

498

THE MICROSCOPE.

invisible, pale yellow germ escapes from the egg ; this, if
placed under the microscope the first day after its birth,
has a very definite form, but not the least like a star-fish.
Four bands of long vibratile cilia guard the body at dif-
ferent points, and by their motion the little animal whirls
about in the water. About the end of the second day two
rows of five each of delicate calcareous trellised plates may
be seen, making a kind of five- sided basket. A dark mass
now collects within the trellised basket, and the rings are
united together by little bundles of rods, till they form
what looks like a joined pillar supporting the basket.
Gradually the plates enlarge and distort the outer wall ;
and the stem-like series of joints lengthen, stretching out
the narrow end with it. The old mouth disappears, the
gelatinous wall settles round the little living skeleton, a
round sucker appears, and the animal fixes itself upright
to a sea- weed or a stone at the bottom of the tank. Five
leaf-like valves, each supported by one of the upper tier of
plates, now open on the top of the wider extremity, and
the little creature looks when these valves are open much
like a microscopic wine-glass, and when closed like a
tulip bud."

Echinidce} — Sea-urchins are found in abundance upon
our sea-shores, lurking among the rocks, where they entrap
their prey. Their spines and suckers are used as feet, or
as a mode of progression, even to the climbing of rocks, in
order to feed upon corallines and zoophytes : they march
along with ease where apparently no footing could be found,
or dig holes with their spines to bury themselves in the
sand, to escape pursuers, or hide from observation. The

(1) Description of Plate 9 :—

ASTEROIDS.

a, Astrophyton scutatum.
n, Ophiocoma rosula.

NaDIBBANCHIATA GASTROPODA.

6, Doris pinnatiflda — back and
side. view.

ACALEPILS.

c, JEquorea Forbesina.

d, Medusce Bud.

e, Thaumantias corynetes
h, Cydippe pyleus.

ECHINOIDE^E.

/, Echinus (A Yonng Sea-urchin).
g, Echinus sphcera.

TUNICA TA.
i, Ascidice.
k, Botryllus violaceus, on a Fucus.

CRUSTACEA.

I, Corystes cossivelaunus.
m, Eurynome aspera.
o, Pagurus Prideaurii.
p, Ebalia Permantii.

PLATE IX. Asteroidea, Echinidea, Crustacea, &c.
K K 2

EOHINIDEA. 501

Echinodermata,1 sea-urchins, or sea-eggs, derive their name
from these curious spinous processes.

In most Echinidea all the feet are expanded into sucker
discs, at their extremities, and are here strengthened by a
calcareous plate or plates ; but in the Echino-ddaris and
some others, the feet of the oral portion of the ambulacra
only have this structure, while those of the apical portion
are pectinated, flattened, and gill-like. Muller distinguishes
four kinds of feet in the Spatangoidea, — simple locomotive
feet, without any sucking disc ; locomotive feet, provided
with terminal suckers, and containing a skeleton ; tactile
feet, whose expanded extremity is papillose ; and gill-like
feet, triangular, flattened, with more or less pectinated
lamellae.

In the Clypeastrodea the petaloid portions of the am-
bulacra possess branchial feet, interspersed with delicate
Icccmotive sucker feet, provided with a calcareous
skeleton. In the Ophiuridea and Crinoidea the feet are
tentaculiform ; and there are no vesicles at the bases of
the feet, while in the Asteridea they are well developed, but
simpler than those of the Echinidea. The madreporic canal
is, in the Asteridea, strengthened by a remarkable cal-
careous framework, which has given rise to the notion
that it is filled with sand, and to the name " sand-canal,"
which has been applied to it. The canal terminates in
the madreporic tubercle, which is always placed inter-
radially on the antambulacral surface of the star-fish.

In some, Holothuridea, the feet are scattered over the
whole ambulacral region, as well in the inter-ambulacra
as in the ambulacra. In others, Psolus, the feet are de-
veloped only from three of the five ambulacra ; while in
the Synaptce and Chirodatce there is only a circlet around
the mouth.

Many star-fishes, and Synapta among the Holothuridea,
have the curious habit of breaking themselves up into
fragments when taken ; Muller has pointed out the very
curious fact, that in Synapta, at any rate, this act may be
prevented by cutting through the oral nervous circle. The
nervous circle in the Echinus surrounds the oesophagus near
the mouth, and is enclosed by the alveoli, between which the

(1) Derived from echinos, a soind and derma, skin.

502 THE MICROSCOPE.

ambulacral nerves pass to reach it. In the Asteridea, the
circle lies at the extreme limit of the soft membrane, which
surrounds the mouth, and may be readily exposed by cut-
ting away the hard inter-ambulacral oral lips, In the
Holothuridea it lies immediately beneatli the perisoma of
the oral disc. The only known organs of sense in the
Echinodermata are the pigmented " eye-spots," developed
in connexion with the ends of the ambulacral nerves, and
on the oral nervous circle in many Holothuridea.

The great majority of the Echinodermata commence
their existence as free-swimming larvae covered with cilia,
but a great difference exists in their further course, accord-
ing as they belong to the Asteridea, the Holothuridea, and
the Crinoidea on the one hand, or to the Echinidea and
Ophiuridea on the other. Of the development of the
Crinoidea we know very little, beyond the observations of
Mr. Thompson, that the larva of the Comatula is provided
with several transverse "bands of cilia, almost like that of
a Holothuria, and that the development of the Echinoderm
commences while the larva is still free. At a later period,
the young Comatula is seated upon a long, jointed stem, so
as to resemble a Pentacrinus; and it becomes detached
from this stem, in assuming its adult condition.

Mr. Huxley, after mature examination of this class of
animals, says, "he can see no reason for retaining them
amongst the Radiata of Cuvier, but. on the other hand,
thinks them properly placed among the Annuloida"

i he skeleton of the Echinoderms generally consists of an
assemblage of plates, or joints, of calcareous matter. The
minute structure of which presents a reticulated character,
and the solid parts are usually composed of a series of
super-imposed laminae or scales. The openings, or areolae,
in one layer being always placed over the solid cell-walls
of the layer beneath it, the spines are situated on the ex-
ternal surface of the shell ; they are generally of a conical
figure, and are articulated with the tubercles by a ball-
and-socket joint. When a thin transverse section of one of
these spines is examined with the naked eye, it appears to
. be made up of a series of concentric layers, varying
considerably in number; not, however, with the size oi
the spine, but with the distance from the base at which

ECHINIDEA.

503

the section was made : when a section taken from the
middle of the spine is examined with a power of fifty
diameters, it will be seen that the centre is occupied by a
reticulated structure ; around the margin of this may be
observed a series of small
structureless spots, ar-
ranged at equal distances
apart (Fig. 240, No. 1) ;
these are the ribs or pil-
lars, and indicate the
external surface of the
first layer deposited ; pass-
ing towards the margin,
other rows of larger pil-
lars may be seen, giving
it a beautiful indented
appearance ; all the other
parts of the section are
occupied by the usual
reticulated tissue. In the
greater number of spines
the sections of the pillars
present no structure, in
others they exhibit a
series of concentric rings
of successive growth,
which strongly remind
us of the medullary rays
of plants ; occasionally
they are traversed by
reticulated structures, as
represented in Fig. 246,
No. 1. When a vertical
section of a spine is ex-
amined, it is found to Fig. 239.

be composed of Cones l» Polypidom of Pennatula phospjiorea. 2,

, , ,, ., Synapta Chirodota. 3, AncMor-shaped

placed one over the Other, spiculum and plate from skin of Sy-

the outer margin of each naPta-

cone being formed by the, series of pillars. In the genus
Echinus the number of cones is considerable, while in that
of Cidaris there are seldom more than one or two ; so that

504

THE MICROSCOPE.

from these species transverse sections may be made, having
no concentric rings, and in which only the external row of
pillars can be seen.

" The skeleton of the Eckinodermata contains very little
organic matter. When it is submitted to the action of
very dilute acid, to dissolve out the calcareous matter, the
residuum is very small in amount. When obtained, it is
found to possess the reticular structure of the calcareous
shell (Fig. 240, No. 1) ; the meshes or areolse being bounded

Fig. 240.

1, Section of spine of Echinus, exhibiting reticulated structure, the calcareous
portion haying been dissolved out by acid. 2, Transverse section of shell
of the Pinna ingens. 3, Horizontal section of shell of Terebratulala rubicunda,
showing its radiating perforations.

by a substance in which a fibrous appearance, intermingled
with granules, may be discerned under a sufficiently high
magnifying power, as originally pointed out by Professor
Valentine. This tissue bears a close resemblance to the
areolar tissue of higher animals ; and the shell may pro-
bably be considered as formed, not by the consolidation of
the cells of the epidermis, as in the Mollusca, but by the
calcification of the fibro-areolar tissue of the true skin.

ECHINIDEA. 505

This calcification of areolar or simply fibrous tissue, oy the
deposit of mineral substance, not in the meshes of areolee,
but in intimate union with the organic basis, is a condition
of much interest to the physiologist; for it presents us
with an example, even in this low grade of the animal
kingdom, of a process which seems to have an important
share in the formation and growth of bone, namely, in
the progressive calcification of the fibrous tissue of the
periosteum membrane covering the bone." l

From their peculiarity of structure they may be said to
be almost imperishable. Their shells exist abundantly in
all our chalky cliffs, innumerable specimens of which may
be obtained, exhibiting the same wondrous forms and
characters as those which now frequent our shores.

The Crinoidea, " Sea-lilies," — so called from the resem-
blance which many of them present to the lily, — were ex-
ceedingly abundant in former ages of the world ; and their
remains often form the great bulk of large masses of rock,
fig. 241. These animals were all supported upon a long
stalk, at the extremity of which they floated in the waters
of those ancient seas, spreading their long arms in every
direction in search of the small animals which constituted
their food. Each of the arms, again, was feathered with
a double series of similarly jointed appendages ; so that
the number of separate calcareous pieces forming the
skeleton of one of these animals was most enormous. It
has been calculated that one species, the Pentacrinus
briareus, must have been composed of at least 150,000
joints; and "as each joint," according to Dr. Carpenter,
" was furnished with at least two bundles of muscular
fibre, — one for its contraction, the other for its extension,
—we have 300,000 such in the body of a single Penta-
crinus— an amount of muscular apparatus far exceeding
any that has been elsewhere observed in the animal
creation." A furrow runs along the inside of the arms,
which is covered with a continuation of the skin of the
disc; and from this the ambulacra are protruded, as in
other Eckinodermata.

In the family of Ophiuridea, so called from the resem-
blance of their arms to a serpent's tail, (Gr. ophis, a snake,

(1) Dr. Carpenter, Cyclopaedia of Anatomy and Physiolcgy.

506

THE MICROSCOPE.

aura, a tail) ; the body forms a roundish or somewhat
pentagonal disc, furnished with five long simple arms,
whioh have no furrow for the protrusion of the ambulacra.
Ophiuridea are exceedingly plentiful in all
our seas, and their remains occur in all
the more recent marine strata of the
earth's crust. They are more commonly
called Sand Stars, or Brittle Stars.

"However much the faunas of the
various geologic periods may have differed
from each other, or from the fauna which
now exists, in their aspect and character,
they were all, if I may so speak, equally
underlaid by the great leading ideas which
still constitute the master types of animal
life. And these leading ideas are four in
number. First, there is the star-like type'
of life, — life embodied in a form that, as
in the corals, the sea anemones, the sea
urchins, and the star fishes, radiates out-
wards from a centre ; second, there is
the articulated type of life, — life embodied
in a form composed, as in the worms,
crustaceans, and insects, of a series of
rings united by their edges, but more or
less moveable on each other ; third, there
is the bilateral or molluscan type of life,
Fig. 24i.— Encrinus, — life embodied in a form in which
there is a duality of corresponding parts,
ranged, as in the cuttle fishes, the claws, and the snails,
on the sides of a central axis or plane ; and fourth there is
the vertebrate type of life — life embodied in a form in
which an internal skeleton is built up into two cavities
placed the one over the other, the upper for the reception
of the nervous centres, central and spinal, — the lower for
the lodgment of the respiratory, circulatory, and digestive
organs. Such have been the four central ideas of the
faunas of every succeeding generation, except perhaps the
earliest of all, that of the Lower Silurian System, in which,
so far as is yet known, only three of the number existed, —
the radiated, articulated, and molluscan ideas or types

ECHINIDEA. 507

That Omnipotent Creator, infinite in His resources — who,
in at least the details of His workings, seems never yet to
have repeated Himself, but, as Lyell well expresses it,
breaks, when the parents of a species have been moulded,
the dye in which they were cast, — manifests Himself, in
these four great ideas, as the unchanging and unchangeable

Fig. 242. — HoIotJiunJea, Sea-cucumbers.

One. They serve to bind together the present with the
past, and determine the unity of the authorship of a wonder-

508 THE MICROSCOPE.

fully complicated design, executed on a groundwork broad
as time, and whose scope and "bearing are deep as
eternity." l

The Synaptidas are characterised by a total absence of
ambulacra, the motions of the animals being assisted by
peculiar anchor-like processes which project from the skin,
and roughen the surface of the animal. The spiculum re-
presented in fig. 239 is serrated on the convex edge, and,
Dr. Herepath says, apparently belongs to S. Galliermii,
but that the drawing of the animal near it is singularly
inaccurate, although taken from Professor Forbes' work ;
and that the oral tentacles are imaginary developments of
S. digitata. See Herepath, " On the Genus Synapta,"
Quar. Journ. Micros. Science, 1865, p. 1. The spicules
are beautiful objects for polarised light. (Plate IV. No.
87, shows a side view of one set in the skin.)
• Holothuridea, " Sea-cucumbers." — In this family the
body acquires a slug-like form. The radiate structure is
in fact scarcely recognisable in these animals, except in
the arrangement of the tentacles which surround the
mouth. The body is always more or less elongated, with
the mouth at one end and the anal opening at the other ;
the calcareous deposit in the skin is reduced to scattered
granules ; and in one family the ambulacra are entirely
wanting.

The integument consists of a number of minute reticu-
lated plates, set closely on the substance of the skin. The
forms of the plates are various, as well as the spicula set
in them. The Australian seas furnish many varieties :
Plate VIII. Nos. 171 and 172, are representations of
plates and spicula under polarised light. Objects of this
class are also well suited for black-ground illumination.

The structure of the spines and other solid parts of the
skeleton of Echinodermata can only be displayed by
making thin sections, in the way described for cutting
bone, at page 209. Their peculiar texture requires that
certain precautions should be taken to prevent the section
from breaking whilst being reduced to a desirable thin-
ness, and to prevent the interspaces of the network from
being clogged by the particles abraded in the reducing

(1) Miller's Testimony of tKe Rocks.

PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES. 509

process. In mounting the specimens, liquid balsam must
be employed, and only a very gentle beat should be ap-
plied ; and if, after it has been mounted, the section
should be found too thick, it will be easy to remove the
glass cover and reduce it further, care being taken to
harden the balsam, as directed in preparing bone sections.

PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES.

The following excellent and simple plan for preserving
zoophytes as fluid preparations, so as to retain the polypes
and their tentacular arms in situ, was adopted by the late
Dr. Golding Bird. For this purpose a lively specimen
should be chosen, and then plunged into cold pure water ; l
the polypes are killed almost immediately, and their ten-
tacles often do not retract : proper-sized specimens should
then be selected, and preserved in weak alcohol. Little
phials about two inches long should be procured, made
from thin flat glass tubes, so as to be half an inch wide,
and about a quarter of an inch, or even less, from back to
front. The specimens should be fixed to a thin platinum
wire, and then placed in one of these phials (previously
filled with weak spirits), so as to reach half-way down.
When several are thus arranged, they should be put on a
glass cylinder, and removed to the air-pump. On pump-
ing out the air, a copious ebullition of bubbles will take
place; and many of the tentacles previously concealed
will emerge from their cells. After being left in vacuo
for a few hours, the bottles should be filled up, closely
corked, and tied over, like anatomical preparations in
general. For all examinations with a one or two-inch
object-glass, these bottles are most excellent, and afford
cheap and useful substitutes for the more expensive and
difficultly-managed cells. In this manner, specimens of
the genera Membraniporce, Alcyonidce, and Crisiadce, &c.,
exhibit their structure most beautifully.

A few dozen of these little bottles hardly occupy any
room, and would form a useful accompaniment to the
microscopist by the sea-side. Any one visiting the caverns

(1) A small quantity of gin thrown into distilled water answers the purpose
etter than pure water, and specimens n ~
are nearly always preserved in their polj

better than pure water, and specimens maybe put up in the same. The animals

lypidoms by using this fluid to kill them.

510 THE MICROSCOPE.

in St. Catherine's Island at Tenby, might reap a harvest
which would afford amusement and instruction for many
weeks. These caverns are so rich in zoophytes and
sponges, that they are literally roofed with the Laomedece,
Grant ice, and their allies ; whilst the elegant Tubularice
afford an ornament to the shallow pools on the floor ; and
the walls are wreathed with the pink, yellow, green, and
purple Actiniae.

When these objects are examined by polarised light,
most interesting results are produced. For this purpose,
let a piece of selenite be placed on the stage of the micro-
scope, and the polarising prisms arranged so that the ray
transmitted is absorbed by the analyser. If a specimen of
Sertularia operculata be placed on the selenite stage, and
examined with a two-inch object-glass, the central stem is
shown to be a continuous tube, assuming a pink tint
throughout its whole extent. The cells appear violet in
colour ; their pointed orifices are seen much more distinctly
than when viewed with common light The vesicles are
paler than the rest of the object ; and their lids, which so
remarkably resemble the operculum of the theca of a
moss, are beautifully distinct, being of an orange-yellowish
colour. This zoophyte is often covered with minute
bivalve shells, distinguished by the naked eye from the
vesicles only by their circular form ; and these, when pre-
sent, add much to the beauty of the specimen, presenting
a striated structure, and becoming illuminated with most
beautiful colours.

*

ECHINODERMATA, HYDKOZOA, POLYZOA, IlELMINTHOIDA.

Tuft'cn West, del.

I'1,ATK IV.

CHAPTEE III.

POtYZOA — MOLLUSCA — GASTEROPODA — BRACHIOPODA — CONCHIFERA
CEPHALOPODA— PTEROPODA— TUNICAT A— CRUSTACEA— EN TOMOSTBACA
ANN ULOS A — CIBRIPEDA — E NTOZOA — ANNELI l> A .

HE term Mollusc, derived from mollis,
soft, is one which at once indicates a
chief structural characteristic of the
class of animals about to occupy our atten-
tion. The body of most of the molluscous
sub-kingdom is soft and fleshy ; and all except
the Tunicata and a few Pteropoda are covered
or protected by a hard calcareous shell. The
shell is of two kinds ; first of an epidermal
character, being formed upon the surface of a
filmy cloak-like organ called a mantle, an-
swering to the true skin of othei animals ;
and next of a dermal character, being con-
cealed within the substance of the mantle,
and frequently moulded into a great diversity
of forms, and coloured with various tints.

The molluscs belonging to the class Gaste-
ropoda have become a large and important
section of the animal series, presenting very
'I many objects of great interest for the micro-
scopist. Of the large family of molluscs, the
only species which bears any resemblance in structure to
the Polyzoa, which now form a portion of the molluscous
division, is the Brachiopoda, and this is confined to a re-
semblance in internal structure.

512

THE MICROSCOPE.

The Polyzoa were placed by Dr. Johnston tinder
the head Ascidioida; in the generality of works they are
named Bryozoa, and the individual, Bryozoon ; derived
from the Greek words fipvov, sea-
moss; £oon/, animal. (Fig. 243.)
The Polyzoa are all compound as-
sociated animals, whence their
name ; but when a polyzoon egg is
hatched, as in the case of Pluma-
tella, it commences life as an iso-
lated being, and by subsequent
growth, resembling budding, mul-
tiplies into a colony. All are most
bountifully supplied with cilia, and
the play of these is most energetic,
for the purpose of securing an
abundant supply of food, and ap-
parently without exertion on the
part of the creature itself. From
this most marked characteristic,
Dr. Farre was induced to give them
the name of Ciliobrachiata. But
it has at length been determined to

Fig. m.-Bryozoon Bower- transfer the Polyzoa, f lustra, Le-
bankia, " Bowertank Bry- praiia Anguinaria spatulatO) &c.

ozoon," showing its inter- * .. , y ., i • j i

»_„_._ _„ -„!..._ to the sub-molluscan kingdom.1

Polyzoa are generally found living
together in great numbers, resem-
bling in this respect some of the Actinozoa, and are
protected by membranaceous coverings or polypidoms.
Protrusion and retraction are performed by two sets of
muscles, one acting on the body of the animal, the other

(1) Mr.^Gosse, in his Manual of Marine Zoology, adopts the idea, now pretty
general, that the Polyzoa belong to the Molluscous division, in spite of their
external resemblances to Polypes, and he places them among Molluscs. In this,
perhaps, he has thought more of systematic views on classification than of the
student's convenience. It seems to us quite clear that, without adopting De
Blainville's principle of classifying animals according to their envelope as the
best principle of scientific classification, we should adopt it in works of refer-
ence like the present, since the external characters are necessarily those most
immediately recognised by the student ; and in the case of the Polyzoa, they are
so remarkably similar in external characteristics to the hydroid polypes, that
they were always classed with them, until the profounder investigations of Van
Beneden, Allman, and others, revealed the resemblances between the internal
characteristics of the Polyzoa and those of Molluscs.

nal ' structure ; another
animal withdrawn mto its
cell.

POLYZOA. 513

upon its cell. The oral extremity is surrounded by a circle
of long tubular tentacles covered with cilia ; at each of these
feelers or arms there is an aperture, the one at the base
communicating with a canal that passes round the edge of
the oral aperture or mouth. The food passes down a long
gullet, that contracts during the process of swallowing. At
the end of this is an orifice that opens into what appears
to be a gizzard, having two bodies opposite to each other,
with a rough surface, as if for the comminution of food,
moved by muscular fibres. Those of the species without
this gizzard have a digestive stomach that secretes a
coloured fluid. From the upper part of the stomach near
the entrance from the gizzard arises an intestine, having
a narrow opening surrounded by cilia that proceeds
upwards, ending in an orifice near to the tentacles, from
which the refuse food is ejected.

Their cells are of various shapes, and from one, a family
of millions come, budding forth from its sides ; and
though the living matter disappears, the catacombs exist
for the foundation of their families, branching out and
enduring for ages.

Bryozoon Bowerbarikia received its name from Dr. Arthur
Farre, in honour of the well-known microscopist, Mr.
Bowerbank. A magnified representation of the animal ia
seen in fig. 243. " When fully expanded, it is about one-
twelfth of an inch in length. In its retracted state, it is
completely enclosed in a delicate horny cell, sufficiently
transparent to admit of the whole structure of the con-
tained animal being seen through its walls. The cells are
connected together by a cylindrical creeping stem, upon
which they are thickly set, sessile, ascending from its
sides and upper surface. The animal, when completely
expanded, is seen to possess ten arms of about one-third
the length of the whole body ; each arm being thickly
ciliated on either side, and armed at the back by about
a dozen fine hair-like processes, which project at nearly
right angles from the tentacles, remaining motionless,
while the cilia are in constant and active vibration."

Notamia, Back-cell, so named from the cells being exactly
opposite, and united back to back with a thick partition,
and having a joint above and below each pair. In some

L L

514

THE MICEOSCOPE.

species of the Flustrce the interior of the cell is protected
by a lid which bears some appearance to the head and
beak of a bird, and hence it is termed the bird's-head
process. This has been made the subject of investigation
by many naturalists. George Busk, Esq., F.R.S.,1 con-
tributed to the Transactions of the Microscopical Society,
1849, an admirable paper on the Notamia bursaria,
"Shepherd's-purse Coralline," (represented in fig. 244,
Nos. 1 and 3), which adds to our knowledge of this
curious process. He says : " This most beautiful pearl-

Fig. 244.

1, Notamia lurtaria, Shepherd's-purse Coralline. 2, Anguinaria spatulata.
Snake Coralline, growing with the Campanularia Integra. 3, The Shepherd's
purse Animalcule withdrawn into its cup, and the internal organism
shown greatly magnified.

coloured coralline adheres by small tubes to fuci, from
whence it changes into flat cells ; each single cell, like

(1) Mr. Busk has added to the description here given of this bird's-head
process in the Quarterly Journal of Microscopical Science, for January 1854.

POLYZOA. 515

the bracket of a shelf, broad at top and narrow at the
bottom : these are placed back to back in pairs, one above
another, on an extremely slender tube that seems to
run through the middle of the branches of the whole
coralline. The cells are open at top. Some of them have
black spots in them ; and from the top of many of them
a figure seems to issue out like a short tobacco-pipe, the
small end of which seems to be inserted in the tube that
passes through the middle of the whole. The cells in pairs
are thought by some to have the appearance of the small
pods of the plant " Shepherd's Purse," by others the shape
of the seed-vessel of the Veronica, Speedwell.

" The polypidom of this bryozoon, like those of most of
its congeners, may be said to consist of a radical portion,
by which it is affixed to the objects upon which it grows,
and of a celliferous portion or branches, upon which the
polypes themselves are lodged. The radical portion in the
present species consists of a central discoid body of a
nearly circular form, and of branches radiating from the
periphery of the disc, which thence exhibits something of
the aspect of the body of an ophiura. The radical tubes
or branches springing from the margin of the disc are
usually five or six in number, and they are given off at
pretty regular distances apart ; but besides these radical
tubes, one or more celliferous branches are not unfrequently
seen to arise immediately from the upper surface of the
discoid portion.

" The central disc, and the radical tubes arising from it,
exhibit a similar structure, and are formed of a thick, firm,
apparently horny envelope, containing a coarse granular
matter, of a yellowish-white colour, and which in some
portions of the tubes assumes the form of distinct irregu-
larly-globular masses, of nearly uniform size. The central
disc is subdivided into distinct compartments by septa of
considerable thickness, and each radiating branch arises
from one of these distinct compartments ; so that there
appears to be no communication between one radical
branch and another. The radical branches give off at
irregular distances secondary branches, which ultimately
become celliferous. Each of these secondary branches,
however, arises from a distinct compartment, as it were, of

LL2

516 THE MICROSCOPE.

the tube from which it springs. This compartment is
formed, like those of the central disc, by a thick septum,
which shuts off the origin of the secondary branch from
the main cavity of the primary one."

The larger, or polypiferous cells, Mr. Busk proposes to
term cells, and the smaller tobacco-pipe-shaped organs
cups; the latter being usually above the former through-
out the polypidom, "excepting immediately below each
fork, where the cup is invariably absent above one of the
cells of the pair from between which the fork springs.
The polype-cells are several times larger than the cups,
and their walls are much thinner ; in fact, sufficiently
transparent to allow of the contents of the cell being
pretty well seen, without any preparation, even during the
life of the animal. In shape they are inversely conical,
and the outer and upper angle is usually produced into a
prominent,, sharp point. From the internal and upper
angle arises the tubular prolongation going to form the
next cell or cup, as the case may be, in succession. They
are entirely closed at the top, contrary to what is stated
by previous observers ; and, as has been shown, there is no
connexion whatever between the cell and the cup placed
immediately above and behind it. The aperture of the cell
is on the anterior face, and towards the upper margin ; it
is of a crescentic form, and placed obliquely, as it were,
across the upper and internal angle of the cell, with the
convexity of the curve directed upwards and inwards. The
lips of the aperture are' strengthened by thin bands of
horny material ; and, under favourable circumstances,
indications of short muscular fibres, for the purpose of
opening or closing the aperture, may be seen."

The shell, which Mr. Busk believes to be entire at the
bottom, though closed only by a very delicate membrane,
contains an ascidoid polype of the usual typical form of
that class. " It has ten tentacles, and no gizzard. Two
sets of muscular fibres at least may be distinguished as
appertaining to the polype. The most important of these
are the retractor muscles, which, arising from the bottom
of the cell, in the form of long, somewhat flattened,
transversely striped, isolated fibres, about the one ten-
thousandth of an inch in width, are inserted, some of them

CELLEPORID.E. 517

at the base of the tentacles, and others lower down the
body of the polype."

When we consider the minuteness of the delicate little
sprig which is the natural size of this polype, we cannot
but wonder at the triumphs of the microscope in giving
such precise details as Mr. Busk relates of the Notamia
bursaria. Its beautiful and perfect organisation, the care-
ful provision for the safety and engagements of this
minute being, make us awe-stricken at the power of Divine
intelligence.

The Halodactylus, better known as Alcyonidium, is re-
markable among the marine forms of Polyzoa, for the large
size of its tentacular crowns; these when expanded are
distinctly visible to the unassisted eye, and present a spec-
tacle of great beauty when viewed with the binocular
microscope. Its polyzoary has a spongy aspect very much
resembling that of the Alcyonian zoophyte : when how-
ever the animals are expanded, they are at once seen to be
widely different, as the plumose turfts which then issue
from the surface of Halodactylus give it the appearance of
a beautiful downy film. The opacity of its polyzoary
renders it unsuited for the examination of anything more
than the tentacular crown.

Lepralia, "Sea-scurf," — from the Greek for marine
leprosy, — is the name given to this family of the Celle-
poridce by Dr. Johnston.

Lepralia nitida, found attached to shells, is thus
described : " Crust spreading circularly, closely adherent,
rather thin, greyish white, calcareous; cells contiguous,
in radiating rows, large, subalternate, ovate, ventricose,
silvery, the walls fissured with six or seven cross slits
which are on the mesial line ; aperture subquadrangular,
depressed, terminal ; anterior to it there is often found a
globular, pearly, smooth, oviferous operculum, with a round
even aperture. The remarkable structure of the -cells
renders this one of the most interesting species under the
microscope. There is sometimes an appearance of a spine
on each side of the lower angle of the mouth, which is
merely the commencement of the walls of the next cell."

L. coccinea, L. variolosa, L. ciliata, L. trispinosa, and
L. immersa, are the other British species.

518 THE MICROSCOPE.

The family Cellularia, little-cells, have a curious and
wonderful provision of nature for their protection, an
operculum, a lid or cover over the apertures of each cell.
Cellularia ciliata is parasitical, branching, calcareous,
white and tufted ; grows about half an inch in height, and
the oblique aperture is armed on the outer edge with four
or five long hollow spines. The operculum is pearly, and
near the base there is that singular appendage, described
as the bird's-head process. Its beauty and transparency
render it a favourite object with microscopists.

The Cellularia (nowJBugula) avicularia are very accurately
described by Mr. Gosse, from his own observations upon
specimens secured on the Devonshire coast, during a resi-
dence there. He says : " Well does it deserve the name of
Bird's-head Coralline, given to it by the illustrious Ellis ;
for it presents those curious appendages that resemble vul-
tures' heads in great perfection. All my specimens were
most thickly studded with them ; not a cell without its
bird's head, and all see-sawing, and snapping, and opening
their jaws with the most amusing activity ; and what was
marvellous, equally so in one specimen from whose cells
all the polypes had died away, as in those in which they
were still protruding their lovely bells of tentacles. The
stem ascends perpendicularly from a slender base, which is
attached to the rock, or to the cells of a Leprcdia growing
from the rock. The central part of the spine is most ex-
panded, the diminution above and below being pretty
regular ; during life, the usual colour is a pale buff, but
the cells become nearly white in death. When examined
microscopically it is, however, that the curious organisa-
tion of this zoophyte is discovered, especially when in full
health and vigour, with all the beautiful polypes protruded
and expanded to the utmost, on the watch for prey. It
seems to me as poor a thing to strain one's eyes at a
microscope over a dead and dry polypidom, as it does to
examine a shrivelled and blackened flower out of a her-
barium ; though I know well that both are often indispen-
sable for the making out of technical characters. But if
you want to get an insight into the structure and functions
of these minute animals, or if you would be charmed
with the perception of beauty, or delighted with new

519

and singular adaptations of means to an end, — or if you
desire to see vitality under its most unusual, and yet most
interesting phases, — or if you would have emotions of
adoring wonder excited, and the tribute of praise elicited
to that mighty Creator who made all things for His own
glory, — then take such a zoophyte as this, fresh from the
clear tide-pool, take him without inflicting injury ; there-
fore detach with care a minute portion of the surface-rock,
and drop your prisoner, with every organ in full activity,
into a narrow glass cell with parallel sides, filled with clear
sea-water, and put the whole on the stage of the micro-
scope, with a power of not more than 100 linear, at least,
for the first examination. I greatly mistake if you will
not confess that the intellectual treat obtained is well
worth — ay, ten times more than worth — all your trouble."

CRISIADJG, signifying a separation; applied to a parasi-
tical family. Crisia cornuta, " Goat's-horn Coralline " of Ellis,
having cells linked in a single series ; the same remark ap-
plies to C. chelata, " Bull's-horn Coralline ;" the latter look
like a number of shoes fitting close to the ancle, joined by
the toe-part to the heel of others. Ellis says : " This beau-
tiful coralline is one of the smallest we meet with. It rises
from tubuli growing upon fuci, and passes from thence into
sickle-shaped branches, consisting of single rows of cells,
looking when magnified like bull's horns inverted, each one
arising out of the top of the other. The upper branches take
their rise from the fore-part of the entrance of a cell, where
we may observe a stiff, short hair, which seems to be the
beginning of a branch. The opening of each cell, which
is in the front of its upper part, is surrounded by a thin
circular rim ; and the substance of the cells appears to
consist of a fine transparent shell or coral-like substance."

Crisia eburnea, "Tufted-ivory Coralline," attains the
height of an inch, and displays its beautiful white, bushy
tufts, with often a dash of light-red intermingled. Its cells
are loosely aggregated and cylindrical, with bent tubular
orifices free ; while the Crisia aculeata have cells closely
aggregated, cylindrical, nearly straight, with long slender
spines springing from the margin of every cell, giving it a
delicate and pretty appearance.

EUCRATIAD.E. — We select from this family a specimen of

520 THE MICROSCOPE.

great interest, the Anguinaria, — from the Latin anguis, a
snake. This, and also Notamia, belong to the class Polyzoa.
An account of the Anguinaria spatulata, "Snake-head
Coralline," appeared in the Transactions of the Microscopical
Society, by Mr. Busk, who corrects the errors of other ob-
servers. The polype is parasitical upon fuci, and is not un-
frequently associated with other kinds on the same plants,
as in fig. 244, No. 2, on Campanularia. The A. spatulata
"as a whole, consists, like all its congeners, of two distinct
portions, one usually termed the radical, and another which
constitutes the proper polype cells. In the present instance,
the arrangement of these parts is in some respects
very peculiar and curious; but it will be found upon
strict examination to accord accurately with the uni-
versal type."

" In the radical tubes, and on the dorsal or upper surface
of the dilated extremity of the polype-cell, represented
at No. 2, this earthy matter is deposited in the form of
minute angular or rounded particles, presenting faint
traces of a linear arrangement ; but in the main body
of the polype-cell, or the upright portion, the calcareous
material is arranged in beautifully regular rings, giving
that part of the zoophyte a peculiarly elegant appear-
ance under the microscope. This calcareous ingredient
is sufficiently abundant to render the contents of the
radical tubes and polype-cells indistinct ; and to obtain
a satisfactory view of these parts it is necessary to remove
the earthy matter by some weak acid. When this is
done, it will be found that the contents of the radical
portion are coarsely granular, and the wall rather thicker
than those of the proper polype-cell. The latter contains
an ascidian polype, which has about twelve tentacles, and
no gizzard." The polype, as far as Mr. Busk has observed,
is always lodged in the upright portion of the cell ; but
the long retractor muscular fibres arise near the com-
mencement of the horizontal portion of the cell, from its
upper wall, and nearly at one point.

The expanded portion of the cell, besides the special
muscles of the aperture, contains other muscular fibres, in
all respects resembling those described by Dr. Farre, aa
conducing to the extrusion of the polype in JBowerbankia,

BSCHARUXffi.

521

and which are also very distinct in the Notamia ; but
which, in the present instance, would seem to have for
their chief function the drawing-up or corrugation of the
membraneous portion of the polype-cell. These muscular
fibres have a distinct central nucleus or thicker portion, as
is the case in the analogous muscles in some other polypes.

ESCHARID.E. — This interesting family justly deserves the
great attention many naturalists have bestowed upon it.
Linnaeus named it Flustra, from the
Saxon word flustran, to weave ; it is
commonly called a Seamat, and re-
sembles fine network spread over
stones, rocks, shells, and marine plants.
This network, when submitted to the
powers of the microscope, is found to
be a cluster of cells, in each of which
dwells an animal, that protrudes its
feelers when searching for food, and
sinks into its little home when tired,
or alarmed by approaching danger.

Dr. Grant estimates that a single
Flustra has as many as four hundred
millions of cilia on these restless ten-
tacles. The tentacula vary from ten to
twelve ; the general organization con-
sists of a gullet, a gizzard, a stomach,
and intestines, the body itself being quite transparent.
When collected together in clusters they take the form of
a delicate minute tree, having cells in all parts, and of
various colours. Larnouroux says : " When the animal
has acquired its full growth, it protrudes from the opening
of its cell a small globular body, which it fixes near the
aperture, and, as it increases in size, soon assumes the form
of a new cell; it is yet closed, but through the trans-
parent membrane that covers its surface the motions of
a polype may be detected ; the habitation at length
bursts, and the tentacles protrude ; eddies are pro-
duced in the water, and conduct to the polype the
atoms necessary for its subsistence. The aperture of
the cells is formed by a semicircular lid, convex ex-
ternally and concave internally, which folds down when

the animal is
represented out of its
polypidom.

522 THE MICROSCOPE

the polype is about to advance from the cell. The opening
of this lid in the F. truncata, where it is very long, appears
through the microscope like the opening of a snake's jaws;
and the organs by which this motion is effected are not
perceptible. The lids of the cells open and shut in the
Flustrce without the slightest perceptible synchronous
motion of tjie polypes."

In the formation of their stony skeletons, the animals
appear to take a most insignificant part ; they are princi-
pally secreted by the integuments or membranes with which
they are invested, in like manner as the bones and nails in
man are secreted by tissues designed for that purpose, and
acting slowly and imperceptibly. From an analysis of the
stony corals, it appears that their composition is very
analogous to that of shells. The porcellaneous shells, as
Jie cowry, are composed of animal gluten and carbonate
of lime, and resemble, in their mode of formation, the
enamel of the teeth; whereas the pearly shells, as the
oyster, are formed of carbonate of lime and a gelatinous or
cartilaginous substance, the earthy matter being secreted
and deposited in the interstices of a cellular tissue, as in
bones. In like manner, some corals yield gelatine upon
the removal of the lime, while others afford a substance in
every respect resembling the membranous structure ob-
tained by an analysis of the nacreous (pearly) shells.
A recent elaborate analysis of between thirty and forty
species of corals, by an eminent American chemist (Mr. B.
Silliman), has shown, contrary to expectation, that they
contain a much larger proportion of fluorine than of
phosphoric acid.

Flustra foliacea, the broad-leaved Horn-wrack of Ellis,
is about four inches high, and of a brown colour. The cells
are small, in alternating rows ; and sometimes covered by
a lid opening downwards. Hook says : " For curiosity and
beauty, I have not, among all the plants or vegetables
I have yet observed, seen any one comparable to this
sea-weed." Flustra truncata is abundant in deep water,
and grows to a height of about four inches ; it is of a
delicate yellow colour, and bushy. This is the narrow-
leaved Horn-wrack of Ellis ; for it must not be forgotten
that the older writers regarded the whole genera as plants.

ESCHARIDJE. 523

Flustra chartacea. — Ellis states : " The cells of this sea
mat are of an oblong square figure, swelling out a little in
the middle of each side. The openings of the cells are
defended by a helmet-like figure ; from hence the polype-
shaped suckers extend themselves. This sea-mat is of a
slender and delicate texture, like a semi-transparent paper,
of a very light straw-colour. It was first found on the
coast of Sussex, adhering to a shell. I have since met, on
the same coast, about Hastings, in the year 1765, with
several specimens whose tops are digitated, and others that
were very irregularly divided."

The Flustra carbasea grow out in a leaf-like manner,
gradually widening to the end : they are found on shells of
a yellowish-brown colour ; on one of the sides the cells are
both large and smooth. The animals have about twenty-
two arms or feelers, which, says Dr. Grant, after a most
careful examination of these polypes, " are nearly a third
of the length of the body; and there appear to be about
fifty cilia on each side of a tentacle, making 2200 cilia
on each polype. In this species there are more than
eighteen cells in a square line, or 1800 in a square inch of
surface ; and the branches of an ordinary specimen pre-
sent about ten square inches of surface ; so that a common
specimen of the F. carbasea presents more than 18,000
polypes, 396,000 tentacles, and 39,600,000 cilia.

" They are very irritable, and frequently observed to
contract the circular margin of their broad extremity,
and to stop suddenly in their course when swimming ;
they swim with a gentle gliding motion, often appear
stationary, revolving rapidly round their long axis, with
their broad end uppermost, and they bound straight for-
ward, or in circles, without any other apparent object than
to keep themselves afloat till they find themselves in a
favourable situation for fixing and assuming the perfect
state. The transformation of the ova, from that moving,
irritable, free condition of animalcules, to that of the fixed
and almost inert zoophytes, exhibits a new metamorphosis
in the animal kingdom not less remarkable than that of
many reptiles from their first aquatic condition, or that of
insects from their larva state."

Flustra amcularis. — This is another of the little beauties

524 THE MICROSCOPE

of the deep, found usually on old shells, an inch in height,
spreading itself fan-like, and of an ashy colour, deeply
divided in a dichotomous manner into narrow, thin, plane
segments, truncate at the end, formed of four or five series
of oblong cells, capped with a hollow, globose, pearly, oper-
culum seated between the spines, of which there is one on
either side of the circular aperture. The opercula are so
numerous, that they give to the upper surface the appear-
ance of being thickly strewn with orient pearls ; the under-
surface is even and longitudinally striated, the number of
striae corresponding to the number of rows in which the
cells are disposed. Dr. Johnston describes, amongst many
other British species, F. membranacea, " a gauze-like incrus-
tation on the frond of the sea-weed, spreading irregularly
to the extent of several square inches."

Dr. Perceval Wright discovered on the western coast of
Ireland a new genus of Alcyonidw, which he named after
the well-known naturalist Mr. Harte, Hartea elegans, Plate
IV. No. 86. This polype is solitary, the body cylindrical,
and fixed by its base to the rock; it has eight ciliated
tentacles, which are knobbed at their base and most freely
displayed. It is a very beautif ul polyzoon of a clear white
colour, and when fully expanded stands three-quarters of
an inch high.1

The fresh-water Polyzoa are peculiarly interesting ob-
jects for microscopic observation, from the very beautiful
manner in which they display their ciliated tentacula, set
upon a crescentic, horseshoe-shaped "lophopore." The
arrangement of the latter appendage has been the cause of
separating the fresh-water Polyzoa, from their marine
allies, into a sub-class ; the former being named Hippocrepa
(horseshoe-like^, and the latter Infundibulata (funnel-
like).2 The most striking form among the Hippocrepa is
the Cristatella Mucedo —a wandering Polyzoon, capable of
moving freely through the water. It may be met with
during a great part of the summer in our ponds and streams,
amidst the sterns and leaves of aquatic plants (Plate IV.

(1) On a new genus of Alcyonidce. By Dr. E. Perceval Wright. Micros.
Journ. Science, vol. v. p. 213. 1865.

(2) The reader is referred to a valuable treatise on the structure and classifi-
cation of this group by Professor Allmtin, Monograph of the British Fresh-
Water Polyzoa, published by the Ray Society, 1857.

POLYZOA. 525

!No. 97). It is always regarded as one of the most exqui-
site specimens of the class Polyzoa ; should there be
any difficulty in finding the animal itself, the eggs, met
with late in the summer or autumn, should be care-
fully stored in an aquarium without fish. The eggs or
" statoblasts," No. 95, are small, dark, circular bodies,
about the size of a pin's head, surrounded by a series of
minute hooked spines ; the animal conceals them among
tangled masses of decayed grasses and confervas. Polyzoa
are known to live upon Desmids and Algae ; and to keep
them alive the tank must be freely supplied with such
kinds of food. Cristatella Mucedo is rarely found in the
same spot a second day, it wanders about apparently in
search of food ; it is, therefore, provided with a contractile
disc or foot, and by means of this it creeps about not far
from the surface of the water, for it delights to display its
beautiful crests of tantacula (about eight in number), in the
"broad light of day or sunlight ; in this respect Cristatella also
differs from most Polyzoa. Below the external margin is
a series of tubular chambers visible through the translucent
membrane ; and the csensecium or common dermal system
is of a light yellow colour, often concealing several dark,
brownish-looking eggs.

Lophopus crystallinus is a finer Polyzoon than the former,
and displays beautiful plumes of transparent tentacles
arranged in a double horseshoe-shaped series. They at
times abound in slow running streams, adhering to the
stems of water-plants. When first removed from the water
they resemble masses of the ova of one of the water snails,
and have often been mistaken for them. On putting one
of those jelly-like masses into a glass trough with some of
the clear water from the stream, delicate tubes will be
cautiously protruded, and then the beautiful fringes of cilia
are soon brought into play. The organization of L. Crys-
tallinus is simple, although it is provided with organs
of digestion, circulation, respiration, and generation. A
nervous1 and muscular system are also tolerably well

(1) It has been demonstrated by Fritz MiiUer that the Polyzoa possess a ner-
vous system : — "The nervous system of each branch consisting of— 1st, a consi-
derable sized ganglion sitnated at its origin ; 2d, of a nervous trunk running the
entire length of the branch, at the upper part of which it subdivides into
branches, going to the ganglia of the internodes arising at this part ; and 3d, of

526 THE MICROSCOPE.

developed. It increases both, by budding and by ova,
both of which conditions are shown in Plate IV. No. 98.
The ova are generally seen enclosed in the transparent
case of the parent. In Lophopus and most other fresh-
water genera, such as Cristatella, Flumatella, and A Icyo-
nella, the neural margin of the lophopore is extended into
two triangular arms, giving it the appearance of a deep
crescent.

Alcyonella is a genus of fresh-water polyzoa, found
usually about the autumnal period of the year in the
several Docks at the East end of London, adhering to
floating pieces of timber. It assumes the form of an
irregular sponge-like mass, with an aggregation of mem-
branaceous tube-like openings covering the surface.
From these openings, the polypes are seen to project, the
mouths of which are encircled with a single series of
filiform ciliated tentacles, which keep the surrounding
water in active motion. The polypidom seen in water
has the appearance of a blackish-green sponge.

Trembley gave an interesting account of the family of
Alcyonella ; and Mr. J. Newton Tomkins favours us with
the following observations on the development of the
Alcyonella stagnorum, (fluviatella) : —

"The ova now under examination (J-inch obj. A. eye-
piece— 100 lin. diam., Wollaston's condenser), are the
products of some healthy specimens of Alcyonella stag-
norum given me by Mr. Lloyd, and sketched in full
activity in September 1856. Soon after this period
their movements decreased in energy, numerous ova were
detached, which floated to the surface of the water of
the jar in which they were confined, and in the course
of a very few weeks no trace remained of the parent
animals, except a spongy mass of an almost gelatinous
character, which still exists, though devoid of definite
form, and appears composed of a mass of broken and
disorganized cells.

" In November, with a view of preserving the water in
a normal condition, I introduced a sprig of Anacharis

a rich nervous plexus resting on the trunk, and connecting the ganglia just
mentioned, as well as the basal ganglia of the individual polypides." For
further account, see paper in the Micros. Journ. vol. i. New Series, p. 330.

POLYZOA. 527

Alsinastrum, and finding it grew freely, but soon covered
with a filamentous confervoid growth, threw in two small
water-snails, which are there still. About January last,
the ova, which till then had floated on the surface of the
water, began to sink and attach themselves to the leaves of
the Anacharis and elsewhere. Latterly, they have all
subsided to the bottom of the jar, where they lie in com-
pany with a quantity of decayed vegetable matter, spawn
of the Limnceus, &c. They are of a light-brown colour,
ovoid in shape, longest diameter -0089, shortest diameter
•0172. The outer rim seems built up of cells of oblong
shape, but necessarily ill-defined, owing to their being ob-
served by light transmitted through two surfaces; the
inner or central portion also cellular, but from the con-
vexity of the object, more easy to determine as to its true
nature, formed of larger hexagonal-shaped cells. Seen by
higher power (J-in. obj. A. eye-piece — 220 lin. diam.),
these central cells, besides being unmistakably hexagonal
in form, have each a distinct dark nucleus in the centre :
this, however, may be an optical fallacy, due to their
peculiar position on a curved surface. No movement yet
visible, April 25, 1857."

Plumatella fiepens, Plate JY. No. 99, so named from its
feather-like crown of tentacles, is a well-known fresh- water
Polyzoon, found in ponds and rivulets attached to aquatic
plants, generally choosing the under-surface for the pur-
pose of avoiding the strong light. It is a very elegant
variety, rather timid, withdrawing on the least disturbance
of the water, and not again venturing to display its beau-
tiful plume until all is once more perfectly quiet. Pro-
fessor Allman says of it : — " Except in the condition of
the dermal system the structure of Plumatella differs in
no essential point from that of A Icyonella. This system,
however, in the coalescence of the tubes into a common
mass in Alcyonella, while they remain totally distinct in
Plumatella, presents us with a difference of sufficient im-
portance to justify the placing the two forms in separate
generic groups. The number of known species are twelve,
of which nine are Britiph. The csensecium consists of a
linear-branched series of tabula, cells of membrano-
corneous consistence, which is terminated by the orifice

528

THE MICROSCOPE

destined for the egress of the polypides. The tentacula
are about sixty in number, long, and ciliated on either
side. The statoblasts are ovoid, of a dark- brown colour
without marginal spines, and contained within the poly-

Fig. 247.

1, Portion of a transverse section of the spine of an Echinus. 2, Crystals of
carbonate of Lime, from the surface of shell of Oyster. 3, Horizontal section
of shell of Haliotis splendens, with stellate pigment in the interior. 4,
Portion of shell of a Crab, showing granules beneath the articular layer, 5,
Another portion of the same shell, showing its hexagonal structure.

pidom, through the transparent walls of which they can be
readily seen. It occurs in greatest perfection during the

SHELL OF MOLLUSC A 529

summer and towards autumn, often obtaining to a consi-
derable size." Most of the species may be found in the
ponds around London, and few objects are capable of
affording greater pleasure than these Polyzoa when examined
in a living state under a moderate power, and with a dark-
ground illuminator. The withdrawal of the Polyzoa
from the Eadiate sub-kingdom, and their location among
Mollusca, was a step in the right direction • while the
important division of the molluscan sub -kingdom by
Milne-Edwards into primary sections of the Mollusca and
Molluscoida, the latter including the Tunicata and the
Polyzoa, is all that can be desired in the systematic
location of the Polyzoa.

Shell of Mollusca. — The simplest form of shell occurs in
the rudimentary oval plate of the common Slug, Limax
rufus ; it is imbedded in the shield situated at the back
and near the head of the animal.

When a molluscous or conchiferous shell is composed of
a single piece, it is then termed univalve ; when of two
pieces, bivalve. The bivalve Mollusca exhibit no trace of
any distinct head ; whilst in the univalve this part of the
body is well-marked, and usually furnished with special
organs of sense (tentacles, eyes, nerves, &c.).

The older naturalists recognised a group of multi-
valve shells, or shells composed of several valves, the
majority of which belonged to the Cirrhopod order of
Crustacea, and were regarded as Mollusca by earlier ob-
servers. The Plwlades, however, which in other respects
are true bivalve Mollusca, are furnished with a pair of
accessory plates in the neighbourhood of the hinge ;
whilst the Chitons, a small but sin-
gular group of Molluscs nearly
allied to the univalve limpets, have
an oval shell composed of eight
movable plates, which gives them a
great resemblance to enormous
woodlice ; and they have been re-
garded as forming a sort of transi-
tion towards the articulated divi- Fis- 248.— Apiysia, sea-
sion. Those Mollusca not furnished

with a shell, or having only a small calcareous plate en-
M M

530 THE MICROSCOPE.

closed within the mantle, are called Nudibranchiata ; an
example of this family is seen in fig. 248, Aplysia ; but it is
remarkable that most of them are provided with a small
shell when they lirst quit the egg. In the shell-bearing
or Testaceous Mollusca, this embryonic shell, which often
differs greatly in shape and texture from the shell of the
mature animal, is, however, a commencement of the latter ;
additions being constantly made to the free edge by the
secretion of calcareous matter at the margin of the mantle.
The delicate membranaceous part of the mantle, which
lines the internal portion of the shell inhabited by the
animal, has also the power of secreting a thin layer of
shelly matter upon its inner surface. This is frequently of
a pearly lustre ; and in many bivalves a new layer of this
substance is deposited at the time when the size of the
shell is increased by additions to its margins, — for it must
be observed that the formation of new shell is not con-
stantly going on, but appears to be subject to periodical
interruptions, as indicated by lines on the surface of the
shell ; which are called lines of growth. In many cases,
the margin of the mantle, instead of being even, presents
lobes of tubercles ; these produce corresponding irregula-
rities,— ribs, tubercles, or spines, — on the surface of the
shell.

Dr. Bowerbank says, " Shell is developed from cells
that in process of growth have become hardened by the
deposition of calcareous matter in the interior." This
earthy matter consists principally of carbonate of lime,
deposited in a crystalline state ; and in certain shell, as in
that of the common Oyster (fig. 247, !N"o. 2), from the
animal-cell not having sufficiently controlled the mode of
deposition of the earth particles, they have assumed the
form of perfect rhomboidal crystals.

The shell of the genus Pinna, " Wing-shells," is com-
posed of a series of hexagonal cells filled with transparent
calcareous matter, seen in fig. 240, No. 2, the outer layer
of which can be split up into prisms, like so many basaltic
columns ; as at No. 1.

Organs of sense are possessed by some of this class in an
advanced state of development. In the Scallop (Peeteri),
tor example, eyes occur in great numbers, placed among

MOLLUSCA. 531

the tentacles on the borders of the mantle. In other
genera, the eyes are differently placed, in Pinna on the
fore part of the mantle, and around the siphon-orifices in
Pholas and Solen. In the Cockle (Cardium) the short
siphons are surrounded with an extraordinary number of
tentacles, capable of protrusion, each of which bears a
pretty little eye; these are beautiful objects under the
microscope. Cockles are able to perform vigorous leaps by
means of a well developed foot, which they possess ; in
other species the foot is grooved j and being associated
with a gland which has the power of secreting a gluti-
nous substance, the latter is drawn out into slender
threads, with a sucker-like or flattened extremity, by
which they attach themselves to rocks. The grooved foot
is then withdrawn, and the thread hardens into an elastic
sort of cord, called a byssus. It is by an aggregation of
these threads that the common Mussel moors itself
securely. The hinge of the shell is formed of variously
shaped dentations ; those under the beak are called car-
dinal teeth ; those on either side are lateral teeth.

The Pholadidce are a series of animals remarkable for
their destructive boring propensities. The Teredo, ship-
worm, is well known for the damage it does to the
bottoms of ships, especially in the tropical seas. Others
of this family give a preference to sandstone, and even the
most compact marble has been found bored through by
them.

Mr. J. Robertson says : — " Having, while residing here
(Brighton), opportunities of studying the Pholas dactylus,
I have endeavoured during the last six months to discover
how this mollusc makes its hole or crypt in the chalk, — by
a chemical solvent 1 by absorption ? by ciliary currents 1
or by rotatory motions ? My observations, dissections, and
experiments set at rest controversy in my mind. Between
twenty and thirty of these creatures have been at work in
lumps of chalk in sea water in a finger glass and a pan, at
my window, for the last three months. The Pholas dac-
tylus makes its hole by grating the chalk with its rasp-like
valves, licking it up when pulverized with its foot, forcing
it up through its principal or branchial siphon, and
squirting it out in oblong nodules. The crypt protects the
M M 2

532 THE MICROSCOPE.

Pholas from Confervce, which, when they get at it, grow
not merely outside, but even within the lips of the
valves, preventing the action of the siphons. In the foot
there is a gelatinous spring, or style, which when taken
out has great elasticity, and which seems the mainspring
of the motion of the Pholas dactylus"

Tunicate, — The most remarkable group of animals be-
longing to this order are the Ascidians. The cell of the
Polyzoon is represented in the Asddian by a, test or tunic —
from which they derive their name — of a membraneous or
cartilaginous consistence, and often including calcareous
spicules, — having two orifices, within which is another
envelope, distinguished as the mantle. Few microscopic
spectacles are more interesting than the sight of the circu-
lation along this network of muslin- like fabric, and that
of the ciliary movement by which the circulating fluid is
kept moving. In the transparent species, such as Clave-
lina and Perophora, this movement is seen to great advan-
tage. The animals are found very commonly adhering to
the broad fronds of fuci, or on pieces of shell, near low
water-mark. They thrive in tanks, and multiply both b)
fissuration and budding. Two species are figured in Plate
IX. i and Jc, Botryllus violaceus belonging to the family
Didemnians, the zooids of which are often arranged in the
beautiful stellate clusters seen in the plate.1

Pteropoda. — The most prominent character of this class
is the possession of two broad muscular fins, one on either
side of the neck, somewhat resembling the expanded
wings of a butterfly, whence Cuvier gave them the name
of Pteropoda, " wing-footed." In Clio, the anatomy of
which has been carefully investigated, there is a very
curious apparatus developed for seizing its prey. On each
side of the mouth are three fleshy warts, covered with
minute red specks. Under the microscope, these specks,
numbering about three thousand on each tentacle, are seen
to be transparent cylinders, each containing in its cavity
twenty stalked discs, and forming so many adhesive
suckers.

(1) For information respecting the Compound Ascidians, see the admirable
monograph of Milne-Edwards, Art. Tunicata in the Cyclop. Anatomy and Phy-
siology, Huxley in Phil. Trans, for 1851, or Journ. Micros. Soc. vol. iv. 1856 ;
also Prof. Allman, same journal, vol. vii. 1859.

MOLLUSCA. 533

The Oyster is the type of the tribe Ostracea, all of
which are Acephalus, that is, animals without a distinct
head. The gills, or breathing apparatus, form what is
commonly called the beard of the oyster. The creature
is attached by strong muscles to its shell. The mouth of
the oyster is a mere opening in the body, without jaws or
teeth ; its food consists of nourishing substances suspended
in the water, and which are drawn into the shell when it
is open by means of cilia. Oysters attach one of their
valves to rocky ground, or some fixed substance, by a mu-
cilaginous liquid, which soon becomes as hard as the shell
itself. They spawn some time in May ; and their growth
is so rapid, that in three days after the deposition of the
spawn, the shell of the young oyster is nearly a quarter of
an inch broad ; in three months it is larger than a shil-
ling. The spawn is a very interesting object for micro-
scopic examination, especially with polarised light. The
young fry is represented in fig. 254 ; some with cilia pro-
truded.

In the stomach of the Oyster, and in the alimentary
canal, myriads of living Paramcecium and other Infusoria
are found swimming in great activity ; swarms of a con-
glomerate and ciliated living organism, somewhat resem-
bling the Volvox globator, and so extremely delicate in
their structure that they require a good objective to define
them.

Pearls are usually met with in the Meleagrina Marga-
ritifera, " Pearl Oyster," which, however, does not belong
to the family Ostracea. They are likewise found in the
Mussel known as Mya Margaritifera, and an inferior kind
in many Mussels of the rivers of Great Britain ; and, at
one time, the pearl-fishery of Ireland was justly cele-
brated. Naturalists somewhat differ in their opinions as
to the mode in which pearls are formed. Some think that
they are produced by particles of sand getting into the
stomach ; the animal, to prevent the roughness of these
particles from injuring its delicate structure, covers them
over with a secretion from a gland, and, by continual ad-
ditions, they gradually increase in size. Mussels, in which
artificial pearls were said to have been formed by tht
Chinese, have frequently found their way to this country.

534

THE MICROSCOPE.

It is now, however, very generally admitted to be a dis-
eased condition. Pearls are matured on a nucleus, con-
sisting of the same matter as that from which the new
layers of shell proceed at the edge of the Mussel or
Oyster. The finest kinds are formed in the body of the
animal, or originate in the pearly-looking part of the shell.
It is from the size, roundness, and brilliancy of pearls
that their value is estimated.

The microscope discloses a difference in the structure of
pearls : those having a prismatic cellular structure have a
brown horny nucleus, surrounded by small iinperfectly-

Fig. 249.

1, A transverse section of a Pearl from Oyster, showing its prismatic structure.
2, A transverse section of another Pearl, showing its central cellular struc-
ture, with outside rings of true pearly matter. (Magnified 50 diameters.)

formed prismatic cells ; there is also a ring of horny
matter, followed by other prisms, and so on, as represented

MOLLUSCA.

535

in fig. 249 ; and all transverse sections of pearls from
Oysters show the same successive rings of growth or
deposit.

In a segment of a transverse section of a small purple
pearl from a species of Mytilus (fig. 250), all trace of
prismatic structure has disappeared, and only a series of
fine curved or radiating lines is seen. This pearl consists
of a beautiful purple-coloured series of concentric laminae ;
many of which have a series of concentric zones, and are
of a -yellow tint. The most beautiful sections for micro-
scopic examination are obtained from Scotch pearls.

Brachiopoda, " Lamp-shells/ ' or, as the name literally

Fie, 250.

1, A transverse section of a small Pearl- from a species of Mytilus. 2, Hori-
zontal section of same Pearl magnified 250 diameters, to show prismatic
structure and transverse striae.

signifies, arm-footed, is intended to express a most re-
markable characteristic of these animals, the presence of a
pair of arms, often of great length, rolled up in a spiral
form, and believed by Cuvier to replace the foot in other
bivalves. Professor Owen has shown that these organs
are tubes closed at each end, and contain a fluid, which by

536 THE MICROSCOPE.

the contraction of the circular muscular fibres of which
the walls of the tube are composed, is propelled from the
base to the extremity, thereby unrolling, as he believes,
the spiral coils. One side of each arm is fringed with a
vast number of long filaments : these are ciliated. The
shell is opened by a peculiar process, which has given to
the Terebratula the name of Coach-spring Shell. In the
shell there are minute openings surrounded by a series of
radiating lines : these at first appear like dark oval spots ;
but in a vertical section they are seen to be perforations or
tubes running obliquely from the inner to the outer surface
of the shell, and having a series of radiating lines on the
edge, as in fig. 240, No. 3. The outer layer has been re-
moved, to show a radiating structure around the perfora-
tions. Dr. Carpenter fully describes Terebratula in the
Philosophical Magazine, 1854.

Not less curious than beautiful is the internal layer of
many kinds of bivalves, which present an iridescent
lustre, the whole surface being varied with a. series of
grooved lines running nearly parallel to each other. The
well-known gorgeously coloured univalve, the Ear-shell,
Baliotus splcndens, has been ascertained to consist of
numerous plates, resembling tortoise-shell, forming a series
of hexagonal cells, in the centre of which the stellate
pigment is deposited (fig. 246, No. 3), alternating with
thin layers of pearl, or nacre ; and this exhibits, when
highly magnified, a series of irregular undulating folds, re-
presented in the upper portion of the section. The iride-
scent lines are often extremely pleasing ; and if a piece be
submitted to the action of diluted hydrochloric acid, until
the calcareous portion of the nacreous layers are dissolved
out, the plates of animal matter fall apart, each one carry-
ing with it the membraneous residuum of the layer of
nacre that belonged to its inner surface. But the nacre
and membrane covering some of these horny plates remain
undisturbed ; and their folded or plaited surfaces, although
divested of calcareous matter, exhibit iridescent hues of
the most gorgeous description. If the membrane be
spread out with a needle, and the plates unfolded to a
considerable extent, the iridescence is no longer seen; a
fact which clearly demonstrates that the beautiful colours

TONGUES, ETC., OF GASTEROPODS.

Tuffen West, del.

W. F. Maples, ad. nat. del.

PLATE V.

Edmund Kvans.

GASTEROPODA. 537

presented "by the nacreous portions of shells, commonly
called mother-of-pearl, are produced solely by the disposi-
tion of single membraneous layers in folds or plaits, lying
more or less obliquely to the general surface.

In the Chitonidce, Coat of mail Shells, the shell consists
of eight transverse plates, imbedded in the mantle ; in the
Limpets, the ordinary form is that of a cone. The
arrangement of the teeth is somewhat remarkable.

The majority of Gasteropoda are furnished with a
shell, denominated spirivahe. The cause of this spiral
arrangement is said to be owing to the shape of the body
of the animal inhabiting the shell, which, as it grows,
enlarges its shell principally in one direction ; thus, of
course, making it form a spire, modified in shape according
to the degree in which each successive turn surpasses in
bulk that which preceded it. It would rather appear that
this is principally owing to the ciliary motion imparted to
th'e early stage of the embryo ; the first deposit of calca-
reous matter forming the axis, the tube continues to rotate
upon its axial pillar or columella, as it is called ; and by
reason of some other peculiar vital tendency, the shell is
gradually deposited in a series of cells ; thus enlarging its
conical form, and winding obliquely from right to left.
Every turn around the axis is termed a whorl; and when
the columella is hollow, it is said to be umbilicated. In
the spirivalve-shelled Gasteropoda, we find a difference in
structure between that part of the mantle which enve-
lopes the viscera, and which is always concealed within
the cavity of the shell, and the portion placed around its
aperture.

The mouths of most Gasteropoda consist of a strong
muscular cavity, and a crescentic-shaped tooth-bearing
membrane, armed with sharp points, and separated by
semi-circular cutting spaces, admirably adapted for the
division of the food upon which they feed. Most of them
are beautiful objects for the microscope.

Professor Huxley very properly objects to the use of the
commonly accepted term tongue for the tooth-bearing
membrane of the mollusca, and more appropriately desig-
nates it " the odontophore."
: " The odontophore consists essentially of a cartilaginous

538

THE MICROSCOPE.

strap, which bears a long series of transversely-disposed
teeth. The ends of the strap are connected with muscles
attached to the upper and lower surface of the hinder ex-
tremities of the cartilaginous cushions ; and these muscles,
by their alternate contractions, cause the toothed strap to
work backwards and forwards over the end of the pulley
former! by its anterior end. The strap consequently acts

Fig. 251.

1, Palate of Buccinum undaium, common Whelk, seen under polarised light.
2, Palate of Doris tuberculata, Sea-slug.

after the fashion of a chain-saw (rather of a rasp,) upon
any substance to which it is applied, and the resulting
wear and tear of its anterior teeth are made good by the
incessant development of new teeth in the secreting sac in
which the hinder end of the strap is lodged. Besides the
chain-saw-like motion of the strap, the odontophore may
be capable of a licking or scraping action as a whole."1

In the constant growth of the band we observe the
development of new teeth. In some the teeth on the
extreme part of the band differ much, both in size and
form, from those in the median line : so much, that if at
any time one portion be separated from the other and
then examined, it might be supposed to belong to another
species.

Since the investigations of Professor Loven, of Stock-
holm, into the lingual dentition of the glossophorous Mol-
lusca, various observers have studied the subject with
great advantage to our knowledge of the affinities of those
animals. Although the patterns or types of the lingual
membranes are, on the whole, remarkably constant, yet

(1) Elements of Comparative Anatomy, p. 36.

3ASTEROPODA. 539

their systematic value is not uniform ; and therefore tha
attempts to remodel the arrangement of the Gasteropoda
by their peculiarities of dentition have not become so com-
plete a success as was at first expected. Some, how-
ever, hold a different opinion ; and Dr. J. E. Gray writes :
— " One result of the study of these papers (Loven's, On
the Tongues of Mollusca) and the examination of the
tongues of several molluscs has been to establish more
firmly the theory which I have long entertained, that no
species of gasteropodus molluscous animal can be properly
placed in the system unless we are enabled to examine the
animal, the shell, the operculum, and the structure of its
tongue ; and as none of these parts but the shell can be
examined in the fossil species, their position in the various
genera must be always attended with more or less uncer-
tainty."1

Dr. Troschel has laboured much in this field of investi-
gation, and in his valuable work on the subject attempts a
classification of the principal types by their lingual den-
tition. The union under one formula of so many creatures
widely differing in anatomy, habits, and shell structure,
clearly indicates that, if the lingual ribbon contains
generic characters, they have not yet been ascertained. At
the same time, it does present differences which may offer
collateral evidence in cases otherwise difficult of discrimi-
nation. It does not help us to separate carnivorous from
phytophagus animals ; but it seems possible to make use
of it as a mark between species ; for, in all, there is a dis-
tinct difference between the tongues even of the most
closely allied. Thus, amongst other changes, it has been
found necessary to remove the Proserpinadce from the
neighbourhood of the Gydophoridce, to which they were
formerly supposed to be nearly related, and to place them
in a more natural position near the Neritidce. That these
investigations are of value is also shown by the light
which has been shed on the true position of Aporrhais,
supposed by so great a naturalist as Forbes to be akin to
the Gerithiidce, but which is shown by its dentition to
belong to the Strombidce?

(1) Annals of Nat. Hist. Ser. ii. vol. x. p. 413.

(2) See a paper on the subject in the Trans. Linn. Soc. 1S67.

540 THE MICROSCOPE.

The relations of the freshwater operculata are as varied
as those of the land. Ampullaria seems to find its nearest
marine relative in Natica, an opinion which seems con-
firmed by the form of the shell. A West Indian species
found on the trees of the forests of those islands, and placed
by Lam arch in the ffelicina, would rather appear to belong
to Neritina. The several peculiarities of their teeth, espe-
cially that of H. nemoralis, with its numerous uncini, its
sub-opaque trapezoid laterals, which seem heretofore to
have been overlooked, confirm the belief in its close rela-
tionship to Neritina. The horny mandibles of the Mol-
lusca may be deserving of some attention with a view to
the elucidation of their affinities. In Cydotus translucidus
the mandible is divided into two portions by a median
articulation, and it is covered with fine denticulations
in regular rows, somewhat like that of Velutina, Plate Y.
No. 109. In most of the inoperculata, the mandible is
horse-shoe-shaped, and striate or corrugate. In Ampul-
laria, the same organ is beak-shaped, like the upper man-
dible of Octopus or Loligo.

11 The lingual band, we should premise, has been, for con-
venience of description, divided into longitudinal areas,
which are crossed by many rows of teeth. There are
five, distinguishable by the different characters of the teeth
they bear ; but the characteristics are not always present.
The teeth are consequently named median, lateral, and
uncini, although the latter are not necessarily more hooked
than the others. The areas bearing the uncini have been
called pleurae. Since each row is a repetition of all the
rest, the system of teeth admits of easy representation by
a numerical formula, in which, when the uncini are very
numerous, they are indicated by the sign oo (infinity), and
the others by the proper figure. Thus, oo • 5 * 1 • 5 • oo ,
which represents the system in the genus Trochus, signifies
that each row consists of one median, flanked on both
sides by five lateral teeth, and these again by a large
number of uncini. When only three areas are found, the
outer ones are to be considered as the pleura3,, inasmuch as
there is frequently a manifest division in the membrane
between them and the lateral areas."

Most of the Cephalopod molluscs are provided with

TEETH OF GASTEROPODA. 541

strong, well developed teeth ; they are all animal feeders.
Loven describes those of the cuttle-fish (Sepia officinalis,
Plate Y. No. Ill), as like Pteropoda, formula of teeth,
3*1 '3. The Sepia is also furnished with a retractile
proboscis, and a prehensile spiny collar, apparently for the
purpose of holding its prey while the teeth are employed
in drilling or abrading it. In the Squid (Loligo, No. 113),
the medians, broad at the base, approach the tricuspid form
with a prolonged acute central cusp ; while the uncini are
much prolonged and slightly curved. The lingual band
increases in breadth towards the hinder part, in some in-
stances to twice the diameter of the anterior. The band,
when mounted dry, forms a fine object for the black-
ground illuminator, or side reflector. The lingual band of
Octopus tuberculatus differs slightly with Sepia.

The Nudibranchiata have become more attractive since
the publication of the valuable and beautifully-illustrated
monograph of Messrs. Alder and Hancock. The nudi-
branchs are without a shelly covering, slug-like in their
appearance, and most voracious feeders, greedily devouring
zoophytes, sponges, &c. (Plate IX. 6.) They possess the
remarkable property of restoring lost parts ; their powers
of endurance are great, so that they may be kept alive for
some time in a small glass jar of sea-water. While keep-
ing a specimen of the Piplida in confinement, the Rev.
Mr. Lowe noticed on several occasions a display of a bril-
liant phosphorescence. Many of the genus Dorididce and
Eolidida are infested with parasitic Entromostraca, which
either live freely on the surface, under the skin, or adhere
to the branchiae of the animals. Oncidoris bilamellata (the
Sea-lemon) belongs to the Dorididse ; its mouth is provided
with a narrow band of strong hooked teeth (Plate V. No.
120), which in some species are serrated ; all are provided
with mandibles, consisting of two homy plates uniting
near the fore part. The median row of teeth are small and
inconspicuous; the band is represented by the formula
2 • 1 • 2. A portion of the mandible of Aplysia hybrida
(the Sea-hare) is shown in Plate V. No. 112.

Patella radiata (the Rock-limpet). — The band of this
mollusc, No. 116, may be readily distinguished from the
common limpet of our coasts ; the remarkably long ribbon-

542 THE MICROSCOPE.

like membrane, which lies folded up in the abdominal
cavity, is furnished with numerous rows of strong, nearly
opaque, dark brown tricuspid teeth. The teeth of Acmcect
(No. 117) are differently arranged ; their formula is 3 • 1 • 3.
Chitonidce are said to be near relatives of the Patellidce ; the
mouths of all are furnished with mandibles.

Testacella maugei, belonging to the Pulmonifera, is slug-
like in its appearance, and, curiously enough, is subter-
ranean in its habits, chiefly feeding on earth-worms. During
winter and in dry weather it forms a kind of cocoon,
and thus completely encloses itself in an opaque white
mantle, which effectually protects it from atmospheric
influences. Its lingual membrane is large, and covered
with about fifty rows of divergent teeth, which gradually
diminish in size towards the median row ; each tooth is
barbed and pointed, broader towards the base, and fur-
nished with an articulating nipple set in the basement
membrane. A few rows are represented slightly mag-
nified, Plate V. No. 121. Their formula is 0 0 • 1 '00.

Cymba olla (the Boat-shell) belongs to the species
Yelutinidae, formula, 0 • 1 • 0, or 1 • 1 • 1. The lingual band,
No. 118, is narrow and ribbon-like in its appearance, with
numerous trident-shaped teeth set on a strong muscular
membrane. The end of the strap and its connexion with
the muscles at the hinder extremity of the cartilaginous
cushion is shown in the drawing. The blueish appearance
seen in the Plate is due to a selenite film and polarised
light. Scapander ligniarim (the Boatman shell). — The
band (Plate Y. No. 119), is narrow, but the teeth are bold
and of extraordinary size ; their formula is 1 • 0 * 1. This
mollusc is said to be without eyes. Pleurobranchus plu-
mula belongs to the same family ; its teeth are simple, re-
curved, and convex, and arranged in numerous divergent
rows ; the medians of which are largest. The mandible
(Plate Y. No. 122), presents an exceedingly pretty tesse-
lated appearance, and the numerous divergent rows have
tricuspided denticulations. Velutina Icevigata (the Yelvety
shell), formula 3 • 1 • 3.— The teeth (Plate Y. No. 108) are
small and fine ; medians recurved, with a series of deli-
cate denticulations on either side of the central cusp,
which is much prolonged : 1st laterals, denticulate, with

GASTEKOPODA. 543

outer cusp prolonged ; 2d and 3d laterals, simple curved
or hooked-shaped. The mandible, No. 109, divided
in the centre, forms two plates of divergent denticu-
lations.

Haliotis tuberculatus (the Ear-shell), is a well-known
beautiful shell much used for ornamental purposes. The
lingual band, Plate Y. No. 114, is well developed. The
medians are flattened out, recurved obtuse teeth ; 1st
laterals, trapezoidal or beam-like ; uncini numerous, about
sixty, denticulate, the few first pairs are prolonged into
strong pointed cusps. Turbo marmoratus (the Top-shell).
After the outer layer of shell is removed, it presents a
delicate pearly appearance. The lingual band, No. 123,
closely resembles Trochus ; it is long and narrow, the
median teeth are broadest, with five recurved laterals, and
numerous rows of uncini, slender and hooked. A single
ow only is represented in the plate. Cydotus translu-
"idus, a family of operculate land-shells, belongs to the
Cydostomatidce. The teeth shown at No. 110, formula
3 • 1 • 3, are arranged in slightly divergent rows on a narrow
band ; they are more or less subquadrate, recurved, with
their central cusps prolonged. Cistula catenata, one of
the family Cydophoridce ; its band, No. 115, formula
2 * 1 • 2, shows teeth resembling those of Littorina, and
should certainly be separated from Cydophoridce. It
would also seem that the teeth of Cydostomatidce point to
a near alliance with the Trochidce; but this question can
only be determined by an examination of several species,
when it may, perhaps, be decided to give them rank as a
sub-order. They are numerous enough ; the West Indian
islands alone furnish us with 200 species.

Professor William Thompson, in his paper " On the
Dentition of British Pulmonifera," Ann. Nat. His. vol.
vii. 1851, pointed out that the length of the lingual band,
and number of rows of teeth borne on it, vary greatly in
different species. The rows, however, being closely set
are usually very numerous ; but it is among the Pul-
monifera we meet with the most astonishing instances
of large numbers of teeth. Limax maximus possesses
26,800, distributed through 180 rows of 160 each; the
individual teeth measuring only one 10,000th of an inch.

544 THE MICROSCOPE.

Helix pomatia has 21,000, and its comparatively dwarfed
congener, H. obvoluta, no less than 15,000. When it is
remembered that these estimates refer to series of forms,
curiously carved and sculptured, the total area sustaining
them not measuring in most of the molluscs half an inch in
length, we must be filled with admiration at the marvellous
creative power bestowed upon the organization of these
lowly-creeping creatures.

The Preparation of Teeth of Mollusca. — The method of
preparing the lingual membranes of Mollusca is as fol-
lows : — The animal having been taken from its shell, pin
down the muscular foot to a piece of cork, pour water upon
it, and let the water be changed as often as it becomes
turbid. Then with a dissecting microscope and a good
bull's eye condenser cut open and expose to view the floor
of the mouth; pin back the cut edges throughout its
whole length, and work out the dental band with knife
and forceps. When the band is detached place it in a
watch-glass, and again clean it well by repeated washings
and a camel's hair brush : then place it in weak spirit and
water, where it must remain for a few days before mount-
ing. If the membrane is dense and fatty it must be soaked
for a time in liquor potassce, and when removed carefully
washed. The best fluids for mounting are glycerine, weak
spirit and water, Eimmington's glycerine-jelly, or Goadby's
solution. Canada balsam renders them so very pellucid
that the finer teeth are completely lost in it.

Thread-cells. — These curious appendages, so commonly
met with in the Actinozoa, and in the tentacles surround-
ing the mouth of the Medusae, are also seen in some
species of Mollusca.

These prehensile threads, now generally termed " urti-
cating organs," were discovered in 1835, in the Hydra, by
Corda and by Ehrenberg. About the same time they were
found by E. Wagner in the Actiniae, who at first regarded
them as zoosperms. Subsequently, however, he recog-
nised their identity with similar organs in the Medusae,
and gave them the name of urticating organs. Since then
numerous observations have shown that these organs exist
in the entire class of polypes ; in that of the Hydra,
Medusse, as well as in the Synaptae, many Turbellarise,

OVA OF MOLLUSCA. 545

some Annelids, and lastly among the Mollusca, the
Eolidae in particular.

Max Schultze has divided these organs into two cate-
gories ; one including those of a rod-like form, or the
bacillar, which are found pretty generally in the Turbel-
larias ; and the other containing the urticating capsules
armed with a long filament. Eut the researches of other
observers, including Dr. Bergh, have shown that this dis-
tinction is unimportant.

Dr. Bergh has devoted much attention to the urticating
filaments or cnida of the Mollusca, which are far less well
known than those of the Caelenterata. The existence of
sacs with cnida — that is to say, the existence of true
urticating batteries — is then at the present day a well-
established fact as regards the typical forms of the Eolidae,
i.e. in the genera Eolidida, Montagna, Facelina.

In every case the urticating batteries are planted at the
extremities of the papillae above the hepatic lobe. The
sac opens to the exterior by a minute pore situated at the
summit. Its walls are muscular, a circular layer of fibres
being the most considerable element. The interior is filled
with urticating cells, together with cysts full of closely-
packed filaments and free filaments. The genus Pleuro-
phyllidium, according to Dr. Bergh, is the only mollusc
besides the Eolidae in which cnida are met with, and it is
to be remarked that in their anatomical conformation these
animals appear to approach very closely to the Eolidae.

The use of these cnida is still involved in doubt. Mr.
Lewes, however, has shown that they do not serve to
paralyse the animals upon which Actiniae feed.

Ova of Mollusca. — It is interesting to watch the develop-
ment of the spawn of the Mollusca under a low magnifying
power. The ova of the Limnceus is usually found adhering
to the surfaces of stones, pieces of weed, or other matters in
the water ; they are always contained in a long ribbon-
like delicate ova-sac of a curious and beautiful form.
The mass of eggs deposited by the Doris resembles a frill
of lace of great beauty. In Aplysia the spawn resem-
bles long strings of vermicelli, of varying tints through-

a) On Urticating Filaments in the Mollusca, by Dr. Bergh. Jmrn. Micros. ScL
vol. ii. p. 274. 1SG2.

N N

546

THE MICROSCOPE.

out the different parts of the thread. The Limnceus stag-
nalis deposits small sacs, containing from fifty to sixty

Fig. 252.— Limncea stagnalis.

ova; one of which is represented at a, fig. 252. When
examined soon after they are deposited, the vesicles appear
to be filled with a perfectly clear fluid; at the end of
twenty-four hours a very minute yellow spot, the nucleus,
or germ, may be seen near., the side of the cell-wall. In
about forty- eight hours afterwards, this small germ has a
smaller central spot rather deeper in colour, which is the
nucleolus. On the fourth day the nucleus has changed its
position, and is enlarged to double the size : a magnified
view is given at b ; upon viewing it more closely, a trans-
verse fissure or depression is seen ; this on the eighth day
most distinctly divides the small mass into the shell and
soft part of the future animal, c. It is then detached from
the side of the cell, and moves with a rotatory motion
around the cell-interior; the direction of this motion is
from the right to the left, and is always increased when
the sunlight falls upon it. The increase is gradual up to
the sixteenth day, when the spiral axis can now be made
out as at d; it presents a striking difference in appearance
to the soft parts. On the eighteenth day, these changes
are more distinctly visible, and the ova crowd down to the
mouth of the ova-sac ; by using a higher magnifying power,
a minute black speck, the future eye, is seen protruded

GASTEROPODA.

547

with the tentacles, at e. Upon closely observing it, a
fringe of cilia is noticed in motion near the edge of the
shell. It is now apparent that the rotatory motion first
observed must have been in a great measure due to this ;
and the current kept up in the fluid contents of the cell
by the ciliary fringes. For days after the young animal
has escaped from the egg, this ciliary motion is carried
on, not alone by the fringe surrounding the mouth, but
by cilia entirely surrounding the tentacles themselves,
which whips up the supply of nourish-
ment, and at the same time the proper
aeration of the blood is effected. Whilst
in the ova, it probably is by this motion
that the cell-contents are converted into
tissues and shell. From the twenty-sixth
to the twenty-eighth day, it appears
actively engaged near the side ojf the
egg, using all its force to break through
the cell- wall, which at length it succeeds
in doing; leaving the shell in the ova-
sac, and immediately attaching itself to
the side of the glass-vase, to recommence
its ciliary play, and appears in the ad-
vanced stage represented at /. It is still
some months before it grows to the
perfect form represented at fig. 253,
Vr here the animal is drawn with its sucker-like foot adhering
closely to the side of the glass-vase. One of these snails
may deposit from two to three of these ova-sacs a week ;
producing, in the course of six weeks or two months, from
900 to 1,000 young, thus supplying food for fish.

The shell itself is deposited in minute cells, which take
up a circular position around the axis; on its under-surface
a hyaline membrane is secreted. The integument expands,
and at various points an internal colouring-matter or pig-
ment is deposited. The increase of the membrane goes
on until the expanded foot is formed, the outer edge of
which is rounded off and turned over by condensed tissue
in the form of a twisted wire ; this encloses a net-work of
small vessels filled with a fluid in constant and rapid
motion. The course of the blood or fluid, as it passes

N N 2

Fig. y&.^

stagnalis.

54:8 THE MICROSCOPE.

from the heart, may be traced through the larger branches
to the respiratory organs, consisting of branchial-fringes
placed above the mouth; the blood may also be seen
returning through other vessels. The heart, a strong mus-
cular apparatus, is pmr-shaped, and enclosed within a
pericardium or enveloping membrane, which is extremely
thin and pellucid. Affixed to the sides of the heart are mus-
cular bands of considerable strength, the action of which
appears very like the alternate to-and-fro motion occasioned
by drawing out bands of India-rubber, and which, although
so minute, must be analogous to the muscular cords of the
mammal heart ; it beats or contracts at the rate of about
sixty times a minute ; and is placed rather far back in the
body, towards the axis of the shell. The nervous system
is made up of ganglia, or nervous centres, and distributed
throughout the various portions of the body.

The singular arrangement of the eye cannot be omitted ;
it appears at an early stage of life to be within the tentacle,
and consequently capable of being retracted into it. In the
adult animal, the eye is situated at the base of the tentacle ;
and although it can be protruded at pleasure for a short
distance, it seems to depend much upon the tentacle for
protection as a coverlid — it invariably draws down the ten-
tacle over the eye when that organ needs protection. The
eye itself is pyriform, somewhat resembling the round
figure of the human eye-ball, with its optic-nerve attached.
In colour it is very dark, having a central pupillary-open-
ing for the admission of light. The tentacle, which is cylin-
drical in the young animal, becomes fiat and triangular in
shape in the adult. The young animal is for some time
without teeth ; consequently, it does not very early betake
itself to a vegetable sustenance : in place of teeth it has
two rows of cilia, as before stated, which drop off when the
teeth are fully formed. The lingual band bearing the
teeth, or the " tongue," as it is termed, consists of several
rows of cutting spines, pointed with silica.

It is a fact of some interest, physiologically, to know
that if the young animal is kept in fresh water alone,
without vegetable matter of any kind, it retains its cilia,
but arrest of development follows, and it acquires no
gastric teeth, and never attains perfection in form or sizo,

GASTEROPODA. 5

If, at the same time, it is confined within a narrow cell, or
space, it grows only to such a size as will enable it to move
about freely ; thus it is made to adapt itself to the neces-
sities of a restricted state of existence. Some young
animals in a narrow glass-cell, at the end of six months,
were alive and well, and the cilia retained around the
tentacles in constant activity ; whilst other animals of the
same brood and age, placed in a situation favourable to
growth, attained their full size, and produced young, which
grew in three weeks to the size of their elder relations.

Should any injury occur to the shell, or a portion of it
become broken off, the calcareous deposit is quickly resumed,
in order to replace the lost part ; the cells being apparently
only half the size of those originally deposited. This
may be thought to afford some proof of the statement
made by Professor Paget, — " that, as a rule, the reparative
power in each perfect species, whether it be higher or
lower in the scale, is in an inverse proportion to the
amount of change through which it has passed in its
development from the embryonic to the perfect state.
And the deduction to be made from them is, that the
powers for development from the embryo are identical
with those exercised for the restoration from injuries ; in
other words, that the powers are the same by which per-
fection is hVst achieved, and by which, when lost, it is
recovered. Indeed, it would almost seem as if the species
that have the least means of escape or defence from
mutilation were those on which the most ample power of
repair has been bestowed, — an admirable instance, if it be
only generally true, of the beneficence that has prepared
for the welfare of even the least of the living world, with
as much care as if they were the sole objects of the Divine
regard."

The primordial cell-wall of the cell does not appear to
enter into the formative process of the embryo — the cell-
contents alone nourishing the vital blastema of the nucleus.
A gradual cycle of progressive development once set up,
goes on, until the animal is sufficiently matured to break
through the cell-wall and escape from the ova-sac. At
the same time, it may be inferred, that all this is in some
measure- aided by the process of endosmose ; and that cer-

550 THE MICROSCOPE.

tain gases or fluids are drawn into the interior, and thus aid
in the supply of nourishment for the growth of the animal.
The cell-wall appears to bear the same relation to the
future perfect animal that the egg-shell of the chick does
to it ; it is, in fact, hut an external covering to a certain
amount of gaseous and fluid matter, used for placing the
germ of life in a more favourable state for development,
assisted, as it is, by an increase of temperature, usually
the resultant of a chemical action, set up or once begun
in an organism and a medium. " The ovum destined to
become a new creature originates from a cell, enclosing
gemmules, from which its tissues are formed, and nutriment
is assimilated, and which eventually enables the animal to
successively renew its organs, through a series of meta-
morphoses that give it permanent conditions, not only
different, but even directly contrary to those which it had
primitively."

Cephalopoda. — Molluscous animals without a foot, or
a distinct head, and covered with fleshy arms, bearing
sucker-like discs. The Cuttles and Squids form the prin-
cipal groups of this class, only a few species of which are
found on our shores. These molluscs are the nearest
approach of all invertebrate animals to the vertebrate
forms; and their organs of sense appear to be highly de-
veloped.1 Cuttle-fish bone, cut in thin sections, or broken
into small fragments, are interesting microscopic objects :
the peculiarities of structure are best seen when small
pieces are detached with a sharp knife. In 'the living
state these creatures have the power of suddenly changing
the colour of their skins.

Structure of Shell. — "We may exhibit the structure of
shell by using an acid solvent in the following manner.
If a sufficient quantity of hydrochloric acid, considerably
diluted with water (say one part acid to twenty-four of
water), be poured upon a shell contained in a glass vessel,
it will soon exhibit a soft floating substance, consisting of
innumerable membranes, which retain the figure of the
shell, and afford a beautiful and popular object for the

(1) In the Cephalopoda \ye hare the first' indication of a true internal
skeleton, in the form of a broad flattened cartilage which protects the central
(optic) ganglia of the nervous system.

STRUCTURE OF SHELL. 551

microscope. In analysing shells of a finer texture than
such as are generally submitted to the test of experiment,
the greatest circumspection is necessary. So much so,
that M. Herissant, whose attention was particularly devoted
to the subject, after placing a porcelain shell in spirits of
wine, added, from day to day, for the space of two months,
a single drop of spirits of nitre, lest the air, generated or
let loose by the action of the hydrochloric acid on the
earthy substance, should tear the net-work of the fine
membranaceous structure. This gradual operation was
attended with complete success, and a delicate and beauti-
fully reticulated film, resembling a spider's web in texture,
rewarded the patience of the operator ; the organization of
which film, from its extreme fineness, he was not, however,
able to delineate. In shells of peculiar delicacy, even five
or six months are sometimes necessary for their complete
development ; but in others of a coarser texture the process
is soon completed. Sections of shells are usually mounted
in Canada balsam, or in shallow cells with glycerine.

Mr. George Eainey pointed out the remarkable fact
that many of the appearances presented by the shell or
hard structures of animals, and which had been usually
referred to cell-development, are really produced by the
physical laws which govern the aggregation of certain crys-
tallizable salts when exposed to the action of vegetable and
animal substances in a state of solution. Mr. Eainey gives
a process for obtaining artificially a crystalline substance
which closely resembles shell in its chemical structure.

" The chemical substances to be employed in the pro-
duction of the artificial calculi are, a soluble compound of
lime, and carbonate of potash or soda, dissolved in separate
portions of water; and some viscid vegetable or animal
substance, such as gum or albumen, mixed with each of
these solutions. The mechanical conditions required to
act in conjunction with the chemical means are, the pre-
sence of such a quantity of the viscid material in each
solution as will be sufficient to make the two solutions,
when mixed together, of about the same density as that of
the nascent carbonate of lime, and a state of perfect rest
of the fluid in which the decomposition is going on, so
that the newly-formed compound may be interfered with

552 THE MICROSCOPE.

as little as possible in its subsidence to the sides and
bottom of the vessel. This will require two or three
weeks, or longer, according to the size and completeness
of the calculi. But I have not found that they increase
at all after six weeks."

Mr. Eainey shows1 the analogy or identity of his arti-
ficially formed crystals with those found in natural pro-
ducts both in animals and vegetables, chiefly confining
himself to the structure and formation of shells and bone,
pigmental and other cells, and the structure and develop-
ment of the crystalline lenses, which he contends are all
formed upon precisely the same physical principles as the
artificial crystals. Take, for instance, the calculi found in
the body : these cannot be distinguished from the crystals
of artifically formed carbonate of lime. Again, the shell
of the crustaceans ; the resemblance between these and the
artificial products is, in some respects, more complete than
in that of calculi. All the appearances in shells can
be best observed by merely cleaning them in water, and
examining them in glycerine, grinding being unnecessary
and injurious. Polarised light is indispensable ; as in the
young hermit-crab, at the part where the calcareous and
membranous portions of the shell are continuous, the cir-
cular forms of globular carbonate are so delicate that no
evidence whatever of its presence can be detected under
powerful lenses, and with the best illumination, until
polarised light is brought to bear upon the specimen. To
obtain the most satisfactory results in the investigation of
the process of calcification of animal tissues, it is indis-
pensably necessary that the parts examined should be in
the earliest stages of the process, and before the calcifying
membrane is entirely covered with the globular coalescing
deposit. The usual plan of examining shells in thin
vertical sections is entirely useless, unless it be simply to
see the number and arrangement of their layers ; the part
of the section in such specimens, in which the calcifying
process ought to be best seen, being entirely ground oft'.
This part, being the softest, can only be preserved in
the process of grinding by extreme care, and by keep-

(1) G. Rainey, " On the Mode of Formation of Shells, Lonz, &c. "by a process of
Molecular Coalescence." 1858.

STRUCTURE OF SHELL. 553

ing the lower edge of the section always thicker than the
upper.

Dr. Carpenter describes the shell of the Crab and Lobster
as being composed of three layers, viz. the epidermis or
cuticle, the rete-mucosum or pigment, and the coriuni.
The epidermis is of a horny nature, being generally more
or less brown in colour, and under the highest magnifying
powers presenting no trace of structure (fig. 247, No. 2) ;
it invests all the outer parts of the shell, and has in many
instances large cylindrical or feather-like hairs developed
from certain portions of its surface. The rete-mucosum,
or pigment cells, consist of either a series of hexagonal
cells, forming a distinct stratum, or of pigmental matter
diffused throughout a certain thickness of the calcareous
layer. (Fig. 247, No. 5.) In the Crab and Lobster it is
very thin, but in the Crayfish it occupies in some parts
more than one-third of the entire thickness of the shell ;
when examined by the microscope, this portion appears to
be composed of a large number of very thin laminse, which
are indicated by fine lines taking the same direction on
the surface of the shell, the number of lines being the
greatest in the oldest specimens ; these layers, even in the
Crayfish, are covered by a thin stratum of very minute
hexagonal cells, without any trace of cell matter in their
interior. The corium is the thickest layer of the three,
being the one on which the strength of the shell depends,
in consequence of the calcareous material deposited in it.
(Fig. 247, No. 4.) "When a vertical section of the shell of
the Crab is examined, it is found to be traversed by parallel
tubes, resembling those in the dentine of the human tooth ;
these tubes extend from the inner to the outer surface of the
shell, and are occasionally covered by wavy lines, probably
those of growth, shown in a portion of No. 3, fig. 247. If
a horizontal section of the same shell be made, so that the
tubes be divided at right angles to their length, the sur-
face will clearly exhibit their open ends, surrounded by
calcareous matter. In Shrimps and very small Crabs, the
deposition of the calcareous matter takes place in concen-
tric rings like those of agate ; and occasionally small cen-
tres of ossification, somewhat like Pinna, with radiating
striae, are met with in the Shrimp. If the calcareous

554

THE MICROSCOPE,

portion of the shell be steeped in hydrochloric acid, a
distinct animal structure or basis is left behind, and the
characters of the part will be very accurately preserved.
The calcareous matter, like that of bone, generally pre-
sents a more or less granular appearance, as at ~No. 4, and
so angular in figure as to resemble certain forms of rhom-
boidal crystals : JSTo. 2 is a section from the outer brown
shell of the Oyster. The beauty of all such structures is
much increased if viewed with polarised light on the
selenite stage.1

Crustacea. — The skeletons of Crustacea are external to
the soft parts ; in a great number of species the shell is
thin and membranous, in others it is of a horny material,
thickened with calcareous matter, having a distinct series
of pigment cells of a stellate
figure, all supplying beautiful
objects for microscopic examina-
tion and polarised light. The
Astacus, Crayfish, may be" taken
as the type of that large and
important group of Crustacea to
which the term Podophthalma,
Stalk-eyed, is applied.2

Cirrhopoda or Cirripedta,
when mature, attach themselves
to rocks and other objects. The
Barnacle (fig. 254) and Acorn-
shell are the best known exam-
ples of this order; they gene-
rally select floating objects to
i, Young fry of the Oyster, a dwell upon ; and bottoms of
£££*" ^tud £5 <*ips have been covered by them
of Barnacles. to such an extent as even to

impede their progress through the water. The soft bodies
of these animals are enclosed in a case composed of five
calcareous plates ; from this circumstance they were
grouped with the multivalve shells of the older concholo-

(1) See Prof. Huxley's articlei on the- "Tegumentary Organs," Cyclop. Anat.
and Physio, vol. v. p. 487.

(2) Some valuable information will be found on the minute structure of shells
in Prof. Williamson's paper, "On some Histological Features in the Shells of
the Crustacea," Journ. Micros. Scien. vol. viii. p. 35, 1860.

Fig. 254.

ENTOMOSTRACA. 555

gists. Their limbs are converted into tufts of jointed
cirri, and protrude through an apening in the mantle
which lines the interior of the shell. The cirri, twelve
in number, are covered with cilia, which, when the animal
is alive, are in continual motion. The intestinal canal is
complete, and the nervous system exhibits the usual
series of ganglia, characteristic of the articulate type.
The head is marked only by the position of the mouth,
and is armed with a pair of jaws, if we may so term
the shells.

Balanidce, " Sea-acorns," a sessile species, whose curious
little habitations may constantly be met with upon the
rocks of the sea-shore, and not unfrequently upon many
species of marine shells. The shell forms a short tube,
and is usually composed of six segments securely united
together. The lower part of the tube is firmly fixed to the
object on which the Balanus has taken up its abode ; whilst
the superior orifice is closed by a movable roof, composed
of from two to four valves, between which the little tenant
of this curious domicile protrudes his delicate cirri in search
of nourishment. In the young state the Balanidce freely
swim about, and somewhat resemble the following group,
En tomostraca.

.Entomostraca, or Water-fleas, undergo a series of remark-
able changes from the moment of their escape from the
egg to the attainment of their fully matured form. And
it is of the highest interest to remark that, in obedience
to a law which, if not universal, is at any rate widely pre-
valent in the animal kingdom, these temporary or larval
forms are themselves closely analogous to the prefect forms
of groups still lower in the scale of existence, so that many
of them in their early forms were formerly, before their
life-history was known, either classed as distinct species, or
placed in a position very far from that which they are now
seen to occupy. The embryo of the Shore-crab (Carcinus
moenas) before, and for a short time after, its liberation
from the ovum, presents both in size and general outline
a strong resemblance to Entomostraca. In this transi-
tion stage it was assigned to a distinct genus under the
name of Zoea ; and having undergone a still further trans-
formation was called Megalopa. In this latter stage it

556

THE MICROSCOPE.

puts on somewhat the appearance of the Lobster crab
(Galathea), and after another step attains its true crab-
form, being the highest development of which it is capable.
These changes are not produced gradually, but by a suc-
cession of " moults," the animal becoming at times sluggish,
casting its hard covering, and reappearing in a new guise.
The after growth of a crustacean is carried on by the system
of moulting ; the hard calcareous case of the animal pre-
venting its growth in any other mode. And as in the
higher orders of Crustacea, so also amongsb the Entomos-
traca, transformations of this kind constantly take place.
Cyclops quadricornis, when first born, is totally unlike its
parents, being of an ovoid shape, having only two shoit
antenna? and two pairs of feet ; in three moults the
animal reaches its perfect form, with its two pairs of an-
tennse, five pairs of feet, and body divided into several
distinct rings or segments.

The animals comprising the order Ostracoda are generally
of very minute size ; the body,
which strongly resembles that
of the Copepoda, is always
enclosed in a little bivalve
shell, the feet and antenna)
being protruded between the
lower edges of the valves.
These little shells so closely
resemble those of minute
bivalve Mollusca, that those
of some of the larger species
have actually been described
by conchologists as the cover-
ing of animals belonging to
that class. The antennae are
often curiously branched ; and
the hinder extremity is usu-
ally prolonged into a sort of
tail, which is seen in constant
action when the animal is in
motion. In Cypridina, the
body is entirely enclosed by
a shell, of which the genus Cypris (fig. 255) is an example ;

Fig. 255.

1, Cypris. 2, Polyphemus, Cyclops.
3, Branchiopus stagnalis.

ENTOMOSTRACA, 557

and in Daphnia, " "Water-fleas," the head is protruded be-
yond the shell. In Polyphemidce the head is large, and
almost entirely occupied by an enormous eye, giving the
creatures a most singular appearance; the Monoculus is
a well-known example of this group. Another family,
not provided with a shell or carapace, called Branchio-
poda, from the name of the typical genus, Branchiopus
stagnalis (fig. 255), is often found after heavy rains in
cart-ruts and other small pools.

Daphnia pulex is found commonly in fresh water, and
is scarcely inferior to its marine relative, Talitrus locusta,
in agility. The Corophium longicorne, remarkable for its
long antennae, is not less so for its singular habits. It
is found at Kochelle, where it burrows in the sand, and
wages constant war with all other marine creatures of
moderate size that come in its way.

Dr. Baird has followed up the successive generations in
Daphnia pulex ; so far as the fourth change in the Daphnia
born from the ordinary ova, and so far as the third in those
born from* the ephippial eggs. These ephippia, or "winter
eggs," require a few words of explanation. They are, in fact,
eggs covered with envelopes of more than usual hardness
and thickness, being enabled to withstand an excess of
cold, which would surely prove fatal to the parent. . This
observer found, upon examining ponds which had been
filled up again by the rain after remaining two months
dry, numerous specimens of the Cyclops quadricornis in
all stages of growth. Dr. Baird, in his "Natural History
of British Entomostraca," 1850, tells us that they have
many enemies.

" The larva of the Coretlira plumicornis, known to micro-
scopical observers as the skeleton larva, is exceedingly rapa-
cious of the Daphnia. Pritchard tells us they are the choice
food of a species of Nais ; and Dr. Parnell states that the
Lochlevin trout owes its superior sweetness and richness of
flavour to its food, which consists of small shell-fish and En-
tomostraca." These animals abound both in fresh and salt
water. Artemice are formed exclusively in salt water, in salt
marshes, and in water highly charged with salt. " Myriads
of these Entomostraca are to be found in the salterns at
Lymington, in the open tanks or reservoirs where the brine

558 THE MICROSCOPE.

is deposited previous to boiling. A pint of the fluid
contains about a quarter of a pound of salt, and this con-
centrated solution destroys most other marine animals."
During the fine days in summer Artemice may be observed
in immense numbers near the surface of the water, and, as
they are frequently of a lively red colour, the water appears
tinged with the same hue.1 There is nothing more elegant
than the form of this little animal. Its movements are
peculiar. It swims almost always on its back, and by means
of its tail it runs in all directions, its feet being in constant
motion. They are both oviparous and ovoviviparous, accord-
ing to the season of the year. At certain periods they only
lay eggs, while during the hot summer months they pro-
duce their young alive. In about fifteen days the eggs are
expelled in numbers varying from 50 to 150. As is the
case with many of the Entomostraca, the young present a
very different appearance from the adult animals ; and
they are so exactly like the young of Chirocephalus, that with
difficulty they can be distinguished the one from the other.
The ova of other species are furnished with thick cap-
sules, and imbedded in a dark opaque substance, presenting
a minutely cellular appearance, and occupying the inter-
space between the body of the animal and the back of the
shell. This is called the ephippium.2 The shell is often
beautifully transparent, sometimes spotted with pigment :
it consists of a substance known as chitine, impregnated
with a variable amount of carbonate of lime, which pro-
duces a copious effervescence on the addition of a small
quantity of acid, and when boiled it turns red, like the
lobster. Their shells vary in structure. Sometimes they
consist of two valves united at the back, and resembling

(1) It is a curious fact that salt-water when highly concentrated frequently
assumes a red colour, and that this should have been attributed to the presence
of the Artemia salina, as in the case of fresh-water noticed elsewhere found
coloured red by a species of Paramcecium. The cause of this red colour, which
was well known to take place in the salt marshes and reservoirs of salt-water
at Montpellier, was made the subject of a very grave discussion in France.
Some maintained that the colour was caused by the presence of Artemice, while
others declared that it arose from vegetable matter, either Hcematococcus or
Protococcus. M. Joly, came to the conclusion, after many careful examinations,
that the red colour depends upon the presence of myriads of monads, and that
the Artemice. living upon these partook of the same red hue, and thus the water
appeared to be of the same colour.

(2) See paper on " Reproduction in Daphnia," by Sir John Lubbock, Philos*
Trans. 1857, p. 79.

ANNULOSA. 559

the bivalve shell of a mussel ; others are simply folded at
the back, so as to appear like a bivalve, but are really
not so ; or they consist of a number of rings or seg-
ments. The body of. the Cypris presents a reticulated
appearance, resembling that of cell structure. All the
Entomostraca are best preserved in a solution of chloride
of calcium.

ANNULOSA. — Articulata. The animals composing the
sub-kingdom Articulata are characterised by having the
body enclosed in a tunic, or integument, consisting of a
series of rings, segments, or joints, " articulated " together
by a flexible membrane.

The Annulosa are divided, by Professor Huxley, into
two principal groups, the Artkropoda and the Annuloida.
TheArthropoda, comprising Insecta, Myriapoda, Crustacea,
and Arachnida, possess a definitely segmented body ; the
segments being provided with appendages, the anterior of
which are so modified as to subserve the functions of sen-
sation and manducation. They have almost always a heart,
communicating with the general cavity of the body, for
propelling the true corpusculated blood which that cavity
contains. The nervous system consists of a longer or a
shorter chain of ganglia.

Nothing can be more variable than the characters of the
body, the appendages, and the nervous system among the
rest of the Annulosa, which are included under the Annu-
loida; nevertheless, there are two features in which they
all agree ; firstly, they possess a remarkable system of
vessels, either ciliated, or deprived of cilia, and containing
a fluid very different from the true blood which fills the
general cavity of the body or perivisceral space ; secondly,
in no annuloid animal has any true heart been hitherto
discovered. Contractile vessels belonging to the system
just referred to abound, but no organ comparable in struc-
ture to the heart of other animals has yet been found in
any of the Annuloida.

The Annuloida, as thus defined and limited, fall into
two parallel series ; in one of which, for the most part,
dioecious forms predominate, as the Annelida, while of
the latter, the Trematoda may be regarded as the typical
example ; on the other hand, the Echinodermata and

560 THE MICROSCOPE.

Rotifera, the Tocniadce and the Nematoidea, may be con-
sidered as the most aberrant groups of their respective
series.

Under the head Annelida, Mr. Huxley includes the
errant and tubicular Annelids of Cuvier, and the Gephyrea
of De Quatrefages; he thinks that the Terricola — the
Earthworms and Naides — should be separated from the
Scoledce of Milne Edwards, and brought into the same
group. So far as external structure is concerned, the
genus Polynoe is, perhaps, the best fitted to serve as the
type to which other Annelida may be referred: the com-
monest form of the genus being the P. squamata.1 The
best developed branchiae among the Annelids are possessed
by the Amphinomidce, the Ennicid-as, the Terelellidce, and
the Serpulidce. The branchiae in the three former families
are ciliated, branched plumes or tufts attached to the
dorsal surface of more or fewer of the segments. In the
last they are exclusively attached to the anterior segments
of the body, and present the form of two large plumes,
each consisting of a principal stern, with many lateral
branches; this stem is itself supported on a kind of
cartilaginous skeleton.

The teeth in a great number of the Annelida are very
curious and distinctive. In the Polynoe there are four,
planted in the muscular wall of the proboscis. In the
Nereis there are two powerful teeth working horizontally,
besides minute accessory denticles. In Syllis there is a
circle of sharp teeth, surrounding a triangular median
tooth. In Glycera there are a pair of teeth ; but the most
complex arrangement of teeth is that presented by the
Ennicidce. 'The tubicular Annelids possess neither pro-
boscis nor teeth.

Many Annelids pass through a larval condition, in
which the body exhibits mere indications of segments,
and the appendages are entirely absent; locomotive
function being performed by a circlet of cilia, disposed
around the anterior part of the body. There is a large
group of very remarkable organisms, observes Mr. Huxley,
the minute " wheel animalcules," Rotifera, whose whole

(1) Consult a valuable paper on this genus in Miiller's Archiv. 1857. Also
Huxley's "Elements of Comparative Anatoiry."

ANNULOSA. 561

organization demonstrates, not merely their annulose •
nature, but their position among the Annuloida, and
which exhibit precisely the same indistinct segmentation,
the same general absence of appendages, and whose means
of locomotion are in like manner confined to one or two
ciliated circlets at the anterior part of the body. The
connexion between the Annelida and the Rotifera, is
further illustrated by such remarkable forms as the
Polyophthalmus of De Quatrefages, a true Annelid, which,
nevertheless, possesses on each side of the head a ciliated
lobe, capable of being voluntarily protruded and retracted,
and presenting a close resemblance to the trochal disc of a
Rotifer. Hydatina senta has been so well and accurately
described by Dr. Cohn,1 and others, that it may be taken
as the typical form of the Rotifera. The trochal disc in
the species, undergoes great changes of form. In Hydatina,
it is circular, and its margin is skirted by two distinct con-
tinuous bands of cilia, the one immediately in front of, the
other behind the mouth. In Brachionus the ciliated circlet
fringing the edges of the trochal disc is horseshoe-shaped,
but the circlet is produced into three lobes or processes,
which stand out perpendicularly to the surface of the
trochal disc. In Stephanoceros it fringes the edges of a
number of tentaculiform processes, into which the trochal
disc is produced, so as to give the whole animal somewhat
the appearance of a Polyzoon.

The Turbellaria, a group of serpent-like worms, for
the most part the inhabitants of fresh and salt waters, a
few only being found in damp siuations on land, are
characterised by the ciliation of the entire surface of the
body. In their internal organisation they approximate in
many respects to the Trematoda, while in others they
exhibit a certain affinity with the other great group of
parasitic Annuloida, the Nematoidea. Polycelis Icevigatits,
one of the Dendrocoela so well described by De Quatrefages
in his Monograph on the Marine Planarice, may be most
advantageously selected as a type of the group. The
Nemertidce have engaged the attention of the same learned
authority, the ova of which undergo a remarkable kind of

(1) Ueler die Fortflawzung der Raderlhiere, Von Dr. F. Cohn, in Breslau.
1S55.

O O

562 THE MICROSCOPE.

metamorphosis. The embryo has at first a ciliated non-
contractile, oval body, exhibiting no structure but a semi-
lunar superficial cleft, provided with raised edges. After
a time, a small actively-contractile, vermiform creature,
resembling the parent, escapes from the interior of the
larval form, which it leaves behind like a cast skin. The
semilunar cleft becomes the mouth of the imago, and is
only part of the larva carried away. The Gordiacei l best
enable us to connect the Turbellaria with the very puzzling
group Nematoidea, and the structure of several species
belonging to the two genera which compose the group
Mermis and Gfordius, have recently been made the subject
of two elaborate monographs by Meissner.2

The Gordiacei are excessively elongated, thread-like
worms, plentiful enough in Thames mud, and, as Von
Siebold discovered, partake both of the free habit of the
Nemertidce, and of the parasitic nature of the Nematoidea.
The young Mermis, for instance, is parasitic upon insects,
inhabiting the peri visceral cavity of the larva or of the
imago.

The NemertidcB seem to differ from their close allies the
Turbellaria, in possessing a vascular system distinct from
and added to the water-vessels. In the Hirudinidce, Leeches
and Earthworms, a system of vessels homologonous with
the pseud-heemal system exists, and, in addition a series
of more or less coiled tubules lie in the perivisceral cavity,
and open, by pores, on the ventral surface of the body.
These organs have been regarded sometimes as secretory,
sometimes as respiratory apparatus; but all that we
know about them in reality is that they are tubular, and
are more or less richly ciliated within, and that, in some
cases (Nais, Lumbricus), they present at their internal ex-
tremities a ciliated aperture, whereby they freely com-
municate with the perivisceral cavity.

There remains, however, yet another system of vessels
in the Annuloida — the ambulacral vessels of the Echino-
dermata. These are frequently termed " water- vessels,"
and, indeed, if we regard the structure with reference to

(1) Huxley, General Natural History.

(2) Beltr'dge zurAnatomie und Physiologic von Mermis Albicaus, v. 2"eitsclirift
fur Wiss.Zoologie, Bd. v 1854; and Beitrdge zurAnat. & Physiol.des Gordiaccn,
Ibid. Bd. vii. 1855.

ANNULOSA. 563

their peculiar functions, they singularly resemble true
water-vessels ; they open by an external pore, and are
ciliated internally ; they unite around the gullet, as do the
water- vessels in some Trematoda, and are eventually shut
off from such communication; the ambulacral vessels of
the Holothuridce undergo precisely this change, and thus
they facilitate our comprehension of a transition from the
water-vessels of the Trematoda to the pseud-hsemal vessels
of the Annelida. We may take it as an established fact
that, whatever the functions of this varied vascular system
and its contents in different classes of the Annuloida,
they have nothing to do with the blood or true blood
vessels. The latter are entirely absent in all the Annu-
loida at present known, the blood (improperly called
" chyle-aqueous fluid ") being simply contained in the peri-
visceral cavity and its processes. The development of
the Nematoidea appears to take place without metamor-
phosis ; the embryo assuming within the egg a form nearly
resembling that of the adult. Encysted asexual nematoid
worms are frequently found in various parts of the body
of fishes; and the remarkable Trichina spiralis is the
asexual state of a nematoid worm, encysted within the
substance of the muscles of man. Zooid development is
only known to occur in one nematoid, the Filaria, Medi-
nensis, Guinea-worm. Mr. Busk's careful observations
have long since placed this fact beyond a doubt.

The TceniadcB and the Acanthocephala, like the Trema-
toda, entirely parasitic in their habits, differ from them in
the total absence of mouth or digestive cavity. The
Taniadce, Tapeworms, are ribbon-like creatures, usually
divided throughout the greater part of their length into
segments, whose usual habitation is the intestinal cavity
of vertebrate animals ; and apparently of a carnivorous
vertebrate, in fact, though capable of existence elsewhere,
it is there alone that they are able to attain their complete
development. The anterior extremity of a taenoid worm
is usually called the head, and bears the organ by which
the animal attaches itself to the mucous membrane of the
creature which it infests. These organs are either suckers
or hooks, or both conjoined. In Tcenia, four suckers are
iombined with a circlet of hooks, disposed around a median
o o 2

564 THE MICROSCOPE.

terminal prominence. The embryo passes through a
similar course of development to the Trematoda ; viz.
four forms or changes : but the embryo itself is very
peculiar, consisting of an oval non-ciliated mass, provided
upon one face with six hooks, three upon each side of the
middle line. The Tceniadce are /ound in many other
situations besides the alimentary canal : the eye, the brain,
the muscular tissues, the liver, &c. ; the following cystic
worms are included in this genera, Cysticercus Anthoce-
phalus, Ccenurus, and T. Echinococcus. Plate IV. No. 100,
this figure shows an entire and full-grown Tcenia with
rostellum and suckers, and then three succeeding segments,
the last of which contains the ova, &c. The water-vascular
system is represented coloured with carmine. This para-
site infests the human body more frequently than other
varieties. This accurately-drawn figure is copied from
Cobbold.

Yon Siebold, Leuckart, and others, have shown, by many
interesting experiments, such as feeding puppies with Cys-
ticercus pisiformis, that in the course of a few weeks these
entozoa are transformed into fully formed Tcenia serrata ,
again, rabbits fed with the embryo of the Tcenia, the
embryo bore their way, by means of hooks, through the
walls of the intestine, until they reach some blood-vessel :
by the current of blood they are carried into the liver,
and here Leuckart has traced their further development.
The embryos grow to the 1-1 6th of an inch in length, and
become elongated, so as almost to resemble an Ascarid in
form ; they then make their way to the surface of the liver,
and pass out into the peritoneal cavity.

In like manner, Cysticercus fasciolaris is rapidly developed
within the liver of white mice ; Cysticercus cellulosce seen
in the muscles of the pig fed with the Tcenia solium, pro-
duces the diseased state of pork familiarly known as
" measly pork." If a lamb is the subject of the feeding
experiment with Tcenia serrata, the final transformation
will be very different ; within a fortnight, symptoms of 'a
disease known as " staggers" are manifested, -and in the
course of a few weeks, the Coenurus cerebralis will be found
transformed and developed within the brain. Yon Siebold
pointed out the bearing of this fact upon the important

TREMATODA. 565

practical problem of the prevention of " staggers." Others
of the same family of parasites are quite as remarkable, in
giving a preference to the alimentary canal of fishes. The
Echinorhynchus is developed in the canal of the Flounder,
Tricenopliorus nodulus in the liver of the Salmon, attain-
ing a more perfect development in the alimentary canal of
the Perch and Pike. Another, found in the Stickleback,
becomes changed in the intestines of water birds, which
devour these fish ; and thus, by careful and repeated
observations with the microscope, the connexion existing
between the Cystic and Cestoid Entozoa have been most
satisfactorily established.

The Fluke belongs to the order Trematoda, which
signifies that they are internal parasites, suctorial worms,
or helminths ; they are all usually visible to the naked
eye, although a few of the smallest scarcely exceed 1-1 00th
of an inch in length ; many are larger, and the species best
known, Fasciola Jiepatica, attains to an inch or more in
length. The Fluke shown in Plate IV. No. 103, is cone-
shaped : it is the Amphistome conicum of liudolphi. This
parasite is common in oxen, sheep, and deer, and it has also
been found in the Dorcas antelope. It almost invariably
takes up its abode in the first stomach, or rumen, attaching
itself to the walls of the interior.1 In the full-grown state
it never exceeds half an inch in length ; in our plate it is
represented magnified. On closer inspection it will be seen
that the animal is furnished with two pores or suckers, one
at either extremity of the body, the lower being by far the
larger of the two. By means of the latter the Amphistome
anchors itself to the papillated folds of the paunch, or first
stomach, as this organ is improperly called.

In the figure the oral sucker at the anterior end, or head,
leads into a narrow tube, forming the throat or oesophagus,
and this speedily divides, or rather widens out, into a pair
of capacious canals. These cavities are correctly regarded

(1) The larval condition of Amphisloma in all probability lives in or upon the
body of snails. This we infer from the circumstance that the larvae, cercarice,
of a closely allied species, the Amphistomasubdavatum, which is known to infest
i he alimentary canal of frogs and newts, have been also found on the surface of
t he body of the Planorbis by ourselves, whilst Van Beneden discovered the
larvae in a species of Cyclas. The cercarice, larvae, are taken, it is supposed, by
the cattle while drinking. They then attach themselves to the walls of the
stomach, where they soon complete their further stages of development.

566 THE MICROSCOPE.

as together constituting the stomach ; but they are caecal,
that is, closed below, having no other outlet than the
entrance above mentioned. The water-vascular system,
artificially coloured in the plate, or rather the vessels thus
named, bear a very striking resemblance to that of arteries
or veins ; and the centrally-placed pouch, shown in the
figure, might very easily be taken to represent the heart.
This large cavity gives origin to two primary trunks, which
pass forward along the inner sides of the digestive caeca ; in
their passage they send off secondary branches, which divide
and sub-divide until we arrive at a series of minute capil-
lary ramifications ; the latter, according to Blanchard,
terminating in small oval-shaped sacs or lacunae.

" It should be further observed, that the surface of the
Amphistome, though quite smooth to the naked eye, is
clothed with a series of minute tubercles, which may be
readily brought into view under a half-inch object glass.
Beneath the cuticle we find a layer of cellules forming the
true skin ; and beneath this, again, there are two, if not
three, layers of muscular fibre ; an anterior longitudinal
series and an inner circular set being readily distinguish-
able. The substance of the body is traversed by bands of
cellular parenchyma or connective tissue, which here and
there form thickened sheaths for the support of the various
delicate organs above described." The reproductive organs
of flukes possess the greatest amount of interest both from
an anatomical and physiological point of view. They are
produced from eggs, which are found in large numbers in
the ova-sac; varying in size from 1-1 50th to l-250th of
an inch.

"'The large fluke (Fasciola hepatica) is not only of
frequent occurrence in all varieties of grazing cattle, but
has likewise been found in the horse, the ass, and also in
the hare and rabbit, and in some other animals. Its occur-
rence in man has been recorded by more than than one
observer ; the oral sucker forming the mouth leads to the
short oesophagus, which very soon divides into two primary
stomachal or intestinal trunks, which latter in their turn
give off branohes and branchlets ; the whole together form-
ing that beautiful dendritic system of vessels which has
often been compared to plant-venation. This remarkably-

TREMATODA. 567

formed digestive apparatus is accurately represented in
Plate IV. Nos. 106 and 107, Fasciola gigantea of Cobbold,
which should be contrasted with the somewhat similarly-
racemose character of the water- vascular system. Let it be
expresely noted, however, that in the digestive system the
majority of the tubes branch out in a direction obliquely
downwards, whereas those of the vascular system slope
obliquely upwards. A further comparison of the dis-
position of these two systems of structure, with the
same systems figured and described as characteristic of
the Amphistome, will at once serve to demonstrate the
important differences which subsist between the several
members of the two genera, if we turn to the con-
sideration of the habits of Fasciola hepatica, which,
in so far as they relate to the excitation of the liver
disease in sheep, acquire the highest practical import-
ance. Intelligent cattle-breeders, agriculturists, and veteri-
narians have all along observed that the rot, as this
disease is commonly called, is particularly prevalent after
long-continued wet weather, and more especially so if
there have been a succession of wet seasons ; and from this
circumstance they have very naturally inferred that the
humidity of the atmosphere, coupled with a moist condi-
tion of the soil, forms the sole cause of the malady. Co-
ordinating with these facts, it has likewise been noticed that
the flocks grazing in low pastures and marshy districts are
much more liable to the invasion of this endemic disease
than are those pasturing on higher and drier grounds ; a
noteworthy exception occurring in the case of those flocks
feeding in the salt-water marshes of our eastern shores." 1
Plate IY. No. 106, Fasciola gigantea : the anterior surface
is exposed to display oral and ventral suckers, and the
dendriform digestive apparatus injected with ultramarine ;
No. 107, shows the dorsal aspect of the specimen and
the multiramose character of the water-vascular system,
the vessels injected with vermilion.

One of the most remarkable of the Trematode helminths
is Billiarzia hcematobra of Cobbold ; Distomia hcematobium
of some other authors. Plate IY. No. 102. This genus

(1) Entozoa: An Introduction to the Study of Helminthology. By T. Spencer
Cobbold, M.D.F.R.S. 1866. P. 14S.

568 THE MICROSCOPE.

of fluke, discovered by Dr. Bilharz in the human portal
system of blood vessels, gives rise to a very serious state of
disease among the people of Egypt. So common is the
occurrence of this worm, that this physician expressed his
belief that half the grown-up people are infested with it.
Griesinger conjectures that the young of the parasite exists
in the waters of the Nile, and in the fishes which abound
therein. Dr. Cobbold thinks " it more probable that the
larvse, in the form of cercarise, redias, and sporocysts, will
be found in certain gasteropod mollusca proper to the
locality." The anatomy of this fluke is fully described in
Kuchenmeister's able work on Parasites, by Leuckart, and
by Cobbold. The eggs and embryos of Bilharzia are
peculiar in possessing the power of altering their forms in
both stages of life ; and it is more than probable that the
embryo form has been mistaken for some extraordinary
form of ciliated infusorial animalcule, their movements
being most quick and lively. We cannot fail to notice
the curious leech-like form of the male animal, and, re-
markable enough, he is generally found carrying the female
about. The whip-like appendage seen in the figure is a
portion of the body of the female. The disease produced
by them is said to be more virulent in the summer months,
which is probably owing to the prevalence of the cercarian
larvae at the spring time of the year.

Trichina spiralis. — This, the smallest of the helminths,
measures only the l-20fch of an inch. The female is a little
larger ; it was discovered by Professor Owen in a portion
of the human muscle sent to him from St. Bartholomew's
Hospital, 1834. The young animal presents the form of
a spirally- coiled worm in the interior of a minute oval-
shaped cyst (Plate IV. No. 104), a very small speck
scarcely visible to the naked eye. In the muscle it resem-
bles a little particle of millet seed, more or less calcareous
in its composition. The history of the development of
Trichinae in the human muscle is briefly that in a few
hours after the ingestion of diseased flesh, Trichinae, dis-
engaged from the muscle, are found free in the stomach :
they pass thence into the duodenum, and afterwards
advance still further into the small intestine, where they
become developed. From the third or fourth day, ova or

TRICH^A SPIRALIS. 569

spermatic cells are found, the sexes in the mean while be-
coming distinctly marked. Shortly afterwards the ova are
impregnated, and young living entozoa are developed within
the bodies of the female. The young have been noticed
(by Yirchbw) under the form of minute Filarice, more
especially in the serous cavities, in the mesenteric glands,
Arc. Continuing their migrations, they penetrate as
far as the interior of the primitive muscular fasciculi,
where they may be found as early even as three days
after ingestion, in considerable numbers, and so far deve-
loped that the young entozoa have almost attained a size
equal to that of the full-grown Trichinae. They pro-
gressively advance into the interior of the muscular fasci-
culi, where they are often seen several in a file one after
the other. Behind them the muscular tissue becomes
atrophied, and around them an irritation is set up, and
from the commencement of the third week they are found
encysted. The sarcolemma is now thickened, and the
contents of the muscular fibres exhibit indications of a
more active cell-growth ; the cyst is the product of a sort
of inflammatory irritation.

Professor Virchow draws the following conclusions : —
"1. The ingestion of pig's-flesh, fresh or badly dressed,
containing Trichina, is attended with the greatest danger,
and may prove the proximate cause of death. 2. The
Trichinae maintain their living properties in decomposed
flesh ; they resist immersion in water for weeks together,
and when encysted may, without injury to their vitality,
be plunged in a sufficiently dilute solution of chromic acid
for at least ten days. 3. On the contrary, they perish and
are deprived of all noxious influence in ham which has
been well smoked, kept a sufficient length of time, and
then well boiled before it is consumed."

The Ecldnococcus found in cysts, chiefly in the human
liver, is represented in Plate IY. No. 101. A large col-
lection was taken from the liver of a boy who died in
Charing-cross Hospital from accidental rupture of the
liver. The cysts containing these parasites are always
situated in cavities in the interior of the body. These
cavities may be situated in any part of the tissues or organs
of the body, but are more frequently found in the solid

570

THE MICROSCOPE.

viscera, and especially in diseased livers. Fig. 256 repre-
sents the microscopical appearance of the contents of a cyst.

Fig. 256.— Cystic Disease of Liver. (Human).

a, Cyst with an echinococcus enclosed. &, Detached booklets from the head of
Echinococcus, magnified 250 diameters, c, Crystals found in the cyst, choles-
terine. d, Cylindrical epithelium, some enclosed in structureless globules.
e, Puro-mucus, and fat corpuscles.

Mr. Busk, who has examined several of these cysts,
says : — "When a large hydatid cyst, — for instance, in the
liver of the sheep, — very shortly after the death of the
animal, is carefully opened by a very small puncture, so. as
to prevent at first the too rapid exit of the fluid, and con-
sequent collapse of the sac, its internal surface will be
found covered with minute granulations resembling grains
of sand. These bodies are not equally distributed over
the cyst, but are more thickly situated in some parts than
in others. They are detached with the greatest facility,
and on the slightest motion of the cyst, ;and are rarely
found adherent after a few days' delay. When detached,
they subside rapidly in the fluid, and consequently will
then be usually found collected in the lowest part of the
cyst, and frequently entangled in fragments of the inner
thin membrane. When some of these granulations are
placed between glass under the microscope, and viewed
with a power of 250 diameters, upon pressure being em-
ployed it will be seen, after rupture of the delicate enve-
loping membrane, that the Echinococci composing the gra-
nulations are all attached to a common central mass by
short pedicles ; which, as well as the central mass, appear
to be composed of a substance more coarsely granular by

AXG UILLULuE. 571

far than that of which the laminae of the cyst are formed.
This granular matter is prolonged beyond the mass of
Echinococci into a short pedicle, common to the whole, and
by which the granulation is attached to the interior of the
hydatid cyst, as represented in !Nb. 101. In specimens
preserved in spirits, Ecliinococci of all imaginable forms and
appearances are to be met with, — differences owing to de-
composition or to mechanical injury ; and in many cases
no traces of them can be found except the hooklets or
spines, "which, like the fossil remains of animals in
geology, remain as certain indications of their source, and
not unfrequently afford the only proof we can obtain of
the true nature of the hydatid."1

The Ecliinorhynchi, or Acantlio cepliali, constitute a
group of entozoa, with respect to whose development and
life-history we are indebted to Prof. Leuckart of Giessen.
Most observers, and in particular Von Beneden and G.
"Wagner, have been disposed to assign to the Echinorhynci
a simple metamorphosis, hardly perhaps more remarkable
than that which has been shown to take place in some
other of the Nematode worms. The latter observer goes
so far even as to believe that the organization of the per-
fect animal may be discerned in the embryo. Leuckart
instituted, in 1861, a series of experiments with the ova
of EchinorhyncJius Proteus, which is found parasitic upon
the Gammarus Pulex. The ova " of E, Proteus resemble
in form and structure those of the allied species. They
are of a fusiform shape, surrounded with two mem-
branes, an external, of a more albuminous nature, and an
internal, chitinous one. When the eggs have reached the
intestine, the outer of these membranes is lost, being in
fact digested ; whilst the inner envelope remains until
ruptured by the embryo."2

Anguillulce are very small eel-like worms, of which one
species,3 Anguillula fluviatilis, is found in rain-water
amongst Gonfervce and Desmidiacece, in wet moss and
moist earth, and sometimes in the alimentary canal of the

(1) Microscopical Society's Transactions. 1st Series.

Monograph on the Anguillulidse." Lin. Soc. Trans, vol.
xxv. p. 75. The "Anguillula Accti." — Popular Ssience Review, January, 1863.

572 THE MICROSCOPE.

Limneus, the frog, fish, &c. ; another species is met with
in the ears of wheat affected with a blight termed the
" cockle ;" another, the A. glutinis, is found in sour paste;
and another, A. aceti, in stale, bad vinegar. If grains
of the affected wheat are soaked in water for an hour
or two before they are cut open, the eels will be seen in
a state of activity when placed under the microscope.
The paste-eel makes its appearance spontaneously 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 show them-
selves, to dry up, and then lay it by for stock ; if at any
time a portion of this is introduced into a little fresh
made paste, and the whole kept warm and moist for a few
days, it will be found to swarm with these curious little
worms. A small portion of paste spread over one face of
a Coddington lens is a ready way of showing them.

Planarice: a genus of the order Turbellaria. Some of the
species are very common in pools, and resemble minute
leeches ; their motion is continuous and gliding, and they
are always found crawling over the surfaces of aquatic
plants and animals, both in fresh and salt water. The
body has the flattened sole-like shape of the Trematode
Entozoa; the mouth is surrounded by a circular sucker,
this is applied to the surface of the plant from which the
animal draws its nourishment. The mouth is also fur-
nished with a long funnel-shaped proboscis, and this, even
when detached from the body, continues to swallow any-
thing presented to it.

"In imitation of the name bestowed on the trunk of
the elephant, the extensile organ serving to imbibe the
nutriment of many of the smaller animals is called a pro-
boscis, whether it simply unfolds from the root, protrudes
from a sheath, or unwinds from a regular series of volu-
tions. But in none is the designation equally strict and
appropriate as in the Planarice. There it "is absolutely the
organ of the elephant in miniature, with this exception,
that it is neither annulated nor composed of segments.
It is of surprising length, being little, if any, shorter when
fully extended than the whole animal. It seems of greater
consistency, harder, and tougher than the rest of the body,

HIRUDINID.E. 573

so as to admit insertion into decaying vegetables, and
when stretched to the utmost the root becomes an apex of
the slenderest cone."1

Planarice multiply by eggs, and by spontaneous figura-
tion, in a transverse direction, each segment becoming a
perfect animal. Professor Agassiz believes that the infu-
sorial animals, Paramcecium and Kolpoda, are nothing else
than Planarian larvae.

Hirudinidce, the Leech tribe, are usually believed to
form a link between the Annelida on the one hand, and
the Trematoda on the other; but their affinities are closer
connected with the latter than the former. Totally deprived
of the characteristic setae of the Annelida, and exhibiting
no sectional divisions, they are provided with suckers so
constantly possessed by the Trematoda, and present no
small resemblance to them in their reproductive organs.
On the other hand, in the arrangement of their nervous
system and in their vascular system, the Hirudinidce
resemble the Annelida. The head in most of these animals
is distinctly marked, and furnished with eyes, tentacles,
mouth, and teeth, and in some instances with auditory
vesicles, containing otolithes. The nervous system con-
sists of a series of ganglia running along the ventral
portion of the animal, and communicating with a central
mass or brain.

The medicinal leech puts forth strong claims to our
attention, on the ground of the services which it renders
to mankind. The whole of the family live by sucking the
blood of other animals ; and, for this purpose, the mouth
of the leech is furnished with an apparatus of horny teeth,
by which they bite through the skin. In the common
leech, three of these teeth exist, arranged in a triangular,
or rather triradiate form, a structure which accounts for
the peculiar appearance of leech-bites in the human skin.
The most interesting part of the anatomy of the leech to
microscopists is the structure of the mouth (fig. 257).
"This piece of mechanism," says Professor Rymer Jones,
" is a dilatable orifice, which would seem at first sight to
be but a simple hole. It is not so ; for we find that just

(1) Sir John Dalyell's Observations on some interesting Phenomena exhibited
by several Species of Planarice. 1814.

574 THE MICROSCOPE.

within the margin of this hole three beautiful little semi-
circular saws are situated, arranged so that their edges
meet in the centre. It is by means
of these saws that the leech makes
the incisions whence blood is to be
procured, an operation which is per-
formed in the following manner :
JSTo sooner is the sucker firmly fixed
to the skin, than the mouth becomes
slightly everted, and the edges of
the saws are thus made to press
upon the tense skin ; a sawing
movement being at the same time
given to each, whereby it is made

Fig. 25r.-Jfo«/* of Leech. gmduallv ^ pierce ^ surfaC6j a]1(j

cut its way to the small blood-vessels beneath. Nothing
could be more admirably adapted to secure the end in view
than the shape of the wound thus inflicted, the lips of which
must necessarily be drawn asunder by the very contrac-
tility of the skin itself ; and that the enormous sacculated
stomach, which fills nearly the whole body of the leech,
was designed to contain its greedily devoured meal, there
can be no reasonable question. The leech, in its native
element, could hardly hope for a supply of hot blood
as food ; and, on the other hand, its habits are most
abstemious, and it may be kept alive and healthy for
years, with no other apparent nourishment than what is
derived from pure water frequently changed ; even when
at large, minute aquatic insects and their larvae form its
usual diet."

In Clepsinidce, the body is of a leech-like form, but very
much narrowed in front, and the mouth is furnished with
a protrusile proboscis. These animals live in fresh water,
where they may often be seen creeping upon aquatic
plants. They prey upon water-snails.

Tubicola. — The worms belonging to this series of
branchiferous Annelida are all marine, and distinguished
by their invariable habit of forming a tube or case,
within which the soft parts of the animal can be en-
tirely retracted. This tube is usually attached to stones
or other submarine bodies. It is often composed of various

ANNELIDA. 575

foreign materials, such as sand, small stones, and the
debris of shells, lined internally with a smooth coating of
hardened mucus- ; in others it is of a leathery or horny
consistency ; and in some it is composed, like the shells of
Mollusca, of calcareous matter secreted by the animal.
The Tubicolce generally live in societies, winding their
tubes into a mass which often attains a considerable size :
a few are solitary in their habits. They retain their posi-
tion in their habitations by means of appendages very
similar to those of free worms, with tufts of bristles and
spines ; the latter, in the tubicular Annelids, are usually
hooked ; so that, by applying them to the walls of its
domicile, the animal is enabled to oppose a considerable
resistance to any effort to draw it out of its case. In the
best known family of the order (Sabellidce), the branchiae
are placed on the head, where they form a circle of
plumes or a tuffc of branched organs. The Serpulce form
irregularly twisted calcareous tubes, and often grow
together in large masses, when they secure themselves to
shells and similar objects j other species, Terebdla, which
build their cases of sand and
stones, appear to prefer a
life of solitude. The curious
little spiral shells seen upon
the fronds of sea-weeds, are
formed by an animal be-
longing to the family Spi-
rorbis.

If the animals be placed
in a vessel of sea-water, a
very pleasing spectacle will
soon be witnessed. The mouth
of the tube is first seen to
open, by the raising of an
exquisitely-constructed door,
and then the creature cauti-
ously protrudes the anterior F5_ 9ra . „ ,"**

i & -j. T j T Flg 258. —^ Serpula protruded from Us

part ot its body, spreading calcareous tube.

out at the same time two beautiful fan-like expansions, of a
rich purple, or scarlet colour, which float elegantly in the sur-
rounding water, and serve as branchial or breathing organs.

576 THE MICROSCOPE.

The Serpula, if withdrawn from its calcareous tube (fig.
260), is found to have the lower part of the hody com-
posed of a series of flattened rings, and entirely destitute
of limbs or other appendages. Its food is brought to its
mouth by currents created by the cilia on the branchial
tufts.

Some of the Annelids are without tubes or cells of any
sort, and simply bury their bodies in the sand about the
tidal mark. The Arenicola, lob-worm, is a well-known
specimen of the class ; its body is so transparent that the
circulating fluids can be distinctly seen under a moderate
magnifying power. Two kinds of fluids flow through the
vessels, one nearly colourless, the other red ; the vessels
through which the latter circulate . are looked upon as
blood-vessels. A few also have not only no tubes but are
free and active swimmers. Drs. Carpenter and Claparede,
during a sojourn at Lamlash Bay, Arran, met with an
interesting member of this class of Annelids, the Tomopteris
onisciformis. It possesses a remarkable pair of "frontal
horns," projecting laterally from the most anterior part of
head, as well as pair of greatly elongated appendages,
designated by those observers as " the second antennce," in
contradistinction to another and a shorter pair of appen-
dages situated just in advance of them, the first pair
being characteristic of the larval, and the second of the
adult state of the annelid.

" The head also bears on its dorsal surface a pair of
ciliated epaulettes, which extend over the edges of the
bilobed nervous ganglion. These, at a certain stage of
development, are fringed with long cilia both at their
margins and their base ; but as the cilia are only occa-
sionally to be seen in activity, they may escape the atten-
tion of the observer. Cilia are likewise distinguishable on
certain parts of that innermost layer of the general integu-
ment which forms the external boundary of the peri-
visceral space, and by their agency a special movement is
imparted to the corpuscles of the fluid contained in the
cavity."

The development of the caudal prolongation is peculiar,
and this as well as other points of interest are given
in the Lin. Soc. Trans, vols. xxii. and xxiii. pp. 335

INSECTS' EGGS, ETC.

ANGUILLUL.E 677

and 59. Dr. Carpenter believes that this creature "ia
a degraded form of the annelidan type — its nearest affi-
nities being (as already pointed out by Drs. Leuckart
and Pagenstecher) the chsetopod or setigerous Annelids.
Every part of the characteristic organization of the type
is here reduced to the extreme of simplicity. The alimen-
tary canal passes in a straight line from one extremity of
the body to the other, without either sacculations or glan-
dular appendages. The nutritive fluid which transudes
through its walls, and which finds its way into the peri-
visceral cavity, is distributed throughout the body solely
by means of extensions of that cavity, through which it is
propelled in part by the agency of cilia that clothe its walls.
This fluid is obviously the homologue of the blood of higher
animals, that we cannot but regard the existence of the type
of structure before us (the wonderful transparency of the
body not permitting the slightest doubt as to the absence
of anything resembling a dorsal vessel) as affording a
further confirmation of the view of the so-called circulat-
ing apparatus of the higher Annelida, which regards their
perivisceral cavity and its extensions as representing the
proper sanguiferous system, and which looks upon the
system of vessels containing coloured fluid as a special
arrangement having reference rather to the respiratory
functions.1 The extreme tenuity of the walls of the body
and its appendages renders it unnecessary that any special
provision should be made for the aeration of the nutritive
fluid ; and we accordingly find neither branchiae nor any
trace of what is commonly described as the- sanguiferous
system in Annelida. The centres of the nervous system
would seem to consist solely of the cephalic ganglia — the
absence of the ordinary longitudinal series being apparently
related to the very incomplete segmentation of the body,
and constituting a link of affinity to the Turbellarian
Worms. The ocelli present a condition of extreme sim-
plicity, yet the duplication of the corneale in each of them
marks that tendency to repetition which so peculiarly
distinguishes the Articulate type. It is, however, the
extreme simplicity of its generative apparatus that con-

(1) See Prof. Huxley's Lectures in Medical Times and Gazette, July 12 and 26»
P P

578 THE MICROSCOPE.

stitutes one of the chief points of interest in the organiza-
tion of Tomopteris."

Not solely in this class, but in that of the Annelida
generally, does much interest attach to the developmental
period. Most of them come forth from the egg in a con-
dition so closely resembling the cililated gemmules of
polypes, that competent observers have been known to
mistake them for animals of a lower class ; fortunately a
few hours' careful watching is sufficient to dispel the
illusory belief, and the embryonic globular shapeless
mass is seen soon to change its form ; segmentation takes
place, and the various internal organs become more and
more developed ; eye spots appear, and the young animal
assumes the likeness of its parent.

The Actinotrocha, even in the adult state, in many parti-
culars resembles the "bipinnarian larva of the star-fish."
Its long body is surmounted by a head, or mouth, around
which is placed a number of ciliated ventacula : they are
not only employed for feeding purposes, but also for
enabling it to swim about ; and in this particular, accord-
ing to Dr. A. Schneider and other competent authorities,
it is quite remarkable.1 Dr. Carpenter tells us that he
lias captured these free-swimming Annelids among other
marine animals by the careful use of the " stick-net."

^l> See Ann. Nat. Hist. vol. ix. 1862, p. 486.

CHAPTER IV.

SUB-KINGDOM ARTICULATA.— INSECTA.— ARACHNIDA.

MONG the numerous objects
which engage the attention
of the microscopist, the in-
sect tribes in general are far
l from being the least
interesting ; their
curious and won-
derful economy is a subject
well deserving especial in-
vestigation. Earth, air, and
water, teem with the
various tribes of insects,
many of which are invisible to the unassisted eye, but
presenting, when viewed with the microscope, the most
beautiful mechanism in their frame-work, the most perfect
regularity in their laws of being, and exhibiting the same
wondrous adaptation of parts to the creature's wants,
which, throughout creation, furnishes traces of the love
and wisdom that so strongly mark the works of God.1

" I cannot," says the learned Swammerdam, " after an
attentive examination of the nature and structure of both
the least and largest of the great family of nature, but
allow the less an equal, perhaps a superior degree of
dignity. Whoever duly considers the conduct and instinct
of the one with the manners and actions of the other,
must acknowledge all are under the direction and control
of a superior and supreme Intelligence ; which, as in the

(1) We commend to the reader the excellent Introduction to Entomology, by
Kirby and Spence. Longmans. Art. "Insec to," Cyclop. Ant. and Physio.

pp 2

580 THE MICROSCOPE.

largest it extends beyond the limits of our comprehension,
escapes our researches in the smallest. If, while we dis-
sect with care the larger animals, we are filled with wonder
at the elegant disposition of their limbs, the inimitable
order of their muscles, and the regular direction of their
veins, arteries, and nerves, to what a height is our astonish-
ment raised when we discover all these parts arranged in
the least of them in the same regular manner ! How is
it possible but that we must stand amazed, when we reflect
that those little animals, whose bodies are smaller than the
point of the dissecting knife, have muscles, veins, arteries,
and every other part common to large animals ! Crea-
tures so very diminutive that our hands are not delicate
enough to manage, nor our eyes sufficiently acute to see
them."

The Articulate sub-kingdom, Insect a, is divided and
sub-.divided into orders, families, genera, species, as for
example : —

Lepidoptera ; typical form, Butterfly, Moth.
Dipteria;1 typical form, Fly, Gnat, &c.
Aptera ; typical form, Flea, Louse, Springtail.
Coleoptera ; typical form, Beetle, Water Beetle, &c.
Orthoptera ; typical form, Locust, Grasshopper.
Neuroptera ; typical form, Dragon-fly, May-fly.
Hymenoptera ; typical form, Bee, Wasp, Ant.
Homoptera; typical form, Plant-louse (Aphis), Lan-
tern-fly.

Hemiptera ; typical form, Water-scorpion, Water-boat-
man.

Arachnida; typical form, Spider, Scorpion, &c. The
Acarina belong to this genus, family Acarea, well known
as "Mites "and "Ticks."

Insects are characterised by a simple breathing ap-
paratus ; by the division of the body into distinct regions.
or segments ; when three, the middle one, the thorax,
bears three pairs of jointed legs, and usually two pairs
of wings • and by the possession of a single pair of jointed

(1) Comprised within the order Diptera, or two-winged flies, are several
genera having no wings, the apterous and suctorial Pulex, and the apterous ami
pupiparous Episboscidce: among the latter, we have the winged Hippobosca, or
horse-fly, and some others.

1NSECTA. 581

antenim The metamorphoses which all undergo, before
they arrive at the perfect state and are able to fulfil all
the ends of their existence, are more curious and striking
than in any other department of nature ; and in the
greater number of species the same individual differs so
materially at the several periods of life, both in its in-
ternal and external conformation, in its habits, locality,
and kind of food, that it becomes one of the most inter-
esting investigations of the physiologist to ascertain the
manner in which these changes are effected, to trace the
successive steps by which that despised and almost un-
noticed larva that but a few days before lay grovelling in
the earth, with an internal organization fitted only for
the reception and assimilation of the crudest vegetable
matter, has had the whole of its external form so com-
pletely changed, as now to have become an object of
admiration and delight, and able to "spurn the dull
earth," and wing its way into the wide expanse of air,
with internal parts adapted only for the reception of the
purest and most concentrated aliment, which is now ren-
dered absolutely necessary for its support, and the reno-
vation increased energies demand.

The greater number of insects undergo a complete series
of changes. They are for the most part oviparous, and
their eggs assume a variety of forms, colour, &c. as
will be seen in Plate VI. On first leaving the egg, they
assume a more or less worm-like appearance, known as
larva, maggot, or caterpillar. The next stage is that of
the nympha, pupa, or chrysalis ; this is succeeded by that
of the perfect insect or imago. In some insects the
changes are incomplete; the body, legs, and antennae
are nearly similar, but wings are wanting. In others the
pupa continues active, is of a large size, and acquires
rudimentary wings ; and some are without material altera-
tion of "structure, the change consisting in what is termed
" ecdysis," a casting off, or moulting only.

The heads of insects present many points of interest;
Plate VI. No. 134, shows the head of the Tortoise butter-
fly in profile, with large compound eye, palpi, and spiral
tongue. JN"o. 131 is a portion of the head with lancets,
&c. of the Glossina morsitans, Tsetse-fly of Africa. In

582

THE MICROSCOPE.

the mouths and tongues of insects, the most admirable art
and wisdom are displayed ; and their diversity of form is
almost as great as the variety of species. The mouth is
usually placed in the fore part of the head, extending
somewhat downwards. Many have the mouth armed with
strong jaws, or mandibles, provided with muscles of great

.Fig. 259. — Under-surface of a Wasp's tongue, Feelers, &c. (Within the circle the
same is seen life-size.)

power, with which they bruise and tear their food, answer-
ing to the teeth of the higher animals ; and in their
various shapes and modifications serving as knives, scissors,
augers, files, saws, trowels, pincers, or other tools, accord-
ing to the requirements of each insect.

The tongue is generally a compact instrument, used
principally to extract the juices on which the insect feeds,
varying greatly in its length in the different species. . It is
capable of being extended or contracted at the insect's

INSECTA. 583.

pleasure ; sometimes it is dexterously rolled up in a taper and
spiral form, as in the Butterfly ; tubular and fleshy, as in the
Wasp. In fig. 259, the under lip of the Wasp is represented
with its brush on either side ; above which are two jointed
feelers (palpi labiates), the use of which is probably for the
purpose of making an examination of the food before it is

Fig. 200.— Eye of Fly (magnified 150 diameters.)

taken into the mouth, or that of cleaning the tongue. Near
these feelers the antennae or horns are placed, as curious in
form as they are delicate in structure. The antennae of the
male generally differ from those of the female : some writers
believe these are organs of smell or hearing ; others that
they are solely intended to add to the perfection of touch
or feeling, increasing their sensibility to the least motion
or disturbance. Apart from their use, they are the most
interesting and distinguishing characteristics of insects,
and appear to be often employed for the purpose of ex-
amining every object they alight upon.

584 THE MICROSCOPE.

The structure of the eye is in all creatures a most
admirable piece of mechanism, in none more so than in
those of the insect tribe. The eyes differ in each species ;
varying in number, situation,
figure, simplicity of con-
struction, and in colour. Fig.
260 represents a portion of
the eye of the common Fly,
drawn by the light of the sun
upon a prepared photographic
surface of wood ready for the
engraver. Fig. 261 repre-
sents a side view of the eye
when thrown down, showing *'ig-

the compound nature of the organ, with its series of
cylindrical tubes ; better seen in fig. 262.

" On examining the head of an insect, we find a couple
of protuberances, more or less prominent, and situated
symmetrically one on each side. Their outline at the base
is for the most part oval, elliptical, circular, or truncated ;
while their curved surfaces are spherical, spheroidal, or
pyriform. These horny, round, and naked parts seem to
be the cornege of the eyes of insects ; at least, they are
with propriety so termed, from the analogy they bear to
those transparent tunics in the higher classes of animals.
They differ, however, from thege ; for, when viewed by the
microscope, they display a large number of hexagonal
facets, which constitute the medium for the admission of
light to as many simple eyes. Under an ordinary lens,
and by reflected light, the entire surface of one cornea
presents a beautiful reticulation, like very fine wire gauze,
with a minute papilla, or at least a slight elevation, in the
centre of each mesh. These are resolved, however, by the
aid of a compound microscope, and with a power of from
80 to 100 diameters, into an almost incredible number
(when compared with the space they occupy) of minute,
regular, geometrical hexagons, well defined, and capable of
being computed with tolerable ease, their exceeding minute-
ness being taken into consideration. When viewed in this
way, the entire surface bears a resemblance to that which
might easily and artificially be produced by straining a

INSECTS EYES.

585

portion of Brussels lace with hexagonal meshes over a
small hemisphere of ground glass. That this gives a toler-
ably fair idea of the intricate carving on the exterior may
be further shown from the fact, that delicate and beautiful
oasts in collodion can be procured from the surface, by
giving it three or four coats with a camel-hair pencil.
When dry it peels off in thin flakes, upon which the
impressions are left so distinct, that their hexagonal form
can be discovered with a Coddington lens. This experi-
ment will be found useful in examining the configuration
of the facets of the hard and unyielding eyes of many of
the Coleoptera, in which the reticulations become either
distorted by corrugation, or broken by the pressure re-
quired to flatten them. It will be observed also, that by
this method perfect casts can be obtained without any dis-
section whatever ; and
that these artificial
exuviae — for such they
really are — become
available for micro-
scopic investigations,
obviating the necessity
for a more lengthened
or laborious prepara-
tion. The dissection
of the cornea of an
insect's eye is by no
means easy. I have A)
used generally a small
pair of scissors, with
well - adjusted and
pointed extremities, and a camel-hair pencil, having a por-
tion of the hairs cut off at the end, which is thereby flat-
tened. The extremity of the cedar handle should be cut
to a fine point, so that the brush may be the more easily
revolved between the finger and thumb ; and the coloured
pigment on the interior may be scrubbed off by this
simple process. A brush thus prepared, and slightly
moistened, forms by far the best forceps for manipulating
these objects preparatory to mounting ; as, if only touched
with any hard-pointed substance, they will often spring
from the table and be lost.

Fig. 262.

a section of the eye of Melolontha wilgans,
Cockchafer. B, a portion more highly mag-
nified, showing the facets of the cornea, and
its transparent pyramids, surrounded with
pigment. At A they meet, and form the optic
nerve.

586

THE MICROSCOPE.

"Each hexagon forms the slightly horny case of an
eye.1 Their margins of separation are often thickly set
with hair, as in the Bee ; in other instances naked, as in
the Dragon-fly, House-fly, &c. The number of these lenses
has been calculated by various authors, and their multi-
tude, cannot fail to excite astonish-
ment. Hooke counted 7,000 in the
eye of a House-fly; Leeuwenhoek
more than 12,000 in that of a
Dragon-fly ; and Geoffry cites a
calculation, according to which
there are 34,650 of such facets in
the eye of a Butterfly." 2

The trunk is situated between
the head and the abdomen ; the legs
and wings are inserted into it. The
thorax is the upper part of the
trunk ; the sides and back of which
are usually armed with points or
hairs. The abdomen forms the
posterior part of the body, and is
generally made up of rings or seg-
ments, by means of which the
jectaboutthenaturaisize.) insect lengthens or shortens itself.
Kunning along the sides of the abdomen are the spiracles,
or breathing apertures, fig. 263, communicating directly
with the internal respiratory organs. Pure air being thus
freely admitted to every part, and the circulating fluids

(1) "Each of the eyelets, or 'ocelli,' which aggregated constitute the com-
pound eye of a Bee, is itself a perfect instrument of vision, consisting of two
remarkably formed lenses, namely, an outer • corneal' lens and an inner or
'conical' lens. The 'corneal' lens is a hexahedral or six-sided prism, and it is
the assemblage of these prisms that forms what is called the ' cornea ' of the
compound eye. This ' cornea ' may easily be peeled off, and if the whole or a
portion be placed under the microscope, it will be seen that each corneal lens is
not a simple lens but a double convex compound one, composed of two plano-
convex lenses of different densities or refracting powers, joined together by their
plane surfaces. The effect of this arrangement is, that if there should be any
aberration of the rays of light during their passage through one portion of the
lens, it is rectified in its transit through the other. It appears questionable
whether the normal shape of these lenses is hexagonal, or whether this form is
not rather a necessity of growth, &c., that is, that they are normally round, but
assume the hexagonal shape during the process of development in consequence
of their agglomeration." J. Samuelson and B. Hicks, ''On the Eye of the
Bee," Journ. Micros. Soc. vol. i. p. 51.

(2) "Remarks on the Cornea of the Eye in Insects/' by John Gorham,
M.R.C.S. Journ. Micros. Science, p. 76, 1853.

INSECTS FEET.

587

kept exposed to the vivifying influence of the atmosphere,
the necessity for more complicated and cumbersome
breathing organs is at once obviated ; and the whole body
is at the same time rendered lighter. The spiracles are
usually nine or ten in num-
ber, and consist of a horny
ring, of an oval form. The
air-tubes are exquisitely
composed of two thin
membranes, between which
a delicate elastic thread or
spiral fibre, is interposed,
forming a cylindrical pipe,
and keeping the tube always
in a distended condition ;
thus wonderfully preserving
the sides from collapse or
pressure in their passage
through the air, which
otherwise might occasion
suffocation. Fig. 264 re-
presents the beautiful me-
chanism of a portion of the tracheae of Hydropilus,
showing the peculiar arrangement of the spiral tubes,
which give it elasticity and strength.

The legs of insects are extremely curious and interest-
ing ; each leg consists of -several horny cylinders, connected
by joints and ligaments, inclosing within them sets of
powerful muscles, whereby their movements are effected.

Feet of Flies, &c. — " The tarsus, or foot of the Fly, con-
sists of a deeply bifid, membranous structure, pulvillus ;
anterior to the attachment of this part to the fifth tarsal
joint, or the upper surface, are seated two claws, or * tarsal
ungues,' which are freely movable in every direction.
These ungues differ greatly in their outline, size, and rela-
tive development to the tarsi, and to the bodies of the
insects possessing them, and in their covering ; most are
naked over their entire surface, having however a hex-
agonal network at their bases, which indicates a rudimen-
tary condition of minute scale-like hairs, such as are common
on some part of the integument of all insects. Flexor and

ig. 264. — Magnified portions of the
trachea of the ffydrophilus, show-
ing spiral tubes on 3. their arrange-
ment.

588

THE MICROSCOPE.

extensor muscles are attached to both ungues and the
flaps ; the flaps, corrugated or arranged on the ridge and
furrow plan, are in some cases perfectly smooth on
their superior surface, in others this surface is covered
with minute scale-like hairs. The thickness of the flaps
on the Blow-fly does not exceed the 1 -2000th of an inch
at the margin ; thence they increase in thickness towards
the point of attachment. Projecting from their inferior
surface are the organs which have been termed ' hairs/
' hair-like appendages/ ' trumpet-shaped hairs/ &c. That

these are the immediate
agents in holding is now
admitted by most obser-
vers, and it will be con-
venient to term them
'"tenent" hairs/ in allu-
sion to their office. Plate
VI. No. 140, the under
surface of left forefoot of
Musca Vomitoria, is shown
with tenent-hairs ; a and b
are more magnified hairs,
a from below, 6 from the

Oside. No. 142 is the left
forefoot of Amara commu-
nis, showing under surface
and form of tenent appen-
dages, one of which is seen
more magnified at a. No. 143, under surface of left forefoot,
Ephydra riparia. This fly is met with sometimes in im-
mense numbers on the water in salt marshes ; it has no
power of climbing on glass, which is explained by the
structure of the tenent-hairs : the central tactile organ is
also very peculiar, the whole acting as a float, one to each
foot, to enable the fly to rest on the surface of the water ; a
is one of the external hairs. No. 1 35, under surface of left
forefoot of Cassida viridis (Tortoise-beetle), showing the
bifurcate tenent appendages, one of which is given at a
more magnified. These, in the ground-beetles, are met
with only in the males, and are used for sexual purposes.
The delicacy of the structure of these hairs in the fly, the

object natural size.)

INSECTS' HAIRS, 589

Tbend near their extremity, in each of which supervenes an
elastic membranous expansion, and from which a very
minute quantity of a clear, transparent fluid is emitted
when the fly is actively moving, explains its capacity for
clinging to polished surfaces. It simply remains to add
that the tubular nature of the shaft of the tenent-hairs on
the foot of this insect has been surmised, although its
minute size and homogeneity hardly admits of actual con-
firmation. At the root of the pulvillus, or its under sur-
face, is a process, which in some instances is short and
thick, in others long and curved, and tapering to its ex-
tremity (Scatophaga), setose (Empis), plumose (Hippobos-
cidce), or, in one remarkable example (Ephydra), so closely
resembling in its appearance the very rudimentary pul-
villus with which it is associated. Just at the base of the
fifth tarsal joint, on its under surface, there is present, in
EristaliSj a pair of short, very slightly curved hairs, which
point almost directly downwards. It became desirable to
endeavour to ascertain how far the structure of these
tenent-hairs agrees with that of true hairs, on which some
valuable critical observations were made last year by Dr.
Hicks.1

" Tenent-hairs are usually present in some modification
or other, that it is really difficult to name a beetle which
has not some form of them ; the only one I yet know that
seems to me really to possess nothing of the kind is a
species of Helops, which lives on sandy heaths ; I suppose
the dense cushion of hairs on the tarsi here to be for the
protection, simply, of the joints to which they are attached.
I have detected them on the tarsal joints of species of
jEphydra, and on the first basal tarsal joint of the Drone
of the Hive-bee. A very rudimentary form of tenent-hairs
is present on the under surface of some of the Tree-bugs
(Pentatomidce), which have in addition a large, deeply-cleft
organ at the extremity of the tarsus, which appears to be
a true sucker.

" When walking on a rough surface, the foot represents
that of a Coleopterous insect without any tenent appen-
dages. The ungues are always attached to the last joint of

(1) Sec Trans. Linn. Soc. vol. xxiii. p. 143.

590 THE MICROSCOPE.

an insect's tarsus. They are not attached to the fifth tarsal
joint of a Dipterous insect ; neither are they attached to
the fifth tarsal joint of a Hymenopterous insect, but to the
terminal sucker, which again, in this great order, is a
sixth tarsal joint, membranous, flexible, elastic in the
highest degree, retractile to almost its fullest extent within
the fifth tarsal joint — a joint modified to an extraordinary
degree for special purposes.

" The plantula of Lucanus, with its pair of minute claws,
at once occurred as a case strictly in point. The ungues
are hairs modified for special purposes ; and they have the
structure of true hairs. The sustentacula of Epeira, the
analogous structures on the entire under surface of the
last tarsal joints in Pholcus, the condition of the parts in
the hind limbs of Notonecta, in both its mature and earlier
conditions, as well as in Sarcoptes, Psoroptes, and some
other Acari, all contribute to the proof of this fact. The
various orders of insects have, for the most part, each their
own type of foot. Thus there is the Coleopterous type, the
Hymenopterous type, the Dipterous type, the Homop-
terous type, &c. ; and so very distinctive, that in critical
instances they will sometimes serve at once to show
to which order an insect should be referred. Thus,
amongst all the Diptera, I have as yet met with but one
subdivision which presents an exception to the structure
described. This exception is furnished by the Tipulidce,
which have the Hymenopterous foot. With hardly an
exception, then, I believe the form of foot described will
be found universal amongst the Diptera, and will be found
amongst the members of this order alone. It may be
desirable to add a few words on the best plan of conduct-
ing observations on these parts. Their action should be
studied in Iwing insects under the influence of chloroform,
careful notes taken of appearances, and accurate drawings
made. It is of the greatest advantage to preserve carefully
all the parts examined : for this purpose Deane's medium
or glycerine jelly suits very well; some of the delicate
preparations, however, can only be kept satisfactorily in a
solution of chloride of zinc. The old plan of soaking in
caustic potash, crushing, washing, putting into spirits of
wine (or pressing and drying first), and then into turpen-

INSECTS TONGUES.

591

tine, and lastly into Canada balsam, is perfectly useless,
except in rare instances where points connected with the
structure of the integument have to be made out. Of
course, the parts should be viewed from above, from below,
and in profile, in order to gain exact ideas of their rela-
tions. The binocular microscope, however, promises to
diminish vastly the difficulties which had until recently
to be encountered, as by its use the parts may be clearly
viewed just as they are, without preparation of any kind." 1

Fig. 266.

1, Foot and leg of OpMon. 2, Foot and leg of Flesh-fly. 3, Foot and leg of
Dfrone-fly. (The small circles inclose objects about natural size.)

Fig. 267 represents the tongue and piercing apparatus
of the Drone-fly. This remarkable compound structure,
together with the admirable form and exquisite beauty of
the apparatus, must strike the mind with wonder and
delight, and lead the observer to reflect on the weakness
and impotence of all human mechanism, when compared
with the skill and inimitable finish displayed in the object
before us. The harder structures which surround it have

(1) Tuffen West, Trans. Linn. Soc. vol. xxiii. p. 393.

592

THE MICROSCOPE.

Pig. 26?. — Tongue and Piercing Apparatus of Drone-fly.

INSECTS' TONGUES. 593

been removed for the purpose of bringing the several parts
into view, and which consist of two palpi, or feelers,
covered with short hairs, and united to the head by a set
of muscles ; these feelers appear to be in frequent requisi-
tion for guarding the other organs from external injury.
The two lancets seen above them are formed somewhat like
a cutlass, or the dissecting knife of the anatomist, and are
purposely intended for making a deep and sharp cut, also
for cutting vertically with a sweeping stroke. The other
and larger cutting instrument appears to be intended to
enlarge the wound, if necessary; or it may be for the
purpose of irritating and exciting the part around, thereby
increasing the flow of blood to the part, being jagged or
toothed at the extremity. The larger apparatus, with its
three peculiar prongs, or teeth, is tubular, to permit of the
blood passing through it and thence to the stomach ; this
is inclosed in a case which entirely covers it. The spongy
tongue itself projects some distance beyond this apparatus,
and is composed of a beautiful network of soft muscular
spiral fibres, forming a series of absorbent tubes; and these
are moved by powerful muscles and ligaments, the retrac-
tile character of which may be seen in the drawing of the
proboscis of the Fly, fig. 268 : by the aid of two booklets
placed in each side, he is enabled to draw in and dart
out the tongue with wonderful rapidity. Another set of
muscles is seen at the root of the whole apparatus.

" In the organization of the mouth of various insects we
have a modification of form, to adapt them to a different
mode of use ; as in the Muscidce, or common House-flies.
When the food is easily accessible, and almost entirely
liquid, the parts of the mouth are soft and fleshy, and
simply adapted to form a sucking tube, which in a state of
rest is closely folded up in a deep fissure, on the under
surface of the head. The proboscis at its base appears to
be formed by the union of the lacinia above and the labium
below, the latter forming the chief portion of the organ,
which-is tenanted by dilated muscular lips. J n the Tabanus
these are exceedingly large and broad, and are widely ex-
panded, to encompass the wound made by the insect with
its lancet-shaped mandibles in the skin of the animal it
attacks. On their outer surface they are fleshy and
Q Q

594 THE MICROSCOPE.

muscular, to fit them to be employed as prehensile organs ;
while on their inner they are more soft and delicate, but
thickly covered with rows of very minute stiff hairs,
directed a little backwards, and arranged closely together.
There are very many rows of these hairs on each of the
lips ; and from their being arranged in a similar direction,
they are easily employed by the insect in scraping or tear-
ing delicate surfaces. It is by means of this curious
structure that the busy House-fly often occasions much
mischief to the covers of our books, by scraping off the
white of egg and sugar varnish used to give them the
polish, leaving traces of its depredations in the soiled and
spotted appearance which it occasions on them. It is by
means of these also that it teases us in the heat of summer,
when it alights on the hand or face, to sip the perspiration
as it exudes from and is condensed upon the skin. The
fluid ascends the proboscis, partly by a sucking action,
assisted by the muscles of the lips themselves, which are
of a spiral form, arranged around a highly elastic, ten-
dinous, and ligamentous structure, with other retractile
additions for rapidity and facility of motion." l

The beautiful form of the spiral structure of the tongue
should be viewed under a magnifying power of 250 dia-
meters, or a quarter-inch object-glass.

These insects are of great service in the economy of
nature, their province being the consumption of decaying
animal matter, which is found about in quantities so small
as to be imperceptible to most people, and is not removable
by ordinary means, even in the best-kept apartments, during
hot weather. It was asserted by Linnaeus, that three flies
would consume a dead horse as quickly as a lion. This
was, of course, said with reference to the offspring of
such three flies ; and it is possible the assertion may be
correct, since the young begin to eat as soon as they are
born. A single Blow-fly has been known to produce twenty
thousand living larvas (one of which is represented in Plate
VI. !No. 141), and in twenty-four hours each has increased
its own weight above two hundred times ; in five days it
attains to its full size. When the larvae are of full size,

(1) Mr. G. Newport, Cyclopaedia of Anatomy and Physiology.

INSECTA

595

they change into the pupa state, and remain in that state
a few days ; they then become flies, soon produce thou-

Fig. 268. — Proboscis of House-fly. — Drawn from a preparation by Topping. (Tin

small circle incloses the same about natural size.)

Q Q 2

596 THE MICROSCOPE.

sands of eggs, larvae, and flies, and this is repeated again
and again until the whole brood is destroyed by winter's
cold.1

The " Tsetse" fly of tropical Africa (Glossina morsitans):
the mouth, proboscis, and piercing apparatus of one, viewed
from the under-side, is represented in Plate VI. ^N"o. 131.
The biting apparatus consists of four parts, of which two
are lateral setose palpi ; if a horny case for the protection
of the proboscis and its contained style can be so called.
The palpi, although arising from two roots, when joined
together, and accurately embracing the proboscis, as they
will do when the fly is at rest, appear as one only ; but
when the insect is in the act of piercing or sucking, they
divide, and are thrown directly upwards. The palpi are
furnished on the outer, or convex sides, with long and
.sharply pointed, dark-brown setae or hairs; while the
inner or concave sides which are brought in contact with
the proboscis are perfectly smooth and fleshy. Three cir-
cular openings seem to indicate the tubular character of
what in the common fly is a fleshy, expanded, and highly-
developed muscular proboscis : in the Glossina it is a
straight, horny-looking, red-coloured bristle, the apex of
which is slightly dilated and rounded, and apparently
barbed, while it expands a little towards the base, and
there dilates into a large-sized fleshy bag, or muscular sac,
filled with a red-coloured fluid. The proboscis is grooved
on the under-side for the purpose of receiving a slender
glassy style, acutely pointed, and equal to it in length.
The style, nicely adapted to the groove, and taking its
rise from the poison gland, is the penetrating instrument.
A series of long and thin muscular bands embrace this
gland, and their tendinous insertions are so arranged as to
bring considerable force to bear upon its contents. Phy-
siological science has made us familiar with the fact, that

(1) Dead flies may be constantly observed, about autumn, surrounded by a
sort of halo, which, upon examination, is found to consist of the spores of a
fungus. The abdomen is much distended, and the rings composing it are
separated from each other, the intervals being occupied by white prominent
xones, constituted of a fungoid growth proceeding from the interior of the
body. Further examination will show that the whole of the contents or the
body of the fly have been consumed by the parasitic growth, and that nothing
remains but an empty shell, lined with a thin felt-like layer composed of the
interlaced mycelia of the innumerable fungi.— See Dr. F. Cohn's observation
upon the parasite in vol. v. p. 154, Jon^n. Micros. Sci. 1857.

WINGS OF INSECTS. 597

all fluid poisons are enormously increased in their power
for good or for evil, when injected beneath the skin ; this
knowledge prepares us to understand how it is that a drop
from the poison gland of that wonderful little fly is suffi-
ciently potent and virulent to destroy a large animal in
a few minutes. Dr. Livingstone tells us that on one
occasion he lost forty-three oxen in as many minutes,
" when not more than a score of the ' Tsetse' flies could
be seen." The tongue is neither large nor well developed,
but this is in a measure balanced by the mouth and lips ;
the latter are muscular, and capable of affording great
assistance while the fly is in the act of sucking the blood
of its victim. The wings are long and powerful ; the legs
strong and muscular ; the feet provided with the usual
appendages, terminating in a pair of strong claws of a
rather large size.

The wings of insects exhibit variety in form and struc-
ture, as well as beauty of colouring ; the art with which
they are connected to the body, the curious manner in
which some are folded up, the fine articulations provided
for this purpose, with the various ramifications by which
the nourishing fluids are circulated and the wings strength-
ened, all afford a fund of rational investigation highly
entertaining, and exhibiting, when examined under the
microscope, beautiful and wonderful design in their forma-
tion. Take the Libellulidce (Dragon-flies) as an example,
whose wings, with their horny framework, are as elegant,
delicate, and as transparent as gauze; often ornamented
with coloured spots, which, at different inclinations of the
sun's rays, show all the tints of the rainbow. One species
(Calepteryx virgo) will be seen sailing for hours over a piece
of water, all the while chasing, capturing, and devouring
the numerous insects that cross its course ; at another time
driving away competitors, or making its escape from an
enemy, without ever seeming tired or inclined to alight.

In fine weather, female Dragon-flies are seen to deposit
their eggs upon the water, making a strange noise, as
though they were beating the water; the cluster of eggs
looks like a floating bunch of small grapes. The larva*
when hatched, live in the water ; and it is scarcely pos-
sible to fancy more strange-looking creatures. They are

598 THE MICROSCOPE.

short and comparatively thick, with movements heavy and
clumsy, and after shedding their skins become pupse : still
continuing to live in the water. The pupse differ from
the larvae principally in having four small scales on their
sides ; these conceal their future wings. While the Dragon-
fly continues in its aquatic state, both as larva and pupa,
it devours all the insects it can entrap ; and as it only
moves slowly, it is furnished with a very curious apparatus
near its head, which it projects at pleasure, and uses as
a trap. This apparatus consists of a pair of very large,
jointed, movable jaws, which the insect keeps closely
folded over its head, like a large mask, till it sees its
prey; when it does, it creeps softly along till it is suffi-
ciently near ; it then darts out those long, arm-like jaws,
and suddenly seizing its prey, conveys it to its mouth.
When the Dragon-fly is about to emerge from its pupa-
case, it places itself on the brink of the pond, or on the
leaf of some water-plant sufficiently strong to bear its
weight, and there divests itself of its pupa-case. When the
perfect insect first appears, it has two very small wings ;
these gradually increase, and in a short time two other
wings appear. As soon as the wings are fully expanded,
and have attained their beautiful gauze-like texture, the
Dragon-fly begins to dart about, and then commences its
work of destruction.

Equally rapid, exactly steered, and unwearied in its
flight is the Gnat. The wings of a Gnat have been calcu-
lated, during its flight, to vibrate 3,000 times in a minute ;
these wonderful wings are covered on surface and edge
with a fine down or hair. The alternations of bright sun-
shine and rain, so commonly seen in March, are extremely
favourable to the appearance of Gnats. The first that
appear are called Winter Midges (Trichocera hy emails). As
the spring advances, these Midges are succeeded by others
somewhat different ; and as the weather becomes warmer,
the true Gnats appear. The sting of the Gnat (Culex
pipiens) is well known ; although the insects themselves,
so very rapid in their movements, are so much dreaded
that very few people care to examine the delicacy and
elegance of their forms. The sting is very curiously con-
trived (see fig. 269), and inclosed in a sheath, folds up

STINGS OF INSECTS.

599

after one or more of the six lancets have pierced the flesh ;
it will inflict a severe though minute wound, the pain of
which is increased by an acrid liquid injected into it
through a curiously-formed proboscis ; this latter is covered
over with feathers or scales. A magnified view of one of
these feathers is seen at No. 3. Another scale from a

Fig. 269.

. Head of Culex pipiens, Female Gnat, detached from the body. 2, Wing.
3, A Scale from the Proboscis. 4, Proboscis and Lancets. The reticulation
on each side of the head shows the space occupied by the eyes. The feather
or scale from proboscis is magnified 250 diameters

600 THE MICROSCOPE.

Gnat's wing is magnified 500 diameters, fig. 273, No. 7.
The proboscis is protected on either side by antennae, or
feelers.

The metamorphosis of the larva of Corethra plumi-
cornis, one of the Gnat tribe, has been carefully in<
vestigated by Professor Bymer Jones, F.RS.1 This
competent observer brings out many points of interest ;
one in particular deserves notice, namely, the use of
the four remarkable-looking jet-black bodies situated
in the body of the larva, two of which are placed in
the thoracic region, and two near the centre of the pos-
terior half of the body. These have hitherto puzzled all
observers, but at length receive elucidation at the hands of
Professor Jones, who had the good fortune to witness the
metamorphosis. In form these bodies are more or less
kidney-shaped, and to all appearance completely isolated
in the body. Upon crushing the insect beneath the com-
pressorum, they are found to b« filled with air, and by their
means the creature is enabled to rise and sink at pleasure.
They are composed of a series of small vesicles, each of
which has several coats : of these the outermost, when feebly
magnified, seems of a uniform hue of black, but under a
higher power is seen to be made up of many pigment cells,
so as to give the organ a reticulated appearance ; and it is
only when this black pigment has been removed, together
with a dull opaque membrane whereon the black patches
rest, that the real air-sac is displayed. When thus denuded,
the true walls of the air-sac appear to be composed of
a dense membrane, possessing great refractive power, the
effect of which upon transmitted light is extraordinary.
When highly magnified, it is found to be entirely com-
posed of numerous coils of a delicate fibre,., similar to that
which maintains the permeability of the trachea of ordi-
nary insects, arranged in several superimposed layers, and
having the appearance of being closed in on all sides. It is
not until the larva thus constituted has arrived at its full
size that the appearances described become complicated by
intermixture with organs belonging to the pupa condition
of the insect. At this period, however, the rudiments of

(1) See Trans. Micros. Soc. Oct. 1867, "On the Structure and Metamorphosis
of the larva of Corethra plumieornis."

INSECTA. 601

future limbs begin to show themselves under the form of
transparent vesicles, which, as they enlarge, crowd the
thoracic region of the body. The change from the larva
to the pupa condition involves phenomena of the most
startling character. The air-sacs, situated both in the
thoracic region and in the hinder portion, burst and
unfold themselves into an elaborate tracheal system, and
a pair of ear-shaped tubes, of which not the slightest trace
could hitherto be discerned, make their appearance upon
the dorsal aspect of the thorax ; two long tracheae seem to
be thus simultaneously produced, occupying the two sides
of the body, and constituting the main trunks, from which
large branches are given off to supply, in front, the head,
the eyes, and the nascent limbs; while posteriorly they
spread over the now conspicuous ovaries, and terminate by
ramifying largely through the thin lamellae that constitute
the caudal appendages. In individuals subjected to micro-
scopic examination within a very brief period after their
assumption of the pupa state, the places originally filled
by the air-sacs of the larva are found to be occupied by
the lateral remnants of their external coats, clearly indi-
cated by ragged membranes, covered with patches of black
pigment, in the immediate vicinity of which numerous
air-bubbles are met with, extravasating, as it were, into
the cellular tissue.

The family Phryganeidce, the larvae of which are aquatic,
present almost as little resemblance to the imago as those
of some metabolous insects. They are long, softish grubs,
furnished with six feet, and with a horny head armed with
jaws, generally fitted for biting vegetable matters, although
some appear to be carnivorous. To protect their soft
bodies, which constitute a very favourite food with fishes,
the larvae are always inclosed in cases formed of bits of
straw and sticks, pebbles, and even small shells. The
materials of these curious cases are united by means of
fine silken threads, spun like those of the caterpillars of
the Lepidoptera, from a spinnaret situated on the labium.
In increasing the size of its case to suit its growth, the
larva is said to add to the anterior part only, cutting off a
portion of the opposite extremity. When in motion, the
larva pushes its head and the three thoracic segments,

602 THE MICROSCOPE.

which are of a harder consistence than the rest of the
body, out of its case ; and as the latter is but little, if at
all, heavier than the water, the creature easily drags it
along behind, thus keeping its abdomen always sheltered.
It adheres stoutly to the inside of its dwelling by means of
a pair of articulated caudal appendages, generally assisted
by three tubercles on the first abdominal segment. Before
changing to the pupa state, the larva fixes his case to some
object in the water, and then closes up the two extremities
with a silken grating, through which the water necessary
for the respiration of the pupa readily passes. The pupa
is furnished with a large pair of hooked jaws, by means of
which, when about to assume the perfect state, it bites
through the grating of its prison, and thus sets itself free
in the water. In this form the pupae of some species
swim freely through the water by means of their long hind
legs, or creep about plants with the other four ; frequently
rising to the surface of the water, they there undergo their
final change, using their deserted skin as a sort of raft,
from which to rise into the air ; others climb to the surface
of aquatic plants for the same purpose.

The perfect insect (Phryganea grandis) has four wings,
with branched nervures, the anterior pair of which, clothed
with hairs, are more frequently used than the posterior.
The organs of the mouth, except the palpi, are rudimen-
tary, and apparently quite unfit for use. The head is fur-
nished with a pair of large eyes, and with three ocelli ;
the antennae are generally very long. Some species are so
exactly like Moths, that they have often been supposed to
belong to the Lepidopterous order ; in point of fact, these
insects may be considered to form a connecting link
between the Neuroptera and the Lepidoptera. The females
have been seen to descend to the depth of a foot or more
in the water, to deposit their eggs.

Eggs of Insects, Plate VI. No. 124, &c. — In form,
colour, and variety of design, the eggs of insects are more
surprisingly varied than those of the feathered tribes ;
but as from their smallness they escape observation, our
acquaintance with their structure and peculiarities is neces-
sarily limited and imperfect. Although the eggs of the
animal series differ much in their external characteristics,

EGGS OF INSECTS. 603

they closely resemble each other while yet a part of the
ovarian ova, and prior to their detachment from the ovary.
At one period of their formation all eggs consist of three
similar parts : — 1st. The internal nucleated cell, or ger-
minal vesicle, with its macula ; 2d. The vitellus, or yolk-
substance ; and 3d. The vesicular envelope, or vitelline
membrane. The germinal vesicle being the first produced
may be regarded as the ovigerm ; then comes the yolk-
substance, which gradually envelopes it, or is deposited
around it ; and the vitelline membrane, the latest formed,
incloses the whole. The chemical constituents of the egg
contents are albumen, fatty matters, and a proportion of a
substance precipitable by water. The production of the
chorion, or shell membrane, does not take place till the
ovum has attained nearly the full size, and it then appears
to proceed, in part at least, from the consolidation over the
whole surface of one or more layers of an albuminous fluid
secreted from the wall of the oviduct. The observations
of H. Meyer have shown that a part of the outer mem-
brane is derived from a conversion into it of the inner
cellular or epithelial lining membrane of the oviduct, at
the place where it is in closest contact with the surface of
the ovum. Dr. Allen Thompson therefore thinks that
" many of the varieties in the appearance and structure of
the external covering of eggs may probably depend on the
different modes of development of these ceils."

The embryo cell is so directly connected with the
germinal vesicle that at a certain period it disappears alto-
gether, and is absorbed into the germinal yolk, or rather
becomes the nucleus of the embryo, when a greater degree
of compactness is observed in the yolk, and all that remains
of the germinal vesicle is one or more highly refracting
fat globules and albuminoid bodies. Towards the end of
the period of incubation, the head of the young cater-
pillar, according to Meissner, lies towards the dot or
opening in the lid, which he terms the micropyle? from its
resemblance to a small gate, or opening through which the
worm emerges forth. From a number of careful observa-

(1) The term micropyle (a little gate) has heretofore only been used in its re-
lation with the vegetable kingdom : it is used to denote the opening or foramen
towards which the radicle is always pointed.

604 THE MICROSCOPE.

tions made on the silkworm, we have not been able to
satisfy ourselves of the correctness of these particulars :
in every case, indeed, the young worm- makes its way out
from a point generally below this spot. Leuckart, how-
ever, expresses his belief in this micropyle, and says, " It
becomes at a later period converted into a funnel, which is
connected directly with the mouth of the embryo, and
serves to convey nourishment from without to it." We,
on the contrary, look upon it as an involuted portion of
membrane, indicating the spot where the formative pro-
cess of the outer membrane terminated, or where at a still
earlier stage, and while the ova was yet in the ova-sac, the
spermatozoa passed in to fecundate the yolk mass.

The germinal vesicle is very large and well marked,
while the egg is yet in the ova-sac of the insect. By pre-
paring sections, after Dr. Hallifax's method,1 we find that
the germinal vesicle in the bee's egg is not situated imme-
diately near or even below the so-called micropyle, but
rather more to the side of the egg ; just in the position
which the head of the embryo is subsequently found to
occupy when it arrives at maturity.

The egg membrane, or envelope, of all the Lepidop-
tera, is composed of three separate and distinct layers :
an external slightly raised coat, tough and hard in its
character, a middle one of united cells, and a line trans-
parent vitelline lining membrane, perfectly smooth and
homogenous in structure, imparting solidity, and giving a
fine iridescent hue to the surface, such as most of us admire
in old glass exhumed from the ruins of Pompeii. The
germinal vesicle is of a proportionately large size for the
egg, and its macula is at first single, then multiple. In
the silk- worm's egg the outer membrane is comprised of
an inner reticulated membrane of non- nucleated cells, and
in the outer layer the cells are arranged in an irregular
circular form, also non-nucleated, with minute interstitial
setae or hairs projecting outward.

The outer surface of the egg-shell of Coccus Fersicce is

(1) Dr. Hallifax adopts the method of killing the insect with chloroform : he
thenimmerses it in a bath of hot wax, in which it is allowed to remain until the
wax becomes cold and hard ; now with a sharp knife a section is easily made in
the required direction without in the least disturbing any of the fragile parts,
or internal organs.

EGGS OF INSECTS. 605

covered by minute rings, of which the ends somewhat over-
lap. These rings are thought to he identical in their
character with the whitish substance which exudes through
pores on the under-side of the body ; and it is more than
probable that these layers of rings and their arrangement
account for the beautiful prismatic hues which they pre-
sent when viewed as opaque objects under the microscope,
and by the aid of the side-condenser. This white sub-
stance, it should be observed, becomes a part of the intimate
structure of the egg-shell, and is in nowise affected by
either strong spirit or dilute acids. Sir John Lubbock1
states that in the greenish eggs of Pkryganea, " the colour
is due to the yolk-globules themselves. In Coccus, how-
ever, this is not so ; the yolk-globules are slightly yellow,
and the green hue of the egg is owing to the green granules,
which are only minute oil globules. When, however, the
egg arrives at maturity, and the upper chamber has been
removed by absorption, these green granules will be found
to be replaced by dark-green globules, regular in size, and
about 1 -8000th of an inch in diameter, and which appear
to be in no way the same in the yolk of Phryganea eggs."
Another curious fact has been noticed, which partially
bears on the question of colour : the production of parasite
bodies within the eggs of some insects. In the Coccus, for
instance, parasitic cells of a green colour occur, " shaped
like a string of sausages, in length about the 1-2 000th of
an inch by about the 1 -7000th in breadth."

The eggs of Moths and Butterflies present many varying
tints of colour ; in speaking of this quality we do not re-
strict the term solely to those prismatic changes to which
allusion is so often made, and which are liable to constant
mutations according to the accident of the rays of light
thrown upon them ; but we more particularly refer to the
several natural transitions of colour, the prevailing tints
of which are yellow, white, grey, and a light-brown. In
some eggs the yellow, white, and grey are delicately blended,
and when viewed with a magnifying power of about fifty
diameters, and by the aid of a side-reflector (parabolic-
reflector), present many beautiful combinations. The
most delicate opalescent or rather iridescent tints appear

(1) Phil Trans. 1859, p. 341.

606 THE MICROSCOPE.

on others, of which, the eggs of the feathered tribes
furnish no example. The egg of the Mottled Umber
Moth (Erannis defolaria), Plate VI. No. 137, is in every
particular very beautiful. It is ovoid, with regular
hexagonal reticulations, and at each corner studded with
a raiyed knob or button ; the space within the hexagon is
finely punctated, and the play of colours is exquisitely
delicate. In this egg no ndcropyle can be seen. The
egg of the Thorn Moth (Ennomos erosaria), Plate VI.
No. 138, is of an elongated brick-looking form, one end of
which is slightly tapered off, while the other in which
the lid is placed is flattened and surrounded by a beauti-
fully white-beaded border, having for its centre a slightly
raised reticulated micropyle. The empty egg-shell gives
a fine opalescent play of colours, while that containing the
young worm appears of a brownish-yellow.

The egg of the Straw-belle Moth (Aspilatcs gilvaria),
Plate VI. No. 139, is delicately tinted, somewhat long
and narrow, with sides slightly flattened or rounded off,
and irregularly serrated. The top is convex, and the base
a little indented, in which are seen the lid and micropyle.
The young worm, however, usually makes its way through
the upper convex side : the indentation represented in the
drawing shows the place of exit.

An example of those eggs possessing a good deal of
natural colour is presented in that of the Common Puss
Moth (C. Vinula), a large spheroidal- shaped egg, having,
under the microscope, the appearance of a fine ripe
orange ; the micropyle exactly corresponds to the depres-
sion left in this fruit by the removal of the stalk ; the sur-
face is finely reticulated, and the natural colour a deep
orange.

The egg of the Mottled Eustic Moth (Caradina
Morpheus), No. 124, is subconical, and equally divided
throughout by a series of ribs, which terminate in a well-
marked geometrically-formed lid. The Tortoise-shell
Butterfly (Vanessa urtica), No. 125, presents us with a
delicate ovoid egg, divided into segments, the ribs of
which turn in towards the micropyle. The Common
Footman (Lithosia campanula), No. 126, produces a per-
fectly globular egg covered with fine reticulations, and of

TONGUES OF INSECTS. 607

a delicate buff colour. The egg of the Shark Moth (Cu-
cullia umbratica), No. 127, is subconical in form, with
ribs and cross-bars passing up from a flattened base to the
summit, and turning over to form the lid. No. 136, the
Egg of Blue Argus Butterfly (Polyommatus Argus). That
of the Small Emerald Moth (Jodis Vernaria), No. 1 34, is
an egg of singular form and beauty, — an oval, flattened on
both sides, of silvery iridescence, and covered throughout
with minute reticulations and dots. It is particularly
translucent, so much so that the yellow-brown worm is
readily seen curled up within. The lid or micropyle is
not detected until the caterpillar eats its way out of the
shell. It should be stated that the whole series of eggs
in the plate are considerably over-coloured, and conse-
quently lose much of their beautiful transparency. The
eggs of Flies and Parasites also present much variety in
form, colour, and construction. Many of their eggs are
provided with a veritable lid, which opens up with a hinge-
like articulation. The cover is shown in Plate VI. No.
144, Egg of Bot-fly, from which the larva is seen just
escaping ; No. 146, Egg of Scatophaga ; No. 147, Egg of
Parasite of Magpie.1

Moths and Butterflies supply the microscopist with
some of the most beautiful objects for examination. What
can be more wonderful in its adaptation than the antenna
of the Moth, represented in fig. 271, No. 1, with a thin,
finger-like extremity almost supplying the insect with a
perfect and useful hand, moved throughout its extent by
a muscular apparatus of the most exquisite construction !
The tongue of Butterfly, No. 2, is evidently made for the
purpose of dipping into the interior of flowers and extracting
the juices ; this is furnished with a spiral band of muscle :
an enlarged view of a portion is given at No. 3. See also
Plate YI. Nos. 132 and 133, Antennae of Vapour Moth.

The inconceivably delicate structure of the maxillae or
tongues (for there are two) of the f>utterfly, rolled up like
the trunk of an elephant, and capable, like it, of every
variety of movement, has been carefully examined and
described by Mr. Newport. " Each maxilla is convex on

(1) A paper on the Eggs of Insects, giving many other forms, will be found in
the Intellectual Observer, Oct. 1867.

608

THE MICROSCOPE.

Fig. 271.

1, The Antenna of the Silkworm-moth. 2, Tongue of a Butterfly. 3, A portion
of the Tongue highly magnified, showing its muscular fibre. 4, The Trachea;
of Silkworm. 5, The Foot of Silkworm. (The small circles enclose each some-
what near tho natural size).

INSECTA. 609

its outer surface, but concave on its inner ; so that when
the two are approximated, they form a tube by their union,
through which fluids may be drawn into the mouth. The
inner or concave surface, which forms the tube, is lined
with a very smooth membrane, and extends throughout
the whole length of the organ; but that each maxilla is
hollow in its interior, forming a tube ' in itself/ as is
generally described, is a mistake; which has doubtless
arisen from the existence of large tracheae, or breathing-
tubes, in the interior of each portion of the proboscis. In
some species, the extremity of each maxilla is studded
externally with a great number of minute papillae, or
fringes — as in the Vanessa atalanta — in which they are
little elongated barrel-shaped bodies, terminated by smaller
papillae at their extremities." Mr. Newport supposes that
the way in which the insect is enabled to pump up the
fluid nourishment into its mouth is this : " On alighting on
a flower, the insect makes a powerful expiratory effort, by
which the air is expelled from the interior air-tubes, and
from those with which they are connected in the head and
body ; and at the moment of applying its proboscis to the
food, it makes an inspiratory effort, by which the central
canal in the proboscis is dilated, and the food ascends it at
the same instant to supply the vacuum produced; and
thus it passes into the mouth and stomach : the constant
ascent of the fluid being assisted by the action of the
muscles of the proboscis, which continues during the whole
time that the insect is feeding. By this combined agency
of the acts of respiration and the muscles of the proboscis,
we are also enabled to understand the manner in which
the Humming-bird sphynx extracts in an instant the honey
from a flower while hovering over it, without alighting;
and which it certainly would be unable to do, were the
ascent of the fluid entirely dependent upon the action of
the muscles of the organ." *

The wings of Moths and Butterflies are covered with
scales or feathers, carefully overlapping each other, as tiles
are made to cover the tops of houses. The iridescent variety
of colouring on their wings arises from a peculiar wavy
arrangement of the scales. Figs. 272 and 273 are magni-

(1) Cyclop. Anat. PhysM., article "Insecta."
R R

610

THE MICROSCOPE.

fied representations of a few of them. No. 1 is a scale of
the Morpho menelaus, taken from the side of the wing, of a

pi£. 272.— Scales from Butterflies' and Moths' wings. (Magnified 200 diameters.)

1, Scale of Morpho Menelaus. 2, Large Scale of Polyommatus Argiolus, azure
blue. 3, Hlpparchia Janira Argiolus. 4, Pontia Brassica. 5, Podura
Plumbea. 6, Small Scale of Azure Blue.

pale-blue colour: it measures about l-120th of an inch in
length, and exhibits a series of longitudinal stripes or lines,
between which are disposed cross-lines or strise, giving it
the appearance of brick- work. The microscope should be
enabled to make out these markings with the spaces
between them clear and distinct, as shown in fig. 273,
No. la.

Polyommatus argiolus, Azure-blue, Nos. 2 and 6, are
large and small scales taken from the under-side of the
wing of this beautiful blue butterfly; the small scale is
covered with a series of spots, and exhibits both longitu-

IXSECTA. 611

dinal and trausverse striae, which should be clearly defined,
and the spots separated : this is a good test of the denning
power of a quarter-inch object-glass.

No. 3, Hipparchia janira, Common Meadow Brown
Butterfly scale : on this we see a number of brown spots
of irregular shape and longitudinal striae.

No. 4, Pontia brassica, Cabbage- butterfly, affords an
excellent criterion of the penetration and definition of a
microscope: it is provided at its free extremity with a
brush-like appendage. With a high power, the longitu-
dinal markings appear like rows of little beads. Cheva-
lier's test-object is the scale of the Pontia brassica, the
granules of which must be rendered distinct. Mohl and
Schacht use Hipparchia janira as a test for penetration,
with a moderate angular aperture and oblique illumina-
tion. Amici's test-object is Navicula Rhomboides, the dis-
play of the lines forming the test ; this is a very good test
for angular aperture.

Fig.273. — Portions of Scales, magnified 500 diameters.

la, Portion of Scale of Morpho Menelaus. 5a, Portion of Large Scale of Podura
Plumbea. 7, Scale from the Wing of Gnat; its two layers are here represented.
8, Portion of a Large Scale of Lepisma Saccharina.

The Tinea vestianella, Clothes-moth, possesses very deli-
cate and unique scales ; two of these are imperfectly
represented near the Acarus taken from one of these moths,
at page 641. The feathers from the under-side of the
R R 2

612 THE MICROSCOPE.

wing are the best, requiring some management of illumi-
nation to bring out the lines sharp and clear.

The common Clothes-moth generally lays its eggs on
the woollen or fur articles it is bent upon destroying ; the
larva begins to eat immediately it is hatched ; then with
the hairs or wool it first gnaws off, it forms a case or
tube, under the protection of which it devours the sub-
stance of the article on which it fixes its abode. This
tube is of parchment-like consistence, and quite white;
is cylindrical in its shape, and furnished at both ends with
a kind of flap, which the insect raises at pleasure, and
crawls out ; or it projects the front part of its body with
its fore-feet through the opening, just enough to enable
it to creep about without removing the rest of its body from
the tube, which it draws after it. There are several kinds
of Clothes-moths, the caterpillars of many bury them-
selves in the article on wnich they feed,
instead of making the tube before-men-
tioned. The moths also differ very much
in appearance ; the commonest is of a light

buff colour '> one sPecies> Tinea tapetzella,
fig. 274, is nearly black, with the larger
wings white tipped, or pale grey.
Mr. Topping, the well known preparer of microscopic
objects, generally furnishes three kinds of test-objects, which
he covers with the thinnest glass, in order that object-
glasses of the highest powers may be used in their exami-
nation. The following are arranged in their order of
value as test-objects ;

Fig. 274.-ro.Bta*

Amician test.
N. v. Rhomboides.
Grammatophora subtilisima.
Pleurosigtna fasciola.

— cuspidata.

— angulatum.

— strigosum.

— prolongation.

— Spencerii.

— Balticum.

— hippocampus.

— strigilis.

— formosum.

SCALES.

Meadow Brown.
Pontia Brassica.
Azure Blue.
From Gnat's Wing.
Tinea Vestianella.
Amathusia Horsefieldii.
Morpho' Menelaus.
Podura plumbea.
Lepisma saccharina.

HAIRS.

Indian Bat.

,, Mouse.

„ Mole.
Larva of Dermest.es.

Mr. J. T. Norman, of City Road, preparer of specimens for the microscope,
furnished our Eggs of Insects.

INSECTA. 613

In a genus Coccina (Dorthesia), several species of which
are found in this country, the female — although apterous
and active in all stages — is completely covered with a
snow-white secretion, which gives it more the appearance
of a little plaster-cast than anything else.

Tn another tribe, the Phytophthiria, both sexes are
either wingless or furnished with four distinctly veined
wings. The rostrum springs apparently from the breast ;
the tarsi are two-jointed, and furnished with two claws.
The most familiar species of this tribe are the Aphides,
Plant-lice, which have ever been regarded with consider-
able interest by the naturalist. Their bodies are flask-
shaped, t and furnished with six feet, a pair of antennae,
and very generally with a pair of short tubes close to the
extremity of the abdomen, from which a clear sweet
secretion exudes. Both sexes are at one period winged,
at another wingless ; and individuals of the same species
are often winged and apterous at different periods of the
year. Perhaps the most remarkable phenomena in the
history of generation was first observed in the Aphis, and
to which great significance has been given by Professor
Owen, under the name Parthenogenesis or virgin-procre-
ation. This mode of generation is not confined to insect-
life, the same has been observed in the Salpce among
mollusca, the Distomata among entozoa, each parent giving
birth to an embryo diiferent to itself; and this embryo
living as an independent animal, gives birth, without inter-
course, to another and to a successive series, until at length
a progeny is formed bearing the likeness of the first parent.
In the Aphis the ova are deposited by the parent insect,
and in due time produce larval wingless Aphides. Each
virgin Aphis of this brood will produce other similar
broods without intercourse; this will go on to the
eleventh generation, the last generation being winged, and
male and female : these have intercourse, and then com-
mence the same series of phenomena over again.

The Maple-aphis, better known as the Leaf Insect
(Plate VI. No. 128), averages about the one-fiftieth of
an inch in length, and, although long sold and exhibited
under the name of the "Leaf Insect," nothing was
known of its origin and history, with the exception of

614 THE MICROSCOPE.

what the Eev. J. Thornton stated in 1852, to whom
we owe its discovery on the leaves of the maple ; he,
believing it to be a species of Aphides, called it Phyl-
lopJwrus testudinatus. Subsequently it attracted the
attention of the Dutch naturalist Van der Hoeven,
who regarded it as the larval form of an undetermined
species of Aphis, and named it Periphyllus. It has more
recently engaged the attention of Dr. Balbiani and M.
Siguoret, whose united investigations are given in the
" Comptes Eendus " of June 17, 1867. They have posi-
tively ascertained that it is the larva of Aphis aceris ; a
brown species is also met with during a great part of the
year upon the young shoots of the maple. At the same
time a curious fact was made out, constituting a new and
remarkable peculiarity in the development of this group
of insects, already presenting so many curious phenomena
in connexion with their reproduction. It really appears
that the female produces two kinds of young — one normal,
the other abnormal; the first arc alone capable of con-
tinuing the course of their development, and capable of
reproducing the species ; whilst the latter retain their
original form, which is never changed throughout their
existence. They increase so little in size, that it appears
almost doubtful whether they eat ; the mouth is so very
rudimentary that this surmise in some measure gains sup-
port from the circumstance ; they undergo no change of
skin, never acquire wings like the reproductive insect,
and their antennae always retain the five joints which
are peculiar to all young Aphides before the first moult.
Neither are they all of the same colour, some being of a
bright green, as represented in our Plate, while others are
of a darker, or brownish-green, colour. The brown-green
embryos differ from the adult female only in those cha-
racters analogous to all other species ; and that chiefly
with regard to the hairs, which are long and simple. In
the green embryos, in the place of hairs, the body is sur-
rounded with scaly, transparent lamellae, more or less
oblong in shape, each of which is traversed by divergent
ramifying nervures. These lamellae not only occupy the
body, but also the anterior part of the head, the first joint
of the antennae, and the outer edge of the tibiae of the

APHIDES. 615

two anterior pair of legs. The dorsal surface in these
insects is covered with a mosaic of hexagonal plates, very
closely resembling the plates of the carapace of the tor-
toise. In this particular our artist has certainly fallen
into an error. Another peculiarity is that the body is
much flattened out, and looks so much like a scale on the
surface of the leaf, that it requires considerable practice,
as well as quickness of sight, to detect the young Maple-
aphis. One of the lamellae is seen highly magnified at c,
and a tenent-hair at 6. The antennae taper off towards the
apex, are serrate on both edges, and terminate in fine
setae, one of which is shown at a. Below the insertions
of the antennae, brilliant scarlet- coloured compound eyes
are placed, which receive their nervous supply from the
central ganglion.

Aphides live upon plants, the juices of which they
suck, and, when they occur in great numbers, cause con-
siderable damage to vegetation ; a fact well known to
the gardener and farmer. Many plants are liable to be
attacked by swarms of these insects, which cause the
leaves to curl up : they grow sickly, and their produce is
greatly reduced. One striking instance is presented in the
devastation caused by the Hop-fly (Aphis humuli).

The Aphrophora bifasciata, common Frog-hopper, has
the antennae placed between the eyes, and the scutellum
visible — that is to say, not covered by a process of the
prothorax. The eyes, never more than two in number,
are sometimes wanting. These little creatures are always
furnished with long hind legs, which enable them to per-
form most extraordinary
leaping feats. The best-
known British species, be-
cause so very abundant in
gardens, is the Cuckoo-spit,
Froth-fly, fig. 275. The
names Cuckoo- spit and

Froth-fly both allude to the Fig- w.-Aphrophora sp-um
peculiar habit of the insect, cuckoo-spit.

while in the larva state, of «> ^ frothy substance, b, The pupa
enveloping itself in a kind of frothy secretion, somewhat
resembling saliva ; and this, indeed, was at one time sup

G16 THE MICROSCOPE.

posed to be the saliva of the cuckoo, being found on the
young shoots of plants just about the time the cuckoo is
heard in the woods.

The Hymenoptera are distinguished from other insects
with membranous wings by the presence of an ovipositor
of peculiar construction at the extremity of the abdomen
of the females, which serves for placing the eggs in the
required position ; and in the males of some (Bees, Wasps.
&c.) constitutes a most formidable offensive weapon. As
the structure of this organ, which is rarely absent, is
essentially the same throughout the order, the form of its
component parts being merely modified to suit the exigencies
of the different insects, a short description of its structure
will not be considered out of place. The ovipositor,
borer, or sting, generally consists of five pieces : a pair of
horny supports (fig. 279) forming a sheath for the borer
or ovipositor, being jointed at the point where they issue
from the cavity of the last abdominal segment, and the
last joint is usually as long as the borer itself. The latter
consists of three bristles, of which the superior is grooved
along its lower surface, for the reception of a pair of finer
styles, and these are barbed at the point. The three
pieces, when fitted together, form a narrow tube, through
which the eggs pass to their destination, the poisonous
fluid also, which renders the sting of the Bee so painful,
is forced down the same into the wound. In the Saw-fly,
a part of this organ remains rudimentary, in other respects
it does not very much differ.

The larvae of most Hymenoptera are footless grubs,
furnished with a soft head, and exhibiting but little, if
any, advance upon those of Diptera (Plate VI. No. '141).
In the Saw-fly, however, the larva, instead of being, as
above described, a mere footless maggot, presents the
closest resemblance to the caterpillar of the Lepidoptera ;
it is provided with a distinct head, with six thoracic legs,
and in most cases, from twelve to sixteen pro-legs are
appended to the abdominal segments.

The Saw-fly, fig. 276, most destructive to the goose-
berry-bush, is remarkable for the way in which the female
provides for the safety of her eggs. This fly has a flat
yellow body, and four transparent wings, the outer two of

OVIPOSITORS OF INSECTS.

61'

which have brown edges. The female lays her eggs on
the under-side of the leaf, along the projecting veins;
these are firmly attached, and cannot be removed without

Ing. '276. — TJa Caterpillar and Saw-fly of Gooseberry tree.

crushing. The instrument which the little insect uses for
the purpose of cutting the leaf is the most remarkable
piece of perfect mechanism imaginable ; securely lodged,

Fig. 277.— Saws of Saw-fly. (The small circle incloses the same nearly the
natural size.)

when not in use, in a long narrow slit beneath the abdomen,
and protected loy two horny plates, which at first appear
to consist of a single piece ; but upon closer inspection

618 THE MICROSCOPE.

four plates are seen to enter into their construction:
namely, two saws, placed side by side, as in fig. 277 ;
and two supports, somewhat like the saws in shape. A
deep groove runs along the thicker edge of the latter,
which is so arranged that the saws glide backwards and
forwards, without a possibility of running out of the
groove. When the cut is made, the four are drawn
together; and through a central canal, which is now
formed by combining the whole, an egg is protruded
into the fissure made by the saws in the leaf. The cutting
edges of the saws are provided with about eighteen or
twenty teeth : these have sharp points of extreme delicacy,
and together make a serrated edge of the exact form
given to the finest and best-made surgical saws. In the
summer-time the proceedings of this little insect can be
watched, and the method of using this curious instrument
seen, by the aid of a hand magnifier ; they are not easily
alarmed when busy at their work.

Many other insects are provided with instruments for
boring into the bark or solid wood itself. The -Qynip bores
a hole into the side of the oak-apple,
/ for the purpose of depositing her egg.
The larva when hatched finds a com-
fortable lodging, and a good supply of
food ; when full grown, it eats its way
out of the nut, and, dropping to the
ground, it assumes the form of the per-
fect fly. The most important of this
" family is the Cynip galloe tinctorive,
Fig. 278.— Female Egian- fig. 278, which is the cause of the gall-
tine Gail-fly and larva. nutj a nut mogt extensively employed

in the manufacture of ink and for dyeing purposes.

Some of the Wasp tribe, so very peculiar in their habits,
are active agents in the economy of nature. The solitary
Mason-wasps curiously construct nests in the form of
cells, for the purpose of carefully rearing their young.
The social-wasps, like bees, live in communities, and
have nearly the same divisions of labour and regulations
for the good government of the colony. The struc-
ture and mechanical contrivance of the wasp's sting can
only be seen under the microscope. The sting consists of

STINGS OP INSECTS. 619

two barbed darts, which will penetrate the flesh deeply,
and, from a peculiar arrangement & their serrated edges,
their immediate withdrawal is prevented ; by the great
muscular effort required for this purpose, a small sac or

Fig. 279.

i Sting of Wasp. 2, Sting of Bee. (The small circles show each nearly tha
full size.)

620 THE MICROSCOPE.

bag near the root is pressed upon, and its irritating con
tents squeezed out iftto the wound. After the fluid is
injected, the wasp has the power of contracting the
barbed points, and then it withdraws the sting from its
victim. In fig. 279 the sting of the wasp is shown, with
its attachments and muscular arrangement ; and it will be
seen that the sting is most wonderfully adapted to become
an instrument of a very effective and dangerous character.
The palpi near it are placed there for the purpose of
cleaning or wiping it ; at all events, this appears to be one
of the uses they are put to.

The proboscis or trunk of the Honey-bee next demands
attention; this is used, with its curious accessories, to
collect the honey while roving about from flower to
flower. The proboscis itself (fig. 280) is very curiously
divided ; the divisions are elegant and regular, beset with
triangular hairs, which, beir.g numerous, appear at first
sight as a number of different articulations. The two
outside lancets are spear-shaped, of a membranaceous or
horny substance, set on one side with short hairs, and
having their interior hollow; at the base of each is a
hinge- articulation, which permits of considerable motion
in several directions, and is evidently used by the busy
insect for the purpose of opening the internal parts of
flowers, and thus facilitating the introduction of its pro-
boscis. The two shorter feelers are closely connected to
the proboscis, and terminate in three-jointed articulations.
Swammerdam thought these were used as fingers in
assisting the removal of obstructions ; but it is more pro-
bable that they are made use of by the insect for storing,
and removing the bee-bread to and from the pocket-
receptacles in the legs. The lower part of the proboscis
is so formed that it can be considerably enlarged at its
base, and thus made to contain a larger quantity of the
collected juice of flowers ; at the same time, it is in this
cavity that the nectar is transformed into pure honey by
some peculiar chemical process. The proboscis tapers off
to a little nipple-like extremity, and at its base will be
seen two shorter and stronger mandibles, which serve the
little insects in the construction of their cells, and from
between which is protruded a long and narrow tongue

TONGUE OF BEE.

621

or lance ; the whole is most ingeniously connected to the
head by a horny sheath, and a series of muscles and
ligaments. The proboscis, being cylindrical, extracts the
juice of the flower in a somewhat similar way to that of
the butterfly ; when loaded with honey, the insect's next

Fig. 2

1, Honey-bee's tongue. 2, Leg, showing pocket for carryin^ the
(The small circles show the objects about the naturaf size.)

the Bee-bread.

622 THE MICROSCOPE.

care is to fill the very ingenious pockets situated in its
hind legs (one of which is shown at No. 2) with bee-bread ;
when these little pockets are filled with as much pollen
as the bee can conveniently carry, it flies back to the hive
with its valuable load, where it is speedily assisted to
unload by its fellow- workers ; the pollen is at once
kneaded and packed closely in the cells provided for its
preservation. The quantity of this collected in one day
by a single hive during favourable weather is said to be
at least a pound ; this chiefly constitutes the food of the
working-bees in the hive. The wax is another secretion
exuding through the skin of the insect ; it is found in
little pouches in the under-part of the body, but is not
collected and brought home ready for use, as has been
generally supposed. The waxen walls of the cells are,
when completed, strengthened by a varnish, called pro-
polis, collected from the buds of the poplar and other
trees, and besmeared over by the aid of the wonderful
apparatus represented in the engraving. If a bee is
attentively observed as it settles down upon a flower,
the activity and promptitude with which it uses the
apparatus is truly surprising ; it lengthens the tongue,
applies it to the bottom of the petals, then shortens it,
bending and turning it in all possible directions, for the
purpose of exploring the interior, and removing the pollen.
In the words of Brook : —

" The dainty suckle and the fragrant thyme,
By chemical reduction they sublime ;
Their sweets with bland attempering suction strain,
And curious through their neat alembics drain ;
Imbib'd recluse, the pure secretions glide,
And vital warmth concocts th' ambrosial tide."

The leading characteristic of the vast order Coleoptera,
Beetles, consists in the leathery or horny texture of the
anterior wings (elytra), which serve as sheaths for the
posterior wings in repose, and generally meet in a straight
line down the back.

The elytra present us with wing-cases of many Curculios,
Diamond beetles, the most brilliant of opaque objects.
Some are improved by being mounted in Canada balsam,
whilst others are more or less injured by it : a trial of a
small portion, by first touching it with turpentine, decides

INSECT A 623

this point. Oblique or side illumination shows the play
of colours on the scale to the greatest advantage.

To the genus Ptinus belongs a small beetle known as
the Death-watch, fig. 281. This and the species AnoUum
are found in our houses, doing much in-
jury whilst in the larval state. The eggs
are often deposited near some crack in a
piece of furniture, or on the binding of an
old book. As the larvse are hatched, they
begin to eat their way into any furniture
on which they may have been deposited :
and, having attained a sufficient depth, Fjo. 281

they undergo transformation, and return, The D^th-watcii,
by other passages, as perfect beetles. In Atropus, magnified,
furniture attacked by them, small round holes, about
the size of the head of a pin, may be seen, and to these
holes the term worm-eaten has been applied; and the
noise, made by the insect striking its head against the
wood, has given rise to the name of Death-watch. The
larva is called a Book-worm when it attacks books ; old
books and those seldom used, are often found bored
through by it. Kirby and Spence mention, that in one
case twenty-seven folio volumes were eaten through, in a
straight line, by this insect. The beetle is very small, and
almost black. The head is particularly small ; and from
the prominence of the thorax, looks as
if it were covered with a hood. The
Anobium puniceum, fig. 282, attacks
dried objects of natural history, and all
kinds of bread and biscuits, particularly
sailors' biscuits, in which maggots fre-
quently abound. In collections of in-
sects, it first consumes the interior;
when the larva assails birds, it is gene-
rally the feet that it devours first ; and
in plants, the stem or woody part. The

, r . ,, , . . , ,, » , niceum, magnified.

larva is a small white maggot, the body
of which is wrinkled, and consists of several segments
covered with fine hairs ; its jaws are strong and horny,
and of a dark brown. The body is white, and so trans-
parent, that the internal organs of the insect can be seen

624 THE MICROSCOPE.

through it. The beetle itself is of a reddish-brown

colour, covered with fine hairs.

The Bacon-beetle (Dermestes lardariw) is another of

the destructive beetle family. The larva of this beetle is
particularly partial to the skin
of any animal that may fall in
its way; consequently it de-
stroys stuffed animals and birds
in collections of natural his-
tory, whenever it can gain ac-
cess to them. It attacks hams
and bacon for the skin's sake ;

Fig. 283.- Dermestes lardarius. and, being a very glutton, ex-
Larva, pupa, and imago. ^ ^ rayageg ^ ^ ^^

This larva is long and slender, its body nearly round, and
is divided into thirteen segments, of a blackish-brown in
the middle, and white at the edge ; the whole being fur-
nished with bristle-shaped reddish-brown hairs.

The Dermestidce belong to the family of Necrophagous
beetles, six genera of which have been found in Great
Britain. The D. lardarius is black about the head and
tail, with an ash-grey band across the back, having three
black spots on each wing-case. Sometimes this band takes
a yellowish tinge, and then the hairs, which are here dis-
posed in tufts, are likewise of a yellowish-grey colour.
The beetle is most destructive in spring. The larvae, like
those of the clothes moths, are but seldom seen, being
careful to conceal themselves in the bodies they attack,
and their presence can only be guessed at by finding
occasionally their cast-off skins, which they change several
times during their larvae state. Specimens of hair put
up by the mounters and labelled "Hair of Dermestes,"
do not belong to the species at all. These hairs, long
favourite objects with microscopists, and placed by them
among test-objects, may, it is believed, be those found in
tufts at the extremity of the body of Anthrenus muse-
orum. Westwood says that the larvae of these beetles
are furnished with tufts of hairs, which are " individually
formed of a series of minute conical pieces placed in suc-
cession, the base being very slender, and the extremity
a large oblong knot, placed on a slender footstalk." This

FOOT OF WATER-BEETLE.

625

description comes very near to that of the hair in question.
It is also suggested that the larvae of another genus, that
of Tiresius serra, furnish these hairs ; but, however that
may he, it is quite clear that the hairs called " Dermestes "
(fig. 307) are not obtained from the Bacon-beetle.

In the Gyrinus, Whirligig, we have a combination of
contrivances to facilitate the creature's movements in the
element in which it lives. The hind legs are converted
into a pair of oars of remarkable efficiency, the point of

Fig. 284.
1, Leg of Gyrinus, Whirligig, with paddle expanded. 2, With paddle closed up.

their connexion with the body being adapted with great
precision to ensure the most effectual application of the
propelling power ; as it strikes out behind in the act of
swimming, a membranous expansion of a portion of the
legs enables the insect to move about with great rapidity ;

rn the legs being drawn back again towards the body,
membrane closes up, and thus offers but a small
resistance to the water (fig. 284). The eyes are not the
least curious part of the merry little creature ; while one
s s

626 THE MICROSCOPE.

portion of them, that fitted for seeing in the air, is fixed
on the upper part of the head, the lower portion, for
seeing under the water, is placed at the lowest part, a
thin division separating the two.

Sir John Lubhock, writing of aquatic insects, says : l
" Though most of the great orders are represented, no
aquatic Hymenoptera or Orthoptera had till now (1864)
been discovered. Great, therefore, was my astonishment,
when I saw a small Hymenopterous insect, evidently quite
at its ease, and actually surimming by means of its wings.
At first I could hardly believe my sight ; but having found
several specimens, and shown them to some of my friends,
there can be no doubt about the fact. Moreover, the same
insect was again observed, within a week, by another ento-
mologist, Mr. Duchess, of Stepney. It is a curious coinci-
dence that, after remaining so long unnoticed, this little
insect should thus be found almost simultaneously by two
independent observers. Mr. Walker at first considered
the insect to be Polynema fuscipes, but thougli allied to
that species, it is not identical with it. So completely
aquatic is it in its habits that it can remain immersed for
at least twelve hours ; but it nevertheless requires to come
to the surface at certain intervals to renew the air in its
tracheae. It is uncertain whether P. natans can also use
its wings in flight. They are at any rate not easily incited
to do so. It is a very minute species, and well fitted for
microscopical observation, the female measuring 0'38 of an
inch, and the male 042."

Dytiscus marginalis, derived from dutes, a diver. Larva
narrow, body composed of twelve segments, including
head, which is large and strong, bearing antennae, and
armed with two powerful jaws. Several varieties of this
beetle are met with in fresh and still waters. The larvae
feed upon other aquatic larvae, such as the Gnat, Dragon-
fly, &c. The suckers on the legs, the feet, &c. are very
interesting objects, and should be mounted for viewing
both as transparent and opaque objects.

To the Orthoptera belong Locustina, Gryllina, and Ache-
tina, all herbivorous insects. The first is represented by our
well-known Grasshopper (Gryllus viridissimus), the second,

(1) Journ. Micros. Soc. vol. iv. p 139. 1864.

SPRING-TAILS. 627

the Gryllina, appear to frequent trees and shrubs more
than the other tribes, the members of which generally
keep among herbage ; and, in accordance with this habit,
many of the exotic species have wing-cases which present
the most perfect resemblance to leaves both in colour and
venation. Of the Achetina, the common Cricket (Acheta
domestica), fig. 285, the noisy little denizen of the kitchen-
hearth, is the best example. These insects have the
antennae slender and tapering, and often considerably
longer than the body. They agree with the Gryllina in
the structure of their singing apparatus ; but the wings,
instead of being arranged in the form of a high-pitched
roof, are laid flat upon the back. Some of them possess
ocelli, whilst others are destitute of those organs. The
wings are very long, and folded up in such a manner as
to project beyond the wing-cases in the form of a pair of
tapering tails ; the abdomen is also furnished, in both
sexes, with a pair of pilose, bristle-shaped, caudal appen-
dages : in the female these form a long slender ovipositor,
the two filaments being placed side by side, and somewhat
thickened at the tip. The tarsi are three- jointed. The
horny covering and muscular apparatus under the wing-
cases of the Cricket
are very curious, and
will repay microscopi-
cal examination. The

Cricket has tWO wings, *"&• 286.— The Cricket.

covered by elytra or wing-cases of a dry membranous consis-
tency, near the base of which is a horny ridge having trans-
verse furrows, exactly resembling a rasp or file ; this it rubs
against its body with a very brisk motion, and produces
the well-known merry chirp ; the intensity of which is
increased by a hollow space, called the tympanum, acting
as a sounding-board. The gastric teeth are numerous.

In Thysanura there is a remarkable diversity of struc-
ture ; they undergo no metamorphosis, and have no wings.
This order contains two families, Spring-tails, Poduridos,
and Lepismence. In the former, the caudal appendage
has the form of a forked tail (Podura, fig. 286), which is
bent under the body when not in use ; by its sudden ex-
tension the insect causes itself to spring to a very great
s 3 2

628 THE MICROSCOPE.

distance, in comparison with its size. The body is
covered with numerous minute scales, mostly of a beau-
tiful silvery or pearly lustre, and curiously striated.

Podura plumbea, Lead-colour Springtails, are generally
found in damp places, leaping about like fleas. They

prefer a moist atmosphere,
some take to the surface
of the water in secluded
places ; their food seems
to be vegetable matter of
any kind in a stage of

Fig.286.-Poduraphi.m6ea. (In the small decay; the little active

circle the insect appears life-size.) creatures are seen to leap
about if a stone in a damp situation in the garden is
turned up, or if a dark, damp corner of the cellar, about
the beer-barrel, is searched; or if we peep among the
roots of the ferns in the fern-case. Poduridae, varying in
form, colour, &c. are produced from eggs, undergo no
metamorphosis, are not parasitic, have from twelve to
sixteen simple eyes ; are furnished with strong mandibles,
and a broad, curious- looking snout, and a rather long
body, terminating in a bifid tail, which by alternately ex-
panding and contracting, enables them to leap great dis-
tances. The antennae are very long, and covered with
scales and fine hairs. To obtain the scales from the body
without damage — which is certain to occur if the Podura
is touched by the fingers — take a small test-tube and
quickly place it over the insect, when it instantly springs
up and clings to the side of the tube ; insert a thin glass-
cover beneath, and close up the open end. One drop of
chloroform carefully administered instantly kills the in-
sect ; in a very short time this evaporates and leaves the
tube quite dry. By gently shaking the tube a number of
scales will drop off and adhere to the thin glass cover ;
remove this, and make it secure to the ordinary glass-slip.

Mr. E. Beck says, "that the best scales are obtained
from insects found in comparatively dry places." Mr.
S. J. Mclntire, in an interesting paper on the Podura,1
confirms this statement, but believes that the "test-scale"
figured by Mr. Beck belongs to a distinct species. The

(1) Science Gossip, March, 18G7.

SCALES OP LEPISMA. 629

markings on the scale are better seen when an achromatic
condenser is employed with a good objective. Under a
power of 500 diameters, the surface appears to be covered
with extremely delicate longitudinal and wavy lines. The
smaller scales are much more difficult to resolve than the
larger, and these form a good test of the defining power
of a l-8th or l-12th object-glass. No. 5 a, fig. 274, is a
portion of a large scale. Fig. 273, No. 5, the longitudinal
markings are shown under a lower power. " But the
transverse striae on the scale of the speckled Podura are
rendered more distinct when the central rays are stopped
out. Any error in the correction of the lenses, whether
in the manufacture or in the adjustment of the thin
covering glass, is immediately detected by the peculiar
appearance which these markings present."

Lepisma saccharina has a spindle-shaped body covered
with silvery scales, the sides of the abdomen being fur-
nished with a series of appendages or false feet, with
long-jointed bristle-like organs at their extremities. The
head is concealed under a pro-thorax ; the eyes are usually
compound, and generally occupy the greater part of the
head. The antennae are very long, and composed of
numerous joints ; the maxillary palpi, which are from five
to seven jointed, are very conspicuous. These insects are
also inhabitants of moist places. The Lepisma saccharina
is commonly found about houses, in sash-frames, old sugar-
casks, &c. ; from the latter circumstance it derives its
name. The scales (fig. 273, No. 8) have long been
favourite objects, and much used for testing the power of
penetration and definition of object-glasses. The scales
should be mounted under thin glass covers ; oblique light
shows some portions of the scale to advantage ; other
parts are rendered more distinct when the central rays of
the achromatic condenser are stopped out.

The metamorphosis is complete in the Suctoria, or
Siphonaptera, a wingless family — the larva, pupa, and
imago of which are very distinct in their appearances —
the well-known Flea is the best example of this small
group. By many authors these insects have been arranged
with the Diptera : this is most decidedly incorrect, since
they differ in many particulars. The external covering of

630

THE MICROSCOPE.

the Flea (fig. 287) is a horny case, divided into distinct
segments ; those upon the thorax being always disunited.
Although apterous, the Flea has the rudiments of four

Fig. 287

1, Female Flea. 2 Male Flea. (The small circles enclose fleas the aclaal or
life size./

THE FLEA. 631

wings, in the form of horny plates on both sides of the
thoracic segments. Its mouth consists of a pair of sword-
shaped mandibles, finely -serrated ; these, with a sharp,
penetrating needle-like organ, constitute the formidable
weapons with which it pierces through the skin.

The neck is long, the body covered over with scales, the
edges of which are set with short spikes or hairs ; from its
head project a pair of antennas, feelers or horns, a pro-
boscis, which forms a sheath to the pair of lance-shaped
weapons. On each side of the head a large compound eye
is placed. It has six many-jointed powerful legs, termi-
nating in two-hooked claws ; a pair of long hind legs are
kept folded up when the insect is at rest, which in the
act of jumping it suddenly straightens out, at the same
time exhausting all its muscular force in the effort. The
female Flea, fig. 287, lays a great number of eggs, sticking
them together with a glutinous secretion • the Flea infest-
ing the dog or cat glues its eggs fast to the roots of the
hairs ; in four days' time the eggs are hatched, and a small
white larva or grub is seen crawling about, and feeding
most actively. No. 4 (fig. 289) is a magnified view of one,
covered with short hairs, doubtless for the purpose of
preventing its dislodgment. After remaining in this
state about nine or ten days, it assumes the pupa form ;
this it retains four days ; and in nine days more it be-
comes a perfect Flea. The head of the Flea found in the
cat (No. 3, fig. 289) somewhat differs in form from that
of the species infesting the human being. Its jaws are
furnished with more formidable-looking mandibles, and
from between the first and second joints behind the head
short strong spines project.

Arachnida. — The animals forming the class Arachnida
include spiders and their allies, most of which are looked
upon with disgust and aversion by the generality of man-
kind. Arachnida are divided into two orders, Trackearia
and Pulmonaria. The first includes the Acaridce or
Mites, in which we find tracheae, as in insects, but no
distinct vascular apparatus : in the second, spiders and
scorpions are included, and these have a pulmonary cavity,
and a well-developed circulatory system. The above are
distinguished from Podopthalmia or Arthropoda by their

632 THE MICROSCOPE.

aerial respiration, their possession of four pairs of legs
attached to an anterior division of the body, and the total
absence of antennae. The body is also covered with a
softish skin, which sometimes attains a horny consistency,
but nothing more. In the higher forms, the body is
divided into two parts, the anterior of which, as in Crus-
tacea, consists of a thoracic segment, amalgamated with
the head, and forming together a whole called the cephalo-
thorax. In the highest classes the division of the thorax
into separate segments becomes apparent; the anterior
segment is, however, amalgamated with the head. The
structure of the abdomen varies greatly. In some cases
it forms a soft round mass, without any traces of seg-
mentation ; whilst in others, as scorpions, it is continued
into a long flexible jointed tail.

Acarea, an order of animals not strictly belonging to
insects, but rather to Arachnida, Spiders, Scorpions, &c.
The general description of the class is that the head
is united with the thorax, forming a cephalo-thorax ; no
antennae, simple eyes, body presenting transverse striae or
furrows between the second and third pair of legs, which
are eight in number, terminated by an acetabulum and
claws. These animals are commonly called mites, and
the best known species is that found in cheese, iheAcarus
domesticus. Most of the species are oviparous and vivi-
parous, their eggs are very numerous. The spider enve-
lopes its eggs in a beautiful silken cocoon. Scorpions
produce their young alive, and it is deserving of notice
that in this family the embryo is developed in the ovum
while it still remains in the ovary. The existence of a
micropyle has not yet been made out in the ova of Arach-
nida. For the sake of convenience we have included
Parasites in this part of our work, and in Plate YI. Nos.
144 to 147 are representations of their eggs, from some of
which the larvae are just emerging.

The MalophaguSj or Sheep-tick, fig. 288, is apterous,
and seems to be a connecting link between acarina and
insects proper. The Sarcoptes scabiei produces the itch in
the human being : it is also found to be the cause of mange
in the dog. In one pustule on a dog suffering from this
as many as thirty parasites have been found.

THE SHEEP-TICK.

633

The Louse (fig. 290, No. 1). — Whenever wretchedness,
disease, and hunger seize upon mankind, this horrid
parasite seldom fails to appear in the train of such
calamities, and to increase in proportion as neglect of

Fig. 288. — Malophagus ovinus, Sheep-tick. (The small circlu encloses one
of life size.)

personal cleanliness engenders loathsome disease. When
examined under the microscope, our disgust of it is in no
way diminished. In the head may he distinguished two
large eyes, and near to them are the two antennae ; the
front of the head is long, and somewhat tapering off to
form a snout, which serves as a sheath to the proboscis
and the instrument of torture with which it pierces the
flesh and draws the blood. To the fore part of its body
six legs are affixed, having each five joints, terminated
by two unequal hooks ; these, with other portions, are
covered with short hairs. Around the outer margin of

G34

THE MICROSCOPE.

the body may be seen small circular dots, the breathing
apertures, with which all the class are freely provided,
rendering them very tenacious of life, and difficult to kill.
There is another louse, rather differing in its characteristics

Fi<r. 289.

i»-vrasite. 2, Rat Acarus. 3, Head of Cat-Flea. 4, Larva, or grub oi
Flea. (The life size of each is given in the small circles, i

ACARINA.

635

Fig. 290.— parasites. Acarino..

1, LonfiO, Human ; magnified 50 diameters. 2, Acarus domestic/us, Choese-
Mite ; tinder surface. 3, Acarus Scabiei, Itch-Insect; magnified 350 dia-
meters. 4, Entozoon folliculorum, Grub from the human skin in various
stages of existence, from the egg upwards : magnified 350 diameters. (The
small circles near represent the objects about the natural size. )

C36 THE MICROSCOPE.

from this, found upon the body of the very poor and dirty
known as the body or crab-louse. Leeuwenhoek carried his
researches on the habits of these insects further than most
investigators, even allowing his zeal to overcome his disgust
for such creatures as the louse. In describing its mode of
taking food, &c., he observes : " In my experiments,
although I had at one time several on my hand drawing
blood, yet I very rarely felt any pain from their punctures ;
which is not to be wondered at, when we consider the
excessive slenderness of the piercer ; for, upon comparing
this with a hair taken from the back of my hand, I judged,
from the most accurate computation I could form by the
microscope, that the hair was 700 times larger than this
incredibly slender piercer, which consequently by its
punctures must excite little or no pain, unless it happens
to touch a nerve. Hence I have been induced to think
that the pain or uneasiness those persons suffer who are
infested by these creatures, is not so much produced from
the piercer as from a real sting, which the male louse
carries in the hinder part of his body, and uses as a
weapon of defence." He found, from experiments made
to ascertain the possible increase of these pests, that from
two females he obtained in eight weeks the almost in-
credible number of 10,000 eggs.

The Itch-insect, Acarus scabiei (fig. 290, No. 3, magni-
fied 350 diameters). Dr. Bononio was among the first to
detect the parasitic character- of the disease known as the
itch. On turning out one of the pustules, or little blad-
ders, from between the fingers, with the points of very
fine needles, under the microscope, a minute animal was
discovered, very nimble in its motion, covered with short
hairs, having a short head, a pair of strong mandibles or
cutting jaws, and eight legs, terminating in remarkable
appendages, each provided with a sucker and setae.

It has no eyes ; but when disturbed it quickly draws in
its head and feet, and then somewhat resembles the tor-
toise in appearance, its march is precisely that of the tor-
toise. It usually lays sixteen eggs, which are carefully
deposited in furrows under the skin, and ranged in pairs ;
these hatch in about ten days.

To find the itch-insect, the operator must examine care-

ACAEUS DOMESTICUS. 637

folly the parts surrounding each pustule, he will then see
a red line or spot communicating with it ; this part, and
not the pustule, must be probed with a fine-pointed instru-
ment ; the operator must not be disappointed by repeated
failures. Dr. Bourguignon bestowed much time in
studying the habits of this troublesome parasite. To
arrive at a knowledge of its haunts he arranged his mi-
croscope so as to enable him to observe it under the skin
of the diseased person. The rays of light from a lamp or
candle must be carefully brought to a brilliant focus by
means of the condensing or bull's-eye lens upon the
chosen point of observation ; a Leiberkiihn should also be
attached to the object-glass.

No. 4, fig. 290, Demodex folliculorum, is another re-
markable parasite found beneath the skin of man : it is
sometimes obtained from a spot where the sebaceous folli-
cles, or fat glands, are abundant ; such as the forehead, the
side of the nose, and the angles between the nose and
lip ; if the part where a little black spot or a pustule is
seen be squeezed rather hard, the oily matter there accu-
mulated will be forced out in a globular form ; if this be
laid on a glass slide, and a small quantity of oil added to
it, to cause the separation of the harder portions, the
parasite in all probability will float out ; after the addition
of more oil, it can then be taken away from the oily
matter by means of a fine-pointed sable pencil-brush, and
transferred to a clean slide ; ^when dry it should be im-
mersed in Canada balsam, covered over with thin glass,
and mounted in the usual way.

The Cheese-mite, A cams domesticus (fig. 290, No. 2),
has a peculiar elongation of its snout, forming strong,
cutting, dart-shaped mandibles, which it has the power of
advancing separately or together. The powder of old and
dry cheese almost entirely consists of mites and their eggs,
which are hatched in about eight days ; if deprived of
food, they have been seen to kill and eat each other.
Acari infest almost the whole of our dried articles of
food. Ac. passularum has two very long buccal bristles ; it
lives upon dried figs, and other saccharine fruits. Ac. de-
structor has long black hairs ; it feeds upon the contents
of entomological cabinets, especially butterflies; Ac. pru-

638

THE MICEOSCOPE.

norum is found on dried plums, &c. ; Ac. favorum finds
its food in old honeycombs ; A earns sacchari (fig. 291) is
commonly present in the more impure kinds of sugar.
The discovery of the general prevalence of this acarus
rests, we believe, with Dr. Hassall.

The Sugar acarus approaches somewhat, in its organisa-
tion and habits, A earns domesticus ; it attains to a size so
considerable, that it is plainly visible to the unaided sight.

Fig. 291.
Ova and young of the Acarus sacchari, Sugar-Insect, after Hassall.

When present in sugar, it may always be detected by the
following proceeding : two or three drachms or teaspoonfuls
of sugar should be dissolved in a large wine-glass of tepid
water, and the solution allowed to remain at rest for an
hour or so ; at the end of that time the acari will be
found, some on the surface of the liquid, some adhering to
the sides of the glass, and others at the bottom, mixed up
with the copious and dark sediment, formed of fragments
of cane, woody fibre, grit, dirt, and starch-granules, which
usually subside on the solution of even a small quantity of
sugar in hot water. The Acarus sacchari, when first
hatched, is scarcely visible ; as it grows it becomes elon-
gated and cylindrical, until it is about twice as long as

ACARINA PAEASITES.

639

broad; after a time the legs and proboscis begin to protrude.
The body is partially
covered by setae, and the
feet terminate in hooks.
These stages of the de-
velopment of the acarus
are exhibited in-fig. 291.
The Acarus faring.
Flour-mite. — This is of
occasional occurrence in
flour, but is never pre-
sent unless it has be-
come damaged. Any
flour, therefore, contain-
ing the animal in ques-
tion is in a state unfit
for consumption. We
believe that it is found
more frequently in the
flour of the Leguminosce
than that of the Gra-
minece.

This acarus differs con-
siderably in structure
from the Sugar-mite,
particularly so in its
pennate setae.

Dr. Burnett esta- Fig. m.—Acariufairina!t Meal-Mite, inagni-

blished to his satisfac-
tion the following facts :
" 1. That though there
are single species of pa-
rasites peculiar to parti-
cular animals, there are
others which are found
on different species of
the same genus; as is
the case in the para-
sites living on birds of
the genus Larus (gulls), Fi&-

1^1 j- i u- j c 1. ffippobosca Hirundinit. 2, Nirmi, mala

and the diurnal DirdS OI and female, parasites infesting Swallow*.

lied 250 diameters.

640

THE MICROSCOPE.

prey, 2. The parasites of the human body confine them-
selves strictly to particular regions ; when they are found

Fig. 294.

1, Parasite of Turkey. 2, A earns of common Fowl, under surface. 3, Parasite
of Pheasant. (The small circle encloses each about life size.)

elsewhere, it is the result of accident. Thus, the Pediculi
capitis live in the head ; P. vestimenti, upon the surface of
the body ; the P. tabescentium, on the bodies of those dying
of marasmus ; and the P. inguinalis, about the groins, arm-

ACARINA PARASITES.

641

pits, mouth, and eyes." From an examination of the
structure of these parasites, Dr. Burnett is of opinion that

Fig. 295.

1, Acarus of Beetle. 2, Acarus of Fly. 3, Acarus of Clothes-Moth. (The
circles enclose each about life size.)

they should be placed in an order by themselves, closely
allied to Insecta ; the mandibulate parasites occupying the
highest, and the haustellate the lowest, position in the
order : thus confirming to some extent the observations
made by Mr. Denny.

There is a remarkable species of acarus described by
T T

642 THE MICROSCOPE.

Dr. Eobins, found spinning a white silken web on the base
of the sparrow's thigh, or on the fore-part of its body ; OD
raising this delicate web, you perceive that it is filled with
minute eggs, from which the young issue, being in due
time hatched by the warmth of the body it is destined to

annoy. In fig. 29 6 are
seen some eggs of a
parasite infesting the
hornbiil ; they are
glued to the feathers
near the head of the
bird ; the larvae are
ready to leave the egg
in two days. Another,
curiously enough, se-
lects the pulmonic ori-
fice of the snail : when

Fig. SOQ.-Larva, of the Parasite of Hornbiil. ^Q animal dilates this

orifice, for the purpose of allowing the air to penetrate its
respiratory cavity, the female acarus slips through the open-
ing, and lays her eggs in the folds of the mucous membrane,
where they are gradually developed. The young, upon
issuing forth from the eggs, select some portion of the
snail's body upon which to feed and perfect their growth.

Ixodidoe are furnished with a powerful rostrum, armed
with recurvate spines, with which they pierce the skin of
the unfortunate animal upon whose blood they live. So
firmly do these anchor-like organs retain their hold, that if
the parasite is pulled away it usually carries a portion of
the skin of its victim with it. These creatures live upon
a great variety of animals. The dog is very liable to their
attacks, and many species fix themselves exclusively upon
serpents and other reptiles. Glyciphagus cursor is found
in the feathers of the owl, and in the cavities of the bones
of skeletons. Gamasidce are furnished with a sucking
apparatus very similar to that of Ixodidoe, usually attaching
themselves to the bodies of beetles ; the common Dung-
beetle (Geotroupes) is often found with its lower surface
nearly covered with them.

There are other families leading a more active life,
being furnished with eyes. One family, Hydrachnidcp.

ACARTNA PARASITES.

643

Water-mites, inhabit the water, where they swim about
with considerable rapidity by means of their fringed leys.

Fig.

1, Parasite of Eagle. 2, Parasite of Vulture. 3, Parasite of Pigeon,
circles enclose each about life size).

(The

In their young state, they attach themselves parasitically
to aquatic animals ; they then possess only six legs, and
pnss through a quiescent or pupa state before acquiring
the fourth pair. Orbitadce, unlike other Acarea, live
upon vegetable matter, principally damp leaves and moss ;

T T 2

644 THE MICROSCOPE

they have a mouth adapted for biting such food, and are
covered with a hard and very brittle skin. The Bdellidae
live among damp moss, have the body divided apparently
into two parts by a constriction, and the rostrum and
palpi very long ; whilst Trombidiidce, of which the little
scarlet mite so often seen in gardens is an example, have
their palpi converted into little raptorial organs.

Another family of parasites are commonly met with in
the bodies of fishes, attaching themselves to the branchiae,
to the soft skin under the fins, or to the eyes, much to
the annoyance .of the unfortunate victim. Some of these
found on fresh-water fish are sufficiently transparent to
show the circulation of their fluids — most interesting
objects for the microscope.

The Water-snail, Limnceus, is tormented by a larva of
the family Amphistoma, which attaches itself by a series
of booklets and bristles to various parts of the body and
mantle ; under a low magnifying power, when congre-
gated together, they appear somewhat like tufts of threads.1

ARACHNIDA, Spiders. — Epeira diadema is the best
known of the British species of Garden Spiders: it
is readily recognised by the beautiful little gem-like
marks -on its body and legs. Spiders abound on every
shrub ; and if we consider that the Spider is destitute of
a distinct head, without antennae, one-half of its body
attached to the other by a very slender connexion, and so
soft as not to bear the least pressure, - its limbs so slightly
attached to its body that they fall off at a very slight
touch, — it appears ill-adapted either to escape the many
dangers which threaten it on all sides or to supply itself
with food ; and the economy of such an animal is deserving
of the microscopist's attention.

The several important organs peculiar to the Spider
tribe are represented in fig. 299. Of these, No. 1 show
the spinning apparatus; four only are the spinnarets, or
organs by which their silky threads are emitted. Their
structure is very remarkable ; the surface of each spinnaret
is pierced by an infinite number of minute holes, shown

(1) The earliest known account of the parasite tribes is given in Redi's
Treatise de Generatione Insectorum; see also H. Denny's Monographia Anoplu-
rorum Britannice. 1842.

AKACHNIDA.

645

in No. 2, from each of which there escapes as many little
drops of a liquid as there are holes, which, drying the
moment they come in contact with the air, immediately
form so many delicate threads. Immediately after the
filaments have passed through the pores, they unite first
together, and then with those of the next, to form one
common thread ; so that the thread of the spider is com-

\

Fig. 298.— Epeira diadema, Diadein Spider.

posed of a large number of minute filaments, perhaps
many thousands, of such extreme tenuity that the eye can-
not detect them until they are twisted together into the
working thread. In the two pairs of spinnarets a different
anatomical structure can be detected; the pair above,
which are a little the longest, show a multitude of small
perforations, the edges of which do not project, and which
therefore resemble a sieve. The shorter pair have pro-
jecting tubes independent of the perforations which exist

646

THE MICROSCOPE.

in those above. The tubes are hollow, and perforated at
their extremities ; and it is supposed that the agglutinating
threads issue from these tubes, while those emitted from
the perforations do not possess that property. It will be
seen, by throwing a little dust on a circular Spider's web,
that it adheres to the threads which are spirally disposed,
but not to those that radiate from the centre to the cir-
cumference ; the latter are also the stronger of the set.

Fig. 29y.

J , Spinnarets of Spider. 2, Extreme end of one of the upper pair of spinna-
rets. 3, End of undor pair of spiunarets. 4, Foot of Spider. 5, Side view
of eye. (3, The arrangement of the four pairs of eyes.

The rapidity with which these webs are constructed is
as astonishing as is the accuracy with which the webs
are formed. There are many different kinds of Spiders ;
but nearly all of them envelop their eggs in a covering of
silk, forming a round ball, which the Spider takes care to
hang up in some sheltered place till the spring. The
mode in which the ball is formed is very curious.: the
mother Spider uses her own body as a guage to measure
her work, in the same way as a bird uses its body to
guage the size and form of its nest. The Spider first
spreads a thin coating of silk as a foundation, taking care
to have this circular by turning its body round during the
process. In the same manner it spins a raised border

ARACHNIDA. 647

round this till it takes the form of a cup ; it is at this
stage of the work that it begins to lay its eggs in the cup,
and not content to fill it up to the brim, it also piles up
a large round heap, as high as the cup is deep. Here,
then, is a cup full of eggs, the under half covered and pro-
tected by the silken sides of the cup, but the upper still
bare and exposed to the air and the cold. She now sets
to work to cover these also : the process is similar to the pre-
ceding, that is, she weaves a thick web of silk all round
them, and, instead of a cup-shaped nest, like some birds,
the whole partakes of the form of a ball much larger than
the body of the Spider.

The feet of the Spider, one of which is represented at
No. 4, are curiously constructed. Each foot, when mag-
nified, is seen to be armed with strong horny claws, with
serrations on the under-surface. By this arrangement the
Spider is enabled to regulate the issue of its rope from the
spinnarets. Some have, in addition, a remarkable comb-
like claw, for the purpose of separating certain threads
which enter into the composition of their delicate webs.

One of the most remarkable members of the family, the
Argyroneta aquatica, Diving Spider, weaves itself a curious
little bell-shaped globule, which it takes with it to the
bottom of the water, whither it retires to devour its prey.
Notwithstanding its aquatic habits, this, like the rest of
its order, is fitted only for aerial respiration ; it therefore
fills its miniature balloon with air, which it carries down
with it entangled amongst the hairs of its body. This
closely resembles the earliest diving-bells.

Mr. Quekett recommended the following as a simple
method of obtaining a perfect system of tracheal tubes
from the larvae of insects : — A small opening having been
made in the body, it is to be placed in strong acetic acid,
which softens or decomposes all the viscera : the trachea
must then be well washed with a syringe, and removed
from the body, by cutting away the connexions of the
main trunks with the spiracles, by means of fine-pointed
scissors. For mounting, they should be floated on to the
glass-slide, and laid out in the position best adapted for
displaying them. If we wish to mount them in Canada
balsam, they should be allowed to dry upon the slide,

648 THE MICROSCOPE.

but their natural appearance is best preserved by mount-
ing in weak spirit and water, or Goadby's solution, using a
very shallow cell, to avoid pressure. The spiracles should
be dissected out with a fine knife and scissors.

Mr. HepwortKs Mode of Preparing and Mounting In-
sects.— He destroys life with sulphuric ether, then washes
the insects thoroughly in two or three waters in a wide-
necked bottle; he afterwards immerses them in caustic
potash or Brandish's solution, and allows them to remain
in it from one day to several weeks or months, according
to the opacity of the insect ; with a camel-hair pencil he
then presses the contents of the abdomen and other soft
parts dissolved by the potash out in a saucer of clean
water, holding the head and thorax with one brush, and
gently pressing the other with a rolling motion against the
body from the head to the extremities. The potash must
afterwards be completely washed out, or crystals may
form. The insects must then be dried, the more delicate
specimens being spread out or floated on to glass- slides,
covered with thin glass and tied down with thread.-
When dry, they must be immersed in rectified spirits of tur-
pentine, and placed under an air-pump. When sufficiently
saturated they are ready for mounting in Canada balsam ;
but they may be retained for months in the turpentine
without injury. Before mounting, as much turpentine as
possible must be drained and cleaned off the slide ; but
the thin glass must not be removed, or air would be re-
admitted. Balsam thinned with chloroform is then to be
dropped on the slide so as to touch the cover, and it will
be drawn under by capillary attraction. After pressing
down the cover, the slide may be left to dry and to be
finished off. If quicker drying be required, the slide
must be warmed over a spirit-lamp, but not made too hot,
as boiling disarranges the object. Vapours of turpentine
or chloroform may cause a few bubbles, but these dis-
appear when condensed by cooling.1

TRANSFORMATION OF INSECTS.

The metamorphoses of the insect race offer some of
the most curious and wonderful of nature's phenomena for

(1) Journ. Micros. Soc, vol. i. p. 73.

TRANSFORMATION OF INSECTS. 649

contemplation. " We see," says an old author, " some of
these creatures crawl for a time as helpless worms upon
the earth, like ourselves ; they then retire into a covering,
which answers the end of a coffin or a sepulchre, wherein
they are invisibly transformed, and come forth in glorious
array, with wings and painted plumes, more like the inha-
bitants of the heavens than such worms as they were in
their former state. The transformation is so striking and
pleasant an emblem of the present, intermediate, and
glorified state of man, that people of the most remote
antiquity, when they buried their dead, embalmed and
enclosed them in an artificial covering, so figured and
painted as to resemble the caterpillar in the intermediate
state ; and as Joseph was the first we read of that was
embalmed in Egypt, where this custom prevailed, it was
probably of Hebrew origin."

Faint and imperfect symbol though it be, yet it may,
perchance, offer a glimpse of the metamorphosis awaiting
our own frail bodies. Between the highest and lowest
degree of corporeal and spiritual perfection, that there are
many intermediate degrees, the result of which is one
universal chain of being, no one can for a moment gain-
say. Thus the angel Eaphael is made to say, in Milton's
Paradise Lost, —

"What surmounts the reach

Of human sense, I shall delineate so,

By likening spiritual to corporeal forms,

As may express them best : though what if earth

Be but the shadow of heaven, and things therein

Each to other like, more than on earth is thought ! "

The great class of insects, which furnishes four-fifths of
the existing species of the animal kingdom, has two chief
divisions. In the one, the Ametabola, we have an imper-
fect, in the other, the Metabola, a perfect metamorphosis ;
that is, in the former there is no quiescent pupa state, and
the metamorphosis is accompanied by no striking change
of form ; in the latter, there is an inactive pupa that takes
no nourishment, and so great a change of form, that only
by watching the progress of the metamorphosis can we
recognise the pupa and the imago as belonging to the
same animal.

The degree of metamorphosis is, however, very different

650 THE MICROSCOPE.

in different groups of insects. In its most complete form,
as exemplified in the Butterflies, Moths, Beetles, and many
other insects, the metamorphosis takes place in three very
distinct stages. In the first, which is called the larva state,
the insect has the form of a grub, sometimes furnished
with feet, sometimes destitute of those organs. Different
forms of insects in this state are popularly known as Cater-
pillars, Grubs, and Maggots. During this period of its
existence, the whole business of the insect is eating, which
it usually does most voraciously, changing its skin repeat-
edly, to allow for the rapid increase in its bulk ; and after
remaining in this ' form for a certain time, which varies
greatly in different species, it passes to the second period
of its existence, in which it is denominated a pupa. In
this condition the insect is perfectly quiescent, neither
eating nor moving. It is sometimes completely enclosed
in a horny case, in which the position of the limbs of the
future insect is indicated by ridges and prominences ;
sometimes covered with a case of a softer consistence,
which fits closely round the limbs, as well as the body,
thus leaving the former a certain amount of freedom.
Pupce of this description are sometimes enclosed within
the dried larva skin, which thus forms a horny case for the
protection of its tender and helpless inmate. After lying
in this manner, with scarcely a sign of life, for a longer or
shorter period, the insect, arrived at maturity, bursts from
its prison in the full enjoyment of all its faculties. It is
then said to be in the imago or perfect state. This meta-
morphosis is one of the most remarkable phenomena in
the history of insects, and was long regarded as perhaps
the most marvellous thing in nature ; although recent
researches have shown that the history of many of the
lower animals presents us with circumstances equally if
not more wonderful, nevertheless the metamorphosis of the
higher insects is a phenomenon which cannot fail to arrest
our attention. To see the same animal appearing first as
a soft worm-like creature, crawling slowly along, and de-
vouring everything that comes in its way, and then, after
an intermediate period of death-like repose, emerging from
its quiescent state, furnished with wings, adorned with
brilliant colours, and confined in its choice of food to the

TRANSFORMATION OF INSECTS. 651

most delicate fluids of the vegetable kingdom, is a spec-
tacle that must be regarded with the highest interest;
especially when we remember that these dissimilar crea-
tures are all composed of the same elements, and that the
principal organs of the adult animal were in a manner
shadowed out in all its previous stages.

Nor is the singularity of their natural history the only
claim that these insects have upon our attention. Lowly
as they seem in point of organization, there are few
animals that exceed them in commercial importance. To
give an instance or two ; the finest red dyes known to our
manufacturers are derived from insects. The Lecanium
ilicis, an inhabitant of the Ilex, Evergreen-oak, growing in
countries near the Mediterranean, was employed for this
purpose by the ancient Greeks and Romans, as it is still
by the Arabs ; and, until the introduction of the Mexican
cochineal, another species, the Coccus polonicus, living
on the roots of the Scleranthus perennis in Central Europe,
was much used for the same purpose. The Mexican cochi-
neal, which has driven all other kinds out of the market, is
one of the species Coccinia ; this pretty insect was long
regarded as a parasite upon the Cactus opuntia, Prickly-
pear — a plant common in Central America. The com-
mercial importance of this insect is shown by a single fact :
in 1850, no less than 2,514,512 Ibs. of cochineal were im-
ported into Great Britain alone (value about 7s. per Ib.) ;
and as about 70,000 insects are required to weigh a
pound, we may form some idea of the almost countless
numbers annually destroyed. For many years the culti-
vation, or rather feeding, of cochineal was entirely confined
to Mexico ; but the insect has lately been introduced into
Spain, and the French possessions in Africa, with every
prospect of success. A fourth species, of great import-
ance, is the Lac insect, Coccus lacca, an inhabitant of the
East Indies, where it feeds upon the Banian-tree, Ficus
religiosa, and other trees. It is to this insect we are
indebted, not only for the dye-stuffs known as lac-dye
and lac-lake, of which upwards of 18,000 cwts. were
imported in 1850, but also for the well-known sub-
substance called shell-lac, so much used in the preparation
of sealing-wax and varnishes. It is somewhat remark-

652 THE MICEOSCOPE.

able that only the female insects yield a good colouring
matter.

Of all the secretions peculiar to insects, silk may well
be regarded as the most valuable, since it has become as
much an essential to the purposes of mankind as to the
economy of its producers. The fluid, before it comes in
contact with the air, is viscous and transparent in the young
larva, but thick and opaque in the more mature. It is found,
by chemical analysis, to be chiefly composed of Bombic
acid, a gummy matter, a portion of a substance resembling
wax, and a little colouring matter. Silk may be placed in
boiling water without undergoing any change ; the strongest
acids are required to dissolve it; and it has never yet been
imitated artificially. More than 500,000 human beings
derive their sole support from the culture and manufacture
of silk ; and the importance of the Silkworm to Great
Britain alone is represented by the large sum of 16,500,000£.
annually. Then we have large sums of money changing
hands from the labours of the useful little Bee ; tons'
weight of honey and wax are yearly consumed ; England
pays more than 50,000/. for foreign honey and wax, in
addition to her own valuable produce. A great variety of
scents, which from their agreeable odours are much used in
perfumery, are manufactured from insects. The Spanish
My is an indispensable article in the treatment of certain
forms of disease ; and that invaluable agent, Chloroform,
was first made from formic acid ; an acid discovered in the
Formic ant, and from which it has derived its name.
Then there are Gall-nuts, produced by a small fly, for which
a substitute could not be found in dyeing and ink-making.

" Much more extensive and important than any of the
foregoing, but, as less palpable, even more disregarded, are
the general uses of insect existence. Disease, engendered
of corruption in substances animal and vegetable, would
defy all the precautions of man, unless these were aided
by scavenger- insects, those myriads of flies and carrion
beetles, whose perpetual labours, even in our tempered
climate — but infinitely more so in warmer regions — are
essentially important to cleanliness and health.

" A use of this nature, and one performed perhaps to an
extent we little think of is the purification of standing

TRANSFORMATION OP INSECTS. 653

waters by the innumerable insects which usually inhabit
them. We have witnessed ample proof of the efficacy in
this respect of Gnat larvae, when keeping them to observe
their transformations. Water swarming with these ' lives
of buoyancy ' has been perfectly sweet at the end of ten
days ; while that from the same pond, containing only
vegetable matter, has become speedily offensive.

" We have already pointed out the utility of insects in
affording ever-new subjects of interesting inquiry. And
let those who will look scorn upon our pursuit ; but few
are more adapted to improve the mind. In its minute
details, it is well calculated to give habits of observation
and of accurate perception ; while, as a whole, the study
of this department of nature, so intimately linked with
others above and below it has no common tendency to lift
our thoughts to the great Creative Source of Being, to
Him who has not designed the minutest part of the
minutest object without reference to some use connected
with the whole."

*' The shapely limb anJ lubricated joint
Within the small dimensions of a point,
Muscle and nerve miraculously spun,
His mighty work, who speaks, and it is done ;
The invisible in things scarce seen revealed,
To whom an atom is an ample field."

CHAPTER Y.

VERTEBRATA.

PHYSIOLOGY — HISTOLOGY — BOUNDAKY BETWEEN THE TWO KINGDOMS- CELT.
IIKVELOPMENT — GKOWTH OF TISSUES — SKIN, CARTILAGE, TEKTH,

BONE, ETC.

HE most complicated state in which
matter exists, is where, under
the influence of life, it forms
bodies with a curious internal
structure of tubes and cavities,
in which fluids are moving and
producing incessant internal
changes. These are called orga-
nised bodies, because of the
various organs which they contain, and
they form two remarkable classes ; those
of the lowest class are for the most part
fixed to the soil, and are recognised as
vegetables, — the structure of these we have
already considered ; those of the higher
order are endowed with power of locomo-
tion, ancf are called animals. Some of the peculiarities
and minute structure of the invertebrate animals have
already been made the subject of investigation, and we
now propose to extend our observations to the vertebrate.
The study of the Science of Life, or the building up of
the living structure, is termed Physiology, or Biology ; 1
and that part of it more particularly relating to the minute
structure of the organs of animals has been termed
Histology.'2'

(1) From /3io9, life, and Xo-yoy, discourse— & discourse on life ; a more expres-
sive term than physiology.

(2) From lo-ror, o tissue, or web, and Xo-yoy, o discourse.

IN.IKCTIOXS, ETC.

~Z&
• ^tSfaXft ' .*,'*., j « *, A A . « A _,fl^Ji__

Tuffen West del.

I'J-ATK VI. I.

ANIMALS AND VEGETABLES. 655

Physiology has for its object the scientific co-ordination
of the phenomena and laws of life ; yet, writes Mr. Lewes,
" the attempts to define what we are to understand by Life,
have hitherto proved almost if not quite valueless." In
our previous investigations, we must have seen the value
and advantage of " studying Life in its simpler forms,
if Life is to be understood in its more complex ; and
no sooner do we comprehend the fact that the lower
animals present to us the more important phenomena of
Life under simpler forms and conditions, than we at once
recognise the study as indispensable."

It was Ehrenberg who first asserted that there was an
absolute boundary between animals and plants ; finding
even, as he fancied he did, in the smallest of the former, —
the Infusoria, — which had previously been regarded as
mere unorganised masses of mucus, the same systems of
organs as those by which the most highly-developed animal
is characterised, that is to say, distinct nutritive, motile,
vascular, sexual, and sensitive systems. Siebold called
the existence of these organs in question, regarding the
organisation of the Infusoria as a homogeneous paren-
chyma, in which he recognised only a nucleus, and in one
division a mouth and oesophagus. Nevertheless he asserted
that plants and animals were essentially distinct, and that
there was no transition from one to the other, the nature
of the plant being always immotile and rigid, whilst the
animal possessed the faculty of contracting and expanding
its body. This contractility is, in his opinion, alone to be
taken as the characteristic feature. It is not, however, the
animal organisation itself which is contractile, but only a
single tissue in it ; all the rest, skin, bones, and connective
tissue, are as rigid or passive as the vegetable membrane,
or, at most, only elastic ; in the higher animals the muscles
only are contractile, and in those of the lowest classes, viz.
the Infusoria, the entire body.

Whence Ecker assumed the existence of a special con-
tractile substance, which sometimes occurs in a formed
state, as a contractile cell or as muscular substance, some-
times amorphous, as in the bodies of the Infusoria, Rhizo-
poda, and Hydrozoa. Kdlliker confirmed this view, and
carried it out, particularly in the case of the Infusoria,

656 THE MICROSCOPE.

which, he at one time declared to be unicellular animals
with a contractile cell-membrane and contents. The con-
tractile substance is characterised by the following attri-
butes : it is homogeneous, or finely granular, transparent,
of the consistence of albumen, gelatiniform, soft, more
refractive than water, but less so than oil ; insoluble in
water, but gradually decomposed ; destroyed by caustic
potash ; coagulated and contracted by carbonate of potash,
as well as by alcohol and nitric acid ; having the power of
forming aqueous cavities, which originate either by the
separation of the water contained in it, or by its reception
from without ; owing to which the remainder becomes
denser and more granular, and lastly, it represents the
appearance, in water, of contractile drops, which move like
an Amoeba. All these properties had already been observed
by Dujardin, in a substance of which the Infusoria and
Bhizopoda are principally composed, and which he termed
" sarcode ; " the aqueous spaces or hollows he named
"vacuoles," regarding them as the most characteristic
features of the substance ; these spaces had been errone-
ously regarded by Ehrenberg as stomachs. All these
properties, however, are possessed by a substance in the
plant-cell, which must be regarded as the prime seat of
almost all vital activity, but especially of all the motile
phenomena in its interior — the protoplasm. Not only do
its optical, chemical, and physical relations coincide with
those of the "sarcode," or contractile substance, but it
also possesses the faculty of forming " vacuoles " at all
times, and even externally to the cell ; a property, it is
true, which has for the most part been hitherto overlooked
or misinterpreted. These clear, aqueous spaces, the so-
termed vesicular contents, are present in all young
cells, and play a considerable part in cell division, and the
sap-currents ; they are in all respects analogous to the
vacuoles of the sarcode.1

(1) Mr. Huxley has satisfied himself that in all the animal tissues the so-
called nucleus (endoplast) is the homologue of the primordial utricle, with
nucleus and contents (endoplast) of the plant, the other histological elements
being invariably modifications of the periplastic substance. Upon this view we
find that all the discrepancies which had appeared to exist between the animal
and vegetable structure disappear : and it becomes easy to trace the absolute
identity of plan in the two, the differences between them being produced merely
by the nature and form of the deposits in, or modifications of, the periplastic

HISTOLOGY. 657

In organised beings, the way in which nature works out
her most secret processes is by far too minute for observa-
tion Hby unassisted vision \ even with the aid of the improved
microscope, comparatively a very small portion has, up to
this time, been revealed to us. To point out in detail the
discoveries made through the employment of this instru-
ment, as regards physiology, would be to give a history of
modern biological science ; for there is no department in
this study which is not more or less grounded upon the
facts and teachings of the microscope.

To the casual observer, the brain and nerves appear to
be composed of fibres. The microscope, however, reveals
to us, as was first pointed out by Ehrenberg, that these
supposed fibres do not exist, or rather, that they all consist
of numerous tubes, the walls of which are distinct, and
contain a fluid which may be seen to flow from their broken
extremities on pressure. In looking at a muscle, it appears
to be made up of fine longitudinal fibres only. The micro-
scope tells us that each of these supposed fine fibres is com-
posed of numerous smaller ones, and that these are crossed
by lines which have received the name of transverse striae ;
that muscular contraction, the cause of motion in animals,
is produced by the relaxation or approximation of these
transverse striae.

The microscope has shown us that a distinct network of
vessels lies between the arteries and veins, partaking of
the properties of neither, and possessed of others peculiar
to themselves. These have been denominated intermediary
vessels by Berres, and, serving to connect the arterial with
the venous system, are commonly known as capillaries.

On regarding with the naked eye the different glands
in which the secretions are formed, how complex they
appear, how various in conformation ! The microscope
teaches us that they are all formed on one type ; that the

substance. In both plants and animals there is but one histological element —
the endoplast — which does nothing but grow and vegetatively repeat itself ;
the other element -the periplastic substance— being the subject of all the che-
mical and morphological metamorphoses in consequence of which specific
tissues arise. The differences between the two kingdoms are mainly, first,
That in the plant the endoplast grows, and the primordial utricle attains a
large comparative size, while in the animal the endoplast remains small, the
principal bulk of its tissues being formed by the periplastic substance ; and
secondly, In the nature of the chemical changes which take place in the peri-
pi nstic substance in each case.

U U

658 THE MICROSCOPE.

ultimate element of every gland is a simple sacculated
membrane, to which the blood-vessels have access; and
that all glands are formed from a greater or less number,
or different arrangement only of the primary structure.

Our notions respecting the skin were vague until the
microscope discovered its real anatomy, and showed us
the existence and relations of the papillae, of the sudorific
organs and their ducts, the inhalent muscular apparatus,
and so on. All our knowledge of epidermic structures,
such as hair, horn, feather, &c., the real structure of
cartilage, bone, tooth, tendon, cellular tissue, and, in a
word, of all the solid textures, has been revealed to us by
the same agency ; so that it may be truly said, that all our
real knowledge of structural anatomy, and all our acquaint-
ance with the true composition of every organ in the body,
have been arrived at by means of the microscope, and
could never have been known without it.

In addition to this, and what is of greater importance,
after having studied the healthy structure of the body,
most beneficial aid is afforded in the investigation ot'
changes produced by disease. We may cite one notable
example. Dr. Andrew Clarke, after having carefully
studied the appearances of sputa from patients under his
care, says, " that the microscopical inspection of expecto-
ration affords, at a very early period of consumption, defi-
nite information, not otherwise attainable, regarding the
nature of the malady; and at all times must furnish
valuable aid in forming a prognosis regarding the cause of
the complaint." The expectoration generally shows pus,
cells, lung tissue, blood corpuscles, and granular material,
mixed with, at times, a small amount of fat corpuscles.

The space allotted to this division of our subject enables
us to give only a short and imperfect sketch of a few of
the fundamental tissues of the animal body. First, enu-
merating merely the elementary substances recognised by
chemistry as entering into the formative processes, we shall
proceed to inquire into that most interesting and wonderful
starting-point of life, the cell ; admitted to be, and indeed
demonstrable as, the common centre alike of animal and
vegetable organisms.

HISTOLOGY.

659

THE HUMAN BODY, ITS PHYSIOLOGICAL COMPOSITION AND
CHARACTER.

The elementary substances found in the human body are
oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur,
chlorine, fluorine, iron, manganese, titanium, and calcium.
Silenium is found in the hair, and fluorine in combination

Fig. 300. — Diagram showing various forms of development in Animal Cells.

1, Shows a newly formed cell. 2, Subdivision of the nucleus. 3, The nucleui
changes its situation, and at 4, subdivides and disappears. 5, The walls of
the cell increase in thickness. 6, the cell becomes branched, or stellate. 7,
Two cells are seen to coalesce. 8, They have coalesced and run into each
other. 9, Again they take another form and become multilocular. 10,11,12,
Cells sprouting out to form membrane and vessels. 14, Development of
complicated cells, which, at 13, have coalesced to form tissue.

with lime forms the enamel of the teeth. Iron is the
chief colouring-matter of the blood, the black pigment of
the choroid of the eye, and the skin of the negro.

u u 2

660 THE MICROSCOPE.

Cells. — All animal and vegetable structures, the micro-
scope has revealed to us, are developed from cells or their
nuclei ; and the materials for building up animal structures
are furnished from the yolk and the blood.

The animal nucleated cell, fig. 300, is more or less of a
globular form ; within the delicate cell-wall a granular
matter is inclosed suspended in a fluid; the wall being
somewhat darker than the rest. There are usually one or
two spherical masses termed nuclei ; these enclose central
dots, termed the nucleoli. The size of a cell may be
1 -300th part of an inch in diameter, some are larger, some
smaller ; the nucleus may be 1,3000th of an inch in dia-
meter ; the nucleolus l-10,000th of an inch in diameter,
more or less.

Of the Cell. — Dr. Beale's views of the cell are so ori-
ginal, and his theory of its development so carefully
studied and worked out, that we shall attempt, in as few
words as possible, to place them before our readers. The
cell has always been considered, and is still so, by many
good authorities, to consist, as just stated, of certain defi-
nite parts, viz. cell-wall, cell-contents, and nucleus ; to each
of which various different functions have been assigned.
Many affirm that the vital force is resident in the nucleus
alone, while others attribute to the cell- wall, or even to the
inter-cellular substance, the power of producing chemical
and other changes. Dr. Beale considers this view to be
entirely erroneous, and states that every cell or " anatomi-
cal elementary part" consists of matter in two different
states or stages of existence — matter which lives (germinal
matter), and matter which is formed (formed material),
and which has ceased to manifest purely vital phenomena ;
all living entities, from the smallest living particle to the
most complex cell, consist of matter in these two states,
the relative proportions of which differ at different periods
of the life of the cell, and vary with the different con-
ditions under which it may be placed. If a tissue be
examined before development has proceeded to any great
extent, masses of germinal matter will be found almost
continuous with each other, without any appearance of the
cells from which all tissues are said to be originally formed.

CELL FORMATION. 661

As growth proceeds, these masses become separated, and
the small processes or tubes which connected them, are
drawn out, as it were, and become thinner and thinner ;
so that, for instance, in the formation of stellate tissue, so
far from the rays having been shot out by unequal growth
from special points of the original cell-wall, they have
been continuous from the very first.

Of the Structure and Formation of the simple Cell Muce-
dines. — The mucedines, commonly called mildews, are
among the simplest living things known, and are therefore
well adapted for observation. If the membranous invest-
ment of a fully developed spore taken from one of these
fungi be ruptured, innumerable minute particles, some not
more than I -100,000th of an inch in diameter, are set free :
these constitute the living growing matter, in contradis-
tinction to the envelope or outer part of the cells. " Ger-
minal matter" may always be readily distinguished from
formed material by its capability of becoming dyed by an
alkaline solution of carmine, while the latter remains
perfectly colourless. Directly such a minute living par-
ticle comes into contact with air or water, a thin layer
upon its outer part becomes changed into a soft, passive,
transparent homogeneous substance (cell-wall), exhibiting
a membranous character, which protects the matter within.
Nutrient matter passes through this into the interior, and
there becomes changed into living matter ; so that growth
takes place, not by additions to the outside, but by the
introduction of new matter into the interior. If pabulum
be abundant, and the external conditions (temperature,
moisture, &c.) favourable, it readily passes through the
thin external membrane, and the living matter rapidly
increases. But if the external conditions be unfavourable,
less pabulum transudes, and the living matter within dies,
layer after layer, until the envelope becomes very much
thickened, with a proportionate decrease in the size of the
living matter. If all this living matter die, and only
formed material remain, no increase can take place ; but if
the smallest particle remain alive, any amount of living
matter, and afterwards of tissue or formed material, may
be produced. The position of the germinal matter in the
cell varies with the direction in which the pabulum reaches

662 THE MICROSCOPE.

it ; thus in the columnar epithelial cells covering the villi
of the intestines, in which the pabulum flows from the
free surface towards the attached extremity, the germinal
mass is found near the centre or near the free edge of the
cells ; but in the mucus-forming cells from the mouth and
fauces, in which the pabulum flows in the opposite direc-
tion, $he germinal mass is found to be placed quite at the
attached end of the cells, where it has consequently easier
access to the pabulum, upon which its growth and secretive
power depends.

Cell-wall and Cell-contents. — In the mucus cells above
mentioned, and in many other cells, two kinds of formed
material are produced from the original germinal matter ;
these are spoken of as the cell-wall, and the peculiar
matter found inclosed in it, the cell-contents. For instance,
in the starch-containing cell of the potato, the cell-wall is
formed around and invests the germinal matter, while the
starch is deposited as small insoluble particles in the very
substance of the germinal matter. So that by the death
of particles on the surface of the cell-wall the cellulose
cell-wall is produced, while by the death of some of the
particles further inwards, and therefore under different
conditions, starch is formed. This outer part of the ger-
minal matter, which eventually lies between the starch
grains on the inside and the cell wall on the outside, is
known as the "primordial utricle" of the vegetable cell.
Fat-cells or adipose vesicles are formed in precisely the
same way ; fat may, moreover, be deposited amongst the
germinal matter of other cells, such as the cartilage or
nerve cell.

Of the so-called Intercellular Substance.— -In cartilage,
tendon, and some other tissues there is no line of sepa-
ration between the portions of formed material which
belong to each respective mass of germinal matter ; and
hence it has been supposed that these tissues were deve-
loped in a diiferent way to the epithelial structures. A
"cell," or elementary part of adult cartilage or tendon,
merely differs from the epithelial cells, spoken of above,
in not having a distinct margin around its own particular
formed material, and if a line were drawn midway between
the various germinal masses, it would roughly mark out

CELL FORMATION. 663

the point to which the formed material corresponding to
each extended; and each cell would then be exactly
analogous to the mucous-forming cells. In all of these cells,
of mucous membrane, tendon, cartilage, muscle, &c., there
is no abrupt demarcation between the germinal matter and
the formed material, but the one passes gradually into the
other. All living cells consist of matter in these two
different states ; the one being an active condition, vital ;
the other merely passive, in which no vital actions are
exhibited : upon matter in this first state, all growth,
multiplication, conversion, all life depends ; while in the
second condition, matter may exhibit many very peculiar
properties, but it does not grow or multiply, or convert or
form ; in short, it does not live, though it may increase by
new matter being superadded to it.

Of the Nucleus and Nucleolus. — A mass of germinal
matter, besides increasing in quantity, may divide into
several, and thus cell-multiplication may occur ; and in all
cases it is to be observed that this multiplication is not
due to a "gro wing-in," or constriction of the cell-wall or
formed material, but entirely to changes occurring in the
germinal matter. In many cases a smaller spherical mass
may be observed in the centre of the germinal mass,
which often divides before the parent mass itself does;
but it is by no means a necessary part of the process, for
division as often takes place where no such bodies are to
be seen ; and it frequently happens that these small
bodies may make their appearance only after the division
of the original mass. And again, within these, other still
smaller ones are sometimes produced The former are
termed nuclei, the latter nucleoli. These are to be regarded
as but new living centres appearing in centres already pre-
existing, and may perhaps mark the commencement of a
set of changes differing in some minor particulars from
the first that have occurred. But although both nuclei
and nucleoli are germinal or living matter, they are not
undergoing conversion into formed material. Nuclei do
not always exhibit their vital powers, but under certain
circumstances they may do so, and then they exhibit the
characters of ordinary germinal matter ; they absorb pabu-
lum and increase in size, and the original germinal matter

664 THE MICROSCOPE.

becomes changed into formed material, while fresh nuclei
and nucleoli are developed. And so far from nuclei bein^
formed first, and the other elements of the cell deposited
around them, they always make their appearance in the
substance of pre-existing matter, and have neither a
different constitution to ordinary germinal matter, nor
perform any special function.

Of the Increase of Cells. — Several distinct modes of cell-
multiplication have been described, but in all cases the
germinal matter divides, and is the only material actively
concerned in the process ; which may, however, take place
in different ways.

1. The parent mass may simply divide into two equal
parts, apparently in obedience to a tendency of the por-
tions to move away from each other as soon as the original
mass has reached a certain size.

2. The parent mass may divide in three, four, or more
equal portions.

3. From every part of the parent mass protrusions may
occur, each of which, when detached, absorbs nutrient
matter, and soon attains the same size as its parent.
During these processes of increase and multiplication, the
formed material is perfectly passive, and when a septum
or partition exists, it does not result from a "growing-in"
of this dead structure, but is produced by the conversion
of part of the germinal matter into a thin layer of formed
material.

Of the Changes of the Cell in Disease. — If the conditions
under which cells ordinarily live be modified beyond a
certain extent, a morbid change may result. For instance,
if cells, which normally grow slowly, be supplied with an
excess of nutrient pabulum, they grow — that is, convert
certain of the constituents of the pabulum that come into
contact with them into matter like themselves — at an
increased rate. In this way the inflammatory product
pus results. " The abnormal pus-corpuscle may be pro-
duced from the germinal or living matter of a normal
epithelial cell, the germinal matter of which has been supplied
with pabulum much more freely than in the normal state."
In cells in which the access of nutrient pabulum is more
restricted than in the abnormal state, as in normal cells

CELL FORMATION. 865

passing from the embryonic to the adult state, the outer
part of the germinal matter undergoes conversion into
formed material, which increases as the supply of pabulum
becomes reduced.

Dr. Beale, in short, considers that " all formed matter
results from changes in the germinal matter, and that the
action of the cell really consists in a change from the living
to the lifeless state of the matter of which it is composed ;
and that the products formed by the cell do not depend
upon any metabolic action exerted by the cell- wall or
nucleus upon the pabulum, nor are they simply separated
from, or deposited by, the blood." And he looks upon
the "living cell" as a minute body, consisting partly of
living matter influenced by vital force, and partly of life-
less matter resulting from the death of the first, in which
chemical and physical changes occur, which may be
modified by the influence of surrounding substances and
external forces.

In pursuing the subject of cell development, we shall
proceed by the aid of our old lights in this intricate path
of physiological science. And it is only right that we
should add, that the views we have endeavoured to place
fairly before our readers have not been unhesitatingly
accepted, but, on the contrary, those of the German school
are greatly preferred by many physiologists.

Change of Cells into Tissues. — This may take place by
a joining together or coalescence of cells in a rudimentary
state. Cells may meet, and at the point of contact coalesce
and run into each other, thus forming a tube ; indeed,
in this manner minute tubular structures are formed.
Another mode is : cells aggregate into a mass, and at the
point of contact run into each other, thus producing a
multilocular cavity ; No. 9, fig. 300. Glandular struc-
tures are formed in this way. Membrane is formed of a
deposit from the cytoblastema ; before the cell-membrane
is formed, the substance from the cytoblastema coalesces
with those particles close at hand, thus forming a delicate
film-like membrane. This membrane Professor T. Whartou
Jones calls endosmotic, retentive membrane. We have
the cells coalescing to form a filament or fibre. The nucleus
may disappear, or form another structure ; and where

666 THE MICROSCOPE.

regeneration of tissue is proceeding, there is found a
larger number of granules.

According to some histologists, cells may be formed in
cytoblastema independent of any pre-existing cells ; this
is cited as an instance of that mysterious agency desig-
nated spontaneous generation. There are cells which, so
far as we know, after full development, undergo no further
metamorphosis ; such as those of the epithelium, the blood
corpuscles, &c.

As an instance where previously-existing cells exert an
influence on those about to be formed, we may adduce a
fractured bone, between the ends of which osseous matter
is deposited. We infer from this, that the substance of the
bone determines, as it were, the formation of other cells,
first into cartilage, and then into bone. Generally, how-
ever, where a part has to be repaired, it does not seem to
determine the generation of a texture similar to itself —
for example, muscle and skin. We have an exception to the
last observation in the case of nerves, which if cut across,
a substance is formed between the ends which transmits
the nervous influence, but the ends must not be separated
to any great distance, or this will not occur. The
same remark applies to bone. There may be a single
layer of cells so arranged side by side, and presenting
a columnar or basaltic form ; this arrangement is seen
in the cells of the intestinal tract, fig. 303 a. Another
change of cell is this : they shoot out processes from
certain parts of them, as seen in fig. 300, Nos. 10, 11;
this kind of formation occurs on the inner surface of
the sclerotic coat of the eye. The cylindrical form of cell
is found with delicate processes shooting out from the
broad end ; these are called ciliated, fig. 303 d, and the
cilia having a vibratile motion urge on the secretions of
the part in a particular direction.

In some cases the walls of the cell increase in thickness
(fig. 300, No. 5). Under the microscope, some cells
appear to be composed of concentric laminae. In plants
this is the common mode of increase in the thickness of
the cell, but the deposit does not take place entirely
around, but only here and there, so that vacant spaces
«ra V>ft which form canals, and may become branched :

CELL-GROWTH. 667

these canals are named pore-canals (fig. 300, No. 6).
They do not perforate the outer layers ; consequently the
blind ends seen through the outer membrane, and which
were supposed to be apertures, are nothing of the kind.
Henle believes he has found canals in cells in animals
similar to those in vegetables — in the cartilage of the
epiglottis, for instance. In other instances, cells may
be aggregated, like a bunch of raisins, and the parts
in contact with each other disappear, so constituting
a multilocular cavity : examples of this are seen in
the racemose glands (fig. 300, No. 9). Schwann
conjectures another mode of coalescence. From cells
formed as usual, processes sprout out ; but this change
takes place at the expense of the cell-membrane itself,
and when it has gone on to some extent, we have
the appearance of a net-work formed (fig. 300, No.
11, and 12). Capillary vessels are formed in this way.
Cells, we thus perceive, coalesce to form tissues, when
they have not attained their full growth as such ; or when
they have been fully formed they become flattened, and
assume the solid form. Deposits of matter may take
place from the cytoblastema with similar adjoining sub-
stance, constituting a delicate membrane, with here and
there nuclei, as in the capsule of the lens, the membrane
of the aqueous humour of the eye, or sheath of the primi-
tive fasciculus of muscle ; or the cells may coalesce in the
linear series, to form fibre.

Development of Complicated Cells. — Here the nucleated
cell is surrounded by a deposit, and that again surrounded
so as to constitute a membrane ; so that the nucleated cell
may be looked upon as the nucleus to the cell so formed
(fig. 300, Nos. 13 and 14). Sometimes the nucleus under-
goes important changes in the development of tissues, as
well as the cell itself. In some cases, where the cells have
joined in the linear series, the nucleus becomes oval, elon-
gated, so that the nucleus of one cell tends to meet the
nucleus of another cell ; they subsequently coalesce, and
thus fibre is said to be formed.

Action of Celh. — The subsequent changes of the cell
depend in a great degree on endosmosis, or diffusion. The
nature of the membrane is a necessary condition, for it

668 THE MICROSCOPE.

determines the way in which the stream should pass ; and
we find in general that the current is from the rarer to the
denser fluid. If we immerse a porous tube half filled with
a strong solution of common salt in a jar of water, we notice
that the level of the fluid inside the tube rapidly rises
above the outside, while the water becomes slightly salt
to the taste. It is not a constant circumstance that the
stream is from the rarer to the denser fluid ; with alcohol
and water, for instance, the stream is from the latter to
the former. Mineral substances, even pipeclay and chalk,
permit of endosmosis in a low degree. In glands, the cells,
being filled with their peculiar fluid, are conveyed to the
wall of the intercellular passage, and through this the
secretion arrives at the surface of the body.

The Epithelium. — If we cut very thin slices from the
superficial portions of the skin, we can raise from it a
delicate membrane ; or, what is better, by using chemical
or mechanical irritation, we obtain what is ordinarily
called a blister ; to it we give the name of epidermis. The
microscope has shown this to be a tissue of high and
remarkable organisation ; being, in point of fact, an aggre-
gation of cells, differing, in different
situations, in regard to form, colour,
and composition. These laminated ele-
^§ BSPS^. men^ary cells, found on the surfaces,
*' ' -^ have generally nuclei. The form of

the nucleus is rounded or oval, and is
the l-3000th to l-5000th of an inch
in diameter. Each nucleus has two or
three nucleoli, with outlines more or
less irregular. The epithelium cells
may be divided into three kinds : the
1st is termed the tesselated or pave-
ment ; 2d, the columnar or basaltic ;
3d, the ciliated or vibratile epithelium.
Fig. SQL— Auction of the Some make a 4th, combining the tesse-
lated and the columnar : this may be
considered as transition epithelium, and is found only in
certain mucous passages. These various cells are repre-
sented in fig. 303, a, 6, c, and d.

EPITHELIAL CELLS.

669

Tesselated epithe-
lium is the simplest
form, and, as its name
implies, resembles flags
of pavement, over-
lapping each other
at their edges. They
assume, more or less,
the polygonal form,
and their size varies in
the different mem-
branes. The cells of the
pericardium, or cover-
ing membrane of the Fig- 302.

heart, are much smaller I, Simple isolated cells containing reproductive

' „ , , granules. 2, Mucous membrane of stomach,

than those 01 the COVer- fhowing nucleated cells. 3, One of the

inrT TnPTYi"hraT>P rvf fhp tubular follicles from a pig's stomach. 4, Sec-

' tne tion of a lymphatic, magnified 50 diameters.

lungs, &c. On some
surfaces we have many
layers — in the skin, for
instance ; if a verti-
cal section of such
be made, and viewed
under the microscope,
it will be seen to be
composed of number-
less layers, shown in
fig. 304. The skin
taken from the sole
of the foot, in con-
sequence of the con-
tinued pressure there Fi S03

(1) a is a diagram of a portion of the involuted mucous membrane, showing
the continuation of its elements in the follicles and villi, with a nerve entering
its submucous tissue. The upper surface of one villus is seen covered with
cylindrical epithelium ; the other is denuded, and with the dark line of base-
ment membrane only running round it ; 6, pavement epithelium scales, sepa-
rated arid magnified 200 diameters ; in the centre of each is a nucleus, with a
smaller spot in its interior, called the nucleoli. c, pavement epithelium scales,
from the mucous membrane of the bronchial or air tubes of the lung ; d
represents another form of epithelium, termed the vibratile or ciliated ; the
nuclei are visible, with cilia at their upper or free surfaces, magnified 250
diameters.

670 THE MICROSCOPE.

experienced, presents a distinctly stratified appearance.
These layers of cells are held together by intercellular
substance, which exists in quantities ; if the epithelium
be taken from these membranes it is more easily seen, be-
cause the cells are not so closely aggregated together as in
the skin ; therefore a piece of epithelium from the mouth
is recommended for display under the microscope, and by
the addition of a drop of the solution of iodine the cells are
much better seen. The cells from serous and mucous mem-
branes are acted upon by acetic acid, and dissolved if the
acid be of considerable strength : but if the acid be weaker,
the cells swell up. Cells are not affected by alcohol, ether,
ammonia, or its salts; but they are dissolved by caustic
potash, which also dissolves the intercellular substance.

Columnar or Cylindrical Epithelium, Fig. 303, a. — The
nucleus is generally better seen than in the former kind of
cells, although formed from them. If we examine a portion
sideways, it resembles those at d, the upper part being
broader, and the nucleus being midway between the two
extremities. When the cells of the cylindrical, epithelium
are closely aggregated together, they become compressed
into the prismatic form ; when they are less so, the rounded
shape prevails. Consequently, when we take a bird's-eye
view of them, from above or below, they appear like the
pavement epithelium, at c, and thus error might creep in ;
but we must become fully satisfied by examining them
sideways, and with various reagents. Their chemical com-
position is the same, and the cells dissolve in strong acetic
acid. As examples of the situations in which this form of
epithelium is found, we may instance the intestinal tract
along the ducts of the glands, as the liver, &c.

In no situations do we find these two kinds of epithe-
lium terminating abruptly the one in the other ; but there
is a gradual change of the one kind into that of the
adjoining; for example, where the tesselated epithelium
is gradually supplanted by the cylindrical, as it passes from
the oesophagus to line the interior of the stomach ; it is
then termed transition epithelium.

Ciliated Epithelium^ig. 303, d. — The cells do not differ
materially from those of the cylindrical ; the great distinc-
tion between he two is, that in the former there are no

CILIATED EPITHELIUM. 671

cilia attached to the broad end. Examples of the situations
in which these are • found are, investing membrane of the
respiratory passages, upper part of the pharynx, larynx,
bronchi, and the lateral ventricles of the brain, &c.

Epithelium is found to grow from the surface of the
cutis outwards — in most places it is constantly growing
outwards, and as continually being thrown off from the
surface : it must at the same time be remembered, that
though the epithelium is in close contact with the cutis,
or true skin, it is not a deposit from it, but derives only
its materials of formation and nourishment from it.

The epidermis is destitute of sensibility, yet it invests
very sensitive parts : it is not vascular, but invests very
vascular parts. Its exfoliation takes place regularly, as
may be exampled in reptiles and the Batrachia, who throw
off their skin : the moulting of birds is analogous. In the
early periods of life in the human subject, exfoliation takes
place from the surface of the skin ; from the mouth the
morsel of food is always mixed with detached cells. In
the process of digestion the same thing occurs — in fact, it
is only wnen the epithelium cells are thrown off that the
gastric juice is secreted by the tubes of the stomach.

Cilia. — The most remarkable circumstance in connexion
with cells is the movement of their cilia. There are three
ways in which the cilia ordinarily move — the rotatory, the
undulatory, and the wavy, like a field of wheat set in
motion by a steady breeze. No satisfactory explanation
has been given of the cause of this vibratile motion. The
current produced by them is from within outwards, in most
places ; in the respiratory passages, on the contrary, it is
from without inwards. In the Frog's mouth, it takes the
same course. The ciliary motion may be seen in the kidney
of the Frog or Newt ; the cilia in the latter continue in
active motion for 'some minutes after the animal is dead.
Make a very thin section of the kidney with a sharp knife,
and take care to disturb the structure as little as possible ;
then moisten it with a little of the serum of the animal,
place it in a glass cell, and cover with thin glass and a
magnifying power of 250 diameters.

Pigment. — Pigment granules are found in greater or
less quantities in the skin and bodies of white and dark

672

THE MICROSCOPE.

Fig. 304. — Pigment cells
from the eye.

races. In the eye there is pigment, and it affords a good
example of nucleated cells, in which are contained the
pigment particles, fig. 304. These are placed there for an
optical purpose, that of absorbing
the rays of light. -In the peculiar
colouration found in the eyes of some
animals, called Tapetum lucidum, the
colour is not owing to the pigment
particles, but to the interference of
the light : it is reflected from it, as
in mother-of-pearl, coloured feathers,
scales of fishes, &c. The colour of
the skin is owing to the granular
contents of the pigment cells ; these
are like ordinary elementary gra-
nules, with the addition of colour ;
and this latter may be removed by
the action of chlorine.

The Nails are appendages to the
epidermis, and present a^ mould of
the cutis beneath ; from the cutis
the materials are furnished for the
formation and growth of the nail.
Like the epidermis, the nail is
stratified, the markings are parallel
to the surface, and the appearance
is produced by the coalescence of the
cells and their lying over each other.
See Plate VII., No. 149, toe of mouse.
The stratified arrangement when a
section is examined by polarised
light, presents the appearance seen
in the processes of the cat's tongue,
Plate VIII. No. 174.

Hairs. — The form and structure
of hairs differ much ; some are cy-
lindrical, others flattened. A hair
is divided into a body or shaft, and
a root which is in the skin (fig.
305.) The shaft is again divided
into two parts : the external is
termed the cortical portion, and the internal the medul-

Fig. 305.— A single Hair,
seen near its bulb.

HAIRS, SECTIONS OP.

673

lary portion ; the latter does not usually exist in the whole
length of the shaft. The cortical part consists of fibres,

Fig. 306.

1, Transverse section of human hair, showing the cylinder of medullary sub-
stance. 2 Longitudinal section, snowing the fibrous character of the same
pigment or colouring matter, and serrated edges.

arranged parallel to each other: besides these there are,
on the exterior, minute epithelial scales, which are ar-
ranged like the tiles on a house, producing the appearance
of transverse markings. The fibres gradually expand out,

Hair from tho Indian Bat, magnified 500 diameters. 2, Hair su'
belong to (Dc, mestes?) Anthrenus, magnified 250 diameters. 3, Hair
Mouse, magnified fc50 diameters.

X X

to

674 THE MICROSCOPE.

forming a wall to the bulb enclosed in its capsule. The
development of a hair commences at the bottom of the
follicle, and by the aggregation of successive cytoblasts,
or new cells, are gradually protruded from the follicle, both
by the elongation of its constituent cells, antl by the addition
of new layers of these to its base ; the apex and shaft of
hair being formed before the bulb, just as the crown of a
tooth is before its fang. The cytoblasts are round and
loose at the base of the hair, but are more compressed and
elongated in the shaft ; and by this rectilinear arrange-
ment the hair assumes a fibrous appearance. Of sixteen
species of the Bat tribe, the hairs of which were examined
by the late Professor Quekett, all were analogous in struc-
ture ; and the diversity of surfaces which these hairs pre-
sent are in reality owing to the development of scales
on their exterior. By submitting hairs to a scraping pro-
cess, these minute scale-like bodies, tolerably constant as
regards their size and figure, can be procured; so that
Bats' hair may be said to consist of a shaft invested with
scales, which are developed to a greater or less degree, and
varying in their mode of arrangement in the different
species of the animal ; that part of the hair nearest the
bulb is nearly free from scales, but as we proceed toward
the apex the scaly character becomes evident. Many of
the scales are not unlike those procured from the wings
of butterflies, but, being very much smaller, exhibit no
trace of striae on their surfaces ; those taken from dark-
coloured hairs have colouring-matter deposited on them in
small patches. In some cases they appear to terminate in
a pointed process ; in others the free margin is serrated. By
scraping, many of them will
be detached separately ; but in
some few cases, as many as
four or five will be found joined
together : in the larger hairs,
the cellular structure of the
interior, as well as the fibrous
Fig. 308. Transversesectionof Hair character of the shaft, are
of Pecari, showing its fibrous better seen after the scales

and cellular structure -i i j

have been removed.
"The hair owes the greater part of its colour to pigment-

SKIN, GLANDS OP.

675

Fig. 309.— Pigment Cells from
the skin.

cells: as these decay, and become gradually divested of
their colouring-matter, they appear whitened, or "turn
grey." These hexagonal cells also give colour to the skin
of the negro, and are situated immediately beneath the
transparent coat. A small por-

tion is shown in fig. 309, the
vacant space denoting the situa-
tion of a lost hair.

Certain parts of the skin and
mucous membranes are espe-
cially supplied with papillse,
which serve as organs of touch ;
throughout the greater part of
the skin there are papillce more
or less sensitive, but only at
the extremities of the fingers,
lips, and in a few other situa-
tions, are these highly dev
loped, as in fig. 310. Papillae
are either filiform or tubiform,
and have entering into them nerves and blood-vessels;
the former supplying the sensibility of the skin, and termi-
nating in loops, as shown in fig. 310. Papillse injected are
shown in Plate VII. No. 150, tongue of mouse ; villi from
small intestine of rat, No. 154.

The skin is the seat of two
processes in particular ; one of
which is destined to free the
blood from a large quantity
of fluid, and the other to
draw off a considerable
amount of solid matter.
To effect these processes we
meet with two distinct classes
of glandulae in its substance :
the sudoriferous, or sweat
glands; and the sebaceous,
or oil glands. They are both
formed, however, upon the same simple plan, and can
frequently be distinguished only by the nature of their
secreted product. The oil-glands of the skin are
x z 2

Fig. 310. — A section of skin from, the
finger, showing the vascular net-
work of pupillce, at the surface of
the cutis.

£76

THE MICROSCOPE.

Fig. 311.— Capillary network and dis-
trioution of papillce over the tongue.

similar in structure to the perspiratory ducts, being com-
posed of three layers derived respectively from the scarf-
skin, which lines their interior ;
the sensitive skin, which is the
medium of distribution for the
vessels and nerves ; and the
corium, with its fibres, giving
them strength and support.
Like the sudoriferous ducts, they
are in some situations spiral ;

this IS not a Constant fea-
, /, . , .,

ture ; more frequently they pass
directly to their destination; they are also larger, as
shown in fig. 312, proceeding from the oil or fat vesicle

situated at its
lower extremity.
Oil - glands are
freely distributed
to some parts,
whilst in others
they are entirely
absent : in a few
situations they are

Fig. 312.— Distribution of the tactile nerves at the Worthy of parti-
extmnity of the fingers, as seen in a thin perpen- Clllar notice, as in
dicular section of the skin. . . . . , ' .

the eyelids, where

they possess great elegance of distribution and form, and
open by minute pores along the edges of the lids ; in the
ear-passages, where they produce that amber-coloured
substance known as the wax of the ears ; and in the scalp,
where they resemble small clusters of grapes, and open in
pairs into the sheath of the hair, supplying it with a
pomade of Nature's own preparing.

Internal parts of the body. — We shall now have under
consideration cells of a much higher order than any before
referred to ; the cell found floating in the animal fluids is
known as the blood-cell, and requires a vascular system of
its own for distribution over the whole animal body.
The red blood cells, or corpuscles, have a circular form,
somewhat flattened ; their size is about 1-3, 200th of an
inch in diameter. It is well known that the blood-cor-

SECTION OP SKIN.

677

puscles, when floating in their own serum, or after having
been treated with acetic acid or water, appear to be fur-
nished with perfectly plain coverings, composed of a simple
homogeneous membrane, without distinction of parts. But,
when the blood is treated with a solution of magenta (nitrate
of rosanilin) or with a dilute solution of tannin, the cor-
puscles present changes which seem irreconcileable with
such a proposition. Dr. W. Eoberts, of Manchester, com-
municated an account of his observations on this subject to

Fig. 313. — A vertical section of the Human Skin, showing the sweat-glands, sur-
rounded by fat-globules, the ducts passing upwards through the epithelial
layer to the epidermis or external cuticle, magnified 250 diameters.

the Royal Society (Proc. Roy. Soc. vol. xii, p. 481), in
which he shows that nearly every disc possessed a parietal
macula, capable of being stained by a dye. It was com-
monly of a lenticular shape, but sometimes square, and as
a rule very minute, not covering more than I -20th or l-30th
of the circumference. Moreover, in the blood of many of

678 THE MICROSCOPE.

the lower animals a similar tinted particle appeared when
the corpuscles were treated with magenta. The conclusion
to be drawn from this and other observations noted by
Dr. Eoberts, is that a duplication at one, or at most at
two points only, is indicated by direct proof; but certain
appearances occasionally observed £ ivour the notion of a
complete duplication.

The wall of the cell is a transparent structureless mem-
brane, and is of greater thickness than we find the analogous
membrane of cells to be generally. The red corpuscles of
birds, reptiles, &c. possess a distinct nucleus ; but, on
examining those of the human subject and other Mam-
malia, no distinct nucleus can be made out. By applying
dilute acetic acid, the red corpuscle becomes bleached, and
its walls distended, but no nucleus appears. If a red cor-
puscle from the Frog be treated in the same manner, we
see a nucleus, and the red colouring matter is drawn out
by exosmosis. Water causes the corpuscle to swell up,
and the colouring-matter disappears, but its real nature is
masked ; upon employing a drop of solution of iodine, the
wall is coloured or tinged, and made distinct. The cells
themselves have a tendency to undergo spontaneously
certain changes, one of the most common is a wrinkling up
of the walls, with a surface somewhat like that of a mul-
berry ; this may also be produced by mechanical pressure,
the addition of oil, &c.

There is another set of corpuscles, slightly larger than
the red set ; these are termed colourless corpuscles, which,
when distended by the action of water, are seen as nucleated
cells, whose diameter is about the 1-2, 500th of an inch,
and a double contour of the walls is observed ; sometimes
there is a slight tinge of colour to be seen in the nucleus.
There is a third kind of corpuscles in the blood, more
numerous than those above referred to, but of about the
same diameter ; when distended, they are seen to be cells
filled with granular matter ; sometimes a clear spot is
noticed on one side ; very dilute acetic acid being applied,
the granules are dissolved out, and a clear central nucleus
remains, if the acid be used stronger, an appearance is
seen as if there were several nuclei aggregated together.
This latter appearance was considered to be the natural

BLOOD CELLS.

679

state of the nucleus, the particles of which were either
tending to unite with one another, or there was a sepa-
ration of the nucleus into several smaller portions.
Wharton Jones, however, says there is no subdivision of
the nucleus.

If we examine a drop of blood under the microscope,

Fig. 314.

1, A portion of the web of a Prog's foot, spread out and slightly magnified to
show the distribution of the blood-vessels. 2, A portion magnified 250 dia-
meters, showing the ovoid form of the blood-discs in the vessel, beneath
which a layer of hexagonal nucleated epithelium-cells appear. 3, Human
blood discs, as they appear when fresh drawn (magnified 250 diameters).

the corpuscles aggregate themselves together like rolls of
coins, fig. 314, No. 3, presenting a kind of network so
long as they remain suspended in their liquor sanguinis.
After the lapse of a few minutes, the fibrin, from its elasti-
city, contracts more and more, and a yellow fluid, called
serum, is pressed out, — or, in other words, the components
of the liquor sanguinis, with exception of the fibrin, — and
only a shrunken, jelly-like mass remains.

The blood-corpuscles of the lower animals Mr. Gulliver
has especially studied. In the blood-corpuscles of birds,

680 THE MICROSCOPE.

and animals below them, there are nuclei ; but the cells,
instead of being circular, as in the human subject, are
elliptical, and larger. The corpuscles in Mammalia in
general are like those of man in form and size, being a
little larger or smaller. The most marked exception is iu
the blood of the Musk-deer, in which the corpuscles are
of extreme smallness, about the 1-1 2,000th of an inch in
diameter. The Elephant has the largest, which are about
1- 2,000th of an inch in diameter. The Goat, of all common
animals, has very small corpuscles ; but they are, withal,
twice as large as those of the Musk-deer. Another excep-
tion in regard to form is in the Camel tribe, where they
are oval, and resemble those of the oviparous Vertebrata,
as the Frog, shown in fig. 314, No. 2. In the Meno-
branchus lateralis, they are of a much larger size than in
any animal, being the 1 -350th of an inch ; in the Proteus,
the l-400th of an inch in the longest diameter ; in the
Salamander, or Water-newt, l-600th; in the Frog, l-900th;
Lizards, l-l,400th ; in Birds, l-l,700th ; and in Man, the
1-3, 200th of an inch. Of Fishes, the cartilaginous have
the largest corpuscles ; in the Gold-fish, they are about the
1-1, 700th of an inch in their longest diameter.

The large size of the blood-discs in reptiles, especially in
the JBatrachia, has been of great service to the physiologist,
by enabling him to ascertain many particulars regarding
their structure which could not have been otherwise deter-
mined with certainty. The value of the spectroscope in
the chemical examination of the blood has been already
pointed out in our remarks on the application of this
instrument to the microscope. See page 119.

An interesting subject to Physiologists has been noticed —
the production from the blood, under certain conditions,
of red albuminous crystals, — which, although formed from
animal matter, and sometimes, in all probability, during
life, have the same regular forms as inorganic crystals.
Virchow was the first who paid particular attention to
their actual nature, and proved them to differ from saline
or earthy crystals. If we add water to a drop of blood
spread out under the object-glass of the microscope, as the
drop is beginning to dry up, the edges of the heaps of blood-
corpuscles are seen to undergo a sudden change : a few

BLOOD-CRYSTALS. 681

corpuscles disappear, others have dark thick edges, become
angular and elongated, and are extended into small well-
defined rodlets. In this manner an enormous quantity of
crystals are formed, which are too small to enable us to
determine their shape ; they rapidly move lengthways, the
entire field of vision being gradually covered by a dense
network of acicular crystals, crossing one another in every
direction, with other crystals presenting a rhomboid form.

Dr. Garrod discovered, that by a slow evaporation of
portions of the serum of blood taken from patients labour-
ing under gout, he could obtain strings of crystals of uric
acid. His mode of procedure is to pour a little serum
into a watch-glass, and add a few drops of acetic acid ;
in this mixture place a few very fine filaments of silk or
tow, and stand it by for twenty-four hours under a glass-
shade. Upon removing the glass and submitting the
filaments to microscopical examination, they are found
studded with minute crystals.

A peculiar fatty matter was discovered by Virchow in the
tissues of the human body and in certain nerves which he
termed Myelin. In the liver it exists in large quantities,
and much is found in the yolk of the egg. It is colour-
less, glistening, semi-fluid, prone to form drops, and capable
of being drawn out into long threads, which curve and
twist into very peculiar forms. The masses often exhibit
double contours, or many lines are observed equi-distant
from one another and vary-
ing in thickness. Choles-
terin is a component of all
forms of nyelin ; Beneke
has, in fact, shown that it
is a mechanical mixture of
cholesterin and cholate of
lipyl. No. 1, fig. 314,

the foot of the Frog, when ^ 315._ffL 0/ Long^red Bat.
stretched out, shows the (Piecotus Auritus.)

distribution of the blood-vessels in the web : the two
sets of vessels — the arteries and veins — are very readily
made out when kept steadily on the stage of the micro-
scope ; the rhythm and valvular action of the latter may
be observed, although they are much better seen in the ear

682

THE MICROSCOPE.

or wing of the Long-eared Bat, as Professor Wharton Jones
pointed out.

To view the circulation of blood in the Frog's foot, the
older microscopists, Baker, Adams, and others, were in the
habit of tying the frog to a frame of brass ; at the present
time the entire body of the animal, with the exception
of the foot about to be examined, is secured in a black
silk bag, and this is fastened to a plate, termed the frog-
plate, shown at a a a in fig. 316. The bag provided should

Fig. 316.

be from three to four inches in length, and two and a half
inches broad, shown at b b, having a piece of tape, c c,
sewn to each side, about midway between the mouth and
the bottom ; and the mouth itself capable of being closed
by a drawing-in string, d d. Into this bag the frog is
placed, and only the leg which is about to be examined
kept outside ; the string d d must then be drawn suf-
ficiently tight around the small part of the leg to prevent
the foot from being pulled into the bag, but not to stop
the circulation ; three short pieces of thread,///, are now
passed around the three principal toes; and the bag with
the frog must be fastened to the plate a a by means of the
tapes c c. When this is accomplished, the threads ///
are passed either through some of the holes in the edge
of the plate, three of which are shown at g g g, in order
to keep the web open ; or, what answers better, in a series

TADPOLE, CIRCULATION IN. 083

of pegs of the shape represented by h, each having a slit »
extending more than half-way down it ; the threads are
wound round these two or three times, and then the end
is secured by putting it into the slit i. The plate is now
ready to be adapted to the stage of the microscope : the
square hole upon which the foot must be placed is brought
over the aperture in the stage through which the light
passes to the object-glass, so that the web may be strongly
illuminated by the mirror.

The circulation of the Tadpole is best seen by placing
the creature on its back, when we immediately observe
the beating heart, a bulbous-looking cavity, formed of the
most delicate, transparent tissues, through which are seen
the globules of the blood, perpetually, but alternately, en-
tering by one orifice and leaving it by another. The heart
is enclosed within an envelope or j>ericardium ; and this
is, perhaps, the most delicate and certainly the most
elegant thing in the creature's organism. Its extreme
fineness makes it often elude the eye under the single
microscope, but under the binocular its form is distinctly
revealed. Passing along the course of the great blood-
vessels to the right and left of the heart, the eye is
arrested by a large oval body, of a more complicated
structure. This is the inner gill, which, in the tadpole, is
formed of delicate, transparent tissue, traversed by arteries,
and presenting a crimson network of blood-vessels.

The Tadpole is hatched with respiratory and circulatory
organs resembling those of the fish. It lives in, and
breathes oxygen from the air contained in, the water,
and during the early period of its existence respires ex
clusively by gills.

It will be remembered that in nearly all fish the heart
has but two cavities, an auricle and ventricle ; that the
blood of the latter is returned by the veins to the auricle,
passes into the ventricle, is then transmitted to the gills,
where, being exposed to the air contained in the water, it
becomes deprived of carbonic acid, aerated, and rendered
fit for recirculation through the system. In the reptile we
find a modification of plan. The heart has three cavities,
two auricles and one ventricle ; by this contrivance there
is a perpetual mixture in the heart of the impure car-

684 THE MICROSCOPE,

bonized blood which has already circulated through the
body, and flows into the ventricle from the right auricle,
with the pure aerated blood returned from the lungs, and
which also flows at the same instant into the ventricle
from the left auricle. Thus the habitual circulation of
this " cold-blooded " mixture is the cause of the low tone
of vitality that distinguishes reptiles.

For the purpose of observation the tadpole must, of
course, be selected during the period in which the skin
is perfectly transparent. The first examinations reveal
plainly enough the appearances abeady described of the
form and situation of the heart, and the three great arte-
rial trunks proceeding (right and left) from it. Many ob-
servations are required to arrive at the true anatomical
arrangement of these vessels. First, they are closely
connected with the corresponding gill. The upper one
(the cephalic) runs along the upper edge of the gill, and
gives off, in its course, a branch which ascends to the
mouth, which, with its accompanying vein, is termed the
labial artery and vein. The cephalic artery continues its
course around the gill, until it suddenly curves upwards
and backwards, and reaches the upper surface of the head,
where it dips between the eye and the brain, towards
which it is evidently travelling.

It would be a mistake to suppose that you can make
this out distinctly, in the average of tadpoles taken,
without some preparation. The great obstacle is the large
coil of intestines, usually distended with dark-coloured
food. This must be got rid of by making your tadpoles
live on plain water for some days. Plate VII. No. 152,
exhibits the view of the vessels obtained under the in-
fluence of low diet, and we are now enabled to trace the
course of the three large arteries. The third trunk,
traversing the lung, is seen to emerge from the lower
edge and descend into the abdomen to form the great
abdominal aorta. A small black-looking starved little
tadpole shows the heart beating and the blood circulating,
but the latter is quite colourless, not a single red globule
visible anywhere. The globules chase one another away
like globules of water, the heart is a colourless globe, the
gills two transparent ovals, and the bowels a colourless,

TADPOLE, CIRCULATION IN, 685

transparent coil. Through the empty coil the artery is seen
on each side descending from the gills, converging to the
spine, meeting its fellow, and with it uniting to form the
abdominal aorta, the large central vessel coloured red in
the figure. After the aorta has supplied the abdominal
viscera, a prolongation, or caudal artery is seen descend-
ing to the tail, the all-important organ of locomotion in
the tadpole. This artery, entering the root of the tail, is
imbedded deeply in the flesh, whence it emerges, and then
continues its course, closely accompanied by the vein, to
within a short distance of the tail's extremity, where,
being reduced to a state of extreme fineness, it terminates
in a capillary loop, which is composed of the end of the
artery and the beginning of the vein. The artery, in its
course, gives off branches continually to supply the neigh-
bouring tissue. We may often observe that the blood-
current in the tail, even in the main artery or vein, is
sluggish or even still. This occurs independently of
the heart, which may continue to beat as usual ; it
happens, because the circulation in the tail depends very
much on the motion of the organ. When this is sus-
pended (as in confining the tadpole under the microscope),
the blood moves sluggishly, or stops, till the tail regains
its freedom and motion, when the activity of the current
is restored. This fact is thus alluded to by Dr.
Grant : — " It is the restless activity of the worm and of
the insect that makes every fibre of their body, as it were,
a heart to propel their blood and circulate their fluids,
while the slow-creeping snail that feeds upon the turf has
a heart as complicated as that of the red-blooded, verte-
brated fish, that bounds with such velocity through the
deep. It is because the fish is muscular and active in
every point that it requires no more heart than a snail to
keep up the necessary movements of its blood."

Having traced the arterial system, which conveys the
blood from the heart to the extremities, we will now note
its return by the veins back again to the heart.

The caudal vein runs near to the artery during the greater
part of its course, with its stream, of course, towards the
heart. This stream is swollen by perpetual tributaries from
vessels so numerous that their loops form a network which

686 THE MICROSCOPE.

covers the entire surface of the tail. As the vein approaches
the root of the tail it lies superficially to the artery, and
diverges from it at the point of entering the abdomen.
Here it approaches the kidneys, sends off branches to
them, while the main trunk continues its course on-
ward ; and, passing upwards behind a coil of intestine, it
approaches the liver, and runs in a curved course along the
margin of that organ. This blood is seen to enter the
vena cava by numerous fine channels, which converge
towards the great vein as it passes in close proximity to
the organ. Beyond the liver the vena cava continues its
course upwards and inwards to its termination in the sinus
venosus or rudimentary auricle of the heart. This ter-
mination is the junction of not less than six distinct venous
trunks, incessantly pouring their blood into the heart.
The circulation in the fringed lips forms a most compli-
cated network of vessels, out of which proceeds a vein
corresponding to the artery already traced. This descends
in a direct course till it joins the principal vein of the
head, which corresponds to our ovrn jugular.

Thus we have traced the blood through its main chan-
nels, and completed the circle of its course.

The blood is driven by the heart into each inner gill
through three large blood-vessels, which arise directly from
the truncus arteriosus, and may be called the afferent vessels
of the gill. (See enlarged view of gill, Plate VII. No. 156).

It will be seen that " each internal gill or entire
branchial organ consists of cartilaginous arches (Xo. 156),
with a piece of additional framework of a solidly tri-
angular form, stretching beyond the arches, and composed
of semi-transparent, gelatinous-looking material. These
parts, forming the framework of the organ, support upon
their upper surface the three rows of crests with their
vascular network, and the main arterial and venous trunks
which lie parallel with and between them. The three
systemic arteries arising, right and left, from the truncus
arteriosus, enter each gill on its cardiac side, and then
follow the course of the crests, lying in close proximity to
them. The upper of these branchial arteries runs alone
on the outside of the upper crest, and another branch
leaving the trunk and passing into the network of the

TADPOLE, CIRCULATION IN. 687

crest, whence a returning vessel may be traced carrying
back the blood across the branchial artery, and to a vessel
lying close to and taking the same course as the artery
itself. Carrying the eye along the latter vessel we find,
at a short distance from the first of these crest branches, a
second, which leaves the main trunk and enters the crest,
when a corresponding returning vessel conveys the blood
across the arterial trunk into the vessel lying beside it, as
in the former instance. A succession of these branches
(each taking a similar course) may be traced from one end
of the crest to the other. But it is now to be observed
that the trunk from which these arterial branches spring
diminishes in size as it proceeds in its course (like the gill
artery in fishes), while the vessel running parallel to it and
receiving the stream as it returns from the crest enlarges in
the same degree. Thus, the artery or afferent vessel which
brings the blood to the gill is large at it» entrance, but
gradually diminishes and dwindles to a point at the op-
posite end of the crest ; while the venous or efferent vessel,
beginning as a mere radical, gradually enlarges, and thus
becomes the trunk that conveys the blood out of the gill
to its ultimate destination. Calling this vessel the upper
branchial vein as long as it remains in contact with the
gill, we subsequently change its name when it leaves the
gill and winds upwards for distribution to the head, and
then designate it the cephalic artery. The middle branchial
artery and vein proceed in like manner in connexion with
the middle crest, and the lower artery and vein in connexion
with the lower crest. The middle and lower venous trunks,
having reached the extremity of the crests, curve down-
wards and inwards, and then leave the gill. The former
trunk, converging towards the spine, meets its fellow, and
with it forms the ventral aorta. The latter gives origin to
the pulmonary artery, and supplies also the integuments
of the neck. Curious and beautiful is the final stage of
the metamorphosis, when the waning tadpole and incipient
frog coexist, and are actually seen together in the same
subject. The dwindling gills and the shrinking tail — the
last remnants of the tadpole form — are yet seen, in com-
pany with the coloured, spotted skin, the newly-formed
and slender legs, the flat head, the wide and toothless

688 THE MICROSCOPE.

mouth, and the crouching attitude of the all but perfect
reptile.

" By the process now described, the three systemic
arteries become continuous with the corresponding efferent
trunks that convey the blood for distribution through the
body, while, simultaneously, the vital fluid is being
abstracted from the special trunks belonging to the gill
and its vascular crests. These, with the gill structure
connected with and dependent upon them, being thus
deprived of their blood, shrink, become absorbed, and
disappear. Such appears to be the beautifully simple
mechanism by which the transition in the type of the
respiratory function from fish to reptile is accomplished.
If we take a tadpole a few days old, when the outer gills
are fully developed, and immerse it for another few days
in a weak solution, of chromic acid (Mr. Archer's method),
we may, by placing the tadpole under a dissecting micro-
scope, and with the aid of a needle and camel-hair brush,
then remove the integuments, disclose the tufts of the
inner gills, and by carefully getting rid of a prominent roll
of intestine that occupies the upper part of the abdomen,
succeed in revealing the incipient lungs. These are situated
behind the gut and close to the spine, and appear as a pair
of minute tubular sacs, united at their upper and open
extremities. The chromic acid renders the tissues friable,
so that they can be readily peeled away."

That we may see how the circulation is carried on during
life in the gills, the outer covering must be carefully raised,
or even stripped off. This can be accomplished by put-
ting the Tadpole under the influence of chloroform — a
drop of the fluid is sufficient for the purpose.1

The blood-vessels of mammals are divided with refer-
ence to their structure into arteries, capillaries, and veins ;
yet these three divisions are by no means broadly separated
from each other, inasmuch as the capillaries are continued
into the veins just as imperceptibly as they arise from the
arteries. But with reference to their structure, while the
capillaries possess only a single coat without any special
structure, the larger vessels present, with but few excep-

(1) We refer the reader to Mr. W U. Whitney's highly interesting and valuable
paper iu the Trans. Micros. Soc. for 1861 and 1867.

CAPILLARY CIRCULATION. 689

tions, three layers, which are designated as the inner coat,
or tunica intima ; the middle coat or circular fibrous coat,
tunica media; and an outer coat, tunica externa or ad-
ventilia. The first is the thinnest coat, and consists of a
cellular layer, the epithelium ; generally, also of an elastic
coat, with the fibres disposed in a longitudinal direction.
The second, middle coat, is a thicker layer, and the principal
seat of the muscular fibres of the vessels ; in the veins,
however, it contains numerous longitudinal fibres, and in
the largest vessels more or less elastic elements and con-
nective tissue. The third coat has its fibres again arranged
for the most part longitudinally, and it is as thick as, or even
thicker than, the middle coat, and consists of connective
and elastic tissues. This coat, the tunica adventitia of
large arteries, contains muscular fibres in animals, but none
in man. According to J. Lister (Quart. Journ. Micros.
Scien. 1857, p. 8), the smallest arteries of the frog's web
show contractile fibre-cells, which measure from the 1-1 00th
to l-200th of an inch, and run in a spiral direction, making
one and a half up to two and a half turns round the inner
coat of the vessel, and such fibre-cells in a single layer
constitute the only muscular elements of the vessel.

The blood-vessels of the eye are extremely numerous,
and present different conditions in the several parts. In
the choroid coat, they are arranged in a most beautiful
stellate manner, and the capillary network of the inner-
most layer of the choroid coat, when injected, forms an
attractive object. A vertical section of the eye of a cat,
showing its several vascular and nervous coats, is given in
Plate VII. No. 157.

The circulation in the foot of the Frog and the tail
of the Newt is, for the most part, the capillary circula-
tion. The ramifications of the minute arteries form a
continuous network, from which the small branches of
the veins take their rise The point at which the arteries
terminate and the minute veins commence, cannot be
exactly defined ; the transition is gradual ; but the inter-
mediate network is so far peculiar, that the small vessels
which compose it maintain nearly the same size through-
out ; they do not diminish in diameter in one direction,
like arteries and veins; hence the term capillary, from

Y Y

690

THE MICROSCOPE.

capillus, a hair. (Fig. 317.) The size of the capillaries
is proportioned in all animals to that of the blood-cor-
puscles ; thus, amongst the Reptilia, where the blood-cor-
puscles. are the largest, the capillaries are also the largest :
but it does not follow that they
should be always of the same
size in all the tissues of one
and the same animal ; for if
we examine and carefully mea-
sure in the human subject
their sizes in different tissues,
we shall find that they vary
greatly even in individual tis-
sues, and, at a rough estimate,
examples may occur as large as
a thousandth, whilst others are
as small as the four or five-
thousandth of an inch. They
should be measured, if possible,
in their natural state ; when in-

their size IS slightly

.-A network of capillaries

Jected»

.

conveying Uood to the lungs. increased ; but, when dried, they
diminish so considerably that in some specimens vessels
imperfectly filled with injection have been known to shrink
from the three to the twenty -thousandth of an inch.

Fig. 318.

1, Blood-vessels of the Eye ; back view of the Iris and ciliary processes. 2, Vessel
of the membrana pupillaris, from the eye of a Kitten. 3, Fibres or tubes from
the lens of the Ox. (A sectional view of a Cat's «ye is given in Plate VII.
No. 157.)

CAPILLARIES.

691

Capillaries are, with very few exceptions, always sup-
ported by an areolar network, which serves not only as an
investment to them, but connects them intimately with
the tissues they are destined to supply. A possibility
arises, in first examinations, of mistaking or confounding
capillaries with nerves,
especially if the part
under observation should
have been left for some
time in strong preserving
or alkaline solutions.

A weak solution of
caustic soda, and also
another of acetic acid, are
both of use ; the first is
available for the purpose
of tracing nerves ; the
latter in making out
vessels, structure of pa-
pillae, unstriped muscle,
&c., inasmuch as it renders
their nucleimore obvious ^ 319_m broncU> a ^ mtwork of

while SOda thickens and air-tubes for supplying the lungs with air.

makes them less so. It is very useful sometimes to use
these re-agents alternately ; the rule is, to apply them to the
object while under
the microscope, so as
to watch their gra-
dual operation.

It is not in the
blood alone that cells
float in a fluid ; the
chyle and lymph are
colourless corpuscles
flowing along their
especially - adapted
tubes and ducts, and
carrying the nutritive
particles gathered

from the food tO the FiS- 320.— A capillary of blood-vessels distributed
iii i * *i. to <*« ft* tissue- Better seen in some of the in-

blood- Vessels, for the jected specimens, Plate VII.

692 THE MICROSCOPE.

reparation of the framework, or growth that incessantly
goes on in the animal body.

Classification of the Animal Tissues. — Professor Schwann
classifies the fundamental tissues of the human body as
follows : — and it will be seen that more than half are
made up of cellular tissue or simple membrane.

1. Simple membrane : employed alone \ Examples : Walls of cells, capsule of
in the formation of compound > lens of the eye, sarcolemma of
membranes ; muscle, <fcc.

} Examples : White and yellow fibrous
tissue, areola tissue, elastic tissue,

3. Cellular tissues jAljn^J.ijj.vg

4. Sclerous, calcareous, or hard tissues j

5. Compound membranes : composed -\

of simple membrane and a layer of / Examples : Mucous membrane, skin,
cells of various forms (ephithelium > true or secreting glands, serous and
or epidermis), or of areola or con- V synovial membranes.
nective tissue and epithelium . . J

6. Compound tissues; a, those com-\

substance ......... )

fll>ro°8

Cellular or Formative Membrane. — Areolar or connective
tissue is generally distributed throughout the body, and

various forms of this tissue are
found ; it is seen uniting to-
gether component parts, tilling
up interstices between them,
and affording a support to the
blood-vessels and nerves, be-
fore they are distributed to the
various organs. This tissue is
soft, clear, smooth, and ex-
tremely minute, being the
1-1 2,000th of an inch in dia-
meter, sometimes less. The
fibre is usually found united
together in bundles; if

Fig. 321.— Fibrous tissue, lining the in- these be acted Upon by dilute
terior of the eggshell, the lime having ,. •-, .1 *i

beenpreviouslyremovedby immersion acetlC acid, they Swell Up,

in dilute hydrochloric Mid. become transparent, and the

appearance of fibrous structure is no longer seen, although

FIBROUS TISSUE.

693

some fibres that were not previously observed may become
more distinct. The first kind does not refract the light
strongly; the second kind does, showing some chemical
difference in their composition.

Cellular tissue, if dried, becomes a yellowish, brittle,
transparent mass ; but regains its former state if placed in
water. The fibres have a remarkable arrangement and
disposition. They are often deposited in a spiral manner;
at other times they are regularly undulating. In fibres
taken from some parts of the body, we find a fasciculus
wound round in a spiral form. As a consequence, when
acetic acid is applied, we perceive projections of swollen
cellular tissue, and the depressions, from not having been
acted on, have a constricted appearance. The fibrous tissue
lining the eggshell, fig. 321, is the simplest form in which
it is found.

Fat is generally found in the cellular tissue ; it is not
secreted from it, but is contained in its proper cells, and
termed adipose tissue ; the elementary cells of which are
from the l-300th to the l-600th of an inch in diameter
(fig. 322). The cell- wall is very delicate and transparent;
sometimes there are one or two nuclei enclosed.
dissolves out the fat- cells from
the tissues. Acetic acid acts
upon the cell-wall, and causes
the contents to pass from within
outwards.

Fibrous tissue, elastic and
non-elastic, is usually divided
into white and yellow fibrous
tissue. The yellow is elastic,
and of great strength, consisting
of bundles of fibres which are
highly elastic. (Fig. 324, No. 2.)
The white (fig. 324, No. 1),
though non-elastic, is of great
strength, and of a shining,
silvery appearance.

These two kinds of fibrous tissue differ from each other
in many respects, but chiefly in their ultimate structure,
their physical properties, and their colour : both are largely

694

THE MICROSCOPE.

employed in those parts subservient to the organs of loco-
motion.

The white fibrous tissue is (when perfectly cleared of
the areolar) of a silvery lustre, and composed of bundles
of fibres running, for the most part, in a parallel direc-
tion ; but if there be more than one
plane of fibres they cross or inter-
lace with each other. In some
specimens it is very difficult to
make out the fibres distinctly,
except with oblique light; from
this circumstance it would appear
that this tissue is composed of
Fig. 323.-Wti~ contents of a longitudinally striated membrane,

single fat-cell, separated and wnich is often found split UD into
magnified 250 diameters. „. -,, i-,ni_ .• •

fibres. Ine white fibrous tissue is

principally employed in the formation of ligaments and
tendons — a purpose for which it is admirably fitted on
account of its inelasticity : it also enters into the formation

1 2

Fig. b24.

1, White fibrous or non-elastic tissue. 2, Yellow fibrous or elastic tissue
taken near a ligament.

of fibrous membranes, viz. the pericardium, dura mater,
periosteum, perichondrium, sclerotic coat of the eye, and

MUSCULAR FIBRE,

695

Fig. 325. — White fibrous tissue from th€
sclerotic coat of the eye.

all the fasciae. It is sparingly supplied with capillaries
and nerves : the former always run in the areolar tissue,
connecting the bundles of fibres together ; in the gene-
rality of the fibrous tissues, the capillaries are not well
seen, except in that of the dura mater and periosteum ;
in other parts it must be injected to show them.

The yellow fibrous tissue
is highly elastic ; it consists
of bundles of fibres covered
with, and connected together
by, areolar tissue : the fibres
are of a yellow colour, some
round, others flattened ;
they are not always paral-
lel, but frequently bifurcate
and anastomose with neigh-
bouring fibres. It is always
difficult to separate the fibres
from each other ; and when
separated, the elasticity of
each individual fibre is shown
by its tendency to curl up at the end. The fibres in the
human subject vary in diameter from the l-5,000th to
l-10,000th of an inch. Acetic acid of ordinary strength
does not act on yellow fibrous tissue; nor for a very
long time after maceration in water or spirit does its
elasticity diminish. Very long boiling extracts from it a
minute quantity of a substance nearly allied to gelatine ;
neither nuclei nor a trace of a cell can be seen in it after
the addition of acetic acid : both are readily seen when
white fibrous element is treated with this acid.

Muscular Fibre. — There are three different kinds of
muscular fibre found in the animal body : 1st, in the
muscle of the skeleton ; 2d, in the muscle of the heart ;
and 3d, in the stomach, intestine, &c. The functions of
muscular fibre may be referred to two kinds — voluntary
and involuntary. The muscles endowed with voluntary
power are those of the skeleton ; the involuntary are those
of the heart, stomach, intestine, &c.

Muscular fibre is held together by a very delicate tubular
sheath, nearly resembling simple structureless membrane.

696

THE MICROSCOPE.

This cannot always be discerned ; but when the two ends
are drawn asunder it will be perceived to rise up in
wrinkles, or the fragments of the torn muscle will be
seen to be connected by the untorn membrane, as at
fig. 326. This membrane is termed Myolemma. It is best
seen when a piece of muscle is subjected to the action of

fluids, as diluted acetic or
citric acid, or the fluid alka-
lies ; which occasion it to swell
and become easy of separa-
tion. It has no share in the
contraction of the muscle itself,
which is made up of a series
of bundles of highly elastic
fibres : portions of a separated

structureless membrane, myolemma. "bundle are shown at fisr. 327
(Magnified 100 diameters.) -1^11^- J>

and the ultimate structure of

a fibre, under a magnifying power of 600 diameters, at
fig. 328, No. 1.

Dr. Hyde Salter pointed out, that in the tongue the
muscles pass directly into the bundles of the submucous

connective tissue, which
serve as their tendons. Such
a transition is shown in fig.
328, No. 2 ; the tendon, the
lower part of which may be
seen passing insensibly into
the striped muscle, the glan-
dular sarcous elements of
the latter appearing, as it
were, to be deposited in the
substance of the tendon (just
as calcareous particles are
deposited in bone), at first leaving the tissue about the
walls of the cavities of the endoplasts, and that in some
other directions, unaltered. These portions, which would
have represented the elastic element in ordinary connective
tissue, disappear in the centre of the muscular bundle, and
the endoplasts are immediately surrounded by muscle ;
just as, in many specimens of bone (see figs, of bone), the
lacunae have no distinguishable walls. On the other hand

Fig. 327.— Muscular fibre, broken up
into irregular and distinct bands;
a few blood globules are distributed
about. (Magnified 200 diameters).

MUSCULAR FIBRE. 697

at the surface of the bundle the representative of the
elastic element remains, and often becomes as much de-
veloped as its sarcolemma. There is no question here of
muscle resulting from the contents of fused cells. It
is obviously and readily seen to be but a metamorphosis
of the periplastic substance, in all respects comparable
to that which occurs in ossification, or in the develop-
ment of tendon. In this case, we might expect that, as
there is an areolar form of connective tissue, so should

Fig. 328.

1, Muscular fibre, and & fasciculus of a muscle taken from a young Pig. (Mag-
nified 600 diameters.) 2, Muscular fibre from the tongue of Lamb, showing
continuity of the upper portion, with connective tissue of the lower portion.
3, Branched muscle, ending in stellate connective cells, from the upper lip of
the Rat.

we find some similar arrangement of muscle ; such may,
indeed, be seen very beautifully in the termination of the
branched muscles, as they are called. In fig. 328, No. 3,
the termination of a muscular fibre from the lip of a Rat,
is shown :. and the stellate " cells" of areolated connective
tissue are seen passing into the divided extremities of
the muscular bundle, becoming gradually striated as they
do so. In the muscle it is obvious enough, that what-
ever homology there may be between the stellate "cells"
and the muscular bundles with which they are con-
tinuous, there is no functional analogy, the stellate bodies
having no contractile faculty. The nervous tubule is
developed in essentially the same manner as a muscular
fasciculus, the only difference being, that fatty matters
take the place of syntonin. Now it commonly happens
that the nerve- tubule terminates in stellate bodies (fig.
330) of a precisely similar nature ; these are supposed to

698

THE MICROSCOPE.

possess important nervous functions ; and are now known
as " ganglionic cells."

The muscular fibre, known as the non-striated, or invo-
luntary, consists of a series of tubes presenting a flattened
appearance, without the transverse striae so characteristic
of the former : elongated nuclei immediately appear upon
the application of a little dilute acetic acid. Professor
Wharton Jones first demonstrated this structure in his
lectures at Charing Cross Hospital, about 1843 : he was
led to infer, from appearances in very young fibre, that
the striped muscular fibre is originally composed of
similar elements to the unstrip&d, or plain muscular tissue,
which, in the process of deve-
lopment, becomes enclosed in a
sarcolemma (simple membrane)
common to many of them ; the
fibres then split into smaller
fibres (fibrillce). Thus account-
ing for the nuclei of striped
muscular fibre ; which, accord-
ing to his views, are " the per-
sistent nuclei of the primitive
muscular-fibre cells."

The non-striated fibre is beau-
tifully seen in connexion with
the skin surrounding the hairs
of the head, a few fibres of
which are separately shown in
fig. 329. Professor Kolliker ori-
ginally described these muscles
of the skin, of which there appear
Fig. 329.— A portion of the invoiun- to be one or two in connexion

tary muscular fibre surrounding •,-, i_ t, • r IT i

the hair. with each hair-follicle, arising

from the more superficial parts

of the outer skin, then passing down to the root of the hair,
close behind the fat-gland, and there embracing it. It is
indeed most remarkable that skin, when covered with
hair, should alone be provided with these muscular
fibres ; the effect of the contraction of which must be
to thrust up the hair-follicles and depress the inter-
mediate portions of skin, and thus produce that peculiar

NERVOUS STRUCTURE.

and before unaccountable state of the surface known as
goose-skin.

Nerves. — The nervous system consists of
brain, spinal marrow, and nerves. There
are two sets of nerves in the body ; in the
one set the nerves are white, firm, shining,
more or less rounded, with transverse mark-
ings ; in the other, they are softer, not so
consistent, of a reddish grey colour, and
generally flat.

Under the microscope, nerves are seen to
be composed of minute fibres or tubules, full
of nervous matter, arranged in bundles, Fig. 330.-^
and connected by an intervening fibro-cel-
lular tissue, through which capillaries ramify.
A layer of the same, or of a more delicate,
transparent, structureless tissue surrounds
the whole nerve, forming a sheath. The
slight pressure of the thin glass, when
placed on the nerve-fibre, causes nearly the
whole of the contents .to flow out in the
form of a granular material ; it therefore
becomes necessary to exercise considerable
care in breaking up structures to view these
tubules, which should be immersed in a
very weak solution of spirit and water.

On Microscopical Examination of Nerves — It would
scarcely be necessary to insist on the great importance of
removing and examining the
nervous centres as soon as
possible after death, were it
not that the practice is too
often neglected. Great cau-
tion also should be exercised
to avoid injuring the parts, so
that when hardened, perfect
or entire sections of them may Fig. ssi.-Termtnatton of new-loop,
be obtained for examination in muscles.

under the microscope. After they have been carefully
examined externally, by the assistance of a lens, if neces-
sary, incisions should be made, not at random, but in a

cle, with tubular
processes issuing
out, which at a
is filled with a
corpuscle con-
taining black
pigment, above
this are corpus-
cles with nuclei
and their nu-
cleoli ; at 6 is a
corpuscle en-
closing within
its sheath gra-
nular matter :
this is taken
from the root of
a spinal nerve.

700 THE MICROSCOPE.

regular manner through them ; and wherever there is
reason to suspect the existence of disease, small portions
should be removed, and examined while perfectly fresh
under high magnifying powers. The nature of the lesion
having been thus ascertained, the morbid parts, with
some of the surrounding healthy tissue, should be re-
moved, and after being divided, if necessary, into smaller
portions, should be macerated in a weak solution of chromic
acid. It is very important to cut and subdivide the
parts, when necessary, in such a manner, that their rela-
tion to the rest may be recognised after they have become
hardened for the purpose of making sections. Thus, —
unless the locality of the lesion require a different course,
— one incision may be made through the crura cerebri,
immediately in front of the small or motor roof of the
trifacial nerves, and a third through the base of the
anterior pyramids, immediately below the attachment of
the sixth pair of cerebral nerves. With regard to the
spinal cord, if it be cut up into small portions and
hardened in chromic acid, it will be found better to divide
it in three places : 1st, through the middle of the cervical
enlargements ; 2d, through the middle of the dorsal
region ; and 3rd, through the middle of the lumbar
enlargement.

I£ however, the lesion be suspected to exist at another
point, the cord must be divided there; as it is highly
important that the nature of any morbid portion that
may be found should be examined under the microscope
in a perfectly fresh state ; for the nerve-fibres undergo a
considerable and very deceptive alteration by the action
of chromic acid. But it is no less important, and indeed is
absolutely necessary for an exact and complete investiga-
tion, that entire portions of the cord, in the locality of the
lesion, be hardened in chromic acid, so that thin, but
perfect sections may be made for examination under the
microscope.

" The strength of the chromic acid solution should differ
for different parts of the cerebro-spinal centres. For the
convolutions of the cerebral hemispheres and cerebellum,
the proportions should be one of the crystallised acid to
about four hundred of water, while for the pons varolii,

SECTIONS OF SPINAL CORD 701

medulla oblongata, and spinal cord, the strength of the
solution may be in the proportion of one of the acid to
about three or even two hundred of water. It is best,
however, to begin with the weaker solution and increase
its strength at the end of some hours. If the cerebral
and cerebellar hemispheres be hardened in a solution of
greater strength, they become friable and unfit for making
perfect sections."1

Method of Preparing Sections of tJie Spinal Cord. — By
a peculiar method of preparation, Mr. Lockhart Clarke
obtains beautiful sections showing the arrangement of the
nerve-fibres and vesicles in the spinal cord and other
parts of the nervous system. The results are recorded in
the Philosophical Transactions for 1851, Part 2. The
cord it appears is first hardened in acetic acid and alcohol,
when excessively thin sections may be readily obtained
with a sharp knife. These are then soaked in pure spirit,
which permeates the texture in every part, and drives out
the acetic acid, and afterwards transferred to turpentine
which expels the spirit, and lastly the sections are
mounted in Canada balsam. By this plan the tissues of
the embryos of mammalian animals can also be rendered so
transparent that the smallest ossific points can be seen in
the temporary cartilages. To render the specimen more
transparent immerse it in alcohol to which a few drops
of a solution of soda have been added, and allow it to
remain quietly for a few days. When sufficiently acted
on, remove it, and preserve permanently in weak spirit. The
principle of the action of the fluid may be explained
thus : alcohol alone tends to coagulate albuminous textures
and render them opaque, at the same time that it hardens
them. The alkali, on the other hand, renders the tissues
soft and transparent, and if time were allowed, would
cause their complete solution. These two fluids in con-
junction harden the texture and at the time make it clear
and transparent. Many soft tissues may thus be hardened
sufficiently to enable us to cut very thin sections.

Nerves may be examined in thin sections of the skin
after the addition of acetic acid and a solution of soda.
Gerber boils the skin until it becomes quite transparent,

(1) Lockhart Clarke on the Microscopical Examination of Nerves.

702 THE MICROSCOPE.

then allows it to remain a few hours in turpentine, or
until the nerves are seen to be white and shining, when
they are ready for cutting into perpendicular sections with
the double (Valentine's) knife.

It is proposed to employ chloride of gold to stain the
tissues of the body. Tissues soaked in a weak solution
of from one to two per cent, of this salt in distilled water,
and afterwards exposed to light, are found to exhibit
certain parts, as nerve-fibres, connective tissue, corpuscles,
and cells generally, stained of violet-red colour, while
other parts, as intercellular substance, &c. are left un-
touched. The soaking must be continued until the tissue
assumes a straw-yellow colour, then taken out of the solu-
tion and placed in dilute acetic acid of one to two per
cent. The colour will be seen to gradually develop itself,
and Kolliker and Cohnheim, who have tried it, say that
nerve-fibre, &c. are exceedingly well shown in this way.

Consolidated Tissues. — Such tissues are formed by a
chemical combination with the albumen and gelatine of
the fibre ; this in cartilaginous
formations is termed chondrine,
the cells of which become con-
solidated by calcareous deposits,
and a gradual transition results
therefrom. Cartilage is the
firmest structure next to bone
met with ; it is very elastic,
and, as an intercellular sub-
stance, is generally divided into
two kinds. Between the ribs
we find this substance presenting
a uniform bluish appearance,
Fig. 332.— Cartilage from ear of and slightly granular ; this is
^Sbn^^th^Trim-true, or white cartilage. The
posed layers. other form of intercellular sub-

stance is developed in fibrous substances ; and it is in
this peculiarly-formed felt-work that cells with nuclei are
found. This is known as yellow, fibrous, or spongy car-
tilage, the yellow colour depending on the mode of fibrous
arrangement of the intercellular substance : it is found in
the ears, and other parts.

CARTILAGE.

703

Cartilage forms the entire skeleton in some kinds of
fishes, the Skate, Lamprey, &c. j and it is nourished with-

Fig. 833.

1, Cartilage from Rabbit's ear, showing large cells embedded in a fibrous
matrix. 2, Cartilage from Human ribs, with cells in groups, each having a
granular nucleus. (Magnified 200 diameters.)

out coming into direct contact with the blood-vessels,
therefore it is said to be non-vascular ; nourishment is
derived by imbitionfrom the surround-
ing blood-vessels. When examined
microscopically, the simplest form of
cartilage is seen to resemble in a
striking manner the cellular tissue of
vegetables ; it consists of an aggre-
gation of cells of a spherical or oval
form, capable in some cases of being
separated from each other, and every
cell having a nucleus, with a'nucleolus
in its interior. In figs. 332, 333, and
334, we have varieties of this structure.
In the more highly organized scale
of animals, a strong fibrous capsule,
or sheath, surrounds the cartilage-
cells; some of the fibres dip in amongst
the cells, and bind them firmly
together. In those inhabitants of the
water, the Ray and Shark, the entire skeleton being car-
tilaginous, the cell is imbedded in a matrix, which ma*

Fig. 334.— Cartilage from
the Cuttle-fish, showing
stellate form of cells.

704

THE MICROSCOPE.

be strictly termed intercellular. Cells are frequently or
entirely isolated, as in the section from the ear of a Mouse
(fig. 332), they then rarely become converted into bone.
In the highest animals it is generally invested by a fine

1 Fig. 335.

1, Cartilage from the head of Skate, with clusters of nucleated cells and
nuclepli inclosed. 2, Cartilago from the Frog, with cells having nucleoli,
magnified 200 diameters.

and delicate membrane, termed perichondrium, which brings
the blood-vessels in close contact with the cartilage ; and,
when in actual contact with the extremities of bones, is
covered by a vascular membrane having a large number of
vessels terminating in it, for the purpose of supplying a
lubricating fluid to the end of the bones : this, the synovial
membrane, is a very beautiful structure when injected and
viewed under a 1-inch power.

In the earliest stages of existence, the entire framework —
or a very large proportion — is composed of cartilage, which,
by a gradual addition of earthy matter, becomes consoli-
dated into bone. The mode of development, and the
change from one to the other, is represented in the section
(fig. 336) ; it will there be seen that the calcareous matter
is deposited in nearly straight lines, which stretch from
the ossified surface into the substance of the matrix of
the cartilage, the amount of calcareous matter in which
gradually diminishes as we recede from the ossified part.
If the deposit has taken place to any great extent, the

TEETH.

705

m

- < . |C> a~~ *=*-'Zi ~*~

=

calcareous matter becomes crowded and consolidated ; as
the process advances, the bone thickens, and a series .of
grooves, of a stellate form as in the annexed cut (fig. 337,
No. 2), are found upon its sur-
face, which become gradually
converted into canals for the
passage of blood-vessels.

In certain forms of disease,
many of the soft parts of the
human body are converted into
cartilaginous and bony masses,
which have received the name
of Enchondroma (figs. 338 and
339). The microscopical cha-
racteristics of this change have
been described by the author
in the Transactions of the Patho-
logical Society of London, vol. iv.

Teeth. — It is desirable to be-
come acquainted with the struc-
ture of teeth under the micro-
scope ; they are highly interest-
ing to the physiologist, and im-
portant guides to the naturalist
in the classification of animals.
Professor Owen has said, "If
the microscope is essential to
the full and true interpretation
of the vegetable remains of a
former world, it is not less in-
dispensable to the investigator
of the fossilised parts of animals.
It has sometimes happened that
a few scattered teeth have been
the only indications of animal
life throughout an extensive stratum; and when these
teeth happened not to be characterised by any well-marked
peculiarity of external form, there remained no other
test by which their nature could be ascertained than that
of the microscopic examination of their intimate tissue.
By the microscope alone could the existence of Keuper-

z z

Fig. 336. — A vertical section oj
cartilage, with clusters of cells
arranged in columns previous to
conversion into lone, which is
seen consolidated at the upper
surface. The greater opacity of
this portion is owing to the in-
crease of osseous fibres, the
opacity of the cell contents,
and the multiplication of oil-
globules ; the dark intercel-
lular spaces become occupied
by vessels.

706 THE MICROSCOPE.

reptiles in the Lower sandstones of the New red system,

Fig. 337.

I, Section of the tendo-Achillis as it joins the oscalcis ; showing the stellate
cells of tendon gradually coalescing to form the round or oval cells of the
cartilage. 2, A small transverse section of enchondroma, showing the gradual
change of the cartilage-cells at a into the true bone-cells, termed lacuna,
at b, with their characteristic eanaliculi.

in Warwickshire, have been placed beyond a doubt. By

the microscope, the
supposed monarch
of theSaurian tribes
— the so-called Ba-
silosaurus — has
been deposed, and
removed from the
I head of the Kepti-

lian to the bottom
of the Mammalian
division. The mi-
croscope has de-
graded the Sauro-
cephalus from the
class of reptiles to
that of fishes. It
has settled the
doubts entertained
by some of the
highest authorities
in paleontology as
to the true affinities
of the gigantic Me-
gatherium ; and by

Fig. 838.— Microscopical character of Enchondroma,
from a finger. The cartilage undergoes a gra-
dual change, and is seen converted into bone
at the upper portion.

TEETH.

707

demonstrating the identity of its dental structure with
that of the Sloth, has yielded us an unerring indication of
the true nature of its food."

The teeth of Man and of most of the higher animals
'are composed of three different
'substances, Dentine (known as
ivory in the tusk of the elephant),
Enamel, and Cementum, or crusta
petrosa. These are variously dis-
posed, according to the purposes
which the tooth is to serve : in
Man the whole crown of the
tooth is covered with enamel,
shown in the darker marginal Fi

part of fig. 340 I its root or fang

is covered with cementum,

whilst the substance or body of the tooth is composed of

dentine.

In the human subject, two sets of teeth are developed,
the milk and permanent : the first are formed from one

S39._Portion of an enchon.

romatovs mass, nucleated cells,

Fig. 340.— Sections of Human Molar Tooth (magnified 50 diameters)
1, Vertical Section. 2, Horizontal Section.

set of bulbs, which in time shrink, and let the teeth fall

out -, the permanent set is then produced from new bulbs,

zz 2

708

THE MICROSCOPE.

situated by the side of the old ones. Blandin was the first
to point out that the teeth are developed in the mucous
membrane, in a similar way to hair and nails. Other ob-
servers have been led to the same conclusion ; and, more
lately, Professor Goodsir demonstrated that the teeth are
first formed in grooves of the mucous membrane, and sub-
sequently converted into closed sacs by a process of involu-
tion, and that their final adhesion to the jaw is a com-
paratively late part of the process. It is now generally
conceded that teeth belong to the muco-dermoid, and not

Fig. 341.

1, A section of a cusp of the posterior molar, upper jaw of a Child, The inner
outline represents it before the addition of acetic acid — the outer after-
wards, when Nasmyth's membrane g is seen raised up in folds ; /, the enamel
organ ; e, the dentine. The central portion is filled up with pulp. 2. Edge
of the pulp of a molar cusp, showing the first rudiment of the. dentine, com-
mencing in a perfectly transparent layer between the nuclei of the pulp and
the membrana preformativa. 3, Nasmyth's membrane detached from the
subjacent enamel by acetic acid. 3, The stellate-cells of the enamel-organ.
5, Tooth of the Frog, acted on by dilute hydrochloric acid, so as to dissolve
out the enamel and free Nasmyth's membrane. The structure of the dentine
e is rendered indistinct. At the base, Nasmyth's membrane is continued over
the bony substance at z, in which the nuclei of the lacunce are visible. (After
Huxley.) 6. Decalcified tooth-structure; a, the dentine; b, enamel organ;
c, enamel ; d, Nasmyth s membrane.

to the periosteal, series of tissues ; that, instead of standing
in close relation to the endo-skeleton, they are part of the
dermal or exo-skeleton ; their true anologues being the
hair, and some other epidermic appendages. Professor
Huxley has proved that, although teeth are developed in

TEETH.

709

two ways, these are mere varieties of the same mode in
the animal kingdom. In the first, which may be typified
by the Mackerel and the Frog, the pulp is never free, but
from the first is inclosed within the capsule, seeming to
sink down as fast as it grows. In the other, the pulp pro-
jects freely at one period above the surface of the mucous
membrane, becoming subsequently included within a cap-
sule formed by the involution of the latter ; this occurs
in the human subject. The Skate offers a sort of inter-
mediate stage.

The enamel forms a continuous layer, and invests the
crown of the tooth; it is thickest upon the masticating
surface, and decreases towards the neck, where it usually
terminates. The external surface of the enamel appears

Fig. 342.— Tootn Structure.

1, Longitudinal section of superior canine tooth, exhibiting general arrange-
ment, and contour markings, slightly magnified. 2 and 3, Portions from same,
highly magnified, showing the relative position of bone-cells, cementum at
2, dentine fibres, and commencement of enamel at 3. 4, Dentine fibres
decalcified. 5, Nasmyth's membrane separated and the calcareous matter
dissolved out with dilute acid. 6, Cells of the pulp lying between it and the
ivory. 7, A transverse section of enamel, showing the sheaths of fibres,
contents removed, and magnified 300 diameters.

smooth, but is always marked by delicate elevations and
transverse ridges, and covered by a fine membrane (Na-
sinyth's membrane), containing calcareous matter : this
membrane is separable after the action of hydrochloric acid ;
it then appears like a network of areolar tissue, shown in
fig. 342, No. 6 ; which is Huxley's " calcified membrana

710 THE MICROSCOPE

preformativa" of the whole pulp. Nasmyth says : " In all
cases where this covering has been removed by means of
acid, it has, of course, the appearance of a simple mem-
brane, in consequence of the earthly deposit having been
dissolved out, and the animal tissue only remaining. The
structure and appearance of the covering detached in this
manner from the enamel is the same in every respect as
that observed in the capsule of the unextruded tooth, and
consisting, like it, of two layers, fibrous externally, and
having on its external surface the peculiar reticulated
appearance common to both."

" On examining carefully fine sections of several teeth
under the microscope, I perceived here also," observes
Nasmyth, " that the structure in question was continuous
with the crusta petrosa of the fang of the tooth."

The enamel has a fibrous bluish aspect, is very brittle,
and much harder than the other dentinal structures ; it
is, indeed, so hard, that it strikes fire with steel ; if an
attempt be made to cut it without the application of water
to keep it cooled down, it burns with an ammoniacal
odour, such as we perceive when horse-hoof is burnt. It is
composed of prisms, about l-5,000th of an inch in breadth,
more or less wavy, and transversely striped. Two kinds of
bands or stripes are seen traversing enamel, the direction
of one of which nearly coincides with that of the dentine
fibres ; the other set of stripes indicate the laminated struc-
ture of enamel. Under polarised light, a third set become
visible, arising from the variable inclination of the axes
of the fibres to the plane of polarisation. The enamel
is often traversed by cracks or fissures, mostly running
parallel with one set of the fibres : these are sometimes
described as canals ; but as they resemble splits, and are
seldom seen in young teeth, it is more likely that they
are caused by the nature of the food and drink, which is
taken into the mouth at temperatures varying many de-
grees ; we also trace the commencement of disease from
a fissure in the enamel. When a section of the enamel
is cut obliquely, it has somewhat of a hexagonal or six-
sided appearance. The dentine consists of a transparent
basement membrane, with alternating layers of cal-
careous matter, traversed by very fine branching tubuli,

TEETH. 711

which commence at the pulp cavity, and pass up to the
enamel.

Czermak discovered that the curious appearances of
globular conglomerate formations in the substance of
dentine depend on its mode of calcification and the
presence of earthy material ; and he attributes the contour
lines to the same cause. Contour markings vary in in-
tensity and number; they are most abundant in the root,
and most marked in the crown. Vertical sections exhibit
them the best; as fig. 342, No. 1. In preparing a specimen,
first make the section accurately,
then decalcify it- by submersion in
dilute muriatic acid ; then dry it
and mount in Canada balsam with
continued heat, so as to allow the
specimen to soak in the fluid resin
for some time before it cools. It is
the white opacity at the extremity

Of the Contour markings which Fig. Z&.— Transverse section of

. -i f • Tooth of Pristis, showing ori-

gives the appearance Ot rings On fices of medullary canals, with

fhp tnnfh-fancr systems of radiating fibres

tnetOOtn lang. ^ analogous to the

" The tOOth-SUbstance appears, Haversian canals in true

says Czermark, " on its inner sur-
face, nob as a symmetrical whole, but consisting of balls
of various diameter, which are fused together into a
mass with one another in different degrees, and on which
the dentinal tubes in contact with the germ cavity are
terminated. By reflected light, back-ground illumination,
one perceives this stalactite-like condition of the inner
surface of the tooth-substance very distinctly, by means of
the varied illumination of the globular elevations, and by
the shadows which they cast. Here one has evidently to
do with a stage of development of the tooth-substance;
for the older the tooth is, the less striking in general are
these conditions, and the more even is the surface of the
wall of the germ-cavity. In very old teeth considerable
unevenness again makes its appearance; these, however,
are not globular, but have a cicatrised, distorted appear-
ance. It is best to make the preparation from a tooth of
which the root is not perfectly completed. With suc:i
preparations, one is readily convinced that the ground-

712 THE MICROSCOPE.

substance of the last-formed layer of the tooth-substance
appears, at least partly, in the form of balls, which are
fused one among another, and with the balls of the penul-
timate layers; and one also perceives that in general their
diameter becomes less and less, somewhat in the form of a
point, towards the periphery of the tooth-substance. To
obtain specimens, procure a tooth of which the fang is
half-grown; then introduce the point of a penknife into its
open extremity, and scraping the inner surface, detach
small portions, which exhibit the globules admirably." l

The cementum is the
cortical layer of osseous tis-
sue, forming an outer coat-
ing to the fangs, which it
sometimes cements toge-
ther. It commences as a
very thin layer at the part

VS. M4. -Transverse section of Tooth of wher.6 the 6namel .CeaS6S>
Myliobates, Eagle-ray, viewed as ail and increases in thlCKUCSS

SE sttSurl? sh°w its radiatfQS towards the ends of the

fangs. Its internal surface

is intimately united with the dentine, and in many teeth
it would appear as if the earliest determined arrangement
of the fibres of the dentine started from the canaliculi, as
they radiate from the lacunae in the cement. The inter-
lacunar layer is often striated, and exhibits a laminated
structure : sometimes it appears as if Haversian canals
were running in a perpendicular direction to the pulp
cavity. The canaliculi frequently run out into numerous
branches, connecting one with another, and anastomising
with the ends of the dentine fibres. The thick layers of
cement which occur in old teeth show immense quantities
of aggregated lacunae of an irregular and elongated form.
Professor Owen believes that by age the pulp ceases to pro-
duce or nourish the dentine, which then becomes converted
into osteo-dentine, and thereby the layer of crusta is so
much increased as often to fill up the pulp cavity of the
tooth. Professor Simonds assures us that this is not the case
in the Herbivora. For instance, in the horse, the oblitera-

(1) Czermak: translated by James A. Salter, M.B., Quarterly Journal oj
Microscopical Science, July, 1823.

BONE.

713

tion of the cavity is gradually effected by an increased
formation of dentine ; and this is not supplanted by an
abnormal or diseased growth, as would be the case were
the pulp to become ossified, but as the pulp diminishes,
so is the supply of nutriment to the tooth lessened, and at
length entirely cut off from the interior. " To provide for
the vitality of the tooth under
these circumstances, the crusta
increases in quantity on the
fang, at the expense of the per-
fectly-formed dentine, which is
lying in immediate contact with
its inner surface. Through the
medium of the canals in the
crusta, which open on its
borders, the tooth now draws
its nourishment from the blood-
vessels of the socket ; and thus
it continues, long after the obli-
teration of its pulp cavity, to
serve all the purposes as a part
of the living organism." l

gone. The elements of bone Fig. 345. -/ transverse section of '-the

are lamellae and small cor-
puscles j the latter are possibly
merely spaces between the for-
mer, in which is deposited the
earthy substance. The lamellae
have for their basis a cartila-
ginous substance combined
with earthy matter, or salts.
These salts are chemically com-
bined with the organic basis,
earthy salts, and leave the organic basis of the same
form as the »bone itself. The lamella are homoge-
neous throughout, like the intercellular substance of car-
tilage, but chemically different, being resolved by boiling
in water into colla, whereas cartilage is resolved into
chondrine.

human clavicle, or collar-bone, mag-
nified 95 diameters ; which ex-
hibits the Haversian canals, the
concentric laminae, and the con-
centric arrangement of bone-cells
around them. Some of the Ha-
versian canals are white, others
black ; the latter are filled with

in t

a deposit of opaque matter, used
he grinding and polishing the
section. When viewed under a
lower power, they appear to be
only a series of small black dots,
as shown in fig. 346.

Acids dissolve only the

(1) Professor Simonds, on the
Animals."

'Structure and Development of Teeth of

714

THE MICROSCOPE.

Professor Quekett's paper in an early number of the
Micros. Soc. Trans, gave an
excellent account of the " In-
timate structure of Bone." To
this paper we are indebted
for the following microscopical
investigation of bone : —

Bone consists of a hard and
soft part ; the hard is com-
posed of carbonate, phosphate,
and fluate of lime, and of car-
bonate and phosphate of mag-
nesia, deposited in a cartila-
ginous or other matrix ; whilst
the soft consists of that matrix,
and of the periosteum which
invests the outer surface of

Fig. 346— The same, viewed under a fu_ -L.nr>0 Qnrl nf fhp mpdnllnrv
lower power, appear to be a series ttie bone> ancl °I tne meCLUllary

of small black dots. membrane which lines its in-

terior or medullary cavity, and
is continued into the minutest
pores. If we take for exami-
nation a long bone of one of
the extremities of the human
subject, or of any mammalian
animal, we shall find that the
bony substance, or shaft, is
slightly porous, or rather oc-
cupied, both on its external
and internal surfaces, by a
series of very minute canals,
which, from their having been
first described by our coun-
tryman Clopton Havers, are

. termed to this day the Haver-
Fig. 347.— A transverse section oj the . , -, £ ,-,

Humerus, or fore-arm bone, of a sian canals, and serve for the
SSt^SS^S^ "nals," transmission of blood-vessels
with a slight tendency to a con- into the interior of the bone.

centric arrangement of bone-cells Jf .1 - fT.aT,a,7p,op QPP

around them. The bone-cells are " now a tmn transverse

large and very numerous, but fcion of the same bone be made,

occur for the most part in parallel . . , -, , -,

rows. and be examined by the micro-

BONE STRUCTURE.

715

scope with a power of 200 linear, we shall see the Haversian
canals very plainly, and around them a series of concentric
bony laminae, from three to ten or twelve in number. If
the section should consist of the entire circle of the shaft,
we shall notice, besides the concentric laminae round the
Haversian canals, two other series of laminae, the one
around the outer margin of the section, the other round
the inner or medullary cavity.
Between the laminae is situ-
ated a concentric arrangement
of spider-like looking bodies,
which have, by different au-
thors, received the name of
osseous corpuscles, lacunae, or
bone -cells, according as to
whether they were ascertained
to be solid or hollow: these
bone- cells have little tubes or
canals radiating from them,
which are termed canaliculi.
The average length of the
lacunae, or bone-cells, in the
human subject is the l-2,000th Fig 5,8._A transverse sectionlof the

Of an inch j they are Of an Femur, or leg-bone of an Ostrich

oval figure, and somewhat flat- ftESS ^t^VecXg
tened on their opposite sur- fisure> !* wil1 ^ noticed that the

f , L-L,, -i j Haversian canals are much smaller

laces, and are USUaliy abOUt and more numerous, and many of
One- third greater in thickness them run in a transverse direction.

than they are in breadth; hence, as will be presently
shown, it becomes necessary to know in what direction
a specimen is cut, in order to judge of their comparative
size. The older anatomists supposed them, from their
opacity, to be little solid masses of bone ; but if the sec-
tion be treated with spirits of turpentine coloured with
alkanet-rcofc, or if it has been soaked in very liquid
Canada balsam for any great length of time, it can
then be unequivocally demonstrated that both these sub-
stances will gain entrance into the bone-cells through the
canaliculi. The bone cells, when viewed by transmitted
light, for the most part appear perfectly opaque ; and they
will appear the more opaque the nearer the section of

716

THE MICROSCOPE.

them approaches to a transverse one : for when the cells
are cut through their shorter diameter, they are often of
such a depth that the rays of light interfere with each
other in their passage through them, and darkness results ;
whereas if the section be made in the long diameter of the
cells, they will appear transparent. When viewed as an
opaque object, with a dark ground at the back and con-
densed light, the bone-cells and canaliculi will appear quite
white, and the intercellular substance, which was trans-
parent when viewed by transmitted light, is now perfectly
dark. The soft part consists
of the periosteum, which in-
vest the outer, and of the
medullary membrane, which
invests the inner surface, lines
the Haversian canals, and is
continued from them, through
the canaliculi, into the interior
of the bone-cells ; and of the
cartilaginous or other matrix,
which forms the investment
of the minute ossific granules.
The earthy matter of the bone
may be readily shown by
macerating the section for a

Fig. 349.— A horizontal section of the short time in a dilute solution

ZSk'SS&S ."££"&.•£ of caustic potash. The animal

bone-cells arrangedin parallel lines, matter mav be procured bv
There are no Haversian canals pre- . »»i .* ' i ITT • •*
sent ; and when this specimen is USing dilute hydrochloric acid
contrasted with that of fig. 347, inafpa/j nf nanafin •nr>fn«>i •
it will be noticed that the canali- inSteaO. C caustic potasn _,—

cuii given off from each of the when all the earthy matter

bone-cells of this fish are very few • i 1-1 -11

in number in comparison with 1S removed the Section Will

that of the reptile. exhibit nearly the same form

as when the earthy constituent was present ; and if then
viewed microscopically, it will be noticed that all the
parts characterising the section previous to its maceration
in the acid will be still visible, but not so distinct as
when both constitutents were in combination. When,
however, the animal matter is removed, the bone will not
exhibit the cells and the canaliculi, but is opaque and
very brittle, and nothing but the Haversian canals and a

BONE STRUCTURE.

717

which are larger in this animal than
in any other yet examined. As in
the preceding specimen, no Haver-
sian canals are present.

granular structure can be seen.
The parts which a transverse
or a longitudinal section of a
long bone of a mammalian
animal exhibits, will be the
Haversian canals, the con-
centric bony laminae, the bone-
cells and their canaliculi ;
even these, except the bony
laminae, may be seen in all
mammalian bones (fig. 345).
Whether long or otherwise,
they are, nevertheless, so dif-
ferently arranged in the flat
bones, such as those of the „.

, ,, ' , ., . i Fig. 350. — A portion of the Cranium

Skull, and in the irregular Of a Siren (Siren lacertina), re-
l->nnp<3 a<5 tVip vprtphriP a<? to markable for the large size of the

Dones, as tne verteorae, as to bone.cellg and of tge canulicuii
require notice. Those of the
head are composed of two thin
layers of compact texture;
enclosed between which is
another layer of variable thick-
ness, of a cellular or cancel-
lated structure. The two outer
layers are called tables — the
one being the outer, the other
the inner table ; and the middle
or cancellated layer is termed
the diploe : in this last the
principal blood-vessels ramify.
The outer table of the skull
is less dense than the inner ;
the latter, from its brittle-
ness, is termed by anatomists
the vitreous table. When
a vertical section of a boneFig ^_A ^ ^.^ of ^

Of the Skull IS made SO as taken from the exterior oj s the shaft
frv irmlnrlo -Hio +Virna lavpra of the Humerus of a Pterodactyle ;

to include tne tnree layeis thig exhibit3 tl?6 elongated bone-
above mentioned, bone-cells cells characteristic of the order
may be seen in all ; but each Reptil™"
of the three layers differ in structure : the middle or can-

718

THE MICROSCOPE.

cellated structure will be found to resemble the cancellated
structure in the long bones — viz. thin plates of bone, with
one layer of bone-cells without Haversian canals ; the outer
layer will exhibit Haversian canals of large size, with bone-
cells of large size, and a slightly laminated arrangement ;
but the inner or vitreous layer resembles the densest bone,
as the outer part of the shaft of a long bone, for instance,
and will exhibit both smaller Haversian canals and more
numerous bone-cells of ordinary shape around them.

A transverse section of the long bone of a bird, when
contrasted with that of a mammal, exhibits the following
peculiarities : the Haversian
canals are more abundant,
much smaller, and often run
in a direction at right angles
to that of the shaft, by which
means the concentric laminated
arrangement is in some cases
lost ; the direction of the canals
follows the curve of the bone ;
the bone-cells also are much
smaller and more numerous ;
but the number of canaliculi
given off from each of the cells
is less than from those of mam-
mals, fig. 348 : the average
length of a bone-cell of the

Fig. M9.-A Aortontal section o/aOstrich is l-2,000th of an inch,
scale, or flattened spine, from the the breadth 1-6, 000th.
slcinofaTrygon,orStingRay;t]i\s T *u r> J.-T ±\ -i
exhibits la?ge Haversian canals, -^ the Meptllia, the bones
with numerous wavy parallel tubes, may be either hollow, Cancel-
like those of dentine, cominunicat- , J , iiV^

ing with them. This specimen lated, Or SOlld ; but the specific
shows, besides these wavy tubes, Q.ravi'tv i«j -nn+- Qrx orouf ao fkaf
numerous bone-cells, whose cana- gravipy 1S n°t SO great as tnat

licuii communicate with the tubes, of birds or mammals. The
dentine- short bones of most of the
Chelonian reptiles are solid, but the long bones of the
extremities are either hollow or cancellated; the ribs of
the Serpent tribe are hollow, the medullary cavity per-
forming the office of an Haversian canal ; the bone-cells
are accordingly arranged in concentric circles around the
canal. The vertebrae of these animals are solid j and the

BONE STRUCTURE. 719

bone, like that of some of the birds, is remarkable for its
density and its whiteness. When a transverse section is
taken from one of the long bones, and contrasted with
that of a mammal or bird, we shall notice at once the
difference which the reptile presents : there are very few,
if any, Haversian canals, and these of large size ; and at
one view, in the section, fig. 347, we shall find the canals
and the bone-cells arranged both vertically and longi-
tudinally : the bone-cells are most remarkable for the
great size to which they attain ; in the Turtle they are
1-3 7 5th of an inch in length, the canaliculi are extremely
numerous, and are of a size proportionate to that of the
bone-cell.

In fishes we have a greater variation in^the minute
structure of the skeleton than in either of the three classes
already noticed. Of all the varieties of structure in the
bones of fishes, by far the greater number exhibit nothing
more than a series of ramifying tubes, like those of teeth ;
others exhibit Haversian canals, with numerous fine tubes
or canaliculi, like ivory tubes, connected with them ; a few
consist of Haversian canals, with fine tubes and bone-
cells, fig. 349; and a rare form, found only as yet in the
sword of the Swordfish (Istiophorus), exhibits Haversian
canals and a concentric laminated arrangement of the
bone, but no bone-cells. The Haversian canals, when
they are present, are of large size, and very numerous, and
then the bone-cells are, generally speaking, either absent
or but few in number; their place being occupied by
tubes or canaliculi, which are often of a very large size.
The bone-cells are remarkable for their graduate figure,
and the canaliculi which are derived from them are few in
number; they are seen to anastomose freely with the
canaliculi given off from neighbouring cells; and if the
specimen under examination is a thin layer of bone, such
as the scale of an osseous fish, from the cells lying nearly
all in one plane, the anastomoses of the canaliculi are
seen beautifully distinct. In the hard scales of many of
the osseous fishes, such as the Lepidosteus and Calicthys,
and in the spines of the Siluridce, the bone-cells are
beautifully seen ; in the true bony scales comprising the
exo-skeleton of the cartilaginous fishes, the bone-cells are

720 THE MICROSCOPE.

to be seen in great numbers. In the spines of some of the
Ray family may be noticed a peculiar structure : the Haver-
sian canals are large and very numerous, and communi-
cating with each canal are an infinite number of wavy
tubes, which are connected with the canals in the same
manner as the dentinal tubes of the teeth are connected
with the pulp-cavity ; and if such a specimen were placed
by the side of a section of the tooth of some of the Shark
tribe, the discrimination of one from the other would be
no easy matter. In the spine of a Eay, fig. 352, the
analogy between bone and the ivory of the teeth is made
more evident ; for in this fish we have tubes, like those of
ivory, anastomosing with the canaliculi of bone-cells.

Now, if we proceed at once to the application of the
facts which have been laid down, and make a fragment of
bone of an extinct animal the subject of investigation;
we first find that the bone-cells in Mammalia are tolerably
uniform in size ; and if we take 1 -2,000th of an inch as a
standard, the bone-cells of birds will fall below that
standard; but the bone-cells of reptiles are very much
larger than either of the two preceding; and those of
fishes are so entirely different from all three, both in size
and shape, that they are not for a moment to be mistaken
for one or the other ; so that the determination of a minute
yet characteristic fragment of fishes' bone is a task easily
performed. If the portion of bone should not exhibit
bone-cells, but present either one or other of the characters
mentioned in a preceding paragraph, the task of discrimi-
nation will be as easy as when the bone- cells exist. We
have now the mammal, the bird, and the reptile to deal
with ; in consequence of the very great size of the cells
and their canaliculi in the reptile, a portion of bone of one
of these animals can readily be distinguished from that of
a bird or a mammal ; the only difficulty lies between these
two last : but, notwithstanding that on a cursory glance
the bone of a bird appears very like that of a mammal,
there are certain points in their minute structure in which
they differ ; and one of these points is in the difference in
size of their bone-cells. To determine accurately, there-
fore, between the two, we must, if the section be a trans-
verse one, also note the comparative sizes of the Haversian

FISH SCALES.

721

canals, and the tortuosity of their course ; for the diameter
of the canal bears a certain proportion to the size of the
bone-cells, and after some little practice the eye will
readily detect the difference.

A curious modification of horn is presented in the ap-
pendage borne by the Ehinoceros u-pon its snout, which
in many points resembles a bundle of hairs. When a
transverse section is made and viewed by polarised light,
each cylinder is seen to have
a cross diverging from a cen-
tral spot; the lights and
shadows of this cross are
replaced by bands of con-
trasted complementary co-
lours, if the selenite plate is
interposed (fig. 353). See

Pifltp VTTT ~NTn T78 Whal P FiS- 953.— Transverse section of Horn

nate v 111. IN o. i / s. w naie- of RUnoceroS) seen by polarised

bone is almost identical in light.

structure, and is similarly affected by polarised light.

A knowledge of the form and structure of scales of
fishes (fig. 354), like that of
teeth, has been "shown by
M. Agassiz to afford an uner-
ring indication of the particu-
lar class to which the fish may
belong : in the examination
of fossil remains, the appli-
cation of this knowledge has
been attended with extraor-
dinary results. As a class of
objects for the microscope, the
scales of fishes are exceedingly
curious and beautiful, especially
when mounted in fluid or
Canada balsam, and viewed by
polarised light. Many are seen
best as opaque objects, and are

then mounted dry between Fig. 354—ScaZe o/ sofc.
glasses. M. Agassiz divides the scales into four orders,
which he names Placoid, Ganoid, Ctenoid, and Cycloid ;
in the first two the scales are more or less coated with
3 A

722 THE MICROSCOPE.

enamel, in the others they are of a horny nature. To the
Placoid order belong the Skates, Dog-fish, Kay, and Sharks ;
cartilaginous fishes, having skins covered with small prickly
or flattened spines. To the Ganoid belong the Sturgeon,
Lepidosteus, Hassar-fish, and Polypterus ; fishes of this
order are more generally found in a fossil state, and the
scales are of a bony character. To the Ctenoid belong the
Pike, Perch, Pope, Basse, Weaver-fish, &c. ; their scales
are notched like the teeth of a comb. To the Cycloid
belong the Salmon, Herring, Eel, Carp, Blenny, and the
majority of our edible fishes ; their scales are circular and
laminated. The scales of the Eel tribe are of an oval
figure, and are among the most remarkable that can be
selected for microscopic examination. To procure them, a
sharp knife must be passed beneath the epidermal layer,
and a portion of it raised, in a similar manner as directed
for tearing off the cuticle from plants : after a few trials
some will be detached. They are of an oval figure, rather
softer than the scales of other fishes, and in some parts of
the skin do not form a continuous layer. When the skin
has been stripped off, previous to the fish being cooked,
the scales can be obtained from the under surface, with a
knife or pair of forceps. The scales of the viviparous
Blenny are of a circular figure, situated under the epider-
mal layer ; they were described by Mr. Yarrell as mucous
glands, from their figure and small number. The surface
of the skin of this fish, when fresh, appears to be covered
with follicles ; if, however, a portion be scraped off, it will
be found to be a mass of delicate circular scales. A piece
of the skin, when dried, exhibits the scales to great
advantage, and, like those of the Eel, are beautiful objects
for polarised light. The prismatic colours exhibited by
fish are said to be due to the presence of fatty matter in
the skin; but the beautiful metallic tints displayed by
so many of them are rather due to the numerous micro-
scopic plates, or scales, distributed over its surface.

Having thus brought our brief examination of a few of
the more important structures of the animal economy to
a close, it only remains for us to express a hope that it
will be found to smooth the way, or in some degree assist
the investigations of the student to a better and more

EERORS OF INTERPRETATION. 723

general survey of the whole fabric. Such a survey will
not be unattended with its difficulties and disappoint-
ments, but it will bring its own reward for any amount
of labour bestowed. To the medical student, desirous
of obtaining further information in his especial depart-
ment of microscopy, we recommend Dr. Beale's book
on " The Microscope, and its Application to Clinical
Medicine."1-

The importance of becoming thoroughly familiar with
the structural and microscopical characters of any par-
ticular organ in a healthy condition, cannot be too strongly
urged upon the attention of the student ; as to a want of
this knowledge must be attributed many erroneous de-
scriptions of morbid appearances. All who wish to use
the microscope successfully, with reference to the exami-
nation of organs in a diseased state, will do well to
acquaint themselves with minute anatomy generally, not
only of the human subject, but of the lower animals ;
without such knowledge it will be found impossible to
study pathology, or prosecute pathological inquiries with
any degree of success.

A large amount of wrong observation has been recorded
on cells and cellular structures : since Schwann announced
his "cell theory," almost everything round has been
regarded as a cell ; any single body within this, or where
there are several, the largest, has been regarded as a
nucleus, and any spot within the nucleus has been viewed
as a nucleolus. Whereas many of the so-called cells are
homogeneous spheres; many of the nuclei are vacuoles,
and so forth.

Such errors are natural, at first inevitable ; they can be
corrected only by practice, by testing observations in other
ways, especially by chemical re-agents, and by comparison
with the observations of others. " The marvel is not that
the microscope should suggest false views — do not otr
eyes play us that trick1? — but that it should reveal so
many astounding facts as it really does ; and the one con-

(1) The Cyclopaedia of Anatomy and Physiology will be found a most valuable
book of reference for the student in all matters relating to physiology and
minute anatomy. Numerous valuable papers are distributed throughout the
Trans, of the Royal Micros. Soc. : Huxley's Lectures on Comparative Anatomy :
Owen's Lectures on Comparative Anatomy ; Carpenter's Physiology, edited by H.
Power, and Kolliker's Manual of Human Microscopic Anatomy.

3 A2

724 THE MICROSCOPE.

solatory reflection which accompanies the difficult task of
microscopic investigation is the unanimity which now
reigns among observers on so vast a body of observations.
If we read in physiological works of the yolk cells and
coloured oil globules of the yolk, and the beautiful
function of assimilation which has been attributed to
them, they exist but in the imagination of the authors
who have regarded the one as cells simply because they
are round, and the other as consisting of fat because they
are highly refractive, — such errors of interpretation do
not discredit it any more than the mis-interpretations,
which have helped to make Ehrenberg's name at once
famous and suspicious, alter the facts which he saw, and
could not rightly interpret. In truth, the eye is only
a preliminary instrument in science. What we see has to
be interpreted ; and, as it is very difficult to confine our-
selves to pure observation unmixed by Irypothetical inter-
pretation, we need many collateral confirmations."

The principal physical characters to be regarded in micro-
scopic examinations may be summed up as follows : —

1. Shape. — Accurate observation of the shape of bodies
is very necessary, as many are distinguished by this phy-
sical property. Thus the human blood-globules present
a round biconcave disc, and are in this respect different
from the oval corpuscles of birds, reptiles, and fishes.
The distinction between round and globular is very requi-
site. Human blood corpuscles are round and flat; but
they become globular on the addition of water. Minute
structures seen under the microscope may also be likened
to the shape of well-known objects, such as that of a pear,
balloon, kidney, heart, &c.

2. Colour. — The colour of structures varies greatly, and
often differs under the microscope from what was pre-
viously conceived regarding them. Thus the coloured
corpuscles of the blood, though commonly called red, are,
in fact, yellow. Many objects present different colours,
according to the mode of illumination ; that is, as the light
is reflected from or transmitted through their substance, as
in the case of certain scales of insects, feathers of birds, &c.
Colour is often produced, modified, or lost, by re-agents ;
as when iodine comes in contact with starch-granules, when

ANIMAL STRUCTURES — MODE OP INVESTIGATING. 725

nitric acid is added to chlorophyle, or chlorine-water to the
pigment-cells of the choroid, and so on.

3. Edge or Border. — This may present peculiarities
worthy of notice. Thus, it may be dark and abrupt on the
field of the microscope ; so fine as to be scarcely -visible ;
or it may be smooth, irregular, serrated, beaded, &c.

4. Size. — The size of the minute bodies, fibres, or tubes,
which are found in the various textures of animals, can
only be determined with exactitude by actual measure-
ment. It will be observed, for the most pai t, that these
minute structures vary in diameter ; so that when their
medium size cannot be determined, the variations in size
from the smaller to the larger should be stated. Human
blood-globules in a state of health have a pretty general
medium size, and these may consequently be taken as a
standard with advantage, and bodies described as being two,
three, or more times larger than this structure ; or all may
be measured with a micrometer, as explained at page 51.

5. Transparency. — This physical property varies greatly
in the ultimate elements of numerous textures. Some
corpuscles are quite diaphanous ; others are more or less
opaque. The opacity may depend upon corrugation or
irregularities on the external surface, or upon contents of
different kinds. Some bodies are so opaque as to prevent
the transmission of the rays of light ; in this case they
look black when seen by transmitted light, though white
if viewed by reflected light ; others, such as fatty particles
and oil-globules, refract the rays of light strongly, and
present a peculiarly luminous appearance.

6. Surface. — Many textures, especially laminated ones,
present a different structure on the surface from that
which exists below. If, then, in the demonstration, these
have not been separated, the focal point must be changed
by means of the fine adjustment. In this way the capil-
laries in the web of the Frog's foot may be seen to be
covered with an epidermic layer, and the cuticle of certain
minute *Fungi or Infusoria to possess peculiar markings.
Not unfrequently, the fracture of such structures enables
us, on examining the broken edge, to distinguish the dif-
ference in structure between the surface and the deeper
layers of the tissue under examination.

726 THE MICROSCOPE.

7. Contents. — The contents of those structures which
consist of envelopes, as cells, or of various kinds of tubes,
are very important. These may consist of included cells or
nuclei, granules of different kinds, pigment matter, or
crystals : a fair illustration of the changes effected by dis-
ease is given in fig. 256, from a cyst in a diseased liver :
occasionally their contents present definite moving cur-
rents, as in the cells of some vegetables ; or trembling
rotatory molecular movements, as in the ordinary globules
of saliva in the mouth.

8. Effects of Re-agents. — These are most important in
determining the structure and chemical composition of
numerous tissues. Thus water generally causes cell- for-
mations to swell out from endosmosis ; while syrup, gum-
water, and concentrated saline solutions, cause them to
collapse from exosmosis. Acetic acid possesses the valu-
able property of dissolving coagulated albumen, and in
consequence renders the whole class of albuminous tissues
more transparent. Thus it operates on cell-walls, causing
them either to dissolve, or become so thin as to display
their contents more clearly. Ether, on the other hand,
and the alkalies, operate on fatty compounds, causing their
solution and disappearance. The mineral acids dissolve
most of the mineral constituents that are met with ; so
that in this way we are enabled to tell with tolerable cer-
tainty, at all events, the group of chemical compounds to
which any particular structure may be referred.

Many, if not all, animal structures require examination
in several ways before an accurate idea of their general
structure can be obtained. It is of much importance
to examine a body by reflected light, transmitted light,
and by polarised light ; when immersed in water, or in a
highly refracting fluid, such as glycerine, oil, turpentine,
and Canada-balsam ; with a cover and without a cover,
with the application of distilled water and of chemical
re-agents. The most scrupulous cleanliness must always
be observed in microscopical examinations ; many errors
have arisen in consequence of a want of sufficient care not
having been taken to prevent the admixture of various
accidental substances. The better way of avoiding errors
from this cause is to become familiar with the characters

ANIMAL STRUCTURES — MODE OF INVESTIGATING. 727

of common substances which are likely to be mixed up
with preparations, as the following : — oil globules, air
bubbles, portions of worsted, cotton, and linen, silk and
wool fibres, hairs from plants, vegetable tissues, human
hair, portions of feathers, and the starches — wheat and
potato starch from bread crumbs. In taking fluids from
bottles and vessels, the possibility of mixing small portions
of their contents must be avoided ; the pipette should be
washed immediately after it has been used. Another
fallacy arises from the great transparency of some struc-
tures ; a membrane may appear perfectly clear and trans-
parent when in reality it is covered with a delicate layer
of epithelium, which only becomes visible after the appli-
cation of some chemical re-agent \ on the other hand, by
the action of re-agents, a fibrous appearance is produced.
Acetic acid, when added to many preparations, frequently
produces a swelling of the tissue, which looks like base-
ment membrane, but which in reality has been formed by
the action of the acid. The mechanical pressure of the
thin glass, if pressed down tightly, alters structures very
much; the appearance of the blood discs are, at times,
much distorted in this way, and lead to false conclusions
and erroneous descriptions.

Should it be desirable to make an examination of the
vital fluid, blood, the smallest drop, caused by the prick of
a fine needle, may be placed on a strip of glass, and waved
backwards and forwards, that the blood may dry as quickly
as possible ; in this way the corpuscles or blood-discs
retain their form j and if the preservation of the specimen
is wished, a thin glass-cover carefully placed over it, and
cemented down, in the way directed at page 217.

To the advanced observer, the examination of the mucous
membrane will afford some instruction. Should the speci-
men be small, it will be better to pin it to a piece of cork;
then well wash it by means of a small syringe. If the
investing epithelium is required for examination, a por-
tion can be detached from the surface by a knife ; when
placed on a glass slide, add a drop of iodine solution, then
view it with a J-inch power. Villi and papillae are best
made out in injected specimens, as will be seen on reference
to Plate VII.

CHAPTER VI.

THE MINERAL KINGDOM.

INORGANIC MATTER— FORMATION OF CRYSTALS— POLARISATION, ETC.

our meagre search through organic nature
we met with an endless variety of beautiful
and instructive materials for the employment
of the microscope. If we now turn our atten-
tion to the inorganic or mineral kingdom we
shall find a vast storehouse filled with objects
of unsurpassed interest to the microscopist.
In the examination of the many beautiful
forms presented to us in the phenomena of crystallisation,
and the study of the varied chemical combinations, the
student will discover a never-ending source of useful occu-
pation.

We are as yet in great ignorance of the manner in
which the majority of crystals belonging to the mineral
kingdom are formed : we know, however, that very few can
be reproduced by the chemist. But, although ignorant of
the means whereby the great majority of crystals have
been formed in the vast laboratory of nature, we can
crystallise an immense number of substances, watch their
numerous intricate modes of formation, and that in the
smallest appreciable quantities, when aided by the micro-
scope. Among natural crystals those employed in the
formation of rocks open up a wide field to our view. The
varieties of granites present us with the earliest crystal-
lised condition of the earth's crust as it cooled down, the
structure of which is beautifully exhibited under polarised
light. Plate VIII. No. 160, is a section of a granite

FORMATION OF CRYSTALS.

729

shown on a red selenite ground. Crystallisation under a
somewhat different condition and combination is seen in
the New Eed Sandstone, No. 158.

The prismatic rings of another crystalline substance,
Quartz, represented in ISTo. 159, possess great interest.
Again, that of Arragonite, Tremolite, and Carbonate of
Lime. The latter is frequently seen in combination with
animal structure, and is then productive of many re-
markable changes and modifications, such as we have
represented in Plate VIII. Nos. 171, 172, 175, and 180,
all of which should be prepared for examination with as
well as without the polariscope.

The formation of artificial crystal may be readily
effected, and the process watched, under the microscope, by
simply placing a drop of a saturated solution of any salt
upon a previously warmed slip of glass. The following
list of salts and other substances form a beautiful series
of objects for polarised light : —

Alum.
Asparagine.

AsparticAcid. Plate VIII. No. 1G8.
Bitartrate of Ammonia.
Boracic Acid.

Borax. Plate VIII. No. 164.
Carbonate of Lime.
Soda.

Chlorate of Potash.
Chloride of Barium.

„ Cobalt.

,, Copper and Ammonia.

,, Sodium.
Cholesterine.
Chromate of Potash.
Cinchonine.
Cinchonidine.
Citric Acid.
Hippuric Acid.
Iodide of Mercury.

,, Potassium.

,, Quinine,
lodo-disulphate of Quinine.
Murexide.
Nitrate of Bismuth.

„ Barytes.

,, Brucine.
Copper.
Potash.

,, Strontian.

,, Uranium.
Oxalate of Ammonia.

,, Chromium.

,, Chromium and Potash.

„ Lime.
Soda.

Oxalic Acid.

Oxalurate of Ammonia.

Permanganate of Potash.

Phosphate of Lead arid Soda.

Platino-cyanide of Magnesia.

Plumose Quinidine.

Prussiate of Potash, red and yellow.

Quinidine.

Santonine.

Salicine.

Salignine. Plate VIII. No. 162.

Sulphate of Cadmium.

Copper.

Copper and Potash.
Sulphate of Iron.

Iron, Cobalt, and Nickel

Magnesia.

Nickel and Potash.

Soda.

Zinc.
Sugar.

Tartaric Acid.
Thionurate of Ammonia.
Triple Phosphate.
Urate of Ammonia.

Soda.

Urea, and all the urinary deposits.
Uric Acid.

MINERALS.

Agates, various.
Asbestiform Serpentine.
Avanturine.
Carbonate of Lime.
Carrara Marble.

730 THE MICROSCOPE.

Indurated Sandstone, Howth. i VTWTARTT1 «5rTRt4TA\rnT?<a

Indurated Sandstone^ Bromsgrove. VEGETABLE SUBSTANCES.

Gibraltar rock. j CUTICLE of Leaf of Correa Cardinalis.

Granite, various localities. No. 160.

Hornblend Schist.

Labrador Spar.

Norway Rock.

Quartz Rock, various. No. 159.

„ in Bog Iron Ore.

Quartzite, Mont Blanc.
Sandstone, Plate VIII. No. 158.
Satin Spar.

Selenites, various colours.
Tin Ore, with Tourmalin.

Dentzia scabra.

PI. vm. NO. 173.

„ „ Elseagnus.

,, ,, Onosma taurica.

Equisetum. No. 174.
Fibro cells from orchid. No. 169.

,, Oncidium bicallosum.
Scalariform vessels from Fern.
Scyllium. No. 177.
SILICIOUS CUTICLES. — Various.
Starch.— Various. No. 167.

Very interesting results will be obtained by combining
two or more chemical salts. Mr. Davies1 succeeded in
forming numerous beautiful double salts in the following
manner. To a nearly saturated solution of the sulphate
of copper and sulphate of magnesia add a drop, on the
glass-slide, and dry quickly. To effect this, heat the
slide so as to fuse the salts in its water of crystallisation,
and there remains an amorphous film on the hot glass.
Put the slide aside and allow it to cool slowly ; it will
gradually absorb a certain amount of moisture from the
air, and begin to throw out crystals. If now placed
under the microscope, numerous points will be seen to
start out here and there. The starting points may be
produced at pleasure by touching the film with a fine
needle point, so as to admit of a slight amount of moisture
being absorbed by the mass of salt. Development is at
once suspended by applying gentle heat; cover the
specimen with balsam and thin glass. The balsam should
completely cover the edges of the thin glass circle, other-
wise moisture will probably insinuate itself, and destroy
the form of the crystals.

Mr. Thomas succeeded in crystallising " the salts of
the magnetic metals " at very high temperatures, which
gave interesting results, and produced curious forms of
crystals. Plate VIII. No. 163 are representations of
crystals of sulphate of iron and cobalt, ISTo. 165, of nickel
and potash, obtained in the following manner : — To form
the sulphate of iron crystal, add to a concentrated solution
of iron a small quantity of sugar, to prevent oxidation.
Put a drop of the solution on a glass slide, and drive out the

(1) Quart. Journ. Micros. Scien. , rol. ii. p. 128. 1862.

SUBLIMATION OF ALKALOIDS. 731

water of crystallisation as quickly as possible, by the
aid of a spirit lamp ; then with a Bunsen's burner bring
the plate to a high temperature. Immediately a remark-
able change is seen to take place in the form of the crystal,
and if properly managed the " foliation " represented in
the plate will be fairly exhibited. The slide must not be
allowed to cool down too rapidly or the crystals will
probably absorb moisture from the atmosphere, and in so
doing the crystals alter their forms. Immerse them in
balsam, and cover in the usual way before quite cold.

/Sublimation of Alkaloids. — Dr. Guy a few years ago
directed the attention of microscopists to the fact that the
crystalline shape of bodies belonging to the inorganic
world might lead to their detection. Subsequently, Dr.
A. Helwig, of Mayence, took the matter up, and showed
that the plan was applicable not only to inorganic but also
to organic substances, and especially to the poisonous alka-
loids. By improving on Dr. A. Hel wig's process, and
substituting a bit of porcelain, Dr. Guy has been able to
watch the process more minutely, and to regulate it more
exactly. He has by this means been able to obtain
characteristic crusts composed of crystals of strychnine
weighing not more than l-3,000th or 1 -5,000th of a grain.
Morphia gives equally characteristic results. For the
examination of these, Dr. Guy recommends the use of a
binocular microscope with an inch object-glass. But it is
not to crystalline forms alone that one need trust ; the
whole behaviour of a substance as it melts and is converted
into vapour is eminently characteristic, and when once
deposited on the microscopical slide, under the object-
glass, the application of re-agents may give still more satis-
factory results. The re-agents, however, which are here to
be applied are not of the kind ordinarily employed. Colour-
tests under the microscope are, comparatively speaking,
useless : those that give rise to peculiar crystalline forms
are rather to be sought after. For instance, the crystals
produced by the action of carbazotic acid on morphia are
by themselves almost perfectly characteristic. These ex-
periments should not, however, be undertaken for medico-
legal purposes by one unskilled in their conduct, for the
effects of the re-agents themselves might be mistaken by

732 THE MICROSCOPE.

the uninitiated for the result of their action on the sub-
stances under examination.

Dr. Guy's1 method of procedure is as follows : — " Pro-
vide small crucibles, covers, slabs, or fragments of white
porcelain ; a few microscopic cell-glasses, with a tTnV.1mp.ss
of about one-eighth of an inch and a diameter of circle of
about two-thirds of an inch : and discs of window-glass
about the size of a shilling. Place the porcelain slab on
the ring of a retort-holder or other convenient support ;
then the glass cell ; and upon the porcelain in the centre
of the cell a minute portion of the alkaloid or other white
powder, or crystal reduced to powder ; then pass the clean
glass dish through the flame of the spirit-lamp till the
moisture is driven off, and adjust it with the forceps over
the glass ring ; now apply the flame of the spirit-lamp to
the porcelain, underneath the powder or crystal, and con-
tinue the heat till the powder undergoes its characteristic
change and gives off vapour. Watch the deposit of this
vapour on the glass dish, and remove the spirit-lamp,
either directly or after a short interval, as experience may
determine.

" The white surface of porcelain being visible through
the glass disc, as through a window, the behaviour of
the substance under examination is easy to observe. It
may be driven off without undergoing change or leaving
residue, and the disc may be covered with crystals, as
happens with arsenious acid, or with an amorphous
sublimate, as happens with calomel ; it may coalesce,
throw out long silky crystals, to be gradually transferred
as crystals to the glass disc, as is the case with corrosive
sublimate; and it may melt, with or without previous
change of colour, retain or shift its place, deposit carbon
more or less abundantly, and yield a sublimate of detached
crystals (veratrine), twigs (solanine), tufts (meconine),
branching patterns (strychnine, morphine, cryptopia, &c.),
watered patterns with or without crystalloids (several alka-
loids and glucosides), the melting and deposition of carbon
being a common property of the alkaloids and of some
analogous active principles.

(1) Dr. W. A. Guy, F.R.S. &c. on the "Sublimation of the Alkaloids."—
Pharmaceutical Journal, June and August, 1867. Micros. Jour. Dec. 1867

SUBLIMATION OP ALKALOIDS. 733

" The principal precaution to be observed in the
application of heat is, that it should be moderate and
gradual. It is best to act on the assumption that the
substance under examination may be one of a considerable
group of bodies, some of which sublime at very moderate
temperatures. The spirit-lamp should, therefore, be placed
at first three or four inches below the slab of porcelain, so
that the point of its flame may not touch it ; and if, under
this low temperature, the disc of glass is not dimmed, the
lamp should be raised by degrees till the mist makes its
appearance. Then, as a general rule, the lamp should be
withdrawn, the disc removed, and a new one put in its
place. It may be well to state that, as the disc has been
passed through the flame to drive off moisture, and has in
this way been heated, the flame of the spirit lamp should
not be allowed to play on the porcelain slab after the mist
has appeared on the disc, at least not for any length of
time ; for, if this precaution be neglected, it may happen
with the alkaloids as with arsenious acid or corrosive sub-
limate, that the mist does not form at all, or that it is
driven off as soon as it is deposited. Perhaps, too, it may
not be quite unnecessary to recommend that each disc of
glass, as it is removed, should be placed with the subli-
mate upwards against a glass slide or fragment of porcelain ;
and that in this position (sublimate upwards) it should be
retained. If this very simple precaution be overlooked, it
is quite possible that we may mistake one surface for the
other, and find ourselves applying our re-agents to the
wrong one. The chief precaution relating to the ex-
amination and disposal of the sublimates consists in
measures for preserving their identity during the examina-
tion to which we may have to subject them. This is best
done by writing the names and that of the reagents on
discs of paper, and placing paper and disk together in
sunken grooves or circular spaces.

" As a precaution omitted by an experimenter so prac-
tised as Dr. Helwig is very likely to be overlooked by
others, it is well to insist upon and to prescribe as the
first step to be taken with a crystalline solution which we
are about to use as a test, the determination of its proper
crystalline form or forms as evaporated on a flat surface of

734: THE MICROSCOPE.

glass. Another mistake, arising out of a similar want of
caution, may consist in confounding the effect of some
saline re-agent with that of the water which holds it in
solution.

"Now these remarks have a direct practical bearing on
the selection of tests. A preference ought to be given to
re-agents which leave no residue of their own : to distilled
water, to alcohol, ether, chloroform, benzole, and fusel oil ;
and to acetic acid and the dilute mineral acids. Then
those salts should be preferred of which the solutions
yield dry residues of one or two definite forms, not such as
put on many different shapes, are deliquescent themselves,
and are likely to leave moist and unstable compounds.
Nor is the strength of the solution a matter of little or no
importance ; for it should be borne in mind that the sub-
limates to which we apply them contain very minute frac-
tions of a grain; and that a very strong solution, after
acting on this minute quantity, would leave a coarse
deposit of its own, both over the general surface and at
the margin of the spot, which, blending with the reaction,
would obscure and confuse it. As a general rule, there-
fore, solutions of a moderate strength are to be preferred,
such as 1 grain of carbazotic acid to 250 of water, and 1
grain of bichromate of potash to 100, the same of the red
prussiate of potash, and of the nitro-prusside of sodium."

Other than the alkaloids and volatile metallic poisons
were found to yield sublimates when heated, as urea,
uric acid, hippuric acid, alloxan, uramile, &c.; but these
results scarcely prepared one to expect a sublimate from a
blood-stain. Yet, on separating the fibres of a small spot
of a cotton texture stained with blood about twenty-five
years since, and submitting a section of the fibre an eighth
of an inch long to heat, a figured pattern of the colour of
blood was obtained, such as might be caused by a solution
of blood in some thin oily liquid : this figured pattern was
surrounded by a colourless border, having bright figured
patterns such as those which mark the less characteristic
portions of crystalline sublimates. Dr. Guy, on repeating
his experiments, found the results constant ; and on con-
ducting them with care, and under the guidance of micro-
scopic examinations, two sublimates were uniformly ob-

SPECTRUM ANALYSTS. 735

tained, the first colourless and apparently crystalline, the
second, under a high temperature, of the colour of the
blood-stain from which it was procured, and of the figured
pattern mentioned.

Mr. Sorby's attention has been directed to obtain a defi-
nite method of qualitative analysis of "animal and vegetable
colouring matters," and of animal substances generally, by
means of the spectrum microscope. He has also so com-
bined the spectroscope with the binocular microscope as
to make it available for the purpose of distinguishing
minute portions of coloured minerals in thin sections of
rocks and meteorites. He employs an ordinary large
binocular microscope, with an object-glass of about three-
inches focal length, corrected for looking through glass an
inch thick ; the lenses being at the top, and as far as pos-
sible from the slit. This objective is placed at the focus,
and between it and the lenses, at a distance of about half
an inch from them, is a compound prism, composed of a
rectangular prism of flint-glass and two of crown-glass, of
about 61°, one at each end. This arrangement gives direct
vision and a spectrum of a suitable size for these inquiries,
since a wide dispersion often produces indistinctness of
the absorption bands. That we may have the opportunity
of comparing two spectra side by side, a small rectangular
prism is fixed over half the slit, and with the acute angle
parallel to it and passing beyond it.1

" This gives an admirable result, the only defect being
that, when the spectra are in focus, their line of junction
is some distance within it ; and therefore to correct this
employ a cylindrical lens of about two feet focal length,
with its axis in the line of the slit, which can easily be
fixed at such a distance between the slit and the prisms
as to bring the spectra and their line of contact to the
same focus. In front of the slit, close to the small rectan-
gular prism, is a stop with a circular opening, to shut out
lateral light, and a small achromatic lens of about half
an inch focal length, which gives a better field, and
counteracts the effect of the concave surface of the liquid
in the tubes used in the experiments, if they are not

(1) Mr. Sorby's prisms and their arrangement have "been entrusted to Mr.
Browning's skilful hands, who is prepared to adapt them to any microscope.

736 THE MICROSCOPE,

quite full. These are cut from barometer-tubes, having
an internal diameter of about one-seventh of an inch, and
an external diameter of about three-sevenths of an inch.
They are made half an inch long, ground flat at each end,
and fixed with Canada balsam on slips of glass two inches
long and about six-tenths of an inch wide, so that the
centre of the tube is about one-fourth of an inch from
one edge. By this arrangement the liquid may be
examined through the length of the tube by laying the
slip of glass flat on the stage of the microscope, or through
the side of the tube, by placing the slip vertical and the
tube horizontal. Cells of this size can be turned upside
down and deposits removed without any liquid being
lost ; and the upper surface of the liquid is sufficiently
flat, even when inclined at a considerable angle. If
requisite, small bits of thin glass can be laid on the top,
which are held on by capillary attraction, or fastened
on with gold-size, if it be desirable to keep the solution
for a longer time. When the depth of colour is too great
in the line of the length of the cell, we can at once see
what would be the effect of about one-fourth of the colour
by turning it sideways ; and thus we can save much time,
and quickly ascertain what strength of solution would
give the best result. Very frequently an excellent
spectrum is obtained in one direction with one reagent,
and in the other with another, without further trouble.

" The scale of measurement consists of two small Mcol's
prisms, and an intermediate plate of quartz. If white
light, passing through two such prisms, without the plate
of quartz, be examined with the spectrum-microscope, it
of course gives an ordinary continuous spectrum ; but if
we place between the prisms a thick plate of quartz or
selenite, with its axis at 45° to the plane of polarisation,
though no difference can be seen in the light with the
naked eye, the spectrum is entirely changed. The light is
still white, but it is made up of alternate black and
coloured bands, evenly distributed over the whole spec-
trum. The number of these depends on the thickness of
the depolarising plate, so that we may have, if we please,
almost innumerable fine black lines, or fewer broader
bands, black in the centre and shaded off at each side.

SPECTRUM ANALYSIS. 737

These facts are of course easily explained by the inter-
ference of waves. It would be impossible to have a mope
convenient or suitable scale for measuring the spectra of
coloured solids and liquids. If we use a micrometer in
the eyepiece, an alteration in the width of the slit modifies
the readings, and the least movement of the apparatus
may lead to error, whereas this scale is not open to either
objection. Besides this, the unequal dispersion of the
spectrum makes the blue end too broad, so that a given
width, as measured with a micrometer in the eyepiece,
is not of the same optical value as the same width in
the red. The divisions in the interference- spectrum
bear, on the contrary, the same relation to the length
of the waves of light in all parts of the spectrum, and
no want of adjustment in the instrument alters their
position. As will be seen from the diagram (fig. 355),
the unequal dispersion makes the distance between the
bands in the blue about twice as great as in the
red. The perfection of a spectrum would be one in
which they were all at equal intervals ; but possibly
no such uniform dispersion could be produced. By
having a direct-vision prism, composed of one of flint-
glass of 60°, and two of crown-glass of suitable angle, we
can place it over the eyepiece, and can diminish the
dispersion at the blue end, or increase that at the red end,
by turning it in one position or the other, and thus see
either end to the greatest advantage.

" Since the number of divisions depends on the thick-
ness of the interference-plate, it became necessary to decide
what number should be adopted. Ten it was thought
would be most suitable ; but, on trying, it appeared to b&
too few for practical work. Twenty is too many, since it
then becomes extremely difficult to count them. Twelve
is as many as can be easily counted ; it is a number easily
remembered, gives sufficient accuracy, and has a variety of
other advantages. With twelve divisions the sodium-line
p comes very accurately at 3^ ; and thus, by adjusting the
plate so that a bright sodium-light is hid in the centre of
the band, when the Nicol's prisms are crossed, it is accu-
jately at 3|, when they are arranged parallel, so as to give
a wider field. The general character of the scale will

SB

738 THE MICROSCOPE.

be best understood from the following figure, in which
the bands are numbered, and given below the principal
Fraunhofer lines. The centre of the bands is black, and

0123456 78 9 10 11 12

<R^> IIHIiillHH

1 1 1 1 i i i

Fig. 355. — A BCD E b F o

they are shaded off gradually at each side, so that the
shaded part is about equal to the intermediate bright
spaces. Taking, then, the centres of the black bands as
1, 2, 3, &c., the centres of the spaces are 1J, 2J, 3|, &c.,
the lower edges of each J, If, &c., and the upper 1J, 2J,
&c., we can easily divide these quarters into eighths by
the eye ; and this is as near as is required in the sub-
ject before us, and corresponds as nearly as possible to
1-1 00th part of the whole spectrum, visible under ordinary
circumstances by gaslight and daylight. Absorption-bands
at the red end are best seen by lamplight, and those at the
blue end by daylight.

On this scale the position of some of the principal lines
of the solar spectrum is about as follows : —

A f B 1J C 2| D 3|

E 5H 6 6^ F,.;...74 G....:10-

At first plates of selenite, which are easily prepared,
were used, because they can be split to nearly the re-
quisite thickness with parallel faces ; but its depolarising
power varies so much with the temperature, that even
the ordinary atmospheric changes alter the position of the
bands. However, quartz cut parallel to the principal
axis of the crystal is so slightly affected in this manner
as not to be open to this objection, but is prepared with
far greater difficulty. The sides should be perfectly
parallel, the thickness about '043 inch, and gradually
polished down with rouge until the sodium- line is seen in
its proper place. This must be done carefully, since a
difference of l-10,000th inch in thickness would make it
decidedly incorrect.

The two Nicol's prisms and the intervening plate are
mounted in a tube, and attached to a piece of brass in such

SPECTRUM ANALYSIS. 739

a manner that the centre of the aperture exactly corre-
sponds to the centre of any of the cells used in the experi-
ments, which are all made to correspond in such a manner
that any of them, or this apparatus, may be placed on the
stage and be in the proper place without further adjust-
ment, which, of course, saves much time and trouble.1

In the preparation of vegetable colouring matters for
the spectroscope, care must be taken to employ a small
quantity of spirits of wine ; filter the solution, and
evaporate it at once to dryness at a very gentle heat,
otherwise if we attempt to keep the colouring matters in
a fluid state they quickly decompose. It is necessary to
employ various reagents in developing characteristic spectra.
The most valuable reagent is sulphite of soda, which
admits of the division of colours into groups. Of the
mode of applying reagents, ample directions are given.

Mr. Sorby's qualitative analysis is just the kind of thing
to employ in detecting adulterations in many substances met
with in commerce, as well as in inquiries where very small
quantities of material are at command. By this method
we might be able in a few minutes to form a very satisfac-
tory opinion, or at least one that might meet all practical
requirements, and narrow the inquiry to a surprising
extent ; if this can be said even now, surely further re-
search cannot fail to make it most useful in cases where
ordinary chemical analysis would be of little or no use ;
for in this way we may be able to detect the presence
of chlorophyll in some of the lower animal forms; as
the amoeba, hydra, &c., or, on the other hand, the red
colouring matter of the blood, cruorine, in worms, molluscs,
and insects. A number of colouring matters can be
obtained, by using ether, from sponges, polyzoa, and the
crustaceans; these, if examined in this way, may give
unexpected results.

For further information on this interesting subject we
must refer the reader to Mr. Sorby's paper " On a Definite
Method of Qualitative Analysis of Vegetable and Animal
Colouring Matter by means of the Spectrum Microscope,"
published in the Proc. Roy. Soc. No. 92, 1867.

(1) See a paper by Dr. Gladstone, on the Spectra of Solutions of Salts.
Quart. Journ. Chem. Soc. vol. xi. p. 36.

3B2

740 THE MICROSCOPE.

It would be a vain attempt were we to try to convey
to our readers any idea of the great discoveries which have
been made by the microscope, or of the important pur-
poses to which it has been applied. Second only to the
telescope, though in many respects superior to it, the
microscope transcends all other instruments in the scientific
value as well as in the social interest of its results. While
the human eye, the telescope and microscope combined,
enables us to enjoy and examine the scenery around us, to
study the forms of life with which we are more imme-
diately connected, it fails to transport us into the depth of
space, to throw into relief the planets and the stars, and
to indicate the forms and arrangements in the worlds of
life and motion, which distance diminishes and conceals.
To these mysterious abodes, so long unrevealed, the tele-
scope has at last conveyed us. It has shown us those
worlds and systems, of which our own earth and our own
system are the types ; but it fails to enlighten us respecting
the nature and constitution of the celestial bodies, and the
forms of life for which they are created.

In its downward scrutiny, as well as in its upward
aspirations, the human eye has equally failed. In the
general view which it commands of animal, vegetable, and
mineral structures, it cannot reach those delicate organiza-
tions on which life depends, or those structures of inor-
ganic matter from which its origin and composition can be
derived. Into these mysterious regions, where the philo-
sopher has been groping his way, the microscope now
conducts him. The dark abodes of unseen life are lighted
up for his contemplation, — organizations of transcendent
beauty appeal to his wonder — new aspects of life, new
forms of being, new laws of reproduction, new functions
in exercise, reward the genius of the theoretical and
practical optician, and the skill and toil of the naturalist.
With wonders like these all nature is pregnant : the earth,
the ocean, and the air — times past and times present, now
surrender their secrets to the microscope.

What we know at present, even of things the most near
and familiar to us, is so little in comparison of what we
know not, that there remains an illimitable scope for our
inquiries and discoveries ; and every step we take serves to

CONCLUSION.

741

enlarge our capacities, and give us still more noble and
just ideas of the power, wisdom, and goodness of God.
This marvellous universe is so full of wonders, so teems
with objects of latent beauty, that perhaps eternity alone
will open up and develop sufficient opportunities to enable
us to survey and admire and appreciate them all

" And lives the man, whose universal eye
Has swept at once th' unbounded scheme of things,
Mark'd their dependence so, and firm accord,
As with unfaltering accent to conclude
That this availeth nought ? Has any seen
The mighty chain of beings, lessening down
From infinite perfection to the brink
Of dreary nothing, desolate abyss !
From which astonish'd thought, recoiling, turns?
Till then, alone let zealous praise ascend.
And hymns of holy wonder, to that Power,
Whose wisdom shines as lovely on our minds
As on our smiling eyes his servant sun." — THOMSON.

APPENDIX.

AN increasing demand for good, useful, and moderately
priced instruments fit for students and others, naturally
enough has had the effect of inducing makers to vie with
each other in their endeavours to give a better class micro-
scope for a small sum. Among those manufacturers who have
effected much for the microscope, not only in the way of
improvements, but in its production at a moderate cost,
we should have mentioned Messrs. E. and I. Beck.
Their Popular Microscope will be readily understood on
reference to fig. 357.

The body, A (in the illustration shown as binocular),
is carried by a strong arm, B ; and this is attached to a
square bar, c, which may be moved up or down by a
rack-work and pinion in the lower part of the stand, where
the stage, D, and the mirror, E, are attached.

The base, F, is triangular; and it is connected with the
parts of the instrument already described by a broad stay,
G, which moves on centres at the top and bottom, so as to
allow the end of the tube, H, to fit by its projecting pin
into various holes along the medial line of the base.
With this arrangement, if the body of the microscope be
required in a more or less inclined position as in the figure,
four holes are provided near the extremity of the base for
the pin of the tube to fit into. A hole near the stout pin, L,
is used when a vertical position is wanted ; while to obtain
the horizontal position, the pin of the tube is placed in a
hole in the stud, K, the inner surface of the stay, G, resting
at the same time on the top of the stout pin, L. This form of
construction is entirely new, and has the following advan-
tages : it is strong, firm, and yet light ; the instrument
cannot alter from any particular inclination it is put into,

744 APPENDIX.

which is not unfrequently the case when the ordinary

Fig. 357. — Beck's Popular Microscope.

joint works loose ; and in every position the heavier part

APPENDIX.

of the stand is brought over the centre of the
ensure an equality of balance.

745

to

P g. 358. - Beck's Student's Microscope.

746 APPENDIX.

To adjust the focus of the object-glass, turn the
milled heads o for a quick movement, or the milled head
p for a slow one.

The stage, D, is circular, and upon it fits a plate, T;
this again carries the object-holder, u, which is provided
with a ledge, v, and a light spring, w ; it is held on the
plate T by a spring underneath, so that it can be moved
about easily and smoothly by one or by both hands. The
small spring, w, is fastened to the object-holder by a
milled head, which will unscrew ; so that the position of
the spring may be altered to give more or less pressure
upon the edge of the object, or it may be removed alto-
gether, if necessary.

When a stage with only a flat surface is required, the
object-holder, u, may be removed by unscrewing, from the
under side of the plate T, two small milled heads which
connect a circular spring with the object-holder; or, by
removing the plain stage altogether, an extra simple flat
plate may be substituted.

Beneath the stage there is a cylindrical fitting for the
reception of a diaphragm, or for any additional apparatus
that may be required in that position.

The mirror, B, besides swinging in a rotating semicircle,
will slide up or down the tube, H, or it will turn on either
side for oblique illumination.

Their Educational and Student's Microscopes, and larger
instruments are well known, and therefore need no
particular mention.

CROUCH'S CHEAP BINOCULAR MICROSCOPE.

The instrument (fig. 359) manufactured by Mr. H. Crouch,
London Wall, possesses many important advantages as a
cheap microscope. First it combines perfect optical per-
formance with good workmanship in the construction of
the stand. It is well balanced, and stands firmly in any
position. The polariscope can be used (the analyser
being adapted to binocular) with the 2-inch. The
stage is of a new construction, giving universal move-
ments of 1 J inch in extent. The condenser is on a separate

APPENDIX.

747

stand, and the accessory apparatus can be adapted at any
time, without returning the instrument to the maker's
'lands.

Fig. 359. — Crouch's Microscope. Scale J.

The latest improvement effected in this cheap instru-
ment is the adaptation of a concentric rotating stage, a
most convenient and useful addition. This stage (tig. 360)
is an adaptation of Nachet's principle, and consists of : A,
a lower plate or stage attached to stand in the ordinary
manner, with fitting beneath (F) to receive the accessory
illuminating apparatus. B is an upper plate rotating con-

748

APPENDIX.

centrically with optic axis of microscope, c a plate of
polished glass let in and secured to upper surface of B.
D D, a v spring attached to outer edge of the plate B and
rotating with it, having at the outer extremities projecting
"ivory" points d d. E the object-carrier, consisting of
another plate of polished glass, mounted in brass frame,

Fig. 360.— Crouch's Concentric Stage. Scale |.

having an attachment for holding the object. The plate
E projecting slightly on the lower surface from the brass
frame is kept in contact with the circular plate o (also
slightly projecting above B), the two glass surfaces being
in contact, and kept so by the pressure of the "ivory
points" dd; thus securing a beautifully smooth and
delicate — though firm — adjustment, which admits of
an object being found with extreme facility under the
highest powers. It is particularly adapted for the ex-
amination of objects in fluid of any kind, the adjustments
not being subject to oxidation; any minute object may
very readily be found, and the slightest change in the
field is easily effected ; there is no slipping back or recoil.

APPENDIX.

749

The whole stage may also be concentrically rotated;
this is most essential in the examination of the markings
on certain test objects ; and, what is very important, there
is no danger of the apparatus getting out of order. For
histological work, and for the teacher who wishes to
demonstrate any peculiar feature of an object, it is

Fig. 361.— Browning's Student's Microscope.

certain to prove exceedingly useful. The stage can be
added to any instrument.

BROWNING'S COMPLETE MICROSCOPE.

Mr. Browning's Student's Complete Microscope differs
from the educational instruments of other makers, possessing

750

APPENDIX.

mechanical motions to the stage. It has a handsome brass
stand, large body, with coarse and fine adjustments, and
drawer tube to eye-piece, and separate 1-inch and J-incb
objectives of very superior quality, of moderate angular
aperture, cut to the Microscopic Society's gauge.

The stage is arranged to receive the polariscope, and the
whole instrument is so made that additional apparatus may
at any time be added to it, at pleasure. The performance
of the objectives is unusually good ; the instrument is well

Tiff. 362. —Ladd's Microscope.

APPENDIX. 751

made, and remarkably cheap at the price, £6 6s. ; we ver}
cordially recommend it for general use.

Mr. Ladd has lately effected improvements in the
manufacture of his instruments in mechanical details,
and in obtaining a perfect centre of gravity. In his best
instrument, such as that represented in fig. 362, he has
taken great care to obtain a perfect balance in any position,
even when placed on its horizontal axis ; no instrument
can be better adapted than this to all the wants of the
microscopist, and which is one combining many of the
advantages of the more expensive forms.

Nachet and Hartnack of Paris, and Merz of Munich,
hold an almost equal rank as makers of first-class micro-
scopes, and in point of excellence of workmanship
fairly rival those of English makers. Hartnack's latest
improvement consists in an exquisitely-fitted concentric
stage, which works with marvellous neatness and pre-
cision. Nachet has also effected considerable improve-
ments in his circular stage, as well as in the arrangement
of his binocular form of body; for fuller particulars of
which we must refer the reader to the Monthly Micro-
scopical Journal.

IMMERSION OBJECTIVES.

Messrs. Hartnack and Merz and others have likewise added
greatly to their well-earned reputations by the construction
of immersion objectives of a very superior order. We have
had especial opportunities of comparing the respective
merits of Hartnack's ^ and J^, Merz's -J^, and Noberts's
Jy, of which we can speak in the highest terms of praise.
All work through ordinary thick glass covers with
great facility, and. are therefore adapted either for the
examination of pathological specimens or for the most
delicately-lined test-objects. The low price at which they
are sold is no unimportant consideration to the student in
microscopical science ; the T^ of either Hartnack or Merz
can be purchased for about £6 6s., while their other powers
are equally cheap. Amici nearly fifty years ago demon-
strated the value of the immersion system : and Scemmering,
writing of one of Amici's microscopes, observes : " Its
magnifying power, and the admirable precision and clear-
ness with which the object is seen, seems astonishing."

752 APPENDIX.

It is not difficult to see that Amici's method of connecting
the objective with the cover-glass by a film of water must
necessarily very much dimmish the reflection which usually
takes place in the incidence of oblique light when the
ordinary or dry objective is employed. The limiting angle
of refraction of water being about 48 degrees, it follows
that whatever is the degree of obliquity in the incident
light falling on the object, the immersion lens never has
to deal with rays of greater obliquity than 48 degrees.
To this, as well as the greater number of parallel rays
brought to a focus, and the increased angle of aperture,
is due the greater clearness and precision of the image
obtained.

" The advantages," writes Mr. J. Mayall,1 " mainly
claimed for the immersion objectives are : greater work-
ing distance between the object and the objective, increase
of light, superior definition and clearness in the optical
image, which image is obtained by much simpler illumi-
nating apparatus, and with less manipulative skill than
that considered indispensable in using high-power dry
objectives."

We are pleased to add that Messrs. Powell and Lealand
are turning their attention to the construction of objectives
on the immersion system. This cannot however be effected
1 y making the front lens moveable, so that the objective
may be used either wet or dry.

(1) The Monthly Microscopical Journal, 1869, p. 92.

INDEX.

ABEBRATION, CHROMATIC, 26.

of lenses, 21.

spherical, 26.

Abraham's reflecting prism, 172.
Absorption bands, 128.
Acalephae, 491.
Acarina, 632.
Acarus beetle, 455.

cloth moth, 641.

- — domesticus, 637.

of dog, 634.

farinse, 639.

of fly, 641.

of fowl, 640.

of rat, 634.

sacchari, 638.

scabiei, 635.

of swallow, 639.

Achetina, 627.
Achnanthes Longipes, 420.
Achorion, 296.
Achromatic condenser, 166.

corrections, 40.

illuminator, 167.

object-glasses, 42.

Acineta-form infusoria, 401.

vorticella, 447.

Acineta tuberosa, 411, 449.
Actinia actinozoa, 465.

rubra, 483.

bellis, 484.

Actiniforum zoophytes, 485.
Actinophrys sol, 374.
Actinotrocha, 578.
Actinozoa, 485.
Adams' microscope, 10.
Adipose tissue, 693.
Adulteration of food, 345.
2Ecistes, 451.
^cidium, 293.
Agates, 399.

Alcyonella stagnorum, 526.
Alcyonidje, 489, 524.
Alcyonium digitatum, 489.

polypidoms, preparation of, 509.

Alder, section of, 334.
Algae, development of, 269.
Alkaloids, sublimation of, 731.
Amici's microscopes, 12.

prisms, 82.

Amphistome conicum, 565.
Amphitetras, 416.

Amoeba, 373.

Amoeboid state of volvox, 277.
Anacharis alsinastrum, 821.
Analysis, spectrum, 786.
Angle of aperture, 44

of incidence, 16.

of refraction, 17.

mode of measuring, 45.

Anguillulae, 571.
Anguinaria spatulata, 520.
Animalcule, snn, 874.
Animalcules, 402.

cage, Varley's, 195.

collecting, 193.

history of, 4C3.

infusorial, 414.

Animal cell, 659.

action of cilia in, 671.

bodies, injecting, 231.

cells, change into tissues, 665.

cellular membrane, 692.

connective tissue, 662.

elementary substance, 659.

epithelium, 668.

fibrous tissue, 694.

kingdom, division of, 866.

life, 655.

structure, 661.

structure, mode of investigating,

724.

tissues classified, 692.

tissue consolidated, 702.

tissues, staining, 225.

Annelida, 575.

Annulosa, 559.

Anobium, 633.

Antennae of insects, 607.

Amyot's finder, 188.

Aphides, 613.

Aphrophora bifasciata, 615.

Aplanatic doublet lensj 26.

Aplysia, 529.

Aquatic box, 194.

Arachnida, 631, 644.

Arachnoidiscus, 432.

Archer on amoeboid bodies, 277.

Arcella acuminata, 372.

Arenicola, 576.

Aristophanes, microscope known to, 2.

Artemise, 557.

Articulata, 579.

Asci of lichens, 306.

C

754

INDEX

Aspergillus, G01.
Astasia, 412.
Asteroidea, 495.
Atropus, 623.
Atlantic soundings, 382.

BAKER on the microscope, 10.
Baker's microscopes, 86.

brachionus, 456.

Baccillaria paradoxa, 269.

Bacterium, 412.

Baird, Dr., on entomostraca, 557. .

Balanidse, 555.

Balbiani, Dr., on paramgecium, 410.

Barnacle, 554.

De Bary on fungi, 291.

Bat, head of, 681.

Beale, Dr. on cell development, 659.

on a new object glass, 73.

on magnifying power, 77.

on glycerine for preserving objects,

on method of staining tissues, 225.

on injecting, 237.

Beck, Mr. R., on errors of interpreta-
tion, 64.

Bee's tongue, leg, &c., 612.

eye, 586.

Beetles, 623.

bacon, 624.

diamond, 622.

tortoise, 588.

water, 625.

Bell-animalcule, 445.

Berg-mehl, 432.

Bergh, Dr., on urticating organs, 545.

on podura scales, 628.

Berkeley on two new British fungi, 304.

on fungi, 290.

Beroe, 492.

Bichromate of potash injection, 236.

Biddulphia, 437.

Bilharzia hsematobra, 567.

Binocular microscope, 117.

Bird's-head coralline, 518.

Blood-corpuscles, 678.

crystallization of, 680,

disc, size of, 680.

spectrum, 128.

vessels, structure of, 688.

Blow-fly, 590.

Beckett's lamp, 185.

Bone, 714.

cutting sections of, 208.

eel, 716.

fishes, 719.

human, 713.

ostrich, 715.

reptiles, 714.

sting ray, 718.

Bonnani's microscope, 8.

Bbtrytis, 301.

Bot-fly, egg of, 607.

Bourgingnon, Dr., on acarus scabiei,
635.

Bowerbank on sponges, 386.

Bowerbankia, 512.

Brachionus, 455.

Brachiopoda, 535.

Brewster, Sir David, on viewing ob-
jects, 160.

Nineveh lens, 3.

on double refractory crystals, 147.

Bridgeman's reflector, 181.

finder, 190.

Brightwell on navicula, 419,

Brooke, Mr., on opaque objects, 183.

on test objects, 57.

Browning's spectre-microscope, 120.

oblique illuminator, 171.

Bryozoa Bowerbankia, 512.

Buccinum undatum, palate, 538.

Burnett, Dr., on parasites, 639.

Busk, Mr., on anguinaria spatulata,
520.

on starch granules, 342.

on echinococci, 570.

volvox, 276.

Butterflies, eggs of, 605.

• tongues of, 607.

CALEPTERYX VIRGO, 597.
Calcification of animal tissues, 552.
Callithamnion, 273.
Camera-lucida, 129.
Oampanukria volubilis, 481.

gelatinosa, 481.

Campilodiscus clypeus, 439.
Cancer-cell, 296.
Cane, section of, 341.
Capillaries, 689.

in fat, 691.

Carbonate of lime in shell, 528.
Carpenter, Dr., on volvocinese, 275

on diatomaceae shell, 553.

on tomopteris, 576.

on eozoon, 379.

Cartilage, 702.

from ear of mouse, 702.

rabbit's ear, 703.

Carter, Mr., on chara development, SIS.

on spongilla, 391.

Cassida viridis, 588.
Cedar, stem of, 357.
Cell formation, 659.

action of, 667.

animal, 660.

changes, 258, 661.

changes in disease, 664.

contents, 662.

development, 239, 659.

nucleus, 663.

pigment, 671.

Cells, complicated, 667.

for desmids, 230.

for mounting, 213.

growing, 198.

motile, 261.

Suffolk's, 221.

vegetable, 257.

INDEX.

756

Cellularia, 518.

avicularia, 518.

Cellular tissue of plants, 323.

in animals, 662.

Cements, 219.

Cephalopod, tongue of, 540.
Cephalopoda, 550.
Cephalosiphon, 451.
Characese, 315.

antheridia of, 317.

development, 318.

Cheese-mite, 637.

Chemical re-agents, 245.

China-grass, 353.

Chitonid*, 537.

Chloride of gold, 701.

Chloroform and balsam mixture for

mounting, 227.
Cilia, 404, 671.

movement of, mode of exhibiting,

406.

Ciliated epithelium, 670.
Cimex leeticularis, egg of, 113.
Circulation of blood in frog, to view,

682.

Cirrhopoda, 554.
Clarke, Lockhart, on the preparation of

spinal cord, 761.
Clematis, section of, 333, 357.
Clepsinidse, 574.
Clionse, 395.
Clip for mounting, 214.
Closterium lunula, 285.
Clothes moth, 612.
Clypeastrodea, 501.
Coal, structure of, 363.
Cobbold, Dr., on helminths, 5«7.
Cocconema, 437.
Coccus persicse, 604.

egg of, 605.

Cochineal insect, its value, 651.
Cocoa, adulteration of, 346.
Coelenterata, 462.
Coddington's lens, 34.
Coffee, structure of, 347.
Cohn on stephanosphsera, 265.
Coleoptera, 622.
Collecting objects, 248.

animalcules, 248.

bottle, 192.

net, 193.

stick, Mr. Williamson's, 193.

Collins' mounting case, 254.

microscope, 95.

Collodion for multiplying objects, 585
Comatula, 496.
Compressorium, 195.
Condensers, Gillett's, 163.

Powell and Lealand's, 169.

Collins's, 169.

Ross's, 167.

J. B. Reade's, 174.

buli's-eye, 182.

Confervoidese, 267.
Conjugation in desmids, 279.

Conochilus, 448.
Consolidated tissues, 702.
Coral reefs, 491.
Corals, 490.
Cordylophora, 463.
Corethra plumicornis larva, 600
Corn-blights, 293.
Corymorpha nutaus, 476.
Coryne-stauridia, 475.
Coscinodiscus, 440.
Cosmarium, 282.
Crabshell, 528.
Crayfish, 553.

- shell of, 553.
Cricket, 627.
Crinoidea, 505.
Crisiadse, 519.
Cristatella mucedo, 524.
Crustacea, 554.
Crystals, formation of, 729.

of snow, 153.

quinine, 151.

urinary salts, 149.

mode of showing optical axis, 14.1.

Cuckoo-spit, 615.
Culcx, head of, 599.
Cutleria dichotoma, 273.
Cutting sections, 203.

glass cells, 213.

Cuttlefish-bone, 546.

Cyclops, 556.

Cymba olla, tongue of, 542.

Cymbella Ehrenbergii, 418.

Cynips gallse, 618.

Cypridse, 556.

Cystic disease of liver, 570.

Cysticercus fasciolaris, 564.

pisiformis, 564.

Czermak on tooth substance, 711.

DALYELL, SIR J. G., on tubularidse, 474

on actiniae, 467.

Dana, Prof., on corals, 490.

Daphnia pulex, 557.

Darkens selenite stage, 142.

Darwin on infusoria, 433.

Dasya Kiitzingiana, 272.

Davis on a new rotifer, 451.

Death-watch beetle, 623.

Deep-sea soundings, 381.

Delabarre's microscope, 10.

Delessaria, 274.

Demodcx folliculorum, 637.

Dentine, 707.

Deparia prolifera, 313.

Dermestes lardarius, 624.

Dermestidse, 624.

Designing from microscopic forms, 440

Desmidiacese, 278.

finding and preserving, 288.

Deutzia scabia, 339.
Diamond beetle, scales of, 622
Diaphragm, description of, 162
Diatomacese, 416.
Kiitzing on, 417, .

756

INDEX.

Diatomacese, on collecting, 428.

Diatoms, movements of, 423.

Difflugia, 372.

Diffraction of light. 68.

Diphydse, 464.

Dipping tubes, 191.

Directions for keeping instrument, 159.

- for mounting and preparing ob-

jects, 215.
Disc, circular, 212.
Dissecting knives and needles, 198.

- microscopes, 98.
— — under water, 200.

- scissors, 202.
Distoma, 567.
Divini's microscope, 7.

Doris tuberculata, palate of, 538.
Dragon-fly, 597.
Drone-fly, 591.
Dytiscus marginalis, 626.

- sucker from leg of, 588.

ECHINIDJS, 498.
Echinococci, 569.
Eehinodennata, 494.
Echinorhynchus, 571.
Ecker, on protozoa, 378.
Eel, scales of, 722.
Eggs of insects, 602.

- of gasteropoda, 545.

Egyptian cloth, 354.
Ehren

berg's brachionus, 455.

- on boundary between plants and
- animals, 655.

Elder-root, section of, 363.
Elm, section of, 356.
Enamel, 709.
Enchondroma, 704.
Encrinus, 506.
Entomostraca, 555.
Entozoa, 565. •-
Eozoon canadense, 378.
Epeira diadem, 645.
Epithelium, tesselated, 668.

- columnar, 670.
Equisetacese, 311.
Equisetum, section of, 332.
Errors of interpretation, 65, 723.
Escharidse, 521.

- foliacea, 522.
Euastrum, 280.
Eucratiadse, 519.
Euglena, 412.
Eunotia, 437.
Euphorbia neriifolia, 329.
Euplectella, 402.
Eye-glass, 31.

Eye, human, vessels in, 689.

- pigment, 672.

- section of cat's, 689.
Eye-piece, the, 47.

- Huyghenian, 47.

- Ramsden, 50.

- micrometer, Jackson's, 52.

- Kelner, 78.

Eyes of insects, 584.

FASCIOLA HEPATICA, 566.
Fat cells, 694.
Favus fungus, 296.
Feather-star, 496.
Feet of insects, 587.
Ferns, 311.

section of root, 335.

Fibre, muscular, 695.

in the tongue, 697.

involuntary, 698.

Fibrous tissue, 693.

white and yellow, 694.

Finders, 187.

Amyot's, 188

Maltwood's, 189.

Fishes' scales, 721.
Flatness of field, 72.
Flax, 353.
Flea, 630.

cat's, 634.

larva of, 634.

Flora of coal measure, 364

Floridese, 271.

Flower buds, 351.

Flowers, colouring matter of, 352.

Flukes, 565.

Floscularia ornata, 458.

Floscularise, 453.

Flustrae, 521.

avicularis, 523.

chartacea, 523.

foliacea, 522.

Ply, foot and leg of, 587, 591.

tongue, 595.

fungoid disease of, 596.

Tsetse, of Africa, 596.

Follicles of pig's stomach, 669
Foraminifera, 375.

skeletons of, 381,

fangasina, section of, 380.

fossU, 377.

Forceps for holding objects, 190.
Fossil infusoria, 431.

mode of preparing, 434.

Fossil plants, 362.
Fraunhofer's glasses, 10.

lines, 738.

Frog-plate, 632.

bit, 321.

circulation, 679.

hopper, 615.

Fungi, 290.

Berkeley on, 290.

De Bary on, 291.

floating, 295.

Fungise, 484.
Fungoid growths, 296.
Furze's spotted lens, 155.
Fragillaria pectinalis, 437.
Funaria, capsule of, 309.

GALL-FLY, 618.
Qallionella sulcata, 438.

INDEX.

757

Garrod's, Dr., crystals in blood, 681.
Gras-lamp, 185.
Gasteropoda, 537.

lingual bands of, 538.

Gemmulea of sponges, 400.

Geodia Barretti, 390.

Gibbons's section-cutter, 205.

QUlett's illuminator, 163.

— measuring angle of aperture, mode

of, 45.

Gill of tadpole, circulation in, 686.
Glass-rope sponge, 401.
Glaucoma, 414.
Globigerina, 384.
Giossina morsitans, 596.
Glycerine for mounting, 224.

Bimmington's, 223.

Gnat, description of, 598.
Goadby's fluid, 227.

process of injecting, 235.

Gomphonema, 419.
Goniometer, Schmidt's, 56.
Gordiacea, 562.
Gorgonidae, 487.

spiculse from, 487.

Gorham, T. on eyes of insects, 584.
Goring, Dr., achromatic object-glasses,

13.
Gosse on notommata, 456.

on cellularia, 518.

on coryne stauridia, 475.

on melicerta ringens, 459.

Gourd seed, section of, 335.

Graminaceae, 840.

Grant, Dr., on flustra, 521.

on alcyonidae, 489.

on plumularia, 478.

on sponges, 386.

Grass, cuticle of, 339.
Gray, Dr. , on mollusca, 539.
Gregarinida, 367.
Gregarina of earth-worm, 270.
Growing cell, 198.
Guinea-worm, 563.
Gulliver on raphides, 337.

on blood discs, 679.

Guy, Dr., on sublimation, 731.
Gyrinus, paddle of, 625.

HAIR, HUMAN, 672.

bat, Indian, 673.

gregarines in, 369.

moss, 311.

mouse, 673.

pecari, 674.

Haliotus splendens, 536.

tuberculatus, tongue of, 543.

Hallifax, Dr., on preparing insects, 604.

Hand magnifiers, 33.

Hard tissues, preparation of, 208.

Hartea elegans, 524.

Hassall, Dr., on the adulteration of

food, 349.

Henfrey, Prof., on ferns, 313.
Hemp, 353.

Hepaticae, 308.

Hepworth, Mr., on mounting insects

648
Herapath's, Dr., polarising crystal, 142.

iodo-quinine, 149.

on polarisation as a test, 148.

Hermia glandulosa, 475.

Herschel's aplanatic doublet lens, 26.

, A., spectroscope, 122.

Hey's mounting fluid, 227.

Hicks, Dr. B., on amoeboid bodies, 227.

on lichens, gonida of, 306.

Highley's gas-lamp, 185.

microscopes, 99.

photographic camera, 157.

Hill's microscope, 10.
Hipparchia janiraL 611.
Hirudinidse, 573.
Holland's eye-piece, 33.
Holothuridae, 508.

drawing of, life-size, 507.

Honey-bee, 620.

Hooke's microscope, 7.

How's microscope, 101.

Horn, rhinoceros, 721.

Human body, composition of, 659.

Huxley, T. H. on animal tissues, 656

on echinidae, 494.

on tongue of mollusca, 538.

on actinozoa, 468.

on rotifera, 560.

on tooth development, 708.

Huyghenian eye-piece, 47.
Hyalonema, 401.
Hydatids, 570.
Hydra, 446, 466, 470.
Hydrachnidae, 642.
Hydractinia, 473.
Hydrophilus, trachea of, 587.
Hymenoptera, 616.
aquatic, 626.

ICELAND SPAR, 135.
Improvements in microscope, 10.
India-rubber tree, 329.

section of leaf, 334.

Indicators, 187.
Infusoria, 402.

cilia, 405.

fossil, 431.

history of, 403.

Infusorial animalcules, 402.

Pasteur's researches on, 414.

Injecting, mode of, 231.

lower animals, 244.

mercurial, 239.

steps of the process, 241.

the duets and glands, 243.

Injected preparations, to mount, 244
Injections, transparent, 226.

coloured, 232.

Insects, 579.

commercial importance of, 651.

dissection of, by Swammerdam,

579.

758

INDEX.

Insects' eggs, 602.

eyes, 584.

feet, 587.

hairs, tenent, 589.

heads, 582.

itch, 635.

injecting, 240.

ovipositors, 616.

preparing and mounting, 590, 648.

proboscis, 599.

spiracles, 586.

stings, 619.

tongues, 582, 607.

transformations of, 648.

wings of, 597.

Interpretation, errors of, 67.
Intercellular substance, 662.
lodo-quinine, 151.
Iris-leaf, 336.
Istlunia enervis, 432.
Ivory nut, section of, 350.
Ixodidse, 642.

JACKSON'S micrometer, 51.

Jelly-fish, 491.

Johnstone, Dr., on sponges, 385.

on hydra, 471.

on campanularia, 481.

Jones, Wharton, on non-striated mus-
cular fibre, 698.

Rymer, on the coretha plumi-

cornis, 600.
Jungermannia bidentata, 310.

KETTLEDRUM condenser, 174.
Kelner eye-piece, 78.
Knives for dissecting, 119.
Kolliker on the muscles of the skin,

698.
Kiitzing on vegetables and animals,

256.
on diatomacese, 417,

LADDS'S microscopes, 84.
Lamps, 184.
Lamp-shells, 535.

Lankester, E. B., on gregarina of earth-
worm, 370.

Lathe for polishing, 209.
Leaf-insect, 613.
Leech, medicinal, 573.
Leeuwenhoek's microscope, 6.
Lenses, achromatic, 28.

chromatic, aberration of, 26.

Coddington, 34.

concavo-convex, 19.

- — condensing, 183.

correction of, 28.

curvature of, 22.

double convex, 18.

forms of, 18.

magnifying power of, 29.

meniscus, 25.

tracing rays through, 17.

Lenses, periscopic, 33.

plano-convex, 24.

refraction of light through, 16.

spherical aberration of, 26.

Stanhope, 35.

Lepidoptera, eggs of, 605.

tongue of, 608.

wing-scales of, 609.

Lepisma, 529.

scale of, as a test, 611.

Lepralia nitida, 517.

Leuchart on echmorhynchus, 571.

Lewes on actiniae, 407.

on life, 655.

thread cells, 467.

Libellulidse, wings of, 597.

Lichens, 304.

Lieberkiihn, Dr. N., on gregarina, 369

microscope, 5.

on spongilla, 389.

Life, animal, 655.
Light, diffraction of, 68,

polarisation of, 132.

Limax rufus, 529.
Limnsea stagnalis, 545.
Limnias ceratophylli, 458.
Lister's lenses, 13.

achromatic corrections, 40.

List of objects, Wheeler's, 253.

Live-box, 194.

Liver, diseased, 567.

Liverworts, 308.

Lobb, Mr., on polarising crystals, 145.

on the illumination of test objects,

61.

micrasterias, 279.

Lob-worm, 576.

Loligo, palate of, 541.

Lophopus crystallum, 525.

Loven on mollusca, 538.

Louse, 633.

Lubbock, Sir J., on the eggs of insects

605.

on aquatic insects, 626.

Lucernaridse, 493.
Luidia fragilissima, 496.
Lung, capillaries of, 690.
Lymphatic, vessels of, 669.

MADREPOBID^E, 486.
Maddox, Dr., wire clip, 214.
Magnifiers, hand, 33.
Magnifying power of single lenses, 2!

of object-glasses, Ross's, 55.

Powell's, 56.

Maltwood's finder, 189.
Maple-aphis, 613.
Marchantia polymorphic, 308.
Mechanical arrangements, 70.
Medusae, 492.

Meissner on the micropyle, 603.
Melicerta ringens, 459.
Melolantha, eye of, 585.
Melting vessel, 233.
Mercurial injections, 239.

INDEX.

75C

Mesoglia vermicularis, 268.
Micrometers, 51.
Microscope, Baker on the, 10.

Baker's binocular, 89.

compound, 86

dissecting, 98.

• student's, 88.

• traveller's, 108.

Bonnani's, 8.

Brewster's diamond, 11.

Collins's binocular, 95.

dissecting, 98.

student's, 97.

compound, 38.

Frauenhofer, lenses for, 10.

G. Adams's, 10.

compound, 39.

• E. Divini's compound, 8.

• Goring's compound, 7.

Highley's clinical, 105..

pocket, 110.

professional, 99.

• ' student's, 100.

Hooke's compound, 7.

• water, 5.

How's student's, 101.

• Huyghenian eye-piece of,

Ladds's, 84.

Lieberkiihn's, 5.

• Lister's, improvements in, 43.

Murray and Heath's, 108.

. class, 104.

pocket, 107.

Newton's speculum, 9.

Norman's, 100.

Pillischer's binocular, 91.

prize, 94.

. student's, 93.

Powell and Lealand's, 82.

arranged for test objects, 62.

Quekett's dissecting, 38.

Ross's, combination of object-
glasses, 43.

compoitnd, 79.

simple, 35.

S. Gray's globule, 4.

simple, 5, 30,

• simple, for dissections, 98.

Valentine's simple, 36.

Warrington's, 106.

-binocular, 112.

Wheeler's, 110.

. Wollaston's doublet, 31.

periscopic, 16.

Microspectroscopy, 119.

Micrasterias, 280.

Miller, Hugh, on fossil plants, 364.

Mineral kingdom, 728.

Mite, cheese, 637.

flour, 639.

Molecular movements, 67.
Mollusca, 511.

injecting, 240.

— — tongues of, 539.
Monads, 411.

Morpho Menelaus, scale of, 611.

Moss-agates, 399.

Mosses, 309.

Moths and butterflies, 607.

Motile organs in cells, 262.

Mottled umber moth, 606.

Mounting and preparing, 215.

spring clip for, 214.

injections, 244.

case, Collin's, 254.

Movements of diatoms, 423.

Mucidines, development of, 661.

Mucor mucedo, 292.

Mucous membrane, 669.

Murray and Heath's microscopes, 103.

Muscular fibre, 695.

Mushroom spawn, 343.

Mussel, 531.

Myelin, 681.

Myolemma, 696.

Mytilus, 535.

NAILS, the, 672.
Naviculse, 419.
Neckera antipyretica, 310.
Nematoidea, 563.
Nemertidse, 562.
Nerves, 699.

perfection of sections, 701.

— - stellate corpuscle, 699.

Newport on moths' tongues, 607.

Nicol's prism, 136.

Nitella, 320.

Nobert's ruled micrometer lines, 54.

Noctiluca miliaris, 409.

Norman on collecting diatoms, 428.

Norman's microscope, 100.

Notommata aurita, 456.

Nudibranchiata, 530.

tongues of, 541 .

Nummufites, 377.

OBJECT-GLASSES, forms of, 72.

Ross's, 55.

Objects, Shadbolt on collecting, 248.

directions for viewing, 160.

mounting and preserving, 215.

Oblique illumination, 171.

J. N. Tomkins's double prism, 17J

Oidium, 293.

Opuntia, 356.

Onion, section of, 338.

Ophiocoma, 495.

Ophiura, 495.

Orchidese, 350.

Orthoptera, 626.

Osborne, Lord S. G., on fungi, 295.

on closterium lunula, 284.

Oscillatoriae, 266.

Ostracoda, 556.

Ova mollusca, 545.

Owen, Major, on foraminifera, 385.

Professor, on animalcule life, 444

on microscopic investigation, 705

Oxytricha, 414.

760

INDEX.

Oyster, 533.

fry, 554.

pearl, 533.

PALATES OF MOLLUSCA, 539.
Panax Lessonii, 329.
Papillae of skin, 675.
Parabolic reflectors, 179.
Paramsecium, 409.
Parasites, 612.

of dog, 634.-

of eagle, 643

of fowl, 640. ,

of hornbill, 642.

human, 633.

of pheasant, 640,

of pigeon, 643.

of sheep, 633.

of swallow, 639.

of turkey, 640.

of vulture, 643.

Parasitic fungi, 293.
Parmelia, 305.

stellata, 306.

Patella, tongue of, 641.

Pear cells, 338.

Pearl oyster, 533.

Pearls, artificial, 533.

Pedicellarise of starfish, 496.

Pediculi, 636.

Penetrating power of object-glasses, 75.

Peniuiu, 283.

Pennatulidse, 488.

phosphorea, 488.

Peziza, 304,

Peronosporae, 290.

Pholas dactylus, 531.

Photography applied to microscope,

155.

Phryganea, eggs of, 605.
Phryganeidse, 601.
Phyllactinia, 294.
Pigment cells from skin, 675.
Pillischer's microscope, 91.
Pinna, 530.
Planarise, 562.
Plants and animals, 257.

annular vessels, 358.

cellular tissue of, 323.

circulation in, 320.

crystals in, 337.

fossil, 362.

hairs of, 324.

lactiferous tissue of, 334.

lice, 613.

pollen grains, 361.

pollen and seeds from, 361.

preparation of tissues, 359.

raphides in, 337.

cutting sections of, 205,

silicia in, 340.

silicious cuticle of, 339.

starch in, 341.

starch of potato, 345.

Plants and animals, starch, wheat
flour, 344.

• stellate tissue, 333.

structure of, 323.

unicellular, 260.

vascular system of, 327.

vascular tissue of, 324.

vital characteristics, 257.

woody tissue, 353.

Phosphorescence, marine, 408.
Pleurobranchus, mandible of, 542.
Pleurosigma, 421.

as a test object, 59.

Plumatella repens, 527.
Plumularia, 478.

pinnata, 480.

Podura plumbia, 628.

scale, as a test, 610.

Polarisation of light, 132, 729.
Polarised light, objects for, 729.
Polariser, 137.
Polyzoa, 512.

mounting, 227.

fresh-water, 524.

Polycystina, 384.
Polygastrica of Ehrenberg, 416.
Polyommatus argiolus, 610.
Polypifera, 462.
Polythalamia, 376.
Pontia brassica, 611.
Potato mould, 290.

starches, 343.

Powell and Lealand's microscopes, 82.
Powell's condenser, 168.
Preparation of insects, 648.
Preparing sections of bone, 209.

tongues of mollusca, 544.

vegetable tissues, 359.

Prism for binocular, 117.

for micro-spectroscope, 121.

polarising, method of using, 138.

Sollitt's, 175.

Propita gigantea, 493.

Proteus, the, 373.

Protococcus pluvialis, 259.

Protozoa, 363*— f

Prussian blue for injections, 238.

Pteropoda, 532.

Puccinia, 292.

buxi, 294.

Pumpkin fungi, 301.

QUEKETT on the vascular tissue of
plants, 358.

on polarised light, 154.

on fossil infusoria, 438.

on the structure of bone, 714.

dissecting microscope, 38.

on resolving test objects, 61.

Quinine, its detection, 149.
Quinidine, test for, 151.
crystals of, 151.

RAINET, on artificial shell, 551.
Ralfs, Mr., on desmidiaceae, 288.

INDEX.

'61

Ralfs, Mr., on preservation of algse, 228.

Raphidea in plants, 337.

Reade's, Rev. J. B., hemispherical

condenser, 174.
Re-agents, effects of, 726.
Redfern on separating naviculse, 435.
Red seaweeds, 271.
Reflector, parabolic, 179, 182.

Shadbolt's, Mr., 179.

side, 182.

Rhinoceros horn, 721.

Rhizopoda, 372.

Rhubarb cells, with raphides and

starch, 388.

spiral vessels, 355.

Ringworm, 296.

Roberts, Dr., on blood cell, 677.
Robertson, J., on pholas, 531.
Ross's compressorum, 195.

microscopes, 78

object-glasses, 74.

Rotiferae, 452.
Rush, stem of, 333

SALTER, DR. HYDE, on muscle, 496.

Salts, urinary, 149.

Samuelson, J., on infusoria, 415.

Sandstone, 729.

Sarcina ventriculi, 295.

Barcode, 656.

Saw-fly, 616.

Scales of fish, 721.

of lepidoptera, 609.

of podura, 628.

Scapander, tongue of, 542.
Schultze, Dr., on rhizopoda, 375.

on the diatom valve, 422.

Schwann's classification of tissues, 692.
Scissors, dissecting, 202.
Sea-cucumbers, 508.

lilies, 497, 505.

jelly-fish, 491.

slug, 529.

soundings, 383.

urchins, 498.

Sections of tissues, 247.
Section-cutting machines, 203.
Selenite, 141.
Sepia, palate of, 541.
Serpula, 575.
Sertulariadse, 476.

pumila, 477.

setacea, 477.

Shadbolt, Mr., on collecting, 248.

Sheep-tick, 633.

Shell, structure of, 546.

artificial formation of, 551.

Sheppard,J.B.,oncolouredmonads,413.

Silk, 354.

Silkworm moth, antenna of, 608.

Silkworm's breathing aperture, 586.

Single microscope, 4.

Skin, capillaries of, 675.

fungoid diseases of 296.

nerves of, 676.

Skin, section of, 677.

Slack, H. J., on a new rotifer, 451.

Smith and Beck's troughs, 197.

oblique illuminator, 170.

Smith's, Prof., condenser, 170.

growing slide, 198.

mechanical finger, 436.

Mr. J., section-cutter, 203.

Snow, crystals of, 152.

Sollitt on diatoms as test objects, 427.

Sollitt's prism illumination, 175.

Sorby's standard interference spec-
trum, 738.

spectroscope, 123.

Sori of ferns, 315.

Sphacelaria cirrhosa, 269.

Spectro-microscopy, 119.

Spectrum analysis, 735.

Speculum, Lieberkiihn's, 181.

Spencer, Herbert, on the formation of
fibre in plants, 325.

Sphagnum, 809.

Sphseriacei, 294.

Sphserosira volvox, 276.

Spiders, 644.

diving, 647.

Spiderwort, 350.

Sponges, 385.

motile phenomena in, 389.

' skeletons of, 396.

spicula from, 387, 390.

Spongia coalita, 388.

geodia, 390.

Spongilla cinera, 391.

alba, 392.

development of, 389.

gemmules of, 400.

Spring clips, 214.

Starches, 343.

in plants, 842.

potato, polarised, 154.

tests for, 283.

Star-fishes, 495.

Staurastrum, 282.

Stellate tissue from a rush, 333.

Stentors, 450.

Stephanoceros, 458.

Stephanosphsera pluvialis, 265.

StichostegidEe, 276.

Stinging-nettle hairs, 324.

Stokes's, Prof., absorption bands, 128.

Stomach, mucous membrane of, 669,

Structure of shell, 529.

Suctoria, 629.

Sugar insect, 638.

cane, section of, 336.

Surirella constricta, 420.

Swammerdam's dissection of insect*,
579.

Synapta chirodota, 503.

Synaptidse, 508.

TADPOLE, circulation of, 683.

gill of, 686.

Tseniadee, 563.

762

INDEX.

Tapeworms, 563.

Tea, adulterated, 349.

Teeth, preparing sections of, 209.

of mollusca, how to prepare, 544.

sections, mounting of, 211.

Terebratula, 536.

Teredo, 531.

Test objects, 57, 61, 65.

Testacella, tongue of, 542.

Thomas, Mr., on crystallization, 730.

Thompson on mollusca tongues, 543.

Prof. W., on sea-lilies, 497.

Thread cells, 544.

in actiniae, 467.

in mollusca, 544.

Thuiarea, 478.
Thysanura, 627.
Tinea vestianella, 611.
Tissue, woody, 353.

animal, 6.

Tissues, consolidated animal, 702.

elastic and non-elastic, 694.

Tomato, diseased, 300.

Tomkins, Mr. J. N. on alcyonella, 526,

double prism illumination, 174.

Tomopteris onisciformis, 576.
Tooth, section of, 707.

structure, 709.

ofprestis, 711.

of eagle-ray, 712.

Topping's test objects, 612.

section-cutter, 206.

Torula cerevisia, 300.

diabetica, 295.

Tourmaline, 138.

artificial, 143.

Tradescantia, circulation in, 350.

Transformation, insect, 648.

Transparent injections, 226.

Trematoda, 563.

Trembley on hydra, 471.

Triceratium, 419.

Trichobasis, 294.

Trichocera hyemalis, 598.

Trichoda, 411.

Trichina spiralis, 568.

Trochell, Dr., onmolluaca, 539.

Troughs for exhibiting circulation, 197

Truffles, 302.

Tsetse-fly of Africa, 596.

Tubercibarium, 302.

Tubicola, 574.

Tubiporidse, 489.

Tnbularidse, 473.

Tubularia Dumortierii, 497.

Tunicata, 532.

Turbellaria, 561.

Turbo marmoratus, tongue of, 543.

ULV.E, development, 271.
Uredo, 291.
Urinary salts, 149.
Uromyces, 291.

Urticating organs in actinse, 467.
in mollusca, 544.

VALENTINE'S knife, 201.

Vallisneria, 321.

Valley's animalculse cage, 195.

on chara, 315.

Vaucheria, 274.
Vegetable structure, 323.

cell, 255.

cellular tissue, 360.

kingdom, 255.

division between animal and,

256.

preparation of, 359.

preparation of tissues, 359

starch, 341.

• vascular tissue, 324.

Velutina, palate of, 540.

Vertebrata, 654.

Vibrio spirilla, 412.

Viewing objects, directions for, 160

Virchow on trichina, 569.

Volvox globator, 275.

Vorticellidse, 445.

WALKER'S trough for fish, 197.
Warington's microscope, 106.
Wasp, 618.

tongue of, 582.

Water-beetle, 625.

Water-microscope, 5.

Water-mites, 643.

Wenham on photography applied to

microscopic drawing, 156.

on the binocular microscope, 112.

on object-glasses, 64.

on a parabolic reflector, 179.

West, Tuffen, on feet of flies, 588.
Wheat, portion of husk of, 340.

flour, adulterations of, 344.

Wheeler's microscopes and cabinets,

110.

list of objects, 253.

Whelk, palate of, 537.

Whirligig, 625.

Whitney, W.U., on the tadpole, 683.

Williamson's collecting stick, 193.

Wing-shell, 530.

Wollaston's lenses, 36.

Wood, cutting sections of, 206.

Woodward, Mr., on polarised light, 139.

Wool, 354.

Wright, Dr., on alcyonida, 524.

XANTHIDI^B, 282, 441.

YEAST-PLANT, 299.
Yew, section of, 356.

ZOOPHYTES, canal-bearing, 385.

a fresh-water group, 463.

preservation of polypidoms of, 50!),

- skeletons of, 490.
Zygoceros rhombus, 432.

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