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UNIVERSITY OF CALIFORNIA.

GIFT OF

MRS. MARTHA E. HALLIDIE.
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THE MICROSCOPE.

PRINTED BY LEVEY, BOBSOX, AXD FKASKLVN,
Great ?sew Street and Tetter I-ane.

ft H| HISTORY, ' ^ »».-,•

* ' CONSTRUCTION. ANDM ff| ^Of ,' 1
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iffy APPLICATIONS. K *?U

THE

MICROSCOPE:

ITS

HISTORY, CONSTRUCTION, AND APPLICATIONS.

FAMILIAR INTRODUCTION TO THE USE OF THE INSTRUMENT

Stutrg of JSicrogcopicaJ Science.

BY JABEZ HOGG, M.R.C.S.

ASSISTANT 8URGEOK TO THE ROYAL OPHTHALMIC HOSPITAL CHASING CROSS,

FELLOW OF THE MEDICAL SOCIETY OF LONDON,

MEMBER OF THE MICROSCOPICAL AND PATHOLOGICAL SOCIETIES OF LONDON,
AUTHOB OF ELEMENTS OF NATURAL PHILOSOPHY, ETC.

fortjj ttpfoarfrs of $tit jjiimbttbr

SECOND EDITION.

LONDON:
HERBERT INGRAM AND CO. 198 STRAND.

1856.

PREFACE TO THE SECOND EDITION,

endeavour, in the First Edition of this work,
to produce a cheap and popular guide to the use
of the Microscope, and thus to supply a want
which I had long believed it very desirable to
see supplied, has been rewarded by a success
which has far exceeded my expectations. In the short space
of twelve months a large edition of five thousand copies has

been sold; and I am now called upon to prepare a Second
(

Edition.

My efforts on this occasion have been directed to the thorough cor-
rection and revision of the whole work, rather than to extending it
with much new matter ; and I trust I shall have succeeded in making
the present Edition more free from blemish and more generally useful
to the public than the preceding one. In endeavouring to do so, I
have fully availed myself of the judicious suggestions and criticisms of
many kind friends ; and I wish to take this opportunity of acknow-
ledging the obligations I am under to those who have so generously
accorded to this small work, whatever its defects, their meed of appro-
bation.

103347

PREFACE TO THE FIRST EDITION.

HE author of the present 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 justifi-
cation, for the work which he now ventures to submit to
the indulgent consideration of his readers.

It had been to him for some time a subject of regret,
that one of the most useful and fascinating of studies — the
study that belongs to the domain of microscopic observation — should
be, if not wholly neglected, at best but coldly and indifferently ap-
preciated, by the great mass of the general public ; and he formed a
strong opinion, that this apathy and inattention were mainly attri-
butable to the want of some concise, yet sufficiently 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 destined for circulation amongst a special class
of readers, were necessarily, from the nature of their contents and th e
style of their production, published at a price that renders them
practically unattainable by the great bulk of the public. They

Vlll PREFACE.

constitute careful and beautiful contributions to the purposes of
science ; but they cannot adequately serve to bring the value and
charm of microscopic studies home, so to speak, to the firesides of
the people. Eepeatedly, day after day, new and interesting disco-
veries, and further amplifications of truths already discerned, have been
made ; but they have been either scattered in serials, or, more usually,
devoted to the pages of class publications. Thus this most important
and attractive study has been, 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, participated, to any
general extent, in the instruction and entertainment which follow in
its train.

The manifold and various uses and advantages of the Microscope
crowd upon us in such profusion, that we can only attempt to enume-
rate them in the briefest and most rapid manner in these few pre-
fatory 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 appreciated,
even by those who formerly were slow to see its benefits. Knowledge
which could not be obtained by the minutest dissection is acquired by
the aid of the Microscope, which has become as essential to the anato-
mist and pathologist as the scalpel to the one and bedside observation
to the other. The smallest portion of a diseased structure, placed
under a Microscope, will tell more in one minute to the experienced
eye than could be ascertained by many days' examination of the gross
masses of disease in the ordinary method. Microscopic agency, in
thus assisting the medical man, materially contributes to the alleviation
of those multiplied " ills which flesh is heir to."

So fully impressed were the Council of the Koyal College of Sur-
geons with the importance of the facts brought to light in a short space
of time, that in 1841 they determined to establish a Professorship of

PREFACE. ix

Histology, and to form a collection of preparations of the elementary
tissues of both animals and vegetables, healthy and morbid, adapted to
illustrate the uses and results of microscopical investigations. From
that time histological anatomy deservedly became an important branch
of the education of the medical student.

By " conducting the eye to the confines of the visible form," the
Microscope proves an effective auxiliary in defining the geometric pro-
perties 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 has enabled us to detect
the smallest structural difference, heretofore inappreciable ; and in our
analysis to define positively the structure of tissues beyond the capa-
bility of the greatest magnifying power to change or modify.

The Microscope, as an ally of Chemistry, enables us to discover very
minutely and completely the changes of form and colour effected by
test-fluids upon solids ; it dissects for us, so to speak, the most multi-
plex compounds ; it opens out to the mind an extended and vast tract,
opulent in wonders, rich in beauties, and boundless in extent.

In prosecuting the study of Vegetable Physiology, the Microscope
is an indispensable instrument ; it empowers 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 detecting the adulteration of our articles of food, as has been verified
by the exposures — which must have done great good — that have from
time to time appeared in the Lancet, and subsequently collected into a
volume by Dr. Hassall. In the examination of suspected flour, an
article of so much importance to all persons, the Microscope enables us
to judge of the size and shape of the starch-grains, the markings of
them, and their isolation and agglomeration, and thus to distinguish
the starch-grains of one meal from those of another. In the necessarily
limited space of this work, the author has only been able to glance at
the subject of the minute structure of vegetables ; but the remarks and

Xll PREFACE.

Finally, it is the author's hope that, by the instrumentality of this
volume, he may possibly assist in bringing the Microscope, and its
most valuable and delightful studies, before the general public in a
more familiar, compendious, and economical form than has hitherto
been attempted ; and that he may thus, in these days of a diffused taste
for reading and the spread of cheap publications, submit some further
food for the exercise of the mental and intellectual faculties, — contri-
bute to the additional amusement and instruction of the family circle
around the domestic hearth, — and aid the student of nature in investi-
gating the wonderful and exquisite works of the Almighty Hand. 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 how-
ever slight a degree, in furthering this design, the author will feel sin-
cerely happy ; and will be fully repaid for the attention, time, and
labour, that he has expended in writing, arranging, and compiling it.

6 Gower Street, Bedford Square,
May 1854.

DIRECTIONS FOR PLACING THE PLATES.

Frontispiece and Engraved Title to face each other, and precede the
printed title-page.

PLATE

II. Fossil Infusoria to face page 154

IV. Sponges, Spicula from • n 175

V. Zoophytes „ 194

VI. Echino-dermata, &c. ...... „ 252

VII. Proboscis of Fly „ 286

VIII. Tongue, &c. of Drone-fly „ 296

IX. Antenna, &c. of Moth „ 304

X. Scales from Wings of Butterflies ... „ 306

XL Parasites „ 326

XII. Animal Structures „ 344

XIII. Animal Tissues „ 352

XIV. Human Skin and Hair „ 360

XV. Vegetable Cells, &c „ 394

XVL Vegetable Structures „ 424

PART I.
flfetorg of % $n&*ntton antt Improvements; of tje 4!Huro$cope.

CHAPTER I.

PAGE

History of the Microscope . . . . . .1

CHAPTER II.

Mechanical and Optical Principles involved in the Construction of the
Microscope — Lenses — Mode of Estimating their Power, <fcc. — Achro-
matic Lenses — Magnifying Power — Wollaston's Doublet — Codding-
ton's Lens — Ross's Simple and Compound Microscopes — Baker's
Microscopes — Micrometers, &c. . . . . .12

CHAPTER III.

Preliminary Directions — Illumination — Accessory Apparatus — Achro-
matic Illuminator — Gillett's Condenser — Preparing and Mounting
Objects — Injecting — Chemical re-agents — Collecting Objects — The
Camera Lucida — Polarised Light — Binocular Instrument — Photo-
graphic Drawing . . . . . . .53

PART II.

CHAPTER I.

Protozoa — Rhizopoda — History of Infusorial Animalcules — Monads —
Diatomaceae, Fossil Infusoria, Vorticellid8e,Stentors, Rotifera, Flos-
cularidae, Xanthidia — Sponges . • . . . 129

XVI CONTENTS.

CHAPTER II. PAGE

Polypifera. Hydroida — Zoophytes, or Polyps — Bryozoa — Acalephae —
Echinidae — Holothuridae . . . . . .195

CHAPTER III.
Mollusca — Gasteropoda — Collecting Specimens . . . 253

CHAPTER IV.
Articulata. Entozoa — Annelida — Crustacea — Arachnidae . . 270

CHAPTER V.
Articulata. Insects — Acarina ...... 286

CHAPTER VI,

Animal Structure. Physiology — Histology — Cell Theory — Growth of
Tissues — Special Tissues — Skin, Cartilage, Teeth, Bone, &c. . 343

CHAPTER VII.

Vegetable Structure — Vital and Chemical Characteristics— The Vege-
table Cell — Fungi — Mosses — Algae — Volvox — Desmidaceae — Struc-
ture of Plants— Fungoid Diseases — Adulteration of Articles used
for Food — Preparation for Microscopic Examination — Cutting Sec-
tions— Warington's Microscope — Magnifying Power of the Eye —
Conclusion ..... . 394

THE MICROSCOPE

PART I.

HISTORY OF THE INVENTION AND IMPROVEMENTS OF THE
MICROSCOPE.

CHAPTEK I.

HISTORY OF THE MICROSCOPE.

HE instrument known as the Microscope de-
rives its name from two Greek words, jj-iKpog
small, and OVCOTTEW to view ; that is, to see or
view such minute objects as without its aid
would be invisible.

The invention of the microscope cannot be
traced with any degree of certainty before the
year 1660, a period fruitful in discoveries.
The honour of the invention is claimed by
the Italians and the Dutch ; the name of the
inventor, however, is lost. Probably the dis-
covery did not at first appear sufficiently im-
portant to engage the attention of those men who, by their reputation
in science, were able to establish an opinion of its merit with the rest
of the world, and to hand down the name of its inventor to succeeding
ages.

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
microscopes before the year 1590 : about that time the ingenious Cor-

B

2 HISTORY OF THE MICROSCOPE.

nelius Drebell brought one made by them with him to England, and
showed it to William Borrell and others. It is possible this instrument
of Drebell'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 j for we have many instances in our own times
of more than 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.

If we consider the microscope as an instrument consisting 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 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 convexi-
ties, 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.

Aristophanes, who lived five centuries before Christ, speaks of a
" burning-sphere." Seneca, who wrote in the first half-century of the
Christian era, says that small and indistinct objects become larger and
more distinct in form when seen through a globe of glass filled with
water. Pliny also mentions the burning property of lenses made of glass.
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 extraordinary 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 fa-
vourable circumstance — the discovery of a new object, or some new
improvement in the instruments of observation — awakened the atten-
tion of the curious, and reanimated their researches. Thus, soon after
the invention of the microscope, the field it presented to observation
was cultivated 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.

HISTORY OF THE MICROSCOPE. 3

We shall first speak of the single microscope, that, as we have
already observed, 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 very 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 Leeuwen-
hoek and Swammerdam, Lyonet and Ellis, examined the invisible
forms of nature, laid open some of her hidden recesses, 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. By these
globules an immense magnifying 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
Micrograpliw Illustrata, published in the year 1656.

Mr. Stephen Gray* having observed some irregular particles within
a glass globule, and finding that they appeared distinct and prodi-
giously 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 distinctly
and highly magnified. The result of this idea far exceeded his expec-
tation. His method was, to take on a pin a small portion of water
which he knew contained some minute animalcules j this he laid on
the end of a small piece of brass wire, till there was formed somewhat
more than a hemisphere of water j on applying it then to the eye, he
found the animalcules most enormously magnified ; for those which
were scarcely discernible with his glass globules, with this appeared as
large as ordinary-sized peas. Montucla observes, that when any ob-
jects are enclosed within this transparent globule, the hinder part of
the globule acts like a concave mirror, provided the objects be situated
between that surface and the focus ; and that by this means they are
magnified three times and a half more than they would be in the usual
way.

An extempore microscope may be formed by taking up a small
drop of water on the point of a pin, and placing it over a fine hole
made in a piece of metal j but as the refractive power of water is less
than that of glass, these globules do not magnify so much as glass ones
of the same size : this was also one of Mr. Gray's magnifiers. The
* Philosophical Transactions, 1696.

4 HISTORY OF THE MICROSCOPE.

same ingenious author invented another water-microscope, consisting
of two drops of water separated in part by a thin brass plate, but
touching near the centre, which were thus rendered equivalent to a
double-convex lens of unequal convexities.

Dr. Hooke described the method of using this single 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 microscopic 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 for-
wards. 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 there-
fore undergone few alterations ; and these have been
chiefly confined to the mode of mounting it, or to
additions to its apparatus. The greatest improve-
ment this instrument has received was made by Dr.
Lieberkuhn,* 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 ob-
ject, which is thus examined with great ease and pleasure.
Before this contrivance, it was almost impossible to exa-
mine small opaque objects with any degree of exactness
and satisfaction; for the dark side of the object being
next the eye, and also overshadowed by the proximity of
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 anatomical
preparations, twelve of which, with their microscopes, are
deposited in the Museum of the Royal College of Sur-
geons.

fig- 1. Lieberkuhn's instrument, fig. 1, is thus described by
Professor Quekett : -)- a b represents a piece of brass tube, about an

* Dr. Nathaniel Lieberkuhn of Berlin.

f Practical Treatise on the Microscope, p. 16.

HISTORY OF THE MICROSCOPE.

inch long and an inch in diameter, which is provided with a cap at each
extremity ; the one at a carries a small double-convex 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 instruments is seen in fig. 2 : a
represents the magnifier, 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 quar-
ter 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 knob d ; upon
this disk the injected object is fastened, and is co- gg> 2.

vered over with some kind of varnish which has Lieberkuhn's
dried of a hemispherical figure. Between this knob Microscope.
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 concentrate the light on the speculum. To the lower part
of the tube a handle of ebony, about three inches in length, is attached
by a brass ferrule and two screws. The use of this instrument is ob-
vious : 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 6, 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 Leeuwenhoek's
microscopes, which were rendered famous throughout all Europe, on
account of the numerous discoveries he had made with them, as well as
from his afterwards bequeathing a part of them to the Royal Society.

The microscopes he used were all single, and fitted up ill a con-
venient and simple manner : each consisted of a very small double-
convex 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 ob-
server, the nature of the object, and the convenient examination of its
parts required.

6 HISTORY OF THE MICROSCOPE.

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 exceedingly 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, pro-
portioned to the nature of the object and the parts designed to he
examined.

He observed, in his letter to the Eoyal Society, that, from upwards
of forty years' experience, he had found the most considerable disco-
veries were to be made with glasses of moderate magnifying power,
which exhibited the object with the most perfect brightness and dis-
tinctness. Each instrument was devoted to one or two objects ; 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 Bonnani. Dr. ^oke
gives 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 the fewer the refractions are, the clearer and brighter the
object appears.

Dr. Hooke also gave us the first and most simple method of find-
ing 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 Eoyal
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 ;

HISTORY OF THE MICROSCOPE. 7

by which means the glass takes in more of an object, the field is larger,
the extremities of it less curved, and the magnifying power greater.
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 16 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 microscopes in
169$. Both were compound. The first was 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, and spread it uniformly over, according to its nature, and the
magnifying power that was used.

A short time before this, Sir Isaac Newton having discovered his
celebrated theory of light and colours, was led to improve the telescope ;
and in 1672 he is said to have applied his principles most successfully
to the construction of a compound reflecting microscope. 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,
m0ra>-chromatic." We find other two plans of this kind; the first that
of Dr. Kobert 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 com-
municated to the public. The vast magnifying power obtained by this
instrument, the colossal grandeur with which it exhibited the " minutiae
of nature," the pleasure 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 polyp. The discoveiy of the
wonderful properties of this little animal, together with the works of

8 HISTORY OF THE MICROSCOPE.

Mr. Trembley, Mr. Baker, and Mr, Adams, combined to spread the
reputation of the instrument.

In 1742, Mr. Henry Baker, F.R.S., published an admirable treatise
on the microscope. He also read several papers before the Royal So-
ciety on the subject of his microscopic discoveries. In our title-page
we have represented an elegant scroll "pocket microscope with a spe-
culum," 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 vari-
ous 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 microscope 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, improved
his father's invention, and rendered it useful for viewing opaque
as well as transparent objects. This instrument, made and described
by him,* continued in use up to the time of the invention of the
achromatic improvement, proposed and made in 1815 for Amici,
who subsequently gave so much time to the investigation of po-
larised light, and the adaptation of a polarising apparatus to the
microscope.

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 were very thick, and of long focus.
Although such considerable improvements had taken place in the mak-
ing 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
compound 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 Mo-

dena, 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

* Microscopical Essays, 1787.

HISTORY OF THE MICROSCOPE.

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. Chevalier, was
presented by M. Selligues to the Academie des Sciences on the 5th of
April, 1824. In the same year, and without a knowledge of what
had been done on the Continent, the late Mr. Tulley, at the sugges-
tion of Dr. Goring, constructed an achromatic object-glass for a com-
pound microscope of nine-tenths of an inch focal length, composed of
three lenses, and transmitting a pencil of eighteen degrees ; this was
the first that had been made in England.

It was at one time hoped, as precious stones are more refrac-
tive than glass, and as the increased refractive power is unaccompanied
by a corresponding increase in chromatic dispersion, that they would
furnish valuable materials for lenses, inasmuch as the refractions would
be accomplished by shallower curves, and consequently with diminished
spherical aberration. But these hopes were disappointed. Every
thing that ingenuity and perseverance could accomplish was tried by
Mr. Varley and Mr. Pritchard, under the patronage of Dr. Goring. It
appeared, however, that the great reflective power, the doubTy-refracting
property, the colour, and the heterogeneous structure of the jewels
which were tried, much more than counterbalanced the benefits arising
from their greater refractive powers, and left no doubt of the supe-
riority of skilfully-made glass doublets and triplets. The idea is now,
in fact, abandoned ; and the same remark is applicable to the attempts
at constructing fluid lenses, and to the projects for giving to glass other
than spherical surfaces ; none of which have come into extensive use.

Mr. Lister, who was engaged with Mr. Tulley in the perfecting
the achromatic object-glass, finding that none of the microscope-stands
hitherto made were sufficiently steady for the use of high powers,
directed his attention to the improvement of this part of the instru-
ment ; and in order to carry out his views, he employed Mr. James
Smith, now one of our first opticians, to execute a stand from his
own drawings, which he completed early in 1826.

In March 1825 M. Chevalier presented to the Society for the En-
couragement 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.

10 HISTORY OF THE MICROSCOPE.

In 1826, Professor Amici, who from the year 1815 to 1824 had
abandoned his experiments on the achromatic object-glass, was in-
duced, after the report of Fresnel to the Academy of Science, to re-
sume them; and in 1827 he brought to this country and to Paris a
horizontal 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.

" 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 micro-
scope, they essentially promoted its improvement."

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 improvements 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 to be taken
as a basis for the microscopic object-glass : it diminishes very nearly
half the loss of light from reflection, 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 sur-
faces. Since this time, Mr. Ross has been constantly employed in
bringing the manufacture of object-glasses to their greatest perfection,
and at length they have attained to their present improved manufac-
ture. Having applied Mr. Lister's principles with a degree of success
never anticipated, so perfect were the corrections given to the achro-
matic object-glass, so completely were the errors of sphericity and
dispersion balanced or destroyed, that the circumstance of covering
the object with a plate of the thinnest glass or talc disturbed the cor-
rections, if they had been adapted to an uncovered object, and ren-
dered an object-glass which was perfect under one condition sensibly
defective under the other. Here was another and unexpected difficulty
to be overcome, but which was finally accomplished ; for in a commu-
nication made to the Society of Arts in 1837, Mr. Ross stated, that by
separating the anterior lens in the combination from the other two, he

HISTORY OF THE MICROSCOPE. 11

had been completely successful. The construction of this object-glass
will be illustrated and explained in a future chapter.

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

To Mr. Solly is due the credit of bringing before the public the
improved microscope of Mr. Valentine, the excellent workmanship of
Mr. Ross j and by his intimate connection with the Society of Arts, he
has been the means of making its Transactions, since 1831, the vehicle
through which nearly all the improvements in the construction of tele-
scopes and microscopes have been made known to the world. 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 the above
makers by far excelled those of all other countries. See Juries' Reports
for much interesting matter on this subject; article "Microscope"
Penny Cyclopaedia, by Mr. Ross j Cyclopaedia of Anatomy and Phy-
siology, by Dr. Carpenter ; Practical Treatise on the Microscope, by
Professor Quekett; Brewster's Treatise on the Microscope; Dujardin's
Observateur; Maudl, Traite pratique du Microscope; Dr. Robin, Ih(,
Microscope, &c.

CHAPTER II.

MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IN THE CONSTRUCTION

OF THE MICROSCOPE LENSES MODE OF ESTIMATING THEIR POWER,

ETC. ACHROMATIC LENSES MAGNIFYING POWER WOLLASTON'S

DOUBLET — CODDINGTON'S LENS — ROSS'S SIMPLE AND COMPOUND
MICROSCOPES MICROMETERS, ETC.

the construction of the modern microscope optical
and mechanical principles of some importance are
involved. These principles we now proceed to no-
tice, together with the more recent improvements
effected in the instrument generally.

The microscope depends for its utility and ope-
ration upon concave and convex lenses, and the
course of the rays of light passing through them.
Lenses are usually defined as pieces of glass, or
other transparent substances, having their two sur-
faces 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 direc-
tion of the ray is changed both on entering and leaving j 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 per-
pendicular, and vice versa.

Dr. Arnott remarks : " But for this fact, which to many persons might
at first appear a subject of regret, as preventing the distinct vision of
objects through all transparent 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

CONSTRUCTION OF THE MICROSCOPE.

13

form a part ; nor even the eye itself." Rays of light falling perpendi-
cularly 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. 3), 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 b in the direction a e
m b, it will be refracted

to d, in a direction ap-
proaching 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 perpen-
dicular 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 d e g which it
makes with the 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 re-
fracted ray e d as that was from the Hue 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 direction 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 g m measures the angle of incidence g e m,
and the arc g d the angle of refraction g e d, A line m o drawn from,
the point m perpendicular to h k is called the sine of the angle of
incidence, and the line d g the sine of the angle of refraction. From
the conclusions drawn from the principles of geometry, it has been
found, that in any particular transparent substance the sine of the
angle of incidence m o has always the same ratio to the sine d g of the

14 CONSTRUCTION OF THE MICROSCOPE.

angle of refraction, no matter what be the degree of obliquity with
which the ray of incidence a e is projected to the surface of the trans-
parent 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 higher in proportion 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 the object must be placed is called the focus of the lens;
and the distance from the middle of the lens to the focus is called the
focal length, or distance. 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 ; the middle point between them the centre ; and the distance
between them the diameter.

Fig. 4 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-con-
cave j d, a plano-concave ;
e, a double-convex; f} a
/ plano-convex.

Refraction of Light through Lenses, and Method of tracing the
Progress of Rays.

"When a ray of light enters the concave surface of a dense medium,
or quits a similar surface and enters the convex surface of a rare
medium, the method of tracing its progress is shown in fig. 5, where m'n
is a dense medium of glass with two concave surfaces, forming a thick con-
cave lens. Let c c be the centres of the two surfaces lying in the axis
c c', and h' r, h"r parallel rays incident on the first surface. As c r is per-

CONSTRUCTION OF THE MICROSCOPE.

pendicular to the surface at r, hrc will be the angle of incidence ; and
if a circle is described with a radius r h, hm will be the sine of the
ano-le : the same happens as was shown occurring with parallel surfaces
in fig. 3. From a scale on which hin is 1'500 take in the compasses
1, and find some point,
b, in the circle, where
when one foot of the
compasses is placed, the
other will fall only on
one point, n, of the per-
pendicular, r c; the line
r b, drawn through this
point, will be the re-
fracted ray. By continuing this ray, b r, backwards, it will be found
that it meets the axis at f. In like manner it will be seen that the
ray h" r' will be refracted in the direction of r r", as if it also diverged
from/! Hence f will be the focus of the parallel rays refracted by a
single concave surface, and may be found by the following rule : Divide
the index of refraction by its excess above unity, and the quotient will
be the principal focal distance fc, the radius of the surface. If, by a
similar method, we find the refracted ray r c at the emergence of the
ray r b from the second surface r r' of the lens, and continue it back-
wards, it will be found to meet the axis at f j so that the divergent
rays r r", r r" are rendered still more divergent by the second surface,
and c will be the focus of the lens m' n.

Kays of light falling upon a convex lens parallel to its axis are
refracted in precisely the same manner as those falling on a sphere ; and
the refracted ray may be found in the very same way. But as a sphere
has an axis in every direction, every incident ray must be parallel to
an axis of it ; whereas in a lens, which has only one axis, many of the
incident rays must be oblique to that axis. In every case, whether of
spheres or of lenses, all the rays that pass along the axis suffer no
refraction at all, because the axis is always perpendicular to the
refracting surfaces.

When parallel rays, r I, r1 c, r" I', fig. G, fall upon a double-convex
lens, II', parallel to its axis, r'f, the ray r' c, which coincides with the
axis, will pass through without suffering any refraction ; but the other
rays, r Z, r" I', will be refracted at each of the surfaces of the lens ; and
the refracted rays corresponding to them, namely If, I' f", will be
found, by the method already given, to meet at some point, /", in the
axis.

16 CONSTRUCTION OF THE MICROSCOPE.

But when the rays are oblique to the_ axis, as 5 I, s" I, 1 1, t" ?', the
rays s' c, t' c, which pass through the centre, c, of the lens, will suffer
refraction at each surface ; but as the two refractions are equal and in
opposite directions, the finally refracted rays ef} cf" will pass from

s' c, t' c ; and it will be found that s I, s" I' will be refracted to a com-
mon point,/", in the direction of the central ray s'f", and 1 1, t" I' to the
point / When the lens is of glass and equally convex, the focal dis-
tance will be equal to the radius. 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 reflection, they will form
a new image, and that repeatedly, so long as their order is not dis-
turbed. It follows also, that when the progress of the luminous ray
is under consideration, we may look on the image as the object, and
the object as the image ; and consider the second image, as if it had
been produced by the first, as an object, and so on. This is one of
the principles involved in the adaptation of these lenses to magnifying
objects. It has been shown in fig 6, that if the point of light be situ-
ated above the line of the axis, the focus will then be below it, and vice
versa; 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.

And if the object be placed at twice the distance of the principal
focus, the image being formed at an equal distance on the other side

CONSTRUCTION OF THE MICROSCOPE. 17

of the lens, will be of the same dimensions with the object, as in fig. 7 ;

fig. 7.

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

Spherical Aberration of Lenses.

We have many imperfections to contend with in our optical arrange-
ments and combinations ; one of which results from the spherical aber-
ration of the rays passing through lenses whose curvatures are equal
over their whole surfaces. If the course of the rays be observed, it
will be seen that they do not all meet exactly in the foci already stated,
but that the focus of the ray& which have passed through the circum-
ferential portion of the lens is much closer to it than that of the rays
which are nearer the line of its axis. This is shown in fig. 9 : a b, the
rays, are seen falling on the circumference and coming to a focus, /;
a b', a" b" are rays falling nearer the centre, and coming to a more dis-
tant focus,/"; so that if a screen be held at cd, the rays which have
passed through the central portion of the lens will be stopped at /be-
fore they come to a focus, or they will come to it in a state of diverg-

c

18

CONSTRUCTION OF THE MICROSCOPE.

ence at c d: in either case the image will have a certain degree of
indistinctness; and the difference between the focal points of their cir-
cumferential and central rays is termed the spherical aberration. It

fig. 9.

therefore becomes apparent that, to produce the desired effect, the cur-
vature of the lens is required to be increased around the centre, so as
to bring the rays which pass through it more speedily to a focus ; and
to be diminished towards the circumference, so as to throw the focus
of the rays influenced by it to a greater distance. This condition is in
a measure fulfilled in the meniscus form of lens, which is shown to be
the segment of an ellipsoid instead of a sphere.

But the ellipse and the hyperbola are curves of this kind, in which
the curvature diminishes from the central ray, or axis, to the circum-
ference b; and mathematicians have sliown how spherical aberration
may be entirely removed by lenses whose sections are ellipses or hy-
perbolas. This curious discovery we owe to Descartes.

If a I, a I' for example, fig.
10, be part of an ellipse whose
greater axis is to the distance
between its foci //as the in-
dex of refraction is to unity,
then parallel rays r /', r" I in-
cident upon the elliptical sur-
face I' a I, will be refracted by
the single action of that sur-
face into lines which would,
meet exactly in the farther
focus/ if there were no second surface intervening between la 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 Id 1? is perpendicular to every one of
the refracted rays, all these rays will go on to /without suffering any

10.

CONSTRUCTION OF THE MICROSCOPE.

19

refraction at the circular surface. Hence it should follow, that a me-
niscus whose concave surface is part of an ellipsoid, and whose con-
vex surface is part of any spherical surface whose centre is in the
farther focus, will have no spherical aberration, and will refract pa-
rallel rays incident on its convex surface to the farther focus.

In like manner, a con-
cavo-convex lens, fig. 11,
II' } whose concave surface
I a I' is -a eircte described
round the farther focus of
the ellipse, will cause paral-
lel rays b I, b' I' to diverge in
directions Ir, I'r", which,
when continued backwards,
will meet exactly in the fo-
cus jfj which will be its vir- fig. 11.
tual focus.

If a plano-convex lens, fig. 12, has its convex surface I a I' part of a
hyperboloid, formed by the revolu-
tion of a hyperbola whose greater
axis is to the distance between
the foci as unity is to the index
of refraction, then parallel rays
r I, r" I' falling perpendicularly in
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 in its plane surface.*

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 its first surface is con-

* It should be borne in mind, that in none of these lenses would the object be cor-
rectly seen in focus, except at the one point known as the mathematical or geometrical
axis of the lens.

fig. 12.

20

CONSTRUCTION OF THE MICROSCOPE.

fig. 13.

vex, 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 is a meniscus, and r I,
r 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 refraction is to unity,
that is as 1-500 to 1 in
glass; then if /is the fo-
cus of the first surface,
describe, with any radius

less than fa, a circle ma' 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
ae or remote from it, will be refracted 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 manner, it is
obvious that rays fl, fl'} diverging from / will be refracted into r I, r I',
which diverge accurately from the virtual focus.* **

There are certain mechanical difficulties in the way of such lenses
as these, but which have to some extent been surmounted by dimin-
ishing the working aperture with stops, for correcting their aberra-
tion. This is still better effected, or even got rid of altogether, by
using combinations of lenses, so disposed that their opposite aber-
rations shall correct each other, whilst magnifying power is gained.
For it is easily seen that, as the aberration of a concave lens is just
the opposite of that of a convex lens, the aberration of a
convex lens placed in its most favourable position may be
corrected by a concave lens of much less power in its most
favourable position. This is the principle of a combina-
tion proposed by Sir John F. W. Herschel, fig. 14, con-
sisting of a plano-convex lens and a meniscus ; and a
doublet of this kind will be found extremely useful and
available for microscopic purposes : it affords a large field,
like the Coddington lens. Another and serious difficulty
arises to the optician in the unequal refrangibility of the different
coloured rays which together make up white light, so that they are not
* Brewster's Optics.

fig. 14.

CONSTRUCTION OF THE MICROSCOPE.

21

all brought to the same focus even by a lens free from spherical aber-
ration. It is, indeed, this difference in their refrangibility which causes
their complete separation by the prism into a spectrum. This is
termed chromatic aberration, and will be best explained by a reference
to fig. 15: ab are rays of white light refracted by a convex lens;

c the focus of the violet rays, which then cross and diverge towards
ef; d is the focus of the red rays, which are crossed at the points
e e by the violet rays ; the middle point, therefore, of this line is the
mean focus, or focus of least aberration.

The correction of chromatic aberration has been accomplished by
bringing into use the different dispersive powers of various materials
which bear no relation to their simple refracting power, — in other words,
by a combination of flint and crown glass ; and by a most curious series
of experiments the dispersive power of flint-glass was found to be so
much greater than that of crown-glass, that if the lens a a (fig. 16)
be made of crown glass, whose index of
refraction is 1-519, and dispersive power
0-036, and the lens b b of flint-glass,
whose index of refraction is 1-589, and
dispersive power 0^0393., and if the
focal length of the convex crown-glass
lens is made 4^ inches, and that of the
concave flint-glass lens 7§ inches, they
will form a lens with a focal length of
ten inches, and will bring rays of light,
c c', to a single focus, d, free of colour.

Such a lens is called an achromatic lens; and when used in combina-
tion with other glasses in constructing the microscope, it is termed
an achromatic microscope.

To assist us in gaining a clearer notion of the mode in which a
single lens serves to magnify minute objects, it is necessary to take a

fig. 16.

22

CONSTRUCTION OF THE MICROSCOPE.

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 impinges, requires the intervention of the crystal-
line 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, in-
deed, the angle it subtends 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.
17. 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 there-
fore appear nearly twice as long as o w,
being seen under twice the angle; and
in the same proportion for any greater
or lesser difference 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 is-
suing from it ; so that they enter the eye in a state of moderate diver-
gence, as if they had is-
sued from an object be-
yond the nearest limit of
distinct vision ; and a
well-defined image is con-
sequently formed upon
the retina. In fig. 18
a double- convex lens is
placed before the eye,
near which is a small
arrow, to represent the
object under examina-
tion ; and the cones

drawn from it are portions of the rays of light diverging from those
points and falling upon the lens. These rays, if permitted to fall

CONSTRUCTION OF THE MICROSCOPE.

at once upon the pupil, would be too divergent to allow of their
being brought to a focus upon the retina by the optical arrangements
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 pre-
cisely as if they had emanated directly from a larger arrow placed at
ten inches from the eye. The difference between the real and the ima-
ginary arrow is called the magnifying power of the lens. Fig 19 will
perhaps convey a clearer idea of the increase of the angle of vision by
interposing a convex lens :
without this lens placed at
f g', the eye would see the
dart at b' c' under the
angle formed by the eye
and b' c ; but the rays b'f
and c g from the extremi-
ties of the dart, in passing
through the lens, are re-
fracted to the eye in the
direction of^and g, which
causes the dart to be seen
under the much larger
angle formed with the eye

and d e ; and it therefore appears so much magnified as to extend from
d to e. 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.* With these preliminary remarks as to the
medium by which microscopic power is obtained, we shall proceed to
apply them to the construction of a perfect instrument. A microscope,
as we have before explained, may be either a single or simple, or a com-
pound instrument. The simple microscope may consist of one, as seen
in fig. 1 8, 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 micro-
scope, not less than two lenses must be employed : one to form the in-
verted 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

* "The Magnifying Power of Short Spaces" has received an able elucidation from
John Gorham, Esq. M.R.C.S. Journal of Microscopical Society, October 1854.

fig. 19.

CONSTRUCTION OF THE MICROSCOPE,

may be formed out of a combination of lenses, as will be hereafter
seen.

We have hitherto considered a lens only in reference to its enlarge-
ment 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 j but it at the same time becomes as important that
we do riot sacrifice definition to this end. 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 re-
fraction.

The first satisfactory arrangement for this purpose was the inven-
tion of the celebrated Dr. Wollaston. His doublet (fig. 20) consisted of

two plano-convex lenses
having their focal lengths
in the proportion of one
to three, or nearly so, and
placed at a distance which
can be ascertained best by
actual experiment. Their
plane sides are placed
towards the object, and
the lens of shortest focal
length ne^t the object.

It appears that Dr.
Wollaston was led to this
invention by considering
that the achromatic Huy-
ghenean eye-piece, which
will be presently de-
scribed, would, if revers-
ed, possess similar good
properties as a simple mi-
croscope. But it will be
evident, when the eye-
piece is understood, that
the circumstances which
**£• ^' render it achromatic are

very imperfectly applic-
able to the simple microscope, and that the doublet, without a nice
adjustment of the stop, would be valueless. Dr. Wollaston makes no

CONSTRUCTION OF THE MICROSCOPE. 25

allusion to a stop, nor is it certain that he contemplated its introduction ;
although his illness, which terminated fatally soon after the presenta-
tion 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 lol' is the object, p a portion
of the pupil, and dd the stop, or limiting aperture.

Now it will be observed that each of the pencils of light from
the extremities IV of the object is rendered excentrical by the stop;
consequently each passes through the two lenses on opposite sides of
their common axis op; thus each becomes affected by opposite errors,
which to some extent 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 moreover
as the blue rays fall 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 dimin-
ished 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 compensation would take
place, quite different in principle, and inferior in degree, to that which
is produced in the excentrical 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 microscope 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 completely balanced

26 CONSTRUCTION OF THE MICROSCOPE.

or corrected at the second bending, in the opposite direction, by the
third lens.

Every increase in the number of lenses is attended with one draw-
back, from the circumstance that a certain portion of light is lost by
reflection and absorption each time that the ray enters a new medium.

The combination of three lenses approaches so very close to the
object under observation as, indeed, to prevent the use of more than
three ; and this constitutes a limit to the improvement of the simple
microscope, — for it is called a simple microscope, although consisting
of three lenses.

Before we proceed to describe the simple microscope and its appen-
dages, it will be well to explain such other points in reference to the
form and materials of lenses as are most likely to be interesting.

A very useful form of lens was proposed by Dr. Wollaston, and
called by him the Periscopic lens. It consisted of two hemispherical
lenses cemented together by their plane faces, having a stop between
them to limit the aperture. A similar proposal was made by Mr.
Coddington, who, however, executed the project in a better manner, by
cutting a groove in a whole sphere, and filling the groove with opaque
matter. His lens, which is the well-known Coddington lens, is shown
at fig. 21 : it gives a large field of view, which is equally good in all direc-
tions, as it is evident that the pencils a b and b a pass through under pre-

* *>

fig. 21. fig. 22.

cisely the same circumstances. Its spherical form has the further ad-
vantage of rendering the position in which it is held of comparatively
little consequence. It is therefore very convenient as a hand mag-
nifier ; but its definition is, of course, not so good as that of a well-made

CONSTRUCTION OF THE MICROSCOPE.

27

doublet or achromatic lens. It is generally set in a folding case, as re-
presented in the figure, and so contrived that it is admirably adapted
for the waistcoat-pocket ; which, together with the small Jwlder, fig. 22,
for securing small objects and holding them during examination, are
all that is required for afield instrument during a day's ramble. The
useful little holder may be purchased in a case of Mr. Weedon, 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, according to circumstances, with lenses and mirrors to
collect and reflect the light upon the object, with other conveniences.

The best of the kind was that contrived by Mr. Ross : it is repre-

fig. 23.

fig. 24.

sented in fig. 23, and consists of a circular foot &, from which rises a
short tubular stem d, into which slides another short tube c, carrying
at its top a joint /; to this joint is fixed a square tube a, through

28 CONSTRUCTION OF THE MICROSCOPE.

which a rod 6 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 in-
creased 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 exami-
nation 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 microscope 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 supported on a firm tripod, made of bell-metal, the
feet of which, a a a, are made to close up for the purpose of packing 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 r r. 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 base d is moved up and
down within the triangular bar c, by turning the milled head t, forming
the coarse adjustment : this bar carries the lens-holder mnop. The
stage e consists 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 ft and has a spring clip h for holding, if necessary,
the objects under examination. By means of two screws placed dia-
gonally, one of which is seen at s, this elevated stage can be moved in
two directions, at right angles to one another; and thus different parts
of objects can be brought successively into 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 it-
self can be lengthened or shortened by means of the rack and pinion
m o ; hence the lens q can be applied to every part of an object without
moving the stage.

The mirror I 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 k ; and the lens is made to slide up

CONSTRUCTION OF THE MICROSCOPE.

29

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 either simple lenses or doublets ;
or it could be easily converted into a compound microscope by insert-
ing a compound body, supported on a bent arm, in the place of the one
carrying the single lenses.

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 to do
what might have been accomplished, though not
so well, by one ; and the third merely effected
certain modifications in the light before it entered
the eye. But in the compound microscope the
two lenses have totally different functions : the
first receives the rays from the object, and bring-
ing them to new foci, forms an image, which the
second lens treats as an original object, and mag-
nifies it just as the single microscope magnified
the object itself,

Fig. 25 shows the earliest form of the com-
pound microscope, with the magnified image of a
fly, as given by Adams, which he describes as con-
sisting of an object-glass, In, and an eye-glass, /#;
the object, b' o, being placed a little further from
the lens than its principal 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 converge by the refractive powers of this
organ, and be collected on the retina. But the
image differs from the real object in a very essen- £„. 25.

tial particular. The light being emitted from the
object in every direction, renders it visible to an eye placed in any

30 v CONSTRUCTION OF THE MICROSCOPE.

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 is converged by the
lens iof, cross each other, and diverge towards h, and therefore would
never arrive at the lens fg, without the interposition of the plano-
convex lens at d e, 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 fg, 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 fb
is greater than the distance from the real object to f; and secondly,
because this picture is again magnified by the eye-glass. The com-
pound 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 enlarged, and is consequently called i\\z 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
called the eye-piece.

Upon the construction of this microscope Mr. Ross observes :
" Since the power depends on the ratio between the anterior and pos-
terior foci of the object-glass, it is evident that by increasing that ratio
any power may be obtained, the same eye-glass being used • or having
determined the first, any further power may be obtained by increasing
that of the eye-glass; and thus, by a pre-arrangement of the relative
proportions in which the magnifying power shall be divided between
the object-glass and the eye-glass, almost any given distance (within
certain limits) between the first and its object may be secured. This
is one valuable peculiarity of the compound instrument ; and another
is the large field, or large angle of view, which may be obtained, every
part of which will be nearly equally good ; whereas with the best sim-
ple microscopes the field is small, and is good only in the centre."

Mr. Lister, as we stated in a previous chapter, first set about in-
vestigations which have ultimately proved of the utmost value. The
results arrived at by him were published in the Philosophical Transac-
tions ; and the principles have since been applied and exhibited by Mr.
Hugh Powell and Mr. Andrew Ross. It is due to the late Mr. Tulley
to say, that he constructed an achromatic object-glass of nine-tenths of
an inch focal length, composed of three lenses, transmitting a pencil of
eighteen degrees; and as regards accurate correction throughout the

CONSTRUCTION OF THE MICROSCOPE. 31

field, his combination has not been excelled by any subsequent set of
three lenses. By Mr. Lister's combination he was enabled to produce
lenses which transmitted a pencil of fifty degrees with a large field cor-
rect in every part. In the paper referred to above he enters into many
interesting particulars, which, however, are not necessary to the com-
prehension of our subject. Mr. Ross presented to the Society of Arts,
in 1837, a paper on the subject, which was published in the 51st volume
of their Transactions. This being essential to a full understanding of
the ultimate refinements of the instrument, we give it in full :

"In the course of a practical investigation, with the view of con-
structing 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 sufficient 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 combination is the thinnest possible, and it follows
that there will be the greatest distance between the object and the
object-glass. The focal length is ^ of an inch, having an angular aper-
ture 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 T^ 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 achromatic 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 aberration 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

32

CONSTRUCTION OF THE MICROSCOPE.

satisfactory judgment of their character may be 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 consequently deteriorate
the definition ; and this defect will be more obvious with the increase
of distance between the object and object-glass.

"If an object-glass is constructed as represented in fig. 26, where
the posterior combination p and the middle m
have together an excess of negative aberration,
and if this be corrected by the anterior combi-
nation a having an excess of positive aberra-
tion, 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 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 di-
verge, the effect of the anterior combination a upon the other two, p
and m, will vary with its distance from thence.

"When, therefore, the correction of the whole is effected for an
opaque object, with a certain distance 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 anterior
combination will act more powerfully, and the whole will have an ex-
cess 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 correc-
tion, by moving the lenses nearer together, till the positive aberration
thereby produced balances the negative aberration caused by the me-
dium.

" 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 j and if diverging rays near the axis and at the margin are pro-

CONSTRUCTION OF THE MICROSCOPE.

33

jected 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, separated, into a beam consisting of the component colours of
the ray, and that each beam is widely different in form. This differ-
ence, being magnified by the power of the microscope, readily accounts
for the chromatic thickening of the outline just mentioned. Therefore,
to obtain the finest definition of extremely delicate and minute objects
they should be viewed without a covering : if it be desirable to im-
merse them in a fluid, they should be covered with the thinnest pos-
sible 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 correction for colour.

" The mechanism for applying these principles to the correction of
an object-glass under the various circumstances is represented in fig. 27,
where the anterior lens is set in the end of a
tube a, which slides on the cylinder b, contain-
ing the remainder of the combination j the
tube a, holding the lens nearest the object,
may then be moved upon the cylinder b, for
the purpose of varying the distance, accord-
ing 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 together when adjusted. An
aperture 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 hundreth 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 adjustment of the microscope. In this
process the milled edge of the object-glass will be employed to adjust
for character 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 correc-

fig-27

CONSTRUCTION OF THE MICROSCOPE.

tion 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 aberration result-
ing from the rest of the lenses ; and as this disturbance is effected at
the first refraction, it is independent of the other part of the combina-
tion. The visibility 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 corrections for chromatism
and the oblique pencils.

" With this adjusting object-glass, therefore, we can have the requi-
sites 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 aberra-
tions j also, by the adjustment, the means of preserving that correction
under all the varied circumstances 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 increased
" angle of aperture." The angle of aperture is that angle which the
most extreme rays that are capable of being transmitted through the
object-glass make with the point of focus: b a b, in figs. 28 and 29, is
the angle of aperture ; but it will be seen that the angle of aperture is

much greater in fig. 28 than in fig. 29, which
represents an uncorrected lens ; consequent-
ly a much larger quantity of light is trans-
mitted by the former than by the latter,
when any object is subjected to examina-
tion. In order to see an object at all dis-
tinctly 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. We shall have
occasion to speak of this again.

A very perfect instrument for measur-
ing the angle of aperture, designed by Mr. Gillett, consists of two
microscopes, the optical axes of which may be adjusted to coincidence.
One of these is attached horizontally to the traversing arm of a hori-

ANGLE OF APERTURE.

35

zontal 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 micro-
scope, 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 nu-
merous 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 the aberration in any
given optical combination.

Fig. 30 represents the body of one of Mr.
Ross's compound microscopes with the triple ob-
ject-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 ; ee being the eye-glass, and ff the field-glass,
and between them, at bb, 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 &; these rays, if not pre-
vented by the lens ff, or the diaphragm at b b,
would form an image at a a; but as they meet
with the lens// in their passage, they are con-
verged 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 further magnified by the lens

fig. 30.

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

36

CONSTRUCTION OF THE MICROSCOPE.

spherical and chromatic aberration, would, nevertheless, be of little
service without an eye-piece of peculiar construction.

If we stopped here, we should convey a very imperfect idea of the
beautiful series of corrections effected by the eye-piece, and which were
first pointed out in detail in a paper on the subject, published by Mr.
Yarley, in the fifty-first volume of the Transactions of the Society of
Arts. The eye-piece in question was invented by Huyghens for tele-
scopes, with no other view than that of diminishing the spherical aber-
ration 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 ar-
rangement, accidentally cor-
rected a great part of the
achromatic aberration. Let
fig. 31 represent the Huyghe-
nian eye-piece of a micro-
scope,^ being the field-glass,
and ee the eye-glass, and
Imn 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 bb blue, and the
intermediate ones green, yel-
low, and so on, corresponding
with the colours of the pris-
matic spectrum. This order
of colours is the reverse of
that of the common compound
microscope, in which the sin-
gle object-glass projects the
red image beyond the blue.
The effect just described, of projecting the blue image beyond the

THE EYE-PIECE. 37

red, is purposely produced for reasons presently to be given, and is
called over-correcting the object-glass as to colour. It is to be ob-
served also, that the images b b and r r are curved in the wrong direc-
tion to be distinctly seen by a convex eye-lens, and this is a further
defect of the compound microscope of two lenses. But the field-glass,
at the same time that it bends the rays and converges them to foci at
b' b' and r 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 pass un coloured
through the eye-glass. To render this important point more intelli-
gible, let it be supposed that the object-glass had not been over-cor-
rected, 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 rr 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 re-
spect,— the blue images are rendered smaller than the red by the su-
perior 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 for-
mer representing the red, and the latter the blue rays. This is the ac-
cidental 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 separa-
tion 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

38

CONSTRUCTION OF THE MICROSCOPE.

sensibly parallel, presenting, in consequence, the perfect definition of a
single point to the eye. The same reasoning is true of the intermediate
colours and of the other pencils.

From what has been stated, it is obvious what we mean by an
achromatic object-glass : one in which the usual order of dispersion is
so far reversed, that the light, after undergoing the singularly beautiful
series of changes effected by the eye-piece, shall come uncoloured to
the eye.

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. 32. The eye and field glasses

fig. 32.

33.

have now their plane faces turned towards the object ; the rays from
the object are made to converge immediately in front of the field-glass ;
and here is placed a plane-glass, on which are engraved divisions of
1-1 00th 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. 33, and at it are seen some magnified grains of starch. Thus the
measure of the magnified image is given by mere inspection ; and the
value of such measures, in reference to the real object, when once ob-
tained, is constant for the same object-glass.

Mr. Lister placed on the stage of his instrument a divided scale,
the value of which was known ; and viewing the scale as the micro-
scopic object, observed how many of the divisions on the scale attached
to the eye-piece corresponded 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 MICROMETER.

SO

tlie 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 were 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 show-
ing the value of each division of the micrometer for every object-glass
with which it may be used.

While on the subject of measuring, it may be well to explain the
mode of ascertaining the magnifying power of the compound micro-
scope, which is generally taken on the assumption before mentioned,
that the naked eye sees most distinctly at the distance of ten inches.

Place on the stage of the instrument, as before, a known divided
scale, and when it is distinctly seen, hold a rule at ten inches distance
from the disengaged eye, so that it may be seen by that eye over-
lapping or lying by the side of the magnified picture of the other
scale; then move the rule till one or more of its known divisions
correspond with a number of those in the magnified scale, and a com-
parison of the two gives the magnifying power.

Mr. Jackson has adopted a simpler and cheaper form of micro-
meter, represented in fig. 34, which is thus described by him in the
Microscopical Society's Transactions: It consists of a slip of glass
placed in the focus of the eye-
glass, and can be used 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- thou-
sandth with the eighth ; and at
the same time the half, or even
the quarter of a division maybe es-
timated, thus affording the means
of attaining all the accuracy that
is really available. It may there-
fore entirely supersede the more
complicated and expensive screw-
micrometer, being much handier
to use, and not liable to derange-
ment in inexperienced hands.

The positive eye-piece gives
the best view of the micrometer,
the negative of the object. The

fig. 34.

40 CONSTRUCTION OF THE MICROSCOPE.

former is quite free from distortion, even to the edges of the field ;
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, how-
ever, to the extent of half its diameter, there is no perceptible dis-
tortion ; and the clearness of the definition gives a precision to the
measurement which is very satisfactory. For this reason Mr. Jackson
gives it the preference.

Short bold lines are ruled on a piece of glass, a, fig. 34 ; 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, fig. 34, 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 adjustment 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 divisions 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-hundreth of an inch. This is the common mode of express-

THE MICROMETER.

41

ing microscopical measurements j 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 measure ten ; which, divided by
2000, gives the decimal fraction -005.

Enter in a table the length to which the tube is drawn. out, and the
number of divisions on the eye-piece micrometer equivalent to an inch
on the stage ; and any measurements afterwards taken with that mi-
crometer 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 hundreth of an inch on the stage will occupy too much of
the field ; the two-hundredth or five-hundreth 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 should 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, provided the object-glass be of the first quality;
otherwise use the eye-piece of lowest power. The lens above the micro-
meter 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. 34.

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

CONSTRUCTION OF THE MICROSCOPE.

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 :

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 microscope 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 2000, and then the lines
which are only l-47000th of an inch apart will be seen as perfectly
traced as the coarser lines. 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, dif-
fering from 2 inches to 1-1 6th of an inch.

Magnifying Power of Mr. Ross's Object-Glasses with his various
Eye-Pieces.

OBJECT-GLASSES.

EYE-GLASSES

1-inch.

2-inch.

-|-inch.

i-inch.

i-inch.

TVinch.

A

20

60

100

220

420

600

B

30

80

130

350

670

870

C

40

100

180

500

900

1200

Value of each

space in the Micro-
meter eye-glass,

Too

9*0

16*00

f£oo

o o o o

TsJtTo

with the various

•0025

•001031

•0005263

•0002325

•0001111

•000074

object-glasses.

EYE-PIECES. 43

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. Across the focus of the eye-piece a single
cobweb is drawn, 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 j the frame-work bearing the cobweb, with the ver-
nier, 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.

The Eye-piece. — To the most complete instruments a set of eye-
pieces, consisting of three, is generally 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 Huyghean plan),
being limited by the diameter of the body. It is usually about 20 de-
grees. The next eye-piece, or middle power, marked B, 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 large ones ; molluscs, or 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 cellu-
lar tissues of plants, the Haversian canals and lacunae of bone, and the
serrated laminae of the crystalline lens in the eyes of birds and fishes.

The eye-piece c is of use when it is requisite to investigate the in-
timate 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, obvi-
ates the necessity of using a deeper object-glass, which always occa-
sions 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 & 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

44 CONSTRUCTION OF THE MICROSCOPE.

microscope is judged of by the distinctness and comfort with which it
exhibits certain objects, the details of which can only be made visible
by combinations of lenses of high magnifying power, and a near ap-
proach to correctness. Such are called by the microscopist test- objects.
Mr. C. Brooke, F.K.S., whose labours have been devoted to the correc-
tion 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 necessary to form some
definite conceptions regarding the external 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, ar\d the siliceous
lories, or valves of the genus Pleurosigma, freed from organic matter :
the former of these is commonly adopted as the test of the defining
power of an achromatic object-glass, and the several species of the lat-
ter as the tests of the penetrating or separating power, as it has been
iermed. The defining power depends only on the due correction of
chromatic and spherical aberrations, 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 constants ; but it is practically perfect when the residual
error is a quantity less than that which the eye can appreciate. The
separation of the markings of the Pleurosigmata 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
\ very delicate transparent lamina or membrane, covered with an im-
yricated arrangement of epithelial 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 subsequently 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

DEFINING AND PENETRATING POWER. 45

scales thus obtained in Canada balsam, and illuminating them by means
of Wenham's parabolic reflector. The structure may also be very
clearly recognised when the scale is seen as an opaque object under a
Boss's TVth (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 glistening surface, with very
slight markings, corresponding 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 Pleuro-
sigma; which, as arranged in the order of easy visibility, are, P.formo-
sum, P. hippocampus, P. angulatum. These appear to consist of a
lamina of homogeneous transparent silex, studded with rounded knobs
or protuberances, which, in P. formosum and P. angulatum, are ar-
ranged 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 de-
scribed j and the visibility of these projections is probably propor-
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 consequently 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 other similar objects, have
been by some writers supposed to be made up of two substances pos-
sessing different degrees of refractive power ; but this hypothesis is
purely gratuitous, since the observed phenomena will naturally result
from a series of rounded or lenticular protuberances of one homoge-
neous 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 lens, it is difficult to conceive why the oblique
rays only should be visibly affected. When P. hippocampus or P. for-

46 CONSTRUCTION OF THE MICROSCOPE.

mosum is illuminated by a Gillett's condenser, with a central stop
placed under the lenses, and viewed by a quarter-inch object-glass of
70° aperture, both being accurately adjusted, we may observe in suc-
cession, 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 same 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 accumulation
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 admit-
ting very oblique rays.

It does not appear to be desirable that objects should be illumi-
nated 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 illumination may be well illustrated by viewing
with a one-inch object-glass the Isthmia, illuminated by Gillett's con-
denser. When this is in focus, and its full aperture open, the markings
above described are wholly invisible ; but as the aperture is succes-
sively diminished by the revolving diaphragm, the object becomes
more and more distinct, and is perfectly defined when the aperture of

MECHANICAL ARRANGEMENTS. 47

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 defi-
nition of objects is always most perfect when an illuminating pencil of
suitable form is accurately adjusted to focus, that is, so that the source
of light and the plane of vision may be conjugate foci of the illumi-
nator. If an object-glass of 120° aperture, or upwards, be used as an
illuminator, the markings of Diatomacese will be scarcely distinguish-
able with an object-glass, the glare of the central rays overpowering
the structure of those that are more oblique."

MECHANICAL ARRANGEMENTS.

Having now explained the more important optical principles of the
achromatic compound microscope, it remains only to describe the me-
chanical and accessory arrangements for giving those principles their
full effect. .The mechanism of a microscope is of much more import-
ance than might be imagined by those who have not studied the sub-
ject. In the first place, steadiness, or freedom from vibrations which
are not equally communicated to the object under examination and to
the lenses by which it is viewed, is a point of the utmost consequence.

One of the best modes of mounting a compound microscope is
that shown, fig. 35, which, although it does not exhibit all the details,
will serve to explain the chief features of the arrangement.

" The mechanical construction," says Mr. Ross, " is derived from
a practical acquaintance with the various improvements made in the
microscope for many years. The general arrangement, which is pro-
perly the province of the mechanic, has been contrived to obtain the
utmost freedom from tremor, and to afford the greatest facility in
using the various movements; while the extent, direction, and num-
ber of these have been collected from the experience of the most
indefatigable observers in all the various branches of microscopic
inquiry.

The optical part, also, has arrived at such perfection, that points
or lines whose distance is such that their separation is bordering on
interfering with the physical constitution of light can be distinctly
separated, thus insuring a reality in the appearance of objects where
the minuteness of the detail approaches the natural limit of micro-
scopic vision."

In the larger instrument, fig. 36, two uprights, J, are strengthened by

48

CONSTRUCTION OF THE MICROSCOPE.

two internal buttresses mounted on a strong tripod ; at the upper part,
and between the uprights, we have an axis, upon which the whole of the
upper part of the instrument turns, so as to enable it to take a hori-
zontal or vertical position, or any intermediate inclination, — such, for
instance, as that shown in the drawing. This movable part is fixed to

fig. 35. Baker's Compound Microscope.

the axis near its centre of gravity, and consists of the stage F G ; the
arm K is screwed into the triangular bar, and carries the microscope
tube or body A, at the upper end of which is the eye-piece B, and at
the lower the object-glasses c. The stage F G has rectangular move-

THE COMPOUND MICROSCOPE.

49

rnents one inch in extent on the racket-cylinders, and are moved by
the pinions connected with the milled-heads at G. The triangular
bar, together with the arm and microscope-tube, is moved by the large

fig. 36. The Compound Microscope.

50 THE MICROSCOPE.

milled-heads at D ; and a more delicate adjustment of this optical parfc
is effected by the milled-head E. The other milled-head fixes the arm
K to the triangular bar. H is the mirror, which slides up or down the
tube to which it is attached ; standing near which is the condenser
M, with its upright support of brass for holding the condensing-lens
L, — this is made to unscrew, for the convenience of packing. Such
instruments are manufactured by Mr. Ross at prices varying from 10£
to 100Z.

Mr. Ross's small achromatic compound microscope is supported on
a firm tripod base, from which rise two strong uprights, supporting at
their upper parts the trunnions to which the square frame, carrying the
stage and triangular bar, with the body, are attached. Within the tube
a smaller one is made to slide up and down by rack and pinion : this
forms the coarse adjustment. The fine adjustment consists of a conical-
pointed steel screw pressing against the top of a slit in the inner tube,
to the end of which the adapter for receiving the object-glasses is fixed.
The stage has the usual rectangular motions, that from the side being
performed by a screw and nut, by turning the milled-head ; whilst the
up-and-down movement is performed by a rack and pinion, turned by
the milled-head below the other. The stage-plate is provided with a
sliding-rest, by which the distance of an object from the central hole
in the plate may be regulated before focussing : this is sometimes made
to answer the purpose of the complicated sliding frame in the more
expensive instruments. At the upper part of this stage-plate there are
two holes for the reception of the forceps and side reflector. To the
under part of the stage, the achromatic condensers, the diaphragm-
plate, and polarising-prism may all be adapted as in the larger instru-
ments ; and for convenience of package, the stage itself may b,e turned
on a pivot, so as to be at right angles with the tube. The mirror is
mounted in the usual manner, and is made to slide up or down the
tube on which it is supported. This is recommended to those whose
means are limited, in consequence of the low price ; it being of a form
which may be added to from time to time, according to the wants of
the employer : thus, for instance, a vertical stand, with two eye-pieces,
exclusive of the object-glasses, may be procured without the stage
movements or the fine adjustment, at the small cost of 41. 10s. ; and
as both the stage and the compound body are of the same size as in the
more perfect instrument, the fine adjustment and the stage movement
may be added to the former at any time, and render it as complete.

A smaller compound achromatic microscope, fig. 37, is particularly
adapted for students : this is packed into a neat mahogany case, com-

THE STUDENT'S MICROSCOPE.

51

plete, with lenses, for the small sum of 51. 15s., by Mr. Baker, 244 Hoi-
born, who likewise furnishes all the requisites for microscopical pur-
poses, with well-selected specimens of mounted objects, at a small cost.
In Messrs. Powell and Lealand's microscope, the body moves on a
triangular bar, having a bearing of three inches, which renders it very
steady. The coarse and fine adjustment are both carefully attended to ;
and the stage is large and convenient. On the same bar that the body
rests, moves the " achromatic condenser;" by such an arrangement it is
certain to move in the same line with the body, which is very essential.

fig. ST. Baker's Student's Microscope.

Their object-glasses are of the most faultless construction, and are pre-
ferred for pathological investigations. Messrs. Smith and Beck, Mr.
Salmon, and other makers, supply cheap and useful forms of instru-
ments. Mr. Warrington has had constructed a very portable and eco-
nomical microscope, adapted either for the examination of objects in a
vivarium, or for dissecting purposes. It is packed in a neat case ; and

52 THE MICROSCOPE.

being of light weight, can be carried in the coat-pocket : the cost com-
plete is 21. 10s.

The following useful remarks on the microscope are extracted
from the Juries' Reports of the Great Exhibition, 1851 : " The powers
varying from one-inch to a quarter-inch focus, inclusive, are by far the
most generally useful in the whole range of microscopic combinations,
especially for educational purposes. It must be remarked, that the
angle of aperture of the combinations should not be extended to its
utmost possible limit when destined for the general purposes of natural
history or anatomical investigation. Combinations of high power, and
extremely extended angle of aperture, are excellent in developing one
class of test objects, viz. minute lines or dots on plane surfaces, and
admirably demonstrate the high perfection to which such glasses are
capable of being carried by scientific opticians; but such combinations,
with a less angle of aperture and more penetrating power, are far more
generally useful and valuable to the minute anatomist and the naturalist.
In regard to the brass-work, the qualities especially requisite in the
stand of a microscope are simplicity of construction, portability, com-
bined with sufficient weight to ensure safety and steadiness, with smooth-
ness and accuracy of action in all the working parts, and such a con-
struction as to distribute any tremor that may be communicated to the
instrument equally over its body, stage, and other working parts."

CHAPTER III.

PRELIMINARY DIRECTIONS — ILLUMINATION ACCESSORY APPARATUS —

ACHROMATIC ILLUMINATOR GILLETT'S CONDENSER — PREPARING AND

MOUNTING OBJECTS POLARISED LIGHT BINOCULAR INSTRUMENT

PHOTOGRAPHIC DRAWING, ETC.

CAVING selected an apartment with a northern
aspect, and, if possible, with only one win-
dow, 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 ob-
servation. A large bell-glass will be found
of great service in keeping dust from a mi-
croscope when set up for use. In winter it
will be proper to slightly warm the instru-
ment before it is used, otherwise the per-
spiration from the eye will be perpetually
condensing on the eye-glass, thus greatly
impeding vision. Always begin the ex-
amination of your object with the lowest
power you have, unless it be very minute.

As a general rule, large objects require low powers, and small ones
high powers : low powers show the whole or general view of an object,
the high ones only its parts in succession 5 and as the power in-
creases, so does the difficulty of finding the object and adjusting the
focus. 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 : recol-
lect 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 your glasses :
a small piece of dried elder-pith is preferred by some for the purpose.

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, moreover, if you see a round disc of light, at least

54 THE MICKOSCOPE.

when the object is not on the slider-holder : if you do not, it is a sign
thatr something is wrong ; perhaps the body is not placed directly before
the aperture of the slider-holder, or may not be truly directed towards
the light. Use the least amount of light possible, if you work for any
length of 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.
Look at the object with both eyes open, and 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 be reflected from the eye-glass,
you are looking upon the eye-glass instead of through it. Take care
also that the mirror is properly arranged.

Sir David Brewster's excellent directions for viewing objects should
be made familiar to the microscopist. He observes :

" First. Protect the eye from all surrounding light, letting 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 small diaphragm : at night, from the con-
centrated light of a sperm-oil or gas lamp, having a faint blue-tinted
chimney-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 con-
densers beneath the stage."

Mr. James Smith contributed the subjoined practical observations
on the same subject to the Microscopical Transactions: Much of the

ILLUMINATING THE OBJECT. 55

beauty of the objects seen depends upon the management of the light
that is thrown upon or behind them, which can only be fully mastered
by practice. It may be remarked, however, as a general rule, that in
viewing those which are transparent, the plane mirror is most suitable
for bright daylight ; the concave for a lamp or candle, which should
have the bull's-eye lens, when that is used, so close to it that the rays
may fall nearly parallel on the mirror.

If the bull's-eye lens is not used, the illuminating body should not
be more than five or six inches from the mirror. The latter is seldom
required to be more than three inches from the object, the details of
which are best shown when the rays from the mirror fall upon it be-
fore crossing ; and the centre should be, especially by lamplight, in the
axis of the microscope. For obscure objects, seen by transmitted light,
and for outline, a full central illumination is commonly best ; but for
seeing delicate lines, like those on the scales of insects, it should be
made to fall obliquely, and in a direction at right angles to the lines
to be viewed.

The diaphragm is often of great use in modifying the light and
stopping such rays as would confuse the image (especially with low or
moderate powers) ; but many cases occur when the effects desired are
best produced by admitting the whole from the mirror. If an achro-
matic condenser is employed instead of the diaphragm, its axis should
correspond with that of the body ; and its glasses, when adjusted to
their right place, should show the image of the source of artificial light;
or by day, that of a cloud or window-bar in the field of the microscope,
while the object to be viewed is in focus. The most pleasing light for
objects in general is that reflected from a white cloud on a sunny day ;
but an Argand's lamp or wax candle, with the bull's-eye lens, is a good
substitute. A large proportion of opaque objects are seen perfectly
xyell (especially by daylight) with the side reflector, and the dark bore
as a background ; and for showing irregularities of surface, this lateral
light is sometimes the best ; but the more vertical illumination of the
Lieberkuhn is usually preferable ; the light thrown up to it from the
mirror below being, with good management, susceptible of much com*
mand and variety.

Mr. Ross very properly remarks, that the manner in which an ob-
ject is lighted is second in importance only to the excellence of the
glass through which it is seen. In investigating auy 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

56 THE MICROSCOPE.

all possible directions. Every change will probably develop 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; which last has a refractive power nearly equal to that of glass.
If the object be delicate vegetable tissue, it will be, in some re-
spects, rendered more visible by gentle heating or scorching before a
clear fire, between two plates of glass. In this way the spiral vessels
of asparagus and other similar vegetables may be beautifully displayed.
Dyeing the objects in tincture of iodine, or some one of the dye-woods,
will, in some cases, answer this purpose better.

But the principal question in regard to illumination is the mag-
nitude of the illuminating pencil, particularly in reference to trans-
parent objects. Generally speaking, the illuminating pencil should be
as large as can be received by the lens, and no larger. Any light be-
yond this produces indistinctness and glare. The superfluous light
from the mirror may be cut off by a screen, having various-sized aper-
tures placed below the stage.

The DiapJiragm, fig. 38, 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 different sizes ; this plate is of a circular

figure, and is made to revolve
upon another plate by a cen-
tral pin or axis ; this last
plate is also provided with
a hole as large as the largest
in the diaphragm-plate, and
corresponds in situation to
the axi» of the compound
body. To ascertain when

either of the holes m the diaphragm-plate is in the centre, a bent
spring is fitted into the second: plate, and rubs against th« edge of
the diaphragm-plate, which is provided with notches. The space be-
tween the smallest and largest is great enough to use for the purpose
of shutting off all the light from the mirror.

A good mode of imitating artificially the light of a white cloud
opposite the sun has been proposed by Mr. Varley : he covers the sur-
face of the mirror under the stage with carbonate of soda, or any similar
material, and then concentrates the sun's light upon its surface by a
large condensing lens.

GILLETT'S ILLUMINATOR.

GILLETT S ILLUMINATOR, OR CONDENSER.

The advantages 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 constructed 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 any where 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. An elastic diaphragm,
or artificial pupil, as it might be called, was first proposed by Mr.
Brooke, which was shown to answer very well in a large model, and
produced a remarkable semblance of vital contractility ; but mechanical
difficulties interfered with its application, and the revolving diaphragm
in the instrument, now well known as Gillett's condenser, was substi-
tuted. It is represented in fig. 39 as manufactured by Mr. Ross, and
consists of an achromatic illuminating lens c, which is 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
which, at an angle of about
25°, is a circular rotating brass
plate a b, provided with a coni-
cal diaphragm, having a series
of circular apertures of differ-
ent sizes hg, each of which in
succession, as the diaphragm is
rotated, proportionally limits
the light transmitted through
the illuminating lens. The
circular plate in which the

fig. 39. Gillett's Condenser.

conical diaphragm is fixed is provided with a spring and catch ef, 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
illumination, allowing only the passage of a hollow cone of light to illu-

58 THE MICROSCOPE.

minate the object. The illuminator above described is placed in the
secondary stage, ii, which is situated below the general stage of the
microscope, and consists of a cylindrical tube having a rotatory motion,
also a rectangular adjustment, which is effected by means of two
screws, / m, one in front, and the other on the left side of its frame.
This tube receives and supports all the various illuminating and
polarising apparatus, and other auxiliaries which are placed under-
neath the object. The tube and its frame are affixed to a dovetailed
sliding bar, k, 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 adjustment 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 re-
gulates the sliding bar, bring the illuminating lens to a level with the
upper surface of the object-stage ; then move the arm which holds the
microscope body to the right until it meets the stop, whereby its cen-
tral 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, a, 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 adjust-
ment now under consideration, namely, the centering of the compound
body of the microscope with the illuminating apparatus of whatever
description.* The centering-glass, being thus affixed to the top of the

* 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,
aud the images of the apertures at the lenses and in the diaphragms contained in the

GILLETT'S ILLUMINATOR. 59

eye-piece, «, is then to be adjusted by its slicling-tube (without dis-
turbing the microscope-tube) until the images of the diaphragms in
the object-glass and centering lens are distinctly seen. The illumi-
nator 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 recognise 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 be-
come deranged.

The second process is to ascertain that the fittest concentration of
light is obtained. For this purpose the mirror should now be so in-
clined that the image of some intercepting distant object, such as a
house-top, or chimney, tree, window-frame, or (if lamp-light be em-
ployed) 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 second-
ary 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 ad-
justment being effected by the movement of the secondary stage alone,
the microscope tube remaining undisturbed, also the object on the ob-
ject-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 lamp; and the eye-piece and object-glass
suitable for examining the object may be employed, and the focus ad-
justed accordingly. The conical diaphragm with its various apertures
may now be rotated, until that quality of illumination is obtained

tube -which holds the illuminating combination, may all be in focus at the same time,
as with the same adjustment they may be brought sufficiently near in focus to recognise
their centricity.

CO THE MICROSCOPE.

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 illuminating condenser
and microscope body has not been deranged.

It has been stated that the image of a white cloud opposite the sun
is the best for illuminating transparent objects when viewed by trans-
mitted light. Mr. Gillett has successfully imitated this natural surface
by an apparatus consisting 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 em-
ployed 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 coin-
cident, and the enamel disc placed between them. The small hyper-
bolic reflector receives the light reflected from the large parobolic re-
flector, and concentrates the rays on the small enamel disc. The sur-
face 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.

BOSS'S ACHROMATIC ILLUMINATOR, OR CONDENSER.

When employing this apparatus, the general practice is to insert in
it, as an illuminating lens, the object-glass next lowest in power to
that which is intended to be attached to the microscope ; so that when
the one-eighth is used on the microscope, the one-fourth is screwed
into the illuminating apparatus ; and so, in like manner, with the rest.
But when economy is not regarded, a system of three achromatic com-
binations is supplied, adapted for the illumination of the whole range
of the powers of the microscope : the whole system being employed for
the highest powers ; two of such combinations with the middle powers ;
and the largest combination by itself for the lowest powers. This illu-
mination is not required for objects when viewed with object-glasses
transmitting small pencils of rays, or whose angular aperture is less
than thirty degrees; that is, where the object-glass is of greater focal
length than half an inch.

The apparatus is fixed to the under side of the stage of the micro-
scope, in the place of the diaphragm-plate; and before fixing, the proper
object-glass, as an illuminating lens, must be screwed on to it. In
fig. 40, two tubes are seen sliding one within the other ; to the outer
one, 6, is attached a flat plate a, which slides underneath the stage,
and is adjusted for distance by the screwy,* at c the milled-head is

BOSS'S ACHROMATIC ILLUMINATOR. 61

connected to a pinion ; and .by means of a rack attached, the inner
tube, carrying the achromatic combination d, is raised or lowered : the
upper part of the outer tube is larger than
that where the milled-head is seen, for the ^M

purpose of allowing the milled ridge of y

the achromatic to pass up and down. For
the i or ^ inch, the combination d is used ;
and for the higher power, ^ or -jL, the
second e is slipped over d. Place the
object to be viewed upon the stage of
the microscope ; and when the instru-
ment is not directed at once to the source
of light, such as the flame of a lamp,
or a white cloud, arrange the reflector
(having the plane mirror upwards) so
as to throw the light up the tube of

the apparatus; which may be ascertained by turning aside the mi-
croscope tube, and observing when the spot of light appears on the
object placed on the stage. The microscope-tube is then to be re-
placed as nearly over the spot of light as possible, and vision of the
object obtained, disregarding the precise quality of the light. Then
proceed for perfect adjustment as directed in using Gillett's con-
denser.

Slight obliquity of the illumination subdues the glare attendant
upon perfectly central and full illumination by lamp-light; and this
obliquity may be obtained by slightly altering the position of the mir-
ror; or if the mirror is not employed, but light is obtained by pointing
the microscope-tube directly to the lamp, then the obliquity required
may be obtained by a small variation of the inclination of the micro-
scope. It is essential that the mirror and lamp-glass be free from dust
and soot.

F. H. Wenham, Esq., (Micros. Trans. 1851) proposed a new illu-
minator, for the purpose 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 bring-
ing 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
ingenious metallic reflector, by which the condensation of lateral light
may be effected.

62

THE MICROSCOPE.

"The apparatus is shown in section in fig. 41 : a a is a parabolic

reflector, of a tenth of an
inch focus, with a po-
lished silver surface, hav-
ing the apex so far cut
away as to bring the focal
point at such a distance
above the top of the ap-
paratus (which is closed
with a screw -cap when
not in use) as may allow
the rays to pass through
the thickest glass com-
monly used for mounting
objects upon before com-
ing to a focus.

At the base of the parabola is placed a disc of thin glass b b, in
the centre of which is cemented a dark well, with a flange equal in dia-
meter 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 adjustments 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 aper-
tures e e, placed diametrically, for the purpose of obtaining two pencils
of oblique light in opposite directions. The effects of the chromatic
and spherical aberrations, in the shape of fog and colour about the ob-
jects, caused by the glass slides upon which they are mounted, fre-
quently 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 illumination is procured ; and as
the silver reflector is now closed with glass, it is hermetically sealed,
and permanently protected from dust and damp, and will therefore re-
tain its polish. The light most suitable for this method of illumination
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 ob-

THE PARABOLIC REFLECTOR. G3

ject 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 the navicula, the circular diaphragm should be slid on the extremity
of the apparatus, and revolved till the two pencils of light are thrown
most suitably across the object.

All objects, either transparent or opaque, with the exception of
white, absorb some of the rays of light, and are rendered visible by
that portion which they radiate : a predomirience of those rays, either
primary or compound, of which ordinary white light is composed, is
the cause of their various colours, the intensity of which depends upon
the quantity radiated ; therefore any object at all capable of radiating
light will be well shown by this mode of illumination, and, if the light
thrown on them is achromatic, in all their natural colours.

In viewing objects by light transmitted directly through them,
we have two sets of rays entering the eye — viz. those emanating from
the source of light, and those radiating from the object; the imperfec-
tions produced by the former passing through and around the object
mingling with the latter, and preventing them from producing their
proper effect."

As the method of illuminating microscopic objects by means of a
large angular pencil of light, having the central rays obscured, is of
recent introduction, we shall mention a few instances where transparent
objects are shown, under similar circumstances, with perfect or im-
proved definition.

The lateral mode of illumination will be found to possess peculiar
advantages in the examination of test-objects and the internal me-
chanism of infusoria. The markings on most of the test-objects are
either depressions or projections by direct light : all parts of an object
are illuminated with equal intensity, and delicate colours are in great
part destroyed, consequently there is a want of contrast. The effect of
an angular pencil of rays of 175°, with the central ones stopped, is,
that there is a greater relative amount of light thrown on these pro-
minences, as they intercept the largest portion of the marginal rays
near the apex of the reflector, leaving the base of the prominence
in comparative shadow, consequently the markings we wish to see are
the most strongly lighted. The different organs in the interior of an
animalcule may be much of the same colour and transparency, and yet
possess a different refraction, according to their density. Direct light
will pass through these transparent membranes in straight lines with-
out being affected by their various refractive powers. The effect of
lateral or oblique light on such tissues is, that the rays are more re-

64 THE MICROSCOPE.

fracted according to their inclination, and proportionate to the various
densities of the medium, the most refractive structure transmitting the
greatest quantity of light, and being in consequence the most illumi-
nated; and this reason is somewhat confirmed by the circumstance
of lateral illumination showing the structure of some objects which,
from slight variation in density, were invisible, except by the use of
polarised light. Mr. Shadbolt has since modified this reflector, which
he denominates " a sphero-annular condenser :" it has superior reflect-
ing arrangments, with less liability of derangement, and is constructed
of a solid cylinder of glass terminating above in a solid cone, the sur-
face of which has the form of a parabola, and replaces the silver reflect-
ing surface.

It is due to Mr. Lister to mention that in his paper on the " Achro-
matic Object-Glass," published in the 120th vol. of the Transactions of
the Royal Society, he makes mention " of some objects being better seen
when the central rays are obscured." This observation has been carried
out in many ways. The Rev. Mr. Reade's " back-ground illuminator" is
one in which the light is thrown under the object in such a direction
as to avoid or pass by the aperture of the object-glass, and give a black
field. The structure under view, if large, must have sufficient trans-
parency to allow the light to enter into its substance, and to be diffused
or radiated therefrom in all directions. This illuminator is very suit-
able for objects requiring a low power to view them.

Condensing lenses are used either for opaque objects, or to condense
the light upon the mirror attached to the microscope. Two lenses, as
represented in fig. 42, are sometimes used. A bull's-eye, or plano-convex
lens, of three inches focal length, is best suited for the larger ; and the
mode of employing the two condensers upon an object placed on the
stage of the microscope at a is here shown. The bull's-eye lens c slides
up and down a brass rod, screwed into a steady foot ; 6, the smaller lens,
working on a joint, or it may be fixed into the stage of the microscope,
through which the light is finally concentrated 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 ^ 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 from this
surface are reflected down on the object by a plane mirror attached to
the object-glass, and on a level with the outer surface. By these means
the structure of the scale of the Podura, and the different characters of
its inner and outer surfaces, are rendered distinctly visible. Silver

THE LIEBERKUHN CONDENSER.

specula, known as Lieberkuhn's, are much employed, and preferred by
some microscopists. The Lieberkuhn is concave, and attached to the

fig. 42.

object-glasses, from the two-inch to the half-inch, in the manner repre-
sented at fig. 43, where a exhibits the lower part of the compound
body; b the object-glass, over which is slid a tube and the Lieber-
kuhn c attached to it ; the rays of light re-
flected 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 forceps/; and when too small to fill up
the entire field of view, or when transparent,
it is necessary 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 fig. 43.

66 THE MICROSCOPE,

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.

Mr. S. Highley's achromatic gas-lamp, fig. 44, is now much in use,
for condensing the light on the mirror. Gas, as a source of light,
presents great advantages over oil and spirit, on account of clean-
liness, being ever ready for use, and affording a perfect control over

fig. 44.

the flame ; but when the ordinary gas-lamps are used for the purpose
of illuminating the field of the microscope, a yellow glaring light is
given, alike injurious to the eye and the definition of the object under
examination. To correct these evils this lamp was arranged, which 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 FORCEPS, ETC. 67

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 j 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. G 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, con-
centrates 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 ; 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 G, and bringing the shade M
over the burner, it may be used as a reading-lamp. A retort ring sr
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.

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. 45, and consists of a piece of steel

fig. 45.

wire, about three inches long, which slides through a small tube, con-
nected 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 object, may be separated

68

THE MICROSCOPE.

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 for taking up Animalcules. — These are tubes of glass,
fig. 46, about nine inches in length, open at both ends, and from one-

fig. 46.

fig. 47.

eighth to one-fourth of an inch in diameter. The ends should be nicely
rounded off in the flame of a blow-pipe ; some of them may be straight,
whilst others should be drawn out to a fine point, and made of either
of the shapes represented at cde. Mr. Varley describes the method of
using them in volume forty-eighth of the Transactions of the Society of
Arts. Supposing the animalcules that are about to be examined to be
contained in a phial or glass jar, as in fig. 47, having observed where
they are most numerous, — either with the naked eye, if they are large,
or with a pocket-magnifier, if they are small, — 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

ON COLLECTING ANIMALCULES. 69

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 may be
withdrawn from the phial ; and as the tube is almost certain to con-
tain much more fluid than is requisite, the entire quantity must be
dropped into a watch-glass, which spreads it, and the insect may be
again caught by putting the tube over it, when a small quantity of
fluid is sure to run in by capillary attraction. This small quantity is
to be placed upon the tablet ; but should there be still too much for
the tablet, if it be touched with the tube again, it will be diminished
accordingly. If we wish to place several individuals together on the
tablet, it is necessary that each should be taken up with the smallest
amount of water : to effect this, Mr. Varley suggests that the tube
should be emptied on a slip of glass, in separate drops ; and with one
of the capillary tubes but little larger than enough to catch them, they
may be lifted out one by one, and be placed on the tablet. Generally
speaking, it is necessary to add a small quantity of vegetable matter
to animalcules, to keep them alive ; and as many species of them are
found on confervse and duck-weed, some instrument is required to take
small portions of these plants out of the jar in which they are growing.
For this purpose Mr. Varley uses the forceps fig. 48. These are made

fig. 48.

of brass ; the points are a little curved, to keep them accurately toge-
ther, and the blades are provided with a hole and steadying-pin. This
instrument serves for transferring small portions of vegetable matter,
or for picking up minute objects.

Collecting Animcdddes. — For collecting the living water animalcules,
the cambric-muslin net, made similar to a landing-net, fig. 49, will be
found very useful ; this should be secured to a brass-ring a, and fitted
into a socket &, by which it can be attached to the end of a walking-
stick, or, when not in use, the socket may be earned in the pocket j and
the net, by contracting the diameter of the ring (which the construction

70

THE MICROSCOPE.

admits of) can be put inside of the hat. Fig. 50, is a box containing six
bottles for holding the animalcules when caught. These bottles should

fig. 49.

fig. 50.

be filled with the water when you collect the insects, and the larger
insects put by themselves. When collecting from different localities,
take care not to mix the insects from one
brook with those from another, otherwise
serious conflicts may take place, and on
reaching home you will find the greater
part of your stock either dead or dying.
Always separate the various sizes and races
as speedily as possible. This can be done
most 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 spe-
cies to its separate "fish-pond." The best
localities in the neighbourhood of London
for collecting are Epping Forest, Hamp-
stead Heath, and Blackheath.

Mr. Williamson has a very cheap and
simple contrivance for converting the end
of a walking-stick or umbrella into what
he terms a "collecting-stick." In fig. 51, a
represents a piece of whalebone, about 1 8
inches long, bent round the end of the stick

or umbrella, 6, 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

fig. 51.

ANIMALCULE CAGE.

71

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 placing it for a short time near the fire.

Animalcule Cage. — Mr. Yarley, in the year 1831, greatly improved
the form of this instrument, and gave to it the name of capillary-tablet,
or cage. He made a channel all round the object-plate, so that the
fluid and the animalcules in it were retained at the top of the object-
plate by capillary attraction ; and they then bear turning about in all
directions without leaving the top, provided the cage be not suddenly
shaken. The cover is made to slide down upon 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 two opposite sides
for convenience of package. One of these instruments is seen in ele-
vation and in section in fig. 52. A B, in both figures, is the 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.

r i

fig. 52.

fig. 53.

Many microscopists make great use of the compressorium, an in-
strument in which an object may be submitted to graduated pressure
between two plates of glass, the parallelism of which is perfectly main-
tained. The class of investigations in which the eompressorium is
valuable, is that in which such structures as the minute ovum need be
closely scrutinised, without any further change in their shape than
may render their contents more distinctly visible. For such purposes

72 THE MICROSCOPE.

a steady hand and a well-made animalcule cage, such as we have pre-
viously described, will answer the purpose sufficiently.

Smith and Beck's troughs for chara and polyps, a sectional view of
which is shown at fig. 53, are 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 times, when used to view chara, the dia-
gonal 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 should be
in a position nearly horizontal. A useful trough, described by Mr.
Varley, in the Transactions of the Society of Arts, consists of a bottom-
plate of stout glass, upon which is cemented with pitch and bees'-wax
a thin one for the top ; slips of glass between it and the bottom-plate
forming the sides. The top-plate is not so broad as the bottom, in
order that a slip of chara may be more readily placed in the trough,
as it can be first laid upon the bottom-plate, and then gradually be slid
down between it arid the other. In order to render the trough more
manageable, it can be cemented to a larger bottom-plate by Canada
balsam; but it will be found far more advantageous if the bottom-
plate itself be large and broad, and the cover cemented to that, and not
to another plate, as two extra surfaces will then be dispensed with.

Dissecting Knives, &c. — Knives and needles of various kinds and
sizes are required for microscopic dissection : the best for the purpose
are represented in fig. 54, 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. Three of the most convenient are shown
in fig. 55 ; which are made expressly by Mr. Weedon for the use of
the microscopist.

In the preparation of objects, no mieroscopist was ever more suc-
cessful than Swammerdam : His chief art seems to have been in con-
structing very fine scissors, and giving them an extreme sharpness ;
these he made use of to cut very minute objects, because they dissected
them equally, whereas knives, if ever so fine and sharp, are apt to dis-
order delicate substances. His knives, lancets, and styles were so fine,
that he could not see to sharpen them without a magnifying glass.

DISSECTING KNIVES, ETC.

73

The mode adopted for breaking up tissues into very small pieces is
usually conducted as represented at fig. 56, with a pair of the small

fig. 54.

needles held firmly between the fore-finger and thumb. The structure
must be teased out ; an operation which requires care and perseverance,

fig. 55.

as most of the animal tissues are very difficult of separation, especially
when it is wished to examine them under high powers. All substances

fig. 56.

should be carefully separated from dust and other impurities which
would render their structure indistinct, or confusing. With very deli-
cate membranes, and with those of the nervous system of the smaller
animals, insects, &c.,-it becomes necessary that the investigation should

74

THE MICROSCOPE.

be carried on under water, or in fluid of some sort, the object being
contained in a glass case, and having a very strong light thrown down
upon it by the aid of the condensing lens, as represented in fig. 57. A
certain amount of change of structure must be expected and allowed
for j nearly all will imbibe some portion of the fluid. The cells or
troughs are generally made of pieces of stout plate-glass, their edges
being accurately ground, and cemented together with marine-glue or
sealing-wax : the size of the trpugh should be about three inches square
and one inch deep.

fig. 57.

If desirable to dissect under the microscope itself, the instrument
must be brought over the trough, and the subject adjusted to the
focus of an inch or a two-inch magnifier, as it is very difficult to em-
ploy a much higher power. The simple microscope (p. 27, fig. 23)
is that generally employed for the purpose. If the object be a por-
tion of an injected animal, it is better to pin it out on a piece of cork
covered with white wax, and then immerse it in the water-trough ; the
more delicate the structure, the sooner after death should it be ex-
amined, especially in animals. With most vegetable structures, the dis-
section should be carried on under water. The separation of the woody
and vascular tissues, and the spiral vessels, is only effected by macera-
tion and tearing with the fine needles under water.

VALENTIN'S DISSECTING KNIFE. 75

TJie improved Valentin's Knife. — For making fine sections of large
substances, or those soft in structure, such as the liver, spleen, and
kidney, the double-bladed knife, the invention of Professor Valentin,
may be used with advantage. An improved construction of this knife
by Professor Quekett is represented in fig. 58. It consists of two
blades, one of which is prolonged by a flat piece of steel to form a
handle, and has two pieces of wood riveted to it for the purpose of its

fig. 58.

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 slits cut out in them exactly opposite to each
other, up and down which slit 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 together as to touch. One head of this rivet, being
smaller than the hole in the end of the slit, can be drawn 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, 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, so 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 regulated by sliding up or 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, and
the part cut will be found between the blades, from which it may be
separated either by opening 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 dissection : of these the most useful

76

THE MICROSCOPE.

are shown in fig. 59. They are either straight or curved ; of the first
kind, two pairs will be required, one having the extremities broad, and
the other sharp-pointed ; and if large dissections be undertaken, a still
stronger pair, with the extremities broad, and made rough like a file,
will also be necessary. In dissecting under the microscope, the curved-
pointed pair shown at f will be found most convenient. In all of these

•.59.

instruments the points should fit accurately together : sometimes those
that are very sharp are apt to cross ; this 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.

Circular Disc. — For the purpose of cutting glass covers, or making
shallow cells with japanners' gold-size for mounting objects, fig. 60

fig. 60.

will be found useful ; it is made of two circular wheels of wood, these
being let into a solid block of wood, and secured there by central

ON MOUNTING OBJECTS. 77

screws. A handle of wood is fixed into the upper part of one, for the
purpose of turning it round, the motion being communicated to the
other by an endless band of catgut running in the grooved edge of
each. On the upper surface of the wheel, under the right hand, are
fixed, by means of screws, two strips of brass, which serve as springs
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 microscopist 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 convenient and
economical : the mode of using it may be learned in any glazier's shop.
On mounting and preserving Objects. — Microscopic objects are
usually mounted on slips of glass three inches by one inch, either dry
or immersed in some fluid. The minute structures, such as the tissues
of animals, parts of insects, vessels of plants, &c., must be preserved in
thin cells, made as directed above, with a small amount of fluid.*
Clean the glass with a weak solution of ammonia or potash from all
grease, and wipe it dry with a piece of chamois leather or cotton velvet ;
cloth generally leaves behind it small filaments, which are always un-
sightly when seen near the object. Let fall a drop of the preserving
fluid or Canada balsam on the centre of the glass; then place the object
in it with a small pair of forceps, and spread it out very carefully with the
point of one of your fine needles. Select a thin glass cover, previously

fig. 61.

cleaned, touch its edges with cement, and let it fall gently and gra-
dually down upon the object, as represented in fig. 61 ; press it lightly

* Cells for microscopic purposes may be purchased of Mr. Bender, 6 Brunswick
Place, City Road, or of Mr. Baker, 244 High Hoiborn.

78

THE MICROSCOPE.

to exclude any excess of fluid, which remove with strips of blotting-
paper, being careful to do all this with a light hand, that small bubbles
of air may not insinuate themselves to replace any lost fluid: air-
bubbles are at all times unsightly, and liable to spoil an object when
allowed to remain. Lastly, cement the edges of the cover to the bottom
glass with japanners' gold-size, or sealing-wax varnish, carefully
drawn around the edges with a camels'-hair pencil. Mr. John
Gorham has lately proposed the use of a " Brass cementing
Pencil,'"1 fig. 62. It is a brass tube, six inches long, with a
conical bore, having a lid to screw on. A small portion of the
cement crumbled into fragments is shot into the tube, which is
then ready for use. In using this instrument, the extremity is
gently heated in the flame of a spirit-lamp; and when the cement
begins to ooze out, holding the pencil like a pen, the point is
traced along each side of the cover, leaving a line of cement in
the angle. It is thus laid on much easier than with ^a brush,
and after a little manipulation, it will be found that the point
will suffice to polish off, instead of using the flattened wire.
The cement recommended by Mr. Quekett for cementing deep
cells is made by melting together two ounces of black resin,
one ounce of bees'-wax, and one of vermilion. Mr. Hett pre-
fers dark-coloured and old japanners' gold-size for securing the
cells of his beautifully delicate injected preparations.* Mr.
Brooke uses Brunswick black, to which has been previously
fig' ' added a little India-rubber dissolved in mineral naphtha, to
prevent its cracking when dry.

Mr. Gorham's drawing and description of a " holder" is similar to

fig. 63.

one long used by the author, fig. 63, for the purpose of pressing toge-
ther objects mounted in the dry way, and during the drying process,

* For methods of making various good cements, consult Ure's Dictionary of Arts
and Manufactures.

ON MOUNTING OBJECTS.

79

after maceration, which facilitates removal of the object from time to
time for the purpose of examining it. It is made of two stout strips
of whalebone three or four inches in length, held together at each end
with square pieces of brass ; these may be moved at pleasure towards
the centre, and thus made to exert considerable pressure upon the
pieces of glass and the object, which are placed crossways between the
strips of whalebone.

For the purpose of more effectually removing bubbles of air from
the cells before cementing them down, the small air-pump, fig. 64,
will be found serviceable. This can be purchased of Baker, Holborn,

nTmniirrnrrmT

fig. 64.

at a moderate price. The mode of using it, is simply to place the
object, after having warmed it and covered it with the thin glass, under
the bell-glass c ; then, by drawing up and pushing down the handle B,
pump out the air until the whole of the small bubbles are withdrawn
from around the object to be secured and preserved. By turning the
small screw at D, you will let in sufficient air to remove the bell-glass ;
or allow your object to remain under it for several hours until the
cement around the edge of the glass-cover becomes perfectly dried and
secure, when exposure to the external air will no longer affect it. It
will be also found useful in withdrawing the air from the cells of woods
or limbs of insects. The pump itself, A, when unscrewed, can be used
as an injecting-syringe for fine anatomical injections.

80 THE MICROSCOPE.

Mr. Thomas Boys, in giving directions for mounting objects in
Canada balsam, says, the first thing to be considered is the apparatus
required.

1st. A small single-wick oil-lamp, having a glass chimney about
four inches long ; the flame to be about the size of that in a hand-
lantern : a spirit lamp will do even better.

2d. Slips of glass of required size, and small pieces of thin glass to
cover the object, all well cleaned.

3d. A pair of nippers to hold the glass-slips.

4th. A pointed iron-piercer in a wooden handle.

5th. A bottle containing the clearest Canada balsam, diluted with
the best spirits of turpentine to a consistency allowing it to drop
readily from one end of the iron-piercer, or Mr. Gorham's cementing-
pencil. The preceding articles being spread before you ready for use,
and the object to be displayed well examined for choice of position,
and cleaned if necessary, fix the glass-slip in the nippers, dip the
piercer into the balsam, and withdraw a full-sized drop to place upon
the slide. The centre of the slide should now be rested across the
chimney of the lamp until the balsam begins to spread, when it must
be immediately withdrawn. The object is then to be placed on this
balsam, and at once covered with a second drop, applied in the same
way as the first ; in this state the slide should remain (covered to
exclude the dust) for two or three minutes, that the balsam may have
time to penetrate ; the thin glass is then to be taken up between the
finger and thumb, and placed gently upon the balsam covering the
object. The slide being now held by the nippers at one end, place
the other extremity over the lamp-chimney, so that the heat may be
gradually extended towards the object. The proof of its having done
so sufficiently will be that the balsam flows to the edge of the thin
glass, taking with it all air-bubbles from that part nearest the heat.
The slide is now to be turned, the heated end being placed in the nip-
pers, and the process repeated. The slide should remain flat till nearly
cool, when pressure should be made with a small piece of wood perpen-
dicularly on the upper glass ; this will expel all superfluous balsam;
and with it all extraneous matter. Should any air-bubbles remain,
they generally disappear in a few days. If the balsam requires harden-
ing, place the slide on the mantel-piece, the gentle heat from which
will prove sufficient.

Mr. Deane recommends a composition of gelatine for mounting
dry or moist animal or vegetable structures in place of Canada balsam ;
his formula for which is as follows : " Take of White's patent size,

ON MOUNTING OBJECTS, 81

6 ounces by weight ; honey 9 ounces by weight j add a little spirits of
wine and a few drops of creosote ; mix and filter whilst hot, to render
perfectly clear. Or take of pure glycerine, 4 fluid ounces ; distilled
water, 2 fluid ounces ; gelatine, 1 ounce by weight ; dissolve the gela-
tine in the water made hot, then add the glycerine and mix with care ;
this need not be filtered.

Fresh animal or vegetable structures containing their natural
juices require little or no preparation before mounting in this sub-
stance. Those contained in water, as the desmidiese, Crustacea, &c.
may, when taken out of their native element, be placed on a proper
slip of glass previously warmed, the superfluous water removed with
blotting-paper, and then mounted at once by dropping a little warm
medium upon them and covering with thin glass. Animalcules
mounted in this way do not appear to alter either in colour or di-
mensions. The latter may be accounted for in this way, viz. that
the contraction of the medium is entirely in thickness, and the pres-
sure of the cover prevents any alteration taking place in the object
laterally.

It is probable that some animalcules may be better shown if some
moisture be allowed to remain in the medium, the evaporation from
which may be stopped at any stage by filling round the edge of the
cover with some gold-size varnish, or even boiled linseed-oil.

For many delicate objects this has a great advantage over Canada
balsam, in not possessing the high refractive power of that substance ;
and the minute hairs and other parts of insects, that are quite oblite-
rated with the balsam, are beautifully shown in this medium."

Glycerine was introduced by Mr. Warington, as a preservative
fluid for mounting organic substances in. The method adopted by
him in the employment of glycerine, is simply to mount the object in
the manner it is usually performed when spirit of wine or creosote-
water is used as a medium, and having covered the immersed object
with the thin glass, and removed all excess of liquid, to cement the
margin with a coating of shell-lac varnish ; the one usually employed
consists of the ordinary black sealing-wax dissolved in rectified spirit
of wine. Care must be taken during this operation to maintain the
slider in a flat position, until the varnish has become dry from the eva-
poration of the spirit, and also until a sufficient number of coatings or
layers of the varnish have been applied to render the subject perfectly
secure, and prevent any escape of the fluid. Gold-size or copal dis-
solved in oil of lavender may be employed to effect the same purpose ;
and the second and third coatings may, with advantage, consist of

G

82 THE MICROSCOPE.

either of these, which yield a tough varnish above the lac, which is
otherwise liable to become brittle.

The glycerine may be used in its concentrated form or treacly
state, or it may be diluted with distilled water to any required extent,
according to the object of the operator, and the subject to be mounted;
if there be extremely fine markings on the subject, it is better to add
about four or five times its volume of water, as otherwise the thick
fluid may prevent these from being so sharply defined as may be de-
sired. " I have," adds Mr. Warington, " a number of slides of Desmi-
diece, which have been mounted from four to ten months by this means,
and they have kept excellently. The glycerine may also be used with
the addition of a small portion of culinary salt, corrosive sublimate,
creosote, or spirit of wine, if considered desirable."

Castor-oil may be used as a medium for mounting crystals of salts
and other objects. The object required to be mounted is placed on
the slider in its dry state, or deposited wet and allowed to dry ; or if
in solution, a drop of the liquid is to be placed on the slip of glass, and
allowed to crystallise by spontaneous evaporation ; in the latter case
I prefer taking a drop of a warm saturated solution of the salt re-
quired, and when a good group of well-defined crystals has been ob-
tained, to break through the marginal ring of crystalline deposit with
a small point of wood, and carefully conduct off the uncrystallised
portion or mother-liquor to the extremity of the slide, at the same time
placing it in a vertical position to drain until it is dry. A small quan-
tity of castor-oil is to be next carefully dropped on the subject, and
guided over the field with the point of a needle ; in this way it readily
displaces the air and occupies the most minute cavities. After a short
time the upper glass is to be placed on the surface, taking care to
lower it gradually so as to exclude the air ; if the field is too full of oil,
the excess may be removed by a small piece of bibulous paper ; and if, on
the contrary, sufficient oil has not been used, an additional portion can
be readily introduced by the capillary action between the glasses. I
mention these points of practical manipulation, because on them the
success of the operation may often depend, as it must be evident, that
in the first case the excess would prevent the cell from being properly
sealed by the varnish, and in the latter it would be drawn into the field,
and the whole operation spoiled. The shell-lac varnish is then to be
used as the cementing medium in the same way as has been described,
and with the same precautions. I may also observe, that this varnish
cannot be replaced by either of the others, as it is actually necessary
(and this should always be borne in mind) that there should exist no

ON MOUNTING OBJECTS. 83

affinity between the fluid in the cell and the varnish used to seal it
permanently. Hundreds of excellent objects have been lost from this
cause, and much valuable time and labour thrown away.

The reason why oil was selected by Mr. Warington for this pur-
pose arose from want of action on most crystalline salts, many of which
could not be preserved uninjured in any other medium. Castor-oil
was chosen in consequence of its not depositing a crystalline stearin
by reduction of temperature, as is the case with most oils, and even in
some specimens of this material ; it therefore requires to be carefully
examined in this respect before it is employed. In the same year I
used this medium as a mounting-fluid for minute fungi and pediculi
with complete success.

Mr. Goadby has succeeded in supplying to microscopists a ready,
cheap, and effectual means for mounting animal structures with the
greatest possible ease and security. The following are his formulae :

Take for No. 1 solution, bay salt, 4 oz. ; alum, 2 oz. ; corrosive
sublimate 2 grains ; boiling-water, 1 quart : mix. For No. 2 solu-
tion, 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 em-
ployed where great astringency is needed to give form and support to
very delicate structures. No. 2 is best adapted for permanent prepara-
tion ; but neither should be used in the preservation of animals con-
taining carbonate of lime (all the mollusca), as the alum becomes de-
composed, sulphate of lime is precipitated, and the preparation 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 cementing 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.

Professor Quekett's preservative fluid is made of creosote, 1J drs. ;
wood naphtha, 3 ounces; distilled water, 32 ounces; chalk, as much as

84

THE MICROSCOPE.

may be required to make the creosote and naphtha into a paste before
adding the water : let it stand by a day or two, then filter through white
blotting-paper. Add to this solution two small lumps of camphor, and
stand it by for a week. At the end of that time filter again through
clean blotting-paper. This is an excellent fluid for mounting all vege-
table substances in, and many of the more delicate animal tissues keep
very well in it ; it has also the advantage of not dissolving the cement
used in making the cells.

INJECTING MINUTE VESSELS.

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 supported between the two fingers. Fig. 65
represents the syringe : a is a cylindrical brass body, with a screw at
the top for the purpose of firmly screwing down the cover b, 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 convenience of cleaning; e is a
stop-cock, on the end of which another stop-cocky
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
intended 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 lesser 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 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
perfectly 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.

The size thus prepared may be coloured with any of the follow-
ing:

INJECTING SMALL VESSELS.

For Red.

„ Yellow.
White.

To a pint of size, add 2 oz. of Chinese vermilion.
„ „ 2^ oz. of chrome-yellow.

„ „ 3|- oz. of flake- white.

,. 6 oz. of fine blue smalts.

It is necessary to remember, that whatever colouring matter is em-
ployed must be very finely levigated before it is mixed with the injec-
tion. This is a matter of great importance ; 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 mixture 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 fur-
thest 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 pre-
vent 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 proportion to the size of the part
and the amount of its rigidity. Euysch (from whom the art of inject-
ing has been called the Ruyschian art) recommends a previous macera-
tion 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 shown in
fig. 66. It consists merely of
a water-bath, in which the cans
containing the injecting fluid
can be kept hot, and their con-
tents protected from dust by

fig. 66.

means of their covers. A small apparatus of this kind could be

TY J

THE MICROSCOPE,

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 for-
ceps, for seizing the vessel or stopping the escape of injection.
A small needle, fig. 67, will be found useful for passing the
thread round the vessel into which the injecting pipe is to
be inserted. Where the vessels are 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 the 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. 65, must then be placed in the largest
artery of the part, and made secure by tying. Put the stop-
cock f 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. Ruysch's method, according to Rigerius, was to em-
ploy melted tallow coloured with vermilion, to which in the summer a
little white wax was added. A material used by some is made of resin
and tallow : take of each two ounces, melted and strained through
linen, to which add three ounces of vermilion or finely ground indigo,
first well rubbed with eight ounces of turpentine varnish. Monro re-
commended coloured oil of turpentine for the small vessels; after the
use of which, he threw in the common coarse injection.

Professor Breschet frequently employed with success milk, isin-
glass, the alcholic solution of gum-lac, spirit varnish, and spirit of
turpentine; but he highly commends the colouring matter extracted
from Campeachy, Fernambone, or Sandal woods. He says : " The co-
louring matter of Campeachy wood easily dissolves in water and in

INJECTING SMALL VESSELS. 87

alcohol; it is so penetrating that it becomes rapidly spread through
the vascular net-works. The sole inconvenience of this kind of injec-
tion is, that it cannot be made to distend any except most delicate
vessels, and that its ready penetration does not admit of distinguishing
between arteries, veins, and lymphatics." He also recommends a solu-
tion 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, 1048
grains to two pints of water, is propelled into the vessels ; and after a
short time, in the same manner and in the same vessels, an aqueous
solution of acetate of lead, 2000 grains to a pint of water, is injected.
This is an excellent method, as the material is quite fluid, and the pre-
cipitation 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 decom-
position, 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 bright-
ness 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 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

88 THE MICROSCOPE.

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 examination by
the microscope, to wet the surface of a preparation 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 subsequent 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
preparations ; the infiltrated gelatine producing appearances of a puz-
zling 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 cor-
roder with very good results. But, probably, liquor potassa would have
answered this purpose better.

When size-injection is to be employed, coloured either with ver-
milion or the chromate of lead, the animal should be previously pre-
pared by bleeding, to empty the vessels ; for if they be filled with
coagulated blood, it is quite impossible to transmit even size, to say
nothing of the colouring matter. Hence the difficulty of procuring
good 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.
The large quantity of infiltrated blood — the invariable concomitant of
Mr. Goadby's process — characterises it from all other modes of inject-
ing, and is a distinctive feature of the preparations.

Still another plan has been suggested. It consists in adding a
quantity of sulphuric ether to the finely levigated colouring matter,
which is also first ground or mixed with linseed-oil, in the manner em-
ployed by painters. Upon this plan (as well as upon the last named)

INJECTING SMALL VESSELS. 89

some beautiful injections of the smallest capillaries are made ; but
sometimes it is a failure, owing to the too rapid evaporation of the
ether, and the clogging up of the vessels from the early deposition
of the solid colouring matter. Perhaps a solution of gum-mastic in
ether, coloured with fine vermilion, will answer the purpose better.
Prussian blue, mixed with an equal quantity of oxalic acid, finely pow-
dered and dissolved in water, which should be gradually added, and
afterwards the strong size solution, forms a very beautiful injection
for the capillaries of the lungs.

A foetus may be injected by the umbilical vein ; the head, by the
carotids ; the liver, mucous membrane of the intestines, &c. by the
portal vein ; an extremity by the principal artery, <fec.

In those cases in which we desire to examine the arrangement of
the different systems of vessels in the same tissue or animal, it becomes
necessary to use a distinct colouring matter for each system. M. Robin
recommends blue for the arteries, yellow for the veins, red for the
portal veins, and white for the bile ducts, or renal tubes.

Before portions of injected preparations are put up in the glass-
cells, they should be allowed to harden some time in the preservative
fluid they are intended to be kept in • clean sections can then be
made with a sharp knife, and slightly washed in fresh fluid. If it is
intended to preserve them in Canada balsam, it will be found advan-
tageous to spread them out to dry, and wet the surface with a drop of
turpentine before they are finally immersed in the balsam, : a thin glass
cover must be pressed down on the injection.

Many parts, after injection, require to be macerated in water, or
corroded by dilute muriatic acid, &c., in order to exhibit the ramifica-
tions of the small vessels. They should be very carefully handled, or
moved, in the macerating liquor, as the slightest force may break the
vessels. When corroded, the pulpy flesh is to be carefully washed away,
by placing it under a stream, of water, flowing very slowly, or by the
use of a syringe with water.

The lymphatics are now usually injected with coloured material
instead of quicksilver, as formerly. M. Rusconi employed a small
silver syringe, together with a kind of trocar, of which the canula is
formed from the quill of the wing-feather of the quail or partridge, —
the trocar being a tolerably large-sized surgical needle, the point having
three facets. When desirous of injecting the lymphatic system of a
lizard, tortoise, &c., he says : " I seize with a small pair of forceps the
mesentery, close to the vertebral column, where the reservoir of the
chyle is situated, and I introduce into it the point of the trocar ; I

THE MICROSCOPE.

then retain the quill, and withdraw the needle from the tube. I then
seize with the small forceps the quill, and introduce into it the small
extremity of the syringe ; and push the piston with a force always
decreasing."

By carefully following out these directions, any one, after a little
practice, will be enabled to succeed in making many useful and valuable
preparations. Injections are best viewed by the aid of the Leiberkuhn,
or under a condensed light with a one or two inch object-glass. For
Harting's process of injecting, see translations in the Edinburgh Monthly
Journal, 1852.

CHEMICAL RE-AGENTS.

Dr. Schacht recommends the following chemical re-agents and pre-
servative fluids for microscopic uses :

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-con-
tents and thickening layers. This solution acts best upon being heated.

4. Solution of Iodine (iodine one grain, iodide of potassium three
grains, distilled water one ounce) for the coloration of the cell-mem-
brane and of the cell-contents.

5. Concentrated Sulphuric Acid, employed chiefly in the examina-
tion 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 after-
wards 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 uni-
form throughout the whole 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.

CHEMICAL RE- AGENTS. 91

This solution, which was first proposed and employed by Professor
Schultz of Rostock, 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 ap-
plied. It is prepared by dissolving zinc in hydrochloric acid; the solu-
tion 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 means, also discovered by Professor Schultz, is as follows : —

The object, a thin section of wood for instance, is introduced, with
an equal bulk of chloride, or chlorate of potass, into a long and moder-
ately 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 removed from the flame,
and the action of the oxidising agent allowed to continue for two or
three minutes. The contents 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 boil-
ing 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.

Thin sections of vegetable tissue are warmed for half a minute, or
a minute, in a watch-glass : boiling is here unnecessary. The section
is taken out, and treated with water in a watch-glass.

9. Oil of Lemons, or any other essential oil, for the investigation of
pollen and spores.

10. A moderately strong solution of Muriate of Lime (one part
dry muriate of lime and three parts distilled water), for the preserva-
tion of microscopical preparations. This is applicable to most things,
even for the most delicate preparations, excepting starch. If it is de-
sired to keep a preparation, which is not to be retained permanently,
for some days, a small drop of the solution may be placed upon it, and
the whole put under a glass cover to keep it from dust.

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

92 THE MICROSCOPE.

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 then removed by means of a hair pencil,
and a drop of the diluted sulphuric acid added j 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 the
case of 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.

The preceding observations must be received with caution ; a very
useful warning having been recently given by Dr. Parkes in reference
to unusual crystalline forms he has found some of these re-agents to
assume, when in use, under the microscope. Without a knowledge of
this singular fact, and a perfect recognition of the crystalline forms,
errors in micro-chemical research cannot but occur. For example, if
a drop of liquor potassa3 be allowed to evaporate on a slip of glass,
crystals appear, chiefly 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.
These crystals do not arise from the presence of impurities ; at least
perfectly pure potash exhibits the same phenomenon.

He also states that the form of the crystals of acetate of potash
varies according to the strength of the acid out of which it crystallises ;
and when formed out of strong acid, very much resembles that of the
crystals of uric acid ; for, mixed up with other forms, long dagger-like
or lancet-shaped crystals are seen, which might well deceive us.

It may also be noticed in this place, that Majendie has lately 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 used without fear in micro-chemistry.

Preparation and Preservation of Algce, &c. — Mr. Half's excellent
directions for making preparations of the alga3 for the microscope are
as follows : " First to obtain a fluid which shall preserve the plant as
little altered as possible from its appearance when living ; and secondly,
to adopt the best means for preventing the escape of this fluid after
the object has been mounted in it. With respect to the first point,
the fluid which I have found to answer best is made in the following

PRESERVATION OF ALGJ3. 93

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 ; and there
is certainly less probability of confervoid filaments making their ap-
pearance in the preparations ; and there would seem to be nothing to
prevent 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.

Fluids containing a larger quantity of spirits of wine, and conse-
quently of creosote also, than the one of which I have given the for-
mula, produce a greater change in the appearance of the endochrome.

My method of making cells in which to mount preparations of
algae is as follows : some objects require very shallow, and others
somewhat deeper cells. The former may be made with a mixture of ja-
panners' 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 pos-
sible, 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 extremely 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 superfluous 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 j 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 object 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 j and, after care-
fully 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

94 THE MICROSCOPE.

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 in an open vessel ; a process which
renders it fit for use. In mounting the Desmidiece, 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 mois-
ture remains on their edge, it should be removed by blotting-paper, in
preference to any other mode. A thin description of glass is manufac-
tured expressly for the purpose of covering specimens when mounted.

The rarer species of Desmidiece are frequently scattered amongst
decayed vegetable matter, so that it is difficult to procure good speci-
mens 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 Desmidiece 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 can 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 occasionally peels off
the glass after the specimen has been mounted for some time. To obvi-
ate 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, com-
posed of japan varnish or gold-size.

* Mr. Penney, of 251 Tottenham Court Road, supplies an excellent varnish, called
" Coachmaker's Black,"

ON COLLECTING OBJECTS. 95

I have tried this method extensively, and have never found my
specimens spoiled by the varnish insinuating itself into the cell. This
process requires less time, and herein it possesses another great advan-
tage over the gold-size method ; for the second coat being applied within
half an hour, the risk of admitting air into the cell is much diminished.
To preserve the brush in a fit state, it should always be cleaned with
spirits of wine whenever it has been used.

The fluid which Mr. Topping uses for mounting consists of one
ounce of rectified spirit to five ounces of distilled water ; this he thinks
superior to any other combination. To preserve delicate colours, how-
ever, 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.

ON COLLECTING OBJECTS.

The following hints for collecting objects for microscopical exami-
nation, by G, Shadbolt, Esq., are exceedingly useful and valuable to
the microscopist.

" Having procured a good microscope, it is often a source of per-
plexity to the novice to obtain a sufficient supply of objects on which
to exercise his powers.

Rivers, brooks, springs, fountains, ponds, marshes, bogs, and rocks
by the sea-side, are all localities that may be expected to be produc-
tive ; some being more prolific than 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 collecting 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, 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 in-
tended ultimately for 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 linen or ca-
lico, two or three inches square, a piece of string, a slip or two of

96 THE MICROSCOPE.

glass, with the edges ground, such as are used for mounting objects ;
and lastly, a good and pretty powerful hand-magnifier. Two Cod-
din gton lenses, mounted in one frame of about half an inch, and one-
tenth of an inch in focal power, are specially convenient.

Perhaps it will be as well, in pointing out a few localities, to de-
scribe some that I have actually visited, with the means of access, and
the appearance of the various species, en 'masse, that I have met with.

Swanscombe Salt-marsh will be found well worth a visit ; and it
can be reached by steam-boat or railway from London-bridge to North-
fleet. On quitting the railway-station, make towards the almshouses
on the top of the hill j and arriving at the road, turn to the left, descend
the hill, and cross a sort of bridge over a somewhat insignificant
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 j 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 consistence 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 con-
trast to the sombre shade. By carefully insinuating 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 pro-
bably be found to consist of myriads of specimens of Pleurosigma (na-
vicula 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 Cyclo-
tella menighiniana, and a surirella or two embedded in a mass of Spi-
rulina hutchinsia ; and another mass of floating weed, which feels harsh
to the touch, proceeding from a quantity of a synedra, closely investing
a filamentous alga j and elsewhere Meloseira nummuloides [gallionella of
Ehrenberg).

In a trench by the sea-wall, as it is termed, is a mass of brown

ON COLLECTING OBJECTS. 97

matter of a shade somewhat different to any hitherto observed, ad-
hering to some of the parts of the trench, being partially submerged,
and having a somewhat tremulous motion on agitating the water. This
is a species of Schizonenia ; 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 Amphisporium 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 indications of the
presence of diatomacece ; and though this is by no means universal,
the variation is most frequently dependent upon the presence of some-
thing 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 creosote water, pre-
serves many of the species in a very natural-looking manner ; but they
are killed by the fresh water, and the endochrome becomes much con-
densed in the Pleurosigmata and some other species. The addition of
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 diatomacece, are April,

H

yo THE MICROSCOPE.

May, September, and October ; but some species are found in perfec-
tion 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 inte-
resting species of desmidiese and other fresh-water algae may be pro-
cured. 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 turn 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 gelatinous nature. It consists of a hyaline
substance, with a comparatively small quantity of a bright green en-
dochrome, disposed in little branches, and this is the Draparnaldia
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 recognised as
Zygnema nitidum. In various parts there are other species of zyg-
nema, tyndaridea, mougeotia, mesocarpus, and many others.

Keeping up the stream, and occasionally diverging a little on
either side of it, amongst the miniature bays 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 appear-
ance of most of the desmidiece, as Micrasteias, Euastrum, 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 portion of it.

Little pools in the bog, made by the footsteps of cattle, are par-

ON COLLECTING OBJECTS.

ticularly 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 de-
partment 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 fascicytata, Gomplw-
nema curvata, Diatoma elongatum, Diatoma vulgare, Surirella ovata, &c. ;
and at this same place a few objects, not of the botanical class, as
Spongilla fluviatilis, Cordylophora, lacustris, Akyonella stagnorum, &c.,
are obtainable in abundance in the autumn.

In the ornamental water in St. James's Park may be found, Cocco-
nema lanceolatum, and other species of this genus, Gomphonenta cris-
tatum, &c. Epping Forest, about the neighbourhood of Leytonstone,
Snaresbrook, Wanstead, and Woodford Bridge, are also capital locali-
ties for the filamentous algae, especially the last-named, where Nitella
translucens and Chara vulga/ris abound."*

On the north side of the Serpentine, Hyde Park, especially near
the bridge, may be found :

Cocconeis placentula.

Uvella hyalina.

Gallionella nummuloides.

Euastrum elegans.

Pixidula operculata.

Cladophora glomerata and Sphaero-

plea crispa, two of the filamentous

algae,

Mr. Topping, of New Winchester Street, Pentonville, has furnished
me with the following list of 100 interesting and popular objects pre-
pared by him :

Fos. Infusoria from Guano.
Fos. infusoria, Barbadoes.

„ Upper Bann, Ireland.

„ Island of Mull.

„ Tuscany.

Infusoria from Thames mud.
Spicules of Gorgonia.
„ sponge.
» ,, fresh water.

Gemmules of a sponge.

Cymbella maculata.
Gomphonema cristatum.
Scenedesmus quadricauda.

„ obliquus.

Ankistrodesmus falcatus.
Pediastrum Heptactys.
Cocconema lanceolatum.
Amphora ovalis.

Tests :

Navicula angulata.

„ strigosa.

„ formosum.
Scales of Podura.

„ Lepisma.
Hair of Indian bat.

,, mouse.

„ Larva of Dermestes.

Triceratium from Thames mud.
Arachnaydiscus.

Section of shell— Pinna.
» ,, crab.

Quarterly Journal of Microscopical Science.

100

THE MICROSCOPE.

Section of shell— Haliotis,
}f spine of Echinus,
,, ,, 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.
Proboscis 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, sect, 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 the

formation of the bone-cells.
Muscle of mammalia.
„ reptile. f
„ bird,
fish.

Injections of
Human lung.

intestine.

skin.

kidney.

stomach.

muscle.

section of finger.

This forms a very nice cabinet. Mr. S. Stevens, 24 Bloomsbury
Street, London, supplies neatly mounted microscopic objects at 10s. 6d.
per dozen in racked boxes.

THE CAMERA LUCIDA.

101

THE CAMERA LUCIDA.

The Camera Lucida, fig. 68, was invented by Dr. Wollaston, in
1807 : it is a valuable addition to the microscope, for making drawings
of structures, and for obtaining, with a micrometer, accurate measure-
ments. It consists 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
heads. So arranged, the camera
may be adapted to the eye-piece,
the microscope having been pre-
viously placed in a horizontal po-
sition j if the light be then re-
flected 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 illumi-
nated, then, either by revolving
the circular plate or turning the
prism upon the screws, the de-
sired object will be effected. The chief difficulty in the use of this
instrument 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.

Professor Quekett gives the following directions for using the Camera

102 THE MICROSCOPE.

Lucida with the microscope : The first step to be taken, after the ob-
ject 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 microscope 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 is 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 illuminated, 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 pencil may be moved
along the outline of the image, so as to trace it on the paper. How-
ever 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 complicated subject. If the operation is con-
ducted by lamp-light, it will be found very advantageous not to illumi-
nate 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 compli-
cated 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 weighty 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 j there will then be no risk

POLARISED LIGHT, 103

of the shifting of the paper, as, when the wood is moved, both micro-
scope and paper will move with it. In all sketches made by the ca-
mera, 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 supporting-
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, 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 mea-
surement of all parts of the object. Some persons cover the whole of
the drawing over with squares, to facilitate, 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 accu-
rate outline is the only thing the camera will give : the finishing of
the picture will depend entirely upon the skill of the artist himself.

ON THE POLARISATION OF LIGHT AS APPLIED TO THE MICROSCOPE.

Huyghens and others having observed that a ray of light has not
the same properties in every part of its circumference, 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 posi-
tions; and thence the term, polarisation, a term having neither re-
ference to cause nor effect. It is to Malus, however, who, in 1808, dis-
covered polarisation by reflection, that we are indebted for the series
of splendid phenomena which have since that period been developed ;
phenomena of such surpassing beauty as far to exceed any thing which
can be presented to our eyes under the microscope. It has been truly
observed by Sir David Brewster, that " the application of the prin-
ciples of double refraction to the examination of structures is of the
highest value. The chemist may perform 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 exquisite skill; but
there are still structures in the mineral, vegetable, and animal king-

104

THE MICROSCOPE.

doms which defy all such modes of examination, and which will yield
only to the magical analysis of polarised light. A body which is
quite transparent 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 mine-
ral, vegetable, and animal structures, the extraordinary organisation
of Apophyllite and Analcime may be referred to ; also the symmetrical
and figurate depositions of siliceous crystals in the epidermis of equi-
setaceous plants, and the wonderful variations of density in the crystal-
line lenses of the eyes of animals.

If we transmit a beam of the sun's light through a circular aper-
ture 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 reflected 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, provided 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 pro-
perties 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 abed, fig. 69 ; and we shall

Otf

fig. 69.

distinguish the section of a beam 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, Oo Ee, formed by
double refraction, we shall find, 1st, that the beams 0 o E e have dif-
ferent properties on different sides, so that each of them differs in this
respect from the beam of common light.

POLARISED LIGHT. 105

2d. That the beam 0 o differs from E e in nothing excepting
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 diameter 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 and d' for example.

These 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, cd; or a b', c df,
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 a b c d of
common light. Hence we infer that a beam of common light, abed,
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 is laid above E e, it will produce a figure like ab cd;
and we shall therefore represent common light by such a figure. If we
were to place 0 o above E e, so that the planes of polarisation 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 pro-
perties ; 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, into its
component parts 0 o and E e. 2d. We may turn round the planes of
polarisation, ab cd, 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."*

The first of these methods of producing polarised light is that in
which we employ a doubly reflecting crystal, which was first discovered
to exist in a transparent mineral substance called Iceland spar, cal-
careous spar, or carbonate of lime. This substance is admirably
adapted for exhibiting 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
* firewater's Optics.

106

THE MICROSCOPE.

can always cleave it or split it into shapes represented by fig. 70,
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, acd, are
101° 55' and 78° 5'. The line ax, 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 gene-
rally colourless. Its natural faces when it is
split are commonly even and perfectly polished ;
but when they are not so, we may by a new cleaverage replace the
imperfect face by a better one, or we may grind and polish an im-
perfect face.

It is found that in all bodies where there seems to be a regularity
of structure, as salts, crystallised minerals, on light passing through
them it is divided into two distinct pencils. If we take a crystal of Ice-
land 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 where it is first observed. In the accompanying diagram, fig. 71,

the line appears double, as a b
and c d, or the dot, as e and f.
Or allow a ray of light, g h, to
fall thus on the crystal, it will
in its passage through be se-
parated into two rays, hf, he;
and on coming to the opposite
surface of the crystal, they will
pass out at ef in the direction
of ik, parallel to g h. The
plane Imno is designated the
principal 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 used, the only difference 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

fig. 71.

POLARISED LIGHT.

107

each other, the ordinary ray refracted in the first will be the extraordi-
nary 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) : " A. rhomb of Iceland spar of one-fourth of an
inch in length, and about four-eighths of an inch in breadth and thick-
ness, 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 refrac-
tive index of which (1-549) is that between the ordinary (1-6543) and
the extraordinary (1*4833) refraction, of calcareous spar, and which will
change the direction of both rays in. an opposite manner before they
enter the posterior half of the combi-
nation." The direction of rays passing
through such a prism is indicated by
the arrow, fig. 72, and the combination
is shown mounted, one for use under fig> 72.

the stage of the microscope, fig. 73,

termed the polariser; another, fig. 74, screwed on to and above the
object-glasses, is called the analyser.

73.

fig. 74.

108 THE MICROSCOPE.

Metfwd of using tlte polarising Prism, fig. 73. — After haying adapted
it to slide into a groove on the under-surface of the stage, it is held in
its place by turning the small railled-head screw at one end : the other
prism, fig. 74, 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 ascer-
tained, and carefully corrected by the maker and adapter of the appara-
tus. If very minute salts or crystals are to be viewed, it is preferable
to place the polariser above the eye-piece ; it will then require to be
mounted as in fig. 75. Thus the polariscope consists of two parts ; one
for polarising, the other for analysing or testing the
light. There is no essential difference between the
two parts, except what convenience or economy may
lead us to adopt j and either part, therefore, 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 ^V^h of an inch thick, and parallel to its axis.
The great objection to it is, that the transmitted polar-
ised beam is more or less coloured. The best tourma-
line to choose is the one that stops the most light when
"^ — IT""" its axis is at right angles to that of the polariser, and

yet admits the most when in the same plane.
In the illumination of objects by polarised light, when under view
with high powers, for the purpose of obtaining the maximum effect, it
is alpo requisite that the angle of aperture of the polariser should be
the same as the object-glass, each ray of which should be directly op-
posed 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 tourmaline, used in combina-
tion 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 most clearly
and comprehensively explained by Mr. Woodward, in his " Introduc-
tion to the Study of Polarised Light."* To render the diagram more
* Mr. Woodward constructed a very available form of polariscope for 'most pur-

POLARISED LIGHT.

109

intelligible, as we are unable to introduce them in the colours given by
the above gentleman, we may state that ordinary light is represented
by a cross, which denotes that its vibrations are in planes at right
angles to each other ; whereas when one set of such vibrations only is
shown, the light is said to be polarised. In fig. 76", abed represent

the rectangular vibrations of common light ; e a plate of tourmaline
placed with its axis in a vertical direction — this is called the polariser ;
fa, beam of polarised light obtained from«6cc?by the stoppage of
plane cd ; g a film of selenite of such a thickness as to produce red or
green light ; h the polarised beam/ split into two planes at right angles
to each other ; i a second tourmaline or analyser, with its axis in the
same direction as that of e ; by this all the vibrations that are not
inclined at a greater angle than 45° to the axis of the analyser can
be transmitted and again brought together; k the waves RoRe of
red light, meeting in the same state of vibration, and forming a wave
of red light of doubled intensity; I'm the waves Ye To and Bo Be
for yellow and blue meeting together, with a difference of an odd num-
ber of half undulations, and thus neutralising each other by interfer-
ence ; n the resultant red light.

In the next line of figures may be seen what takes place by turning
the analysing tourmaline one quarter of a circle, h represents the polar-
ised beam split into two rays ; i the tourmaline turned so that its axis is
at right angles to that in the preceding figure; k the waves 12 o Re of
red light destroying each other by interference ; Im the waves To T e
and Bo Be for yellow and blue, meeting together in the same state of
vibration, and by their coincidences, waves of doubled intensity for
yellow and blue light ; n green light, resulting from the mixture of the
yellow and blue light respectively. By substituting Nichol's prisms for

poses ; the instrument is described in Elements of Natural Philosophy, by J. Hogg,
p. 281.

110 THE MICROSCOPE.

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 microscope, put
upon the stage of a film of selenite, which exhibits, under ordinary cir-
cumstances, the red ray in one position of the polarising prism, and the
green ray in another; each arc will assume one of these complemen-
tary colours, whilst the centre of the field will remain colourless. Into
this field introduce any microscopic object which in the usual arrange-
ment of the polariscope undergo no change in colour, when it will
immediately display the most brilliant effects. Sections of wood, fea-
thers, 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 in-
tensity of colour, as well as the separating power of the prism, being-
impaired under much higher amplification ; although in some few in-
stances, such as in viewing animalcules, the inch-object-glass is perhaps
to be preferred.

Mr. J. King attributes the foregoing phenomenon to the double-
image prism separating the constituents of the polarised ray into two
planes, and causing them to overlap each other, except at the edges
where the light is analysed ; and of course, the combination of comple-
mentary colours in the centre of the field produces white light. Any
object, therefore, placed in the white field, partakes of the characters of
the selenite ; one image being refracted into the plane which exhibits
the green ray, assumes that colour ; whilst the second image, being re-
fracted into the plane of the red ray, partakes of that tint. Should the
object, however, be so large that actual separation of the images is not
effected, the extremities and interstices only will be polarised, whilst
the middle will remain dark, or present only its natural hue.

Selenite is the native crystallised hydrated sulphate of lime. A beau-
tiful 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 rectangular direc-
tions they allow perpendicular rays of polarised light to traverse them
unchanged ; these directions are called the neutral axis. In two other

POLARISED LIGHT. Ill

directions, however, which form respectively angles of 45° with the
neutral axis, these films have the property of double refraction. These
directions are known as the depolarising doubly refracting axis.

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 beautiful 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." Mr. Darker has constructed a very neat stage of brass for this
purpose, and that of producing a mixture of all the colours by super-
imposing 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.

Dr. Herapath, of Bristol, has recently 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 elytrse of cantharides, and are also very
similar to murexide in appearance. When examined by transmitted
light, they scarcely possess 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 crys-
tals are not one five-hundreth of an inch in thickness. 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. As the result of a series of very elaborate experi-
ments, 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

112 THE MICROSCOPE.

ifc. Dr. Herapath lias succeeded in making artificial tourmalines large
enough to surmount the eye-piece of the microscope ; so that all expe-
riments 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 advan-
tages over the Nicol's prism in the sante position, as it gives a perfectly
uniform tint of colour over a much more extensive field than can be
had with the prism."*

A variety of interesting phenomena have been described by Mr.
S. Legg in the Transactions of the Microscopical Society. He says :

" 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.

A plate of brass, fig. 77, three inches by one, perforated with a
series of holes from about one-sixteenth to one-fourth of an inch in

fig. 77.

diameter • the size of the smallest should be in accordance with the
power of the object-glass, and the separating power of the double re-
fraction.

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
(1^ or 2 inch) object-glass, and adjust the focus as for an ordinary
microscopic object ; place the doubly-refracting crystal over the eye-
piece, and there will appear two distinct images ; then, by revolving
the eye-piece, 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 com-
pletely separated, but will overlap, as represented in the figure.

* 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. Also, for further researches on its polarising properties, see Philosophical
Magazine, May 1855.

POLARISED LIGHT.

113

Experiment 2. Screw the Nicol's prism into its place under the
stage, still retaining the double refractor 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 com-
pletion 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 by noticing the natural
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 selenite thus pre-
pared, 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 constituents 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 produced. If, by accident,
the prism is 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 refractor, and a film of selenite adapted between the double
refractors. The systems of coloured rings in crystals cut perpendicu-
larly to the principal axis of the crystal are best seen by screwing the
Nicol's prism under the stage, and employing the lowest object-glass :
place the crystals over the eye-piece, and use a tourmaline as the ana-
lyser."

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 refraction as well as of polarisation.

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 2J° to the axes

I

114 THE MICROSCOPE.

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 axis 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 axis of the prism, we shall
see the double system of rings shown in figs. 78 and 79.

fig. 78. fig. 79.

When the line connecting the two axes of the crystal is inclined
45° to the plane of primitive polarisation, the cross seen as first de-
scribed, on revolving the nitre, opens, and gradually assumes the form
of two hyperbolic curves, fig. 79. But if the tourmaline be revolved,
the black crossed lines will be replaced by white spaces, and the red
rings by green ones, 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 corresponds 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.

A large number of crystals exhibit this curious and beautiful sys-
tem of coloured rings. Small specimens of salts may also be crystal-
lised 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 may 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 in the same fluid, some of which
are shown in fig. 80.

Dr. W. B. Herapath has contributed an interesting addition to the
uses of polarised light, by applying it to discover the salts of alka-
loids, quinine, &c. in the urine of patients. He says : " It has long

POLARISED LIGHT.

115

been a favourite subject of inquiry with the professional man to trace
the course of remedies in the system of the patient under his care, and

fc*l

*i <

*r«

c,

fig. 80. Urinary Salts.

a, Uric acid deposit. 1), 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 form.

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 ex-
treme 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 de-
tection 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 ta obtain demon-
strative evidence of the presence of quinine, even if in quantities not
exceeding the 1-1 00,000th 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 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,

116

THE MICEOSCOPE.

which forms as a small circular spot; the alcohol separates in little
drops, which, by a sort of repulsive movement, drive the fluid away ;
after a time, the acid liquid again flows over the spot, and the polar-
ising crystals of sulphate of iodo-quinine are slowly produced in beauti-
ful 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 complementary colours of the stage; red and green, sup-
posing that the pink stage is employed, or blue and yellow, provided the

fig. 81. In this figure the heraldic lines are adopted to denote colour. The dotted
parts indicate yellow, the straight lines red, the horizontal lines blue, and the dia-
gonal, or oblique lines, green. The arrows show the plane of the tourmaline,
a, blue stage ; b, red stage of selenite employed.

blue selenite is made use of. All those crystals at right angles to the
plane of the tourmaline, producing that tint which an analysing-plate
of tourmaline would produce when at right angles to the polarising-
plate; 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. 81, a and 6.

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 proper-

POLARISED LIGHT.

117

ties of that remarkable salt of quinine, so fully described by me in the
Philosophical Magazine for March ] 852, and the chemical analysis of
which was published in the number for September in the same year.
In fact, these crystals are perfectly identical with the sulphate of iodo-
quinine in every respect.

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 tourmalines, 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
shown in fig. 82.

fig. 82.

If we employ the selenite stage in the examination of this object,
we obtain one of the most gorgeous appearances 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 having a red and green fringe, whilst the four intermediate
sectors are of a gorgeous orange-yellow. These appearances 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, accord-
ing to the position of the analysing-plate. These phenomena are ana-
logous to those exhibited by certain circular crystals of boracic acid,
and to those circular discs of salicine (prepared by fusion) ; the differ-

118

THE MICROSCOPE.

ence being, that the salts of quinidine 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 the quinidines has a very different
mode of crystallisation ; but it occasionally presents 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
discriminate the two. — Philosophical Magazine, 1853.

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 this system. A sheet of clear ice, of about
one inch thick, and slowly formed in still weather, will show the
circular rings and cross when viewed by polarised light. Some of the
Wenham Lake ice answers very well.

During the intense frost of February 1855, Mr. Glaisher made
many beautiful drawings of snow crystals, figs. 83, 84, 85, and 86.

He writes: "This morning, February 21, with a temperature of
21°, they are falling sparingly, but are intensely beautiful; they are
also minute, and highly crystalline. Up to the present time, 9h. 30m.,
all that I have observed are made up of prisms of six facets; and many
are double, that is, two crystals alike in form are falling, united to an
axis at right angles to the plane of each. These are generally fine
specimens, and less minute ; the rays of the under crystal in most cases
filling the intermediate spaces between those of the upper, and, as

fig. 83. /Snow Crystals.

SNOW CRYSTALS.

119

crystals of a complex order, exhibiting a richness of effect hardly to be
exaggerated.

It is a pleasant feature in the study of these figures that they give

fig. 84. Snow Crystals.

pleasure to the observer, whether as seen by the naked eye with a lens
of moderate power, or as expanded in all their beauty beneath the mi-
croscope. I received, a few days ago, from a gentleman at Huntingdon,
drawings of twenty-four varieties, which he had observed in the year
1841. They were drawn about their natural size, with a fine pen; and,

fig. 85. Snow Crystal

if less wonderful in detail, were scarcely less beautiful than any I had
seen with my highest-power lens.

My own observations of some of the more simple forms have been
very satisfactorily confirmed by a lady, residing at Richmond, who has
obligingly forwarded to me several of her sketches, made at the same
time with many of my own. A collection of snow crystals, as observed

120

THE MICKOSCOPE.

fig. 86. Snow Crystals.

and accurately recorded, would be an interesting feature in meteoro-
logical investigation. At the same time, it is probable that the con-
ditions of their forma-
tion 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 ap-
parent connection be-
tween the form of the
compound varieties of
snow crystals and the
electrical condition of
the atmosphere, whe-
ther negative or positive; and is, he informs me, instituting experi-
ments for his better information on the subject."

A great variety of animal, vegetable, and other substances possess
a doubly refracting or depolarising structure, as : a quill cut and laid
out flat on glass ; the cornea of a sheep's eye ; skin, hair, a thin sec-
tion of a finger-nail ; sections of bone, teeth, horn, silk, cotton, whale-
bone ; stems of plants containing silica or flint ; barley, wheat, &c.
The larger-grained starches form splendid objects ; tons les niois, being
the largest, may be taken as the type of all the others. It presents a
black cross, as at a, fig. 87, the arms of which meet at ttie hilum. On

rotating the analyser, the black cross
disappears, and at 90° is replaced by a
white cross, as at b ; another, but much
fainter black cross being perceived
between the arms of the white cross.
Hitherto, however, no colour is per-
ceptible. But if a thin plate of sele-
nite be interposed between the starch-
fi §7 grains and the polariser, most splendid

and delicate colours appear. All the

colours change by revolving the analyser, and become complementary
at every quadrature of the circle. West and East India arrow-root,
sago, tapioca, and many other starch-grains, present the same appear-

THE BINOCULAR MICROSCOPE. 121

ance; but in proportion as the grains are smaller, so are their mark-
ings 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 j 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, vegetable, or mi-
neral kingdom, in which the power of unequal or double refraction is
suspected to be present, are those that should especially be investigated
by polarised light. Some of the most delicate of the elementary tis-
sues of animals, such as the tubes of nerves, the ultimate fibrillse of
muscles, &c. are amongst the most striking subjects that may be studied
with advantage under this method of illumination. 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."*

APPLICATION OF BINOCULARITY TO THE MICROSCOPE.

The application of this principle to microscopic purposes seems to
have been tried as early as 1677, by a French philosopher, le Pere
Cherubin, of Orleans, a Capuchin 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 ad-
vantages above the single instrument so extraordinary and so surpris-
ing, 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 appears to have long slumbered and been forgotten; and
nothing more was heard of the subject until Professor Wheatstone's
very surprising invention of the stereoscope, when it again attracted
the attention of the above philosopher, who applied to both Ross and
Powell to construct him an instrument. But this was not done ; and
during the year 1853 a notice appeared in jSillimans American Journal
* Quekett's Practical Treatise on the Use of the Microscope.

122 THE MICROSCOPE.

of a binocular instrument constructed by Mr. J. L. RiddelL This even
had many disadvantages and inconveniences, which Mr. F. H. Wenham
has very ingeniously succeeded in modifying and improving.

In describing his improvements, he observes : " That in obtaining
binocularity with the compound achromatic microscope, in its com-
plete acting state, there are far greater practical difficulties to contend
against ; and which it is highly important to overcome, in order to cor-
rect 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 microscope ; then, with a card held
close to the object-glass, stop off alternately the right or left hand por-
tion of the front lens : it will be seen that during each alternate change
certain parts of the object will alter in their relative position. To
illustrate this, figs. 88 a b are enlarged draw-
ings 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 in-
clined orifice will occupy when the right and left
hand portions of the object-glass are stopped
off. It was illuminated 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. The two dif-
ferent images just produced are such as are required for obtaining
stereoscopic vision. It is therefore evident that if, instead of bringing
them confusedly together into one eye, we can separate them so as to
bring figs. 88 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

THE BINOCULAR MICROSCOPE.

123

form a correct judgment of the solidity and distances of the various
parts of the object.

If a rectangular plate of speculum-metal is ground and polished,
so as to form two reflecting facets inclined to each other at the required
angle, as represented at 4, fig. 89, and this is placed at an angle of
45° with the division of the facets intersecting the axis of the object-
glass, we shall divide the rays, and reflect them horizontally by one
single reflection. Any other direction than a right angle, with respect
to the axis of the object-glass, may, of course, be given to the rays by
inclining the reflector more or less. From the simplicity of this con-
trivance, and the facility with which it may be constructed, I shall take
an early opportunity of giving it a trial. The only question I have
is, whether a material may not be found that will reflect more light
than even speculum-metal. I have heard an alloy of cast-steel and
platinum well spoken of, but have never seen any of it.

In considering the aberrations which the thickness of glass con-
tained in the reflecting prisms must inevitably produce, when placed
immediately behind the object-glass, it occurred to me that if the same
prisms were placed close to the top lens of the eye-piece, these errors,
not being magnified, would be less sensibly felt.

fi. 89.

Diagram 3, fig. 89, represents the methods that I have contrived for
obtaining the effect of bringing the two eyes sufficiently close to each
other to enable them both to see through the same eye-piece together.
aaa are rays converging from the field lens of the eye-piece; after pass-

124 THE MICKOSCOPE.

ing 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 sub-
stance of the glass at e. The rays then diverge, and after being re-
flected by the second inclined surface f, 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 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.

I have constructed an adjusting binocular eye-piece, not differing
in principle from the last. The first reflection is performed by means
of a triangular steel prism, with the two inclined facets very highly
polished ; this is represented by the dotted outline g g. The rays,
after having been reflected at right angles, are taken up by two rect-
angular glass prisms, shown by the dotted lines at//!

The loss of light in this is much greater than in the former instance,
and the field of view more contracted ; for the rays from the eye-piece,
after being reflected from the surface of the steel prism, fall to their
natural focal distance, instead of being elongated, as in the solid prism ;
consequently the eye is still further removed from the focus. I had
chosen hard steel for the reflector, on account of the property this ma-
terial possesses of allowing the figure of a small flat surface to be re-
tained, or even perfected, during the operation of polishing. I have
also tried a combination of prisms over the field-glass, using two eye-
lenses ; but with no good result. The best effect that I have yet pro-
duced in the way of binocular vision applied to the microscope, is that
next to be described, in which I. have altogether dispensed with reflect-
ing surfaces, merely using three refracting prisms, which, when placed
together, are perfectly achromatic, 'a a, diagram 2, fig. 89, is a single
prism of dense flint-glass, with the three surfaces well polished ; b b
are two prisms of crown-glass of half the length of the under flint-

THE BINOCULAR MICROSCOPE.

125

prism, to the upper inclines of which they are cemented with Canada
balsam.

The angle of inclination to be given to the prisms must depend
upon the dispersive power of the flint and crown-glass employed. In
the combination that I have worked out, I have used, for the sake of
simplicity, some flint and crown that Mr. Smith kindly furnished me
with, in which the dispersive powers are exactly as two to one ; conse-
quently I have had to make the angle of the crown just double that of
the flint, in order to obtain perfect achromatism. The refractive power
of each must also be known, that we may determine the angles of the
prisms suitable for refracting the rays from the object-glass into the
two eyes, at a distance of nine inches, c, fig. 89, represents a ray of
light incident at right angles upon the under-surface of the flint-prism.
On leaving the second surface, and entering the crown-prism, it is
slightly bent inwards ; and on finally emerging, it is refracted outwards
in the direction required. On looking through this prism, I could not
discover the slightest colour or distortion — it is almost like looking
through a piece of plain glass ; and the loss of
light is so inappreciable, that it is difficult to
distinguish any difference between an object
and its refracted image. The base of the
compound prism should not be larger than
is sufficient to cover the stop of the lowest
object-glass, in order that they may be made
very thin.

The method of applying the prism to
the binocular microscope is shown by fig.
90 : a a is the object-glass, b the prism placed
as close behind it as the fittings will admit.
The prism is set in an aperture in a flat disc
of brass, which has a horizontal play in every
direction, in order that it may be adjusted
and fixed in such a position that the junc-
tion of the prisms may bisect the rays from
Se object-glass, and at the same time be at
jht angles to the transverse centres of the
e-piece ; c c are the two bodies of the mi-
croscope, provided with draw-tubes and the
usual eye-pieces dd. The distance between

them should be rather less than the average distance asunder of the
eyes ; and in cases where these are very wide apart, we can pull

tic
thi

3

fig. 90.

126 THE MICROSCOPE.

out the draw-tubes, which will increase the distance between the eye-
pieces.

With this apparatus I obtain the whole of the field of view in
each eye; which circumstance I was not prepared to expect, as this
must, in some measure, depend upon the correction of the oblique
pencils of the object-glass, for we cannot expect to look obliquely
through the objective of a compound achromatic microscope in the
same way as in the single lens arrangement, but can only avail our-
selves of such oblique pencils of rays as are corrected for passing-
through the axis of the microscope."

During the past year Mr. Wenham succeeded in further improving
and simplifying this arrangement, a detailed account of which will
be found in the volume of the Journal of Microscopical Science for 1854.

APPLICATION OF PHOTOGRAPHY TO THE MICROSCOPE.

When this book was first projected, it was thought that if the ob-
jects so beautifully exhibited under the microscope could be drawn by
light on the page of the book, or on the wood-block, so that the en-
graver might work directly from the drawing thus made, truthfulness
would be insured, and we should present to the reader a valuable re-
cord of microscopic research never before seen or attempted. But in
this we were doomed to disappointment by the existence of a patent,
which presented obstacles too great to be surmounted at that time ;
and the idea was abandoned, with the exception of a few drawings
then prepared, and now 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 whirligig, with a few
others, were first taken on a film of collodion, and then floated off
the glass to the surface of a block of wood ; the wood having been
previously and lightly inked with printer's ink or amber- varnish ; the
film was then gently rubbed or smoothed down to an even surface, at
the same time carefully pressing out 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 must 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 should not
exceed eighteen inches in length ; for if longer, the pencil of light trans-

APPLICATION OF PHOTOGRAPHY TO THE MICROSCOPE. 127

mitted by the object-glass is diffused over too large a surface, and a
faint and unsatisfactory 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 better pictures are
produced by taking away the eye-piece 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 produce pictures
nearly equal to the sunlight. Collodion offers the best medium, as a
strong negative can be made to produce any number of printed posi-
tives.

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 has given directions for improving " microscopic
photography" in the Quarterly Journal of Microscopical Science for
January 1855. In this paper he has shown how to ensure 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, acting 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.

Mr. S. Highley's mode of adapting an object-glass to the ordinary
camera, for the purpose of taking microscopic objects on collodion and
other surfaces, is shown in fig. 91 ; a sectional view of his arrangement
is given, which is 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 c,
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 graduated head, K, acting on a fine
screw, likewise attached to the stage-plate, after the manner of Ober-
hauser's microscopes. An index, L, is fixed opposite the graduated
head, K. The stage and clamp slides vertically on H ; and by sliding

128 THE MICROSCOPE.

this up or down, and the glass object-slide horizontally, 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 j 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

fig. 91.

object-glass. The difference in each glass employed should be ascer-
tained by experiment in the first instance, and then noted. By em-
ploying a finely-ground focussing-glass greased with oil, this arrange-
ment 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.

Two exquisitely delineated negative objects obtained in this way
by Mr. Delves were afterwards printed as positives, for the purpose of
illustrating an excellent paper on the "Application of Photography
to Microscopy," in No. 3 of the Quarterly Journal of Microscopical
Science.

PAET II.

CHAPTER I.

PROTOZOA — RHIZOPODA HISTORY OF INFUSORIAL ANIMALCULES

MONADS FOSSIL INFUSORIA, ROTIFERA, VORTICELLA, STENTORS,

HYDRA, ZOOPHYTES, SPONGES, MOLLUSCA, CRUSTACEA, ETC.

1 CIENCE has defined matter, space, time, and na-
tural history so infinitesimally, that the brain
becomes bewildered from want of some familiar
object to convey to the mind by comparison
the results exhibited.

The precious metal gold can be reduced to a
film the four- millionth part of an inch in thick-
ness by manual ingenuity ; space measured and
divided the hundred-thousandth part of an inch
with truthfulness by a machine j electricity
proved to pass along a wire with the velocity
of five hundred and seventy-six thousand miles
in a second, and an object of the most elaborate
workmanship seized in every detail, and faithfully por-
trayed, by electricity and the camera, in the one-mil-
lionth part of the fraction of time denominated a
second. At the least, a million of living creatures of
delicate structure may be seen in active pursuit of
prey in a space not larger than a mustard-seed, and
a single one, increasing in twenty-four hours to the
enormous number of one hundred and forty millions,
is demonstrated by means of the philosophical instru-
ment the microscope, the construction of which we have been de-
scribing.

130

THE MICROSCOPE.

PROTOZOA.

The first division, or lowest forms of the animal kingdom, appear
as creatures of a low type of organisation, and have been considered to
hold a medium state between animals and vegetables. Almost all of
them live in water; and it would be a fruitless search to look for dis-
tinct internal organs, as the small bladder-looking spaces enclosed within
their substance, — believed by Ehrenberg to be stomachs, and which
have been termed by Dujardin sarcode, — present only the appearance
of a transparent gelatinous cell, with or without moving spaces in

fig. 92. A drop of Water display
Larva of Dytiscus, Cup Moss, Spurge Laurel, &c.

PROTOZOA. 131

their interior ; they may be regarded as the earliest dawn of a circu-
latory system.

The Protozoa, are divided into three classes. In the first, to which
the name of Rhizopoda has been given, the body is composed entirely
of the gelatinous matter above described, motion being effected by the
extension of portions of the substance into filaments or processes of
various forms.

The second class, including the sponges, consists entirely of asso-
ciated cell animals, the individual cells resembling those of the preced-
ing class in their power of extending the substance of their bodies
in all directions ; but in this class they are united by a mucilagi-
nous intercellular substance, and supported upon a horny framework.
From the masses formed by these creatures being perforated in
every part with minute orifices, they have received the denomination
of Porifera.

The animals constituting the third class of the Protozoa have been
called Infusoria. They are generally solitary unicellular animals, and
differ from the Rhizopoda in having the outer surface of the body of a
somewhat firmer consistence than the rest of their substance. They
are usually furnished with a mouth, and their movements are effected
by means of cilia, or of one or more long filiform appendages attached
to one extremity of the body.

In the valuable voluminous treatises on this interesting department
of nature, the above division would be strictly adhered to ; but as our
object is to give a popular account of the wonders disclosed by the
microscope, we will not closely follow the path of the learned investi-
gators of this branch of science ; and hence will avoid as much as pos-
sible the adoption of those terms so alarming to the uninitiated, culling,
as we pass, only those objects of most interest, and likely to create a
desire for further knowledge; whereby there will be found a future
pleasure in overcoming the obstacles by which the learned render so
mysterious and repugnant to the popular mind the stores of their
gathered wealth.

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, which it appears to have the power of shooting
out from any part of its substance. This shapeless mass is well known
to microscopic observers under the name of the Proteus (Amceba dif-

132 THE MICROSCOPE.

fluens, fig. 95, 4, 5, and 6). From the continual changes of shape which
it presents, it is honoured with the name of a fabled god, who could be
either animal, vegetable, or elemental in his nature. This curious ani-
mal presents us with the essential characters of the class Rhizopoda in
the simplest form. It appears to be of an exceedingly voracious dis-
position, 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 composed is capable, as we have seen, of extension
in every direction ; accordingly, when the Amceba meets with any
thing that it regards as suitable for its support, the substance of the
creature, as it were, grows round the object until this is completely
enclosed within the body, when it is gradually dissolved. 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 contractile 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 further organisation. 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, perfectly transpa-
rent 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 Amceba there occur, besides the granules, clear spaces
with fluid contents, which are sometimes unchangeable in form, and
sometimes exhibit rhythmical contractions."

Owing to the general similarity which exists apparently throughout
the rhizopodous class in the intimate structure of the soft part, their
systematic arrangement can only be founded upon their shells, which
exhibit an astonishing diversity of form. Out of these forms, it would
appear that the labours of various naturalists in the last hundred years
have made known nearly 2000 species of recent and fossil Foramini-
fera; and although the observations of Dr. Carpenter tend to show
the probability 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 subject. Dr. Schultze acknowledges the

KHIZOPODA. 133

difficulties attending the study of the Rhizopoda, and insists very pro-
perly 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 conformation.

When recent Foraminifera are dissolved 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 Polystomella strigttata from the Adriatic.

The solitary Rhizopoda, furnished with a horny shell or capsule,
forming a case for the animal, constitute the family Arcellidce. In the
genus Arcella, from which the family derives its name, the shell is some-
what of a bell-shape, with a very large round opening. In Englypha
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 the shell is often globular.

All the Polythcdamw, QY Foraminifera, inhabit the sea, and fre-

fig. 93.

1. Separated prisms from outer layer of Pinna shell.

2. Skeletons of Foraminifera from limestone.

3. Eecent shell of Polystomella. crispa ; seen by the aid of the dark-ground.
*•• illuminator.

134 THE MICROSCOPE.

quently 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 constituents of several very important geologi-
cal 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 ; and they occur in great quantities in the
marly and sandy strata of the tertiary epoch. The stone which is uni-
versally employed in Paris as a building stone is almost entirely
composed of the fossil shells of an animal belonging to the order
Miliola.

In the tStichostegidce the chambers are placed end to end in a row,
so as to 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 j and as the construction of the shell is always
commenced with a single small chamber, the whole necessarily acquires
a more or less pyramidal form. The third family, the Helicostegidce,
presents us with some of the most beautiful forms that we meet with
in these 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
cephalopodous mollusca, of which the nautilus and the argonaut are
examples. The fourth family, the Entomostegidce, stand in the same
relation to the preceding as the Enallostegidce to the 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 cham-
bers 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 fur-
nished with a curious tooth or process. The Miliola will serve as an
example of this family.

It is probable, although by no means certain, that the animals whose
fossil shells, termed Nummidites, are found in great quantities in the
chalk and lower tertiary strata, are also to be regarded as members of
this class. No living example of this form of animal has yet be^n met
with ; but in a fossil state whole mountains consist almost entirely of
their shells.

The great Pyramid of Egypt, covering eleven acres of ground, is

RHIZOPODA. 135

based on blocks of lime-stone consisting of Foraminifera, nummidites,
or stone coin, and other fossil animalcules. The nummulites vary in
size, from that of a most minute object to that of a crown-piece, and
many appear like a snake coiled in a round form. A chain of moun-
tains in the United States, 300 feet high, seems to be wholly formed
of one kind of this fossil-shell. The crystalline marble of the Pyre-
nees, and the lime-stone ranges at the head of the Adriatic gulf, are
composed of small nummulites. Vast deposits of Foraminifera have
;een 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 fossilised Foraminifera in the Poorbandar 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 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 portion 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 dis-
tinctly seen, and their bond of union consisting of many thread-like
filaments. To ascertain the mineral composition of the amber-coloured
particles or casts, after having found that it was carbonate of lime with
which they were surrounded, they were placed for a few moments in
the reducing flame of a blow-pipe, and it was observed that on sub-
sequently exposing them to the influence 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.

Truthfully does Lamarck say of the Foraminifera : " Their small-
ness renders their bodies contemptible to our eyes; in fact, we can
hardly distinguish them ; but we cease to think thus when we consi-
der that it is with the smallest objects that nature produces the most
imposing and remarkable phenomena. Now, it is here again that we
have one of the numerous instances which attest that, in her production
of living bodies, all that nature appears to lose on one side in volume,
she regains on the other in the number of individuals, which she mul-
tiplies to infinity."

INFUSORIA.

The class Infusoria, described by Ehrenberg in his work Infu-
sionsthierehen, published in 1838, was divided into two great groups, the

136 THE MICROSCOPE.

Polygastrica, or many-stomached', and the Rotifer a, or rotating, wheel-
animalcules : the latter are now classed with animals of a higher
type of organisation. The classification of the Infusoria presents
considerable . difficulties, partly arising from their excessive minute-
ness, which renders the assistance of our best microscopes necessary
to enable us even to see many of them, and partly from the impossi-
bility of avoiding confusion from the intermixture of the genus of
more highly organised animals, and some plants, as the Volvodnece,
the Desmidiacece or Hacillariw of Ehrenberg, in various stages of de-
velopment.

The term Infusoria* is applied to them because they were first dis-
covered in water where vegetable matter was decomposing, and there-
fore, the infusion was considered necessary for their production. Now,
however, it is an established fact, that they are in a higher state of
organisation 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 containing 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 vegetables seems to be to facilitate the
development of the latent life of the atoms of organic matter, and per-
haps as the first sources of their food.

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 nu-
merous 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 j
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 as their prey.

The forms of the Infusoria are endless ; some changing their shape
* Infusoria (from infiisor, a pourer-in).

INFUSORIAL ANIMALCULES. 137

at pleasure, some 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 sponta-
neous division or fissuration, in others by gemmation or budding ;
whilst some species are oviparous, and others viviparous. 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 the or-
ganisms which subsequently 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 cease-
less state of motion ; their term is short, they have no time for rest,
and therefore have but one day, which ends only with their death and
decomposition. Nevertheless, they appear to love that which pro-
motes life, — the light of heaven j but others, born in the bowels of the
earth, and who never partook of the blessing, still, like the ignorant
among mankind, have their own contracted round of unenlightened
joys ; they perform their mechanical duties, and expire hidden and
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 pre-
vious 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 func-
tions of life perform their allotted duties perishes, the shell that pro-
tected it from injury during its hours of existence remains as a token
of the past labours of- nature ; this sometimes consists entirely of flint,
and in other cases of lime united with oxide of iron, destructible in
some instances by fire, and in others not so.

Some of these minute beings have apportioned to them setae, 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 them-
selves, or as feelers. Others are possessed of unci, or hooks, pro-
jecting from the under part of the body, which are capable of motion ;
and by their means the animalcule can attach itself to any particular
thing that it desires. 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

138 THE MICROSCOPE.

summit. Many, also, can extend and withdraw their bodies at plea-
sure, in a similar manner to the snail or leech.

One of the most interesting and important organs possessed by the
infusorial animalcule 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 duties 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 gills or
beard of the tadpole, the oyster, and mussel, it would appear that they
are serviceable as organs of respiration, by imbibing oxygen, and emit-
ting 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 satisfactorily 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 deli-
cate 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 projections 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, and death, do not immediately stop the motion of the cilia, as
they will continue in action 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 their muscular development, from their
extreme minuteness ; but there can be no doubt of the existence of this
structure in all. Now in the wheel-animalcules the cilia are in circular

INFUSORIAL ANIMALCULES. 139

rows; and each revolves around its bulb, giving a singular appearance,
seeming to move together like a wheel upon its axle, whence their
name Rotifera ; in some of these muscles may be traced. The cilia
must not be mistaken by young microscopists for the stiff hairs and
bristles found on some animalcules, serving 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 membrane 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 provided with a locomotive apparatus
of the same description, and has frequently been mistaken for such.
The animals more commonly employed for the examination of the cilia
are the oyster and the mussel j 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, and 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 producing 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 above
given ; the movements then will have become sluggish. If a power of
400 diameters be used, and that part of the cilia attached to the epi-
thelium scale carefully watched, each one will be found to revolve a
quarter of a circle, whereby a " feathering movement" is effected, and a
current in one direction constantly produced. In the higher animals
the action of the cilia can only be observed a 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 epithelium is found, it would be almost im-
possible ever to see it in action, unless the body were opened imme-

140 THE MICROSCOPE.

diately after death. In some animals it may be seen in the interior of
the kidney, as was first discovered by Professor Bowman in the ex-
panding 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.

These 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 ma-
chinery 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 ful-
ness of buoyant health becomes dried up, they lie in an inanimate speck
of matter ; but after months, nay years, a drop of water being applied,
their bodies will be resuscitated, and in a short time their frames be
active with life. Leeuwenhceck kept some in a hard and dry condition,
and restored them to life after a sleep of death of 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 wonderful works.

The infusorial animalcules vary in their capabilities of the endur-
ance of heat and cold; some of them retaining life in water 200° Fall.,
while others expire from the heat of a warm room. Many die when
the mercury is as low as 80° Fah., while others survive. They have
been found embedded in ice at the arctic regions, surrounded by a little
water, which Ehrenberg supposes is not frozen from the natural heat
of their bodies. Air is as necessary to their existence as it is to supe-
rior animals ; for if placed in a tightly-corked bottle in water, where

INFUSORIAL ANIMALCULES. 1-11

oil is poured on its surface, or underneath the receiver of an air-pump,
they are killed. They will live in water where poisons which mingle
mechanically, not chemically, are infused. But all sudden transitions
are destructive, as the mixture of sea with fresh water ; still, if the
change be gradual, they will adapt themselves to the new element and
survive. The phosphorescent appearance of the ocean, arising chiefly
from the presence of animalcules, is thus described by Darwin : " While
sailing a little south of the River La Plata, on one very dark night, the
sea presented a wonderful an,d most beautiful spectacle. There was a
fresh breeze, and every part of the surface, which during the day is seen
as foam, now glowed with a pale light. The vessel drove before her
bows two billows of liquid phosphorus, and in her wake she was fol-
lowed by a milky train. As far as the eye reached, the crest of every
wave was bright ; and the sky above the horizon, from the reflected
glare of these livid flames, was not so utterly obscure as over the vault
of the heavens. Near the mouth of the Plata some circular and oval
patches, from two to four yards, shone with a steady but pale light,
while the surrounding water only gave out a few sparks. The appear-
ance resembled the reflection of the moon or some luminous body, for
the edges were sinuous from the undulations of the surface."

Naturalists consider the phosphoric light of the marine animalcule
to be the effect of vital action. The sparks are intermittent like the
fire-fly; they measure from the 12,000th to 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. 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 lumiuousness of the
sea is attributed. One of my large glass vases of sea- water I had ob-
served to become suddenly at night, when tapped with the finger,
studded with minute but brilliant sparks at various points on the sur-
face 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 Noctilucu miliaris swimming about in various direc-
tions. 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

142 THE MICROSCOPE.

their minuteness. They were, in fact, distinctly appreciable by the
naked eye, measuring from ^th to ^th of an inch in diameter." With

fig. 94. Noctiluca miliaris.

a power of about 200 diameters they are seen of various forms and
stages of growth, as represented in fig. 94.

" Awaked before the rushing prow,
The mimic fires of ocean glow,

Those lightnings of the wave ;
Wild sparkles crest the broken tides,
And, flashing round the vessel's sides,

With elfish lustre lave ;
While far behind their livid light
To the dark billows of the night

A gloomy splendour gave."

SCOTT.

MONADIC M — MONADS.

Monads. — These are amongst the smallest atoms of matter possess-
ing the mysterious principle of life, discernible by the extraordinary
magnifying power of the microscope. Minute, however, as they are,
no one can say but that they derive their sustenance by preying on
animals even less than themselves, as larger ones of the same species
do upon them.

A drop of water only a tenth of an inch in diameter may glitter
like a diamond from its translucency, and yet under the microscope be
seen to hold 500 millions of these animated beings; an amount about
equal to the human race now existing on the surface of our globe.
Vainly does man, with all the subtlety of his mind, endeavour to con-
ceive an object the twenty-four thousandth of an inch in length ; yet
this is the size of the monad : some have been discovered twice this
length, but still they are inconceivably small when attempted to be de-
fined by comparison. If each be allowed three times its bulk to move
about in, a cubic inch of water will then contain 800,000 millions of
these organised beings. Nay, some philosophers say this family of

INFUSORIAL ANIMALCULES. 143

Infusoria are seen only the one forty-thousandth of an inch in length.
What incalculable numbers of animalcules must swarm the waters of
creation !

Monads vary in their colours, some being red, green, yellow, and
others colourless; in shape they are round or oval (5 and 6, fig. 100),
and possessed of immense activity, having one or more parts devoted
to the purpose of locomotion. Monads have been claimed by the
botanist, and accordingly placed among the genus Volvocinece, confer-
void algse. Ehrenberg'* regarded and described them as Infusoria.
He says : "All true Infusoria, even the smallest monads, are organised
animal bodies j some consist of a homogeneous jelly, and are dis-
tinctly provided with at least a mouth and internal nutritive appa-
ratus." Perceiving small round spots within the bodies of these
animalcules, he judged them to be stomachs, in contradiction to the
supposition of the former great philosopher in this branch of science,
M tiller, in whose work, published in 1773, they were stated to be the
animal's eggs. To test the truth of his idea, and convince the world,
Ehrenberg fed the little things with colouring matter diffused in the
water which contained them. If the water be clear in which the ani-
malcule is living, the stomachs are transparent, more so than the other
parts of the body ; but are rendered visible by tinting the water with
pure sap green, carmine, or indigo. Some of one of these colours is
rubbed on a piece of glass, then a few drops of water added ; a portion
of the water is then allowed to run off by tilting the glass on one side,
and a little of the remainder of the coloured matter dropped into the
water containing the animalcule. Portions of the coloured fluid are
swallowed by the animalcule, when the stomachs, from their transpa-
rency, are distinctly seen of the same colour as the liquid, while the
other portions of the body remain unchanged. Some species of the
polygastrica have upwards of 100 stomachs, others only four. Sap
green is the colour most easily imbibed by the tiny beings ; carmine
shows development better than any other ; whilst the indigo, which
Ehrenberg found to answer his purpose most satisfactorily, is rather
difficult to manage. Care has always to be observed that the colours
are not those that chemically combine with water, but only such as are
diffusible through the fluid in a state of minute subdivision, as other-

* Christian Gottfried Ehrenberg, medical counsellor and professor at Berlin, was
born at Delitzoch in 1795, and educated at Schulpforta and Leipzig. In 1820-25, he,
in company with Hemprich, visited Egypt and Nubia at the expense of the Berlin
Academy ; and in 1829 ho accompanied Alexander von Humboldt to the Ural Moun-
tains. The results of these journeys he published in various invaluable works, which
will hand his name down to posterity with undying honour.

144 THE MICROSCOPE.

wise they are poisoned by it. This important discovery of feeding the
little things on colour set aside the opinion of previous naturalists,
that they effected nutrition by cuticular absorption ; it also led to a
classification, not, as formerly, by shape, but structure.

Monas Termo, or End Monad. — The name given these animalcules
is from their appearing, under the greatest power of the microscope, as
mere ends or points ; in fact, to catch a glimpse of them is very diffi-
cult, as they are round in shape, and of a bright transparent appear-
ance.

Monas Atomus. — The atom monad has always a round body, and
varies from the 6000th to the 3000th of an inch in diameter ; it is of
the colour of water.

Monas Grandis. — The great monad appears in a variety of bright
colours ; it is oval in form, and when floating on the tops of ponds and
ditches, the water seems encrusted with slime.

Monas Mica. — The grain monad is about the 1500th of an inch in
size, and two oval-shaped bodies are perceptible in it ; but that which
renders it an object of interest when viewed through the microscope,
is a beautiful halo that surrounds it, which is supposed to proceed from
cilia, or hair in motion; it is often seen to revolve on its own axis.

Monas Uva. — The grape monad is so named from a resemblance to
a bunch of grapes, when the animals form themselves into clusters, as
they usually do. They are oval in form, have two cilia, and are won-
drously active in pursuing and devouring their lesser brethren, several
of whom they consume at a meal, having, according to Ehrenberg, no
less than twelve stomachs to fill. They multiply both by eggs and
self-division ; scientifically, they are termed oviparous and gemmipa-
rous, When they propagate in the latter mode, their bodies divide
into four parts, forming as many distinct animals.

The Gonium, or Tablet Monad. — Enclosed in a flat hyaline envelope,
irregular in shape, and not larger than one three-hundredth of an inch
in length, is discovered a happy community of sixteen bright green-
coloured cell masses, which at times exhibit a rhythmical contraction
and expansion, as in the Volvox. These are sometimes called Breast-
plate Animalcules (fig. 95, No. 3). They move about in all directions,
upwards and downwards, forwards and backwards, and rolling on the
edge like a wheel. The twenty-four cilia projecting from the sides,
and eight from the centre, appear to be actively engaged in satis-
fying that first law of nature, self-preservation by food. They are
bound to each other, not only by mutual will,, but by six threads or
tubes. The four centre animals are usually bigger than the others.

INFUSORIAL ANIMALCULES.

145

When they have all attained their growth, the shell divides into four
parts, leaving four monads on each ; these four grow in size, and each
again divide into four, hence arises their magic number of sixteen ;
then, as soon as the sixteen are of a mature size, they divide into a
community of four ; and thus go on dividing and subdividing, end-
lessly fulfilling their appointed destiny in links of creation.

fig. 95. Infusorial Animalcules.

Group of Vibrio Spirilla. 2. Enchelis, or Flask Animalcules. 3. Gonium pec-
tor ale, or Breast- plate Animalcules. 4, 5, 6. Amceba, or the Proteus, represented
in the forms it commonly assumes. 7. Vorticella cyanthina, or bell-shaped ani-
malcules. 8. Berg-mehl, or Mountain-meal Animalcules. 9. Echinella, or Fan-
shaped Animalcules ; an enlarged view of one is seen by the side of the cluster.

VIBRIO. VIBRIONES.

In this family Ehrenberg includes the well-known eels of paste and
vinegar, which must be altogether rejected.

Vibrio Spirilla, Trembling Animalcules, when motionless, are seen
as very minute hairs ; but when they exert the powers of locomotion,
they take a spiral form, like the threads of a fine screw, and by undu-

146 THE MICROSCOPE.

lations wind themselves through the water with rapidity. Each appa-
rent hair is a collection of animals bound together by a pliant band ;
thus, as they are individually so small, little is known of their struc-
ture. 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 at No. 1, fig. 95.
One in particular has been the especial subject of investigation by the
medical microscopist : it is somewhat of an oval shape, and found in
many forms of diseased structure ; doubtless it precedes or leads to the
entire destruction of the tissue it is found in. This shape of the
curious little animalcule, it should be observed, is confined to animal
substances ; whereas the long, or hair-shaped, is generally to be met
with in the disorganisation of vegetable matters.

These hair-like animalcules were very accurately described by Baker,
who ascribes the discovery of them to Mr. Anderson. He says : " They
were discovered in a large ditch running into a river near Norwich,
the bottom of which was covered with them to some thickness ; when
first examined, being motionless, they were taken for vegetable fibres ;
but on keeping them under the microscope, and occasionally viewing
them, they were seen to move in various forms."

ASTASIJEA.

Astasia. — Astasia, signifying without a station, in contradistinc-
tion 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 enor-
mous numbers, and give the waters in which they live the appearance
of their bodies.

Astasia Hcematodes. — The blood-like astasia is first of a green
colour ; but as it matures, becomes red, the tint by which it is desig-
nated.

Astasia Viridis. — On the surface of ponds and stagnant waters
is sometimes seen a crimson covering, which, when examined by a
microscope, is found to consist of a mass of oblong blood-red eye-ani-
malcules the 300th of an inch in length. Ehrenberg states, that in the
early part of their existence they are green ; and that the red and green
spots on their bodies are caused by the condition of the eggs at different
periods in their stomach-cells. A sparkling red eye is possessed by the
living atom ; and a cilium proceeding from its mouth gives it motion,
sometimes in a straight line, at others rolling about in all manner of
ways. When two cilia are seen, then the animal is about to divide

INFUSORIAL ANIMALCULES. 147

into two perfect and separate beings, to proceed again in the career of
its original. They seem to have the power of changing their shapes
at will ; at one time they have a rolling-pin form, at another that of a
fish without a tail, and are also seen with their bodies extended at the
side like wings. This family corresponds to the Englenia of Dujardin;
but they are still very imperfectly known. Astasla are distinguished
from Amoeba by the absence of the irregular foot-like process sent out
by the latter from all parts of the body.

Enchelia, Flask Animalcule (fig. 95, No. 2). These are described
by Miiller as simple invisible animalcules of a cylindrical form. On
the surface of the waters of ponds and ditches is often seen a
kind of green scum, from which people are accustomed to turn with
disgust, and ascribe to it some injurious property. When this is
brought under the powers of the microscope, the water is seen to be
pure and clean, and the green found to consist of innumerable slender
. cylindrical- formed animalcules, whose stomachs, or interiors, impart
the colour from being distended with vegetable matter. The wise and
loving decrees of Providence are here exemplified, as, by the innate
wants of this growing and living speck, varying in size from 1-1 200th
to 1 -400th of an inch, the decaying and putrefying matter is removed,
and the noxious effects on man and beast prevented. Others, of the
same species of these industrious and useful mites in the animal eco-
nomy of nature, with their little active ruby-coloured eye, whose masses
alone render them visible to the human eye as a coloured substance,
exhibit much variety in form and habit.

ACINETIN^EA.

The Acineta of Ehreriberg. — Actinoplirys Sol, " sun-animalcule,"
abounds in pools, where Desmidiacece are founji, in many parts of Dorset-
shire ; they are ravenous feeders, not only upon the Desmidiacece, but also
upon all kinds of minute spores and animalcules. 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. The creature also
seems to be capable of altering its entire form to a certain extent, and
to be able to expand and again contract itself in toto. Stein's researches
render the existence of this species doubtful, by showing that similar
forms are but the intermediate stages of development of vorticella.

148

THE MICROSCOPE.

DIATOMACE.E.

Among the organic beings, whose existence the microscope has
revealed, few possess a higher interest than the group of Infusoria now
known as Diatomacece, or Brittleworts. Appearing every where as the

fig. 96. Skeletons of Diatomacece.

Gomphonema capitatum and elongatum ; Diatoma vulgare ; Achnanthidum lineare,
and coarelatum ; Amphitetras antediluviana, front view ; Orthosira spinosa, front
view ; with globular and oval forms, found at Springfield, Barbadoes.

first-born of life, and wherever inorganic matter is found in a condition
fit for their development, and being provided with a siliceous shell,
their forms remain unchanged from the remotest periods of this world's
history. Recent specimens are of a green colour, with a tinge of
brown ; in form generally that of a prism, or four-sided ; and their
flinty remains consist of one or more pieces, the delicate lines of which,
and the fineness of their tracing, set at defiance the most wonderful
efforts of imitation. They are found abundantly, both in the inland
waters and the ocean, often carried through the air as particles of fine
dust. The earliest observers considered them to be animals, undoubt-
edly; and animals they were decidedly pronounced by Ehrenberg.
Later investigators have declared them to belong to vegetables. I be-
lieve, with Kutzing and others, that they are rightly placed by Ehren-
berg among the earliest forms of animal life. During my examina-
tions of the ciliary motion in the Desmidiacece, near the end of the

INFUSORIAL ANIMALCULES. 149

summer of 1854, I frequently noticed in many of the more common-
met-with forms of the Diatomaceae a similar arrangement of cilia. I
have attentively watched a diatomean moving slowly across the field
of the microscope ; when upon meeting with an obstacle to its progress,
it has changed its course, or pushed the obstacle aside, as if conscious
of an impediment. I have again and again satisfied myself that their
motive power is derived from cilia, so arranged at either end, in some
apparently around central openings, that they might readily act as
propellers, or paddles. This arrangement is merely indicated in the
very rough sketch I made at the time, hoping to have had other op-
portunities of rendering my illustra-
tions more perfect. Before satisfying
myself of the presence of cilia, I thought
the motion of these little creatures
somewhat remarkable, steering their
course as they did by a power which
they evidently were able to call into
action, or restrain at will. I was there-
fore agreeably surprised to find this
motive power due to cilia. The distri-
bution of the cilia differs from that observed in the Desmidiacece ; the
ciliary motion seen in which I believe to be due to a physical force
acting independently of any controlling power. On the contrary, with
the Diatomacese, their cilia may be said to act in obedience to a will,
for intervals of rest and motion are clearly perceptible.

With Kiitzing, we may say that every diatomean is formed of a
siliceous shield, and a soft substance therein contained ; this shield
consists of pure silica, or in some cases, perhaps, of silica combined
with alumina. Nageli believes the silica is deposited in the outside
organic membrane, but this he believes to be of a vegetable nature.
In fact, an organic membrane ought to exist ; for the silica could not
become solid, except by crystallising or depositing itself on some pre-
existing substance. On the other hand, we cannot admit, with Nageli,
that it has been deposited externally ; for in many genera, and espe-
cially in the Achnanthidia, the siliceous shield is covered with a very
delicate dilatable membrane, itself containing silica, as is proved by
its sustaining unchanged the action of fire and acids. Therefore, com-
paring this shield with other organic formations, whether animal or
vegetable, containing, in like manner, either silica or some other so-
called mineral element, we might reasonably consider it to be formed
of an organic tissue permeated by silica.

150 THE MICROSCOPE.

Comparing the arguments which seem to indicate the vegetable
nature of Diatom acese with those which favour their animal nature, we
are of necessity 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 in-
ternal substance corresponded with the genimic substance, and that the
oil globules could take the place of starch. The multiplication 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 unexplained the ex-
ternal motions and the internal changes ; and we must prove Ehren-
berg's observations on the exterior organs of motion to be false. But
again, admitting their animal nature, much would remain to be investi-
gated, both in their organic structure and their vital functions ; except-
ing this, so far as we know, we have only one difficulty 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, so the
absence of it is not a proof of vegetable. And in order that the objec-
tion should really have some weight, it would be well to demonstrate
that this substance is isomeric with starch. For then, supposing all
the arguments in favour of the animal nature of Diatomaceee were
proved by new and more circumstantial observations, this peculiarity,
if it deserve the name of objection, might still be regarded as an im-
portant discovery. We should then have in the animal, as well as in
the vegetable kingdom, a ternary substance similar to that forming
the basis of the vegetable tissue. " I conclude," observes Kutzing,
ft however, that in the present state of science, the Diatomacese are
to be enumerated among animals."

I should recommend microscopists to conduct their observations of
these and similar bodies in very shallow cells, say of from l-50th to
l-100th of an inch deep, covered with glass of from l-150th to 1 -250th
of an inch thick. The objective must be a l-4th or 1-Sth, with a
good eye-piece, and careful illumination — Eainey's moderator with a
Gillett's condenser or parabolic reflector. The examination should be
conducted during very bright weather, or sunlight.

INFUSORIAL ANIMALCULES.

151

Bid our space permit, many other arguments might be adduced in
favour of the views we have herein advocated ; but we must refer the
reader to the works of Kiitzing and Ehrenberg for further informa-
tion.

Dr. Gregory believes that a large number of those Diatomacese
usually given as separate species, are nothing more than transition
forms of the same ; and that more extended observation has proved
that form, shape, or outline is not nearly so permanent a character as
had been imagined ; and he adds, " the more the Diatomacese are
studied, the more we perceive that, in many species at least, the shape
or outline is subject to endless variations."*

The markings of the Diatomaceae are best seen when mounted dry :
they are usually mounted in Canadian balsam, or weak spirit and
water. Before quitting these interesting objects, we shall notice a few
of the commoner forms, reserving our remarks upon other species
until we come to fossil Infusoria.

Naviculce. — Navicula is the Latin word for ship, and has been ap-
plied to these little creatures from
their resemblance in form to a
long ship or boat. In the cata-
logue of the microscopist there are
upwards of twenty-four different
species named, fourteen of which
are at the present day found alive,
fig. 98, Nos. 1, 2, and 3. From
their beauty and minuteness, they
are used as test objects. It was
only in 1841 that Mr. Harrison, of
Hull, discovered the beautiful longi-
tudinal and transverse sir ice (groov-
ings) on the Navicula hippocampus,
or sea-horse ship, No. 1. A curved
graceful line runs down the shell,
in the centre of which is an ex-
panded oval opening, and smaller
ones at each end. Near to the fi

central opening the dots elongate L Navicuia hippocampus. 2. NavULla an-
crossways, presenting the appear- gulata, magnified 250 diameters. 3. Navi-
ance of small short bands. The cula Spencerii, magnified 350 diameters.

* Dr. Gregory, " On a remarkable group of Diatomaceous Forms/' — Quarterly
Journal of Microscopical Science.

152

THE MICROSCOPE.

Navicula angulata, No. 2, cornered little ship, was first discovered in
the Humber; the lines upon its surface resemble the most elegant

tracery, which are resolva-
ble into raised minute dots.
The markings are seen to
be longitudinal, transverse,
and oblique. Man boasts
of the fineness and perfec-
tion of his handicraft ; his
manufacture will be so
small that a magnify ing-
glass is required to observe
it ; he will proudly display
a piece of lace of most fra-
gile material ; but when he

fig. 99.

once gazes through the mi-

1. Pleurosigma angulatum. 2. Portion of the same, croscope at these objects,
magnified 1200 diameters. 3 Portion of P. for- invigible t hj naked
mosum magnified 5500 diameters. . J '

and sees the perfection of

Nature's works, he feels abashed, and sinks, conscious of the futility
of his attempts to rival the accuracy and completeness given by a
guiding power to the most insignificant of its creations.

The Green Navicula was found by Dr. Mantell in a pool on Clap-
ham Common ; it is about the 100th part of an inch in length. In
this specimen the ribbed division is distinctly seen, extending the
whole length of its shell.

The Golden Navicula is another beautiful species, and was so named
from the numerous points within the shell giving it a bright yellow
appearance. The shell is an oblong oval, and has upon it numerous
delicate and regular flutings.

The Eunotia. — In this species a furrow is seen the entire length of
the shell, from which spring numerous ribs tending towards the edges ;
of these, eight maybe counted in the 1200th of an inch; there can
also be traced, in the length, a line, by which, when at maturity, the
animal divides, and in this manner preserves its generation from age to
age. See Plate II. No. 13.

Siebold says : " I have been unable to detect six openings in the
Navicula; and precisely at the spots which Ehrenberg and others
suppose they have seen openings, the siliceous cell-membrane becomes
thickened, and forms rounded eminences which project internally. On
the same two surfaces upon which the thickenings of the siliceous

COLLECTING AND PRESERVING DIATOMACE^E. 153

shield of Navicula are placed, there may be observed four lines pass-
ing along the middle of the surfaces from one thickening to another.
These lines — which have been long known, but hitherto little noticed
— are to be referred to a suture, fissure, or rather gap, in which no
siliceous matter is deposited ; so that in these places the delicate prim-
ordial membrane which lines the siliceous shield can be brought in
close relation with the outer world. It is exactly at these four sutures
or fissures that the water surrounding the Navicula is set in motion.
The existence of this current is readily demonstrated if some minute
solid particles be added to the water in which are some fresh Naviculae.
When water coloured with indigo has come to a state of rest on the
object-glass, it will soon be perceived by the microscope that those
particles which come in contact with the living Naviculse are set into
a quivering motion, though previously quite still. It will also be per-
ceived, that only those particles of indigo are set in motion which are
in contact with the four sutures of the siliceous shield ; whilst the par-
ticles adherent to the other parts of the shield remain altogether mo-
tionless. Another striking motion is perceptible in these particles
when they come in contact with the sutures of the siliceous shield,
feeing forced rapidly up and down upon it. Those particles which are
propelled from the terminal towards the two central eminences, are
never observed to pass beyond the latter; at this point there is always
a quiet space, from which the particles are again repelled towards the
extremities. This proves that the linear sutures do not extend over
the central eminences of the shield. At these clefts the current is
sometimes so strong, that comparatively large bodies are set in motion
by it."

COLLECTING AND PRESERVING DIATOM ACE m.

The following directions by the Rev. W. Smith for collecting and
preserving the Diatomacese, may prove useful to the student : " Let
him provide himself, in the first place, with the necessary apparatus
for the field : this includes a good stock of small wide -mouthed bottles,
that each gathering may be kept perfectly distinct ; a long rod or
stick, to which can be attached a small muslin net ; a cutting-hook
of about three inches in length, and a broad flat spoon ; the first, to
collect such specimens as float upon the surface, or are held in sus-
pension by the water ; the second, to remove the larger algae which
may be covered with parasitic Diatorus ; and the third, to skim the
surface of the mud for those which lie at the bottom of the pool.

He will probably find, notwithstanding every care, that his speci-

154 THE MICROSCOPE.

mens 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 students may remove in various ways : by re-
peated washings in pure water, and at the same time profiting by the
various specific gravities of the Diatorus and the intermixed substances,
to secure their separation ; but, more particularly, by availing himself
of the tendency which the Diatomacese 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 sun-
light, 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 scientific observer, is simply to dry them
upon small portions of talc, which can at any time be placed under the
microscope, 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."

In the vicinity of Hull many very interesting varieties of Diato-
maceaB have been found, the beauty of the varied forms of which are
such as to delight the microscopist ; and, at the same time, some of
them are highly useful, as forming that class of test objects which are
best calculated of all others for determining the excellence and powers
of our object-glasses. It has been shown by Mr. Sollitt that the mark-
ings on some of the shells were so fine as to range between the 30,000th
and 60,000th of an inch ; the Pleurosigma strigilis having the strongest
markings, and the Navicula acus the finest.

DESCRIPTION OF PLATE II.

1. Shell of Arachnoidiscus. 2. Shell of Actinocyclus (Bermuda). 3. Shell of
Cocconeis (Algoa Bay). 4. Shell of Coscinodiscus (Bermuda). 5. Shell of Isthmia
enervis. 6. Zygoceros rhombus. 7. Campylodiscus clypeus. 8. Amphitetras. 9.
Gallionella sulcata. 10. Triceratium, found in Thames' mud. 11. Gomphonema ge-
minatum, with their stalk-like attachments. 12. Dictyocha fibula. 13. Eunotia.
14. Cocconema. 15. Fragilaria pectinalis. 16. Meridion circulare. 17. Diatoma
flocculosum.

PLATE II.

SILICEOUS SHELLS OF FOSSIL INFUSORIA.

FOSSIL INFUSORIA.

FOSSIL INFUSORIA.

'TARTLING and almost incredible as the asser-
tion may appear to some, it is none the less
a fact, established beyond all question by the
aid of the microscope, 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 also our massive lime-
stone rocks ; the sand that covers our bound-
less 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 individual 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 pro-
perties being the same, in commerce they both pass under the name of
Tripoli. One merchant alone in Berlin disposes annually of twenty
tons weight. The thickness of a single shell is about the sixth of a
human hair, and its weight the hundred-and-eighty-seven-millionth part
of a grain. The well-known Turkey-stone, so much used for the pur-
pose of sharpening razors and tools ; the Rotten-stone of commerce, a
polishing material ; and the pavement of the quadrangle of the Royal
Exchange, are all composed of infusorial remains.

The bergh-mehl, or mountain-meal, in Norway and Lapland, has
been found thirty feet in thickness ; in Saxony twenty-eight feet thick ;

156 THE MICROSCOPE.

and it has also been discovered in Tuscany, Bohemia, Africa, Asia,
the South Sea Islands, and South America ; of this, almost the entire
mass is composed of flinty skeletons of Diatomacese. That in Tuscany
and Bohemia resembles pure magnesia, and consists entirely of a shell
called campilodiscus, about the two-hundredth of an inch in size.

Dr. Darwin, writing of Patagonia, says : " Here along the coast, for
hundreds of miles, we have our great tertiary formation, 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
Professor Ehrenberg has already recognised 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 thickness 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 organisation. At Kichmond 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 animalcules ; for in the slightest particles of it they are disco-
verable. On these myriads of skeletons are built the towns of Rich-
mond and Petersburg. The species in these earths are chiefly the Navi-
cula ; but the most attractive, from the beauty of its form, is the Cos-
cinodiscus, 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 computes, 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 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

FOSSIL INFUSORIA. 157

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 incomprehensible, 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 become ultimately deposited on the island, 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 civilised
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 micro-
scopically by Ehrenberg, was found chiefly to consist of the flinty shells
of Infusoria, and the siliceous tissue of plants : of these Infusoria, sixty-
four proved to belong to fresh-water 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 j and
he found the nutritive principle to consist of fossil Infusoria. So pro-
fusely 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 submerged forest on the coast, numbers of fresh-water
fossil Diatomacese have been discovered, although the sea flows over
the place at every tide.

Before entering on further details of the fossil Infusoria, we would
first state how they may be prepared for microscopic examination.
A great many of the infusorial earths may be mounted as objects with-
out any previous washing or preparation ; some, such as chalk, how-
ever, must be repeatedly washed, to deprive the Infusoria of all im-
purities ; 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

158 THE MICROSCOPE.

take place, which may be assisted by the application 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 consists of silica, will con-
tain all the infusorial forms ; and some of this may be taken up by a
fishing-tube, laid on a slide, and examined in the usual manner. Should
perfect specimens of the Coscinodiscus, Gallionella, or Navicula 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 ; or, if good, after being dried, may be
mounted in Canada balsam.

Dr. Redfern has given us an excellent mode of isolating Naviculse
and other test- objects. He says : Having found the methods ordinarily
employed very tedious, and frequently destructive of the specimens, I
adopted the following 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 through a slit in a
piece of cork, use it as a forceps under a two-thirds of an inch objec-
tive, 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 being brought up to the object,
are easily made to seize it, when it can be transferred as a single spe-
cimen 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 extremity 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.

We now proceed to notice in detail some of the most interesting of
the fossil Infusoria.

Professor J. W. Bailey, of New York, has enriched the Museum of
the College of Surgeons with several valuable specimens of the skele-
tons of Infusoria ; among them is a fresh-water Bacillaria, named

FOSSIL INFUSORIA. 159

Meridian 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 certain positions,
they resemble circles ; each lorica is articulated by two lateral sur-
faces. It is asserted that they can creep about when free from the
stalk-plate. (Plate II. No. 16.)

Cocconimo Eoeckii is composed of 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. (Plate II. No. 14.)

Achnanthes Longpipes 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. They pro-
pagate by self-division.

In a specimen of a fossil Eunotia, found in some Bermuda earth,
the flinty case is in four parts ; it is of a half-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. Ehren-
berg says they have four openings, all on one side (Plate II. No. 13),
presenting a row of dots varying very much in number ; minute strise
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 Fragillaria pectinalis, which consists of a number of bivalve
parts : on the articulating surface there are small grooves, represented
in Plate II. No. 15. A singular class of objects are Diatomce floccu-
losce, being rather oblong-looking, and joined to each other at oppo-
site corners ; sometimes they are grooved on each side. (Plate II.
No. 17.)

A recent specimen of the flinty, wedge-shaped Gomphonema gemi-
natum (No. 11), fixed on a horny stalk, is in the Museum of the Col-
lege of Surgeons. Ehrenberg states they have two openings at their
hemispherical or indented broad ends. The surfaces are grooved cross-
ways. There is another kind, commonly called the Swollen Eunotia,
which is generally about from the eleventh to the two-hundreth of
an inch in length. A groove, that is widest in the centre, and tapers
off to the ends, passes along its centre on both sides, with curved lines
proceeding from it. So wonderfully close are these lines or ribs, that as

160 THE MICROSCOPE.

many as eight of them have been counted in the space of the twelve-hun-
dredth 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 de-
veloped as a distinct object ; and thus from age to age they grow and
separate, filling the earth with their flinty shells. The earth found in
the river Upper Baun, Ireland, contains an abundance of Gallionella
distans, so plentiful in the State of Bilin, and the bergh-mehl of
Sweden.

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 loricae, having their outer
surfaces marked or furrowed with longitudinal striae ; short joints may
occasionally be seen having their ends uppermost, the depth of the
furrows being shown on the margin j within the margin is a thin trans-
parent rim having radiating striae. Sometimes as many as forty will
be found joined together (See Plate II. No. 9). The Gallionella received
its designation from a celebrated French naturalist named Gaillon, and
is often termed the Box-chain Animalcule; and when the flinty case is
seen lying on its face, it much resembles a coin. These animalcules
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 pro-
duced 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 will be found three inches
long ; the size is from the 14th to the 400th part of an inch.

The beautiful Navicula, or Little Ship, is found in all parts of the
world ; and from being met with most readily near London, has been
minutely examined and carefully described. Professor Quekett, in the
catalogue we have before referred to, describes an " Earth from Bo-
hemia, particularly rich in fossil specimens of Navicula viridis, which
consists of four prismatic loricse, two ventral and two lateral; the
former having round, the latter truncate extremities; and both pro-
vided with two rows of transverse markings and dots, longer and
more marked on the ventral than on the lateral surfaces. The speci-
mens having their ventral surfaces uppermost, exhibit a longitudinal
marking in the centre, with a slight dilitation or knob at each extre-
mity ; 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

FOSSIL INFUSORIA. 161

two of the same spots will be seen, one on each side ; they are of tri-
angular 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 con-
siderably; some exceed l-100th, whilst others are even smaller than
1-1 000th of an inch.

Isthmia Enervis (No. 5) is 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 are Amphitetras antedilu-
viana ; they are of a cubical or box-like figure, and consist of three
portions, the one in the centre being in the form of a band, as shown
at Plate II. No. 8, and the two lateral ones having four slightly-pro-
jecting 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.

Oocconeis is oval, and is marked with eight or ten lines proceeding
from the inner margin to the centre; between which are dotted fur-
rows, which leave a small elder spot in the centre. (Plate II. No. 3.)
Campylodiscus Clypeus is oval, and curved in opposite 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. (Plate II. No. 7.)

Actinocydus has a round bivalve flinty case, with numerous cells
formed by radiating partitions. Sometimes only every alternate cell
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 minute circles. One of the valves of this specimen
is represented in Plate II. No. 2.

M

162 THE MICROSCOPE.

Artists who design for art-manufacturers might derive many use-
ful hints from the revelations of the microscope, as evidenced in the
arrangement of the shell last noticed, and in that of the genus Cos-
cinodiscus, another handsome object; the shells are marked with a
network of cells in a hexagonal form, arranged in radiating lines or
circles ; they vary 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 ; they are
gradually larger from the centre to the margin. The angles of the
cross are filled with the hexagonal cells previously noticed. (Plate II.
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 or
cells are beautiful, and at each corner there is a curved projecting horn
or foot. (Plate II. fig. 10.) In Bermuda earth there is a small species
found, which has its three margins curved ; and also a curious species,
which resembles a triradiate spiculum of 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 any generic types, as in the 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 encountered on every
side by forms which set at nought our definitions.

Zygoceros rhombus is in three parts ; one central, which is like a
broad band, the others lateral, of a rhomboidal shape, and curved;
while at each corner is a projecting piece like a spine. It is en-
tirely marked with very small dots. (Plate II. No. 6.)

As well as the beautiful shell of the Cosdnodiscus, 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. (Plate II.
No. 1.) This is met with in the guano of Ichaboe; it is also found in
the United States, as well as among the sea-weed from Japan, and the
algse of the Cape of Good Hope. Mr. Shadbolt says : " These shells
are not, strictly speaking, bivalves, although capable of being separated
into two corresponding portions ; but are more properly multivalves,
each shell consisting of two discoid portions, and two annular valves

VOKTICELLID^E. 163

exactly similar respectively to one another." See Microscopical Society's
Transactions for an excellent paper on these shells by Mr. Shadbolt.

Man even uses infusorial remains as food ; for the berg-mehl, or moun-
tain-meal (represented in fig. 95, No. 8), 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, Navicula viridis, and GompJwnema gemminatum. Dr. Trail,
on analysing it, found it to consist of 22 per cent of organic matter, 72
of silica, 5-85 of alumina, and 0'15 of oxide of iron. This would 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 sea-
sons of extreme dearth. One of our Christians, who, at the period of the
last famine, fed upon this substance, with five other individuals com-
posing his family, informed me, when they made use of it, they bruised
it into a very fine powder, mixing three parts with two of rice-powder,
or, better, the flour of wheat, to make small eakes, which were seasoned
with salt or sugar. Kecourse was only had to this in times of great
want ; and this being over, no one ever dreamt of making use of it as
an article of food. Those accustomed to partake of it complained of a
weight at the stomach and constipation. They could subsist for two
months on this material formed into cakes ; whilst without its assist-
ance, their provisions would only suffice as food for one month. Those
persons who employed the fossil-flour without mixing it with vegetable
meal, scarcely ever escaped disease."

VORTICELLIDJ2.

We now come to a family which includes some of the most beauti-
ful of the infusorial animalcules, and in which we meet with phenomena
more curious than any we have yet witnessed, and perhaps as wonderful
as any that will be presented to our notice, when studying the natural
history of the higher classes of animals. This is the family of the Vor-
ticellidce, or bell-animalcules. The animals of which it is composed are
characterised by the possession of a fringe of rather long cilia, surround-
ing the anterior extremity, which can be exerted and drawn in at the
pleasure of the creature. Some are furnished with a horny case for
the protection of their delicate bodies, 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

164 THE MICROSCOPE.

nevertheless 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 Vorticella 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, rooted,
as it were, to a single spot by its slender stalk; its Creator has fore-
seen the probable arrival of a period in its existence when the power
of locomotion would become 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 developed; 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 phenomena.

The Vorticella possess means of propagation which is denied to
other Infusoria, with the exception of a few nearly allied genera,
although we shall meet with it again in other classes of animals. The
mode of reproduction is called gemmation. It consists in the produc-
tion 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 ex-
tremity, and fix themselves in a new habitation in exactly the same
manner as the individuals produced by the division of the bell.

At an earlier or later period of their existence, the Vorticellce with-
draw the disc surrounded by cilia, which forms the anterior portion of
their bodies, and contracting themselves into a ball^ secrete a gela-
tinous covering, 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 complicated. 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 into which
the substance of the 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 con-

VORTICELLID^:. 165

siderable 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, the enclosed embryos, are suddenly shot out into
the water, there to become diffused, and give rise to a new generation.
From the name Acineta given by Ehrenberg to these, 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 ani-
malcule into the Acineta-form was still distinctly observable, becomes
entirely and altogether converted into an active young Vorticella, ac-
quiring an ovate form, with a circlet of cilia round its narrower extre-
mity, 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 mem-
branes inclosing the Acineta, which however immediately close again.
The latter continues protruding and retracting its filaments, and soon
produces in its interior a new nucleus, which in its turn becomes
metamorphosed into young Vorticella.

The same faculty of inclosing themselves in a cyst is said to be
made use of by the Vorticella, as a means of self-preservation when the
water in which they have been residing dries up. When the animal is
thus encased, the mud of 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 surface of the parched ground and borne along to great dis-
tances, so as to cause their appearance in most unexpected localities
(they are frequently found in roof gutters), where the first shower of
rain calls them back to active life. These processes are repeated in
several of the allied genera with so little variation, as far as observa-
tions have hitherto shown, that it will be unnecessary to mention them
more particularly.

Vorticella cyanthina, fig. 95, No. 7, has a fringe of cilia surrounding
the margin of its cup. A single animal is first seen, which increases
and then divides into two perfect animals, joined by a stem.

Stentor, or Trumpet Animalcule, belongs to this family, fig. 100,
No. 4. Its body is of a trumpet-shape, and it adheres to its point of
attachment by a pointed extremity. They are of various colours — white,
blue, yellow, red, and green. They swim in a parallel line to their sides,
sometimes tail first, rotating on their own axis. They attach them-

166

THE MICROSCOPE.

selves to objects by a sucker at the lower part. Some of them have
cilia over their entire bodies, and a good fringe over their gaping
mouths, which is a type of their ravenous nature. The prey may be
seen in their row of stomachs, as if strung like a strap of beads up and
down its interior. They differ from many gluttons by possessing great
activity, moving swiftly through the water. They are said to increase
both by eggs and self-division. There are many species, differing in
size, shape, and colour. Usually they are about the hundredth part of
an inch in size. When found, they appear a mass of green jelly encir-
cling a twig. Often, when swimming, they take the form of a cup,
having their tails drawn within their bodies.

fig. 100.

1, 2, 3. Hydrce, or fresh-water Polyps, attached to the stem of a plant 4. A group
of Stentor polymorphus, or Multi-shaped Stentor. 5, 6. Monads, Viviparous and
Cloak Monads.

Stentor Cceruleus, or Blue Stentor, is remarkable from having a crest
extending along its body \ it assumes a peculiar shape when swimming,
appearing to possess a thick tail nearly one half the breadth and
length of its body.

Upon quitting these animalcules, we may notice this peculiarity,
that when they are procured from infusions the first instances of life

ROTATORI.E.

167

are generally the Monads, which in a very short period increase to a
most extraordinary extent. These afterwards gradually decrease, larger
and more perfect creatures supplying their place, as the Peridinida,
Paramesia, Trachelina, Acineta, and others ; and these, again, are sup-
planted by the Vorticellse and Branchionsea. Though the generations
thus rise up, there is no regular order in their doing so, even in the
same infusions.

THE ROTATORI.E, ROTATING OR WHEEL-ANIMALCULES.

This higher grade of the Infusoria, now classed among the Articu-
lata, derives its name from the appearance presented by the motion of
its circles of cilia on the superior part of its body, which resembles the
turning round of a wheel, as they rapidly vibrate. Many have been

fig. 101.

1. The common Wheel- Animalcule, with its cilia or rotators pbinted. 2. The same
in a contracted state at rest : at g is seen the development of the eyes in the
young. 3. Pitcher-shaped Brachionus : a the jaws ; b the shell ; c the cilia, or
rotators ; d the tail. 4. Baker's Brachionus : a the jaws and teeth ; b the shell ;
c the rotators ; e the stomach. 5 and 6. Other forms of the same family,

the speculations as to the mechanism of this beautiful movement : some
have considered it as a magnetic or electrical force; and as one passes

168 THE MICROSCOPE.

out of sight while the next appears, adding to the optical illusion, a
philosopher of considerable note was led to look upon the whole as a
deception of the sight, and affirmed they had no existence. The cilia
processes appear but in one part of the Rotifera ; whereas in the Vor-
ticellidse, cilia are seen in various parts of the body.

These animalcules are only discovered in water, which is their
native element ; still they are found in damp earth, and are indwellers
of the cells of rnoss and sea-weed. They possess but one stomach, and
generally have teeth and jaws to supply its wants. They can elongate
and contract their bodies ; and some species have at their extremity a
kind of tail with a sucker, by which they affix themselves to extraneous
substances while the cilia is in rapid motion, and thus prevent the su-
perior portion of the body being drawn in by the force of the rotatory
action. They multiply by eggs j but some bring forth their young
alive. Both the animal and its eggs possess extraordinary tenacity of
life, and will undergo the most opposite extremes of circumstances
without destruction to the living principle.

In the atmosphere the eggs may often be discovered whirling along
by the force of the wind to some resting-place, where, when circum-
stances admit, they spring into active life, and fulfil their appointed
destiny. Ehrenberg accurately described the upper part of a common
wheel-animalcule, with the cilia, jaws, teeth, eyes, as seen under a mag-
nifying power of 200 diameters, represented at 1, fig. 101.

The small arrows show the direction of the currents produced by
the cilia turning on their base. At the will of the animal a change is
made in the direction in which the wheels appear to revolve, and they
have the power of withdrawing, with the quickness of thought, the
whole of the wheel-work ; when this is done, the head is elongated, and
with a telescopic appearance, as if capable of sliding within itself. On
assuming this form, a cluster of hairs appears at the extremity, that
do not revolve, and are considered different from the cilia : as they are
usually protruded when the creature is moving from place to place, their
functions have been imagined to be that of feelers, shown in No. 2.

The red spots supposed to be the eyes of the Rotatoria are generally
of a bright red colour; but the number and arrangement of these organs
vary. In some kinds there have been discovered as many as eight,
sometimes placed on each side of the head, in a row, in a circle, or in
clusters ; and in others, in a triangular shape.

Ehrenberg, from actual observation, found that the Rotatoria laid
four eggs a day ; that the young, when two days old, followed the same
law as their parents ; consequently, a single one in ten days had a

ROTATORIA. 169

family of 1,000,000, in eleven days 4,000,000 ; and in twelve days the
venerable progenitor was surrounded by 16,000,000 of an active,
happy, energetic race, ceaseless in search of prey, and a famous feast
for a larger animal.

The Rotatoria delight in the sunshine ; and when the bright lumi-
nary is hidden behind clouds, the animals sink down to the bottom of
the water, and there remain. When the water of their haunts is be-
coming much evaporated, they rise to the top, arid 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 swimming, the ro-
tatory action of the crowns of cilia impelling it forward ; in other
instances it bends its body, then moves its tail up towards the head,
which it can do from having two processes that serve as feet near to
the tail ; it then jerks its head to a further distance, again draws up its
tail, and so proceeds on its journey. Another peculiarity they possess
of drawing in the head and tail until nearly globular, from remaining
in this condition fixed by the sucker • at other times they become
a complete ball, and can be rolled about by any agitation in the water.
The eggs are of an oval form, and from twenty to thirty may be
seen in an animal. Some are of a brown colour, and others of a deli-
cate pink and deep golden yellow. In those of a light colour, the
young may be seen with their cilia in active vibration.

The body of the wheel-animalcule is of a whitish colour j its form
will be seen by the engraving ; and its tail has six points. 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 of the wheels, it
passes down canals in the neck to the mouth, which is situated at the
lower extremity of that part of the body. The food is crushed by the
teeth on the plates of the jaw, with an action like a hammer. From
this it passes on to the alimentary canal for the sustenance of the
animal.

BRACHIONJEA.

Ehrenberg's genus Brachionus, or Spine-bearing Animalcule, be-
longing to the Rotatoria, are truly interesting from their perfect, high,
and complex organisation. Some are entirely enclosed in a shell, and
others only partially covered. Their structure is so beautiful and sym-
metrical as to cause them to be favourites with those who delight
in the studies of microscopic observation.

Brachionus Striatus, or Striped /Shell Animalcule (No. 3, fig. 101), is
of an elegant, jug-like form, the transparent shell being fluted length-

170 THE MICROSCOPE.

wise, and having six scallops at the upper part, whence the pale citron-
coloured inhabitant protrudes itself. Two horn-like processes are ap-
pended to its under-side. As occasions require, it sinks firmly and
securely within its crystal home, through the sides of which its organi-
sation can be distinctly seen. Its progress is effected by means of its
rowing cilia.

Brachionus Pala, or Bent Horn Animalcule, Anurce Cervicornis, is
possessed of double rotatory organs, and four long processes, that pro-
ject above the oval shell. It measures the 90th part of an inch.

Brachionus Ovalis, or ^Egg-shaped Brachionus, is remarkable for the
strength of its transparent shell, which is beyond that of other shelled
creatures. Its projecting tail, as well as head, can at pleasure be with-
drawn into its powerful case. It attains to about the 250th of an inch
in size.

Brachionus Tripos, or Three-spined Brachionus, has its shell in two
parts, united by a joining at the back; it ends in three spines, and be-
tween the two first projects its cleft tail.

Brachionus Dentatus, or TootJied Brachionus. This active, bright,
pink-eyed little creature, the 90th part of an inch in size, is enclosed in
a two-valved shell, having each end indented so .as to form two pair of
teeth. Mr. Pritchard says : " In addition to the rotatory organs for
supplying it with food, I have observed it attached to a stem of con-
fervse, and abrading it with its teeth fixed in the bulbous oesophagus,
which, during the operation, oscillates quickly ; the rotatory cilia at the
same time move rapidly, which makes it highly probable that they per-
form some office connected with the organs of respiration, as their
motion seems altogether unnecessary while the creature is feeding in
this manner."

Brachionus Urceolarie, or Mower-pot Brachionus, resides in a shell
one-half its own length, from which it thrusts out its tail at one end,
and its vibrating cilia at the other : at this latter part it has sharp in-
dentations at one side, and flowing scallops at the other.

Brachionus BaJceri, or Baker's Brachionus (fig. 101, 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 proceeding to a point in the lower
part, while a square seems taken out of its body, forming thus two
spines ; from the centre projects a long tail. The eggs are sometimes
attached to the spines, and in other instances to the tail.

Notom/mata Aurita, the Eared Notommata. — The anatomy of this
animal, of the Rotatoria family, is most lucidly explained and beauti-

ROTATORIES. 171

fully 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 Walthamstow, 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 some-
what 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 pro-
jection higher up the body. When not swimming or rotating, the
head assumes a rounded outline, displaying through the transparent
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 integu-
ment. 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, ordi-
narily 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
every where seen, particularly all about the head."

Mr. Gosse, on puttiijg carmine into the water, saw the jaws work-
ing slightly, the points opening a little way, and then closing; the rods
of the hammers were drawn towards the bottom for opening, and up-
wards 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 j nor did an atom at this time go into the
stomach.

After entering into further minute details of the little animal, he ob-
serves : " They possess organs that many others do not, and want some

172 THE MICROSCOPE.

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
Rotifera occupy a place in the scale of animal life much higher than
that which has been commonly assigned to them."

Of the manners of the species, this careful observer states, that, in
a phial, it frequently clings to the sides of the glass, and appears sluggish ;
but when put into a live-box it is active, especially if there be any con-
fervee, or leaves of chara, or roots of lemna, in the water. Among these
it crawls about nimbly and impatiently, like a caterpillar, pushing itself
in every direction, by means of its two-toed foot, and by the elongation
and contraction of its body, but without any definite course.

It commonly keeps its ear-like lobes concealed while crawling ; but
will often suddenly protrude them, and in the same instant shoot off
through the water with considerable rapidity, and with a smooth, gliding
motion, partially revolving on the longitudinal axis as it proceeds.

Like most of the class, this Notommata is predatory. Mr. Gosse
once saw one eagerly nibbling at the contracted body of a sluggish
Rotifera vulgaris ; the mouth was drawn obliquely forward, and the
jaws were protruded to the food, so as to touch it. It did not appear,
however, to do the rotifer much damage. It seemed chiefly to feed on
monads.

FLOSCULARIDJS.

The /Slephanoceros, or Crowned Animalcule. — This beautiful little
creature is about the 36th of an inch in length. It is enclosed in
a transparent cylindrical flexible case, over which it protrudes five
long arms in a graceful manner, which, touching at their points, give
the 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 is 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. Tp the bottom of its home
it is fastened 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 and into the sheath. Its mouth differs a little from the
common wheel-animalcule, as it has two distinct sets of teeth, with
which it tears and crushes its food. The eggs of the Stephanoceros,
after leaving the animal's body, remain in the crystal-like shell until
hatched, when they escape from the lower part. A cluster of eggs may
be generally seen in the ovisac. Dr. Mantell, from close observation,

FLOSCULARIDJE. 173

found that about eighty hours elapsed before their organs were all
developed.

Limnias Ceratophylli, or Water- Nymph, is of this family, and is
about one-twentieth of an inch in size, residing 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 rotatory apparatus is divided into two lobes, possessing vibrating
cilia, as well as a singular projecting angular chin. The Water Nymph,
when young, is said to have two red eyes; but they fade away as the
term of their existence draws to a close. The body of the animal is
fixed to the bottom of its little horn; and, by means of the attach-
ment, it can retire on the slightest symptom of danger, or protrude
itself out of it in search of that sustenance requisite to its existence.
In the rows of little eggs seen in the body of the parent may clearly
be distinguished many of the particular organs in a state of activity.
From its fondness for hornwort, it often receives the name of that
plant.

Floscularia Ornata, or Elegant Floscularia, is a beautiful type of this
family, and has its rotatory organs divided into several parts ; when it
draws itself into a small compass, its transparent covering becomes
wrinkled. This forms an interesting object, as its internal structure
can be well seen through the translucent sheath that constitutes its
dwelling. The little beings are very rapacious, although but the 108th
part of an inch in size.

Floscularia Probosddea, or Horned Floscularia, has six lobes
fringed with cilia shorter than in the preceding kind. The name that
distinguishes it arises from a kind of horn or proboscis, also having
cilia, that is placed in the centre of the lobes. The eggs cast off by
the parent are seen in the sheath, and are very pretty objects for
microscopic observation. In fact, the tinted case, the light ethereal
frame of the tiny animal, and the various colours of the food in the
stomach, combine in rendering it deeply interesting.

Melicerta Eingens, or Beaded Melicerta. — Among the Melicerta, 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 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 that,
appearing as rows of beads, give the name to the animal.

Mr. Gosse has given an excellent account of the "architectural
instincts of Melicerta Ringens" which is not only truly surprising, but

174 THE MICROSCOPE.

full of interest. He says, it 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 ingeniously-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 exposure; 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. The appearance is
not unlike that of a flower of four unequal petals, from which circum-
stance Linnaeus 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, he,
Mr. Gosse, can compare 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-hemi-
spherical 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 Rotifera, but in this genus very small.

The pellets composing the case are very regular in form and posi-
tion: in a fine specimen, about l-28th of an inch in length when fully
expanded, of which the tube was 1-3 6th 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 & fine specimen attached to a
submerged moss from a pond at Hackney; this he saw engaged in

FLOSCULARIDJS. 175

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 pedicle. On mixing car-
mine 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, be-
tween the larger petals. If the pigment be abundant, the cloudy tor-
rent 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, following the irregularities of outline with beautiful pre-
cision, 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, believing 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 j
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
minutes to make and deposit a pellet. Some atoms of the floating
carmine now and then passed down the gullet into the gizzard, and
thence into the stomach ; but these were quite independent of, and
unconnected with, the pellets, which were composed exclusively out of
the torrent that had passed off the disc. On one occasion the cup was
brought down to the margin, but, from some cause or other, failed to
deposit its pellet ; it was raised for a moment, and then a second
attempt was made, which was successful.

Such is the vivid picture and perfect description of the wondrous
mechanism and ingenuity of this singular and beautiful animal.

176 THE MICROSCOPE.

Before quitting the consideration of the Protozoa, we must refer
to a curious group of minute parasitic creatures, the genus Gregarina,
of which we know six distinct species, all of them Entozoa, and all
organised as simple cells, but endowed with contractility and expansi-
bility quite sufficiently to put their animal nature beyond a doubt, and
which appear to be more nearly allied to the Infusoria than to any
other class in the animal kingdom. They are to be found in the intes-
tines of the common garden worms, insects, and many other members
of the articulate division of animals, and are but rarely to be met with
in animals of any other group. These animals are generally of a cylin-
drical 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 move-
ments, although a few possess true cilia. Their curious mode of deve-
lopments, with other points in the history of these minute parasites,
are well worthy of investigation.

We have taken a rapid survey of some of the marvellous creations
in the busy invisible world ; every glimpse inspiring awe, from the im-
mensity, variety, beauty, and minuteness of the organised habitants.

Immensity, 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, ochre, and
the limestone 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 vege-
table and animal bodies which they are appointed to devour and assi-
milate. Surely we must, in some degree, be indebted 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 im-
portant 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 comminution and
decay which immediately precedes its final decomposition into the ele-
mentary gases, and its consequent return from the organic to the inor-
ganic world, these wakeful members of nature's invisible police are
every where ready to arrest the fugitive organised particles, and turn
them back into the ascending stream of animal life. Having converted
the dead and decomposing particles into their own living tissues, they

PLATE IV.

SPICULA FROM SPONGES.

f/'^' OF TH£

UNIVERSITY

OF

PORIFERA. 177

themselves become the food of larger Infusoria, and of numerous other
small animals, which in their turn are devoured by larger animals ;
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. 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 sub-
division, 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 j
and they are all obedient. All things are double one against another ;
and He hath made nothing imperfect. One thing establisheth the
good of another ; and who shall be filled with beholding His glory f '

PORIFERA..

SPONGES.*

THE term Porifera, or Canal-bearing Zoophytes, was applied by Pro-
fessor Grant to designate the remarkable class of organised beings
usually known as sponges, which are met with in most seas, growing
in great abundance on the surface of rocks.

Ellis, in the course of his investigations, was astounded by disco-
vering that sponges possessed a system of pores and vessels, in which
sea-water passed, with all the appearance of the regular circulation of
fluids in animal bodies, and a seeming purpose of conveying animal-
cules to the animal for food. Professor Owen gives it as his opinion

* DESCRIPTION OF PLATE IV.

1. Portion of sponge, showing siliceous spicula imbedded in a soft matrix. 2.
Skeleton of sponges of the acerate form, covered with rows of spines. 3. Showing
rings of growth, and a portion of horny fibre, enclosing a bundle of spicula of the genus
Verongia. 4. Sphero-stellate spicula of Tetkea. 5. Portion of sponge mounted in
Canada balsam, showing the spicula more plainly. 6. Tricuspid-anchorate spicula,
sphero-stellate. 7. Acuate-biclavate, double recurvo-ternate, expando^ternate, detri-
radiate spicula. 8. Gemmules of- Ckodia. 9. Gemmules of Spongilla fluviatilis
enclosed in spicula. 10. Clavate spicula, covered with short spines. 11. Gemmules
ofGeodia in an advanced stage of growth. 12. Birotulate spicula from the Fluviatilis.
13. Gemmules of Spongilla fluviatilis immersed in acid, to show its coating of birotu-
late spicula.

N

178 THE MICROSCOPE.

that sponges should be placed in the vegetable kingdom : " The living
sponge, when highly magnified, exhibits a cellular tissue, permeated by
pores, which unite into cells or tubes, that ramify through the mass in
every direction, and terminate in larger openings. In most sponges
the tissue is strengthened and supported by spines, or spicula of va-
rious 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, by
which large animalcules or noxious particles are excluded ; water inces-
santly enters into these pores, traverses the cells or tubes, and is finally
ejected from the larger 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."

On the disputed point of sponges being animals, Dr. Johnston re-
marks : " Although I agree with the advocates of the animality of
zoophytes in general, I cannot go the length of Ellis in considering it
proved that sponges and corallines belong to the same class. Ellis,
we have seen, knew that no polyps were to be found in sponge ; and
their existence in the pores of corallines was inferred merely from the
structure of these latter, and their chemical composition. They have
been examined by subsequent naturalists fully competent to the task ;
and under the most favourable circumstances, — in particular by Cavo-
lini and Schweigger, — and the result has been a conviction that these
productions are truly apolypous. Now this fact, in my opinion, deter-
mines the point ; for if they are not the productions of polyps, the
zoologist who retains them in his province must contend that they
are individually animals ; an opinion to which I cannot assent, seeing
that they have no animal structure or individual organs, and exhibit
no one function usually supposed to be characteristic of that kingdom.
Like vegetables, they are permanently fixed ; like vegetables, they are
non-irritable ; their movements, like those of vegetables, are extrinsical
and involuntary ; their nutriment is elaborated in no appropriate diges-
tive sac ; and, like cryptogamous vegetables, or alga3, they usually grow
and ramify in forms determined by local circumstances ; and if they
present some peculiarities in the mode of the imbibition of their food,
and in their secretions, yet even in these they evince a nearer affinity
to plants than to any animal whatever."

Miiller writes on this question : " If, therefore, it is still a matter

PORIFEKA. 179

of doubt whether certain simple organised beings, such as the Sponges
and several so-called Alcyonetta, are animal or vegetable, the absence
of all voluntary motion in these bodies, whether of the whole or of in-
dividual parts of it, must determine the question ; and they must more
properly be numbered among the vegetable marine structures. It may
certainly be said, that the embryo of sponges (as Dr. Grant has shown),
like the embryo of polyps and corals, moves by means of cilia ; but
the distinctive marks between the embryo of sponges and marine In-
fusoria are by no means certain, and similar motions have been many
times observed in the embryo of true vegetables, — of the alg89, for
example."

Again, we read that " M. Dujardin, having repeated his observa-
tions on spongillae, or fresh-water sponges, as well as others on marine
sponges, thinks he has proved that these ambiguous beings are posi-
tively groups of animals, capable of contraction and extension. If a
piece be detached from a living sponge, and submitted to a microscope,
it will be seen to group itself into irregularly-rounded masses, and
change the form of its edges incessantly : isolated portions, detached
from the general mass, move slowly in the liquid, and creep along by
means of their alternate contraction and expansion."

The description given of sponges by Dr. Johnston is, that they are
" organised bodies growing in a variety of forms, permanently rooted,
unmoving and irritable, fleshy, fibro-reticular, or irregularly cellular ;
elastic and bibulous, composed of a nbro-corneous axis or skeleton,
often interwoven with siliceous or calcareous spicula, and containing
an organic gelatine in the interstices and interior canals ; they are
reproduced by gelatinous granules called gemmules, which are generated
in the interior, but in no special organ. All are aquatic, and with few
exceptions marine." The same author says : " Mr. J. Hogg, in a letter
dated June 25, states that the green colour of the fresh- water sponge
(iSpongilla fluviatilis) depends upon the action of light, as he has
proved by experiments 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. He therefore
infers the vegetable nature of this sponge ; but leans to the opinion
that the sea sponges are animals."

Dr. Lankester has given a somewhat better definition for the deter-
mination of animal and vegetable life than other investigators. He
proposes that the general fact of vegetables giving off oxygen gas and
absorbing carbonic acid, whilst animals absorb oxygen and give off

180

THE MICROSCOPE.

carbonic-acid gas, should be generally admitted to constitute the true
line of demarcation between the two, and would thus remove the ob-
jections raised by those who will not admit the presence of starch as
sufficient to determine the point. Professor Grant has more recently
examined the sponges ; and from his patient and careful observations
of them, they have been finally classed amongst the animal creation.
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 inter-
esting, that we cannot resist giving, in his own words, the results
arrived at in these investigations : " Having placed a portion of live
sponge (Spongia coalita, fig. 102, No. 1) in a watch-glass with some sea-
water, I beheld for the first time the splendid spectacle of this living

fig. 102. 1.

ia coalita. 2. A piece of /Spongia panicea highly magnified. '.

fountain, represented in fig. 102, 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 panicea), 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 its surface and highest orifice with

PORIFERA. 181

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."

Sponges grow attached to almost every thing which may serve them
as a point of support, whether fixed or floating; some cover rocks,
shells, and other submarine objects, with a close spongy incrustation;
whilst others shoot up a branched stem into the water; and others
again hang freely from the seaweeds floating in the ocean. Sometimes
they select very unexpected objects on which to take up their abode.
Thus, in one case recorded by Dr. Johnston in his Natural History of
British Sponges, a specimen of the Halichondria oculata, a sponge
not uncommon on some parts of the British coasts, was found growing
from the back of a small live crab, — " a burden," says the learned
Doctor, " apparently as disproportionate as was that of Atlas, — and yet
the creature has been seemingly little inconvenienced with its arboreous
excrescence."

In the second order, the Hyppocrepia, all the members are inha-
bitants of fresh water; one of the most common species, and that
which attracted the attention of Trembley as long ago as 1741, is the
AlcyoneUa stagnorum. It occurs in great abundance, attached to the
leaves of aquatic plants, on floating logs of timber, in the West India
Docks. When first taken out of the water it is of a lobulated form
and brown colour; the polypidom is soft and elastic, and feels very
much like a sponge; but, as Mr. Teale observes, this polyp "is organi-
cally connected with the mass, the tube forming its tunic, from which
the animated body issues by a process of evolution similar to that
which develops the horn of a snail. When developed, the head pro-
jects a short way, and is crowned with a beautiful expansion of tenta-
cula, about fifty in number, arranged in an unbroken circle, which is,
however, depressed into a deep concavity on one of its sides, so as to
produce the appearance of a double row of tentacula, in a horse-shoe
form. About 1600 polyps are situated on a square inch of surface of
the mass, consequently the number of polyps in one specimen, which
weighed 17 ounces, and measured 14^ inches in circumference, 'may
be computed at 106,000, and the tentacula at 5,320,000 !'"

Trembley gave an excellent and interesting account of one of the
family of AlcyoneUa, as far as the powers of the microscope at that time
allowed. " This is one of the many kinds of water animals which live
as it were in societies ; of which some sorts hang together in clusters,

182 THE MICKOSCOPE.

but can detach themselves at pleasure ; whilst others are so intimately
joined and connected together, that no one seems capable of moving or
changing place without affecting the quiet arid situation of all the rest.
But this creature forms as it were an intermediate gradation between
the other two, dwelling in the same general habitation with others of
its own species, from whence it cannot entirely separate itself; and yet
therein it appears perfectly at liberty to exert its own voluntary
motions; and can either retire into the common receptacle, or push
itself out from thence, and expand its curious members, without inter-
fering with or disturbing its companions.

" They dwell together from the numbers of ten to fifteen (seldom
exceeding the latter or falling short of the former number), in a filmy
kind of mucilaginous or gelatinous case, which out of the water has no
determined form, appearing like a lump of slime ; but when expanded
therein, resembles nearly the figure of a bell with the mouth upwards,
and is usually about the length of half an inch, and one quarter of an
inch in breadth or diameter. This case being very transparent, all the
motions of its inhabitants may be discerned through it distinctly. It
seems divided internally into several apartments, or rather, to contain
several smaller sacculi, each of which encloses one of these animals.
The openings at the tops of these sacculi are but just sufficient to admit
the creature's head, and a very small part of its body, to be thrust
beyond them, the rest remaining always in the case. The animal can,
however, when it pleases, draw itself down entirely within the case,
which is an asylum to secure it from its enemies (for it is not unlikely
many of the larger aquatic insects prey upon it).

" The arms are set round the head to the number of forty, having
each the figure of a long^ one of whose hooked ends is fastened to its,
head; and altogether, when expanded, compose a figure somewhat of
a horse-shoe shape, convex on the side next the body, but gradually
opening and turning outwards, so as to leave a considerable area within
the outer extremities of the arms. And when thus extended, by giving
them a vibrating motion, the creature can produce a current in the
water, which brings the animalcules, or whatever other minute bodies
are not beyond the sphere of its action, with great velocity to its
mouth, whose situation is between the arms ; where they are taken in
if liked, or else, by a contrary current^ which the creature can excite,
they are carried away again; whilst at the same time other minute
animalcules or substances that, by lying outside the enclosure made by
the arms, are less subject to the force of the stream, are seized by
them ; for their sense of feeling is so exquisite, that on being touched

FRESH-WATER SPONGES. 183

ever so slightly by any such little body, it is caught immediately and
conveyed to the mouth. One may observe the creature, when disap-
pointed of its prey, slowly extending itself again without retiring into
its case.

" The bells or colonies of these animals are to be found adhering to
the large leaves of duckweed and other aquatic plants ; and may easiest
be discovered by letting a quantity of water, with duckweed in it,
stand quietly for three or four hours in glass vessels, in some window
or other place where a strong light comes ; for then, if any are about
the duckweed, they will be found, on careful inspection, extending
themselves out of their cases, spreading their plumes, and making an
elegant appearance.

" They are extremely tender, and require no little care to preserve
them; their most general disorder is a kind of slime or mouldiness,
which will sometimes envelope them in such a manner as to prove
mortal. The best way of curing this is by gently pouring a large
quantity of water (perhaps two or three quarts) into the vessel where
they are kept, and letting it run off slowly ; by which means the slimi-
ness will gradually be loosened, and carried away with the water.

" As to food, if fresh water be given them daily, they will find suffi-
cient for themselves ; and it is dangerous to try any other way of feed-
ing them; for the smallest worms, or other visible insects one can think
of giving them, will tear their delicate frame in pieces."

In the journal of the Bombay branch of the Royal Asiatic Society
for 1849, Surgeon H. J. Carter gives a minute and able account of the
fresh-water sponges in the water-tanks of Bombay. Of five species
that he discovered, one was the Spongilla friabilis, the others he named
Sp. cinerea, Sp. alba, Sp. meyeni, Sp. plumosa.

SpongiUa 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 thickness. It
is found on the sides of fresh-water tanks, on rocks, stones, or gravel.
Seed-like bodies spheroidal, about l-63d of an inch in diameter, pre-
senting rough points externally. 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 1 -380th of an inch in length.

Spongilltij friabilis. — Growing in circumscribed masses, on fixed
bodies, or enveloping floating objects; seldom attaining more than

184 THE MICROSCOPE.

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; structure reti-
culated. The investing membrane abounds in minute spicula; has
seed-like spheroidal bodies about l-30th of an inch in diameter, with
rough points externally. 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 l-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
spiniferous spicula when dry present a white lacey appearance, from
which Mr. Carter gives them the name of alba.

SpongiUa meyeni is massive, having large lobes, mammillary emi-
nences, 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 disks.

Spongilla plumosa. — This is much the same in appearance and
colour as the last, but looser and coarser in its texture and structure.

Mr. Carter states : " That fresh-water sponge is composed of a fleshy
mass, supported on a fibrous, reticulated, horny skeleton. The fleshy
mass contains a great number of seed-like bodies in all stages of deve-
lopment, and the horny skeleton is permeated throughout with siliceous
spicula. When the fleshy mass is examined by the aid of a micro-
scope, it is found to be .composed of a number of cells, imbedded in and
held together by an intercellular substance.

The granules are round or oval ; translucent, and of an emerald
or yellowish-green colour, varying in diameter below the 12,000th part
of an inch, which is the average linear measurement of the largest. In
some cells they are so minute and colourless as to appear only under
the form of a .nebular mass ; while in others they .are of the largest
kind, and few in number.

The hyaline vesicles, on the other hand, are transparent, colourless,
and globular; and although variable in point of size, like the green
granules, are seldom recognised before they much exceed the latter in
diameter. They generally possess the remarkable property of slowly
dilating and contracting themselves, and present in their interior mole-
cules of extreme minuteness in rapid commotion.

The intercellular substance, which forms the bond of union between

FRESH-WATER SPONGES. 185

the cells, is mucilaginous. When observed in the delicate pellicle,
which, with its embedded cells and granules, it forms over the surface,
and throughout the canals of the sponge, it is transparent ; but when a
portion of this pellicle is cut from its attachments, it collapses, and
becomes semi-opaque. In this state, the detached portion immediately
evinces a tendency to assume a spheroidal form ; but whether the in-
tercellular substance participates in this act, or remains passive while it
is wholly performed by the habit of the cells which are imbedded in it
to approximate themselves, Mr. Carter has not been able to determine.
The seed-like bodies occupy the oldest or first-formed portions of
the sponge, near its periphery. They are round or oviod, according
to the species, and each presents a single infundibular depression on its
surface, which communicates with the interior. At the earliest period
of development in which Mr. Carter recognised the seed-like body, it
has been composed of a number of cells, united together in a globular
or oviod mass, according to the species, by an intercellular substance
similar to that just described. The seed-like body passes from the
state just mentioned into a more circumscribed form; then becomes
surrounded by a soft, white, compressible capsule ; and finally thickens,
turns yellow, and develops upon its exterior a firm crust of siliceous
spicula.

Thus matured, its cells, which were originally unequal in size, now
become nearly all equal, almost motionless, and a little exceed the
average diameter of the largest sponge-cells ; while their germs, which
in the first instance so nearly resembled the gemmules of the sponge-
cells, are now four or five times larger ; and vary in diameter below the
3000th part of an inch, which is the average linear measurement of the
largest of their kind.

The capsule passes from a soft, white state, into a tough, yellow,
coriaceous membrane, presenting in meyeni and plumosa a hexagonally-
tessellated appearance, on the divisions of which rest asteroid disks of
the vertically- placed spicula which surround it.

On the development of Spongilla Mr. Carter remarks : " When the
cells of the seed-like body are forcibly expelled from their natural
cavity under water, they are irregular in form and motionless, but soon
swell out (by endosmose?), become globular, and after a few hours
burst. At the time of bursting, their visible contents, which consist of a
mass of germs, occupying about two-thirds of the cavity of the cell, sub-
side, and afterwards gradually become spread over the bottom of the
vessel in which they are contained. They are of various diameters
below the 3000th part of an inch, which is the average linear measure-

186 THE MICROSCOPE.

ment of the largest, and they appear to be endowed with the power of
locomotion in proportion to their size."

Not the least wonderful circumstance connected with the history of
the 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 re-
duced to such a state as to render substances 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, and some allied
genera. 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 communication with the water by means of
perforations in the outer wall of the shell. The mechanism by which a
creature 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 satisfactory conclusions upon the
habits of an animal that works so completely in the dark as the Cliona
— 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 exca-
vating power to the presence of a multitude of minute siliceous crystal-
line 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 dis-
integration of submarine calcareous bodies — the shelly coverings, it may
be, of animals far higher in organisation than they ; nay, in many in-
stances they prove themselves formidable enemies even to living mol-
lusca, by boring completely through the shell. In this case the animal
whose domicile is so unceremoniously invaded, has no alternative but
to raise a wall of new shelly matter between himself and his unwelcome
guest j and in this manner generally succeeds at last in barring him out.

SKELETONS OF SPONGES.

The skeletons of Sponges, as well as those of Zoophytes, possess no
blood-vessels ; they are secreted by the fleshy mass of the animal, and

SKELETONS OF SPONGES.

187

some of them are partially formed before the birth of the polyps
which have to become their inhabitants.

The skeletons of some of the Campanularia, consist of tubular
granular matter, encased in a horny translucent substance, which is
enlarged at the end of each branch into cells for the domiciliation of
the polyps. The outline is waved from the cells with a jointed appear-
ance, which allows of a certain elasticity to the cells.

Alcyonium digitatum are branched, and have tubes; some are curved,
others straight, and many take the form of a cross. The dark-red
margin of Gorgonia petechialis is a mass of large, red, flattened, angular
spicula ; while inside they are small and in bundles, forming a net-
work around the pores or canals, thin and slightly-curved, with a small
swelling in the centre.

fig. 103.

1. Transverse section of a branch ofMyriapore. 2. A section of the stem of Virgu-
laria mirabilis. 3. A spiculum from the outer surface of a Sea-pen. 4. Spicula from
crust of his hippuris. 5. Spicula from Gorgonia elongata. 6. Spicula from Alcyo-
nium. 7. Spicula from Gorgonia umlraculum.

In a New Zealand specimen of Alcyonium the spicula are calcareous,
of a brown colour, shaped like a cucumber, having all parts of their
outer surface studded with conical tubercles j some of them exceed the

188 THE MICROSCOPE.

l-8fch of an inch in length, others are as small as the 1-2 00th of an
inch. (Fig. 103, No. 6.)

The purple-coloured spicula of the outer surface of the Sea-pen
(Renilla Americana) are cylindrical, a little twisted, and seem to have
a central canal ; they are the l-70th of an inch long, by the 800th in
the short diameter. (Fig. 103, No. 3.)

The dull lake or dirty-white spicula of the crust of Gorgonia elon-
gata are bowed with projecting^ from one side (fig. 103, No. 5) ; but
they are commonly elongated, covered with tubercles arranged in rings.

Muricca elongata are yellowish-brown, of a pine-apple shape ; one
extremity covered with short sharp-pointed tubercles, the other ex-
panded with spines ; the free extremities of which all point in one
direction.

Spicula from the fleshy crust of Isis hippuris, mostly of a quadrate
or clavate figure, covered with large modulated tubercles, are repre-
sented in fig. 103, No. 4.

The Gorgonia umbraculum present two kinds, one found in the
crust, of large stellate angular figure and rich brown colour ; the
other much smaller, and covered with modulated tubercles. (Fig. 103,
No. 7.)

When a section is made of the Myriapora, Nullepora alciformis, it
is seen, as in fig. 103, No. 1, to be of a reticulated structure, the diameter
of each cell of which is about the l-300th of an inch.

Professor Quekett states that 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 consists of a network of smooth, and more or less
cylindrical threads, of a light-yellow colour, and, with few exceptions,
always solid ; they frequently anastomose, and vary considerably in
size ; when developed to a great extent, needle-shaped siliceous bodies
termed spicula (little spines) are formed in their interior j 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 ; the fibres,
however, in these cases are represented by siliceous needle-shaped spicula,
and the horny matter serves the important office of binding them firmly
together, as shown in Plate IV. No. 1. There is, however, one remark-
able exception to this rule, viz. Dictyochalix pumiceus, described by
Mr. S. Stutchbury, in which the fibrous skeleton is composed of threads
of silex quite as transparent as glass.

SPICULA FEOM SPONGES. 189

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-sfiaped to that of a star. The calca-
reous spicula, on the contrary, are more simple in their form, being
principally acicular, but not unfrequently branched or even tri or quad-
riradiate ; the two kinds, the siliceous 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, 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 crystalline, 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 Plate IV. No. 3. The spicula occupy
certain definite situations in sponges; some are peculiar to the crust,
others to the flesh, others to the margins of the large canals, others to
the fibrous network of the skeleton, and others belong exclusively to
the gemmules. Thus, for instance, in Pachymatisma, Johnstonia, ac-
cording 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 flesh 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 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.

190 THE MICROSCOPE.

The Moss-agates, found among the pebbles at Brighton and else-
where, are flints containing the fossilised remains of sponges. The
coloured fibres seen in the 6rm?n-jaspers of the east are of the same
character. There is reason to believe that most flints were originally
sponges j 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 trans-
parent, for examination under the microscope, that we learn their true
nature and origin.

Every horny sponge, when living, was 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
occasionally form the skeleton of the geimnules, and may be 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 Plate IV. Nos. 9 and 13. 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, or Spongia officinalis, is brought from the Medi-
terranean, has a horny network skeleton rather fine in the fibres,
solid, small iu size, and light in colour (Plate IV. No. 1.) In some
larger specimens there is a single large fibre, or a bundle of smaller
ones.

In Halicliondria 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 Halicliondria have siliceous spicula pointed at both
extremities — acerate (Plate IV. No. 7) ; while the spicula of some are
round at one end and pointed at the other — acuate (see No. 7) ; and
also spicula round at one end, the former being dilated into a knob —
spinulate ; some have a spinous surface.

From the South Seas specimens are found having spicula with both
ends rounded ; cylindrical ; some curved, others straight.

In an unclassed genus, the spicula are discovered rather cylindrical
in form, pointed at both ends, having the surface covered with spines

SPICULA FROM SPONGES. 191

placed in an annular form (Plate IV. No. 2), and another in which the
spicula exhibit many curious forms ; within the circle may be seen
one spiculum of remarkable beauty, being of large size, rounded at both
ends, and slightly bent ; its outer surface is covered with rows of tuber-
cles of circular figure, which project some little distance beyond the
free margin.

In HalicJiondria from New Zealand there are found some with
the spicula of the acuate form covered with spines, blunt at one end
and sharp at the other ; the spines are small, without order in their
situation, but greater in number at the middle.

In the genus Pachymatisma some spicula are sharp at one ex-
tremity and expand into two points at the other — expando-binate ;
they are large, and their purpose is that of connecting the crust and
the fleshy matter compactly together. The P. Johnstonia spicula are
sharp at one end and expand into three points at the other — expando-
ternate ; arranged at angles at 45° to the other part of the stem
(Plate IV. No. 7); there is also in this kind a variety having spicula
sharp at one end and expanding into three branches at the other, each
of which again divides into two dichotoino-expando-ternate kinds.

In the genus Tethea there are spicula having hooks at both ex-
tremities— bi-recurvo-ternate : at one end they are not so large or so
numerous as at the other ; the stem is a little spinous.

In TetJiea Lyncurium the ends of the branches of the spicula are re-
curved, forming two, three, or four hooks, which serve to anchor the
crust to the soft central fleshy part ; their term is recurvo-binate,
ternate, &c. Of the recurvo-ternate we give a specimen from a species
of Pachymatisma. (Plate IV. No. 6.)

Among the genus Grantia, Geodia, and Levant sponge, are found
spicula of a large size, radiating in three directions — triradiate. In
the Levant specimen, a central communicating cavity can be distinctly
seen. Some Smyrna "sponge, and a species of Geodia, have four rays
— quadriradiate.

There are spicula in P. Johnstonia and Geodia that have as many
as ten rays — multiradiati ; they vary in number. (No. 12.)

In some species of Tethea the spicula consist of a central sphe-
rical body, from which short conical spines proceed — stellate spi-
cula. (Plate IV. No. 4.) These are also found in some of the genus
Geodia.

Branched spicula, some covered with spines, have been taken from
sponge brought from Ceylon ; and from sponge from the same place,
spicula more or less curved — curvate.

192 THE MICROSCOPE.

Spicula having both extremities bent alike — bicurvate — have been
obtained from Trieste sponge. (See Plate IV. No. 3.)

Some South Sea sponges have spicula twice bent; and have extre-
mities like the flukes of an anchor — bicurvate-anchorate \ sometimes
the flukes have three pointed ends. (Plate IV. 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 frame-
work of bundles of acerate spicula of the flesh, as shown in Plate IV.
No. 9 • but in many marine species, Geodia and Pachymatisma, they
are principally confined ta the crust. In the fresh-water sponges, the
amount of animal matter in the gemmules is considerable ; but in
Pacliymatisma, 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 ; and if they be
viewed when taken fresh from the sponge, and after boiling in acid to
remove the animal matter, a slight increase in transparency is the only
perceptible difference of appearance in these two opposite conditions.

XANTHimA.

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 or double-bar animalcules belong to the
Desmidiacese. In proof of this it can be shown that their skeletons are
composed of horn, and not of silica, as was once supposed.

The name Xanthidia is derived from a Greek word signifying
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 shape
in different species. One kind was found by Dr. Bailey in the United
States of an oval shape, the 288th of an inch in length ; and another
kind, round in form, by the late Dr. Mantell, at Clapham ; both these
kinds were of a beautiful green colour. Specimens of the Branched
Xanthidium, found in flint by Dr. Mantell, were from the 300th to the
500th of an inch in diameter. (Plate III. No. 4.) Mr. Ralfs says :
"That the orbicular spinous bodies so frequent in flint are fossil sporangia
of Desmidiacese, cannot, I think, be doubtful, when they are compared
with figures of recent ones. Indeed, the late Dr. G. Mantell, who, in

XANTHIDIA. 193

his Medals of Creation, without any misgiving, had adopted Ehrenberg's
ideas concerning them, changed his opinion ; and in his last work re-
gards them as having been reproductive bodies, although he is still
uncertain whether they are of vegetable origin."

Ehrenberg and his followers describe these bodies as fossil species
of Xanthidium ; but no doubt erroneously, since their structure is very
different. For the true Xanthidium has a compressed, bipartite, and
bivalved cell; whilst these fossils have a globose and entire one.

The fossil forms vary like recent Sporangia, in being smooth, bristly,
or furnished with spines, which in some are simple, and in others
branched at the extremity. Sometimes, too, a membrane may be
traced, even more distinctly than in recent specimens, either covering
the spines, or entangled with them. Some writers describe the fossil
forms as having been siliceous in their living state j 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 sili-
ceous before they were imbedded in the flint. In the present state of
our knowledge, it would be premature to attempt identifying the fossil
with recent species ; it is better, therefore, at least for the present, to
retain the names bestowed on the former by those who have described
them.

Near to Sydden Spout 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, the Xanthidia in flints j . and clearly recognised X.
spinosum, ramosum, tubiferum, simplex, tubiferum reeurvum, malleo-
ferum, and pyxidwulum, 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 re-
semblance to some gemmules of sponge, and having 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 to be 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 pressure 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 eva-
porated away, the spines or arms fell inclined to the glass. These cir-

o

194 THE MICROSCOPE.

cumstances 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 Xanthidia, some modifi-
cation 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.

These investigations corroborate Mr. Kalfs, and also show that the
same fossil remains, so abundant in flint, are to be found in the beds of
chalk by which it is surrounded.

Mr. Wilkinson, who examined some Xanthidia found in the Thames
mud and slime on piles and stones at Greenhithe, gives it as his
opinion that they are not siliceous, but of a horny nature, similar to
the wiry sponges, which Mr. Bowerbank describes as being very diffi-
cult to destroy without the action of fire.

He also met with a peculiarity in a X. spinosum, which he had
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 circumference,
similar to that formed by two cups when placed on each other, so as
to make their rims or upper edges meet. There also seemed to be a
peculiarity in the arrangement of the tentacula : the tentacula of Xan-
thidia generally pass from the body in a direction perpendicular to its
centre, without any apparent fixed arrangement of position ; but in this
instance, both in the upper and lower portions, there were two circlets
of tentacula ; one placed round each extremity, and another round that
part where the specimen appeared to be separated. The size was the
325th part of an inch in diameter, and the number of tentacula about
twenty-five.

The other fossil Infusoria, found most abundantly in the chalk and
flint of England, are the Rotalia or wheel-sliaped, and the Textularia 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 lessen-
ing towards the apex.

PLATE V.

ZOOPHYTES, POLYPS, XANTHIDIA, ETC.

1. FUNOIA agariciformis.

2. ALCYONIUM, CYDONIUM MULLERI.

3. CYDONIUM, with polyps protruding and tentacles expanded, others closed.

4. XANTHIDIA in flint.

5. MADREPORE ABROTANOTDE.

6. MADREPORE cell magnified, showing its internal structure.

7. CORALLID^E: Corals.

8. CORAL, with polyps magnified and protruding from the cells.

9. GOBOONIA nobilis, with polyps magnified and expanded.

10. TUBIPOBA MUSIC A.

11. Tube of same, with polyp expanded, one being cut longitudinally to show its

internal structure.

12. SERTULARIA, with polyps protruding; others being withdrawn into their cells.

CHAPTER II.

POLYPIFERA.
ZOOPHYTES, OK POLYPS.

Y the term Zoophytes, taken in its strictly
limited sense, is understood a class of
creatures which, in their form, or most
remarkable characters, recall the appear-
ance of a vegetable, or its leading pro-
perties. The most obvious character
common to this vast race of animals is,
that their mouths are surrounded by ra-
diating tentacula arranged somewhat like
the ray of a flower ; and hence the term
Zoophyte. So plant-like, indeed, are
their forms, that the ancients regarded
them as vegetating stones, and invented many theories to explain their
growth. They are usually divided into two classes, the AntJiozoa and
Polyzoa. The first of these is again subdivided into three orders, the
Hydroida, Asteroida, and Helianthoida ; the second, or Polyzoa, into
two orders, the Infundibulata and the Hyppocrepia.

The mass of scattered information that the investigators of this
branch of natural history had published, has been collected and arranged,
with refreshing enthusiasm, by Dr. George Johnston, of Berwick-upon-
Tweed, under the title of A History of the British Zoophytes ; in which
work the ardent naturalist has not only combined " the whole under a
system more in harmony with the anatomy of the objects than has
hitherto been done," but enriched it by many personal researches and
observations on the species found in his own neighbourhood. Of
Polyps/' Dr. Johnston gives the following definition : "Animals aver-
tebrate, inarticulate, soft, irritable, and contractile, without a vascular
or separate respiratory or nervous system ; mouth superior, central, cir-
cular, edentulous, surrounded by tubular, or more commonly by filiform

* TfoAvs, many, and irovs, a foot.

196 THE MICROSCOPE.

tentacula ; alimentary canal variable ; where there is an intestine, the
anus opens near the mouth ; asexual ; gemmiparous ; aquatic. The in-
dividuals (Polyps) of a few families are separate and perfect in them-
selves ; but the greater number of Zoophytes are compound beings, viz.
each Zoophyte consists of an indefinite number of individuals or polyps
organically connected, and placed in a calcareous, horny, or membranous
case or cells, forming by their aggregation corals, or plant-like Polypi-
doms * * which is the house or support of the polyps ; and which,
though commonly present, is yet not necessary to the existence of a
Zoophyte."

Opposed to all our common ideas of animal life is this singular
creation. If we cut a limb off a tree, or sever that of an animal, these
parts will wither and decompose, by passing into other forms of matter.
Cut a tree across its middle, and its natural symmetry is irreparably
disfigured ; slit it down its centre, and it is destroyed : all animals so
treated suffer instant death, with the sole exception of the polyp ; for
it will put forth new limbs, form a new head or tail, and if slit, become
two separate existences.

fig. 104.

Hydra, with its tentacles displayed and magnified, adhering to a stalk of the
Anacharis.

The animals of the first order, the Hydroida, are generally com-
pound, and invested with a horny tubular polypidom; the digestive

HYDROIDA. 197

cavity is excavated in the substance of the body without any proper
lining membrane, and the reproductive organs are always external.
In the second order, the Asteroida, the polyps are always compound;
the mouth is surrounded by eight tentacles; the digestive cavity is
lined with a membrane, and the ovules are produced in the interior of
the animal. The polyps in this order are imbedded in a more or less
fleshy mass, which is generally supported on a horny or calcareous axis.
The polyps of the third order, the Hdiantlwida, are single, and either
possessed of a certain power of locomotion, or imbedded in a calcareous
polypidom. The mouth is generally surrounded by a great number of
tubular tentacles : the stomach is furnished with a distinct lining, and
the ovaries are internal.

HYDROIDA HYDRA, OR FRESH-WATER POLYPS.

It is in the polyps of this order that we find the nearest approach
to the preceding division. The body in these generally consists of a
homogeneous aggregation of visicular 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 tentacula which sur-
round the anterior extremity are irregular in number ; they are capable
of extension to a very great length when seeking for prey; and on
coming in contact with any object floating through the water, they
immediately twine round it, and convey it to the mouth. In some
genera the tentacles appear to be tubular, the internal cavity being
continuous with that of the stomach. To assist in the capture of living
prey, their surface is commonly roughened with a series of granules,
which in some cases contain a curious poisonous or urticating apparatus.
The mouth, which is situated in the centre of the circle of tentacles,
leads directly into a simple digestive cavity, which is not lined with
membrane.

In ponds and rivulets, adhering to the leaves of aquatic plants, or
twigs and sticks that have fallen into the water, are found the Hydraa.
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 sup-
posed to resemble the fifty-headed water-serpent called Hydra, and

198 THE MICROSCOPE.

destroyed by Hercules in the lake of Lerna, as we are informed in
fabulous history.

Leeuwenhceck, in 1703, was the first to draw attention to the
Hydra; and in 1739, M. Trembley, from, the Hague, most accurately
described the habits of the animal.

The extraordinary attenuation of the arms, until they can with
difficulty be detected, renders it surprising that they possess strength
sufficient to cope with the struggles of large worms and insects, round
which the hydra wraps them; but, as the victim seems powerless when
once in the fatal coil, it has been thought they possess some electric
power similar to the eel and torpedo, that stun or destroy their prey
by electrical force; and this belief is more especially entertained, as the
little creature rests, like the above-named fish, before regaining power
to resume its pursuit of prey.

Polyps are not vegetarians, and were fed by M. Trembley 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 carefully 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 round 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 polyp thrown over two worms at the same time ; yet they
could not escape, and lost all power of motion.

Dr. Johnston writes : " Sometimes it happens that two polyps will
seize upon the same worm, when a struggle for the prey ensues, in
which the strongest gains, of course, the victory ; or each polyp 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 con-
tact. The rest that now ensues, appears to prove that they are sensible
of their untoward position, from which 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 I 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 polyp is
engulfed ! But a polyp is no fitting food for a polyp, 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,"

IIYDROIDA. 199

This fact is the more remarkable, when it is contrasted with the
fate which awaits the worms on which they feed. ~No sooner are these
laid hold upon than they evince every symptom of painful suffering ;
but their violent contortions are momentary, and a certain death sud-
denly follows their capture. How this effect is produced, is mere
matter of conjecture. Worms, in ordinary circumstances; are most
tenacious of life, even under severe wounds; and hence one is inclined
to suppose that there must be something eminently poisonous in the
Hydra's grasp; as it is impossible to believe, with Baker, that this
soft toothless creature can bite and inject a venom into the wound it
gives. " I have sometimes," says Baker, " forced a worm from a polyp
the instant it has been bitten (at the expense of breaking off the polyp's
arms), and have always observed it to die very soon afterwards, with-
out one single instance of recovery." Trembley states as a fact, that
fishes cannot be made to swallow hydrse, seeming to prove the presence
of some irritating quality in the latter.

The body of the Hydra viridis is said by Ecker to be composed of
a vital contractile substance, soft, granular, and elastic, which is reti-
culated with clear spaces, containing more or less clear fluid. This
contractile substance, from its want of definite form, cannot, according
to Ecker, be termed muscular. " It is distributed throughout the whole
body, and not formed into filaments or fasciculi ; nor any more is the
sensitive substance yet collected into nerves, but must be assumed to
be dispersed through the whole body. The one is always most inti-
mately connected with the other, as the investigation of all the lower
animal forms teaches us. It is not until nerves are developed, that
even scattered muscles are assigned for any given purpose in the
economy. Muscles are not possible without a connecting nervous
system."

The tentacles, or feelers, are tubular, and filled with an albuminous
fluid. They are furnished with a variable number of tubercles, arranged
in a spiral manner on the surface. These tubercles are beset with a
number of spinigerous vesicles, which serve as organs of touch, in the
midst of which, at the apex of the tubercle, a very singular organ of
prehension is situated. Each spinigerous vesicle consists of two sacs,
placed one within the other, with a small cavity in the centre of the
inner one. At the point of contact of the two sacs is placed a long
ciliary hair, which projects from the surface of the tentacle. The organ
of prehension, which is called the hasta, consists 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

200 THE MICROSCOPE.

bears a sharp calcareous piece called the sagitta, or arrow. This can be
pushed out at the pleasure of the animal, serving to roughen the sur-
face of the tentacle, and afford a much firmer hold of its living prey.

The polyp 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 communicating with that of its
parent, and participating in the fears and actions of its progenitor ;
finally, it is cast off to wander the world of waters. Betimes, 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 ex-
traordinary 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 polyp 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 polyp has been cut lengthways at seven in the morning, and in
eight hours afterwards each part has devoured a worm as long as
itself."

Still equally -wonderful is the fact, that if turned inside out, the parts
at once accommodate themselves to their new condition, and carry on
all ^iieir 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 every one 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 polyp affixes itself by its tail to various substances, and fre-
quently is a parasite to other animals, which it annoys, while benefited
itself by taking advantage of their locomotive powers : this is more
especially the case with the water-snail, on the body of which may
often foe found the polyp.

Dr. Roget, in his Bridgewater Treatise, copying Trembley, says :
" The position in which they appear to take most delight is that of
remaining suspended from the surface of the water by means of the
foot alone ; and this they effect in the following manner : When the
flat surface of the foot Is exposed for a short time to the air, above the

HYDROIDA. 201

surface of the water, it becomes dry, and in this state exerts a repulsive
action on the liquid ; so that when dragged below the level of the sur-
face, by the weight of the body, it still remains uncovered, and occupies
the bottom of the cup-shaped hollow in the fluid, thereby receiving a
degree of buoyancy sufficient to suspend it at the surface. The principle
is the same as that by which a dry needle is supported on water, in the
boat-like hollow which is formed by the cohesive force of the liquid, if
care be taken to lay the needle down very gently on the surface. If,
while the hydra is floating in this manner, suspended by the extremity
of the foot, a drop of water be made to fall upon that part, so as to wet
it, this hydrostatic power will be destroyed, and the animal will imme-
diately sink to the bottom."

The Hydroida, with the exception of the genera Hydra and Cordy-
lophora, are all marine ; and vary in height from a line to that of a foot
or more. A few of them are naked ; but the remainder are invested
with a transparent horny-sheath, or skeleton, termed the Polypidom,
which is of a tubular form, investing the soft parts. In the families
Sertidaria, Tubularia, Plumularia, Antenmdaria, and Campamdaria,
their names serve to a certain extent to explain the shape of the poly-
pidom. We proceed to notice briefly a few individuals of the species
Hydra.

Hydra vidgaris, or Common Polyp (No. 3, fig. 100), is often found
upon plants, branches of trees, pieces of wood, rotten leaves, stones, and
other substances in the water. They are of an orange-brown or oil-
green colour, and round in shape. The number of its arms, or, as they
are technically called, tentacula, vary, and are usually a little longer
than the outstretched body of the animal itself. On moving from place
to place, they dispose themselves in an arched position, grasping some
object with their arms ; they then draw the tail towards the hea'd, fix it,
throw their head out again, and seizing some other substance, thus
proceed onwards. A young one is seen sprouting from the body of
this Hydra.

Hydra viridis, or Green Polyp (No. 2, fig. 100), differs little from
the common polyp, except as regards its beautiful light-green colour,
and its having shorter arms.

Hydra fusca, Brown or Long-Armed Polyp, is, like other polyps,
composed of a jelly-like matter, formed into cells, which perform certain
functions with a large mouth and a sucker at the opposite extremity j
the difference between it and the others named consists in the length of
its arms, which will elongate several inches (see No. 1, fig. 100). In the
extraordinary foresight of nature, it ia provided that during the cold

202

THE MICROSCOPE.

weather the polyp shall continue its propagation not by budding, but
by eggs ; the latter being better calculated to protect the tender thread
of life within against the destructive frosts of winter, than could pos-
sibly be resisted by the delicate construction of a new-born fragile
creature thrust into its nipping influence.

There are other British kinds : the Hydra verrucosa, which is of a pale
ashy colour, with six moderately long arras ; and the Hydra lutea, a
marine species, with a large head and ten very short arms.

Every reflecting person who reads even the slight sketch we have
given of this polyp tribe must be struck with astonishment at a creature
so primitive in structure, possessing the actions, sensations, and powers
of higher organised beings. The stomach is but one simple structure-
less membrane, or cell, the external surface-cells condensed so as to
form a kind of double skin ; and the inside a mere wall of cells running
crosswise, possessed of a velvet- like surface, the substance being red or
brown grains held together by a sort of gluey substance.

This singular formation for the functions of animal life has led to
many learned surmises and discussions tending to the most important
results in the science of physiology.

SERTULARIDJ3.

The second family of polyps are the interesting and beautiful Ser-
tularidce ; they are readily attainable on our own sea-shores. Linnaeus
made a large genus of them ; but Lamarck considerably reduced his
classification. The usual type presented is the beautiful Sertularia

pluma, fig. 105, which Dr. Fleming pro-
poses to divide into two groups, accord-
ing as the stems are simple or compound.
The Sertularia have arms or feelers,
which are abundantly supplied with cilia,
with pitcher-shaped, dwarfish cells, ar-
ranged alternately, or in pairs obliquely,
not exactly opposite, on the stem and
branches of the polypidom, which is
horny, fistulous generally, but attached
in zigzag radiant fibres.

Within this family come the Thoa,
of Lamouroux, of which there have been
several kinds found in Great Britain.

fig. 105. A single branch of Ser-
tularia.

The name is supposed to be derived from

SERTULARIDyE.

203

the Greek word for sharp ; but we think with Dr. Johnston, that it

more probably is a

mis-spelling of Thoe,

one 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 j but rarely at-
tains more than half
an inch in height.
Stewart says, this
species, and probably
many others, in some
particular states of the
atmosphere, emits a
phosphorescent light
in the dark. If a leaf
of the above fucus
(serratus), with the
Sertularia upon it, re-
ceives a smart stroke
in the dark, the whole
coralline is most beau-
tifully illuminated, ev-
ery denticle seeming
to be on fire.

Sertularia Hiber-
nica is thus named
from being found near
Donaghadee. Tem-

pleton savs " The
* '

,
branching of this and other sea-side plants.

> Pollicipes, Chiton Marginatus ;
Eggs of Cuttle-fish, or Sea-grapes ; Armeria maritima,

204 THE MICROSCOPE.

species is somewhat peculiar, each of the primary and secondary
branches springing out at an angle of 40° or 50°. That part of
the stem which bears the denticles is waved so as to bear each
denticle on the projecting part; the denticles are elliptic, and the
mouth of each apparently a little hollowed inwards, perhaps arising
from the extremity being fractured; the vesicles are ovate, with four
or five blunt teeth surrounding the mouth, and divided into six or eight
portions by annulated undulating lines. It might be classed among
the large and strong SertularidaB, the principal shoot being of the thick-
ness of a sparrow's quill at its base, and four inches or five inches long.
The branches shoot forth from opposite sides; the whole coralline thus
assuming a flat form, to the extent of four or five inches.

On the south-eastern coast of England the most common kind found
is the Sertularia setacea, which, after rough weather, is cast on the
shore attached to sea-weed. The stem and branches seem composed of
separate pieces, fitting into each other as some foreign trees do, and
terminate in a star-like head, from which radiate the feelers or arms.
Dr. Mantell states he was present on one occasion when Mr. Lister
was observing ,a living specimen : a little globular animalcule swam
rapidly by one of the expanded polyps, the latter immediately con-
tracted, seized the globule, and brought it to the mouth or central
opening by its tentacula; these gradually opened again, with the ex-
ception of one, which remained folded, with its extremity on the ani-
malcule. The mouth instantly seemed filled with cilia, which, closing
over the prey, was carried slowly down its stomach; here it was im-
perfectly seen, and soon disappeared.

Appertaining to this family are the Thuiarea, so named from re-
sembling a cedar-tree ; but some kinds look more like a knobbed thorn-
stick with a bottle-clearer at the top; others resemble a fir-tree.
Antennularia are so called from resembling the lobster's antenna.
They are found fixed to shells and rocks, are plentiful on the north-
eastern coast of England and the coast of Ireland. They are of a brown
colour, and covered with hair-like little branches ; and as the hairy
process is continued up its jointed stem, it is sometimes denominated
Sea-beard.

The Plumularia, so named from the shoots and offsets being
plumous, are an extensive and beautiful branch .of this family. Pro-
fessor Grant thus describes the Plumidaria falcata : " This species is
very common in the deeper 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

SERTULARID^E. 205

spherical, composed of minute transparent granules, 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 Campanularia, 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 off 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 they have fixed,
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 inter-
stices 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 sub-
stance of the roots ; and the portion, of that substance which grows
perpendicularly 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 polyp. Polyps, 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 to fuci and sea-side shells in abundance on the southern
coast of England, is found Plumularia cristata* It is affixed by a
horny, branching, interlacing, tubular fibre to the object on which it
grows. At different parts there are plumous shoots, usually about a
little more than 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 polyp
minute, delicate; tentacles ten, annulated; mouth infundibuliform.

206 • THE MICROSCOPE.

" Each plume," says Mr. Lister, in reference to a specimen of this
species, "might comprise from 400 to 500 polyps;" "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 men-
tioned; thus giving 6000 polyps as the tenantry of a single polypidom !
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 population, which nor London nor Pekin can rival."

Plumulatia pinnata, or Feather Polyp (represented magnified in
Plate I. No. 3), " is as remarkable for the elegance 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 woodcuts 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 assist-
ance. From this devotion to, 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 Catharina :
whose stem is plumous, pinnae opposite, bent inwards ; cells distant, carn-
panulate, with an even margin ; vesicles scattered, pear-shaped, smooth.
Found on old shells, corallines, and ascidia, in deep water. At Scar-
borough it is rare. In Frith of Forth by Dr. Coldstream, and fre-
quently in Berwick Bay. This equals P. pinnata in size and delicacy,
but differs from it very obviously in having opposite pinna?, which, in-
stead of being arched, are bent inwards, so as to render the general form
of the coralline concave on a front view ; an appearance produced by
the pinna3 originating, not from the sides, but from the anterior face of
the stein. The stem itself is straight or slightly bent, jointed, pellucid,
filled with a granular fluid matter ; and in which it differs from its con-
geners, bearing cells, there being always one at the base and between
the insertion of the pinna?, and generally another on the interval be-
tween them. Between the cells there is a series of minute tubular or
tooth-like cells, visible only with a high magnifier. The ovarian vesicles
are produced in summer ; they are stalked, shaped like a pear or vase,
solitary, scattered, and originating always at the base of a polyp cell.

CAMPANULARIA. 207

From the intermediate cellules, particularly from the one next the
polyp-cell, there often grows up a small trumpei-like tube ; and I have
seen in one specimen, all the ends of the branches terminated by four
of these tubes, diverging in pairs."

The sub-family Campanularia 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.

The Campanularia volubilis, or Twining Polyp (Plate I. No. 4), is
the common type : it is parasitical, and infests the antennae of the crab
to a great extent ; its stem is filiform, and at the end of its slender
branches are situated the cells containing the polyps. The polyp itself
is slender when protruded, as seen in the figure, and becomes dilated
at the base into a sort of foot which spreads over the diaphragm,
widening 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, surrounded by the tentacles, a large fleshy
mouth protrudes, somewhat funnel-shaped, with lips, endowed with
the power of protrusion and contraction ; these appear to be very
sensitive. Mr. Gosse found them in great abundance round Small-
mouth Caves.

The Campanularia gelatinosa has beautiful bell-shaped cells, out of
which the animal protrudes, giving it the semblance of a green flower
with a delicate pink stalk. It is indeed an interesting object for ob-
servation, as the currents in the tubes may be detected. Dr. Johnston
says, " On Saturday, May 29th, 1837, a specimen of Campanularia
gelatinosa was procured from the shore ; and after having ascertained
that the polyps were active and entire, it was placed in a saucer of
sea-water. Here it remained undisturbed until Monday afternoon,
when all the polyps had disappeared. Some cells were empty, or
nearly so ; others were half -filled with the wasted body of the polyp,
which had lost, however, every vestige of their tentacula. The water
had become putrid, and the specimen was therefore removed to ano-
ther 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 j but on the afternoon of Friday,
June 2d, every cell had its polyp complete, and displayed in the
greatest perfection. Had these singular facts been known to Linnseus,
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,

208 THE MICROSCOPE.

which after a time fall like blighted blossoms off a tree; they do be-
come ' old in their youth/ and, rendered hebetous and unfit for duty or
ornament by age or accident, 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 unde-
niable ; 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, the more I look into Nature's
works, the sooner am I induced to believe of her even those things that
seem incredible' " — Baker.

TUBULARID^E.

The third family are the Tubular or Vaginated Polyps : of an arbo-
rescent appearance, the animals live near the end of the branches, and
are found attached to stones, sea-weeds, and shells. The Tubularia
indivisa, or individed tubes, rise up like a tuft of herbage, of a horn
colour, to the height of twelve inches. Ellis says, " they seem part of
an oat-straw with the joints cut off." At the summit protrudes the
scarlet-coloured polyp, well furnished with tentacula, and connected
with a pinkish fluid that fills the tubes. It was in this that Dr. Eoget
discovered the singular peculiarity of a circulation, similar to that in
many plants, carried on without the mechanism necessary in higher
organised animals : he says, " In a specimen of the Tubulama indivisa,
when magnified one hundred times, a current of particles was seen
within the tubular stem of the polyp, strikingly resembling, in the
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 particles 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 on 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 ofliee they perform, as well as the true character of their

TUBULARIDvE. 209

remarkable activity and seemingly spontaneous motions ; for the hypo-
thesis of their individual vitality is too startling to be adopted without
good evidence." Dr. Johnston cautions his readers against confounding
this sort of circulation " with those aqueous currents which flow over
the surfaces of the external organs of the ascidian polyps;" he adds,
that innumerable cilia " clothe the surfaces of their tentacula, and
by their rapid vibrations drive a constant equable stream of water
along one side, which returns along the other in an opposite direction ;
and by this means the purposes of respiration are effected, and the nu-
trient fluid fitted for assimilation with the body."

Respecting the singular property of the head dropping off, Sir J. G.
Dalyell says of the Tubularia indivisa, " 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 seems to rise within this tubular stem from below, and to be de-
pendent 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 j and a redundance of heads may be obtained
from artificial sections, apparently beyond the ordinary provisions of
nature. Thus twenty-two heads were produced through the course of
150 days from three sections of a single stem."

One mode of propagation exhibited by these animals is that of the
production of what have been called by Professor Van Beneden, " free
or motive buds." They are produced in little clusters of bulbs, which
grow from the bases of the tentacles at certain seasons, and for a certain
period, after exclusion, possess a considerable power of locomotion.
Sir J. G. Dalyell informs us, that on quitting the parent the bud of this
species develops some little tubercles, the rudiments of the tentacles
ffom its under-surface, and on these, as on so many feet, moves about
the bottom of the water. After a time it appears to select a position
in which to fix its permanent abode, when " it reverses itself to the
natural position, with the tentacles upwards, and is then rooted per-
manently by a prominence, which is the incipient stalk, originating from
the under part of the head. Gradual elongation of the stalk afterwards
continues to raise the head, and the formation of the zoophyte is per-
fected." Other ovules undergo a certain degree of development whilst
still enclosed in the ovisac, and are excluded from this shelter in a form
somewhat resembling that of the common hydra. They then fix
themselves, and become gradually developed into the form of the parent
animal. Many polyps, apparently belonging to this family, give origin,

210 THE MICROSCOPE.

by a process of gemmation, to young Medusae, which again produce
ova, from which similar polyps are developed. The observation of this
fact has given rise to the theory of what is called the " alternation of
generations/' — a theory which has been applied by its originator,
Steenstrup, to several other classes of animals.

Tubularia Icurynx is a most beautiful object ; it is so named from
its slender clustered tubes, which are of a horny texture, having the ap-
pearance of the windpipe of a bird. They are about three inches high,
and the polyps have a delicate red colour, with white arms ; one circle
around the body, and the other round the oral opening.

In this family are the T. ramous, T. ramea, perfect trees in minia-
ture ', and the 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 heads were the guar-
dians of the animal, its "sphery eyne," suggested the name here adopted.
These polyps are adherent by a tubular fibre, which creeps along the
surface of the object on which they grow, 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 which 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 perforated,
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 tentaculum a distinct motion and direction ; but all its move-
ments are very slow and leisured.

We likewise have the Coryne sqiwtmata, and the Coryne stcwridia,
or Slender Coryne (fig. 107, No. 4), a sea-water polyp, thus described
by Mr. Gosse : " It was 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 cellular in texture, and hollow ; within which
a rather slow circulation of globules, few in number, and remote, is
perceived. 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. 5, detached, and

ASTEROIDA. 211

more highly magnified. It is much infested with parasites ; a vorti-
cella 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 -fa inch, with
a diameter of yoVo" inch. They are straight, equal in thickness
throughout, and marked with distinct transverse lines ; they bend them-
selves about with considerable activity, and frequently adhere to the
polyp by one extremity, while the remainder projects freely."

Some of this family attain a considerable size ; the Gorymorpha
nuians, 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 dis-
covered 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 appro-
priate specific appellation given it by Sars), bending the upper part
of its stem. It waved it» long tentacula to and fro at pleasure, but
seemed to have no power of contracting them. It could not be re-
garded 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 Tubularidce inhabit the sea ; but one species,
the Cordyloplwra lacustris, is found in the dock of the Grand Canal,
Dublin, in water which is perfectly fresh.

ASTEROIDA.

The next, or second order of Zoophytes is named Ast&roida from
the polyps presenting the form of a star on the surface of the fleshy
mass in which they reside. (In title-page various species are dis-
tributed over the rock-work at the base.) Their organisation is supe-
rior to those previously described ; and there exists this difference,
that instead of the animals domiciling in a hard cell, they exist in a fleshy
tough crust, which is supported by hard calcareous spicula, and others
with thick branching processes, performing 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
ramified by various tubes and canals for the sustenance and other func-
tions of life of the polyp. This order contains three families, the Gor-
goniadce, Pennatulidce, and the Alcyonidce.

212 THE MICROSCOPE.

The family Gorgoniadce are named after the three celebrated sisters,
daughters of Phorcus and Ceto, who turned to stone all on whom they
fixed their eyes, and one of whom had her hair turned into serpents.
They are of a large size, rising to a foot or more in height, and being
from fifteen to sixteen inches in width (see Plate V. No. 9, and
branches surrounding the title-page).

A widely-diffused class are the Gorgoniadse in every sea ; and
though they naturally seem to dwell in deep water, yet when found in
that more shallow, their colours are richer, deeper, and brighter. They
are flexible, and seem like plants growing to the rocks to which
they are fixed. Some are branching, covered with lace-like work j
others like a feather or fan ; while some, again, are straight, and others
of a drooping form. The stems flat, angular, or round, of a dark
colour, with an outer crust of a soft substance full of pores, out of
which the polyps thrust themselves. The flesh when dry is earthy and
friable, a considerable proportion of carbonate of lime entering into
its composition ; but in a recent state it is soft and fleshy, and exca-
vated with numerous cells for the lodgment of the polyps. When a
portion of a branch is macerated in a weak acid, the lime is entirely
removed ; but the branch retains its original size and figure, and
shows the frame-work to., be an irregular close texture of corneous
fibres, the interstices of which had been, probably, filled with a gela-
tinous fluid.

The Gorgonia patula of Ellis and Solander is beautiful from its
bright red colour ; on its opposite sides it has holes projecting forwards,
through which the polyps protrude in search of food.

Gorgonia flabellum, sometimes called the Sea-fan, Flabellum Veneris,
or Venus 's fan, may often be seen of the height of five feet. It grows
in the form of a net, with its branches compressed inwardly ; the flesh
is yellow, sometimes purple, with small mouths placed irregularly, hav-
ing polyps with eight tentacles ; the bone is black, horny, and slightly
striated on the large branches. When alive, the colour is most beauti-
ful, generally yellow with red spots, and is of a tough nature ; but it
varies much both in shape and colour, presenting some of the most
delicate and graceful forms that can be conceived. Its elegant skeleton
is generally seen decorating the houses of seafaring persons. Kay, re-
ferring to the fan- shape of some marine objects, says, "That the motion
of the water descends to a good depth, I prove from those plants that
grow deepest in the sea, because they all generally grow flat, in the man-
ner of a fan, and not with branches on all sides like trees ; which is so
contrived by the providence of nature, for that the edges of them do in

PENNATULID^E. 213

that posture with most ease cut the water flowing to and fro ; and
should the flat side be objected to the stream, it would soon be turned
edgewise by the force of it, because in that site it doth least resist the
motion of the water ; whereas, did the branches of these plants grow
round, they would be thrown backward and forward every tide. Nay,
not only the herbaceous and woody submarine plants, but also the litho-
phyta themselves affect this manner 'of growing, as I have observed in
various kinds of corals."

In the British family there are also (?. verucosa, G. placomus,
G. anceps, G. lepadifera, G. umbraculum, G. nobilis.

The Isis, sea-shrubs belong to this class ; they are small, but nume-
rously scattered in the soft fleshy integument, Isis hippuris, or
Horse-tails, so called from its" resemblance to the Equisetse, is the
type by which this family is illustrated ; it has a jointed stony stem,
which rises into many loose branches. The stem or support of the
animal consists of white, cylindrical, stony channelled joints, connected
together by black, contracted, horny intermediate ones. The flesh is
whitish, plump, and full of minute vessels ; the surface of it is full of
the little mouths of the cells, which are disposed in a quincunx order,
covering the polyps with eight claws.

PENNATULIDJ2.

This family derives its name from penna, a quill, which the animal
much resembles ; a spiculum from one is shown at No. 3, fig. 103. Natu-
ralists call them Sea-pens ; and had they generally applied such simple
appropriate terms to the objects of nature, they would have removed a
bar to the study of science, and overcome a repugnance commonly felt
on entering the enchanting field of knowledge.

The polypiferous mass of the Pennatula is fleshy or jelly-like ; and
the polyps are always found on the margin of the appendages of the
polypidom. The skin is tough and horny, and has numerous calcareous
spicula in a parallel position to each other, which Dr. Coldstream is of
opinion are solid ; and when connected with the body of the animal,
seem to be red ; but a slight degree of heat is sufficient to bleach
them : they consist of phosphate and carbonate of lime, making thus
a near approach to the bone of vertebrate animals.

On many parts of the coast, when the fishermen haul in their lines,
and more especially if baited with mussels, there are found attached to
the bait a number of polyps, which the boatmen call Cocks' -combs, but
naturalists, Pennatula phosphorea ; they are from two to four inches

214 THE MICROSCOPE.

long, of a purplish-red colour, except at the base of the smooth stalk,
which is a pale yellow, from, as the fishermen say, this part being im-
bedded in the mud at the bottom of the sea. They are built up in
the same manner as the former. The papillae on the back of the rachis,
and between the pinnae, are disposed in close rows, and do not differ
from the polyp-cells except in size. The latter are placed along the
upper margin of a flattened fin; they are tubular, and have the aper-
ture armed with eight spinous points, which are movable, and contract
and expand at the will of the animated inmates. These 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, and a series of lesser ones to the latter cilia. The
mouth, in the centre of the tentacula, is somewhat angular, bounded
by a white ligament, a process from which encircles the base of each
tentaculum, which thus seems to issue from an aperture. The ova lie
between the membranes of the pinnae ; they are globular, of a yellow-
ish 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 phospJiorea,
with all its delicate transparent polyps 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 polyps." The power of locomotion is doubted by other
writers, and the pale blue light is said only to be emitted when under
the influence of some painful irritation.

In some genera, Virgularia mirabUis and pavonaria, to which the
name of Sea-rushes has been given, the central stem is from six to ten
inches long (see fig. 103). Sowerby describes them as like a quill stripped
of its feathers. The base has some resemblance to a pen, as in the other
species, swelling a little from the end, and then tapering. The upper
part is thicker, with alternate semicircular pectinated swellings, larger
towards the middle, tapering upwards, and terminating in a thin bony
substance, which passes through the whole. Professor Grant writes :
" Their axis is calcareous, solid, white, brittle, flexible, cylindrical, of
equal thickness throughout, and exhibits no mark of attachment at
either end. When broken, it exhibits a radiated surface, like the
broken spine of an echinus. The axis appears to have little connection
with the fleshy part, and to consist of concentric layers deposited by
the soft parts surrounding it. When a portion of the axis is broken

ALCYONIDJE. 215

off from either extremity, the animal retracts at that part, so as con-
tinually to expose a fresh naked portion of the axis ; hence we can
take out the axis entirely from its soft sheath, and we always find the
lower pinnae of the animal drawn up closely together, as if by the fre-
quent breaking of the base. These very delicate and brittle animals
seem to be confined to a small circumscribed part of the coast, which
has a considerable depth and a muddy bottom j and the fishermen ac-
customed to dredge at that place believe, from the clearness of the Vir-
gularise when brought to the surface, that they stand erect at the bottom
with one end fixed in the mud or clay. Miiller's specimens were like-
wise found on a part of the Norwegian coast with a muddy bottom.
The polyps much resembling those of the common Ldbularia digitata,
are long, cylindrical, transparent, marked with longitudinal white lines,
and have eight tentacula, which present long slender transparent fila-
ments or cilia on each of the lateral surfaces when fully expanded. The
polyps are easily perceived extending through the lateral expansions or
pinnae, to near the solid axis, where we observe two transverse rows of
small round white ova placed under each pinna, and contained within
the fleshy substance. These ova appear to pass along the pinnae, to be
discharged through the polyps, as in the Lobularia, Gorgonia, Caryo-
phyllea, Alcyonia, &c."

ALCYONID^J.

The family of the Alcyonium derives its name from Alcyone or
Halcyone, the daughter of Neptune and wife of Ceyx, who, hearing of
her husband's death at sea, cast herself into it ; and was, with her hus-
band, changed into birds of the same name, to keep the waters calm
while they sit in their nests of sea-foam for the space of seven, eleven, '
or fourteen days. Thus Alcyon signifies kingfisher, or sea-foam. The
term Lobularia is sometimes applied to this family, but generally re-
jected from its botanical appellation.

Alcyonium digiiatum, PI. V. No. 2. Its name is derived from its
fingered appearance ; the French call it Main de Mer, or " sea-hand,"
the Germans Diebs/iand, or " thief's hand." Sometimes they are very-
small ; but when larger are named by the fishermen Cow's-paps, and
others, differing a little in form, Dead Mens Toes, or Dead Men's
Hands. Their spiculae are calcareous or siliceous crystalline, in the
form of a cross, toothed at the sides, and lie scattered through the
jelly-like mass.

The cells occupied by the polyps are placed at the terminations of
canals which run through the polypidom, and which, by their union

216 THE MICROSCOPE.

with each other, serve to maintain a communication between the indi-
vidual polyps constituting the mass. The rest of the polypidom is
made up of a transparent gelatinous substance, containing the calcare-
ous spicula above mentioned, and pervaded by numerous small fibres,
which form a sort of irregular network. Alcyonidse are always
attached to submarine bodies. The species already mentioned is ex-
ceedingly 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," says Professor Grant, " when placed under the micro-
scope, and viewed by transmitted light, appeared as opaque spheres
surrounded with a thin transparent margin, which increased in thick-
ness when the ova began to grow, and such of the ova as lay in contact
united and grew as one ovum. A rapid current in the water imme-
diately around each ovum, drawing along with each all the loose
particles and floating animalcules, was distinctly seen moving with
an equal velocity as in other ciliated ova ; and a zone of very minute
vibrating cilia was perceptible, surrounding the transparent margin of
all the ova. The progressive motion of the ova, always in a direction
contrary to that of the current created by their cilia, was very obvious,
though less rapid than in any other zoophyte in which I have observed
the same remarkable phenomenon. The specimen, suspended in a glass
jar filled with pure sea-water, I now brought so close to the transparent
side of the vessel, that I could examine through it, with the assistance
of a powerful lens, and without disturbing the animal, the motions and
progress of the groups of ova passing through the colourless bodies of
the polyps. To the naked eye, at first sight, all appeared motionless.
The deep vermilion hue of the small round ova, and the colourless
transparency of the outer covering of the polyps, formed a beautiful
contrast with the pure white colour of the delicate longitudinal folds,
the central open canal, and the slender filaments which wind down
from its sides towards the clusters of white ova at the base : but the
living phenomena discovered within were even more admirable than
the beautiful contrast of colours, the elegant forms, and the exquisite
structure of all the parts ; when observed with a lens, the ova were
seen to be in constant motion, and quite free within the bodies of the
polyps. They moved themselves backwards and forwards, and fre-
quently contracted their sides, as if irritated or capable of feeling. I
could observe none passing upwards between the stomach and the sides
of the polyps. They never assumed the appearance of a string of beads
enclosed in a narrow, short, curved tube, as represented by Spix, but

ALCYONIDvE. 217

swam freely in the water which distended the polyp, as figured by
Ellis. Their motions in the polyps, though circumscribed, were so in-
cessant, that, by watching attentively, I could observe them with the
naked eye ; and they became more conspicuous as the ova advanced to
the open base of the stomach. From their restlessness, as they ap-
proached the last passage which separates them from the sea, they
seemed to feel the impulse of a new element, which they were im-
patient to enjoy ; and by following the direction of that impulse, they
appeared to find their way into the lower extremity of the stomach,
without any organic arrangement to lead them into that narrow canal.
In their passage through the stomach, which was effected very slowly,
the spontaneous motions of the ova were arrested, unless some imper-
ceptible action of their cilia, or some contraction of their surface,
might tend to irritate the sides of that canal, and thus direct or hasten
their escape."

Alcyoniwn, gelatinosum. — Attached to old stones and shells is this
jelly-like transparent spongy zoophyte, growing to a height of nearly
a foot, and sometimes much longer. It is branched, and of a brown
or yellow colour, dotted with polyps, which are attached to the cells.
Through angular openings they protrude their arms or feelers. Dr.
Farre states, " The tentacula are sixteen in number (occasionally fifteen),
fully two-thirds the length of the body of the animal, and extremely
slender and flexible. When expanded they are frequently seen to roll
up closely upon themselves, even down to their base; the revolution
taking place either inwardly or outwardly, and in one or more arms at
the same time. Their full expansion affords a more perfect cam-
panulate form than is usually met with in this class, each of the arms
having a slight curve outwards towards its extremity, which gives to
the whole a very elegant appearance. It is remarkable that in some
specimens the arms are much shorter on one side of the body than on
the other."

The last specimen we notice, belonging to this family, is the
handsome Tubipora musica, or Organ-pipe Coral, fig. 10, Plate V.
This coral is composed of parallel tubes, united by lateral plates,
or transverse partitions, placed at regular distances ; in this manner
large masses, consisting of a congeries of pipes or tubes, are formed.
When the animals are alive, each tube contains a polyp of a beautiful
bright-green colour, and the upper part of the surface is covered with
a gelatinous mass, formed by the confluence of the polyps. This species
occurs in great abundance on the coasts of New South Wales, of the
Red Sea, and of the Molucca Islands, varying in colour from a bright

218 THE MICROSCOPE.

red to a deep orange. It grows in large hemispherical masses, from
one to two feet in circumference : these 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 the other tubes are produced on
the transverse plates ; thus filling up the intervals, and constituting
a uniform tubular mass ; the surface being covered with a green fleshy
substance beset with stellular animalcules.

ACTINIAE.

All persons accustomed to wander by the sea-shore must have ad-
mired the livid green, dark little jelly-masses adhering to the rocks, —
called Actinia, from a Greek word signifying a ray, — and le.ft in some
little pool by the ebbing tide, living as they do principally within high
and low-water mark, and expanding their broad surfaces and fringing
feelers to the finger of inquisitive youth, so often thrust into the centre
to feel the effect of the suction, as the poor animal draws itself up in the
form of a little fleshy hillock. TheActinice have the power of secreting
some adhesive substance at their base, by which they affix themselves to
rocks and other objects..; but can release their bodies when necessary,
and, either by creeping on their feelers, or filling their bodies with
water, and gliding along, change their location. Much interest has
been excited by the exhibition of many of this class in the tanks in the
Zoological Gardens. These zoophytes are more familiarly known by
the name of Sea-Anemonies, or Animal Flowers : they belong to the
order Helianthoida ; the polyps are single, free, or permanently attached;
fleshy, naked, or encrusted with a calcareous polypidom, the upper sur-
face of which is crossed by radiating lamella?. Eepresentations are
given of them in the Frontispiece, Nos. 5, 6, and 7, and elsewhere.

In their appetites they are voracious, and seize the little shelled in-
habitants of the sandy shores. Dr. Johnston says : " I had once brought
me a specimen of Actinia gemmacea, that might have been originally
two inches in diameter, and that had somehow contrived to swallow a
valve of Pecten maximus, of the size of an ordinary saucer. The shell,
fixed within the stomach, was so placed as to divide it completely into
two halves ; so that the body, stretched tensely over, had become thin,
and flattened like a pancake. All communication between the inferior
portion of the stomach and the mouth was of course prevented; yet,
instead of emaciating and dying of atrophy, the animal had availed it-
self of what had undoubtedly been a very untoward accident, to increase
its enjoyments and its chances of double fare. A new mouth, furnished

ACTINIA. 219

with two rows of numerous tentacula, was opened up on what had been
the base, and led to the under-stomach : the individual had, indeec7,
become a sort of Siamese twin, but with greater intimacy and extent
in its unions." The following curious observations made by Dicque-
mare upon these rivals of the weather-wise leeches, may be useful to
some residents at the sea-shore ; " My very earliest observation showed
that the sea-anemonies feel, and prognosticate within doors, the differ-
ent changes of temperature in the atmosphere. I had not leisure at
that time to form tables of their various indications j but I have since
done it. This fact, if applied to practice, might be of use in the for-
mation of a sea-barometer ; an object of no small importance, which
several ingenious men have hitherto endeavoured in vain to furnish us
with. I should prefer the anemonies of the third species for this pur-
pose, their sensation being very quick ; they are also easily procured,
and may be kept without nourishment. Five of them may be put in
a glass vessel four inches wide and as many in depth, in which they
will soon cleave to the angle formed by the sides and the bottom. The
water must be renewed every day ; and as they do not require a great
quantity of it, as much may be fetched from the sea (if they be kept on
land) as will supply them for several days ; its settling some time will
only improve it. If the anemonies be at any time shut .or contracted,
I have reason to apprehend an approaching storm ; that is, high winds
and an agitated sea. When they are all shut, but not remarkably con-
tracted, they forbode a weather somewhat less boisterous, but still at-
tended with gales and a rough sea. If they appear in the least open,
or alternately and frequently opening and closing, they indicate a mean
state both of winds and waves. When they are quite open, I expect
tolerably fine weather and a smooth sea. And lastly, when their
bodies are considerably extended, and their limbs divergent, they
surely prognosticate fixed fair weather and a calm sea. There are
times when some of the anemonies are open, and others shut ; the
number must then be consulted ; the question is decided by the ma-
jority. The anemonies used as barometers should not be fed ; for then
the quantity of nourishment might influence their predictions. Ane-
monies *>f this, and of the first species, live and do well for several
years without taking any other food but what they find disseminated
in the sea-water ; but should a respite of some days be granted them,
they might then be fed with some pieces of muscles, or soft fish, and
thus restored to their original vigour. Whenever the vessel is sullied
by the sediments of salts, slime, the first shoots of sea-plants, &c. the
animals may, on changing the water, be cleansed, by wiping them with

220 THE MICROSCOPE.

a soft hair pencil, or even with the finger, carefully avoiding to rub or
press hard on the anemonies. Should any of them drop off during this
operation, they may be left at liberty ; for they will soon of their own
accord fix themselves to some other place. Should any of them die,
which will soon be discovered by the milky colour of the water, and
an offensive smell on changing it, it must be taken out, and on the first
opportunity another of the same species be put in its place ; those of a
moderate size are the most eligible."

Actinia bring forth their young alive ; one or more appear first
in the tentacles, from whence they can be withdrawn and transmitted
to others by the parent, and are at last produced by the mouth. In
the course of six years, one specimen was found to produce above
276 young.

Like the Hydra?, the Actinia may be cut and its members lopped
off without injury, the parts becoming perfect animals, or the limbs
rebudding ; in fact, the tentacles will be reproduced as often as the
sympathising experimenter may choose to perform amputation. If the
animal be divided in two, separating the base from the head, the former
will become a perfect animal, and the latter industriously swallow food ;
which passes freely through it, but in time is retained, and a finished
stomach effects the necessary function of digestion. Upon trying this
experiment, there have been instances of a new head coming at the part
where the separation from the base was effected ; thus at each end the
active and powerful feelers captured prey and conveyed it to the stomach.
Hot water may blister its skin, and a transparent palace of ice encase
its body, or an air-pump deprive it of air, the animal will not die ; but
fresh-water is the swift and sure messenger of death.

The commonest kind of this family, Actinia mesembryanthemum, or
Smooth Anemone., is of a dark-flesh or olive colour; some are streaked
with white, blue, or green, or spotted. The feelers, when stretched out,
are about the same length as the body ; the animal generally measures
about an inch and a half in diameter. Dr. Johnston says: " The tubercles
within the margin of the oral disk are formed by papillary projections
of the parenchyma — spongy or porous flesh — of the body, covered over
" on the top with a thick layer of dense blue matter ; in it, as well as in
the skin generally, minute fusiform calcareous spicula, some slenderer
than others, may be detected in abundance with the microscope."

Actinia rubra and Bellis (Nos. 4, 5, 6, and 7, Plate I.) generally live
together in groups of four or five. Goertner thus describes them : "From
the small base arises a cylindric stalk, which- supports the roundish body
of the animal, and from whence afterwards the calyx, being a continued

ACTINIAE. 221

membrane of the body, draws its origin. The stalk, or pedunculus of
the polyp is quite smooth, and its colour inclines towards the carna-
tion. The outside of the calyx, and the body of this animal, are marked
with a number of small white protuberances resembling warts, to which
fragments of shell, sand-grains, &c. adhere, and hide the beautiful
colour of these parts, which, from that of carnation, are insensibly
changed towards the border of the calyx, first into purple, then violet,
and at last into a dark brown. The inside of the calyx is covered with
the feelers that grow in several ranges upon it ; they differ considerably
in length, those that are near the edge of the calyx being but small
papillee, in proportion to those that surround the disk, or the central
part of the body. They are almost transparent, and some of them of
a pale ash colour, with brown spots ; others, on the contrary, are of a
chestnut colour, marked with white spots. The disk is formed like'a
star, which, according to the figure that is traced out by the innermost
row of the feelers, consists of many angles. The colour of this part of
the body is a beautiful mixture of brown, yellow-ash colour, and white,
which together form variegated rays, that, from the centre or the mouth
of the animal, are spread over the whole surface of the disk. The
polyp, contracting itself, changes its body into an irregular hemisphere,
which is so covered with the several extraneous bodies that stick to it,
that it is extremely difficult to know the animal in this state, and to
discern it from the rubbish that commonly surrounds it."

Actinia gemmacea is larger than those previously named ; it has
three or four rows of thick short feelers around the oral disk, which
have suckers at the ends, by which they seize and hold their unfortunate
victims. This is a large and varied species of different colours, the
feelers being usually variegated with red and white rings. Its body is
rough, with glandular warts ; and being covered by the sand, shells, or
gravel surrounding it, is hidden from objects that may prey upon it,
or unobserved by those upon which it preys. So singular is Nature in
adapting its productions to the circumstances by which they are sur-
rounded, that when this species becomes an inhabitant of waters that
do not leave it dry, the masquerading-dress is cast aside, the warts
almost disappear, and it stands forth in all its beauty, proving the words
of the poet, that "when unadorned, adorned the most."

What will man not venture to eat, in hope of tickling the appetite
with some new excitement ! Dicquemare says : " Of all the kinds of
sea-anemonies, I would prefer this for the table ; being boiled some
time in sea-water, they acquire a firm and palatable consistence, and
may then be eaten with any kind of sauce. They are of an inviting

222 THE MICROSCOPE.

appearance, of a light silvery texture, and of a soft white and pinkish
hue. Their smell is not unlike that of a warm crab or lobster."

Actinia maculata. — This is a curious and interesting object, as it is
found enveloping a snail-like or periwinkled shell, having the superior
part of a species of small crab projecting from the inside of the shell.
Its body is of a reddish colour, marked with beautiful purple spots, and
in its thickest part is not more than three-tenths of an inch ; it is about
three inches in diameter, and furrowed longitudinally.

Among the largest of the British species of Actinia is one found on
the north-east coast, which, when contracted, usually measures three
inches in length. Dr. Johnston, as sponsor, gives it the name of Actinia
Tuedice, the ancient appellation of the maritime parts of Berwickshire,
to indicate the place of its first discovery, where it is often dredged from
deep water by the fishermen. It is of a uniform reddish or brownish-
orange colour, and either smooth or contracted at pleasure into circular
folds. The base is smooth and orange-coloured. The mouth is ever
varying in size and form, and there are often protruded from it vesi-
cular-like lobes of a reddish colour, scored with fainter lines.

Anttiea, a flower, is a name applied by Dr. Johnston to a branch of
the order 'Helianthoida. Anthea cereus is of a pretty light-brown
colour, having a somewhat cylindrical furrowed body. About 200
feelers arise from the disk of the animal, which, when expanded, are
longer than the body, and of a bright sea-green colour tipped with red.
But in some kinds this colour varies. They are common on the Corn-
wall coast : Ellis observes, " Their tentacula being disposed in regular
circles, and tinged with a variety of bright lively colours, very nearly
represent the beautiful petals of some of our most elegantly fringed and
radiated flowers, such as the carnation, marigold, and anemone."

EUCERNAE1D.E.

These beautiful and singular animals may be seen swimming quickly
through the waters, or more generally adhering to sea-weed, and spread-
ing out and contracting their bodies as they seize their prey ; for as soon
as the suckers at the end of their feelers have got a little animal within
its power, it is carried to the mouth, and the body contracts to enclose
and consume it. They are of a jelly-like nature, with a smooth and
thickish skin ; their bodies are arborescent, with bell-shaped cells,
having a small sucker at the bottom, and are divided into eight com-
partments, as are others of the Actinia.

Lucernaria campanulata. — This graceful animal is about an inch

LUCERNARID.E. 223

in height, of a bell-shape, terminating in a sucker resembling the stand
of a stalked drinking-glass. The upper part is indented by eight short
processes or arms, stretching upward, and terminated by a delicate tuft
of a blossom-like appearance ; these, about sixty in number, are glands
or suckers, by which prey is caught. Its colours are various and rich.
The interior is hollow like a flower, in the centre of which a square
mouth is seen ; from this seems to spread four leaves, which add to the
beauty of the appearance.

Dr. Johnston mentions in the British family of Lucernaria, L. fasci-
cularis and L. auricula; they differ but little from L. campanulata.
They propagate by ova, which are seen as two rows of spots in the arms
that extend around the mouth,

Nearly allied to the family Actiniae, are those laminated, circular-
form corals, called Fungice, or Sea-Mushrooms (Plate V. No. 1).
They are found in great variety; are white, of a flattened round
shape, made up of thin plates or scales, around which is a translucent
jelly-like substance, and amidst it a large polyp ; for, unlike others,
they exist as individuals : the lower part is of a stony nature, by
which the animal is affixed to the rock whereon it lives.

In Ellis's Zoophytes is the following passage, quoted from Kum-
phius in regard to the Fungia agariciformis : " 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 gela-
tinous 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 lamellae, and which shrink between them
when the animal contracts itself on being disturbed. They are con-
stantly moving in tremulous undulations ; but the vesicles appeared
to me to be air-vessels placed along the edges of the folds, and the
vesicles disappeared when the animal was touched."

In the British Museum there is a splendid specimen of the Brain-
stone Coral, or Meandrina cerebriformis, so named by the appearance
of its surface resembling the convolutions of the medullary substance of
the human brain. In a living state the mass is invested with a fleshy
substance, variously coloured, and having numerous short, conical
polypiform, confluent cells, arranged in rows between the ridges. It
attaches itself by a strong stony secretion to rocks ; and as one genera-
tion passes away, on the shelly remains another arises; and thus the
imperishable charnel-houses are built upon and increased in magni-
tude.

224 THE MICROSCOPE.

MADREPORID.E.

Madrepores, Mother-pores, or " tree corals," differ from other corals
in not having a smooth 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 polyp is dead and decomposed ; but
most distinct in the Oculina ramea, or Abrotanoide, as they are situated
at the apparently broken stumps that branch from the trunk of the
skeleton (Plate V. fig. 5). Every branch is seen to be covered
with multitudes of small pits or dots, scarcely visible to unassisted
vision ; but when viewed under the microscope, will be found to
be cells of the most beautiful construction, remarkable alike for their
mathematical regularity and the exquisite fineness of the materials em-
ployed in their composition. A magnified drawing of one of the cells
is given at No. 6. The living polyps are most beautiful in their native
waters ; their varying colours adding to the richness of the hues cover-
ing the plains of the ocean.

Caryophillia, or Nut-leaf. The Caryopliittia Smithii is found
tightly fixed to rocks ; it is round, of a dirty white colour. Dr. Fle-
ming says of the plates : " The lamellae are disposed in fours, and may
be distinguished into three different kinds. The first are the highest
and the broadest at the margin ; but as they descend into the disk, they
become narrower before they join the central plate. The second kind
are narrower than the preceding at the margin, but towards the middle
they suddenly enlarge and join the middle plate. The third kind are
the smallest, and terminate before reaching the middle plate. The
space included between a pair of the first kind of plates contains one
of the second kind in the middle, with one of the third kind in each of
the lateral spaces. Those on the sides are rough, with small scattered
tubercles, and their margins are curled. This last circumstance occa-
sions the roughness externally, where the longitudinal striae are the
remains of the gills. The plate which occupies the bottom of the
cavity is smooth, variously twisted, and connected with the base of the
lateral plates."

Dr. Coldstream, writing to his friend Dr. Johnston, gives the fol-
lowing interesting account of the animal : " When the soft parts are
fully expanded, the appearance of the whole animal resembles very
closely that of an Actinia. When shrunk, they are almost entirely hid
amongst the radiating plates. The specimens I have seen have varied
in size from three-tenths to half an inch in height. They are found
pendent from large boulders of sandstone, just at low-water mark;

CELLEPORID2E. 225

sometimes they are dredged from the middle of the bay (Torquay).
Their colour varies considerably ; I have seen the soft parts white, yel-
lowish, orange-brown, reddish, and of a fine apple-green. The ten-
tacles are usually paler. During expansion, the soft parts rise above
the level of the calcareous disk to about twice its height. The tenta-
cles are pushed forth very slowly, but sometimes are as long as the
whole height of the body. They are terminated by a rounded head.
The mouth has the appearance of an elongated slit in the centre of the
disk ; it is prominent, and the lips are marked with transverse striae of
a white colour. When a solid body is brought into contact gently
with the tentacles, they adhere pretty strongly to it, just as the Ac-
tinia do ; but when they are rudely touched, they contract very
quickly, and if the irritation be continued, the whole soft parts sink
within the calcareous cup."

The species best known from its skeleton is Corallium rubrum, or
Red Coral. It is the coral of commerce, and is an inhabitant of the
Mediterranean and adjacent seas. In appearance it resembles a tree
devoid of leaves and small branches. It requires about ten years to
arrive at maturity, and is then about a foot in length. Its skeleton or
axis is the polished brilliant red-stone used in ornamentations. It is
solid, channelled, ramified, and fixed by a broad base, with a thin ex-
ternal, fleshy covering, of a pale blue colour, and studded over with
star-like polyps, that extend their feelers to grasp at prey. When
brought into the air, the pulpy body of the animal soon decays, when
its remains are prepared for market, and the neck or arm of matchless
beauty is endeavoured to be rendered more attractive by being adorned
with the pretty skeleton forms of the dead animal.

CELLEPORID^E.

This family have calcareous polypidoms, cellular, irregularly -lobed,
or branched, formed of pitcher-shaped cells, heaped together or arranged
in quincunx, that is, resembling the five on playing-cards.

On the British shores are found C- pumicosa, C. ramulosa, C. Skenei
(named after the talented Dr. David Skene), C. cervicornis, and C.
Icevis. This last, Dr. Fleming says, is " in height an inch and a quarter;
diameter, one-tenth ; the branches are smooth, with the orifices of
the cells smooth and concave ; towards the extremities the branches
are rough with the forming cells, and the orifices are more declining,
circumscribed, a little prominent, with a blunt process at the proximal
margin."

Q

226 THE MICROSCOPE.

Lepralia, Sea-scurf, — from the Greek for marine leprosy, — is the
name given to this branch of the Celleporidae by Dr. Johnston.

Lepralia nitida, found attached to shells, is thus described: "Crust
spreading circularly, closely adherent, rather thin, greyish white, cal-
careous ; cells contiguous, in radiating rows, large, subalternate, orate,
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.

The family Cellularia, or little cells, have mostly that wonderful
provision of nature for their protection, an operculum, a lid or cover
over the apertures of their cells. 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.

Cellidaricu avicvlaria has been more accurately described by Mr.
Gosse, from his own observations upon specimens secured on the Devon-
shire coast, during a residence 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 vultures' 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 polyps
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 Lepralia
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 organisation of this zoophyte is discovered, especially when in

CBISIAD^E. 227

full health and vigour, with all the beautiful polyps 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 herbarium ; 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 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 ; therefore 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 mi-
croscope, 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."

CRISIAD^L

The Crisiadce, signifying a separation, are generally parasitical.
Crisia cornuta, or Goafs-horn Coralline of Ellis, have the cells linked
in a single series, as well as C. cfielata, or BulVs-Jwrn Coralline; the
latter look like a number of shoes that come close to the ancle, joined
by the toe-part to the heel of others. Ellis says : " This beautiful
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 begin-
ning 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, or 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, cylindrical,

228 THE MICROSCOPE.

bent and tubular orifices, free ; while the Crisia aculeata has 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.

Of the family Eucratiados, we have to notice a specimen of great
interest, the Anguinaria, — from the Latin anguis, a snake. This is now
classed with the Bryozoa, but from its external form, and resemblance
to the Hydra-form zoophytes, we prefer to retain and describe it where
it was originally placed. An account of the Anguinaria spatulata, or
Snake-head Coralline, appeared in the Transactions of the Microscopical
Society, by Mr. Busk, who corrects many errors before existing re-
specting this zoophyte. This polyp is parasitical upon fuci, and is not
unfrequently associated with other kinds on the same plants, as in fig.
107, No. 2; it is there associated with Campanularia Integra. The
A. spatulata "as a whole, consists, like all its congeners, of two dis-
tinct portions, one usually termed the radical, and another which con-
stitutes the proper polyp-cells. In the present instance, the arrange-
ment of these parts is in some respects very peculiar and curious ; but
it will be found upon strict examination to accord accurately with the
universal type. The origin, or base, as it may termed, of the zoophyte,
is a more or less rounded disk of small size, probably divided into com-
partments, as in the Notamia, from each of which arises a primary
radical branch, in this species very short; these primary radical
branches or tubes are directly continued into a polyp-cell; but the
cavities of the tube and cell are not continuous, being separated by a
distinct dissepiment, so that the coarsely-granular contents of the
radical tube have no communication with the polyp-cell. The growth
of the polyp-cell appears to precede in some degree that of the radical
tube continuous from it ; and the development of these two parts seems
to be carried on in the usual way, viz. first, in the appearance of a
rounded bud filled with granular matter, which gradually increases in
length, and the contents of which are finally moulded or resolved into
the proper contents of the cell, of which the bud constitutes the origin.
In some cases, more than one bud of a radical tube arises at the angle
of the polyp-cell ; and in this way arise the apparent branches of the
creeping- stem. The walls of the radical tubes and of the polyp-cells
consist of a thin transparent horny material, which is insoluble in weak
acids, and strengthened or rendered rigid, except in one part, by the
deposit of calcareous matter. In the radical tubes, and on the dorsal

ESCHARID^. 229

or upper surface of the dilated extremity of the polyp-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 polyp- cell, or the upright portion, the
calcareous material is arranged in beautifully regular rings, giving
that part of the zoophyte a peculiarly elegant appearance under the
microscope. This calcareous ingredient is sufficiently abundant to
render the contents of the radical tubes and polyp-cells indistinct;
and to obtain a satisfactory view of these parts it is necessary to re-
move 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 polyp-cell. The
latter contains an ascidian polyp, which has about twelve tentacles,
and no gizzard. The polyp, as far as Mr. Busk has observed, is always
lodged in the upright portion of the cell ; but the long retractor mus-
cular fibres arise near the commencement of the horizontal portion of
the cell, and from its upper wall, 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, as conducing to the extrusion of the
polyp in Bowerbankia, and which are also very distinct in iheNotamia;
but which, in the present instance, would seem, to have for their chief
function the drawing-up or corrugation of the membranous portion of
the polyp-cell. These muscular fibres have a distinct central nucleus
or thicker portion, as is the case in the analogous muscles in the other
cases just cited."

From the above description, the student in natural history will
perceive the discoveries of Mr. Busk so far differ from the accepted
account of this zoophyte as to remove it from the family in which it is
generally placed, as well as Notamipu bursaria, to the class Bryozoa.

ESCHARID.E.

This interesting family justly deserves the great attention many
naturalists have bestowed upon it. Linnaeus named it Flustra, from
the Saxon word flustrian, to weave; they are commonly called Sea-
mats, and resemble 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 fearful of danger.

230 THE MICROSCOPE.

Dr. Grant estimates that a single Flustran has as many as four
hundred millions of these useful and restless appendages. The feelers
vary from ten to twelve ; their organisation consists of a long gullet, a
gizzard, a stomach and intestines; the body being of a transparent
substance. Some take the form of a delicate minute tree, having cells
in all parts; and vary in colour, inhabiting every sea. Lamouroux
says : " When the animal has acquired its full growth, it flings from
the opening of its cell a small globular body, which fixes near the
aperture, increases in size, and soon assumes the form of a new cell ;
it is yet closed, but through the transparent membrane that covers its
surface the motions of the polyp may be detected ; the habitation at
length bursts, and the tentacles protrude ; eddies are produced in the
water, and conduct to the polyp the atoms necessary for its sub-
sistence."

Dr. Grant writes : " The aperture of the cells is formed by a semi-
circular lid, convex externally and concave internally, which folds down
when the polyp 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 Flustrae without the slightest perceptible synchronous
motion of the polyps."

Milne Edwards, in writing on the Eschares, remarks, " that the cell,
in which it is said the polyp retires as into a shell, is a component part
of the animal itself, in which it conceals itself, if we may use the com-
parison, as the hedgehog enters into the thorny skin of his back. It is
not a calcareous crust, which is moulded on the surface of its body,
but a portion of the general tegumental membrane of the skin of the
polyp, which, by a molecular deposit of earthy matter in the meshes of
its tissue, ossifies as the cartilages of superior animals ossify, without
ceasing to be the seat of the nutritive movement."

In the formation of their stony skeletons, the animals appear to
take no part, " being secreted by the integuments or membranes with
which it was permeated and invested, in like manner as the bones
and nails in man are secreted by the tissues designed for that purpose,
and acting without his knowledge or control. From an analysis of
the stony corals, it appears that their composition is very analogous to
that of shells. The porcellaneous shells, as the 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 cartila-

FLUSTER. 231

ginous 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
obtained by an analysis of the nacreous (pearly) shells. A recent ela-
borate 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 is the broad-leaved Horn -wrack of Ellis ; it is about
four inches high, brown, and the polypidom is horny. The cells are
small, in alternating rows; sometimes covered by a lid that opens down-
wards. 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. The cells have lines in an oblong direction. It is the nar-
row-leaved Horn-wrack of Ellis.

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 j
from hence the polyp-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."

Flustra carbasea grows out in a leaf-like manner, gradually widening
to the end. It is 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 Dr. Grant, who has written a
most careful paper on these polyps, says, 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 polyp." 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 present about
ten square inches of surface ; so that a common specimen of the F.
carbasea presents more than 18,000 polyps, 396,000 tentacles, and
39,600,000 cilia. The ova of the F. carbasea make their first ap-
pearance as a small yellow point, a little below the aperture of the
cell, and behind the body of the polyp ; they are unconnected with

232 THE MICROSCOPE.

the polyp, and appear to be produced by the posterior wall of the
cell, in the same manner as the axis, or common connecting sub-
stance of polyps, produced them in other zoophytes. In this rudimen-
tary state they are found in the same cells with the healthy polyps ;
but, before they arrive at maturity, the polyps of such cells perish and
disappear, leaving the entire cavity for the development of the ovum.
There is never more than one ovum in a cell, and it occupies about
a third of the cavity when full-grown and ready to escape. When
first visible, it has a round or slightly oblong and regular form ; when
mature, it is ovate, with the small end next the aperture of the cell.
The ova do not appear in all the cells at one time ; nor is there any
discernible order as to the particular cells which produce ova, or the
part of the branch which contains them. Cells containing ova are
found alike on every part of the branches, from the base to within two
or three rows of the apex occupied only by young polyps.

Dr. Grant, in writing more especially of the F. carbasea, says :
" They are very irritable, and are 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 forward, 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 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 appearance of being thickly strewn with orient
pearls ; the under surface is even and longitudinally striated, the num-
ber of stria3 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 incrustation on the frond of

CORALLINES. 233

the sea-weed, spreading irregularly to the extent of several square
inches."

Eschara foliacea (Frontispiece, No. 2). — "This curious polypi-
dom," writes Dr. Johnston, " attains a large size, being often three or
four inches high, and from twelve to twenty inches in diameter. It
may be described as a broad membrane, twisted into winding folds,
leaving large sinuosities and cavernous interstices ; it is very light, and
floats in water ; crisp when dry, membrano-calcareous, cellular, of a
yellowish-brown colour, roughish, and punctured with the numerous
pores which open on both sides. The membrane is less than a line in
thickness, and consists of two layers of cells, separated behind from one
another by a thin plate down the middle. The cells open obliquely by
contracted roundish apertures disposed in a quincunx order on the sur-
face, and which, more especially when recently formed, are often covered
by a small operculum . When a portion of its skeleton is macerated in
diluted muriatic acid, it retains the original form, but becomes soft and
flaccid from the subtraction of the carbonate of lime. The cells are
liable to all the changes of form and character resulting from age in
general."

The Corallines were at one time considered to be animals, and
polyp cells were described by Ellis and Lamarck as existing upon their
outer surface ; such, however, has been shown to be an erroneous de-
scription, and the calcareous material existing in the form of a coating
of variable thickness to a mass of cells evidently is of the vegetable
character. In the Nullapores all the intercellular spaces are filled with
lime, so that it would appear that the external surface of the cell- wall
possesses the power of separating lime from the sea-water, the crystals
of which take a certain definite form of arrangement. They are now
classed among plants, under the scientific terms of Lithophytes, or Stone
Plants, Corallines, and Nullapores.

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 reflect, that these islands, bearing on their bosoms gar-
dens of Eden, are entirely formed by the slow-growing corallines,
which, rising up in beautiful and delicate forms, displace the mighty
ocean, defy its gigantic strength, and display a shelly bosom to the ex-
panse of day ! The vegetation of the sea, cast on its surface, under-
goes a chemical change ; the deposit frc m rains aids in filling up the
little gaping catacomb, the fowls of the air and the ocean find a rest-
iug-place, and assist in clothing the rocks ; mosses carpet the surface,

234 THE MICROSCOPE.

seed brought by birds, plants carried by the oceanic currents, animal-
cules floating in the atmosphere, live, propagate, and die, and are suc-
ceeded, by the assistance 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.

Dr. Maccullock, in his Highlands and Western Islands, observes :
"Their plants are made of stone, and they construct islands and conti-
nents for the habitation of man. The labours of a worm, which man
can barely see, form mountains like the Apennines, and regions to
which Britain is as nothing. The invisible, insensible toil of an ephe-
meral point, conspiring with others in one great design, working un-
seen, unheard, but for ever guided by one volition, — by that One Voli-
tion which cannot err, — converts the liquid water into the solid rock,
the deep ocean into dry land ; and extends the dominions of man, who
sees it not, and knows it not, over regions which even his ships had
scarcely traversed. This is the Great Pacific Ocean, destined at some
future day to be a world. That same Power, which has thus wrought,
by means which blind man would have despised as inadequate, by
means which he has just discovered, here too shows the versatility, the
contrast of its resources. In one hour it lets loose the raging engines,
not of its wrath, but of its benevolence ; and the volcano and the
earthquake lift up to the clouds the prop and foundation of new
worlds, that from those clouds they may draw down the sources of
the river, the waters of fertility and plenty."

Ehrenberg, on beholding the coral-beds in the Ked Sea, exclaimed :
" Where is the paradise of flowers that can rival in variety and beauty
these living wonders of the ocean V

In the Narrative of tlw Surveying Voyage of H.M.S. Fly, J. B.
Jukes, Esq., naturalist of the expedition, thus writes : " In a small
bight of the inner edge of the coral reef was a nook, where the ex-
treme slope was well exposed, and where every coral was in full life
and luxuriance. Smooth round masses of meandrinse and astrese
were contrasted with delicate, leaf-like, and cup-shaped expansions of
explanarise, and with an infinite variety of branching madreporae, and
some with mere finger-shaped projections ; others with large branching
stems; and others again exhibiting an elegant assemblage of interlacing
twigs, of the most delicate and exquisite workmanship. Their colours
were unrivalled : vivid greens, contrasting with more sober browns or

CORALLINES. 235

yellows, mixed with rich shades of purple, from pale pink to deep blue.
Bright red, yellow, and peach-coloured millepores clothed those fleshy
masses that were dead, mingled with beautiful pearly flakes of escharse
and reteporse ; the latter looking like lace- work in ivory. Amidst the
branches of the corals, like birds among trees, floated many beautiful
fish, radiant with metallic greens or crimsons, or fantastically banded
with black and yellow stripes. Patches of clear white sand were seen
here and there on the floor, with dark hollows and recesses, beneath
overhanging masses and ledges. All these, seen through the clear
crystal water, the ripple of which gave motion and quick play of light
and shadow to the whole, formed a scene of the rarest beauty ; and left
nothing to be desired by the eye, either in elegance of form or bril-
liancy and harmony of colouring."

Captain Basil Hall thus describes a coral-reef near Loo Choo :
" When the tide has left the rock for some time dry, it appears to be a
compact mass, exceedingly hard and rugged ; but as the water rises,
and the waves begin to wash over it, the polyps protrude themselves
from holes which were before invisible. These animals are of a great
variety of shapes and sizes, and in such prodigious numbers, that in a
short time the whole surface of the rock appears to be alive and in
motion. The most common form is that of a star, with arms, or ten-
tacles, which are moved about with a rapid motion in all directions,
probably to catch food. Others are so sluggish, that they maybe mis-
taken for pieces of the rock, and are generally of a dark colour. When
the coral is broken above high-water mark, it is a solid hard stone j but
if any part of it be detached at a spot where the tide reaches every day,
it is found to be full of polyps of different lengths and colours ; some
being as fine as a thread, of a bright yellow, and sometimes of a blue
colour. The growth of coral appears to cease when no longer exposed
to the washing of the sea. Thus a reef rises in the form of a cauli-
flower, till the top has gained the level of the highest tides, above which
the animalcules have no power to advance ; and the reef, of course, no
longer extends upwards."

Of the myriads upon myriads of organised beings created to work
out the grand designs of Providence, all calculation seems futile ; as the
result would be beyond the grasp of our comprehension. The Poly-
nesian Archipelago, now dubbed one of the great divisions of the globe,
has its foundation formed of coral reefs, the spontaneous growth of once-
living zoophytes. Of the immense extent of the geographical changes
effected by the tiny polyps, Dr. Mantell observes : " We may form
some idea, from the facts stated by competent observers, that in the

236 THE MICROSCOPE.

Indian Ocean, to the south-west of Malabar, there is a chain of reefs
and islets 480 geographical miles in length ; on the east coast of New
Holland, an unbroken reef of 350 miles long ; between that and New
Guinea, a coral formation which extends upwards of 700 miles ; and
that Disappointment Islands and Duff's Group are connected by 600
miles of coral reefs, over which the natives can travel from one island
to another."

Nothing can be more impressive than the manner in which these
diminutive creatures carry out their stupendous undertakings, which
we denominate instinct, intelligence, 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 proceed; by which means the wall
protects the busy millions at work beneath and within. These
breakwaters will resist 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. It is almost unnecessary to remark, that the formations here re-
ferred to are not those of corallines alone, but of zoophytes also.

BRYOZOA.

Bryozoa were placed by Dr. Johnston under the head Ascidioida ;
in the generality of works they are named Bryozoa, and the individual,
Bryozoon ; derived from the Greek words fipvov, sea-moss ; £wov, ani-
mal. (Plate I. Nos. 1, 2.) The distinction to be drawn between it
and those already described, consists in the polypidom being a living
portion of the polyp, while all others are unorganised ; and that most
of the zoophytes we have examined are devoid of cilia, whilst in the
Bryozoon these are most bountifully supplied. The play of the cilia

DESCRIPTION OF PLATE I. (FRONTISPIECE.)

1. Bryozoa Bowerbankia, or Bowerbank Bryozoon, showing its internal structure :
near it is a smaller animal completely withdrawn into its cell. 2. Eschara cervicornis,
or Sea-moss polyp : the animal is seen drawn out from its shell or chalky covering1.
3. Plumulaiia pinnata, or Feather polyp. 4. Campanularia volubilis, or Twining
polyp. These polyps are all represented slightly magnified. 5. Actinia rubra, or
Sea-marigold, near which is one shown retracted into its cell. 6. Actinia Bellis, or
Daisy sea-anemone ; a side view of the animal. 7. The same animal seen with its
crown of tentacles fully expanded. 8. Doris tuberculata. 9. Laniogerus Elfortii.
10. Aplysia ; all species of water-snails, the last without a shell-covering. Fronds of
Algse are represented growing amongst the rocks. In the title-page many other
specimens of marine Polyps, Actiniae, &cv are given.

BllYOZOA. 237

is most energetic, for the purpose of securing an abundant supply of
food, almost 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 since been discovered that
the Bryozoa possess a higher organisation than any of the preceding
families of zoophytes ; and also, from the presence of striped muscular
fibre in their bodies, naturalists have transferred them, with other ani-
mals, the Mustra, Lepralia, Anguinaria spatulata, Notamia, &c., to
the sub-kingdom Mottusca.

Bryozoa are generally found living together in great numbers, and
always clothed with hardy coverings or polypidoms. They subsist on ani-
mal bodies, and differ from most other mollusca in being able to protrude
themselves from their cells. When the animals draw themselves within
their protective homes, to the bottom of which they are attached by a
sinewy ligament, they double themselves up by bending the lower part
of the body upwards. When the creature stretches forth, it presents a
beautiful sight, from its blossom-like appearance and busy cilia; its
protrusion and retraction are performed with surprising quickness, as
it has two sets of muscles for the purpose, one acting on the body of
the animal, the other 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 com-
municating with a canal that passes round the edge of the oral aper-
ture 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 oppo-
site 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.

" The connection of the polypidom with the soft portion of the
polyp is effected," says Dr. Johnston, " by means of an inner tunic,
which, after enclosing the polyp's body as in a pouch, is afterwards re-
flected over the aperture of the cell, — the reflected portion becoming
exterior and solidified, either by calcareous depositions in its texture,
or by a mutation of its thin membranous character into a horny in-
vestment, better suited to the office it has now to perform, of protect-
ing the sentient body from a too rough contact of the medium in which

238 THE MICROSCOPE.

the animals live, and from worse foes. From this mode of connection
it results, that when the animals retire within, they at the same time
must close the aperture to their cells ; for that portion of the inner
tunic which is pushed outwards by their exit, in their withdrawal
follows the body by a process of invagination, becoming at one and the
same time a sheath for the column of tentacles, and a plug to the aper-
ture, which, when of a flexible material, has its margins also drawn
tighter and closer together."

The cells are of various shapes, and from one, grow into a family
of millions, budding forth from the sides ; and though the living matter
disappears, the catacombs exist for the foundation of their families,
branching out and enduring for ages.

Bryozoon Bowerbankia received its name from Dr. Arthur Farre,
in honour of the well-known microscopist, Mr. Bowerbank. A mag-
nified representation of the animal is seen in the frontispiece, Plate
I. No. 1.

Dr. Farre gives the following description of Bowerbankia densa:
" 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 contained
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 com-
pletely expanded, is seen to possess ten arms of about one-third the
length of the whole body ; and 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, or Back-cell, so named from the cells being exactly oppo-
site, and united back to back with a thick partition, and having a joint
above and below each pair.

In some 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 long been
a subject of investigation by naturalists : George Busk, Esq., F.E.S.*
contributed to the Transactions of the Microscopical Society 1849 an
admirable paper on the Notamia busaria, or Shepherd' s-purse Coral-
line (represented in fig. 107, Nos. 1 and 3), which adds to our know-

* Mr. Busk Las added much to the description here given of this bird's-head pro-
cess in the Quarterly Journal of Microscopical Science for January 1854.

BRYOZOA.

239

ledge of tliis curious process. He says : "This most beautiful pearl-
coloured coralline adheres by small tubes to fuci, from whence it
changes into flat cells ; each single cell, like 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,
or Speedwell.

fig. 107.

1. Notamia busaria, or Shepherd' s-purse Coralline. 2. Anguinaria spatulata, or
Snake Coralline, growing with the Campanularia integra* 3. The Shepherd's-
purse Animalcule drawn into its cup, the internal organism of which is shown
greatly magnified. 4. Coryne stauridia, or Slender Coryne. 5. One of the tubercles
detached and magnified.

The polypidom of this bryozoon, like those of most of its con-
geners, may be said to consist of a radical portion, by which it is affixed

240 THE MICROSCOPE.

to the objects upon which it grows, and of a celliferous portion or
branches, upon which the polyps 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 disk, which thence exhibits something of the aspect of the body of
an ophiura. The radical tubes or branches springing from the margin
of the disk are usually live or six in number, and they are given off at
pretty regular distances apart j but besides these radical tubes, one or
more celliferous branches are not unfrequently seen to arise immedi-
ately from the upper surface of the discoid portion.

The central disk, and the radical tubes arising from it, exhibit
a similar structure, and are formed of a thick, firm, apparently horny
envelope, containing a course granular matter, of a yellowish- white
colour, and which in some portions of the tubes assumes the form of
distinct irregularly-globular masses, of nearly uniform size. The cen-
tral disk is subdivided into distinct compartments by septa of consider-
able 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 the tube from which it springs.
This compartment is formed, like those of the central disk, 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 throughout 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 polyp-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 prepara-
tion, 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 in all previous notices ; and, as has been shown, there
is no connection whatever between the cell and the cup placed imme-
diately above and behind it. The aperture of the cell is on the anterior

PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES. 241

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 observed."

The shell, which Mr. Busk believes to be entire at the bottom,
though closed only by a very delicate membrane, contains an ascidioid
polyp, of the usual typical form of that class. '* It has ten tentacles,
and no gizzard. Two sets of muscular fibres at least may be distin-
guished as appertaining to the polyp. 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 at the base of the tentacles, and others lower down the
body of the polyp."

When we consider the minuteness of the delicate little sprig which
is the natural size of this polyp, 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.

PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES.

The following excellent and simple plan for preserving Zoophytes
as wet preparations, so as to retain the polyps and their tentacular arms
in situ, was proposed by the late Dr. Golding Bird. " For this pur-
pose a lively specimen should be chosen, and then plunged into cold
pure water; the polyps 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 pumping out the air, a copious ebullition of bubbles will take
place; and many of the tentacles previously concealed will emerge

242 THE MICKOSCOPE.

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 use-
ful substitutes for the more expensive and difficultly-managed cells. In
this manner specimens of the genera Cycloum, Membranipora, Alcyoni-
dium, and Crisia, 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 in St. Catherine's Island at Tenby,
could 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 Laomedea3, Grantise, and their
allies; whilst the elegant Tubularise 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 inte-
resting results are produced. For this purpose, let a piece of selenite
be placed on the stage of the microscope, and the polarising prisms
arranged so that the ray transmitted is absorbed by the analyser.

If a specimen of Sertularia operculuta, 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 orange-yellowish colour.

This zoophyte is often covered with minute bivalve shells, distin-
guished by the naked eye from the vesicles only by their circular form;
and these, when present, add much to the beauty of the specimen, pre-
senting a striated structure, and becoming illuminated with most beau-
tiful colours.

Sertularia JUicula forms an interesting object ; the waved stem
becoming of a dusky-red, whilst the cells assume but little colour, ren-
ders their mutual relation very obvious. Sertularia abietina is also a
fine object, especially when loaded with vesicles, as it often is in the
autumn. Plumularia falcata acquires fresh beauty under polarised
light, the cells being a pale green, whilst the tubular stem becomes
of a crimson hue j thus presenting a feathered appearance.

The most splendid tints are exhibited by the calcareous structure

PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES. 243

of the Polyzoa, and of these the Flustra truncata, when viewed on
the selenite stage. The Cellularia avicularia is very brilliant when
viewed in the same way ; its cells being covered with plates of carbo-
nate of lime, it presents a fine display of beautiful tints, especially its
bird's-head appendages."

The wonders we have brought to view in our glance at the families
constituting the zoophytic kingdom, must be regarded with wonder and
astonishment by every reflective being. We have seen how wonder-
fully and fearfully they are made ; we have seen the surprising facul-
ties with which they are endowed ; we have seen the perfection and
order bestowed upon them ; we have seen the singular 'faculties they
possess to perform the allotted duties of their destiny ; and seeing all
these things, we read in plain intelligible language the wisdom, power,
and goodness, of an almighty and beneficent Being. We may here
state, that we have taken a somewhat more extended view of this de-
partment of animated nature, from the very circumstance of its pre-
senting a wider field of deeply interesting and curious subjects for
inquiry to the microscopist ; and the more especially have these sub-
jects attracted great public attention, from the spirited attempt on the
part of the Zoological Society of London to afford us the opportunity
of more closely and frequently observing their remarkable habits, en-
closed in glass tanks, forming what we now recognise as marine vivaria.
In our frontispiece, and elsewhere, we have attempted to represent one
of these glass cases, merely adding a few magnified figures of the
Bowerbankii, &c. There the visitor may see the Sabellce, the Ac-
tiniae, of brilliant hues, and many kinds; Mollusca, both shelled and
naked ; Crustacea, Annelida, &c. ; all pursuing their various avoca-
tions, enjoying themselves without restraint, under circumstances
scarcely distinguishable from those of nature. Mr. Warington and
Mr. Gosse made the experiment about the same time ; and from Mr.
Gosse's delightful book, entitled A Naturalist's Rambles on the Devon-
shire Coast, we extract the plan he adopted to preserve his marine ani-
mals alive for many months in London. He says : " The following facts
may be considered as established : marine animals and plants may be
kept in health in glass vases of sea- water for a period of greater or less
length, provided they be exposed to the influence of light. The oxygen
given off by healthy vegetation under this stimulus, is sufficient for the
support of a moderate amount of animal life ; and this amount can be
ascertained by experiment.

But another element in the question soon obtrudes itself. The
Actiniee and other animals habitually throw off a mucous epidermis, and

244 THE MICROSCOPE.

other excretions, which fall to the bottom of the vessel, or accumulate
around them. The progress of actual decay also continually goes on in
the older fronds of the algae ; after a while the presence of this sub-
stance becomes too manifest in the offensive odour of the water ; in a
very short time this leads to disease, and the death of the animal. To
prevent this, it is absolutely necessary to present the water to the action
of the atmosphere in a divided state, which can only be effected by
passing it in driblets, or in a slender stream, from another vessel
suspended above that which contains the animals and plants. An-
other advantage is secured by this process, viz. the aeration of the
water ; for though the requisite oxygen may be supplied by the
agency of the plants alone, the mechanical admixture of the atmo-
spheric air with the water by artificial aeration is highly conducive to
the health and comfort of the animals."

We must, as a fitting addenda to the above, give the plan pursued
by Mr. Gosse, to establish his marine vivarium on a small scale. " The
first thing to be done, is to obtain the algsd in a growing state. As
they have no proper roots, but are generally found closely attached to
the solid rock, from which they cannot be torn without injury by
laceration, I have always used a hammer and chisel to cut away a
small portion of the rock itself, having ready a jar of sea-water, into
which I dropped the fragment with its living burden, exposing it as
little as possible to the air. The red sea-weeds I have found most
successful ; the Fuci and Laminarice, besides being unwieldly, discharge
so copious a quantity of mucus as to thicken and vitiate the water.
The Ulvce and Enteromorphce> on the other hand, are apt to lose their
colour, or become a colourless membrane, and decay from their attach-
ments. The species most capable of being preserved are Chondrus
crispus, the Delessaria, and Iridea edulis. The last named is the best
of all, and next to it the Delessaria sanguinea, for maintaining the
purity of the water ; while the colours and forms of these render them
very beautiful objects in the vase. Into this were placed specimens of
Anthea cereus, Actinia, Crisia denticulata, Coryne, Pedicillina Belgica,
Membranipora pilosa, Doris, Polycera, /Serpula, Acarida, Entomos-
traca, Infusoria, Grantia nivea, and other smaller zoophytes and
sponges." Most of these appeared to enjoy existence, and afforded, no
doubt, months of most interesting microscope examinations j at the
same time the vivarium will form a beautiful and attractive ornament
for the conservatory or drawing-room.

Mr. Warington, in his trials, found that it was not sufficient that
there be plants alone ; but where the higher animals, such as fish, are

THE AQUARIUM. 245

kept, it is necessary that some beings should be introduced for the pur-
pose of feeding on the decaying vegetable matter. This desideratum
is supplied by the various forms of phytophagous mollusca. So that,
to maintain perfect health, it is necessary to place in the glass sea-
weeds, mollusca, fish, &c. ; but those should not be put together which
will devour each other. The sea-water should be kept near the same
temperature always, about 60° Far. ; and the loss by evaporation
supplied by adding rain or distilled-water from time to time. All
dead animal or vegetable matter should be removed, and the glass vase
kept near the window, exposed to the influence of light.

It is quite possible to make an artificial sea-water, for the purpose
of supplying these tanks. In water manufactured as follows, the ani-
mals and plants will thrive and do well. Take 15 pints of water from
the house- cistern, and add to it 7 ozs. of table-salt, \ oz. of Epsom
salts, 80 grains of chloride of potass, and 400 grains of chloride of mag-
nesia. Any chemist can supply or prepare this.

Mr. N. B. Ward, whose fern-cases have now become universal
favourites, made the earliest attempt to establish, on a small scale, an
" aquarium for fish and plants." He writes :* "I placed ten or twelve
gold and silver fish, in company with several aquatic plants, viz.
Villisneria spiralis, Anacharis alsinastrwn, Pontederia crassipes, Pa-
pyrus elegans, and Pistia Stratiotes, which plants, by means of their
vital actions, as had long been well-known, maintained the purity of
the water, and, as in the atmosphere, kept up the balance between
the animal and vegetable respirations. Placed in the centre of my
fern-house, and nearly surrounded by rock-work (rising five or six
feet above the margin of the vessel), clothed with Adiantum and
other lovely ferns, and partially overshadowed with the palmate leaves
of Corypha australis, the plants and fish continued to flourish for
years, The only enemy I had to contend with was a species of Vau-
cJieria, which from its rapid growth, required to be kept constantly
in check. My friend, Mr. Bowerbank, always alive to scientific in-
quiries, followed up these experiments with equal success ; but sub-
stituted sticklebacks and minnows for the gold fish, and a few snails
(Limeus stagnalis) to get rid of the decaying leaves of Vallisneria
spiralis, &c."

* "On the Growth of Plants in closely-glazed cases," by N. B. Ward, Esq.,
F.R.S.

246 THE MICKOSCOPE.

ACALEPH^E.

In great variety of form and colour, swimming freely about the waters
of the ocean, are found in abundance the beautiful Acalephse. From
some of them having a remarkable stinging property, they have derived
their name of Sea-nettles, while others, from their gelatinous nature, are
commonly called Sea-jelly, or Jelly-fish; one of which is shown in the
title-page of this work, depending from the top.

These interesting animals were first arranged in three orders: A.
stabiles (fixed), A. liber ce (free), and A. hydrostaticce (hydrostatic).
Cuvier classed them in two orders : A. swiplices, and A. hydrostaticce.
They are now, however, divided into four orders, and classed in groups
according to the peculiar mode in which they effect their locomotion.

The Medusae, spread on the surface of the water, a beautiful jelly-
like mass, that in form resembles an umbrella ; and by a continual con-
traction and opening out of this part, they pass along in the path they
desire. They are all more or less phosphorescent. The Jleroe, like
many of the Infusoria, propel themselves with active ciliated arms. (See
fig. 115.) The Physalidce have an organ common to fishes, — swimming
bladders, — Iby filling or emptying which they rise or sink, and move
along in their watery home.

The Portuguese Men-of-war have a large bladder, which, when
filled with air, rises above the surface of the waves, and is propelled by
the wind; a contrivance something similar to, though more successful,
we suspect, than the proposition to drag along land-carriages by means
of balloons.

The flat circular horny disk 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 occur 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; andplicse
or folds of the mantle fit accurately into the furrows, from which they
can easily be removed by the application of a gentle force. The con-
centric markings have in all cases small scalloped edges ; they occur at
certain regular intervals, 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 pro-

ACA.LEPH.E. 247

cesses like hairs projecting from them. In no part of this horny tissue
is there a trace of a cellular or a reticular structure.

The most singular incidents in the history of the Medusas are the
circumstances connected with their reproduction. They are all propa-
gated by eggs, which the females produce in glandular organs, some-
times arranged in bands or patches on the surface of the sub-umbrella,
and sometimes in cavities at the base of the peduncle. But these ova,
when excluded from the body of the parent, develop an animal quite
different in form from that from which they sprang ; and it is only in
the second generation that the original Medusa is reproduced. The
eggs are developed, to a certain extent, in small pouches, placed beneath
the body, and in the arms of the mother, whence they are not excluded
until they have acquired the form of an active infusorial animalcule, fur-
nished with cilia, enabling them to swim freely in the water. After a
time, the little animal attaches itself by one extremity in some suitable
position, and awaits its further development. Arms are soon formed
at its upper extremity, and it now presents the appearance and takes
its food in the manner of a hydraform polyp. At this stage of its
growth buds are often produced, just as in a true hydra. The body now
increases considerably in length, and becomes constricted, or divided
by wrinkles of the surface into numerous segments ; these become
more and more distinct, their edges become notched, and at length the
animal resembles a pile of jagged saucers placed one upon another,
and surmounted by a crown of tentacles. At length these separate,
and swim about like little Medusce ; and, after undergoing some
changes, they acquire the form and colouring of the common Medusa
aurita of our coasts. So completely do what, for want of a better term,
we must call the preparatory state of these animals, resemble hydroid
polyps, that their connection with the Medusce has only been quite
recently discovered ; and the species just referred to has been described
under the name of Hydratuba ; and from their great resemblance to
the Tubularian and Sertularian polyps, some zoologists have proposed
the removal of the whole of the hydroid polyps into the present
class, of which many of them are certainly only stages of development.
Opinions are still so much divided, however, as to the true affinities of
these animals, that we have preferred leaving the hydroid polyps in
their old position to placing them where few of our readers would think
of looking for them.

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 substance appears to consist of a fluid, dif-

248 THE MICROSCOPE.

fering 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 only two pounds, which was examined by Professor
Owen, weighed only thirty grains.

The transparency of the tissues renders the whole of the Acalephce
delightful objects for the microscope. (See an excellent paper in the
Transactions of tJie Microscopical Society, " On the Anatomy of Two
Species of Naked-eyed Medusae," by G. Busk, Esq. ; also Professor
Forbes' various works on this family.)

ECHINID^E.

These creatures form an extensive class, to which the above name
has been applied, as well as that of Echino-dermata, Sea-urchins, or
Sea-eggs. Asterias, or Star-fish, are the best known family of this class.

The Echino-dermata are divided into four orders. In two of these
the body is more or less flattened or discoid in its form, and usually
furnished with five or more arms. These in the first order, the
Crinoidea, are slender, and formed of complete calcareous rings or
cylinders ; whilst in the second, the Stellerida, the calcareous covering
of the arms is composed of separate plates. In the third order, the
Echinida, the calcareous plates have become united into a regular
shell ; and the fourth includes the worm-like forms, the Holothurice.

The amount of the calcareous deposit in the skin varies greatly
in the different animals composing the class. In some (as the Holo-
thurice) it forms small irregular grains, scattered, not very plentifully,
through the substance of the skin ; in others, as the Star- fishes (Stel-
lerida), it constitutes plates of various forms, fitting closely to one
another, but only connected by the agency of the true skin ; so that
although the body is completely encased in a suit of calcareous armour,
every part of it still retains considerable flexibility. In others again,
as the Sea-eggs or Sea-urchins (Echinida), these plates are positively
united together, forming a continuous shell, within which all the
organs of the animal are enclosed. Upon most of these calcareous
plates tubercles are to be seen, which serve for the articulation of
movable spines, often of considerable size. These assist the animal
in its motions ; and it is from their almost universal presence that
the name of the class (Echino-dermata, — echinos, a spine, and derma,
skin) is derived.

Echinida may be found in abundance upon our sea-shores, lurk-

ECHINID^E.

249

ing among the rocks, where they entrap their prey. The spines and
suckers are used as feet, or as a mode of progression, even to the
climbing of rocks, in order to feed upon the corallines and zoophytes :
he marches along with ease where apparently no footing could be found,
or digs a hole with his spines to bury himself in the sand, to escape
his pursuer, or to hide himself from observation.

The skeleton of these animals generally consists of an assemblage
of plates, or joints, of calcareous matter. The minute structure of
which presents more or less a reticu-
lated character ; and the solid parts are
usually composed of a series of super-
imposed lamina? or scales. The open-
ings, or areolse, in one layer being
always placed over the solid cell- walls
of the layer beneath it, the spines are
situated on the external surface of the
shell ; they are generally of a conical
figure, and are articulated to the tu-
bercles 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, how-
ever, with the size of the spine, but
with the distance from the base at
which 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, arranged at equal
distances apart (Plate VI. No. 2) ; these
are the ribs or pillars, and indicate the
external surface of the first layer de-
posited; passing towards the margin,
other rows of larger pillars 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

fig. 108.

Polypidom of Pennatula phos-
phorea. 2. Synapta. 3. Anchor-
shaped spiculum and plate from
its skin.

250 THE MICROSCOPE.

greater number of spines the sections of the pillars present no struc-
ture, 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 Plate VI. No. 1. When a vertical section of a spine is examined, it
will be found to be composed of a series of cones placed one over the
other ; the outer margin of each 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
from such species transverse sections may be made, having no concen-
tric rings, and in which only the external row of pillars may be seen.

" The skeleton of Echino-dermata contains very little organic mat-
ter. When it is submitted to the action of very dilute acid, to dis-
solve 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 (Plate VI. No. 7); the meshes or areolse being bounded
by a substance in which a fibrous appearance, intermingled with gra-
nules, may be discerned under a sufficiently high magnifying, power, as
was first pointed out by Professor Valentine. This tissue bears a close
resemblance to the areolar tissue of higher animals ; and the shell may
probably 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. This calcification of areolar or simply
fibrous tissue, by the deposit of mineral substance, not in the meshes
of areolaB, but in intimate union with the organic basis, is a condition
of much interest to the physiologist ; for it presents us with an ex-
ample, 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."*

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, or Sea-lilies, — so called from the resemblance which
many of them present to flowers, — were exceedingly abundant in for-
mer ages of the world ; and their remains often form the great bulk of
large masses of rock. During the whole or a part of their existence,

* Dr. Carpenter, Cyclopaedia of Anatomy and Physiology.

ECHINID^.

251

these animals are attached to submarine bodies by a longer or shorter
stalk, composed of calcareous rings similar to those of which the arms
are composed.

The family Encrinidce, or Sea-lilies, fig. 109, includes an immense
number of fossil forms ; and one or two are still to be found in the
West Indian seas. 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 these arms,
again, was feathered with a double series of similarly jointed append-
ages ; so that the number of separate calcareous pieces forming the
skeleton of one of these animals was most enormous. It has been cal-
culated that one species, the Pentacrinus Uriareus,
must have been composed of at least one hundred and
fifty thousand 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 three thousand such
in the body of a single Pentacrinus — 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?
covered with a continuation of the skin of the disk ;
and from this the ambulacra are protruded, as in other
Echino-dermata.

The third family, the Comatulidce, or Hair-stars,
includes a considerable number of animals, which
bear a great resemblance, both in form and structure?
to the Encrinidce.

The Encrinus being supported upon a long flexible
stalk, formed of calcareous cylinders, is so close a re-
semblance, that when first discovered the young of Co-
matula was described as a Pentacrinus. These animals
are tolerably numerous in the seas of the present day,
and may be said to represent the living type of this
and the preceding class ; they are shown in fig. 116.

In the family of Ophiuridce, so called from the resemblance of their
arms to serpents' tails (Gr. ophis, a snake, oura, a tail), the body forms a
roundish or somewhat pentagonal disk, furnished with five long simple
arms, which have no furrow for the protrusion of the ambulacra. The
Ophiuridce are exceedingly plentiful in all our seas, and their remains

fig. 109.

Encrinus, or
Sea-lily.

252 THE MICROSCOPE.

occur in all the more recent marine strata of the earth's crust. They
are commonly called Sand Stars, or Brittle Stars, fig. 110.

The family Asteridce, the common Star-fish, so abundant on our
coasts, is an example. In this family the arms appear to be merely
prolongations of the disk j they are usually five in number, and the
plates from which the ambulacra are exserted are placed in deep fur-
rows, which run along the lower surface of the arms.

HOLOTHURI^E, OR SEA- CUCUMBERS.

In this order the body , acquires a worm-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.

This order is divided into two families. The first, the Synaptidce,
are characterised by the total absence of ambulacra, the motions of the
animals being assisted by peculiar anchor-like processes of the cal-
careous grains which project from the skin, and roughen the surface of
the animal. The spiculum represented at fig. 108 is serrated on the
convex edge, and the opposite extremity is recurved, and appears to
be connected in some peculiar way with the oval plate upon which it
lies. It is a beautiful object for polarised light.

In the Holothurice, on the contrary, the ambulacra, although short,
exactly resemble those of the. other Echino-dermata in their structure
and action. The mouth is surrounded by a ring of calcareous plates
serving for the attachment of the longitudinal muscles, by which the
contractions of the body are effected. These animals inhabit the seas
of most parts of the world. Some of them are eaten even by Euro-
pean populations ; and the Trepang (Holothuria edulis) is an article of
luxury amongst the Chinese. A few living specimens have been lately
introduced into the tanks at the Zoological Gardens, where they are
established as objects of great interest to the naturalist.

PLATE VI.

SHELL OF ECHINO-DERMATA, GASTEROPODA, ETC.

1. Portion of a transverse section of the Spine of an Echinus. 2. Another section, exhibiting reticulated structure,
the calcareous portion having been dissolved out by acid. 3. Horizontal section of shell of Hnliotis splendens,
with stellate pigment in the interior. 4. Portion of Shell of a Crab, showing granules beneath the articular
layer. 5. Another portion of same Shell, showing its hexagonal structure. 6. Horizontal section of Shell
of Terebratula rubicunda, showing the radiating perforations. /. Transverse section of shell of Pinna ingens.
8. Crystals of Carbonate of Lime, from the outer brown shell of the oyster.

CHAPTER III.

MOLLUSCA.

:HE term Mollusc is derived from the Latin, and
signifies soft ; the body of the animal being soft and
fleshy, partly or entirely covered by a shell attached
to it by means of muscles. The shells are of two kinds ;
those of an epidermal character being formed upon the sur-
face of a filmy cloak-like organ called a mantle, answering
to the true skin of other animals ; and those of a dermal
character being concealed within the substance of the man-
tle, and frequently moulded into a great diversity of forms,
and coloured with various tints.

The animals belonging to the molluscous sub-kingdom
are divided into the following orders, viz. Bryozoa, Tuni-
cata, Conchifera, Gasteropoda, Pteropoda, and Cephalopoda;
of these, all, except the Tunicata and a few of the Pteropoda,
are provided with a hard calcareous shell. In the first
class of the Mollusca, the Bryozoa approximating so closely
to Zoophytes, and from their having been until lately
classified with them, we have thought it more convenient
to the microscopist to retain them in that class with the Eschara.

In the Conchifera the most simple rudimentary form of shell is met
with j for example, in the common slug, Limax rufus, it occurs as a thin
oval plate, imbedded in the shield situated on the back and near the
head of the animal. The shell of all the oyster genus (Pinna) is com-
posed of a series of hexagonal cells filled with transparent calcareous
matter, seen at fig. 7, Plate VI. Dr. Carpenter has shown that the
outer layer of the shell can be split up into prisms, like so many
basaltic columns, fig. 93, No. 1.

When molluscous shells are composed of a single piece, they are
termed univalves ; when of two pieces, bivalves. The bivalve Mollusca
exhibit no traces of any distinct head ; whilst, in the univalves, this
part of the body is well-marked, and usually furnished with special
organs of sense (tentacles, eyes, &c.).

The older naturalists also recognised a group of multivalve shells, or

254

THE MICROSCOPE.

shells composed of several valves. The majority of these belonged to
the Cirrhopod order of Crustacea, which were regarded as Mollusca by

fig. 110.

Mollusca, &c. Padina pavonia, Peacock's- tail, from south-coast; Ophiura, Sand
star, Purpura lapillus, Whelk, Limpet, &c.

MOLLUSCA. 255

the earlier observers. The P/iolades, however, which in other respects
are true bivalve Mottusca, are furnished with a pair of accessory plates
in the neighbourhood of the hinge; whilst the Chitons, fig. 106, a small
but singular group of Mollusca 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 regarded
as forming a sort of transition towards the articulated division.

Many Mollusca are not furnished with a shell, or have only a small
calcareous plate enclosed within the mantle. These are called naked
Mollusca, an example of this family is seen in the frontispiece, Aplydcb;
but it is remarkable, that most of them are provided with a small shell
at their first quitting the egg. In the shell- bearing, or testaceous Mol-
lusca, this embryonic shell, which often differs greatly in shape and
texture from the shell of the mature animal, forms the commencement
of the latter, additions being constantly made to its free edge by the
secretion of calcareous matter at the edge of the mantle. The delicate
membranous part of the mantle, which lines the interior of that part
of the shell inhabited by the animal, has, however, the power of secret-
ing a thin layer of shelly matter upon the inner surface. This is
frequently of a pearly lustre ; and in many bivalves a new layer of this
substance is deposited at the same time that 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 constantly going on, but appears to
be subject to periodical interruptions, indicated by lines on the surface
of the shell ; these are called lines of growth. In many cases the
margin of the mantle, instead of being even, presents lobes or tubercles,
which produce corresponding irregularities, — ribs, tubercles, or spines,
— on the surface of the shell.

Mr. 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 (Plate VI. No. 8), from, the animal-cell not
having sufficiently controlled the mode of deposition of the earth par-
ticles, they have assumed the form of perfect rhomboidal crystals.

The Oyster belongs to the class called AcepJialus, or non-headed,
as it has no 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 ; and its food con-
sists of nourishing substances contained in the water, and which are

256 THE MICKOSCOPE.

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 mucilaginous liquid, which soon becomes as hard as the shell. They
generally spawn 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 ; and in three months it is larger
than a shilling. The spawn is a very interesting object for micro-
scopic examination, especially when viewed under polarised light. The
young fry is shown in fig. 121, nearly ready to escape from the shell.

The well-known ciliary currents in the fringes of the oyster in-
duced me to examine the contents of the stomach, under the expecta-
tion of finding some minute forms of Infusoria ; for it seemed but
reasonable to infer that the absence of locomotive power, and the con-
sequent inability of seeking for food, might be compensated by so
beautiful a contrivance for ensuring constant nourishment. My expec-
tations were fulfilled and surpassed. In the stomach of every oyster
I examined, and in the alimentary canal, I found myriads of living
Monads, the Yibrio also in great abundance and activity, and swarms
of a conglomerate and ciliated living organism, which may be 'named
Volvox ostrearius, somewhat resembling the Volvox globator, but of so
extremely delicate a structure, that it must be slightly charred to be
rendered permanently visible.

The Pearl Oyster. — At one time a most extravagant value was set
upon pearls : for one of these molluscous secretions, it is recorded that
Tavernier paid the sum of 110,000?. ; it was found at the Catifa fishery,
off the coast of Arabia. At the Bahrein Islands, Persian Gulf, the
produce of the two months' fishing is said to average 90,000?.

Pearls are usually found in the Meleagrina Margaritifera, or Pearl
Oyster; also in a mussel termed Mya Margaritifera. An inferior
kind of pearl is also found in many mussels of the rivers of Great
Britain ; and, at one time, the pearl-fishery of Ireland was greatly
celebrated. The oysters on our coasts have frequently a dull, common
kind of pearl within their shells.

Naturalists somewhat differ in their opinions as to the mode in
which pearls are formed. Some think that they are caused by par-
ticles of sand having got into the stomach ; the animal, to prevent the
roughness of these particles from injuring its delicate structure, covers
them over with a secretion from its body, and by continual additions,
they are gradually increased in size. It is now, however, pretty gene-
rally admitted to be a disease ; and it is quite certain that the pearls
are matured on a nucleus, consisting of the same matter as that from

MOLLUSCA.

257

which the new layers of shell proceed at the edge of the mussel or
oyster. The finest kind are formed in the body of the animal, or
originate in the pearly part of the shell. It is by the size, roundness,
and brilliancy of pearls that their value is estimated. They are found
either in the mantle of the animal, or attached to the inner surface of
the shell.

Pearls have been produced in an artificial manner; Apollonius,
the philosopher of Tyana, who is supposed to have died at an advanced

'

fig. 111. Artificial Pearls in the shell of My a margaritifera.

age in the year 97, being the first to notice such a practice, on the
borders of the Red Sea. Sir Joseph Banks had specimens of some
Chinese mussels, in which were small pieces of iron covered with a

s

258

THE MICROSCOPE.

pearly substance, that at first seemed to give countenance to such a
story.

Mussels, in which these artificial pearls had been formed by the
Chinese, have been recently brought to this country by Mr. Raw son, from
one of which the preceding drawing was made (fig. Ill); it is repre-
sented of the natural size, with the simple pearls adhering to the shell.
The account furnished by this gentleman at the same time is, "that they
are only obtained near Ning-po. The Herm.es steamer being on a visit
to that place, he was able to obtain a few living specimens ; in which,
on being opened, several pearls, as many as eighteen or twenty, were
found in the course of formation. It appears they are formed by

fig. 112.

1. A transverse section of a Pearl from the Oyster, showing its prismatic structure.
2. A transverse section of another Pearl, showing its central cellular structure and
outside rings of true pearly matter. Magnified fifty diameters.

introducing some pieces of wood or baked earth into the animal while
alive, which, irritating it, cause it to cover the extraneous substance
with a pearly deposit. Little figures made of metal are frequently
introduced ; and, when covered with the deposit, are valued by the

MOLLUSCA.

259

Chinese as charms. These figures generally represent Buddha in the
sitting position, in which that image is most frequently portrayed."

The microscope discloses the different structure of pearls : those
having a prismatic cellular structure, have a brown horny nucleus, sur-
rounded by small imperfectly- formed prismatic cells ; then there is a
ring of horny matter, followed by other prisms, and so on, as repre-
sented in fig. 112, which are transverse sections of pearls from oysters,
showing successive rings of growth, or deposits.

In a horizontal section (fig. 113) of another pearl, the prismatic
structure and the transverse grooves of the prisms are very well

fig. 113.

1. A transverse section of a small pearl from a species of Mytilus. 2. A horizontal
section of a Pearl magnified 250 diameters, showing its prismatic structure, and
the transverse striae of the prisms.

shown. The prisms are smallest in the centre, and nearly filled with
dark matter, as are also some nearer the edge. In a segment of a
transverse section of a small purple pearl from a species of Mytilus, all
trace of prismatic structure has gone, and only a series of fine curved
or radiating lines are seen. It consists of a beautiful purple-coloured
series of concentric laminse (fig. 113). Many of this kind of pearls
have a series of concentric zones, and some are of a yellow tint. The
most beautiful sections for microscopic examination are obtained from
Scotch Pearls.

260 THE MICROSCOPE.

The true pearls are composed entirely of nacre, and are exquisite
in their colouring. Their structure is shown highly magnified at No. 2,
fig. 113. Some, again, are composed of nacre and prismatic cellular
structure ; the centre having the prismatic formation, banded outside
by two rings of the true pearly matter — nacre, or " mother-of-pearl"

In the shell of the Terebratula, or Coach-spring shell, there are
openings surrounded by a series of radiating lines, which at first appear
like dark oval spots ; but in a vertical section they will be 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 No. 6, Plate VI. The outer layer has here been removed to show
the radiating structure around the perforations. Dr. Carpenter has
elaborately described the Terebratula in the Philosophical Magazine,
1854.

Not less curious than beautiful is the internal layer of different
kinds of bivalves, which present a nacreous or iridescent lustre, the
whole of its surface being varied with a series of grooved lines running
nearly parallel to each other. One of the most remarkable is the well-
known Ear-shell, Haliotus splendens ; this has been ascertained to con-
sist of numerous plates, resembling tortoise-shell, forming a series of
hexagonal cells, in the centre of which the stellate pigment is deposited
(Plate VI. No. 3), alternating with thin layers of pearl, or nacre ; and
this exhibits, when highly magnified, a series of irregular undulating
folds, represented in the upper portion of the section. The iridescent
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 be dissolved out, the plates of animal matter fall apart,
each one carrying 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, ex-
hibit iridescent hues of the most gorgeous description. But if the
membrane is 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 effects presented by the nacreous
portions of shells, commonly called mother-of-pearl, are produced solely
by the disposition of single membraneous layers in folds or plaits, lying
more or less obliquely to the general surface.

GASTEROPODA. 261

GASTEROPODA.

The Gasteropoda (belly-creeping animals) are characterised by their
being provided with a fleshy disk, serving as a foot upon which to
creep. The back is covered with a cloak, in or upon which the shell
is secreted, and may consist of one or more pieces. All the shells are
remarkable for the small amount of the animal as compared with that
of the earthy matter, so that they are extremely brittle, and their frac-
tured surfaces have a crystalline appearance. In some the shell is of
a horny texture, for example, in the Aplysia, Sea-hare (Plate I. No.
10) ; it is also transparent and flexible.

The majority of the Gasteropoda are furnished with a shell, which
has been denominated spirivalve. The cause of this spiral arrange-
ment is said to be owing to the shape of the body of the animal inha-
biting the shell, which, as it grows, principally enlarges its shell in one
direction ; thus, of course, making it form a spine, 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 the early stage of the embryo ;
the first deposit of calcareous matter forming the axis, the tube con-
tinues to rotate upon its axial pillar or columella, as it is called j 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 wJwrl ; 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 envelopes the viscera, and which is always
concealed within the cavity of the shell, and the more vascular portion
placed around its aperture.

The mouth of such of the Gasteropoda as devour vegetable matter
consists of a strong muscular cavity, with a single crescent-shaped
horny tooth, furnished along its upper edge with sharp points, sepa-
rated by semicircular cutting spaces, admirably adapted for the divi-
sion of vegetable food, and furnishing beautiful objects for the micro-
scope— especially under polarised light. Several kinds of molluscous
animals are to be found in shallow water, in brooks, and ditches. One
of the most frequent of these is commonly known as the horny coil-
shell, or Planorbis corneus. The shell of this creature at first sight
looks like that of one of those little flat snails which are sometimes

262

THE MICROSCOPE.

found in cellars ; but, on examination, it will be found to differ from
these creatures in being exactly the same on both sides ; or, in the
language of a naturalist, having neither spine nor column. The animal
belonging to this shell is extremely like a snail, when it is crawling
with its tentacles extended ; but it is much smaller in all its parts. It
is found in ditches and ponds. The amber snail (Succinea amphibia)

fig. 114. The Amber Snail. Physafontinalis. Moor Snail and Mountain Bulimus,

has a beautiful transparent shell of a light amber colour ; and it is from
this that it derives its scientific name — as Succinum signifies amber.
The puddle-mud snail (Limnceus peregra) is also very generally found
in this country. Its shell bears considerable resemblance to that of
Succinea; but it is less transparent, and has a more horny look. The
shells of all the species of Limncea have the aperture on the right hand,
and the plait on the left hand, which distinguishes them from Succinea.
Another kind of pond-snail, called the stream-bubble shell (Physafon-
tinalis), is distinguished from Limnceus by its opening being on the left
handinstead of the right.

fig. 115. Limnoea stagnalis.

It is extremely curious to watch the development of the spawn of
these animals under a magnifying-glass. The spawn of the water-snail

GASTEROPODA. 263

is usually found attached to the surface of stones, pieces of weed, or
other matters, under the water ; and generally connected together in
long ribbons or delicate ova-sacs of a curious and beautiful form. The
mass of eggs deposited by the Doris resembles a frill of lace of great
beauty. In the Aplysia the spawn resembles long strings of vermicelli,
of varying tints throughout the different parts of the thread. In the
LimncKus stagnalis it is deposited in small sacs, containing from fifty to
sixty ova; one of which is represented at a, fig. 115. If 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 may be detected adhering to one side of the cell-wall. In
about forty-eight hours afterwards, this small spot is seen to have a
smaller central spot of a rather deeper colour ; this is the nucleolus.
On the fourth day the spot or nucleus may be observed to have changed
it position, and enlarged to double the size : a magnified view is shown
at b ; upon viewing it closely, a transverse fissure or depression may
be seen, which on the eighth day most distinctly divides the small mass
into shell and soft part of the future animal, as at c. It then becomes
detached from the side of the cell, and moves with a rotatory motion
around the whole of the cell-interior ; the direction of this motion is
from the right to the left, and is always increased when sunlight, and
consequently heat, is thrown upon it. The increase is gradual up to
the sixteenth day, when the greater half appears to be the shell por-
tion, as seen magnified at d. The spiral axis can now be traced and
seen by oblique light from its darker colour ; offering a striking differ-
ence 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; when, by using a higher magnifier, a minute
black speck, the future eye, may be seen protruded with the tentacles,
as at e. Upon closely observing it, a fringe of cilia will be seen in
motion near the edge of the shell : it now became apparent that the
rotatory motion first observed must have been in a great measure due
to this ; a current, no doubt, being 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 brings the whole supply of nourishment required ;
at the same time, and by the same means, the proper aeration of the
blood is effected. Whilst in the ova, it is, no doubt, by this motion
that the cell-contents are converted into the various tissues of the body
and shell. From the twenty-sixth to the twenty- eighth day, it appears

264 THE MICROSCOPE.

actively engaged near the side of the egg, using all its force to break
through the cell-wall, which it at length succeeds in doing ; leaving
the shell in the ova-sac, and immediately attaching itself to the side of
the glass-vase, to recommence the ciliary motion ; it then appears in
the advanced stage of life seen at/. It is still some months before it
grows to the perfect form represented at g, where the animal is drawn
with its sucker-like foot adhering closely to the side of the glass-vase.
One of these animals will deposit from two to three of these ova-sacs
a week ; thus producing, in the course of six weeks or two months,
from 900 to 1000 young, upon which the smaller kinds of fish feed.

The shell itself is deposited in minute cells, that take up a cir-
cular position around the axis, on the under-surface of which a hyaline
membrane is secreted, soon to become permeated with vessels ; at the
same time the integument expands, and at various points an internal
colouring-matter or pigment is deposited ; the point of one cell being
in contact with those of others, thus form the ribs seen in the shell.*
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 a
condensed tissue having the form of a twisted wire, enclosing 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 from the heart, may be
traced through the large branches to the respiratory organs, con-
sisting of branchial-fringes placed above the mouth ; the blood may
also be seen returning through other trunks. The heart itself is a
strong muscular apparatus. It is pear-shaped, with a pericardium or
external wall- enveloping membrane, extremely thin and pellucid. Af-
fixed to the sides of the heart are muscular 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, they being
analogous to the muscular cords of the mammal heart. The heart
beats or contracts at the rate of about sixty times a minute ; and it is
placed rather far back in the body, towards the terminal portion of the
shell.

The nervous system is made up of many ganglia, or nervous cen-
tres, distributed through the different portions of the body, but con-
nected with each other by cords of communication ; the nerve-fibres
proceeding to the different parts of the body from the ganglia.

The singular arrangement of the eye must not be omitted; it
appears in the early stage to be situated within the tentacle, and con-

* See further researches by the author, published in the Microscopical Journal
1854.

GASTEROPODA. 265

sequently capable of being withdrawn with it. In the adult animal,
the eye is found to be at the base of the tentacle ; and although it can
be protruded at pleasure for a short distance, it seems to be de-
pendent upon the tentacle only for an external coverlid — as it inva-
riably draws it down over the eye whenever that organ needs protec-
tion. 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, with a single central pupillary-opening for the admis-
sion of light. The tentacle, which is rounded in the young animal,
becomes flat 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, as it is termed, the
"tongue" of the mollusc, consists of several rows of cutting spines,
pointed with silica, which, as we have before stated, is a most interest-
ing object seen under the microscope.

It is an interesting physiological fact, to find that if the young
animal be kept in fresh water alone, without vegetable matter of any
kind, it retains its cilia, and arrest of development follows ; it acquires
no gastric teeth, and never attains perfection in form or size. If, at
the same time, it be confined within a narrow cell, or space, it grows
only to such a size as will enable it to move about freely; thus
adapting itself to the necessities of its restricted state of existence.
Some young animals in a glass-cell were, at the end of six months,
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 only half the size of those first
deposited in the original formation. This may be cited in proof of
what was stated by Professor Paget, in his lectures delivered at the
Royal College of Surgeons, 1852, — "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 embyronic to the per-
fect 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

266 THE MICROSCOPE.

powers are the same by which perfection is first 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 mutila-
tion, 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 each cell does not appear to enter into
the formative process of the embryo — the cell-contents alone nourish-
ing the vital blastema of the nucleus. A gradual cycle of progressive
development, once set up, goes on until the animal is sufficiently ma-
tured to break through the cell-wall, and thus 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 in this way certain gases or
fluids may become drawn into the interior, and thus aid in the supply
of nourishment for the growth of the animal.

The cell-wall would appear to bear the same relation to the future
perfect animal, that the egg-shell of the chick does to it; it is, in
fact, but an external covering to a certain amount of gaseous and
fluid matter, thus placing the germ of life in a more favourable state
for development, assisted, as it is known to be, by an increase of tem-
perature, usually the resultant of a chemical action, set up or once
begun in an organism and a m/edium.

The ovum destined to become a new creature originates from a
cell, enclosing gemmules, from which its tissues are formed, and nu-
triment is assimilated, and which eventually enables the animal to
successively renew its organs, through a series of metamorphoses that
give it permanent conditions, not only different, but even directly con-
trary to those which it had primitively.

" Oh, there are curious things of which men know-
As yet but little ! secrets lying hid
Within all natural objects. Be they shells,
Which ocean flingeth forth from off her billows
On the low sand, or flowers, or trees, or grasses,
Covering the earth ; rich metals or bright ores,
Beneath the surface. He who findeth out
Those secret things hath a fair right to gladness ;
For he hath well performed, and doth awake
Another note of praise on Nature's harp
To hymn her great Creator."

The Structure of Shells. — We may exhibit the structure of shells by

COLLECTING SALT-WATER SPECIMENS. 267

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 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 beautifully reticulated film, re-
sembling a spider's web in texture, rewarded the patience of the
operator • the organisation 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.

ON COLLECTING SALT-WATER SPECIMENS.

" Nothing," as Dr. Harvey says, "can exceed the beauty of a clear
rock-pool, seen under strong sunlight, and through a calm surface,
tenanted by its various animated tribes all fulfilling the duties allotted
to their several kinds. Careful examination with a lens will generally
detect a multitude of minute shells, some of very strange shapes, and
others possessing structures of great elegance. These are the various
species of Foraminifera. We should recommend these species to be
studied in a living condition, whenever opportunity presents, as it
will prove a study of great interest. The drift-sand will often be
found to contain a wonderful variety of minute spiral univalve shells,
though these are scarcely of so small a size as to come Avithin the list of
microscopic objects. Others may be obtained by the gatherers of sea-
weeds, with little trouble, if they will only preserve the sediment that
collects in the water in which the sea-weeds are washed. When the
sea-weeds are plunged into fresh water, these minute molluscs (Eissoce)
are quickly killed, and fall to the bottom, and may then be secured
by simply straining the water through a piece of canvas. Many other

268 THE MICROSCOPE.

minute and curious animals, and sometimes Diatomacece, may be col-
lected in a similar way.

Having thus surveyed the rocks, sands, and weeds of the shore
above low-water mark, if we launch upon the deep itself a similar
abundance of minute and interesting forms is still presented to us. A
small muslin bag, the mouth of which is kept open by a wire ring
about four inches in diameter, towed slowly behind a boat, on a calm
and bright day, in any sheltered bay or inlet, will be found to have
gathered multitudes of creatures of the most beautiful forms, and
occasionally of the most brilliant colours, — creatures whose crystalline
substance affords to our wondering gaze a ready insight into many
things connected with the structure of the lower animals, which will in
vain be sought elsewhere. In this way are collected the numerous
species of minute Naked-eye Medusae.

Nothing can be conceived more elegant and graceful than the
motions of these minute crystalline bodies in a glass of water. On
almost every part of the coast, besides the beautiful Tunis neglecta and
the allied Beroes, the towing- net will gather innumerable specimens of
a creature resembling a slender spicula of glass, about an inch in
length, but which is so slender and transparent as to be almost invi-
sible except in a particular direction of the light : this is the Sagitta
bipunctata; and its simple structure affords an excellent subject for
microscopic research. When fishing for objects of this kind, it is best
to have in the boat a large white basin half filled with sea water ; and
into this the towing-net is to be inverted and gently shaken every now
and then. In this way the delicate creatures it contains will come out
of it without injury ; and though themselves perhaps at first wholly
invisible, their shadows will be seen with great distinctness at the
bottom of the basin ; and thus many forms which might otherwise
escape observation be rendered evident.

The microscopic wonders of the sea, however, are still far from
being exhausted ; it presents as many, if not more, curiosities at the
bottom, where its depths are never opened to view, than at the surface.
The best and most convenient mode of obtaining these, is by the use
of an instrument, with which all perhaps are acquainted in one shape
or another, — we mean the dredge.

The essential qualities of a microscopist's dredge are, a small and
convenient size, with sufficient weight to ensure its sinking to and
keeping at, the bottom, even when at a considerable depth and drawn
with some velocity through the water. The dredge we should recom-
mend is made of cast iron, which reduces the cost considerably ; and it

COLLECTING SALT-WATER SPECIMENS.

269

is, in practice, found to be sufficiently strong. It is about 18 inches
in length, and the opening is about 4 inches wide, the two sides
diverging outwards at a slight angle, and coming to a sharp edge.

tig. 116.

Young of Comatula, usually described as Pentacrinus Europceus, Beroe. Actinia;,
closed and expanded specimens. Caryophillea Smithii. . Spider crab, Velvet crab,
and Flustra.

CHAPTER IV.

ARTICULATA.

HE animals composing the sub-kingdom Ar-
ticulata 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 lowest of
the order, Vermes, may be divided into four classes
which are generally distinguishable by their external
appearance. Of these, the first two are for the most
part parasitic, living in the interior of other animals,
few of which are, in fact, exempt from the visits of
these unwelcome guests. Of these, the first, the Flat-
worms (Platyelmia) have the body flattened, and gene-
rally more or less ovate and leaf-like ; these present the
greatest divergence from the articulate type. In the
second, the Nematelmia, or Round-worms, the body is
usually elongated and cylindrical, and the division into
segments is often indicated by annulations of the skin.
The other two classes are composed principally of aquatic
animals. One of these, the Rotifer a, or WJieel Animalcules, we have
already seen, includes a number of minute creatures. The Annelida,
or true worms, have the body distinctly divided into segments, gene-
rally furnished with lateral appendages, with a well-developed nervous
system. The blood, in this last class, is also generally of a red colour.
We shall first notice the Entozoa, or internal parasites ; few animals
can present a better claim to our notice, from the circumstance that
many of them find their natural residence in our own bodies, and in
those of our domestic animals, where they often do us a great amount
of injury. They have a still stronger claim to the attention of the
scientific zoologist, from the number of points connected with their

ARTICULATA. 271

natural history, which still remain to be cleared up, and from the
wonderful nature of those portions of the history of their development
which have been revealed by the recent researches of some of our most
eminent naturalists.

The two parasitic orders are the Cestoidea, or Tape-worms, with
long jointed bodies ; and the Frematoda, with short elliptical or discoid
forms.

Two species of Cestoid worms inhabit the human intestines, — the
Tcenia solium and the Bothrioceplmlus latus. The former is the ordi-
nary Tape-worm,ihQ second occurs only in particular countries, — in
Holland, Poland, and Switzerland, In the Cystic form some of these
worms do great injury to domestic animals ; one of the most noxious
is the so-called Ccenurus cerebralis, inhabiting the brains of sheep.
Many interesting facts are connected with the history of these animals ;
but our space forbids us from entering into further details.

In the Distomidce, the animals possess two suckers, of which the
anterior contains the mouth. Of these the Fluke (Distoma hepaticum),
which infest the livers of sheep, is a well-known example. Other
species live in the intestines, and even the eyes, of other animals.

The Tristomidce are furnished with three suckers ; two small ones
at the anterior extremity, between which the mouth is situated, and a
larger one at the hinder extremity. These worms principally infest
the gills of fishes, as do also Polystomidce, characterised by the presence
of several suckers at the hinder extremity of the body, whilst the
anterior extremity is either entirely destitute of those organs, or only
possesses a small one, in which the mouth is situated. This family
includes the singular Diplozoon paradoxuin, — an animal which appears
to be compounded, like the Siamese twins, of two perfect individuals,
each containing precisely the same organs.

The Gordicea, or Hair-worms, are at once distinguishable by the
extraordinary length of their bodies, which frequently present a close
resemblance to a horse-hair ; so close, indeed, that in former times the
popular belief ascribed their origin to the introduction of horse-hairs
into the water in which they are found. One of the most singular
circumstances connected with their history is, that if by any chance, on
breaking out of their insect-home, they find that dry weather has
produced a state of things incompatible with their notions of comfort,
they quietly allow themselves to be dried up, when they become per-
fectly hard and brittle ; but, strange to say, the moment a shower of
rain comes to refresh the earth with its moisture, the dormant Gordii
immediately recover their activity, and start off in search of their prey.

272 THE MICROSCOPE.

With the exception of one family, all the worms included in the
order Nematoidea are parasitic in the bodies, and principally in the
intestines of other animals ; they are, in fact, amongst the most common
and the most injurious of Entozoa.

\ This order includes the common Ascaris, or Sound-worm of the
human subject, as well as the little Thread-worms (Oayuris) which are
often so troublesome to children ; the Strongylus gigas, a worm some-
times attaining a length of two or three feet, and the thickness of a
garden worm, which usually inhabits the kidneys of swine, but some-
times finds its way into the same organ in man. This tremendous
worm, by destroying the organ in which it has taken up its abode,
frequently causes the death of its host.

In this order we also place the Anguillulidce, the so-called Eels of
paste and vinegar. These are minute thread-like worms, exhibiting
distinct digestive and generative organs, which occur often in great
numbers in putrefying substances.

This order also includes the dreaded Guinea-worm (Filaria medi-
nensis, fig. 117), which appears to occur in most parts of tropical
Africa. This worm lives in the cellular tissue beneath the skin of
man, confining its attacks principally, though not exclusively, to the
lower extremities, where it often produces considerable pain. It is
said occasionally to attain a length of twenty or thirty feet ; but its
average length is five or six. It is extracted by winding it very slowly
upon some object, an operation in which great care is said to be neces-
sary, as if the worm be broken, its fluids produce a very painful effect.

In man, and some of the lower animals also, the muscles are fre-
quently attacked by Cysticercus cellulosce ; a well-known disease in the
pig is caused by them, it is then called by pork-dealers " measly pork."
Becent researches have shown this Entozoa is but the larva of Tcenia.

The EcJdnococcus, another Entozoa, is found in cysts, both in the
body of man and sheep.

Fig. 118 represents a bunch taken from the liver of a boy who died
in Charing-cross Hospital from rupture of the liver, occasioned by the
wheel of an omnibus passing over him. The simple cysts containing
these animals are always situated in cavities in the interior. These
cavities may be situated in any part of the tissues or organs of the
body ; they are more frequently found in the solid viscera, and especi-
ally in diseased livers.

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

ARTICULATA.

273

small puncture, so as to prevent at first the too-rapid exit of the fluid,
and consequent 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 col-
lected in the lowest part of the cyst, and frequently entangled in frag-
ments of its innermost thin membrane. When some of these granu-

fig. 117. The Guinea-worm, taken from the leg of a Negro.

1. Represents the form of the worm when first taken from one of the sacs seen at fig. 2.
3. The young worm rolled up. 4. The worm extended.

lations are placed between glass under the microscope, and viewed with
a power of 250 diameters, upon pressure being employed it will be
seen, after rupture of the delicate enveloping membrane, that the
Echinococci composing the granulations are all attached to a common
central mass by short pedicles ; which, as well as the central mass, ap-
pear to be composed of a substance more coarsely granular by 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, com-
mon to the whole, and by which the granulation is attached to the in-
terior of the hydatid cyst, as represented in fig. 118.

In specimens preserved in spirits, Echinococci of all imaginable

T

274 THE MICKOSCOPE.

forms and appearances are to be met with, — differences owing to decom-
position or to mechanical injury ; and in many cases no trace of them
can be found except the booklets or spines, which, like the fossil re-
mains 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.

In almost all the aggregations of Echinococci, besides the perfect
specimens, there are to be seen one or more of a different appearance
and of various shapes — round, clavate, or oval — like the others, attached
to the common mass by a pedicle : they are composed of granular mat-

fig-. 118. JEcMnocoeci found in the human liver, magnified 250 diameters.

ter, denser apparently, and of a deeper colour, than that of which the
bodies of the perfect animals are composed, and increasing in density
towards the free extremity."

ANNELIDA.

The Annelida, in general, present a more complicated organisation
than any of the preceding animals ; the division of the body into seg-
ments is usually distinctly recognisable, and the segments are almost
universally furnished with external appendages, which are sometimes
jointed. The majority live in water, or in damp situations ; a very
few only are parasitic in their habits.

ANNELIDA. 275

The head in most of these animals is distinctly marked, and furnished
with organs of sense, such as eyes, tentacles, and in some instances
auditory vesicles, containing otolithes. The nervous system, in the
higher forms, exhibits the articulate type of structure very distinctly ;
it usually consists of a series of ganglia running along the ventral por-
tion of the animal, and united by a pair of slender filaments, by which
they also communicate with the central mass, or brain, which is en-
closed in the head. They are divided into two groups, characterised
by the presence or absence of external respiratory organs. The abran-
chiate Annelides include the Suctoria or Leeches, and the Scoledna or
Earthworms. The branchiferous group are again subdivided into
two orders : the Tufiicola, animals having a tube for their habita-
tion, and the Errantia, those having no such protection. Of the ani-
mals belonging to the order Suctoria, the medicinal leech is a familiar
example. Their motions are effected by undulations of the body whilst
swimming, or by the alternate attachment of the sucking disks with
which the two extremities of their bodies are furnished.

The medicinal leech puts forward strong claims to our attention, on
the ground of the services which it renders to mankind. The whole of
this 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.
119). "This piece of mechanism," says Profes- ^

sor 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 within
the margin of this hole three beautiful little
semicircular 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 performed in the following manner: No
sooner is the sucker firmly fixed to the skin,
than the mouth becomes slightly everted, and Mo
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 gradually to pierce the surface, and cut its way to the small

276 THE MICROSCOPE.

blood-vessels beneath. Nothing conld 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
contractibility 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 the Clepsinidce, the body is of a leech-like form, but very much
narrowed in front, and the mouth is furnished with a protrusible pro-
boscis. These animals live in fresh water, where they may often be seen
creeping upon aquatic plants. They prey upon the water-snails
(Limnece).

Some species of this family, forming the genus Piscicola, live as
parasites upon various fresh-water fishes ; whilst those of the genus
BranchiobdeUd) which are quite destitute of eyes, inhabit the branchia3
of some Crustacea. The Scolecina, of this order, the well-known earth-
worm so common in our gardens, is an example. Naids are inhabi-
tants of water.

The Tubicola. — The worms belonging to this series of branchiferous
Annelida are all marine, and are distinguished by their invariable habit
of forming a tube or case, within which the soft parts of the animal
can be entirely retracted. This tube is usually attached to stones or
other submarine bodies. It is often composed of various foreign
materials, such as sand, small stones, and the debris of shells, lined in-
ternally 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 the Mollusca, of calcareous matter secreted by the animal.
These animals frequently live together in societies, winding their tubes
into a mass which often attains a considerable size; others are more
solitary in their habits. They retain their position in their habitations
by means of appendages very similar to those of the free worms, and
furnished like these with tufts of bristles and spines ; the latter, in the
tubicolar Annelid es, are usually hooked ; so that, by applying them to
the walls of its domicile, the animal is enabled to oppose a consider-
able resistance to any effort to draw it out of its case.

In the best known family of the order (Sabellidce), the branchiae

ANNELIDA. 277

are placed on the head, where they form a circle of plumes or a tuft of
branched organs. The Serpulce, which form irregularly twisted cal-
careous tuhes, often grow together in large masses, generally attached
to shells and similar objects ; whilst those genera which, like Terebella,
build their residences of sand and stones, appear to prefer a life of
solitude. The curious little spiral shells often seen upon the fronds of
sea-weeds, are formed by an animal belonging to this family (Spirorbis).

If, while the contained animals are alive, these be placed in a
vessel of sea- water, a very pleasing spectacle may 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
cautiously protrudes the anterior part of
its body, spreading out at the same time
two beautiful fan-like expansions of a rich
purple or scarlet colour, which float ele-
gantly in the surrounding water, and serve
as branchial or breathing organs. The Ser-
pula, which fabricates these tubes, when
withdrawn from its residence (fig. 120), is
seen to have the lower part of its body
composed of a series of flattened rings, en-
tirely destitute of limbs or any other ap-
pendages. Its food is brought to its mouth
by the currents created by the cilia on the
branchial tufts. Many very beautiful speci- Tke Ser?ulcl in its cal™™ous tule.
mens of this family may be seen alive in the tanks of the Zoological Society.

Of the jErrantia, the highest of the order, we are unable to notice
more than one ; that of the family of Aphroditce, some species of
which are known as Sea-mice. In these worms the body is generally
broad, or ovate ; the head small, and furnished with very short tenta-
cles ; the feet large, with immense tufts of bristles and spines, often of
the most remarkable forms, and exhibiting the most brilliant metallic
colours. Each of these hairs is retractile within a horny sheath,
which serves to protect the soft parts of the animal from injury by its
own weapons. Their most remarkable peculiarity is, that the dorsal
surface is entirely or partially covered by a double series of large mem-
branous scales attached to the alternate segments, between which the
beautiful bristles of the feet make their appearance. These animals
generally inhabit deepish water; but numbers of them are often thrown
upon our coasts after a storm.

278 THE MICROSCOPE.

We may here remark, that Dr. Carpenter divides the articulate sub-
kingdom into eight classes, viz. Entozoa, Rotifera, Annelida, Myriapoda,
Insecta, Crustacea, Cirrhipoda, and Arachnida. The immense number
and variety of this portion of the animal kingdom necessitates a corre-
sponding multiplicity of subordinate divisions, which it would be quite
impossible for us to attempt a detailed description of. Our space will
only permit of a few remarks upon the Artlvropoda, or True Articulata ;
the first of which is the Crustacea.

The skeletons of Crustacea* are external to the soft parts ; in a
great number of species it 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 ob-
jects for microscopic examination.

A crustaceous animal consists of three parts : the head, the body,
and the carapace, which is covered with one entire shell, and is popu-
larly called the tail, consisting of seven rings, or joints. There are
properly fourteen rings in that part of the body which is called the
carapace; but they are only used when the animal changes its shell.
The joints in the tail are to enable the animal to spring forward, which
it does frequently when it wishes to change its position. It can also
crawl ; but it moves in this manner awkwardly, and in an oblique di-
rection. The river crawfish belongs to the same genus (Astacus) as
the lobster, and both have long tails, which are spread out when they
crawl, and numerous legs and claws, with which they can pinch se-
verely when they wish to defend themselves. The crab has a short
tail, and belongs to the genus Cancer. The shrimp, though it has no
claws, properly so called, has two feet larger than the others, each of
which has a hooked jointed nail. The prawn, which is quite different
from the shrimp, is nearly allied to the crawfish, or thorny lobster. All
the Crustacea have the power of renewing their claws if they are torn
off at a joint, and they change their shells every year.

Dr. Carpenter describes the shell of the crab and lobster as being
composed of three layers, viz. the epidermis or cuticle, the rete-muco-
sum or pigment, and the corium. 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 (Plate VI. No. 7) ;
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
* Criistacea (from crusta, a shell).

CRUSTACEA. 279

matter diffused throughout a certain thickness of the calcareous layer.
(Plate VI. 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 laminae, 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 speci-
mens ; 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 cal-
careous material deposited in it. (Plate VI. No. 4.) When a vertical
section of the shell of the crab is examined, it is found to be traversed
by parallel tubes, like 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, Plate VI. If a horizontal section of the same shell
be made, so that the tubes be divided at right angles to their length,
the surface will clearly exhibit their open mouths, surrounded by cal-
careous matter. In shrimps and very small crabs, the deposition of the
calcareous matter takes place in concentric rings, like those of agate \
and occasionally small centres of ossification somewhat similar to No.
3, with radiating strise, are to be met with in the former animal. If
the calcareous 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 presents a more or less granular appearance as
at No. 4, and so angular in figure as to resemble certain forms of
rhomboidal crystals, as shown at No. 8, from the outer brown shell of
the oyster. The beauty of all these structures is much increased when
viewed by polarised light on the selenite stage.

The sub-class Cirrhipoda includes only a single order. They are
all marine animals, which, when mature, attach themselves to rocks or
other submarine objects; the common Barnacle (fig. 121), perhaps the
best known example of the order, generally selecting floating objects
for this purpose, and frequently covering the bottoms of ships to such
an extent as even to impede their progress through the water. The
bodies of these animals are soft, and enclosed in a case composed of
several calcareous plates j they formed part of the group of multivalve
sJiells of the older conchologists. The limbs are converted into a tuft
of jointed cirri, which can be protruded through an opening in the

280

THE MICROSCOPE.

sort of mantle which lines the interior of the shell. The cirri are
twelve in number, and beset with bristles. When the animal is alive
they may be seen in continual motion, exserted
and retracted every moment in search of prey.
The intestinal canal is complete, furnished with
a mouth and an anal opening j and the nervous
system exhibits the usual series of ganglia,
which we have seen to be characteristic of the
articulate type. The head is marked only by
the position of -the mouth, which is armed
with a pair of jaws; but all traces of any of
the organs that we are accustomed to see at
this part of the body have completely disap-
peared.

The second family, the Balanidce or sea-
acorns, includes the sessile species, whose cu-

1. Young fry of the Oyster, a . ' ,,.,,. , ,, ,
portionofthemnearlyready rlous llttle habitations may constantly be met
to escape from the shell. with upon the rocks of the sea-shore, and not

2. Body andshell of Barnacle, unfrequently upon many species of marine
shells. The shell forms a short tube, usually composed of six segments
firmly united together. The lower part of this tube is firmly fixed to
the object on which the JBalanus 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
can protrude his delicate cirri in search of nourishment. In their
young state the Balanidse resemble the following group, the Ento-
mostraca.

These animals occur in countless swarms in all waters, whether salt
or fresh j and, minute as they are, one species is said to constitute the
principal food of the whale.

The best known form is the genus Cyclops (fig. 122), specimens of
which may be found in every stagnant pool ; it is the type of the
family Cyclopidce, characterised by the possession of a single eye. In
the Cetochilidce there are two of these organs.

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 antennae 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 coverings of animals belonging to that class. The antennas

CRUSTACEA.

281

are often curiously branched j and the hinder extremity is usually pro-
duced into a sort of tail, which is seen in constant action when the
animal is in motion.

This order divides into two families — the Cypridoe, in which the body
is entirely enclosed by the shell, of which
the genus Cypris (fig. 122) is an example;
and the Dapliniadce, in which the head is
protruded beyond the shell. In the Poly-
pliemus, belonging to this group, the head,
which is large, is almost entirely occupied
by an enormous eye, giving the creature a
most singular appearance.

The Monoculus is a well-known example
of this group. Another family, not pro-
vided with a shell or carapace, are called
Branchipodidce, from the name of the typi-
cal genus, Branchipus stagnalis (fig. 122),
an animal which is often found after heavy
rains in cart-ruts and other small pools.
Another species, the Artemia salina, in-
habits a still more curious situation, namely,
the salt-pans at Lymington, where it is usu-
ally found in those pans in which the evapo-
ration of the water has proceeded to a considerable extent.

A few years since only a small number of the Entomostraca were
described. Dr. Baird, of the British Museum, has lately published a
valuable volume upon the British species alone.

The Gammaridce are characterised by the large size of the foot-
jaws, which cover the whole mouth. The common Talitms locusta, or
sand-hopper, which may be met with in thousands upon the sands of
our shores, is a well-known example of this family. Although its
length is not .much more than half an inch, it can leap several inches
into the air, and the facility with which it escapes pursuit by burrowing
into the soft wet sand is truly wonderful. Another species, Gammarus
pulex, is found commonly in fresh water, and is scarcely inferior to its
marine relative in agility.

The CorypJiium longicorne, remarkable for its long antennae, is not
less so for its singular habits. It is found at Rochelle, where it bur-
rows in the sand, and wages constant war with all other marine crea-
tures of moderate size that come in its way. To discover their prey
they beat about in the mud with their large antennae.

fig. 122.

I. Cypris. 2.- Cyclops-.
3. Branchipus stagnalis.

282 THE MICROSCOPE.

In the family Maiada, or sea-spiders, the carapace is more or less
narrowed in front, forming a projecting beak or rostrum • the legs are
long and hairy ; the back covered with spines and hairs, much resem-
bling some spiders, whence the name of spider-crabs or sea-spiders, by
which these animals are known.

Arachnidce. — The animals forming the class Arachnida, which in-
cludes the spiders and their allies, are amongst those which are viewed
with disgust and aversion by the generality of mankind. Confounded,
in the popular mind, with the reptiles, they of course come in for
their share of the bad reputation of those creatures, and some of them,
no doubt, not without reason ; but on a closer examination we find
that, however unattractive they may be in appearance, they present
much that is interesting both in their structure and habits.

They are distinguished from the other Arthropoda by their aerial
respiration, their possession of four pairs of legs attached to the ante-
rior division of the body, and the total absence of antennae. The body
is usually covered with a softish skin, which, however, sometimes attains
a horny consistency. In the lower forms, the division of the body into
separate regions is quite unrecognisable, and the whole forms a roundish
or oval mass, which does not even present traces of segmentation. In
the higher groups the body is composed of two principal divisions, of
which the anterior, as in the Crustacea, consists of the thoracic seg-
ments, amalgamated with those of the head, and forming together a
mass called the cephalothorax. In the highest forms the division of
the thorax into separate segments becomes apparent ; but the anterior
segment is still amalgamated with the head. The structure of the
abdomen varies greatly. In some cases it forms a soft round mass,
without any traces of segmentation j whilst in others, as the scorpions,
it is produced into a long flexible jointed tail.

The Arachnida are divided into two orders : Tracliearia and Pul-
monaria. The first includes the Acaridce or Mites, in which there are
tracheae, as in insects, but no distinct vascular apparatus : in the
second, which includes spiders and scorpions, there are pulmonary
cavities, and a well-developed circulating system.

Of spiders, the diadem (Epeira diad&ma) is one of the largest of the
British species ; it is a garden spider, and is easily recognised by the
beautiful little gem-like marks on its body and legs. Spiders abound
on every shrub ; and when we consider that the spider is destitute of a
distinct head, without horns, one-half of its body attached to the other
by a very slender connection, and so soft as not to bear the least pres-
sure,— its limbs so slightly attached to its body that they fall off at a

ARACHNIDS.

283

very slight touch, — it appears ill adapted either to escape from danger
which threatens it on all sides, or to supply itself with food : the eco-
nomy of such an animal deserves our notice.

The several small appendages, represented in fig. 124, it is import-
ant not to confound with each other. Of these the two longest, No.

\

f Fig. 123. Epeira diadema, or Garden Spider.

1, having articulated processes, seem to be feelers ; the others, being
the organs by which their silky threads are emitted, are four in num-
ber. Their structure is very remarkable ; the surface of each of the
spinnarets is pierced by an infinite number of minute holes, as seen in
No. 2, from each of which there escape as many little drops of a liquid,
which, drying the moment they come in contact with the air, form so
many delicate threads. Immediately after the filaments have passed
out of 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
composed of a large number of minute filaments, perhaps many thou-
sands, of such extreme tenuity, that the eye cannot detect them until
they are twisted together into the working thread. In the two pairs
of spinnarets a different anatomical structure is to be detected ; the pair
above, which are a little longer than the lower, show a multitude of

284

THE MICROSCOPE.

small perforations, the edges of which do not project, and which there-
fore resemble a sieve. The other shorter pair have projecting tubes
independent of the perforations which also exist (No. 3). 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 may
be observed, 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 circumference ; the latter are also
stronger than the others. The rapidity with which these webs are
constructed is astonishing, as is also 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 gauge to measure her work,
in the same way as a bird uses its body to gauge 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 round its body during the

1. Spinnarets of the spider. 2. Extreme end of one of the upper pair of spinnarets.
3. End of under pair of spinnarets. 4. Foot of the spider. 5. Side view of eye of
spider. 6. The arrangement of the eight eyes.

process. It then, in the same manner, spins a raised border round this
till it takes the form of a cup, and at this stage of the work it begins
to lay its eggs in the cup, not only filling it with these up to the brim,
but piling them up above it into a rounded heap, as high as the cup is

ARACHNIDS. 285

deep. Here, then, is a cup full of eggs, the under half covered and
protected by the silken sides of the cup, but the upper still bare and
exposed to the air and the cold. It is now the spider's task to cover
these, and the process is similar to the preceding, that is, she weaves a
thick web of silk all round them, and, instead of a cup-shaped nest like
some birds, the whole eggs are enclosed in a ball much larger than the
body of the spider that constructed it.

The feet of the spider, one of which is represented at No. 4, are
curiously constructed. Each foot, when magnified, is seen to be armed
with strong, horny claws, furnished with bent teeth on the under-sur-
face, which gradually diminish towards the extremity of the claw. By
this apparatus the spider is enabled to regulate the issue of its rope
from the spinnarets, and also to suspend itself with the greatest ease by
the larger central claw. Some have, in addition, a remarkable comb-
like claw, for the purpose of separating certain fibrous bands that enter
into the composition of their delicate webs.

One of the most remarkable members of this family is the Argy-
roneta aquatica, or Diving Spider, which weaves itself a curious little
bell-shaped dwelling at the bottom of the water, whither it retires to
devour its prey. As, notwithstanding its aquatic habits, this animal,
like the rest of its order, is fitted only for aerial respiration, it takes
care to fill its miniature dome with air, which it carries down with it
from the surface amongst the hairs with which its body is thickly
clothed ; a process very closely resembling that by which the earliest
diving-bells were supplied with air.

The Lycosidce agree in the structure of their jaws and palpi, and
in the number of their spinnarets, with the Araneidce ; but the eyes are
arranged in three rows. Unlike the Araneidce, the animals of this
family never construct regular webs for the capture of prey; their
utmost exertion of instinct in this direction consisting in laying a few
threads in the neighbourhood of their dwelling-places. They generally
live under stones, in holes in the earth, or in old walls, sometimes
lining their habitations with a silken tapestry; and some, which live
upon trees, weave themselves a silken nest amongst the leaves or on
the branches. A common example is the Salticus scenicus, a small
species banded with black and white, which may frequently be met
with on garden-walls.

CHAPTER V.

ARTICULATA. INSECTS.

AMONGST the numerous objects which en-
gage the attention of the microscopist, the
insect tribes in general are far from being
the least interesting ; and their
curious and wonderful economy is
a subject well deserving especial investiga-
tion. Earth, air, and water, teem with the
various tribes of insects, for the most part
invisible to the unassisted eye of man, but
presenting, when viewed with the micro-
scope, 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, through-
out all creation, furnishes traces of the love and wisdom that so
strongly mark the works of God.

" I cannot," says the excellent 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 largest it extends beyond the
limits of our comprehension, escapes our researches in the smallest.
If, while we dissect 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 astonishment raised when we discover
all these parts arranged in the least 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

PLATE VII.

PROBOSCIS OF HOUSE-FLY.

DRAWN FROM A PREPARATION BY TOPPING.
(THE SMALL CIRCLE ENCLOSES THE PROBOSCIS OF THE NATURAL SIZE.)

INSECTS. 287

the dissecting knife, have muscles, veins, arteries, and every other part
common to the larger animals ! Creatures, so very diminutive, that
our hands are not delicate enough to manage, nor our eyes sufficiently
acute to see them.

Insects constitute the fourth class of the sub-kingdom Articulata.
They are characterised by their aerial respiration ; by the division of
the body into three very distinct regions (of which 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 antennae.

fig. 125. Female Crane-fly.

The number of species is greater than is known in any other division
of the animal kingdom, and is only exceeded, as in fishes, by the
almost countless myriads of individuals which every species produces.
The metamorphoses which most of them 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 class ; and in the
greater number of species the same individual differs so materially at
its different periods of life, both in its internal as well as external con-
formation, in its habits, locality, and kind of food, that it becomes one
of the most interesting investigations of the physiologist to ascertain
the manner in which these changes are effected, to trace the successive

288

THE MICROSCOPE.

steps by which that despised and almost unnoticed larva, that but a
few days before was grovelling in the earth, with its internal organisa-
tion fitted only for the reception of, and assimilation of, the grossest
vegetable matter, has had the whole of its internal form so completely
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 open at-
mosphere, with its internal parts adapted only for the reception of the
purest and most concentrated aliment, now rendered absolutely neces-
sary for the support and renovation of its redoubled energies.

Our space will not admit of an examination of every part of the
insect ; we therefore content ourselves with noticing only such as pre-

fig. 126.

Under- surface of a Wasp's Tongue, Feelers, &c. Within the circle is represented
the life-size of same.

sent some point of interest to the microscopist. The various parts will
be easily recognised by referring to the illustration of the common
Crane-fly (fig. 125). The insect has its body constructed with a view
to its being furnished with wings for the purpose of poising itself in the
air. The number of segments of which the body is normally composed
is thirteen ; but some of them are so joined together, or concealed, as
to make it appear that fewer segments are present.

INSECTS. 289

The heads of all kinds of insects are good objects for the microscope.
This will be seen by reference to fig. 133, which shows the head of a
gnat, detached from the thorax, and drawn under a magnifying power
of 50 diameters, by the aid of the camera lucida ; the eyes cover nearly
two-thirds of the head ; and from the fore part are projected the pro-
boscis, lancets, antennae, &c.

In 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 their mouths
armed with strong jaws or mandibles, provided with muscles of great
power, with which they bruise and tear their food, answering to the
teeth of the higher animals ; and in their various shapes and modifica-
tions serving as knives, scissors, augurs, files, saws, trowels, pincers,
or other tools, according to the requirements of the insect.

fig. 127. Eye of Fly, magnified 100 diameters.

The tongue is generally a compact instrument, used principally to
extract the juices on which the insect feeds, varying greatly in its
length in different species. It is capable of being extended or con-
tracted at the insect's pleasure ; sometimes dexterously rolled up ;
taper and spiral, as in the butterfly ; tubular and fleshy, as in the
wasp. In fig. 126 the under-lip of the wasp is shown, with its brush

u

290

THE MICROSCOPE.

on either side ; above which are two jointed feelers (palpi labiales), the
use of which is probably for the purpose of examining the food before
it is taken into the mouth, and afterwards to clean the tongue. Near
these feelers the antennae or horns are placed, curious in form as they
are delicate in structure. The antennae of the male generally differ from
those of the female : some writers have believed them to be the organs
of smell or hearing ; others that they are solely intended to add to the
perfection of their touch or feeling, being sensible to the least motion
or disturbance of the air. They are amongst the most interesting and
distinguishing characteristics of insects ; and appear to be always em-
ployed for the purpose of examining every object they alight upon.

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 construction, and in colour.

Fig, 127 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, not a line
being added by the hand of the draughts-
man.

Fig. 128 represents a side view of the
eye when thrown down, and showing the
compound eye to be made up of a large
number of cylindrical tubes.

11 On examining the head of an insect,
we shall find a couple of protuberances, more
128- or less prominent, and situated symmetri-

cally 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 cornese 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,
these ; 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 re-
flected light, the entire surface of one of these cornese presents a beauti-
ful 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

INSECTS. 291

compared with the space they occupy) of minute, regular, geometrical
hexagons, well defined, and capable of being computed with tolerable
ease, their exceeding minuteness 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 por-
tion of Brussels lace with hexagonal meshes over a small hemisphere of
ground glass. That this gives a tolerably fair idea of the intricate
carving on the exterior, may be further shown from the fact, that deli-
cate and beautiful casts in collodion may be procured from the surface,
by giving this three or four coats with a camel-hair pencil. When dry,
it is peeled off in thin flakes, upon which the impressions are left so
distinct, that their hexagonal form can be discovered with a Coddington
lens. This experiment will be found useful in examining the configu-
ration of the facets of the hard and unyielding eyes of many of the Co-
leoptera, in which the reticulations become either distorted by corruga-
tion, or broken by the pressure required to flatten them. It will be
observed also, that by this method perfect casts can be obtained without
any dissection whatever ; and that these artificial exuviae — for such they
really are — become available for microscopic investigations, obviating
the necessity for a more lengthened or laborious preparation. The dis-
section of the cornea of an insect's eye is by no means easy. I have
used generally a small pair of scissors, with well-adjusted and pointed
extremities, and a camel-hair pencil, having a portion of the hairs cut
off at the end, which is thereby flattened. 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 j and the coloured pig-
ment on the interior may be scrubbed off by this simple process, A
brush thus prepared, and slightly moistened, forms, as far as my expe-
rience goes, by far the best forceps for manipulating these objects pre-
paratory to mounting ; as, if only touched with any hard-pointed sub-
stance, they will often spring from the table from mere elasticity, and
thus the labour of hours be lost in a moment. It does not appear to
me desirable to attempt to flatten an entire cornea by pressure and
maceration, although this is generally recommended, as -ifc does not
either aid in developing the beauty, or counting the number of its
lenses. On the contrary, the rounded membrane becomes, if the mar-
gin remains intact, corrugated ; and so one hexagon overlaps the other.
It will be useful, therefore, to make two preparations of the eyes of one
insect : the one entire, retaining its natural curved form, not having
been subjected to pressure ; the other nicked at its margin, or cut into
small fragments, and pressed between two slides.

292

THE MICROSCOPE.

Each hexagon forms the slightly horny case of an eye. 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 multitude cannot fail to excite astonishment. Hooke counted
7000 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."*

The trunk is situated between the head and the abdomen ; the less

' O

and wings are inserted into it. The thorax is the upper part of the
trunk ; the sides and back of which are usu-
ally armed with points or hairs. The abdomen
forms the posterior part of the body, and is
generally made up of rings or segments, by
means of which the insect can lengthen or
shorten itself. Eunning along the sides of
the abdomen are the spiracles, or breathing
apertures, fig. 129, communicating directly
with the internal respiratory organs. Pure
air being thus freely admitted to every part,
and the circulating fluids kept exposed to the
vivifying influence of the atmosphere, the ne-
cessity for more complicated and cumbersome
breathing organs is at once obviated ; and thus
the whole body is at the same time rendered
lighter. They are usually nine or ten in
The number, and consist of a horny ring, gene-

fig. 129.

Breathing-aperture or spi-
racle of Silkworm.

circle encloses the object rally of an oval form. The air-tub es are ex-
of the natural size. quisitely 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 dis-
tended condition ; thus wonderfully preserving the sides from collapse
or pressure in their passage through the air, which would occasion
suffocation. No. 4, Plate IX. represents the beautiful mechanism
of, a portion of the tracheae of the silk-worm moth. Fig. 129 is a
small portion of a tracheae, highly magnified, and showing the peculiar
arrangement of the spiral tubes, giving elasticity and strength to
the air-tubes of the Hydrophilus.

The legs of insects are extremely curious and interesting, each leg
consisting of several horny cylinders, connected by joints and liga-
* John Gorham, Esq., Microscopical Journal, 1853.

INSECTS.

293

fig. 130.

Highly magnified portions of the
trachea of the Hydrophilus,
showing the spiral tubes, and
their arrangement.

ments ; enclosing within them sets of powerful muscles, whereby their
movements are effected. The first is
called the hip ; it is short, and is con-
nected by a ball-and-socket joint to the
thorax ; the second, called the trocfianter,
is connected with the former by a tough
membrane, fitting to a corresponding
socket ; the third, the femur, or thigh, is
the largest and strongest, serving as a
fulcrum, upon which the leg depends for
strength and motion ; the fourth is named
the tibia, or shank ; this is connected
to the thigh by a beautiful hinge-joint,
which permits of both bending and ex-
tension ; to the end of this is attached
the tarsus, or foot, generally terminated
by two horny hooks or claws, whereby
the insect holds to the object upon which it moves ; between these
hooks, in most species, is situated a cushion, sucker, or broad flaps
(pulvilli), wherewith to take hold of a
smooth surface. In fig. 132 the lower
joints, with the feet of flies, are beau-
tifully represented, marking peculiari-
ties of structure in each ; and in fig.
131, we have a sucker somewhat re-
sembling the admirably -constructed
sucker attached to the under-surface
of the feet of house-flies, by means of |
which " they tread the ceiling or in-
verted floor, and from its precipice de-
pend secure." It was formerly sup-
posed, from the experiments of Sir
Everard Home, that flies were enabled
to walk against glass, and with the

back downwards in various situations, gucker on the Jot O'f Water-beetle.
solely by the formation of a vacuum The circle encloses the object of
under the soles of their feet, if they the natural size-
may be so termed ; as it was observed that the margins of the feet
were closely applied to the glass, while the central part was drawn up.
It has, however, now been discovered that this hypothesis was not cor-

294

THE MICKOSCOPE.

rect, as Mr. Blackwell (a gentleman residing in Manchester, and an
acute observer of nature) noticed that flies remained attached to the

fig. 132. Feet and Legs, magnified 150 diameters.

1. Foot and leg of Ophion. 2. Foot and leg of Blow-fly. 3. Foot and leg of Drone-
fly. The small circle encloses each object of about the natural size.

sides of an exhausted glass receiver of an air-pump, even after they had
entirely lost the power of locomotion, and an evident distension of the
body had been occasioned by the exhaustion of the air. To detach
them from these stations, Mr. Westwood adds, the employment of a
small degree of force was found requisite. In prosecuting this subject,
clean phials of transparent glass, containing spiders and various insects
in the larva and imago (perfect) states, capable of walking on their up-
right sides, were breathed into, till the aqueous vapour expelled from
the lungs was copiously condensed on their inner surface. The result
was remarkable ; the moisture -totally prevented those animals from
obtaining any effectual hold on the glass, and the event was equally
decisive if a small quantity of oil was substituted for the aqueous
vapour. In fact, it was found that powder, or any substance on the
inside of the phials, prevented the flies from climbing ; and the idea
naturally suggested itself that some glutinous substance was emitted
by the feet of the flies, which enabled them to adhere to the glass.
The next point to be determined, therefore, was, whether spiders and

INSECTS. 295

insects in the larva and perfect states were found to leave any visible
track behind them when they crawled over glass ; and, by the aid
of powerful magnifying-glasses, it was found that traces were left of
an exceedingly minute quantity of glutinous matter, which appeared
to have been emitted by the feet of these creatures ; and subsequent
experiments proved that the hair-like appendages which form the
brushes of spiders and flies are all tubular.

Plate VIII. represents the tongue and piercing apparatus of the
Droiw 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 fleshy outer case which encloses it has been removed for the
purpose of viewing the several parts, which consist of two spongy
guards or feelers, covered with short hairs, united to the head by
muscles ; these feelers appear to be merely used as a preservative
apparatus, in guarding the organs from external injury. The two
lancets seen above them are formed somewhat like a cutlass, or the dis-
secting knife of the anatomist, and purposely intended for making a
deep and sharp cut, and also for cutting vertically with a sweeping
stroke. The other and larger cutting instrument appears to be in-
tended 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 tubu-
lar, to permit the drawing up of the blood and conveying it to the
stomach ; it is enclosed 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 retractile character of which may be there seen in
the drawing of the proboscis of the fly, Plate VII. : by the aid of these
booklets he is enabled to draw in and dart out the tongue with won-
derful rapidity. The striated appearance of another set of muscles may
be seen at the root of the whole.

" In the organisation 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 acces-
sible, 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

296 THE MICROSCOPE.

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 Idbium below, the latter forming the
chief portion of the organ, which is tenanted by dilated muscular lips.
In the Tabanus these are exceedingly large and broad, and are widely
expanded, 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 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
tearing 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 u's 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, tendinous, and
ligamentous structure, with other retractile additions for rapidity and
facility of motion."* The beautiful form of the spiral will be best
seen under a magnifying power of 250 diameters, or quarter-inch
object-glass.

These insects are of great service in the economy of nature, their
province being the consumption of decaying animal matter, given out
in such small quantities, that they are not perceptible to common
observers, neither removable by the ordinary means of cleanliness,
even in the best-kept apartments, in hot weather. It was asserted by
Linnseus, that three of these 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
maggots ; and each of these continues eating so voraciously, that in
twenty-four hours it has increased its own weight above two hundred

* Mr. G. Newport, Cyclopedia of Anatomy and Physiology*

PLATE VIII.

TONGUE AND PIERCING-APPARATUS OF THE DRONE-FLY.

(THE SMALL CIRCLE ENCLOSES THE TONGUE, ETC. OF THIC NATURAL SIZE.)

/jy OF THE *>

DIVERSITY

OF

INSECTS. 297

times ; and in five days it has attained its full size. When the maggots
attain their full size, they change into the pupa state, and remain in that
only a few days ; they then become flies, ready to produce thousands
more maggots, and afterwards flies, till the whole brood is destroyed
by cold.

We cannot resist an apt quotation on this wonderful little insect :
" A fly on the wing is no less curious an object than one on foot ; yet,
when do we trouble our heads about it, except as a thing which troubles
us ? The most obvious wonder of its flight is its variety of direction,
most usually forwards, with its back upwards like a bird, but on occa-
sions backwards, with its back downwards, as when starting from the
window and alighting on the ceiling. Marvellous velocity is another
of its characteristics. By fair comparison of sizes, what is the swift-
ness of a race-horse clearing his mile a minute to the speed of the fly
cutting through her third of the same distance in the same time?
And what the speed of our steaming giants, the grand puffers of the
age, compared with the swiftness of our tiny buzzers; of whom a
monster train, scenting their game afar, may even follow partridges
and pheasants on the wings of steam in their last flight as friendly
offerings 1 But, however, with their game the flies themselves would
be most in ' keeping' on the atmospheric line, — a principal agent in
their flight, as well as in that of other insects, being the air. This
enters from the breathing organs of their bodies, in the nerves and
muscles of their wings, from which arrangement their velocity depends,,
not alone on muscular power, but also on the state of the atmosphere,
1 How does a fly buz V is another question more easily asked than
answered. ' With its wings, to be sure,' hastily replies one of our
readers. ' With its wings as they vibrate upon the air,' responds
another, with a smile, half of contempt, half of complacency, at his
own more than common measurement of natural philosophy. But how,
then, let us ask, can the great dragon-fly, and other similar broad-
pinioned, rapid-flying insects, cut through the air with silent swiftness,
while others go on buzzing when not upon the wing at all 1 Rennie,
who has already put this posing query, himself ascribes the sound par-
tially to air ; but to air as it plays on the ' edges of their wings at
their origin, as with an Eolian harp-string/ or to the friction of some
internal organ on the root of the wing nervures. Lastly, how does the
fly feed ? The busy, curious, thirsty fly, that ' drinks with me,' but
does ' not drink as I,' his sole instrument for eating or drinking being
his trunk or suck ; the narrow pipe by means of which, when let
down upon his dainties, he is enabled to imbibe as much as suits his

298

THE MICROSCOPE.

rx

fig. 133.

Calepteryx Virgo, Dragon-fly. Melitcea Euphrosyne, Pearl-bordered fritillary butter-
fly. Ceramlyx Moschata, Musk-beetle. Polyommatis Argiolus, Azure-blue butter-
fly. Lyccena phlceas, Small copper butterfly ; found throughout the month of July.

INSECTS. 299

capacity. This trunk might seem an instrument convenient enough
when inserted into a saucer of syrup, or applied to the broken surface
of an over-ripe blackberry, but we often see our sipper of sweets quite
as busy on a solid lump of sugar, which we shall find on close in-
spection growing { small by degrees' under his attack. How, without
grinders, does he accomplish the consumption of such crystal condi-
ment 1 A magnifier will solve the difficulty, and show how the fly
dissolves his rock, Hannibal fashion, by a diluent, a salivary fluid
passing down through the same pipe, which returns the sugar melted
into syrup."*

The wings are of great variety in form and structure ; the beauty
of their 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 wing strengthened, all afford a
fund of rational investigation highly entertaining, and exhibiting,
when examined under the microscope, beautiful and wonderful design
in their formation. Take the Libdlulidce, 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, fig, 133) may be seen sailing
for hours over a piece of water, all the while chasing, capturing, and
devouring the various insects that come athwart its course, or driving
away its competitors, without ever seeming tired or inclined to alight.

In fine weather, the female dragon-flies deposit their eggs, which
they lay in water, making a strange noise, as though they were beating
the water ; and the eggs themselves look like a floating bunch of small
grapes. The larvae, when hatched, live in the water ; and it is scarcely
possible to fancy more strange-looking creatures. They are short,
comparatively thick, and their motions are heavy and clumsy. They
shed their skins and become pupa3 j still continuing to live in the
water. The pupa differs from the larva principally in having four
small scales on its sides, which conceal the future wings. While the
dragon-fly continues in its aquatic state, both as larva and pupa, it
devours all the insects it can catch ; but as it can only move slowly,
it is furnished with a very curious apparatus to its head, which it can
project at pleasure, and use as a trap. This apparatus consists of a
pair of very large, jointed, movable jaws, which the insect keeps

* Episodes of Insect Life, a charming book, published by Keeve, 1851.

300

THE MICROSCOPE.

closely folded over its head, like a kind of mask, till it sees its prey.
When it does, it creeps softly along till it is sufficiently near, and then
darts out those long, arm-like jaws, and seizing the insect it had
marked, conveys it to its mouth. When the dragon-fly emerges from

fig. 134. Head and Wing of Culex pipiens, Female Gnat.

1. Head of Female Gnat, detached from the bodj-. 2. Wing. 3. A Scale from the
Proboscis. 4. The Proboscis and Lancets. The reticulation on each side of the
head shows the space occupied by the eyes. The small circles enclose the objects
of natural size. The feather or scale from proboscis 250 diameters.

its pupa-case, it places itself on the brink of the pond, or on the leaf
of some water-plant which is sufficiently strong to bear its weight, and
there it divests itself of its pupa-case. When the insect first appears,
it has two very small wings ; these gradually swell out, the veins fill

INSECTS. 301

with coloured liquid globules, and then two other wings gradually
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 to catch any insect that may fall in its way.

Equally rapid, exactly steered, and unwearied in its flight, is the
gnat. The wing of a gnat has been calculated, during its flight, to
vibrate 3000 times in a minute : these wonderful wings are covered on
surface and edge with a fine down or hair.

The alternations of bright sunshine and rain which are common in
March, are extremely favourable to the appearance of gnats. The first
that appear are called the winter midges (Trichocera Jiyemalis). As
the spring advances, these midges are succeeded by others of a dif-
ferent species ; and as the weather becomes warmer, the true gnats
appear. The sting of the gnat (Culex pipiens) is well known; though
gnats themselves are generally so rapid in their movements, and so
much dreaded, that very few people care to examine the delicacy and
elegance of their forms. The sting is very curiously formed (see fig.
134). The sucker is enclosed in a sheath, which folds up after one or
more of the six lancets have pierced the flesh j it thus inflicts a severe
though minute wound, the pain of which is increased by an acrid
liquor injected into it through the curiously-formed proboscis, which is
covered with feathers or scales. A magnified view of one of these
feathers is seen at No. 3, fig. 134. A scale
from a gnat's wing is seen magnified 600 dia-
meters in Plate X. No. 7. The proboscis is
protected on either side by antennae, or feelers.
Those who will take the trouble to watch the
operations of the female (fig. 135), when she fig. 135. Female Gnat de-
is about to make her nest, will be very much positing her eggs.
struck with the ingenuity and admirable instinct which this little
creature displays.

The bodies of insects are covered with a hard skin ; this answers
the purpose of an internal skeleton, and is one of their chief cha-
racteristics. All animals, and most fishes, have an internal skeleton
of bones, to which the muscles are fixed ; but the interior of an insect
is composed of a soft mass, and the muscles are affixed to the exterior
casing or horny skin, which answers all the purposes of bone, con-
necting the various parts, and maintaining them in their proper places ;
at the same time it is a perfect covering to the body. In some in-
sects this horny skin is remarkable for its strength, as in the beetle
tribe, many of which are exceedingly curious objects.

302

THE MICROSCOPE.

fig. 136.

Cadis-worm cases and Fly. Phryganea, grandis — Coccinella septem punctata, Seven-
spot Lady Bird. Miklia Aprilina, Marvel- du-j our Moth. Eucldoe, Cardamines,
Orange-tip Butterfly ; all to be met with, during the month of April.

INSECTS. 303

The family of 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 veget-
able matters, although some appear to be carnivorous. To protect
their soft bodies, which constitute a very favourite food with fishes,
these larvae always enclose themselves in cases formed of various mate-
rials j bits of straw and sticks, pebbles, and even small shells, being
commonly employed in this manner. 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 only to the anterior end, cutting off a portion of the opposite ex-
tremity. When in motion, the larva pushes its head and the three
thoracic segments, 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 can readily drag it along behind
it, thus keeping its abdomen always sheltered. It adheres stoutly to
the inside of its dwelling by means of a pair of articulated caudal ap-
pendages, generally assisted by three tubercles on the first abdominal
segment.

Before passing 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 can easily pass. 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 pupse of some species swim freely
through the water by means of their long hind legs, also creeping
upon the other four limbs ; these frequently rise to the surface of the
water, and there undergo their final change, using their deserted skin
as a sort of raft, from which to rise into the air, whilst others generally
creep up the stems of aquatic plants for the same purpose.

The perfect insect (P/iryganea grandis, shown in fig. 136, near its
larva-case), has four wings, with branched nervures, of which the an-
terior pair are clothed with hairs ; the posterior are folded in repose.
The organs of the mouth, except the palpi, are rudimentary, and appa-
rently quite unfit for use. The head is furnished with a pair of large
eyes, and with three ocelli, and the antennae are generally very long.
Some species are so exactly like Moths, that they have often been sup-
posed to belong to the Lepidopterous order j and, in fact, these insects

304 THE MICROSCOPE,

may be considered to form a connecting link between the Neuroptera
and the Lepidoptera. The females have been observed to descend to
the depth of a foot or more in water, in order to deposit their eggs.

Many species of these insects are found in Britain. The larvae are
well known to anglers under the names of Caddis-worms and Straw-
worms. They are said to be excellent baits.

LEPIDOPTERA. BUTTERFLIES AND MOTHS.

In this, the highest order of the suctorial insects, with a complete
metamorphosis, we meet with creatures which must be ranked with the
most elegant denizens of the air.

Who has not seen and admired the elegant butterfly, fluttering over
flowers, which they frequently excel in splendour of colour, and at
length resting on them with a touch so light as not to appear to be
resting there ? Who has not seen them, whilst reposing on the flower,
opening and shutting their beautiful wings, alternately erecting and
depressing their long and slender antennae, popularly called horns 1
and who has not seen the beautiful apparatus by which they extract
the nectar from the flowers ?

All butterflies and moths proceed from caterpillars, which after-
wards change into chrysalides ; out of which, after a certain time, pro-
ceed the perfect insects. The female butterfly deposits her eggs upon
such substances as are proper to nourish the caterpillars which proceed
from them : thus, the common cabbage-butterfly places them on cab-
bage ; the peacock-butterfly on nettles ;
the swallow-tailed butterfly on fennel
or rue ; the atalanta-butterfly on net-
tles, &c. These eggs are simply at-
fi 137 tached by some glutinous secretion to

Eggs of the LacJcey Moth. leaV6S °r stemS > in tlie Same Wa? are

the eggs of moths placed, a few of

the latter are enclosed in down. The Lepidoptera are divided into
two great groups, the Heteroscera and the RJwpalocera.

The distinguishing characteristics of butterflies are, that the horns
terminate in small knobs ; and the wings, when the insects are at rest,
are so placed that they meet upwards. Moths, on the contrary, have
sharp-pointed horns, which in many are simple, in others beautifully
feathered along the sides ; while the wings, when at rest, lie in a hori-
zontal position.

Moths and butterflies supply the microscopist with some of the most
beautiful objects for examination. What can be more wonderful in

PLATE IX.

MOTH, SILKWORM.

1. Antenna of Moth. 2. Tongue of Moth. 3. A portion of the Tongue highly magnified,
showing circular muscular fibre. 4. Trachete of Silkworm. 5. Foot of Silkworm.

(THE SMALL CIRCLES ENCLOSE THE OBJECTS OF THE NATURAL SIZE.)

INSECTS. 305

their adaptation than the antennas of the moth, represented in Plate
IX., No. 1, with thin finger-like extremities almost supplying the
insect with a perfect and useful hand, moved throughout its extent by
a muscular apparatus, the whole being of a feathery construction !
The tongue, No. 2, for the purpose of dipping into the interior of the
flower and extracting the honey, is endowed with a series of muscles :
an enlarged view of a portion of the same is seen at No. 3.

The inconceivably delicate structure of the maxillae or tongues (for
there are two) of the butterfly, 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 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 de-
scribed, is a mistake ; which has doubtless arisen from the existence of
large trachse, 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 papilla? at their extremities." Mr. New-
port 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 ex-
pelled 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 sphinx
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."*

* Cyclop. Anat. and Pkysiol,, article "Insecta."

306 THE MICROSCOPE.

In the wings of moths and butterflies we have them also covered
with scales or feathers, carefully overlapping each other, as the tiles
cover the tops of our houses. The irridescent variety of colouring on
the wings arises from the peculiar wavy arrangement of these scales.
In Plate X. are seen magnified representations of a few of them.
No. 1 is a scale of the Morpho-Menelaus, taken from the side of the
wing, of a 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 stria9, 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
at No. 1 a.

Polyommatus Argiolus, or 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 longitudinal and transverse striae, which should be most
clearly defined, and the spots separated : it is a very good test of the
defining power of a quarter-inch object-glass.

No. 3. Hipparchia Janira, or Common Meadow Brown Butterfly :
on this may be seen a number of brown spots of irregular shape and
longitudinal striae. Arnici used this as a test-object.

No. 4. Pontia Brassica, or Cabbage-butterfly, affords an excellent
criterion of the penetration and definition of a microscope : it is pro-
vided at its free extremity with a brush-like appendage. With a high
power, the longitudinal markings appear to be rows of little beads.

The Tinea Vestianella, or Clothes-moth, possesses very delicate and
unique scales : two of these are imperfectly represented near the
Acarus found on one of these moths, at page 334. The feathers from
the under-side of the wing are the best, requiring some management
of illumination to bring out the lines sharp and clear.

The common clothes-moth generally lays its eggs on the woollen or
fur articles it intends to destroy; and when its larva appears, it begins
to eat immediately; with the hairs or wool it has gnawed off, it
forms a silken case or tube, under the protection of which it devours
the substance of the article on which it has fixed its abode. This tube
is of parchment-like consistence, and quite white ; it is cylindrical in
its shape, and furnished at both ends with a kind of flap, which the
insect can raise at pleasure, and crawl out ; or it can project the front
part of its body with its fore-feet through the opening, so as to crawl
about without removing the rest of its body from the tube, which it
drags after it. There are several kinds of clothes-moths ; and the

PLATE X.

SCALES FROM BUTTERFLIES' WINGS, ETC.

1. Scale of Morpho Menelaus, magnified 250 diameters, la. Portion of Scale of Morpho Menelaus, magni-
fied 500 diameters. 2. Large Scale of Polyommatus Argiolus, azure blue, magnified 250 diameters.
3. Hipparchia Janira, magnified 250 diameters. 4. Pontia Brassica, magnified 250 diameters. 5. Podura
Plumbea, magnified 250 diameters. 5n. Portion of Large Scale of Podura Plumbea, magnified 500
diameters. 6. Small Scale of Azure Blue, magnified 250 diameters. 7. Scale from the Wing of Gnat,
magnified 500 diameters. 8. Portion of a Large Scale of Lepisma Saccharine, magnified 500 diameters.

<*

INSECTS. TEST-OBJECTS. 307

caterpillars of some of them bury themselves in the article on which
they feed, instead of making the silken tube spoken of. The moths
also differ very much in appearance : the commonest kind is of a light
buff; one species, Tinea Tapetzella, fig. 138, is nearly black, with the
tips of its larger wings white, or pale grey.

Mr. Topping, the careful 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 fi 138
the examination of them. The following are arranged The Black Clothes-
according to their difficulty as test- objects : moth.

Fos. N. gracilis.
Amician test.
Grammatophora.
Ceretonis faschiota..
Navicula cuspidata.

— angulata.

— strigosa.

— lineata.

— Spencerii.

N. baltica. HAIRS,

— hippocampus.

— strigitate.

— formosum.

SCALES.

Meadow Brown.
Pontia Brassica.
Azure Blue.
From Gnat's Wing.
Tinea Vestianella.
Amathusia Horsefieldiii
Morpho Menelaus.
Podura plumbea.
Lepisma saccharina.

Indian Bat.
)r Mouse.
Mole.

Larva of Dermistes.

Mr. J. T. Norman, preparer of specimens for the microscope, 10 Fountain Place,
City Koad, furnished the author with a similar list for publication.

The caterpillar's foot is made up of a series of booklets, which
enable him to cling with ease to the surface of a leaf or stalk of a plant.
A magnified view of one is given at No. 5, Plate IX.

The Homoptera form three great groups or tribes. The first, the
Cocdna, is composed of numerous minute insects, of which the history
is still very imperfectly known. Of these the tarsi have only one joint.
The males are furnished with two wings, with a few straight nervures ;
they are destitute of a rostrum, and pass their pupa stage in a state of
repose. The females are destitute of wings, possess a rostrum, and
appear to undergo no metamorphosis whatever. These curious little
creatures, whose history is so singular that some authors have pro-
posed the formation of a separate order for their reception, are princi-
pally inhabitants of the warmer regions of the earth, although many
species are found in our own country, where some of them are well

308 THE MICEOSCOPE.

known to gardeners under the name of " the bug," from the injury
they do to many plants, especially in hothouses.

Nothing can be more dissimilar in appearance than the two sexes
of the singular insects Homoptera (fig. 139). The females usually
form a mere fleshy mass, often nearly destitute of limbs, and remaining
attached to one spot upon the branches of the plant infested by them,
from which they continue to suck nutriment, by the agency, of their
rostrum, until they attain a considerable size.
The males, on the contrary, are generally very
minute and really elegant creatures, furnished
with a single pair of filmy wings ; the only
representatives of the hinder wings being a
pair of organs somewhat similar to the ImUeres

»of the Diptera. Hence some etymologists
have put forward the opinion that the males of
the Coccina are, in reality, dipterous parasites.
The abdomen of the male is generally furnished

with a pair of long filaments. In some in-
fig. 139. Cochineal Insect. r. f ,& . . . ,

1. Male. 2. Female. stances the females retain their limbs and

power of motion through life.

In one genus of Coccina (Dorthesia), several species of which are
found in this country, the female — which, although apterous, is active
in all stages — is completely covered with a snow-white secretion,
which gives it more the appearance of a little plaster-cast than any
thing else.

Iii a second tribe, the Phytoplithiria, or Plant-lice, both sexes are
either wingless or furnished with four distinctly veined wings. The
rostrum springs apparently from the breast, and the tarsi are two-
jointed and furnished with two claws.

The greater part of this tribe is composed of the Aphides, or Plant-
lice, whose extraordinary history renders them one of the most inter-
esting groups of insects. These creatures must be well-known to every
one. They are all small animals, with a more or less flask-shaped body,
furnished with six feet and a pair of antenna, and usually with a pair
of short tubes close to the extremity of the abdomen, from which a
clear sweet secretion exudes. Both sexes are sometimes winged, some-
times apterous ; and the individuals of the same species are often
winged and apterous at different periods of the year. They all live
upon plants, the juices of which they suck ; and when they occur in
great numbers, often cause great damage to vegetation. Gardeners
and farmers are well aware of this. Many plants are liable to be

INSECTS. HOMOPTERA. 309

attacked by vast swarms of Aphides, when their leaves curl up, they
grow sickly, and their produce is certain to be greatly reduced. One
striking instance is presented by the Hop-fly (Aphis Humuli).

The Cicadellina or Cercopidae, of which the Aphrophora bifasciata,
or common Frog-hopper, have the antennae placed between the eyes,
and the scutellum visible — that is to say, not covered by a process of
the prothorax. The ocelli, which are sometimes wanting, are never
more than two in number. These little creatures are always furnished
with long hind legs, which assist them in performing most extraordi-
nary leaps.

The best-known British species, so very abundant in gardens, is the
Cuckoo-spit, or Froth-fly. The names of cuckoo-spit and froth-fly both
allude to the peculiar habit of the insect, when in the larva state, of
enveloping itself in a kind of frothy secretion, somewhat resembling
saliva; and which, indeed, was formerly supposed to be the saliva of
the cuckoo, it being found on the young shoots of plants just about the
time that the cuckoo is heard in the woods. The frothy secretion is
supposed to be intended to preserve the tender body of the insect from
the overpowering effects of the sun, as it has been observed to be pro-
duced in exact proportion to the heat of the weather. It is not known
exactly how the froth is produced. When by any chance it becomes

Aphrophora spumaria, Cuckoo-spit. Perfect Insect of

a. The frothy substance. 5. The pupa. the Cuckoo-spit.

fig. 140.

condensed, it drops like rain from the trees on which the insect is
found. It is only in its larva or infant state that it produces the froth.
The larva and the pupa resemble the perfect insect, except that the
larva has no wings, and the pupa has very small ones. The perfect
insect, however, has both wings and wing-cases ; and it has the power
of flying to a considerable distance. Sometimes, indeed, these insects
are seen in vast multitudes on the wing. One of the peculiarities of
this insect is its power of leaping, which is so great, that, being assisted
by its wings, it will sometimes leap a distance of five or six feet ;
which is more than two hundred and fifty times its own length, or as

310 THE MICROSCOPE.

much as if a man were to take a leap a quarter of a mile high. This
extraordinary activity appears to be principally occasioned by the great
length of the thighs of the insect, which are also furnished on their
outer margin with a fringe of stiff hairs or strong spines, which are of
great use to the insect in leaping.

The Hymenoptera are distinguished from the other insects with
membranous wings, by the presence of an ovipositor of peculiar con-
struction at the extremity of the abdomen in the females, which not
only serves for placing the eggs in the required position, but also in
many species (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 exigences of the different
insects, a short description of its general construction will not be out of
place here. The ovipositor, or sting, generally consists of five pieces :
a pair of horny valves (fig. 144), which form a sheath for the true
sting or ovipositor j these are 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 sting itself. - The latter consists of three bristles,
of which the superior is channelled along its lower surface, for the
reception of a pair of finer bristles, which are toothed at the tip. These
three pieces, when fitted together, form a narrow tube, through which
the egg passes to its destination ; and through this also the poisonous
fluid, which renders the sting of the bee so painful, is injected into the
wound. In the saw-fly one of these parts remains rudimentary ; but
in other respects the organ is the same.

The larvae of most of the Hymenoptera are footless grubs, usually
furnished with a soft head, exhibiting but little, if any advance upon
the maggots of the Diptera. In the saw-flies, however, the larva,
instead of being, as above described, a mere footless maggot, presents
the closest resemblance to the caterpillars of the Lepidoptera, being
provided with a distinct horny head, and not only with six thoracic
legs, but also, in most cases, with from twelve to sixteen pro-legs,
situated upon the abdominal segments.

The Saw-fly, fig. 141, so destructive to gooseberry-bushes, is remark-
able for the manner 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 which are marked with brown on the edge. The female
lays her eggs on the under-side of the leaf, on the projecting veins ; and
these are so firmly attached, that they cannot be removed without
crushing them. The instrument which the little insect uses for the

INSECTS. HYMENOPTERA.

311

purpose of cutting the leaf, is one of the most remarkable pieces of per-
fect mechanism : it is securely lodged, when not in use, in a long nar-
row slit beneath the hinder part of the abdomen, bounded by two horny

fig. 141. The Saw-fly of the Gooseberry.

plates. At first these appear to consist of a single piece ; but upon
closer inspection four plates are found to enter into their construction :
namely, two saws, placed side by side, as in fig. 142 ; and two supports,
very like the saws in shape. A deep groove runs along the thick edge

fig. 142. Saws of Saw-fly,

In the small circle is represented the comparative size of these instruments ; they are
drawn rather too small.

of the latter, which is so arranged that the saws run backwards or for-
wards, without the possibility of getting out of the groove. When the
cut is made, the four are drawn together ; and through the central
canal, which is now formed by combining the whole, an egg is pro-
truded into the fissure made by the saws in the leaf. The cutting
edges of the saws are provided with about eighteen or twenty teeth,

312 THE MICROSCOPE.

having sharp points of extreme delicacy ; together forming a good ser-
rated edge of exactly the form given to the finest and best-made sur-
gical saws. In the summer-time the proceedings of this little insect
may be watched, and the mode of using this curious instrument seen,
by the aid of a hand magnifying-glass ; as they are not easily alarmed
when busy at this work.

Many other insects are provided with instru-
ments for boring into the bark or solid wood it-
self. The Cynip bores a hole into the side of the
oak-apple, for the purpose of depositing its larva,
whence, as well as being comfortably lodged, it
receives its early food. When full grown, it eats its
way out of the nut ; and dropping to the ground, it
assumes its pupa form, which in a short time is

fig" ' exchanged for that of the perfect fly. The most

Female Eglantine . . . x J.

Gall-fly and Larva, important ot these insects is the Cynip gallce tine-

torice, fig. 143, which causes the formation of the
gall-nut, so extensively employed in the manufacture of ink and for
dyeing purposes.

Some of the wasp tribe are very peculiar in their habits, and are
active agents in the economy of nature. The solitary, or mason wasps,
curiously construct their nests, forming cells, in which they most care-
fully rear their young. The social wasps, like the bees, live in commu-
nities, and have nearly the same divisions of labour and regulations for
the government of their colony. The structure and mechanical con-
trivance of their stings can only be seen under the microscope. The
stings consist of two barbed darts, which penetrate the flesh deeply ;
and from the peculiar arrangement of their serrated edges, their
immediate withdrawal is prevented ; while, by the muscular effort
required for this purpose, a small sack or bag near the root is
pressed upon, and its irritating contents squeezed into the wound.
After the fluid is injected, the insect possesses the power of contracting
the barbed points ; it then withdraws the sting from the flesh. In fig.
144 the sting of the wasp is shown, with its attachments and muscular
arrangements ; and it can be seen that the sting is most wonderfully
adapted to become an instrument of a very effective and deadly con-
struction. The brushes near it are evidently placed there for the pur-
pose 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 our atten-
tion ; this it uses, with its accessories, to collect the honey for its food

INSECTS. HYMENOPTERA.

313

when roving about from flower to flower. The proboscis itself (fig.
1 45) is very curiously divided ; the divisions are elegant and regular,
beset with triangular hairs j and being numerous, appear at first sight

©

fig. 144.

1. Sting of Wasp. 2. Sting of Bee.
The small circle encloses the object of the natural size.

as a number of different articulations. The two exterior lancets are
spear-shaped, and 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, permitting considerable motion in several
directions ; evidently used by the little busy insect for the purpose of
distending the internal parts of flowers, and thus facilitating the intro-

314

THE MICROSCOPE.

duction of the proboscis. The two shorter feelers are closely connected
to the proboscis, and terminate in three jointed articulations. Swam-
merdam thought these were used as fingers in assisting the removal of
obstructions ; but it is more probable that they are used by the insect
for the purpose of storing and removing the bee-bread to the pocket-
receptacle in the legs. The lower part of the proboscis is so formed
that it may be considerably enlarged at its base, and thus made to con-

fig. 145.

1. Honey-bee's tongue. 2. Leg, showing pocket for carrying tlie Bee-bread.
The small circles enclose the objects of their natural size.

tain a larger quantity of the collected juice of flowers ; while, at the
same time, in this cavity the nectar is soon transformed into pure honey

INSECTS. BEETLES. 315

by some peculiar chemical process of its own ; the proboscis tapers off
to a little nipple-like extremity. At its base may be seen two shorter
and stronger mandibles, serving the little insects for tools in construct-
ing their cells ; from between these is protruded a long and narrow
tongue or lance ; the whole most ingeniously connected to the head by
a cartilaginous structure, with a series of muscles and ligaments. The
proboscis being cylindrical, extracts the juice of the flower in a some-
what similar way to that of the butterfly ; when loaded with honey,
the next 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 the bee is speedily
assisted to unload by its fellow- workers ; and the pollen is at once
kneaded and packed close 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 seems to consti-
tute the food of the working-bees in the hive. The wax is another
secretion exuding from the skin of the insect, and is found in little
pouches in the under-part of the body ; it 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 be-
smeared over them by the wonderful apparatus we have shown in the
engraving. If a bee is attentively observed when it has placed itself
upon a flower, the activity and promptitude with which it uses this
apparatus is truly surprising. It lengthens it, 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
whole of 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."

BEETLES.

The leading characteristic of the vast order of Coleoptera, or 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.

316

THE MICROSCOPE.

The common Black-beetle (Blatta orientalis, fig. 146) is not, strictly
speaking, one of the beetle tribe, but more nearly allied to the cricket
and grasshopper. All the insects belonging to this class are very de-
structive, as they continue eating through all their transformations.
The female black-beetle does not lay her eggs singly, but always sixteen
at a time ; and these eggs are enclosed in a capsule, which resembles a
small oblong box (see upper part of cut). The mother carries this
capsule about with her, until the sides of it have attained a proper
firmness, and become changed from white to brown. If this recep-
tacle for the eggs is more closely examined, it will be seen that one of
the two longer margins is very finely toothed, and is composed of two

layers, and so constructed that
the teeth of one of the layers
easily go into the spaces between
the teeth of the other. This
margin is also so firmly united by
means of a gummy substance,
that it might be easier opened at
any other part than at the
toothed edge. As soon as the
young are hatched, and have
quitted the egg, they emit a fluid
from their mouths, by which they
soften the cement that united the
two layers, of the capsule toge-
ther, and thus contrive to open
the door of their prison-house.

fig. 146.
Male and female JBlatta orientalis.

Melolontha Vulgaris, or Cockchafer, is very abundant in our island,
and it has a variety of names, — the brown tree-beetle, blind-beetle,
May-bug, chaffer, May-bob, or oak-web, jack-horner, geffry-cock, acre-
bob, as it is termed in different parts of the country. The larva is soft
and grey, with the head and legs protected by a shelly covering of a
yellow-brown colour. While in the larva state, which continues for a
space of two or three years, it devours the roots of corn, grass, and
other vegetables.

The eggs are laid in small detached heaps, beneath the surface of
some clod ; and the young, when first hatched, are scarcely more than
one-eighth of an inch in length, gradually increasing in their growth,
occasionally changing their skins, until they are of the size of two
inches or more. At this time they descend to the depth of two feet,
where they construct an oval cell, very smooth in the inside ; and after

INSECTS.

317

fig. 147.

Geotrupes stercorarius, Dor beetle. Bombus terrestris, Humble bee. Vanessa urticce,
Small tortoiseshell butterfly. Apis mellifera, Honey-bee. Arum, Narcissus, &c.,
frequently found during the month of March.

318

THE MICROSCOPE.

fig1. 148. Melolontka V^dgar^s, or Cockchafer.

a certain time, divest themselves of their last skin, and appear in the
chrysalis form, in which they continue till the succeeding spring, when
they assume the perfect beetle ; but remain for a considerable time in
a weak state, not venturing out till the fine days of May or the begin-
ning of June, at which time the beetle emerges from its retirement,
and commits its depredations on the leaves of trees, <fec. The antennae
have a remarkable cornb-shaped appearance, and, with other parts of
this insect, generally find a place in the microscopist's cabinet.

The elytra or wing-cases of the diamond beetles are amongst the

most brilliant of
opaque objects. Some
are improved by being
mounted in Canada
balsam, whilst others
are more or less in-
jured by it : a trial of
a small portion, by
first touching it with turpentine, will decide this point.

To the genus Ptinus belongs a small beetle, known as the Death-
watch, fig. 149. This and the species Anobium are found in our
houses, doing much injury whilst in the larva state. The eggs are
often deposited near some crack in a piece of furniture, or on the bind-
ing of an old book. As the larvse are hatched, they begin to eat their
way into the furniture on which they have been deposited ; and when
they have attained a sufficient depth, they undergo their transforma-
tions, and return, by another passage, as beetles. In furniture attacked
by them, little round holes, about the size of the head of a pin, may be
seen ; and these are the holes that have been made by the beetles.
The noise, which has given rise to the name of death-watch, is made by
the insect striking its head against the wood. The larva is called a
book-worm when it attacks books ; and old books when 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 promi-
nence of the thorax, looks as if it were covered with a
fig. 149. hood. The Anobium puniceum, fig. 150, attacks dried
The Death-watch objects of natural history, and all kinds of bread and
(Atropus), biscuits, particularly sailors' biscuits, in which its mag-
gots frequently abound. In collections of insects, it

magnified.

INSECTS. BEETLES. 319

first consumes the interior ; when the larva assails
birds, it is generally the feet that it devours first ;
and in plants, the stem or ligneous part. The
larva is a small white maggot, the body of which
is wrinkled, consisting of several segments covered
with fine hairs ; its jaws are strong and horny^
and of a dark brown. The pupa is white, but so
transparent, that every part of the perfect insect \.

may be seen through it. The beetle itself is of a fi£- 15°- .

,,.,. , , , .., ,. i . Anobium puniceum,

reddish-brown colour, and covered with line hairs. magnified

The Bacon-beetle (Dermesteslardarius)is one whose

ravages are very extensive. The larva of this insect is particularly
partial to the skin of any animal that falls in
its way ; and consequently it destroys stuffed
animals and birds in collections of natural
history, whenever it can gain access to them.
It attacks hams and bacon for their skin;
but as it is very gluttonous, it extends its
ravages to the flesh. The larva is long and
slender : its body, being nearly round, con- fig- 151« Dermestes lardarius.

. . f ,-, • , 111-11 • Larva, pupa, and imago.

sists of thirteen segments, blackish-brown in

the middle, and white at the edge. The whole body is furnished with
bristle-shaped reddish-brown hairs. The beetle is black at 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 j and the
whole beetle is furnished here and there with tufts of ash-grey or yellow-
ish-grey hairs. The beetle is most destructive in spring. Their larvae
are very seldom seen, as they conceal themselves in the bodies they
attack j and their presence can only be guessed by finding occasionally
their cast-off skins, as they change their skins several times while in
their larva state. Whenever, therefore, little rolls of black skin are
found near where ham or bacon is kept, or in cases containing
objects of natural history, it is probable this beetle has attacked
them. The small scales covering many species of Dermestes, as well
as their hairs, are very beautiful microscopic objects.

The Heteroptera, or Bugs, form two principal groups, distinguished
by their structure and habits, — the Hydrocores, or Water-bugs, and
the Geocores, or Land-bugs. The latter never possess wings : the
disagreeable Bed-bug (Cimex lectularius) and its allies belong to
this group. The former are at once recognisable by the small size
of their antennae, which are composed of three or four short joints,

320 THE MICROSCOPE.

and are concealed beneath the eyes. Of these, the Notonectida are
distinguished by their broad, rounded head, which occupies the whole
width of the front of the body. They swim rapidly about in the
water, with their bellies directed upwards, rowing themselves along
by means of their flattened hinder legs, which are extended on each
side of them like oars. Hence the Notonecta is generally known as
the ~boat-fly. They carry the air required for their respiration in a
space left for this purpose between the wings and the back. They
are very active and predaceous animals, and when captured some of
them often inflict a painful wound with their powerful rostrum. Se-
veral species may be met with in almost any piece of water. In the
second group, the N&pina, the head is small and triangular, and gene-
rally considerably narrower than the thorax. Their legs are generally
less distinctly formed for swimming than in the preceding group j but
the anterior pair are converted into powerful raptorial organs.

The Nepa cinerea is a British example of this group, to be met with
in every pond. These insects respire by means of the filaments of the
caudal extremity, which they place at the surface of the water, the
only available stigmata being situated at the base of these filaments.

The Dytiscus, the principal genus of this tribe, is common in fresh
and placid waters. Its larva, represented in fig. 92, feeds upon other
aquatic larvse, such as those of gnats, dragon-flies, &c.

In the Gyrinus, Whirligigs, we have combined contrivances to
facilitate the creature's movements in the element it frequents. The
hinder legs are converted into a pair of oars of remarkable efficiency,
the point of their connection with the body being adapted with great
precision to insure the most effectual application of the propelling
power ; and as they are struck out behind in the act of swimming,
there is a membranous expansion, which enables the insect to move
about with great rapidity ; while, on their being drawn back towards
the body, the membrane closes up again, and thus offers but a small
resistance to the water (fig. 152). If the insect wishes to remain below
the surface of the water, he employs the small hooks at the extremity
of the leg, for the purpose of adhering to the roots or stem of some
aquatic plant. The eyes are not the least curious part of the merry
little creature; the upper portions of them, being fitted for seeing in the
air, are placed on the upper part of the head ; whilst the other portions,
fitted for seeing in water, are placed in the lower part, a thin division
separating the two.

To the Orthoptera belong the Locustina, Gryllina, and the Achetina,
all herbivorous insects. The first is represented by our well-known grass-

INSECTS. CRICKET.

321

hopper : the second, the Gryttina, 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

fig. 152.

1. Leg of Gyrinus. 2 Leg with paddle expanded.
In the small circle the object is represented of the natural size.

exotic species have wing-cases, which present the most perfect resem-
blance to leaves both in colour and veining. There are several British
species, one of which (the Gryttus viridissi<mus, Grasshopper,) is very
common in marshy situations.

Of the tribe Achetina, the common Cricket (Acheta domestica),
fig. 154, the noisy little denizen of our kitchen-hearths, serves as an ex-
ample. These insects have the antennae slender and tapering, and often
considerably longer than the body. They agree with the Gryllina in
the structure of the 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 hinder wings are very long, and folded up in such a manner that
they 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 appendages, and in the female with a
long, slender ovipositor, composed of'two filaments, laid side by side,
and somewhat thickened at the tip. The tarsi are three-jointed.

The horny covering and muscular apparatus under the wing-case

322

THE MICROSCOPE.

fig. 153.

Lizard. " Sillercups," Polyommatus carydon, Chalk-hill blue butterfly. Gryllus xiri-
dissimus, Grasshopper. Polyommatus Adonis, Clifden blue butterfly ; and flower-
ing plants found during the month of July.

INSECTS. PODURID^E. 323

of the cricket offer many curious points for microscopic examination.
The cricket has two wings, which are covered with wing-cases of a
leathery consistency, near the base
of which is a horny ridge having
transverse furrows, exactly re-
sembling a rasp or file ; this the
cricket rubs against its body with fi^154' The Cricket'

a very brisk motion, whereby it produces its sound. It has been
remarked that the chirp becomes louder in proportion as the heat
increases ; and it is extremely difficult to silence the cricket in any way
but by putting out the fire near which the little animal is chirping.

In the order Thysanoura there is a remarkable diversity of struc-
ture. They undergo no metamorphosis, and have no wings. The
order contains two families, the Podu-
ridce, or /Spring-tails, and the Lepismidce.
In the former, the caudal appendage
has the form of a forked tail {Podura,
fig. 155), which is bent under the animal

when not in use, and by its sudden ex- % 155 PoduraplumJ)ea.
tension causes the animal to spring, often The small circle encloses the insect
to a great distance in comparison with of life size.

its size. The body is covered with numerous minute scales, often of .a
beautiful silvery or pearly lustre, and curiously striated. Some species
may be found jumping about on the surface of the water, whilst others
are met with in profusion upon snow and ice.

The Lepismidce have a spindle-shaped body, usually covered with
silvery scales, and furnished along the sides of the abdomen with a
series of appendages or false feet, besides several long-jointed, bristle-
like organs at its extremity. The head is concealed under the pro-
thorax • the eyes are usually compound, and frequently occupy the
whole of the head. The antennae are very long, and composed of
numerous joints ; and the maxillary palpi, which consist of from five
to seven joints, are very conspicuous. These insects generally inhabit
moist places. The most common species, Lepisma saccliarina, is fre-
quently found about houses, especially in sash-frames, or old sugar-
casks, from which it derives its name. The scales from these little
insects have always been favourite objects with microscopists, and are
generally used to test the power of penetration and definition of the
instrument itself.

Podura plumbea, or Lead-colour Springtail, are usually found in
wine-cellars, amongst the sawdust, leaping about like fleas, and are

324 THE MICROSCOPE.

therefore difficult to take. The following is generally the plan resorted
to : sprinkle a little oatmeal on a piece of black paper near their
haunts ; after a few hours, remove it carefully to a large glazed basin,
so that when they leap from the paper, as they will when brought to
the light, they may fall into the basin, and thus become separated from
the meal. The best way of separating the very fine scales from their
bodies has been previously explained (See page 44). The markings
cannot be seen with a lower power than a quarter-inch object-glass.
Under a power of 500 diameters, the surface appears to be covered
with extremely delicate wedge-shaped dots or scales, as seen at No. 5 a,
Plate X. The smaller scales are much more difficult to resolve than
the larger ; and they form a good test of the defining power of a l-8th
or 1-1 2th object-glass, No 8, a portion of a large scale of Lepisma
sacclmrina, showing the longitudinal markings.

The family Aphaniptera, in which the metamorphosis is what is
termed complete — the larva, pupa, and imago being very distinct in
their appearance : the well-known flea is the best example of this small
group. By many recent authors these insects have been arranged with
the Diptera, which would appear to be incorrect, as they differ in many
particulars. The external covering of the flea (fig. 156) is a horny case,
formed of very distinct segments ; those of the thorax being always
disunited. Although apparently apterous, the flea has the rudiments of
four wings, in the form of horny plates on the sides of the thoracic
segments. Its mouth consists of a pair of sword-shaped, finely-serrated
mandibles, which, with a sharp, needle-like organ, appears to constitute
the formidable weapon with which it -pierces the skin of its victim.

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 antenna, or horns, its proboscis, and a pair of sharp lancets, with
which it penetrates the skin. On each side of the head a large sharp
eye is placed. It has six many-jointed powerful legs, terminating in
two sharp-hooked claws, which are so constructed, that they can be
folded up, as it were, and when it leaps it springs them out ; so that
its whole strength is excited at the same moment. The female flea,
fig. 156, lays a great number of eggs, sticking them together with a
glutinous matter ; those of fleas infesting the dog or cat are made fast
to the roots of the hairs ; in four days' time the eggs are hatched,
and a small white worm or grub is seen crawling about, and feeding
most actively. No. 4, fig. 157, is a magnified view of one ; it is
covered with short hairs, which prevent its being easily dislodged.
After remaining in this state about nine or ten days, it assumes the

INSECTS. FLEA.

325

pupa form, which it retains for four days ; and in nine days more it
becomes a perfect flea. The head of the flea found in the cat (No. 3,
fig. 157) is seen to be very different in its form from that of the

fig. 155.

1. Female Flea. 2. Male Flea.
The small circles enclose the little animals of the natural size.

human flea (fig. 156). Its jaws are supplied with formidable booklets,
and from the first and second joints behind the head project short and
strong spines ; these are, no doubt, for the purpose of enabling it to
maintain a firmer and better hold on the animal.

326 THE MICROSCOPE.

ACARINA PARASITES.

Nearly all the animals that we include in this order, of which the
common Mites are the best known examples, are recognisable at the
first glance by the form of the body, which usually constitutes a roundish
or oval mass, without any trace of segmentation. They are mostly
parasitic animals, furnished with a proboscis containing a pair of sharp
spines, which serve for wounding their prey, and bearing a palpus oil
each side. The proboscis is jointed and retractile. Sometimes it is
furnished with a swollen base, which has been taken for a head. The
eyes, which are often wanting in the parasitic forms, are two in num-
ber when present, and are placed on each side of the anterior portion
of the body.

The Acarina are generally oviparous; a few bear living young.
The young generally possess only three pairs of feet j the fourth pair
not making their appearance until after the first moult.

Parasites infest the skin, lurk among the hairs and feathers of
quadrupeds and birds, and even of other insect races, whence they
draw an abundant supply of support for their singular mode of exist-
ence. Mr, Henry Denny has figured and described a greater number of
parasitic insects in his Monographic** Anoplurorum than any previous
observer. He says, " that the opinion entertained of each animal having
its peculiar parasite, is not entirely borne out by facts ; nevertheless,
that those infesting the quadruped will not be found in the bird, being
almost always confined to animals of the same species, or of similar
habits. For instance, the Docophorus icteroides is to be found on nearly
every species of duck. The Neimus obscurus infests several species of
sandpipers, godwits, &c. ; the Neimus rufus, the hawks and falcons ;
the Docophorus lari, all the gulls. In quadrupeds it is rather more
doubtful, as they are frequently transferred by association ; for instance,
the Trichodectes scalaris has been found upon both the ox and the ass
feeding in the same stall. The Hcematopinus piliferus, infesting dogs,
have been found in swarms upon the ferret. The Pediculus, besides
being found on man, is also found on the Quadrumana, Eodentia,
Camivora, Pachydermata, and the Ruminantia. We include in this
group both Acari and Parasites ; though from the former having eight
legs, and the latter six only, they are not generally admitted as belong-
ing to the same class of insect life.

Respiration goes on simply through the skin in Acarus and Sar-
coptes ; while in Gamasus, Cheyletus, and various kinds with pincer-

PLATE XI.

PARASITES.

1. LOUSE, HUMAN; magnified 50 diameters.

2. ACABUS DOMESTICUS, Cheese-Mite; magnified 50 diameters.

3. SARCOPTES SCABIEI, Itch-Insect; magnified 350 diameters.

4. DEMODEX FOLLICULORUM, or Gmb from Human Skin, in its various stages of

existence, from the Egg upwards ; magnified 250 diameters.

(THE SMALL CIRCLES ENCLOSE THE OBJECTS OF THE NATURAL SIZE.)

•MVE'RSITY

v r-. OF

ACARIXA — PARASITES. 327

shaped mandibles, there is a complete system of tracheae with spiracles,
as in true insects. Besides these two there is an intermediate plan of
respiration not known before, combining both the other modes, in
which inspiration takes place through the skin, and expiration through
a system of tracheae, which have their outlet above the insertion of the
mandibles. " Trombidiun is an example in which a latticed aperture at
the root of the mandibles forms the anterior outlet of two large air-
pipes running from the hinder end to the front, each subdivided into a
tuft of numerous unbranched simple tracheae. Besides these, there is
under the skin a round meshed network of a transparent and seemingly
homogeneous substance, resembling the respiratory network under the
skin of certain Trematoda.

" The importance of a thorough examination of these microscopic
pests is at once evident, in the fact that the type of the family to which
the whole of them belong is the noisome parasite of the human subject;
that another, as yet undetermined form of the same tribe, is thought by
some to be connected with one of the most fatal ailments of our frame
— dysentery ; that two distinct Sarcoptes, yet undescribed, affect the
horse and sheep ; and that even the common sparrow, our little pet
canary-bird, and even the useful bee, do not escape the ravages of one
of the family.

When, therefore, we reflect on the ailments which these produce,
and on the diminutive size of the creature which in its effects is so
destructive to other tribes ; and bear in mind that this mere speck,
this particle of dust, is organised for all its purposes as completely as
the most perfect of any of the whole sub-kingdom to which it belongs,
even to the flexor, the extensor, and the rotator muscles of its truly
atomic limbs ; while the entire body of the creature, when first pro-
duced, measures scarcely more than the sixteen -thousandth of an
inch in length ; and then call to mind that the mere foot of the Di-
nornis, or of the Palapteryx, the ancient colossal bird of the antipodes,
measures, as shown by Professor Owen, more than seven hundred and
fifty times the whole size of this little body, — who can but feel astonished
at this range of creation 1 Who can but feel that the study of natural
history, not as the amusement of an hour, but as a sober contempla-
tion, must tend to exalt as well as to extend the human intellect, and
that the most microscopic atom of organised life, considered as part of
the world, is as deserving of our fullest attention as the most gigantic V3*

The Louse (Plate XI. No. 1). Whenever wretchedness, disease, and

* George Newport, Esq., F.R.S., "On a new genus of the family Chalcididce, found
n the nest of the bee." — Linnean Society's Transactions, 1853.

328

THE MICROSCOPE.

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 personal cleanliness engenders loathsome disease. When examined
under the microscope, our disgust of it is in no way diminished. In the

fig. 157.

1. Dog's Parasite. 2. Eat Acarus. 3. Head of Cat-Flea. 4. Larva or grub of Flea.
The life size of each is shown within the small circles.

head may be distinguished two large eyes, near-to which are situated
the 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

ACARINA PAKASITES. 329

five joints, terminated by two unequal hooks ; these, with the other
portions, are covered with short hairs. Around the outer margin of the
body may be seen small circular dots, the breathing apertures, with
which all this class of animals are provided, rendering them very
tenacious of life, and difficult to kill. There is another louse, rather
differing in its characteristics from this, formed about the body of the
very poor and dirty, called 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 ex-
cessive 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 seven
hundred times the size of this incredible slender piercer, which conse-
quently 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 hind part of his body, and uses as a weapon
of defence." He found from experiments made to ascertain the in-
crease of these vermin, that from two females he obtained in eight
weeks the incredible number of 10,000 esrafs.

* OO

The Itch-insect, Sarcoptes scabiei (Plate XI. No. 3, magnified 350
diameters). Dr. Bononio made out the true character of the very
troublesome disease known as the itch. Upon examining one of the
pustules, or little bladders, from between the fingers, with the points of
very fine needles, under the microscope, he perceived a very small ani-
mal, very nimble in its motion, covered with short hairs, having a for-
midable head with a pair of strong mandibles or cutting jaws, and
eight legs, from the extremities of which are appended remarkable
feet, each provided with a sucker, by means of which it no doubt sucks
or draws its way beneath the skin, having first cut out a small section
with its mandibles ; here the insects form a nest, lay eggs, and mul-
tiply rapidly, being most difficult to dislodge.

To find the itch-insect, the operator must examine carefully the
x parts surrounding each pustule, and he will see a red line or spot com-
municating with it ; this part, and not the pustule, must be probed
with a fine-pointed instrument ; the operator must not be disappointed

330 THE MICROSCOPE.

by repeated failures. As it is often very difficult to detect the haunts
of the insect, an eye-magnifier will greatly assist.

Dr. Bourguignon has of late bestowed much time in studying the
habits of this troublesome parasite. To arrive at this knowledge, the
Doctor had recourse to a peculiar kind of movable microscope, which
enabled him to observe it under the skin of the diseased person. The
microscope is composed of the frame of an ordinary instrument, the
optical and essential parts of which have been raised from the socket
that supported it, and articulated to a movable knee at the extremity
of a lever. The rays of light from a lamp or candle are brought to a
brilliant focus by means of the condensing or bull's-eye lens ; which
focus is directed upon the chosen point of observation.

He then saw that the feet were armed with suckers, which enabled
it to fasten itself in the furrows under the skin, aided by the small
bristles ; and being likewise covered by the same in various parts of
the body, it more firmly fixes itself there ; and with its terrible man-
dibles it accomplishes its destructive mission. It has no eyes j but in
the moment of danger it quickly draws in its head and feet, somewhat
resembling the tortoise ; its march is precisely that of the tortoise. It
usually lays sixteen eggs, which are carefully deposited in furrows un-
der the skin, and ranged in pairs ; these are hatched in about ten
days.

No. 4, Plate XL, Demodex folliculorum, is another very remarkable
parasite found beneath the skin of man : it may be obtained from a
spot where the sebaceous follicles, or fat glands, are very abundant ;
such as the forehead, the side of the nose, and the angles between the
nose and lip j if the part where a little black spot or a pustule is seen
be squeezed rather hard, the oily matter accumulated will be forced out
in the globular form and various stages of growth, as represented in the
drawing ; if this be laid on a glass-slide, and a small quantity of oil be
added to it, so as to separate the harder portions, the little insect in all
probability will be floated out j after the addition of more oil, it may
be taken away from the oily matter by means of a fine- pointed sable
pencil-brush, and transferred to a clean slide, where it may be covered
over with thin glass, and mounted in the usual way.

The Cheese-mile, Acarus domesticus (Plate XI. No. 2), has a peculiar
elongation of its snout, forming strong, cutting, dart-shaped mandibles,
which can be advanced separately or together. Their legs are brown. All
indeed present a great diversity of form, size, and colour ; and in the
cheese-mite we observe the peculiar adaptation of form and apparatus ne-
cessary for cutting its way into or through the food on which it is destined

AC ARINA— PARASITES.

331

to exist. Mites multiply very rapidly ; they are hatched from eggs in
about eight days ; and if deprived of food, will kill and eat each other
very greedily. They infest almost the whole of our dried articles of
food. The parts of the mouth and legs of these acari can be best made
out by crushing the animal upon a glass slide, with a thin glass cover ;
then washing away the exuded substance with water — sometimes a hot
solution of potash is requisite, with the subsequent addition of acetic
acid and washing ; after drying, mount them in Canada balsam.

The Acarus saccJmri, or Sugar Insect. — There is very commonly
present in the more impure kinds of sugar a beetle-like animalcule of
the genus Acarus. The discovery of the very general presence of this
acarus rests, we believe, entirely with Dr. Hassall.

The sugar acarus approaches somewhat, in organisation and habits,
the louse and the itch-insect ; it is in size so considerable, that it is
plainly visible to the unaided sight. 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 animalcules will be found, some on the
surface of the liquid, some adhering to the sides of the glass, and

fig. 153.

Ova and young of the A cams sacchari, or Sugar-insect, after Hassall,
magnified 200 diameters.

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 subsides on the solution of even a small quantity of sugar
in water.

We will now proceed to give a description of the acarus in question,

332

THE MICROSCOPE,

and observe, in the first place, that the whole of its development may
be clearly traced out in almost every sample of brown sugar. The

Acarus sacchari is first visible as a
rounded body, or egg ; this gradu-
ally enlarges, and becomes elon-
gated and cylindrical, until it is
about twice as long as broad ; after
a time, from the sides and one ex-
tremity of this ovum the legs and
proboscis begin to protrude. These
stages of the development of the
acarus are exhibited in fig. 158.

The Acarus farince, or Flour-
mite. — This is of occasional occur-
rence in flour, but is never present
unless it has become damaged.
Any flour, therefore, containing
the insect in question 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 Graminece.

This acarus differs considerably
in structure from the sugar-mite,
and particularly in its pennate setee.
fig. 159. Acarus farince, or Meal-mite, Dr. Burnett established to his

magnified 250 diameters. satisfaction the following facts : « 1 .

That although there are single species of parasites peculiar to particular

fig. 160.
Larva of Parasite of Hornlill.

fig. 161.

1. Hippolosca Hirundinis.

2. Nirmi, parasites infesting the Swallow.

ACARINA — PARASITES.

333

animals, there are others which are found on different species of the
same genus ; as is the case in the parasites living on birds of the genus
Larus (gulls), and the diurnal birds of prey. 2. The parasites of the
human body confine themselves strictly to particular regions ; when
they are found elsewhere, it is the result of accident. Thus, the Pedi-

fig. 162.

1. Parasite of Turkey. 2. A cams of common Fowl, under surface. 3. Parasite of
Pheasant. The small circles enclose each object about life size.

culi 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. inyuinalis about the groins, armpits, mouth, and eyes."
From an examination of the structure of these animals, Dr. Burnett is
of opinion that they should be placed in an order by themselves, closely
allied to Insecta ; the mandibulate parasites occupying the highest, and

334

THE MICROSCOPE.

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 Dr. Robins,
found spinning a white silky web on the base of the sparrow's thigh,
or on the fore-part of its body ; on raising this delicate web, you per-
ceive 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

fig. 163.

1. Acarus of Beetle. 2. Acarus of Fly. 3. Acarus of Clothes-Moth.
The circles enclose the objects about life size.

annoy. In fig. 160 are seen some eggs of a parasite infesting the horn-
bill j they were glued to the feathers near the head of the bird. The
insect is nearly ready to leave the egg. Another, curiously enough,
selects the pulmoiiic orifice of the snail : when the animal dilates this
orifice, for the purpose of allowing the air to penetrate its respiratory ca-

ACARINA PARASITES.

335

vity, the female acarus slips through it, lays her eggs in the folds of the
mucous membrane, where they are gradually developed ; issuing forth
from the egg, they select some portion of the snail's body upon which
to feed and perfect their growth.

The Ixodidce are furnished with a powerful rostrum, armed with
recurved spines, with which they pierce the skin of the unfortunate

fig. 164.

1. Parasite of Eagle. 2. Parasite of Vulture. 3. Parasite of Pigeon.
The circles enclose the objects of about life size.

animals upon whose blood they live. So firmly does this anchor-like
organ retain its hold, that if the parasite be 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 attach themselves exclusively to serpents and

336 THE MICROSCOPE.

other reptiles. The animal known as the Harvest-bug, which is often
so troublesome in summer and autumn, also belongs to this group.
The Gamaside, which are furnished with a sucking apparatus very
similar to that of the Ixodidce, usually attach themselves to the bodies
of beetles ; the common Dung-beetles (Geotroupes) may often be found
with the lower surface nearly covered with them.

The remainder generally lead a more active life, and are always
furnished with eyes. One family, the Hydrachnidce, or Water-mites,
inhabit the water, where they swim about with considerable rapidity
by means of their fringed legs. In their young state, they attach
themselves parasitically to aquatic insects ; they then possess only six
legs, and pass through a quiescent or pupa state before acquiring the

fig. 165. The Sheep-tick. The small circle shows one of life size.

fourth pair. The Oribatidce — which, unlike the other Acarina, live
upon vegetable matter, principally the leaves of mosses, — are covered
with a hard and very brittle skin, and have the mouth adapted for
biting. The Bdellidce, which live amongst damp moss, have the body
divided apparently into two parts by a constriction, and the rostrum
and palpi very long ; whilst the Trombidiidce, of which the little Scarlet
Mite so often seen in gardens is an example, have the palpi converted
into little raptorial organs.

PREPARATION OF INSECTS. 337

Another family of parasites are commonly met with in the bodies
of fishes, attaching themselves to the branchia, to the soft skin under
the fins, or to the eyes, much to the annoyance of the unfortunate vic-
tim. Some of those found on fresh-water fish are sufficiently transparent
to show the circulation of their fluids — a most interesting sight.

The water-snail, Liinneus, is infested with a parasite of the family
Clepsinidce, which attaches itself by a series of hooklets and bristles to
such parts of the body and mantle as give a secure lodgment to it ;
they look like little tufts of thread hanging from the sides of the ani-
mal, without its having the power to dislodge them,*

We have before referred to Swammerdam's careful dissections
under the microscope. In no department of nature did he bestow more
care than in his many examinations of insects. He first killed them
by immersion in spirits of wine and water, or in spirits of turpentine ;
preserving them for some time in the same fluid, to give firmness, and
render his dissections more easy. When he had divided the insect
transversely with his fine scissors, he particularly noted the relative
position of the various parts, and then proceeded to remove the viscera
very cautiously with fine-pointed instruments, carefully washing away
all the fat and other matters with fine camels'-hair pencils ; or, by
putting the whole into water and then shaking them gently, he se-
parated the air-vessels, or trachsea, in a perfect state from the other
parts. At other times he made use of a very fine syringe to inject water
into and thoroughly cleanse them j after which they were distended by
blowing in air, and hung up to dry. He is said to have often suc-
ceeded by immersing insects in balsam. Again, he frequently made
punctures in some insects with a fine needle, and after squeezing out
all their moisture through the holes made in this manner, he filled
them with air by means of very slender glass tubes, then dried them in
the shade, and afterwards anointed them with oil of spike in which a
little resin had been dissolved : those prepared in this way retained
their forms and kept well for years. Swammerdam discovered that
the fat of all insects was perfectly soluble in spirit of turpentine ; after
steeping them in it, he washed them well in water, and was thus en-
abled to show the viscera plainly. He frequently spent whole days in
thus cleansing a single caterpillar of its fat, in order to discover the
structure of its heart. His singular mode of stripping off the skin
of the caterpillar, just as it was on the point of spinning its cone, was

* A very interesting account of the parasite tribes is given in Rhedi's Treatise de
Generatione Insectorum, and in H. Denny's Monographia Anoplurorum Britannia?,
Bohn, London, 1842.

Z

338 THE MICROSCOPE.

effected by taking hold of its thread and letting it drop into scalding-
water, and then suddenly withdrawing it : the skin easily peels off.
After this it was put into distilled vinegar and spirits of wine mixed in
equal proportions; this gave a firmness to the parts, and the exuvia or
skin readily separated ; the pupa is then seen to be enclosed, and the
butterfly traced in the pupa.

Parasites may be quickly killed by immersing them in spirits of
wine or spirits of turpentine ; in a short time take them out, and dry
them ; if transparent, they may be at once mounted in glycerine or
Goadby's solution : if opaque, they must be mounted in Canada
balsam.

TRANSFORMATION OF INSECTS.

The metamorphoses of the insect race offer some of the most
curious and wonderful of nature's phenomena for 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 inhabitants of the heavens
than such worms as they were in their former state. This trans-
formation is so striking and pleasant an emblem of the present, inter-
mediate, 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 original."

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 per-
fection, that there are many intermediate degrees, the result of which
is one universal chain of being, no one can for a moment gainsay. Thus
the angel Raphael 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

JSach to other like, more than on earth is thought !"

The great class of insects, which furnishes four-fifths of the existing

TRANSFORMATION OF INSECTS. 339

species of the animal kingdom, has two chief divisions. In the one,
the Ametabola, we have an imperfect, 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 Metabola correspond,
as it were, to the flowering plants ; the Ametabola to the Cryptogamia.
It is well worthy of remark, that among plants the Cryptogamia, and
among insects the Ametabola, first appeared on our earth. The most
ancient forests, composed of tree-ferns, club-mosses, and equisetse, were
inhabited by Locustce and Blattce, the first insects. " There have not
yet been found," says Professor Heer, in his History of Imects, " in the
carboniferous and triassic rocks any traces of insects that can be with
certainty referred to any of the other insect orders."

The degree of this metamorphosis is, however, very different in dif-
ferent 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 caterpillars, grubs, and maggots. Dur-
ing this period of its existence the whole business of the insect is eating,
which it usually does most voraciously, changing its skin repeatedly 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. Pupae of this
description are sometimes enclosed within the dried larva skin, which
then 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 metamorphosis is one of the
most remarkable phenomena in the history of insects, and was long

340 THE MICROSCOPE.

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 ap-
pearing first as a soft worm-like creature, crawling slowly along, and
devouring every thing that comes in its way, and then, after an inter-
mediate 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 most delicate fluids of the vegetable kingdom,
is a spectacle that must be regarded with the highest interest; especially
when we remember that these dissimilar creatures 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 may be, in point
of organisation, there are few insects that exceed them in commercial
importance. The finest red dyes known to our manufacturers are de-
rived from these creatures. The Lecanium Ilicis, which inhabits the
Ilex or evergreen oak of the countries round 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 Porphyrophora polonica, which lives on the roots of
the Scleranthus perennis in Central Europe, was much used for the
same purpose. The Mexican cochineal, which has driven the others
out of the field, is also a species belonging to this group, the Coccus
cacti (fig. 139), which lives as a parasite upon the Nopal, or Cactus
opuntia — a plant very common in Central America. The commercial
importance of this insect is shown by the fact, that in 1850 no less
than 2,514,512 Ibs. of cochineal were imported into Great Britain
alone (value about 7s. per Ib.) ; and as about 70,000 insects are sup-
posed to be contained in a pound of this substance, we may form some
idea of the numbers annually destroyed. For many years the culti-
vation of cochineal was entirely confined to Mexico ; but the insect has
lately been introduced into Spain and the French possessions in Africa,
with some prospect of success. A fourth species, of great importance,
is the lac insect (Coccus lacca), an inhabitant of the East Indies, where
it feeds upon the Banian-tree (Ficus religiosa), and some other trees.
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. wrere imported
iii 1850, but also for the well-known substance called shell-lac, so

IMPORTANCE OF INSECTS. 341

much used in the preparation of sealing-wax and varnishes. In all
these cases it is only the female insects that yield the colouring
matter.

Of the secretions peculiar to insects silk may well be regarded
as the most valuable, since it has become nearly as essential to our
own purposes as it is to the economy of the producers of it. The
vessels which secrete it consist of two tubes ; these unite at the ex-
tremity, and open into a small perforated filiform organ, placed
between the palpi on the under lip j this is termed the spinnaret,
and the size of its aperture determines the thickness of the thread.
The fluid, before it comes in contact with the air, is viscous and trans-
parent in the young larva, but thick and opaque in the mature ones.
It is found, by chemical analysis, to be chiefly composed of Bombic acid,
a gumrny matter, a portion of a substance resembling wax, and a little
colouring-matter. It may be placed in boiling water without under-
going any change ; the strongest acids are required to dissolve it ; and
it has never yet been imitated artificially. More than 500,000 of human
beings derive their sole support from the culture and manufacture of
silk ; and upwards of 200,000^. may be said to be annually circulated
by the silk- worm. Then we have large sums of money changing hands
from the labours of the useful little bee j tons weight of honey and wax
are yearly consumed ; England pays more than 50,0001. for foreign
honey and wax, besides her own produce. A great variety of scents,
which from their agreeable odour are much used in perfumery, are
manufactures from insects. The Spanish Fly is absolutely indispen-
sable in the treatment of certain forms of disease; and that invaluable
agent, chloroform, was first produced from Formic acid ; this acid
was discovered in the Formic-ant, from which it derives its name.
Then there are the Gall-nuts, produced by a small fly, so useful in
dyeing, ink-making, &c.

" 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 car-
rion 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 waters by the innumer-
able insects which usually inhabit them. We have witnessed ample

342

THE MICROSCOPE.

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." Episodes of Insect Life.

" The shapely limb and 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."

»***

fig. 166.
Pupa of Hawk- Moth. Excrescences on oak-leaf produced

CHAPTER VI.

ANIMAL STRUCTURE.

PHYSIOLOGY HISTOLOGY — CELL THEORY — GROWTH OF TISSUES —

SPECIAL TISSUES SKIN, CARTILAGE, TEETH, BONE, ETC.

'HE most complicated state in which matter ex-
ists, is where, under the influence of life, it
forms bodies with a curious internal struc-
ture of tubes and cavities, in which fluids
are moving and producing incessant internal
change," says the philosophic Dr. Arnott.
These are called organised bodies, because
of the various organs which they contain \
and they form two remarkable classes j the
individuals of one of which are fixed to the soil, and
are called vegetables, — of these we shall consider the
structure at a future stage j the individuals of the
other are endowed with power of locomotion, and
are called animals : it is some of the peculiarities and
minute structure of this latter class that we are now
about to examine. The phenomena of growth, decay, death, sensation,
self-motion, and many others, belong to life ; but, from occurring ali
in material structures, which subsist in obedience to the laws of phy-
sics and chemistry, the life is truly a superstructure on the other two,
and cannot be studied independently of them. Indeed, the greater
part of the phenomena of life are merely chemical and physical pheno-
mena, modified by an additional principle. The phenomena of life,
from thus involving generally the agency of all the sets of laws, are by
far the most complex of any ; and the discovery or detection of the
peculiar laws of life, although they are fixed as the laws of chemistry
or physics, has been very slow, and is as yet far from being completed.
The study of the Science of Life, or the building up of the living

344 THE MICROSCOPE.

structure, is termed Physiology, or Biology ;* and that part of it more
particularly relating to the minute structure of the organs of animals
has been termed Histology.^ It is generally divided into animal and

DESCRIPTION OF PLATE XII.— ANIMAL STRUCTURES.

No. 1. a, Simple isolated cells containing reproductive granules ; b, mucous mem-
brane of stomach, showing cells, with the open mouths of tubes at the bottom of each,
magnified 50 diameters.

No. 2. 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 sub-
mucous tissue. The upper surface of one villus is seen covered with cylindrical epi-
thelium ; the other is denuded, and with the dark line of basement membrane only
running around it. b, epithelium scales, separated and magnified 200 diameters ; in
the centre of each is a nucleus, with a smaller spot in its interior, called the nucleolus.
c, pavement epithelium scales, from the mucous membrane of the bronchial or air-
tubes of the lung, showing nuclei, with double nucleoli in some, 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.

No. 3. a, is one of the tubular follicles from a pig's stomach, cut obliquely to dis-
play the upper part of its cavity, and the cylindrical epithelium forming its walls, with
a few of them detached, to show their true form ; and at the lower part, the nucle-
ated extremities of the cylinders of epithelium are seen. No. 3. b shows a section of
the lymphatics, and capillary blood-vessels, distributed beneath the mucous surfaces ;
the lymphatics take their origin from the radiated cells.

No. 4. Cells of adipose tissue, or fat, magnified 100 diameters.

No. 5. A single fat-cell separated, and magnified 250 diameters.

No. 6. A capillary of blood-vessels distributed in the fat-tissue.

No. 7. Section^ of the tendo-Achillis as it joins the cartilage, showing the stellate
cells of tendon gradually coalescing to form the round or oval cells of the cartilage.

No. 8. A vertical section of cartilage, with clusters of cells arranged in columns
previous to their conversion into bone, which is seen condensed at the upper surface.
The greater opacity of this portion is owing to the increase of osseous fibres, the
opacity of the cell-contents, and the multiplication of the oil-globules ; the dark inter-
cellular spaces become filled up with vessels.

No. 9. A small transverse section of the same, showing the gradual change of the
cartilage cells at a into the true bone-cells termed lacunce, at b} with their character-
istic canaliculi.

No. 10 is a stellate nerve corpuscle, with tubular processes issuing from them : at a
it is filled with corpuscles containing black pigment, above which is a corpuscle in the
nucleus of which is seen nucleoli ; at & is a corpuscle enclosed within its sheath, and
filled with granular matter : this is taken from the root of a spinal nerve.

No. 11 shows the continuity of muscle, the upper portion, with connective tissue ;
the lower portion, from the tongue of a lamb.

No. 12. Branched muscle, ending in stellate connective cells, from the upper-lip of
the rat.

No. 13. Black pigment-cells from the human eye, lining the internal surface of the
eye, magnified 150 diameters.

* From jStos, life, and \oyos, discourse — a discourse on life ; a more expressive
term than physiology.

•f From to-ros, a tissue or web, and \oyos, a discourse.

PLATE XII.

ANIMAL STRUCTURES.

ANIMAL STRUCTURE. 345

vegetable life. Bichat terms it organic life and relative life. In organ-
ised beings, the way in which nature works out her most secret pro-
cesses is by far too minute for observation by unassisted vision ; even
with the aid of the improved microscope, only a small portion has, up
to this time, been revealed to us. To point out in detail the disco-
veries made through the employment of this instrument, as regards
physiology, would be to give a history of modern biological science j
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 ex-
tremities on pressure. In looking at a muscle, it appears to be made
up of fine longitudinal fibres only. The microscope tells us that each
of these supposed fine fibres is composed of numerous smaller ones,
and that these are crossed by lines which have received the name of
transverse strite ; that muscular contraction, the cause of motion in
animals, is produced by the relaxation or approximation of these trans-
verse striae.

The microscope has shown us that a distinct network of vessels
lies between the arteries and veins, partaking of the properties of nei-
ther, and possessed of others peculiar to themselves. These have been
denominated intermediary vessels by Berres, and serve to connect the
arterial with the venous system.

On regarding with the naked eye the different glands in which the
secretions are formed, how complex they appear, how various in con-
formation ! The microscope teaches us that they are all formed on
one type ; that the ultimate element of every gland is a simple saccu-
lated membrane, to which the blood-vessels have access ; and that all
glands are formed from the greater or less number, or different arrange-
ment 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 iuhalent
muscular apparatus, and so on. All our knowledge of epidermic struc-
tures, such as hair, horn, feather, &c., the real structure of cartilage,
bone, tooth, tendon, cellular tissue, and, in a word, of all the solid tex-
tures, 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

346 THE MICROSCOPE.

our acquaintance 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 diagnosis of diseases, which in many cases were overlooked
or undistinguishable without the assistance of this instrument. It is
on this account constantly resorted to by the medical profession for the
benefit of their fellow-creatures.

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, enumerating 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; now admitted to be, and indeed
demonstrable as, the common centre alike of the animal and vegetable
organism.

THE HUMAN BODY, ITS PHYSIOLOGICAL COMPOSITION AND
CHARACTER.

The elementary 'substances found in the human body are oxygen,
hydrogen, carbon, azote, phosphorus, sulphur, chlorine, fluorine, iron,
manganese, titanium, and lime. Silinium is found in the hair, and
flourine in combination with lime forms the enamel of the teeth. Iron
is the colouring-matter of the blood, the black pigment of the choroid
of the eye, and in the skin.

Manganese is found in the bones, hair, blood ; titanium in the
salts from the supra-renal capsule. Other substances and gases are
found distributed throughout the body.

Azotised and now-azotised substances constitute the proximate or-
ganic principles. The azotised are, protein and its compounds, albu-
men, fibrin, casein, and pepsin ; extractive matters, gelatin, hsematin,
colestrin or bile matters, urea, and uric acid. The now- azotised are,
lactine, or sugar of milk, and fatty matters.

Cells. — All animal and vegetable structures, it has been found by
microscopists, are developed from cells ; the materials for these in ani-
mals are furnished from the yelk and the blood.

A nucleated cell, 1 a, Plate XII., is a delicate membrane of a glo-
bular form, enclosing a granulous fluid j in the wall on one side is a
dark oval body— this is the nucleus : there are one or two, seldom

CELL FORMATION. 347

more ; these enclose what are 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 l-3000th of an inch in diameter ; the
nucleoli are 1-1 0,000th of an inch in diameter, more or less.

The wall of a cell is chemically different from the nucleus ; for if
treated with dilute nitric acid, the wall is dissolved, and the nucleus
unaffected, so that we can in this manner isolate the nucleus. It is
not known whether there exists any chemical difference between the*
latter and the nucleolus ; and it is probable that the nucleolus is a
space in the nucleus containing a fluid.

The elementary cell is imbedded in an amorphous matter, which is
termed cytoblastema, and is a fluid of greater or less consistence ; so
that in one case the cell may float, and in the other it may be im-
bedded. The matter between the cells is called intercellular substance.
Cells differ in their contents, which implies a difference in their walls,
inasmuch as they secrete the interior.

The nucleolus was first discovered by Robert Brown in plants, and
its use made out by Schleiden. He discovered that the nucleus was
formed before the cell, and the latter was formed around it. After
this cells of different kinds were found in animals ; and Schwann
collected many instances, showing that animal and vegetable tissues
were developed from cells : this was an important generalisation.

The mode of origin of the nucleated cell is this : cytoblastema first
exists ; in it is developed the nucleus, and around the latter is formed
the membrane of the cell from matters drawn from the cytoblastema.
The way in which the cell itself is formed is this : around a granule
we have a deposit forming a nucleolus ; round it again is formed the
nucleus ; a swelling of this membrane takes place, and is situated
over the others like a watch-glass, and thus the exterior cell is
formed. Coalescence of the granules forms a nucleus, and in the inter-
stices between these we find a fluid which is thought by Henle to form
the nucleoli. It has been observed, that a globule of oil in contact
with a small quantity of albumen drew from it a thin coating, which
enveloped the globule of oil ; and this albumen became coagulated, form-
ing a cell. When this globule was so surrounded, the coating became
wrinkled ; but when placed in contact with water it became distended,
thus proving it to be capable of endosmosis, or more probably an ab-
sorption of water by the wall of the cell, which consequently became
distended or swollen up, as there is no attraction between oil and
water. Nevertheless, elementary granules appear to be granules of
oil, surrounded by a covering of a protein compound. Milk globules.,

348 THE MICROSCOPE.

being composed of oil, surrounded by a covering of casein and dis-
solved fibrin, have been shown to attract a covering of albumen.

In this way the chyle, for instance, is taken as food into the
body. The chyle is composed of protein compounds and fatty mat-
ters, which are reduced to a pulp by the digestive process ; the pro-
tein compounds being converted into albuminous matters. The villi
throughout the intestinal canal are permeable to these fluids ; the oily
particles meeting with a protein compound, are attracted to them, form-
ing a covering; and so an elementary granule is formed. In their sub-
sequent development, cells, when fully formed, never lose their cha-
racter as cells while they exist ; but they may dissolve other cells before
they are changed into certain tissues. Cells may receive additional
parts, which may remain as such, or form tissues ; such are termed
complicated cells: nerves and muscular fibre are formed from these.
Examples of cells that undergo no further metamorphosis after ful]
development are found in the cells of the epithelium, epidermis, and
in the corpuscles of the blood. The elementary constituents of glands
are cells, and the fluids are absorbed by them : cells are the greal
agents of absorption and secretion.

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. Glandular structures 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 Wharton Jones calls endosmotic, or retentive mem-
brane. We may have the cells coalesce to form a filament or fibre.
The nucleus may disappear, or form another structure. Where rege-
neration of tissue is proceeding, there is found a larger number oi
granules.

Multiplication of Cells. — Cells may be formed in cytoblastema inde-
pendent of any pre-existing cells : this is indeed an instance of that
mysterious agency designated spontaneous generation. As an example
of independent formation, we may instance the epithelium and epider-
moid cells, corpuscles of the blood, and other juices of the body. Cells
are formed from cells in three ways. First, there is gemmiparous
generation, that is to say, sprouts occur from previous cells and be-

CELL FORMATION. 340

come detached, forming in their turn cells ; this is also termed exogenous
generation, inasmuch as the process takes place from the exterior.
Endogenous generation is the second mode, and by it is meant that
one cell is formed within the body, as it were, of the parent cell.
The third manner is denominated fissiparous generation, and is where
one cell becomes constricted, and eventually, at the point of constric-
tion, divides into two. Of these three kinds or modes of multiplica-
tion, one only is found to occur in animals — it is the endogenous. The
exogenous is only seen in the lowest plants. Fissiparous generation
occurs in vegetables, and has been supposed by some to occur in
animals also. The most striking example of endogenous generation
that can be adduced, is that which takes place in the ovum of animals
or birds. The first part formed of the ovum is the germinal cell, in
the centre of the yolk ; this approaches the surface, is dissolved, and
there is then developed a new cell, which is called the embryo cell,
from which is generated a numerous progeny ; the contents of these
cells are the cytoblastema to other nucleated cells.

As an instance where cells are not directly derived from cells, but
previously-existing cells exert an influence on those to be formed,
we may instance 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. This change is shown at figs. 8 and 9,
Plate XII. Generally, however, where a part has to be repaired, it
does not seem to determine the generation of a texture similar to
itself — muscle and skin, for examples. 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 c£n transmit 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. Cells may retain an
independent existence, although changes may take place in their walls
and contents, or they may become eventually dissolved and be succeeded
by new ones. They may change their form, that is, a globular cell may
pass to the compressed form ; and this may arise from the difference
of the contents to the material outside it, as in the corpuscles of the
blood. Flattening of cells may arise from the pressure they exert
upon each other, as, for example, in the cells of the epidermis and the
epithelium. In some cases the cells become so thin, that their thick-
ness cannot be measured. Sometimes, where there is but a single
layer of cells, flattened, the hexagonal form of cell is assumed ; at
other times the polygonal. When a mass of cells compress each other,

350 THE MICROSCOPE.

they take the polygonal form, and have length, breadth, and thickness,
as in the fat-cells of ruminating animals ; this is readily seen in the
fat of beef, but in human fat the round form is maintained. There
may be a single layer of cells so arranged side by side, and presenting
a columnar or basaltic form j this arrangement is seen in the cells of
the intestinal tract, fig. 2 a, Plate XII. Another change of cell is this :
they shoot out processes from certain parts of them, as may be seen at
fig. 10 a, Plate XII. ; this may be found also in the choroid plexus,
on the inner surface of the sclerotic coat of the eye, or lamina fusca,
as it is called. The cylindrical form of cell is found with delicate
processes shooting out from the broad end ; these are called ciliated,
seen at fig. 2 b, Plate XII., and the cilia are endowed with the power
to move spontaneously, having a vibratile motion, intended to urge on
the secretions of the part in a particular direction.

Change of the Nucleus. — The nucleus may undergo a change; it
may be smooth, round, compressed, like the cell to which it belongs ;
it may disappear altogether, and the cell which contained it remain.
The corpuscles of the blood and the epidermic scales in the last
stage of development are examples. The contents may change with
the membrane itself. Some cells are filled with a granulous matter,
others with pigment, or colouring-matter, as the cells of the choroid of
the eye. Others, again, become filled with matters which form the
secretions ; the cell-membrane breaking, and pouring out its contents.
The cell-membrane may become so changed, as to be of a horny con-
sistence, not capable of being acted on by acetic acid, as it could have
been before; this is well seen in the last changes of the epidermoid
and epithelium cells.

In some cases the walls of the" cell increase in thickness. Under
the microscope, some cells appear to be composed of concentric la-
minse. In plants this is the common mode of increase in the thick-
ness of the cell, but the deposit does not take place entirely around,
but only here and there, so that vacant spaces are left which form
canals, and may become branched, and these canals are named pore-
canals. They do not perforate the outer layers, consequently the blind
ends are seen through the outer membrane, and were supposed, indeed,
to be apertures ; but they are not so. Henle thinks he has found canals
in such cells in animals, similar to those in vegetables — in the cartilage
of the epiglottis, for instance. Another mode of development is, that
the cells may not remain free and independent, but may coalesce with
each other. Of this there are two modes : the first is, before coalescence
the cell may have attained its full development as a cell ; or secondly,

CELL DEVELOPMENT. 351

when this occurs, the cell may be simply solid plates or cells in a
rudimentary state. The first kind is seen in cartilage ; here the walls
of the cell become increased in thickness and coalesce with each other,
mixing at the same time with the intercellular substance, while the
cavities or vacuolm remain distinct, but are rendered smaller by this
process of deposition. In the second kind, cells coalesce, but their
cavities or vacuolce run into each other : the tubules of some glands are
thus formed. Where the cells touch they coalesce, and the thin walls
dissolving, a single elongated cavity is formed.

Another mode is, the cells may be aggregated, like a bunch of
raisins, and the parts in contact with each other disappear, so con-
stituting a multilocular cavity : examples of this are seen in the
racemose glands. Schwaun 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. Capillary vessels are in this way formed, as shown at
fig. 3 b and fig. 6, Plate XII. 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 cyto-
blastema with similar adjoining substance, constituting a delicate mem-
brane, 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 sur-
rounded 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. Sometimes the nucleus undergoes im-
portant changes in the development of tissues, as well as the cell it-
self. In some cases, where the cells have joined in the linear series,
the nucleus becomes oval, elongated, so that the nucleus of one cell
tends to meet the nucleus of another cell ; they subsequently coalesce,
and thus fibre is formed. That so-constituted filament differs from
that formed by the coalescence of the cells themselves, which is acted
upon by nitric acid, whilst that formed from the nucleus resists it.
The nucleus may be on the exterior of the cell, and sometimes im-
bedded in the wall. As an example of the first, may be instanced the
nucleus of the pigment-cell of the eye, fig. 1 3, Plate XII. If, instead of
the fibre being flat, it is cylindrical, it is formed by the nucleus. When

352 THE MICROSCOPE.

tlie nucleus is outside, the fibres of the cell and those of the nucleus
unite, fibre by the side of fibre. As an example, we have the bone of
the tooth ; in this the fibres of the cell and nucleus alternate. Again,
if the nucleus be arranged externally, it unites across either behind or
in front, and thus a spiral filament is formed : this is seen in cellular
tissue and tendon. The last-described form may alternate with that
described before it, and there are all intermediate shades of difference.
Nuclei sometimes disappear when they are very nearly developed, as in
the cornea of the eye.

Action of Cells. — The subsequent changes of these depend in a
great degree on endosmosis. The nature of the membrane is a neces-
sary condition, for it 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 take common salt and fill a tube with it, and put the
latter in water, we find that the salt rises, from the water having passed
into the tube, and at the same time the water outside is saltish 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 permit of
endosmosis, as pipeclay and chalk, in a low degree ; but sandstone does
not allow of endosmosis at all ; thus proving that there must be some-
thing in the nature of the material to be permeated.

As to the processes of secretion, these depend in a great degree on
endosmosis, inasmuch as the materials are drawn from the blood, and
so thrown off.

Intercellular Substance. — In certain tissues the basis is made up of
a homogeneous matter, granular or fibrous, or of a tissue composed of
cells. The intercellular tissue must be the cytoblastema after the cells
have been formed from it, and differs in quantity in different tissues ;
in some it is very slight in quantity, so that it has been overlooked ;
but still the parts are held together, and this must be by cytoblastema,
which is proved by chemical action. In epithelium and other parts, on
the contrary, it is in great quantity. This intercellular substance is
sometimes formed into fibre, whether it be constituted of cytoblastema
or of cells, and may exist in three conditions : 1st, as a homogeneous
substance ; 2d, as granular matter ; 3d, as fibre. As an example of
the first kind we have the epidermis, and of the second the cellular
tissue. As hyaline membrane it exists in cartilage. In some carti-
lages it is by age developed into fibre, called cartilage fibre — an ex-
ample is that between the vertebra ; for the part in immediate connec-
tion with the bone, Wharton Jones has shown to be true cartilage.

PLATE XIII.

ANIMAL TISSUES.

1. Yellow fibrous, or elastic tissue, taken near a ligament. 2. White-fibrous, or non-dastic tissue.
3. Fibrous tissue, lining the interior of the egg-shell, the lime having been removed by diluted
hydrochloric acid. 4. White-fibrous tissue connecting the Tendons. 5. Muscular fibre, broken
across, the fragments connected by the untorn structureless membrane, or Myolemma, magnified 100
diameters. 0. Muscular fibre, broken up into irregular and distinct bands, with a f-w blood-globules
distributed about, magnified 200 diameters. 7. Muscular fibre, or a fasiculus of muscle taken from
a young pig, magnified 000 diameters.

DEVELOPMENT OF CELLS. 353

Sometimes the spaces between cells have no intercellular substance,
there may be instead fluid or air ; such cavities may present different
forms — they are termed intercellular passages, and are for the con-
veyance of fluid or the passage of secretions : they exist in animals
and vegetables, but are more highly developed in animals. In vege-
tables there are other cells lining these intercellular passages, so as to
form a regular tube, with walls consisting of different coats. Cells
exist in the neighbourhood of these passages, and have shot out pro-
cesses and coalesced to form vessels with similar offsets from other
cells : ultimately these are seen to join the intercellular passages, and
become continuous with them. In glands, the cells being filled with
their peculiar fluid, are conveyed to the wall of the intercellular pas-
sage, 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 mi-
croscope has shown this to be a tissue of high and remarkable organisa-
tion, being, in point of fact, an aggregation of laminated cells, differing,
in different situations, in regard to form, colour, and composition. This
investment serves to protect the delicate structures beneath, and is
likewise a bad conductor of heat, — thus tending to maintain the tempe-
rature of the body ; besides these uses, it answers the purposes of ex-
cretion, and is sometimes an agent of motion. These laminated elemen-
tary cells, found on the surfaces, have generally nuclei. The nucleus is
rounded or of oval form, and is the 1-3000 to 1-5000 of an inch in dia-
meter. Each nucleus has two or three nucleoli, with outlines more or
less irregular; a cell surrounds the whole, which has transparent walls.
The cell varies in this latter arrangement : it may be flattened, and
the nucleus maybe attached to one side of it; or again, the nucleus
may be in the centre, and the cell prolonged at either end. The cells
of the epithelium may be divided into three kinds : the 1st is termed
the tesselated or pavement; 2d, the columnar or basaltic; 3d, the
ciliated or vibratile epithelium. Some make a 4th, combining the tes-
selated and columnar : this may be considered as transition epithelium,
and is found only in certain mucous passages. These cells are repre-
sented in Plate XII., figs. 1, 2, and 3.

Tesselated epithelium is the simplest form, and, as its name
implies, resembles flags of pavement, overlapping each other at
their edges. They assume more or less the polygonal form, and
their size varies in the different serous membranes. The cells of the

A A

354 THE MICROSCOPE.

pericardium, or covering membrane of the heart, are much smaller than
those of the covering membrane of the lungs, or the serous surface
of the cornea, &c. On some surfaces we have many layers ; in the
skin it will be found of comparatively great consistence. If a vertical
section of such be made, and viewed under the microscope, it will be
seen to be composed of numberless layers, as shown in fig. 167. The
skin taken from the sole of the foot, in con-
sequence of the continued pressure there expe-
rienced, presents this distinctly stratified appear-
ance. These layers of cells are held together by
intercellular substance, which exists in quantities
in the epithelium of the mucous membranes; if the
epithelium is taken from these membranes, it is
more easily seen, because the cells are not so closely
aggregated together as in the skin ; therefore a
piece of epithelium from the mouth is recom~
mended for display under the microscope, and by
the addition of a drop of the solution of iodine the
fig. 167. ceijg are still better seen. The cells from serous

and mucous membranes 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, sether, ammonia or its salts,
but they are dissolved by caustic potash, which dissolves the intercel-
lular substance also.

Columnar or cylindrical epithelium, No. 2, a, Plate XII. — The nu-
cleus is generally better seen than in the former kind of cells, although
formed from them. If we examine a portion sideways it appears as
at a, the upper being broader, and the nucleus being midway
between the two extremities. When the cells of the cylindrical epi-
thelium 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, as at c ; and thus
error would creep in ; but we must satisfy ourselves by examining them
sideways, and in various modes. Their chemical composition is the
same, and the cells dissolve in strong acetic acid. As examples of the
situations in which this form of epithelium may be found, we may in-
stance the intestinal tract, along the ducts of the glands, as the liver, &c.
In no situations do we find these two kinds of epithelium terminat-
ing abruptly the one in the other ; but there is a gradual change of the
one kind into that of the adjoining ; as, for example, where the tesse-

EPITHELIAL CELLS. 305

lated epithelium is gradually supplanted by the cylindrical, as it passes
from the sesophagus to line the interior of the stomach. This is termed
transition epithelium.

Ciliated epithelium, No. 2, b, Plate XII. — The cells of this do not
differ materially from those of the cylindrical ; the great distinction
between the two is, that in the former there are 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, and bronchi, 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 j it must at the same time be remem-
bered, that though the epithelium is in close connection with the cutis,
or true skin, it is not a deposit from it, but derives only its materials of
formation and nourishment from it. Cytoblastema is given out from the
blood ; the nucleus is first formed by granules, and around the nucleus
is established the cell-membrane, taking, at the same time, the parti-
cular form of the epithelium to be developed ; and this development is
dependent upon the individual energies of the cell itself, and not the
cutis, whence it derives its nourishing materials. Its uses would seem
to be to protect the delicate cutis from friction and external agents.

The epidermis is destitute of sensibility, yet it invests very sensitive
parts. It is not vascular, but invests very vascular parts. Its exfoli-
ation takes place regularly, as may be exampled in reptiles and the
batrachia, who throw off their skin : the moulting of birds is analo-
gous. 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 when the epithelium cells are
thrown off that the gastric juice is secreted by the tubes of the stomach.

Cilia. — The most remarkable circumstance in connection with cells
is the movement of the cilia : these are delicate processes, microscopi-
cally thin, and square at the end in man generally, but tapering in ani-
mals. These cilia are in constant motion, by them fluids and particles
suspended in fluids are carried along, and in this manner reach the sur-
face. There are three ways in which the cilia ordinarily move : the
rotatory, the undulatory, and the waving, like a field of wheat set in
motion by a steady breeze. No satisfactory explanation has be.en
given of the cause of this vibratile motion. The current produced by
them is from within outwards, in most places ; in the respiratory pas-
sages, on the contrary, it is from without inwards. In the frog's mouth

356 THE MICROSCOPE.

it takes the same course. The ciliary motion may be seen in the kicl-
neyttof the frog or newt ; the cilia in the latter continue in active mo-
tion for some minutes after the animal is dead. A thin section must
be made, with a very sharp knife and care taken to disturb the structure
as little as possible. The section should be moistened with a little of the
serum of the animal, and examined in a glass cell, covered with thin glass.
Pigment. — Pigment granules are found in greater or less quantities
in the skin and bodies of white and dark races.
In the eye there is pigment, and it affords a
good example of nucleated cells, in which are
contained the pigment particles, fig. 168. These
are placed there for an optical purpose, that of
absorbing the rays of light. In the peculiar co-
louration 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
fig. 168. 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 granulous contents of the pigment cells j these are like
ordinary elementary granules, 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 ap-
pearance is produced by the coalescence of the cells and their lying
over each other. This arrangement causes an irridescent appearance of
the section, when viewed with polarised light under the microscope.

Hairs. — The form of these differs in different parts of the body :
some are cylindrical, others flattened. A hair is divided into a body
or shaft, and a root which is in the skin (Plate XIV., No. 2). The
shaft is again divided into two parts : the external is termed the cor-
tical portion, and the internal the medullary portion ; the latter does
not usually exist in the whole length of the shaft. The cortical part
consists of fibres, arranged parallel to each other : besides these there
are, on the exterior, minute scales, like an epithelium ; which are
.arranged like the tiles of a house, and produce the appearance of trans-
verse markings. The fibres gradually expand out, forming a wall to
the bulb enclosed in its capsule. The development of a hair com-
mences at the bottom of the follicle, and by the aggregation of succes-
sive cytoblasts or new cells is gradually protruded from the follicle,

STRUCTURE OF HAIR.

357

both by the elongation of its constituent cells, and 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 rectilineal-
arrangement the hair assumes a fibrous character (see Plate XIV,, No.
2). Of sixteen species of the Bat tribe, the hairs of which have been
examined by Professor Quekett, all were analogous in structure to fig.

fig. 169.

1. Hair from the Indian Bat, magnified 500 diameters. 2. Hair from the Dermestes,
magnified 250 diameters. 3. Hair from the Mouse, magnified 250 diameters. 4.
Pigment cells giving colour to the skin.

169, No. 1 ; and the curious surfaces which these hairs present, are in
reality owing to the development of scales on their exterior. By sub-
mitting hairs to a scraping process, these minute scale-like bodies, toler-
ably constant as regards their size and figure, can be procured ; so that
Bat's hair may be said to consist of a shaft invested with scales, which
are developed to a greater or less degree, and vary in the mode of their
arrangement in 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 in shape those from the wings of butterflies, but are much

358 THE MICROSCOPE.

more minute, and exhibit no trace of striae on their surfaces j but 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, like the quill part of butterflies' scales; and 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 character of the shaft, are better seen
after the scales have been removed.

The hair owes the greater part of its colour to pigment- 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 portion is shown in fig. 169, No. 4,
the vacant space denoting the situation of a lost hair.

Certain parts of the skin and mucous membranes are especially sup-
plied with papillae,
which serve as or-
gans of touch ; ne-
vertheless, through-
out the skin there
are papillae more or
less sensitive ; but

fi -J7Q it is only at the ex-

No. 1. A section of the skin of finger, showing the vascular tremities of the fin-
network ofpapiU.ce at the surface of the cutis. No, 2. Ca- gers, lips, and in a
pillary network and distribution of papilla of the tongue. few other situations,

that these are highly developed, as in fig. 170. Papillae are either fili-
form or tubeform, and have entering into them nerves and blood-
vessels j the former supplying the sensibility of the skin, and termi-
nating in loops, as shown in fig 171.

In Plate XIV., No, 1, we have represented a vertical section of the
skin, drawn under a ^-inch object-glass.

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 pro-
cesses, 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 secieted product.

The sudoriferous or perspiratory glands form small oval or globular

THE SKIN. 359

masses, situated just beneatli the cutis, in almost every part of the sur-
face of the body. Each is formed by the convolution of a single tube,
which thence runs towards the surface, as the efferent duct, making
numerous spiral turns in its passage through the skin, and penetrat-
ing the epidermis rather obliquely ; so that its orifice is covered by a

1

f.1-71.

No. 1. Distribution of the tactile nerves at the extremity of the fingers, as seen in a
thin perpendicular section of the skin. No. 2. Termination of loops of nerve- in
the muscles.

sort of little valve of scarf-skin, which is lifted up as the fluid issues
from it. Mr. Erasmus Wilson says : " To arrive at something like an
estimate of the value of the perspiratory system, in relation to the rest
of the organism, I counted the perspiratory pores on the palm of the
hand, and found 3528 in a square inch. Now, each of these pores
being the aperture of a little tube of about a quarter of an inch long, it
follows that in a square inch of skin on the palm of the hand there
exists a length of tube equal to 882 inches, or 73i feet. Surely such
an amount of drainage as 73 feet in every square inch of skin — assum-
ing this to be the average for the whole body — is something wonderful ;
and the thought naturally intrudes itself, What if this drainage were
obstructed ?"* Could we furnish a stronger illustration, of the neces-
sity for maintaining the skin in a healthy state 1

The oil-glands of the skin are similar in structure to the perspira-
tory ducts, being composed 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 per-
spiratory tubes, they are in some situations spiral ; but this is not a
constant feature ; more frequently they pass directly to their destina-
tion • they are also larger, as shown in the drawing, 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

* Wilson on the Management of the Skin.

360 THE MICROSCOPE.

absent : in a few situations they are worthy of particular notice \ as in
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 clus-
ters 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 have now to consider a cell of a much higher order than any
before referred to ; it is found floating in the animal fluids, and is known
as the blood-cell ; this requires a vascular system of its own for distribu-
tion over the whole of the animal body. The red blood corpuscles have
a rounded form, somewhat flattened; and under the microscope it is
clearly seen that the central portion is hollowed out. Their size is about
1 -3200th of an inch in diameter ; but in consequence of the form of the
corpuscle, the thickness is different at the circumference to what it is
at the centre; in the former situation, it is about the l-12,000th of an
inch in thickness. It is a cell, possessing a biconcave form in conse-
quence of being empty or collapsed. This we can readily understand ;
for when the thick walls of a cell are collapsed, the central portion, in
consequence of the approximation of the sides, appears thin, whilst the
circumference, presenting an edge formed by a fold, must be thicker.
This structure of the corpuscle is further proved to be its condition
from the changes which it is made to assume by the action of re-
agents ; these in some cases produce endosmosis, causing the corpuscle
to become distended, and of a globular form like a cell. Again, re-
agents may cause exosmosis, or a drawing out the fluid from the inte-
rior, and thus render the corpuscle again biconcave.

The wall of the cell is a transparent structureless membrane, and is
of greater thickness than we find the analogous membrane of cells to
be generally. The contents, being thicker than the outer membrane,
and composed of a protein compound, are the colouring-matter consti-
tuting the redness of the corpuscles. The red corpuscles of birds, rep-
tiles, &c., possess a distinct nucleus ; but on examining those of the
human subject and other mammifera, 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
corpuscle from the frog be treated in the same manner, we see a nu-
cleus, and the red colouring-matter is drawn out by exosmosis.

Water causes the corpuscle to swell up, and the colouring-matter

PLATE XIV.

HUMAN SKIN AND HAIR.

1. A vertical section of Epidermis, Human Skin, showing the sweat-glands, surrounded

by the fat-globules, the ducts passing upwards through the epithelial layer to the
external cuticle, magnified 250 diameters.

2. A single Hair, seen near its bulbous extremity, and surrounded by involuntary

muscular fibre.

3. A portion of involuntary muscular fibre isolated, and magnified 350 diameters.

BLOOD CELLS. 361

disappears ; but its real nature is masked ; upon employing a drop of
solution of iodine the wall becomes tinged, and is made distinct.

The cells themselves have a tendency to undergo spontaneously cer-
tain changes : one of the most common is a wrinkling up of the walls,
with a surface somewhat like that of a mulberry ; this may also be pro-
duced by mechanical pressure, 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 -2500th 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; some-
times a clear spot is seen on ope 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 used
to be considered the natural state of the nucleus, the particles of which
were either tending to unite with one another, or there was a separation
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, the corpuscles
aggregate themselves together like rolls of coins, fig. 172, JSTo. 3,
which present 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 elasticity, contracts more and more, and a yellow fluid called
serum is pressed out, — or, in other words, the components of the liquor
sanguinis, with the exception of the fibrin; and only a shrunken, jelly-
like mass remains.

The blood corpuscles of the lower animals were formerly much
studied. In the blood corpuscles of birds, and animals below them,
there are nuclei ; but the cells, instead of being round, as in the hu-
man subject, are elliptical and larger. The corpuscles in mammifera
in general are like those of man in form and size, being a little larger
or smaller. The most marked exception is in 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 the l-2000th 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 exception in regard

362

THE MICROSCOPE.

to form is in the camel-tribe, where they are oval, and resemble those
of the oviparous vertebrata ; those of the frog are shown in fig. 172,
No. 2. In the proteus, they are of a much larger size than in any
animal, being the l-400th of an inch in the longest diameter ; in the
salamander, or water-newt, 1 -600th ; in the frog, l-900th ; lizards,
l-1400fch; in birds, l-1700th ; and in man, the l-3200th of an inch.
Of fishes, the cartilaginous have the largest corpuscles ; in the gold-
fish, they are about the 1-1 7 00th of an inch in their longest diameter.
The large size of the blood-disks 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 determined with certainty. Among

fig. 172.

1. A portion of the web of a frog's foot, spread out and slightly magnified to show
the distribution of the blood-vessels. 2. A portion of same highly magnified,
showing the ovid form of the blood disks in the vessel, beneath which a layer of
hexagonal nucleated epithelium-cells appear. 3. Human blood-disks, magnified
200 diameters, as they appear when fresh drawn.

other facilities which this occasions, is that of procuring their separa-
tion from the other constituents of the blood ; for they are too large to
pass through the pores of ordinary filtering-paper, and are therefore
retained upon it after the fluid part of the blood has flowed through,

A new and very interesting subject has lately been noticed — the
production from the blood, under certain circumstances, of red albumi-

BLOOD CRYSTALS. 363

nous crystals, — which, though formed of animal matter, and sometimes,
in all probability, during life, have forms as regular as any inorganic
crystals.

Various authors, Sir E. Home, Scherer, and others, described reddish
crystals in blood which had been effused into tissues or organs j but
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 cor-
puscles are seen to undergo a sudden change : a few corpuscles dis-
appear, 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 en-
able 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 the form of rhombic plates.

Dr. Garrod discovered, that by a slow evaporation of portions of
the serum of blood taken from patients labouring under gout, he
could obtain strings of crystals of uric acid : this may prove of great
value as a diagnostic sign of this disease. His mode of proceeding is
to pour a little serum into a watch-glass, and add a few drops of acetic
acid ; place in this mixture a few very fine filaments of silk or tow,
and stand it by for twenty-four hours under a glass-shade. Upon
removing and submitting the filaments to microscopical examination,
they will be seen to be studded with minute crystals of uric acid.

No. 1, fig. 172, the foot of the frog
is stretched out, to show the distribu-
tion 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

c ,-, 7 , -, M ,, Head of Long -eared Bat. Plecotus

or wing of the long-eared oat, as first Auritus.

pointed out by Wharton Jones.

The circulation in the foot of the frog and the tail of the newt is,
for the most part, the capillary circulation. 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

364

THE MICROSCOPE.

terminate and the minute veins commence cannot be exactly defined :
the transition is gradual; but the intermediate network is so far peculiar,
that the small vessels which compose it maintain nearly the same size
throughout ; they do not diminish in diameter in one direction, like
arteries and veins; hence the term capillary, from capillus, a hair.
(Fig. 175.) The size of the capillaries is proportioned in all animals to
that of the blood corpuscles; thus, amongst the reptilia, where the
blood corpuscles 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

fig. 174.

1. Blood-vessels of the Eye ; back view of the Iris and ciliary processes. 2. Vessels of
the membrana pupillaris from the eye of a Kitten. 3. Fibres or tubes from the
lens of the Ox.

the tissues of one and the same animal ; for if we examine and care-
fully measure in the human subject their sizes in different tissues, we
shall find that they vary greatly even in individual tissues ; and, at a
rough estimate, examples may occur as large as a thousandth, whilst
others are so small as the four or five-thousandth of an inch. They
should be measured, if possible, in their natural state ; when injected,
their size is slightly increased ; but when dried, they diminish so con-
siderably, that in some specimens vessels imperfectly filled with injec-
tion have been known to shrink from the three to the twenty-thou-
sandth of an inch.

We here digress for the purpose of saying a word or two on a
popular belief; that the precious organ of vision is liable to injury
from using the microscope. We have taken some trouble to look
through the records of a large hospital devoted to diseases of the eye,
and have likewise made many inquiries amongst microscopists, and
can come to no other conclusion, than that such a belief is without
foundation ; the eye, on the contrary, which may be most used in
making microscopic examinations, becomes the strongest and best.

CAPILLARIES.

365

It is perfectly natural to believe that this would be the result ; know-
ing, as we do, that every organ of the human body is both improved
and strengthened by careful cultivation. With our many excellent
contrivances for moderating the intensity of artificial light, when em-
ployed, there is, indeed, but small risk of injury to the eye.

Capillaries are, with very few exceptions, always supported by an
areolar network, which serves not only as an investment to them, but
connects them in timately with the tissues they are destined to supply.

No. 1 represents the fine network of air- tubes that supply the lungs with air.
No. 2 the network of capillaries for conveying blood to the lungs.

There is a possibility, in first examinations, of mistaking or con-
founding capillaries with nerves, especially if the part under observation
should have been left for some time in the strong preserving or alka-
line solutions in the act of cleansing. A weak solution of caustic soda,
and also another of acetic acid, are both made use of : the first is more
generally available for the purpose of discovering nerves ; the latter in
tracing out vessels, structure of papillaB, unstriped muscle, &c. ; inas-
much as it renders their nuclei more obvious, while soda makes them
less so. It is very useful sometimes to use these re-agents alternately ;
and the rule is, to apply them to the object while under the microscope,
BO as to watch their gradual operation.

It is not in the blood alone that cells float in a fluid ; the chyle and
lymph are but colourless corpuscles, flowing along their especially-
adapted ducts and tubes, and carrying the nutritive particles gathered

366 THE MICROSCOPE.

from the food to the blood-vessels, for the reparation of the framework
or growth that so incessantly goes on in the animal body. In Plate
XII. No. 3 b is shown the arrangement of the chyliferous tubes, with
their corpuscles enclosed in a structureless membrane.

And thus we shall find that all the tissues most actively engaged
in the maintenance of the vital functions of the human body are per-
formed by these cells or globules, varying in size from infinite mi-
nuteness to forms visible to the unassisted eye ; that one system
of cells secretes the bile, another the fat, another the nerve-matter,
and so forth. But how these special products are formed by cells
apparently of similar organisation, we know not. Whether the
special endowment belonging to the system of cells of a particular
organ depends on the intimate structure of the wall or tissue of such
cells, and this structure be so attenuated and infinitesimal as to
elude our observation, or whether it results from the transmission
of some peculiar modification of that mysterious vital force we term
nervous influence, are questions to which no satisfactory reply can be
given.

Mr. Huxley has ascertained, 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 histo-
logical 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 dis-
appear ; 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 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 chemical and morphological
metamorphoses in consequence of which specific tissues arise. The
differences between the two kingdoms are mainly, firstly, That in the
plant the endoplast grows, and, as 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 periplastic substance in each case.

A CLASSIFICATION OF THE ANIMAL TISSUES. 367

A CLASSIFICATION OF THE ANIMAL TISSUES.

Professor Schwann's classification of the fundamental tissues of the
human body is that generally adopted, more than half of which tissues
are formed out of the cellular or simple membranes.

1. Simple membrane : employed alone "1 Examples : Walls of cells, capsule of

in the formation of compound y lens of the eye, sarcolemma of muscle,

membranes ..... J &c.

"I Examples : White and yellow fibrous

2. Fibrous tissues L tissue, areolar tissue, elastic tissue,

J &c.

3. Cellular tissues I ExamPles : Cartilage, fat, pigment,

J grey nervous matter, &c.

4. Sclerous or hard tissues 1 Examples: Rudimentary skeleton of in -

J vertebrata, bone, teeth, &c.

5. Compound membranes : composed of ~)

simple membrane and a layer of Examples : Mucous membrane, skin,

cells of various forms (epithelium ^ true or secreting glands, serous and
or epidermis), or of areolar tissue synovial membranes,

and epithelium . . J

6. Compound tissues ; a, those com- "1

posed of tubes of homogeneous

membrane, containing a peculiar f ExamPles : Musde, nerve.

substance J

Z», those composed of white fibrous ~|

tissues and cartilage . . . } Example : Fabro-cartilage.

Cellular Membrane, or Tissue. — Cellular or areolar tissue is gene-
rally distributed throughout the body, and various forms of this cell-
fibre are found ; it is seen uniting together component parts, filling up
interstices between them, and affording a support to the blood-vessels
and nerves, before they are distributed to the various organs. This
fibre is soft, clear, smooth, and extremely minute, being the 1-1 2,000th
of an inch in diameter, sometimes less. The fibre is usually found
united together in bundles, the 1 -2000th of an inch broad: if these
be acted upon by dilute acetic acid they swell up, become transparent,
and the appearance of fibrous structure is no longer seen, although
some fibres that were not previously observed may become more dis-
tinct. The first kind does not refract the light strongly j 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 that a fasciculus is

368 THE MICROSCOPE.

wound round in a spiral form. As a consequence, when acetic acid is
applied, we perceive projections of swollen cellular fibre ; and in the
depressions the spiral fibre, which, from not having been acted on, has
formed the constriction, and with the acid has given rise to the ap-
pearance. This forms a striking instance of the constancy of the
spiral, which perhaps will be seen to take on a definite course, as ob-
served by M. Wichura in many other departments of nature. He says,
"that the circularly or heliacally acting forces of nature follow an
unchanging, definite, lateral direction in their course. The planets
describe heliacal lines, winding to the right in space by virtue of their
circulation from west to east, since this is combined with the advance
iu company with the sun towards a point in the northern hemisphere.
In the department of physics we meet with allied phenomena in the
circular polarisation of light, and in the course of electro-magnetic
spirals. Organic life exhibits similar laws in the circulation of the
blood, in all cases starting from the left side of the animal's body ; and
in the heliacal windings of the shells of molluscs, which follow a
direction determinate for every species. But plants, above all, give
evidence of a wonderful obedience to such laws, in the direction of the
spiral vessels, the heliacally winding trunks of trees, winding stems
and leaves ; and probably, also, in the circulation of their saps." In
the lowest forms of animal life, and in those of insects, the spiral form
will be seen to be most extensively distributed throughout ; as may be
observed by referring to our woodcuts.

Sometimes fat is 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 1-3 00th to the
1 -600th of an inch in diameter, Plate XII., No. 4. The cell-wall is
very delicate and transparent : sometimes there are one or two nuclei
enclosed. ^Ether 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 yelloiv fibrous tissue. The yellow is elastic and of great strength,
consisting of bundles of fibres which are highly elastic (Plate XIII.,
No. 2). The white, 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 employed in those parts subservient to the organs of loco-
motion.

ANIMAL TISSUES. 369

The white fibrous tissue is (when perfectly cleared of the areolar)
of a silvery lustre, and is composed of bundles of fibres running for
the most part in a parallel direction ; but if there be more than one
plane of fibres, they often cross or interlace with each other : in some
specimens it is difficult to make out the fibres distinctly, except in cer-
tain lights ; and in these cases it appears that this tissue may be com-
posed of a longitudinally striated membrane, which may be now and
then split up into fibres. The white fibrous tissue is principally em-
ployed in the formation of ligaments and tendons, — a purpose for
which it is admirably fitted on account of its inelasticity ; it also is
concerned in the formation of fibrous membranes, viz. the pericardium,
dura mater, periosteum, perichondrium, the sclerotic coat of the eye,
and all the different fasciae. It is sparingly supplied with blood-vessels
and nerves : the former always run in the areolar tissue, connecting
the bundles of fibres together ; but in the generality of the fibrous
tissues the blood-vessels are not well seen, except in the dura mater
and in the periosteum.

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, in some cases round, in others flattened ;
they are not always parallel, but frequently bifurcate and anastomose
with other neighbouring fibres. It is always rather difficult to separate
the fibres from each other ; and when they are 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 1 -5000th
to 1-1 0,000th of an inch. The acetic acid of ordinary strength does
not act on the yellow fibrous tissue ; nor after maceration in water or
spirit for a very long time does its elasticity diminish. Very long
boiling is said to extract from it a minute quantity of a substance
allied to gelatine ; neither nuclei nor a trace of cells can be seen in it
after the addition of acetic acid : these 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, muscle of the skeleton; 2d, muscle of
the heart ; and 3d, muscle of the stomach, intestines, &c. The func-
tions of muscular substance 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, &c.

Muscular fibre is held together by a very delicate tubular sheath,
nearly resembling simple structureless membrane. It cannot always
be discerned ; but when the two ends are drawn asunder it will be

B B

370 THE MICROSCOPE.

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 No. 5,
Plate XIII. 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 alkalies; which occasion it to swell and
become easy of separation. 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 bundle are shown at No. 6 ; and the
ultimate structure of a fibre, under a magnifying power of 600 dia-
meters, at No. 7, Plate XIII.

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. We have figured such a transition at Plate XII., No. 1 1 :
the tendon, the lower part of which may be seen passing insensibly into
the striped muscle, the glandular sarcous elements of the latter appear-
ing, as it were, to be deposited in the substance of the tendon (just as
the 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 lacunse have no distinguishable walls. On the other hand,
at the surface of the bundle the representative of the elastic element
remains, and often becomes as much developed as the sarcolemma.
There is no question here of muscle resulting from the contents of
fused cells, &c. It is obviously and readily seen to be nothing but a
metamorphosis of the periplastic substance, in all respects comparable
to that which occurs in ossification, or in the development of ten-
don. In this case we might expect, that as there is an areolar form of
connective tissue, so we should find some similar arrangement of
muscle ; and such may indeed be seen very beautifully in the termina-
tion of the branched muscles, as they are called. In Plate XII., No. 12,
the termination of such a muscle 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 mus-
cular bundles with which they are continuous, there is no functional
analogy, the stellate bodies having no contractile faculty. But the
nervous tubule is developed in essentially the same manner as a

ANIMAL TISSUES. 371

muscular fasciculus, the only difference being, that fatty matters take
the place of syntonin. Now it commonly happens, that the nerve-
tubules terminate in stellate bodies (Plate XII., No. 10) of a precisely
similar nature ; and these, in this case, are supposed to possess im-
portant nervous functions, and go by the name of " ganglionic cells."

The muscular fibre, known as the non-striated, or involuntary, con-
sists of a series of tubes presenting a flattened appearance, without the
transverse striae so characteristic of the former : elongated nuclei are
developed immediately upon the application of a little diluted acetic acid.
Wharton Jones, F.R.S., first demonstrated this structure in his lectures
at Charing-Cross Hospital about 1843 : he was led to infer from ap-
pearances in very young fibre, that the striped muscular fibre is ori-
ginally composed of similar elements to the unstriped, or plain mus-
cular tissue ; which, in the process of development, become enclosed
in a sarcolemma (simple membrane) common to many of them : the
fibres then split into smaller fibres (JibriUce). Thus accounting for the
nuclei of striped muscular fibre ; which, according to his views, are
the persistent nuclei of the primitive muscular-fibre cells.

The non-striated fibre is beautifully seen in connection with the
skin surrounding the hair, a few fibres of which are separately shown
at No. 3, Plate XIV. Professor Kolliker originally described these
muscles of the skin, of which there appear to be one or two in connec-
tion 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 remarkable that the skin, where 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 intermediate portions of the skin, and thus produce that peculiar
state of the surface well known as goose-skin, a condition of the skin
before unaccounted for.

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
markings; 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, connected
by intervening fibro-cellular tissue, in which blood-vessels ramify. A
layer of the same, or of a delicate, transparent, structureless tissue,
also surrounds the whole nerve, and forms a sheath for it. The slight

372 THE MICROSCOPE.

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 requisite to exercise more care in the breaking up
of structures to view these tubules, which should be immersed in a
very weak solution of spirit and water. Mr. Clarke, in his very im-
portant investigations on the structure of the spinal cord, placed the
cord, immediately after removal from the animal, into strong spirits of
wine. This hardened it, and enabled him to make very thin sections of
the spine. As nerves approach the brain or spinal cord, they gra-
dually become smaller, and do not measure more than from l-10,000th
to l-14,000th of an inch in diameter. The difference in the nervous
substances is not an affair of colour only; it refers also to their intimate
structure and organisation : the white matter is made up of bundles of
tubular fibres j whilst the grey is composed of aggregated cells, and is
often denominated the vesicular neurine. To collections of this vesi-
cular substance the term " ganglion" is applied ; because the knots of
nervous matter, which were formerly supposed to give origin to the
nerves, and which are distributed so largely throughout the body, are
vesicular in their composition. And thus the identity in structural
constitution has led to the employment of the word ganglion as a
common term ; although the ganglionic or spheroidal form is not at
all essential, as was at one time supposed, to the constitution of what
is now called ganglionic substance. Physiological and pathological
researches have rendered it more than probable that the vesicular and
the fibrous substances have universally separate and distinct offices in
the animal economy ; the ganglionic structures being the source of
functional change, and the fibrous matter being simply for the conduc-
tion of impressions originating in the former. This theory, in the
promulgation of which Mr. Solly shares probably in the most eminent
degree, is now received very generally as a scientific truth. The
nerve-corpuscles and stellate nerve-fibres are represented in Plate XII.
No. 10.

All the sensory ganglia, it may here be noticed, besides their in-
strumentality in inducing the simpler forms of consciousness, react
upon the muscular system, when stimulated from without ; and that,
too, in apparent independence of thought or volition. The movements
thus arising Dr. Carpenter very aptly designates consensual : they are
seen when the dazzled eye withdraws instinctively from the light, or
when the startle follows upon a loud and unexpected sound.

Consolidated Tissues. — These tissues are formed by a chemical com-
bination with the gelatine of the fibre, which in cartilaginous forma-

ANIMAL TISSUES.

373

tions is termed chondrine ; the cells of which become consolidated by
calcareous deposits, and a gradual transition results therefrom. Car-
tilage is the firmest structure next to bone ; it is very elastic, and
is converted by the intercellular substance into two kinds. In a rib
we find that this substance is uniform, and has a bluish appearance, or
is slightly granulous ; this is termed true, or white cartilage. The
other form of intercellular substance is developed in fibrous substances ;
and in this peculiarly-formed felt-work, cells and nuclei are imbedded.
It is termed yellow, fibrous, or spongy cartilage ; the yellow colour
depends on the mode of fibrous arrangement of the intercellular sub-
stance : it is found in the ear, &c.

Cartilage forms the entire skeleton in some kinds of fishes, as the
skate, lamprey, &c. It is nourished without coming into direct con-
tact with the blood-vessels, and is therefore said to be non-vascular,
deriving nourishment by imbibition from the surrounding blood-vessels.
When examined microscopically, the simplest form of cartilage is found
to resemble in a striking manner the cellular tissue of vegetables ; it
consists of an aggregation of cells of a spherical or oval figure, capable
in some cases of being separated from each other, but every cell having
a nucleus, with a nucleolus in its interior. In figs. 176 and 177 we have
given varieties of this structure. In the more highly advanced scale
of animals a strong fibrous capsule or sheath surrounds the cartilage-
cells, and some of the fibres dip in amongst the cells, and bind them
firmly together. In those of the Ray and Shark kind, where the entire

2 1

fig. 176.

1. Cartilage from ear of mouse, resembling a section of vegetable tissue, with several
superimposed layers. 2. Cartilage from rabbit's ear, showing large cells imbedded
in a fibrous matrix. 3. Cartilage from human ribs, with cells in groups, each
having a granular nucleus : magnified 200 diameters.

skeleton is cartilaginous, the cell is imbedded in a matrix, which may

374

THE MICROSCOPE.

be strictly termed intercellular. The cells are frequently or entirely
isolated, as seen in the section from the ear of a mouse (Fig. 176,
No. 1); and it then rarely becomes converted into bone. In the
higher animals it is generally invested by a fine and delicate mem-
brane, termed perichondrium, which brings blood-vessels into close

fig. 177.

1. Cartilage from the cuttle-fish, showing a peculiar form of cell. 2. Cartilage from
the head of skate, with nucleated cells in clusters, and nucleoli in their interior.
3. Cartilage from the frog, and cells having nucleoli : magnified 200 diameters.

contact with the cartilage ; and when in actual contact with the ex-
tremities of bones, it is covered by a fringed 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 is the synovial mem-
brane, a very beautiful structure when injected and viewed with the
1 or 2 inch object-glass.

In the early stages of existence, the framework, — or a very large
proportion of it, — is composed of cartilage, which, by the gradual addi-
tion of earthy matter, becomes consolidated into bone. The mode of
development, and the change from one to the other, is represented in
the section, Plate XII. No. 8 ; 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 calcareous matter becomes crowded and consolidated ;
as the process advances, the bone thickens, and a series of grooves, of
a stellate figure, No. 9, are found upon its surface, which are gradually
converted into canals for the passage of blood-vessels.

ANIMAL TISSUES. TEETH. 375

Iii certain forms of disease many of the soft parts of the human
body become converted into cartilaginous and bony masses, which have
received the name of Enchondrorrta. The microscopical characteristics
of this change have been described by the author, in the Transactions
of the Pathological Society of London, vol. iv.

Teeth. — The teeth are nearly allied to bone in structure ; and in
some of the lower vertebrata there is an actual continuity between the
bone of the jaw and the teeth. It is desirable to become acquainted
with the structure of teeth under the microscope : they are always in-
timately related to the food and habits of the animal, and are there-
fore highly interesting to the physiologist; they form for the same
reason important guides to the naturalist in the classification of ani-
mals ; and their value as zoological characters is enhanced by the faci-
lity with which, from their position, they can be examined in living or
recent animals.

Professor Owen has said, " If the microscope be essential to the
full and true interpretation of the vegetable remains of a former world,
it is not less indispensable 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 stra-
tum ; 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-reptiles in the lower sandstones of the new red
system, in Warwickshire, have been placed beyond a doubt. By the
microscope, the supposed monarch of the Saurian tribes — the so-called
Basilosaurus — has been deposed, and removed from the head of the
reptilium to the bottom of the marnmiferous class. The microscope has
degraded the tiaurocephalus 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 Megatherium ;
and by 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 disposed, according to the purpose which the tooth is to serve :
in man the whole crown of the tooth is covered with enamel, shown in
the dark marginal part of fig. 178; its root or fang is covered with

376

THE MICROSCOPE.

fig. 178.

Sections of Human Teeth.
1. Vertical Section. 2. Horizontal Section.

cementum, whilst the substance or body of the tooth is composed of
dentine. The enamel is composed of solid prisms or fibres, of about

l-5500th of an inch in
diameter, arranged side
by side, and closely adhe-
rent to each other..

The dentine consists
of a fine substance in
which mineral matter
largely predominates,
though to a less degree
than in the enamel. It
is traversed by a vast
number of very fine cy-
lindrical, branching, wavy
tubuli, which commence
at the pulp cavity and
radiate towards the sur-
face. The cementum cor-
responds in all essential particulars with bone, preserving its charac-
teristic lacunae, traversed by vascular medullary canals.

The very interesting structural characters of teeth in some of the
lower animals, called forth an able work from the pen of Professor
Simon ds, of the Royal Veterinary College : to his book upon this sub-
ject we beg to refer the reader.

Czermak discovered that the curious appearances of globular con-
glomerate formations in the substance of dentine, are entirely depend-
ent on its mode of calcification ; and he attributes the contour lines to
the same cause. Contour markings vary in intensity and number ;
they are most abundant in the root, and most marked in the crown.
Vertical sections exhibit them the best. In preparing the specimen,
first make the section accurately, then decalcify it by submersion in
dilute muriatic acid. It should then be dried and mounted 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 of the
extremity of the contour markings that produces the appearance of
rings on a tooth-fang.

" The tooth-substance appears," says Czermak, " on its inner sur-
face, not as a symmetrical whole, but consisting of balls of various
diameter, which are fused together into a mass with one another in dif-
ferent degrees, and on which the denterial tubes in contact with the

ANIMAL TISSUES. TEETH. 377

germ cavity are terminated. By reflected light, back-ground illumina-
tion, 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-sub-
stance ; for the older the tooth is, the less striking in general are these
conditions, and the more even is the surface ,pf the wall of the germ-
cavity. In very old teeth considerable unevenness again makes its
appearance j these, however, are not globular, but have a cicatrised,
distorted appearance. It is best to make the preparation from a tooth of
which the root is not perfectly completed. With such preparations, one
is readily convinced that the ground-substance of the last-formed layer
of the tooth-substance appears, at least partly, in the form of balls,
which are fused among one another, and with the balls of the penulti-
mate 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. The majority of these balls are
pierced through by one or more tubes, crosswise, passing from within
outwards. Very frequently, however, they appear homogeneous, and
contain no tubes." 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.

"Another method of obtaining specimens which further illustrate
the internal surface of the dentine is the following : In rubbing down
a section of a tooth, as the operator approaches the pulp-cavity the
last fibre of dentine frequently bulges into the unresisting cavity ; and
instead of grinding up into particles, comes away in a small sheet, — a
little film of dentine parallel with the pulp-cavity's surface, the inner-
most layer, and the one last formed. This should be carefully preserved
and mounted. On viewing such a specimen by transmitted light, one
sees the globules scattered about — some isolated, others more or less
confluent ; and between them a pale, rather indefinite structure, uniting
the whole into a sheet.

But the most instructive specimens are to be obtained from the
very thin cap of dentine found upon the foetal pulp. The thin edge
should be cut off, and examined on the inner surface ; it should be
moist, and never allowed to get dry. In such specimens the globules
are very apparent ; but, as Czermak observes, they do not appear
superficial, but in the substance of the dentine. It is here, in the
moist specimens, that the focus reaches the globules ; and, consequently,

378

THE MICROSCOPE.

there is no superficial stalactite-like bulging of globules, it is only in
dry specimens that that is seen. Now, if such a specimen be steeped in
dilute hydrochloric acid, so as to remove all the earthy matters, the glo-
bules instantly vanish, and the dentine where they were seen assumes the
same aspect as that where they were not seen. No other change is pro-
duced. The existence of the globules, therefore, seems dependent upon
the presence of earthy material." *

BONE.

The elements of bone are lamellae and small corpuscles ; the latter
are possibly merely spaces between the former, in which is deposited
the earthy substance. The lamellse have for their basis cartilaginous
substance combined with earthy matter, or salts. These salts are
chemically combined with the organic basis. Acid dissolves only the
earthy salts, and leaves the organic basis of the same form as the bone
itself. The lamellse are homogeneous throughout like the intercellular
substance of cartilage, but chemically it is different, being resolved by
boiling in water into cotta, whereas cartilage is resolved into chondrin.

1 2

fig. 179.

A transverse section of the human clavicle, or collar-bone, magnified 95 diameters ;
which exhibits the Haversian canals, the concentric laminae, and the concentric
arrangement of bone-cells around them. Some of the Haversian canals are white,
others black : the latter are filled with a deposit of opaque matter, used in the
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 No. 2.

Professor Quekett has given, in the Microscopical /Society's Trans-
* James A. Salter, M.B., Quarterly Journal of Microscopical Science, July 1853.

BONE.

379

actions, a most excellent account of the " Intimate Structure of Bone.1'
From this paper we propose to show the valuable results to be ob-
tained by a microscopic investigation of bone.

" Bone consists of a hard and soft part ; the hard is composed of
carbonate, phosphate, and fluate of lime, and of carbonate and phos-
phate of magnesia, deposited in a cartilaginous or other matrix ; whilst
the soft consists of that matrix, and of the periosteum which invests
the outer surface of the bone, and of the medullary membrane which
lines its interior or medullary cavity, and is continued into the mi-
nutest pores. If we take for examination a long bone of one of the
extremities of the human subject, or of any mammalian animal, we
shall find that it consists of a body or shaft and two extremities ; if
a vertical section of such a bone be made, we shall also find that the
middle of the shaft contains a central cavity termed the medullary
cavity, which extends as a canal throughout the whole of it, or else is
entirely or partially filled up with a cellular bony strupture, which
cells are termed cancelli, and the structure a cancellated structure. On

fig. 180.

1. A transverse section of the humerus, or fore-arm bone, of a Turtle (Chelonia mydas).

It exhibits traces of Haversian canals, with a slight tendency to a concentric ar-
rangement of bone-cells around them. The bone- cells are large and very numerous,
but occur for the most part in parallel rows.

2. A transverse section of the femui", or leg-bone, of an Ostrich, magnified 95 diameters.

When contrasted with the preceding figure, it will be noticed that the Haversian
canals are much smaller and more numerous, and many of them run in a trans-
verse direction.

a more careful examination of the bony substance, or shaft, we shall
find it to be slightly porous, or rather occupied, both on its external
and internal surfaces, by a series of very minute canals, which, from

380

THE MICROSCOPE.

their having been first described by our countryman Clopton Havers,
are termed to this day the Haversian canals, and serve for the trans-
mission of blood-vessels into the interior of the bone. Further than
this we cannot proceed without optical assistance ; but if now a thin
transverse section of the same bone be made, and be examined by the
microscope 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 situated
a concentric arrangement of spider-like looking bodies, which have, by
different authors, 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

fig. 181.

1. A horizontal section of the lower jaw-bone of a Conger eel, which exhibits a single
plane of bone-cells arranged in parallel lines. There are no Haversian canals pre-
sent ; and when this specimen is contrasted with that of fig. 180, No. 1, it will be
noticed that the canaliculi given off from each of the bone-cells of this fish are very
few in number in comparison with that of the reptile.

2. A portion of the cranium of a Siren (Siren lacertina), which is remarkable for the
large size of the bone-cells and of the canaliculi, they being larger in this animal
than in any other yet examined. As in the preceding specimen, no Haversian
canals are present.

them, which are termed canaliculi by some authors, and tubes and
pores by others : those bone-cells which are nearest the Haversian
canals have the canaliculi of that side radiating towards the opening

BONE. 381

into the Haversian canals ; whilst the canaliculi of the opposite side
communicate with those of the layer of canaliculi more external to
them ; and those in the outer row have most of their canaliculi given
off from that side of the bone-cell which is nearest its own Haversian
canal : hence arises the transparent white line which often may be
noticed as surrounding each concentric system of laminae and bone-
cells : in some cases, however, part of the bone-cells of the external
row anastomose with another series of bone-cells, which are situated
between the concentric laminae. The average length of the lacunae, or
bone-cells, in the human subject is the l-2000th of an inch ; they are of
an oval figure, and somewhat flattened on their opposite surfaces, and
are usually about one-third greater in thickness than they are in
breadth ; hence, as will be presently shown, it will become 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 section be treated
with spirits of turpentine coloured with alkanet-root, or if it have been
soaked in very liquid Canada balsam for any great length of time, it
can then be unequivocally demonstrated that both these substances will
gain entrance into the bone-cells through the canaliculi. The bone-
cells, when viewed by transmitted light, for the most part appear per-
fectly opaque ; and they will appear the more opaque the nearer the
section of them approaches to a transverse one : for when the cells are
cut through their short 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 condensed light,
the bone-cells and canaliculi will appear quite white ; and the intercel-
lular substance, which was transparent when viewed by transmitted
light, is now perfectly dark.

Thus much may be said to compose the hard part of the bone; we
must now turn our attention to the soft part. This, as has been before
stated, consists of the periosteum, which invests the outer, and of the
medullary membrane, which invests the inner surface, lines the Ha-
versian 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 short time in a dilute solution of caustic potash.

The animal matter may be procured by using dilute hydrochloric

382

THE MICROSCOPE.

acid instead of caustic potash, when the earthy matter will be removed,
and the section will exhibit nearly the same form as when the earthy
constituent was present ; and when viewed microscopically, it will be
noticed that all the parts characterising the section previous to its ma-
ceration in the acid will be still visible, but not so distinct as when
both constituents were in combination. When, however, the animal
matter is removed, the bone will not exhibit the cells and the canali-
culi, but will be opaque and very brittle, and exhibit nothing but the
Haversian canals and a granular structure.

If we consider what has been already mentioned as entering into
the composition of a bone, viz. the medullary cavity, the Haversian
canals, the canaliculi, and the bone -cells, we shall find that every part
thus described has been more or less hollow ; where, then, is the true

1 2

fig-. 182.

1. A small portion of bone, taken from the exterior of the shaft of the htimerus of a
Pterodactyle, which exhibits the elongated bone-cells characteristic cf the orders of
Eeptilia.

2. A horizontal section of a scale, or flattened spine, from the skin of a Trygon, or
Sting Ray, which exhibits large Haversian canals, with numerous wavy parallel
tubes, like those of dentine, communicating with them. It will be noticed that this
specimen shows, besides these wavy tubes, numerous bone-cells, whose canaliculi
communicate with the tubes, as in many specimens of dentine.

bony substance 1 This is no other than the small granules of ossific
matter, which are situated between the canaliculi of the bone-cells, each
granule having an investment of soft animal matter, by which the whole
mass of granules is kept in firm apposition.

The parts, then, which a transverse or a longitudinal section of a
long bone of a mammalian animal will exhibit, will be the Haversian

BONE. 383

canals, the concentric bony laminae, the bone-cells and their canaliculi ;
although all these parts, except the bony laminae, may be seen in all
mammalian bones. Whether long or otherwise, they are, nevertheless,
so differently arranged in the flat bones, such as those of the skull, and
in the irregular bones, such as the vertebra, as to require a short de-
scription at this stage of our inquiry.

The bones of the cranium are in all cases composed of two thin
layers of compact texture, which enclose another layer of variable thick-
ness, which is cellular or cancellated. The two outer layers are called
tables. — the one being the outer, the other the inner table j and the
middle or cancellated layer is termed the diploe : in this last the prin-
cipal blood-vessels ramify. The outer table of the skull is less dense
than the inner ; the latter, from its brittleness, is termed by anatomists
the vitreous table. When a vertical section of a bone of the skull is
made so as to include the three layers above mentioned, bone-cells may
be seen in all ; but each of the three layers will differ in structure : the
middle or cancellated structure will be found to resemble the cancel-
lated structure in the long bones, viz. thin plates of bone, with one
layer of bone-cells without Haversian canals ; the outer layer will ex-
hibit Haversian canals of large size, with bone-cells of large size, and a
slightly laminated arrangement ; but the inner or vitreous layer will
be found to resemble 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, will exhibit the following peculiarities ; the
Haversian canals are much more abundant, and much smaller ; and
they 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 often follows the curve of the bone ;
the bone-cells also are much smaller and much more numerous ; but
the number of canaliculi given off from each of the cells is much less
than from those of mammals : the average length of a bone-cell of the
ostrich is 1 -2000th of an inch, the breadth 1 -6000th.

In the Reptilia, the bones may be either hollow, cancellated, or
solid ; and, generally speaking, whichever form prevails, the bone may
be said to be very compact and heavy, but the specific gravity not so
great as that of birds or mammals.

The 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 performing the

384 THE MICROSCOPE.

office of an Haversiaii canal ; the bone-cells are accordingly arranged in
concentric circles around the canal. The vertebrae of these animals are
solid ; and the 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, we shall find the canals and the bone-cells
arranged both vertically and longitudinally : the bone- cells are most
remarkable for the great size to which they attain ; in the turtle they
are l-375th of an inch in length: the canaliculi, too, are extremely nu-
merous, 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 ; and there
are certain remarkable peculiarities in the bones of fishes which are so
characteristic, that a bone of one of these creatures can never be con-
founded with that of any animal of a higher class, when once the true
structure has been satisfactorily understood. Of all the varieties of
structure in the bones of fishes, by far the greater number exhibit no-
thing 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 ; others consist of Haversian canals,
with fine tubes and bone-cells ; whilst 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 canali-
culi, which are often of a very large size. The bone-cells are remarkable
for their graduate figure, and for the canaliculi which are derived from
their being few in number ; they are readily seen to anastomose freely
with the canaliculi given off from neighbouring cells; and if the speci-
men under examination be a thin layer of bone, such as the scale of an
osseous fish, from the cells lying nearly all in one plane, the anastomose
of the canaliculi will be rendered beautifully distinct. In the hard
scales of many of the osseous fishes, such as the Lepidosieus and Cal-
licthys, and in the spines of the /Siluridce, the bone-cells are beautifully
seen ; in the true bony scales comprising the exo-skeleton of the carti-
laginous fishes, the bone-cells are to be seen in great numbers. In the
spines of some of the Ray family may be noticed a peculiar structure :
the Haversian canals are large and very numerous, and communicating

BONE. 385

with each canal are an infinite number of wavy tubes, which are con-
nected 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 Ray 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.

Having said thus much on the minute structure of the bone com-
posing the skeleton in the four vertebrated classes, let us proceed at
once to the application of the facts which have been laid down ; and
let us, for example, suppose that a fragment of bone of an extinct ani-
mal be the subject of investigation. It has been stated, that the bone-
cells in mammalia are tolerably uniform in size ; and if we take
l-2000th 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 discrimination 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, therefore, between the two, we must, if the
section be a transverse one, also note the comparative sizes of the
Haversian 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. The
fragments necessary for the purpose of examination are to be selected
with some little care ; and on the whole, a small chip (or two) from
the exterior of the shaft of a long bone is sufficient : but as many
fossil bones are coated with a layer of earthy deposit on their external
surface, it will be requisite to get beneath this deposit, as it very sel-

c c

386 THE MICROSCOPE.

dom happens that the bone-cells are visible in it ; but by a fragment
from about the middle of the laminae of the shaft the characteristic
bone-cells can at once be recognised. But in the comparison of the
bone of a mammal with that of a bird, from the peculiarity in the
arrangement of the Haversian canals in the latter class, it is highly
important always to bear in mind that the specimens used for compari-
son should be cut in one and the same direction ; for as it has been
stated that the bone-cells, on which we are to rely for our determina-
tion, are always longest in the direction of the shaft of the bone, it
would follow, that if one section were transverse and the other longitu-
dinal, there might be a vast difference in the measurement of the bone-
cells, in consequence of their long diameter being seen in the one case,
and their short diameter in the other : hence the caution of having all
the sections made in one direction. In all doubtful cases, the better
plan is to examine a number of fragments, both transverse and longi-
tudinal, taken from the same bone, and to form an opinion from the
shape of bone-cell which most commonly prevails.

Preparing Sections of Bone. — Sections of bone or teeth may be
cut with a fine saw, such as is used for cutting metal ; then filed down
with a flat safe-edged fine file, and afterwards polished between two hones
of the Water of Ayr stone, or two pieces of very smooth boxwood ;
finally polish off on a strop of buff-leather charged with putty powder.

Should the specimen be small or brittle, after it has been filed and
rubbed down on the hone, and polished on one side, dry it, and cement
it — polished side downwards — with Canada balsam to a slip of glass ;
when the balsam is dry and hard, proceed to file and polish the other
side ; the section must be examined from time to time under the
microscope, and when found to be thin enough, it can be easily re-
moved from the glass by steeping it for a short time in ether. After
the section has been dried, it is ready for permanent mounting : this
may be done by immersing it in a thin cell of fluid, or in Canada
balsam ; if in the latter, it should be imbedded in it, and heat em-
ployed to expel all air-bubbles, and fill up the lacunae and canals in the
bone.

When we wish 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 hammer used by mineralogists : carefully
select the thinnest of the chips, and mount them at once without grind-
ing in Canada balsam.

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

ANIMAL STRUCTURES— MODE OF INVESTIGATING. 387

saw, file, and hone j by dissolving out the grease, the lacunas and
canaliculi show up very much better. A lapidary's wheel will be a
most useful article for grinding and polishing sections of bone or teeth.

Having thus briefly examined a few of the more important struc-
tures of the animal economy, and imperfect in a detailed point of
view though that examination be, we trust it may be found to smooth
the way, or in some degree assist the investigations of the student to a
better and more general survey of the whole fabric. Such a survey will
not be unattended with its difficulties and disappointments; nevertheless,
it will fully reward him for any amount of labour he may bestow.

The importance of being thoroughly familiar with the structure and
microscopical characters of any particular 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 descriptions
of morbid appearances. All who wish to use the microscope success-
fully, with reference to the examinations of organs in disease, will do
well to become acquainted with minute anatomy generally, not only of
the human subject, but of the lower animals ; without such knowledge
it will be found impossible to prosecute pathological inquiries with any
degree of success.

To the medical student, desirous of obtaining further information
in this especial department of microscopy, we can recommend a very
valuable little book by Dr. Beale, on The Microscope, and its Applica-
tion to Clinical Medicine. Also Dr. Bennett's Lectures on the Study of
Clinical Medicine, where some excellent hints will be found on the
proper mode of investigating animal structures.

The principal physical characters to be regarded in microscopic
examinations may be summed up as follows :

1. Slwpe. — Accurate observation of the shape of bodies is very neces-
sary, as many are distinguished by this physical property. Thus the
human blood-globules presenting a round biconcave disk, and are in this
respect different from the oval corpuscles of birds, reptiles, and fishes.
The distinction between round and globular is very requisite. 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 previously conceived regarding
them. Thus the coloured corpuscles of the blood, though commonly
called red, are, in fact, yellow. Many objects present different colours,

388 THE MICROSCOPE.

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 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 j 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 measurement. It will be observed, for the most
part, 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 con-
sequently be taken as a standard with advantage, and bodies may be
described as being two, three, or more times larger than this structure.

5. Transparency. — This physical property varies greatly in the ulti-
mate elements of numerous textures. Some corpuscles are quite dia-
phanous ; others are more or less opaque. The opacity may depend
upon corrugation or irregularities on the external surface, or upon con-
tents 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 peculiar luminous appearance.

6. Surface. — Many textures, especially laminated ones, present a dif-
ferent 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
capillaries 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
difference in structure between the surface and the deeper layers of the
tissue under examination.

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,

CIRCULATION IN THE FROG'S FOOT. 389

pigment matter, or crystals : occasionally their contents present definite
moving currents, as in the cells of some vegetables ; or trembling rota-
tary 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-formations to swell out from endosmosis ; while
syrup, gum-water, and concentrated saline solutions cause them to col-
lapse from exosmosis. Acetic acid possesses the valuable 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 disap-
pearance. The mineral acids dissolve most of the mineral constituents
that are met with ; so that in this way we are enabled to tell with tole-
rable certainty, at all events, the group of chemical compounds to which
any particular structure may be referred.

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 -disks will retain their form ; and if the preservation of the speci-
men is wished, a thin glass-cover must be placed over it, and cemented
down in the way directed at page 77.

To the advanced observer, the examination of the mucous mem-
brane will afford some instruction. Should the specimen 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 be required for examina-
tion, a portion may be detached from the surface by a knife, placed on
a glass slide, and viewed as a transparent object with a £-inch power.
Villi and papilla? are best seen upon injected specimens.

TO VIEW THE CIRCULATION OF BLOOD IN THE FROG.

The part most commonly employed for this purpose is the trans-
parent web of the hind foot ; and in order to secure the animal, and
keep its web open, various contrivances have been had recourse to.
The older microscopists, Baker, Adams, and others, were in the habit of
tying the frog to a frame of brass with some fine cord ; in the present
day the entire body of the animal, with the exception of the foot to be.

390

THE MICEOSCOPE.

examined, is secured in a black silk bag ; and this is fastened to a plate
of brass, termed the frog-plate, shown at a a a in fig. 183 : this should
be contrived so as to be held firmly by some part of the stage of the
microscope, and permit of its being moved about with it. Although
the shape of the plate differs with every maker, the mode of using it,
nevertheless, is nearly the same in all. The bag provided should be
about three or four inches in length, and two and a half inches broad,
as 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
out of the mouth ; the string d d is then to be drawn so tight around
the small part of the leg, as to prevent the foot from being pulled into

fig. 183.

the bag, but not to stop the circulation ; three short pieces of thread,
fff, are now to be passed around the three principal toes ; and the bag
with the frog is to be fastened to the plate a a by means of the tapes
c c. When this is accomplished, the threads ///are to be 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
is a series of pegs of the shape represented by h, each having a slit i
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 over which the foot is placed must be
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 power required to view the circulation will be a one-inch

CIRCULATION IN THE TAIL OF NEWT. 391

or half-inch object-glass ; a higher power will be needed to show the
rhythm of the veins.

In the common newt, as well as the frog, the circulation may be
viewed : the tail of the young animal being much used for this purpose,
and showing other interesting points of structure.

fig. 184. TJie common smooth Newt :

The warty newt is in a state of great activity early in spring. It is
common in ponds and large ditches, where it feeds upon the tadpole of
the common frog. The male and female newt are nearly the same in
appearance during winter ; but in spring a beautifully-cut crest rises
from the back of the male, which is highly ornamental.

The manner in which the eggs are deposited is very interesting.
The female, selecting the leaf of some aquatic plant, sits, as it were,
upon its edge ; and folding it by means of her two hinder feet, deposits
a single egg in the duplicature of the folded part of the leaf, which is
thereby glued most securely together, and the egg is thus effectually
protected from injury. As soon as the female has in this way de-
posited an egg, she seeks another leaf, on which she deposits another
egg in the same manner • and in this way she proceeds till she has de-
posited as many eggs as she requires. The egg is very slightly tinged
with buff, and is surrounded by a substance resembling the white of a
common egg, in which it keeps continually whirling round. It now
goes through nine changes from the egg till it becomes a perfect animal ;
and for a considerable time it remains in a tadpole state, almost like the
common frog.

Newts are readily found in many of the ponds around London.
The watercress-gatherers meet with them in large numbers.

FISH.

It has often been observed, that we are surrounded by wonders
which we do not notice because they are of daily occurrence, but which

392 THE MICROSCOPE.

excite the greatest surprise when they are pointed out to us. The
truth of this observation is forcibly exemplified as regards fish. We
see them every day exposed for sale on stalls, and we eat them fre-
quently at our tables, without once considering by what a curious and
delicate organisation these creatures are enabled to see and breathe in
an element that carries death to us and to quadrupeds. The sight of
fishes appears to be remarkably strong, as it is by sight chiefly that
they discover their prey. Hence a fish is easily deceived by an arti-
ficial fly, or the imitation of a frog or other small aquatic or amphi-
bious animal ; which, if it were guided by the smell, or any other
sense than the sight, could not happen. The mode in which fishes
breathe is, however, the most curious. They have no lungs ; but,
instead of them, they have gills, carefully covered with a lid and a
flap, both of which the fish can open or keep closed at pleasure. The
gills are composed of arches bordered by a kind of fringe, which, when
examined through the microscope, is seen to be covered with a velvet-
like membrane, over which myriads of wonderfully minute blood-ves-
sels are spread, like a delicate network. There are commonly four of
these fringed arches : they are movable, and allow the currents of
water driven down by the action of the mouth to flow freely through
them, so as to lave every fibril. It is absolutely necessary that this
should be the case, since the gills lose their power of acting as soon as
they become dry; and hence a fish cannot live long after it is taken
out of the water. As there is danger, however, of the food taken by
the fish being carried through the gills by the stream of water con-
stantly flowing through them, the minor curve of the arch formed by
the gills is studded with spines, which prevent any thing but air or
water passing through them.

A knowledge of the form and structure of scales of fishes, like that
of teeth, has been shown by M. Agassiz to afford an unerring indication
of the particular class to which the fish may belong : in the examination
of fossil remains, the application of this knowledge has been attended
with extraordinary 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 glasses. M. Agassiz divided the scale into four orders,
which he named Placoid, Ganoid, Ctenoid, and Cycloid ; in the first
two the scales are more or less coated with enamel, in the others they
are of a horny nature. To the Placoid order belong the skates, dog-
fish, ray, and sharks ; cartilaginous fishes, having skins covered with

STRUCTURE OP FISHES. 393

small prickly or flattened spines. To the Ganoid belong the sturgeon,
lepidosteus, hassar-fish, and polypterus ; the fish of this order are more
generally found in a fossil state, and their scales are of a bony struc-
ture. 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 amongst the most remarkably
that can be selected for microscopic examination. To procure them, a
sharp knife must be passed underneath the epidermal layer, and a por-
tion of this raised, in the same manner as described for tearing off the
cuticle of plants : after some trials a few 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 may be
obtained from the under surface by tearing them away either with a
knife or pair of forceps. The scales of the viviparous blenny are of a
circular figure, and situated under the epidermal layer ; they have been
described by Mr. Yarrell as mucous glands, in consequence of their
figure and the smallness of their numbers. The surface of the skin of
this fish, when fresh, appears to be covered with follicles ; if, how-
ever, a portion be scraped
off, it will be seen to be a
mass of delicate circular
scales. A piece of the skin,
when dried, will exhibit the
scales to great advantage,

and, like those of the eel, is a fig. 185. The Stickleback.

beautiful object for polarised

light. The colours of fishes 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 produced by the numerous microscopic plates, or
scales, which are distributed over the surface of the true skin.

It will interest our readers to know, that Mr. Lloyd, of 164 St.
John Street Koad, has taken steps to fit-up and stock marine and
fresh-water aquwtia with fish and appropriate plants, at very moderate
prices.

CHAPTER VII.

VEGETABLE STRUCTURE VITAL AND CHEMICAL CHARACTERISTICS THE

VEGETABLE CELL FUNGI ALGJ2 MOSSES VOLVOX DESMIDACEvE

— -STRUCTURE OF PLANTS FUNGOID DISEASES ADULTERATION OF

ARTICLES USED FOR FOOD PREPARATION FOR MICROSCOPIC EXAMI-
NATION— CUTTING SECTIONS — WARINGTON's MICROSCOPE MAGNIFY-
ING POWER OF THE EYE— CONCLUSION.*

INGE fhe introduction of the achromatic micro-

scope, we have obtained nearly the whole of the
valuable information which we now possess re-
lative to the minute structure of vegetables.
Before that time, although some progress had
been made in vegetable physiology, yet the
means of distinguishing one structure from an-
other, with their several external characters,
comprehended the amount of our botanical know-
ledge. " The vegetation which every where
adorns the surface of the globe, from the moss
that covers the weather-worn stone, to the cedar
that crowns the mountain, is replete with mat-
ter for reflection. Not a tree that lifts its
branches aloft, not a flower or leaf that expands
beneath the sunlight, but has something of ha-
bit, of structure, or of form, to arrest the atten-

* DESCRIPTION OF PLATE XV.— DESMIDACE.E, AFTER RALFS.

Euastrum oblongum
Micrasterias rotata

,, denticu]
Desmidium quadran:
Didymoprium Grevillii

„ ' Borreri
Sphserozosma vertebratum

Staurastrum, tumidum
„ dilat

„ hirsu

Cosmarium Ralfsii

Closteria

ata
^ulatum
llii .
ri .
ratum
8, 10, 13

14

No.
1
2
6
3
4
5
7
17 19

Penium .
Staurastrum
„ gracilis
Pediastrum biradiatum
„ pecticum
Volvox globator .
Penium Jenneri
„ margaritaceurr
Aptogonum desmidiuir
Ankistrodesmus falcati

L
IS

No.
21
22
23
24
29
26
27
33
28
30
34
32

im
um
im

: 20

'26,

15
16
18
11,12
31, 35

Docidium clavatum

PLATE XV.

VEGETABLE CELLS, DESMIDACEyE.

VITAL CHARACTERISTICS OF PLANTS. 395

tion." The microscopist sees proof of a higher life in plants than he
before conceived ; and he becomes convinced, after examining the
functions which their organs are destined to perform, that animals and
plants are only separate links in the great chain of organic nature.

Plants are organised beings ; that is, individuals composed of a
number of essential and mutually dependent parts : in common, there-
fore, with animals, they possess a principle which is in continued
action; and which operates in such a manner, that the individual parts
which it forms in the body are adapted to the designs of the whole.
Or, in more intelligible language, plants are living bodies. Like ani-
mals, they are the offspring of other beings similar to themselves; they
grow, are endowed with excitability, have their periods of infancy, adult
age, decay, and death. Their affinity to animals is much closer than is
commonly supposed. The vital or creative power exists already in the
germ, in plants as well as in animals ; and by its influence the essential
parts of the future plant are formed. It might be supposed that the
lateral generation of plants — namely, that renewal of the individual
which is the result of budding or gemmation — is sufficient to distin-
guish them from animals ; but this opinion is erroneous, as we find
that the formation of gems or buds is common in animals belonging to
the Protozoa. In the hydra, we perceive the germs developed as small
ovoid elevations upon the cylindrical body of the animal, and when
examined in this state, they are, like the first formation of the buds in
plants, mere masses of cells ; but as their growth proceeds, these cells
undergo a special arrangement, so as to produce the different tissues
of the body, and acquire the proper form of the polyp : on the same
principle, the bud in the plant is gradually developed, until it termi-
nates, and becomes a branch.

Plants, like animals, possess excitability, or the faculty of being
acted upon by external stimuli, impelling them to the exertion of their
vegetable powers. Light acts on plants, directing the growth of the
stem, vigour, and colour, the direction of the branches, position of
leaves, the opening and shutting of flowers. Heat influences the pro-
trusion of buds, and other stimulants affect the vegetable irritability ;
as an instance of this, cut plants, when fading, revive if placed in water
impregnated with certain chemicals.

Besides the physical and physiological distinctions generally pointed
out as marking the line between animals and plants, chemistry furnishes
many others. Thus, one of the great functions of a plant is to decom-
pose water, and assimilate its components to the vegetable tissues ;
whilst it is a property of animal life constantly to reform it from its

396 THE MICROSCOPE.

elements. The oxygen derived from the atmosphere, by whatever
means it is introduced into the animal system, is expended in the pro-
duction of carbonic acid and water, both of which are thrown off as
excretions. It is true that water is exhaled in great quantities from
the surfaces of plants ; but it is that fluid which has been taken into
the system of the plant, and has not undergone decomposition ; it is,
therefore, not actually found in the body of the vegetable, as it is in
that of the animal. During the process of vegetation, protein is formed
from the constituents of water with carbonic acid and ammonia ; pro-
tein is formed in the animal body, and enters largely into the blood
and muscle.

There is the closest affinity in the chemical nature of the products
between plants and animals. Vegetable albumen is identical in com-
position with that in blood and in eggs; casein does not materially
differ in milk and the juices of some plants: we have many other
equally striking characteristics, which modern chemical investigations
have unfolded. Plants in some characteristics differ most strikingly,
in being almost destitute of voluntary sensation and motion : here we
would not have sensibility confounded with irritability, a principle
which plants, in common with animals, possess. The simplest forms
of animal life manifest both sensation and volition, even those that
are fixed to rocks and other bodies presenting a ramified and vegeta-
tive form ; for instance, in the compound polyps, each individual
polyp displays both sensation and voluntary motion. It is, neverthe-
less, difficult to attribute satisfactorily the movement of some plants to
irritability alone. Thus we find plants, in an apartment with light
admitted on one side, not only turn the upper surface of their leaves
to the light, but bend their sterns and branches towards it. Many
other instances might be cited; but none of them, excepting the move-
ments of the OsciUatoria, more closely resemble volition. Plants,
again, differ from animals in having no nervous system. All animals,
without distinction, have a nervous system. Ehrenberg traced and
described "vessels and nerves in the Rotatoria and some Infusoria"

Another great distinction is connected with the function of diges-
tion, which the simplest form of animals possess : those even which
turn inside out, the hydra, &c. have an internal cavity, into which
their food is taken at intervals ; but vegetables are nourished from the
surface, and by continual imbibition.

It has been supposed, because the sap rises in plants, and in the
interior of some internodia and cells of some simple plants a rotatory
motion of fluid can be perceived, that plants, like animals, have a cir-

VITAL CHARACTERISTICS OF PLANTS. 397

culation of fluids. This opinion is at least disputable, the sap of plants
ascending only once, — for that which is termed the descending sap of
the plant is the proper juice prepared in the leaf; and the fact of
currents being observed in opposite directions, is no proof of the
existence of a circulation. But it may be asked, is the motion in the
Chara or the cells of the Vallisneria spiralis, or in the hairs of the
radicle fibres offrog's-bit, any proof of a circulation ? It is certainly a
proof of the motion of a fluid in the cells of a plant, and is very dif-
ferent from a general circulation of the sap ; which is the only answer
that can be made to such an inquiry : and the true circulation in
animals is derived from an internal impelling power, and not from
external influences.

A more distinctive character is obtained in the products of the
respiratory function in plants": respiration is performed by the entire
surface in most animals, as it is by all plants ; but the products are
different. In plants, the process consists chiefly in the conversion of
carbonic acid and water into vegetable matter j hence oxygen is ex-
haled from the leaves, and carbonic acid absorbed by them from
the atmosphere ; and it is by the decomposition of that acid in the
leaf, that the greater part of the oxygen is restored to the air. And
although plants exhale carbonic acid during the night and in the shade,
yet the quantity is small ; and plants are, in reference to their respira-
tion, a balance in the opposite scale to animals ; they remove from the
air the carbonic acid exhaled from the lungs and spiracles of animals,
and re-supply the oxygen requisite for their respiration. Without the
vegetable tribes, the atmosphere would soon cease to be fitted for the
present race of animals ; without the carbonic acid formed by animal
respiration, plants would lose the greater part of their nutriment ; and
by their reciprocal action the atmosphere is preserved very nearly un-
changed. Therefore the most important difference between the two
may be said to be essentially that pointed out by Dr. Lankaster, in the
nature of the distinctive character of the gases inhaled and exhaled
by animals and by plants. With this brief survey, we may conclude
our comparative view of plants and animals by stating, that whilst they
are endued with many properties and functions common to both, they
possess others sufficiently distinctive, which prevent them from being
regarded as parts of the same link in the chain of vital existence.

As we pass on to a more intimate examination of the various struc-
tures entering into a plant, it will be seen that we have objects of the
deepest interest presented to our notice ; and strikingly differing as
we find plants and animals in some essentials, we shall here, at our

398 THE MICROSCOPE.

starting-point, find them gradually coalescing, until they meet in a
common granule — " that of the simple and individual cell."

Mulder, in describing this starting-point of life, says : " The cell is
a concave globule. This concave globule is an individual ; in the most
simple form in which it can possibly exist (in the lowest moulds), it
possesses all the powers of the molecules united into one whole, and
thus reduced to a state of equilibrium. This state depends, not only
on the nature of the substances and of their elements, carbon, hydrogen,
oxygen, and nitrogen, but also on their form. The state of equili-
brium, therefore, could not exist, unless this concave globular form
existed. Moreover, this hollow globule possesses the whole of these
forces in a state of mutual combination, co-operating for one end ;
this being a peculiarity which also apparently depends on the globular
form."

Cells from which plants are formed are very small delicate closed
sacs, partaking of many forms, and enclosed in a perfectly transpa-
rent membrane, so excessively thin, that it is with difficulty detected,
unless iodine or some colouring-matter be previously added. Dead
and old cells form an exception, as they become thickened, and the
broken surfaces are then readily detected. At one time the cells
were said to be developed by an extrication of gaseous matter among
mucus ; but the double walls which separate cells are irreconcilable
with such an origin. Mr. Thwaites regards the original wall of the
cell as a mere shell, having quite a subordinate office to perform in
the growth of plants ; and he ascribes all the vital powers of growth
to the cytoblast and colouring-matter of the central nucleolus. He
supposes the cell-membrane to arise from the action of electrical cur-
rents upon mucus, and that fissiparous division is caused by the
presence of two centres of electrical force, each giving rise to a set of
currents, and producing two cell-membranes instead of the original
one. For further information on this very interesting subject, see
Henfrey's translation of Mohl's Vegetable Cell; and Dr. J. B. Sanderson,
on "Vegetable Reproduction," Cyclopaedia of Anatomy and Physiology.

The first and most curious exemplification of the simple cell is the
fungi known as the Yeast Plant : it consists of two parts, the cell-wall,
composed of a matter termed cellulose, and the contents of the cells,
resembling fat or oil. The notion that yeast was an organised being,
in fact a living plant, was at first strongly opposed by even Berzelius
and Liebig ; but by the microscope they have been convinced both of
its organisation and vitality. The scientific name by which it is known
is Fermentum cervisia, or Torula cervisia ; it consists of globular or

VEGETABLE CELLS.

399

ovoidal transparent nucleated cells, represented in the accompanying
fig. 186, and showing its stages of growth as first observed by Turpin,

fig. 186. The growth of the Yeast Plant.

who carefully watched the changes after mixing it with some newly-
made beer. Fresh yeast has the appearance seen at No. 1 ; one hour
after it had been added to the wort, germination commenced, and
produced two buds or cells, as at No. 2. In three hours they were
doubled, as at No. 3, and attained the size of the maternal cell. In
eight hours the plants began to ramify, as at No. 4, and some to
explode, emitting a fine powder; and in three days jointed filaments
with lateral branches were produced, as at No. 5.

Yeast-cells occasionally form in the human body under certain
states of disease, principally occurring in the urine of patients ; hence
the cell has been named Torula diabetica : for the sake of comparison
a few of those cells, highly magnified, are represented at No. 9, fig. 187.
Mr. Busk met with a peculiar disease of the stomach, in some patients
under his care vomiting another form of this remarkable fungi, named
by Professor Goodsir Sarcina ventriculi ; this presented under the
microscope an appearance very nearly resembling the Gonium pectorcde
represented in fig. 95. Dr. John Ogle tells us that he has met with
Sarcina where disease was never previously suspected to exist, averag-
ing one out of every five or six stomachs examined. Are not these
Sarcina taken into the stomach with impure water ?

The Mycoderma cervisia of Desmaziers is another stage of growth
of the same plant deposited in porter-vats. Its various stages are
shown in fig. 187, Nos. 6, 7, and at 8 ; the perfect plant is seen, with

400

THE MICROSCOPE.

its granular contents in the stem. One of the most remarkable of this
tribe has been committing great devastation among our grape crops

fig. 187. Fungoid disease.

1. A section of the Tomata, showing the sporangiae growing from the spawn or root
(mycelium). 2 shows a budding from the upper part of a branch. 3. Vertical and
lateral view of sporangiae, with their granular contents turned ,out. 6, 7, and 8
show different stages of growth of Mycoderma cervisia. 9. Torula diabetica.

during the past two years. A section of the grape, magnified 75
diameters, is seen in fig. 188 j the fungi or mildew is growing from a
section of the skin of the grape.

" Grapes," says Mr. Harris, " when blighted, are covered with
what appears to be a white powder, like lime, a little darkened with
brown or yellow. These fungi send forth laterally, in all directions,
thread-like filaments, which become so completely interwoven with
one another as entirely to cover and enclose the skin of the grape in a
compact and firm network, and on each is seen the egg-shaped capsule
or seed-pod."

FUNGI.

401

Fungoid diseases among our growing crops attracted but little
attention until the mischief produced by them became serious ; and the
microscope has enabled us to determine and grapple with the destroyer
in its variety of forms ; thus, we have our corn-crops withering under
the blighting influence of the Uredos and Pucemias, our vines, &c.,

fig. 188. Section of a Grape.

under that of the Oidium, our esculents under the Botrytis infestans
(potato-blight): the same disease is seen to infect the tomata, fig. 187.

The microscope has revealed to us that many of the skin diseases
attacking the human frame are but other forms of the same growth of
parasitic fungi, or cryptogamia, another low form of plant, presenting
at first filaments simple, then ramified, and formed by a single elon-
gated cell, or several cells placed end to end, as in those of the yeast-
plant. The disease known as Ringworm, infesting the heads of children,
is one out of forty-eight different species of Cryptogamia. The con-
ditions of growth of this low form of vegetable life on the human body
are the same as in other situations. Dr. Gudden, who has lately pub-
lished a work upon Cutaneous Diseases caused by " Parasitic Growths"
describes Ringworm under the name of Porrigo-fungus ; the spores of
which are round on the upper, and filamentous on the under surface.
Whenever the healthy chemical processes of nutrition are impaired, and
the incessant changes between the solids and the fluids slacken, then
the skin may furnish a proper soil for the fungi to take root in, should
the sporules come in contact with it. That dreadful disease known as
cancer will no doubt ultimately prove of vegetable growth, or a conver-
sion of the nutritive animal cell into that of a fungoid vegetable cell.

The Rev. S. G. Osborne, during the cholera visitation of 1854, en-
deavoured to direct public attention to the very general distribution of
fungi. He says, " Only those who have closely studied these fungi can

D D

402 THE MICROSCOPE.

be aware how very minute and yet how systematically formed they
are. Preparations of a dozen different species, taken from the grape,
potato, parsnip, bean, cucumber, cineraria, veronica, &c., many of which
have been in fluid for more than a year, retain their form as perfectly
as if only taken from the plant a day. No two are alike in form ; but
all are alike in this — under the very high powers of the microscope, they
show an external hyaline case, with a second utricle, or inner case, full
of minute spores.

If a few leaves of the infected haulm of the potato are taken and
gently shaken over a piece of black paper, a quantity of very fine white
powder is obtained : place a little of this in fluid, under a power of
500 linear ; every atom of this powder will resolve itself into a distinct
cell, somewhat of the form of an ace of spades, varying more or less
in size from about 3-5000ths of an inch in length. There will be seen
a well-defined outline of an inner cell, in which are many hundred
greenish-looking spores ; some of the cells will burst, and by using a
still higher power it will be seen that these have all the shape and cha-
racteristics of the parent cell. Several of them lie easily between the
lines on a micrometer, which lines are just 1 -5000th of an inch apart.
In Plate XV. the destructive effects upon the tuber are shown.

There can scarcely be one spot of earth on which these fungi
do not fall in their thousands. Insoluble in nature, they wait where
they fall the growth of the particular plant for which each has its own
affinity, that if that plant grows on that spot, its enemy is near, on
the very soil from which it is to draw life. But I further believe that
there must be some peculiar disposition yet to be developed in the
plant before the fungus will act upon it, to its own rapid development,
and the destruction of the said plant."

Fig. 189, 4 and 6, represents forms of fungi taken in London by
the author during the cholera visitation, September 1854.

Our limited knowledge of the matter does not forbid the suppo-
sition that there may be some, even among the purely vegetable fungi,
which might, in certain conditions of the human body, when taken into
the frame, produce immediate severe constitutional disturbance. The
Sarcina may be cited as an instance of this fact. It strikes us, however,
as far more probable, that from drains and cesspools — reservoirs as
they are for excrementitious animal matter — may emanate certain spe-
cific fungi, the spores of which, under certain conditions of atmosphere,
would be given out in such quantities, and in such minute particles, as
easily to be carried about by every current of air. Persons in health may
inhale and swallow these spores, and escape injury from them. Other

FUNGI.

403

persons, depressed physically from local or accidental causes, may afford
to them just the pabulwni which will develop their poisonous quality.

Many animal organisms, such as infusorial animalcules and their
ova, are frequently found floating about in the air, as well as the fungi
spoken of.

fig. 189. Fungi. Magnified 200 diameters.

1. Brachycladium penicilatum, found on the stem of plant. 2. Aspergillus glaucus,
found on cheese, &c. 3. Botrytis : the common form of mould on decaying vege-
table substances. 4. Fungi caught over a sewer (foul air). 5. Fungi growing from
a pumpkin. 6. Fungi caught in the air at the time of the cholera. (Aerozoa ?)

Animals, birds, insects, and fishes, alike suffer from the ravages
of fungi. One of the most prevalent of these observed among our
domestic pets is the fungi growing over the upper surface of the gold-
fish j death is almost certain when this white fungoid disease once com-
mences its ravages. Great devastation is at times committed amongst
silkworms by the Botrytis, causing a disease called Musccvrdine, just as
they are about to enter the chrysalis state.

We must range by the side of these the fungi known as mush-
rooms, toadstools, puff-balls ; and also a large number of microscopic
plants forming those appearances which are referred to generally
under the terms of mouldiness, mildew, blight, smut, dry-rot, &c. It
is well known that fruit-preserves are very liable to be attacked by
the common bead-mould (No. 3, fig. 189) ; which no care employed
in completely closing the mouths of the jars can prevent. We may
remark, however, that they are much less liable to suffer in this way,

404

THE MICROSCOPE.

if not left open for a night before they are tied down : it is therefore
probable that the germs of the mould sow themselves before the jar is
covered. Some particular kinds of cheese derive their flavour from
the quantity of a fungous growth which spreads through the mass
whilst it is yet soft.

The power of reproduction of the vegetable mould-plant, or mucor,
is so great, that extensive tracts of snow are suddenly reddened by the
Gory -dew, Protococcus nivalis (red-snow) of the northern regions. That
the Bed-snow plant consists of a cellular or filamentous tissue, may be
easily ascertained by means of a microscope of even moderate powers ;
and one of a higher power demonstrates that the filaments are nothing
more than cells drawn out. Sometimes, as in the genus Uredo, the
cells are spheroidal, having little connection with each other ; each cell
containing propagating matter, and all separating from each other in
the form of a fine powder when ripe. In plants of a more advanced
organisation, as the genus Monilia, the constituent cells are connected
in series which preserve their spherical, and also contain their own re-
productive matter j while in such
plants as Aspergillas (No. 2), the
cells partly combine into threads
forming a stem, and partly preserve
their spheroidal form for fructifica-
tion. It is probable, however, that
in all fungi, and certain that in
most of them, the first development
of the plant consists in what we
here call a filamentous matter, which
radiates from the centre formed by
the space or seeds ; and that all
the cellular spheroidal appearances
are subsequently developed, more
especially with a view to the dis-
persion of the species.

That very curious fungus, known
in Scotland as Siller-cups (Nidula-
ria campanulata), fig. 190, consists

fig. 190.
Siller-cups (Nidularia campanulata).

of a curious leathery cup, in which are a number of small thecse, which
contain the sporules ; and each plant looks like a bird's nest with
several eggs in it. It generally grows on a twig, or a bit of rotten
wood, and one has been found growing on a wooden tally, fixed in a
pot containing a green-house plant. Several kinds of Agaricus have

MOSSES. 405

blue stems, others orange, yellow, and green, with caps of various
colours, some of which are scarlet or crimson, and others have beau-
tiful shades of purple or violet.

fig. 191. Screw Moss. fig. 192. Scale Moss.

The mosses are another low form of vegetable life j and Linnaeus
called them servi, — servants, or workmen, — 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 winter's cold.
The common or Wall Screw-moss, fig. 191, which grows 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 of which terminates in a dark brown case, which is, in fact, its
fruit. As the fruit ripens, a little cap, which covers it like an ex-
tinguisher, rises gradually, and is at last thrown off; and when the
lid of the fruit, which is also conical, falls off, a curious tuft of twisted
hairs appears, forming a kind of fringe ; and it is from these twisted
hairs that the plant takes its popular name of Screw-moss. If a patch
of the moss is gathered when in this state, and the green part at
the base is put into water, the threads of the fringe will uncoil and
disentangle themselves in a most curious and beautiful manner, and
thus afford an opening to the seeds, which are exceedingly small, and
are contained within a thin bag, attached to the central column of the
case. 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 stu-
died in winter. One of the commonest, Scale- moss, fig. 192 (Junger-
niannia bidentala), grows in patches, in moist, shady situations, near
the roots of trees, upon commons, and on hedge-banks. The seed-ves-
sels are little oval bodies, which, if gathered when unexpanded, and
brought into a warm room, burst under the eye with violence the mo-
ment a drop of water is applied to them, the valves of the vessel taking

406

THE MICROSCOPE.

the shape of a cross, and the seeds distending in a cloud of brown dust.
If this dust be examined by the 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 ; and if the seed-vessel
be examined while in the act of bursting, these
little springs will be found twisting and writh-
ing about like a nest of serpents. The undu-
lated Hair-moss (Polytrichum undulatum), fig.
194, is found on moist shady banks, and in
woods and thickets. The seed-vessel has a cu-
rious shaggy cap ; but in its construction it is
very similar to that of the Screw-moss, except
that the fringe round its opening is not twisted.
The Funaria hygrometrica is a remarkable
moss, differing widely in its powers of adapta-
tion, and, consequently, in its 'greater geogra-
phical range, from most of its congeners. The
Funaria is found in fruit, not only in London,
but in every brick-field around it. The peris-
tome of this moss is one of our most beautiful
microscopic objects.

CONFERVOIDE^E. ALGM.

The jointed conferva and some algse are
met with in the smallest accumulations of fresh

water standing for any length of time in the
Undulated Hair Moss. J

open air. They present the appearance of

thread-like tubes, having joints differing in length, and the manner in
which their contents are arranged. They multiply by means of little
granules contained in their tubes, which are enclosed in tube after tube
gradually added to the end of the previous one. Among these con-
fervaB, the most remarkable are the Zognema and Oscillatoria, both of
which evince certain degrees of approach to the animal kingdom. The
species of the latter genus form dark green and purple slimy patches
in damp places, or in water, and are exceedingly remarkable for the
power they possess of moving spontaneously. When in an active
state, their tubes are seen to unite and twist about, just as if they were
vegetable worms ; but they grow like plants, and their manner of
increase is also vegetable. Disjointed algse are extremely curious ;
they are characterised by their original or final spontaneous separa-

CONFERVOIDE^E.

407

tion into distinct fragments, which have a common origin, but an indi-
vidual life. They multiply by spontaneous division, as represented
in fig. 194, N"os. 6 and 7 ; and are generally found attached to the stems
of other plants immersed in water, or floating in pools or ditches.

In the algae, the seeds are imbedded either in the frond itself or
in some especial recep-
tacle ; the fronds develop
cellules, in which the re-
productive nucleolus is
enclosed ; and acquiring
a deeper colour with age,
becomes finally a sepa-
rate plant. The higher
kinds of algae inhabit
sea- water only ; they
then assume the forms
of more perfect plants,
forming vast submarine
forests of the most lux-
uriant vegetation. A
few species are repre-
sented in our frontis-
piece. Many kinds fur-
nish to man a whole-
some and palatable food :
the Laver of our sea-

fig. 194.

, 1. Volvox globator. 2. A section ofvolvox, showing the

Shores, the Carrageen, cuiated margin of the cell. 3. A portion more highly

magnified, to show the young Volvicinae, with their
nuclei and filamentary attachments. 4, 5, 6, and 7.
Confervoidese, showing their modes of growth.

or Irish Moss, with

others, belonging to this

group ; and from them

are formed the edible birds'-nests, which are considered so great a

delicacy by the Chinese. That valuable medicinal substance, Iodine, is

also procured from certain algse.*

We now arrive at a more complex form of cell, one that has at-
tracted the attention of all microscopists from its earliest discovery to
the present day. It was for a very long time classed with the lower
forms of animal life; and there it remained, for the micro-chemical in-
vestigators of the present time to settle the perplexing question, and
by truly assigning to it a place amongst vegetables. The cell referred
to is recognised as the Volvox globator, or revolving-cell, represented
* For further information see Dr. Hassall on the Fresh- Water Algce.

408 THE MICROSCOPE.

in fig. 194, Nos, 1, 2, and 3. These revolving globular bodies are
found of various sizes, some large enough to be discernable by the
naked eye.

Leeuwenhoek first perceived the motion of what he termed globes,
" not more than the 30th of an inch in diameter, through water ; and
judged them to be animated." These globes are studded with innumer-
able minute green spots at their surface, each of which is a cell about
the 3500th part of an inch in size, with a vivid nucleus having many
ever-active cilia, that bristle over their spherical home and are bound to
each other by bands forming a beautiful network. Within this globe,
busy active nature is at work carefully providing a continuance of the
species ; and from six to twenty little bright-green spheres have been
found enclosed in the larger transparent case. As one of these arrives
at maturity, the parent cell enlarges j then bursts asunder to launch
forth its offspring into a watery world. Both the older and younger
spheres possess openings through which the water freely flows, affording
food and air to the little organised beings.

Dr. Carpenter says, "The Volvocince, whose vegetable nature has been
made known to us by observation of certain 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 globator,
has shown that the increase of internal cells is carried on in a manner
precisely analogous to that of the algae ; that between the outer inte-
gument and the primordial cell-wall of each cell a hyaline membrane
is secreted, causing the outer integument to expand ; and as the prim-
ordial cell-wall is attached to it at various points, it causes the internal
colouring-matter, or endochrome, to assume a stellate form (see fig.
194, No. 3), 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. Mr. 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, consisting of a slender elastic filament, by
which it is attached 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 re-
cover its former nestling-place by contracting the tether.

DESMIDACE^E. 409

" Wonderful as it may appear, we have here an example of all the
functions of vegetable life — namely, absorption, assimilation, exhala-
tion, secretion, reproduction, &c. — effected by a single cell. This is
ever continued in the highest and most complicated orders of vegetable
life, in which there is a variety of organs adapted for the performance
of different offices, the functions of which are effected by the agency of
cells, obtaining materials of formation and support from the ordinary
chemical agents around them. Thus the more man gains a knowledge
of the wonders displayed in these minute objects of creation, the more
is the mind humbled and inspired with reverence fofr the First Great
Cause."*

DESMIDACE^E.

The disputed question of the animal or vegetable nature of these
cells has received much valuable elucidation from Mr. Ralfs, who has
given to the world the results of his laborious researches in his excel-
lent work on The British Desmidiece, published in 1848 ; and the con-
clusions of 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 ourselves for that purpose of Mr. Ralfs' labours, with a recom-
mendation to those of our readers who would wish to familiarise them-
selves more completely with this peculiar species, to consult the pages
of the book above referred to.

Desmidacece 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 peculiari-
ties are the beauty and variety of their forms and their external mark-
ings and appendages ; but their most distinctive character is their evi-
dent division into two or more segments. Each cell or joint in the
Desmidaceae generally consists of two symmetrical valves or segments ;
and the suture or line of junction is in general well marked. The mul-
tiplication of the cells by repeated transverse division is full of interest,
both on account of the remarkable manner in which it takes place, and
because it unfolds the nature of the process in other families, and fur-
nishes a valuable addition to our knowledge of their structure and phy-
siology.

The compressed and deeply-constricted cells of Euastruin 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
* Dr. Mantell's Wonders of Geology.

410 THE MICROSCOPE.

appears like two, the segments being always distinct, even from the
commencement. As the connecting portion is so small, and neces-
sarily 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 por-
tions. At first they are devoid of colour, and have much the appear-
ance of condensed gelatine; but as they increase in size, the internal
fluid acquires a green tint, which is at first very faint, but soon be-
comes darker ; at length 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. And lastly, in Xanthidium and Staurastrum the spines and
processes make their appearance, beginning as mere tubercles, and
then lengthening until they attain their perfect form and size, and
armed with setaa; 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, pre-
cisely similar to what has been described by Agardh and others as
occurring in the Confervse. This movement has been aptly termed a
swarming. All the Desmidacese are gelatinous. In some the mucus
is condensed into a distinct and well-defined hyaline sheath or cover-
ing, as in Didymoprium Grevittii and Staurastrum tumidum ; in others
it is more attenuated, and the fact that it forms a covering is discerned
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 he has " distinctly seen that
the large and small granules contain starch, and were sometimes even
entirely composed of it ;" and that " in the month of May he had ob-
served many specimens of Closterium in which the whole interior sub-

DESMIDACEJE. 411

stance was granulated, and all the grains gave with iodine a beautiful
blue colour, as is the case with starch."*

Did we trust solely to the eye, we should indeed be very liable to
pronounce these variable and beautiful forms to far more closely re-
semble animals than vegetables in their appearance. All favours this
supposition. Their symmetrical division into parts ; the exquisite disk-
form, finely cut and toothed Micrasterias ; the lobed Euastrum ; the
Cosmarium, glittering as it were with gems ; the Xanthidium, 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 ob-
server to belong rather to the lowest forms of animal, than vegetable
life. Another indication may be adduced by rendering apparent their
power of motion, as Dr. Bailey did : taking a portion 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 will work
their way to the surface, and cover it with ' a green stratum : this is
no doubt owing to the stimulus of the light exerted upon all matter,
although at first appearing very like a voluntary effort. Another is
afforded by their retiring beneath the surface when the pools dry up.
Mr. Ralfs states, that he has taken advantage of this circumstance to
obtain specimens less mingled with foreign matter than they would
otherwise have been.

During the summer of 1854, the Rev. S. G. Osborne drew our
attention to the economy of an interesting specimen of this family,
the Closterium Lunula. After many careful investigations, we have
been enabled to satisfy ourselves 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, and the cilia which give to it its impulse, are ob-
tained by the use of sunlight, transmitted through the combination of
coloured glass proposed by Mr. Rainey, and adapted to a l-4th achro-
matic condenser ; with which must be used a l-6th objective of Ross's.

* 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 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 characteristic purple tint; and then, by
applying the highest power of the microscope, the peculiar colour of the purple iodide
of starch can in general be easily perceived.

412

THE MICROSCOPE.

The Gillet's condenser, or parabolic reflector, will do equally well with
a l-8th objective. In diagram A, fig. 195, is given a sketch of a speci-
men of the C. Lunula ; with the above arrangement of microscopic

fig. 195.

power, and a deep eye-piece, the cilia will be seen 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 cir-
culation becomes fainter, and the cilia are seen with more distinct-
ness.

In diagram A, a line is drawn at & to a small oval mark ; these
exist at intervals, and more or less in number over the surface of the
endochrome itself, beneath the membrane 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
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

DESMIDACE^. 413

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 circu-
lation, use a Gillet 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 circulation 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 uninterrupted 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 be-
tween the outer and inner case, and again the mere sluggish move-
ment between the inner case and the endochrome.

At B is given an enlarged sketch of one extremity of a C. 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 distinctly ; 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. 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 twist-
ing motion to the free bodies. The line — a, in this diagram, denotes
the outline of the membrane 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,

414 THE MICROSCOPE.

however, do enter the chamber ; occasionally, 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 C. Lunula, we have never
seen any thing like conjugation ; but we have repeatedly seen what we
shall now describe — 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 j 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 ob-
served, 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
an elongation of the membranous sac appear, giving a semi-lunar sort
of chamber j this, as the endochrome elongates, becomes more denned,
until it has the form and outline of the chamber at the perfect ex-
tremity. The obtuse end — b of the frond is at the same time elon-
gating 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 circulation 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 full beautiful construction.
E is a diagram of one end of a C- didymotocum, 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 Micrasteria. This is im-
perfectly shown in fig. 196.

The Mode of Finding and Taking Desmidacece. — As the difficulty of

DESMIDACE^. 415

obtaining specimens is very great, it will materially assist the efforts
of the microscopist to learn the method adopted by Mr. Ralfs, Mr.
Jenner, and Mr. Thwaites. " In the water the filamentous species re-
semble 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 of Euastrum, Micrasterias, Clos-
terium, &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 surface in little masses, and with care may be removed and 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 considerable 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 employment 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 Staurastrum,
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. I would recommend the following
method as the best adapted 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 in-
verted 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 Des-
midacea3, in this way brushed off, will be found lying in the palm. The
greatest difficulty is in withdrawing the hand from the surface of the
water, and probably but little will be retained at first ; practice, how-
ever, will soon render the operation easy and successful. The contents
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.

416

THE MICROSCOPE.

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.

Sporangia are collected more frequently by the last than the
preceding methods. When carried home, the bottles will apparently
contain only foul water ; but if it remain undisturbed for a few hours,
the Desmidacese will sink to the bottom, and most of the water may
then be poured off. If a little filtered rain-water be added occasion-
ally, to replace what has been drawn off, and the bottle be exposed to
the light of the sun, the Desmidacese will remain unaltered for a long
time."

fig. 197. a, elementary cells. I, branched cellular tissue.

The Desmidacese prefer an open country. They abound on moors
and in exposed places, but are rarely found in shady woods or in deep
ditches. To search for them in turbid waters is useless ; such situa-
tions are the haunts of animals, not the habitats of the Desmidaceae ;
and the waters in which the latter are present are always clear to the
very bottom.

To proceed in our inquiry : we now find the cell converted into
other forms, and the transparent membranous cell-wall becoming
thickened ; spontaneous fissure then takes 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
before observed, of the vegetable cell is spheroidal ; but when deve-
loped under pressure within walls, or denser tissues, they take other
shapes, as the oblong, lobed, square, prismatical, cylindrical, fusiform,
muriform, stellate, jttamentous, &c. : it is then termed Parenchym ;
and the cells woven together are called cellular tissue. In pulpy
fruits the cells may be easily separated one from the other : a thin
transverse section of a strawberry is represented at No. 15, Plate
XVI.: within the cells are smaller cells, commonly known as pulp.
Fig. 197, a, is the elementary form of oval cells or vesicles, passing
on to form branched cellular tissue, b. Kemarkable specimens of the

CELLULAR TISSUE.

417

filamentous tissue may be seen in No. 19, Plate XVI., the fungiform
elongated cells from the Mushroom,; only another and more closely

fig. 198.

1. Vertical section of root of Alder, with outer wall. 2. Spiral vessels from the
Opuntia vulgaris. 3. Section of a Nut, showing cells with small radiating pores.
4. Interior cast of the siliceous portion of spiral tubes of the Opuntia. 5.
Vertical section of Elm ; in the lower portion small spiral fibres are seen between
the pores.

connected growth of the mucedinous fungi, or, as it is commonly
called, the spawn of the mushroom.

No. 20, Plate XVI., is stellate tissue cut from the stem of a rush ;
here we have the formative network dividing into ducts for the pur-
pose of conveying the juices to the leaves of the plant. These ducts
undergo other transformations ; and the cell itself may become gradu-
ally changed into a spiral continuous tube or duct, as seen in No. 21,
Plate XVI. ; these are sometimes formed by the breaking down of
the partitions, as shown in the previous figure — in the centre we have a
compound spiral duct, much resembling a portion of tracheae from the
silkworm. Another important change occurring in the original cell is
that of its conversion into woody fibre, so largely entering into the
texture of vegetables. These fibres are elongated cells of a spindle
shape, or tubes drawn out to a point at each end, whose internal cavi-
ties become gradually filled up, as represented occurring at b, fig. 197.
The spiral thread may be either free, or adhering to the side of the
tube. In the first case it forms the so-called sperm animalcules of the
antheridise of mosses ; its elastic and hygrometric properties giving
some resemblance to motion, fig. 198, No. 2. Nageli believes this to

E E

418

THE MICROSCOPE.

arise from the terminal enlargement of each fibre being its free nucleolus ;
and he also assumed that the motile threads, or vibratory cilia, found

fig. 199.

1. Woody fibre from the root of the Elder, exhibiting small pores. 2. Woody fibre of
fossil wood, showing large pores. 3. A section of stem of Clematis, with pores.
At 4 the pores are highly magnified, to show the line which passes round them.

5. A vertical section of a leaf of the India-rubber tree, exhibiting a central gland.

6. Woody fibre, bordered with pores and spiral fibres. 7. Portions of fossil wood
taken from coal.

on the spores of some alga3, &c., are of an analogous nature, each spore
being a nucleolus.

In fig. 199, "No. 1, we have a modification of the cellular tissue,
with its sides marked by pits or dots, produced in consequence of the
cell contents being unequally deposited over the inside of the cell-wall
or membrane. The office of this peculiar tissue is said to be for the
purpose of conveying fluids with rapidity in the direction of the woody
tissues that surround it, or from the lower to the upper limbs : it is
commonly recognised as the porosity of wood. Common woody fibre
(Pluerenchyma) has its sides free from definite markings. In the
coniferous plants, the tubes are furnished with circular disks, shown
at No. 6, fig. 199. These disks are thought to be contrivances to
enable the tubules of the woody tissue to discharge their contents from
one to the other, or into the cellular spaces. Such as have aromatic

CELLULAR TISSUE.

419

secretions are furnished with glands, a circumstance which has led to
the division of woody tissue into simple and glandular. A large cen-
tral gland is seen in a section of a leaf from the Ficus elastica, India-
rubber-tree, No. 5, fig. 199. Professor Quekett says, "The nature of
the pores, or disks, 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 bicon-
vex, Nos. 3, 4 ; and in their centre is a small circular or oval spot,
No. 6, fig. 199, and Nos. 1 and 5, fig. 198: the latter may occur
singly, or be crossed by another at right angles, which gives the ap-
pearance of a cross. No. 2, fig. 19 9-, is a vertical section of fossil
wood, remarkable for having three or four rows of woody tissue occu-
pied by large pores without central markings."

At No. 7, fig. 199, we have represented fragments of Durham coal,
composed almost entirely of woody cells, in which are two flattened
spiral bands interlacing each other at regular distances, and having
small central spaces between them.*

Plants are likewise furnished with lactiferous ducts or tissue, the
proper vessels- of the old writers. These ducts convey a peculiar fluid,

WIKB

Lactiferous ti$s^te.

fig. 200.

Reticulated ducts.

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 aggre-
gation of cells, the yeast-plard> and therefore has some claim to being
considered the stage of development preceding that of the reticulated

* In the January number, 1854, of the Microscopical Journal will be found a most
interesting account of the microscopical characters of coal, by Professor Quekett.

420

THE MICROSCOPE.

ducts seen near it in fig. 200. In the section from the India-rubber
tree, fig. 199, a network of these lactiferous tubes may be found filled
with a brownish or granular matter j that in fig. 200 is an enlarged
view of this tissue from the liber of an exogen, taken near the root.

Among the cell-contents of some plants we have beautiful crystals
known as Raphides: the term is derived from patpiQ, a needle; the
crystals, when first noticed, were of this shape. They are composed of
the phosphate and oxalate of lime ; their use in the economy of the
plant is unknown. " Whether the result of chemical affinity, or of a
vital process, cannot be decided j but it is certain that they can be
produced artificially in the tissue of plants."

The French philosopher, Geoffrey St. Hilaire, has endeavoured
to prove that crystals are the possible transition of the inorganic
to organic matter. Crystals have naturally been supposed to conceal
the first beginnings of the phase na*med organic, because in crystals
we first meet with determinate form as a constituent element. The
matter named inorganic has no determinate form ; but a crystal is
matter arranged in a particular and essential form. The differences,
however, between the highest form of crystal and the lowest form of
organic life known — a simple reproductive cell — are so manifold and
striking, that the attempt to make crystals the bridge over which in-
organic matter passes into the organic is almost universally regarded
as futile.

1 fig. 201. 2

1. A Section from the outer layer of the bulb of an Onion, showing a crystal of oxalate
of lime, with raphides. 2. A vertical section of root of a Fern.

If we examine a portion of the layers of an onion, fig. 201, or
take a thin section of the stem or root of the garden rhubarb, fig. 202,
No. 4, we shall observe many cells in which either bundles of needle-
shaped crystals or masses of a stellate form occur.

Kaphides were first noticed by Malpighi in Opuntia, and were
subsequently described by Jurine and Raspail. According to the

CELL-CONTENTS.

421

latter observer, the needle-shaped or acicular are composed of phos-
phate, and the stellate of oxalate of lime. There are others having
lime as a basis, combined with tartaric, malic, or citric acid. These
are easily destroyed by acetic vacid ; they are also very soluble in many
of the fluids employed in the conservation of objects ; 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 parts of the plant; in the stem, bark,
leaves, stipules, sepals, petals, fruit, root, and even in the pollen, with
few exceptions. They are always situated in the interior of cells, and
not, as has been stated by Raspail and others, in the intercellular pas-
sages.* Some of the containing cells become much elongated j but still
the cell-wall can be readily traced. In some species of Aloe, as, for
instance, Aloe verrucosa, with the naked eye you will be able to discern
small silky filaments. When these are magnified, they are found to be
bundles of the acicular form of raphides.

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

fig. 202.

1. A Transverse section of stem of Equisetum, showing the hexagonal shape of cells.
2. A vertical section, showing the elongated cell. 3. Cells of the Pear, showing
Sclerogen, or gritty tissue. 4. Cells of garden Khubarb, filled with raphides. 5.
Cells from same, filled with starch-grains.

cell is occupied either by an octahedral or a prismatic crystal of oxalate
of lime : in some specimens the octahedral form predominates ; but in

* 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 would not be
considered as an exceptional case, the vessels being regarded as elongated cells.

422 THE MICROSCOPE.

others from the same plant the crystals may 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, ren-
dering the plant so exceedingly brittle, that the least touch will occa-
sion a fracture ; so much so, that some specimens of Cactus senilis, said
to be one thousand years old, which were sent a few years since to
Kew from South America, were obliged to be packed in cotton, with
all the care of the most delicate jewellery, to preserve them during
transport.

Raphides, of peculiar figure, are common in the bark of many trees.
In the hiccory (Caryaalbd) maybe observed masses of flattened prisms
having both extremities pointed. In vertical sections of the stem of
Elceagnus angustifolia, numerous raphides of large size may be seen in
the pith. Raphides are also found in the bark of the apple-tree, and in
the testa of the seeds of the elm ; each cell contains two or more very
minute crystals.

In fig. 203 we have other representations of the crystalline struc-
ture of plants, in sections taken from wheat, grass, and the leaf of
Deutzia scabia. This insoluble material is called silica, and is abun-
dantly distributed throughout certain orders of plants, forming a skele-
ton after the soft vegetable matters have been destroyed : masses of it,
having the appearance of irregularly-formed blackened glass, may
always be found after the burning of hay or straw ; it 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 dissolve the tissue by
boiling it in nitric acid for several hours ; the organic portion is thus
destroyed, and the siliceous matter remains a perfect cast of the ori-
ginal structure.

In the Graminacece, especially the canes ; in the Equisetum hye-
male, 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. 203, No. 2, we have beautifully-arranged masses of silica with
raphides. The leaves of the Deutzia, No. 3, are remarkable for their
stellate hairs, developed from the cuticle of both their upper and under
surfaces; forming most interesting and attractive objects when ex-
amined under the microscope, either by polarised or condensed light.

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-

CELL-CONTENTS. STAKCH.

423

forming a similar office in the economy of plants as that of fat in ani-
mals. It occurs in all plants at some period of their existence, and is
the chief and great mark of distinction between the vegetable and ani-
mal kingdoms. Its presence is detected by testing with a solution of

fig. 203.

1. Portion of the husk of Wheat, showing siliceous crystals. 2. Siliceous cuticle of
blade of Grass (Pha.rus cristatus). 3. Siliceous cuticle from under surface of leaf of
Deutzia scahia. 4. Section of a Cane ; the cell-walls of silica, and internal pores
filled with granular matter.

iodine, which changes it to a characteristic blue or violet colour. Being
insoluble in cold water, it can be readily washed away and separated
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,

424 THE MICROSCOPE.

as shown in fig. 202, and Plate XVI. from the garden rhubarb. Starch-
grains are variable in size : the tous-les-mois, 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 present the appearance of concentric irre-
gular circles ; and most of the granules have a circular spot termed the
hilum, around which a large number of curved lines are arranged : seen
best by polarised light.

Leeuwenhoek, to whom we are indebted for the earliest notice of
starch-granules, enters with considerable minuteness into a description
of those of several plants — such as wheat, barley, rye, oats, peas, beans,
kidney-beans, buckwheat, maize, and rice ; and very distinctly describes
experiments made by him in order to investigate the structure of their
starch-granules. Dr. Reissek regards the 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 of a solid homogeneous structure.

Mr. Busk, after devoting considerable attention to the subject,
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 microscope, 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."* The
mode of applying the concentrated 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 in-
clination 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 ^-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-

* G. Busk, F.R.S., on the Structure of the Starch-granule; Quarterly Journal of
Microscopical Science, April 1853.

PLATE XVI.

VEGETABLE STRUCTURES.

1. Cells of Torula Cerevisia, or Yeast Plant. 2. Hairs of Urtica Dioica, or Stinging-Nettle. 3. Ciliated
spores of Confervse. 4. Starch-grains broken by applying heat. 5. Starch from Tous-les-mois.
6. Starch from Rice. 7. Starch from Sas?o. 8. Imitation- Sago Starch. 9. Wheat Starch. 10. Rhu-
barb Starch retained in their cells. 11. Maize Starch. 12. Oat Starch. 13. Barley Starch. 14. Potato
Starch. 16. Section of Potato attacked by fungoid disease. 17. Section of Potato, showing total
absence of Starch grains. 18. Section of Potato, cells filled with healthy Starch grains. 15. Section
of a ripe Strawberry, cells ovoid, and containing a brown nucleus. 19. Mushroom Spawn, elongated
cells. 20. Simple stellate tissue from the stem of a Rush. 21. Spiral vessels from the Leek and
Rhubarb. 22. Radiating cells or pores from the outer shell of the Ivory-Nut.

CELL- CONTENTS. STARCH.

425

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 disk becomes torn, and is then dis-
tinctly seen, especially in those coloured blue, to 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 the central opening into the interior of the ovate vesicle.

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.

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 adulteration remain undissolved.

Wheat-flour is frequently adulterated with various substances ; and
in the detection of these adulterations, the microscope, together with a
slight knowledge of the action of chemical re- agents, lends important

fig. 204.

W/wat-Flour Starch-granules, with a small portion of its cellulose. Magnified 420

diameters.

assistance. It enables us to judge of the size, shape, and markings on
the starch-grains, and thereby to distinguish the granules of one meal

42 G THE MICROSCOPE.

from that of another. In some cases the microscopic examination is
aided by an application of the solution of potash. Thus we may
readily detect the mixture of wheat-flower with either potato-starch,
meal of the pea, and 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-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 ren-
dered very obvious under the microscope. Polarised light may be used
as an additional aid in this detection ; wheat-starch presents a beau-
tiful black cross proceeding from the central hilum, whereas the starch
of the oat shows nothing of the kind.

The diseases of wheat and corn are most readily detected under the
microscope ; these will be seen to be produced by a parasitic fungus, as
well as the animalcule represented in a previous chapter : all of which
are more or less dangerous if used as articles of food when in this state.

Adulteration of bread with boiled and masJied 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 of an article very much more nutritious.

This adulteration may be readily detected by means of the micro-
scope. The cells which contain the starch-corpuscles are in the potato
very large, fig. 205 ; 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 much less distinct and much altered in
their form. »

Adulteration with alum and " stuff ? — This adulteration is prac-
tised with a twofold object : first to render flour of a bad colour and
inferior quality white and equal, in appearance only, to flour of supe-
rior quality ; and secondly, to enable the flour to retain a larger propor-
tion of water, by which the loaf is made to weigh heavier.

Before leaving the subject of starch, allusion may be made to the
prevalent and destructive epidemic among 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, Plate XVI. Hence it may

ADULTERATION OF WHEAT-FLOUR.

427

be 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 are developed as in most other decaying vegetable substances.

fig. 205.

Potato Starch-granules, sold under the name of British Arrow-root, and used to
adulterate flour and bread. Magnified 240 diameters.

This will undoubtedly explain the most prominent symptom of the
potato-disease, the tendency to decomposition ; and is a point in which
the microscope confirms the result of chemical experiment : for it has
been found that the diseased potatoes contain a larger proportion of
water than those that are healthy. A want of organising power is evi-
dently 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."*

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 Mitchell, Normandy, Chevalier, Jules Garnier, and Harel ;
and has now at length derived a singularly lucid exposition from the
researches — so far as they have extended, and their extent has been

* Professor Quekett's Histology of Vegetables. We would also refer the reader to
an admirable work on Fungi, by Arimini, an Italian botanist, 1759,

428 THE MICROSCOPE.

very large — of Dr. Hassall.* The report of these inquiries fills be-
tween 600 and 700 closely printed pages of a large octavo, replete with
details of the fraudulent contaminations commonly practised by the
people's purveyors, at the people's expense of health and pocket.

By the help of modern chemistry, a wonderfully small fractional
part of many substances contained in, or mingled with some other
substance, may be discovered. The grave gives up its secret to the
chemist, who detects the minutest particle of arsenic in the body of the
victim long murdered. But every body who is poisoned is not poisoned
by an agent so responsive as arsenic to chemical tests. Most poisons
of the vegetable class soon decompose, and cannot be recomposed or
reproduced. If 'they contained permanent active principles, the quan-
tity of these is commonly too small to admit of any demonstration
which is practically trustworthy. Much of the vegetable rubbish with
which articles of food are poisoned, in a comparatively mild degree, by
adulteration, is undiscoverable by chemical science. Sloe-leaves among
tea defy the examination of the detective chemist. He may demon-
strate the tea not to contain as much of its active principle " thein," as
it ought ; he may prove that its quality is bad, — but he cannot show
why, he cannot elicit from the fragments of the Chinese leaf the pro-
duce of the British blackthorn. But the problem that baffles chemistry,
is solved by vegetable anatomy. The microscope supplies the short-
comings of the crucible and the test-tube. The root, leaf, stalk, bark,
flower, fruit of each plant, herb, or tree, has its peculiar structure, dis-
cernible by microscopical examination in the minutest portion of each
of those parts. The fragment of tea presents a different arrangement
of cells, vessels, and other parts, from that exhibited by the piece of
sloe-leaf; and the difference is distinguished with certainty by the
aid of the microscope.

If gratitude is due to those who discover antidotes to disease, or
invent appliances for relieving pain, the same obligation must un-
doubtedly be admitted to the man whose researches, by detecting the
hidden seeds of sickness, must directly tend to prolong life and increase
its comforts. The facts of the case, though already more or less known
to the public, are really startling when presented in so large a mass
and on such formal authority. " In nearly all articles," said Dr. Hassall,
before a committee appointed by the House of Commons to inquire
into these adulterations, " whether food, drink, or drugs, iny opinion is

* Food and its Adulterations ; comprising the Reports of the Analytical Sanitary
Commission of the Lancet, for the years 1851 to 1854 inclusive. By Arthur Hill
Hassall, M.D.

ADULTERATION OF FOODS.

429

that adulteration prevails." And many of the substances, he added, em-
ployed in the adulterating process, were not only injurious to health,
but even poisonous. The investigations were conducted in the most
practical and business-like manner. Samples of the articles to be
analysed were purchased to the number of twenty or forty specimens
from different classes of traders; the powers of the microscope, as well
as other tests, were then brought to bear upon them, and a report was
drawn up embodying the general conclusions. The microscope seems
to have been the more effective instrument in the work. Less than

fig. 206.

Tea adulterated with foreign leaves.

a, upper surface of leaf ; &, lower surface, showing cells ; c, chlorophylle cells ; d, elon-
gated 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 : after Hassall.

five years ago, for instance, it would, we are told, have been impos-
sible to detect the presence of chicory in coffee : in fact, the opinion of
three distinguished chemists was actually quoted in the House of Com-
mons to that effect ; whereas by the use of the microscope the differ-
ences of structure in these two substances, as in many other cases, can
be promptly discerned. Out of thirty-four samples of coffee purchased
at. the outset of the investigation, chicory was discovered in thirty-one;
chicory itself being also adulterated with all manner of compounds.

430

THE MICROSCOPE.

fig. 207.
Structure and character of genuine ground Coffee : after Hassall.

fig. 208.

Sample of Coffee adulterated with loth Chicory and Roasted Wheat : after Hassall.
a a a, small fragments of coffee j 1 1 b, portions of chicory ; c c c, starch-granules of wheat.

ADULTERATION OF FOODS.

431

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 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.1'

In this country cocoa is sold under the names of flake, rock, granu-
lated, soluble, dietetic, homoeopathic cocoa, &c., fig. 209. Now these
names are merely employed to show that they are compounds of sugar,
starch, and often other substances. Unfortunately, however, many of

fig. 209.

Adulterated Cocoa, sold under the name of Homoeopathic Cocoa, a a a, granules and
cells of cocoa ; b b b, granules of Canna-starch, or Tous-les-mois ; c, granules of
tapioca starch : after Hassall.

the preparations of the cocoa-nut sold under the names of chocolate and
of cocoa-flakes, consist of a most disgusting mixture of bad or musty
cocoa-nuts, with their shells, coarse sugar of the very lowest quality,
ground with potato-starch, old sea-biscuits, coarse branny flour, animal
fat (generally tallow, or even greaves), &c.

Were we to extend our inquiries to drugs and pharmaceutical pre-
parations, the immense importance of the question would become still

432 THE MICROSCOPE.

more strikingly manifest. Nearly all the most useful and important
articles of the Materia Medica are grossly and systematically adulte-
rated, often to an enormous extent; so that it is impossible to estimate
the strength of the different remedies administered, or the extent
and character of the effects produced. The greatest confusion and un-
certainty are thus introduced into the practice of medicine, and, no
doubt, many valuable lives are annually sacrificed. For confirmation
of this statement, see Keports of the Analytical Sanitary Commission,
in the Lancet, 1853 and 1854, on the Adulteration of Jalap, Scammony,
Opium, &c.

We nevertheless believe that the growing intelligence and inquir-
ing spirit of the masses, with the greatly increased facilities of detec-
tion so ably pointed out by Dr. Hassall, and afforded by modern
science, will tend not merely to check the evil for the time being, but
ultimately suppress 'such dangerous practices. A remedy is in the
hands of the people ; let them only interest themselves in that which
so nearly concerns their health — nay, lives. Every man should be
able to ascertain the quality and general purity of the substances that
form his daily food : this he may do by acquiring a knowledge of the
microscope ; and by taking such a book as Dr. Hassalls for his guide,
he will soon learn where to look for adulterations, what to look for, and
how to find them out easily for himself.

All plants are provided with hairs ; and a few, like insects, with
weapons of a defensive character. Those in the Urtica dioica, com-
monly 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 appear-
ance seen at No. 2, Plate XVI. At No. 3, same plate, we have repre-
sented a few of the interesting ciliated spores from Confervce.

The next of the cell-contents falling under our notice is that to
which leaves owe their green colour, and is known as Chlorophyl. It
is of a resinous nature, containing nitrogen formed under the action
of light, and not otherwise. In the autumn its colour changes to red
or yellow. It is soluble in spirits of wine or ether, but not in water ;
and is usually contained in cells lying below the surface. The astonish-
ing circulation of the fluid-contents of vegetable cells may be examined
at the same time as the Chlorophyl granules, by selecting for the pur-
pose the transparent water-plants Chara, Nitella, Anacharis, and Val-
lisneria, or the hairs of Groundsel and Tradescantia. The circulation
of the sap in plants growing in water is now termed by botanists Cydosis.

CHLOROPHYL.

433

It is necessary to take a thin section or strip from the flattened
leaf of Vallisneria, which will exhibit a series of oblong cells, as seen in
fig. 210, No. 4. Among the granules a few of a larger and more

• 1 '(,

1 -'

'-' §

f »'
^ ^

, \.

o* (o

H

i

it

(J
t ^

1 %

y o

w!

" rO

.Y^A

ao

!«PlS

I 0

HI

M
y o

y

5 »

, 0

3 >

9 ^

fig. 210.

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, showing the budding at
joints. 4. Portion of a leaf of Vallisneria spiralis, with its cells and granules.

transparent character than the rest may be seen, having the nucleolus
of the cell within them.

Chara vulgaris is the plant in which the important fact of vegetable
circulation was discovered, and in which, from the extreme simplicity

F F

434 THE MICROSCOPE.

of its structure, much more is possibly observable, and with lower mag-
nifying powers than other plants require. Fig. 210, No. 1, is a por-
tion of the plant of the natural size. Every knot may produce roots ;
but it is remarkable, that they always proceed from the upper surface
of the knot, and then turn downwards ; so that it is not peculiar that
the first roots also should rise upwards with the plant, and come out of
the seed-skin, and then turn downwards.

The stems and arms are tubular, and entirely covered with smaller
tubes ; the circulation can mostly be observed in these : see No. 2.
Any ordinary cutting 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 number 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.

Mr. Varley gives the following directions for cultivating these plants.
He says :

" 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 various joints
very long roots into the water, and these would by agitation be
destroyed, and then the plant 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 clone 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.

Imitate the freshness of the water by having an extent of the
surface, which it is requisite to skim frequently, or suffer to overflow
by the addition of more water. These precautions being attended to,
a clear bright surface is kept. It is also desirable to change a small
portion of the water ; but this should be done without agitation. The
best vessels for cultivating this plant are either wide pans holding
three or four gallons, or glass jars a foot or more high ; into these the

CHARA. VALLISNERIA. 435

Chara may be placed, either with clean water alone, or a little earth
may be sprinkled over it, so as to keep it at the bottom ; or the bottom
may be covered one inch with closely-pressed mould, in order that the
water may be put in without disturbing it. On this lay the Chara,
with a little earth over the lower ends to fix it. The vessels kept in-
doors have a film which is always forming on the water, and which re-
quires to be frequently removed. By letting the water overflow the
surface becomes skimmed, though dipping out gently will do ; but in all
cases of pouring in water, hold something, such as a saucer or flat piece
of wood, to receive the pouring, and make it spread, instead of allowing
it to descend at once on the surface. Pans in the open air nearly full
of water will be kept in order by the wind and rain ; only take care to
supply the deficiency (the effect of evaporation), and to change some of
the water if it is considered necessary.

Imitate the equal temperature of its native holes, by sinking the
pan a short way in the earth ; but during frosty weather keep the pan
wi thin-doors, and at the lower part of the house, as this situation is
generally the most uniform in its temperature.

The Chara will live in any temperature above freezing, and grows
quicker as the warmth increases ; but above the earth, as outside of a
first-floor window, it will not bear the daily difference between the
mid-day sun and the cold of sun-rising. The glass jars I keep within
the house as nearly uniform in warmth as convenient. 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 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.

TJie New Water-weed (Anacharis alsinastrum). — This remarkable
plant has recently made its appearance in the rivers Ouse and Cam.
It is so unlike any other water-plant, that it may be at once recognised

436 THE MICROSCOPE.

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 in-
creased so much, that the river might be said to be full of it.

The colour of the plant is deep green ; the leaves are 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 inde-
pendent 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, at
page 196.

Mr. Lawson has pointed out the particular cells in which the current
or circulation may most readily be 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 dis-
tinct, without changing the form of the leaf.

VASCULAR TISSUE.

This tissue in plants is somewhat analogous to the vascular system
of animals ; for this reason, and also for that of its tubular appear-
ance, it was called by the older botanists trachece. It consists of rounded,
square, columnar, and elongated tubes or cells, with membranous walls,
having spiral fibre within. In some cases many fibres are seen run-
ning in the same direction, forming a band, when they are termed com-
pound-spiral. Spiral fibres are represented in Plate XVI., No. 21.
Under this head other membranous tubes are included, in which the

VASCULAR TISSUE. 437

arrangement of the fibre has been considerably modified in its depo-
sition. 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 %as 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 dispute between botanists. The
late Mr. Edwin Quekett gave much attention to the subject ; and in
an excellent paper published in the Microscopical Society's Transac-
tions, 184.0, gave the result of his observations.

In order to watch the development of the membranous tube of a
vessel, no better example can be chosen than the young flower- stalk of
the long-leek (Allium pornwn), in the state in which this vegetable is
usually sent to market ; it is then most frequently found to be about an
inch or more in length, and from a quarter to half an inch in diameter.
This organ occurs very low down amidst the sheathing bases of the
leaves ; and from having to lengthen to two or three feet, and contain-
ing large vessels, 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 part ; 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 dis-
appeared 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 vegetable
jelly ; by boiling which, or by the addition of alcohol, the contents, or
at least the albuminous portion, become coagulated. From this circum-
stance, every cell appears 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. When the granules have arranged

438

THE MICROSCOPE.

themselves throughout the entire length of the tube, those which were
first deposited, and had then some slightly visible space between them,
become reinforced by others, or nourished by the contents of the vessel ;
so that space becomes obliterated, the fibre assuming a thread-like shape
with defined borders, and sufficiently large to allow of the transmission
of white light. When this action has progressed throughout the entire
vessel, the transparency is restored, and the entire mass of granules
disappears. The vessel having arrived at maturity, the liquid contents
are absorbed, as happens in the cells of the pith ; the vessel is then
empty. Probably its being seen in these different states, at one time

fig. 211.

. A portion of the leaf of Sphagnum, showing ducts, vascular tissue, and spiral fibre,
in the interior of its cells. 2. Porous cells obtained from the testa of Gourd-seed,
communicating with each other, and resembling ducts. 3. A transverse section of
Taxus lacwita (Yew), showing the woody fibre. 4. Vertical section of the same,
exhibiting pores and spiral fibres. 5. A section from the stem of a coniferous
plant, with a transverse cutting magnified, and showing the zones of annual growth,
or annual rings.

full and at others empty, may account for the discrepancies existing
among botanists as to the functions these vessels perform. 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 membrane
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

VASCULAR TISSUE.

439

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
indicates a low degree of organisation ; as shown by its occurrence in
Sphagnum, Equisetum, and Lycopodium, which plants, in the ascending
scale of 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 pro-
ceeding 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 modifi-
cations of the above process are to be observed, as in the reticulated
vessels met with in the common balsam (Balsamina hortensis). The
primary formation of fibre in these vessels is marked by the tendency
of the granules to take a spiral
course, when it happens that some
one of the granules becomes en-
larged 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 gra-
nules into bead-like strings, taking
a contrary direction to the original
fibre, forming a cross-bar, or rami-
fying, thereby causing the appear-
ance by which the vessel is recog-
nised.

In the exogenic vessel, the de-
velopment 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 some-
what hollowed or cupped, and the centre only thin membrane. These
vessels are best seen in the young shoots of the Willow. In the endo-

fig. 212. -

A portion of the epidermis of the sugar-
cane, showing the two kinds of cells of
which it is composed, magnified 200
diameters.

440 THE MICROSCOPE.

genie vessel the connecting branches are given off beneath each other,
so that the dots, which are rounded, are arranged in longitudinal rows j
but inthe acrogenic, or scalariforra, in which the vessels are generally an-
gular, 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 entertained by
Mirbel, Kichard, 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.

Vegetable tissues are best prepared for the microscope by making
thin sections, either by maceration, by tearing between 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 magnify ing-glass. Take, for instance, a piece of aspa-
ragus, 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 to its sepa-
ration. The cuticle or external covering of plants assumes various at-
tractive forms, best seen in the pelargonium, oleander, &c. j it may be
mounted either 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

PREPARATION OF VEGETABLE TISSUES.

441

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,
: id 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 surrounding 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 ap-
pearance to the petal.

Fibro-cellular tissue is found readily in Sphagnum or bog-moss,
and in the elegant creeper Cobsea 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 develop-

fig. 213. Male Fern.

ment of ferns may be observed by placing the seeds in moistened flan-
nel, 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. It must be

442 THE MICROSCOPE.

observed, that ferns do not form buds like other plants ; but that their
leaves, or fronds as they are properly called, when they first appear, are
rolled up in a circular form, and gradually unfold, as in fig. 213.
Ferns have no visible flowers ; and their seeds are produced in clusters,
called sori, on the backs of the leaves. Each sorus contains numerous
thecse, and each theca encloses almost innumerable spores, and these
again the seeds. There are numerous kinds of fern, all remarkable for
some interesting peculiarity ; but which from want of space we cannot
here enumerate.

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, mis-
taking 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 rela-
tions 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 into
an error in certain important respects ; for example, he has represented
what is undoubtedly an archegonium filled with cellules, sperm-cells,
which, he states, " emerged from it as from the antheridia" This is
undoubtedly incorrect.

With regard to the spermatozoids, his description is imperfect, the
only indication of the existence of cilia being a statement that he
occasionally saw a long filiform appendage, like that represented by
Meyen in the spermatozoids of Chara. On the other hand, the mathe-
matical definition of the movements of the spermatozoids is surely mis-
placed, since nothing can be more arbitrary or irregular than their course.

These observations on the Ferns have acquired vastly-increased
interest from the subsequent investigations of Hofmeister, Mettenius,
and Suminski, on the allied Cryptogams, and above all, from Hof-
meister's observations on the processes occurring in the impregnation
of the Conifers. 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 exist-
ence of analogous phenomena in the Equisetaceae, Lycopodiacese, and
Rhizocarpese, and shown, moreover, that the bodies described by
Mr. Brown in the Conifers, under the name of "corpuscles," are
analogous to the archegonuo of the Cryptogams ; so that a lin k is
hereby formed between these groups and the higher flowering plants.

PREPARATION OF VEGETABLE TISSUES. 443

For a detailed examination of these very interesting discoveries,
we must refer the reader to excellent papers, published by Mr. Henfrey,
in the Annals of Natural History, and in the Transactions of the Lin-
nean Society of London, vol. xxi., part 2, 1853.

To return from this digression upon ferns. The siliceous cuticle
from the stems of grasses exhibits the beautiful arrangement of
silica so constant in exogenous plants, all of which are very in-
teresting objects for polarised light : Equisetum, wheat, barley, oat
or rye straw, Malacca cane, bamboo, &c. Hairs are found prin-
cipally upon the under surface of leaves; they are best seen when
viewed as opaque objects. Good specimens may be obtained from
leaves of Deutzia, Anchusa tinctoria, Borago officinalis, Dolichos pru-
riens, &c. Pollen should be viewed by the dark-ground illuminator,
and with a magnifying power of 100 diameters. That of the Passion-
flower is curious, and if immersed in dilute sulphuric acid is seen to
open and disperse the grains. The pollen of the Datura Stramonium, if
placed on a slide, and a few drops of dilute acid added, will send forth a,
tube of some length ; the granular matter in the pollen may be seen to
pass along the tube until it is emptied. For these observations a half-inch
power is required. Remarkable forms of pollen are found in the follow-
ing plants : Anagallis arvensis, Fuchsia globosa, Convolvolus, Jasmine,
Lychnis, Penstemon, Polygonum orientale, Tulip, Marvel of Peru, &c.

The following are amongst the most characteristic examples of
woody fibre : flax, hemp, China-grass, section of pine, yew, date-palm,
cedar- wood, cork, oak, mahogany, root of gooseberry, sycamore, furze,
apple, vine, cotton, lace-tree bark, &c. In the cotton-plant, the hairs
are attached to and envelop the seeds ; their fibres are readily distin-
guished from those of linen, wool, &c. : being tubular fibres of cellular
tissue, these tubes, from the thinness of their sides, collapse, and
appear like flat ribbons or bands, woven or interlaced together ; which
is a reason for cotton being preferred to linen (flax) in making lint for
surgical purposes.

Thin sections of charred wood sometimes show structures not seen
in any other way. In fossil woods, after making thin sections, it is
necessary to grind them on a lapidary's wheel, and afterwards polish
them. In the ashes of coal a variety of vegetable structures may be
discovered ; which must be rendered transparent by immersion in Ca-
nada balsam. Stones and shells of nuts are prepared in the same
way ; or we may grind them between a piece of cork and boxwood,
with fine emery-powder, as we should sections of bone.

Sections of woods, if cut from hard woods, containing gum, resin,

444

THE MICROSCOPE.

&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 best instrument is the one used by Mr. Topping,

fig. 214. ab is a flat piece of ma-
hogany, 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 represents
a flat plate of brass, four inches long
and three wide, screwed to the upper
surface of ab ; 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 sere w^ work,
ing in a nut, and having a disk k
exactly adapted to the bore of the

tube ; this disk is connected 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 to be cut is put into the
tube e, and is raised or depressed by the screw/; whilst, before cutting,
the curved piece of metal h should be firmly pressed against it by the
screw c. This instrument is to be fastened to the edge of a bench or
table, where it may be always kept ready for use. The knife to be
employed may be one constructed for the purpose ; or a razor ground
flat on one side will be found to answer very well.

MetJiod 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 greenwood. If the machine to be employed
be such as described, the wood (if sufficiently 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 after-

MAKING SECTIONS.

445

wards be easily separated. The process of cutting consists in raising
the wood by the micrometer screw, so that the thinnest possible slice
may be taken off by the knife ; after a few thick slices have been re-
moved 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 exami-
nation. 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 (seen at No. 5,
fig. 211), vertical, and tangental : each of these will exhibit different
appearances, as may be seen upon reference to fig. 215. b is a vertical
section through the pith

of a coniferous plant : this
exhibits the medullary
rays, which are known 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 indicating the me-
dullary rays cut length-

wise ; whilst at c is a tan-

gental section, andya por-
tion of the same magnified : the openings of the medullary rays m m, and
the woody fibres with vertical slices of the dots, are to be 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 wall* of some of them may oftentimes be examined.
The diagram above given refers only to sections of a pine ; all exoge-
nous stems, however, will exhibit three different appearances, according

446

THE MICROSCOPE.

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 re-
quired. 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 other structures besides wood, it may here be stated, that all
horny tissues may also be considerably softened by boiling, and can
then be cut very easily.*

fig. 216.

Mr. Waringtoris Microscope. — The maker of this instrument, Mr.
Salmon, 100 Fenchurch Street, has enabled us to give a drawing of

* Professor Quekett on the Microscope.

WARINGTON'S MICROSCOPE-STAND. 447

this useful and ingenious microscope, referred to at page 51 of our
book. Fig. 216 is a representation of it as it appears when put
together ready for use ; and fig. 217 shows it taken to pieces, and ready
for packing in a leather case. The simplicity of arrangement here
exhibited must commend itself to every microscopist. It is unneces-
sary to give a lengthy description of it : and we content ourselves by
observing, that it is firmly clamped to the stand or wood bottom, and
by means of this same clamp it can be fixed to the side of a vivarium
or table. 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
screwed. With an additional arm for the reception of a single lens,
it can be converted into a dissecting microscope. It is a cheap
and useful form of instrument, either for the student or sea-side
purposes.

fig. 217.

Other makers have turned their attention to the manufacture of
cheap instruments to meet the requirements of students; among whom
we may mention Messrs. Smith and Beck, and Messrs. Field and Son
of Birmingham.

M. Dujardin found that, to produce the best effects, a prism of
glass should be used instead of a mirror. The prism should be so
arranged as to slide upon the end of the condenser, and turn upon it
in such a manner, that in whatever position the lamp or light may be,
the prism may be adjusted to it. The quantity of light passing through
it is greater than with the mirror ; and those test objects in which deli-
cate markings exist, are seen to much greater advantage in consequence
of all the rays being reflected from the same surface, which is not so
with a silvered glass mirror.

Mr. John Furze has lately directed the attention of microscopists
to a beautiful arrangement for the " illumination of objects by polarised
light on a dark field, in such a manner as to give the object a stereo-
scopic effect by a due contrast of light and shade." To obtain this re-
sult, he uses a plano-convex lens, three-fourths of an inch in diameter.
This, when fitted, is of so small a size, that it can be adapted to any

448 THE MICROSCOPE.

instrument. Such an illuminating lens should be arranged with a sys-
tem of both central and external stops, each revolving on a separate
axis ; and an adjustable cap to slide over the top of the lens, containing
a crystal of herapathite mounted between thin glass; also a plate of
selenite mounted in the same way, to use on the stage above it. Ob-
jects of too great density for transmitted light will appear under this
mode of illumination as if in relief ; and the definition of the various
parts will be so accurately displayed as to constitute a most perfect
method of viewing them.

Before we conclude, we beg to direct the attention of the reader
to the beautiful experiments of Mr. John Gorham,* as illustrating the
wonderful magnifying power of the human eye. The fact itself is
one of great interest to the microscopist, who has hitherto almost ex-
clusively availed himself of the optician's aid in his examination of
minute bodies.

We are only able to notice the results arrived at by this able in-
vestigator, which are as follows : " That when small bodies are brought
very near to the eye, their images are magnified, just as images of
larger objects, when seen at a distance, are diminished, and by the same
law. The apparent magnitude of objects depends on their visual angle.
The visual angle, for short distances, may be well illustrated by em-
ploying a small circular disk of light. This minute circular disk of
light is procured by perforating a card with a needle. A sewing-
needle, of the size marked No. 7, produces an aperture about the one-
fortieth of an inch in diameter. In order to examine the light which
is transmitted through such an aperture, all extraneous rays should be
excluded ; hence the plane in which the opening is made should be
placed at the end of a tube. The pencil of light admitted through an
opening of this kind, held within an inch or so of the eye, consists of
rapidly-diverging rays falling upon the cornea. Some of these are
entirely lost, others are intercepted by the iris, while the remainder
pass on through the pupil, which communicates to the image formed
on the retina its circular form.

For the purpose of presenting very small objects mounted on
microscopic slides in the usual way before the eye, and to exclude the
surrounding rays of light, take an upright box of pasteboard about one
inch and a half deep, and an inch and a quarter in diameter (two pill-
boxes joined will do very well); cut a couple of slits through one of its
sides, sufficiently large to admit of the slips of glass sliding to and
fro. Make two apertures (perforations with a needle) opposite to each

* Published in the Quarterly Journal of Microscopical Science, October 1845.

THE MAGNIFYING POWER OF THE EYE.

449

other — the first the l-30th of an inch, and the second the l-40th of
an inch in diameter ;* let these be so disposed, that when the glass
slip, with a small object mount-
ed on its centre, is introduced
through the slits, the two aper-
tures and the object shall all cor-
respond, and be in one straight
line, while the slide is about a
quarter of an inch behind the
smaller opening, as in fig. 218.

The image becomes more dis-
tinct when more than one aper-
ture is used ; for the intensity of
light by which it is illuminated fig. 218.

is thereby increased, being almost
in a direct ratio with the number of the openings which are employed.

It is found that the magnifying power of the eye is limited by
the magnitude of the visual angle on the one hand, and by the in-
tensity of light on the other. If the visual angle be too large, the
rays are not sufficiently refracted by the humours of the eye to con-
verge to a focus and form an image on the retina ; and if too small,
the image is reduced to a mere point. The exact amount of diver-
gence of the rays, therefore, for any individual eye, lies somewhere be-
tween these two extremes. Again, however accurately adjusted the
visual angle may be to the refractive powers of the eye, if the light be
too strong the pupil becomes so contracted that only the innermost
rays are admitted; while if it be of small intensity, the object is so
dimly illuminated as to be scarcely visible. If, then, whilst a small
object is held very near to the eye, so as to ensure a rapid divergence
of the rays proceeding from it, the pupil can be dilated by the small
quantity of light which is used, and to which, like a photometer, it
immediately responds, so as to admit as large an angle as the lens
and humours of the eye are capable of refracting, at the same time
that the object is rendered distinctly visible, then, under such circum-
stances, we have arrived at the utmost limit to the available magnify-
ing power of the eye/'

Well may we inquire with the immortal Newton : " Was the eye

* Sewing-needles are ordinarily sold in papers, numbered from 1 to 12, according
to their thickness. The diameters of apertures made with needles from the papers
marked Nos. 6, 1, 8, 9, and 10, when measured with the micrometer, are equal to the
l-36th, the l-38th, the l-44th, the l-50th, and the l-70th of an inch.

G G

450 THE MICROSCOPE.

contrived without skill in optics T or with the divine Psalmist : " He
that formed the eye, shall He not see ?"

By vision, aided by knowledge, we pierce into the heavens and
the interior of bodies, examine the minutest fragments of matter, and
the universe of stars ; by our motion on the surface of the globe, and
by its motion, we measure space, and are at once convinced that the
infinitely small, and the infinitely great, of which we get an idea by
vision, have for us no bounds — nothing that we can reach and measure.
Infinity is every where around us, and the evidences of this revealed
by the microscope carry with them convictions that are not to be sur-
passed for their solemnity and grandeur.

The restless curiosity of the human intellect led to the invention
of the telescope, by which man daringly pierced the mysterious and
illimitable space above us ; revealing to his understanding a great and
wonderful series of worlds lost to his unaided powers of vision ; while,
by the microscope, he has discovered an animal, vegetable, and mineral
kingdom, of which he was previously ignorant, on account of its minute-
ness placing it beyond the keenest observation of the naked eye. In
this last-named, new, and amazing world there is displayed a beauty,
a perfection, adaptation, and reproduction, surprisingly surpassing
those objects with which we are familiar in every-day life. With the
microscope we search into the mysteries of creation, and detect many
of the secret workings of nature. We see the utility of a busy, mul-
titudinous, invisible world of animal life, to the health, comfort, and
preservation of human-kind ; and the unbounded love of God in the
admirable secret provisions for the unceasing changes in the form of
matter. The more powerful the instrument, the more astounding its
revelations; until we marvel in what sized atom organic matter ceases;
and our facts become stranger than fiction, and far beyond the ima-
ginings of the most poetic brain.

How vast, indeed, is the variety of forms under which organised
nature exists ! How endless the number of animals and plants that
people and adorn the globe ! Day after day brings us acquainted with
species hitherto unknown ; and it seems as if the door of discovery is
never to be closed. Whenever a new country is visited, animals and
plants, different from what had before either been known or imagined,
are discovered ; but how many regions will remain to be explored in
that, as yet almost unknown country, which belongs to the microscope,
after every spot of the earth shall have been described and laid down
accurately in the map 1

What we know at present, even of things the most near and

CONCLUSION.

451

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 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.

S

INDEX.

ACALEPH.E, 24.
Acarina, 326.
Acarus of beetle, 334.

— of cloth moth, 334.
farinse, 332.

of fly, 334.

— of fowl, 333.

— of rat, 328.

sacchari, 331.

scabiei, 329.

Achetina, 321.
Achnanthes, 159.
Achromatic illuminator, 60.

object-glasses, 34.

Acinetinaea, 147.
Actiniaegemmacea, 218.
maculata, 222.

mesembryanthemum, 220.

rubra, 220.

Tuedise, 222.

Actinocyclus, 161.

Adams'* microscope, 8.

Alcyonella, 181.

Alcyonidae, 215.

Alcyonium, digitatum of, 87.

Algse, 406.

Air-pump for removing air-bubbles, 79.

Amseba, 131.

Amici's microscopes, 10.

Anacharis alsinastrum, 435.

Angle of aperture, 34.

Anguinaria, 228.

Animalcules, cilia of, 1 38.

, collecting, 69.

history of, 138.

infusorial, 136.

marine, 141.

polygastric, 136.

rotating, 167.

Animal cell, 346.

— action of cells, 352.

action of cilia, 355.

articulata, 286.

cell, history of, 346.

cells, change of into tissues, 348.

Animal cells, change of into intercellular

substance, 352.

connective tissue, 367.

elementary tissue, 367.

epithelium, 353.

fibrous membrane, 368.

membrane, 367.

multiplication of cells, 348.

— structure, 343.
structure, mode of investigating,

379.

tissue consolidated, 372.

Annelida, 274.

Anthea, 222.

Aquarium for fish and plants, 245.

Arachnidse, 282.

Arachnoidiscus, 162.

Aristophanes, microscope known to, 2.

Articulata, 270.

Artists, designs for, 162.

Astasisea, varieties of, 146.

Asteroidse, 211.

BAKER ox THE MICROSCOPE, 8.

Balanidse, 280.

Barnacle, 280.

Bee's tongue, leg, Sec., 314.

Beetles, description of, 315.

Bennett, Dr., on investigating animal

structure, 387.
Berg-mehl, 163.

Binocularity, applied to microscope, 121.
Binocular microscope, Wenham's, 122.
Blackwell, Mr., on flies, 294.
Blood corpuscles, 360.

crystallization of, 363.

Blow-fly, 296.
Bone, birds', 383.

cutting sections of, 386.

fishes', 384.

human, 379.

reptiles1, 383.

Bonnani's microscope, 7.

Boys, Mr. Thomas, on mounting objects,

80.

INDEX.

453

Brachionae, 169.

Brewster, Sir David, on viewing objects,

54.
Brooke, Mr., on viewing opaque objects,

64.

on test objects, 44.

Bryozoa, 236.

— Bowerbankia, 238.
Burnett, Dr., on parasites, 332.

Busk, Mr., on Anguinaria spatulata, 228.

— on Hydatids, 274.

on Notamia, 238.

on starch granules, 424.

Butterflies and moths, 304.

CALEPTERYX VIRGO, 299.

Camera- lucida, 101.

Quekett, Professor, on the use of

the, 101.
Campanularia, 207.

volubilis, 207.

Campylodiscus clypeus, 161.

Capillaries, 363.

Cartilage, 373.

Caryophillia, 224.

Celleporidae, 225.

Cells of glass for dissections, 77.

Cellulariae, 226.

Cellular tissue of plants, 419.

in animals, 368.

Cementing pencil, 78.

Cements, 77.

Chara vulgaris, 433.

Cheese-mite, 330.

Chemical re-agents, 90.

Circulation of blood in frog, how to view,

389.

Cirrhipoda, 279.
Clepsinidae, 276.
Clionze, 186.
Cocconeis, 161.
Cocconimo Bb'eckii, 159.
Cochineal insect, 308.
Cockchafer, 316.
Collecting objects, 95.

animalcules, 69.

stick, Mr. Williamson's, 70.

Collodion for multiplying objects, 291.
Comatulidse, 251.
Confervoideee, 406.

Consolidated tissues, 272.

Corallines, 233.

Coral reefs, Captain Basil Hall on, 235.

- Dr. Macculloch on, 234.
Coryne-stauridia, 210.
Coscinodiscus, 162.
Crane-fly, 28&.

Cricket, 323.
Crinoidea, 250.
Crisiadae, 227.
Crustacea, 278.
Crystals of snow, 118.

- quinine, 116.

- urinary salts, 115.
Cutting machine, 444.
Cyclops, 280.
Cypridae, 281.

Czermak upon tooth substance, 376.

DAPHINAD^E, 281.

Deane, Mr., on mounting objects, 80.
Death-watch beetle, 31-8,
Delabarre's microscope, 8.
Demodex folliculorum, 330.
Denny, Mr., on parasites, 326.
Desmidaceae, 409.
Deutzia scabia, 422.
Diaphragm, description of, 56.
Diatomaceae, 148.

- Kiitzing on, 149.

- Rev. W. Smith on collecting and
preserving, 153.

Dipping-tube for animalcules, 68.
Disk, circular, 76.
Dissecting knives and needles, 72.
Divini's microscope, 6.
Dragon-fly, description of, 299.
Drone-fly, 295.

Echinococci, 274.
Egg of bed-bug, 122.
Eggs of insects, 304.
Ehrenberg on infusoria, 143.
Enchelia, 147.
Encrinidae, 251.
Entomostraca, 281.
Entozoa, 270.
Epizoa, 270.
Errantia, 277.

454

INDEX.

Escharidse, 229.
Eye, magnifying power of, 448.
Eye-pieces, value of, 43.
Eyes of insects, 290.
Eucratiadae, 228.

FEET of insects, 293.

Ferns, 441.

Fibre, muscular, 369.

Fibrous tissue, 368.

Fish, 391.

Fishes' scales, 392.

Flea, 324.

cat's, 325. .

larva of, 325.

Floscularidse, 172.

Gosse 's description of, 174.

Stephanoceros, 172.

Flustraa, 231.

carbasea, 231.

chartacea, 231.

— — foliacea, 231.

Lamouroux on, 230.

Fly, foot and leg of, 29 3.

Foraminifera, 133.

Forceps for holding objects, 67.

— — Varley's, 68.

Fossil Infusoria, 155.

Frauenhofer's glasses, 8.

Frog-plate, 390.

circulation, 363.

Fungoid growths, 401.

Furze, Mr. J., on illumination, 447.

GALLIONELLA Sulcata, 160.
Gammaridse, 281.

Garrod's, Dr., crystals in blood, 363.
Gas-lamp, Highley's, 66.
Gasteropoda, 261.
Gillett's Illuminator, 57.
Glycerine for mounting objects, 81.
Gnat, description of, 301.
Goadby's fluids, 83.
Gorgoniadae, 212.

spicuke of, 188.

Gorham's, Mr., holder, 78.

on eyes of insects, 291.

on the magnifying power of the

eye, 448.
Gosse, Mr., on marine animalcules, 141.

Gosse, Mr., on marine vivaria, 243.
Grant, Dr., on Flustra, 230.
Grape blight, 400.

section of, 401.

Guinea worm, 273.
Gyrinus, 320.

HAIR, 356.

Harris, Mr., on the grape-blight, 400.

Hassall, Dr., on the adulteration of
food, 428.

Herapath on the uses of polarised light,
111.

iodo-quinine, 114. ,

Highley's photographic camera for mi-
croscope objects, 127.

gas-lamp, 66.

Hill's treatise on the microscope, 8.

History of animalcules, 155.

Holland's eye-piece, 25.

Holothuridae, 252.

Homoptera, 306.

Hooke's microscope, 6.

Human body, 346.

Huxley ,T.H.,Mr., on the cell theory,366.

Huyghenian eye-piece, 36.

Hydatids, 272.

Hydra, 197.

Hydrachnidae, 336.

Hydrophilus, 292.

Hymenoptera, 310.

ICELAND spar, 107.
Importance of insects, 341.
Improvements in microscope, 8.
Infusoria, Ehrenberg's account of, 143.

fossil, 155.

history of, 136.

Infusorial animalcules, 129.
Injecting, mode of, 84.
Insects, 286.

changes of, 338.

commercial importance of, 340.

• dissection of, by Swammerdam,
337.

• distribution of, 339.

eggs, 304.

feet, 293.

itch, 329.

mouths, 295.

INDEX.

455

Insects, parts of, for examination, 288.

proboscis, 301.

stings, 312.

tongues, 275, 383.

uses of, 296.

wings, 299.

Internal parts of the body, 360.
Isis hippuris, 169.
Isthmia enervis, 161.
Ixodidse, 333.

JACKSON'S Mr., micrometer, 39.
Johnston, Dr., on sponges, 178.
Jones, Mr. Wharton, on non-striated

muscular fibre, 371.
on the circulation in frog's foot,

363.

KING, Mr., on polarised light, 110.
Knives, Quekett's and Valentin's, 75.
Kolliker on the muscles of the skin, 371.

LANKESTER, Dr., on sponges, 179.

on the distinction between plants

and animals, 179.
Leech, medicinal, 275.
Leeuwenhoek's microscope, 5.
Lenses, achromatic, 21.

chromatic aberration of, 21.

Coddington, 26.

concavo-convex, 19.

condensing, 64.

different forms of, 14.

double convex, 20.

meniscus, 20.

method of tracing progress of rays

through, 14.
periscopic, 26.

plano-convex, 18.

refraction of light through, 14.

spherical aberration of, 1 7.

Stanhope, 27.

Lepidoptera, 304.
Lepismidae, 323.
Lepralia, 226.
Libellulidae, 299.
Lieberkhun's microscope, 4.

specula, 65.

Life, theory of animal, 344.
Limneus stagnalis, 263.

Linnaeus on drone- fly, 296.
Lister's lenses, 10,
Louse, 327.
Lucernaridae, 222.

campanulata, 222.

Lycosidae, 285.

MADREPORID.E, 224.
Marine vivaria, 243.
Micrometers, 38.
Microscope, Baker on the, 8.

Baker's student's, 50.

Bonnani's, 7.

compound, 29.

Huyghenian eye-piece of, 36.

Lieberkhun's, 4.

Powell and Leland's, 51.

Ross's, body of, 35.

Ross's large compound, 47.

Ross's small compound, 50.

simple, 27.

simple for dissections, 27.

Warington's, 446.

Mollusca, 253.

Monads, 142.

Mosses, 405.

Moths and butterflies, 304.

MUlder on the vegetable cell, 398.

Muscular fibre, 369.

NAVICUL^E, 151.

— Quekett on, 234.
Nerves, 371.
Newport on Moths, 305.
Newt, 391.

Nicols' prism, 107.
Nitella, 432.
Noctiluca miliaris, 141.
Notamia, 238.

OBJECT-GLASSES, 32.

Ross's, 42.

Objects, Shadbolt on collecting, 95.

— mounting and preserving, 77.
Boys on mounting, 80.

On collecting salt-water specimens, 267.

Ophiuridae, 251.

Osborne, Rev. S. G., on fungi in the air,

40 L
Owen, Professor, on animalcules, 176.

456

INDEX.

Owen, Professor, on microscopic inves-
tigation, 375.
Oyster, 255.
Oyster Fry, 280.

PARABOLIC reflectors, 62.
Parasites, 326.

of cat, 328.

— of dog, 328.

of engle, 335.

of fowl, 333.

ofhornbill, 332.

human, 327.

of pheasant, 333.

of pigeon, 335.

of sheep, 336.

of swallow, 332,

of turkey, 333.

of vulture, 335.

Parkes', Dr., caution on using re-agents,

92.
Pearls, 256.

artificial, 257.

Pediculi, 333.

Pennatulidae, 213.

Photography applied to microscope, 126.

Phryganeidffi, 303.

Pigment cells, 356.

Plants, chorophyl in, 432.

cellular tissue of, 419.

circulation in, 433.

crystals in, 42U.

lactiferous tissue of, 419.

lice, 308.

preparation of tissues, 440.

raphides in, 420.

sections of, 443.

siliceous cuticle of, 443.

starch in, 422.

starch of potato, 426.

structure of, 394.

vascular tissue of, 436.

vital characteristics, 395.

Podura plumbea, 323.

Polarisation of light as applied to the

microscope, 103.
Polygastria of Ehrenberg, 1 36.
Polypifera, 195.
Polythalamia, 133.
Porifera. 177.

Potato, disease of, 426.
Preparation of insects, 337.
Preparing sections of bone, 386.
Preservation of algse, 92.

zoophytes, 241.

Prism, Dujardin's, 447.
Proteus, the, 131.
Protozoa, 130.

QUEKETT, Edwin, Mr., on the vascular
tissue of plants, 437.

Professor, on. advantages of polar-
ised light, 121.

on raphides in plants, 420.

on the structure of bone, 378.

RALFS, Mr., on Desmidacete, 409.
Read, Rev. J. B., on the background

illuminator, 64.
Reflector, parabolic, 62.

Shadbolt's, Mr., 64.

Rhizopoda, 133.

Ross, Mr., on illumination, 55.

Rotatorice, 1G7.

SALTER, Dr., on dentine, 376.

Dr. Hyde, on muscle, 370.

Salt water, artificial, 245.

Sarcina ventriculi, 399.

Sarcoptes scabiei, 329.

Saw-fly, 310.

Schacht's, Dr., preservative fluid for

microscopic uses, 90.
Scissors for dissecting, 75.
Sea-mice, 277.

Section cutting-machine, 444.
Selenite, 110.
Serpula, 277.
Sertularia filicula, 242.
Sertularidse, 202.

Shadbolt, Mr., on collecting objects, 95.
Silkworm's breathing-aperture, 292.
Siller-cups, 404.
Single microscope, 3.
Skeletons of zoophytes, 241.
Skin, fungoid diseases of, 401.

section of, 358.

Smith's and Beck's troughs, 72.

Smith, James, Mr., on management of

light in viewing objects, 54.

INDEX.

457

Snow, crystals of, 118.

red, 404.

Sphagnum, leaf of, 438.
Spider tribes, 282.

diving, 285.

Sponges, 177.

skeletons of, 186.

Starch in plants, 422.

tests for, 411, 424.

Stentor, 165.

Stinging-nettle, leaves of, 432.
Structure of shells, 266.
Sugar insect, 331.

cane, 439.

Swammerdam's dissection of insects,

286.
Synaptidae, 252.

TEETH, 375.

Test objects, 44, 306.

Tissues, consolidated animal, 372.

elastic and non-elastic, 368.

Tomata, diseased, 400.

Topping's, Mr., fluid for mounting, 95.

— test- objects, 307.
Torula cerevisia, 398.

• diabetica, 399.

Tourmaline, 109.
Transformation of insects, 338.
Trichocera hyemalis, 301.
Troughs for animalcules, 72.
Tubicola, 276.
Tubularidee, 208.

WARD, N. B., Mr., on aquaria, 245.
Warington's, Mr., microscope, 447.

preservative fluid, 81.

Wasp's tongue, 289.
Water-beetle, sucker of, 292.
Water microscope, 3.

Water-mites, 336.

Wenham, Mr., binocular microscope,
121.

illuminator, 62.

West wood on insects, 294.

Wheat-flour, adulterations of, 425.

portions of husk, 423.

Wichura, M., on the spiral forces of na-
ture, 368.

Wollaston's and Coddington's lenses, 26.

Wonders of microscope, 155.

Wood, cutting sections of, 444.

Woodward, Mr., on polarised light, 108.

VALLISNERIA, 433.

Varley, Mr., on the culture of water-

plants, 434.
Vegetables, structure of, 394.

cellular tissue of, 419.

fungi, 401.

hairs in, 432.

preparation of tissues, 440.

raphides in, 420.

starch in, 424.

vascular tissue in, 436.

Vibrio spirilla, 145.
Virgularia mirabilis, 214.
Vivaria, the mode of forming, 244.

by Mr. Gosse, 243.

by Mr. Lloyd, 393.

Volvox, 407.
Vorticellid^, 163.

XANTHIDIA, 192.
YEAST-PLANT, 399.

ZOOLOGICAL Society's marine vivaria,

243.
Zoophytes, 195.

preservation of polypidoms of, 241.

Zygoceros rhombus, 162.

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BOSWELL'S LIFE OF DR. JOHN-
SON. Complete in Four Volumes.

THE ILLUSTRATED BOOK OF

BRITISH SONGS, from the Sixteenth to the
Nineteenth Century. With Fifty Engravings.

THE MORMONS, OR LATTER-
DAY SAINTS. An Account of the Rise and
Progress of this new Religious Sect.

THE ORBS OF HEAVEN ; or the
Planetary and Stellar Worlds. A Popular Expo-
sition of the Great Discoveries and Theories of
Modern Astronomy.

PICTURES OF TRAVEL IN THE
SOUTH OF FRANCE. From the French of
ALEXANDRE DUMAS.

HUG'S TRAVELS IN TARTAR Y,
THIBET, AND CHINA, in 1844, 5, and 6. Un-
abridged Edition. Two Volumes. With numerous
Daguerreotyped Illustrations, and a Map of the
Countries.

A WOMAN'S JOURNEY ROUND
THE WORLD. Unabridged. From the German
of IDA PFEIFFER.

MEMOIRS OF EXTRAORDI-
NARY POPULAR DELUSIONS. Two Vo-
lumes. By CHARLES MACKAY, LL.D. Illus-
trated with One Hundred and Twenty Engravings
from Authentic Sources.

BOSWELL'S JOURNAL OF A
TOUR TO THE HEBRIDES. Companion Vo-
lume to " Boswell's Life of Johnson," with the
Index to the " Life." ByR. CARRUTHERS, Esq.,
of Inverness.

THE ILLUSTRATED BOOK OF
SCOTTISH SONGS, from the Sixteenth to the
Nineteenth Century.

PICTURESQUE SKETCHES OF

LONDON, PAST AND PRESENT. By THOMAS
MILLER.

MADAME PFEIFFER'S VISIT
TO ICELAND AND THE SCANDINAVIAN
NORTH. Companion Volume to " A Woman's
Journey Round the W'orld."

THE ISRAEL OF THE ALPS. A
History of the Persecutions of the Waldenses. By
the Rev. Dr. ALEXIS MUSTON.

A NARRATIVE OF THE UNITED
STATES EXPLORING EXPEDITION. Two

Volumes. With numerous Drawings, illustrative
of the Manners, Customs, and Personal Appear-
ance of the Inhabitants, and Views of the Scenery
of the Countries Visited.

THE ILIAD OF HOMER. Trans-
lated into English Verse by ALEXANDER POPE.
A New Edition, with Notes, Illustrations, and In-
troduction. By the Rev. THEODORE ALOIS
BUCKLEY, M.A., Chaplain of Christ's Church,
Oxford. Two Volumes.

THE ODYSSEY OF HOMER. With)
FLAXMAN'S Illustrations, &c. One Volume.
Edited by the REV. THEODORE ALOIS BUCKLEY. I

MADAME PFEIFFER'S VISIT TO
THE HOLY LAND, EGYPT, AND ITALY.

Uniform with "A Woman's Journey Round the
World."

THE COMPLETE ANGLER OF
IZAAK WALTON AND CHARLES COTTON.

New Edition, superbly Illustrated with Fifty En-
gravings of Fishes, Fishing Tackle, Flies, and
Portraits and Landscapes. Edited by EPHEMERA,
of " Bell's Life in London."

EXTRAORDINARY MEN;
THEIR BOYHOOD AND EARLY LIFE. By
W. RUSSELL, Esq.

THE PILGRIM'S PROGRESS
FROM THIS WORLD TO THAT WHICH IS
TO COME. By JOHN BUNYAN. A New Edition,
with a Memoir by J. M. HARE. The Allegory
illustrated with Thirty Outline Drawings by
CLAYTON, and the Biographical Sketch with
Interesting Relics and Recollections of the
Author, by J. L. WILLIAMS.

TRAVELS IN SPAIN. From the
French of THEOPHILE GAUTIER.

THE LIFE, PUBLIC AND DO-
MESTIC, OF THE RIGHT HON. EDMUND
BURKE. By PETER BURKE, Esq., of the Inner
Temple.

THE NATURAL HISTORY AND
ANTIQUITIES OF SELBORNE. By the Rev.
GILBERT WHITE, M.A. Edited, with Notes and
Additions, by Sir WILLIAM JARDINE, Bart.,
F.R.S.E., F.L.S., M.W.S. Fully Illustrated.

THE LIFE AND POETICAL
WORKS OF ALEXANDER POPE, with Ex-
tracts from his Correspondence. Four Volumes.
The " Life" by R. CARRUTHERS, Esq., of Inver-
ness ; and the " Works" edited by the same Gen-
tleman.

THE LIFE AND TIMES OF SIR
WALTER RALEIGH, with copious Extracts
from his " History of the World." By C. WHITE-
HEAD.

JOHNSON'S LIVES OF THE

POETS. Completed by WILLIAM HAZLTTT. In
Four Volumes.

THE HISTORY OF RUSSIA, from
the Foundation of the Monarchy by Rourick to
the close of the Hungarian War. To which are
added Dissertations on Serfdom, Landed Tenure,
the Nobility, the Church, Trade, &c. By AL-
PHONSE RABBE and JONATHAN DUNCAN, B.A.
With Tinted Illustrations by S. READ, of the
principal Cities, Ports, and Harbours; and Maps
of the Russian Empire. In Two Volumes.

THE ILLUSTRATED BOOK OF
FRENCH SONGS. (In French and English.)
Being a careful collection of the most popular
Military, Patriotic, Satirical, Sporting, and Ro-
mantic effusions of the best French writers, from
the Sixteenth to the Nineteenth Century. Illus-
trated with numerous highly-finished and original
Engravings. Translated and edited by JOHN
OXENFORD, Esq.

THE SHILLING

ILLUSTRATED LONDON ALMANAC

FOR

1856.

Containing Twelve Splendid Engravings Emblematical of the Months ; Twelve Beautiful
Botanical Engravings, by W. S. CO LEM AN, Esq. ; and Notes of the Months, by JOHN"
TIMBS, Esq. The Astronomical Department by J. GLAISHER, Esq., F.R.S., of the
Royal Observatory, Greenwich.

The whole of the back Almanacs are now Reprinted, and may be obtained by order
of the local Booksellers, price ONE SHILLING EACH, or the Set from 1845 to 1852
inclusive, in One Handsome Volume, cloth, price Six SHILLINGS.

OFFICE, 198 STKAND.

W. J. SALMON,

100 FENCHURCH STREET,
AND SOUTH-WEST GALLERY, CRYSTAL PALACE, SYDENHAM.

W. J. S. would call the attention of his Friends and the Public to his new and much
improved Microscopes, adapted for all purposes, and suited to all classes — the Drawing-
room, Cottage, and School-room, and for Medical and other Students.

A superior Microscope, with Rack, Stage, coarse and fine Adjustment, two
Achromatics (£ and 1 inch), two Eye-pieces, packed in Mahogany case, 13/. 13s.

Salmon's best Student's Microscope, with two Achromatics, coarse and fine
Adjustment, in case, 61. 10s.

Salmon's small Student's or School Microscope, with two Eye-pieces, and two
Achromatics, in case, 41. 12s.

Mr. Warington's Travelling Microscope, 21. 10s.

A large assortment of Telescopes, Spectacles, Opera, Race, Field, and Marine
Glasses of the best make, Barometers, Thermometers, &c.

AQUARIUMS,

MANUFACTURED BY

WILLIAM THOMAS SALTMARSH,
Carpenter,

4 SALISBURY COURT, FLEET STREET.

Area. Depth. £ s. d.

14 inches by 10 inches . . .12 inches . . . 0 19 0

18 „ " 12 „ . . . 14 „ . . .150

22 „ 14 „ . . . 16 „ . . . 1 12 0

26 „ 16 „ . . . 18 „ . . . 1 16 0

N.B. Larger Sizes at proportionate Prices.

Warranted thoroughly Waterproof

DISSOLVING VIEWS.

AMUSEMENT and INSTRUCTION by means of

CARPENTER and WESTLEY'S

Improved Phantasmagoria Lanterns with the Chromatrope and Dissolving Views,

and every possible variety of Sliders, including
Natural History, Comic, Lever, Movable, and Plain,
Astronomical, Views in the Holy Land, Scriptural Portraits, &c.
No. 1. Lantern, with Argand Lamp, in a box, 21. 12s. 6d.
No. 2. ditto, of a larger size, 4/. 14s. 6d.
A pair of Dissolving-View Lanterns, No. 2, with Apparatus, 111. Us.

The above are supplied with a Lucernal Microscope and 7 Sliders at 31s. 6d.
extra.

The Lamp for the No. 2 Lanterns is very superior.
(The price of the Lanterns, is without Sliders.)

Lists of the Sliders and prices upon application to the Manufacturers,
MESSRS. CARPENTER AND WESTLEY, OPTICIANS,

24 REGENT STREET, WATERLOO PLACE, LONDON.

W. ALFORD LLOYD,

164 ST. JOHN STREET ROAD, LONDON.

Dealer in Marine Living Animals, Sea-Weed, Artificial Sea- Water,
and Marine and Fresh-water Aqnaria.

A stock of small Aquaria, ready fitted up with Weed, Shells, Rockwork, and
Marine Life, always on hand, at very moderate prices.

Valisneria, Chara, Nitella, Anacharis, and other living fresh-water Plants,
Insects, Mollusks, Fish, &c.

SOCIETY OF ARTS PRIZE MICROSCOPES.

R. FIELD & SON, NEW STREET, BIRMINGHAM, have had

awarded to them both of the Special Prizes of the Society of Arts for the best
Students' and School Microscopes.

Student's Achromatic Microscope, with two Eye-pieces and two Objectives, in
Mahogany Cabinet, 31. 3s.

Ditto, superior and more complete, 41. 10s.

Ditto, 61. 6s. and 121.

Movable Stages, from 11. 15*. to 4/. extra.

School Microscope, Rack Adjustment, three Powers, and Instruments, 10*. 6d.

Superior ditto, upwards to 50s.

MICROSCOPIC OBJECTS FOR SALE.

ME. SAMUEL STEVENS,
NATURAL HISTORY AGENT,

&c.,

24 BLOOMSBURY STREET, LONDON.

HAS on sale the following objects, neatly mounted, for microscopic examination. The pricf
is 10s. 6d. per dozen, packed in racked boxes containing one or two dozen? It is sufficient i
gentlemen favouring him with their orders indicate the number prefixed to each specimen.

(b.) Mounted in balsam.

(f.) in fluid.

Trans. Sect, of Cherry Stone (f.)
Palate of Lymnaeus Stagnalis (f.)
Cells contg. Starch from Peony (f.)
Scales of Ourapteryx Machaon-

aria (d.)

Parietal of Foetus, 3 months (b.)
Cocoa-nut Shell (Trans. sect.)(b.)
Cocconeis Scutellum (b.)
Palate of Whelk (f.)
Infusorial Earth from Obero in

Germany (b.)

Trans. Sect, of Lebanon Cedar (b.)
Tusk of Sus Indicus (b.)
Foot of the Hive Bee (b,)
Cuticle of Yucca Gloriosa (f.)
Infusorial Earth from West

Point, New York (b.)
Hair of Bat, Taphozous perfora-

tus (b.)

Humerus of Opossum (Tr. s.)(b.)
Starch from Arrowroot (f.)
Xanthidia in Flint (b.)
Mouse Hair (b.)
Ditto, Albino variety (b.)
Pollen of Hollyhock (f.)
Infu.Earth.Wreatham, Mass, (b.)
Palate of Lymnaeus Palustris (f.)
Infu. Earth, Manchester, U.S. (b.)
Hair of Albino Rat (b.)
Spiral Vessels from Testa of Co-

lomnia(f.)
Femur of Emu (b )
Infusorial Earth, Rappanhannah

Cliff, U.S. (b.)
Sporules of Anemedectyon Fraxi-

ni folium (b.)
Starch from Rice (f.)
Scales of Podura Plumbea (d.)
Palate of Planorbis Corneus (f.)
Tooth of Sawfish (Tr. sect.) (b.)
Ducts and Spiral Vessels from

Carrot (f.)

I. Earth, Schockhoe Hill,U.S. (b.)
Hair of Bat , Dy sopes Nasutus (b. )
Starch of Maple (f.)
Trans. Sect. Elephant's Hair (b.)
Palate of Winkle (f.)
R aphides of Rhubarb (b.)
Infusorial Earth, Piscataway (b.)
Femur of Dinornis Mantelli

(Trans. sect.)(b.)
Hair of Bat, MegadermaLyra(b.)
The Blight Wheat (b.)
Starch from Potato (f.)
Infusorial Earth, Lunenberg (b.)
Elytron of Cyphus Germari (d.)

48. Femur of Poliocephalus Ed-

wardsii (b.)

49. Sponge Spicules, Thames (d.)

50. Hair of Bat, Cynopterus Brevi-

caudatus (b.)

51. Thecae and Sporules of Pteris

Crenata(b.)

52. Scales of Nodura Nigra (d.)

53. Humming Bird Feather (d.)

54. Cuticle of Indian Corn (f.)

55. Infusorial Earth, Italy (b.)

56. Femur of Eagle (Tr. sect.) (b.)

57. Hair of Bat, Taphozous Philli-

pensis (b. )

58. Spicules of Gorgonia tricolor (b.)

59. Infusiorial Earth, Barbadoes (b.)

60. Scales of Vanessa Erythyia (d.)

61. Polishing Slate Bilin (b.)

62. Bird Cherry (Trans, sect.) (b.)

63. Infusorial Earth, Mull (b.)

64. Coquilla Nut (Trans, sect.) (f.)

65. Ulna of Australian Cat (b.)

66. Infusorial Earth, Algiers (b.)

67. Wing of Morpho Menelaus (b.)

68. Spine of Echinus (b.)

69. Infu. Earth, Virginia, U. S. (b.)

70. Palate of Helix Aspersa (f.)

71. Infu. Earth, Bangor, U. S. (b.)

72. Elytron Diamond Beetle (d.)

73. Foot of Wasp (b.)

74. Scales of Cyphus Germari (b.)

75. Bone of Alligator (b.)

76. Scales of Morpho Menelaus (d.)

77. Sponge Spicules from Sark (b.)

78. Metacarpal Bone, Man (b.)

79. Pin shaped Spicules of Sponge (b.)

80. Bone of Turtle (Trans, sect.) (b.)

81. Ivory (Trans, sect.) (b.)

82. Vegetable Ivory (f.)

83. Palateof Trochus Umbilicatus(f.)

84. Pith of Elder (f.)

85. Cuticle of Iris (f )

86. Palate of Nassa Reticulata (f. )

87. Star-shaped Spicules, Sponge (b.)

88. Apricot Stone, &c., sect, (f.)

89. Thecae and Sporules of Blechnum

occidentale (b.)

90. Polishing Slate, Habichtswald(b.)

91. Rhinocerus Horn (Trans, sect.)

92. Spicules of Malataea ochracea(b.)

93. Spicules of Gorgonia Zingiber(b.)

94. Monkey Femur (Trans, sect.) (b.)

95. Beech Wood (Trans, sect.) (b.)

96. Rib of Python (b.)

97. bpicules of Gorgonia rugosa (b.)

98. Gemmules of Geodia (b.)

(d.) dry.

99. Mylobates Jaw (Trans. sect.)(h,

100. Whalebone (Trans, sect.) (b.)

101. Cuticle of Oncidium (f.)

102. Rib of Porpesse (Tr. sect.) (b.)

103. Trifid Spicules of Sponge t

104. Battledore Scales, Polyommatu

Arion (d.)

105. Testa of Illicum anisatum (b.) -v

106. Spicules of Gorgonia miniata(b,j

107. Hair of Taphozous metanopogeu

108. Scales Lepisma Saccharina (d.)

109. Fibro cellular tissue, Cobae*

Scandeus (f.)

110. Palate, Helix caperata (f.)

111. Cuticle, Saccolabium guttatura

(f.)

112. Parallel spined Sponge Spicules

(b.)

113. Starch of Sago (f.)

114. Claws of Astrophyton Linckil

(b.)

115. Starch, Sweet Casava (f.)

116. Scale of Lepidosteos (Tr. sec.

(b)

117. Porcupine Quill (Tr. sect.) (b.)

118. Anchor-shaped Sponge Spic. (b.)

119. Bone of Antelope (Tr. sec.) (b.)

120. Yew (Tr. sec ) (b.)

121. Infu. Earth, Slico Moc. Hill(b.)

122. Cuticle, Agave Americana (f.)

123. Spicules, Muricaea elongata (b.)

124. Carapace of Turtle (b.)

125. Palate of Helix Hortensis (f.)

126. Palate of Helix Nemoralis (f.)

127. Spicules of Gorgonia plicata (b }

128. Portland Meal, Arum Macula-

turn (f.)

129. Femur of Tetrao Urogallus (b.)

130. Raphides, Agave Americans (b.)

131. Palate of Helix Rulescens (f.)

132. Gemmules of Sponge (b.)

133. Cuticle of Aloe Spicata (f.)

134. Fibres,Fos. Coniferous Wood (b)
1S5. Spicules of Gorgonia Gelata (b.)

136. Hair of Ornithorynchus paro-

doxus (b.)

137. Spic. Alcyonium digitatum (b.)

138. Cuticle Opuntia Vulgaris (f.)

139. Truncated Sponge Spicules (b.)

140. Scales of Polyommatus Acis(d.)

141. Fin Bone of Lepidosteos (Trans.

sect.)(b.)

142. Gemmules of Pachymatisma(b.)

143. Testa of Bignonia (f.)

144. Spicules, Gorgonia Guttata (b.)

Mr. S. STEVENS has also on Sale—
A Collection of INFUSORIAL EARTHS,

from twenty-four different localities

price per Set, mounted . 20s.
12 Palates of Mollusca „ ,, . 10s.

24 Spicules of Gorgonia per Set, mounted 20s.

12 Hairs, various „ „ 10s.

12 Scales of Lepidoptera ,, „ . 10s.

24 Sections of Bones and Teeth ,, . 20s.

A CATALOGUE

ACHROMATIC MICROSCOPES

PHOTOGRAPHIC APPARATUS,

MADE AND SOLD BY

C. BAKER,

Nos. 243 & 244, HIGH HOLBORN,

LONDON.

ESTABLISHED 1765.

ACHROMATIC MICROSCOPES,

MADE AND SOLD BY

C. BAKER,

243 AND 244, HIGH HOLBORN,
LONDON.

£ s. d.

No. 1. — Highly finished large Compound Microscope, with
all the latest improvements, having double supports to
prevent vibration, with quick and slow motion for the
most delicate optical adjustment, a mechanical stage
with one-inch motion in opposite directions, a sliding
and revolving object holder, wheel of diaphragms,
apparatus for the reception of the polariscope, achro-
matic condenser, &c., large plain and concave adjusting
mirror with two hiiyghenian eye pieces of the best
construction ... ... ••• ... 13 10 0

Solid Spanish mahogany Case for ditto, with drawer

beneath, and packed complete for apparatus ... 200

The above without the mechanical stage, but having all

the other motions and fittings ... ... ... 10 10 0

No. 2. — A smaller Microscope, having mechanical stage,
quick and slow motion, double mirror, &c., and similar
in all parts to No. 1 ... ... ... 9 10 0

Ditto ditto, without mechanical stage, but having

a sliding object holder, and all the other motions, with
one hiiyghenian eye piece ... ... ... 615 0

Solid Spanish mahogany Case for ditto, with drawer

beneath, and packed complete for apparatus ... 176

No. 3. — A beautifully finished Student's Microscope, with
sliding stage, quick and slow motion, one-inch, half-
inch, and quarter-inch achromatic object glass, live box,

4 CATALOGUE OF ACHROMATIC MICROSCOPES,

£ s. cl

with stage and dissecting forceps, all packed in a neat

mahogany case ... ... ... ... 6 10 0

Ditto ditto, without slow motion ... 5 15 0

N.B. — This instrument is strongly recommended to Surgeons and others for its
completeness, as it answers the purpose of a more expensive instrument for
physiological and general purposes.

No. 4. — A Portable Microscope, with lever or rack motion

to the stage, and fitted complete as No. 3 ... ... 4 15 0

No. 5. — A superior finished Microscope, without joints to
the stand, but having a delicate optical adjustment,
with one-and-a-half-inch, one-inch, and half-inch achro-
matic object glasses, in mahogany case .. 220

No. 6. — A Compound Microscope, (not achromatic), with
six various powers, live box, condenser, forceps, stage
forceps, and other apparatus, packed complete in a
mahogany case ... ... ..t ... 2 10 0

ACHROMATIC OBJECT GLASSES.

Ang-ular Aperture.

Two inch ... ... ... ... 12 degrees 176

One inch ... ... ... 13 „ 1 10 0

Ditto ... ... ... ... 23 „ 1 15 0

Half inch, without adjustment ... 50 „ 200

Ditto, with adjustment ... ... 65 ,, 300

Quarter inch, without adjustment ... 55 „ 220

Ditto, with adjustment ... ... 85 „ 350

A beautifully-defining combination of German Powers, half-
inch, dividing so as to form one-inch and one-and-
a-half- inch, mounted in a superior form ... ... 1 2 6

Ditto ditto, of quarter-inch power, and forming if

divided one-third inch ... ... ... 150

N.E. — These Object Glasses are the finest that can be made, and for denning and
penetrating power cannot be surpassed.

APPARATUS FOR ACHROMATIC MICROSCOPES.

Polariscope, with extra large pair of prisms, fitted and

attached complete ... ... ... ... 1 12 6

Ditto ditto, for Student's Microscope ... 150
Extra Eye -pieces ... ... ... from 6s. to 0 10 6

Achromatic Condenser (mechanical part) for the better

definition of delicate structures, fitted complete ... 1 2 6

Ditto ditto, for Students ... ... 076

Large Condenser, for illuminating opaque objects, with

universal motion and dividing stand ... ... 0 15 6

Ditto ditto, for Students ... ... 0116

Ditto ditto, for adapting to stage ... ... 0 7 6

SOLD BY C. BAKER, 243 & 244, HIGH HOLBORN. 5

£ *. d

Camera Lucida, for drawing the magnified image ... 0 15 0

Stage Forceps ... ... ... from 3s. 6d. to 0 5 6

Dissecting Forceps ... ... ... Is. to 0 1 9

Micrometer, for stage ... ... ... ... 046

Ditto, for eye-piece, mounted in brass ... ... 076

Ditto ditto, unmounted ... ... ... 050

Parabolic Condenser ... ... ... ... 150

Silver Reflector ... ... ... from 6s. to 0 15 0

Animalculse Cages ... ... ... ,, 4s. to 0 5 0

Frog Plate ... ... ... ... ... 0 5 0

Glass Troughs for viewing circulation of plants ..,from 040

Hollow Glass Slides ... ... ... ... 004

Compressoriums ... ... ... ... 0 15 0

HAND MAGNIFIERS FOR DISSECTING, &c.

Pocket Magnifier, with one lens, horn mounting/row Is. to 0 2 0

Ditto ditto, two lenses ... ... ... 030

Ditto ditto, three lenses ... ... 036

Ditto ditto, one lens, tortoiseshell mounting ... 0 3 6

Ditto ditto, two lenses ... ... ... 046

Ditto ditto, three lenses ... ... ...060

Double and Treble ditto, in tortoiseshell, with diaphragm

from 6s. to 0 10 0

Stanhope Lenses, in ivory mounting ... ... ... 026

Coddington ditto, ditto... ... ... 030

Ditto ditto, in silver ... from 6s. to 0 12 6

CABINETS FOR MICROSCOPIC OBJECTS.

Flat French polished mahogany Case to hold three dozen

objects ... ... ... .. ... 0 3 6

Ditto ditto, with lock and key, to hold six dozen

objects ... ... ... ... ... 070

Ditto * ditto, 12 dozen ... ... ... 0 li> G

Superior French polished mahogany Cabinet, with drawer
to hold 480 objects, in a vertical position, and flat
drawer for injections ... ... ... 200

Ditto ditto, with 22 drawers, to hold 276 objects,

in a horizontal position ... ... ... 210 0

LARGER CABINETS MADE TO ORDEK.

6 CATALOGUE OF ACHROMATIC MICROSCOPES,

£ s. d.

PREPARED MOUNTED OBJECTS.

Every variety of Physiological, Entomological, Vegetable,
Recent and Fossil Infusoria, Wood, and other Sections,
and Polariscope Objects ... ... from Is. to 1 6

Anatomical Injected Preparations ... ... from Is. 3d. to 2 0

MATERIALS AND INSTRUMENTS.

Air Pumps, with receiver, complete ... ... ... ... 016 6

Injecting Syringe, with stop cocks ... ... ... ... 0106

Writing Diamond ... ... ... ... ... ... 050

Diamond for cutting slips of plate glass ... ... ... 080

Instrument for cutting circles of thin glass to any size ... ...100

Valentine's Knife, for cutting thin sections of soft animal and vegetable

substances ... ... ... ... ... ... 0 12 0

Machines for cutting sections of wood ... ... ... ... 0176

Revolving Tables for cementing cells with gold size, &c. ... 050

Ditto ditto, of best construction ... ... ... ... 0150

Needle Holders, with ivory handles ... ... ... ... 026

Dissecting Knives, with ditto ... ,.. ... ... ...019

Fine Scissors ... ... ... ... ... from 020

Thin Glass in squares ... ... ... ... per ounce 036

Ditto in circles .... ... ... ... ... ... 059

Plate Glass Slides for mounting ... ... ... ...per dozen 0 0 3

Ditto ditto, ground edges ... ... ... ... 008

Canada Balsam ... ... ... ... ... per bottle 0 1 0

Gold Size ... ... ... ... ... ... ... ,,010

Asphalte ... ... ... ... ... ... ...010

Cells of all kinds for injections ... ... ... per dozen from 013

SUPERIOR MICROSCOPE LAMPS, from 16s.

Every Article manufactured on the Premises by superior Workmen, and Repairs
and Alterations will receive immediate attention at the Lowest Price.

TELESCOPES.

A portable six-draw Telescope, four inches long when
closed, and sixteen inches when drawn out ; of great
magnifying power, sufficient to show the satellites of
Jupiter ... ... ... ... ...150

Ditto ditto, with German silver mounting ... 1 15 0

The above in brass mounting, fitted with a portable stand
and extra eye piece, for astronomical purposes, all
packed in a neat morocco case, 4 J by 3 £ ... ... 2 5 0

Ditto ditto, in German silver ... ... 3 10 0

A portable Reconnoitring powerful Military or Tourist's
Telescope, fitted with leather caps, and sling ; when
drawn out sixteen inches, and closed eight inches, the
object glass one -and- a-half inches clear aperture ... 1 13 6
Ditto ditto, of less power, for general purposes 176

SOLD BY C. BAKER, 243 & 244, HIGH HOLBOKN. 7

£ 8. d.

A very superior three-draw Military or Reconnoitring Tele-
scope, thirty inches when drawn out, and nine inches
when closed, the object glass of two inches clear
aperture ; giving an amount of power and brilliancy
of definition not to be surpassed, leather covered and
leather caps, and sling ... ... ... 330

Ditto ditto, with two draws ... .. ... 2150

A beautifully finished portable four-draw German silver
Telescope, with sliding sun shade and whalebone
body, when drawn oat twenty-eight inches, and
closed eight inches, object gla^s one-and-five- eighth
inch diameter ; the most powerful of its size that can
be manufactured ... ... ... ... 300

Ditto ditto, with 3 draws ... ... ... 2 15 0

Leather Case, with sling, for ditto ... ... 086

A well finished three-draw brass mounted Telescope,
covered with leather, and sliding sun shade, and
pancreatic eye piece for any increase of power ;
30 inches when drawn out, and 10 inches when closed,
object glass one-and- five-eighth diameter ... ... 2 2 0

Ditto ditto, without pancreatic eye piece or sun

shade ... ... ... ... ... 1 15 0

Ditto ditto, with mahogany or rose\vood body ... 1 L2 6

A great variety of every description of second-hand Astronomical and Day Telescopes
at every variety of price, and size always in stock.

BAROMETERS AND THERMOMETERS.

Beautifully finished exposed tube rosewood pediment

Barometer, ivory scale, with sliding vernier ... 176

Ditto ditto, with large column of mercury, and

adjusting rack vernier, massively mounted in oak
frame ... ... ... ... ...200

Ditto ditto, in mahogany or rosewood frame 220

Massively mounted oak Barometer, with extra large
column of mercury, having a double scale, with
double rack verniers ... ... ... 276

Ditto ditto, in rosewood or mahogany ... 2 10 0

Ditto ditto, in carved mahogany or rosewood

frames, beautifully executed with very large columns
of mercury ... ... ... ... ...440

The improved aneroid Barometer, with case complete 250

Ditto ditto, with thermometer attached ... 2 10 0

Ditto ditto, and silver dial ... ... ... 2 15 0

8 CATALOGUE OF ACHROMATIC MICROSCOPES,

£ s. d.
Registering Thermometer, mounted in ivory, with japan

or zinc case ... ... ... .. 0 16 6

Ditto ditto, in box, with similar cases, from lls. to 0 13 6

Bath thermometers ... ... ... from 026

Box ditto ... ... ... ... from 012

OPERA OB RACE GLASSES.

Tourist's exceedingly portable double achromatic Opera,
having additional Lens for increase of power, beauti-
fully finished with morocco case complete ... 1 7 6

Ditto ditto, covered with morocco leather, and

bronzed ... ... ... ... 1 10 0

The best ivory mounted and gilt double achromatic Operas,

by the finest makers of Vienna and Munich, from ... 110 0

Ditto ditto, in buffalo, tortoiseshell, or japan

mountings ... ... ... ... from 150

Extra powerful double achromatic Tourist's Race or
Reconnoitring Operas, covered with morocco leather,
and having sliding sun shade and portable morocco
case ; the most powerful made ... ... ... 2 15 0

Ditto ditto, having achromatic eye piece, whereby

great portability is obtained with the same degree
of power ... ... ... ... 350

Ditto ditto, with a jointed frame, to lessen the

distance between the axis of vision ... ... 3 12 6

Japanned leather Cases to ditto, with a sling ... 0 12 0

SPECTACLES, EYE GLASSES, &c.

Plain steel Spectacles, strongly made ... ... 0 2 6

Ditto ditto, with double temples ... 030

Superior ditto, extra quality glasses ... ... ... 039

Very superior ditto, the best made ... ... 056

Ditto ditto, with pebbles ... ... 0 8 6

Tortoiseshell Eye Glasses, all kinds ... ... 019

Beautifully finished tortoiseshell Hand Spectacles, with

double and counter springs ... ... ... 096

Ditto ditto, with plain spring ... ... 076

Every variety of Gold and Silver Spectacles at equally low prices.

SOLD BY C. BAKER, 243 & 244, HIGH HOLBORN. 9

PHOTOGRAPHIC APPARATUS,

CAMERAS.

£ s. d.

No. 1.— Improved French polished SPANISH MAHO-
GANY CAMERA, of the finest workmanship, fitted
with ground focussing glass, dark frame, six plate or
glass holders, and the best compound, or double
combination Achromatic Lenses, of one-and-a-half-inch
diameter, with delicate rack work adjustment, suitable
for Daguerreotype, Calotype, or the Collodion proces-
ses, producing portraits 4^ by 3 J, and under ... 3 0 0

No. 2. — Ditto ditto, with Lenses two-and-a-quarter-

inch diameter, for portraits 6J by 4J, and under ... 5 10 0

No. 3. — Ditto ditto, with Lenses three -and-a- quarter-

inch diameter, for portraits 8J by 6J, and under, and
views 9 by 9, with sliding frame for adjustment of
foreground and sky ... ... ... ... 10 10 0

No. 4. — Improved Expanding CAMERA of WALNUT WOOD,
with two dark frames, three plate or glass holders,
ground focussing glass, and double Achromatic combi-
nation of Lenses of the finest quality, as attached to
No. 1 Camera, producing portraits 4J by 3^ and under 250

No. 5. — Ditto ditto, with half-plate Lens, two-and-

half-inch diameter, for portraits 6^ by 4J, as No. 2 ... 4 7 6

No. 6. — Ditto ditto, with whole plate Lenses of

three-and-a-quarter-inch diameter, producing portraits
for 8J by 6J, and under, as No. 3 ... ... 9 0 0

N.B. — These Lenses are of the best construction and quality, and are similar to
those supplied with Camera Nos. 1, 2, and 3; the difference of price being in
the Cameras only.

PHOTOGRAPHIC LANDSCAPE LENSES.

No. 1. — A Landscape Lens, consisting of one Achromatic
combination, with delicate rackwork adjustment, the
Lenses one-and -three-quarter-inch diameter, producing
views 5 by 4 ... ... ... ... 110

No. 2. — Ditto ditto, with Lens two-and-a-quarter-

inch diameter, producing views 8 by 6 ... ... 2 0 0

No. 3. — Ditto ditto, with Lens, three-arid-a- quarter-

inch diameter, for pictures or views of large dimensions 3 10 0

10 CATALOGUE OF PHOTOGRAPHIC APPARATUS,

PORTRAIT LENSES.

£ s. d.

No. 1. — Quarter size Portrait Lens of the best quality, with
double achromatic combination, delicate rack and pinion
adjustment, the Lenses one-and-a-quarterinch diameter,
for portraits, 4J by 3J and under £l 2s. Qd. to 1 15 0

No. 2.— Half size ditto ditto, for portraits, 6£ by 4f

and under ... ... ... ... £3 to 3 15 0

No. 3. — Whole size ditto ditto, for portraits, 8-J- by 6^

and under £5 10s. to" 8 10 0

MAHOGANY CAMERAS.

Expanding Camera of French polished mahogany, with
sliding body, focussing glass in frame, and single back,
for taking pictures on glass or paper, up to 5 by 4 and
under ... ... ... ... ... 0 17 6

No. 1. — Expanding Spanish mahogany Camera, with dark
frame, three plate or glass holders, focussing glass, &c.,
beautifully finished and French polished, adapted for
sizes 5 by 4 and under ... ... ... 150

No. 2. — Ditto ditto, for sizes to 8 by 6 ... 2 2 0

No. 3. — Ditto ditto, for sizes up to 8 J by 6 J portraits,

and 9 by 9 views, with sliding front for adjustment of
foreground and sky ... ... ... 2 12 6

SPANISH MAHOGANY Double Back for Paper, fitted to No. 1
Camera, 13s.; No. 2, 16s.; No. 3, £1.

WALNUT WOOD CAMERAS.

No. 1. — Superior well-made walnut- wood Cameras, with two
dark frames, focussing glass, and three plate or glass
holders, ^for sizes 5 by 4 and under ... ... 0 14 0

No. 2.— Ditto ditto, for 6J by f>J ... 0 18 6

No. 3.— Ditto ditto, for 9 by 6 J ... ... 1 7 6

N.JB. — These Cameras are suitable for Plates, Glass, or Paper.
*#* The foregoing Lenses are all of the best German and French manufacture, and
being selected with the greatest care, can be confidently recommended ; but
Operators in the Photographic Art, who may be desirous of having Lenses of
first-rate English manufacture, can be supplied at the following prices :

ENGLISH MANUFACTURED PORTRAIT LENSES.

No. 1. — Portrait Lens of the highest finished English manu-
facture, with delicate rack and pinion adjustment, the
Lenses one-and-three quarter-inch diameter, for portraits
4j by 3| and under ... ... ... ...330

SOLD BY C. BAKER, 243 & 244, HIGH HOLBORN. 11

£ s. d.

No. 2. — A similarly made Lens, with Lenses two-and-a-
half- inch diameter, for portraits 6J by 4j and under 510 0

No. 3. — Ditto ditto, with Lenses three-and-one-

eighth-inch diameter, for portraits SJ by 6J and under 10 10 0

N.B. — These Lenses can be adapted also for Views at a trifling additional
expense.

ENGLISH MANUFACTURED LANDSCAPE LENSES.

No. 1. — Landscape Lens of the highest finished English
workmanship of one achromatic combination, with
delicate rack and pinion adjustment, the Lenses two
inches diameter, producing views 6J by 5J and under 2 10 0

No. 2. — Ditto ditto, with Lenses two-and-half inch

diameter, producing views 9 by 7 and under ... 3 10 0

No. 3. — Ditto ditto, with Lenses three-and-one-

eighth-inch diameter, producing views 10 by 8 and
under ... . ... ... ... ... 4 10 0

No. 4 — Ditto ditto, with Lenses three-and-a-half-

inch diameter, producing views 12 by 10 and under 600

N.B. — The foregoing English Lenses are of the highest possible finish and
quality, and being entirely manufactured on the premises by the most skilful
workmen, each one can be specially guaranteed to perform in the most
efficient manner.

EXPANDING CAMERAS,

SUITABLE FOR THE FOREGOING ENGLISH LENSES.

No. 1. — Improved Expanding Spanish mahogany Camera,
suitable both for views and portraits, with focussing
frame, dark frame, and three plate or glass holders,
beautifully finished and French polished, for sizes
61 by 5J and under ... ... ... ... 200

No. 2. — Ditto ditto, for sizes 9. by 7 and under 300

No. 3.— Ditto ditto, for sizes 10 by 8 and under 3150

No. 4. — Ditto ditto, for sizes 12 by 10 and under 440

Adjustment for foreground and sky, extra 10s.

RIGID CAMERAS.

No. 1. — Improved Rigid Spanish mahogany Camera, suit-
able for views or portraits 6^ by 5t^ and under, as
above, with adjustment for foreground and sky ... 1 10 0
No. 2.— Ditto ditto, 9 by 7 and under ... 200

No. 3. — Ditto ditto, 11 by 9 and under ... 2 10 0

No. 4.— Ditto ditto, 12 by 10 and under ... 3 10 0

Improved Double Backs for No. 1, 15*. ; No. 2, 20s. ; No. 3, 25s.;

No. 4, 30s.

12 CATALOGUE OF PHOTOGRAPHIC APPARATUS,

FOLDING CAMERAS. £ «• <*•

No. 1. — Improved portable Folding Camera, with one single
back for glass or plates, and the necessary frames, one
double back for paper, focussing glass, and adjusting
front for foreground and sky, for sizes 9 by 7 and under
of the finest Spanish mahogany French polished ... 4 15 0
No. 2. — Ditto ditto, for sizes 10 by 8 and under 600

No. 3. — Ditto ditto, for sizes 11 by 9 ... ... 6 10 0

No. 4. — Ditto ditto, for sizes 12 by 10 and under 700

MAHOGANY IODISING AND BEOMISING BOXES.

No. 1. — Quarter-size French polished Spanish mahogany
Bromising and Iodising Boxes (double), with glass
pans, mirrors, &c., and six coating frames ... 1 12 6

No. 2.— Ditto ditto, half-size ... ... 2 12 6

No. 3. — Ditto ditto, whole-size ... ... 440

WALNUT-WOOD IODISING AND BROMISING BOXES.

No. 1. — Quarter-size walnut wood Iodising and Bromising
Double-Boxes, with porcelain pans, and coating frames,
(without mirror) ... ... ... ... 0 .17 6

No. 2.— Half-size ditto ditto ... ... ... 126

No. 3.— Whole-size ditto ditto ... ... ... 110 0

MAHOGANY MERCURY BOXES.

No. 1. — Quarter- size Mercury Boxes of French polished
Spanish mahogany, with thermometer and rising legs,
yellow glass windows, and plate holder ... ... 1 2 6

No. 2. — Ditto ditto, half size ... ... 176

No. 3. — Ditto ditto, whole size ... ... 1 15 0

WALNUT-WOOD MERCURY BOXES.

No. 1. — Quarter-size in walnut wood, with Thermometer,

and rising legs, &c. ... ... ... ...080

No. 2. — Ditto ditto, half size ... ... 0 10 6

No. 3. — Ditto ditto, whole size ... ... 0 15 0

TRIPOD STANDS with double legs and mahogany tops, combiningthe
necessary firmness with durability. No. 1,9s.; No. 2, 12s. 6d. ;
No. 3, 17s. Qd. ; No. 4 (which are of very superior construc-
tion), 25s. and upwards. No. 5, a portable sliding ditto, on
an improved principle, with clamps complete, 32s. 6 d.
MAHOGANY PRESSURE FRAMES, for copying from Negative
Pictures, with stout plate glass and hinged joints to allow for
examination. No. 1, 6s. Gd. ; No. 2, 8s. 6d. j No. 3, 12s. 6d.
Extra large size for views, 14 by 12, 16s.

SOLD BY C. BAKER, 243 & 244, HIGH HOLBOEN. 13

SPANISH MAHOGANY DITTO, beautifully made and French

polished. No. 1, 8s. Qd. ; No. 2, 13s,; No. 3, 16s.; No. 4, £1 ;

No. 5, £1 5s.

GILDING STANDS, mounted with levelling screws, from 3s. Qd.
HEAD RESTS, ordinary, 3s. Gd. each

Ditto ditto, with universal joints, 7s. Qd.
HAND BUFFS, for polishing of silver plate— No. 1, 2s.; No. 2, 3s. ;

No. 3, 5s. Qd. each

PLATE BENDERS, for turning the edges of plate, 5s. Qd.
GLASS SPIRIT LAMPS, from Is. ±d. each
POLISHING BLOCKS, with brass corners and wood binding Screws,

from Is. 3d.
FOCUSSING EYE PIECES, from 10s. to 15s.

PLATE BOXES IN WALNUT WOOD.

1\ inches by 2 ...

a* ;; 2f... "' ... "

4 ,,3

MAHOGANY DITTO, AND OTHERS TO HOLD SEVARAL DOZEN MADE TO ORDER.

s. d.

». rf.

1 3

4J inches by 3J ...

1 7

1 4

5 „ 4

2 0

1 5

6i „ 4|

2 3

1 6

84 ,, 6J

2 9

Every variety of Colours in bottles 9d. each.

Scales with Weights, complete, 3s.

Ditto ditto, in mahogany case, 5s.

Ditto ditto, superior, with glass pans, 7s. 6c?.

Pneumatic Plate Holders, Is. each.

Vertical Glass Trough, or Nitrate of Silver Baths, with mahogany or

glass stand and dipper, No. 1, 3s. Qd. ; No. 2, 4s. 9rf. ; No. 3,

12s. Gd.
Gutta Percha ditto, No. 1, 2s. 6d. ; No. 2, 3s. 9 d. ; No. 3, 5s. 6 d. ;

No. 4, 8s. 6d.

PHOTOGRAPHIC PAPERS, PLAIN AND PREPARED.

Per Quire.

£ s. d.

Canson's Negative, 23 by 17£ ... ... ... 0 3 6

Ditto Positive, 22 by 17 £ ... ... ... 046

Ditto Waxed Negative, 17 by 11 ... ...070

Ditto ditto ditto, Iodised, 17 by 11 ... 0150

Ditto Albumenised Positive, in Ammonia or Sodium,

Ilby9 ... ... ... ... ...050

Whatman's Positive or Negative, 19 by 15 J ... 030

Turner's Positive, 9 by 15... ... ... ... 0 1 6

Ditto Negative, 9 by 15 ... ... 026

Ditto ditto, large 24 by 19

Iodised Calotype Paper, 9 by 7 •** ... 050

Bibulous ... ... ... ... 0 1 3

14

CATALOGUE OF PHOTOGRAPHIC APPARATUS,

SHALLOW PORCELAIN PANS, WITH LIPS.

*. d.

a. d

6 inch by 5 inch

0 8

10 inch by 9 inch ...

2 0

8 , * 5 ,

1 0

11 „ 9 „

2 3

8 i. 64 ' ,

1 2

11 ,, 10 „

2 6

8| , Gf ,

... 1 4

13 „ 11 „

4 0

9 , 8 ,

1 6 15 „ 11 „

5 0

10 , 74 ,

... 1 9 ' Larger ditto to order.

GUTTA PERCIIA

BATHS AND PANS OF ANY SIZE, AT THE LOWEST 1

RICK.

GLASS PLATES.

Glass Plates for

the Collodion Process, of the best patent plate,

with

ground edg

'6 I

SIZE.

s. d.

STXR.

s. rf.

3$ inches by 2|-

... per doz, 1 B

fi^ inches by 4|- ... />er rfos.

5 0

4 „ 3 ..

... „ 2 0

7 „ " 6 „

7 0

2 0

8 „ 6

8 0

5 4 ..

... „ 3 6

8| ,, GT^ ... ... ,,

9 G

6 ,, 5

50

»1 ' "• 5?

10 G

COMPLETE SET OF PHOTOGRAPHIC APPARATUS.

For taking Portraits or Views up to 5 by 4, with Expanding
Camera and double combination of Achromatic Lenses,
mounted in brass, with rack and pinion adjustment,
camera stand, printing frame for producing positive
impression from negative proofs, arranged as to examine
the progress of the printing without disturbing its
position ; gutta percha bath, dipper, glass plate in
box, graduated glass measure showing half drachms,
glass funnel, box of scales and weights, two porcelain
washing trays, levelling stand ; collodion, nitrate of
silver, pyrogallic acid, acetic acid, hypo-sulphate of
soda, varnish, &c .

Complete Set, as above, for sizes up to 6 by 7 ...

Ditto

ditto, for sizes up to 9 by 7

STEREOSCOPIC PICTURES.

Calotype Views in France
Ditto ditto in England
Interiors and Studies from Life
Transparent Albumen Views in France
Ditto ditto ditto England

Ditto ditto . ditto Rome

Ditto ditto ditto Rhine

... 4

4

0

... 8

8

0

16

16

0

Per Slide.

.9.

d,

. . .

1

3

.

1

6

from

1

9

,

4

0

1 ...

5

0

.

4

0

5

6

SOLD BY C. liAKKR, 243 & 244, HIGH HOLBOKN. 15
STEREOSCOPES,

£ .<?. d.

French polished mahogany, with brass adjusting eye piece 080
Ditto ditto, with sliding ditto for adjusting the axis of

vision, and open bottoms for viewing transparencies... 0 10 6
Ditto ditto, of very superior construction and fmish,/rom 0 15 0
Yellow Glass Lanterns, 3s. each.

Books of Instruction for Collodion, Is. Oc?., per post Is. Qd.
Ditto ditto, for every process, Is. Qd. „ 2s. Od.

IODISING AND BKOMISING FANS OF FLINT GLASS.

PLATES.

PER DOZEIv7.

Sl/ES.

30th.

40th.

Galvanized.

Birmingham.

£ a.

d.

£

s.

d.

£

s.

d.

£ *.

d.

2i

by 2

0 4

0

0

3

6

0

4

6

0 5

3

8|

bv 2|

0 6

0

0

5

0

0

7

0

0 8

0

4

by 3

0 8

6

0

7

6

0

10

0

0 11

6

41

by 3{

0 8

6

0

8

0

0

10

0

0 12

0

5

by 4

0 11

6

0

11

0

0

If)

0

0 16

0

M

bv 4{

0 17

6

0

16

0

1

0

0

1 5

6

S^

by 64

1 10

0

1

10

0

1

17

6

2 7

6

PASSE PARTOUT.

PER DOZEN.

SIZES.

Bevilled sight, cushion, or oval shape,

brown ground

Bevilled sight, dome shape, brown ground
Bevilled sight, cushion or oval shape, white

ground

Ditto ditto dome shape

Bevilled sight, gold ground, cushion, oval

or dome shape

Artistic with white ground, particularly

adapted for Calotype, oval or cushion.
Ditto ditto dome shape

24 by 2

31 by 23

41 by 3J

5 by 4

6J by 4|

s. d.

s. d.

s. d.

s. d.

s. d.

2 6
3 0

3 0
3 9

3 6
4 6

5 9

7 0

6 9

8 6

3 6
4 0

4 0
5 0

4 9
5 6

7 0
9 0

9 6
11 6

9 0

10 0

11 0

16 6

23 0

9 0
10 0

10 0

11 0

12 0
12 6

6$ by 84

s. d.
14 0
16 6

17 6
17 6

MOROCCO CASES, TRAYS, &c.

PER DOZEN.

2.1 by 2

31 by 2J

3^by2f

4 by 3

41 by 3]

5 by 4

6}by4J

Morocco Cases, with Mats and

a. d.

8 0

s. d.

10 0

*. d.
12 6

*. d.
16 6

*. d.

17 6

*. d.
25 0

s. d.
45 0

Ditto, best quality, best Silk Vel-
vet Lining and Mats complete
Double Cases, to receive two Pic-
tures, fitted complete
Trays fitted with King:; for sus-
pending, and Gilt Mats

10 0
13 0
6 0

12 0

ie o

7 0

15 0
20 0
8 0

18 0
24 0
10 0

.21 0
27 0
11 0

36 0

i.) 0
18 0

60 0
72 0
30 0

Country Orders must be accompanied by an approximate Remittance,

PUKE PHOTOGKAPHIC CHEMICALS

FOR

CALOTYPE AND COLLODION PROCESSES,

AS SOLD BY

C. B A K E K,

243 AND 244, HIGH H O L B O R N.

*. d.

Acid, Acetic Glacial ... ... ... ... ... per oz. 0 8

Gallic ... ... ... ... ... „ 16

Pyrogallic ... ... ... ... per drachm, Is. 6d. „ 10 -0

Hydrochoric (pure) ... ... ... ... „ 02

Nitric ... ... ... ... ... ... „ 02

Sulphuric ... ... ... ... ... ,,02

Succinic ... ... ... ... ... ... ,, 36

Muriatic ... ... ... ... ... . ,, 02

Ammonia (pure liquid) ... ... ... ... ... „ 02

Iodide ... ... ... ... ... ,,-26

Muriate ... ... ... ... ... „ 02

Barium, Chloride (pure) ... ... ... ... „ 02

Barytes, Nitrate ... ... ... ... .... „ 03

Cadmium, Bromide ... ... ... ... ... „ 50

Iodide ... ... ... ... ... „ 40

Collodion, Iodised ... ... ... ... ... „ 09

best for Negatives ... ... ... „ 1 0

Ether, Sulphuric ... ... ... ... ... „ 06

Gold, Chloride of, in 15 grain bottles ... ... ... „ 30

Salt of, (Sal d'Or) in 15 grain bottles ... ... „ 39

Iron, Protosulphate of ... ... ... ... ... per Ib. 1 4

Lead, pure Acetic ... ... ... ... ... per oz. 0 3

pure Nitrate ... ... ... ... ... „ 04

Magnesia, Nitrate of ... ... ... ,,06

Mercury, Bychloride of ... ... ... ... ... „ 06

Potassium, Bromide ... ... ... ... ... „ 20

Iodide of ... ... ... ... ... „ 26

Fluoride of ... ... ... ... „ 20

Ferrocyanide of ... ... ... ,, 04

Cyanide of ... ... ... ... ,, 04

Potash, Nitrate ... ... ... ... ... ... „ 02

Silver, Acetate ... ... ... ... ... „ 10 0

Iodide ... ... ... ... „ 60

Chloride ... ... ... ... ... „ 60

Oxide ... ... ... ... ... ... „ 90

Nitrate (pure crystallized) „ 40

Soda, Hyposulphate ... ... ... ... ... perlb. 0 10

Sodium, Chloride ... ... ... ... ... per oz. 0 2

Milk, Sugar of ... ... ... ... „ 03

Tripoli (finest prepared) ... ... ... „ 06

Varnish (best crystal) ... ... ... ... ... „ 13

Black Jet for Positives ... per bottle 1 0

An extensive assortment of every description of Optical, Mathematical,
Astronomical, Surveying, and other Scientific Instruments both new and second-
hand, at very low prices. /

— ~ — : - / £ 7 ^

N.B. — Second-hand Instruments of all kinds, purchased or taken in Exchange.

LONDON: PRINTED BY THOMAS SCOTT, WARWICK COURT, HOLBORN.

>F THE ^

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

AN INITIAL FINE OF 25 CENTS

WILL BE ASSESSED FOR FAILURE TO RETURN
THIS BOOK ON THE DATE DUE. THE PENALTY
WILL INCREASE TO SO CENTS ON THE FOURTH
DAY AND TO $1.OO ON THE SEVENTH DAY
OVERDUE.

MAR 25 1938

10 1938

--X

JAN 15 1952^

LD 21-100m-8,'34

•IOLOG\
LIBRARY

THE UNIVERSITY OF CALIFORNIA LIBRARY

I 5 I

^^Hpllli/f/Wllml^MT