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THE

MICROSCOPE

AND ITS

REVELATIONS

WILLIAM B. CARPENTER, C.B. M.I). LL.D.

F.R.S. F.G.S. F.L.S.

CORRESPONDING MEMBER OP THE INSTITUTE OP PRANCE,
AND OP THE AMERICAN PHILOSOPHICAL SOCIETY,
ETC., ETC.

SIXTH EDITION-
ILLUSTRATED BY TWENTY-SIX PLATES
AND 'FIVE MWlibfikv WOOD ENQStJLVINOS

VOLUME II.

NEW YORK
WILLIAM WOOD & COMPANY

56 & 58 Lafayette Plage
1883

TABLE OF CONTENTS.

CHAPTER X.

MICROSCOPIC FORMS OF ANIMAL LIFE:— PROTOZOA.

PAGE

Protozoa, 1

Monerozoa, 2

Rhizopoda, 7

Reticularia, .... 7

Infusoria,
Flagellata,
Cilio-flagellata,
Suctoria, .

FORAMINIFERA, . . . .64

Porcellanea, . , . .70

Arenacea, . . . .77

Vitrea, . . . . 85

Eozoon Canadense, . . .101

Sponges, 117

Zoophytes, 122

Hydrozoa, . . . .123
Production of Medusoids, . 126

Structure of Shells, . . .171
Palate of Gasteropods, . . .180
Development of Mollusks, . ,183

Heliozoa, 11

Lobosa, 14

Coccoliths and Coccospheres . . 19

Gregarinida, 21

. 41

. 53
. 62

Radiolaria, 109

Discida, 112

Polycystina, . . . . 113
Acantbometrina, . . .113
Colloza, 115

Zoophytes continued: —

Acalephae, • . . .132
Actinozoa, .... 134
Ctenophora, . . . .137

. 150

163

Ciliary motion on Gills, . . 189
Organs of Sense of Mullusks, . 190
Chromatophores of Cephalopods, . 191

CHAPTER XL
animalcules: — INFUSORIA and rotifera.

. 24 I Infusoria continued:-

. 26 | Ciliata,

, Ti j Rotifera,

. 39 i Tardigrada,

CHAPTER XII.

FORAMINIFERA AND POLYCYSTINA.

CHAPTER XIII.

SPONGES AND ZOOPHYTES.

CHAPTER XIV.

ECHINODERMATA.

Structure of Skeleton, . • . 140 | Echinoderm-Larvao,

CHAPTER XV.

POLYZOA AND TUNICATA.
POLYZOA, 157 | TUNICATA,

CHAPTER XVI.

MOLLUSCOUS ANIMALS GENERALLY.

7 73^r/

TABLE OF CONTENTS.

CHAPTER XVII.

ANNULOSA OR WORMS.

PAGE PAGE

Entozoa, 192 I Annelida, 195

T urbell aria, .... 194 | Development of Annelids, . 197

CHAPTER XVIII.

CRUSTACEA.

Pycnogonida, .... 205
Entomostraca, , . . .207
Suctoria, 212

ClRRHIPEDA, 213

Malacostraca, . . . .214
Metamorphosis of Decapods, 215

CHAPTER XIX.

INSECTS and arachinda.

Number and variety of Objects af-
forded by Insects, . . .218
Structure of Integument, . .219
Scales and Hairs, . . . 220

Eyes, 229

Antennae, 232

Mouth 233

Circulation of the Blood, . . 237
Respiratory Apparatus, . . . 238

Wings, .
Feet,

Stings and Ovipositors,
Eggs,

Agamic Reproduction,
Embryonic Development

Acarida, .
Parts of Spiders,

CHAPTER XX.

VERTEBRATED ANIMALS.

Elementary Tissues, . . . 252
Cells and Fibres, . . .253

Bone, 255

Teeth, 258

Scales of Fish, . . , .261

Hairs, 263

Feathers, 266

Hoofs Horns, etc., . . . 267

Blood, 267

White and Yellow Fibres, . 271
Skin, Mucous and Serous Mem-
branes, 274

Epidermis, .... 275
Pigment-Cells, . . . .275
Epithelium, . . . .276
Fat, . . . . . .277

Cartilage, 278

Glands, . . . . . 279

Muscle, 281

Nerve, 284

Circulation of the Blood, . . 286
Injected Preparations, . . . 292
Vessels of Respiratory Organs, . 299

CHAPTER XXI.

APPLICATION OF THE MICROSCOPE TO GEOLOGY.

Fossilized Wood, Coal, . . .302
Fossil Foraminifera; Chalk, . . 304
Organic Materials of Lime-stones, 308

Fossil Bones, Teeth, etc., . .310
Inorganic materials of Rocks, . 312
Nachet's Mineralogical Microscope, 315

CHAPTER XXII.

INORGANIC OR MINERAL KINGDOM. — POLARIZATION.

Mineral Objects, . . . .318 Organic Structures suitable for
Crystallization of Salts, . . .319 Polariscope, .... 323
Molecular Coalescence, . . . 323 Micro-Chemistry, .... 326

APPENDIX.

••Numerical Aperture" and " An-
gular Aperture, " .... 327
Watson's New Model Microscopes, 331

Swift's < 'Wale" Model Students'

Microscope, 332

Nachet's Objective-carrier, . . 333

THE MICROSCOPE.

CHAPTER X.

MICROSCOPIC FORMS OF ANIMAL LIFE:— PROTOZOA.

391. Passing-on, now, to the Animal Kingdom, we begin by direct-
ing our attention of those minute and simple forms, which correspond in
the Animal series with the Protophyta in the Vegetable (Chap. VI.); and
this is the more desirable, since the formation of a distinct group to
which the name of Protozoa (first proposed by Siebold) may be appro-
priately given, is one of the most interesting results of Microscopic
inquiry. This group, which must be placed at the very base of the Animal
scale, beneath the great Sub-Kingdoms marked-out by Cuvier, is character-
ized by the extreme simplicity that prevails in the structure of the beings
composing it; the lowest of them being single protoplasmic particles or
' jelly specks;' whilst even among the highest, however numerous their
units may be, these are (as among protophytes. § 227) mere repetitions
of one another, each capable of maintaining an independent existence.
In this there is a very curious and significant parallelism to the earliest
embryonic stage of higher Animals. For the fertilized germ of any one
of these first shapes itself as a single cell; and then, by repeated binary
subdivisions, develops itself into a morula or 6 mulberry-mass 9 of cells
(Fig. 403), corresponding to the 6 multicellular ' organisms met with
among the higher Protozoa (Fig. 350). There is, so far, in neither case,
any sign of that ' differentiation , of organs which is characteristic of the
higher Animals; but whilst, in the Protozoon, each cell is not merely
similar to its fellows, but is independent of them, the morula, in such as
go on to a higher stage, becomes the subject of a series of developmen-
tal changes, tending to the production of a single whole, whose parts are
mutually-dependent. The first of these changes is its conversion into a
gastrula or primitive stomach, whose wall is formed of a double mem-
brane,— the outer lamella, or ectoderm, being derived directly from the
external cell-layer of the morula, whilst the inner, or endoderm, is formed
by the ' invagination ' of that layer into the space left void by the disso-
lution of the central cells of the ' morula.'1 This gastrula-stage, as we

1 It has not yet been certainly ascertained that the endoderm is formed by
invagination in all cases ; but as several of the supposed exceptions have dis-
appeared under the light of fuller investigation, it seems probable that the re-
mainder will be found conformable to the general rule.
1

THE MICROSCOPE AND ITS REVELATIONS.

shall see hereafter (§ 513), remains permanent in the great group of
Ccelenterata; though the endoderm and ectoderm are separated from each
other in its higher forms by the development of generative and other
organs between them. Bat in all Classes above the Coelenterates, the
primitive stomach has only a transitory existence, being superseded by
the permanent structures that have their origin in its walls. — Thus the
whole Animal Kingdom may be divided, in the first place, into the
Protozoa, which are either single cells, or aggregates of similar cells
corresponding to the morwto-stage of higher types; and the Metazoa, in
which the morula takes-on the condition of an individualized organism,
the life of every part of which contributes to the general life of the
whole.

392. The lowest of the Protozoa, however, like the simplest Proto-
phytes, do not even attain the rank of a tmQcell, — understanding by that
designation a definite protoplasmic unit, limited by a cell-wall, and con-
taining a ' nucleus.' For they consist of particles of protoplasm, termed
('cytodes5 or 'plastids') of indefinite extent, which have neither cell-
wall nor nucleus, but which yet take-in and digest food, convert it into
the material of their own bodies, cast out the indigestible portions, and
reproduce their kind, with the regularity and completeness that we have
been accustomed to regard as characteristic of higher Animals. Between
some of these Monerozoa (as they have been designated by Prof. Haeckel,
who first drew attention to them and the Myxomycetes (§ 222) the Chla-
midomyxis (§ 324) already described, no definite line of division can be
drawn; the only justification for the separation here adopted 'being that
the affinities of the former seem to be rather with the lowest forms of
Vegetation, whilst the whole life-history of the types now to be described
and the connected gradation by which they pass into undoubted Bhizo-
pods, leave no doubt of their claim to a place in the Animal Kingdom.

Monerozoa.

393. A characteristic example of this lowest Protozoic type is pre-
sented by the Protomyxa aurantiaca (Fig. 279), a marine c Moner ' of
an orange-red color, found by Professor Haeckel upon dead shells of
Spirula near the Canary Islands. In its active state is has the stellar
form shown at f; its arborescent extensions dividing and inosculating
so as to form a constantly changing network of protoplasmic threads,
along which stream in all directions orange-red granules obviously belong-
ing to the body itself, together with foreign organisms (b c)-such as
marine Diatoms, Eadiolarians, and Infusoria, — which, having been en-
trapped in the pseudopodial network, are carried by the protoplasmic
stream into the central mass, where the nutrient matter of their bodies
is extracted, the hard skeletons being cast out. Neither nucleus nor
contractile vesicle is to be discerned; but numerous floating and incon-
stant vacuoles (a) are dispersed through the substance of the body. —
After a time, the currents become slower; the ramified extensions are
gradually drawn inwards; and, after ejecting any indigestible parti-
cles it may still include, the body takes the form of an orange-red sphere,
round which a cyst soon forms itself, as shown at A. After a period of
quiescence, the protoplasmic substance retreats from the interior of the
cyst, and breaks up into a number of small spheres (b), which, at first
inactive, soon begin to move within the cyst, and change their shape to
that of a pear with the small end drawn out to a point. The cyst then

MICROSCOPIC FORMS OF ANIMAL LIFE.

bursts, and the red pear-shaped bodies issue forth into the water (c),
moving freely about by the vibrations oiflagella formed by the drawing-
out of their small ends, — just as do the flagellated zoospores of proto-
pliytes (§ 231). These bodies, being without trace of either nucleus,
contractile vesicle, or cell-wall, are to be accounted as particles of simple
homogeneous protoplasm, to which the designation plastidules has been
appropriately given* After about a day the motions cease; the flagella
are drawn in, and the plastidules take the form and lead the life of
Amwbm (§ 403), putting forth inconstant pseudopodial processes, and
engulfing nutrient particles in their substance (d). Two or more of
these anicebiform bodies unite to form a fc Plasmodium 9 (as in the Myxo-

Fig. 279.

Protomyxaaurantiaea:—A^ encysted statospore; b, incipient formation of swarm- spores, shown
at c escaping from the cyst, at d swimming freely by their flagellate appendages, and at e creep-
ing in the amoeboid condition; f, fully-developed reticulate organism, snowing numerous vacuoles,
a, and captured prey, 6, c.

mycetes, § 222); its pseudopodial exten&ions send out branches which
inosculate to form a network; and the body grows, by the ingestion of
nutriment, to the size of the original. — In this cycle of change there
seems no intervention of a generative act, the coalescence of the amoebi-
form plastidules having none of the characters of a true * conjugation.'
But it is by no means improbable that after a long course of multiplica-
tion by successive subdivisions, a sexual act of some kind may intervene.

394. Another very interesting 'moneric' type is, the Vampyrella;
of which one form (Fig. 280, b) lias long been known in its encysted con-

THE MICROSCOPE AND ITS REVELATIONS.

dition as a minute brick-reel sphere attached to the filaments of the Con-
jugate Spirogyra: whilst another (Fig. 281, a, a) similarly attaches itself
to the branches of Gomphonema (§ 294). The wails of the cysts are com-
posed of two membranes; of which the interior gives the characteristic
reaction of cellulose, whilst the softer external layer is nitrogenous.
After remaining some time in the quiescent condition, the encysted pro-
toplasm breaks up into two or four 6 tetraspores * (Fig. 281, b, d); these
escape by openings in the cyst (Fig. 280, c); and soon take the spherical
form, emitting very slender pseudopodial filaments (Figs. 280, d, 281, b)
like those of an Actinoplirys, but possessing neither nucleus nor contrac-
tile vesicle. In this condition they show great activity; moving about in
cearch of the special nutriment they require, drawing themselves out in
strings and fine filaments which tear asunder and again unite to send off
branches and form fine fan-like expansions, and these occasionally contract-
Fig, m

Vampyrella spirogprce. as seen at a socking out contents of Spirogyra-cel]: at r. in encysted
condition, the cyst a inclosing granular protoplasm b; at c, division of contents of cyst into tetra-
spores, of which one is escaping in the amoeboid condition, to develop itself into the adult form
shown at n.

ing again into minute spheres. When the V. spivogyrm is watched in
water containing some filaments of Spirogyra, it may be seen to wander
until it meets one of these filaments, to which, if it be healthy and loaded
with chlorophyll, it attaches itself. It soon begins to perforate the wall
of the filament; and when the interior of this has been reached, its endo-
plasm, carrying with it the chlorophyll -granules it includes, passes slowly
into the body of the Vampyrella. In this manner, cell after cell is
emptied of its contents; and the plunderer, satiated with food, resumes
its quiescent spherical form to digest it. The chlorophyll granules which
it has ingested become diffused through the body, but gradually cease to
be distinguishable, the protoplasmic mass assuming a brick-red color.

MICROSCOPIC FORMS OF ANIMAL LIFE.

The first layer it exudes to form its cyst is the outer or nitrogenous in-
vestment, within which the cellulose layer is afterwards formed, — The
V. gomphonematis in like manner creeps over the stems and branches of
the Gomphonema (Fig. 281, e), adapting itself to the form of its support;
and as soon as it has reached one of the terminal siliceous cells of the Dia-
tom, it extends itself over it so as completely to envelop the cell in a thin
layer of protoplasm. From tho surface of this, a number of fine pseudo-
podia radiate into the surrounding water (/); whilst another portion of the
protoplasm finds its way between the two siliceous valves into the interior,

Fig. 281.

ampyrella gomphonematis: — A, colony of Gomphonema attacked by Vampyrellce; a, encysted
state; 5, 6, cysts with contents breaking-up into tetraspores, d, d, seen escaping at e; at /is shown
a Vampyrella sucking- out contents of Gomphonema-cells, the emptied frustults of which, g, h,
are cast forth.— b, isolated Vampyrella, creeping about by its extended pseudopodia.

and appropriates its contents. The valves, when emptied, break off from
their support, and are cast out of the body of the Vampyrella, which soon
proceeds to another Gomphone?na-ce\l and plunders it in the same manner.
After thus ingesting the nutriment furnished by several cells, and ac-
quiring its full size, it passes, like V. spirogyrw, into the encysted con-
dition, to recommence — after a period of quiescence — the same cycle of
change.

395. Intermediate between the foregoing and the ' reticularian ■

THE MICROSCOPE AND ITS REVELATIONS.

Rhizopods to be presently described, is another simple Protozoon discovered
in ponds in Germany by M.M. Claparede and Lachmann, and named by
them Lieberkuhnia Wageneri.1 The whole substance of the body of this
animal and its pseudopodial extensions (Fig. 282) is composed of a homo-
geneous, semifluid, granular protoplasm; the particles of which, when
the animal is in a state of activity, are continually performing a circula-
tory movement, which may be likened to the rotation of the particles in
the protoplasmic network within the cell of a Tradescantia (§ 355). It is
a marked peculiarity of the pseudopodial extension of this type, that it
does not take place by radiation from all parts of the body indifferently;

but that it proceeds entirely from a sort
of trunk that soon divides into branches,
which, again, speedily multiply by further
subdivision, until at last a multitude of
finer and yet finer threads are spun-out,
by whose continual inosculations a com-
plicated network is produced, which may
be likened to an animated Spider's web.
The entire absence of anything like a
membranous envelope is clearly evidenced
by the readiness with which the subdivi-
sion and the coalescence of the pseudo-
podia alike take place. Any small ali-
mentary particles that may come into con-
tact with the glutinous surface of the
pseudopodia, are retained in adhesion by
it, and speedily partake of the general
movement going-on in their substance.
This movement takes place in two prin-
cipal directions; from the body towards
the extremities of the pseudopodia, anil
Lieberkuhnia Wageneri. from these extremities back to to the body

again. In the larger branches a double
current may be seen, two streams passing at the same time in opposite direc-
tions; but in the finest filaments the current is single, and a granule may be
seen to move in one of them to its very extremity, and then to return, per-
haps meeting and carrying back with it a granule that was seen advancing
in the opposite direction. Even in the broader processes, granules are
sometimes observed to come to a stand, to oscillate for a time, and then
to take a retrograde course, as if they had been entangled in the opposing
current, — just as often is to be seen in Chara. When a granule arrives
at a point where a filament bifurcates, it is often arrested for a time,
until drawn into one or the other current; and when carried across one of

1 "Etudes sur les Infusoires et les Rhizopods;" Geneva, 1850-1861. The beauti-
ful figure of Lieberkuhnia, given by M. Claparede, has been reproduced by the
Author in Plate 1 of his ' Introduction to the Study of the Foraminifera.,— A Rhizo-
pod of the same type has been discovered by Mr. Siddall (of Chester) in Sea- water
from the North and South Coasts of Wales, which he regards as especially identi-
cal withi. Wageneri ("Quart. Microsc. Journ.," N. S., Vol. xx., p. 144), but which
the Author (who has great confidence in the accuracy of the excellent observers
by whom the latter was described) must regard as differentiated from it (1) by the
existence of a pellucid flexible investment (foreshadowing the 6 test ' of Gromia),
having a definite orifice bordered by four infolded lips, through which the sarco-
dic trunk issues forth; and (2) by the presence of a number of highly refractive,
short, rod-like spicu'es set at various angles on the external surface.

MICROSCOPIC FORMS OF ANIMAL LIFE.

the bridge-like connections into a different band, it not unfrequently
meets a current proceeding in the opposite direction, and is thus carried
back to the body without having proceeded very far from it. The pseu-
dopodial network along which this 'cyclosis' takes place, is continually
undergoing changes in its own arrangement; new filaments being put
forth in different directions, sometimes from its margin, sometimes from
the midst of its ramifications, whilst others are retracted. Not unfre-
quently it happens that to a spot where two or more filaments have met,
there is an afflux of the protoplasmic substance that causes it to accumu-
late there as a sort of secondary centre, from which a new radiation of
filamentous processes takes place. Occasionally the pseudopodia are en-
tirely retracted, and all activity ceases; so that the body presents the ap-
pearance of an inert lump. But if watched sufficiently long, its activity
is resumed; so that it may be presumed to have been previously satiated
with food, which is undergoing digestion during its stationary period.
No encysting process has been noticed in Lieberkuhnia; and the manner
in which this type reproduces itself is at present entirely unknown. As
the marine type of it occurs on our own coasts, the fresh- water type may
very likely be found in our ponds; and either may be recommended as a
most worthy object of careful study.

Rhizopoda.

396. We now arrive at the group of Rhizopods, or ' root-footed '
animals, first established by Dujardin for the reception of the Amoeba
(§ 403) and its allies, which had been included by Prof. Ehrenberg
among his Infusory Animalcules, but which Dujardin separated from
them as being mere particles of sarcode (protoplasm), having neither the
definite body-wall nor the special mouth of the true Infusoria, but put-
ting forth extensions of their sarcodic substance, which he termed
pseudopodia (or false feet), serving alike as instruments of locomotion,
and as prehensile organs for obtaining food. According to Dujardin's
definition of this group, the Monerozoa already described would be
included in it; but it seems on various grounds desirable to limit the
term Rhizopoda to those Protozoa in which the presence of a nucleus,
the differentiation of an ectosarc (or firmer superficial layer of proto-
plasm) from the semi-fluid endosarc, together with the more definite
form and restricted size, indicate a distinct approach to the condition of
true cells. — Many different schemes for the classification of the Rhizopods
have been proposed; but none of them can be regarded as entirely satis-
factory, our knowledge of the Reproductive processes, and of other
important parts of the life-history of these creatures, being still extremely
imperfect. And as some parts of the scheme proposed by the Author
twenty years ago,1 based on the characters of the pseud opodial extensions,
have been accepted by more recent systematists, he thinks it best still to
adhere to it, as seeming to him to be on the whole most natural.

I. In the First division, Reticularia, the pseudopodia freely ramify
and inosculate, so as to form a network, exactly as in Lieberkuhnia ;
from which they are distinguished by the possession of a nucleus, and by
the investment of their sarcodic bodies in a firm envelope. This is most
commonly either a calcareous shell of very definite shape, or a test built
up of sand-grains or other minute particles more or less firmly united by

1 Natural History Review," 1861, p. 4~6; and "Introduction to the Study of
the Foraminifera "' (1863;, Chap. II.

THE MICROSCOPE AND ITS REVELATIONS.

a calcareous cement exuded from the sarcodic body. These testaceous
forms, which are exclusively marine, constitute the group of Foramini-
fera; whose special interest to the microscopist entitles it to separate
consideration (Chap. xn.). And it is only for convenience, that two
Reticularia which inhabit fresh water also, and the envelopes of whose
bodies are usually membranous, are here separated from the Foraminifera
(to which they properly belong) for description as types of the group.
The Reticularia have little locomotive power, and only seem to exercise
it to find a suitable situation for their attachment; the capture of their
food being effected by their pseudopodial network.

ii. The Second division, Heliozoa,1 consists of the Ehizopods whose
pseudopodia extend themselves as straight radiating rods, having little
or no tendency to subdivide or ramify, though they are still sufficiently
soft and homogeneous (at least in the lower types, § 399), to coalesce
when they come into contact with each other. These have usually
(probably always) a contractile vesicle as well as a nucleus; and the
higher forms of them are characterized by the inclosure of peculiar
yellow corpuscles (whose import is unknown) in the substance of their
endosarc. By far the larger number of this group also have skeletons of
Mineral matter, which are always siliceous ; and these are sometimes
perforated casings of great regularity of form, as in the marine Poly-
cystina; sometimes internal frameworks of marvellous symmetry, as in
the marine Radiolaria. These two groups, also, will be reserved for
special notice (Chap, xn.); the simple Heliozoa which are among the
commonest inhabitants of fresh water, furnishing the best illustrations
of the essential characters of the type. They seem for the most part to
have but little locomotive power, capturing their prey by their extended
pseudopodia.

in. The Third group, Lobosa, contains the Ehizopods which most
nearly approach the condition of true Cells, in the differentiation of their
almost membranous ectosarc and their almost liquid endosarc, and in the
non-coalescence of their pseudopodial extensions, which, instead of being
either thread-like or rod-like, are lobate, that is, irregular projections of
the body, including both ectosarc and endosarc, which are continually
undergoing change both in form and number. The Lobosa are com-
paratively active in their habits, moving freely about in search of food,
which is still received into the substance of their bodies through any part
of their surface, — unless this is inclosed in envelopes, such as are formed
by many of them, either by exudation from the surface of their bodies of
some material (probably chitinous) which hardens into a membrane, or
by aggregating and uniting grains of sand or other small solid particles,
which they build up into i tests/ A large proportion of them are inhabi-
tants of fresh water, and some are even found in damp earth.

397. Reticularia. — This type is very characteristically represented by
the genus Gromia (Fig. 283); some of whose species are marine, and are
found, like ordinary Foraminifera, among tufts of Corallines, Algae, etc. ;
whilst others inhabit fresh water, adhering to Confervae and other Plants
of running streams. It was in this type that the presence of a nucleus
formerly supposed to be wanting in Reticularia generally, was first estab-

1 To this group the Author formerly extended the name Radiolaria given by
Muller to one section of it; but he now thinks it preferable to employ the general
term Heliozoa given to it by Hertwig and Lesser, restricting the term Radiolaria
to the group to which it was originally applied.

MICROSCOPIC FORMS OF ANIMAL LIFE.

T.shed by Dr. Wallich. The sarcode-body of this animal is incased in an
egg-shaped, brownish-yellow, chitinous envelope, which may attain a dia-
meter of from l-12th to l-10th of an inch, looking to the naked eye so
like the egg of a Zoophyte or the seed of an aquatic Plant, that its real
nature would not be suspected as long as it remains quiescent. The
'test' has a single round orifice, from which, when the Animal is in a
state of activity, the sarcodic substance streams forth, speedily giving off
ramifying extensions, which, by further ramification and inosculation,
form a network like that of Lieberktihnia. But the sarcodc also extends
itself so as to form a continuous layer over the whole exterior of the ' test;'
and from any part of this layer fresh
pseudopodia may be given off. By
the alternate extension and contrac-
tion of these, minute Protophytes
and Protozoa are entrapped and
drawn into the interior of the test,
where their nutritive material is ex-
tracted and assimilated; and if the
6 test 9 (as happens in some species) be
sufficiently transparent, the indiges
tible hard parts (such as the siliceous
valves of Diatoms, shown in Fig.
283) may be distinguished in the
midst of the sarcodic substance. By
the same agency, the Gromia some-
times creeps up the sides of a glass
vessel. In the intervals of quies-
cence, on the other hand, the whole
sarcodic body, except a film that
serves for the attachment of the test,
is withdrawn into its interior.

398. Another example of the Re-
ticularian group la afforded by the
curious little Microgromia socialis
(Fig. 284), first discovered by Mr.
Archer, and further investigated with
great care by Hertwig;1 which has
the curious habit of uniting with
neighboring individuals, by the fus-
ion of the pseudopodia, into a com-
mon 'colony;' the individuals some-
times remaining at a distance from
one another as at A, but sometimes
aggregating themselves into compact
masses as at B. The nearly globular
thin calcareous shell is prolonged into
a short neck having a circular orifice,
from which the sarcode-body extends itself, giving off very slender pseudo- '
podia which radiate in all directions. A distinct nucleus can be seen in
the deepest part of the cavity; while a contractile vesicle lies imbedded in
the sarcodic substance nearer the mouth. Multiplication by duplicative
subdivision has been distinctly observed in this type; but with a peculiar

1 'Ueber Microgromia; 9 in " Archiv fur Mikr. Anat.," Bd. x., Supplement.

THE MICROSCOPE AND ITS REVELATIONS.

departure from the usual method. A transverse constriction divides the
body into two halves — as shown in two individuals of colony a, — each half
possessing its own nucleus and contractile vesicle; the posterior seg-
ment, which at first lies free at the bottom of the cell, then presses for-
wards towards its orifice, as shown at c, and finally, by amoeboid move-
ments, escapes from it, sometimes stretching itself out like a worm (as
seen at d), sometimes contracting itself into a globe, and sometimes

Fig. 284.

Microgromia socialist—A, colony of individuals in extended state, some of them undergoing trans-
verse fission ; b, colony of individuals (some of them separated from the principal mass) in com
pact state ; c, d, formation and escape of swarm-spore, seen free at e.

spreading itself out irregularly over the pseudopodia of the colony.
But it finally gathers itself together and takes an oval form; and either
develops a pair of flagella, and forsakes the colony as a free swimming
Monad (§ 416), or assumes the form of an Actinophrys, moving about
by three or four pointed pseudopodia, — probably in each case coming after
a time to rest, excreting a shell, and laying the foundation of a new
colony. There is reason to think that a multiplication by longitudinal fis-

MICROSCOPIC FOKMS OF ANIMAL LIFE.

sion also takes place, in which the escaping segment and the one left be-
hind in the old shell remain attached by their pseudopodia, and the
former develops a new shell without undergoing any change of condition.

399. Heliozoa. — The Actinophrys sol, sometimes termed the ' sun-ani-
malcule' (Fig. 285), is one of the commonest examples of this group;
being often met-with in lakes, ponds, and streams, amongst Confervse
and other aquatic plants, as a whitish-gray spherical particle distinguish-
able by the naked eye, from which (when it is brought under a suffi-
cient magnifying power) a number of very pellucid, slender, pointed
rods are seen to radiate. The central portion of the body is composed
of homogeneous sarcode, inclosing a distinct nucleus with a large nucle-
olus (as in Fig. 287, n); but the peripheral part has a ' vesicular' aspect,
as in the type next to be described (Fig. 286). This appearance is due
to the number of 'vacuoles' filled with a watery fluid, which are included
in the sarcodic substance, and which maybe artificially made either to
coalesce into larger ones, or to subdivide into smaller. A 'contractile
vesicle,' pulsating rhythmically with considerable regularity, is always to
be distinguished, either in the midst of the sarcode-body, or (more com-
monly) at or near its surface; and it sometimes projects considerably
from this, in the form of a flattened sacculus with a delicate membra-
nous wrall, as shown at o. The cavity of this sacculus is not closed ex-
ternally, but communicates with the surrounding medium; not, however,
by any distinct and permanent orifice, the membraniform wall giving
way when the vesicle contracts, and then closing-over again. This al-
ternating action seems to serve a respiratory purpose, the water thus
taken-in and expelled being distributed through a system of channels
and ATacuoles excavated in the substance of the body; some of the vacuoles
which are nearest the surface being observed to undergo distention when
the vesicle contracts, and to empty themselves gradually as it re-fills.
The body of this animal is nearly motionless, but it is supplied with
nourishment by the instrumentality of its pseudopodia; its food being
derived not merely from Vegetable particles, but from various small
Animals, some of them (as the young of Entomostraca) possessing great
activity as well as a comparatively high organization. When one of
these happens to come into contact with one of the pseudopodia (which
have firm axis-filaments clothed with a granular sarcode), this usually
retains it by adhesion, but the mode in which the particle thus taken
captive is introduced into the body, differs according to circumstances.
If the prey is large and vigorous enough to struggle to escape from its
entanglement, it may usually be observed that the neighboring pseudo-
podia bend over and apply themselves to it, so as to assist in holding it cap-
tive, and that it is slowly drawn by their joint retraction toward the
body of its captor. Any small particle not capable of offering active re-
sistance, on the other hand, may be seen after a little time to glide towards
the central body along the edge of the pseudopodium, without any visi-
ble movement of the latter, much in the same manner as in Gromia.
When in either of these modes the food has been brought to the surface
of the body, this sends over it on either side a prolongation of its own sar-
code-substance; and thus a marked prominence is formed (Fig. 285 c),
which gradually subsides as the food is drawn more completely into the
interior. The struggles of the larger Animals, and the ciliary action of
Infusoria and Rotifera, may sometimes be observed to continue even after
they have been thus received into the body; but these movements at
hist cease, and the process of digestion begins. The alimentary sub-

THE MICROSCOPE AND ITS REVELATIONS.

stance is received into one of the vacuoles of the endosarc (Fig. 287, f),
where it lies in the first instance surrounded by liquid; and its nutri-
tive portion is gradually converted into an undistinguishable gelatinous
mass, which becomes incorporated with the material of the sarcode-body,
as may be seen by the general diffusion of any coloring particles it may

Fig. 285.

Actinophrys sol, in different states: — A, in its ordin-
ary sun-like form, with a prominent contractile vesi

b, in the act of division or of conjugation, with cnrfnpp
«fT.o^tii^ ^oi^w ^ n • c in the act of feeding- BUllcl^?

cle o ,

two contractile vesicles o, o
d, in the act of discharging faecal (?) matters, a and

contain. Several vacuoles may
be thus occupied at one time by
alimentary particles; frequently
four to eight are thus distin-
guishable, and occasionally ten
or twelve ; Ehrenberg, in one
instance, counted as many as six-
teen, which he describedas mul-
tiple stomachs. Whilst the di-
gestive process, which usually
occupies some hours, is going on,
a kind of slow circulation takes
place in the entire mass of the
endosarc with its included va-
cuoles. If, as often happens, the
body taken-in as food possesses
some hard indigestible portion
(as the shell of an Entomostra-
can or Rotifer), this, after the
digestion of the soft parts, is
gradually pushed towards the
and is thence extruded
by a process exactly the converse
of that by which it was drawn
in. If the particle be large, it usually escapes at once by an opening
which (like the mouth) extemporizes itself for the occasion (d); but, if
small, it sometimes glides along a pseudopodium from its base to its
point, and escapes from its extremity.

400. The ordinary mode of Reproduction in Actinophrys seems to be
by binary subdivision: its spherical body showing an annular constric-
tion, which gradually deepens so as to separate its two halves by a sort
of hour-glass contraction; and the connecting band becoming more and
more slender, until the two halves are completely separated. This pro-
cess of fission, which may be completed within half an hour from its
commencement, seems to take place first in the contractile vesicle; for
each segment very early shows itself to be provided with its own (b, o,
o), and the two vesicles are commonly removed to a considerable distance
from one another. The segments thus divided are not always equal, and
sometimes their difference in size is very considerable. A junction of
two individuals, on the other hand, has been seen to take place in Actino-
phrys, and has been supposed to correspond to the ' conjugation 9 of Pro-
tophytes; it is very doubtful, however, whether this junction really in-
volves a complete fusion of the substance of the bodies which take part
in it; and there is not sufficient evidence that it has any true generative
character. Certain it is that such a junction or 6 zygosis ' may take place,
not between two only, but between several individuals at once, their
number being recognized by that of their contractile vesicles; and that,
after remaining thus united for several hours, they may separate again
without having undergone any discoverable change.

MICROSCOPIC FORMS OF AU1MAL LIFE.

401. Under the generic name Actinophrys was formerly ranked the
larger but less common Heliozoon now distinguished as Actinosphcerium
Eichornii (Fig. 286); one important difference consisting in the struc-
ture of the radiating pseudopodia, each of which has here a firm axis-fila-
ment or ' spine/ which passing through the superficial zone, rests on the
surface of the central sphere, as shown at a a, Fig. 287. This axis is
clothed with a layer of soft sarcode derived from the superficial or cor-
tical zone of the body. Several nuclei (ri, n) are usually to be seen em-
bedded in the protoplasmic mass. — The general life-history of this type
corresponds with that of tho preceding; but its mode of reproduction
presents some marked peculiarities. The binary segmentation is pre-
ceded by a withdrawal of the pseudopodia, even their clearly-defined axis
becoming indistinct and finallydisappearing; the body becomes enveloped,

Fig. 286.

Actinosphcerium Eickornii:-m, endosarc ; r, ectosarc ; c, c, contractile vacuoles.

by a clear gelatinous exudation, which forms a kind of cyst; and within
this the process of binary subdvision is repeatedly performed, until the
original single mass is replaced by a sort of morula (§ 391), each spherule
of which shows the distinction between the central and cortical regions,
the former including a single nucleus, whilst the latter is strengthened
by siliceous deposit into a firm investment. After remaining in this
state during the winter, the young Actinosphmrm come forth in the
spring without this siliceous investment; and gradually grow into the
likenesses of their parent.

402. A large number of new and curious fresh-water forms of this
type have been recently brought under notice; of which the Clathrulina i
elegans (Fig. 288) may be specially mentioned as presenting an obvious
transition to the Polycystine type (§ 504). This has been found in various

THE MICROSCOPE AND ITS REVELATIONS.

parts of the Continent, and also (by Mr. Archer1) in Wales and Ireland;
occurring chiefly in dark ponds shaded by trees and containing decaying
leaves. Its soft sarcode body is incased by a siliceous capsule of spheri-
cal form, regularly perforated with oval apertures, and supported on a
long silicified peduncle. The body itself, and the pseudopodia which it
puts forth through the apertures of the capsule, seem closely to corre-
spond with those of Adinoplirys. — Reproduction here takes place not
only by binary fission, but by the formation of 'swarm spores.' In the
first mode, one of the two segments remains in possession of the silice-
ous capsule, whilst the other finds its way out through one of the aper-
tures, lives for some hour3 in a free condition as an Actinophrys, and
ultimately produces the capsule and stem characteristic of its type. In
the second mode, numerous small rounded sarcode-masses, each possess-
ing a nucleus, are produced within the capsule, in what manner cannot

Fig. 287.

Marginal portion of Actinosphcerium Eichomii, as seen in optical section under a higher mag-
nifying powder:— m, endosarc; r, ectosarc; a, a, a, pseudopodia; n, n, nuclei with nucleoli ; /,
ingested food-mass.

be clearly made-out; and every one of these is enveloped in a firm envel-
ope, set round with short spines, probably siliceous. These cysts remain
for months within the common capsule; and when the time arrives for
their further development, the sarcode-corpuscles slip out of their cysts,
and escape through the orifices of the capsule as flagellated Monads of
oval form (Fig. 288, B,) each having a nucleus, n, near the base of the
flagella, and two contractile vesicles near its opposite end. After swarm-
ing for some hours in this condition, they change to the free Actinophrys
form, and finally acquire the siliceous capsule and stem of the Clathru-
lina.

403. Lobosa. — No example of the Rhizopod type is more common in

1 See his Memoir on Fresh-water Radiolaria in ' ' Quart. Journ. of Micros.
Sci.," N.S., Vol. ix. (18G9\ p. 230.

MICROSCOPIC FORMS OF ANIMAL LIFE.

streams and ponds, vegetable infusions, etc., than the Amoeba (Fig. 289);
a creature which cannot be described by its form, for this is as changeable
as that of the fabled Proteus, but may yet be definitely characterized by
peculiarities that separate it from the two groups already described.

The distinction between '

Fig. 288.

ecto-
sarc' and ' endosarc ' is here
clearly marked, so that the
body approaches much more
closely in its characters to an
ordinary 'cell' composed of
cell-wall and cell-contents. It
is through the 'endosarc'
alone, en, that those colored
and granular particles are dif-
fused, on which the hue and
opacity of the body depend ; its
central portion seems to have
an almost watery consistence,
the granular particles being
seen to move quite freely upon
one another with every change
in the shape of the body; but
its superficial portion is more
viscid, and graduates insensibly
into the firmer substance of
the 'ectosarc.' The ectosarc,
EC, which is perfectly pellucid,
forms an almost membranous
investment to the endosarc;
still it is not possessed of such
tenacity as to oppose a solution
of its continuity at any point,
for the introduction of alimen-
tary particles, or for the ex-
trusion of effete matters; and
thus there is no evidence, in
Amoeba and its immediate
allies, of the existence of any
more definite orifice, either oral
or anal, than exists in other
Rhizopods. The more advanc-
ed differentiation of the ecto-
sarc from the endosarc of
Amoeba, is made evident by
the effects of re-agents. If an
Amoeba radiosa be treated with
a dilute alkaline solution, the
granular and molecular endo-
sarc shrinks together and re-
treats towards the centre,
leaving the radiating exten-
sions of the ectosarc in the
condition of csecal tubes, of

Diagrammatic representation of Amoeba proteus e c, which the Walls are not soluble
ectosarc; en, endosarc; cv, contractile vesicle; n, nuc- » n „ _ t • _

leus; p, pseudopodia; vil, villous tuft. at the ordinary temperature,

Clathrulina elegans : — a, complete organism ; b, swarm-
spore, showing nucleus, n, and two contractile vesicles
near its opposite end.

Fig. 289.

VIL

THE MICROSCOPE AND ITS REVELATIONS.

either in acetic or mineral acids, or in dilute alkaline solutions; thus
agreeing with the envelope noticed by Colin as possessed by Paramecium
and other ciliated Infusoria, and with the'eontaining membrane of ordi-
nary animal cells. A 8 nucleus/ N, is always distinctly visible in Amoeba,
adherent to the inner portion of the ectosarc, and projecting from this
into the cavity occupied by the endosarc; when most perfectly seen, it
presents the aspect of a clear flattened vesicle surrounding a solid and
usually spherical nucleolus; it is readily soluble in alkalies, and first ex-
pands and then dissolves when treated with acetic or sulphuric acid of
moderate strength; but when treated with dilute acid it is rendered
darker and more distinct, in consequence of the precipitation of a finely
granular substance in the clear vesicular space that surrounds the nucle-
olus. A 6 contractile vesicle/ cv, seems also to be uniformly present,
though it does not usually make itself so conspicuous by its external
prominence as it does in Actinophrys ; and the neighboring part of the
body is often prolonged into a set of villous processes vil, the presence
of which has been thought by some to mark a specific distinction, but
which seems too variable and transitory to be so regarded.

404. The pseudopodia, which are not so much appendages, as lobato
extensions of the body itself, are few in number, short, broad, and
rounded; and their outlines present a sharpness which indicates that the
substance of which their exterior is composed possesses considerable tena-
city. No movement of granules can be seen to take place along the sur-
face of the pseudopodia: and when two of these organs come into contact,
they scarcely show any disposition even to mutual cohesion, still less to
fusion of their substance. Sometimes the protrusion seems to be formed
by the ectosarc alone, but more commonly the endosarc also extends into
it, and an active current of granules may be seen to pass from what was
previously the centre of the body into the protruded portion, when the lat-
ter is undergoing rapid elongation; whilst a light current may set towards
the centre of the body from some other protrusion which is being with-
drawn into it. It is in this manner that an Amoeba moves from place to
place; a protrusion like the finger of a glove being first formed, into
which the substance of the body itself is gradually transferred; and
another protrusion being put forth, either in the same or in some different
direction, so soon as this transference has been accomplished, or even
before it is complete. The kind of progression thus executed by an
Amo&ba is described by most observers as a ' rolling 9 movement, this being
certainly the aspect which it commonly seems to present; but it is main-
tained by M.M. Claparede and Lachmann that the appearance of rolling
is an optical illusion, for that the nucleus and contractile vesicle always
maintain the same position relatively to the rest of the body, and that
' creeping' would be a truer description of their mode of progression. It
is in the course of this movement from place to place, that the Amoeba
encounters particles which are fitted to afford it nourishment: and it
appears to receive such particles into its interior through any part of the
ectosarc, whether of the body itself or of any of its lobose expansions; in-
soluble particles which resist the digestive process being got rid of in the
like primitive fashion.

405. It may often be seen that portions of the sarcode-body of an
Amoeba, detached from the rest, can maintain an independent existence;
and it is probable that such separation of fragments is an ordinary mode
of increase in this group. When a pseudopodial lobe has been put-forth
to a considerable length, and has become enlarged and fixed at its extrem-

MICROSCOPIC FORMS OF ANIMAL LIFE.

ity, the subsequent contraction of the connecting portion, instead of either
drawing the body towards the fixed point, or retracting the lobe into the
body, causes the connecting band to thin-away until it separates; and
the detached portion speedily shoots out pseudopodial processes of its own,
and comports itself in all respects as an independent Amoeba. Multipli-
cation also takes place by regular binary subdivision. And an issue of
6 swarm-spores,' which swim about for a time like Infusoria, has been
witnessed by a competent observer.1 In the A. terricola discovered by
Greef in earth and dry sand, this process is seen to commence in the nu-
cleus, which breaks-up into rounded corpuscles that diffuse themselves
through the substance of the endosarc. The creature then ceases to take-

FlG. 290.

Pelomyxa palustris:—k% as it appears when in amoeboid motion:— b, portion more highly magni-
fied; showing a, a, the hyaline ectosarc,' 6, one of the vacuoles of the endosarc; c, rod-like bodies
scattered through the endosarc; d, protruded extension of ectosarc, with endosarc passing into it;
e, e, nuclei; /,/, globular hyaline bodies.

in food : its motions become less active, and its functions seem to be entirely
confined to the nurture of the germs, which finally make their way out,
and soon attain the size and aspect of their parent. — No sexual act has
been certainly recognized as part of the life-history of Amoeba, the union
of two or more individuals, which may be occasionally witnessed, having
more the character of the i zygosis' of Actinophrys (§ 400).

406. A sarcodic organism discovered by Greef, and named by him
Pelomyxa palustris (Fig. 290), which spreads over the bottom of stagnant
ponds in the condition of slimy masses of indefinite form, exhibits a

!Prof. A. M. Edwards (U. S.) in 66 Monthly Microsc. Journ.," Vol. viii. (1872), p.
2

THE MICROSCOPE AND ITS REVELATIONS.

further advance upon the Amoeban type. The substance of its body ex-
hibits a very clear differentiation between the homogeneous hyaline ecto-
sarc (b, a, d), and the contained endosarc, which contains such a multi-
tude of spherical vacuoles, b, as to have a 'vesicular' or frothy aspect.
When it feeds upon the decomposing vegetable matter at the bottom of
the pools it inhabits, its body acquires a blackish hue; but in other sit-
uations it may be colorless. Besides the vacuoles, there are seen in the
endosarc a great number of nucleus-like bodies, e, e, and also many hya-
line globular brilliant bodies, /, /, which are regarded by Greef as germs
or swarm-spores, developed from nucleoli set free within the general cav-
ity of the body by the bursting of the nuclei. This creature, during the
active period of its life, moves like an Amoeba, either by general undula-
tions of its surface, or by special pseudopodial extensions d. After a
time, however, its movements cease, and it looks as if dead; but by the
giving- way of its ectosarc, a multitude of minute amoebiform bodies break
forth, each having its nucleus and contractile vesicle. These at first live
as Amcebce, but afterwards pass into a resting state, assuming a spherical
or oval shape, and then put-forth flagella, by which they swim actively
for a time, — probably then settling-down to develop themselves into the
parental form.

Fig. 291.

Testaceous forms of Amoeban Rhizopods: — a, Difflugia proteiformis; b, Difflugia oblonga\ c,
drcella acuminata-, d, Arcella dentata.

407. The Amoeban like the Actinophryan type shows itself in the testa-
ceous as well as in the naked form; the commonest examples of this being
known under the names Arcella and Difflugia. The body of the former
is inclosed in a ' test * composed of a horny membrane, apparently resem-
bling in constitution the chitine which gives solidity to the integuments
of Insects: it is usually discoidal (Fig. 291, c, d) with one face flat and
the other arched, the aperture being in the centre of the flat side; and
its surface is often marked with a minute and regular pattern. The test
of Difflugia, on the other hand, is more or less pitcher-shaped (a, b), and
is chiefly made up of minute particles of gravel, shell, etc., cemented to-
gether. In each of these genera, these sarcode-body resembles that of
Amoeba in every essential particular; the contrast being very marked be-
tween its large, distinct lobose extensions, and the ramifying and inoscu-
lating pseudopodia of Gromia (Fig. 283). In each case a detached portion
of the sarcodic body will put forth pseudopodia of its own type; and the
separation of a bud or gemmule put forth from the mouth of the test seems
to be an ordinary mode of propagation among the Amoebans thus inclosed.
In Arcella it has been observed that the pseudopodia of two or more
individuals unite by bridges of protoplasm, and afterwards separate; but
it seems doubtful whether this is a true generative * con jugation/ or a
mere 'zygosis.5 It has been observed by Biitschli, however, that after
the separation of three individuals which had been thus united, the sar-

MICROSCOPIC FORMS OF ANIMAL LIFE.

codic body of one of them had withdrawn itself for a considerable space
from the wall of the test, and that in the liquid which filled the inter-
val a number of Vibrio-like bodies (spermatozoids?) swarmed; while
numerous disk-shaped masses of protoplasm lay on the surface of the
body. After some time these showed lively amoeboid movements, creep-
ing about between the body of the parent and the wall of the test, and
ultimately escaping through its orifice. Each of them contained a nu-
cleus and contractile vesicle, and moved by means of blunt pseudopodia;
and it seems probable that they were embryoes which would in time
form the characteristic Arcella-test.

408. Many testaceous Ammbans have been recently discovered, which
form tests of remarkable regularity and sometimes of singular beauty; and
it is difficult to determine, in many cases, whether the minute plates of
which they are composed have been formed by exudation from their own
bodies, or have been picked up from the surface over which the animals
crawl.1 There can be no doubt of this kind, however, in regard to the
Quaclrula symmetrica represented in Fig. 292, whose sarcode-body is en-
cased in a pear-shaped test of glassy transparence, made up of a great

masses which he designated as ' coccospheres ' (3 ). Regarding the gelatin-
ous matrix in which they were imbedded as a new type of the Monerozoa
described by Haeckel, having the condition of an indefinitely extended
Plasmodium, Prof. Huxley proposed to designate it by the name Bathy-
bius, indicative of its habitat in the depths of the sea; and this idea was

1 See especially the recent admirable work of Prof. Leidy on the Freshwater
Rhizopods of the United States (1880).— It is to be regretted that its able Author s
time and opportunities did not permit him to follow-out the life-histories ot the
many interesting forms which he has described and figured.

Fig. 292.

number of square plates which
touch each other by their edges.
The sarcode body does not usually
fill the test; the intervening space
being occupied by a clear liquid,
and traversed by bands of proto-
plasm. In the posterior part of
the body is seen a large clear
spherical nucleus, with a distinct
dark nucleolus; and in front of this
are contractile vesicles, usually two
in number.

Quadrvla symmetrica, with extended pseudo-
podia.

409. Coccoliths mid Coccospheres.
— This would seem the most appro-
priate place for the description of
certain peculiar little bodies found
very extensively diffused over the
deep-sea bottom, especially abound-
ing in the Globigerina-mud (§480),
which may be considered as Chalk
in process of formation. It was in
the specimens of this mud brought
up by the ' Cyclops ' soundings in
1857, that Prof. Huxley first
found the Coccoliths (Fig. 293, 1,
2) which Dr. Wallich in 1860
found aggregated in the spherical

THE MICROSCOPE AJSTD ITS REVELATIONS .

accepted by Haeckel, whose representation of a living specimen of Batliy-
Mus, with imbedded coccoliths, is given in Fig. 293, 4. The observations
made in the ' Challenger ' Expedition, however, have not confirmed this
view; the supposed Batliybius being a gelatinous precipitate, consisting of
sulphate of lime, slowly deposited in water to which strong spirit has
been added. Whatever be their nature, Coccoliths and Coccospheres are
bodies of great interest; since their occurrence in Chalk and in very early
Limestones (§ 699) is an additional link in the evidence of the similarity
of the conditions under which they were formed, to those at present pre-
vailing on the sea-bed of the Atlantic and others oceans. — Two distinct
types are recognizable among the Coccoliths, which Prof. Huxley has
designated respectively discoliths and cyatholiths. The former are round or
oval disks, having a thick strongly-refracting rim and a thinner internal
portion, the greater part of which is occupied by a slightly-opaque, cloud-
like patch lying round a central corpuscle (Fig. 293, 5). In general, the
6 discoliths ' are slightly convex on one side, slightly concave on the other,
and the rim is raised into a prominent ridge on the more convex side;

Fig. 293.

Coccoliths and Coccospheres:—ty 2, 7, Cyatholiths seen obliquely;— 3, Coccosphere, with im-
bedded cyatholiths;— 4, Coccoliths imbedded in supposed protoplasmic expansion; — 5, Discolith
seem in front view; —6, Cyatholith seem in fron*; view, showing (1) central corpuscle, (3) granular
zone, (3) transparent outer zone;— 8, 9, Discoliths seen edgeways.

so that when viewed edgewise, they present the appearances shown in figs.
8, 9. Their length is ordinarily between l-4000th and l-5000th of an
inch; but it ranges from l-2700th to l-ll,000th. The largest are com-
monly free; but the smallest are generally found imbedded among heaps of
granular particles, of which some are probably discoliths in an early stage
of development. — The 6 cyatholiths, y also, when full grown, have an oval
contour; though they are often circular when immature. They are convex
on one face and flat or concave on the other; and when left to themselves,
they lie on one or other of these two faces. In either of these aspects, they
seem to be composed of two concentric zones (fig. 6, 2, 3) surrounding
an oval thick-wall central corpuscle (1), in the centre of which is a clear
space sometimes divided into two. The zone (2) immediately surround-
ing the central corpuscle is usually more or less distinctly granular, and
sometimes has an almost bead-like margin. The narrower outer zone (3)

MICROSCOPIC FORMS OF ANIMAL LIFE.

is generally clear, transparent, and structureless; but sometimes shows
radiating striae. When viewed sideways or obliquely, however, the * cyatho-
liths ' are found to have a form somewhat resembling that of a shirt-stud
(tigs. 1, 2, 7). Each consists of a lower plate, shaped like a deep saucer
or watch-glass; of a smaller upper plate, which is sometimes flat, some-
times more or less concavo-convex; of the oval, thick-wall, flattened cor-
puscle, which connects these two plates together at their centres; and of
an intermediate granular substance, which more or less completely fills
up the interval between the two plates. The length of these cyatholiths
ranges from about l-1600th to l-8000th of an inch, those of l-3000th of an
inch and under being always circular. — It appears from the action of
dilute acids upon the Coccoliths, that they must mainly consist of calcareous
matter, as they readily dissolve, leaving scarcely a trace behind. When
the cyatholiths are treated with very weak acetic acid, the central corpuscle
rapidly loses its strongly refracting character; and there remains an ex-
tremely delicate, finely-granular membranous framework. When treated
with iodine, they are stained, but not very strongly; the intermediate sub-
stance being the most affected. Both discoliths and cyatholiths are com-
pletely destroyed by strong hot solutions of caustic potass or soda. — The
Coccospheres (Fig. 3) are made up by the aggregation of bodies resembling
' cyatholiths ' of the largest size in all but the absence of the granular
zone; they sometimes attain a diameter of l-760th of an inch. — What is
their relation to the Coccoliths, and under what conditions these bodies
are formed, are questions whereon no positive judgment can be at pres-
ent given. (See § 710.)

Gregarinida.

410. A very curious animal parasite is often to be met with in the
intestinal canal of Earthworms, Insects, etc., and sometimes in that of
higher animals, the simplicity of whose structure requires that it should
be ranked among the Protozoa. Each individual Gregarina (Fig. 294, a)
essentially consists of a large single cell, usually more or less ovate in form,
and sometimes attaining the extraordinary length of tivo-thirds of an
inch.1 A sort of beak or proboscis frequently projects from one extrem-
ity; and in some instances this is furnished with a circular row of hook-
lets, closely resembling that which is seen on the head of Taenia. There
is here a much more complete differentiation between the cell-membrane
and its contents, than exists either in Actinophrys or in Amoeba; and in
this respect we must look upon Gregarina as representing a decided ad-
vance in organization. Being nourished upon the juices already prepared
for it by the digestive operations of the animal which it infests, it has no
need of any such apparatus for the introduction of solid particles into
the interior of its body, as is provided in the ' pseudopodia ? of the Khizo-
pods and in the oral cilia of the Infusoria. Within the cavity of the cell,
whose contents are usually milk-white and minutely granular, there is
generally seen a pellucid nucleus; and when, as often happens, the cell
undergoes duplicative subdivision, the process commences in a constric-
tion and cleavage of this nucleus. The membrane and its contents,
except the nucleus, are soluble in acetic acid. Cilia have been detected
both upon the outer and the inner surface; but these would seem destined,
not so much to give motion to the body, as to renew the stratum of fluid

1 See Prof. Ed. Van Beneden on Gregarina gigantia, in " Quart. Journ. Microsc.
Sci," N. S„ Vol. x. (1870), p. 51, and Vol. xi„ p. 242.

THE MICROSCOPE AND ITS REVELATIONS.

in contact with it; for such change of place as the animal does exhibit,,
is effected by the contractions and extensions of the body generally, as
in Amoeba (§ 403). An ' encysting process/ very much resembling that
of the lower Protophytes, is occasionally observed to take place in Gre-
garince, and seems to be preparatory to their multiplication. Whatever
the original form of the body may be, it becomes globular, ceases to
move, and becomes invested by a structureless * cyst/ within which the
substance of the body undergoes a singular change. The nucleus dis-
appears; and the sarcodic mass breaks up into a series of globular parti-
cles, which gradually resolve themselves (as shown at B, c) into forms
very like those of Naviculm. These ' pseud o-navicellae' are set-free, in
time, by the bursting of the capsule that incloses them; and they develop
themselves into a new generation of Gregarinse, first passing through an
Amceba-like stage. — A sort of ' con jugation ' has been seen to take place
between two individuals, whose bodies, coming into contact with each

Fig. 294.

Gregarina of the Earthworm :— a, in its ordinary aspect ; b, in its encysted condition ; c, d, show-
ing division of its contents into pseudo-navicellse; e, f, free pseudo-navicellae : g, h, free amoeboids
produced from them.

other by corresponding points, first become more globular in shape, and
are then encysted by the formation of a capsule around them both; the
partition-walls between their cavities disappear; and the substance of
the two bodies becomes completely fused together. But as the product
of this ' zygosis' is the same as that of the ordinary encysting process,
there seems no sufficient reason for regarding it, like the 6 con jugation 9
of Protophytes, as a true Generative act.

Prof . Haeckel's Memoirs on Mov,era and the Gastrcea Theory will be found in
the successive Nos. of the " Jenaische Zeitschrift " beginning with 1868; and in
a collected form, in the two parts of his 4 4 Biologische Studien." The first of
his Memoirs on Monera is translated in " Quart. Journ. Microsc Sci.," N.S., Vol.
ix. (1869); and the first of his Papers on the Gastrcea Theory in Vol. xiv. (1874)

MICROSCOPIC FORMS OF ANIMAL LIFE.

of the same Journal. See also the valuable series of papers on the Freshwater
Rhizopods by Mr. Wm. Archer, in the current series of the " Quart. Journ. Microc.
Sci.;" the important Memoirs of Hertwig and Lesser in the " Archiv fur Mikr.
Anat." (especially the Suppl. Heft to Bd. x., 1874), and the Presidential Addresses
of Prof. Allman to the Linnaean Society for 1876 and 1877 (in Nos. 69 and 71 of its
Journal) on " Recent Researches on some of the more simple Sarcode-Organisms,"
of which the Author has freely availed himself.

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTEE XL
ANIMALCULES.— INFUSORIA AND ROTIFERA.

411. Nothing can be more vague or scientifically inappropriate than
the title Animalcules; since it only expresses the small dimensions of the
beings to which it is applied, and does not indicate any of their character-
istic peculiarities. In the infancy of Microscopic knowledge, it was natural
to associate together all those creatures which could only be discerned at
all under a high magnifying power, and whose internal structure could
not be clearly made out with the instruments then in use; and thus the
most heterogeneous assemblage of Plants, Zoophytes, minute Crustaceans,
larvae of Worms, Mollusks, etc., came to be aggregated with the true
Animalcules under this head. The Class was being gradually limited by
the removal of all such forms as could be referred to others; but still very
little was known of the real nature of those that remained in it, until the
study was taken up by Prof. Ehrenberg, with the advantage of instru-
ments which had derived new and vastly improved capabilities from the
application of the principle of Achromatism. One of the first and most
important results of his study, and that which has most firmly maintained «
its ground, notwithstanding the overthrow of Prof. Ehrenberg's doctrines
on other points, was )he separation of the entire assemblage into two dis-
tinct groups, having scarcely any feature in common except their minute
size; one being of very low, and the other of comparatively high organiza-
tion. On the lower group he conferred the designation of Polygastrica
(many- stomached), in consequence of having been led to form an idea
of their organization which the united voices of the most trustworthy ob-
servers now pronounces to be erroneous; and as the retention of this term
must tend to perpetuate the error, it is well to fall back on the name In-
fusoria, or Infusory Animalcules, which simply expresses their almost
universal prevalence in infusions of organic matter. To the higher group,
Prof. Ehrenberg's name Rotifera or Rotatoria is on the whole very appro-
priate, as significant of that peculiar arrangement of their cilia upon the
anterior parts of their bodies, which, in some of their most common
forms, gives the appearance (when the cilia are in action) of wheels in
revolution; the group, however, includes many members in which the
ciliated lobes are so formed as not to bear the least resemblance to wheels.
In their general organization, these ' Wheel-animalcules ' must certainly
be considered as members of the Articulated division of the Animal King-
dom; and they seem to constitute a Class in that lower portion of it, to
which the designation Worms is now commonly given. — Notwithstanding
the wide zoological separation between these two kinds of Animalcules,
it feems most suitable to the plan of the present work to treat of them in
connection with one another; since the Microscopist continually finds
them associated together, and studies them under similar conditions.

MICROSCOPIC FORMS OF ANIMAL LIFE.

Section" I. — Infusoria.

412. This term, as now limited by the separation of the Rhizopoda
on the one hand, and of the Rotifera on the other, is applied to a far
smaller range of forms than was included by Prof. Ehrenberg under the
name of * polygastric' animalcules. For a large section of these, includ-
ing the DesmidiacecB, Diatomacece, Volvocinece, and many other Proto-
phytes, have been transferred, by general (though not universal) consent,
to the Vegetable kingdom. And it is not impossible that many of the
reputed Infusoria may be but larval forms of higher organisms, instead
of being themselves complete animals. Still an extensive group remains,
of which no other account can at present be given, than that the beings
of which it is composed go through the whole of their lives, so far as we
are acquainted with them, in a grade of existence which is essentially
Protozoic (§ 391); each individual apparently consisting of but a single
cell, though its parts are often so highly differentiated, as to represent
(only, however, by way of analogy) the 'organs' of the higher animals
after which they are usually named.

413. Among the ciliate Infusoria, which form not only by far the
largest, but also the most characteristic division of the group, there is
probably none which has not a mouth, or permanent orifice for the intro-
duction of food, which is driven towards it by ciliary currents; while a dis-
tinct anal orifice, for the ejection of the indigestible residue, is also gen-
erally present. The mouth is often furnished with a dental armature;
and leads to an oesophageal canal, down which the food passes into the
digestive cavity. This cavity is still occupied, however, as in Rhizopods
(403), by the enaosarc of the cell; but instead of lying in mere vacuoles
formed in the midst of this, the food-particles are usually aggregated,
during their passage down the oesophagus, into minute pellets, each of
which receives a special investment of firm protoplasm, constituting it a
digestive vesicle (Fig. 299); and these go through a sort of circulation
within the cell-cavity.

414. The 'contractile vesicles' again, attain a much higher develop-
ment in this group, and are sometimes in a connection with a network of
canals chanelled-out in the 'ectosarc' while their rhythmical action
resembles that of the circulatory and respiratory apparatuses of higher
animals. There is ample evidence, also, of the presence of a specially
contractile modification of the protoplasmic substance, having the action
(though not the structure) of muscular fibre; and the manner in which
the movements of the active free-swimming Infusoria are directed, so as
to avoid obstacles and find-out passages, seems to indicate that another
portion of their protoplasmic substance must have to a certain degreee
the special endowments which characterize the nervous systems of higher
animals. Altogether, it may be said that in the Ciliate Infusoria the
Life of the Single Cell finds its highest expression.1

1 The doctrine of the unicellular nature of the Infusoria has been a subject
of keen controversy among Zoologists, from the time when it was first definitely
put forward by Von Siebold (** Lehrbuch der vergleich. Anat.," Berlin, 1845) in
opposition to the then paramount doctrine of Ehrenberg as to the complexity of
their organization, which had as yet been called in question only by Dujardin
'•Hist. Nat. des Infusoires," Paris, 1841). Of late, however, there has been a
decided convergence of opinion in the direction above indicated; which has been
brought about in great degree by the contrast between the Protozoic simplicity
of the reproductive and developmental processes in Infusoria, and the com-

THE MICROSCOPE AND ITS REVELATIONS.

415. Before proceeding to the description of the ciliate Infusoria,
however, it will be of advantage to notice two smaller groups — the flagellate
and the suctorial — which, on account of the peculiarities of their struc-
ture and actions, are now ranked as distinct, and of whose 6 unicellular '
character there can be no reasonable doubt, since they are for the most
part ' closed ' cells, scarcely distinguishable morphologically from those
of Protophytes.

416. Flagellata. — Our knowledge of this tribe has been greatly
augmented in recent years, not only by the discovery of a great variety
of new forms, but still more by the careful study of the life history of
several among them. The Monads, properly so called,1 which are the
smallest animals at present known, are its simplest representatives; but
it also includes organisms of much greater complexity; and some of its
composite forms have a very remarkable relation to Sponges (§ 508). The
monas lens, long familiar to Microscopists as occurring in stagnant waters
and infusions of decomposing organic matter, is a spheroidal particle of
protoplasm, from l-2000th to l-5200th of an inch in diameter, inclosed
in a delicate hyaline investment or 'ectosarc' and moving freely through
the water by the lashing action of its slender flagellum, whose length is
from three to five times the diameter of the body. Within the body may
be seen a variable number of vacuoles; aud these are occasionally occu-
pied by particles distinguishable by their color, which have been intro-
duced as food. These seem to enter the body, not by any definite mouth
(or permanent opening in the ectosarc), but through an aperture that
forms itself in some part of the oral region near the base of the flagellum.
In the smallest Monadinm, neither nucleus nor contractile vesicle is dis-
tinguishable; but in larger forms a nucleus can be clearly seen. The
life-history of several simple Monadince, presenting themselves in infu-
sions of decaying animal matter (a cod's head being found the most pro-
ductive material), has been studied with admirable perseverance and
thoroughness by Messrs. Dallinger and Drysdale, of whose important
observations a general summary will now be given.2

417. The Monad-form most recently and completely studied by Mr.
Dallinger — with all the advantages derived from trained experience, and
under objectives of the highest quality and greatest magnifying power —
is the Dallingeria Drysdali (Kent) represented in Plate xiii. Its normal
shape, as seen in fig. 1, is a long oval, slightly constricted in the middle,
and having a kind of pointed neck (a), from which proceds a flagellum
about half as long again as the body. From the shoulder-like projections
behind this (b, c) arise two other long and fine flagella, which are directed
backwards. The sarcode body is clear, and apparently structureless, with
minute vacuoles distributed through it; and in its hinder part a nucleus
(d) is distinguishable. The extreme length of the body is seldom more than
the 1-4, 000th of an inch, and is often less. This Monad swims with

plexity of the like processes as seen even in the lowest of the Metazoa (§ 391)
which has been specially and forcibly insisted on by Haeckel ("Zur Morphologie
der Infusorien," Jenaische Zeitschr., Bd. vii., 1873). — An excellent summary of
the whole discussion was given by Prof. Allman, in his Presidential Address to
the Linnsean Society in 1875.

1 The Family monadina of Ehrenberg and Dujardin consists of an aggregate
of forms now known to be of very dissimilar nature, many of them belonging to
the Vegetable Kingdom.

2 See their successsive Papers in the " Monthly Microsc. Journ.," Vol. x. (1873),
pp. 53, 245; Vol. xi. (1874), pp. 7, 69, 97; Vol. xii. (1874), p. 261; and Vol. xiii
(1875), p. 185;— and "Proceed. Roy. Soc," Vol. xxvii. (1878), p. 332.

MICSOSCOPIC FORMS OF ANIMAL LIFE.

PLATE XIII.

✓ ^ >»

life-history OF flagellatk infusorium (after Dallinger).

Fig. 1. Normal form, showing three flagella, a, 6, c, and nucleus d.

2. Anterior flagellum, a, 6, double ; c, nucleus.

3. Fission commencing in nucleus c, and in anterior portion of body, a.

4. Fission more advanced, and showing itself also in posterior portion of body, a.

5. Fission still more advanced, both in nucleus, a, b, and in body.

6. 7. Fission proceeding to completion.

8. Change to amoeboid condition, with single flagellum and granular band a.

9. Conjugation of this with free-swimming form.

10, 11. Stages of progressive fusion, terminating in production of still sac, 12 which afterwards
opens and pours out spores, as at 13, 14, tho progressive growth of which is shown in figs. 15-21.

THE* MICROSCOPE AND ITS REVELATIONS.

great rapidity; its movements, which are graceful and varied, being pro-
duced by the action of the fiagella, which can not only impel it in any
direction, but can suddenly reverse its course or check it altogether. But
besides this free-swimming movement, a very curious * springing' action
is performed by this Monad when the decomposing organic matter of the
infusion is breaking up, the process of disintegration being apparently
assisted by it. The two posterior fiagella anchor themselves and coil into
a spiral, and the body then darts forwards and upwards, until the anchored
fiagella straighten out again, when the body falls forward to its horizon-
tal position, to be again drawn back by the spiral coiling of the anchored
fiagella. This Monad multiplies by longitudinal fission; the first stage
of which is the splitting of the anterior flagellum into two (fig. 2, a, b),
and a movement of the nucleus (c) towards the centre. In the course of
from thirty to sixty seconds the fission extends down the neck fig. 3, a;
a line of division is also seen at the posterior end (c), and the nucleus
(b) shows an incipient cleavage. In a few seconds the cleavage-line
runs through the whole length of the body, the separation being widest
posteriorly (fig. 4, a); and in from one to four minutes the cleavage
becomes almost complete (fig. 5), the posterior part of the body, with the
two halves (a and b) of the original nucleus, being now quite disconnected,
though the anterior parts are still held together by a transverse band of
sarcode, as seen in fig. 6. This soon narrows and elongates, as shown in
fig. 7; and at last it gives way, setting the two bodies entirely free. The
whole process of fission, from first to last, is completed in from four to
seven minutes; and being repeated at intervals of a few minutes, this
mode of multiplication produces a rapid increase in the number of the
Monads.

418. Such fission does not, however, continue indefinitely; for certain
individuals undergo a peculiar change, which shows itself first in the
absorption of the two lateral fiagella and the great development of the
nucleus, and afterwards in the formation of a transverse granular band
across the middle of the body (fig. 8, a). One of these altered forms
swimming into a group in the ' springing ' state, within a few seconds
firmly attaches itself to one of them, which at once unachors itself, and
the two swim freely and vigorously about, as shown in fig. 9, generally
for from thirty-five to forty-five minutes. Gradually, however, a ' fusion '
of the two bodies and of their respective nuclei takes place, the two trail-
ing fiagella of the ' springing 7 form being drawn-in (fig. 10); and in a
short time longer the two anterior fiagella also disappear, and all trace of
the separate bodies is lost, the nuclei vanish, and the resultant is an
irregular amoeboid mass (fig. 11), which gradually acquires the smooth,
distended, and ' still' condition represented in fig. 12. This a cyst filled
with reproductive particles of such extraordinary minuteness, that, when
emitted from the ends of the cyst (fig. 13) after the lapse of four or five
hours, they can only be distinguished under an amplification of 5,000
diameters, with perfect central illumination through an aperture in the
diaphragm of from l-80th to the l-100th of an inch in diameter. Yet
these particles, when continuously watched, are soon observed to enlarge
and to undergo elongation (figs. 15-17); and within two hours after their
emission from the sac, the anterior flagellum, and afterwards the two
lateral fiagella (fig. 18) can be distinguished. Slight movements then
commence; the neck-like protrusion shows itself (rig. 19, a, b), and in
about half an hour more the regular swimming action begins. About
four hours after the escape of its germ from the sac, the Monad acquires

MICROSCOPIC FORMS OF ANIMAL LIFE.

its characteristic form (fig. 20), though still only one-half the length of
its parent; but this it attains (passing through the stage shown in fig. 21)
in another hour, and the process of multiplication by fission, as already
d scribed, commences very soon afterwards. — There can be no reasonable
doubt that the 6 conjugation ' of two individuals, followed by the trans-
formation of their fused bodies into a sac filled with reproductive germs,
is to be regarded (as in protophytes) in the light of a true generative pro-
cess; and it is interesting to observe the indication of sexual distinction
here marked by the different states of the two conjugating individuals.
— There is every reason to believe that the entire life-cycle of this Monad
has thus been elucidated; and it will now be sufficient to notice the
principal diversities observed by Messrs. Dallinger and Drysdale in the
life-cycles of the other Monadine forms which they have studied.

419. Their simple uniflagellate Monad {Monas Dallingeri, Kent),
having an ovate form with a long diameter never exceeding l-4000th of
an inch, and advancing slowly with a straight, uniform motion like that
of Monas termo, differs from the preceding in its mode of multiplication;
for this takes place, not hy duplicative fission, but by the breaking- up of
the sarcodic substance (as in the production of ' swarm spores' by Proto-
phytes) into from thirty to sixty segments, which, at first lying closely
packed together, make their escape as free-swimming Monads, each pro-
vided writh its flagellum. Conjugation, in this type, occurs between the
ordinary forms and certain individuals distinguished between their some-
what larger size, and by the granular aspect of their sarcode towards the
flagellate end; and there is reason to think that the latter have never un-
dergone the segmentation by which the former have been multiplied.
The smaller are absorbed, as it were, into the larger; and the latter passes
after a time into the encysted state, corresponding in its subsequent his-
tory with the preceding type. — The bi-flagellate or 6 acorn' Monad of
the same observers (identified by Kent with the Polytoma uvella of Ehren-
berg) presents some remarkable peculiarities in its mode of reproduction.
Its binary fission extends only to the protoplasmic substance of its body,
leaving its envelope entire; and by a repetition of the process, as many
as 16 segments, each attaining the likeness of the parent, are seen thus
inclosed, their flagella protruding through the general investment.
This compound state being supposed by Ehrenberg to be the normal one,
he named it accordingly. But the parent-cyst soon bursts, and sets free
the contained ' macro-spores/ which swim about freely, and soon attain
the size of the parent. Again, the posterior part of the body of certain
individuals shows an accumulation of granular protoplasm, giving to that
region a roughened acorn-cup-like aspect; the bursting of the projection,
while the creature is actively swimming through the water, sets free a
multitude of shapeless granular fragments, within each of which a
minute bacterium-like corpuscle is developed; and this, on its release,
acquires in a few hours the size and form of the original monad. This
process seems analogous to the development of 6 micro-spores ' among
Protophytes, by the direct breaking-up of the protoplasm. It is, like
the previous process, non-sexual or gonidial; the true generative process
consisting here, as in the preceding cases, in the ' conjugation ' of two in-
dividuals, with the usual results.

420. A Cercomonas (0. typicus, Kent), characterized by the posses-
sion of a flagellum at each end, was found to multiply, during eight days
(and nights) of continuous observation, by transverse duplicative subdivi-
sion alone. But certain individuals then exhibited a remarkable change,

THE MICROSCOPE AND ITS REVELATIONS.

becoming amoeboid and less active; and when two of these came into con-
tact, they underwent a complete fusion, the product of which was a
globular cyst, witli a very definite investment, filled with reproductive
germs. — The 6 springing Monad 9 of the same observers {Heteromita ros-
trata, Kent) is of a long ovate form, with an average length of about
l-3000th of an inch. From its narrower extremity a sort of beak arises,
from which proceeds a fine flagellum about half as long again as the body;
and at a little distance behind this, another and longer flagellum arises,
with which the Monad anchors itself to the covering-glass, constantly
springing backwards and forwards by its recurrent coil and uncoil. A
nucleus shows itself near the rounded posterior end of the body. This
Monad multiplies by longitudinal fission, commencing at the beaked end,
and completed in six or seven minutes; and the process may be repeated
continuously for many days. Among enormous numbers, there are a
few distinguishable from the others by a slight excess of size, and by the
power to swim freely; these become ' still ' — for a time amoeboid — then
round; a small cone of sarcode pushes out, dividing and increasing into
another pair of flagella; the disk splits, each part becomes possessed of a
nuclear body, and two well-formed free-swimming Monads are set free.
These conjugate with individuals of the ordinary form which have just
undergone fission, the nuclei of the two approximating to each other; a
complete fusion of sarcode and nuclei takes place; the body, at first
motile, conies to rest, assumes a triangular form, and loses its flagella;
it then becomes clear and distended, and emits its contained reproductive
granules at the angles. — The 6 hooked Monad' (Heteromita uncinata,
Kent) is another bi-flagellate form, usually ovate with one end pointed,
and from l-3000th to l-4000th of an inch in length; being distinguished
from the preceding by the peculiar character of its flagella, of which the
one that projects forward is not more than half the length of the body,
and is permanently hooked, while the other, whose length is about twice
that of the body, is directed backwards, flowing in graceful curves. Its
motion consists of a succession of springs or jerks rapidly following each
other, which seems produced by the action of the hooked flagellum.
Multiplication takes place by transverse fission, and continues uninter-
ruptedly for several days. A difference then becomes perceptible between
larger and smaller individuals; the former being further distinguished by
the presence of what seems to be a contractile vesicle in the anterior part
of the body. Conjugation occurs between one of the larger and one of
the smaller forms, the latter being, as it were, absorbed into the body of
the larger; and the resulting product is a spherical cyst, which soon begins
to exhibit a cleavage-process in its interior. This continues until the whole
of its sarcodic substance is subdivided into minute oval particles, which
are set free by the rupture of the cyst, and of which each is usually fur-
nished with a single flagellum, by whose lashing movement it swims
freely. These germs speedily attain the size and form of the parent, and
then begin to multiply by transverse fission — thus completing the 'gene-
tic ' cycle.

421. The ' calycine Monad' of the same observers (Tetramitns rostra-
tus, Perty), has a length of from l-900th to l-1000th of an inch, and a
compressed body tapering backwards to a point. Its four flagella (which
constitute its generic distinction) arise nearly together from the flattened
front of the body; and its swimming movement is a graceful gliding.
Near the base of the flagella is a pair of contractile vesicles; and further
behind is a large nucleus. Multiplication takes place by longitudinal

MICROSCOPIC FORMS OF ANIMAL LIFE.

fission, which is preceded by a change to a semi-amoeboid state. This
gives place to a more regular pear-like form, the four flagella issuing
from the large end; and the fission commences at their base, two pairs
being separated by the cleavage-plane. The nucleus also undergoes
cleavage, and its two halves are carried apart by the backward extension of
the cleavage. The two half-bodies at last remain connected only by their
hinder prolongations, which speedily give way, and set them free. Each,
however, has, as yet, only two flagella; but these speedily fix themselves by
their free extremities, undergo a rapid vibratory movement, and in the
course of about two minutes split themselves from end to end. A still more
complete change into the amoeboid condition, in which the creature not
only moves, but also feeds, like an Amoeba (devouring all the living and
dead Bacteria in its neighborhood), occurs previously to ' conjugation;'
and this takes place between two of the amoeboid forms, which begin to
blend into one another almost immediately upon coming into contact.
The conjugated bodies, however, swim freely about for a time, the two
sets of flagella apparently acting in concert. But by the end of about
eighteen hours, the fusion of the bodies and nuclei is complete, the fla-
gella are retracted, and a spherical distended sac is then formed, which,
in a few hours more, without any violent splitting or breaking up, sets
free innumerable masses of reproductive particles. These, under a mag-
nifying power of 2,500 diameters, can be just recognized as oval granules,
which rapidly develop themselves into the likeness of their parents, and
in their return multiply by duplicative fission, — thus completing the
' genetic ' cycle.

422. One of the most important researches thus ably prosecuted by
Messrs. Dallinger and Drysdale, has reference to the Temperatures re-
spectively endurable by the adult or developed forms of these Monads,
and by their reproductive germs. A large number of experiments upon
the several *forms now described, indubitably led to the conclusion that
all the adult forms, as well as all those which had reached a stage of
development in which they can be distinguished from the reproductive
granules, are utterly destroyed by a temperature of 150° Fahr. But, on
the other hand, the reproductive granules emitted from the cysts that
originate in 6 conjugation 9 were found capable of sustaining a fluid heat
of 220°,. and a dry heat of about 30° more, — those of the Cercomonad
surviving exposure to a dry heat of 300° Fahr. This is a fact of the high-
est interest in its bearing on the question of 'spontaneous generation'
or Abiogenesis; since it shows (1) that germs capable of surviving desic-
cation may be everywhere diffused through the air, and may, on account
of their extreme minuteness (as they certainly do not exceed l-200,000th
of an inch in diameter), altogether escape the most careful scrutiny and
the most thorough cleansing processes; while (2) their extraordinary
power of resisting heat will prevent these germs from being killed either
by boiling, or by dry-heating up to even 300° Fahr.1

423. The structural resemblance of these simple Flagellate Infusoria
to the ' Monads 9 of Volvox and its allies (§ 237), is so close that no other
than physiological reasons can be assigned for separating them. Whilst
the Volvocinem grow and multiply under conditions which seem to jus-
tify our regarding them as members of the Vegetable Kingdom (§ 220),

1 Descriptions of the special apparatus used by Messrs. Dallinger and Drysdale
in their researches will be found in " Monthly Micr. Journ.," Vol. xi. (1874), p.
97; ibid., Vol. xv. (1876), p. 165; and "Proceed. Roy. Soc," Vol. xxvii. (1878),
p. 343.

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 295.

the 6 flagellated ' agree with the t ciliated' Infusoria in ordinarily drawing
their nutriment from organic compounds; and it seems clear that,
although unpossessed of a mouth, they can introduce solid food-particles
into the interior of their bodies. It is, however, not a little remarkable
that (according to the statement of Messrs. Dallinger and Drysdale)1
these Flagellata — like Bacteria and other forms referred to the group of
Fungi — can be cultivated in Cohn's 6 nutritive fluid' (§303, note), which
consists only of tartrate of ammonia and mineral salts, without any al-
buminous matter.

424. A large series of more complex forms of Flagellate Infusoria has
been recently brought to our knowledge by the researches of the late
Prof. James-Clark (XL S.),2 followed by those of Stein and Saville Kent.
In some of these, a sort of collar-like extension of what appears to be
the sarcodic ectosarc, proceeds from the anterior extremity of the body
(Fig. 295, cT)y forming a kind of funnel, from the bottom of which the
flagellum arises; and by its vibrations a current is produced within
the funnel, which brings down food-particles to the 6 oral disk' that
surrounds its origin, where the ectosarc seems softer than that which
envelops the rest of the body. Towards the base of the collar, a nucleus
(n) is seen; while, near the posterior termination of the body, is a single

or double contractile vesicle cv. The body
is attached by a pedicle proceeding from its
posterior extremity, which also seems to be a
prolongation of the ectosarc. — These Ani-
malcules multiply by longitudinal fission; and
this, in some cases (as in the genus Monosiga),
proceeds to the extent of a complete separa-
tion of the two bodies, which henceforth, as
in the ordinary MonacMna, live quite inde-
pendently of each other. But in other forms,
as Codosiga, the fission does not extend
through the pedicel; and the twin bodies be-
ing thus held together at their bases, and
themselves undergoing duplicative fission,
clusters are produced which spring from com-
mon pedicels (Fig. 296). And by the exten-
sion of the division down the pedicels, them-
selves, composite arborescent fabrics, like
those of Zoophytes, are produced.

425. In an another group, a structureless
and very transparent horny calyx, closely re-
sembling in miniature the polype-cell of a
Campanularia (Plate xx.), forms itself around
the body of the Monad, which can retract
itself into the bottom of it. And in the
genus Salpmgoeca both calyx and collar are
present. In some forms of this group, mul-
tiplication seems to take place, not by fis-
sion, but by gemmation; and, as among
Ilydroia Polypes, the gemmce may either detach themselves and live inde-
pendently, or may remain in connection with their parent-stocks, form-

1 " Monthly Microscopical Journal," Vol. xiii. (1875\ p. 190.

2 See his Memoirs in "Ann. Nat. Hist.," Ser. 3, Vol. xviii. (1866); ibid., Ser.
4, Vol. i. (1868); Vol. vii. (1871); and Vol. ix. (1872).

Single zooid of Codosiga umbel-
lata: — cl, collar; n, nucleus; cv,
double contractile vesicle.

MICROSCOPIC FORMS OF ANIMAL LIFE.

ing composite fabrics, in some of which the calyces follow one another in
linear series, whilst in others they take on a ramifying arrangement.
While some of these composite organisms are sedentary, others, as Dino-
bryon, arc free-swimming.

426. Two solitary Flagellate forms, Anthophysa and Anisonema,
may be specially noticed as presenting several interesting points of resem-
blance to the peculiar type next to be described; the most noticeable
being the presence of a distinct mouth, and the possession of two dilferent
motor organs — one a comparatively stout and stiff bristle of uniform
diameter throughout, which moves by occasional jerks; and the other a very
delicate tapering flagellum, which is in constant vibratory motion. If, as
appears from the recent observations of Biitschli, the well-known Astasia
— of which one species has a blood-red color, and sometimes multiplies to
such an extent as to tinge with it the water of the ponds it inhabits — has

Fig. 296.

osiga umhellata :— colony-stock, springing from single pedicel tripartitely branched.

a true mouth for the reception of its food, it must be regarded as an
Animal, and separated from the Euglena (with which it has been gener-
ally associated), the latter being pretty certainly a Plant belonging to the
same group as Volvox.1

427. There can be no longer any doubt that the well-known Nocii-
luca miliaris — to which is attributable the diffused luminosity that fre-
quently presents itself in British seas — is to be regarded as a gigantic
type of the ' unicellular 9 Flagellata. This animal, which is of spheroidal
form, and has an average diameter of about 160th of an inch, is just large
enough to be discerned by the naked eye when the water in which it may
be swimming is contained in a glass jar held up to the light; and its tail-
like appendage, wThose length about equals its own diameter, and which
serves as an instrument of locomotion, may be discerned with a hand-

1 See the Memoir by Prof. Butschli, in " Zeitsohrift f. Wissensch. Zool ." Bd.
xxx.; of which an abridgment (with Plate) is given in " Quart. Journ. Microsc.
Sci.," Vol. xix. (1879), p. 63.
3

THE MICROSCOPE AND ITS REVELATIONS.

magnifier. The form of Noctiluca is nearly that of a sphere, so com-
pressed that while on one aspect (Fig. 297, a) its outline, when projected
on a plane, is nearly circular, it is irregularly oval in the aspect (b) at
right angles to this. Along one side of this body is a meridional groove,
resembling that of a peach; and this leads at one end into a deep depres-
sion of the surface, a, termed the atrium, from the shallower commence-
ment of which the tentacle, d,1 originates, whilst it deepens down at the
base of the tentacle to the mouth, e. Along the opposite meridian
there extends a slightly elevated ridge, c, which commences with the ap-
pearance of a bifurcation at the end of the atrium farthest from the ten-
tacle; this is of a firmer consistence than the rest of the body, and has
somewhat the appearance of a rod imbedded in its walls. The mouth
opens into a short oesophagus, which leads directly down to the great
central protoplasmic mass; on the side of this canal farthest from the

Fig. 297.

Noctiluca miliaris, as seen at a on the aboral side, and at b on a plane at right angles to it:— a,
entrance to atrium; 6, atrium: c, superficial ridge; d, tentacle: e, mouth leading to oesophagus
withm which are seen the flagellum springing from its base, ana the tooth-like process projecting
into it from above; /, broad process from the central protoplasmic mass, proceeding to superficial
ridge; gr, duplicature of wall; ht nucleus.— Magnified about 90 diameters.

tentacle, is a firm ridge that forms a tooth-like projection into its cavity;
whilst from its floor there arises a long flagellum, which vibrates freely
in its interior. The central protoplasmic mass sends off in all directions
branching prolongations of its substance, whose ramifications inosculate;
these become thinner and thinner as they approach the periphery; and
their ultimate filaments, coming into contact with the delicate membran-
ous body- wall, extend themselves over its interior, forming a protoplasmic

1 The organ here termed * tentacle ' is commonly designated Flagellum; while
what is here termed the flagellum is spoken of by most of those who have recog-
nized it, as a cilium. The Author agrees with M. Robin in considering the former
organ, which has a remarkable resemblance to a single fibrilla of striated muscle
(§ 678), as one peculiar to Noctiluca ; and the latter as the true homologue of the
flagellum of the ordinary Flagellata.— It is curious that several observers have
been unable to discover the so-called cilium, which was first noticed by Krohn.
Prof. Huxley sought for it in at least fifty individuals without success; and out
of the great number which he afterwards examined, did not get a clear view of
it in more than half-a-dozen.

MICROSCOPIC FORMS OF ANIMAL LIFE.

network of extreme tenuity (Fig. 298). Besides these branching prolon-
gations there is sent off from the central protoplasmic mass a broad,
thin, irregularly quadrangular extension (Fig. 297 B,/), which extends
I to the superficial rod-like ridge, and seems to coalesce with it; its lower
' free edge has a thickened border; whilst its upper edge becomes continu-^
ous with a plate-like striated structure, g, which seems to be formed by a
I peculiar duplicative of the body-wall. At one side of the protoplasmic
mass is seen a spherical vesicle, h, of about 3-2000ths of an inch in diam-
eter, having clear colorless contents, among which transparent oval
corpuscles may usually be detected. This, from the changes it undergoes
in connection with the reproductive process, must be regarded as a
nucleus.

428. The particles of food drawn into the mouth (probably by the vi-

Fig. 298.

Portion of superficial protoplasmic reticulation, formed by ramification of an extension ct, of
Central mass.— Magnified 1000 diameters.

brations of the flagellum) seem to be received into the protoplasmic mass
at the bottom of the oesophagus by the extensions of its substance, which
envelop them in filmy envelopes that maintain themselves as distinct from
the surrounding protoplasm, and thus constitute extemporized digestive
vesicles. These vesicles soon find their way into the radiating extensions
of the central mass (as shown in Fig. 297, A, B), and are ensheathed by
the protoplasmic substance which goes-on to form the peripheral network
(Fig. 299). Their number and position are alike variable; sometimes
only one or two are to be distinguished; more commonly from four to
eight can be seen; and even twelve or more are occasionally discernible.
The place of each in the body is constantly being changed by the contrac-
tions of the protoplasmic substance; these in the first place carrying it
from the centre towards the periphery of the body, and then carrying it
back to the central mass, into whose substance it seems to be fused as
soon as it has discharged any indigestible material it may have contained,
which is got rid of through the mouth. Every part of the protoplasmic
reticulation is in a state of incessant change, which serves to distribute
the nutrient material that finds its way into it through the walls of the
digestive vesicles; but no regular cyclosis (like that of plants) can be ob-

THE MICROSCOPE AND ITS REVELATIONS.

served in it. Besides the ' digestive vesicles,7 vacuoles filled with clear
fluid may be distinguished, alike in the central protoplasmic mass, and
in its extensions, as is shown in the centre of Fig. 297. There is no con-
tractile vesicle.

429. The peculiar * tentacle 9 of Noctiluca is a flattened whip-like fila-
ment, gradually tapering from its base to its extremity; the two flattened
faces being directed respectively towards and away from the oral aperture.
When either of its flattened faces is examined, it shows an alternation
of light and dark spaces, in every respect resembling those of striated
muscular fibre, except that the clear spaces are not subdivided. But
when looked-at in profile, it is seen that between the striated band and
the aboral surface is a layer of granular protoplasm. The tentacle slowly
bends over towards the mouth about five times in a minute, and straight-
ens itself still more slowly; the middle portion rising first, while the
point approaches the base, so as to form a sort of loop, which presently
straightens. It seems probable that the contraction of the substance f orm-

Pair of Digestive Vesicles of Noctiluca, lying in a course of extension of central protoplasmic
mass a, to form peripheral reticulation 6, and containing remains of Algae.— Magnified 480 diam-
eters.

ing the dark bands, produces the bending of the filament; whilst, when
this relaxes, the filament is straightened again by the elasticity of the
granular layer.1

430. The extreme transparence of Noctiluca renders it a particularly
favorable subject for the study of the phenomena of phosphorescence.
When the surface of the sea is rendered luminous by the general diffu-
sion of Noctilucce, they may be obtained by the tow-net in unlimited
quantities; and when transferred into ajar of sea-water, they soon rise to
the surface, where they form a thick stratum. The slightest agitation
of the jar m the dark causes an instant emission of their light, which is
of a beautiful greenish tint, and is vivid enough to be perceptible by
ordinary lamp-light. This luminosity is but of an instant's duration,
and a short rest is required for its renewal. A brilliant, but short lived
display of luminosity, to be followed by its total cessation, may be pro-
duced by electric or chemical stimulation. Professor Allman found the
addition of a drop of alcohol to the water containing specimens of Nocti-
luca^ on the stage of the microscope, produce a luminosity strong
enough to be visible under a half-inch objective, lasting with full intens-

1 According to Robin, the ' tentacle ' of Noctiluca is derived conjointly from the
cell-wall and from its contained protoplasm; being thus differentiated alike from
the 'flagellum,' which he regards as an extension of the latter alone, and from
a ' ciliunV which is an extension of the former.

Fig. 299.

MICROSCOPIC FORMS OF ANIMAL LIFE.

ifcy for several seconds, and then gradually disappearing. He was thus
able to satisfy himself that the special seat of the phosphorescence is the
peripheral protoplasmic reticulation which lines the external structureless
membrane.

431. The reproduction in this interesting type is effected in various
ways. According to Cienkowsky, even a smali portion of the protoplasm
of a mutilated Noctiluca will (as among Rhizopods) reproduce the entire
animal. Multiplication by fission or binary sub-division, beginning in
the enlargement, constriction, and separation of the two halves of the
nucleus, has been frequently observed. Another form of non-sexual repro-
duction, which seems parallel to the 6 swarming ' of many Protophytes,
commences by a kind of encysting process. The tentacle and flagellum
disappear, and the mouth gradually narrows, and at last closes up ; the
meridional groove also disappears, so that the animal becomes a closed
hollow sphere. The nucleus elongates, and becomes transversely con-
stricted, and its two halves separate, each remaining connected with a
portion of the protoplasmic network. This duplicative subdivision is
repeated over and over again, until as many as 512 ' gemmules ' are formed,
each consisting of a nuclear particle enveloped by a protoplasmic layer,
and each having its flagellum. The entire aggregate forms a disk-like
mass projecting from the surface of the sphere; and this mass sometimes
detaches itself as a whole, subsequently breaking up into individuals;
whilst, more commonly, the gemmules detach themselves one by one, the
separation beginning at the margin of the disk, and proceeding towards
its centre. —The gemmules are at first closed monadiform spheres, each
having a nucleus, contractile vesicle, and flagellum; the mouth is subse-
quently formed, and the tentacle and permanent flagellum afterwards
make their appearance. — A process of 'conjugation y has also been ob-
served alike in ordinary Noctiluccs and in their closed or encysted forms,
which seems to be sexual in its nature. Two individuals, applying their
oral surfaces to each other, adhere closely together, and their nuclei be-
come connected by a bridge of protoplasmic substance. The tentacles
are thrown off, the two bodies gradually coalesce, and the two nuclei fuse
into one. The whole process occupies about five or six hours, but its re-
sults have not been followed out.1

432. Intermediate between the proper flagellate, and the true ciliate
Infusoria, is the small group of Cilio-flagellata, in which, while the body
is furnished with rows of cilia, a flagellum is also present. Although
this group does not contain any great diversity of forms, yet it is specially
worthy of notice, on account of the occasional appearance of some of
them in extraordinary multitudes. This is the case, for example, with
the Peridinmm observed by Prof. Allman, in 1854, to be imparting a
brown color to the water of some of the large ponds in Phoenix Park,
Dublin; this color being sometimes uniformly diffused, and sometimes
showing itself more deeply in dense clouds, varying in extent from a few
square yards to upwards of a hundred. The animal (Fig. 300, A, B)
has a form approaching the spherical, with a diameter of from l-1000th
to l-5000th of an inch; and is partially divided into two hemispheres, by

1 Noctiluca has been the subject of numerous Memoirs, of which the following
are the most recent: Cienkowski, "Arch. f. Micr. Anat.," Bd. to. (1871), p. 131,
and Bd. ix. (1873), p. 47; Allman, 44 Quart. Journ. Micr. Sci.," N.S., Vol. xii. (1872),
p. 327; Robin. 44 Journ. de l'Anat. et de Physiol.," Tom. xiv. (1878), p. 586 ; and
Vignal, "Arch, de Physiol.," Ser. 2, Tom. V. (1878), p. 415.

THE MICROSCOPE AND ITS REVELATIONS.

a deep equatorial ftfrrow, a, whilst the flagellum-bearing hemisphere, A,
has a deep meridional groove on one side, b, extending from the equatorial
groove to the pole; the flagellum taking its origin from the bottom of this
vertical groove, near its junction with the equatorial. The cilia, in thi^
form, do not seem to be disposed in special bands, but are distributed

Fig. 300.

Peridinium uberrimum; -a, b, Front and back views; c, Encysted stage; d, Duplicative subdivi-
sion.

over the general surface of the body; but in several other Peridinians
(Fig. 301), whose bodies are partially invested by a firm lorica, the cilia
are arranged in special zones. It is questionable whether any definite
mouth exists in this type; but it seems certain that alimentary particles

Fig. 301.

1, Ceratium tripos; 2, Ceratium furca.

arc received into the interior of the body, becoming inclosed in ' diges-
tive vesicles.' A 6 contractile vesicle' has been rarely observed; but a
large nucleus,* sometimes oval, and sometimes horseshoe-shaped, seems
always present. — The Peridinia multiply by transverse fission (Fig. 300,
d), which commences in the subdivision of the nucleus, and then shows
itself externally in a constriction of the ungrooved hemispha re, par

MICROSCOPIC FORMS OF ANIMAL LIFE.

to the equatorial furrow. They pass into a quiescent condition, subsid-
ing towards the bottom of the water; and the loricated forms appear to
throw off their envelopes. But whether these changes are preparatory
to any process of conjugation, is not known. — Some of the Peridinia are
found in sea-water; but the most remarkable marine forms of the cilio-
flagellate group belong to the genus Ccratiam (Fig. 301), in which the
cuirass extends itself into long horny appendages. In the Ceratium
tripos (1), there are three of its appendages; two of them curved, pro-
ceeding from the anterior portion of the cuirass, and the third, which is
straight or nearly so, from its posterior portion. They are all more or
less jagged or spinous. In Ceratium furca (2), the two anterior horns
are prolonged straight forwards, one of them being always longer than
the other; whilst the posterior is prolonged straight backwards. The
anterior and posterior halves of the cuirass are separated by a ciliated
furrow, from one point of which the flagellum arises; and at the origin of
this is a deep depression, into which the flagellum may be completely
and suddenly withdrawn. Whether this is, or is not, a true mouth lead-
ing into the cell-cavity, has not yet been ascertained. — The Author has
found the Ceratium tripos extremely abundant in Lamlash Bay, Arran;
where it constitutes a principal article of the food of the Comatulce that
inhabit its bottom.1

433. Suctoria. — The suctorial Infusoria constitute a well-marked
group, — all belonging to one family, Acinetina, — the nature of which
has been until recently much misunderstood, chiefly on account of the
parasitism of their habit. Like the typical Monadina, they are closed
cells, each having its nucleus and contractile vesicle; but instead of freely
swimming through the water, they attach themselves by flexible pedun-
cles, sometimes to the stems of Vorticellinm, but also to filamentous
AlgaB, stems of Zoophytes, or the bodies of larger amimals. Their nutri-
ment is obtained through delicate tubular extensions of the ectosarc,
which act as suctorial tentacles (Fig. 302); the free extremity of each
being dilated into a little knob, which flattens out into a button-like
disk when it is applied to a food-particle. Free-swimming Infusoria are
captured by these organs, of which several quickly bend over towards the
one which was at first touched, so as firmly to secure the prey; and when
several have thus attached themselves, the movements of the imprisoned
animal become feebler, and at last cease altogether, its body being drawn
nearer to that of its captor. Instead, however, of being received into its
interior like the prey of Actifiophrys (§ 399), the captured Animalcule
remains on the outside; but yields up its soft substance to the suctorial
power of its victor. As soon as the sucking disk has worked its way
through the envelope of the body to which it has attached itself, a yery
rapid stream, indicated by the granules it carries, sets along the tube,
and pours itself into the interior of the Acineta-body. Solid particles
are not received through these suctorial tentacles, so that the Acinetina
cannot be fed with indigo or carmine; but, so far as can be ascertained
by observation of what goes on within their bodies, there is a general pro-
toplasmic cyclosis, without the formation of any special * digestive vesi-
cles.'— The ordinary forms of this group are ranked under the two genera
Acineta and Podophrya; which are chiefly distinguished by the presence
of a firm envelope or lorica in the former, while the body of the latter is

1 See A 11m an in " Quart. Micr. Journ." Vol. iii. ,'1855), p. 24; and H. James-
Clark in "Ann. Nat. Hist.," Ser. 3, Vol. xviii. (1866), p. 429.

THE MICROSCOPE AND ITS REVELATIONS.

miked. In one curious form, the Ophiodendron, the suckers are borne
in a brush-like expansion on a long retractile proboscis like organ. And
the rare Dendroso7na, whose size is comparatively gigantic, forms by con-
tinuous gemmation an arborescent i colony/ of which the individual
members remain in intimate connection with one another.

434. Multiplication in this group seems occasionally to take place by
longitudinal fission; but this is rare in the adult state. Sometimes exter-
nal gemnice are developed by a sort of pinching-off of a part of the free
end of the body, which includes a portion of the nucleus; the ten taenia
of this bud disappear, but its surface becomes clothed with cilia; and,
after a short time, it detaches itself and swims away — comporting itself
subsequently like the internal embryos, whose production seems the more
ordinary method of propagation in this type. These originate in the
breaking-up of the nucleus into several segments, each of which incloses
itself in a protoplasmic envelope; and this becomes clothed with cilia, by

Fig. o02.

Suctorial Infusoria:— \. Con juration of Podophryv quadripartita : 2. Formation of embryos
by enlargement and subdivision of the nucleus; 3, Ordinary form of the same; 4, Podophrya
elongata.

the vibrations of which the embryos are put in motion within the body
of the parent (Fig. 302, 2), from which they afterwards escape by its
rupture. In this condition (a) they swim about freely, and seem identical
with what has been described by Ehrenberg as a distinct generic form,
Megatriclia. And according to the recent observations of Mr. Badcock,1
these Megatricha-forms multiply freely by self division. After a short
time, however, they settle down upon filamentous Algae or other supports,
lose their cilia, put forth suctorial tentacles (which seem to shoot out
suddenly in the first instance, but are afterwards slowly retracted and
protruded with a kind of spiral movement), and assume a variety of
amoebiform shapes (Fig. 303, 1, 2, 3), some of them corresponding to
that of the genus Trichophrya. In this stage they become quiescent at

1 " Journ. of Roy. Microsc. Soc," Vol. iii. (1880), p. 563.

MICROSCOPIC FORMS OF ANIMAL LIFE.

the approach of winter, the suctorial tentacles and the contractile vesicles
disappearing; they do not, however, seem to acquire any special envelope,
remaining as clear, motionless, protoplasmic particles. But with the
return of warmth their development recommences, a footstalk is formed,
and they gradually assume the characteristic form of Podoplirya quadri-
partite.— A regular * con jngation ' baa been observed in this type, the
body of one individual bending down so as to apply its free surface to the
corresponding part of another, with which it becomes fused (Fig. 302, 1);
but whether this always precedes the production of internal embryos, or
is any way preparatory to propagation, has not yet been ascertained

435. Ciliata. — As it is in this tribe of Animalcules that the action of
the organs termed Cilia has the most important connection with the vital
functions, it seems desirable here to introduce a more particular notice
of them. They are always found in connection with cells, of whose pro-
toplasmic substance they may be considered as extensions, endowed in

Fig. 303.

Immature forms of Podoplirya quadripartita:—!, Amoeboid state (Trichophrya of Claparcde
and Lachmann); The same more advanced; 3, Incipient division into lobes.

a special degree with its characteristic contractility. The form of the
filaments is usually a little flattened, tapering gradually from the base to
the point. Their size is extremely variable ; the largest that have been
observed being about l-500th of an inch in length, and the smallest
about l-13,000th. When in motion, each filament appears to bend
from its root to its point, returning again to its original state, like the
stalks of corn when depressed by the wind ; and when a number are
affected in succession with this motion, the appearance of progressive
waves following one another is produced, as when a corn-field is agitated
by successive gusts. When the ciliary action is in full activity, however,
little can be distinguished save the whirl of particles in the surrounding
fluid ; but the back stroke may often be perceived, when the forward-

1 The Acwetina were described both by Ehrenberg and Dujardin; but the first
full account of their peculiar organization was given by Stein in his " Organ ismus
der Infusionsthierchen." Misled, however, by their parasitic habits, Stein origi-
nally supposed them not to be independent types, but to be merely transitional
stages in the development of Vorticellince and other Ciliate Infusoria. This doc-
trine he has long since abandoned; but it is not a little singular that the young of
several true Ciliata come forth provided with suctorial tentacles as well as with
cilia, losing the former as they approximate with advancing growth towards the
parental type. Much information as to this group will also be found in the beau-
tiful " Etudes sur les Infusoires et les Rhizopodes" of MM. Claparede and Lach-
mann, Geneva, 1858-61.

THE MICROSCOPE AND ITS REVELATIONS.

stroke is made too quickly to be seen ; and the real direction of the
movement is then opposite to the apparent. In this back-stroke, when
made slowly enough, a sort of ' feathering' action may be observed ; the
thin edge being made to cleave the liquid, which has been struck by the
broad surface in the opposite direction. It is only when the rate of
movement has considerably slackened, that the shape and size of the
cilia, and the manner in which their stroke is made, can be clearly seen.
Their action has been observed to continue for many hours, or even days,
after the death of the body at large. — As cilia are not confined to Ani-
malcules and Zoophytes, but give motion to the zoospores of many Proto-
phytes (§ 248), and also clothe the free internal surfaces of the respiratory
and other passages in all the higher Animals, including Man (our own
experience thus assuring us that their action takes place, not only with-
out any exercise of will, but even without consciousness), it is clear that

Fig. 304. Fig. 305.

A, Kerona silurus :— a, contractile vesicle; 6, mouth; Group of Vorticella nebuliferu show-
c, c, Animalcules swallowed by the Kerona, after hav- ing a, the ordinary form ; b, the same
ing themselves ingested particles of indigo, b, Parame- with the stalk contracted ; c, the same
cium caudatum :— a, a, contractile vesicles; b, mouth, with the bell closed ; d, e, f, successive

stages of fissiparous multiplication.

to regard Animalcules as possessing a ' voluntary ' control over the action
of their Cilia, is altogether unscientific.

436. In the Ciliated Infusoria, the differentiation of the sarcodic sub-
stance into 'ectosarc' or cell-wall, and ' endosarc ' or cell-contents,
becomes yery complete ; the ectosarc possessing a membranous firmness
which prevents it from readily yielding to pressure, and having a definite
internal limit, instead of graduating insensibly (as in Khizopods) into
the protoplasmic layer which lines it. A ' nucleus 9 seems always present;
being sometimes ' parietal' (or adherent to the interior of the ectosarc),
in other cases lying in the midst of the endosarc. In many Ciliata a
distinct 6 cuticle or exudation-layer may be recognized on the surface
of the ectosarc ; and this cuticle, which is studded with regularly
arranged markings like those of Diatomacese, seems to be the representa-
tive of the carapace of Arcella, etc. (Fig, 291), as of the cellulose coat of

MICROSCOPIC FORMS OF ANIMAL LIFE.

Protophytes. It is sometimes hardened, so as to form a ' shield 9 that
protects the body on one side only, or a 'lorica' that completely invests
it ; and there are other cases in which it is so prolonged and doubled
upon itself, as to form a sheath resembling the 'cell' of a Zoophyte,
within which the body of the Animalcule lies loosely, being attached
only by a stalk at the bottom of the case, and being able either to project
itself from the outlet or to retract itself into the interior. In a curious
group lately described by Haeckel, consisting of Infusoria that spend
their lives in the open sea, the body is inclosed in a siliceous lattice-work
shell, usually bell-shaped or helmet-shaped, which bears so strong a
resemblance to the shells of many Eadiolaria as to be easily mistaken
for them. The form of the body is usually much more definite than
that of the naked Khizopods ; each species having its characteristic
shape, which is only departed from, for the most part, when the Animal-
cule is subjected to pressure from without, or when its cavity has been
distended by the ingestion of any substance above the ordinary size.
The cilia and other mobile appendages of the body are extensions of the
outer layer of the ' ectosarc ' proper ; and this layer, which retains a high
degree of vital activity, is sometimes designated the ' cilia-layer.' Be-
neath this is a layer in which (or in certain bands of which) regular,
parallel, fine striae may be distinguished ; and as this striation is also
distinguishable in the eminently contractile footstalk of Vorticella (Fig.
305, b), there seems good reason to regard it as indicating a special
modification of protoplasmic substance, which resembles muscle in its
endowments. Hence this is termed the ' myophan-layer.' Beneath
this, in certain species of Infusoria, there is found a thin stratum of
condensed protoplasm, including minute ' trichocysts,' which resemble
in miniature the 'thread-cells' of Zoophytes (§ 528); and this, where it
exists, is known as the i trichocyst-layer.'

437. The vibration of ciliary filaments, — which are either disposed
along the entire margin of the body, as well as around the oral aperture,
(Fig. 305, a, b), or are limited to some one part of it, which is always in
the immediate vicinity of the mouth (Fig. 304), — supplies the means in
this group of Infusoria, both for progression through the water, and for
drawing alimentary particles into the interior of their bodies. In some,
their vibration is constant, whilst in others it is only occasional. The
modes of movement which Infusory Animalcules execute by means of
these instruments, are extremely varied and remarkable. Some propel
themselves directly forwards, with a velocity which appears, when thus
highly magnified, like that of an arrow, so that the eye can scarcely fol-
low them ; whilst others drag their bodies slowly along like a leech.
Some attach themselves by one of their long filaments to a fixed point,
and revolve around it with great rapidity; whilst others move by undu-
lations, leaps, or successive gyrations : in short, there is scarcely any
kind of animal movement which they do not exhibit. But there are
cases in which the locomotive filaments have a bristle-like firmness, and,
instead of keeping themselves in rapid vibration, are moved (like the
spines of Echini) by the contraction of the integument from which they
arise, in such a manner that the Animalcule crawls by their means over
a solid surface, as we see especially in Triclioda lynceus (Fig. 308, p, q).
— In Cliilodon and Nassula, again, the mouth is provided with a circlet
of plications or folds, looking like bristles, which, when imperfectly
seen, received the designation of 'teeth;' their function, however,
is rather that of laying hold of alimentary particles by their expansion

THE MICROSCOPE AND ITS REVELATIONS.

and subsequent drawing-together (somewhat after the fashion of the
tentacula of Zoophytes), than of reducing them by any kind of masti-
catory process. — The curious contraction of the foot-stalk of the Vorticella
(Fig. 305), again, is a movement of a different nature, being due to the
contractility of the tissue that occupies the interior of the tubular
pedicle. This stalk serves to attach the bell-shaped body of the Animalcule
to some fixed object, such as a leaf or stem of duck-weed ; and when the
animal is in search of food, with its cilia in active vibration, the stalk is
fully extended. If, however, the Animalcule should have drawn to its
mouth any particles too large to be received within it, or should be
touched by any other that happens to be swimming near it, or should be
' jarred' by a smart tap on the stage of the Microscope, the stalk sud-
denly contracts into a spiral, from which it shortly afterwards extends
itself again into its previous condition. The central cord, to whose con-
tractility this action is due, has been described as muscular, though not
possessing the characterictic structure of either kind of muscular fibre ;
it possesses, however, the special irritability of muscle ; being instantly
called into contraction (according to the observations of Kuhne) by
electrical excitation. The only special 6 impressionable' organs1 for the
direction of their actions, with the possession of which Infusoria can be
credited, are the delicate bristle-like bodies which project in some of
them from the neighborhood of the mouth, and in Stentor from various
parts of the surface. The red spots seen in many Infusoria, which have
been designated as eyes by Prof. Ehrenberg from their supposed corre-
spondence with the eye-spots of Rotifera (§ 447), really bear a much
greater resemblance to the red spots which are so frequently seen among
Protophytes (§ 230).

438. The interior of the body does not always seem to consist of a
simple undivided cavity occupied by soft sarcode; for the tegumentary
layer appears in many instances to send prolongations across it in differ-
ent directions, so as to divide it into chambers of irregular shape, freely
communicating with each other, which may be occupied either by sar-
code, or by particles introduced from without. The alimentary particles
which can be distinguished in the interior of the transparent bodies of
Infusoria, are usually protophytes of various kinds, either entire or in a
fragmentary state. The Diatomaceae seem to be the ordinary food of
many; and the insolubility of their loricce enables the observer to recog-
nize tlrem unmistakably. Sometimes entire Infusoria are observed within
the bodies of others not much exceeding them in size (Fig. 308, b); but
this is only when they have been recently swallowed, since the prey
speedily undergoes digestion. * It would seem as if these creatures do not
feed by any means indiscriminately, since particular kinds of them are
attracted by particular kinds of aliment; the crushed bodies and eggs of
Entomostraca, for example, are so voraciously consumed by the Coleps,
that its body is sometimes quite altered in shape by the distention. This
circumstance, however, by no means proves that such creatures possess a
sense of taste and a power of determinate selection; for many instances
might be cited, in which actions of the like apparently- conscious nature
are performed without any such guidance. — The ordinary process of
feeding, as well as the nature and direction of the ciliary currents, may

1 The term ' organs of sense ' implies a consciousness of impressions, with which
it is difficult to conceive that unicellular Infusoria can be endowed. The com-
ponent cells of the Human body do their work without themselves knowing it

MICROSCOPIC FORMS OF ANIMAL LIFE.

be best studied by diffusing through the water containing the Animal-
cules a few particles of indigo or carmine. These may be seen to be
carried by the ciliary vortex into the mouth, and their passage may be
traced for a little distance down a short (usually ciliated) oesophagus.
There they commonly become aggregated together, so as to form a little
pellet of nearly globular form; and this, when it has attained the sizo of
the hollow within which it is moulded, seems to receive an investment of
firm sarcodic substance, resembling the ' digestive vesicles' of Noctiluca
(§ 428), and to be then projected into the softer endosarc of the interior
of the cell, its place in the oesophagus being occupied by other particles
subsequently ingested. (This ' moulding/ however, is by no means uni-
versal; the aggregations of colored particles in the bodies of Infusoria
being often destitute of any regularity of form.) A succession of such
pellets being thus introduced into the cell-cavity, a kind of circulation
is seen to take place in its interior; those that first entered making their
way out after a time (first yielding up their nutritive materials), generally
by a distinct anal orifice, but sometimes by the mouth. When the pellets
are thus moving round the body of the Animalcule, two of them some-
times appear to become fused together, so that they obviously cannot have
been separated by any firm membranous investment. When the animalcule
has not taken food for some time, ' vacuoles/ or clear spaces, extremely
variable both in size and number, filled only with a very transparent
fluid, are often seen in its sarcode; and their fluid sometimes shows a
tinge of color, which seems to be due to the solution of some of the vege-
table chlorophyll upon which the Animalcule may have fed last.

439. Contractile Vesicles (Fig. 304, a, a), usually about the size of
the ' vacuoles/ are found, either singly or to the number of from two to
sixteen, in the bodies of most ciliated Animalcules; and may be seen to
execute rhythmical movements of contraction and dilatation at tolerably
regular intervals; being so completely obliterated, when emptied of their
contents, as to be quite undistinguishable, and coming into view again as
they are refilled. These vesicles do not change their position in the indi-
vidual, and they are pretty constant, both as to size and place, in differ-
ent individuals of the same species; hence they are obviously quite
different in character from the ' vacuoles.' In Paramecium there are
always to be observed two globular vesicles (Fig. 304, b, a, a), each of
them surrounded by several elongated cavities, arranged in a radiating
manner, so as to give to the whole somewhat of a star-like aspect (Plate
xiv., fig. 1, v, v); and the liquid contents are seen to be propelled from
the former into the latter, and vice versa. Further, in Stentor, a com-
plicated network of canals, apparently in connection with the contractile
vesicles, has been detected in the substance of the 'ectosarc;' and traces
of this may be observed in other Infusoria. In some of the larger Ani-
malcules, it may be distinctly seen that the contractile vesicles have
permanent valvular orifices opening outwards, and that an expulsion of
fluid from the body into the water around it is effected by their contrac-
tion. Hence it appears likely that their function is of a respiratory
nature; and that they serve, like the gill-openings of Fishes, for the
expulsion of water which has been taken in by the mouth, and which has
traversed the interior of the body. (See § 399.)

440. Of the Reproduction of the Ciliated Infusoria, our knowledge is
still very imperfect; for although various modes of multiplication have
been observed among them, it still remains doubtful whether any process
takes place, that can be regarded — like the conjugation of the Monadina

THE MICROSCOPE AND ITS REVELATIONS.

(§418) — as analogous to the sexual Generation of higher organisms.
Binary subdivision would seem to be universal among them; and has in
many instances been observed (as elsewhere) to commence in the nucleus.
The division takes place in some species longitudinally, that is in the
direction of the greatest length of the body (Fig. 305, D, e, f), in other
species transversely (Fig. 308, c, d), whilst in some, as in Chilodon cucul-
lulus (Fig. 306), it has been supposed to occur in either direction
indifferently. But it may be questioned whether, in this latter case, one
set of the apparent 'fissions' is not really ' conjugation ' of two indi-
viduals.— This duplication is performed with such rapidity, under favor-
able circumstances, that, according to the calculation of Prof. Ehrenberg,
no fewer than 268 millions might be produced in a month by the
repeated subdivisions of a single Paramecium. When this fission occurs
m Vorticella (Fig. 305), it extends down the stalk, which thus becomes
double for a greater or less part of its length; and thus a whole bunch of
these Animalcules may spring (by a repetition of the, same process) from
one base. In some members of the same family, arborescent structures
are produced resembling that of Codosiga (Fig. 296), by the like process of

Fig. 306.

A B C » S V

Fissiparous multiplication of Chilodon cucullulus :— a, b, c, successive stages of longitudinal
fission (?); d, k, f, successive stages of transverse fission.

continuous subdivision. — Another curious result of this mode of multi-
plication presents itself in the family Optirydina ; masses of individuals,
which separately resemble certain Vorticellina, being found imbedded in
a gelatinous substance of a greenish color, sometimes adherent, and
sometimes free. These masses, which may attain the diameter of four or
five inches, present such a strong general resemblance to a mass of Nostoc
(§ 247), or even of Frogs' spawn, as to have been mistaken for such;
but they simply result from the fact, that the multitude of individuals
produced by a repetition of the process of self-division, remain connect
with each other for a time by a gelatinous exudation from the surface of
their bodies, instead of at once becoming completely isolated. From a
comparison of the dimensions of the individual Ophrydia, each of which
is about 1-1 20th of an inch in length, with those of the composite masses,
some estimate may be formed of the number included in the latter; for a
cubic inch would contain nearly eight millions of them, if closely packed;
and many times that number must exist in the larger masses, even mak-
ing allowance for the fact that the bodies of the Animalcules are sepa-
rated from each other by their gelatinous cushion, and that the masses
have their central portions occupied by water only. Hence we have, in
such clusters, a distinct proof of the extraordinary extent to which multi-
plication by duplicative subdivision may proceed, without the inter-
position of any other operation. These Animalcules, however, free
themselves at times from their gelatinous bed, and have been observed to

MICROSCOPIC FORMS OF ANIMAL LIFE.

undergo an * encysting process ' corresponding with that of the Vorticel-
lina.

441. Many, perhaps all, ciliated Infusoria at certain times undergo
an encysting process, resembling the passage of Protophytes into the
1 still 9 condition (§ 231), and apparently serving, like it, as a provision
for their preservation under circumstances which do not permit the con-
tinuance of their ordinary vital activity. Previously to the formation of
the cyst, the movements of the animalcule diminish in vigor, and grad-
ually cease altogether; its form becomes more rounded; its oral aper-
ture closes; and its cilia or other

filamentous prolongations are FlQ> 307,

either lost or retracted, as is well
seen in Vorticella (Fig. 307, a).
A new wreath of cilia, however,
is developed near the base, and
in this condition the animal de-
taches itself from its stem, and
swims freely for a short time,
soon passing, however, into the
' still ' condition. The surface
of the body then exudes a gela-
tinous excretion that hardens
around it so as to form a com-
plete coffin-like case, within
which little of the original struc-
ture of the animal can be dis-
tinguished. Even after the Com- Encysting process in Vorticella microstoma :— A,
„l_ i; ^ p n i i full-grown individual in its encysted state ; a, retrac-

pietion 01 tlie Cyst, no Wever, ted oval circlet of cilia ; 6, nucleus; c, contractile vesi-
the Contained animalcule may cle' B> *°yst separated from its stalk; -c, the same
£, , , , : J more advanced, the nucleus broken-up into spore-

Olten be Observed to move tree- like globules; d, the same more developed, the origi-
Iv within it and mav snmp nal body of the Vorticella, d, having become saccu-
rjr wibimi it, dim may bOllie- jated, and containing many clear spaces; — at e, one
times be Caused to Come forth of the sacculations having burst through the envelop-
/» • i xl i • ingcyst, a gelatinous mass, e, containing the gem-

f rom its prison by the mere appli- mules, is discharged,
cation of warmth and moisture.

In the simplest form of the ' encysting process/ indeed, the animalcule
seems to remain altogether quiescent through the whole period of its
torpidity; so that, however long may be the duration of its imprison-
ment, it emerges without any essential change in its form or condition.
But in other cases, this process seems to be subservient either to multi-
plication or to metamorphosis. For in Vorticella, the substance of the
encysted body (b) appears to break up (c, d) into eight or nine segments,
which, when set free by the bursting of the cyst, come forth as sponta-
neously moving spherules. Each of these soon increases in size, develops
a ciliary wreath within which a month makes its appearance, and grad-
ually assumes the form of the Trichodina grandinella of Ehrenberg. It
then develops a posterior wreath of cilia, and multiplies by transverse
fission; each half fixes itself by the end on which the mouth is situated,
a short stem becomes developed, and the cilia-wreath disappears. A new
mouth and cilia- wreath then form at the free extremity; and the growth
of the stem completes the development into the true Vorticellan form.1 —
In Trichocla It/nceus, again, the ' encysting process ' appears subservient
to a like kind of metamorphosis; the form which emerges from the cyst

1 Everts, " Untersuchungen an Vorticella nebulifera," quoted by Prof. Allman,
loc. ext.

THE MICROSCOPE AND ITS REVELATIONS.

differing in many respects from that of the animalcule which, became en-
cysted. According to M. Jules Haime, by whom this history was very
carefully studied,1 the form to be considered as the larval one, is that
shown in Fig. 308, a-e, which has been described by Prof. Ehrenberg
under the name of Oxytriclm. This possesses a long, narrow, flattened
body, furnished with cilia along the greater part of both, margins, and
having also at its two extremities a set of larger and stronger hair-like
filaments; and its mouth, which is an oblique slit on the right-hand side
of its fore-part, has a fringe of minute cilia on each lip. Through this
mouth large particles are not unfrequently swallowed, which are seen
lying in the midst of the endosarc without any surrounding vesicle; and
sometimes even an Animalcule of the same species, but in a different
stage of its life, is seen in the interior of one of these voracious little de-
vourers (b). In this phase of its existence, the Trichoda undergoes mul-
tiplication by transverse fission, after the ordinary mode (c, d); and it is
usually one of the short-bodied ' doubles' (e) thus produced, that passes
into the next phase. This phase consists in the assumption of the globu-

Fig. SOS.

Metamorphoses of Trichoda lynceus :— a, larva {Oxy tricks ; b, «a similar larva, after swallow-
ing the animalcule represented at m; c, a very large individual on the point of undergoing fission;
d, another in which the process has advanced further; e, one of the products of such fission; f,
the same body become spherical and motionless; g, aspect of this sphere fifteen days afterwards;
h, later condition of the same, showing the formation of the cyst; I, incipient separation between
living substance and exuvial matter; k, partial discharge of the latter, with flattening of the
sphere; l, more distinct formation of the confined animal; m, its escape from the cyst; n, its ap-
pearance some days afterwards; o, more advanced stage of the same; i% q, perfect Aspidiscce, one
as seen sideways, moving on its bristles, the other as seen from below ^magnified twice as much as
the preceding figures).

lar form, and the almost entire loss of the locomotive appendages (f);
in the escape of successive portions of the granular sarcode, so that
6 vacuoles 9 make their appearance (g); and in the formation of a gelatinous
envelope or cyst, which, at first soft, afterwards acquires increased firm-
ness (h). After remaining for some time in this condition, the contents
of the cyst become clearly separated from their envelope; and a space
appears on one side, in which ciliary movement can be distinguished (i).
This space gradually extends all round, and a further discharge of gran-
ular matter takes place from the cyst, by which its form becomes altered

1 «■ Annales des Sci. Nat.," Ser. 3, Tom. xix. (1853), p. 109.

MICROSCOPIC FORMS OF ANIMAL LIFE.

(k); and the distinction between the newly-formed body to which the
cilia belong, and the effete residue of the old, becomes more and more
apparent (l). The former increases in size, whilst the latter diminishes;
and at last the former makes its escape through an aperture in the wall
of the cyst, a part of the latter still remaining within its cavity (m).
The body thus discharged (n) does not differ much in appearance from
that of the Oxytricha before its encystment (f), though of only about
two-thirds its diameter; but it soon develops itself (o, p, q) into an
Animalcule very different from that in which it originated. First it
becomes still smaller, by the discharge of a portion of its substance;
numerous very stiff bristle-like organs are developed, on which the Ani-
malcule creeps, as by legs, over solid surfaces; the external integument
becomes more consolidated on its upper surface, so as to become a kind
of carapace; and a mouth is formed by the opening of a slit on one side,
in front of which is a single hair-like flagellum, which turns round and
round with great rapidity, so as to describe a sort of an inverted cone,
whereby a current is brought towards the mouth. This latter form has
been described by Prof. Ehrenberg under the name of Aspidisca. It is
very much smaller than the larva; the difference being, in fact, twice as
great as that which exists between A and P, Q (Fig. 308), since the last
two figures are drawn under a magnifying power double that employed
for the preceding. How the Aspidisca-fovm in its turn gives origin to
the Oxytricha-fovm, has not yet been made out. — A similar ' encysting
process ' has been observed to take place among several other forms of
ciliated Infusoria; so that, considering the strong general resemblance in
kind and degree of organization which prevails throughout the group, it
does not seem unlikely that it may occur at some stage of the life of
nearly all these Animalcules. And it is not improbably in the ' encysted '
condition that their dispersion chiefly takes place, since they have been
found to endure desiccation in this state, although in their ordinary con-
dition of activity they cannot be dried-up without loss of life. When
this circumstance is taken into account, in conjunction with the extraor-
dinary rapidity of multiplication of these Animalcules, there seems no
difficulty in accounting for the universality of their diffusion. It may
be stated as a general fact, that wherever decaying Organic matter exists
in a liquid state, and is exposed to air and warmth, it speedily becomes
peopled with some or other of these minute inhabitants: and it may be
fairly presumed that, as in the case of the Fungi, the dried cysts or
germs of Infusoria are everywhere floating about in the air, ready to
develop themselves wherever the appropriate conditions are presented;
while all our knowledge of their history seems further to justify the
belief, that (in some instances, at least) the same germs may develop
themselves into a succession of forms so different, as to have been re-
garded as distinct specific or even generic types.

442. A very important advance was supposed to have been made in
this direction by the asserted discovery of M. Balbiani1 that a true
process of sexual generation occurs among Infusoria; his observations
having led him to the conclusion that male and female organs are com-
bined in each individual of the numerous genera he has examined, but
that the congress of two individuals is necessary for the impregnation of

*See his "Recherches sur les Phenomenes Sexuels des Infusoires," in Dr.
Brown-Sequard's "Journal de la Physiologie," for 1861. An abstract of these
researches is contained in the " Quart. Journ. of Microsc. Science," for July and
October, 1862.
4

THE MICROSCOPE AND ITS REVELATIONS,
PLATE XIV

1 2 3 4

^3 li 15 16 M 19

sexual (?) reproduction op infusoria (after Balbiani).

Fig. 1. Conjugation of Paramecium aurelia : a, ovarium (nucleus) ; b, seminal capsule (nucleo-
lus): c, oviducal canal; d, seminal canal; e, buccal fissure.

2. The same, more advanced; a, ovary, showing lobulated surface; 6, 6, secondary seminal
capsules.

3. One of the individuals in a still more advanced state of conjugation, showing the ovary a, a,
broken up into fragments connected by the tube m ; 6, 6, seminal capsules ; v, contractile vesicle.

4. Paramecium, ten hours after the conclusion of the conjugation ; a, a, unchanged granular
masses of the ovary, of which other portions have been developed into the ova, o, o, still contained
within the connecting tube m ; b, 6, seminal capsules.

5. The same, three days after the completion of the conjugation.
6-12. Successive stages in the development of the seminal capsules.
13-18. Successive stages in the development of the ovules.

19. Acinetai in different stages, a, b, c.

20. Paramecium containing three Acine fa-parasites, q, g, q, lying in introverted pouches, of
which the external openings are seen at a?, x.

21. Stentor in conjugation.

MICROSCOPIC FORMS OF ANIMAL LIFE.

the ova, those of each being fertilized by the spermatozoa of the other.
He regards the < nucleus ' as an ovarium or aggregation of germs,
whilst the * nucleolus' is really a testis or aggregation of spermatozoids.
The particular form and position which these organs present, and the
nature of the changes which they undergo, vary in the several types of
Infusoria; but as we have in the common Paramecium aurelia an exam-
ple, which, although exceptional in some particulars, affords peculiar
facilities for the observation of the process, and has been most com-
pletely studied by M. Balbiani, it is here selected for illustration. — This
Animalcule, as is well known, multiplies itself with great rapidity (under
favorable circumstances) by duplicative subdivision, which always takes
place in the transverse direction; and the condition represented in Plate
xiv., Figs. 1, 2, is not, as has been usually supposed, another form of
the same process, but is really the sexual congress of two individuals
previously distinct. When the period arrives at which the Paramecia are
to propagate in this manner, they are seen assembling upon certain parts
of the vessel, either towards the bottom or on the walls; and they are
soon found coupled in pairs, closely adherent to each other, with their
similar extremities turned in the same direction, and their two mouths
closely applied to one another, but still continuing to move freely in the
liquid, turning constantly round upon their axes. This conjugation
lasts for five or six days, during which period very important changes
take place in the condition of the reproductive organs. In order to dis-
tinguish these, the Animalcules should be slightly flattened by compres-
sion, and treated with acetic acid, which brings the reproductive
apparatus into more distinct view, as shown in Figs. 1-5. In Fig. 1,
each individual contains an ovarium a, which is shown to present in the
first instance a smooth surface; and from this there proceeds an excretory
canal or oviduct c, that opens externally at about the middle of the
length of the body into the buccal fissure e. Each individual also contains
a seminal capsule b, in which is seen lying a bundle of spermatozoids
curved upon itself, and which communicates by an elongated neck with
the orifice of the excretory canal. The successive stages by which the
seminal capsule arrives at this condition, from that of a simple cell,
whose granular contents resolve themselves (as it were) into a bundle of
filaments, are shown in Figs. 6-10. In Fig. 2, the surface of the ovary
a, is seen to present a lobulated appearance, which is occasioned by the
commencement of its resolution into separate ova; while the seminal
capsule is found to have undergone division into two or four secondary
capsules b, b, each of which contains a bundle of spermatozoa now
straightened out. This division takes place by the elongation of
the capsule into the form represented in Fig. 11, and by the narrowing
of the central portion whilst the extremities enlarge; the further multi-
plication being effected by the repetition of the same process of elonga-
tion and fission. In Fig. 3, which represents one of the individuals still
in conjugation, the four seminal capsules b, b, are represented as thus
elongated in preparation for another subdivision, whilst the ovary a, a,
has begun, as it were, to unroll itself, and to break up into fragments
which are connected by the tube m. It is in this condition that the
object of the conjugation appears to be effected, by the passage of the
seminal capsules of each individual, previously to their complete matura-
tion, into the body of the other. In Fig. 4 is shown the condition of a
Paramecium ten hours after the conclusion of the conjugation; the
ovary has here completely broken up into separate granular masses, of

THE MICROSCOPE AND ITS REVELATIONS.

which some a, a, remain unchanged, whilst others, o, o, o, o, either two,
four, or eight in number, are converted into ovules that appear to be
fertilized by the escape of the spermatozoa from the seminal capsules,
these being now seen in process of withering. Finally, in fig. 5, which
represents a Paramecium three days after the completion of the conjuga-
tion, are seen four complete ova, o, o, o, o, within the connecting tube
m, m ; whilst the seminal capsules have now altogether disappeared. In
figs. 13-18 are seen the successive stages of the development of the
ovule, which seems at first (tig. 13) to consist of a germ-cell having
within it a secondary cell containing minute granules, which is to become
the ' vitelline vesicle.' This secondary cell augments in size, and becomes
more and more opaque from the increase of its granular contents (figs.
14, 15, 16), forming the 6 vitellus' or yolk; in the midst of which is seen
the clear ' germinal vesicle/ which shows on its wall, as the ovule
approaches maturity, the 'germinal spot' (fig. 17). The germinal
vesicle is subsequently concealed (fig. 18) by the increase in the quantity
and opacity of the vitelline granules. The fertilized ova seem to be ex-
pelled by the gradual shortening of the tube that contains them; and
this shortening also brings together the scattered fragments of the-gran-
ular substance of the original ovarium, so as to form a mass resembling
that shown in fig. 1, a, by the evolution of which, after the same fashion,
another brood of ova may be produced.

443. Now there can be no doubt as to the occurrence of ' conjuga-
tion 9 among Ciliated Infusoria; and this not only in the free-swimming,
bat also in the attached forms, as Stentor (Plate xiv., fig. 21). . £n
Vorticella, according to several recent observers, what has been regarded
as gemmiparous multiplication — the putting-f orth of a bud from the base
of the body — is really the conjugation of a small individual in the free-
swimming stage with a fully-developed fixed individual, with whose
body its own becomes fused. But it is doubtful whether such conjuga-
tion has any reference to the encysting process. According to Butschli
and Engelmann, the conjugating process results in the breaking up of
the nucleus and (so-called) nucleolus of the conjugating individuals;
these individuals separate again, and after the expulsion of the broken-
up nuclear structures, the characteristic nucleus and nucleolus are
reformed. The same excellent observers adduce strong grounds for
distrusting Balbiani's assignment of sexual characters to the nucleus and
nucleolus. For although a striation may be observed on the surface
of the latter, no one has witnessed its subdivision into spermatozoidal
filaments. And if embryos are really produced at the expense of the
nucleus, what Balbiani described as sexual ova are really non-sexual
gemmules, each consisting (like the zoospore of Protophytes) of a seg-
ment of the nucleus surrounded by an envelope of protoplasm. — There is
still much uncertainty in regard to the embryonic forms of Ciliate Infu-
soria; some eminent observers asserting that the 'gemmule ' in the first
instance, besides forming a cilia-wreath, puts forth suctorial appendages
(Plate xiv., fig. 19, a, b, c), by means of which it imbibes nourishment
until the formation of its mouth permits it to obtain its supplies in the
ordinary way; whilst others maintain these acinetiform bodies to be
parasites, which even imbed themselves in the substance of the Infusoria
they infest. 1

1 There can be no doubt that Stein was wrong in his original doctrine that the
fully-developed Acinetina are only transition-stages in the development of Vorti-
cellina and other Ciliated Infusoria. But the balance of evidence seems to the

MICROSCOPIC FORMS OF ANIMAL LIFE.

444. It is obvious that no Classification of Infusoria can be of any
permanent value, until it shall have been ascertained by the study of
their entire life-history, what are to be accounted really distinct forms.
And the differences between them, consisting chiefly in the shape of their
bodies, the disposition of their cilia, the possession of other locomotive
appendages, the position of the mouth, the presence of a distinct anal *
orilice, and the like, are matters of such trivial importance as compared
with those leading features of their structure and physiology on which
we have been dwelling, that it does not seem desirable to attempt in this
place to give any detailed account of them. The life-history of the
ciliate Infusoria is a subject pre-eminently worthy of the attention of
Microscopists, who can scarcely be better employed than in tracing out
the sequence of its phenomena, with the same care and assiduity as have
been displayed by Messrs. Dallinger and Drysdale in the study of the
Monadina. — *" In pursuing our researches/' say these excellent observers,

' ' we have become practically convinced of what we have theoretically
assumed — the absolute necessity for prolonged and patient observation of
the same forms. Two observers, independently of each other, examining
the same Monad, if their inquiries were not sufficiently prolonged, might,
with the utmost truthfulness of interpretation, assert opposite modes of
development. Competent optical means, careful interpretation, close
observation, and time, are alone capable of solving the problem."

Section II. — Rotifera, or Wheel- Animalcules.

445. We now come to that higher group of Animalcules, which, in
point of complexity of organization, is as far removed from the preced-
ing, as Mosses are from the simplest Protophytes; the only point of real
resemblance between the two groups, in fact, being the minuteness of
size which is common to both, and which was long the obstacle to the
recognition of the comparatively elevated character of the Rotifera, as it
still is to the precise determination of certain points of their structure.
Some of the Wheel- Animalcules are inhabitants of salt water only; but
by far the larger proportion are found in collections of fresh water, and
rather in such as are free from actively decomposing matter, than in
those which contain organic substances in a putrescent state. Hence
when they present themselves in Vegetable infusions, it is usually after
that offensive condition which is favorable to the development of many
of the Infusoria has passed-away ; and they are consequently to be
looked-for after the disappearance of many successions (it may be) of
Animalcules of inferior organization. Rotifera are more abundantly
developed in liquids which have been long and freely exposed to the open
air, than in such as have been kept under shelter; certain kinds, for
example, are to be met with in the little pools left after rain in the
hollows of the lead with which the tops of houses are partly covered ;
and they are occasionally found in enormous numbers in cisterns which
aie not beneath roofs or otherwise covered over.1 They are not, how-
ever, absolutely confined to collections of liquid : for there are a few
species which can maintain their existence in damp earth ; the common
Rotifer is occasionally found in the interior of the leaf-cells of Sphagnum
(§ 339); and at least two species oiNotommata also are known to be para-
writer to be in favor of his later statement, that the bodies figured in PI. Xiv.,
fig. 19, are really Infusorian embryos, and not parasitic Acinetae.

1 See a remarkable instance of this in vol. L, p. 232, note.

THE MICROSCOPE AND ITS REVELATIONS.

sitic, the one in the large cells of Vaucheria (§ 219), and another in the
sphere of Volvox (§ 236). — The Wheel-like organs from which the class
derives its designation, are most characteristically seen in the common
Rotifer (Fig. 310), where they consist of two disk-like lobes or projections
of the body, whose margins are fringed with long cilia; and it is the
uninterrupted succession of strokes given by these cilia, each row of
which nearly returns (as it were) into itself, that gives rise by an optical
illusion to the notion of ' wheels.' This arrangement, however, is by no
means universal; in fact, it obtains in only a small proportion of the
group ; and by far the more general plan is that seen in Fig. 309, in

Fig. 309. Fig. 310.

muscles; i, t\ tubes of water- vascular system; fc,
young animal ; Z, cloaca.

which the cilia form one continuous line across the body, being disposed
upon the sinuous edges of certain lobes or projections which are borne
upon its anterior portion. Some of the chief departures from this plan
will be noticed hereafter (§ 453).

446. The great transparence of the Eotifera permits their general
structure to be easily recognized. They have usually an elongated form,
similai on the two sides; but this rarely exhibits any traces of segmental
division. The body is covered with a double envelope, both layers of
which are extremely thin and flexible in some species, whilst in others
the outer one seems to possess a horny consistence. In the former case
the whole integument is drawn together in a wrinkled manner when the

MICROSCOPIC FORMS OF ANIMAL LIFE.

body is shortened ; in some of the latter the sheath has the form of a
polype-cell, and the body lies loosely in it, the inner layer of the integu-
ment being separated from the outer by a considerable space (Fig. 312);
whilst in others the envelope or lorica is tightly fitted to the body, and
strongly resembles the horny casing of an Insect or the shell of a Crab,
except that it is not jointed, and does not extend over the head and tail,
which can be projected from the openings at its extremities, or com-
pletely drawn within it for protection (Fig. 313). In those Rotifera in
which the flexibility of the body is not interfered with by the consolida-
tion of the external integument, we usually find it capable of great varia-
tion in shape, the elongated form being occasionally exchanged for an
almost globular one, as is seen especially when the animals are suffering
from deficiency of water; whilst by alternating movements of contraction
and extension, they can make their way over solid surfaces, after the
manner of a Worm or a Leech, with considerable activity, — some even of
the loncated species being rendered capable of this kind of progression
by the contractility of the head and tail. All these, too, can swim
readily through the water by the action of their cilia ; and there are
some species which are limited to the latter mode of progression. The
greater number have an organ of attachment at the posterior extremity
of the body, which is usually prolonged into a tail, by which they can
affix themselves to any solid object; and this is their ordinary position,
when keeping their ' wheels ' in action for a supply of food or of water;
they have no difficulty, however, in letting-go their hold and moving
through the water in search of a new attachment, and may therefore be
considered as perfectly free. The sessile species, in their adult stage, on
the other hand, remain attached by the posterior extremity to the spot
on which they have at first fixed themselves ; and their cilia are conse-
quently employed for no other purpose than that of creating currents in
the surrounding water.

447. In considering the internal structure of Eotifera, we shall take
as its type the arrangement which it presents in the Rotifer vulgaris
(Fig. 310); and specify the principal variations exhibited elsewhere.
The body of this animal, when fully extended, possesses greater length
in proportion to its diameter than that of most others of its class; and
the tail is composed of three joints or segments, which are capable cf
being drawn up, one within another, like the sliding tubes of a telescope,
each having a pair of prongs or points at its extremity. Within the ex-
ternal integument of the body are seen a set of longitudinal muscular
bands (A), which serve to draw the two extremities towards each other;
and these are crossed by a set of transverse annular bands, which also are
probably muscular, and serve to diminish the diameter of the body, and
thus to increase its length. Between the wheels is a prominence bearing
two red spots (#), and having the mouth (a) at its extremity; these red
spots differ altogether from those common in Infusoria and Protophyta,
each having a minute highly-refracting spherical lens set in red pigment,
and being clearly a rudimentary eye; and the prominence that bears them
may be considered, therefore, as a true head, notwithstanding that it is
not clearly distinguishable from the body. This head also bears upon its
under surface a projecting spur-like organ (d)> which was thought by
Prof. Ehrenberg to be a siphon for the admission of water to the cavity
of the body for the purpose of respiration; this, however, is certainly not
the case, the 'spur' being imperforate at its extremity; and there seems
much more probability in the idea of Dujardin, that it represents the

THE MICROSCOPE AND ITS REVELATIONS.

antennce or palpi of higher Articulata, the single organ being replaced in
many Eotifera by a pair, of which each is furnished at its extremity with
a brush-like tuft of hairs that can be retracted into the tube. The
oesophagus, which is narrow in the Rotifer, but is dilated into a crop in
Stephanoceros (Fig. 312) and in some other genera, leads to the masti-

cating apparatus (Fig. '310, e), which in these animals is placed far

behind the mouth," and in close proximity to the stomach.— The Masti-
cating apparatus has been made the subject of attentive study by Mr. P.
H. Gosse; who has given an elaborate account of the various types of
form which it presents in the several subdivisions of the group.1 The
following description of one of the more complicated will serve our
present purpose. The various movable parts are included in a muscular
bulb, termed the mastax (Fig. 311, a), which intervenes between the
buccal funnel (m) and the oesophagus (p). The mastax includes a pair
of organs, which, from the resemblance of their action to that of
hammers working on an anvil, may be called mallei, and a third, still

more complex, termed the incus.
Fig. 311. Each malleus consists of two prin-

cipal parts placed nearly at right
angles to each other, the manu-
brium (c), and the uncus (e); these
are articulated to one another by
a sort of hinge-joint. The former,
as its name imports, serves the
purpose in some degree of a han-
dle; and it is the latter which is
the instrument for crushing and
dividing the food. This is done
by means of the finger-like pro-
cesses with which it is furnished
at the edge where it meets its fel-
low; these being five or six in
number, set parallel to each other
like the teeth of a comb. The in-
cus also consists of distinct arti-
culated portions, namely two
stout rami (a) resting on what
seems a slender footstalk (ft)
termed the fulcrum ; when viewed laterally, however, the fulcrum is seen
to be a thin plate, having the rami so jointed to one edge of it that they
can open and close like a pair of shears. The uncus of each malleus falls
into the concavity of its respective ramus, and is connected with it by a
stout triangular muscle (i), which is seen passing from the hollow of the
ramus to the under surface of the uncus. It is difficult to say with cer-
tainty what is the substance of which these firm structures are composed;
it is not affected by solution of potass, but is instantly dissolved without
effervescence by the mineral acids and by acetic acid. Besides the mus-
cles already described, a thick band (j) embraces the upper and outer
angle of the articulation of the malleus; and is inserted in the adjacent
wall of the mastax; and a semi-crescentic band (Jc) is inserted by its broad
end into the inferior and basal part of the uncus, and by its slender end
into the middle of the inner side of the manubrium; the former of these

Masticating Apparatus of Euchlanis deflexa:
— a, Mastax; c, manubrium, and e, uncus, of
Malleus; g, rami, and h, fulcrum, of Incus; i, mus-
cle connecting ramus and uncus ; j, mucles pass-
ing from malleus to mastax: fc, muscle connecting
uncus and manubrium ; m, buccal funnel ; n, saliv-
ary glands; p, oesophagus.

1 44 Philosophical Transactions," 1856, p. 419.

MICROSCOPIC FORMS OF ANIMAL LIFE.

may be considered as an extensor, and the latter as a flexor, of the mal-
leus. By these and other muscles which cannot be so clearly distin-
guished, the two unci are made to approach and recede by a perpendicular
motion on the hinge-joint, so that their opposing faces come into contact,
and their teeth bruise down the particles of food; but at the same time
they are carried apart and approximated laterally by the movement of the
free extremities of the manubria. The rami of the incus also open and
shut with the working of the mallei: and by the conjoint action of the
whole, the food is effectually comminuted in its passage downwards.1

448. The Alimentary Canal, which lies loose in the ' general cavity of
the body,' is sometimes a simple tube, passing without enlargement or con-
striction from the masticating apparatus to the anal orifice at the posterior
part of the body; whilst in other instances there is a marked distinction
between the stomach and intestinal tube, the former being a large globu-
lar dilatation immediately below the jaws, whilst the latter is cylindrical
and comparatively small. The alimentary canal of Rotifer (Fig. 310)
most resembles the first of these types, but presents a dilatation (/) close
to the anal orifice, which may be considered as a cloaca; that of Braclii-
onas (Fig. 309) is rather formed upon the second. Connected with the
alimentary canal are various glandular appendages, more or less devel-
oped; sometimes clustering round its walls as a mass of separate follicles,
which seems to be the condition of the glandular investment ( g) of the
alimentary canal in Rotifer ; in other cases having the form of caecal
tubuli. Some of these open into the stomach close to the termination of
the oesophagus, and have been supposed to be salivary or pancreatic in
their character, whilst others, which discharge their secretion into the
intestinal tube, have been regarded, and probably with correctness, as the
rudiment of a liver. — In the genus Asplanchna (Gosse), there is a wide
departure from the ordinary Rotifer type; as the species belonging to it
have neither intestine nor anus. The stomach consists of a large bag at
the end of the gullet, about which, when the animals are quiet, the ovary
is bent in a horseshoe form. The indigestible matters are ejected through
the mouth. The curious absence of any digestive apparatus in the males
of this group, will be presently noticed (§ 450). 2

449. There does not appear to be any special Circulating apparatus in
these animals; but the fluid which is contained in the perivisceral cavity
is probably to be regarded as nutritive in its character; and its aeration
is provided for by a peculiar apparatus, which seems to be a rudimentary
form of the ' water- vascular system,' that attains a high development in
the class of Worms. On either side of the body there is usually to be
observed a long flexuous tube (Fig. 309), which extends from a contrac-
tile vessel common to both and opening into the cloaca (Fig. 310, i, i),
towards the anterior region of the body, where it frequently subdivides
into branches, one of which may arch over towards its opposite sides, and
inosculate with a corresponding branch from its tube. Attached to each
of these tubes are a number of peculiar organs (usually from two to eight
on each side), in which a trembling movement is seen, very like that of
a flickering flame; these appear to be pear-shaped sacs, attached by
hollow stalks to the main tube, and each having a flagelliform cilium in

1 See also the description of the mastax of Melicerta ringens and Conochilus by
Mr. Bedwell in " Journ. of Roy. Micr. Soc Vol. i. (1878), p. 176.

2 See Brightwell in " Ann. Nat. His ," Ser. 2, Vol. ii. (1848), p. 153; Dalrymple
in "Philos. Trans." (1849), p. 339; and Gosse in " Ann. Nat. Hist.," Ser. 2, Vols,
iii. (1848), p. 518; vi. (1850), p. 18; and viii. (1851), p. 198.

THE MICROSCOPE AND ITS REVELATIONS.

its interior, that is attached by one extremity to the interior of the sac,
and vibrates with a quick undulatory motion in its cavity; and there can
be little doubt that their function is to keep up a constant movement in
the contents of the aquiferous tubes, whereby fresh water may be contin-
ually introduced from without for the aeration of the fluids of the body.1
The Nervous system is represented by only a single ganglionic body
(sometimes bilobed, however), which lies at one side of the oesophagus,
in near proximity to the eye-spots, the spur-like organ, and the ciliated
pit, and has also, in some Kotifers, an auditory vesicle attached to it.
No nerve-trunks proceeding to the muscular bands have as yet been cer-
tainly distinguished.

450. The Reproduction of the Eotifera has not yet been completely
elucidated. Although they were affirmed by Prof. Ehrenberg to be herm-
aphrodite, yet the existence of distinct sexes has been detected in so
many genera (for the most part by Mr. Gossea), that it may fairly be
presumed to be the general fact. The male is inferior in size to the fe-
male; and sometimes differs so much in organization, that it would not
be recognized as belonging to the same species, if the copulative act had
not been witnessed. In all the cases yet known, as in the Asplanchna of
which the separate male was the first discovered, there is an absolute and
universal atrophy of the digestive system; neither mas tax, jaws, oesopha-
gus, stomach, nor intestines being discoverable in any male; no other
organs, in fact, being fully developed, than those of generation. The
male would appear, therefore, quite unfit to obtain aliment for itself;
and its existence is probably a very brief one, being continued only so
long as the store of nutriment supplied by the egg remains unexhausted.
In the remarkable six-limbed Rotifer discovered by Dr. Hudson, and
named by him Pedalion mira, the virgin female was found to lay female
eggs during the greater part of the year, while male eggs, which are not
found in tiie same individuals, " are half the size of the female ones, and
are carried in clusters of often a score at a time." The males are very
small in comparison with the females, and are very short-lived, sometimes
dying within an hour. In Rotifer*, however, as in a large proportion of
the group, no males have yet been discovered, probably because they are
produced only at certain times. The- female organ consists of a single
ovarian sac, which frequently occupies a large part of the cavity of the
body, and opens at its lower end by a narrow orifice into the cloaca. —
Although the number of eggs in these animals is so small, yet the rapid-
ity with which the whole process of their development and maturation is
accomplished, renders the multiplication of the race very rapid. The
egg of the Hydatina is extruded from the cloaca within a few hours after
the first rudiment of it is visible; and within twelve hours more the
shell bursts, and the young animal comes forth. Three or four eggs
being deposited at once, it was calculated by Prof. Ehrenberg that nearly
seventeen millions may be produced within twenty-four days from a sin-
gle individual. In Rotifer and several other genera, the development of
the embryo takes-place whilst the egg is yet retained within the body of
the parent (Fig. 310, k), and the young are extruded alive; whilst in

1 See Prof. Huxley's account of these organs in his description of Lacinularia
socialis, "Transact, of Microsc. Soc.," N.S., Vol. i. (1853), p. 1.

2 " Philosophical Transactions," 1853, p. 313. See also Dr. Hudson in " Monthly
Microsc. Journ.," Vol. xiii. (1875), p. 45.

3 " Monthly Microsc. Journ.," Vol. viii. (1872), p. 209; and " Quart. Journ. Mic.
Sci„" Vol. xii. (1872), p. 333.

MICROSCOPIC FORMS OF ANIMAL LIFE.

some other instances the eggs, after their extrusion, remain attached to
the posterior extremity of the body (Fig. 309), until the young are set
free. The transparence of the egg-membrane, and also of the tissues, of
the parent Rotifer, allows the process of development to be watched,
even when the egg is retained within the body; and it is curious to ob-
serve, at a very early period, not merely the red eye spot of the embryo,
but also a distinct ciliary movement. In general it would seem that
whether the rupture of the egg-membrane takes- place before or after the
egg has left the body, the germinal mass within it is developed at once
into the form of the young animal, which usually resembles that of its
parent; no preliminary metamorphosis being gone through, nor any

Earts developed which are not to be permanent. In Floscularia ornata,
owever, the young leave the eggs in the shape of little maggots, from
one end of which a tuft of cilia soon appears. The form changes in a
few hours, the ciliated end becoming lobed, and the body rounded. The
foot is developed later.1 — In the curious Notommata Werneckh, which is
found parasitic in the reproductive capsules of Vaucheria (§ 249), the
young animal has the general organization of the free-swimming Rotifers,
and leads a similarly active life; but when its eggs are becoming mature,
it finds its way into one of these capsules and there undergoes a remark-
able deformation, its characteristic organs disappearing, and its body be-
coming a large egg-sac, which seems to be nourished by absorption.2

451. Even in those species which usually hatch their eggs within
their bodies, a different set of Ova is occasionally developed, which are
furnished with a thick glutinous investment; these, which are extruded
entire, and are laid one upon another, so as at last to form masses of
considerable size in proportion to the bulk of the animals, seem not to be
destined to come so early to maturity, but very probably remain dormant
during the whole winter season, so as to j>roduce a new brood in the
spring. These ' winter-eggs ' are inferred by Prof. Huxley, from the
history of their development, to be really gemmce produced by a non-
sexual operation; while the bodies ordinarily known as ova, he considers
to be true generative products. Prof. Cchn, however, states that he has
ascertained, by direct experiment upon those species in which the sexes
are distinct, that the bodies commonly termed ' ova' (Figs. 309, 310) are

• really internal gemmm, since they are reproduced, through many succes-
sions, without any sexual process, just like the external gemmae of Hydra
(§ 515), or the internal gemmae of Entomostraca (§ 609) and Aphides
(§ 643); whilst the i winter-eggs,' are only produced as the result of a
true generative act.3 By M. Balbiani, however, :.t is affirmed (loc. cit.)
that the 6 winter-eggs,' like the ordinary eggs, are produced non-sexually;
so that it would seem as if the intervention of the true generative act is
only occasionally required for the continued propagation of these inter-
esting creatures.

452. Certain Rotifera, among them the common Wheel-Animalcule,
are remarkable for their tenacity of life, even when reduced to such a
state of dryness that they will break in pieces when touched with the
point of a needle (as the Author Jias himself ascertained); for they can
be kept in this condition for any length of time, and will yet revive very
speedily upon being moistened. Taking advantage of this fact, some

1 See Mr. Slack's " Marvels of Pond Life," 2d Edit , p. 54.
* See Balbiani in " Journ. Roy. Microsc. Soc," Vol. ii. (1879), p. 580.
3 See his Memoir, * Ueber die Fortpflanzung der Raderthiere,' in " Siehok? and
Kolliker's Zeitschrift," 1855.

THE MICROSCOPE AND ITS REVELATIONS.

Microscopists are in the habit of keeping by them stocks of desiccated
Rotifers, which can be distributed in the condition of dry dusty powder.
The desiccating process has been carried yet farther with the tribe of Tar-
digrada (§ 453, rv.); individuals of which have been kept in a vacuum
for thirty days, with sulphuric acid and chloride of calcium, and yet have
not lost their capability of revivification. These facts, taken in connec-
tion with the extraordinary rate of increase mentioned in the preceding
paragraph, remove all difficulty in accounting for the extent of the dif u-
sion of these animals, and for their occurrence in incalculable numbers in
situations where, a few days previously, none were known to exist. For
their entire bodies may be wafted in a dry state by the atmosphere from
place to place; and their return to a state of active life, after a desicca-
tion of unlimited duration, may take place whenever they meet with the
requisite conditions — moisture, warmth, and food. It is probable that the
Ova are capable of sustaining treatment even more severe than the fully
developed Animals can bear; and that the race is frequently continued
by them when the latter have perished. — It is not requisite to suppose,
however, that in any of the foregoing cases the desiccation is com-
plete; for it appears that Wheel- Animalcules, in drying, exude a glutinous
matter that forms a sort of impervious casing, which may keep-in the re-
maining fluid.1 When acted on by heat as well as by drought, Rotifers
and Tardigrades lose their vitality; yet the former have survived a grad-
ual heating up to 200° Fahr.

453. The principles on which the various forms that belong to this
Class should be systematically arranged, have not yet been satisfactorily
determined. By Prof. Ehrenberg, the disposition of the ciliated lobes or
wheel-organs, and the inclosure or non-inclosure of the body in a lorica or
case, were taken as the basis of his classification; but as his ideas on both
these points are inconsistent with the actual facts of organization, the
arrangement founded upon them cannot be received. Another division
of the class has been propounded by M. Dujardin, which is based on the
several modes of life of the most characteristic forms. And in a third,
more recently put forth by Prof. Leydig, the general configuration of the
body, with the presence, absence, and conformation of the foot (or tail)
are made to furnish the characters of the subordinate groups. Either of
the two latter is certainly more natural than the first, as bringing *
together for the most part the forms which most agree in general orga-
nization, and separating those which differ; and we shall adopt that of
M. Dujardin as most suitable to our present purpose.

I. The first group includes those that habitually live attached by the
foot, which is prolonged into a pedicle; and it includes two families, the
Floscularians and the Melicertians, the members of which are commonly
found attached to the stems and leaves of aquatic plants, by a long pedi-
cle or foot-stalk, bearing a somewhat bell-shaped body. In one of the
most beautiful species, the Stephanoceros Eicliornii (Fig. 312), this body
has five long tentacles, beset with tufts of cilia, whilst the body is'inclosed
in a gelatinous cylindrical cell. At first sight, the tenacles of this Roti-
fer may seem to resemble those of the Polyzoa; but, if there are carefully
illuminated, the filaments which beset them will be found to be much
larger, to be arranged differently, and to exhibit only an occasional
motion, not at all resembling the regular rhythmical vibrations of the

1 See Davis in " Monthly Micros. Journ Vol. ix. (1863), p. 207; also Slack, at
p. 241 of same volume.

MICROSCOPIC FORMS OF ANIMAL LIFE.

Fig. 312.

cilia of Polyzoa.1 In fact, they seem rather to deserve the designation
of set(B (bristles); for " their action is spasmodic, it creates no vortex,
and it is only by actual contact with these setce that floating particles are
whipped within the area inclosed by the lobes, where by the same whip-
ping action they are twitched from point to point irregularly downwards,
until they come within the range of a vortex that is due, not to any
action of the setce, but to a range of minute cilia in the funnel."8 A
careful comparison of Stephanoceros with other forms,
shows that its tentacles are only extensions of the
ciliated lobes which are common to all the members
of these families; and the cylindrical ' cell ' which en-
velops the body is formed by the gelatinous secretion
from its surface, thrown-off in rings, the indications
of which often remain as a series of constrictions. In **3|tfSigT3
respect of the length of the filaments projecting from
its lobes, and the breadth of these expansions, Flos-
cularia is still more aberrant. — The body of Melicerta
is protected by a most curious cylindrical tube, com-
posed of little rounded pellets agglutinated together;
this is obviously an artificial construction, and the
process by which it is built may be watched by any
Microscopist who is fortunate enough to capture it?
Beneath a projection on its head, there is observed a
small disk-like organ, in which, when the ' wheels 9
are at work, a movement is seen very much resembling
that of a revolving ventilator. Towards this disk the
greater proportion of the solid particles that may be
drawn from the surrounding liquid into the vortex of
the wheel-organs, are driven by their ciliary movement,
a small part only being taken into the alimentary
canal; and there they accumulate until the aggrega-
tion (probably cemented by a glutinous secretion fur-
nished by the organ itself) acquires the size and form
of one of the globular pellets of the case; the time
ordinarily required being about three minutes. The
head of the animal then bends itself down, the pellet-
disk is applied to the edge of the tube, the newly-
formed pellet is attached there, and, the head being lifted into its
former position, the formation of a new pellet at once commences. —
Another curious example of this family is presented by the Conochilus
volvox; which is found in spherical clusters composed of a considerable
number of individuals adherent by their tails, their bodies being arranged
in a radiating manner, and the intervals between them being filled up by
a gelatinous substance. There is not, however, any such organic connec-

Stephanoceros Eich-
omii.

1 In ordinary drawings, the filaments of the Stepharioceros are represented as
short bristles; this is an error arising from bad instruments or defective illumina-
tion. It requires considerable skill to show these filaments, or those of the Flos-
cularia, in their true length; but the beauty of the object is geatly increased
when this is accomplished.

2 See Mr. C. Cubitt's * Observations on the Economy of Stephanoceros,' in
'Monthly Microsc. Journ.," Vol. iii. (1870), p. 242.

3 See Gosse ' On the architectual instincts of Melicerta ringens,' in * Trans, of
Microsc. Soc," Vol. iii. (1852), p. 58; also Bedwell in " Monthly Microsc. Journ.,"
Vol. xvi. (1877), p. 214; and Hudson in " Journ. Roy. Microsc. Soc," Vol. ii. (1879),
p. 1.

THE MICROSCOPE AND ITS REVELATIONS.

tion between them as exists in the Ophrydium (§ 440); and the uniting
substance seems to be nothing else than the clear slimy secretion which
probably all Rotifera exude from the surface of their bodies. It is into
this that the eggs are extruded; and as they are hatched in it, the young
-produced from them remain to form part of the cluster; but, as its num-
bers increase, the cluster breaks up into two or more, which in their turn
enlarge and then subdivide, so that a pond to whose bottom the * winter
eggs' of the year before have subsided, becomes alive with them in the
early summer of the following year.1 — The Lacinidaria socialis, in like
manner, forms transparent gelatinous-looking globular clusters, about
l-5th of an inch in diameter, which attach themselves to the leaves of
aquatic plants.

ii. The next of M. Dujardin's primary groups (ranged by him, how-
ever, as the third) consists of the ordinary Rotifer and its allies, which
pass their lives in a state of alternation between the conditions of those
attached by a pedicle, of those which habitually swim freely through the
water, and of those wl. ich creep or crawl over hard surfaces. — As these
have already been fully described, it is not requisite to dwell longer upon
them.

in. The next group consists of those Rotifera which seldom or never
attach themselves by the foot, but habitually swim freely through the
water; and putting aside the peculiar aberrent form Albertia which has
only been found as a parasite in the intestines of Worms, it may be
divided into families, the Brachionians and the Fur cular tans. The for-
mer are for the most part distinguished by the short, broad, and flattened
form of the body (Figs. 309, 313); which is, moreover, inclosed in a sort
of cuirass formed by the consolidation of the external integument. This
cuirass is often very beautifully marked on its surface, and may be pro-
longed into extensions of various forms, which are sometimes of very
considerable length. The latter (corresponding almost exactly with the
Hydatinece of Prof. Ehrenberg) derived their name from the bifurcation
of the foot into a sort of two-bladed forceps; their bodies are ovoidal or
cylindrical, and are inclosed in a flexible integument, which is often seen
to wrinkle itself into longitudinal and transverse folds at equidistant
lines. To this family belongs the Hydatiyia senta, one of the largest of
the Rotifera, which was employed by Prof. Ehrenberg as the chief sub-
ject of his examination of the internal structure of this group; as does
also the Asplanchna, the curious condition of whose digestive apparatus
has been already noticed (§ 448).

iv. The fourth of M. Dujardin's primary orders consists of the very
curious tribe, first carefully investigated by M. Doyere, to which the
name of Tardigrada has been given, on account of the slowness of their
creeping movement. It seems now clear, however, that they have no
near relationship to the true Rotifera; corresponding to them only in
their minute size and simple structure. They are found in the same lo-
calities with the Rotifers, and, like them, can be revivified after desicca-
tion (§ 452): but they have a vermiform body, divided transversely into
five segments, of which one constitutes the head, whilst each of the others
bears a pair of little fleshy protuberances, furnished with four curved
hooks, and much resembling the pro-legs of a caterpillar. The head is
entirely unpossessed of ciliated lobes; and the mouth, situated at the end
of a sort of beak furnished with two longitudinal stylets, leads, through

1 See Davis in " Monthly Microsc. Journ.," Vol. xvi. (1876), p. 1.

MICROSCOPIC FORMS OF ANIMAL LIFE.

a muscular pharynx, into a wide alimentary canal, which gradually nar-
rows to the anus. There are no special organs of circulation or respira-
tion, but the nervous system is much more developed than in the Koti-
fera; a cerebral mass, bearing two eyes, giving origin to two longitudinal
cords, on which are seated
pairs of ganglia in connec-
tion with the members, as
in Articulated animals gen-
erally. Their nearest affini-
ties seem with the lowest
forms of the Arachnida.

454. Noth withstand i n g
that all the best-informed
Zoologists are now agreed in
ranking the true Rotifera
among Articulated animals,
yet there is still a consider-
able discordance of opinion
as to the precise part of that
series in which they should
stand. Prof. Leydig, who
has devoted much attention
to the study of the class,
regards them as most allied
to the Crustacea, and terms
them * Cilio-crustaceans; *
and the curious Entomos-
tracan-looking Pedalion of Dr. Hudson might seem a link with that
group.1 Prof. Huxley, on the other hand, has argued that they are
more connected with the Annelida, through the resemblance which they
bear to the early larval forms of that class (§ 595); while in their single
bilobed nerve-ganglion and water-vascular system, they seem allied to
Planar ia (§ 593) .

1 See Prof. E. Ray Lankester's * Remarks on Pedalion,'' in ''Quart. Journ.
Microsc. Sci.," Vol. xii. (1878), p. 338.

2 The following Treatises and Memoirs (in addition to those already referred
to) contain valuable information in regard to the life-history of Animalcules and
their principal forms: — Ehrenberg, "Die Infusionsthierchen, ' Berlin, 1838; Du-
jardin, " Histoire Naturelle des Zoophytes Infusoires," Paris, 1841; Pritchard,
M History of Infusoria," 4th Ed., London. 1861 (a comprehensive repertory of in-
formation); Stein, "Der Organismus der Infusionsthiere," Leipzig, Erste Abthei-
lung, 1859, Zweite Abtheilung, 1867, Dritte Abtheilung, Halfte i , 1878: Saville
Kent's 44 Manual of the Infusoria," 1880-1; and Prof. Biitschli's Protozoa (1880,
1881) in the new edition of 44 Bronn's Thierreich." — For the Rhizopoda and In-
fusoria specially, see Claparede and Lachmann, 44 Etudes surles Infusoires et les
Rhizopodes," Geneva, 1858-1861; Cohn, in 44Siebold and Kolliker's Zeitschrift,"
1851-4, and 1857; Lieberkiihn, in "Miiller's Archiv," 1856, and 44 Ann. of Nat.
Hist.," 2d Ser., Vol. xviii., 1856; Engellmann, 44 Zur Naturgeschichte der Infusions-
Thiere" (1862); and Prof. Butschli's 44Studien liber die Conjugation der Infuso-
rien," etc., 1876. — For the Rotifera specially, see Leydig, in 44 Siebold and Kolli-
ker's Zeitschrift," Bd. vi., 1854; Gosse on Melicerta ringens, in "Quart. Journ. of
Microsc. Science," Vol. i. (1853), p. 1; Huxley on Lacinularia socialis in 4 4 Trans-
act, of Microsc. Soc," Ser. 2, Vol. i (1853). p. 1; and Cohn, in 44 Siebold and Kolli-
ker's Zeitschrift," Bde. vii., ix. (1856, 1858). Mr. Slack's 44 Marvels of Pond Life "
(2d Edit., London, 1871) contains many interesting observations on the habits of
Infusoria and Rotifera.

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XII.
FORAMINIFERA AND RADIOL ARIA.

455. Returning now to the lowest or Rhizopod type of Animal life
(Chap, x)., we have to direct our attention to two very remarkable series
of forms, almost exclusively Marine, under which that type manifests
itself; all of them distinguished by skeletons so consolidated by Mineral
deposit, as to retain their form and intimate structure long after the
Animals to which they belonged have ceased to live, even for those un-
defined periods in which they have been imbedded as Fossils in strata of
various geological ages. In the first of these groups, the Foraminifera, the
skeleton usually consists of a calcareous many-chambered Shell, which
closely invests the sarcode-body, and which, in a large proportion of the
group, is perforated with numerous minute apertures; this shell, how-
ever, is sometimes replaced by a 6 test/ formed of minute grains of sand
cemented together; and there are a few cases (§ 397) in which the Ani-
mal has no other protection than a membranous envelope. — In the sec-
ond group, the Radiolaria, the skeleton is always siliceous; and may
be either composed of disconnected spicules, or may consist of a symme-
trical open framework, or may have the form of a shell perforated by
numerous apertures, which more or less completely incloses the body.
— The Foraminifera probably take, and always have taken, the largest
share of any Animal group in the maintenance of the solid carcareous
portion of the Earth's crust; by separating from its solution in Ocean-
water the Carbonate of Lime continually brought down by rivers from
the land. The Radiolaria do the same, though in far less measure, for
the Silex. And both extract from Sea- water the organic matter univer-
sally diffused through it, converting it into a form that serves for the
nutrition of higher Marine animals.

Section I. — Foraminifera.

456. The animals of this group belong to that Reticularian form of
the Rhizopod type (§ 397), in which, — with a differentiation between the
containing and the contained sarcodic substance which is involved in the
formation of a definite. investment, — a distinct nucleus (sometimes sin-
gle, in other cases multiple) is probably always present.1 The Shells of

1 The absence of a nucleus was long supposed to be a characteristic of the ani-
mal of the Foraminifera ; and its presence in Gromia (first detected by Dr. Wal-
lich) was regarded as differentiating that type from the Foraminifera proper.
But the researches of Hertwig and Lesser having established its presence in sev-
eral true Foraminifera, and the Author's own observations on other forms having
confirmed theirs, its general presence may be fairly assumed, until contradicted
by more extended observation.

FOBAMINIFBKA AND KADIOLAKIA.

VARIOUS FORMS OF FORAMINIFERA (Original).

Fig. 1.
2.
3.
4.
5.
6.
7.

10.

Cornuspira.

Spiroloculina.

Triloculina.

Biloculina.

Peneroplis,

Orbiculina (cyclical f orm\
Orbiculina (young^
Orbiculina (spiral form).
Lagena.
Nodosaria.

Fig. 11. Cristellaria.
1 J. Globigerina.

13. Polymorphina,

14. Textularia.

15. Discorbina.

16. Polystomella.

17. Planorbulina.

18. Rotalia.

19. Nonionina.

THE MICROSCOPE AND ITS REVELATIONS.

Foraminifera are, for the most part, polythalamous or many-chambered
(Plate xv.); often so strongly resembling those of Nautilus, Spirula,
and other Cephalopod Mollusks, that it is not surprising that the older
Naturalists, to whom the structure of these animals was entirely un-
known, ranked them under that Class. But independently of the entire
difference in the character of the animal bodies by which the two kinds
of shells are formed, there is a most important distinction between them
in regard to the relation of the animal to the shell. For whilst, in the
chambered shells of the Nautilus and other Cephalopods, the animal is
a single individual tenanting only the last formed chamber, and with-
drawing itself from each chamber in succession, as it adds to this another
and larger one, the animal of a nautiloid Foraminifer has a composite
body, consisting of a number (sometimes very large) of 6 segments/ each
repeating the rest, which continues to increase by gemmation or budding
from the last-formed segment. And thus each of the chambers, how-
ever numerous they may be, is not only formed, but continues to be oc-
cupied, by its own segment; which is connected with the segments of
earlier and later formation by a continuous ' stolon ' (or creeping stem),
that passes through apertures in the septa or partitions dividing the
chambers. — From what wre know of the semi-fluid condition of the sar-
code-body in the Eeticularian type (§ 397), there can be little doubt that
there is an incessant circulatory change in the actual substance of each
segment; so that the material taken-in as food by the segment nearest
the surface or margin, is speedily diffused through the entire mass. The
relation between these ■ polythalamous 9 forms, therefore, and the mono-
thalamous or single-chambered, — of which we have already had an exam-
ple in Gromia (§ 397), and of which others will be presently described,
— is simply that whereas any buds produced by the latter detach them-
selves to form separate individuals, those put forth by the former remain
in continuity with the parent stock and with each other, so as to form
a 6 composite 9 Animal and a * polythalamous' Shell.

457. According to the plan on which the gemmation takes place, will
be the configuration of the shelly structure produced by the segmented
body. Thus, if the bud should be put forth from the aperture of a La-
gena (Plate xv., fig. 9) in th# direction of the axis of its body, and a
second shell should be formed around this bud in continuity with the
first, and this process should be successionally repeated, a straight rod-
like shell would be produced (fig. 10), whose multiple chambers commu-
nicate with each other by the openings that originally constituted their
mouths; the mouth of the last-formed chamber being the only aperture
through which the sarcode-body, thus composed of a number of segments
connected by a peduncle or f stolon 9 of the same material, could now
project itself or draw-in its food. The successive segments may be all
of the same size, or nearly so, in which case the entire rod will approach
the cylindrical form, or will resemble a line of beads; but it often hap-
pens that each segment is somewhat larger than the preceding (fig. 11),
so that the composite shell has a conical form, the apex of the cone
being the original segment, and its base the one last formed. — The
method of growth now described is common to a large number of Fora-
minifera, chiefly belonging to the genus Nodosarina; but even in that
genus we have every gradation between the rectilineal (fig. 10), and the
spiral mode of growth (fig. 11); whilst in the genus Peneroplis (fig. 5)
it is not at all uncommon for shells which commence in a spiral to ex-
change this in a more advanced stage for the rectilineal. When the

FORAMINIFERA AND RADIOL ARE A .

successive segments are added in a spiral direction, the character of the
spire will depend in great degree upon the enlargement or non-enlargement
of the successively-formed chambers; for sometimes it opens out very
rapidly, every whorl being considerably broader than that which it sur-
rounds, in consequence of the great excess of the size of each segment
over that of its predecessor, as in Peneroplis ; but more commonly there
is so little difference between the successive segments, after the spire has
made two or three turns, that the breadth of each whorl scarcely exceeds
that of its predecessor, as is well seen in the section of the Rotalia rep-
resented in Fig. 330. An intermediate condition is presented by such a
Rotalia as is shown in Fig. 314, which may be taken as a characteristic
type of a very large and important group of Foraminifera, whose general
features will be presently described. Again, a spiral may be either ' nau-

Fiq. 314.

Rotalia ornata, with its pseudopodia extended.

tiloid 9 or 1 turbinoid': the former designation being applied to that form
in which the successive convolutions all lie in one plane (as they do in
the Nautilus), so that the shell is i equilateral ' or similar on its two sides;
whilst the latter is used to mark that form in which the spire passes
obliquely round an axis, so that the shell becomes 6 inequilateral/ hav-
ing a more or less conical form, like that of a Snail or a Periwinkle, the
first-formed chamber being at the apex. Of the former we have charac-
teristic examples in Polystomella (Plate xv., fig. 16) and Nonionina
(fig. 19); whilst of the latter we find a typical representation in Rotalia
Baccarii (fig. 18). Further, we find among the shells whose increase
takes place upon the spiral plan, a very marked difference as to the de-
gree in which the earlier convolutions are invested and concealed by the
latter. In the great Rotaline group, whose characteristic form is a tur-

THE MICROSCOPE AND ITS REVELATIONS.

binoid spiral, all the convolutions are usually visible, at least on one side
(figs. 15, 17, 18), but among the Nautiloid tribes it more frequently hap-
pens that the last-formed whorl incloses the preceding to such an extent
that they are scarcely, or not all, visible externally, as is the case in Oris-
tellaria (fig. 11), Poly ^tomella (fig. 16), and Nonionina (fig. 19). — The
turbinoid spire may coil so rapidly round an elongated axis, that the
number of chambers in each turn is very small; thus in Globigerina (fig.
12) there are usually only four; and in Valvulina the regular number
is only three. Thus we are led to the Userial arrangement of the cham-
bers which is characteristic of the Textularian group (fig. 14); in which
we find the chambers arranged in two rows, each chamber communicat-
ing with that above and that below it on the opposite side, without
any direct communication with the chamber of its own side, as will be
understood by reference to Fig. 328, A, which shows a 'cast' of the sar-
code body of the animal. On the other hand, we find in the nautiloid
spire a tendency to pass (by a curious transitional form to be presently
described, § 464) into the cyclical mode of growth; in which the original
segment, instead of budding-forth on one side only, develops gemmce all
round, &o that a ring of small chambers (or chamberlets) is formed around
the primordial chamber, and this in its turn surrounds itself after the
like fashion with another ring; and by successive repetitions of the same
process the shell comes to have form of a disc made up of a great num-
ber of concentric rings, as we see in Orbitolites (Fig. 316) and in Cyclo-
clypeus (Plate xvi., fig. 1).

458. These and other differences in the plan of growth were made by
M. D'Orbigny the foundation of his Classification of this group, which,
though at one time generally accepted, has now been abandoned by most
of those who have occupied themselves in the study of the Foraminifera.
For it has come to be generally admitted that ' plan of growth ' is a
character of very subordinate importance among the Foraminifera, so
that any classification which is primarily based upon it must necessarily
be altogether unnatural; those characters being of primary importance
which have an immediate and direct relation to the Physiological condi-
tion of the Animal, and are thus indicative of the real affinities of the
several groups which they serve to distinguish. The most important of
these characters will now be noticed.1

459. Two very distinct types of Shell-structure prevail among ordi-
nary Foraminifera — namely, the porcellanous and the hyaline or vitreous.
The shell of the former, when viewed by reflected light, presents an
opaque-white aspect which bears a strong resemblance to porcelain; but
when thin natural or artificial laminae of it are viewed by transmitted
light, the opacity gives place to a rich brown or amber color, which in a
few instances is tinged with crimson. No structure of any description
can be detected in this kind of shell substance, which is apparently
homogeneous throughout. Although the shells of this £ porcellanous '
type often present the appearance of being perforated with foramina, yet
this appearance is illusory, being due to a mere 'pitting' of the external
surface, which, though often very deep, never extends through the
whole thickness of the shell. Some kind of inequality of that surface,
indeed, is extremely common in the shells of the 6 porcellanous 9 Fora-

1 This subject will be found amply discussed in the Author's " Introduction to
the Study of the Foraminifera," published by the Ray Society; to which work lie
would refer such of his readers as may desire more detailed information in regard
to it.

FOR AMINIFER A AND RADIOL ARIA.

minifera; one of the most frequent forms of it being a regular alterna-
tion of ridges and farrows, such as is occasionally seen in Miliola (Plate
xv., fig. 3), but which is an almost constant characteristic of Peneroplis
(fig. 5). But no difference of texture accompanies either this or any
other kind of inequality of surface; the raised and depressed portions
being alike homogeneous. — In the shells of the vitreous or hyaline type,
on the other hand, the proper shell-substance has an almost glassy trans-
parence, which is shown by it alike in thin natural lamella, and in arti-
ficially prepared specimens of such as are thicker and older. It is
usually colorless, even when (as in the case with many Rotalinm) the
substance of the animal is deeply colored; but in certain aberrant Rota-
lines the shell is commonly, like the animal body, of a rich crimson hue.
All the shells of this type are beset more or less closely with tubular perfo-
rations, which pass directly, and (in general) without any subdivision,
from one surface to the other. These tubuli are in some instances suffi-
ciently coarse for their orifices to be distinguished with a low magnifying
power, as i punctations5 on the surface of the shell, as is shown in Fig.
314; whilst in other cases they are so minute as only to be discernible in
thin sections seen by transmitted light under a higher magnifying power,
as is shown in Figs. 335, 336. When they are very numerous and closely
set, the shell derives from their presence that kind of opacity which is
characteristic of all minutely-tubular textures, whose tubuli are occupied
either by air or by any substance having a refractive power different from
that of the intertubular substance, however perfect may be the transpar-
ence of the latter. The straightness, parallelism, and isolation of these
tubuli are well seen in vertical sections of the thick shells of the largest
examples of the group, such as Nummulvna (Fig. 335). It often hap-
pens, however, that certain parts of the shell are left unchannelled by
these tubuli; and such are readily distinguished, even under a low mag-
nifying power, by the readiness with which they allow transmitted light
to pass through them, and by the peculiar vitreous lustre they exhibit
when light is thrown obliquely on their surface. In shells formed upon
this type, we frequently find that the surface presents either bands or
spots which are so distinguished; the non-tubular bands usually marking
the position of the septa, and being sometimes raised into ridges, though
in other instances they are either level or somewhat depressed; whilst the
non-tubular spots may occur on any part of the surface, and are most
commonly raised into tubercles, which sometimes attain a size and num-
ber that give a very distinctive aspect to the shells that bear them.

460. Between the comparatively coarse perforations which are com-
mon in the Rotahne type, and the minute tubuli which are characteris-
tic of the Nummuline, there is such a continuous gradation as indicates
that their mode of formation, and probably their uses, are essentially the
same. In the former, it has been demonstrated by actual observation
that they allow the passage of pseudopodial extensions of the sarcode-
body through every part of the external wall of the chambers occupied
by it (Fig. 314); and there is nothing to oppose the idea that they
answer the same purpose in the latter, since, minute as they are, their
diameter is not too small to enable them to be traversed by the finest of
the threads into which the branching pseudopodia of Foraminifera are
known to subdivide themselves. Moreover, the close approximation of
the tubuli in the most finely-perforated Nummulines, makes their col-
lective area fully equal to that of the larger but more scattered pores of
the most coarsely-perforated Rotalines. Hence it is obvious that the

THE MICROSCOPE AND ITS REVELATIONS.

tubulation or non-tubulation of Foramini feral shells is the key to a very
important Physiological difference between the Animal inhabitants of
the two kinds respectively; for whilst^ very segment of the sarcode-body
in the former case gives off pseudopodia, which pass at once into the sur-
rounding medium, and contribute by their action to the nutrition of the
segment from which they proceed, these pseudopodia are limited in the
latter case to the final segment, issuing forth only through the aperture
of the last chamber, so that all the nutrient material which they draw-in
must be first received into the last segment, and be transmitted thence
from one segment to another until it reaches the earliest. With this dif-
ference in the physiological condition of the Animal of these two types,
is usually associated a further very important difference in the conforma-
tion of the Shell — viz., that whilst the aperture of communication be-
tween the chambers, and between the last chamber and the exterior, is
usually very small in the s vitreous ' shells, serving merely to give passage
to a slender stolon or thread of sarcode from which the succeeding seg-
ment may be budded-off, it is much wider in the ' porcellanous 9 shells,
so as to give passage to a 6 stolon' that may not only bud-off new seg-
ments, bi]t may serve as the medium for transmitting nutrient material
from the outer to the inner chambers.

461. Between the highest types of the Porcellanous and the Vitreous
series respectively, which frequently bear a close resemblance to each
other in form, there are certain other well-marked differences in struc-
ture, which clearly indicate their essential dissimilarity. Thus, for ex-
ample, if we compare Orbitolites (Fig. 316) with Cycloclypeus (Plate xvi.,
fig. 1), we recognize the same plan of growth in each, the chamberlets
being arranged in concentric rings around the primordial chamber; and
to a superficial observer there would appear little difference between
them. But a minuter examination shows that not only is the texture of
the shell ' porcellanous 9 and non-tubular in Orbitolites, whilst it is 6 vit-
reous 9 and minutely tubular in Cycloclypeus; but that the partitions be-
tween the chamberlets are single in the former, whilst they are double in
the latter, each segment of the sarcode-body having its own proper shelly
investment. Moreover, between these double partitions an additional
deposit of calcareous substance is very commonly found, constituting
what may be termed the intermediate skeleton; and this is traversed by a
peculiar system of inosculating canals, which pass around the chamber-
lets in interspaces left between the two laminae of their partitions, and
which seem to convey through its substance extensions of the sarcode-
body whose segments occupy the chamberlets. We occasionally find this
6 intermediate skeleton 9 extending itself into peculiar outgrowths, which
have no direct relation to the chambered shell; of this we have a very
curious example in Calcarina (Plate xvi., fig. 3); and it is in these tlr';
we find the 6 canal-system ' attaining its greatest development. Its most
regular distribution, however, is seen in Polystomella and in Operculina;
and an account of it will be given in the description of those types.

462. Porcellanea. — Commencing, now, with the Porcellanous se-
ries, we shall briefly notice some of its most important forms, which are
so related to each other as to constitute but the one family Miliolida. Its
simplest type is presented by the Cornuspira (Plate xv., fig. 1) of our
own coasts, found attached to Sea-weeds and Zoophytes; this is a minute
spiral shell, of which the interior forms a continuous tube not divided
into chambers; the latter portion of the spire is often very much flat-
tened-out, as in Peneroplis (fig. 5), so that the form of the mouth is

FORAMINIFERA AND RADIOL ARIA .

changed from a circle to a long narrow slit. — Among the commonest of
the Foraminifera, and abounding near the shores of almost every sea, are
some forms of the Milioline type, so named from the resemblance of
some of their minute fossilized forms (of which enormous beds of lime-
stone in the neighborhood of Paris are almost entirely composed) to mil-
let-seeds. The peculiar mode of growth by which these are characterized,
will be best understood by examining in the first instance the form which
has been designated as Spiroloculina (Plate xv., fig. 2). This shell is a
spiral, elongated in the direction of one of its diameters, and having in
each turn a contraction at either end of that diameter, which partially
divides each convolution into two chambers; the separation between the
consecutive chambers is made more complete by a peculiar projection
from the inner side of the cavity, known as the 6 tongue ' or ' valve,'
which may be considered as an imperfect septum; of this a characteristic
example is shown in the upper part of fig. 4. Now it is a very general
habit in the Milioline type, for the chambers of the later convolutions to
extend themselves over those of the earlier, so as to conceal them more
or less completely; and this they very commonly do somewhat unequally,
so that more of the earlier chambers are visible on one side than on the
other. Miliolce thus modified (fig. 3) have received the names of Quin-
queloculina and Triloculina according to the number of chambers visible
externally; but the extreme inconstancy which is found to mark such
distinctions, when the comparison of specimens has been sufficiently ex-
tended, entirely destroys their value as differential characters. Some-
times the earlier convolutions are so completely concealed by the later,
that only the two chambers of the last turn are visible externally; and in
this type, which has been designated Biloculina, there is often such an
increase in the breadth of the chambers as altogether changes the usual
proportions of the shell, which has almost the shape of an egg when so
placed that either the last or the penultimate chamber faces the observer
(Plate xv., fig. 4). It is very common in Milioline shells for the exter-
nal surface to present a 'pitting,' more or less deep, a ridge-and-furrow
arrangement (fig. 3), or a honeycomb division; and these diversities have
been used for the characterization of species. Not only, however, may
every intermediate gradation be met-with between the most strongly
marked forms, but it is not at all uncommon to find the surface smooth
on some parts, whilst other parts of the surface in the same shell are
deeply pitted or strongly ribbed or honeycombed; so that here again the
inconstancy of these differences deprives them of all value as distinctive
characters.

463. Reverting again to the primitive type presented in the simple
spiral of Cornuspira, we find the most complete development of it in
Peneroplis (Plate xv., fig. 5), a very beautiful form, which, although
very rare on our own coasts, is one of the commonest of all Foraminifera
in the shore-sands and shallow water dredgings of the warmer regions of
every part of the globe. This is a nautiloid shell, of which the spire
flattens itself out as it advances in growth; it is marked externally by a
series of transverse bands, which indicate the position of the internal
septa that divide the cavity into chambers; and these chambers commu-
nicate with each other by numerous minute pores traversing each of the
septa, and giving passage to threads of sarcode that connect the seg-
ments of the body. At a is shown the ' septal plane' closing in the
last-formed chamber, with its single row of pores through which the
j)seudopodial filaments extend themselves into the surrounding medium.

THE MICROSCOPE AND ITS REVELATIONS.

The surface of the shell, which has a peculiarly ' porcellanous ' aspect, is
marked by closely-set strics that cross the spaces between the successive
septal bands; these markings, however, do not indicate internal divisions,
and are clue to a surface-furrowing of the shelly walls of the chambers.
This type passes into two very curious modifications; one having a spire
which, instead of flattening itself out, remains turgid like that of a
Nautilus, having only a single aperture, which sends out fissured exten-
sions that subdivide like the branches of a tree, suggesting the name of
Dendriiina ; the other having its spire continued in a rectilineal direc-
tion, so that the shell takes the form of a crosier, this being distin-
guished by the name of Spirolina. A careful examination of inter-
mediate forms, however, has made it evident that these modifications,
though ranked as of generic value byM. D'Orbigny, are merely varietal;
a continuous gradation being found to exist from the elongated septal
plane of Peneroplis, with its single row of isolated pores, to the arrow-
shaped, oval, or even circular septal plane of Dendritina, with all its
pores fused together (so to speak) into one dendritic aperture; and a like
gradation being presented between the ordinary and the 'spiroline'
forms into which both Peneroplis and Dendritina tend to elongate
themselves.

404. From the ordinary nautiloid multilocular spiral, we now pass to
a more complex and highly-developed form, which is restricted to
tropical regions, but is there very abundant — that, namely, which has
received the designation Orbiculina (Plate xv., figs. 6, 7, 8). The
relation of this to the preceding will be best understood by an examina-
tion of its earlier stage of growth, represented in fig. 7; for here we see
that the shell resembles that of Peneroplis in its general form, but that
its principal chambers are divided by 1 secondary septa' passing at right
angles to the primary, into ' chamberlets 9 occupied by sub-segments of
the sarcode-body. Each of these secondary septa is perforated by an
aperture, so that a continuous gallery is formed, through which (as in
Fig. 316) there passes a stolon that unites together all the sub-segments
of each row. The chamberlets of successive rows alternate with one
another in position; and the pores of the principal septa are so disposed,
that each chamberlet of any row normally communicates with two
chamberlets in each of the adjacent rows. The later turns of the spire
very commonly grow completely over the earlier, and thus the central
portion or 6 umbilicus 9 comes to be protuberant, whilst the growing edge
is thin. The spire also opens out at its growing margin, which tends to
encircle the first-formed portion, and thus gives rise to the peculiar shape
represented in fig. 8, which is the common aduncal type of this organ-
ism. But sometimes, even at an early age, the growing margin extends
so far round on each side, that its two extremities meet on the opposite
side of the original spire, which is thus completely inclosed by it; and
its subsequent growth is no longer spiral but cyclical, a succession of
concentric rings being added, one around the other, as shown in fig. 6.
This change is Extremely curious, as demonstrating the intimate relation-
ship between the spiral and the cyclical plans of growth, which at first
sight appear essentially distinct. In all but the youngest examples of
Orbiculina, the septal plane presents more than a single row of pores,
the number of rows increasing in the thickest specimens to six or eight.
This increase is associated with a change in the form of the sub-segments
of sarcode from little blocks to columns, and with a greater complexity
in the general arrangement, such as will be more fully described here-

FORAMINIFERA AND KADIOLARIA.

after in Orbit oKtes (§ 466). The largest existing examples of this type
are far surpassed in size by those which make up a considerable part of a
Tertiary Limestone on the Malabar coact of India, whose diameter
reaches 7 or 8 lines.

4G5. A very curious modification of the same general plan is shown
in Alveolina. a genus of which the largest existing forms (Fig. 315) are
commonly about one third of an inch long, while far larger specimens

Fig. 315.

Alveolina Quoii :— a, a, septal plane, showing multiple pores.

Fm, 316.

are found in the Tertiary Limestones of Scinde. Here the spire turns
round a very elongated axis, so that the shell has almost the form of a
cylinder drawn to a point at each extremity. Its surface shows a series
of longitudinal lines which mark the principal septa; and the bands that
intervene between these are marked transversely by lines which show the
subdivision of the principal chambers into ' chamberlets.' The chamber-
lets of each row are con-
nected with each other,
as in the preceding type,
by a continuous gallery;
and they communicate
with those of the next
row by a series of multi-
ple pores in the principal
septa, such as constitute
the external orifices of
the last-formed series,
seen on its septal plane
at a, a.

466. The highest de-
velopment of that cycli-
cal plan of growth which
we have seen to be some-
times taken-on by Orbi-

pnlim is frmnrl in Or hi- > Simple disk of Orbitolites complanatus, laid open to show its
uumnt, lb louiiu ill ur UL- interior structure: —a, central chamber; 6, circumambient cham-
toliteS : a tVPC Which ber» surrounded by concentric zones of chamberlets connected
t i J * 9 with each other by annular and radiating passages.

long known as a very
abundant fossil in the

earlier Tertiaries of the Paris basin, has lately proved to be scarcely less
abundant in certain parts of the existing Ocean. The largest recent speci-
mens of it, sometimes attaining the size of a shilling, have hitherto been
obtained only from the coast of New Holland, the Fijian reefs, and various
other parts of the Polynesian Archipelago; but disks of comparatively mi-
nute size and simpler organization are to be found in almost all Foraminif-
eral sands and dredgings from the shores of the warmer regions of the
globe, being especially abundant in those of some of the Philippine Islands,
of the Eed Sea, of the Mediterranean, and especially of the iEgean. When

THE MICROSCOPE AND ITS REVELATIONS.

such disks are subjected to microscopic examination, they are found (if
uninjured by abrasion) to present the structure represented in Fig. 316;
where we see on the surface (by incident light) a number of rounded ele-
vations, arranged in concentric zones around a sort of nucleus (which has
been laid-open in the figure to show its internal structure); whilst at the
margin we observe a row of rounded projections, with a single aperture
or pore in each of the intervening depressions. In very thin disks the
structure may often be brought into view by mounting them in Canada
balsam and transmitting light through them; but in those which are too
opaque to be thus seen-through, it is sufficient to rub-down one of the
surfaces upon a stone, and then to mount the specimen in balsam. Each
of the superficial elevations will then be found to be the roof or cover of
an ovate cavity or ' chamberlet,' which communicates by means of a
lateral passage with the chamberlet on either side of it in the same ring;
so that each circular zone of chamberlets might be described as a continu-
ous annular passage, dilated into cavities at intervals. On the other hand,
each zone communicates with the zones that are internal and external to
it, by means of passages in a radiating direction; these passages run,
however, not from the chamberlets of the inner zone to those of the
outer, but from the connecting passages of the former to the chamberlets
of the latter; so that the chamberlets of each zone alternate in position
with those of the zones internal and external to it. The radial passages
from the outermost annulus make their way at once to the margin, where
they terminate, forming the ' pores ' which (as already mentioned) are to
be seen on its exterior. The central nucleus, when rendered sufficiently
transparent by the means just adverted-to, is found to consist of a ' pri-
mordial chamber' (a), usually somewhat pear-shaped, that communicates
by a narrow passage with a much larger 6 circumambient chamber' (#),
which nearly surrounds it, and which sends off a variable number of ra-
diating passages towards the chamberlets of the first zone, which forms a
complete ring around the circumambient chamber.1

467. The idea of the nature of the living occupant of these cavities
which might be suggested by the foregoing account of their arrangement,
is fully borne-out by the results of the examination of the sarcode-body,
which may be obtained by the maceration in dilute acid (so as to remove
the shelly investment) of specimens of Orbitolite that have been gathered
fresh and preserved in spirit. For this body is found to be composed
(Fig. 317) of a multitude of segments of sarcode, presenting not the least
trace of higher organization in any part, and connected together by
6 stolons' of the like substance. The 6 primordial' pear-shaped segment,
a, is seen to have budded-off its i circumambient' segment, b, by a narrow
footstalk or stolon; and this circumambient segment, after passing almost
entirely round the primordial, has budded-ofE three stolons, which swell
into new sub-segments from which the first ring is formed. Scarcely any
two specimens are precisely alike as to the mode in which the first ring

1 Although the above may be considered the typical form of the Orbitolite,
yet, in a very large proportion of specimens, the first few zones are not complete
circles, the early growth having taken place from one side only; and there is a
very beautiful variety in which this one-sidedness of increase imparts a distinctly
spiral character to the early growth, which soon, however, gives place to the
cyclical. — In the Orbitolites tenuissimus (Fig. 318) brought up from depths of
1,500 fathoms or more, the ' nucleus' is formed by three or four turns of a spiral
closely resembling that of a Cornuspira (§ 462), with an interruption at every
half -turn as in Spiroloculina; the growth afterwards becoming purely concentric.

FORAMINIFERA AND RADIOL ARIA,

originates from the 6 circumambient segments;' for sometimes a score or
more of radial passages extend themselves from every part of the margin
of the latter (and this, as corresponding with the plan of growth after-
wards followed) is probably the typical arrangement); whilst in other
cases (as in the example before us) the number of these primary offsets is
extremely small. Each zone is seen to consist of an assemblage of ovate
sub-segments, whose height (which could not be shown in the figure)
corresponds with the thickness of

the disk ; these sub-segments, FlG- 317-

which are all exactly similar and
equal to one another, are connec-
ted by annular stolons; and each
zone is connected with that on its
exterior by radial extensions of
those stolons passing-off between
the sub-segments.

468. The radial extensions of
the outermost zone issue-forth as
pseudopodia from the marginal
pores, searching-for and drawing-
in alimentary materials in the
mannner formerly described (§
397); the whole of the soft body,
which has no communication
whatever with the exterior save
through these marginal pores, be-
ing nourished by the transmission
of the products of digestion from
zone to zone, through similar
bands of protoplasmic substance.

In all cases in which the growth ^Z^Z^?™8 '
of the disk takes place with nor-
mal regularity, it is probable that a complete circular zone is added
at once. Thus we find this simple type of organization giving origin
to fabrics of by no means microscopic dimensions, in which, ^ how-
ever, there is no other differentiation of parts than that concerned in the
formation of the shell; every segment and every stolon (with the exception
of the two forming the ' nucleus') being, so far as can be ascertained, a
precise repetition of every other, and the segments of the nucleus differ-
ing from the rest in nothing else than their form. The equality of the
endowments of the segments is shown by the fact — of which accident has
repeatedly furnished proof — that a small portion of a disk, entirely sepa-
rated from the remainder, will not only continue to live, but will so in-
crease as to form a new disk (Fig. 318); the want of the ' nucleus ' not
appearing to be of the slightest consequence, from the time that active
life is established in the outer zones.

469. One of the most curious features in the history of this type is its
capacity for developing itself into a form which, whilst fundamentally
the same as that previously described, is very much more complex.
In all the larger specimens of Orbitolite, we observe that the mar-
ginal pores, instead of constituting but a single row, form many rows
one above another, and besides this, the chamberlets of the two
surfaces, instead of being rounded or ovate in form, are usually oblong
and straight-sided, their long diameters lying in a radial direction,

Composite Animal of Simple type of Orbitclites
complanatus:—a, central mass of sarcode; 6, cir-
cumambient segment, giving off peduncles, in which
originate the concentric zones of sub-segments con-

THE MICROSCOPE AND ITS REVELATIONS.

like those of the cyclical type of Orliculina (Plate xv., fig. G). When a
vertical section is made through such a disk, it is found that these oblong
chambers constitute two supej-ficial layers, between which are interposed
columnar chambers of a rounded form; and these last are connected to-

FlG. 318.

Disk of Orbitolites tenuissimw> formed round fragment of previous disk.

gether by a complex series of passages, the arrangement of which will be
best understood from the examination of a part of the sarcode-body that
occupies them (Fig. 319). For the oblong superficial chambers are occu-
py pied by sub-segments of sarcode, c c, d d,
lying side by side, so as to form part of an
annulus, but each of them disconnected
from its neighbors, and communicating
only by a double footstalk with the two
annular * stolons/ a a', b V which obvious-
ly correspond with the single stolon of
* simple ' type (Fig. 317). These indirect-
ly connect together not merely all the
superficial chamberlets of each zone, but
also the columnar sub-segments of the
intermediate layer; for these columns (e
e, e! ef) terminate above and below in the
annular stolons, sometimes passing direct-
ly from one to the other, but sometimes
going out of their direct course to coalesce
with another column. The columns of
the successive zones (two sets of which arc
shown in the figure) communicate with
* ^p?^1?nof Animaiof Complex type cach other by threads of sarcode, in such

of Orbitolites complanatus:—a cr, b b\ j.i i. / • j.i • i j. \ i

the upper and lower rings of two con- a manner that (as m the simple type) each
^J^U^^M^ column is thus brought into connection

lower layer, connected with the annular With two Columns 01 the Zone next lllte-

&dSsub-^e» Z Xto e^Ter" "or, to which it alternates in position.

FORAMINIFERA AND RADIOLARIA.

Similar threads, passing off from the outermost zone, through the mul-
tiple ranges of marginal pores, would doubtless act as pseudopodia.

470. Now this plan of growth is so different from that previously
described, that there would at first seem ample ground for separating the
simple and the complex types as distinct species. But the test furnished
by the examination of a large number of $pecime?is, which ought never
to be passed-by when it can possibly be appealed to, furnishes these very
singular results : — 1st. That the two forms must be considered as speci-
fically identical ; since there is not only a gradational passage from one
to the other, but they are often combined in the same individual, the
inner and first-formed portion of a large disk frequently presenting the
simple type, whilst the outer and later-formed part has developed itself
upon the complex: — 2d. That although the last mentioned circumstance
would naturally suggest that the change from the one plan to another
may be simply a feature of advancing age, yet this cannot be the case ;
since, although the complex sometimes evolves itself even from the very
first (the ' nucleus/ though resembling that of the simple form, sending
out two or more tiers of radiating threads), more frequently the simple
prevails for an indefinite number of zones, and then changes itself in the
course of a few zones into the complex. — No department of Natural
History could furnish more striking instances than are afforded by the
different forms presented by the Foraminiferal types now described, of
the wide range of variation that may occur within the limits of one and
the same species ; and the Microscopist needs to be specially put on his
guard as to this point, in respect to the lower types of Animal as to those
of Vegetable life, since the determination of form seems to be far less
precise among such than it is in the higher types.

471. In what manner the reproduction of Orbitolites is accomplished,
we can as yet do little more than guess; but from appearances sometimes
presented by the sarcode-body, it seems reasonable to infer that gemmules,
corresponding with the zoospores of Protophytes (§ 244), are occasionally
formed by the breaking-up of the sarcode into globular masses; and that
these, escaping through the marginal pores, are sent forth to develop
themselves into new fabrics. Of the mode wherein that sexual operation
is performed, however, in which alone true Generation consists, nothing
whatever is known.

472. Arenacea. — In certain forms of the preceding family, and
especially in the genus Miliola, we not unfrequently find the shells
encrusted with particles of sand, which are imbedded in the proper shell-
substance. This incrustation, however, must be looked on as (so to
speak) accidental ; since we find shells that are in every other respect of
the same type, altogether free from it. A similar accidental incrustation
presents itself among certain i vitreous ' and perforate shells; but there,
too, it is on usually a basis of true shell, and the sandy incrustation is
often entirely absent. There is, however, a group of Foraminifera in
which the true shell is constantly and entirely replaced by a sandy enve-
lope, which is distinguished as a 'test;' the arenaceous particles being
held together only by a cement exuded by the animal. It is not a little
curious that the forms of these arenaceous ' tests' should represent those
of many different types among both the ' porcellanous' and the ' vitreous *
series; whilst yet they graduate into one another in such a manner, as to
indicate that all the members of this ' arenaceous' group are closely
related to each other, so as to form a series of their own. And it is
further remarkable, that while the Deep-sea dredgings recently carried

THE MICROSCOPE AND ITS REVELATIONS.

down to depths of from 1,000 to 2,500 fathoms, have brought up few
forms of either ' poreellanous ' or 6 vitreous ' Foraminifera that were not
previously known, they have added greatly to our knowledge of the
* arenaceous ' types, the number and variety of which far exceed all
previous conception. These have not yet been systematically described;
but the following notice of a few of the more remarkable, will give some
idea of the interest attaching to this portion of the new Fauna which has
been brought to light by Deep-sea exploration.

473. In the midst of the sandy mud which formed the bottom where
the warm area of the ' Globigerina-mud 5 ( § 480) abutted on that over
which a glacial stream flowed, there were found a number of little pellets,
varying in size from a large pin's head to that of a large pea, formed of
an aggregation of sand-grains, minute Foraminifers, etc., held together
by a tenacious protoplasmic substance. On tearing these open, the whole
interior was found to have the same composition; and no trace of any
structural arrangement could be discovered in their mass. Hence they
might be supposed to be mere accidental agglomerations, were it not for
their conformity to the ' monerozoic ' type previously described (§ 393);
for just as a simple 'moner,' by a differentiation of its homogeneous sar-
code, becomes an Amoeba, so would one of these uniform Mendings of
sand and sarcode, by a separation of its two components, — the sand form-
ing the investing 6 test/ and the sarcode occupying its interior, — become
the arenaceous Astrorhiza. This type, which abounds on the sea-bed in
certain localities, presents remarkable variations of form: being sometimes
globular, sometimes stellate, sometimes cervicorn. But the same general
arrangement prevails throughout; the cavity being occupied by a dark-
green sarcode, whilst the 'test' is composed of loosely aggregated sand-
grains not held together by any recognizable cement, and has no definite
orifice, so that the pseudopodia must issue from interstices between the
sand-grains, which spaces are probably occupied during life with living
protoplasm, that continues to hold together the sand-grains after death,
These are by no means microscopic forms; the ' stellate ' varieties ranging
to 0.3 or even 0.4 inch in diameter, and the ' cervicorn ' to nearly 0.5
inch in length.1

474. The purely Arenaceous Foraminifera are arranged by Mr. H. B.
Brady2 (by whom they have been specially studied) under two Families:
the first of which, Astrorhizida, includes with the preceding a number
of coarse sandy forms, usually of considerable size, and essentially
monothalamous, though sometimes imperfectly chambered by constric-
tions at intervals. Some of the more interesting examples of this family
will now be noticed; beginning with the Saccamina (Sars), which is a
remarkably regular type, composed of coarse sand-grains firmly cemented
together in a globular form, so as to form a wall nearly smooth on the
outer, though rough on the inner surface, with a projecting neck sur-
rounding a circular mouth (Fig. 319,*«, b, c,). This type, which occurs
in extraordinary abundance in certain localities (as the entrance of the
Christiania-f jord), is of peculiar interest from the fact that it has been
discovered in a fossil state by Mr. H. B. Brady, in a clay seam between
two layers of Carboniferous Limestone. Its size is that of very minute
seeds. — In striking contrast to the preceding is another single-chambered

1 See the description and figures of this type given by the Author in " Quart.
Journ. Microsc. Sci.." Vol. xvi (1876), p. 221.

2 See his " Notes "in 44 Quart Journ. of Microsc. Soc," N.S., Vol. xix. (1879), p.
20 ; and Vol. xxi. (1881), p. 31.

FOR A MIN1FER A AND RADIOL ARIA.

type, distinguished by the whiteness of its ' test/ to which the Author
has given the name of Pilulina, from its resemblance to a homoeopathic
'globule' (Fig. 319,* d, c). The form of this is a very regular sphere;
and its orifice, instead of being circular and surrounded by a neck, is a
slit or fissure with slightly raised lips, and having a somewhat S-shaped
curvature. It is by the structure of its 'test,' however, that it is espe-
cially distinguished; for this is composed of the finest ends of sponge-
spicules, very regularly 'laid' so as to form a kind of felt, through the
substance of which very fine sand-grains are dispersed. This 'felt' is
somewhat flexible, and its components do not seem to be united by any
kind of cement, as it is not affected by being boiled in strong nitric acid;
its tenacity, therefore, seems entirely due to the wonderful manner in
which the separate siliceous fibres are ' laid.' — It is not a little curious that

Arenaceous Foraminifera:— a, Saccamina spherica; 6, the same laid open; c, portion of the fcept
enlarged to show its component sand-grains:— a, Pilulina Jeffreysii: e, portion of the test enlarged,
showing the arrangement of the sponge-spicules.

these two forms should present themselves in the same dredging; and
that there should be no perceptible difference in the character of their
sarcode-bodies, which, as in the preceding case, have a dark-green hue. —
The Marsipetta elongata (Fig. 320, d), on the other hand, is somewhat
fusiform in shape, and has its two extremities elongated into tubes, with
a circular orifice at the end of each. The materials of the 'tests' differ
remarkably according to the nature of the bottom whereon they live.
When they come up with 'Globigerina mud,' in which sponge-spicules
abound, whilst sand-grains are scarce, they are almost entirely made up
of the former, which are ' laid ' in a sort of lattice-work, the interspaces
of which are filled up by fine sand-grains; but when they are brought up
from a bottom on which sand predominates, the larger part of the 'test'
is made up of sand-grains and minnte Foraminifera, with here and there
a sponge-spicule (Fig. 320, d, /). In each case, however, the tubular
extensions (one of which sometimes forms a sort of proboscis, e, nearly
equalling the body itself in length) are entirely made up of sponge-spic-

Fig. 319*

THE MICROSCOPE AND ITS REVELATIONS.

ules laid side by side with extraordinary regularity. — The genus Rhab-
dammina (Sars) resembles Saccamina in the structure of its ' test/ which
is composed of sand-grains very firmly cemented together; but the grains
are of smaller size, and they are so disposed as to present a smooth sur-
face internally, though the exterior is rough. What is most remark-
able about this, is the geometrical regularity of its form, which is typically
triradiate (Fig. 321, c), the rays diverging at equal angles from the
central cavity, and each being a tube (d) with an orifice at its extremity.
Not unfrequently, however, it is quadri-radiate, the rays diverging at
right angles; and occasionally a fifth ray presents itself, its radiation,
however, being on a different plane. The three rays are normally of equal
length; but one of them is sometimes shorter than the other two; and
when this is the case, the angle between the long rays increases at the
expense of the other two, so that the long rays lie more nearly in a straight
line. Sometimes the place of the third ray is indicated only by a litttle
knob: and then the two long rays have very nearly the same direction.

Fig. 320.

Arenaceous Foraminifera:— a, 6, upper and lower aspects of Halophragmium globigeriniforme;
c, Hormosina globulifera; d, Marsipella elongata; e, terminal portion, and /, middle portion of
the same, enlarged; g, Thurammina papillata; h, portion of its inner surface enlarged.

We are thus led to forms in which there is no vestige of a third ray, but
merely a single straight tube, with an orifice at each end; and the length
of this, which often exceeds half an inch, taken in connection with the
abundance in which it presents itself in dredgings in which the triradiate
forms are rare, seems to preclude the idea that these long single rods are
broken rays of the latter. — It is undoubtedly in this group that we are
to place the genus Haliphysema; which, from constructing its 6 test 9 en-
tirely of sponge-spicules, and even including these in its pseudopodial ex-
pansions, has been ranked as a Sponge, although observation of it in its
living state leaves no doubt whatever of its Rhizopodal character.1

1 See Saville Kent in "Ann. of Nat. Hist.." Ser. 5, Vol. ii. (1878); 1 rof. R.
Lankester in " Quart. Journ. Microsc. Sci.," Vol. xix. (1868), p. 476; and Prof.
Mobius's "Foraminifera von Mauritius."

FOR AMLNTFER A. AND RADIOL ARIA .

475. Lituolida. — The type of this family, which is named after it, is
a large, sandy, many-chambered fossil form occurring in the Chalk, to
which the name Lituola was given by Lamarck, from its resemblance in
shape to a crozier. A great variety of recent forms, mostly obtained by
deep-sea dredging, are now included in it; as bearing a more or less close
resemblance to it and to each other in their chambered structure, and in
the arrangement of the sand-grains of which their tests are formed. —
These grains are, for the most part, finer than those of which the tests
of the preceding family are constructed, and are set (so to speak) more
artistically; and a considerable quantity of a cement exuded by the ani-
mal is employed in uniting them. This is often mixed up with sandy
particles of extreme fineness, to form a sort of ' plaster 9 with which the
exterior of the test is smoothed off, so as to present quite a polished sur-
face.— It is remarkable that the cement contains a considerable quantity
of oxide of iron, which imparts a ferruginous hue to the 6 tests 9 in which
it is largely employed. The forms of the Lituoline 6 tests ' often simulate
in a very curious way those of the simpler types of the Vitreous series.

Fig. 321.

Arenaceous Foraminifera: — a, 6, Exterior and sectional views cf Reophax rudis; c, Rhabdarrt"
mina abyssorum ; <2, cross section of one of its arms; e, Reophax scorpiurus; f, Hormosina Car-
penteri.

Thus, the long, spirally coiled undivided sandy tube of Ammodiscus
is the isomorph of Spirillina (§ 479). In the genus Halophragmium
(Fig. 320 a, b), we have a singular imitation of the Globigerine type; and
in Thurammina papillata (Fig. 320, g) a not less remarkable imitation
of the Orbuline. This last is specially noteworthy for the admirable
manner in which its component sand-grains are set together; these being
small and very uniform in size; and being disposed in such a manner as
to present a smooth surface both inside and out (Fig. 320, h), whilst
there are at intervals nipple-shaped protuberances, in every one of which
there is a rounded orifice. A like perfection of finish is seen in the test
of Hormosina globulifera (Fig. 320, c), which is composed of a succession
of globular chambers rapidly increasing in size, each having a narrow
tubular neck with a rounded orifice, which is received into the next seg-
ment. In other species of the same genus, there is a nearer approach to
6

THE MICROSCOPE AND ITS REVELATIONS.

the ordinary nodosarine type, their tests being sometimes constructed
with the regularity characteristic of the shells of the true Nodosaria
(Plate xv., fig. 10); whilst in other cases the chambers are less regularly
disposed (Fig. 321, /), having rather the character of bead-like enlarge-
ments of a tube, whilst their walls show a less exact selection of material,
sponge-spicules being worked-in with the sand-grains, so as to give them
a hirsute aspect. A greater rudeness of structure shows itself in the
nodosarine forms of the genus Reophax; in which not only are the sand-
grains of the test very coarse, but small Foraminifera are often worked-
up with them (Fig. 321, e). A straight, many-chambered form of the
same genus (Fig. 321, a, i) is remarkable for the peculiar finish of the
neck of each segment; for whilst the test generally is composed of sand-
grains as loosely aggregated as those of which the test of Astrorliiza is
made up, the grains that form the neck are firmly united by ferruginous
cement, forming a very smooth wall to the tubular orifice.

Fig. 322.

Cyclammina cancellata: — showing at a, its external aspect; o, its internal structure; c, a por-
tion of its outer wall more highly magnified, showing the sand-grains of which U is built up, and
the passages excavated in its substance.

476. The highest development of the ' Arenaceous ' type at the pres-
ent time is found in the forms that imitate the very regular nautiloid
shells, both of the ' porcellaneous ' and the ' vitreous' series; and the
most remarkable of these is the Cyclammina cancellata (Fig. 322), which
has been brought up in considerable abundance from depths ranging
downwards to 1,900 fathoms, the largest examples being found within
700 fathoms. The test (Fig. 322, a) is composed of aggregated sand-
grains firmly cemented together and smoothed over externally with
' plaster/ in which large glistening sand-grains are sometimes set at regu-
lar intervals, as if for ornament. On laying open the spire, it is found to
be very regularly divided into chambers by partitions formed of cemented
sand-grains (b); a communication between those chambers being left by
a fissure at the inner margin of the spire, as in Operculina (Plate xvi.,
fig. 2). One of the most curious features in the structure of this type,
is the extension of the cavity of each chamber into passages excavated in
its thick external wall; each passage being surrounded by a very regular
arrangement of sand-grains, as shown at c. It not unfrequently happens

FORAMINIFERA AND RADIOL ARIA.

that the outer layer of the test is worn-away, and the ends of the passages
then show themselves as pores upon its surface; this appearance, how-
ever, is abnormal, the passages simply running from the chamber-cavity
into the thickness of its wall, and having (so long as this is complete) no
external opening. This ' labyrinthic y structure is of great interest, from
its relation not only to the similar structure of the large Fossil examples
of the same type, but also to that which is presented in other gigantic
Fossil arenaceous forms to be presently described.

477. Although some of the Nautiloid Lituolce are among the largest
of existing Foraminifera, having a diameter of 0.3 inch, they are mere
dwarfs in comparison with two gigantic Fossil forms, whose structure
has been elucidated by Mr. H. B. Brady and the Author.1 Geologists,

Fig. 323.

General view of the internal structure of Parkeria :— In the horizontal section, l\ F, P, l\ mark
the four thick layers; in the vertical sections, a marks the internal surface of a layer separated by
concentric fracture ; b, the appearance presented by a similar fracture passing through the radiat-
ing processes; c, the result of a tangential section passing through the cancellated substance of a
lamella; d, the appearance presented by the external surface of a lamella separated by a concen-
tric fracture which has passed through the radial processes; e, the aspect of a section taken in a
radial direction, so as to cross the solid lamellae and their intervening spaces; c\ c2, c3, c4, succes-
sive chambers of nucleus.

who have worked over the Greensand of Cambridgeshire have long been
familiar with solid spherical bodies which there present themselves not
unfrequently, varying in size from that of a pistol-bullet to that of a
small cricket-ball; and whilst some regarded them as Mineral concretions,
others were led by certain appearances presented by their surfaces, to
suppose them to be fossilized Sponges. A specimen having been fortu-
nately discovered, however, in which the original structure had remained
unconsolidated by mineral infiltration, it was submitted by Prof. Morris
to the Author, who was at once led by his examination of it to recognize
it as a member of the Arenaceous group of Foraminifera, to which he
gave the designation Parkeria. in compliment to his valued friend and
coadjutor, Mr. W. K. Parker. A section of the sphere taken through its
centre (Fig. 323) presents an aspect very much resembling that of an

1 See their 'Description of Parkeria and Loftusia,' in " Philosophical Trans-
actions," 1869, p. 721.

THE MICROSCOPE AND ITS REVELATIONS.

Orbitolite (§ 466), a series of chambeiiets being concentrically arranged
round a 6 nucleus'; and as the same appearance is presented, whatever be
the direction of the section, it becomes apparent that these chamberlets,
instead of being arranged in successive rings on a single plane, so as to
form a disk, are grouped in concentric spheres, each completely investing
that which preceded it in date of formation. The outer wall of each cham-
berlet is itself penetrated by extensions of the cavity into its substance,
as in the Cyclammina last described; and these passages are separated by
partitions very regularly built up of sand-grains, which also close-in their
extremities, as is shown in Fig. 324. The concentric spheres are occa-
sionally separated by walls of more
than ordinary thickness; and such a
wall is seen in Fig. 323 to close-in the
last formed series of chamberlets.
But these walls have the same ' laby-
rinthic ' structure as the thinner ones;
and an examination of numerous
specimens shows that they are not
formed at any regular intervals. The
' nucleus' is always composed of a
single series of chambers arranged
end to end, sometimes in a straighc

Fig. 324.

line, as in Fig. 323, c\ c*
times forming a spiral,

Portion of one of the lamellae of Parkeria,
showing the sand-grains of which it is built up,
and the passages extending into its subtance.

c , o , some-
and in one

instance returning upon itself. But
the outermost chamber enlarges, and
extends itself over the whole ' nu-
cleus/ very much as the 6 circumam-
bient' chamber of the Orbitolite extends itself round the primordial
chamber (§ 466); and radial prolongations given off from this in every
direction form the first investing sphere, round which the entire series
of concentric spheres are successively formed. Of the sand of which
this remarkable fabric is constructed, about 60 per cent consists of
phosphate of lime, and nearly the whole remainder of carbonate
of lime. — Another large Fossil arenaceous type, constructed upon the
same general plan, but growing spirally round an elongated axis after the
manner of Alveolina (Fig. 315), and attaining a length of three inches,
has been described by Mr. H. B. Brady (loo. ext.), under the name Lof-
tusia, after its discoverer, the late Mr. W. K. Loftus, who brought it
from the Turko-Persian frontier, where he found it imbedded in " a blue
marly limestone " probably of early Tertiary age.

478. There is nothing, it seems to the Author, more wonderful in
Nature, than the building-up of these elaborate and symmetrical struc-
tures by mere " jelly-specks,' presenting no trace whatever af that definite
' organization ' which we are accustomed to regard as necessary to the
manifestations of Conscious Life. Suppose a Human mason to be put
down by the side of a pile of stones of various shapes and sizes, and to be
told to build a dome of these, smooth on both surfaces, without using
more than the least possible quantity of a very tenacious but very costly
cement in holding the stones together. If he accomplished this well, he
would receive credit for great intelligence and skill. Yet this is exactly
what these little 6 jelly-specks ' do on a most minute scale; the 6 tests'
they construct, when highly magnified, bearing comparison with the most
skilful masonry of Man. From the name sandy bottom, one species picks

FOR A MINIFER A AND RADIOL ARIA.

up the coarser quartz-grains, unites them together with a ferruginous
cement secreted from its own substance, and thus constructs a flask-
shaped 'test' having a short neck and a single large orifice. Another
picks up the finer grains, and puts them together with the same cement
into perfectly spherical 'tests' of the most extraordinary finish, perfo-
rated with numerous small pores, disposed at pretty regular intervals. "
Another selects the minutest sand-grains and the terminal portions of
sponge-spicules, and works these up together — apparently with no cement
at all, but by the mere 'laying' of the spicules — into perfect white
spheres, like homoeopathic globules, each having a single fissured orifice.
And another, which makes a straight many-chambered 'test,' the conical
mouth of each chamber projecting into the cavity of the next, while
forming the Avails of its chambers of ordinary sand-grains rather loosely
held together, shapes the conical mouths of the successive chambers by
firmly cementing to each other the quartz-grains which border it. — To
give these actions the vague designation 'instinctive,' does not in the
least help us to account for them; since what we want is, to discover the
mechanism by which they are worked out; and it is most difficult to con-
ceive how so artificial a selection can be made by creatures so simple.

470. Vitrea. — Returning now to the Foraminifera which form true
shells by the calcification of the superficial layer of their sarcode-bodies,
we shall take a similar general survey of the vitreous series, whose shells
are perforated by multitudes of minute foramina (Fig. 314). Thus, Spi-
rillina has a minute, spirally convoluted, undivided tube, resembling that
of Cornuspira (Plate xv., fig. 1), but having its wall somewhat coarsely
perforated by numerous apertures for the admission of pseudopodia.
The 6 monothalamous ' forms of this growth mostly belong to the Family
Lagenida ; which also contains a series of transition-forms leading up
gradationally to the 6 polythalamous ' Nautiloid type. In Lagena (Plate
xv., fig. 9) the mouth is narrowed and prolonged into a tubular neck,
giving to the shell the form of a microscopic flask; this neck terminates
in an everted lip, which is marked with radiating furrows. — A mouth of
this kind is a distinctive character of a large group of many- chambered
shells, of which each single chamber bears a more or less close resemblance
to the simple Lagena, and of which, like it, the external surface generally
presents some kind of ornamentation, which may have the form either of
longitudinal ribs or of pointed tubercles. Thus the shell of Nodosaria
(fig. 10) is obviously made up of a succession of lageniform chambers, the
neck of each being received into the cavity of that which succeeds it;
whilst in Oristellaria (fig. 11) we have a similar succession of chambers,
presenting the characteristic radiate aperture, and often longitudinally
ribbed, disposed in a nautiloid spiral. Between Nodosaria and Oristel-
laria, moreover, there is such a gradational series of connecting forms, as
shows that no essential difference exists between these two types, which
must be combined into one genus, Nodosarina ; and it is a fact of no lit-
tle interest, that these varietal forms, of which many are to be met-with
on our own shores, but which are more abundant on those of the Medi-
terranean and especially of the Adriatic, can be traced backwards in
Geological time even as far as the New Red Sandstone period. — In
another genus, Polymorphina, we find the shell to be made up of lageni-
form chambers arranged in a double series, alternating with each other on
the two sides of a rectilinear axis (fig. 13); here, again, the forms of the
individual chambers, and the mode in which they are set one upon
another, vary in such a manner as to give rise to very marked differences

THE MICROSCOPE AND ITS REVELATIONS.

in the general configuration of the shell, which are indicated by the name
it bears.

480. Globigerinida. — Keturing once again to the simple 6 monothala-
mous ? condition, we have in Orbulina — a minute spherical shell that
presents itself in greater or less abundance in Deep-sea dredgings from
almost every region of the globe — a globular chamber with porous walls,
and a simple circular aperture that is frequently replaced by a number of
large pores scattered throughout the wall of the sphere. It is maintained
by some that Orbulina is really a detached generative segment of Globi-
gerina, with which it is generally found associated. — The shell of Globi-
gerina consists of an assemblage of nearly spherical chambers (Fig. 325),
having coarsely porous walls, and cohering externally into a more or less
regular turbinoid spire, each turn of which consists of four chambers
progressively increasing in size. These chambers, whose total number
seldom exceeds sixteen, do not communicate directly with each other,
but open separately into a common 6 vestibule ' which occupies the centre
of the under side of the spire. — This type has recently attracted great
attention, from the extraordinary abundance in which it occurs at great
depths over large areas of the Ocean-bottom. Thus its minute shells

Fig. 325.

Olobigerina bulloides, as seen in three positions.

have been found to constitute no less than 97 per cent of the 'ooze'
brought up from depths of from 1260 to 2000 fathoms in the middle of
the northern parts of the Atlantic Ocean. The surface-layer of this ooze,
the thickness of which is entirely unknown, consists of Globigerinae
whose chambers are occupied by the sarcodic bodies of the animals, and
which may therefore be presumed to be living on the bottom; whilst its
deeper layers are almost entirely composed of dead and disintegrating
shells of the same type. The younger shells, consisting of from eight to
twelve chambers, are thin and smooth; but the older shells are thicker,
their surface is raised into ridges that form a hexagonal areolation
round the pores (Fig. 326, a); and this thickening is shown by examina-
tion of thin sections of the shell (b) to be produced by an exogenous de-
posit around the original chamber- wall (corresponding with the ' inter-
mediate skeleton 9 of the more complex types), which sometimes contains
little flask-shaped cavities filled with sarcode — as was first pointed-out by
Dr. Wallich. But the sweeping of the upper waters of the Ocean by the
' tow-net ' (§ 217), which was systematically carried-on during the voyage
of the 6 Challenger/ brought into prominence the fact that these waters
in all but the coldest seas are inhabited by floating Globigerinae, whose
shells are beset with multitudes of delicate calcareous spines, which ex-
tend themselves radially from the angles at which the ridges meet, to a
length equal to four or five times the diameter of the shell (Fig. 327).
Among the basis of these spines, the sarcodic substance of the body

FORAMIN1FERA AND RADIOLARIA.

exudes through the pores of the shell, forming a flocculent fringe around
it; and this extends itself on each of the spines, creeping up one side to
its extremity, and passing down the other, with the peculiar flowing
movement already described (§ 395). The whole of this sarcodic ex-
tension is at once retracted if the cell which holds the Globigerina receives
a sudden shock, or a drop of any irritating fluid is added to the water it
contains. — It is maintained by Sir Wyville Thomson that the bottom-de-
posit is formed by the continual ' raining-down 9 of the Globigerinae of
the upper waters, which (he affirms) only live at or near the surface, and
which, when they die, lose their spines and subside. But it has been
shown by the careful comparison made by Mr. H. B. Brady between the
surface-gatherings and the bottom-deposits of the same areas, that the
two are often so marked, as to forbid the idea that the latter are solely
derived from the former.1 For not only are there several specific types

Fig. 3:6.

Globigeria a, f row Atlantic ooze showing thickening of shell by exogenous deposit: — a, entire
*?lfeU( showing ^./e^laibJ iidges of surface; b, portion of shell more highly magnified, showing ori-
fi\ ss of tubuli a^d large cavities filled with sarcode; c, section of shell showing exogenous deposit
upon original uhainber-wall, which is raised into ridges with tubuli between them, and includes
sarcodic cavities.

found in each, which do not present themselves in the other, but, as a
rule, the shells of the types common to both are larger and thicker in
the latter than they are in the former. This evidence strongly supports
the conclusion originally drawn by the Author from his own examination
of the Globigerina-ooze, that the shells forming its surface-layer must
live on the bottom, being incapable of floating in consequence of their
weight; and that if they have passed the earlier part of their lives in the
upper waters, they drop down as soon as the calcareous deposit continu-
ally exuding from the body of each animal, instead of being employed in
the formation of new chambers, is applied to the thickening of those

" Quart. Journ. Microsc. Sci., " Vol. xix. (1879), p. 295.

THE MICROSCOPE AND ITS REVELATIONS.

previously formed. — That many types of Foraminifera pass their whole
lives at depths of at least 2000 fathoms, is proved, in regard to those
forming Calcareous shells, by their attachment to stones, corals, etc. ; and
in the case of the Arenaceous types, by the fact that they can only pro-
cure on the bottom the sand of which their 6 tests ' are made up.

481. A very remarkable type has
recently been discovered, adherent
to shells and corals brought from
tropical seas, to which the name
Carpenteria has been given; this
may be regarded as a highly devel-
oped form of Globigerina, its first-
formed portion having all the es-
sential characters of that genus.
It grows attached by the apex of
its spire; and its later chambers
increase rapidly in size, and are
piled on the earlier in such a man-
ner as to form a depressed cone
with an irregular spreading base.
The essential character of Globi-
gerina— the separate orifice of each
of its chambers — is here retained
with a curious modification; for the
central vestibule, into which they
all open, forms a sort of vent whose
orifice is at the apex of the cone,

Globigerina, as captured by tow-net, floating ar\d is sometimes prolonged into a

at or near surface. "tube that proceeds from it; and the

external wall of this cone is so mark-
ed-out by septal bands, that it comes to bear a strong resemblance to a mi-
nute Balanus (acorn-shell), for which this type was at first mistaken.
The principal chambers are partly divided into chamberlets by incomplete
partitions, as we shall find them to be in Eozoon (§ 494). The presence
of sponge-spicules in large quantity in the chambers of many of the best-
preserved examples of this type, was for some time a source of perplexity;
but this is now explained by the interesting observations made by Prof.
Mobius1 on a large branching and spreading form of Carpenteria, which
he recently met-with on a reef near Mauritius, and to which he has given
the name of C. raphidodendrou. For the pseudopodia of this Rhizopod
have the habit, like those of Haliphysema (§ 474), of taking into them-
selves sponge-spicules, which they draw into the chambers, so that they
become incorporated with the sarcode-body.

482. A less aberrant modification of the Globigerine type, however,
is presented in the two great series which may be designated (after the
leading forms in each) as the Textularian and the Rotalian. For not-
withstanding the marked difference in their respective plans of growth,
the characters of the individual chambers are the same; their walls being
coarsely-porous, and their apertures being oval, semi-oval, or crescent-
shaped, sometimes merely fissured. In Textularia (Plate xv., fig. 14)
the chambers are arranged biserially along a straight axis, the position
of those on the two sides of it being alternate, and each chamber opening

See his " Foraminifera von Mauritius," Plates v., vi.

FORAMINIFERA AND RADIOLARIA.

into those above and below it on the opposite side by a narrow fissure; as
is well shown in such ' internal casts ' (Pig. 328, a) as exhibit the forms
and connections of the segments of sarcode by which the chambers were
occupied during life. In the genus Bulimina the chambers are so
arranged as to form a spire like that of a Bulimus, and the aperture is a
curved fissure whose direction is nearly transverse to that of the fissure of
Textularia; but in this, as in the preceding type, there is an extraordi-
nary variety in the disposition of the chambers. In both, moreover, the
shell is often covered by a sandy incrustation, so that its perforations are
completely hidden, and can only be made visible by the removal of the
adherent crust. And so many cases are now known, in which the shell
of Textularinm is entirely replaced by a sandy test, that some Systematists
prefer to range this group among the Arenacea.

483. In the Rotalian series, the chambers are disposed in a turbinoid
spire, opening one into another by an aperture situated on the lower and
inner side of the spire, as shown in Plate xv., fig. 18; the forms and con-
nections of the segments of their sarcode-bodies being shown in such
6 internal casts ' as are represented in Fig. 328, B. One of the lowest
and simplest forms of this type is that very common one now distin-

Fig. 328. Fig. 329.

Internal siliceous Casts, representing the forms of Tinoporus baculatus.

the segments of the animals, of a, Textularia, b, Rotalia.

guished as Discorhina, of which a characteristic example is represented
in Plate xv., fig. 15. The early form of Planorhulina is a rotaline spire,
very much resembling that of Discorbina; but this afterwards gives place
to a cyclical plan of growth (fig. 17); and in those most developed
forms of this type which occur in warmer seas, the earlier chambers are
completely overgrown by the latter, which are often piled-up in an
irregular 'acervuline' manner, spreading over the surfaces of shells, or
clustering round the stems of zoophytes. — In the genus Tinoporus there
is a more regular growth of this kind, the chambers being piled succes-
sively on the two sides of the original median plane, and those of adja-
cent piles communicating with each other obliquely (like those of Textu-
laria) by large apertures, whilst they communicate with those directly
above and below by the ordinary pores of the shell. The simple or
smooth form of this genus presents great diversities of shape, with great
constancy, in its internal structure; being sometimes spherical, some-
times resembling a minute sugar-loaf, and sometimes being irregularly
flattened-out. A peculiar form of this type (Pig. 329), in which the

THE MICROSCOPE AND ITS REVELATIONS.

walls of the piles are thickened at their meeting-angles into solid columns
that appear on the surface as tubercles, and are sometimes prolonged
into spinous outgrowths that radiate from the central mass, is of very
common occurrence in shore-sands and shallow-water dredgings on some
parts of the Australian coast and among the Polynesian islands. — To the
simple form of this genus we are probably to refer a large part of the
fossils of the Cretaceous and early Tertiary period, that have been de-
scribed under the name Orbitolina, some of which attain a very large size.
Globular Orbitolince, which appear to have been artificially perforated
and strung as beads, are not unfrequently found associated with the
"flint-implements" of gravel-beds. — Another very curious modification
of the Kotaline type is presented by Polytrema, which so much resem-
bles a Zoophyte as to have been taken for a minute Millepore; but which
is made up of an aggregation of ' globigerine 9 chambers communicating
with each other like those of Tinoporus, and differs from that genus
in nothing else than its erect and usually branching manner of growth,
and the freer communication between its chambers. This, again, is of
special interest in relation to Eozoon; showing that an indefinite zoo-
phytic mode of growth is perfectly compatible with truly Foraminiferal
structure.

484. In Rotalia, properly so called, we find a marked advance towards
the highest type of Foraminiferal structure; the partitions that divide
the chambers being composed of two laminae, and spaces being left
between them which give passage to a system of canals, whose general
distribution is shown in Fig. 330. The proper walls of the chambers,
moreover, are thickened by iu\ extraneous deposit or 6 intermediate skel-
eton/ which sometimes forms radiating outgrowths; but this peculiar-
ity of conformation is carried much further in the genus Calcarina,
which has been so designated from its resemblance to a spur-rowel
(Plate xvi., fig. 3). The solid club-shaped appendages with which the
shell is provided, entirely belonging to the ' intermediate skeleton 9 b,
which is quite independent of the chambered structure a; and this body
is nourished by a set of canals containing prolongations of the sarcode-
body, which not only furrow the surface of these appendages, but are
seen to traverse their interior when this is laid open by section, as
shown at c. In no other recent Foraminifer does the 6 canal system'
attain a like development; and its distribution in this minute shell,
which has been made out by careful microscopic study, affords a val-
uable clue to its meaning in the gigantic fossii organism Eozoon Cana-
dense (§ 494). The resemblance which Calcarina bears to the radiate
forms of Tinoporus (Fig. 329), which are often found with them in the
same dredgings, is frequently extremely striking; and in their early
growth the two can scarcely be distinguished, since both commence in a
'rotaline' spire with radiating appendages; but whilst the successive
chambers of Calcarina continue to be added on the same plane, those of
Tinoporus are heaped-up in less regular piles.

485. Certain beds of Carboniferous Limestone in Russia are entirely
made up, like the more modern iiummulitic Limestone (§ 489), of an
aggregation of the remains of a peculiar type of Foraminifera, to which
the name Fusulina (indicative of its fusiform or spindle-shape) has been
given (Fig. 331). In general aspect and plan of growth it so much re-
sembles Alveolina, that its relationship to that type would scarcely be
questioned by the superficial observer. But when its mouth is examined,
it is found to consist of a single slit in the middle of the lip; and the

FORAMINIFERA AND RADIOL ARIA.

consist of a regular

interior, instead of being minutely divided into cnamberlets, is found to
series of simple chambers; while from each of these

the 'alar
but which,
the

proceeds a pair of elongated extensions, which correspond to
prolongations' of other spirally growing Foraminifera (§ 48G), b

Fia. 330.

Section of Rotalia Schroetteriana near its
base and parallel to it; showing c, a, the radiat-
ing interseptal canals; 6, their internal bifurca-
tions ; c, a transverse branch ; d, tubuiar wall of
the chambers.

instead of wrapping round the preceding whorls, are prolonged
direction of the axis of the spire,
those of each whorl projecting be-
yond those of the preceding, so that
the shell is elongated with every in-
crease in its diameter. Thus it ap-
pears that in its general plan of
growth, Fusulina bears much the
same relation to a symmetrical Eo-
taline or Nummuline shell, that
Alveolina bears to Orbiculina ; and
this view of its affinities is fully con-
firmed by the Author's microscopic
examination of the structure of its
shell. For although the Fusulina-
Limestone of Russia has undergone
a degree of metamorphism, which
so far obscures the tubularity of its
component shells, as to prevent him
from confidently affirming it, yet
the appearances he could distin-
guish were decidedly in its favor.
And having since received speci-
mens from the Upper Coal Mea-
sures of Iowa, U. S., which are in a much more perfect state of pre-
servation, he is able to state with certainty, not only that Fusulina is
tubular, but that its tubulation is of the large coarse nature that marks
its affinity rather to the Rotaline than to the Nummuline series. — This
type is of peculiar interest, as having long been regarded as the oldest
form of Foraminifera which was known to have occurred in sufficient
abundance to form Eocks by the aggregation of its individuals. It will
be presently shown, however, that in point both of antiquity and of
importance, it is far surpassed by another (§ 493).

486. Nummulinida. — All the most elaborately constructed, and the
greater part of the largest, of the ' vitreous ' Foraminifera belong to the
group of which the well-known Nummulite may be taken as the repre-
sentative. Various plans of growth prevail in the family; but its distin-
guishing characters consist in the completeness of the wall that surrounds
each segment of the body (the septa being double instead of single as
elsewhere), the density and fine porosity of the shell-substance, and the
presence of an f intermediate skeleton/ with a ' canal-system ' for its
nutrition. It is true that these characters are also exhibited in the high-
est of the Eotaline series (§ 484), whilst they are deficient in the genus
Amphistegina, which connects the Nummuline series with the Eotaline;
but the occurrence of such modifications in their border-forms is common
to other truly Natural groups. With the exception of Amphistegina, all
the genera of this family are symmetrical in form; the spire being nauti-
loid in such as follow that plan of growth, whilst in those which follow
the cyclical plan there is a constant equality on the two sides of the
median plane: but in Amphistegina there is a reversion to the rotalian

THE MICROSCOPE AND ITS REVELATIONS.

type in tlie turbinoid form of its spire, as in the characters already speci-
fied, although its general conformity to the Nummuline type is such as
to leave no reasonable doubt as to its title to be placed in this family.
Notwithstanding the want of symmetry of its spire, its accords with
Operculi?ia and Nummulina in having its chambers extended by 'alar
prolongations' over each surface of the previous whorl; but on the under
side these prolongations are almost entirely cut off from the principal
chambers, and are so displaced as apparently to alternate with them in
position; so that M. D'Orbigny, supposing them to constitute a distinct
series of chambers, described its plan of growth as a biserial spiral, and
made this the character of a separate Order.1

487. The existing Nummulinida are almost entirely restricted to tropi-
cal climates; but a beautiful little form, the Polystomella crispa (Plate xv.,
fig. 1G), the representative of a genus that presents the most regular and
complete development of the 6 canal system' anywhere to be met with, is

Fig. 331.

Section of Fusulina-IAmestone.

common on our own coasts. The peculiar surface-marking shown m the
figure consists in a strongly marked ridge and furrow plication of the
shelly wall of each segment along its posterior margin; the furrows being
sometimes so deep as to resemble fissures opening into the cavity of the
chamber beneath. No such openings, however, exist; the only com-
munication which the sarcode-body of any segment has with the exterior,
being either through the fine tubuli of its shelly walls, or through the
row of pores that are seen in front view along the inner margin of the
septal plane, collectively representing a fissured aperture divided by
minute bridges of shell. The meaning the plication of the shelly wall
comes to be understood, when we examine the conformation of the seg-
ments of the sarcode-body, which may be seen in the common Polysto-
mella crispa by dissolving away the shell of fresh specimens by the action
of dilute acid, but which may be better studied in such internal casts (Fig.
332) of the sarcode-body and canal-system of the large P. craticulata of the
Australian coast, as may sometimes be obtained by the same means from

1 For an account of this curious modification of the Nummuline plan of
growth, the real nature of which was first elucidated by Messrs. Parker and
Rupert Jones, see the Author's ' Introduction to the Study of the Foraminifera '
(published by the Ray Society).

FORAMINIFERA. AND RADIOL ARIA.

dead shells which have undergone infiltration with ferruginous silicates.1
Here wTe see that the segments of the sarcode-body are smooth along
their anterior edge b, il, but that along their posterior edge, a, they are
prolonged backwards into a set of 'retral processes;' and these processes
lie under the ridges of the shell, whilst the shelly wall dips down into tho
spaces between them, so as to form the furrows seen on the surface.
The connections of the segments by stolons, c, c\ passing through the
pores at the inner margin of each septum, are also admirably displayed in
such ' casts/ But what they serve most beautifully to demonstrate is tho
canal-system, of which the distribution is here most remarkably complete
and symmetrical. At d, d,1 d,* are seen three turns of a spiral canal
which passes along one end of all the segments of the like number of
convolutions, whilst a corresponding canal is found on the side which in
the figure is undermost; these two spires are connected by a set of
meridional canals, e, e\ e2, which pass down between the two layers of
the septa that divide the segments; whilst from each of these there
passes off towards the surface a set of pairs of diverging branches,/,/1,

Internal Cast of Polystomella craticulata : — a, retral processes, proceeding from the posterior
margin of one of the segments; b, 6*, smooth anterior margin of the same segment; c, ci, stolons
connecting successive segments, and uniting themselves with the diverging branches of the
meridional canals; d, d\ d2, three turns of one of the spiral canals; e, e1, e2, three of the meridi-
onal canals; /, />, p, their diverging branches.

/2, which open upon the surface along the two sides of each septal band,
the external openings of those on its anterior margin being in the furrows
between the retral processes of the next segment. These canals appear
to be occupied in the living state by prolongations of the sarcode-body;
and the diverging branches of those of each convolution unite themselves,
when this is inclosed by another convolution, with the stolon-processes

1 It was by Prof. Ehrenberg that the existence of such ' casts ' in the Green
Sands of various Geological periods (from the Silurian to the Tertiary) was first
pointed out, in his Memoir 4 Ueber den Griinsand und seine Einlauterung des
organischen Lebens,' in ' 4 Abhandlungen den Konigl. Akad. der Wissenschaften,"
Berlin, 1855. It was soon afterwards shown by the late Prof. Bailey (" Quart.
Journ. Microsc. Sci.," Vol. v., 1857, p. 83) that the like infiltration occasionally
takes place in recent Foraminif era, enabling similar ' casts ' to be obtained from
them by the solution of their shells in dilute acid; the Author, as well as Messrs.
Parker and Rupert Jones, soon afterwards obtained most beautiful and complete
internal casts from recent Foraminif era brought from various localities; and a
large collection of green sands yielding similar casts was made in the ' Chal-
lenger.'

Fig. 332.

THE MICROSCOPE AND ITS REVELATIONS.

connecting the successive segments of the latter, as seen at c1. There
can be little doubt that this remarkable development of the canal-system
has reference to the unusual amount of shell-substance which is deposited
as an 6 intermediate skeleton ' upon the layer that forms the proper walls
of the chambers, and which fills up with a solid 'boss' what would other-
wise be the depression at the umbilicus of the spire. The substance of
this 'boss' is traversed by a set of straight canals, which pass directly
from the spiral canal beneath, towards the external surface, where
they open in little pits, as is shown in PI. xv., fig. 16; the umbilical boss
in P. crispa, however, being much smaller in proportion than it is in P.
craticulata. There is a group of Foraminifera to which the term
Nonionina is properly applicable, that is probably to be considered as a
sub-genus of Polystomella; agreeing with it in its general conformation,
and especially in the distribution of its canal system; but differing in its
aperture, which is here a single fissure at the inner edge of the septal
plane (Plate xv., fig. 19), and in the absence of the 'retral processes' of
the segments of the sarcode-body, the external walls of the chambers
being smooth. This form constitutes a transition to the ordinary
Nummuline type, of which Polystomella is a more aberrant modification.

488. The Nummuline type is most characteristically represented at
the present time by the genus Operculina; which is so intimately united
to the true Nummulite by intermediate forms, that it is not easy to sep-
arate the two, notwithstanding that their typical examples are widely
dissimilar. The former genus (Plate xvi., fig. 2) is represented on our
own coast by very small and feeble forms; but it attains a much higher
development in Tropical seas, where its diameter sometimes reaches
l-4th of an inch. The shell is a flattened nautiloid spire, the breadth of
whose earlier convolutions increases in a regular progression, but of
which the last convolution (in full-grown specimens) usually flattens
itself out like that of Peneroplis, so as to be very much broader than the
preceding. The external walls of the chambers, arching over the spaces
between the septa, are seen at b, b; and these are bounded at the outer
edge of each convolution by a peculiar bandtf, termed the 6 marginal cord.'
This cord, instead of being perforated by minute tubuli like those which
pass from the inner to the outer surface of the chamber-walls without
division or inosculation (Fig. 335), is traversed by a system of compara-
tively large inosculating passages seen in cross section at af; and these
form part of the canal-system to be presently described. The principal
cavities of the chambers are seen at c, c; while the 6 alar prolongations '
of those cavities over the surface of the preceding whorl are shown at
c\ c'. The chambers are separated by the septa, d, d, d, formed of two
laminae of shell, one belonging to each chamber, and having spaces
between them in which lie the ' interseptal canals,' whose general distri-
bution is seen in the septa marked e, e, and whose smaller branches are
seen irregularly divided in the septa d\ d', whilst in the septum d" one
of the principal trunks is laid open through its whole length. At the
approach of each septum to the marginal cord of the preceding, is seen
the narrow fissure which constitutes the principal aperture of communica-
tion between the chambers; in most of the septa, however, there are
also some isolated pores (to which the lines point that radiate from e, e)
varying both in number and position. The interseptal canals of each
septum take their departure at its inner extremity from a pair of spiral
canals, of which one passes along each side of the marginal cord; and
they communicate at their outer extremity with the canal-system of the

FORAMINIFERA AND RADIOL ARIA,

PLATE XVI.

Fig. I.

VARIOUS FORMS OF FORAMINIFERA (Original).

Fig. 1. Cycloclypeus, showing external surface, and vertical and horizontal sections.

2. Operculina, laid open to show its internal structure : a, marginal core, seen in cross section
at a' ; 6, 6, external walls of the chambers; c, c, cavities of the chambers; & c\ their alar prolonga-
tions; d, d, septa, divided at d' d' and at d", so as to lay open the interseptal canals, the general
distribution of which is seen in the septa e, e ; the lines radiating from e, e, point to the secondary
pores ; g, g, non-tubular columns.

3. Calcarina, laid open to show its internal structure :— a, chambered portion ; b, intermediate
skeleton ; c, one of the radiating prolongations proceeding from it, with extensions of the canal-
system.

THE MICROSCOPE AND ITS REVELATIONS.

6 marginal cord/ as shown in Fig. 337. The external walls of the
chambers arc composed of the same finely-tubular shell-substance that
forms them in the Nummulite; but, as in that genus, not only are the
septa themselves composed of vitreous non-tubular substance, but that
which lies over them, continuing them to the surface of the shell, has
the same character; showing itself externally in the form sometimes of
continuous ridges, sometimes of rows of tubercles, which mark the posi-
tion of the septa beneath. These non-tubular plates or columns are
often traversed by branches of the canal-system, as seen at g, q. Similar
columns of non -tubular substance, of which the summits show them-
selves as tubercles on the surface, are not unfrequently seen between the
septal bands, giving a variation to the surface-marking, which, taken in
conjunction with variations in general conformation, might be fairly held
sufficient to characterize distinct species, were it not that on a com-
parison of a great number of specimens, these variations are found to be
so gradational, that no distinct line of demarcation can be drawn
between the individuals which present them.

Fig. 333.

a, piece of Nummulitic Limestone from Pyrenees, showing Nummulites laid open by fracture
through median plane; b, vertical section of Nummulite; c, Orbitoides.

489. The Genus Nummulina, of which the fossil forms are commonly
known as Nummulites, though represented at the present time by small
and comparatively infrequent examples, was formerly developed to avast
extent; the Nummulitic Limestone chiefly made-up by the aggregation
of its remains (the material of which the Pryamids are built) forming a
band, often 1,800 miles in breadth and frequently of enormous thick-
ness, that may be traced from the Atlantic shores of Europe and Africa,
through Western Asia to Northern India and China, and likewise over
vast areas of North America (Pig. 333). The diameter of a large pro-
portion of fossil Nummulites ranges between half an inch and an inch;
but there are some whose diameter does not exceed l-16th of an inch,
whilst others attain the gigantic diameter of inches. Their typical
form is that of a double-convex lens; but sometimes it much more nearly
approaches the globular shape, whilst in other cases it is very much flat-
tened; and great differences exist in this respect among individuals of
what must be accounted one and the same species. Although there are
some Nummulites which closely approximate Operculince in their mode
of growth, yet the typical forms of this genus present certain well-marked
distinctive peculiarities. Each convolution is so completely invested by
that which succeeds it, and the external wall or spiral lamina of the new
convolution is so completely separated from that of the convolution it

FORAMINIFERA AND RADIOL ARIA.

incloses by the 'alar prolongations ' of its own chambers (the peculiar
arrangement of which will be presently described), that the spire is
scarcely if at all visible on the external surface. It is brought into view,
however, by splitting the Nummulite through the median plane, which
may often be accomplished simply by striking it on one edge with a
hammer, the opposite edge being placed on a firm support; or, if this
method should not succeed, by heating it in the flame of a spirit-lamp,
and then throwing it into cold water or striking it edgeways. Nummu-
lites usually show many more turns, and a more gradual rate of increase
in the breadth of the spire, than Foraminifera generally; this will be
apparent from an examination of the vertical section shown in Fig. 334,
which is taken from one of the commonest and most characteristic fossil
examples of the genus, and which shows no fewer than ten convolutions
in a fragment that does not nearly extend to the centre of the spire.
This section also shows the complete inclosure of the older convolutions
by the newer, and the interposition of the alar prolongations of the
chambers between the suc-
cessive layers of the spiral FlG* 334-
lamina. These prolonga-
tions are variously arranged
in different examples of the
genus: thus in some, as JV".
distansy they keep their own
separate course, all tending
radially towards the centre;
in others, as N. l<%vigatay
their partitions inosculate
with each other, so as to di-
vide the Space intervening Vertical section of portion of Nummulina laevigata;—
between each lavcr and thea'mar£in of external whorl; 6, one of the outer row of
j • j • -i , chambers; c, c, whorl invested by a; d, one of the chambers
next into an irregular net- of the fourth whorl from the margin; e, e'. marginal por-
wnrlr nrPQPn finer in vprfi'pql ti^ns of the inclosed whorls; /, investing portions of outer

woik, piesennng in vertical whorl. ^ ^ spaces left between the inV(fsting portion of

Section the appearance Shown successive whorls; h, h, sections of the partitions dividing

in Fig. 334; whilst in N.gar- these'

ansensis they are broken up into a number of chamberlets, having little
or no direct communication with each other.

490. Notwithstanding that the inner chambers are thus so deeply
buried in the mass of investing whorls, yet there is evidence that the
segments of sarcode which they contained were not cut off from commu-
nication with the exterior, but that they may have retained their vitality
to the last. The shell itself is almost everywhere minutely porous,
being penetrated by parallel tubuli which pass directly from one surface
to the other. These tubes are shown, as divided lengthways by a ver-
tical section, in Fig. 335, a, a ; whilst the appearance they present when
cut across in a horizontal section is shown in Fig. 336, the transparent
shell-substance a, a, a, being closely dotted with minute punctations
which mark their orifices. In that portion of the shell, however, which
forms the margin of each whorl (Fig. 335, b, b), the tubes are larger,
and diverge from each other at greater intervals; and it is shown by
'horizontal sections that they communicate freely with each other later-
ally, so as to form a network such as is seen at b, b, Fig. 337. At cer-
tain other points, d, d, d (Fig. 335), the shell-substance is not perfo-
rated by tubes, but is peculiarly dense in its texture, forming solid pil-
lars, which seem to strengthen the other parts; and in Nummulites whose
7

THE MICROSCOPE AND ITS REVELATIONS.

surfaces have been much exposed to attrition, ifc commonly happens that
the pillars of the superficial layer, being harder than the ordinary shell-*
substance, and being consequently less worn down, are left as promi-
nences, the presence of which has often been accounted (but erroneously)
as a specific character. The successive chambers of the same whorl
communicate with each other by a passage left between the inner edge"

of the partition that sepa-
Fig. 335. rates them, and the 'mar-

ginal cord ' of the preced-
ing whorl; this passage is
sometimes a single large
broad aperture, but is more
commonly formed by the
more or less complete co-
alescence of several separ-
ate perforations, as is seen
in Fig. 334, b. There is
also, as in Operculina, a
variable number of isolated

Portion of a thin Section of Nummulina laevigata, taken in Por^S in most of the Septa,

the direction of the preceding, highly magnified to show the forming a Secondary means

minute structure of the shell:— a, a. portions of the ordinary « & r ,

shell-substance traversed by parallel tubuli; 6, 6, portions 01 Communication between

forming the marginal cord, traversed by diverging and larger /->ViQrn>iorQ TIip f!a-

tubuli; c, one of the chambers laid open; d, d. d, pillars of inY ^n^mu^fe- — 1 Ilt} yd

solid substance not perforated by tubuli. nal-System of Nummulina

seems to be distributed
upon essentially the same plan as in Operculina; its passages, however, are
usually more or less obscured by fossilizing material. A careful exami-
nation will generally disclose traces of them in the middle of the parti-

Fig. 336.

Fig. 337.

Portion of Horizontal Section of
Nummulite, showing the structure of
the walls and of the septa of the
chambers:— a, a, a, portion of the wall
covering three chambers, the puncta-
tions of which are the orifices of tubuli ;
fe, b, septa between these chambers,
containing canals which send out late-
ral branches, c, c, entering the cham-
bers by larger orifices, one of which is
seen at d.

Internal cast of two of the chambers,

a, a, of Nummulina striata, with the
network of Canals, b, 6, in the marginal
cord, communicating with canals pass-
ing between the chambers.

tions that divide the chambers (Fig. 336, b, b), while from these may be
seen to proceed the lateral branches (c, c), which, after burrowing (so to
speak) in the walls of the chambers, enter them by large orifices (d).
These ' interseptal 9 canals, and their communication with the inosculat-

FORAMINIFERA ANF RADIOL ARIA.

ing system of passages excavated in the marginal cord, are extremely
well seen in the 'internal cast' represented in Fig. 337.

491. A very interesting modification of the Nummuline type is pre-
sented in the genus Heterostegina (Fig. 338), which bears a very strong
resemblance to Orbiculina in its plan of growth, whilst in every other
respect it is essentially different. If the principal chambers of an Oper-
culina were divided into chamberlets by secondary partitions in a direc-
tion transverse to that of the principal septa, it would be converted into
a Heterostegina ; just as a Peneroplis would be converted by the like subdi-
vision into an Orbiculina (§ 464). Moreover, we see in Heterostegina, as
in Orbiculina, a great tendency to the opening- out of the spire with the
advance of age; so that the apertural margin extends round a large part
of the shell, which thus tends to become discoidal. And it is not a little

Fig. 338. Fig. 339.

Heterostegina, Section of Orbitoides Fortisii, paral-

lel to the surface; traversing at a. a, the
superficial layer, and at b, £>, the median
layer.

curious that we have in this series another form, Cycloclypeus, which bears
exactly the same relation to Heterostegina, that Orbitolites does to Orbi-
culina; in being constructed upon the cyclical plan from the commence-
ment, its chamberlets being arranged in rings around a central chamber
(Plate xvi., fig. 1). This remarkable genus, at present only known by
specimens dredged up from considerable depths off the coast of Borneo,
is the largest of existing Foraminifera; some specimens of its discs in
the British Museum having a diameter of inches. Notwithstanding
the difference of its plan of growth, it so precisely accords with the Num-^
muline type in every character which essentially distinguishes the genus,
that there cannot be a doubt of the intimacy of their relationship. It
will be seen from the examination of that portion of the figure which
shows Cycloclypeus in vertical section, that the solid layers of shell by
which the chambered portion is inclosed are so much thicker, and con-4
sist of so many more lamellae, in the central portion of the disk, than

100

THE MICROSCOPE AND ITS REVELATIONS.

they do nearer its edge, that new lamellaB must be progressively adJed
to the surfaces of the disk, concurrently with the addition of new rings
of chamberlets to its margin. These lamellse, however, are closely applied
one to the other, without any intervening spaces; and they are all tra-
versed by columns of non-tubular substance, which spring from the sep-
tal bands, and gradually increase in diameter with their approach to the
surface, from which they project in the central portion of the disk as
glistening tubercles.

492. The Nummulitic Limestone of certain localities (as the South-
west of France, North-eastern India, etc.) contains a vast abundance of
discoidal bodies termed Orbitoides (Fig. 333, c), which are so similar to
Nummulites as to have been taken for them, but which bear a much

closer resemblance to Cyclo-
clypeus. These are only known
in the fossil state; and their
structure can only be ascer-
tained by the examination of
sections thin enough to be
translucent. When one of
these disks (which vary in size,
in different species, from that
of a four-penny piece to that
of half-a-crown) is rubbed-
down so as to display its inter
nal organization, two different
kinds of structure are usually
seen in it; one being com-
posed of chamberlets of very definite form, quadrangular in some species,

Fig. 341.

Fig. 340.

Portions of the Section of Orbitoides Fortisii shown
in Fig. 339. more highly magnified ; —a superficial lay-
er; 6, median layer.

Fig. 342.

Vertical Sections of Orbitoides Fortisii, showing the large central chamber at a, and the median
layer surrounding it, covered above and below by the superficial layer.

circular in others, arranged with a general but not constant regularity in
concentric circles (Figs. 339, 340, b, b); the other, less transparent, being

formed of minuter chamberlets which have
no such constancy of form, but which might
almost be taken for the pieces of a dissected
map [a, a). In the upper and lower walls
of these last, minute punctuations may be
observed, which seem to be the orifices of

the connecting tubes whereby they are per-
forated. The relations of these two kinds
of structure to each other are made evident
by the examination of a vertical section (Fig.

Internal Cast of portion of median 341) 1 which sll0WS that th* portion b, FigS.

ata«a v^^J^S" ^?x*chambOWinf ' ms ^'ie median plane, its con-

each of three zone^s, Vuh theh^mituai centric circles of chamberlets being arrang-

communications; and at b 6, b' b\ b'' ed round a larp-fi central Phflmhpv as in Cn-
b", portions of three annular canals. 7 7 ??, ceni1 dL Cliamoer, as m Vy-

cloclypeus; whilst the chamberlets of the
portion a are irregularly superposed one upon the other, so as to form sev-

FOEAMIN1FERA AND RADIOL ARIA.

101

eral layers which are most numerous towards the centre of the disk, and
thin-away gradually towards its margin. The disposition and connec-
tions of the chamberlets of the median layer in Orbitoides seem to corre-
spond very closely with those which have been already described as pre-
vailing in Cycloclypeas; the most satisfactory indications to this effect
being furnished by the siliceous * internal casts' to be met with in cer-
tain Green Sands, which afford a model of the sarcode-body of the ani-
mal. In such a fragment (Fig. 342) we recognize the chamberlets of
three successive zones, a, a', a", each of which seems normally to com-
municate by one or two passages with the chamberlets of the zone inter-
nal and external to its own; whilst between the chamberlets of the same
zone there seems to be no direct connection. They are brought into rela-

Fig. 343.

Vertical Section of Eozoon Canadense^ showing alternation of Calcareous (light) and Serpentin-
ous (dark) lamellae.

tion, however, by means of annular canals, which seem to represent the
spiral canals of the Nummulite, and of which the ' internal casts 9 are
seen at b b, V V9 b" b".

493. A most remarkable Fossil, referable to the Foraminiferal type,
has been recently discovered in strata much older than the very earliest
that were previously known to contain Organic remains; and the deter-
mination of its real character may be regarded as one of the most inter-
esting results of Microscopic research. This fossil, which has received
the name Eozoon Canadense (Fig. 343), is found in beds of Serpentine,
Limestone that occur near the base of the Laurentian formation1 of

1 This Laurentian formation was first identified as a regular series of stratified
rocks, underlying the equivalents not merely of the Silurian, but also of the
Upper and Lower Cambrian systems of this country, by Sir William Logan, the
former able Director of the Geological Survey of Canada.

102

THE MICROSCOPE AND ITS REVELATIONS .

Canada, which has its parallel in Europe in the ' fundamental gneiss ' of
Bohemia and Bavaria, and ifl the very earliest stratified rocks of Scandi-
navia and Scotland. These beds are found in many parts to contain
masses of considerable size, but usually of indeterminate form, disposed
after the manner of an ancient Coral Reef, and consisting of alternating
layers — frequently numbering from 50 to 100 — of Carbonate of Lime and
Serpentine (silicate of magnesia). The regularity of this alternation,
and the fact that it presents itself also between other Calcareous and
Siliceous minerals, having led to a suspicion that it had its origin in
Organic structure, thin sections of well-preserved specimens were sub-
mitted to microscopic examination by Dr. Dawson of Montreal, who at
once recognized its Foraminiferal nature:1 the calcareous layers present-
ing the characteristic appearances of true shell, so disposed as to form an
irregularly chambered structure, and frequently traversed by systems of
ramifying canals corresponding to those of Calcarina (§ 484); whilst the
serpentinous or other siliceous layers were regarded by him as having
been formed by the infiltration of silicates in solution into the cavities
originally occupied by the sarcode-body of the animal, — a process of
whose occurrence at various Geological periods, and also at the present
time, abundant evidence has already been adduced. Having himself
taken up the investigation (at the instance of Sir William Logan), the
Author was not only able to confirm Dr. Dawson's conclusions, but to
adduce new and important evidence in support of them.2 Although
this determination has been called in question, on the ground that some
resemblance to the supposed organic structure of Eozoon is presented by
bodies of purely Mineral origin,3 yet, as it has been accepted not only by
most of those whose knowledge of Foraminiferal structure gives weight
to their judgment (among whom the late Prof. Max Schulze may be
specially named), but also by Geologists who have specially studied the
Micro-mineral ogical structure of the older Metamorphio rocks,4 the
Author feels justified in here describing Eozoon as he believes it to have
existed when it originally extended itself as an animal growth over vast
areas of the sea-bottom in the Laurentian epoch.

1 This recognition was due, as Dr. Dawson has explicitly stated in his original
Memoir (''Quarterly Journal of the Geological Society," Vol xxi., p. 54), to
his acquaintance not merely with the Author's previous researches on the mi-
nute structure of the Foraminifera, but with the special characters presented by
thin sections of Calcarina which had been transmitted to him by the Author.
Dr. D. has given an excellent account of the Geological and Mineralogical rela-
tions of Eozoon, as well of its Organic structure, in a small book entitled " The
Dawn of Life."

2 For a fuller account of the results of the Author's own study of Eozodn, and
of the basis on which the above reconstruction is founded, see his Papers, in
" Quart. Journ. of Geol. Soc," Vol. xxi., p. 59, and Vol. xxii., p. 219, and in the
" Intellectual Observer," Vol. vii. (1865), p. 278; and his * Further Researches,' in
" Ann. of Nat. Hist.," June, 1874.

3 See the Memoirs of Profs. King and Rowney, in " Quart. Journ. of Geol.
Soc," Vol. xxii., p. 185; and " Ann. of Nat. Hist.," May, 1874.

4 Among these the Author is permitted to mention Prof. Geikie, of Edinburgh,
who has thus studied the older rocks of Scotland, and Prof. Bonney, of Cam-
bridge and London, who has made a like study of the Cornish and other Serpen-
tines. By both these eminent authorities he is assured that they have met with
no purely Mineral structure in the least resembling Eozoon, either in its regular
alternation of Calcareous and Serpentinous lamellae, or in the dendritic exten-
sions of the latter into the former; and while they accept as entirely satisfactory
the doctrine of its Organic origin maintained by the Author, they find them-
selves unable to conceive of any Inorganic agency by which such a structure
could have been produced.

FOR AMINIFER A. AND RADIOL ARIA.

103

494. Whilst essentially belonging to the Nummuline group, in virtue
of the fine tribulation of the shelly layers forming the ' proper wall ' of
its chambers, Eozoon is related to various types of recent Foraminifera
in its other characters. For in its indeterminate zodphytic mode of
growth, it agrees with Polytrema (§ 483); in the incomplete separation
lof its chambers, it has its parallel in Carpenteria (§ 481); whilst in the
I high development of its ' intermediate skeleton' and of the ' canal-sys-
tem ' by which this is formed and nourished, it finds its nearest represen-
tative in Calcarina f§ 484). Its calcareous layers were so superposed, one
upon another, as to include between them a succession of ' storeys ' of
chambers (Plate xvn., fig. 1, a1, a1, a2, a2); the chambers of each 'storey'
'usually opening one into another, as at a, a, l'ike apartments en suite;
but being occasionally divided by complete septa, as at b. b. These septa
are traversed by passages of -

communication between the Fig. 344.

chambers which they separate;
resembling those which, in
existing types, are occupied
by stolons connecting together
the segments of the sarcode-
body. Each layer of shell
consists of two finely-tubulat-
ed or 4 nummuline' lamellae,
B, B, which form the boun-
daries of the chambers be-
neath and above, serving (so
to speak) as the ceiling of the
former, and as the floor of the
latter; and of an intervening
deposit of homogeneous shell-
substance c, o, which consti-
tutes the ' intermediate ske-
leton.' The tubuli of this

, t -| » /-Tv o^^\ vertical Section of a portion of one of the Calcareous

nummuline layer (±< lg. 344) lamellae of Eozoon Canadense:— a a, Nummuline layer,
nVA ii an oil xr -ft 1 *W1 nn ( o a \ n perforated by parallel tubuli, which show a flexure along

are usuany nnea-up ^as mthe line a, y. beneath this is seen the intermediate

the JNummullteS of the i num.- skeleton, c, c, traversed by the large canals, 6, b, and by

mulitic limestone') by min-^S^asep,anes' ^Mch extend also into the Num-
eral infiltration, so as in

transparent sections to present a fibrous appearance; but it fortunately
happens that through their having in some cases escaped infiltration, the
tubulation is as distinct as it is even in recent Nummuline shells (Fig.
344), bearing a singular resemblance in its occasional waviness to that of the
Crab's claw (§ 613). The thickness of this interposed layer varies con-
siderably in different parts of the same mass; being in general greatest
near its base, and progressively diminishing towards its upper surface.
The 6 intermediate skeleton' is occasionally traversed by large passages
(d), which seem to establish a connection between the successive layers
of chambers; and it is penetrated by arborescent systems of canals (e, e),
which are often distributed both so" extensively and so minutely through
its substance, as to leave very little of it without a branch. These canals
take their origin, not directly from the chambers, but from irregular
lacunce or interspaces between the outside of the proper chamber-walls
and the ' intermediate skeleton,' exactly as in Calcarina (§ 484); the ex-
tensions of the sarcode-body which occupied them having apparently

104

THE MICROSCOPE AND ITS REVELATIONS.

PLATE XVII,

Fig. L

structure op eozoon canadense (Original).

Fig. 1. Portion of its calcareous Shell, as it would appear if the Serpentine fthat fills its cham-
bers were dissolved away :— a1, a1, chambers of lower story, opening into each other at a, a, but
occasionally separated by a septum 6, b ; a\ a2, chambers of upper story; b, b, proper walls of the
chambers, formed of a finely-tubular or nummuline substance; c, c, intermediate skeleton, occa-
sionally traversed by large stolon-passages, d, connecting the chambers of different stories, and
penetrated by the arborescent systems of canals e, e, e.

2. Decalcified portion showing the Serpentinous internal cast of the chambers, canals, and
tubuli of the original; presenting an exact model of the animal substance which originally filled
them.

FORAMINIFERA AND RADIOLARIA.

105

been formed by the coalescence of the pseudopodial filaments that passed
through the tubulated lamellae.

495. In the fossilized condition in which Eozoon is most commonly
found, not only the cavities of the chambers, but the canal-systems to
their smallest ramifications, are filled up by the siliceous infiltration
which has taken the place of the original sarcode-body, as in the cases
already cited (§487 note); and thus when a piece of this fossil is sub-
jected to the action of dilute acid, by which its calcareous portion is
dissolved-away, we obtain an internal cast of its chambers and canal-
system (Plate xvn., fig. 2), which, though altogether dissimilar in ar-
rangement, is essentially analogous in character to the ' internal casts'
represented in Figs. 328, 332. This cast presents us, therefore, with a
model in hard Serpentine of the soft sarcode-body which originally occu-
pied the chambers, and extended itself into the ramifying canals, of the
calcareous shell; and, like that of Polystomella (§ 487), it affords an
even more satisfactory elucidation of the relations of these parts, than
we could have gained from the study of the living organism. We see
that each of the layers of serpentine, forming the lower part of such a
specimen, is made up of a number of coherent segments, which have
only undergone a partial separation; these appear to have extended
themselves horizontally without any definite limit; but have here and
there developed new segments in a vertical direction, so as to give origin
to new layers. In the spaces between these successive layers, which
were originally occupied by the calcareous shell, we see the ' internal
casts' of the branching canal-system; which give us the exact models of
the extensions of the sarcode-body that originally passed into them. —
But this is not all. In specimens in which the nummuline layer consti-
tuting the 6 proper wall5 of the chambers was originally well preserved,
and in which the decalcifying process has been carefully managed (so as
not, by too rapid an evolution of carbonic acid gas, to disturb the ar-
rangement of the serpentinous residuum), that layer is represented by a
thin white film covering the exposed surfaces of the segments; the super-
ficial aspect of which, as well as its sectional view, are shown in fig. 2.
And when this layer is examined with a sufficient magnifying power, it
is found to consist of extremely minute needle-like fibres of Serpentine,
which sometimes stand upright, parallel, and almost in contact with each
other, like the fibres of asbestos (so that the film which they form has
been termed the 'asbestiform layer '), but which are frequently grouped
in converging brush- like bundles, so as to be very close to each other in
certain spots at the surface of the film, whilst widely separated in others.
Now these fibres, which are less than 1-10, 000th of an inch in diameter,
are the ' internal casts' of the tubuli of tho Nummuline layer (a precise
parallel to them being presented in the 6 internal cast 5 of a recent Am-
phistegina in the Author's possession); and their arrangement presents
all the varieties which have been mentioned (§ 488) as existing in the
shells of Operculina. — Thus these delicate and beautiful siliceous fibres
represent those pseudopodial threads of sarcode, which originally tra-
versed the minutely-tubular walls of the chambers; and a precise model
of the most ancient animal of which we have any knowledge, notwith-
standing the extreme softness and tenuity of its substance, is thus pre-
sented to us, with a completeness that is scarcely even approached in any
later fossil.

496. In the upper part of the ' decalcified 9 specimen shown in Plate
xvn., fig. 2, it is to be observed that the segments are confusedly heaped

106

THE MICROSCOPE AND ITS REVELATIONS.

together, instead of being regularly arranged in layers; the lamellated
mode of growth having given place to the acervuline. This change is
by no means uncommon among Foraminifera; an irregular piling-together
of the chambers being frequently met-with in the later growth of types,
whose earlier increase takes place upon some much more definite plan.
After what fashion the earliest development of Eozdon took place, we
have at present no knowledge whatever; but in a young specimen which
has been recently discovered, it is obvious that each successive 6 storey'
of chambers was limited by the closing-in of the shelly layer at its edges,
so as to give to the entire fabric a definite form closely resembling that of
a straightened Peneroplis (Plate xv., fig. 5). Thus it is obvious that
the chief peculiarity of Eozdon lay in its capacity for i?idefinite extension ;
so that the product of a single germ might attain a size comparable to
that of a massive Coral. — Now this, it will be observed, is simply due to
the fact that its increase by gemmation takes place continuously; the
new segments successively budded-off remaining in connection with the
original stock, instead of detaching themselves from it as in Foramini-
fera generally. Thus the little Globigerina forms a shell of which the
number of chambers does not usually seem to increase beyond sixteen,
any additional segments detaching themselves so as to form separate
shells; but by the repetition of this multiplication, the sea-bottom of
large areas of the Atlantic Ocean at the present time has come to be cov-
ered with accumulations of Globigeri7ics, which, if fossilized, would form
beds of Limestone not less massive than those which have had their
origin in the growth of Eozdon. — The difference between the two modes
of increase may be compared to the difference between a Plant and
a Tree. For in the Plant the individual organism never attains any con-
siderable size, its extension by gemmation being limited; though the
aggregation of individuals produced by the detachment of its buds (as
in a Potato field) may give rise to a mass of vegetation as great as that
formed in the largest Tree by the continuous putting forth of new buds.

497. It has been hitherto only in the Laurentian Serpentine-Lime-
stone of Canada, that Eozdon has presented itself in such a state of pres-
ervation as fully to justify the assumption of its Organic nature. But
from the greater or less resemblance which is presented to this by Ser-
pentine-Limestones occurring in various localities, among strata that seem
the Geological equivalents of the Canadian Laurentians, it seems a justifi-
able conclusion that this type was very generally diffused in the earlier ages
of the Earth's history; and that it had a large (and probably the chief)
share in the production of the most ancient Calcareous strata, separat-
ing Carbonate of Lime from its solution in Ocean-water, in the same
manner as do the Polypes by whose growth Coral-reefs and islands are
being upraised at the present time.

An elaborate work, " Der Bau des Eozoon Canadense" (1878) has been re-
cently published by Prof. Mobius of Kiel, in which the structure of Eozoon is
compared with that of various types of Foraminifera, and, as it differs from
that of every one of them, is affirmed not to be organic at all, but purely Min-
eral. Upon this the Author would remark, that if the validity of this mode of
reasoning be admitted, any Fossil whose structure does not correspond with that
of some existing type, is to be similarly rejected. Thus, the Stromatopora of
Silurian and Devonian rocks, which some Palaeontologists regard as a Coral,
others as Polyzoary, others as a Calcareous Sponge, and others as Foraminifer,
would not be a fossil at all, because it differs from every known living form.
Yet the suggestion that it is of Mineral origin would be scouted as absurd by
every Palaeontologist. Again, it is urged by Prof. Mobius that as the supposed
canal- system of Eozoon has not the constancy and regularity of distribution which

FOJRAMINIFERA AND RADIOLARIA.

107

It presents in existing Foraminifera, it must be accounted a Mineral infiltration.
To this the Author would reply: — (1) That a prolonged and careful study of this
'canal-system,' in a great variety of modes, with an amount of material at his
disposal many times greater than Prof. Mobius could command, has satisfied him
that in well-preserved specimens the canal-system, so far from being vague and
indefinite, has a very regular plan of distribution; — (2) That this plan does not
differ more from the arrangements characteristic of the several types of existing
Foraminifera, than these differ from each other, its general conformity to them
being such as to satisfy Prof. Max Schultze (one of the ablest Foraminiferalists
of his time) of its Foraminiferal character; — and (3) that not only does the distri-
bution of the canal-system of Eozoon differ in certain essential features from
every form of Mineral infiltration hitherto brought to light, but that canal-sys-
tems in no respect differing from each other in distribution are occupied by dif-
ferent minerals, — a fact which seems conclusively to point to their pre-existence
in the Calcareous layers, and the subsequent penetration of these minerals into
the passages previous occupied by sarcode, — precisely as has happened in those
4 internal casts ' of existing Foraminifera (§ 497) which Prof. Mobius altogether
ignores.

The argument for the Foraminiferal nature of Eozoon is essentially a cumula-
tive one, resting on a number of independent probabilities, no one of which, taken
separately, has the cogency of 2, proof ; yet the accordance of them all with that
hypothesis has an almost demonstrative value, no other hypothesis accounting at
once for the whole assemblage of facts. — As it is the Author's intention to set
forth this in the best and completest form he can devise, at the earliest possible
period, he would beg for a suspension of judgment on the part of those who have
credited Prof. Mobius with having completely settled the question; the small
amount of evidence contained in his Memoir bearing no comparison to that of an
opposite bearing of which the Author is in possession.

498. Collection and Selection of Foraminifera, — Many of the Forami-
nifera attach themselves in the living state to Sea-weeds, Zoophytes, etc.;
and they should, therefore, be carefully looked-for on such bodies, espe-
cially when it is desired to observe their internal organization and their
habits of life. They are often to be collected in much larger numbers,
however, from the sand or mud dredged-up from the sea-bottom, or even
from that taken from between the tide-marks. In a paper containing
some valuable hints on this subject,1 Mr. Legg mentions that, in walking
over the Small-mouth Sand, which is situated on the north-side of Port-
land Bay, he observed the sand to be distinctly marked with white
ridges, many yards in length, running parallel with the edge of the
water; and upon examining portions of these, he found Foraminifera in
considerable abundance. One of the most fertile sources of supply that
our own coasts afford, is the ooze of the Oyster-beds, in which large
numbers of living specimens will be found; the variety of specific forms,
however, is usually not very great. In separating these bodies from the
particles of sand, mud, etc., with which they are mixed, various methods
may be adopted, in order to shorten the tedious labor of picking them
out, one by one, under the Simple Microscope; and the choice to be
made among these will mainly depend upon the condition of the Foram-
inifera, the importance (or otherwise) of obtaining them alive, and the
nature of the substances with which they are mingled. — Thus, if it be
desired to obtain living specimens from the oyster-ooze, for the examina-
tion of their soft parts, or for preservation in an Aquarium, much
time will be saved by stirring the mud (which should be taken from the
surface only of the deposit) in a jar with water, and then allowing it to
stand for a few moments; for the finer particles will remain diffused
though the liquid, while the coarser will subside; and as the Forami-
nifera (in the present case) will be among the heavier, they will be found

1 " Transaction of Microscopical Society," 2d Series, Vol. ii. (1854), p. 19.

108

THE MICROSCOPE AND ITS REVELATIONS.

at the bottom of the vessel with comparatively little extraneous matter,
after this operation has been repeated two or three times. It would
always be well to examine the first deposit let fall by the water that has
been poured-away; as this may contain the smaller and lighter forms of
Foraminifera. — But supposing that it be only desired to obtain the dead
shells from a mass of sand brought-up by the dredge, a very different
method should be adopted. The whole mass should be exposed for
some hours to the heat of an oven, and be turned-over several times,
until it is found to have been thoroughly dried throughout; and then,
after being allowed to cool, it should be stirred in a large vessel of
water. The chambers of their shells being now occupied by air alone
(for the bodies of such as were alive will have shrunk-up almost to
nothing), the Foraminifera will be the lightest portion of the mass; and
they will be found floating on the water, while the particles of sand, etc.,
subside. Another method, devised by Mr. Legg, consists in taking ad-
vantage of the relative sizes of different kinds of Foraminifera and of
the substances that accompany them. This, which is especially applica-
ble to the sand and rubbish obtainable from Sponges (which may be got
in large quantity from the sponge-merchants), consists in sifting the
whole aggregate through successive sieves of wire-gauze, commencing
with one of 10 wires to the inch, which will separate large extraneous par-
ticles, and preceeding to those of 20, 40, 70, and 100 wires to the inch,
each (especially that of 70) retaining a much larger proportion of Foram-
iniferal shells than of the accompanying particles; so that a large portion
of the extraneous matter being thus got rid of, the final selection becomes
comparatively easy. — Certain forms of Foraminifera are found attached
to Shells, especially bivalves (such as the Chamacece) with foliated sur-
faces; and a careful examination of those of tropical seas, when brought
home 6 in the rough/ is almost sure to yield most valuable results. — The
final selection of specimens for mounting should always be made under
some appropriate form of Single Microscope (§§ 43-48); a fine camel-
hair pencil, with the point wetted between the lips, being the instrument
which may be most conveniently and safely employed, even for the most
delicate specimens. In mounting Foraminifera as Microscopic objects,
the method to be adopted must entirely depend upon whether they are
to be viewed by transmitted or by reflected light. In the former cask it
should be mounted in Canada balsam (§ 210); the various precautions to
prevent the retention of air-bubbles, which have been already described,
being carefully observed. In the latter no plan is so simple, easy, and
effectual, as the attaching them with a little gum to wooden slides (Fig.
124). They should be fixed in various positions, so as to present all the
different aspects of the shell, particular care being taken that its mouth
is clearly displayed; and this may often be most readily managed by at-
taching the specimens sideways to the wall of the circular depression of
the slide. Or the specimens may be attached to disks fitted for being
held in Morris's Disk-holder (Fig. 95); whilst for the examination of
specimens in every variety of position, Mr. R. Beck's Disk-holder (Fig.
94) will be found extremely convenient. Where, as will often happen,
the several individuals differ considerably from one another, special care
should be taken to arrange them in series illustrative of their range of
variation and of the mutual connections of even the most diverse forms. —
For the display of the internal structure of Foraminifera, it will often
be necessary to make extremely thin sections, in the manner already de-
scribed (§§ 192-194); and much time will be saved by attaching a num-

FORAMTNIFERA AND RADIOL ARIA.

109

ber of specimens to the glass slide at once, and by grinding them down
together (§ 192, note). For the preparation of sections, however, of the
extreme thinness that is often required, those which have been thus
reduced should be transferred to separate slides, and finished-off each one
by itself.

Kadiolaria.

499. It has been shown that one series of forms belonging to the
Rhizopod type is characterized by the radiating arrangement of their rod-
like pseudopodia (§ 399), suggesting the designation Heliozoa or ' sun-ani-
malcules;' and that even among those fresh-water forms that do not depart
widely from the common Actinophrys (Fig. 285), there are some whose
bodies are inclosed in a complete siliceous skeleton. Now just as the

Fig. 345.

Fossil Radiolaria from Barbadoes.— a, Podocyrtis mitra; 6, Rhabdolithus sceptrum; c, Lych-
nocanium falciferum; c£, Eucyrtidium tubulus; e, Flustrellaconcentnca; /, Lychnocanium lucerna;
gr, Euryrtidium elegans; h% Dictyospyris clathrus; i% Eucyrtidium Mongolfleri; fc, Stephanolithis
spinescens; 1,8. nodosa; m, Lithocyclia ocellus; n, Cephalolithis sylvina; o, Podocyrtis cothur-
nata; p, Rhabdolitnus pipa.

Reticularian type of Rhizopod life culminates in the marine calcareous-
shelled Foraminifera, so does the Heliozoic type seem to culminate in
the marine Radiolaria; which, living for the most part near the surface
of the ocean, form siliceous skeletons (often of marvellous symmetry and
beauty), that fall to the bottom on the death of the animals that pro-
duced them, and may remain unchanged, like those of the Diatoms,
through unlimited periods of time. Some of these skeletons, mingled
with those of Diatoms, had been detected by Prof. Ehrenberg in the
midst of various deposits of Foraminiferal origin, such as the Calcareous
Tertiaries of Sicily and Greece, and of Oran in Africa; and he established
for them the group of Polycystina, to which he was able also to refer a
beautiful series of forms making-up nearly the whole of a siliceous

110

THE xMICROSCOPE AND ITS REVELATIONS.

sandstone prevailing through an extensive district in the island of Bar-
badoes (Fig. 315). Nothing, however, was known of the nature of the
animals that formed them, until they were discovered and studied in the
living state by Prof. J. Muller;' who established the group of Radiolaria,
including therein, with the Polycystina of Ehrenberg, the Acanthome-
trina (§ 505) first recognized by himself, and the Thalassicolla (§ 506)
which had been discovered by Prof. Huxley. Not long afterwards ap-
peared the magnificent and 6 epoch-making' work of Prof. Haeckel;2 and
since that time much has been added by various observers to our knowl-
edge of this group, which still remains, however, very imperfect. For
the following general account of its characters, the Author is indebted to
the valuable summary of " Kecent Researches in regard to the Kadio-
laria 99 lately given by Prof. Mivart.3

500. Each individual Radiolarian consists of two portions of colored
or colorless sarcode: one portion nucleated and central; the other portion
peripheral, and almost always containing certain yellow corpuscles.
These two portions are separated by a chitinous membrane called the
capsule; but this is so porous as to allow of their free communication
with each other. The yellow corpuscles seem to be true ' cells;' having
a regular membranous wall, with protoplasmic contents (including
starch-granules), and distinct nuclei; and multiplying themselves by sub-
division. But there is considerable doubt whether they are really parts
of the animal body, as they have been found in vigorous life when the
rest of the animal is dead and decaying; and they are regarded by Cien-
kowski as parasites. The pscudopodia radiate in all directions (Plate
xviii., figs. 3, 4) from the deeper portion ot the extra-capsular sarcode;
they have generally much persistency of direction, and very little flexi-
bility; in some species (but not ordinarily) they branch and anastomose;
while in others they are inclosed in hollow rods that form part of the
siliceous skeleton, and issue forth from the extremities of these. A flow
of granules takes place along them; and the mode in which they obtain
food-particles (consisting of Diatoms and other minute Algae, marine In-
fusoria, etc.), and draw them into the sarcode-bodies of the Kadiolarians,
appears to correspond entirely with their action in Actinophrys and
other Heliozoa (§ 399).

501. In most Radiolaria, skeletal structures are developed in the sar-
code-body, either inside or outside the capsule, or in both positions; some-
times in the form of investing networks having more or less of a spheroi-
dal form (Plate xix., figs. 1, 2), or of radiating spines (fig. 3), or of
combinations of these (figs. 4, 5). But in many cases the skeleton con-
sists only of a few scattered spicules; and this is especially the case in
certain large composite forms or ' colonies ' (Fig. 350) which may consist
of as many as a thousand zooids, aggregated together in various forms,
discoidal, cylindrical, spheroidal, chain-like, or even necklace-like. The
' colonies ' seem to be produced, like the multiple segments of the bodies
of Foraminifera (§ 456), by the non-sexual multiplication of a primordial
zooid; but whether this multiplication takes place by fission, or by the
budding-off of portions of the sarcode-body, has not yet been clearly

1 * Ueber die Thalassicollen, Polycystinenund Acanthometren des Mittelmeeres,'
in " Abhandlungen der Konigl. Akad. der Wissensch. zu Berlin," 1858, and sepa-
rately published; also * Ueber die im Hafen von Messina beobachteten Polycysti-
nen,' in the " Monatsberichte " of the Berlin Academy for 1855, pp. 671-676.

2 " Die Eadiolarien (Rhizopoda Radiaria)," Berlin, 1862.

3 "Journal of the Linnaean Society," Vol. xiv. (Zool.), p. 136.

FOR AMINIFER A AND RADIOLARIA.

Ill

PLATE XVIII.
Fta. 1. Fio. 2

various forms op polycystina (after Ehrenberg).

Fi^. 1 • Podoyrtis Schomburgkii.

2. Rhopalocanium ornatum.

3. Haliomma hystrix.

4. Pterocanium, with animaL

112

THE MICROSCOPE AND ITS REVELATIONS.

made-out. The emission of flagellated zoospores, very similar to those
of Clathrulina (Fig. 288), has been observed in many Kadiolarians; but
of the mode in which they are produced, and of their subsequent history,
very little is at present known. — Until the structure and life-history of
the animals of this very interesting type shall have been more fully elu-
cidated, no satisfactory classification of them can be framed; and nothing
more will be here attempted than to indicate some of the principal forms
under which the Radiolarian type presents itself.

502. Discida* — Among the beautiful siliceous structures which are met
with in the Radiolarian sandstone of Barbadoes (Pig. 345) there is none
more interesting than the skeleton of Astromma (Fig. 34(J); in which we
have a remarkable example of the range of variation that is compatible
with conformity to a general plan of structure. As in other forms of
Haeckel's group of Discida, there is in this skeleton a combination of

Fig. 346

Varietal modifications of Astromma.

radial and of circumferential parts; the former consisting of solid spoke-
like rods, whilst the latter is composed of a siliceous network more or
less completely filling up the spaces between the rays. The radial part
of the skeleton predominates in the beautiful 4-rayed example represented
at D, having the form of a Maltese cross; whilst m F and G it still shows
itself very conspicuously, though the spaces between the rays are in great
part filled up by the circumferential network. In the 5-rayed specimens
a and B, on the other hand, the radial portion is much less developed,
whilst the circumferential becomes more discoidal. And in c and E,
while the circumferential network forms a pentagonal disk, the radial
portion is represented only by solid projections at its angles. The transi-
tion between the extreme forms is found to be so gradual when a number
of specimens are compared, that no lines of specific distinction can be
drawn between them; and the difference in the number of rays is probably

FORAMINIFERA AND RADIOL ARIA.

113

of no more account in these low forms of Animal life, than it is in the
discoidal Diatoms (§ 290). — Other discoidal forms, showing a like com-
bination of radial and circumferential parts are represented in Figs. 347
and 348, and also in Fig. 345, 0, tn.

503. Entosphcerida. — In this group the siliceous shell is spheroidal,
and is formed within the capsule; and it is not traversed by radii, al-
though prolongations of the shell often extend themselves radially out-
wards, as in Cladococcus (Plate xix., fig. 5). Sometimes the central
sphere is inclosed in two, three, or even more concentric spheres con-
nected by radii, as in the beautiful Actinomma (Plate xix., fig. 2);
reminding us of the wonderful concentric spheres carved in ivory by the
Chinese. — One of the most common examples of this group is the Hali-
omma Humboldt ii (Fig. 349), in which the shell is double.

504. Polycystina. — This name, which originally included the pre-
ceding group, is now restricted to those which have the shell formed
outside the capsule. This shell may, as in the preceding, be a simple
sphere composed of an open siliceous network, as in Etlimo splicer a (Plate
xix., fig. 1); or it may consist of two or three concentric spheres con-
nected by radii; or, again, it may put forth radial outgrowths, which

Fig. 347. Fig. 348.

Perichlamydium prcetextum. Stylodyctya gracilis,

sometimes extend themselves to several times the diameter of the shell,
and ramify more or less minutely, as in Arachno splicer a (Plate xix., fig.
4). But more frequently the shell opens-out at one pole into a form
more or less bell-like, as in Podocyrtis (Plate xviii., fig. 1, and Fig. 345,
a, o), Ehopalocanium (Plate xviii., fig. 2), and Pterocaninm (Plate xviii.,
fig. 4); or it may be elongated into a somewhat cylindrical form, one
pole remaining closed, while the other is more or less contracted, as in
Eucyrtidium (Fig. 345, d, g, i). — The transition between these forms
again, proves to be as gradational, when many specimens are compared,1
as it is among Foraminifera (§ 488).

505. Acanthometrina. — In this group the animal is not inclosed with-
in a shell, but is furnished with a very regular skeleton composed of
elongated spines, which radiate in all directions from a common centre
(Plate xix., fig. 3). The soft sarcode-body is spherical in form, and
occupies the spaces left between the bases of these spines, which are some-
times partly inclosed (as in the species represented) by transverse projec-

1 The general Plan of structure of the Polycystina, and the signification of
their immense variety cf forms, were ably discussed by Dr. Wallich, in the
"Tran-. of the Mxrosc. Soc, ' N.S., Vol. xii. (1865), p. 75.
8

114

THE MICROSCOPE AND ITS REVELATIONS.

PLATE XIX.

various forms op radiolaria (after Haeckel).

Fig. 1. Ethmosphcera siphonophora.

2. Actinomma inerme.

3. Acanthometro xiphicantha.

4. Arachnosphcera obligacantha.

5. Cladococcus viminalis.

FOR A MINIFE R A. AND RADIOL ARIA.

115

tions. The c capsule' is pierced by the pseudopodia, whose convergence
may be traced from without inwards, after passing through it; and it is
itself enveloped in a layer of less tenacious protoplasm, resembling that
of which the pseudopodia are composed. One species, the Acantlwmetra
echinoides, which presents itself to the naked eye as a crimson-red point,
the diameter of the central part of its body being about 6-1000ths of an *
inch, is very common on some parts of the coast of Norway, especially
during the prevalence of westerly winds; and the Author has himself
met with it abundantly near Shetland, in the floating brown masses
termed madre by the fishermen (who believe them to furnish food to the
herring), which consist mainly of this Acanthometra mingled with
Entomostraca.

506. Collozoa,— -To this group belong these remarkable composite
forms, which, exhibiting the characteristic Eadiolarian type in their indi-
vidual zooids, are aggregated into masses in which the skeleton is repre-

Fig. 349. Fig. 350.

Haliomma Humboldtii. Sphcerozoum ovodimare.

sented only by scattered spicules, as in Sphcerozoum (Fig. 350) and
Thalassicolla. — These * sea-jellies/ which so abound in the seas of warm
latitudes as to be among the commonest objects collected by the Tow-net,
are small gelatinous rounded bodies, of very variable size and shape, but
usually either globular or discoidal. Externally they are invested by a
layer of condensed sarcode, which sends forth pseudopodial extensions
that commonly stand out like rays, but sometimes inosculate with each
other so as to form network. Towards the inner surface of this coat are
scattered a great number of oval bodies resembling cells, having a toler-
ably distinct membraniform Avail and a conspicuous round central nucleus.
Each of these bodies appears to be without any direct connection with
the rest; but it serves as a centre round which a number of minute yel-
lowish-green vesicles are disposed. Each of these groups is protected by
a siliceous skeleton, which sometimes consists of separate spicules (as in
Fig. 350), but which may be a thin perforated sphere, like that of cer-
tain Polycystina, sometimes extending itself into radial prolongations.

116

THE MICROSCOPE AND ITS REVELATIONS.

The internal portion of each mass is composed of an aggregation of large
vesicle-like bodies, imbedded in a softer sarcodic substance.1

507. From the researches made during the 6 Challenger 9 expediti* i,
it appears that the Radiolaria are very widely diffused through the waters
of the ocean, some forms being more abundant in tropical and others in
temperature seas; and that they live not only at or near the surface, but
also at considerable depths. Their siliceous skeletons accumulate in some
localities (in which the calcareous remains of Foraminifera are wanting)
to such an extent as to form a 'Radiolarian ooze;' and it is obvious that
the elevation of such a deposit into dryland would form a bed of siliceous
sandstone resembling the well-known Barbadoes rock, which is said to
attain a thickness of 1100 feet, or a similar rock of yet greater thickness
in the Nicobar Islands. — Few Microscopic objects are more beautiful
than an assemblage of the most remarkable forms of the Barbadian Poly-
cystina (Fig. 345), especially when seen brightly illuminated upon a
black ground; since (for the reason formerly explained, § 103) their solid
forms then become much more apparent than they are when these ob-
jects are examined by light transmitted through them. And when they
are mounted in Canada-balsam, the Black-ground illumination, either by
the Webster-condenser (§ 100), the Spot-lens (104), or the Paraboloid
(§ 105), is much to be preferred for the purpose of display, although
minute details of structure can be better made out when they are viewed
as transparent objects with higher powers. Many of the more solid forms,
when exposed to a high temperature on a slip of platinum foil, undergo
a change in aspect which renders them peculiarly beautiful as opaque ob-
jects; their glassy transparence giving place to an enamel-like opacity.
They may then be mounted on a black ground, and illuminated either
with a Side-condenser, or with the Parabolic Speculum (§ 114). — No
class of objects is more suitable than these to the Binocular Microscope;
its stereoscopic projection causing them to be presented to the mind's eye
in complete relief, so as to bring-out with the most marvellous and beauti-
ful effect all their delicate sculpture.2

1 See Prof. Huxley (to whom we owe our first knowledge of these forms) in
"Ann. Nat. Hist.,'' Ser. 2, Vol. viii. (1851), p. 433; also Prof. Muller, of Berlin, in
" Quart. Journ. Microsc. Sci.," Vol. iv. (1856), p. 72, and in his Treatise " Ueber
die Thalassicollen, Polycystinen, und Acanthometren des Mittelmeeres; ' and the
magnificent work of Prof. Haeckel, "Die Radiolarien."— Great additions to our
knowledge of this group may be expected from the collections made in the
* Challenger ' expedition.

2 For a fuller description of the Fossil forms of this group, see Prof. Ehren-
berg's Memoirs in the k' Monatsberichte,' of the Berlin Academy for 1846, 1847,
and 1850; also his 4 Microgeologie,' 1854; and "Ann. of Nat. Hist.," Vol. xx.
(1847). — The best method of separating the Polycystina from the Barbadoes sand-
stone is described by Mr. Furlong in the " Quart. Journ. of Microsc, Sci.," N. S.,
Vol. i. (1861), p. 64.

SPONGES AND ZOOPHYTES.

117

CHAPTER XIII.
SPONGES AND ZOOPHYTES.
I. Sponges.

508. The determination of the real character of the animals of this
Class has been entirely effected by the Microscopic examination of their
minute structure; for until this came to be properly understood, not only
was the general nature of these organisms entirely misapprehended, but
they were regarded by many naturalists as having no certain claim to a
place in the Animal Kingdom. It may now be unhesitatingly affirmed
that a Sponge is essentially an aggregate of Protozoic units, of which
some correspond in every particular to the collared Flagellata (Fig. 295),
whilst others resemble Amcebce (Fig. 289), — the two conditions being
probably only different stages of the same life-history. These units are
held together by a continuous sarcode-body, which clothes the skeletal
framework that represents our usual idea of a Sponge. In the simpler
forms of sponges, however, this framework is altogether absent; in
others it is represented only by calcareous or siliceous ' spicules/ which
are dispersed through the sarcodic substance (Fig. 352, b); in others,
again, the skeleton is a keratose (horny) network, which may be entirely
destitute (as in our ordinary Sponge) of any mineral support, but which
is often strengthened by calcareous or siliceous spicules (Fig. 352, a);
whilst in what may be regarded as the highest types of the group, the
siliceous component of the skeleton increases, and the keratose dimin-
ishes, until the skeleton consists of a beautiful siliceous network re-
sembling spun-glass (§ 511). But whatever may be the condition of the
skeleton, that of the body that clothes it remains essentially the same;
and the peculiarity that chiefly distinguishes the Sponge-colony from the
plant-like colonies of the Flagellate Infusoria (Fig. 296), is that whilst
the latter extend themselves outwards by repeated ramification, sending
their zooid-bearing branches to meet the water they inhabit, the surface
of the former extends itself inwards, forming a system of passages and
cavities lined by these and the amoeboid zooids, through which a current
of water is drawn-in to meet them by the action of the flagella. The
minute pores (Fig. 351, b, b) with which the surface a, a, of the living
Sponge is beset, lead to incurrent passages that open into chambers lying
beneath it (c, c); and it is especially on the walls of these 6 ampullaceous
sacs/ that the flagellate zooids present themselves. The water drawn-in
by their agency is driven outwards through a system of excurrent canals,
which, uniting into larger trunks, proceed to the oscula or projecting
vents d, from each of which, during the active life of the Sponge, a
stream of water, carrying out excrementitious matter, is continually

118

THE MICROSCOPE AND ITS REVELATIONS.

issuing. The in-current brings into the chambers both food-material
and oxygen; and from the manner in which colored particles experiment-
ally diffused through the water wherein a Sponge is living, are received
into its sarcodic substance, it seems clear that the nutrition of the entire
fabric is the resultant of the feeding action of the separate amoeboid and
flagellate units, each of which takes-in, after its kind, the food-particles
brought by the current of water, and imparts the product of its digestion
of them to the general sarcodic mass.1

509. The continuous sarcode-substance or ' cyloblastema ' that clothes
the skeleton of the Sponge and constitutes its living body, includes great
numbers of 'cytodes (§ 392), in various stages of development; which,
like isolated Amwbce, are constantly undergoing changes in form and
position. Their long slender pseudopodia, radiating towards those of
their neighbors, often unite together to form a complex network; and it
seems to be by their agency, that the continual contractions and expan-
sions of the oscula are produced, which are very characteristic of the
living Sponge. It would seem, indeed, as if they combined in them-
selves the functions of nerve and muscle-elements, which are differenti-
ated in the higher forms of
fig. 351. animal life. Any one of

these amoeboids, again, de-
tached from the mass, may
lay the foundation of a new
' colony/ In the aggregate
mass produced by its con-
tinuous segmentation, cer-
tain globular clusters are
distinguishable, each hav-
ing a cavity in its interior;
and the amoeboids that form
the v/all of this cavity be-
come metamorphosed into
collared flagellate zooids
whose flagella project into it.
Thus is formed one of the characteristic c ampullaceous sacs;' which, at
first closed, afterwards communicates with the exterior, on the one hand,
by an incurrent passage, and on the other with theexcurrent canal-system
leading to the oscula. — Besides this reproduction by * micro-spores/
there is another form of non-sexual reproduction by ' macro-spores f
which are clusters of amoeboids encysted in firm capsules, frequently
strengthened on their exterior by a layer of spicules of very peculiar
form. These ' seed-like bodies/ which answer to the encysted states of
many protophytes, are met with in the substance oi* the sponge, chiefly
in winter; and after being set free through the oscula, they give exit to
their contained amoeboids, each of which may found a new colony. — A

1 This view of the nature and living action of Sponges, originally suggested by
Dujardin, was definitely put forth by the late Prof. H. James-Clark, as the result
of an admirable series of researches on Sponges and Flagellate Infusoria, in the
Transactions of the Boston Society of Natural History for 1868, reproduced in the
' 'Ann. Nat. Hist." for the same year. See also his Memoir on Spongilla in
" Amer. Journ. Sci.," 1871, pp. 426-436; reproduced in ' Monthly Microsc. Journ.,'
Vol. vii., (1872), p. 104. - His observations have been since fully confirmed by
Messrs. Carter and Saville Kent; who have published a succession of Papers in
the " Annals of Natural History," the general conclusions of which are embodied
in Chap. v. of Mr. S. Kent's " Manual of the Infusoria."

Diagrammatic section of Spongilla: — a, a, superficial
layer; 6, inhalant apertures; c, c, flagellated chambers,' d,
exhalant oscule ; e, deeper substance of the sponge.

SPONGES AND ZOOPHYTES.

119

true process of sexual generation, moreover, is said to take place in
Sponges; certain of the amoeboids, like certain cells of Volvox (§ 240),
becoming ' sperm-cells/ and developing spermatozoa by the metamor-
phosis of their nuclei; while others become 6 germ-cells/ developing them-
selves by segmentation (when fertilized) into the bodies known as
' ciliated gemmules/ which are set free from the walls of the canals,
swim forth from the vents, and for a time move actively through the
water. According to Prof. Haeckel, the fertilized germ-cells are to be
regarded as true ova, and the products of their segmentation as morulas,
which, by invagination (§ 391), become go&trulce; and he argues that the
whole system of canals and ampullaceous sacs is really, like the system of
canals in the Sponge-like Ahyonium (§ 529), an extension of the primi-
tive gastric cavity; the oscula of Sponges being the undeveloped repre-
sentatives of the polypes of the Zoophyte. — As it is doubtful, however,
whether the supposed Sponge-spermatozoa are anything else than
ordinary flagellated monads, and as the development of the supposed
ovum by no means conforms to the ordinary gastrcea type, the question

Fig. 352.

a. Portion of Halichondria (?) from Madagascar, with siliceous spicules projecting from the
keratose network.

b. Triradi'ate spicules of Grantia compressa, lying in the midst of its cytoblastema.

whether Sponges are strictly Protozoa, or are to be regarded as consti-
tuting the lowest form^of the Metazoic type, must be considered (in the
Author's opinion) as still an open one.1

510. The arrangement of the keratose reticulation in the Sponges
with which we are most familiar, may be best made out by cutting thin
slices of a piece of Sponge submitted to firm compression^ and viewing
these slices, mounted upon a dark ground, with a low magnifying power,
under incident light. Such sections, thus illuminated, are not merely
striking objects; but serve to show, very characteristically, the general
disposition of the larger canals and of the smaller pores with which they
communicate. In the ordinary Sponge, the fibrous skeleton is almost
entirely destitute of spicules; the absence of which, in fact, is one lm-

!See Chap. v. of Mr. Saville Kent's " Manual of the Infusoria," and Chap. v.
of Mr. Balfour's "Comparative Embryology," as well as Prof. Haeckel s impor-
tant work on the Calcareous Sponges.

120

THE MICROSCOPE AND ITS REVELATIONS.

portant condition of that flexibility and compressibility on which its uses
depend. When spicules exist in connection with such a skeleton, they
are usually either altogether imbedded in the fibres, or are implanted into
them at their bases, as shown in Fig. 352, A. But smaller and simpler
Sponges, such as Grantia, have no horny skeleton; and their spicules are
imbedded in the general substance of the body (Fig. 351, b). — Sponge-
spicules are much more frequently Siliceous than Calcareous; and the
variety of forms presented by the siliceous spicules is much greater than
that which we find in the comparatively small division in which they are
composed of carbonate of lime. The long needle-like spicules (Fig.
353), which are extremely abundant in several Sponges, lying close to-
gether in bundles, are sometimes straight, sometimes slightly curved;
they are sometimes pointed at both ends, sometimes at one only; one or
both ends may be furnished with a head like that of a pin, or may carry
three or more diverging points which sometimes curve back so as to form
hooks (Fig. 488, h). When the spicules project from the horny frame-
work, they are usually somewhat conical in form, and their surface is often
beset with little spines, arranged at regular intervals, giving them a jointed
appearance (Fig. 352, a). Sponge-spicules frequently occur, however,

under forms very different from
the preceding; some being short
and many-branched, and the
branches being themselves very
commonly stunted into mere tu-
bercles (some examples of which
type are presented in Fig. 488, A,
c); whilst others are stellate, hav-
ing a central body with conical
spines projecting from it in all
directions (as at D of the same
figure). Great varieties present
themselves in the stellate form,
according to the relative predomi-
nance of the body and of the rays:
in those represented in Fig. 353, the rays, though very numerous, are ex-
tremely short; in other instances the rays are much longer, and scarcely
any central nucleus can be said to exist. The varieties in the form of
Sponge-spicules are, in fact, almost endless; and a single Sponge often pre-
sents two or more (as shown in Fig. 353), the stellate spicules usually occur-
ring either in the interspaces between the elongated kinds, or in the exter-
nal crust.1 The spicules of Sponges cannot be considered, like the r aphides
of Plants (§ 359), simply as deposits of Mineral matter in a crystalline
state; for the forms of many of them are such as no mere crystallization
can produce; they generally (at least in the earlier stage of their forma-
tion) possess internal cavities, which contain organic matter; and the
calcareous spicules, whose mineral matter can be readily dissolved away
by an acid, are found to have a distinct animal basis. Hence it seems
probable that each spicule was originally a segment of sarcode, which has

1 A minute account of the various forms of spicules contained in Sponges is
given by Mr. Bowerbank in his First Memoir ' On the Anatomy and Physiology
of the Spongiadae,' in < Philos. Transact.," 1858, pp. 279-332; and in his "Mono-
graph of the British Spongiadae" published by the Ray Society. — The Calcareous
Sponges have been made by Prof. Haeckel the subject of an elaborate Monograph,
" Die Kalkschwamme," Berlin, 1872.

SPONGES AND ZOOPHFTES.

121

undergone either calcification or silification; and by the self-shaping
power of which, the form of the spicule is mainly determined.

511. There is an extremely interesting group of Sponges, in which
the horny skeleton is entirely replaced by a siliceous framework of great
firmness and of singular beauty of construction. This framework mav
be regarded as fundamentally consisting of an arrangement of six-rayed
spicules, the extensions of which come to be, as it were, soldered to one
another; and hence the group is distinguished as hexiradiate. Of this
type the beautiful Euplectella of the Manilla Seas — which was for a long
time one of the greatest of zoological rarities, but which now, under the
name of ' Venus's flower-basket/ is a common ornament of our drawing-
rooms — is one of the most characteristic examples. Another example is
presented by the Holtenia Carpenteri, of which four specimens, dredged
up from a depth of 530 fathoms between the Faroe Islands and the North
of Scotland, were among the most valuable of the 'treasures of the deep'
obtained during the first Deep-sea Exploration (1868), carried on by Sir
Wyville Thomson and the Author. This is a turnip-shaped body, with
a cavity in its interior, the circular mouth of which is surrounded with a
fringe of elongated siliceous spicules; whilst from its base there hangs a
sort of beard of siliceous threads, that extend themselves, sometimes to a
length of several feet, into the Atlantic mud (§ 480) on which these
bodies are found. The framework is much more massive than that of
Euplectella, but it is not so exclusively mineral; for if it be boiled in
nitric acid it is resolved into separate spicules, these being not soldered
together by siliceous continuity, but held together by animal matter.
Besides the regular hexiradiate spicules, there is a remarkable variety of
other forms, which have been fully described and figured by Sir Wyville
Thomson.1 One of the greatest features of interest in this Holtenia, is
its singular resemblance to the Ventriculites of the Cretaceous formation
(§ 699). Subsequent investigations have shown that it is very widely
diffused, and that it is only one of several Deep-sea forms, including
several of singularly beautiful structure, which are the existing represen-
tatives of the old Ventriculite type. One of these was previously known,
from being occasionally cast up on the shores of Barbadoes after a storm.
This Dictyocalyx pumiceous has the shape of a mushroom, the diameter
of its disk sometimes ranging to a foot. A small portion of its reticu-
lated skeleton is a singularly beautiful object, when viewed with incident
light under a low magnifying power.

512. With the exception of the genus Spongilla, all known Sponges are
marine; but they differ very much in habit of growth. For whilst some
can only be obtained by dredging at considerable depth, others live near
the surface, whilst others attach themselves to the surfaces of rocks,
shells, etc., between the tide-marks. The various species of Grantia, in
which, of all the marine Sponges, the flagellate zooids can most readily
be observed, belong to this last category. They have a peculiarly simple
structure, each being a sort of bag whose wall is so thin that no system
of canals is required; the water absorbed by the outer surface passing
directly towards the inner, and being expelled by the mouth of the bag.
The flagella may be plainly distinguished with a l-8th inch objective on
some of the cells of the gelatinous substance scraped from the interior of
the bag; or they may be seen in situ, by making very thin transverse

1 See his elaborate Memoir in " Philos. Transact.," 1870; and his " Depths of
the Sea "(1872), p. 71.

122

THE MICROSCOPE AND ITS REVELATIONS.

sections of the substance of the sponge. It is by such sections alone that
the internal structure of Sponges, and the relation of their spicular and
horny skeletons to their fleshy substance, can be demonstated. They are
best made by the imbedding process (§§ 189, 190). — In order to obtain
the spicules in an isolated condition, the animal matter must be got rid
of, either by incineration, or by chemical reagents. The latter method
is preferable, as it is difficult to free the mineral residue from carbonace-
ous particles by heat alone. If (as is commonly the case) the spicules
are siliceous, the Sponge may be treated with strong nitric or nitro-
muriatic acid, until its animal substance is dissolved away; if, on the
other hand, they be calcareous, a strong solution of potass may be em-
ployed instead of the acid. The operation is more rapidly accomplished
by the aid of heat; but if the saving of time be not of importance, it is
preferable on several accounts to dispense with it. The spicules, when
obtained in a separate state, should be mounted in Canada balsam. —
Sponge-tissue may often be distinctly recognized in sections of Agate,
Chalcedony, and other siliceous concretions, as will be more fully stated
hereafter (§ 699).

Zoophytes.

513. Under the general designation Zoophytes it will be still conve-
nient to group those animals which form composite skeletons or ' poly-
paries ' of a more or less plant-like character; associating with them the
Acalephs, which are now known to be the i sexual zooids/ of Polypes
(§ 518); but excluding the Polyzoa (Chap, xv.) on account of their truly
Molluscoid structure, notwithstanding their Zoophytic forms and habits
of life. The animals belonging to this group may be considered as
formed upon the primitive gastrula type (§391): their gastric cavity
(though sometimes extending itself almost indefinitely) being lined by
the original endoderm, and their surface being covered by the original
ectoderm; and these two lamellae not being separated by the interposition
of any body-cavity or ccelom. It is a fact of great interest, that although
the product of the development of a morula is here a distinctly indivi-
dualized Polype, in which several mutually dependent parts make up a
single organic whole, yet that these parts still retain much of their inde-
pendent Protozoic life; which is manifested in two very remarkable
modes. In the first place, the digestive sac is observed to be lined by a
layer of amoeboid cells, which send out pseudopodial prolongations into
its cavity, by whose agency (it may be pretty certainly affirmed) the
nutrient material is first .introduced into the body-substance. This
was first noticed by Prof. Allman in the beautiful Hydroid polype
Myriothela;1 the like has been since shown by Mr. Jeffery Parker to be
true of the ordinary Hydra f and Prof. E. Eay Lankester has made the
same observation upon the curious little Medusa lately found in a fresh-
ivater tank.3 (It may be mentioned in this connection, that Metschni-
koff has seen the cells which line the alimentary canal of the lower
Planarian worms gorging themselves with colored food-particles, exactly
in the manner of Amcebm.) — The second ' survival 9 of Protozoic inde-
pendence is shown in the extraordinary power possessed by Hydra, Acti-
nia, etc., to reproduce the entire organism from a mere fragment

1 "Philos. Transact.," 1875, p. 552.

2 " Proceed, of Roy. Soc.," Vol. xxx. (1880), p. 61.

3" Quart. Journ. Microsc. Sci.," M.S., Vol. xx. (1880), p. 37L

SPONGES AND ZOOPHYTES.

123

(§ 515). — This great division includes the two principal groups, the Hy-
drozoa and the Actinozoa; the former comprehending the Polypes, and
the latter the Anemonies. In the Hydrozoa there is no separation be-
tween the digestive cavity and the external body-wall; and the reproduc-
tive organs are external. In the Actinozoa the wall of the digestive sac
is separated from the external body- wall by an intervening space, which
communicates with it, and must be regarded as an extension of it; and
this is subdivided into chambers by a series of vertical partitions, to
which the reproductive organs are attached. — As most of the Hydrozoa
or Hydroid Polypes are essentially Microscopic animals, they need to be
described with some minuteness; whilst in regard to the Actinozoa those
points only will be dwelt-on, which are of special interest to the Micro-
scopist.

514. Hydrozoa. — The type of this group is the Hydra or fresh-water
polype, a very common inhabitant of pools and ditches, where it is most
commonly to be found attached to the leaves or stems of aquatic plants,
floating pieces of stick, etc. Two species are common in this country,
the H. viridis or green Polype, and the H. vulgaris, which is usually
orange-brown, but sometimes yellowish or red (its color being liable to
some variation according to the nature of the food on which it has been
subsisting); a third less common species, the H. fusca, is distinguished
from both the preceding by the length of its tentacles, which in the
former are scarcely as long as the body, whilst in the latter they are,
when fully extended, many times longer (Fig. 354). The body of the
Hydra consists of a simple bag or sac, which may be regarded as a
stomach, and is capable of varying its shape and dimensions in a very
remarkable degree; sometimes extending itself in a straight line so as to
form a long narrow cylinder, at other times being seen (when empty) as
a minute contracted globe, whilst, if distended with food, it may present
the form of an inverted flask or bottle, or even of a button. At the
upper end of this sac is a central opening, the mouth; and this is sur-
rounded by a circle of tentacles or ' arms/ usually from six to ten in
number, which are arranged with great regularity around the orifice.
The body is prolonged at its lower end into a narrow base, which is fur-
nished with a suctorial disk; and the Hydra usually attaches itself by
this while it allows its tendril-likj3 tentacles to float freely in the water.
The wall of the body is composed of cells imbedded in sarcode-substance;
and between its two layers there is a space chiefly occupied by undiffer-
entiated sarcode, having many ' vacuoles' or 'lacunaa' (which often seem
to communicate with one another) excavated in its substance. The arms
are made-up of the same materials as the body: but their surface is beset
with little wart-like prominences, which, when carefully examined, are
found to be composed of clusters of ' thread-cells,' having a single large
cell with a long spiculum in the centre of each. The structure of these
thread-cells or 6 urticating organs' will be described hereafter (§ 528); at
present it will be enough to point-out that this apparatus, repeated many
times on each tentacle, is doubtless intended to give to the organ a great
prehensile power; the minute filaments forming a rough surface adapted
to prevent the object from readily slipping out of the grasp of the arm,
whilst the central spicule or ' dart ' is projected into its substance, prob-
ably conveying into it a poisonous fluid secreted by a vesicle at its base.
The latter inference is founded upon the oft-repeated observation, that
if the living prey seized by the tentacles have a body destitute of hard
integument, as is the case with the minute aquatic Worms which consti-

124

THE MICROSCOPE AND ITS REVELATIONS.

tute a large part of its aliment, this speedily dies, even though, instead
of being swallowed, it escapes from their grasp; whilst, on the other
hand, minute Entomostraca, Insects, and other animals with hard enve-
lopes, may escape without injury, even after having been detaiued for
some time in the polype's embrace. The contractility of the tentacles
(the interior of which is traversed by a canal that communicates with
the cavity of the stomach) is very remarkable, especially in the Hydra
fusca ; whose arms, when extended in search of prey, are not less than
seven or eight inches in length; whilst they are sometimes so contracted,
when the stomach is filled with food, as to appear only like little tubercles

Fig. 354. Fia. 355.

Hydra fusca, with a young bud at Hydra fusca in gemmation ; a, mouth ; b,

6, and a more advanced bud at c. base ; c, origin of one of the buds.

around its entrance. By means of these instruments the Hydra is
enabled to draw its support from animals whose activity, as compared
with its own slight powers of locomotion, might have been supposed to
remove them altogether from its reach; for when, in its movements
through the water, a minute Worm or a Water-flea happens to touch one
of the tentacles of the Polype, spread-out as these are in readiness for
prey, it is immediately seized by this, other arms are soon coiled around
it, and the unfortunate victim is speedily conveyed to the stomach,
within which it may frequently be seen to continue moving for some
little time. Soon, however, its struggles cease, and its outline is

SPONGES AND ZOOPHYTES.

125

obscured by a turbid film, which gradually thickens, so that at last its
form is wholly lost. The soft parts are soon completely dissolved, and
the harder indigestible portions are rejected through the mouth. A
second orifice has been observed at the lower extremity of the stomach; but
this would not seem to be properly regarded as anal, since it is not used
for the discharge of such exuviae; it is probably rather to be considered
as representing, in the Hydra, the entrance to that ramifying cavity,
which, in the Compound Hydrozoa, brings into mutual connection the
lower extremities of the stomachs of all the individual polypes (Plate xx.).

515. The ordinary mode of reproduction in this animal is by a 'gem-
mation ' resembling that of Plants. Little bud-like processes (Fig. 354,
b, c) developed from its external surface gradually come to resemble the
parent in character, and to possess a digestive sac, mouth, and tentacles;
for a long time, however, their cavity is connected with that of the parent,
but at last the communication is cut-off by the closure of the canal of the
foot-stalk, and the young polype quits its attachment and goes in quest
of its own maintenance. A second generation of buds is sometimes ob-
served on the young polype before quitting its parent; and as many as
nineteen young Hydrce in different stages of development have been seen
connected with a single original stock (Fig. 355). This process takes
place most rapidly under the influence of warmth and abundant food; it
is usually suspended in winter, but may be made to continue by keeping
the polypes in a warm situation and well supplied with food. Another
very curious endowment seems to depend on the same condition — the ex-
traordinary power which one portion possesses of reproducing the rest.
Into whatever number of parts a Hydra may be divided, each may retain
its vitality, and give origin to a new and entire fabric; so that thirty or
forty individuals may be formed by the section of one. — The Hydra also
propagates itself, however, by a truly sexual process; the fecundating ap-
paratus, or vesicle producing 6 sperm-cells/ and the ovum (containing the
4 germ-cell/ imbedded in a store of nutriment adapted for its early devel-
opment) being both evolved in the substance of the walls of the stomach
— the male apparatus forming a conical projection just beneath the arms,
while the female ovary, or portion of the body- substance in which the
ovum is generated, has the form of a knob protruding from the middle
of its length. It would appear that sometimes one individual Hydra de-
velops only the male cysts or sperm-cells, while another develops only
the female cysts or ovisacs; but the general rule seems to be that the same
individual forms both organs. The fertilization of the ova, however,
cannot take-place until after the rupture of the spermatic cyst and of the
ovisac, by which the contents of both are set entirely free from the body
of the parent. — The autumn is the chief time for the development of the
sexual organs; but they also present themselves in the earlier part of the
year, chiefly between April and July. According to Ecker, the eggs of
H. viridis produced early in the season, run their course in the summer
of the same year; while those produced in the autumn, pass the winter
without change. When the ovum is nearly ripe for fecundation, the
ovary bursts its ectodermal covering, and remains attached by a kind of
pedicle. It seems to be at this stage that the act of fecundation occurs;
a very strong elastic shell or capsule then forms round the ovum, the sur-
face of which is in some cases studded with spine-like points, in others
tuberculated, the divisions between the tubercles being polygonal. The
ovum finally drops from its pedicle, and attaches itself by means of a
mucous secretion, till the hatching of the young Hydra, which comes

126

THE MICROSCOPE AND ITS REVELATIONS.

forth provided with four rudimentary tentacles like buds. — The Hydra
possesses the power of free locomotion, being able to remove from the
spot to which it has attached itself, to any other that may be more suita-
ble to its wants; its changes of place, however, seem rather to be per-
formed under the influence of light, towards which the Hydra seeks to
move itself, than with reference to the search after food.1

516. The Compound Hydroids may be likened to a Hydra whose
gemmae, instead of becoming detached, remain permanently connected
with the parent; and as these in their turn may develop gemmae from
their own bodies, a structure of more or less arborescent character, termed
a polypary, may be produced. The form which this will present, and the
relation of the component polypes to each other, will depend upon the
mode in which the gemmation takes-place: in all instances, however, the
entire cluster is produced by continuous growth from a single individual;
and the stomachs of the several polypes are united by tubes, which pro-
ceed from the base of each, along the stalk and branches, to communicate
with the cavity of the central stem. Whatever may be the form taken
by the stem and branches constituting the polypary of a Hydroid colony,
they will be found to be, or to contain, fleshy tubes having two distinct
layers; the inner (endoderm) having nutritive functions; the outer (ecto-
derm) usually secreting a hard cortical layer, and thus giving rise to
fabrics of various forms. Between these a muscular coat is sometimes
noticed. The fleshy tube, whether single or compound, is called a cceno-
sarc; and through it the nutrient matter circulates. The 'zooids/ or
individual members of the colony, are of two kinds: one, the polypite, or
alimentary zooid, resembling the Hydra in essential structure, and more
or less in aspect; the other, gonozooid, or sexual zooid, developed at cer-
tain seasons only, in buds of particular shape.

517. The simplest division of the Hydroida is that adopted by Mr.
Hincks,2 who groups them under the sub-order Athecata and Thecata,
the latter being again divided into the Thecaphora and the Gymnochroa.
In the first, neither the 'polypites' nor the sexual zooids bear true pro-
tective cases; in the second, the polypites are lodged in cells, or, as Mr.
Hincks prefers to call them, calycles, many of which resemble exquisitely
formed crystal cups, variously ornamented, and sometimes furnished with
lids or opercula; in the third, which contains the Hydras, there is no
polypary, and the reproductive zooids (gonozooids) are always fixed and
developed in the body-walls. According to Mr. Hincks, the two sexes
are sometimes borne on the same colony, but more commonly the zoo-
phyte is dioecious. The cases, however, are much less rare than has been
supposed, in which both male and female are mingled on the same
shoots. The sexual zooids either remain attached, and discharge their
contents at maturity, or become free and enter upon an independent
existence. 'The free forms nearly always take the shape of Meduscs (jelly
fish), swimming by rhythmical contractions of their bell or umbrella.
The digestive cavity is in the handle (manubrium) of the bell; and the
generative elements (sperm-cells or ova) are developed either between the
membranes of the manubrium, or in special sacs in the canals, radiating

1 A very full account of the structure and development of Hydra has recently
been published by Kleinenberg; of whose admirable Monograph a summary is
given by Prof . Allman, with valuable remarks of his own, in * 4 Quart. Journ.
Microsc. Sci.," N.S., Vol. xiv. (1874), p. 1. See also the important Paper by Mr.
Jeffery Parker already cited.

54 " History of British Hydroid Zoophytes/' 1868.

SPONGES AND ZOOPHYTES.

127

from it. The ova. when fertilized by the spermatozoa, undergo 6 seg-
mentation' according to the ordinary type (§ 581), the whole yolk-mass
subdividing successively into 2, 4, 8, 16, 32 or more parts, until a
6 mulberry mass' is formed; this then begins to elongate itself, its surface
being at first smooth, and showing a transparent margin, but afterwards
becoming clothed with cilia, by whose agency these little planulce, close! v
resembling ciliated Infusoria, first move about within the capsule, and
then swim forth freely when liberated by the opening of its mouth. At
this period the embryo can be made out to consist of an outer and an
inner layer of cells, with a hollow interior; after some little time the cilia
disappear, and one extremity becomes expanded into a kind of disk by
which it attaches itself to some fixed object; a mouth is formed, anil
tentacles sprout forth around it; and the body increases in length and
thickness, so as gradually to acquire the likeness of one of the parent
polypes, after which the 'polypary' characteristic of the genus is gradu-
ally evolved by the successive development of polype-buds from the first-
formed polype and its subsequent offsets. — The Medusae of these polypes
(Fig. 358) belong to the division called 6 naked-eye/ on account of the
(supposed) eye-spots usually seen surrounling the margin of the bell at
the base of the tentacles.

518. A characteristic example of this production of Medusa-like
'gonozooids' is presented by the form termed Syncoryne Sarsii (Fig.
356) belonging to the sub-order Atliecata. At a is shown the alimentary
zooid, or polypite, with its tentacles, and at b the successive stages a, b,
c9 of the sexual zooids, or medusa-buds. When sufficiently developed,
the medusa swims away, and as it grows to maturity enlarges its manu-
brium, so that i t hangs below the bell. The Medusa3 of the gen us Syncoryne
(as now restricted) have the form named Sarsia in honor of the Swedish
naturalist Sars. Their normal character is that of free swimmers;" but
Agassiz ascertained that in some cases, towards the end of the breeding
season, the sexual zooids remain fixed, and mature their products while
attached to the zoophyte.1 This condition of the sexual zooids is very
common amongst the Hydroida; and various intermediate stages may be
traced in different genera, between the mode in which the gonozooids are
produced in the common Hydra, as already described, and that of Syn-
coryne. In Tulularia the gonozooids, though permanently attached,
are furnished with swimming bells, having four tubercles representing
marginal tentacles. A common and interesting species Tulularia indi-
visa receives its specific name from the infrequency with which branches
are given off from the stem, these for the most part standing erect and
parallel, like the stalks of corn, upon the base to which they are attached.
This beautiful Zoophyte, which sometimes grows between the tide-marks,
but is more abundantly obtained by dredging in deep water, often attains
a size which renders it scarcely a microscopic object; its stems being
sometimes no less than a foot in height and a line in diameter. Several
curious phenomena, however, are brought into view by Microscopic
examination. The Polype-stomach is connected with the cavity of the
stem by a circular opening, which is surrounded by a sphincter; and an
alternate movement of dilatation and contraction takes place in jt, fluid
being apparently forced up from below, and then expelled again, after
which the sphincter closes in preparation for a recurrence of the opera-
tion; this, as observed by Mr. Lister, being repeated at intervals of

1 Hincks, op. ext., p. 49.

128

THE MICROSCOPE AND ITS REVELATIONS.

PLATE XX.

campanularia gelatinosa (after Van Beneden).
A, Upper part of the stem and branches, of the natural size.

b, Small portion enlarged, showing the structure of the animal ; a, terminal branch bearing
polypes; 6, polype-bud partially developed; *' horny cell containing the expanded polype d; ey
ovarian capsule, containing medusiform gemmae in various stages of development;/, fleshy sub-
stance extending through the stem and branches, and connecting the different polype-cells and
ovarian capsules; g, annular constrictions at the base of the branches.

SPONGES AND ZOOPHYTES.

129

eighty seconds. Besides the foregoing movement, a regular flow of fluid
carrying with it solid particles of various sizes, may be observed along the
whole length of the stem, passing in a somewhat spiral direction. — It is
worthy of mention here, that when a Tubularia is kept in confinement,
the polype-heads almost always drop off after a few days, but are soon
renewed again by a new growth from the stem beneath; and this exuvi-
ation and regeneration may take plac^ many times in the same indi-
vidual.1

519. It is in the Families Campanularida and Sertularida (whose
polyparies are commonly known as ' corallines '), that the horny branch-

Fig. 356. Fig. 357.

shaped body covered with tentacles:— b, a pol- Sertularia cupressina : a, natural size; B, portion
ype putting forth Medusoid gemmae ; a, a very magnified,
young bud; 6, a bud more advanced, the qua-
drangular form of which, with the four nuclei
whence the cirrhi afterwards spring, is shown
at d ; c, a bud still more advanced.

ing fabric attains its completest development; not only affording an in-
vestment to the stem, but forming cups or cells for the protection of
the polypites, as well as capsules for the reproductive gonozooids. Both
these families thus belong to the Sub-order Thecata. In the Campanu-
larida the polype-cells are campanulate or bell- shaped, and are borne at
the extremities of ringed stalks (Plate xx., c); in the Sertularida, on
the other hand, the polype-cells lie along the stem and branches, at-

1 The British Tubularida form the subject of a most complete and beautiful
Monograph by Prof. Allman, published by the Ray Society.
9

130

THE MICROSCOPE AND ITS REVELATIONS.

taclied either to one side only, or to both sides (Fig. 357). In both, the
general structure of the individual polypes (Plate xx. , d) closely corre-
sponds with that of the Hydra; and the mode in which they obtain
their food is essentially the same. Of the products of digestion, how-
ever, a portion finds its way down into the tubular stem, for the nour-
ishment of the general fabric; and very much the same kind of circula-
tory movement can be seen in Campanularia as in Tubularia, the
circulation being most vigorous in the neighborhood of growing parts.
It is from the 6 coenosarc' (/) contained in the stem and branches, that
new polype-buds (b) are evolved; these carry before them (so to speak) a
portion of the horny integument, which at first completely invests the
bud; but as the latter acquires the organization of a polype, the case
thins away at its most prominent part, and an opening is formed through
which the young polype protrudes itself,

520. The origin of the reproductive capsules or 'gonothecae' (e) is
exactly similar; but their destination is very different. Within them
are evolved, by a budding process, the generative organs of the Zoophyte;
and these in the Campanularida may either develop themselves into the
form of independent Medusoids, which completely detach themselves
from the stock that bore them, make their way out of the capsule, and
swim-forth freely, to mature their sexual products (some developing
sperm-cells, and others ova), and give origin to a new generation of po-
lypes; or, in cases in which the Medusoid structure is less distinctly pro-
nounced, may not completely detach themselves, but (like the flower-
buds of a Plant) expand one after another at the mouth of the capsule,
withering and dropping-off after they have matured their generative pro-
ducts. In the Sertularida, on the other hand, the Medusan conforma-
tion is wanting, as the gonozooids are always fixed; the reproductive cells
(Pig. 357, a), which were shown by Prof. Edward Forbes to be really meta-
morphosed branches, developing in their interior certain bodies which
were formerly supposed to be ova, but which are now known to be 6 me-
dusoids' reduced to their most rudimentary condition. Within these
are developed, — in separate gonothecae, sometimes perhaps on distinct
polyparies, — spermatozoa and ova; and the latter are fertilized by the
entrance of the former whilst still contained within their capsules. The
fertilized ova, whether produced in free or in attached medusoids, de-
velop themselves in the first instance into ciliated 'gemmules,' which
soon evolve themselves into true polypes, from every one of which a new
composite polypary may spring.

521. There are few parts of our coast which will not supply some or
other of the beautiful and interesting forms of Zoophytic life which have
been thus briefly noticed, without any more trouble in searching for
them than that of examining the surfaces of rocks, stones, sea-weeds,
and dead shells between the tide-marks. Many of them habitually live
in that situation; and others are frequently cast-up by the waves from
the deeper waters, especially after a storm. Many kinds, however, can
only be obtained by means of the dredge. For observing them during
their living state, no means is so convenient as the Zoophyte-trough
(§ 124). — In mounting Compound Hydrozoa, as well as Polyzoa, it will be
found of great advantage to place the specimens alive in the cells they
are permanently to occupy, and to then add Osmic acid drop by drop to
the sea-water; this has the effect of causing the protrusion of the ani-
mals, and of rendering their tentacles rigid. The liquid may be with-
drawn, and replaced by Goadby's solution, Dean's Gelatine, Glycerine

SPONGES AND ZOOPHYTES.

131

jelly, weak Spirit, diluted Glycerine, a mixture of Spirit and Glycerine
"•with Sea-water or any other menstruum, by means of the Syringe; and it
is well to mount specimens in several different menstrua, marking the
nature and strength of each, as some forms arc better preserved by one
and some by another.1 The size of the cell must of course be propor-
tioned to that of the object; and if it be desired to mount such a speci-
men as may serve for a characteristic illustration of the mode of growth
of the species it represents, the large shallow cells, whose walls are made
by cementing four strips of glass to the plate that forms the bottom
(§ 174), will generally be 'found preferable. — The horny polyparies of
the Sertularida, when mounted in Canada balsam, are beautiful objects
for the Polariscope; but in order to prepare them successfully, some nicety
of management is required. The following are the outlines of the
method recommended by Dr. Golding Bird, who very successfully prac
tised it: — The specimens selected, which should not exceed two inches in
length, are first to be submitted, while immersed in water of 120°, to the
vacuum of an air-pump. The ebullition which will take-place within
the cavities, will have the effect of freeing the polyparies from dead
polypes and other animal matter; and this cleansing process should
be repeated several times. The specimens are then to be dried, by first
draining them for a few seconds on bibulous paper, and then by sub-
mitting them to the vacuum of an air-pump, within a thick earthenware
ointment-pot fitted with a cover, which has been previously heated to
about 200°; by this means the specimens are very quickly and com-
pletely dried, the water being evaporated so quickly that the cells and
tubes hardly collapse or wrinkle. The specimens are then placed in
camphine, and again subjected to the exhausting process, for the dis-
placement of the air by that liquid; and when they have been thoroughly
saturated, they should be mounted in Canada balsam in the usual mode.
When thus prepared, they become very beautiful transparent objects
for low magnifying powers; and they present
a gorgeous display of colors when examined by FlG* 3**

Polarized light, with the interposition of a plate
Selenite, the effect being much enhanced by
the use of Black-ground illumination.

522. No result of Microscopic research was
more unexpected than the discovery of the close
relationship subsisting between the Hydroid
Zoophytes and the Medusoid Acaleplm (or 6 jel-
ly-fish'). We now know that the small free-
swimming Medusoids belonging to the ' naked- ''''^^fffj^ffflff^
eyed 'group, of which Tkaumantias (Fig. 358)
may be taken as a representative, are really to th^^yS^u^aS!
be considered as the detached sexual apparatus oraJ tentacles; b, stomach; c,

r, ^ r, « i-tji i i gastro-vascular canals, having

oi the Zoophytes irom which they have been the ovaries, a a, on either side,
budded-off, endowed with independent organs S^7einatin8 in theraar^inal
of nutrition and locomotion, whereby they be-
come capable of maintaining their own existence and of developing their
sexual products. The general conformation of these organs will be under-
stood from the accompanying figure. Many of this group are very beautiful
objects for Microscopic examination, being small enough to be viewed

1 See Mr. J. W. Morris in ''Quart. Journ. of Microsc. Science," N.S., Vol. ii.
(1862), p. 116.

132

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 359.

entire in the Zoophyte-trough. There are few parts of the coast on
which they may not be found, especially on a calm warm day, by skim-
ming the surface of the sea with the Tow-net (§ 217); and they are capa-
ble of being stained and preserved in cells, after being hardened by osmic
acid.

523. The history of the large and highly-developed Medusa or Aca-
LEPHiE which are commonly known as ' jeliy-flsh/ is essentially similar;
for their progeny have been ascertained to develop themselves in the first
instance under the Polype-form, and to lead a life which in all essential
respects is zoophytic; their development into Medusae taking place only
in the closing phase of their existence, and then rather by gemmation
from the original polype, than by a metamorphosis of its own fabric.
The huge Rhizostoma found commonly swimming round our coasts, and
the beautiful Chrysaora remarkable for its long ' furbelows 9 which act as
organs of prehension, are Oceanic Acalephs developed from very small
polypites, which fix themselves by a basal cup or disk. The embryo
emerges from the cavity of its parent, within which the first stages of its
development have taken place, in the condition of a ciliated i getnmule,'

of rather oblong form, very closely re-
sembling an Infusory Animalcule, but
destitute of a mouth. One end soon
*"7\"* ^P^li contracts and attaches itself, however,

"| _J m^-Jr so as to form a foot; the other enlarges

and opens to form a mouth, four tuber-
cles sprouting around it, which grow
into tentacles; whilst the central cells
melt-down to form the cavity of the
stomach. Thus a Hydra-like polype is
formed, which soon acquires many addi-
tional tentacles; and this, according to
the observations of Sir J. G. Dalyell on
the Hydra tuba, which is the polype-
stage of the Chrysaora, leads in every
important particular the life of a
Hydra; propagates like it by repeated
gemmation, so that whole colonies are
formed as offsets from a single stock;
and can be multiplied like it by artifi-
cial division, each segment developing
itself into a perfect Hydra. There
seems to be no definite limit to its con-
tinuance in this state, or to its power
of giving origin to new polype- buds;
but when the time comes for the devel-
opment of its sexual gonozooids, the
polype quits its original condition of a
minute bell with slender tentacles (Fig.
359, c, a), assumes a cylindrical form,
and elongates itself considerably; a
constriction or indentation is then seen
around it, just below the ring which encircles the mouth and gives origin
to the tentacles; and similar constrictions are soon repeated round the
lower parts of the cylinder, so as to give to the whole body somewhat the
appearance of a rouleau of coins (Fig. 359, a); a sort of fleshy bulb, a,

Successive stages a, b, c, d, of devel-
opment of Chrysaora: — a, elongated and
constricted Polype-body; 6, its original cir-
cle of tentacles; c, its secondary circle of
tentacles; d, proboscis of most advanced
Medusa-disk; e, polype-bud from side of
polype-body.

SPONGES AND ZOOPHYTES. 133

somewhat of the form of the original polype, being still left at the at-
tached extremity. The number of circles is indefinite, and all are not
formed at once, new constrictions appearing below, after the upper por-
tions have been detached; as many as 30 or even 40 have thus been pro-
duced in one specimen. The constrictions then gradually deepen, so as
to divide the cylinder into a pile of saucer-like bodies; the division being
most complete above, and
the upper disks usually pre-
senting some increase in
diameter; and whilst this is
taking place, the edges of
the disks become divided
into lobes (b), each lobe soon
presenting the cleft with
the supposed rudimentary
aye at the bottom of it,
which is to be plainly seen
in the detached Medusae
(Pig. 360, c). Up to this
period, the tentacles of the
original polype surmount
the highestof the disks; but
before the detachment of
the topmost disk, this circle
disappears, and a new one
is developed at the summit
of the bulb which remains
at the base of the pile (c, c).
At last the topmost and
largest disk begins to ex-
hibit a sort of convulsive
struggle; it becomes detach-
ed, and swims freely away;
and the same series of changes takes-place from above downwards, until
the whole pile of disks is detached and converted into free-swimming
Medusae. But the original polypoid body still remains, and may return
to its original polype-like mode of gemmation (d, e); becoming the pro-
genitor of a new colony, every member of which may in its turn bud-off
a pile of Medusa-disks.

524. The bodies thus detached have all the essential characters of the
adult Mednsce. Each consists of an umbrella-like disk, divided at its
edge into a variable number of lobes, usually eight; and of a stomach,
which occupies a considerable proportion of the disk, and projects down-
wards in the form of a proboscis, in the centre of which is the quadrangu-
lar mouth (Fig. 360, A, b). As the animal advances towards maturity,
the intervals between the segments of the border of the disk gradually
fill-up, so that the divisions are obliterated; tubular prolongations of the
stomach extend themselves over the disk; and from its border there
sprout forth tendril-like filaments, which hang down like a fringe around
its margin. From the four angles of the mouth, which, even in the
youngest detached animal, admits of being greatly extended and pro-
truded, prolongations are put forth, which form the four large tentacles
of the adult. The young Medusae are very voracious, and grow rapidly,
so as to attain a very large size. The Cyanew and Chrysaorce, which are

Development of Chrysaora from Hydra tuba:—x< de-
tached individual viewed sideways, and enlarged, showing
the proboscis a, and b the bifid lobes: b. individual seen
from above, showing the bifid lobes of the margin, and the
quadrilateral mouth; c, one of the nifid lobes still more en-
larged, showing the rudimentary eye (?) at the bottom of
the cleft; d, group of young Medusae, as seen swimming in
the water, of the natural size.

134

THE MICROSCOPE AND ITS REVELATIONS.

common all round our coasts, often have a diameter of from 6 to 15
inches; while the Rhizostoma sometimes reaches a diameter of from two
to three feet. The quantity of solid matter, however, which their fabrics
contain is extremely small. It is not until adult age has been attained,
that the generative organs make their appearance, in four chambers dis-
posed around the stomach, which are occupied by plaited membranous
ribands containing sperm-cells in the male and ova in the female, and the
embryoes evolved from the latter, when they have been fertilized by the
agency of the former, repeat the extraordinary cycle of phenomena which
has been now described, developing themselves in the first instance into
Hydroid Polypes, from which Medusoids are subsequently budded-off.

525. This cycle of phenomena is one of those to which the term
' alternation of generations 3 was applied by Steenstrup,1 who brought
together under this designation a number of cases in which generation a
does not produce a form resembling itself, but a different form, b; whilst
generation b gives origin to a form which does not resemble itself, but
returns to the form A, from which B itself sprang. It was early pointed
out, however, by the Author,2 that the term 'alternation of generations'
does not appropriately represent the facts either of this case, or of any of
the other cases grouped under the same category: the real fact being that
the two organisms, A and B, constitute two stages in the life-history of
one generation; and the production of one form from the other being in
only one instance by a truly generative or sexual act, whilst in the other
it is by a process of gemmation or budding. Thus the Medusm of both
orders (the 6 naked-eyed ' and the ' covered-eyed ' of Forbes) are detached
flower-buds, so to speak, of the Hydroid Zoophytes which bud them off;
the Zoophytic phase of life being the most conspicuous in such Thecata
as Campanularida and Sertularida, whose Medusa-buds are of small size
and simple conformation, and not unfrequently do not detach themselves
as independent organisms; whilst the Medusan phase of life is the most
conspicuous in the ordinary Acalephs, their Zoophytic stage being passed
in such obscurity as only to be detected by careful research. — The
Author's views on this subject, which were at first strongly contested by
Prof. E. Forbes, and other eminent Zoologists, have now come to be
generally adopted.

526. Actinozoa. — Of this group, the common Sea- Anemonies maybe
taken as types; constituting, with their allies, the order Zoantharia, or
Helianthoid polypes, which have numerous tentacles disposed in several
rows. Next to them come the Alcyonaria, consisting of those whose
polypes, having only six or eight broad short tentacles, present a star-
like aspect when expanded; as is the case with various composite Sponge-
like bodies, unpossessed of any hard skeleton, which inhabit our own
shores, and also with the Red Coral and the Tubipora of warmer seas,
which have a stony skeleton that is internal in the first case and external
in the second, as also with the Sea-pens, and the Gorgonim or Sea-fans.
A third order, Rugosay consists of fossil Corals, whose stony polyparies
are intermediate in character between those of the two preceding. And
lastly, the Ctenophora, free swimming gelatinous animals, many of which
are beautiful objects for the Microscope, are by most Zoologists ranked
with the Actinozoa.

1 See his Treatise on " The Alternation of Generations," published by the Ray
Society.

2<k Brit, and For. Med.-Chir. Review," Vol. i. (1848), p. 192, et seq.

SPONGES AND ZOOPHYTES.

135

527. Of the Zoantharia, the common Actinia or ' sea anemone 9 may
be taken as the type; the individual polypites of all the composite fabrics
included in the group being constructed upon the same model. In by
far the larger proportion of these Zoophytes, the bases of the polypites,
as well as the soft flesh that connects together the members of aggregate
masses, are consolidated by calcareous deposit into stony Corals; and the
surfaces of these are beset with ' cells,' usually of a nearly circular form,
each having numerous vertical plates or lamellce radiating from its centre
towards its circumference, which are formed by the consolidation of the
lower portions of the radiating partitions that divide the space interven-
ing between the stomach and the general integument of the animal into
separate chambers. This arrangement is seen on a large scale in the
Fungia or 6 mushroom-coral ' of tropical seas, which is the stony base of
a solitary Anemone-like animal; on a far smaller scale, it is seen in the
little Caryophyllia, a like solitary Anemone of our own coasts, which is
scarcely distinguishable from an Actinia by any other character than the
presence of this disk, and also on the surface of many of those stony
corals known as ' madrepores;' whilst in some of these the individual
polype-cells are so small, that the lamellated arrangement can only be
made-out when they are considerably magnified. Portions of the surface
of such Corals, or sections taken at a small depth, are very beautiful
objects for low powers, the former being viewed by reflected, and the
latter by transmitted light. And thin sections of various fossil Corals of
this group are very striking objects for the lower powers of the Oxy-
hydrogen Microscope. t

528. The chief point of interest to the Microscopist, however, in the
structure of these animals, lies in the extraordinary abundance and high
development of those ' filiferous capsules,' or ' thread-cells,' the presence
of which on the tentacles of the Hydroid polypes has been already
noticed (§ 514), and which are also to be found, sometimes sparingly,
sometimes very abundantly, in the tentacles surrounding the mouth of
the Medusas, as well as on other parts of their bodies. If a tentacle
of any of the Sea-anemonies so abundant on our coasts (the smaller and
more transparent kinds being selected in preference) be cut-off, and be
subjected to gentle pressure between the two glasses of the Aquatic-box
or the Compressorium, multitudes of little dart-like organs will be seen
to project themselves from its surface near its tip; and if the pressure be
gradually augmented, many additional darts will every moment come into
view. Not only do these organs present different forms in different
species, but even in one and the same individual very strongly marked
diversities are shown, of which a few examples are given in Fig. 361.
At a, B, c, d, is shown the appearance of the 6 filiferous capsules,' whilst
as yet the thread lies coiled-up in their interior; and at E, f, g, h, are
seen a few of the most striking forms which they exhibit when the thread
or dart has started-forth. These thread-cells are found not merely in the
tentacles and other parts of the external integument of Actinozoa, but
also in the long filaments which lie in coils within the chambers that
surround the stomach, in contact with the sexual organs which are
attached to the lamellae dividing the chambers. The latter sometimes
contain ' sperm-cells ' and sometimes ova, the two sexes being here
divided, not united in the same individual. — What can be the office of
the filiferous filaments thus contained in the interior of the body, it is
difficult to guess-at. They are often found to protrude from rents in the
external tegument, when any violence has been used in detaching the

136

THE MICROSCOPE AND ITS REVELATIONS.

animal from its base; and when there is no external rupture, they are
often forced through the wall of the stomach into its cavity, and may be
seen hanging out of the mouth. The largest of these capsules, in their
unprotected state, are about l-300th of an inch in length; while the
thread or dart, in Corynactis Allmanni, when fully extended, is not less
than l-8th of an inch, or thirty-seven times the length of its capsule.1

Fig. 361.

Fig. 362.

Spicules of Alcyonium and Gorgonia*

Fig. 363.

Flliferous Capsules of Actinozoaf— a. b,
Corynactis Allmanni; c, e, p, Caryophyllia
Smithii ; d, g. Actinia crassicornis; h, Ac-
tinia Candida.

A, Spicules of Gorgania guttata.

B, Spicules of Muricia elongata.

529. Of the Alcyonaria a characteristic example is found in the
Alcyonium digitatum of our coasts; a lobed sponge-like mass, covered
with a tough skin; which is commonly known under the name of ' dead-
man's toes/ or by the more elegant name of 6 mermaids ' fingers.' When

1 See Mr. Gosse's " Naturalist's Rambles on the Devonshire Coast," and Prof.
Mobius 'Ueber den Bau, etc., der Nesselkapseln einiger Polypen und Quallen,' in
" Abhandl. Naturw. Vereins zu Hamburg," Band v., 1866.

SPONGES AND ZOOPHYTES.

137

a specimen of this is first torn from the rock to which it has attached
itself, it contracts into an unshapely mass, whose surface presents nothing
but a series of slight depressions arranged with a certain regularity. But
after being immersed for a little time in a jar of sea-water, the mass
swells-out again, and from every one of these depressions an eight-armed
polype is protruded, "which resembles a flower of exquisite beauty and
perfect symmetry. In specimens recently taken, each of the petal-like
tentacula is seen with a hand-glass to be furnished with a row of deli-
cately-slender pinnce or filaments, fringing each margin, and arching
onwards; and with a higher power, these pinnae are seen to be roughened
throughout their whole length, with numerous prickly rings. After a
day's captivity, however, the petals shrink up into short, thick, unshapely
masses, rudely notched at their edges" (Gosse). When a mass of this
sort is cut-into it is found to be channelled-out somewhat like a Sponge,
by ramifying canals; the vents of which open into the stomachal cavities
of the polypes, which are thus brought into free communication with
each other, — a character that especially distinguishes this Order. A
movement of fluid is kept-up within these canals (as may be distinctly
seen through their transparent bodies) by means of cilia lining the inter-
nal surfaces of the polypes; but no cilia can be discerned on their external
surfaces. The tissue of this spongy polypidom is strengthened through-
out, like that of Sponges (§ 510), with mineral spicules (always, however,
calcareous), which are remarkable for the elegance of their forms; these
are disposed with great regularity around the bases of the polypes, and
even extend part of their length upwards on their bodies. In the Gor-
gonia, or sea-fan, whilst the central part of the polypidom is consolidated
into a horny axis, the soft flesh which clothes this axis is so full of
tuberculated spicules, especially in its outer layer, that, when this dries-up
they form a thick yellowish or reddish incrustation upon the homey
stem; this crust is, however, so friable, that it may be easily rubbed
down between the fingers, and when examined with the Microscope, it is
found to consists of spicules of different shapes and sizes, more or less
resembling those shown in Figs. 362, 303, sometimes colorless, but some-
times of a beautiful crimson, yellow, or purple. These spicules are best
seen by Black-ground illumination, especially when viewed by the Bino-
cular Microscope. They are, of course, to be separated from the animal
substance in the same manner as the calcareous spicules of Sponges
(§ 512); and they should be mounted, like them, in Canada balsam. The
spicules always possess an organic basis; as is proved by the fact, that
when their lime is dissolved by dilute acid, a gelatinous-looking residuum
is left, which preserves the form of the spicule.

530. The Ctenophora, or ' comb-bearers/ are so named from the
comb-like arrangement of the rows of tiny ' paddles/ by the movement
of which the bodies of these animals are propelled. A very beautiful
and not uncommon representative of this order is furnished by the Cy-
dippe pileus (Fig. 364), very commonly known as the Beroe, which
designation, however, properly appertains to another animal (Fig. 365)
of the same grade of organization. The body of Cydippe is a nearly-
globular mass of soft jelly, usually about 3-8ths of an inch in diameter;
and it may be observed, even with the naked eye, to be marked by eight
bright bands, which proceed from pole to pole like meridian lines.
These bands are seen with the Microscope to be formed of rows of flat-
tened filaments, far larger than ordinary cilia, but lashing the water in
the same manner; they sometimes act quite independently of one

138

THE MICROSCOPE AND ITS REVELATIONS.

another, so as to give to the body every variety of motion, but sometimes
work altogether. If the sunlight should fall upon them when they are
in activity, they display very beautiful iridescent colors. In addition to
these ' paddles,' the Cydippe is furnished with a pair of long tendril-like
filaments, arising from the bottom of a pair of cavities in the posterior
part of the body, and furnished with lateral branches (a); within these
cavities they may lie doubled-up, so as not to be visible externally; and
when they are ejected, which often happens quite suddenly, the main
filaments first come-forth, and the lateral tendrils subsequently uncoil
themselves, to be drawn-in again and packed-up within the cavities with
almost equal suddenness. The mouth of the animal, situated at one of
the poles, leads first to a quadrifid cavity bounded by four folds which
seem to represent the oral proboscis of the ordinary Medusae (Fig. 359);
and this leads to the true stomach, which passes towards the opposite
pole, near to which it bifurcates, its branches passing towards the polar

Fig. 364. Fig. 365.

Cydippe pileus, with its tentacles Beroe Forskalii, showing the tubular
extended. prolongations of the stomach.

surface on either side of a little body which has every appearance of
being a nervous ganglion, and which is surmounted externally by a
fringe-like apparatus that seems essentially to consist of sensory ten-
tacles.1 From the cavity of the stomach, tubular prolongations pass-off
beneath the ciliated bands, very much as in the true Beroe (b); these
may easily be injected with colored liquids, by the introduction of the
extremity of a fine-pointed glass-syringe (Fig. 106) into the mouth.
The liveliness of this little creature, which may sometimes be collected

1 It is commonly stated that the two branches of the alimentary canal open on
the surface by two pores situated in the hollow of the fringe, one on either side
of the nervous ganglion. The Author, however, has not been able to satisfy him-
self of the existence of such excretory pores in the ordinary Cydippe or Beroe,
although he has repeatedly injected their whole alimentary canal and its exten-
sions, and has attentively watched the currents produced by ciliary action in the
interior of the bifurcating prolongations, which currents alwaysappear to him to
return as from csecal extremities. He is himself inclined to believe that this ar-
rangement has reference solely to the nutrition of the nervous ganglion and ten-
tacular apparatus, which lies imbedded (so to speak) in the bifurcation of the
alimentary canal, so as to be able to draw its supply of nutriment direct from
that cavity.

SPONGES AND ZOOPHYTES.

139

in large quantities at once by the Stick-net, renders it a most beautiful
subject for observation when due scope is given to its movements; but
for the sake of Microscopic examination, it is of course necessary to con-
fine these. — Various species of true Beroe, some of them even attaining
the size of a small lemon, are occasionally to be met with on our coasts;
in all of which the movements of the body are effected by the like agency
of paddles arranged in meridional bands. These are splendidly luminous
in the dark, and the luminosity is retained even by fragments of their
bodies, being augmented by agitation of the water containing them. —
All the Ctenopliora are reproduced from eggs, and are already quite ad-
vanced in their development by the time they are hatched. Long before
they escape, indeed, they swim about with great activity within the
walls of their diminutive prison; their rows of locomotive paddles early
attaining a large size, although the long flexile tentacles of Cydippe are
then only short stumpy protuberances. Through the embryonic forms
of the two groups, Prof. Alex. Agassiz considers the Ctenophora as re-
lated to Eclmiodermata.

Those who may desire to acquire a more systematic and detailed acquaintance
with the Zoophyte-group, may be especially referred to the following Treatises
and Memoirs, in addition to those already cited, and to the various recent syste-
matic Treatises on Zoology: — Dr. Johnston's 44 History of British Zoophytes,"
Prof. Milne-Ed wards's 44 Recherches sur les Polypes," and his 44 Histoire des Co-
rallaires " (in the 4 Suites a BufTon'), Paris, 1857, Prof. Van Beneden 4 Sur lesTubu-
laires,'and * Sur lesCampanulaires,' in 44 Mem. de l'Acad. Roy. deBruxelles,"Tom.
xvii., and his 44 Recherches sur l'Hist. Nat. des Polypes qui frequentent les C6tes
de Belgique," Op. cit., Tom. xxxvi., Sir J. G. DalyelFs 4 Rare and Remarkable
Animals of Scotland," Vol. i., Trembley's 44 Mem. pour servir a l'histoire d'un
genre de Polype d'Eau douce," M. Hollard's 4 Monographie du Genre Actinia,1 in
Ann. des Sci. Nat." Ser. 3, Tom. xv., Prof. Max Schultze, 4 On the Male Repro-
ductive Organs of Campanularia genictdata,' in 44 Quart. Journ. of Microsc. Sci.,"
Vol. iii. (1855), p. 59, Prof. Agassiz's beautiful Monograph on American Medusas,
forming the third volume of his 44 Contributions to the Natural History of the
United States of America," Mr. Hincks's 44 British Hydroid Zoophytes," Prof.
Allman's admirable Memoirs on Cordylophora and Myriothela in the Philos.
Transact, for 1853 and 1875, Prof. J. R. Greene's 44 Manual of the Sub- Kingdom
Cazlenterata" which contains a Bibliography very complete to the date of its
publication, and the articles 4Actinozoa,' 4 Ctenophora,' and 4 Hydrozoa,' in the
Supplement to the Natural History Division of the 44 English Cyclopaedia." The
Ctenophora are specially treated of in Vol. iii of Prof Agassiz's 44 Contributions
to the Natural History of the United States." See also Prof. Alex. Agassiz 44 Sea-
side Studies in Natural History," and his 44 Illustrated Catalogue of the Museum
of Comparative Anatomy at Harvard College," Prof James-Clark in 44 American
Journal of Science," Ser. 2, Vol. xxxv., p. 348, Dr. D. Macdonald in 44 Transact.
Roy. Soc. Edinb.," Vol. xxiii.. p 515, Mr. H. N. Moseley 4 On the Structure of a
species of MilleporaS in 44 Philos Trans.," 1877, p. 117, and 4 On the Structure of
the Stylasteridce,' Ibid., 1878, p 425; and on the 'Acalephce' Prof. Haeckel's 44 Bei-
trage zur Naturgeschichte der Hydromedusen," the masterly work of the brothers
Hertwig, '4 Das Nervensystem und die Sinnesorgane der Medusen," 1878, and the
Memoir of Prof. Schafer ' On the Nervous System of AureliaauritaJ in 44 Philos.
Trans.," 1878, p. 563.

140

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XIV.
ECHINODERMATA.

531. As we ascend the scale of Animal life, we meet with such a
rapid advance in complexity of structure, that it is no longer possible to
acquaint one's-self with any organism by Microscopic examination of it
as a whole; and the dissection or analysis which becomes necessary, in
order that each separate part may be studied in detail, belongs rather to
the Comparative Anatomist than to the ordinary Microscopist. This is
especially the case with the Echinus (Sea-Urchin), Asterias (Star-fish),
and other members of the class Echinodermata; even a general account
of whose complex organization would be quite foreign to the purpose of
this work. Yet there are certain parts of their structure which furnish
Microscopic objects of such beauty and interest that they cannot by any
means be passed by; while the study of their Embryonic forms, which
can be prosecuted by any Sea-side observer, brings into view an order of
facts of the highest scientific interest.

532. It is in the structure of that Calcareous Skeleton which proba-
bly exists under some form in every member of this class, that the ordi-
nary Microscopist finds most to interest him. This attains its highest
development in the Echinida; in which it forms a box-like shell or ' test,'
composed of numerous polygonal plates jointed to each other with great
exactness, and beset on its external surface with 6 spines/ which may
have the form of prickles of no great length, or may be stout club-
shaped bodies, or, again, may be very long and slender rods. The inti-
mate structure of the shell is everywhere the same; for it is composed of
a network, which consists of Carbonate of Lime with a very small quan-
tity of animal matter as a basis, and which extends in every direction
(i.e., in thickness as well as in length and breadth), its areola or inter-
spaces freely communicating with each other (Figs, 366, 367). These
6 areolae/ and the solid structure which surrounds them, may bear an ex-
tremely variable proportion one to the other; so that in two masses of
equal size, the one or the other may greatly predominate; and the tex-
ture may have either a remarkable lightness and porosity, if the network
be a very open one like that of Fig. 366, or may possess a considerable
degree of compactness, if the solid portion be strengthened. Generally
speaking, the different layers of this network, which are connected to-
gether by pillars that pass from one to the other in a direction perpen-
dicular to their plane, are so arranged that the perforations in one shall
correspond to the intermediate solid structure in the next; and their
transparence is such that when we are examining a section thin enough
to contain only two or three such layers, it is easy, by properly focussing
the Microscope, to bring either one of them into distinct view. From
this very simple but very beautiful arrangement, it comes to pass that
the plates of which the entire 6 test 9 is made-up possess a very consider-

ECHINODERMATA.

able degree of strength, notwithstanding that their porousness is such,
that if a portion of a fractured edge, or any other part from which the
investing membrane has been removed, be laid upon fluid of almost any
description, this will be rapidly sucked-up into its substance. — A very
beautiful example of the same kind of calcareous skeleton, having a more
regular conformation, is furnished by the di^k or i rosette' which is con-
tained in the tip of every one of the tubular suckers put forth by the

Fig. 366. Fig. 367.

Section of Shell of Echinus, showing
the calcareous network of which it is
composed :— a a, portions of a deeper
layer.

Transverse Section of central portion
of Spine of Acrocladia, showing its more
open network.

living Echinus from the 'ambulacral pores' that are seen in the rows of
smaller plates interposed between the larger spine-bearing plates of its
box-like shell. If the entire disk be cut-off, and be mounted when dry
in Canada balsam, the calcareous rosette maybe seen sufficiently well;
but its beautiful structure is better made-out when the animal membrane
that incloses it has been got-rid of by boiling in a solution of caustic
potass; and the appearance of one of the five segments of which it is
composed, when thus prepared, is shown in Fig. 368.

533. The most beautiful display Fig 368

of this reticulated structure how-
ever, is shown in the structure of
the 6 spines' of Echinus, Cidaris,
etc. ; in which it is combined with
solid ribs or pillars, disposed in such
a manner as to increase the strength
of these organs; a regular and ela-
borate pattern being formed by
their intermixture, which shows
considerable variety in different
species. — When we make a thin
transverse section (Plate n., fig. 1)
of almost any spine belonging to
the genus Echinus (the small spines
of our British species, however,
being exceptional in this respect)
or its immediate allies, we see it to be made up of a number of
concentric layers, arranged in a manner that strongly reminds us of
the concentric rings of an Exogenous tree (Fig. 254). The number of
these layers is extremely variable; depending not merely upon the age

One of the segments of the calcareous skeleton of
an Ambulacral Disk of Echinus.

THE MICROSCOPE AND ITS REVELATIONS.

of the spine, but (as will presently appear) upon the part of its length
from which the section happens to be taken. The centre is usually occu-
pied by a very open network (Fig. 367); and this is bounded by a row
of transparent spaces (like those at a, a', b b\ c c/ etc., Fig. 369), which
'*on a cursory inspection might be supposed to be void, but are found on
examination to be the sections of solid ribs or pillars, which run in the
direction of the length of the spines, and form the exterior of every layer.
Their solidity becomes very obvious, when we either examine a section
of a spine whose substance is pervaded (as often happens) with a coloring
matter of some depth, or when we look at a very thin section by black-
ground illumination. Around the innermost circle of these solid pillars
there is another layer of the calcareous network, which again is surrounded
by another circle of solid pillars; and this arrangement may be repeated
many times, as shown in Fig. 369, the outermost row of pillars forming
the projecting ribs that are commonly to be distinguished on the surface
of the spine. Around the cup-shaped base of the spine is a membrane
which is continuous with that covering the surface of the shell, and serves
not merely to hold-down the cup upon the tubercle over which it works,
but also by its contractility to move the spine in any required direction.

Fig. 369.

Portion of transverse section of Spine of Acrocladia mammillata.

This membrane is probably continued onwards over the whole surface of
the spine, although it cannot be clearly traced to any distance from the
base, and the new formations may be presumed to take place in its sub-
stance. Each new formation completely ensheathes the old; not merely
surrounding the part previously formed, but also projecting considerably
beyond it; and thus it happens that the number of layers shown in a trans-
verse section will depend in part upon the place of that section. For if
it cross near the base, it will traverse every one of the successive layers
from the very commencement; whilst if it cross near the apex, it will
traverse only the single layer of the last growth, notwithstanding that,
in the club-shaped spines, this terminal portion may be of considerably
larger diameter than the basal; and in any intermediate part of the spine,
so many layers will be traversed, as have been formed since the spine
first attained that length. The basal portion of the spine is enveloped
in a reticulation of a very close texture, without concentric layers; form-
ing the cap or socket which works over the tubercle of the shell.

534. Their combination of elegance of pattern with richness of
coloring, renders well-prepared specimens of these Spines among the
most beautiful objects that the Microscopist can anywhere meet with.

ECHINODERM AT A .

143

The large spines of the various species of the genus Acrocladia furnish
sections most remarkable for size and elaborateness, as well as for depth
of color (in which last point, however, the deep purple spines of Echinus
lividus are pre-eminent); but for exquisite neatness of pattern, there are
no spines that can approach those of Echinometra heteropora (Plate n.,
fig. 1) and E. lucunter. The spines of Heliocidaris variolaris are also
remarkable for their beauty. — No succession of concentric layers is seen
in the spines of the British Echini, probably because (according to the
opinion of the late Sir J. G. Dalyell) these spines are cast off and
renewed every year; each new formation thus going to make an entire
spine, instead of making an addition to that previously existing. — Most
curious indications are sometimes afforded by sections of Echinus-spines,
of an extraordinary power of reparation inherent in these bodies. For
irregularities are often seen in the transverse sections, which can be
accounted for in no other way than by supposing the spines to have
received an injury when the irregular part was at the exterior, and to
have had its loss of substance supplied by the growth of new tissue, over
which the subsequent layers have been formed as usual. And sometimes

Fig. 370.

Spines of Spatangus,

a peculiar ring may oe seen upon the surface of a spine, which indicates
the place of a complete fracture; all beyond it being a new growth,
whose unconformableness to the older or basal portion is clearly shown
by a longitudinal section.1 — The spines of Cidaris present a marked
departure from the plan of structure exhibited in Echinus; for not only
are they destitute of concentric layers, but the calcareous network which
forms their principal substance is encased in a solid calcareous sheath
perforated with tubules, which seems to take the place of the separate
pillars of the Echini. This is usually found to close in the spine at its
tip also; and thus it would appear that the entire spine must be formed
at once, since no addition could be made either to its length or to its
diameter, save on the outside of the sheath, where it is never to be
found. The sheath itself often rises up in prominent points or ridges
on the surface of these spines; thus giving them a character by which
they may be distinguished from those of Echini.— The slender, almost
filamentary spines of Spatangus (Pig. 370), and the innumerable minute

'See the Author's description of such Reparations in the * < Monthly Micro-
scopical Journal," Vol. iii. (1870), p. 225.

144 THE MICROSCOPE AND ITS REVELATIONS.

hair-like processes attached to the shell of Clypeaster, arc composed of
the like regularly-reticulated substance; and these are very beautiful
objects for the lower powers of the Microscope, when laid upon a black
ground and examined by reflected light without any further preparation.
— It is interesting also to find that the same structure presents itself in
the curious Pedicellarice (forceps-like bodies mounted on long stalks),
which are found on the surface of many Echinida, and the nature of
which was formerly a source of much perplexity to Naturalists, some
having maintained that they are parasites, whilst others considered them
as proper appendages of the Echinus itself. The complete conformity
which exists between the structure of their skeleton and that of the
animal to which they are attached, removes all doubt of their being
truly appendages to it, as observation of their actions in the living state
would indicate.

535. Another example of the same structure is found in the peculiar
framework of plates which surrounds the interior of the oral orifice of
the shell, and which includes the five teeth that may often be seen
projecting externally through that orifice; the whole forming what is
known as the 'lantern of Aristotle/ The texture of the plates or jaws
resembles that of the shell in every respect, save that the network is
more open; but that of the teeth differs from it so widely, as to have
been likened to that of the bone and dentine of Vertebrate animals.
The careful investigations of Mr. James Salter,1 however, have fully
demonstrated that the appearances which have suggested this compari-
son are to be otherwise explained; the plan of structure of the tooth
being essentially the same as that of the shell, although greatly modified
in its working-out. The complete tooth has somewhat the form of that
of the front tooth of a Rodent; save that its concave side is strengthened
by a projecting 'keel/ so that a transverse section of the tooth presents
the form of a This keel is composed of cylindrical rods of carbonate
of lime, having club-shaped extremities lying obliquely to the axis of the
tooth (Fig. 371, A, d)\ these rods do not adhere very firmly together, so
that it is difficult to keep them in their places in making sections of
the part. The convex surface of the tooth (c, c, c) is covered with a
firmer layer, which has received the name of 6 enamel; ' this is composed
of shorter rods, also obliquely arranged, but having a much more inti-
mate mutual adhesion than we find among the rods of the keel. The
principal part of the substance of the tooth (a, b) is made-up of what
may be called the ( primary plates; ' these are triangular plates of
calcareous shell-substance, arranged in two series (as shown at b), and
constituting a sort of framework with which the other parts to be
presently described become connected. These plates may be seen by
examining the growing base of an adult tooth that has been preserved
with its attached soft parts in alcohol, or (which is preferable) by exam-
ining the base of the tooth of a fresh specimen, the minuter the better.
The lengthening of the tooth below, as it is worn-away above, is mainly
affected by the successive addition of new 6 primary plates.' To the
outer edge of the primary plates, at some little distance from the base,
we find attached a set of lappet-like appendages, which are formed of
similar plates of calcareous shell-substance, and are denominated by Mr.
Salter 6 secondary plates.' Another set of appendages termed 'flabelli-

*See his Memoir ' On the Structure and Growth of the Tooth of Echinus,' in
" Philos. Transact." for 1861, p. 387.

ECHINODERMATA.

145

form processes 9 is added at some little distance from the growing base-
these consist of elaborate reticulations of calcareous fibres, endmo* in
fan-shaped extremities. And at a point still further from the baset we
find the different components of the tooth connected together by ' solder-
ing particles/ which are minute calcareous disks interposed between the
previously-formed structures; and it is by the increased development of
this connective substance, that the intervening 'spaces are narrowed into
the semblance of tubuli like those of bone or dentine. Thus a vertical
section of the tooth comes to present an appearance very like that of the
bone of a Vertebrate animal, with its lucunae, canaliculi, and lamellae'
but in a transverse section the body of the tooth bears a stronger
resemblance to dentine; whilst the keel and enamel-layer more resemble
an oblique section of Pinna than any other form of shell-structure.

Fig. 371.

£3

Structure of the Tooth of Echinus:— a, vertical section, showing the form of the apex of the
tooth as produced by wear, and retained by the relative hardness of its elementary parts; a, the
clear condensed axis; 6, the body formed of plates; c, the so called enamel; d, the keel:— b, com-
mencing growth of the tooth, as seen at its base, snowing its two systems of plates ; the dark
appearance in the central portion of the upper part is produced by the incipient reticulations of
the flabelliform processes:— c, transverse section of the tooth, showing at a the ridge of the keel,
at b its lateral portion, resembling the shell in texture; at c, c, the enamel.

536. The calcareous plates which form the less compact skeletons
of the Asteriada (' star-fish ' and their allies), and of the Ophuirida
(' sand-stars ' and ' brittle-stars'), have the same texture as those of the
shell of Echinus. And this presents itself, too, in the spines or prickles
of their surface, when these (as in the great Goniaster equestris) are
large enough to be furnished with a calcareous framework, and are not #
mere projections of the horny integument. An example of this kind,
furnished by the Astrophyton (better known as the Euryale), is repre-
sented in Fig. 372. The spines with which the arms of the species of
Ophiocoma ('brittle-star') are beset, are often remarkable for their
beauty of conformation; those of 0. rosula, one of the most common
kinds, might serve (as Prof. E. Forbes justly remarked), in point of
lightness and beauty, as models for the spire of a cathedral. These are
seen to the greatest advantage when mounted in Canada# balsam, and
viewed by the Binocular Microscope with black-ground illumination.
—It is interesting to remark that the minute tooth of Ophiocoma
10

146

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 372.

Calcareous plate and claw of Astrophyton
(Euryale).

clearly exhibits, with scarcely any preparation, that gradational trans-
ition between the ordinary reticular structure of the shell and the peculiar
substance of the tooth, which, in the adult tooth of the Echinus, can
only be traced by making sections of it near its base. The tooth of
Ophiocoma may be mounted in balsam as a transparent object, with
scarcely any grinding down; and it is then seen that the basal portion of

the tooth is formed upon the open re-
ticular plan characteristic of the 6 shell/
whilst this is so modified in the older
portion by subsequent addition, that the
upper part of the tooth has a bone-like
character.

537. The calcareous skeleton is very
highly developed in the Crinoidea;
their stems and branches being made-up
of a calcareous network closely resem-
bling that of the shell of the Echinus.
This is extremely well seen, not only in
the recent Pentacrinus Caput Medusce,
a somewhat rare animal of West Indian
seas, but also in a large proportion of
the fossil Crinoids, whose remains are so abundant in many of the older
Geological formations; for notwithstanding that these bodies have been
penetrated in the act of fossilization by a Mineral infiltration, which
seems to have substituted itself for the original fabric (a regularly-crys-
talline cleavage being commonly found to exist in the fossil stems of
Encrinites, etc., as in the fossil spines of Echinida), yet their organic
structure is often most perfectly preserved.1 In the circular stems of
Encrinites, the texture of the calcareous network is uniform, or nearly
so, throughout; but in the pentangular Pentacrini, a certain figure or
pattern is formed by variations of texture in different parts of the trans-
verse section.2

538. The minute structure of the Shells, Spines, and other solid
parts of the skeleton of Echinodermata can only be displayed by thin
sections made upon the general plan already described (§§ 192-195).
But their peculiar texture requires that certain precautions should be
taken; in the first place, in order to prevent the section from breaking
whilst being reduced so the desirable thickness; and in the second, to
prevent the interspaces of the network from being clogged by the particles
abraded in the reducing process. — A section of the Shell, Spine, or other
portion of the skeleton should first be cut with a fine saw, and be rubbed
on a flat file until it is about as thin as ordinary card, after which it
should be smoothed on one side by friction with water on a Water-of-Ayr
stone. It should then, after careful washing, be dried, first on white
blotting-paper, afterwards by exposure for some time to a gentle heat, so

1 The calcareous skeleton even of living Echinoderms has a crystalline aggre-
gation, as is very obvious in the more solid spines of Eehinometrce, etc. ; for it is
difficult, in sawing these across, to avoid their tendency to cleavage in the oblique
plane of calcite. And the Author is informed by Mr. Sorby, that the calcareous
deposit which fills up the areolae of the fossilized skeleton has always the same
crystalline system with the skeleton itself, as is shown not merely by the uni-
formity of their cleavage, but by their similar action on Polarized light.

2 See Figs. 74-76 of the Author's Memoir on " Shell Structure" in the Eeport
of the British Association for 1847.

ECHINODERMATA.

147

that no water may be retained in the interstices of the network, which
would oppose the complete penetration of the Canada balsam. Next' it is to
be attached to a glass-slip by balsam hardened in the usual manner; but
particular care should be taken, first, that the balsam be brou°'ht to
exactly the right degree of hardness, and second, that there be enough
not merely to attach the specimen of the glass, but also to saturate its
substance throughout. The right degree of hardness is that at which
the balsam can be with difficulty indented by the thumb-nail; if it be
made harder than this, it is apt to chip-off the glass in grinding, so that
the specimen also breaks away; and if it be softer, it holds the abraded
particles, so that the openings of the network become clogged with them.
If, when rubbed-down nearly to the required thinness, the section appears
to be uniform and satisfactory throughout, the reduction may be com-
pleted without displacing it; but if (as often happens) some inequality
in thickness should be observable, or some minute air bubbles should
show themselves between the glass and the under surface, it is desirable
to loosen the specimen by the application of just enough heat to melt the
balsam (special care being taken to avoid the production of fresh air-
bubbles), and to turn it over so as to attach the side last polished to the
glass, taking care to remove or to break with the needle-point any air-
bubbles that there may be in the balsam covering the part of the glass
on which it is laid. The surface now brought uppermost is then to be very
carefully ground down; special care being taken to keep its thickness uni-
form through every part (which may even be better judged-of by the touch
than by the eye), and to carry the reducing process far enough, without
carrying it too far. Until practice shall have enabled the operator
to judge of this by passing his finger over the specimen, he must have
continual recourse to the Microscope during the latter stages of his work;
and he should bear constantly in mind, that, as the specimen will become
much more transparent when mounted in balsam and covered with glass,
than it is when the ground surface is exposed, he need not carry his
reducing process so far as to produce at once the entire transparence he
aims at, the attempt to accomplish which would involve the risk of the
destruction of the specimen. In 6 mounting 9 the specimen, liquid bal-
sam should be employed, and only a very gentle heat (not sufficient to
produce air-bubbles, or to loossen the specimen from the glass) should
be applied; and if, after it has been mounted, the section should be
found too thick, it will be easy to remove the glass cover and to reduce it
further, care being taken to harden to the proper degree the balsam
which has been newly laid-on.

539. If a number of sections are to be prepared at once (which it is
often useful to do for the sake of economy of time, or in order to com-
pare sections taken from different parts of the same spine), this may be
most readily accomplished by laying them down, when cut-off by the
saw, without any preliminary preparation save the blowing of the cal-
careous dust from their surfaces, upon a thick slip of glass well covered
with hardened balsam; a large proportion of its surface may thus be
occupied by the sections attached to it, the chief precaution required
being that all the sections come into equally close contact with it. Their
surfaces may then be brought to an exact level, by rubbing them down,
first upon a flat piece of grit (which is very suitable for the rough grind-
ing of such sections), and then upon a large Water-of-Ayr stone whose
surface is 'true.' When this level has been attained, the ground surface
is to be well washed and dried, and some balsam previously hardened is

148

THE MICROSCOPE AND ITS REVELATIONS.

to be spread over it, so as to be sucked-in by the sections, a moderate
heat being at the same time applied to the glass slide; and when this has
been increased sufficiently to loosen the sections without overheating
the balsam, the sections are to be turned-over, one by one, so that the
ground surfaces are now to be attached to the glass slip, special care
being taken to press them all into close contact with it. They are then
to be very carefully rubbed-down, until they are nearly reduced to the
required thinness; and if, on examining them from time to time, their
thinness should be found to be uniform throughout, the reduction of the
entire set may be completed at once; and when it has been carried
sufficiently far, the sections, loosened by warmth, are to be taken-up on
a camel-hair brush dipped in turpentine, and transferred to separate
slips of glass whereon some liquid balsam has been previously laid, in
which they are to be mounted in the usual manner. It more frequently
happens, however, that, notwithstanding every care, the sections, when
ground in a number together, are not of uniform thickness, owing to
some of them being underlaid by a thicker stratum of balsam than others;
and it is then necessary to transfer them to separate slips before the
reducing process is completed, attaching them with hardened balsam,
and finishing each section separately.

540. A very curious internal skeleton, formed of detached plates or
spicules, is found in many members of this class; often forming an in-

vestment like a coat of mail to some of the viscera, especially the ovaries.
The forms of these plates and spicules are generally so diverse, even in
closely-allied species, as to afford very good differential characters. — This
subject is one that has been as yet but very little studied, Mr. Stewart
being the only Microscopist who has given much attention to it;1 but it
is well worthy of much more extended research.

541. It now remains for us to notice the curious and often very
beautiful structures, which represent, in the order Holothurida, the
solid calcareous skeleton of the others already noticed. All the animals
belonging to this Order are distinguished by the flexibility and absence
of firmness of their envelopes; and excepting in the case of certain
species which have a set of calcareous plates, supporting teeth, disposed
around the mouth, very much as in the Echinida, we do not find among
them any representation that is apparent to the unassisted eye, of that
skeleton which constitutes so distinctive a feature of the class generally.
But a microscopic examination of their integument at once brings to
view the existence of great numbers of minute isolated plates, every one

Fig. 373.

Calcareous plates in skin of Holotlmria.

1 See his Memoir in the " Linneean Transactions," Vol. xxv., p. 365.

ECHINODERMATA.

149

of them presenting the characteristic reticulated structure, which are
set with greater or less closeness in the substance of the skin. Various
forms of the plates which thus present themselves in Holothuria are
shown in Fig. 373; and at a is seen an oblique view of the kind marked
a, more highly magnified, showing the very peculiar manner wherein
one part is superposed on the other, which is not at all brought into
view when it is merely seen through in the ordinary manner. — In the
Synapta, one of the long-bodied forms of this order, which abounds in
the Adriatic Sea, and of which two species (the 8. digitata and 8. in-
hcsrens) occasionally occur upon our own coasts,1 the calcareous plates of
the integument have the regular form shown at a, Fig. 374 ; and each

Fig. 374.

Fig. 375.

Calcareous Skeleton of Synapta:—A, plate imbedded in Skin; b, the same, with its anchor-like
spine attached ; c , anchor-like spine separated.

of these carries the curious anchor-like appendage, c, which is articu-
lated to it by the notched piece at the foot, in the manner shown (in
side view) at b. The anchor-like appendages project from the surface of
the skin, and may be considered as representing the spines of Echinida.
— Nearly allied to the Synapta is the Cliirodota, the integument of which
is entirely destitute of ' anchors/ but is furnished with very remarkable
wheel-like plates; those represented in Fig. 375 are found in the skin of
Cliirodota violacea, a species inhabiting
the Mediterranean. These ' wheels' are
objects of singular beauty and delicacy,
being especially remarkable for the very
minute notching (scarcely to be discerned
in the figures without the aid of a magni-
fying-glass) which is traceable around the
inner margin of their ' tires' — There can
be scarcely any reasonable doubt that
every member of this Order has some kind
of calcareous skeleton, disposed in a man-
ner conformable to the examples now
cited ; and it would be very valuable to
determine how far the marked peculiar-
ities by which they are respectively distinguished, are characteristic of
genera and species. The plates may be obtained separately by the usual
method of treating the skin with a solution of potass; and they should
be mounted in Canada balsam. But their position in the skm can only
be ascertained by making sections of the integument, both vertical and
parallel to its surface; and these sections, when dry, are most advan-
tageously mounted in the same medium, by which their transparence is

1 See Woodward in " Proceedings of Zoological Society," July 13, 1858.

Wheel-like plates from Skin of Cliiro-
dota violacea.

150

THE MICROSCOPE AND ITS REVELATIONS.

greatly increased. All the objects of this class are most beautifully dis-
played by the Black-ground illumination; and their solid forms are seen
with increased effect under the Binocular. The Black-ground illumina-
tion applied to very thin sections of Echinus spines brings out some
effects of marvellous beauty; and even in these the solid form of the net-
work connecting the pillars is better seen with the Binocular than it can
be with the ordinary Microscope.1

542. Echinoderm-Larvce. — We have now to notice that most remark-
able set of objects furnished to the Microscopic inquirer by the larval
states of this class; for our knowledge of which we are chiefly indebted
to the painstaking and widely-extended investigations of Prof. J. Miiller.
All that our limits permit is a notice of two of the most curious forms of
these larvae, by way of sample of the wonderful phenomena which his
researches brought to light, and to which the attention of Microscopists
who have the opportunity of studying them should be the more assid-
uously directed; as even the most delicate of these organisms have been
found capable of such perfect preservation, as to admit of being studied,
when mounted as preparations, even better than when alive (§ 545, a).
The peculiar feature by which the early history of the Echinoderms
generally seems to be distinguished is this, — that the embryonic mass of
cells is converted, not into a larva which subsequently attains the adult
form by a process of metamorphosis, but into a peculiar i zooid ' or
pseudembryo, which seems to exist for no other purpose than to give
origin to the Echinoderm by a kind of internal gemmation, and to carry
it to a distance by its active locomotive powers, so as to prevent the spots
inhabited by the respective species from being overcrowded by the accu-
mulation of their progeny. The larval zooids are formed upon a type
quite different from that which characterizes the adults; for instead of a
radial symmetry, they exhibit a bilateral, the two sides being precisely
alike, and each having a ciiliated fringe along the greater part or the
whole of its length. The two fringes are united by a superior and an
inferior transverse ciliated band : and between these two the mouth of
the zooid is always situated. Further, although the adult Star-fish and
Sand-stars have usually neither intestinal tube nor anal orifice, their
larval zooids, like those of other Echinoderms, always possess both.
The external forms of these larvae, however, vary in a most remarkable
degree, owing to the unequal evolution of their different parts; and
there is also a considerable diversity in the several Orders, as to the pro-
portion of the fabric of the larva which enters into the composition of
the adult form. In the fully developed Star-fish and Sea-urchin, the
only part retained is a portion of the stomach and intestine, which is
pinched-off, so to speak, from that of the larval zooid.

543. One of the most remarkable forms of Echinoderm-larvae is that
which has received the name of Bipinnaria (Fig. 376), from the symme-
trical arrangement of its natatory organs. The mouth (a), which opens
in the middle of a transverse furrow, leads through an oesophagus a' to a
large stomach, around which the body of a Star-fish is developing itself;
and on one side of this mouth are observed the intestinal tube and anus
(b). On either side of the anterior portion of the body are six or more

1 It may be here pointed out that the reticulated appearance is sometimes de-
ceptive; what seems to be solid network being in many instances a hollow net-
work of passages channelled-out in a solid calcareous substance. Between these
two conditions, in which the relation beween the solid frame-work and the inter-
vening space is completely reversed, there is every intermediate gradation.

ECHLNODERMATA.

151

Fig. 376.

narrow fin-like appendages, which are fringed with cilia; and the poste-
rior part of the body is prolonged into a sort of pedicle, bilobed towards
its extremity, which also is covered with cilia. The organization of this
larva seems completed, and its movements through the water become very
active, before the mass at its anterior extremity presents anything of the
aspect of the Star-fish; in this respect corresponding with the movements
of the pluteus of the Echinida (§ 545). The temporary mouth of the
larva does not remain as the permanent mouth of the Star-fish; for the
oesophagus of the latter enters on what is to become the dorsal side of its
body, and the true mouth is subsequently
formed by the thinning-away of the in-
tegument on its ventral surface. The
young Star-fish is separated from the Bi-
pinnarian larva by the forcible contrac-
tions of the connecting stalk, as soon as
the calcareous consolidation of its integ-
ument has taken-place and its true mouth
has been formed, but long before it has
attained the adult condition; and as its
ulterior development has not hitherto
been observed in any instance, it is not
yet known what are the species in which
this mode of evolution prevails. The lar-
val zooid continues active for several
days after its detachment; and it is pos-
sible, though perhaps scarcely probable,
that it may develop another Asteroid by
a repetition of this process of gemmation.

544. In the Bipinnaria, as in other
larval zooids of the Asteriada, there is
no internal calcareous frame- work; such
a frame-work, however, is found in the
larvae of the Ecliinida and Ophiurida, of
which the form delineated in Fig. 377 is
an example. The embryo issues from the
ovum as soon as it has attained, by repeat-
ed ' segmentation 9 of the yolk (§ 581),
the condition of the ' mulberry-mass;' and the superficial cells of this are
covered with cilia, by whose agency it swims freely through the water.
So rapid are the early processes of development, that no more than from
twelve to twenty-four hours intervene between fecundation and the
emersion of the embryo; the division into two, four, or even eight seg-
ments taking-place within three hours after impregnation. Within a few
hours after its emersion, the embryo changes from the spherical into a
sub-pyramidal form with a flattened base; and in the centre of this base
is a depression, which gradually deepens, so as to form a mouth that
communicates with a cavity in the interior of the body, which is sur-
rounded by a portion of the yolk-mass that has returned to the liquid
granular state. Subsequently a short intestinal tube is found, with an
anal orifice opening on one side of the body. The pyramid is at first tri-
angular, but it afterwards becomes quadrangular; and the angles are
greatly prolonged round the mouth (or base), whilst the apex of the
pyramid is sometimes much extended in the opposite direction, but is
sometimes rounded off into a kind of dome (Fig. 377, a). All parts of

Bipinnaria asterigera, or Larva of
Star-fish:— a, mouth; a', oesophagus; b,
intestinal tube and anal orifice ; c, furrow-
in which the mouth is situated ; d d', bi-
lobed peduncle; 1, 2,3, 4, 5, 6, 7, ciliated
arms.

152

THE MICROSCOPE AND ITS REVELATIONS.

this curious body, and especially its most projecting portions, are strength-
ened by a frame-work of thread-like calcareous rods (e). In this condi-
tion the embryo swims freely through the water, being propelled by the
action of the cilia, which clothe the four angels of the pyramid and its
projecting arms, and which are sometimes thickly set upon two or four
projecting lobes (/); and it has received the designation of pluteus. The
mouth is usually surrounded by a sort of proboscis, the angles of which
are prolonged into four slender processes (g, g, g, g), shorter than the
four outer legs, bat furnished with a similar calcareous frame-work.

545. The first indication of the production of the young Echinus
from its 'pluteus/ is given by the formation of a circular disk (Fig. 377,
A, c), on one side of the central stomach (#); and this disk soon presents
five prominent tubercles (b), which subsequently become elongated into
tubular cirrhi. The disk gradually extends itself over the stomach, and
between its cirrhi the rudiments of spines are seen to protrude (c); these,
with the cirrhi, increase in length, so as to project against the envelope

Fig. 377.

Embryonic development of Echinus:— a, Pluteus larva at the time of the first appearance of
the disk; a, mouth in the midst of the four-pronged proboscis; 6, stomach; c, Echinoid disk; d, d,
d, d, four arms of the pluteus-body ; e, calcareous framework; /, ciliated lobes; g, g, g, </, ciliated
processes of the proboscis;— b, Disk with the first indication of the cirrhi:— c, Disk with the origin
of the spines between the cirrhi ;— d, more advanced disk, with the cirrhi, g, and spines, x, project-
ing considerably from the surface. (N.B —In b, c, and d, the Pluteus is not represented, its parts
having undergone no change, save in becoming relatively smaller.)

of the pluteus, and to push themselves through it; whilst, at the same
time, tiie original angular appendages of the pluteus diminish in size, the
ciliary movement becomes less active, being superseded by the action of
the cirrhi and spines, and the mouth of the pluteus closes-up. By the
time that the disk has grown over half of the gastric sphere, very little
of the pluteus remains, except some of the slender calcareous rods; and
the number of cirrhi and spines rapidly increases. The calcareous frame-
work of the shell at first consists, like that of the Star-fishes, of a series
of isolated networks developed between the cirrhi; and upon these rest
the first-formed spines (d). But they gradually become more consoli-
dated, and extend themselves over the granular mass, so as to form the
series of plates constituting the shell. The mouth of the Echinus (which

ECHINODERMATA.

153

is altogether distinct from that of the pluteus) is formed at that side of
the granular mass over which the shell is last extended; and the first in-
dication of it consists in the appearance of the five calcareous concretions,
which are the summits of the five portions of the frame-work of jaws and
teeth that surround it. All traces of the original pluteus are now lost;
and the larva, which now presents the general aspect of an Echinoid
animal, gradual augments in size, multiplies the number of its plates,
cirrhi, and spines, evolves itself into its particular generic and specific
type, and undergoes various changes of internal structure, tending to the
development of the complete organism.

a. An excellent summary of the developmental history of the several Echino-
derm-types, with references to the principal Memoirs which treat of it, will be
found in Chap. xx. of Mr. Balfour's "Comparative Embryology." — In collecting
the free-swimming larvae of Echinodermata, the Stick-net should be carefully
employed in the manner already described (§ 217); and the search for them is of
course most likely to be successful in those localities in which the adult forms of
the respective species abound, and on warm calm days, in which they seem to
come to the surface in the greatest numbers. The following mode of preparing
and mounting them has been kindly communicated to the Author by Mr. Percy
Sladen: — " For killing and preserving Echinoderm zooids, I have come to prefer
either Osmic acid or the Picro-sulphuric mixture of Kleinenberg (§ 199, e) of one-
third strength. The latter, of course, destroys all calcareous structures, but the
soft parts are preserved in a wonderful manner. If the diluted Kleinenberg's
mixture is used, let the zooids remain in it for one or two hours; then wash them
thoroughly in 70 per cent Spirit until all trace of acid is removed; then stain;
then again wash in 70 per cent Spirit, transfer them to 90 per cent Spirit for
some hours, and lastly to absolute Alcohol. Transfer them from this to Oil of
Cloves; and finally mount in Canada balsam in the usual manner. — If Osmic acid
be used, place three or four of the living zooids in a watch-glass of sea- water, and
add a drop of the 1 per cent solution. They should not remain even in this weak
solution for more than a minute; and should then be thoroughly washed in a
superabundance of 35 per cent Spirit, to prevent the deposit of crystals of salt
consequent on the action of the osmic acid. Then transfer the specimens to 70
per cent Spirit; and proceed as in the other case.

546 . One of the most interesting to the Microscopist of all Echino-
dermata is the Antedon 1 (more generally known as Comatula), or
' feather-star ' (Fig. 378), which is the commonest existing representative
of the great fossil series Crinoidea, or 'lily star/ that were among the
most abundant types of this class in the earlier epochs of the world's his-
tory. Like these, the young of Antedon is attached by a stalk to a fixed
base, as shown in Fig. 379; but when it has arrived at a certain stage of
development, it drops off from this like a fruit from its stalk; and the
animal is thenceforth free to move through the ocean- water it inhabits.
It can swim with considerable activity; but it exerts this power chiefly
to gain a suitable place for attaching itself by means of the jointed
prehensile cirrhi put forth from the under side of the central disk (Fig.
378); so that, notwithstanding its locomotive power, it is nearly as sta-
tionary in its free adult condition, as it is in its earlier Pentacrinoid
stage. The pentacrinoid larva 2 — first discovered by Mr. J. V. Thomp-

1 The Author has found himself obliged, by the accepted rules of Zoological
nomenclature, to adopt the designation Antedon, instead of the much better known
and very appropriate name given to this type of Lamarck. See his ' Researches
on the Structure, Physiology, and Development of Antedon rosaceus,' Part. I., in
" Philos. Transact.," 1866, p. 671.

2 The Pentacrinoid larvae of Antedon have been found abundantly (attached to
Sea-weeds and Zoophytes) at Millport on the Clyde, and in Lamlash Bay, Arran;
in Kirkwall Bay, Orkney; in Lough Strangford, near Belfast, and in the Bay of
Cork; and at Ilfracombe, and in Salcombe Bay, Devon.

154

THE MICROSCOPE AND ITS REVELATIONS.

son of Cork, in 1823, but originally supposed by him to be a perma-
nently attached Crinoid — forms a most beautiful object for the lower
powers of the Microscope, when well preserved in fluid, and viewed by
a strong incident light (Plate xxi., fig. 3); and a series of specimens in
different stages of development, shows most curious modifications in the
form and arangement of the various component pieces of its calcareous
skeleton. In its earliest stage (Fig. 379, a), the body is inclosed in a
calyx composed of two circles of plates; namely, five basals, forming
a sort of pyramid whose apex points downward, and is attached to the
highest joint of the stem: and five orals superposed on these, forming
when closed a like pyramid whose apex points ^ upwards, but usually
separating to give passage to the tentacles, of which a circlet surrounds
the mouth. In this condition there is no rudiment of arms. In the
more advanced stage shown at b, the arms have begun to make their

Fig. 378. Fig. 379.

Antedon (Comatula) or Feather-star, seen from its Crinoid Larva of Antedon :— A, b, c,

under side. successive stages of development.

appearance; and the skeleton, when carefully examined, is found to con-
sist of the following pieces, as shown in Plate xxi., fig. 3L: — b, b, the cir-
clet of basals supported on the top of the stem: r1 the circlet of first
radials, now interposed between the basals and the orals, and alternating
with both; between two of these is interposed the single anal plate, a;
whilst they support the second and the third radials (r2, r3), from the
latter of which the bifurcating arms spring; finally, between the second
radials we see the five orals, lifted from the basals on which they origi-
nally rested, by the interposition of the first radials. In the more ad-
vanced stage shown in Fig. 379, c, and on a larger scale in Plate xxi.,
figs. 2, 3, we find the highest joint of the stem beginning to enlarge, to
form the centro-dorsal plate (fig. 2, c d), from which are beginning to
spring the dorsal cirrhi (c i r), that serve to anchor the animal when it
drops from the stem; this supports the basals (b), on which rest the

ECHINODERMATA.

155

PLATE XXI.

PENTACRINOID LARVA OF ANTEDON (Original).

Fig. 1. Skeleton of early Pentacrinoid, under Black-ground illumination, showing its component
plates:— 6, 6, basals, articulated below to the highest point of the stem; t* r\ first radials, between
two of which is seen the single anal plate, a; r2, second radials; r\ third radials, giving oil the
bifurcating arms at their summit ; o, o, orals. , .... ,

2, 3. Back and front views of a more advanced Pentacrinoid, as seen by incident light, one or
the pair of arms being cut away in Fig. 3, in order to bring the mouth and its surrounding parts
into view :— 6,6, basals , r\ r'\ r\ first, second, and third radials; a, anal, now carried upwards by
the projection of the vent v; o, o, orals; cir, dorsal cirrhi, developed from the highest joint of the
stem.

156

THE MICROSCOPE AND ITS REV EL A HONS.

first. radials (r1); whilst the anal plate (a) is now lifted nearly to the
level of the second radials (r2), by the development of the anal funnel
or vent (v) to which it is attached. The oral plates are not at first appa-
rent, as they no longer occupy their first position; but on being carefully
looked-for, they are found still to form a circlet around the mouth (fig.
3, o, o), not having undergone any increase in size, whilst the visceral disk
and the calyx in which it is lodged have greatly extended. These oral
plates finally disappear by absorption; while the basals are at first con-
cealed by the great enlargement of the centro-dorsal (which finally ex-
tends so far as to conceal the first radials also); and at last undergo
metamorphosis into a beautiful ' rosette/ which lies between the cavity
of the centro-dorsal and that of the calyx. — In common with other mem-
bers of its Class, the Antedon is represented in its earliest phase of develop-
ment by a free-swimming ' larval zooid ' or pseudernbryo, which was first
observed by Busch, and has been since carefully studied by Pro. Wyville
Thomson 1 and Goette.2 This zooid has an elongated egg-like form, and
is furnished with transverse bands of cilia, and with a mouth and anus of
its own. After a time, however, rudiments of the calcareous plates form-
ing the stem and calyx begin to show themselves in its interior; a disk
is then formed at the posterior extremity, by which it attaches itself to a
Sea- weed (very commonly Laminar ia), Zoophyte, or Polyzoary; the calyx,
containing the true stomach, with its central mouth surrounded by ten-
tacles, is gradually evolved; and the sarcodic substance of the pseudem-
bryo, by which this calyx and the rudimentary stem were originally in-
vested, gradually shrinks, until the young Pentacrinoid presents itself in
its charateristic form and proportions.3

1 'On the Development of Antedon rosaceus' in "Philos. Transact." for 1865,
p. 513.

2" Archiv f. Mikrosk. Anat.," Bd. xii., p. 583.

3 The general results of the Author's own later studies of this most interesting
type (the key to the life-history of the entire Geological succession of Crinoidea)
are embodied in a notice communicated to the "Proceedings of the Royal Society,"
for 1876, p. 211, and in a subsequent note, p. 451. Of the further contributions re-
cently made to our knowledge of it, the Memoir of Dr. H. Ludwig ' Zur Anatomie
der Crinoideen' (Leipzig, 1877), forming part of his i ' Morphologische Studien an
Echinodermen, " is the most important.

POLYZOA AND TUNIC ATA

157

CHAPTEE XV.
POLYZOA AND TUNICATA.

547. At the lower extremity of the great series of Molluscous animals,
we find two very remarkable groups, whose mode of life has much in
common with Zoophytes, whilst their type of structure is conformable in
essential particulars to that of the true Mollusks. These animals are for
the most part microscopic in their dimensions; and as some members of
both these groups are found on almost every coast, and are most interest-
ing objects for anatomical examination, as well as for observation in the
living state, a brief general account of them will be here appropriate.

548. Polyzoa. — The group which is known under this name to
British naturalists (corresponding with that which by Continental Zoolo-
gists is designated Bryozoa) was formerly ranked as an order of Zoophytes;
and it has been entirely by Microscopic study that its comparatively high
organization has been ascertained. — The animals of the Polyozoa, incon-
sequence of their universal tendency to multiplication by gemmation, are
seldom or never found solitary, but form clusters or colonies of various
kinds, and as each is inclosed in either a horny or a calcareous sheath or
6 cell/ a composite structure is formed, closely corresponding with the
'polypidom' of a Zoophyte, which has been appropriately designated the
polyzoary. The individual cells of the polyzoary are sometimes only con-
nected with each other by their common relation to a creeping stem or
stolon, as in Laguncula (Plate xxn. ); but more frequently they bud-forth
directly, one from another, and extend themselves in different directions
over plane surfaces, as is the case with Flustrce, Lepralics, etc. (Fig. 380);
whilst not unfrequently the polyzoary develops itself into an arborescent
structure (Fig. 381), which may even present somewhat of the density
and massiveness of the Stony Corals. Each individual, designated as a
polypide or polype-like animal, is composed externally of a sort of sac, of
which the outer or tegumentary layer is either simply membranous, or is
horny, or in some instances calcified, so as to form the cell; this investing
sac is lined by a more delicate membrane, which closes its orifice, and
which then becomes continuous with the wall of the alimentary canal;
this lies freely in the visceral sac, floating (as it were) in the liquid which
it contains.

549. The principal features in the structure of this group will be best
understood from the examination of a characteristic example, such as the
Laguncula repens; which is shown in the state of expansion at A, Plate
xxii., and in the state of contraction at B and c. The mouth is sur-
rounded by a circle of tubular tentacles, which are clothed by vibratile
cilia; these tentacles, in the species we are considering, vary from ten to
twelve in number, but in some other instances they are more numerous.

158

THE MICROSCOPE AND ITS REVELATIONS.

By the ciliary investment of the tentacles, the Polyzoa are at once dis-
tinguishable from those Hydroid polypes to which they bear a superficial
resemblance, and with which they were at one time confounded; and
accordingly, whilst still ranked among Zoophytes, they were characterized
as ciliobrachiate. The tentacula are seated upon an annular disk, which is
termed the lophophore, and which forms the roof of the visceral or peri-
gastric cavity; and this cavity extends itself into the interior of the tenta-
cula, through perforations in the lophophore, as is shown at D, Plate

xxii., representing a portion of the
tentacular circle on a larger scale,
a a being the tentacula, b b their
internal canals, c the muscles of the
tentacula, d the lophophore, and e
its retractile muscles. The mouth
situated in the centre of the lopho-
phore, as shown at A, leads to a
funnel-shaped cavity or pharynx, b,
which is separated from the oeso-
phagus, d, by a valve at c; and this
oesophagus opens into the stomach e,
which occupies a considerable part
of the visceral cavity. (In the Bozv-
erbanhia and some other Polyzoa,
a muscular stomach or gizzard for
the trituration of the food inter-
venes between the oesophagus and
the true digestive stomach). The
walls of the stomach, h, have con-
siderable thickness; and they are
beset with minute follicles, which

Cells of Lepralice.—A, L. Hyndmanni; b, L. figu- seem to have the character of a

laris; c, l. verrucosa. rudimentary liver. This, however,

is more obvious in some other mem-
bers of the group. The stomach is lined, especially at its upper
part, with vibratile cilia, as seen at c, g; and by the action of these the
food is kept in a state of constant agitation during the digestive process.
From the upper part of the stomach, which is (as it were) doubled upon
itself, the intestine i opens, by a pyloric orifice, /, which is furnished
with a regular valve; within the intestine are seen at k particles of excre-
mentitious matter, which are discharged by the anal orifice at I. No
special circulating apparatus here exists; but the liquid which fills the
cavity that surrounds the viscera contains the nutritive matter which has
been prepared by the digestive operation, and which has transuded
through the walls of the alimentary canal; a few corpuscles of irregular
size are seen to float in it. The visceral sacs of the different polypides
put forth from the same stem appear to communicate with each other.
No other respiratory organs exist than the tentacula; into whose cavity
the nutritive fluid is probably sent from the perivisceral cavity, for aera-
tion by the current of water that is continually flowing over them.

550. The production of gemmce or buds may take place either from
the bodies of the polypides themselves, which is what always happens
when the cells are in mutual apposition; or from the connecting stem or
' stolon,' where the cells are distinct one from the other as in Laguncula.
In the latter case there is first seen a bud-like protuberance of the horny

Fig. 380.

POLYZOA AND TUNIC ATA.

159

PLATE XXII.

structure of laguncula repens (after Van Beneden).

A, Polypide expanded; b, polypide retracted; c, another view of the same, with the visceral
apparatus in outline, that the manner in which it is doubled on itself, with the tentacular crown
and muscular system, maybe more distinctly seen:— a, a, tentacula ; 6, pharynx ; c, pharyngeal
valve ; d, oesophagus; e, stomach ; /, its pyloric orifice ; g, cilia on its inner surface ; K biliary fol-
licles lodged in its wall ; i, intestine; k, particles of excrementitious matter; Z, anal orifice; m, tes-
tis; n, ovary; o, ova lying loose in the peri-visceral cavity; p, outlet for their discharge; q, sperma-
tozoa in the perivisceral cavity; r, s, t, u, v, w, x, muscles.

d, Portion of the Lophophore more enlarged:- a, a, t3ntacula; b, b, their internal canals; c,
their muscles; d, lophopnore; e, its retractor muscles.

160

THE MICROSCOPE AND ITS REVELATIONS.

external integument, into which the soft membranous lining prolongs
itself; the cavity thus formed, however, is not to become (as in Hydra
and its allies) the stomach of the new zooid; but it constitutes the cham-
ber surrounding the digestive viscera, which organs have their origin in
a thickening of the lining membrane, that projects from one side of the
cavity into its interior, and gradually shapes itself into the alimentary
canal with its tentacular appendages. Of the production of gemni83
from the polypides themselves, the best examples are furnished by the
Flustrm and their allies. From a single cell of the Flustra, five such
buds may be sent-off, which develop themselves into new polypides
around it; and these, in their turn, produce buds from their unattached
margins, so as rapidly to augment the number of cells. To this extension
there seems no definite limit; and it often happens that the cells in the
central portion of the leaf like expansion of a Flustra are devoid of con-
tents and have lost their vitality, whilst the edges are in a state of active
growth. — Independently of their propagation by gemmation, the Polyzoa
have a true sexual generation; the sexes, however, being usually, if not
invariably, united in the same polypides. The sperm-cells are developed
in a glandular body, the testis m, which lies beneath the base of the
stomach; when mature they rupture, and set free the spermatozoa q q,
swim freely in the liquid of the visceral cavity. The ova, on the other
hand, are formed in an ovarium n, which is lodged in the membrane
lining the tegumentary sheath near its outlet; the ova, having escaped
from this into the visceral cavity, as at 0, are fertilized by the spermato-
zoa which they there meet with; and are finally discharged by an outlet
at j9, beneath the tentacular circle.

551. These creatures possess a considerable number of muscles, by
which their bodies may be projected from their sheaths, or drawn within
them; of these muscles, r, s, t, u, vy w, x, the direction and points of attach-
ment sufficiently indicate the uses; they are for the most part retractors,
serving to draw-in and double up the body, to fold-together the circle
of tentacula, and to close the aperture of the sheath, when the animal
has been completely withdrawn into its interior. The projection and
expansion of the animal, on the contrary, appear to be chiefly accom-
plished by a general pressure upon the sheath, which will tend to force-
out all that can be expelled from it. The tentacles themselves are
furnished with distinct muscular fibres, by which their separate move-
ments seem to be produced. At the base of the tentacular circle, just
above the anal orifice, is a small body (seen at A, a), which is a nervous
ganglion; as yet no branches have been distinctly seen to be connected
with it in this species; but its character is less doubtful in some other
Polyzoa. — Besides the independent movements of the individual poly-
pides, other movements may be observed, which are performed by so
many of them simultaneously, as to indicate the existence of some con-
necting agency; and such connecting agency, it is affirmed by Dr. Fritz
Miiller,1 is furnished by what he terms a 6 colonial-nervous system/ In
a Serialaria having a branching polyzoary that spreads itself on sea-weeds
over a space of three or four inches, he states that a nervous ganglion
may be distinguished at the origin of each branch, and another ganglion
at the origin of each polypide-bud; all these ganglia being connected
together, not merely by principal trunks, but also by plexuses of nerve-

!See his Memoir in " Wiegmann's Archiv," 1860, p. 311; translated in
''Quart. Journ. of Microsc. Science," New Ser., Vol. i. (1861), p. 300.

POLYZOA AND TUNICATA.

161

fibres, which may be distinctly made-out with the aid of Chromic acid in
the cylindrical joints of the polyzoary. His views, however, have not
been universally accepted; some observers still maintaining that what he
regards as nerve-fibres are only connective tissue.

552. Of all the Polyzoa of our own coasts, the Flustrm or ' sea-mats'
are the most common; these present flat expanded surfaces, resembling
in form those of many sea-weeds (for which they are often mistaken)?
but exhibiting, when viewed with even a low magnifying power, a most
beautiful network, which at once indicates their real character. The
cells are arranged on both sides; and it was calculated by Dr. Grant, that
as a single square inch of an ordinary Flustra contains 1800 such cells,
and as an average specimen presents about 10 square inches of surface, it
will consist of no fewer than 18,000 polypides. The want of trans-
parence in the cell- wall, however, and the infrequency with which the
animal projects its body far beyond the mouth of the cell, render the
Polyzoa of this genus less favorable subjects for microscopic examination
than are those of the Bowerbarikia, a Polyzoon with a trailing stem and
separated cells like those of Laguncula, which is very commonly found
clustering around the base of masses of Flustrae. It was in this that
many of the details of the organization of the interesting group we are
considering were first studied by Dr. A. Farre, who discovered it in
1837, and subjected it to a far more minute examination than any Poly-
zoon had previously received;1 and it is one of the best adapted of all
the marine forms yet known, for the display of the beauties and wonders
of this type of organization. — The Halodactylus (formerly called Alcyo-
nidium), however, is one of the most remarkable of all the marine forms
for the comparatively large size of the tentacular crowns; these, when
expanded, being very distinctly visible to the naked eye, and presenting
a spectacle of the greatest beauty when viewed under a sufficient magni-
fying power. The polyzoary of this genus has a spongy aspect and
texture, very much resembling that of certain Alcyonian Zoophytes
(§ 529), for which it might readily be mistaken when its contained
animals are all withdrawn into their cells; when these are expanded,
however, the aspect of the two is altogether different, as the minute
plumose tufts which then issue from the surface of the Halodactylus,
making it look as if it were covered with the most delicate downy film,
are in striking contrast with the larger, solid-looking polypes of Alcyo-
nium. The opacity of the polyzoary of the Halodactylus renders it
quite unsuitable for the examination of anything more than the tentacu-
lar crown and the oesophagus which it surmounts; the stomach and the
remainder of the visceral apparatus being always retained within the
cell. It furnishes, however, a most beautiful object for the Binocular
Microscope, when mounted with all its polypides expanded, in the man-
ner described in § 521. — Several of the fresh-water Polyzoa are pecu-
liarly interesting subjects for Microscopic examination; alike on account
of the remarkable distinctness with which the various parts of their
organization may be seen, and the very beautiful manner in which their
ciliated tentacula are arranged upon a deeply-crescentic or horseshoe-
shaped lopliophore. By this peculiarity the fresh-water Polyzoa are
separated as a distinct sub-class from the marine; the former being
designated as Hippocrepia (horseshoe-like), while the latter are termed

1 See his Memoir ' On the Minute Structure of some of the higher forms of
Polypi, in the " Philosophical Transactions" for 1837, p. 387.
11

162

THE MICROSCOPE AND ITS REVELATIONS.

Infundibulata (funnel-like). The cells of the Hippocrepia are for the most
part lodged in a sort of gelatinous substratum, which spreads over the
leaves of aquatic plants, sometimes forming masses of considerable size;
but in the very curious and beautiful Cristatella, the polyzoary is unat-
tached, so as to be capable of moving freely through the water.1

553. The Infundibulata or Marine Polyzoa, constituting by far the
most numerous division of the class, are divided into four Orders, as fol-
lows:— i. Cheilostomata, in which the mouth of the cell is sub-terminal,
or not quite at its extremity (Fig. 380), is somewhat crescentic in form,
and is furnished with a movable (generally membranous) lip, which
closes it when the animal retreats. This includes a large part of the
species that most abound on our own coasts, notwithstanding their wide
differences in form and habit. Thus the polyzoaries of some (as F lustra)
are horny and flexible, whilst those of others (as Eschara and Retepora)
are so penetrated with calcareous matter as to be quite rigid; some
grow as independent plant-like structures (as Bugula and Gemellaria),
whilst others, having a like arborescent form, creep over the surfaces of
rocks or stones (as Hippothoa); and others, again, have their cells in
close apposition, and form crusts which possess no definite figure (as is
the case with Lepralia and Membranipora). — n. The second order,
Cyclostomata, consists of those Polyzoa which have the mouth at the
termination of tubular calcareous cells, without any movable appendage
or lip (Fig. 381). This includes a comparatively small number of
genera, of which Crisia and Tubulipora contain the largest proportion
of the species that occur on our own coasts. — ill. The distinguishing
character of the third order, Ctenosomata, is derived from the presence
of a comb-like circular fringe of bristles, connected by a delicate mem-
brane, around the mouth of the cell, when the animal is projected from,
it; this fringe being drawn in when the animal is retracted. The
Polyzoaries of this group are very various in character, the cells being
sometimes horny and separate (as in Laguncula and Bowerbankia),
sometimes fleshy and coalescent (as in Halodactylus). — iv. In the fourth
order, Pedicellinem, which includes only a single genus, Pedicellina, the
lophophore is produced upwards on the back of the tentacles, uniting
them at their base in a sort of muscular calyx, and giving to the animal
when expanded somewhat the form of an inverted bell, like that of
Vorticella (Fig. 305). — As the Polyzoa altogether resemble Hydroid
Zoophytes in their habits, and are found in the same localities, it is not
requisite to add anything to what has already been said (§ 521), respect-
ing the collection, examination, and mounting of this very interesting
class of objects.2

554. A large proportion of the Polyzoa of the first Order are
furnished with very peculiar motile appendage**, which are of two kinds,
avicularia and vibracula. The avicularia or c bird's-head processes/ so
named from the striking resemblance they present to the head and jaws
of a bird (Fig. 381, b), are generally * sessile ' upon the angles or

!See Prof. Allman's beautiful " Monograph on the British Fresh-water Poly-
zoa," published by the Ray Society, 1857.

2 For a more detailed account of the Structure and Classification of the Marine
Polyzoa, see Prof. Van Beneden's ' Recherches sur les Bryozoaires de la Cote
• d'Ostende,' in ''Mem. de TAcad. Roy. de Bruxelles," torn, xvii ; Mr. G. Busk's
" Catalogue of the Marine Polyzoa in the Collection of the British Museum;" Mr.
Hincks's ' 4 British Marine Polyzoa," 18<Q0; and Nitsche, ' Beitrage zur Kenntniss
der Bryozoen, in Zeitschrift f. wiss. Zool.," Bde. xx., xxi., xxiv.

POLYZOA AND TUNIC ATA.

163

once to them without
either 6 projecting '

Fig. 381.

margins of the cells, that is, are attached at
the intervention of a stalk, as at A, being
6 immersed;' but in the genera
Bugula and Bicellaria, where
they are present at all, they are
' pedunculate/ or mounted on
footstalks (b). Under one form
or the other, they are wanting in
but few of the genera belonging
to this order; and their presence
or absence f urnishes valuable char-
acters for the discrimination of
species. Each avicularium has
two ' mandibles/ of which one is
fixed, like the upper jaw of a
bird, the other movable, like its
lower jaw; the latter is opened and
closed by two sets of muscles which
are seen in the interior of the
'head;' and between them is a
peculiar body, furnished with a
pencil of bristles, which is prob-
ably a tactile organ, being brought
forwards when the moutlvis open,
so that the bristles project beyond
it, and being drawn back when the

mandible Closes. The avicularia A Portion of Cellularia ciliata, enlarged; b, one
keep UP a Continual Snapping ac- of the 4 bird's-head ' processes of Bugula avicularia,
i • -t • a >\ L i more highly magnified, and seen in the act or grasp-

tion during the hie ot the polyzo- mg another,
ary ; and they may often be observed

tolay hold of minute Worms or other bodies, sometimes even closing upon
the beaks of adjacent organs of the same kind, as shown at B. In the
pedunculate forms, besides the snapping action, there is a continual
rhythmical nodding of the head upon the stalk; and few spectacles arc
more curious than a portion of the polyzoary of Bugula avicularia (a very
common British species) in a state of active vitality, when viewed under
a power sufficiently low to allow a number of these bodies to be in sight
at once. It is still very doubtful what is their precise function in the
economy of the animal; whether it is to retain within the reach of the
ciliary current, bodies that may serve as food; or whether it is, like the
Pedicellariae of Echini (§ 534), to remove extraneous particles that may
be in contact with the surface of the polyzoary. The latter would seem
to be the function of the vibracula, which are long bristle-shaped organs
(Fig. 380, a), each one springing at its base out of a sort of cup that
contains muscles by which it is kept in almost constant motion, sweep-
ing slowly and carefully over the surface of the polyzoary, and removing
what might be injurious to the delicate inhabitants of the cells when
their tentacles are protruded. Out of 191 species of Cheilostomatous
Polyzoa described by Mr. Busk, no fewer than 126 are furnished either
with Avicularia, or with Vibracula, or with both these organs.1

555. Tunicata.— The Tunicated Mollusca are so named from the in-

1 See Mr. G. Busk's ' Remarks on the Structure and Function of the Avicula-
rian and Vibracular Organs of Polyzoa,' in " Transact, of Microsc. Soc, ber. a,
Vol. ii. (1854), p. 26.

164

THE MICROSCOPE AND ITS REVELATIONS.

closure of their bodies in a ' tunic/ which is sometimes leathery or even
cartilaginous in its texture, and which very commonly includes calcare-
ous spicules, whose forms are often very beautiful. They present a strong
resemblance to the Polyzoa, not merely in their general plan of conforma-
tion, but also in their tendency to produce composite structures by gem-
mation; they are differentiated from them, however, by the absence of
the ciliated tentacles which form so conspicuous a feature in the external
aspect of the Polyzoa, by the presence of a distinct circulating apparatus,
and by their peculiar respiratory apparatus, which may be regarded as a
dilatation of their pharynx. In their habits, too, they are for the most
part very inactive, exhibiting scarcely anything comparable to those rapid
movements of expansion and retraction which it is so interesting to watch
among the Polyzoa; whilst, with the exception of the Salpidm and other
floating species which are chiefly found in seas warmer than those that
surround our coast, and the curious Appendicularia to be presently no-
ticed (§ 560), they are rooted to one spot during all but the earliest period
of their lives. The larger forms of the Ascidian group, which constitutes
the bulk of the class, are always solitary; either not propagating by gem-
mation at all, or, if this process does take place, the gemmae being de-
tached before they have advanced far in their development. — Although
of special importance to the Comparative Anatomist and the Zoologist,
this group does not afford much to interest the ordinary Microscopist,
except in the peculiar actions of its respiratory and circulatory apparatus.
In common with the composite forms of the group, the solitary Ascidians
have a large branchial sac, with fissured walls, resembling that shown in
Figs. 382 and 384; into this sac water i3 admitted by the oral orifice, and
a large proportion of it is caused to pass through the fissures, by the
agency of the cilia with which they are fringed, into a surrounding
chamber, whence it is expelled through the anal orifice. This action
may be distinctly watched through the external walls in the smaller and
more transparent species; and not even the ciliary action of the tentacles
of the Polyzoa affords a more beautiful spectacle. It is peculiarly re-
markable in one species that occurs on our own coasts, the Ascidia pa-
rallelogramma,1 in which the wall of the branchial sac is divided into a
number of areolae, each of them shaped into a shallow funnel; and round
one of these funnels each branchial fissure makes two or three turns
of a spiral. When the cilia of all these spiral fissures are in active
movement at once, the effect is most singular. — Another most remarka-
ble phenomenon presented throughout the group, and well seen in the
solitary Ascidian just referred-to, is the alternation in the direction of
the Circulation. The heart, which lies at the bottom of the branchial
sac, is composed of two chambers imperfectly divided from each other;
one of these is connected with the principal trunk leading to the body,
and the other with that leading to the branchial sac. At one time it will
be seen that the blood flows from the respiratory apparatus to the cavity
of the heart in which its trunk terminates, which then contracts so as to
drive it into the other cavity, which in its turn contracts and propels it
through the systemic trunk to the body at large; but after this course
has been maintained for a time, the heart ceases to pulsate for a moment
or two, and the course is reversed, the blood flowing into the heart from
the body generally, and being propelled to the branchial sac. After this

1 See Alder in " Ann. of Nat. Hist.," 3d Ser., Vol. xi. (1863), p. 157; and Han-
cock in "Journ. of Linn. Soc.," Vol. ix., p. 333.

POLYZOA AND TUNIC AT A.

165

Compound mass of Amoroucium
proliferum with the anatomy of a
single zooid:— a, thorax; b, abdomen;
c, post-abdomen ;— c, oral orifice; e,
branchial sac; /, thoracic sinus:
anal orifice; i', projection overhanging
it; j, nervous ganglion; k, oeosphagus;
I, stomach surrounded by biliary tu-
buli; m, intestine; n, termination of

intestine in cloaca; o, heart; o\ peri-
cardium; p, ovarium; p', egg ready to
escape; testis; r, spermatic canal;
r', termination of this canal in the
cloaca.

reversed course has continued for some time, another pause occurs, and
the first course is resumed. The length of time intervening between the
changes does not seem by any means constant. It is usually stated at from
half-a-minute to two minutes in the composite forms; but in the solitary
Ascidia parallelogramma (a species very common in Lamlash Bay,
Arran), the Author has repeatedly observed an interval of from five to
fifteen minutes, and in

some instances he has Fig. 382.

seen the circulation
go-on for half -an-hour,
or even longer, without
change, — always, how-
ever, reversing at last. V V* 1 p ^ JSSRjtit y\

556. The Compound
Ascidians are very
commonly found ad-
herent to Sea* weeds, /P^p J^^^d^ c ffji^M^^ " \\
Zoophytes, and stones
between the t i d e-
marks; and they pre-
sent objects of great
interest to the Micro-

scopist, since the small b ( ft/^3jy| 1*

size and transparence
of their bodies when
they are detached from
the mass in which they
are imbedded, not only
enables their structure
to be clearly discerned
without dissection, but
allows many of their
living actions to be

watched. Of these we have a characteristic example
in Amoroucium proliferum; of which the form of u \ $

the composite mass and the anatomy of a single
individual are displayed in Fig. 382. Its clusters
appear almost completely inanimate, exhibiting no
very obvious movements when irritated; but if they
be placed when fresh in sea-water, a slight pouting
of the orifices will soon be perceptible, and a constant
and energetic series of currents will be found to
enter by one set and to be ejected by the other,
indicating that all the machinery of active life is
going-on within these apathetic bodies. In the tribe
of Polyclinians to which this genus belongs, the body
is elongated, and may be divided into three regions,
the thorax (a) which is chiefly occupied by the respiratory sac, the abdo-
men (b) which contains the digestive apparatus, and the post-abdomen
(c) in which the heart and generative organs are lodged. At the summit
of the thorax is seen the oral orifice c, which leads to the branchial sac e;
this is perforated by an immense number of slits, which allow part of the
water to pass into the space between the branchial sac and the muscular
mantle, where it is especially collected in the thoracic sinus /. At k is

166

THE MICROSCOPE AND ITS REVELATIONS.

seen the oesophagus, which is continuous with the lower part of the pha-
ryngeal cavity; this leads to the stomach I, which is surrounded by biliary
follicles; and from this passes-off the intestine mf which terminates at n
in the cloaca, or common vent. A current of water is continually drawn-
in through the mouth by the action of the cilia of the branchial sac and
of the alimentary canal; a part of this current passes through the fissures
of the branchial sac into the thoracic sinus, and thence into the cloaca;
whilst another portion, entering the stomach by an aperture at the bottom
of the pharyngeal sac, passes through the alimentary canal, giving up any
nutritive materials it may contain, and carrying away with it any excre-
mentitious matter to be discharged; and this having met the respiratory
current in the cloaca, the two mingled currents pass forth together by
the anal orifice i. The long post-abdomen is principally occupied by the
large ovarium, p, which contain ova in various stages of development.
These, when matured and set-free, find their way into the cloaca; where
two large ova are seen (one marked p', and the other immediately below
it) waiting for expulsion. In this position they receive the fertilizing
influence from the testis, q, which discharges its products by the long
spermatic canal, r, that opens into the cloaca, r'. At the very bottom of
the post-abdomen we find the heart, 0, inclosed in its pericardium, 0'. —
In the group we are now considering, a number of such animals are im-
bedded together in a sort of gelatinous mass, and covered with an integu-
ment common to them all; the composition of this gelatinous substance
is remarkable as including Cellulose, which generally ranks as a Vegetable
product. The mode in which new individuals are developed in this mass,
is by the extension of stolons or creeping stems from the bases of those
previously existing; and from each of these stolons several buds may be
put-forth, every one of which may evolve itself into the likeness of the
stock from which it proceeded, and may in its turn increase and multiply
after the same fashion. A communication between the circulating sys-
tems of the different individuals is kept-up, through their connecting
stems, during the whole of life; and thus their relationship to each other
is somewhat like that of the several polypes on the polypidom of a Cam-
panularia (§ 519).

557. In the family of Didemnians the post-abdomen is absent, the
heart and generative apparatus being placed by the side of the intestine
in the abdominal portion of the body. The zooids are frequently ar-
ranged in star-shaped clusters, their anal orifices being all directed to-
wards a common vent which occupies the centre. — This shortening is still
more remarkable, however, in the family of Boctryllians, whose beautiful
stellate gelatinous incrustations are extremely common upon Sea-weeds
and submerged rocks (Fig. 383). The anatomy of these animals is very
similar to that of the Amoroucium already described; with this exception,
that the body exhibits no distinction of cavities, all the organs being
brought together in one, which must be considered as thoracic. In this
respect there is an evident approximation towards the solitary species.1

558. This approximation is still closer, however, in the 6 social'
Ascidians, or Clavellinidce; in which the general plan of structure is
nearly the same, but the zooids are simply connected by their stolons

1 For more special information respecting the Compound Ascidians, see espe-
cially the admirable Monograph of Prof. Milne-Edwards on that group; Mr.
Lister's Memoir * On the Structure and Functions of Tubular and Cellular Polypi,
and of Ascidiae,' in the " Philos. Transact.," 1834; and the Art. Tunicatay by Prof.
T. Rupert Jones, in the " Cyclopaedia of Anatomy and Physiology."

POLYZOA AND TUNIC ATA.

167

Fig. 383.

(Fig. 384), instead of being included in a common investment; so that
their relation to each other is very nearly the same as that of the poly-
pides of Laguncula (§ 549), the chief difference being that a regular
circulation takes place through the stolon in the one case, such as has no
existence in the other. A better opportunity of studying the living
actions of the Ascidians can scarcely be found, than that which is afforded
by the genus Perophora, first discovered by Mr. Lister; which occurs not
unfrequently on the south
coast of England and in the
Irish Sea, living attached to
Sea-weeds, and looking like
an assemblage of minute
globules of jelly, dotted with
orange and brown, and link
ed by a silvery winding
thread. The isolation of the
body of each zooid from that
of its fellows, and the ex-
treme transparence of its
tunics, not only enable the
movements of the fluid with-
in the body to be distinctly
discerned, but also allow the
action of the cilia that bor-
der the slits of the respiratory
sac to be clearly made out.
This sac is perforated with
four rows of narrow oval
openings, through which a portion of the water that enters its oral
orifice (g) escapes into the space between the sac and the mantle, and is

Fig. 384.

Botryllus violaceus:—A, cluster on the surface of a
Fucus : — b, portion of the same enlarged.

A, Group of Perophora (enlarged^ growing from a common stalk: -b, single Perophora; a, test;
b, inner sac; c, branchial sac, attached to the inner sac along the linec' c' ; e e, finger-like processes

• ~, oral ori-
vent; i,

thus discharged immediately by the annal funnel (/). Whatever little

168

THE MICROSCOPE AND ITS REVELATIONS.

particles, animate or inanimate, the current of water brings, flow into
the sac, unless stopped at its entrance by the tentacles (#'), which do not
appear fastidious. The particles which are admitted usually lodge some-
where on the sides of the sac, and then travel horizontally until they
arrive at that part of it down which the current proceeds to the entrance
of the stomach (i), which is situated at the bottom of the sac. Minute
animals are often swallowed alive, and have been observed darting about
in the cavity for some days, .without any apparent injury either to them-
selves or to the creature which incloses them. In general, however,
particles which are unsuited for reception into the stomach are rejected
by the sudden contraction of the mantle (or muscular tunic), the vent
being at the same time closed, so that they are forced out by a powerful
current through the oral orifice. — The curious alternation of the circula-
tion that is characteristic of the Class generally (§ .555), may be particu-
larly well studied in Perophora. The creeping-stalk (Fig. 384) that
connects the individuals of any group, contains two distinct canals,
which send off branches into each peduncle. One of these branches
terminates in the heart, which is nothing more than a contractile dilata-
tion of the principal trunk; this trunk subdivides into vessels (or rather
sinuses, which are mere channels not having proper walls of their own),
of which some ramify over the respiratory sac, branching off at each of
the passages between the oval slits, whilst others .are first distributed to
the stomach and intestine, and to the soft surface of the mantle. All
these reunite so as to form a trunk, which passes to the peduncle and con-
stitutes the returning branch. Although the circulation in the different
bodies is brought into connection by the common stem, yet that of each
is independent of the rest, continuing when, the current through its own
footstalk is interrupted by a ligature; and the stream which returns from
the branchial sac and the viscera is then poured into the posterior part of
the heart, instead of entering the peduncle.

559. The development of the Ascidians, the early stages ot which are
observable whilst the ova are still within the cloaca of the parent, pre-
sents some phenomena of much interest to the Microscopist. After the
ordinary repeated segmentation of the yolk, whereby a ' mulberry mass '
is produced (§ 531), a sort of ring is seen encircling its central portion;
but this soon shows itself as a tapering tail-like prolongation from one
side of the yolk, which gradually becomes more and more detached from
it, save at the part from which it springs. Either whilst the egg is still
within the cloaca, or soon after it has escaped from the vent, its envelope
bursts, and the larva escapes; and in this condition it presents very much
the appearance of a tadpole, the tail being straightened out, and pro-
pelling the body freely through the water by its lateral strokes. The
centre of the body is occupied by a mass of liquid yolk; and this is con-
tinued into the interior of three prolongations which extend themselves
from the opposite extremity, each terminating in a sort of sucker. After
swimming about for some hours with an active wriggling movement, the
larva attaches itself to some solid body by means of one of these suckers;
if disturbed from its position, it at first swims about as before; but it
soon completely loses its activity, and becomes permanently attached;
and important changes manifest themselves in its interior. The pro-
longations of the central yolk-substance into the anterior processes and
tail are gradually drawn back, so that the whole of it is concentrated into
one mass; and the tail, now consisting only of the gelatinous envelope, is
either detached entire from the body by the contraction of the connect-

POLYZOA AND TUNICATA. 109

ing portion, or withers, and is thrown off gradually in shreds. The
shaping of the internal organs out of the yolk-mass takes place very
rapidly, so that by the end of the second day of the sedentary state the
outlines of the branchial sac and of the stomach and intestine may be
traced; no external orifices, however, being as yet visible. The pulsal ion
of the heart is first seen on the third day, and the formation of the
branchial and anal orifices takes-place on the fourth; after which the
ciliary currents are immediately established through the branchial sac
and alimentary canal. — The embryonic development of other Ascidians,
solitary as well as composite, takes-place on a plan essentially the same
as the foregoing, a free tadpole-like larva being always produced in the
first instance.1

560. This larval condition is represented in a very curious adult free-
swimming form, termed Appendicular 'ia, which is frequently to be taken
with the Tow-net on our own coasts. The animal has an oval or flask-
like body, which in large specimens attains the length of one-fifth of an
inch, but which is often not more than one-fourth or one-fifth of that
size. It is furnished with a tail-like appendage three or four times its
own length, broad, flattened, and rounded at its extremity; and by the
powerful vibrations of this appendage it is propelled rapidly through the
water. The structure of the body differs greatly from that of the Asci-
dians, its plan being much simpler; in particular, the pharyngeal sac is
entirely destitute of ciliated branchial fissures opening into a surrounding
cavity; but two canals, one on either side of the entrance to the stomach,
are prolonged from it to the external surface; and by the action of the
long cilia with which these are furnished, in conjunction with the cilia
of the branchial sac, a current of water is maintained through its cavity.
From the observations of Prof. Huxley, however, it appears that the
direction of this current is by no means constant; since, although it
usually enters by the mouth and passes out by the ciliated canals, it
sometimes enters by the latter and passes out by the former. The caudal
appendage has a central axis, above and below which is a riband-like layer
of muscular fibres; a nervous cord, studded at intervals with minute
ganglia, may be traced along its whole length. — By Mertens, one of the
early observers of this animal, it was said to be furnished with a peculiar
gelatinous envelope or Haus (house), very easily detached from the body,
and capable of being re-formed after having been lost. Notwithstanding
the great numbers of specimens which have been studied by Muller,
Huxley, Leuckart, and Gegenbaur, neither of these excellent observers
has met with this appendage; but it has been since seen by Prof. Allman,
who describes it as an egg-shaped gelatinous mass, in which the body is
imbedded, the tail alone being free; whilst from either side of the
central plane there radiates a kind, of double fan, which seems to be

1 The study of the development of Ascidians has derived a new interest and
importance from the discovery made by Kowalevsky in 1857, that their free-
swimming larvae present a most striking parallelism to Vertebrate embryoes, in
exhibiting the beginnings of a spinal marrow and a spinal column; thus bridging
over the gulf that was supposed to separate them from Invertebrata, and (when
taken in connection with the curious Ascidian affinities of Amphyoxus, the low-
est Vertebrate at present known) affording strong reason to believe in the deriva-
tion of the Vertebrate and Tunicate types from a common original. See his
Memoir ' Entwickelungsgeschichte der einfachen Ascidien,' in " Mem. St. Petersb.
Acad. Sci.,"Tom. x., 1867, and the abstract of it in " Quart. Journ. Microsc.
Sci.," Vol. x., N.S. (1870), p. 59; also Prof. Haeckel's " History of Creation," Vol.
ii., pp. 152, 200.

THE MICROSCOPE AND ITS REVELATIONS.

formed by a semicircular membranous lamina folded upon itself. It is
surmised by Prof. Allman, with much probability, that this curious
appendage is * nidamental/ having reference to the development and
protection of the young; but on this point further observations are
much needed; and any Microscopist, who may meet with Appendicularia
furnished with its ' house/ should do all he can to determine its struc-
ture and its relations to the body of the animal.1

1 For details in respect to the structure of Appendicularia, see Huxley, in
"Philos. Transact." for 1851, and in "Quart. Journ. of Microsc. Science," Vol.
iv. (1856), p. 181; also Allman in the same Journal, Vol. vii. (1859), p. 86; Gegen-
baur in Siebold and Kolliker's 44 Zeitschrift," Bd. vi (1855\ p. 406; Leuckart's
" Zoologische Untersuchungen," Heft ii., 1854; and Fol's 'Etudes sur les Appen-
diculaires' in " Archiv. Zool. Experim.," Tom. i. (1872), p. 57. — For the Tunicaia
generally, see Prof. T. Rupert Jones, in Vol. iv. of the *' Cyclop, of Anatomy and
Physiology;" Mr. Alder's 'Observations on the British Tunicata,' in 44 Ann. of
Nat. Hist.," Ser. 4, Vol. xi. (1863), p. 153; and Mr. Hancock's Memoir 4 On the
Anatomy and Physiology of the Tunicata,' in the ''Journal of the Linnaean
Society," Vol. ix., p. 309.

MOLLUSCOUS ANIMALS GENERALLY.

171

CHAPTER XVI.
MOLLUSCOUS ANIMALS GENERALLY.

561. The various forms of 9 Shell-fish,' with their ' naked' or shel-
less allies, furnish a great abundance of objects of interest to the Micro-
scopist; of which, however, the greater part may be grouped under three
heads: — namely, (1) the structure of the shell, which is most interesting in
the Conchifera and Brachiopoda, in both of which classes the shells
are 9 bivalve,' while the animals differ from each other essentially in gen-
eral plan of structure; (2) the structure of the tongue or palate of the
Gasteropoda, most of which have ' univalve' shells, others, however,
being 6 naked;' (3) the developmental history of the embryo, for the study
of which certain of the Gasteropods present the greatest facilities. — These
three subjects, therefore, will be first treated of systematically; and a few
miscellaneous facts of interest will be subjoined.

562. Shells of Mollusca. — These investments were formerly regarded
as mere inorganic exudations, composed of calcareous particles, cemented
together by animal glue; Microscopic examination, however, has shown
that they possess a definite structure, and that this structure presents
certain very remarkable variations in some of the groups of which the
Molluscous series is composed. — We shall first describe that which may
be regarded as the characteristic structure of the ordinary Bivalves; tak-
ing as a type the group of Margaritacece, which includes the Avicula or
9 pearl-oyster ' and its allies, the common Pinna ranking amongst the
latter. In all these shells we readily distinguish the existence of two dis-
tinct layers; an external, of a brownish-yellow color; and an internal,
which has a pearly or 9 nacreous ' aspect, and is commonly of a lighter
hue.

563. The structure of the outer layer may be conveniently studied in
the shell of Pinna, in which it commonly projects beyond the inner, and
there often forms lamina sufficiently thin and transparent to exhibit its
general characters without any artificial reduction. If a small portion
of such a lamina be examined with a low magnifying power by trans-
mitted light, each of its surfaces will present very much the appearance
of a honeycomb; whilst its broken edge exhibits an aspect which is evi-
dently fibrous to the eye, but which, when examined under the Microscope
with reflected light, resembles that of an assemblage of segments of
basaltic columns (Fig. 488, p). This outer layer is thus seen to be com-
posed of a vast number of prisms, having a tolerably uniform size, and
usually presenting an approach to the hexagonal shape. These are
arranged perpendicularly (or nearly so) to the surface of the lamina of
the shell; so that its thickness is formed by their length, and its two
surfaces by their extremities. A more satisfactory view of these prisms
is obtained by gnnding-down a lamina until it possesses a high degree of

172

THE MICROSCOPE AND ITS REVELATIONS.

transparence; the prisms being then seen (Fig. 385) to be themselves
composed of a very homogeneous substance, but to be separated by definite
and strongly marked lines of division. When such a lamina is submitted to
the action of dilute acid, so as to dissolve-away the carbonate of lime,
a tolerably firm and consistent membrane is left, which exhibits the
prismatic structure just as perfectly as did the original shell (Fig. 386);
its hexagonal divisions bearinga strong resemblance to the walls of the cells
of the pith or bark of a Plant. By making a section of the shell perpen-
dicularly to its surface, we obtain a view of the prisms cut in the direction
of their length (Fig. 387); and they are frequently seen to be marked by

Fig. 385. Fig. 386.

Section of Shell of Pinna, taken transversely to Membranous basis of the same,

the directions of its prisms.

delicate transverse striae (Fig. 388), closely resembling those observable
on the prisms of the enamel of teeth, to which this kind of shell struc-
ture may be considered as bearing a very close resemblance, except as
regards the mineralizing ingredient. If a similar section be decalcified
by dilute acid, the membranous residuum will exhibit the same resem-

Fig.387. Fig. 388

Section of the shell of Pinna, in the Oblique Section of Prismatic Shell-substance,

direction of its prisms.

blance to the walls of prismatic cells viewed longitudinally, and will be
seen to be more or less regularly marked by the transverse stride just
alluded to. It sometimes happens in recent, but still more commonly in
fossil shells, that the decay of the animal membrane leaves the contained
prisms without any connecting medium; as they are then quite isolated,

MOLLUSCOUS ANIMALS GENERALLY.

173

they can be readily detached one from another; and each one may be
observed to be marked by the like striations, which, when a sufficiently
high magnifying power is used, are seen to be minute grooves, apparently
resulting from a thickening of the intermediate wall in those situations.
These appearances seem best accounted-for, by supposing that each is
lengthened by successive additions at its base, the lines of junction of
which correspond with the transverse striation; and this view corresponds
well with the fact, that the shell-membrane not unfrequently shows a
tendency to split into thin laminae along the lines of striation; whilst we
occasionally meet with an excessively thin natural lamina lying between the
thicker prismatic layers, with one of which it would have probably coa-
lesced, but for some accidental cause which preserved its distinctness.
That the prisms are not formed in their entire length at once, but that
they are progressively lengthened and consolidated at their lower extremi-
ties, would appear al o from the fact that where the shell presents a deep
color (as in Pinna nigrum), this color is usually disposed in distinct
strata, the outer portion of each layer being the part most deeply tinged,
whilst the inner extremities of the prisms are almost colorless.

564. This ' prismatic ' arrangement of the carbonate of lime in the
shells of Pinna and its allies, has been long familiar to Conchologists,
and regarded by them as the result of crystallization. When it was first
more minutely investigated by Mr. Bowerbank1 and the Author/ and
was shown to be connected with a similar arrangement in the membran-
ous residuum left after the decalcification of the shell-substance by acid,
Microscopists generally3 agreed to regard it as a ' calcified epidermis: '
the long prismatic cells being supposed to be formed by the coalescence
of the epidermic cells in piles, and giving their shape to the deposit of
carbonate of lime formed within them. The progress of inquiry, how-
ever, has led to an important modification of this interpretation; the
Author being now disposed to agree with Prof. Huxley4 in the belief
that the entire thickness of the shell is formed as an excretion from the
surface of the epidermis, and that the horny layer which in ordinary
shells forms their external envelope or 'periostracum,' 6 being here
thrown out at the same time with the calcifying material, is converted
into the likeness of a cellular membrane by the pressure of the prisms
that are formed by crystallization at regular distances in the midst of it.
— The peculiar conditions under which calcareous concretions form
themselves in an organic matrix, have been carefully studied by Mr.
Rainey and Dr. W. M. Ord; of whose researches some account will be
given hereafter (§ 711).

565. The internal layer of the shells of the Margaritacece and some
other families has a 6 nacreous 9 or iridescent lustre, which depends (as
Sir D. Brewster has shown6) upon the striation of its surface with a

1 4 On the Structure of the Shells of Molluscous and Conchiferou* Animals,' in
" Transact, of Microsc. Society," 1st Ser. (1844\ Vol. i., p. 123.

2 4 On the Microscopic Structure of Shells/ in 44 Reports of British Association "
for 1844 and 1847.

3 See Mr. Quekett's 44 Histological Catalogue of the College of Surgeons' Mu-
seum," and his 44 Lectures on Histology," Vol. ii.

4 See his article 4 Tegumentary Organs,' in 44 Cyclopaedia of Anatomy and Phy-
siology," Supplementary Volume, pp. 489-492.

5 The Periosiracum is the yellowish-brown membrane covering the surface of
many shells, which is often (but erroneously) termed their epidermis.

6 4 4 Philosophical Transactions," 1814, p. 397.— The late Mr. Barton (of the
Mint) succeeded in producing an artificial iridescence on metallic buttons, by

174

THE MICROSCOPE AND ITS "REVELATIONS .

series of grooved lines, which usually run nearly parallel to each other
(Fig. 389). As these lines are not obliterated by any amount of polish-
ing, it is obvious that their presence depends upon something peculiar in
the texture of this substance, and not upon any mere superficial arrange-
ment. When a piece of the nacre (commonly known as 'mother-of-
pearl') of the Avicula or 'pearl-oyster ' is carefully examined, it becomes
evident that the lines are produced by the cropping-out of laminae of
shell situated more or less obliquely to the plane of the surface. The
greater the dip of these laminae, the closer will their edges be; whilst the
less the angle which they make with the surface, the wider will be the
interval between the lines. When the section passes for any distance in
the plane of a lamina, no lines will present themselves on that space.
And thus the appearance of a section of nacre is such as to have been

section of 'mother-of-pearl' ought to contain many hundred laminae, in
accordance with the number of lines upon its surface; these being fre-
quently no more than l-7500th of an inch apart. But when the nacre is
treated with dilute acid so as to dissolve its calcareous portion, no such
repetition of membranous layers is to be found; on the contrary, if the
piece of nacre be the product of one act of shell-formation, there is but a
single layer of membrane. This layer, however, is found to present a
more or less folded or plaited arrangement; and the lineation of the
nacreous surface may perhaps be thus accounted for. — A similar arrange-
ment is fouitd in pearls; which are rounded concretions projecting from
the inner surface of the shell of Avicula, and possessing a nacreous
structure corresponding to that of 'mother-of-pearl.' Such concretions
are found in many other shells, especially the fresh-water mussels, Unto
and Anodon; but these are usually less remarkable for their pearly lustre;
and, when formed at the edge of the valves, they may be partly or even
entirely made-up of. the prismatic substance of the external layer, and
may be consequently altogether destitute of the pearly character.

drawing closely-approximating lines with a diamond-point upon the surface of
the steel die by which they were struck.

Section of nacreous lining of Shell of Avicula marga-
ritacea (Pearl-oyster).

Fig. 389.

aptly compared by Sir J. Her-
schel to the surface of a
smoothed dealboard, in which
the woody layers are cut per-
pendicularly to their surface
in one part, and nearly in their
plane in another. Sir D. Brew-
ster (loc. tit.) appears to have
supposed that nacre consists of
a multitude of layers of carbon-
ate of lime alternating with
animal membrane; and that the
presence of the grooved lines
on the most highly-polished
surface is due to the wearing
away of the edges of the ani-
mal laminae, whilst those of
the hard calcareous laminae
stand out. If each line upon
the nacreous surface, however,
indicates a distinct layer of
shell-substance, a very thin

MOLLUSCOUS ANIMALS GENERALLY.

175

566. In all the genera of the MargaritacecB, we find the external layer
of the shell prismatic, and of considerable thickness; the internal layer
being nacreous. But it is only in the shells of a few families of Bivalves,
that the combination of organic with mineral components is seen in the
same distinct form; and these families are for the most part nearly allied
to Pinna. In the TJnionidm (or ' fresh- water mussels '), nearly the whole
thickness of the shell is made-up of the internal or 6 nacreous ' layer; but
a uniform stratum of prismatic substance is always found between the
nacre and the periostracum, really constituting the inner layer of the
latter, the outer being simply horny. — In the Ostracem (or oyster tribe)
also, the greater part of the thickness of the shell is composed of a 6 sub-
nacreous 9 substance (§ 568) representing the inner layer of the shells of
Margaritaceae, its successively-formed laminae, however, having very lit-
tle adhesion to each other; and every one of these laminae is bordered
at its free edge by a layer of the prismatic substance, distinguished by
its brownish-yellow color. In these and some other cases, a distinct
membranous residuum is left after the decalcification of the prismatic
layer by dilute acid; and this is most tenacious and substantial, where
(as in the Margaritacem) there is no proper periostracum. Generally
speaking, a thin prismatic layer may be detected upon the external sur-
face of Bivalve shells, where this has been protected by a periostracum,
or has been prevented in any other manner from undergoing abrasion;
thus it is found pretty generally in
Chama, Trigonia, and Solen, and oc-
casionally in Anomia and Pecten.

567. In many other instances, how-
ever, nothing like a cellular struc-
ture can be distinctly seen in the deli-
cate membrane left after decalcifica-
tion; and in such cases the animal
basis bears but a very small propor-
tion to the calcareous substance, and
the shell is usually extremely hard.
This hardness appears to depend upon
the mineral arrangement of the car-
bonate of lime; for whilst in the
prismatic and ordinary nacreous layer
this has the crystalline condition of

calcite, it Can be Shown in the hard Section of hinge-tooth, of Mya arenaria,

shell of Pholas to have the arrange-
ment of arragonite; the difference be-
tween the two being made evident by Polarized light. A very
curious appearance is presented by a section of the large hinge-tooth of
Mya arenaria (Fig. 390), in which the carbonate of lime seems to be de-
posited in nodules that possess a crystalline structure resembling that of
the mineral termed Wavellite. Approaches to this curious arrangement
are seen in many other shells.

568. There are several Bivalve shells which almost entirely consist of
what may be termed a sab-nacreous substance; their polished surfaces
being marked by lines, but these lines being destitute of that regularity
of arrangement which is necessary to produce the iridescent lustre. This
is the case, for example, with most of the Pectinidw (or scallop tribe),
also with some of the Mytilacece (or mussel tribe), and with the common
Oyster. In the internal layer of by far the greater number of Bivalve

Fig. 390.

176

THE MICROSCOPE AND ITS REVELATIONS.

shells, however, there is not the least approach to the nacreous aspect;
nor is there anything that can be described as definite structure;1 and
the residuum left after its decalcification is usually a structureless 'base-
ment-membrane.'

569. The ordinary account of the mode of growth ot the shells ot
Bivalve Mollusca,— that they are progressively enlarged by the deposition
of new laminae, each of which is in contact with the internal surface of
the preceding, and extends beyond it,— does not express the whole truth;
for it takes no account of the fact that most shells are composed of two
layers of very different texture, and does not specify whether both these
layers are thus formed by the entire surface of the ' mantle' whenever
the shell has to be extended, or whether only one is produced. An ex-
amination of Fig. 391 will clearly show the mode in which the operation
is effected. This figure represents a section of one of the valves of Unio
occidens, taken perpendicularly to its surface, and passing from the
margin or lip (at the left hand of the figure) towards the hinge (which
would be at some distance beyond the right). This section brings into
view the two substances of which the shell is composed; traversing the

Fig. 391.

Vertical section of the lip of one of the valves of the shell of Unio:— a, 6, c, successive forma-
tions of the outer prismatic layer; a', b\ c\ the same of the inner nacreous layer.

outer or prismatic layer in the direction of the length of its prisms, and
passing through the nacreous lining in such a manner as to bring into
view its numerous laminae, separated by the lines a a\ b b\ c c', etc.
These lines evidently indicate the successive formations of this layer; and
it may be easily shown by tracing them towards the hinge on the one
side and towards the margin on the other, that at every enlargement of
the shell its whole interior is lined by a new nacreous lamina in imme-
diate contact with that which preceded it. The number of such laminae,
therefore, m the oldest part of the shell, indicates the number of enlarge-
ments which it has undergone. The outer or prismatic layer of the
growing shell, on the other hand, is only formed where the new structure
projects beyond the margin of the old; and thus we do not find one layer
of it overlapping another, except at the lines of junction of two distinct
formations. When the shell has attained its full dimensions, however, new
laminae of both layers still continue to be added, and thus the lip becomes
thickened by successive formations of prismatic structure, each being ap-
plied to the inner surface of the preceding, instead of to its free margin.
— A like arrangement may be well seen in the Oyster; with this differ-

1 For an explanation of the real nature of what was formerly described by the
Author as * tubular 1 Shell-substance, see § 316.

MOLLUSCOUS ANIMALS GENERALLY.

177

A, Internal surface (a), and oblique section (6), of Shell
of Terebratula (Waldheimia) australis; b, external sur-
face of the same.

Fig. 393.

ence, that the successive layers have but a comparatively slight adhesion
to each other.

570. The shells of Terebratulce, however, and of most other Bracliio-
pods, are distinguished by peculiarities of structure which differentiate
them from all others. When thin sections of them are microscopically
examined, they exhibit the appearance of long flattened prisms (Fig. 392,
A, b), which are arranged

with such obliquity that Fig. 392,

their rounded extremities a b

crop-out upon the inner
surface of the shell in an
imbricated (tile-like) man-
ner (a). All true Terebra-
tididce, both recent and
fossil, exhibit another very
re markable peculiarity;
namely, the perforation of
the shell by a large number
of canals, which generally
pass nearly perpendicularly
from one surface to the other
(as is shown vertical sections,
Fig. 393), and terminate
internally by open orifices
(Fig. 392, a), whilst exter-
nally they are covered by the
periostracum (b). Their dia-
meter is greatest towards
the external surface, where
they sometimes expand sud-
denly, so as to become trum-
pet-shaped; and it is usually
narrowed rather suddenly,
when, as sometimes hap-
pens, a new internal layer is
formed as a lining to the
preceding (Fig. 393, A,dd).
Hence the diameter of these
canals, as shown in different
transverse sections of one
and the same shell, will vary
according to the part of
its thickness which the sec-
tion happens to traverse. —
The shells of different species
of perforated Brachiopods,
however, present very striking diversities in the size and closeness of their
canals, as shown by sections taken in corresponding parts; three examples
of this kind are given for the sake of comparison in Figs. 394-396.
These canals are occupied in the living state by tubular prolongations of
the mantle, whose interior is filled with a fluid containing minute cells
and granules, which, from its corresponding in appearance with the fluid
contained in the great sinuses of the mantle, may perhaps be considered
to be the animal's blood. Of their special function in the economy of
12

Vertical Sections of Shell of Terebratula (Wald-
heimia) australis; showing at a the canals opening by
large trumpet- shaped orifices on the outer surface, and
contracting at d, d, into narrow tubes; and showing at b a
bifurcation of the canals.

178

THE MICROSCOPE AND ITS REVELATIONS,

the animal, it is difficult to form any probable idea; but it is interesting
to remark (in connection with the hypothsek of a relationship between
Brachiopods and Polyzoa) that they seem to have their parallel in exten-
sions of the peri-visceral cavity of many species of Flustra, Eschara,
Lepralia, etc., into passages excavated in the walls of the cells of the
polyzoary.

571. In the Family EhynchonellidcB, which is represented by only two
recent species (the Eh. psittacea and Eh. nigricans, both formerly rank-
ing as Terebratulae), but which contains a very large proportion of fossil
Brachiopods, these canals are almost entirely absent; so that the uniform-
ity of their presence in the Terebratulidse, and their general absence in
the Khynchonellidae, supplies a character of great value in the discrimi-
nation of the fossil shells belonging to these two groups respectively.
Great caution is necessary, however, in applying this test; mere surf ace-
mar kings cannot be reiied-on; and no statement on this point is worthy
of reliance, which is not based on a Microscopic examination of thin sec-
tions of the shell. — In the Families Spiriferidce and Strophomenidce, on
the other hand, some species possess the perforations, whilst others are desti-

Fig. 394. Fig. 395. Fig. 396.

Fig. 394. Horizontal section of Shell of Terebratula bullata (fossil. Oolite).
Fig. 395. Ditto . . of Megerlia lima (fossil. Chalk).

Fig. 396. Ditto . . of Sptriferina rostrata (Triassic).

tute of them; so that their presence or absence there serves only to mark-
out subordinate groups. This, however, is what holds-good in regard to
characters of almost every description, in other departments of Natural
History; a character which is of fundamental importance from its close
relation to the general plan of organization in one group, being, from its
want of constancy, of far less account in another.1

572. There is not by any means the same amount of diversity in
the structure of the Shell in the class of G aster opods; a certain typical
plan of construction being common to by far the greater number of them.
The small proportion of animal matter contained in most of these shells,
is a very marked feature in their character; and it serves to render other

1 For a particular account of the Authors researches on this group, see his
Memoir on the subject, forming part of the introduction of Mr. Davidson's
" Monograph of the British Fossil Brachiopoda," published by the Palseontogra-
phicai Society. — A very remarkable example of the importance of the presence or
absence of the perforations, in distinguishing shells whose internal structure
shows them to be generically different, whilst from their external conformation
they would be supposed to be not only generically but specifically identical, will
be found in the " Annals of Natural History," Ser. 3, Vol. xx. (1867), p. 68.

MOLLUSCOUS ANIMALS GENERALLY.

179

features indistinct, since the residuum left after the removal of the cal-
careous matter is usually so imperfect, as to give no clue whatever to the
explanation of the appearances shown by sections. Nevertheless, the
structure of these shells is by no means homogeneous, but always exhibits
indications, more or less clear, of a definite arrangement. The ' porcel-
lanous' shells are composed of three layers, all presenting the same kind
of structure, but each differing from the others in the mode in which
this is disposed. ^ For each layer is made-up of an assemblage of thin
laminae placed side-by-side, which separate one from another, apparently
in the planes of rhomboidal cleavage, when the shell is fractured; and
as was first pointed out by Mr. Bowerbank, each of these laminae consists
of a series of elongated^ spicules (considered by him as prismatic cells
filled with carbonate of lime) lying side-by-side in close apposition; and,
these series are disposed alternately in contrary directions, so as to inter-
sect each other nearly at right angles, though still lying in parallel
planes. The direction of the planes is different, however, in the three
layers of the shell, bearing the same relation to each other as have those
three sides of a cube which meet each other at the same angle; and by
this arrangement, which is better seen in the fractured edge of the
Cyprcea or any similar shell, than in thin sections, the strength of the
shell is greatly augmented. — A similar arrangement, obviously answering
the same purpose, has been shown by Mr. Tomes to exist in the enamel
of the teeth of Eodentia.

573. The principal departures from this plan of structure are seen
in Patella, Chiton, Haliotis, Turbo and its allies, and in the 6 naked
Gasteropods, many of which last, both terrestrial and marine, have some
rudiment of a shell. Thus in the common Slug, Limax rufus, a thin
oval plate of calcareous texture is found imbedded in the shield-like fold of
the mantle covering the fore-part of its back; and if this be examined in an
early stage of its growth, it is found to consist of an aggregation of minute
calcareous nodules, generally somewhat hexagonal in form, and sometimes
quite transparent, whilst in other instances it presents an appearance
closely resembling that delineated in Fig. 390. — In the epidermis of
the mantle of some species of Doris, on the other hand, we find long
calcareous spicules, generally lying in parallel directions, but not in con-
tact with each other, giving firmness to the whole of its dorsal portion;
and these are sometimes covered with small tubercles, like the spicules
of Gorgonia (Fig. 363). They may be separated from the soft tissue in
which they are imbedded, by means of caustic potash; and when treated
with dilute acid, whereby the calcareous matter is dissolved-away, an
organic basis is left, retaining in some degree the form of the original
spicule. This basis cannot be said to be a true cell; but it seems to be
rather a cell in the earliest stage of its formation, being an isolated parti-
cle of sarcode without wall or cavity; and the close correspondence
between the appearance presented by thin sections of various Univalve
shells, and the forms of the spicules of Doris, seems to justify the con-
clusion that even the most compact shells of this group are constructed
out of the like elements, in a state of closer aggregation and more definite
arrangement, with the occasional occurrence of a layer of more spheroidal
bodies of the same kind, like those forming the rudimentary shell of
Limax.

574. The structure of Shells generally is best examined by making
sections in different planes as nearly parallel as may be possible to the
surfaces of the shell, and other sections at right angles to these: the

180

THE MICROSCOPE AND ITS REVEL ATIO N 5 .

former may be designated as horizontal, the latter as vertical. Nothing
need here be added to the full directions for making such Sections,
which have already been given (§§ 192-194). Many of them are beau-
tiful and interesting objects for the Polariscope. — Much valuable infor-
mation may also be derived from the examination of the surfaces
presented by fracture. The membranous residua left after the decalcifi-
cation of the shell by dilute acid, may be mounted in weak spirit or in
Goadby's solution.

575. The animals composing the class of Cephalopoda (cuttle-fish and
nautilus tribe) are for the most part unpossessed of shells; and the struc-
ture of the few that we meet-with in the genera Nautilus, Argonaut a
(' paper-nautilus'), and Spirula, does not present any peculiarities that
need here detain us. The rudimentary shell or sepiostaire of the com-
mon Cuttle-fish, however, which is frequently spoken-of as the ' cuttle-
fish bone/ exhibits a very beautiful and remarkable structure, such as
causes sections of it to be very interesting Microscopic objects. The
outer shelly portion of this body consists of horny layers, alternating
with calcified layers, in which last may be seen a hexagonal arrangement
somewhat corresponding with that in Fig. 390. The soft friable sub-
stance that occupies the hollow of this boat-shaped shell, is formed of a
number of delicate calcareous plates, running across it from one side to
the other in parallel directions, but separated by intervals several times
wider than the thickness of the plates; and these intervals are in great
part filled-up by what appear to be fibres or slender pillars, passing
from one plate or floor to another. A more careful examination shows,
however, that instead of a large number of detached pillars, there ex-
ists a comparatively small number of very thin sinuous laminae, which pass
from one surface to the other, winding and doubling upon themselves,
so that each lamina occupies a considerable space. Their precise ar-
rangement is best seen by examining the parallel plates, after the sinuous
lamina have been detached from them; the lines of junction being dis-
tinctly indicated upon these. By this arrangement each layer is most
effectually supported by those with which it is connected above and
below; and the sinuosity of the thin intervening laminae, answering ex-
actly the same purpose as the ' corrugation ' given to iron plates for the
sake of diminishing their flexibility, adds greatly to the strength of this
curious texture; which is at the same time lightened by the large amount
of open space between the parallel plates, that intervenes among the
sinuosities of the laminae. The best method for examining this struc-
ture, is to make sections of it with a sharp knife in various directions,
taking care that the sections are no thicker than is requisite for holding-
together; and these may be mounted on a Black Ground as opaque ob-
jects, or in Canada balsam as transparent objects, under which last
aspect they furnish very beautiful objects for the Polariscope.

576. Palate of Gasteropod Mollusks. — The organ which is sometimes
referred to under this designation, and sometimes as the ' tongue,' is one
of a very singular nature; and cannot be likened to either the tongue or
the palate of higher animals. For it is a tube that passes backward and
downwards beneath the mouth, closed at its hinder end, whilst in front
it opens obliquely upon the floor of the mouth, being (as it were) slit-up
and spread-out so as to form a nearly flat surface. On the interior of
the tube, as well as on the flat expansion of it, we find numerous trans-
verse rows of minute teeth, which are set upon flattened plates; each
principal tooth sometimes having a basal plate of its own, whilst in

MOLLUSCOUS ANIMALS GENERALLY.

181

other instances one plate carries several teeth. — Of the former arrange-
ment we have an example in the palate of many terrestrial Gasteropods,
such as the snail (Helix) and Slug (Limax), in which the number of
plates in each row is very considerable (Figs. 397, 398), amounting to 180
in the large garden Slug (Limax maximus); whilst the latter prevails in
many marine Gasteropods, such as the common Whelk (Buccimim unda-
tum), the palate of which has only three plates in each row, one bearing
the small central teeth, and the two others the large lateral teeth (Fig.

Fig. 397. Fig. 398.

Portion of the left half of the Palate of Palate of Zonites cellar ius.

Helix hortensis ; the rows of teeth near
the edge separated from each other to show
their form.

401). The length of the palatal tube, and the number of rows of teeth,
vary greatly in different species. Generally speaking, the tube of the
terrestrial Gasteropods is short, and is contained entirely within the
nearly globular head; but the rows of teeth being closely set together are
usually very numerous, there being frequently more than 100, and in

Fig. 399. Fig 400

some species as many as 160 or 170; so that the total numer of teeth
may mount-up, as in Helix pomatia, to 21,000, and in Umax maximus,
to 26,800. The transverse rows are usually more or less curved, as
shown in Fig. 398, whilst the longitudinal rows are quite straight: and

182

THE MICROSCOPE AND ITS REVELATIONS.

the curvature takes its departure on each side from a central longitudi-
nal row, the teeth of which are symmetrical, whilst those of the lateral
portions of each transverse row present a modification of that symmetry,
the prominences on the inner side of each tooth being suppressed, whilst
those on the outer side are increased; this modification being observed
to augment in degree, as we pass from the central line towards the
edges.

577. The palatal tube of the marine Gasteropods is generally longer,
and its teeth larger; and in many instances it extends far beyond the
head, which may, indeed, contain but a small part of it. Thus in the
common Limpet {Patella), we find the principal part of the tube to lie
f olded-up, but perfectly free, in the abdominal cavity, between the in-
testine and the muscular foot; and in some species its length is twice or
even three times as great as that of the entire animal. In a large pro-
portion of cases, these palates exhibit a very marked separation between
the central and the lateral portions (Figs. 399, 401); the teeth of the
central band being frequently small and smooth at their edges, whilst
those of the lateral are large and serrated. The palate of Troclms zizy-
pliinus, represented in Fig. 399, is one of the most beautiful examples
of this form; not only the large teeth of the lateral bands, but the deli-
cate leaf-like teeth of the central portion, having their edges minutely
serrated. A yet more complex type, however, is found in the palate of
Haliotis ; in which there is a central band of teeth having nearly straight
edges instead of points: then, on each side, a lateral band consisting of
large teeth shaped like those of the Shark; and beyond this, again,
another lateral band on either side, composed of several rows of smaller
teeth. — Very curious differences also present themselves among the dif-
ferent species of the same genus. Thus in Doris pilosa, the central band
is almost entirely wanting, and each lateral band is formed of a single row
of very large hooked teeth, set obliquely like those of the lateral band in
Fig. 399; whilst in Doris tubercalata, the central band is the part most
developed, and contains a number of rows of conical teeth, standing
almost perpendicularly, like those of a harrow (Fig. 400).

5/8. Many other varieties might be described, did space permit; but
we must be content with adding, that the form and arrangement of the-
teeth of these ' palates 9 afford characters of great value in classification,
as was first pointed out by Prof. Loven (of Stockholm) in 1847, and has
been since very strongly urged by Dr. J. E. Gray, who considers that
the structure of these organs is one of the best guides to the natural
affinities of the species, genera, and families of this group, since any im-
portant alteration in the form or position of the teeth must be accom-
panied by some corresponding peculiarity in the habits and food of the
animal.1 Hence a systematic examination and delineation of the struc-
ture and arrangement of these organs, by the aid of the Microscope and
Camera Lucida, would be of the greatest service to this department of
Natural History. The short thick tube of Limax and other terrestrial
Gasteropods, appears adapted for the trituration of the food previously
to its passing into the oesophagus; for in these animals wre find the roof
of the mouth furnished with a large strong horny plate, against which
the flat end of the tongue can work. On the other hand, the flattened
portion of the palate of Buccinum (whelk) and its allies is used by these
animals as a file, with which they bore holes through the shells of the

1 "Annals of Natural History," Ser. 2, Vol. x. (1852), p. 413.

MOLLUSCOUS ANIMALS GENERALLY.

183

Mollusks that serve as their prey; this thev are enabled to effect by evert-
ing that part of the probosis-sliaped mouth whose floor is formed by the
flattened part of the tube, which is thus brought to the exterior* and
by giving a kind of sawing-motion to the organ by means of the alter-
nate action of two pairs of muscles,— a protractor, and a retractor —
which put-forth and draw- back a pair of cartilages whereon the tongue
is supported, and also elevate and depress its teeth. Of the use of the
long blind tubular part of the palate in these Gasteropods, however,
scarcely any probable guess can be made; unless it be a sort of ' cavity
of reserve/ from which a new toothed surface may be continually sup-
plied as the old one is worn- away, somewhat as the front teeth of the Ro-
dents are constantly being regenerated from the surface of the pulps
which occupy their hollow conical bases, as fast as they are rubbed-down
at their edges.

579. The preparation of these Palates for the Microscope can, of
course, be only accomplished by carefully dissecting them from their
attachments within the head; and it will be also necessary to remove the
membrane that forms the sheath of the tube, when this is thick enough
to interfere with its transparence. The tube itself should be slit up
with a pair of fine scissors through its entire length; and should be so
opened out, that its expanded surface may be a continuation of that
which forms the floor of the mouth. The mode of mounting it will de-
pend upon the manner in which it is to be viewed. For the ordinary
purposes of Microscopic examination, no method is so good as mofthting
in fluid; either weak Spirit or Goadby's solution answering very well
But many of these palates, especially those of the marine Gasteropods, be-
come most beautiful objects for the Polariscope when they are mounted
in Canada balsam; the form and arrangement of the teeth being very
strongly brought-out by it (Fig. 401), and a gorgeous play of colors being-
exhibited when a selenite plate is placed behind the object, and the
analyzing prism is made to rotate.1

580. Development of Mollusks. — Leaving to the scientific Embryologist
the large field of study that lies open to him in this direction,2 the ordi-
nary Microscopist will find much to interest him in the observation of cer-
tain special phenomena of which a general account will be here given. At-
tached to the gills of fresh-water Mussels (Unio and Anodon) there are
often found minute bodies, which, when first observed, were described as
parasites, under the name of Glochidia, but are now known to be their
own progeny in an early phase of development. When a Fish is near,
they are expelled from between the valves of their parent, and attach
themselves in a peculiar manner to its fins and gills (Fig. 402, a). In
this stage of the existence of the young Anodon, its valves are provided
with curious barbed or serrated hooks (d, b), and are continually snap-
ping together (so as to remind the observer of the avicularia of Polyzoa,
§ 554), until they have inserted their hooks into the skin of the Fish,
which seems so to retain the barbs as to prevent the reopening of the
valves. In this stage of its existence no internal organ is definitely
formed, except the strong ' adductor muscle' (c, a) which draws the
valves together, and the long, slender, byssus-filament (b, a, d) which
makes its appearance while the embryo is still within the egg membrane,

1 For additional details on the organization of the Palate and Teeth of the
Gasteropod Mollusks, see Mr. W. Thomson, in "Cyclop, of Anat. and Physiol. "
Vol. iv., pp. 1142, 1143; and in "Ann. of Nat. Hist.," Ser. 2 Vol. vii., p. 86.

2 See Balfour's " Comparative Embryology," Chap. ix.

184:

THE MICROSCOPE AND ITS REVELATIONS.

lying coiled-up between the lateral lobes. The hollow of each valve is
filled with a soft granular-looking msss, in which are to be distinguished
what are perhaps the rudiments of the branchiae and of oral tentacles;
but their nature can only be certainly determined by further observation,
which is rendered difficult by the opacity of the valves. By keeping a
supply of Fish, however, with these embryoes attached, the entire history
of the development of the fresh-water Mussel may be worked out.1

581. In certain members of the Class Gasteropods, the history of em-
bryonic development presents numerous phenomena of great interest.
The eggs (save among the terrestrial species) are usually deposited in
aggregate masses, each inclosed in a common protective envelope or
nidamentum. The nature of this envelope, however, varies greatly :
thus, in the common Limnceus stagnalis or f water-snail ' of our pondf

Fig. 401. Fig. 402.

4 !V:

:,><

Parasitic Larva (Glochidium) of Anodon:— a, glochidia at-
tached to the tail of a Stickleback; b, side view of glochidium
still inclosed in the egg-membrane, showing the hooks of its
valves and the byssus-filamenta,* c, glochidium with its valves
widely opened, showing the adductor-muscle a; d, side view
of glochidium; with the valves opened to show the origin of
Palate of Buccinum undatum as the byssus-filament and the three pairs of tentacular ( ?) or-
seen under Polarized Light. gans, the barbed hooks 6, and the muscular or membran-
ous folds c, c, connected with them.

and ditches, it is nothing else than a mass of soft jelly about the size of
a sixpence, in which from 50 to 60 eggs are imbedded, and which is at-
tached to the leaves or stems of aquatic plants; in the Buccinum unda-
tum, or common Whelk, it is a membranous case, connected with a con-
siderable number of similar cases by short stalks, so as to form large
globular masses which may often be picked-up on our shores especially
between April and June ; in the Purpura lapillus, or ' rock-whelk,' it is
a little flask-shaped capsule, having a firm horny wall, which is attached
by a short stem to the surface of rocks between the tide-marks, great
numbers being often found standing erect side by side; whilst in the

1 See the Rev. W. Houghton ' On the Parasitic Nature of the Fry of the Ano-
donta cygnea? in " Quart. Journ. of Microsc. Sci.," N.S., Vol. ii. (1861), p. 162;
and Balfour, op. cit, pp. 220-223.

MOLLUSCOUS ANIMALS GENERALLY.

185

Nudibranchiate order generally (consisting of the Doris, Eolis, and other
'sea-slugs') it forms a long tube with a membranous wall, in which inu
mense numbers of eggs (even half a million or more) are packed closely
together in the midst of a jelly-like substance, this tube being disposed
in coils of various forms, which are usually attached to the Sea-weeds or
Zoophytes. — The course of development, in the first and last of these
instances, may be readily observed from the very earliest period down to
that of the emersion of the embryo; owing to the extreme transparence

Fig. 403.

Embryonic development of Doris bilamellata:—A, Ovum, consisting of enveloping membrane a
and yolk b ; b, c, d, e, f, successive stages of segmentation of yolk; g, first marking-out or tne
shape of the embryo ; h, embryo on the 8th day; i, the same on the 9th day; k, the same on tne
12th day, seen on the leftside at l; m, still more advanced embryo, seen at n as retracted within
its shell:— a, superficial layer of yolk-segments coalescing to give origin to the shell; c, c, ciliated
lobes; <2, foot; g, hard plate or operculum attached to it; h, stomach; *, intestine; m, n, masses
(glandular ?) at the sides of the oesophagus; o, heart (?); s, retractor muscle (:); t, situation or
funnel; v, membrane enveloping the body; x, auditory vesicles; y, mouth.

of the nidamentum and of the egg-membranes themselves. The first
change which will be noticed by the ordinary observer, is the 6 segmenta-
tion ' of the yolk-mass, which divides itself (after the manner of a cell
undergoing binary subdivision) into two parts, each of these two into

186

THE MICROSCOPE AND ITS REVELATIONS.

two others, and so on until a morula or mulberry-like mass of minute
yolk-segments is produced (Fig. 403, a-f), which is converted by 6 in-
vagination 9 into a 'gastrula' (§ 391), whose form is shown at g. This
'gastrula' soon begins to exhibit a very curious alternating rotation
within the egg, two or three turns being made in one direction, and the
same number in a reverse direction : this movement is due to the cilia
fringing a sort of fold of the ectoderm termed the velum, which after-
wards usually gives origin to a pair of large ciliated lobes (h-l, c) resem-
bling those of Rotifers. The velum is so little developed in Limnceus,
however, that its existence has been commonly overlooked until recog-
nized by Prof. Ray Lankester,1 who also has been able to distinguish its
fringe of minute cilia. This, however, has only a transitory existence; and
the later rotation of the embryo, which presents a very curious spectacle
when a number of ova are viewed at once under a low magnifying power,
is due to the action of the cilia fringing the head and foot.

582. A separation is usually seen at an early period, between the
anterior or 6 cephalic' portion, and the posterior or 'visceral' portion, of
the embryonic mass; and the development of the former advances with
the greater activity. One of the first changes which is seen in it, con-
sists in its extension into a sort of fin-like membrane on either side, the
edges of which are fringed with long cilia (Pig. 403, h-l, c), whose move-
ments may be clearly distinguished whilst the embryo is still shut-up
within the egg; at a very early period may also be discerned the 6 auditory
vesicles' (k, x) or rudimentary organs of hearing (§ 587), which scarcely
attain any higher development in these cxeatures during the whole of
life; and from the immediate neighborhood of these is put-forth a pro-
jection, which is afterwards to be evolved into the ' foot 'or muscular
disk of the animal. While these organs are making their appearance,
the shell is being formed on the surface of the posterior portion, appear-
ing first as a thin covering over its hinder part, and gradually extending
itself until it becomes large enough to inclose the embryo completely,
when this contracts itself. The ciliated lobes are best seen in the embryoes
of Nudibranclis; and the fact of the universal presence of a shell in the
embryoes of that group is of peculiar interest, as it is destined to be cast-
ofi2 very soon after they enter upon active life. These embryoes may be
seen to move-about as freely as the narrowness of their prison permits,
for some time previous to their emersion; and when set free by the rup-
ture of the egg-cases, they swim forth with great activity by the action
of their ciliated lobes, — these, like the ' wheels' of Rotifera, serving also
to bring food to the mouth, which is at that time unprovided with the
reducing apparatus subsequently found in it. The same is true of the
embryo of Lymnwus, save that its swimming movements are less active,
in consequence of the non -development of the ciliated lobes; and the
currents produced by the cilia that fringe the head and the orifice of the
respiratory sac, seem to have reference chiefly to the provision of sup-
plies of food, and of aerated water for respiration. The disappearance
of the cilia has been observed by Mr. Hogg to be coincident with the
development of the teeth to a degree sufficient to enable the young water-
snail to crop its vegetable food; and he has further ascertained that if the
growing animal be kept in fresh water alone for some time, without vege-

1 See his valuable * Observations on the Development of Limnceus stagnalus,
and on the other stages of other Mollusca,' in " Quart. Journ. Microsc. Science,"
Oct. 1874. See also Lereboullet, ' Recherches sur le Developpement du Limnee,'
in " Ann. des Sci. Nat. Zool.," 4ieme Ser., Tom. xviii., p. 47.

MOLLUSCOUS ANIMALS GENERALLY.

187

table matter of any kind, the gastric teeth are very imperfectly developed
and the cilia are still retained.1 1 9

583. A very curious modification of the ordinary plan of development
is presented in the Purpura lapillus; and it is probable that something
of the same kind exists also in Buccinum, as well as in other Gasteropoda
of the same extensive Order (Pectmibranchiata).—Eixch of the capsules
already described (§ 581) contains from 500 to 600 egg-like bodies (Fig.
404, a), imbedded in a viscid gelatinous substance; but only from 12 to
30 embroyes usually attain complete development; and it is obvious from
the large comparative size which these attain (Fig. 405, b), that each of
them must include an amount of substance equal to that of a great num-
ber of the bodies originally found within the capsule. The explanation
of this fact (long since noticed by Dr. J. E. Gray, in regard to Buccinum)
seems to be as follows:— Of those 500 or 600 egg-like bodies, only a small
part are fertile ova, the remainder being unfertilized eggs, the yolk-

Fig. 404. Fig. 405.

of Purpura lapillus:— A.egg-like spherule; Later stages of embryonic Development of Pur-

b, c, e, f, g, successive stages of segmenta- pura lapillus: — a, conglomerate mass of vitelline

tion of yolk-spherules; d, h, i, j, k, succes- segments, to which were attached the embryoes, a,

sive stages of development of early em- b, c, d, e:-B, full-size embryo, in more advanced

bryoes. stage of development.

material of which serves for the nutrition of the embryoes in the later
stages of their intra-capsular life. The distinction between them mani-
fests itself at a very early period, even in the first segmentation; for
while the latter divide into two equal hemispheres (Fig. 404, n), the
fertilized ova divide into a larger and a smaller segment (d); in the cleft
between these are seen the minute 4 directive vesicles/ which appear to be
always double or even triple, although from being seen ' end on/ only one
may be visible; and near these is generally to be seen a clear space in each
segment. The difference is still more strongly marked in the subsequent
divisions; for whilst the cleavage of the infertile eggs goes-on irregularly,
so as to divide each into from 14 to 20 segments, having no definiteness
of arrangement (c, E, p, g), that of the fertile ova takes place in such a
manner as to mark-out the distinction already alluded-to between the

!See " Transact, of Microsc. Soc," 2d Ser., Vol. ii. (1854), p. 93.

188

THE MICROSCOPE AND ITS REVELATIONS.

6 cephalic' and the ' visceral ' portions of the mass (h); and the evolution
of the former into distinct organs very speedily commences. In the first
instance, a narrow transparent border is seen around the whole embryonic
mass, which is broader at the cephalic portion (i); next, this border is
fringed with short cilia, and the cephalic extension into two lobes begins
to show itself; and then between the lobes a large mouth is formed, open-
ing through a short, wide oesophagus, the interior of which is ciliated,
into the visceral cavity, occupied as yet only by the yolk-particles origi-
nally belongiug to the ovum (k).

584. Whilst these developmental changes are taking place in the em-
bryo, the whole aggregate of segments formed by the yolk-cleavage of
the infertile eggs coalesces into one mass, as shown at A, Fig. 405; and
the embryoes are often, in the first instance, so completely buried within
this, as only to be discoverable by tearing its portions asunder: but some
of them may commonly be found upon its exterior; and those contained
in one capsule very commonly exhibit the different stages of development
represented in Fig. 404, h-k. After a short time, however, it becomes
apparent that the most advanced embryoes are beginning to swalloiv the
yolk-segments of the conglomerate mass; and capsules will not unfre-
quently be met- with, in which embryoes of various sizes, as a, b, c, d, e
(Fig. 405, a), are projecting from its surface, their difference of size not
being accompanied by advance in development, but merely depending
upon the amount of this 6 supplemental 9 yolk which the embryoes have
respectively gulped- down. For during the time in which they are engaged
in appropriating this additional supply of nutriment, although they in-
crease in size, yet they scarcely exhibit any other change; so that the large
embryo, Fig. 405, e, is not apparently more advanced as regards the for-
mation of its organs, than the small embryo, Fig. 404, K. So soon as
this operation has been completed, however, and the embryo has attained
its full bulk, the evolution of its organs takes-place very rapidly; the cili-
ated lobes are much more highly developed, being extended in a long
sinuous margin, so as almost to remind the observer of the ' wheels' of
Eotifera (§ 445), and being furnished with very long cilia (Fig. 405, b);
the auditory vesicles, the tentacula, the eyes, and the foot, successively
make their appearance; a curious rhythmically-contractile vesicle is seen,
just beneath the edge of the shell in the region of the neck, which may,
perhaps, serve as a temporary heart; a little later, the real heart may be
seen pulsating beneath the dorsal part of the shell; and the mass of yolk-
segments of which the body is made-up, gradually shapes itself into the
various organs of digestion, respiration, etc., during the evolution of
which (and while they are as yet far from complete) the capsule thins-
away at its summit, and the embryoes make their escape from it.1

585. It happens not unfrequently that one of the embryoes which a
capsule contains does not acquire its 6 supplemental ' yolk in the manner
now described, and can only proceed in its development as far as its ori-
ginal yolk will afford it material; and thus, at the time when the other
embryoes have attained their full size and maturity, a strange-looking

1 The Author thinks it worth while to mention the method which he has found
most convenient for examining the contents of the egg-capsules of Purpura; as
he believes that it may be advantageously adopted in many other cases. This
consists in cutting off the two ends of the capsule (taking care not to cut far
into its cavity), and in then forcing a jet of water through it, by inserting the end
of a fine-pointed syringe (§127) into one of the orifices thus made, so as to drive
the contents of the capsule before it through the other. These should be received
into a shallow cell, and first examined under the Simple Microscope.

MOLLUSCOUS ANIMALS GENERALLY.

189

creature, consisting of two large ciliated lobes with scarcely the rudiment
of a body, may be seen in active motion among them. This may happen,
indeed, not only to one but to several embryoes within the same capsule,'
especially if their number should be considerable; for it sometimes appears
as if there were not food enough for all, so that whilst some attain their
full dimensions and complete development, others remain of unusually
small size, without being deficient in any of their organs, and others
again are more or less completely abortive, — the supply of supplemental
yolk which they have obtained having been too small for the develop-
ment of their viscera, although it may have afforded what was needed for
that of the ciliated lobes, eyes, tentacles, auditory vesicles, and even the
foot, — or, on the other hand, no additional supply whatever having been
acquired by them, so that their development has been arrested at a still
earlier stage. — These phenomena are of so remarkable a character, that
they furnish an abundant source of interest to any Microscopist who may
happen to be spending the months of August and Septembor in a locality
in which the Purpura abounds; since, by opening a sufficient number of
capsules, no difficulty need be experienced in arriving at all the facts which
have been noticed in this brief summary.1 It is much to be desired that
such Microscopists as possess the requisite opportunity, would apply
themselves to the study of the corresponding history in other Pectini-
branchiate Gasteropods, with a view of determining how far the plan now
described prevails through the Order. And now that these Mollusks
have been brought not only to live, but to breed, in artificial aquaria, i t
may be anticipated that a great addition to our knowledge of this part of
their life-history will ere long be made.

586. Ciliary Motions on Gills. — There is no object that is better
suited to exhibit the general phenomena of Ciliary motion (§ 435), than
a portion of the gill of some bivalve Mollusk. The Oyster will answer
the purpose sufficiently well; but the cilia are much larger on the gills of
the Mussel,2 as they are also on those of the Anodon or common ' fresh-
water mussel' of our ponds and streams. Nothing more is necessary than
to detach a small portion of one of the riband-like bands, which will be
seen running parallel with the edge of each of the valves when the shell
is opened; and to place this, with a little of the liquor contained within
the shell, upon a slip of glass, — taking care to spread it out sufficiently
with needles to separate the bars of which it is composed, since it is on
the edges of these, and round their knobbed extremities, that the ciliary
movement presents itself, — and then covering it with a thin-glass disk.
Or it will be convenient to place the object in the Aquatic-box (§ 122),
which will enable the observer to subject it to any degree of pressure that

1 Fuller details on this subject will be found in the Author's account of his
researches, in 4 4 Transactions of the Microscopical Society," 2d Ser., Vol. iii.
(1855), p. 17. His account of the process was called in question by MM. Koren
and Danielssen, who had previously given an entirely different version of it, but
was fully confirmed by the observations of Dr. Dyster; see "Ann. of Nat.
Hist." 2d Ser., Vol. xx. (1857), p. 16. The independent observations of M. Clapa-
rede on the development of Neritina fluviatilis (Muller's ' ' Archiv," 1857, p. 109,
and abstract in " Ann. of Nat. Hist.," 2d Ser., Vol. xx. (1857), p. 196, showed the
mode of development in that species to be the same in all essential particulars as
that of Purpura. The subject has again been recently studied with #reat minute-
ness by Selenka, " Niederlandisches Archiv fur Zoologie," Bd. i., July, 1862

2 This Shell-fish may be obtained, not merely at the sea-side, but likewise at
the shops of the fishmongers who supply the humbler classes, even in midland
towns.

190

THE MICROSCOPE AND ITS REVELATIONS.

he may find convenient. A magnifying power of about 120 diameters is
amply sufficient to afford a general view of this spectacle; but a much
greater amplification is needed to bring into view the peculiar mode in
which the stroke of each cilium is made. Few spectacles are more
striking to the unprepared mind, than the exhibition of such wonderful
activity as will then become apparent, in a body which to all ordinary ob-
servation is so inert. This activity serves a double purpose; for it not only
drives a continual current of water over the surface of the gills them-
selves, so as to effect the aeration of the blood, but also directs a portion
of this current (as in the Tunicata, § 555) to the mouth, so as to supply
the digestive apparatus with the aliment afforded by the Diatomacece,
Infusoria, etc., which it carries-in with it.

" 587. Organs of Sense of Mollusks, — Some of the minuter and more
rudimentary forms of the special organs of sight, hearing, and touch,
which the Molluscous series presents, are very interesting objects of Mi-
croscopic examination. Thus, just within the margin of each valve of
Pecten, we see (when we observe the animal in its living state, under
water) a row of minute circular points of great brilliancy, each surrounded
by a dark ring; these are the eyes, with which this creature is provided,
and by which its peculiarly-active movements are directed. Each of them,
when their structure is carefully examined, is found to be protected by a
sclerotic coat with a transparent cornea in front; and to possess a colored
iris (having a pupil) that is continuous with a layer of pigment lining the
sclerotic, a crystalline lens and vitreous body, and a retinal expansion pro-
ceeding from an optic nerve which passes to each eye from the trunk that
runs along the margin of the mantle.1 — Eyes of still higher organization
are borne upon the head of most Gasteropod Mollusks, generally at the
base of one of the pairs of tentacles, but sometimes, as in the Snail and
slug, at the points of these organs. In the latter case, the tentacles are
furnished with a very peculiar provision for the protection of the eyes;
for when the extremity of either of them is touched, it is drawn-back into
the basal part of the organ, much as the finger of a glove may be pushed-
back into the palm. The retraction of the tentacle is accomplished by a
strong muscular band, which arises within the head, and proceeds to the
extremity of the tentacles; whilst its protrusion is effected by the agency
of the circular bands with which the tubular wall of the tentacle is itself
furnished, the inverted portion being (as it were) squeezed-out by the
contraction of the lower part in which it has been drawn back. The
structure of the eyes, and the curious provision just described, may easily
be examined by snipping-off one of the eye-bearing tentacles with a pair
of scissors. — None but the Cephalopod Mollusks have distinct organs of
hearing; but rudiments of such organs may be found in most Gasteropods
(Fig. 403, K, x), attached to some part of the nervous collar that sur-
rounds the oesophagus; and even in many Bivalves, in connection with
the nervous ganglion imbedded in the base of the foot. These 6 auditory
vesicles,' as they are termed, are minute sacculi, each of which contains
a, fluid, wherein are suspended a number of minute calcareous particles
(named otoliths or ear-stones), which are kept in a state of continual
movement by the action of cilia lining the vesicles. This " wonderful spec-
tacle," as it was truly designated by its discoverer Siebold, may be brought
into view without any dissection, by submitting the head of any small

1 See Mr. S. J. Hickson on 'The Eye of Pecten,' in " Quart. Journ. Microsc.
.Sci.," Vol. xx., N.S. (1880), p. 443.

MOLLUSCOUS ANIMALS GENERALLY.

191

and not very thick-skinned Gasteropod, or the young of the larger forms,
to gentle compression under the Microscope, and transmitting a strong
light through it. The very early appearance of the auditory vesicles in
the embryo Gasteropod has been already alluded-to (§ 582).— Those who
have the opportunity of examining young specimens of the common
Pecten, will find it extremely interesting to watch the action of the very
delicate tentacles which they have the power of putting-forth from the
margin of their mantle, the animal being confined in a shallow cell, or in
the zoophyte-trough; and if the observer should be fortunate enough to
obtain a specimen so young that the valves are quite transparent, he will
find the spectacle presented by the ciliary movement of the gills, as well
as the active play of the foot (of which the adult can make no such use),
to be worthy of more than a cursory glance.

588. Chromatophores of Cephcdopods. — Almost any species of Cuttle-
fish (Sepia) or Squid (Loligo) will afford the opportunity of examining
the very curious provision which their skin contains for changing its hue.
This consists in the presence of numerous large c pigment-cells/ contain-
ing coloring-matter of various tints; the prevailing color, however, being
that of the fluid of the ink-bag. These pigment-cells may present very
different forms, being sometimes nearly globular, whilst at other times
they are flattened and extended into radiating prolongations; and, by the
peculiar contractility with which they are endowed, tiiey can pass from
one to the other of these conditions, so as to spread their colored con-
tents over a comparatively-large surface, or to limit them within a com-
paratively small area. Very commonly there are different layers of these
pigment-cells, their contents having different hues in each layer and thus
a great variety of coloration may be given, by the alteration in the form
of the cells of which one or another layer is made-up. It is curious
that the changes in the hue of the skin appear to be influenced, as in
the case of the Chameleon, by the color of the surface with which it
may be in proximity. The alternate contractions and extensions of
these pigment-cells or cliromatopliores may be easily observed in a piece
of skin detached from the living animal and viewed as a transparent ob-
ject; since they will continue for some time, if the skin be placed in sea-
water. And they may also be well seen in the embryo cuttle-fish, which
will sometimes be found in a state of sufficient advancement in the grape-
like eggs of these animals attached to Sea- weeds, Zoophytes, etc. — The
eggs of the small cuttle-fish termed the Sepiola, which is very common
on our southern coasts, are imbedded, like those of the Doris, in gelati-
nous masses, which are attached to Sea weeds, Zoophytes, etc.; and their
embryoes, when near maturity, are extremely beautiful and interesting
objects, being sufficiently transparent to allow the action of the heart to
be distinguished, as well as to show most advantageously the changes
incessantly occurring in the form and hue of the 'chromatophores.'

192

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XVII.
ANNULOSA, OR WORMS.

589. Under the general designation of i Annulose ' animals, or Worms,
may be grouped-together all that lower portion of the great Articulated
Sub-kingdom, in which the division of the body into longitudinally-
arranged segments is not'distinctly marked-out, and there is an absence of
those ' articulated 9 or jointed limbs that constitute so distinct a feature
of Insects and their allies. This group includes the classes of Entozoa
or Intestinal Worms, Rotifer a or wheel-animalcules, Turbellaria, and
Annelida; each of which furnishes many objects for Microscopic exami-
nation, that are of the highest scientific interest. As our business, how-
ever, is less with the professed Physiologist, than with the general inquirer
into the minute wonders and beauties of Nature, we shall pass over these
classes (the Rotifera having been already treated-of in detail, Chap, xi.)
with only a notice of such points as are likely to be specially deserving
the attention of observers of the latter order.

590. Entozoa. — This class consists almost entirely of animals of a
very peculiar plan of organization, which are parasitic within the bodies
of other animals, and which obtain their nutriment by the absorption of
the juices of these, — thus bearing a striking analogy to the parasitic Fungi
(§§ 312-316). The most remarkable feature in their structure consists in
the entire absence or the extremely low development of their nutritive sys-
tem, and the extraordinary development of their reproductive apparatus.
Thus, in the common Tce?iia (' tape-worm '), which may be taken as the
type of the Cestoid group, there is neither mouth nor stomach, the
so-called 'head' being merely an organ for attachment, whilst the seg-
ments of the 'body* contain repetitions of a complex generative appa-
ratus, the male and female sexual organs being so united in each as to en-
able it to fertilize and bring to maturity its own very numerous eggs;
and the chief connection between these segments is established by two
pairs of longitudinal canals, which, though regarded by some as represent-
ing a digestive apparatus, and by others as a circulating system, appear
really to represent the ' water- vascular system/ whose simplest condi-
tion has been noticed in the wheel-animalcule (§ 449). — Few among the
recent results of Microscopic inquiry have been more curious, than the
elucidation of the real nature of the bodies formerly denominated Cystic
Entozoa, which had been previously ranked as a distinct group. These
are not found, like the preceding, in the cavity of the alimentary canal
of the animals they infest; but always occur in the substance of solid
organs, such as the glands, muscles, etc. They present themselves to the
eye as bags or vesicles of various sizes, sometimes occurring singly, some-

ANNULOSA, OR WORMS.

193

times in groups; but upon careful examination each vesicle is found to
bear upon some part a 'head' furnished with hooklets and suckers; and
this may be either single, as in Gysticercus (the entozoon whose presence
gives to pork what is known as the ' measly ' disorder), or multiple, as in
CcBnuruSy which is developed in the brain, chiefly of sheep, giving rise
to the disorder known as ' the staggers.' Now in none of these Cystic
forms has any generative apparatus ever been discovered, and hence they
are obviously to be considered as imperfect animals. The close resem-
blance between the 'heads' of certain Cysticerci and that of certain Tcenice
first suggested that the two might be different states of the same animal;
and experiments made by those who have devoted themselves to the work-
ing-out of this curious subject have led to the assured conclusion, that
the Cystic Entozoa are nothing else than Cestoid Worms, whose develop-
ment has been modified by the peculiarity of their position, — the large
bag being formed by a sort of dropsical accumulation of fluid when the
young are evolved in the midst of solid tissues, whilst the very same
bodies, conveyed into the alimentary canal of some carnivorous animal
which has fed upon the flesh infested with them, begin to bud-forth
the generative segments, the long succession of which, united end-to-end,
gives to the entire series a Worm-like aspect.

591. The higher forms of Entozoa, belonging to the Nematoid or
thread-like Order, — of which the common Ascaris may be taken as a
type, one species of it (the A. Iwnbricoides, or ' round worm') being a
common parasite in the small intestine of man, while another (the A. ver-
micularis, or thread-worm ') is found rather in the lower bowel, — approach
more closely to the ordinary type of conformation of Worms; having a
distinct alimentary canal, which commences with a mouth at the anterior
extremity of the body, and which terminates by an anal orifice near the
other extremity; and also possessing a regular arrangement of circular
and longitudinal muscular fibres, by which the body can be shortened,
elongated, or bent in any direction. The smaller species of Ascaris, by
some or other of which almost every Vertebrated animal is infested, are
so transparent that every part of their internal organization may be made-
out, especially with the assistance of the Compressor (§ 125) without any
dissection; and the study of the structure and actions of their Generative
apparatus has yielded many very interesting results, especially in regard
to the first formation of the ova, the mode of their fertilization, and
the history of their subsequent development. — Some of the Worms belong-
ing to this group are not parasitic in the bodies of other animals, but live
in the midst of dead or decomposing Vegetable matter. The Gordius or
' hair worm/ which is peculiar in not having any perceptible anal orifice,
seems to be properly a parasite in the intestines of water-insects; but it
is frequently found in large knot-like masses (whence its name) in the
water or mud of the pools inhabited by such insects, and may apparently
be developed in these situations. The AnguillulcB are little eel-like worms
of which one species, A. fluviatilis, is very often found in fresh water
amongst Desmidiem, Confervce, etc., also in wet moss and moist earth, and
sometimes also in the alimentary canals of snails, frogs, fishes, insects,
and larger worms; whilst another species, A. tritici, is met-with in the
ears of Wheat affected with the blight termed the ' cockle;' another, the
A. glutinis, is found in sour paste; and another, the A. aceti, was often
found in stale vinegar, until the more complete removal of mucilage and
the addition of sulphuric acid, in the course of the manufacture, ren-
dered this liquid a less favorable ' habitat 9 for these little creatures. A
13

194:

THE MICROSCOPE AND ITS REVELATIONS.

writhing mass of any of these species of i eels/ is one of the most curious
spectacles which the Microscopist can exhibit to the unscientific observer;
and the capability which they all possess (in common with Rotifers and
Tardigrades, § 452), of revival after desiccation, at however remote an
interval, enables him to command the spectacle at any time. A grain of
wheat within which these worms (often erroneously called Vibriones)
are being developed, gradually assumes the appearance of a black pepper-
corn; and if it be divided in two, the interior will be found almost
complete filled with a dense white cottony mass, occupying the place of
the flour, and leaving merely a small place for a little glutinous matter.
The cottony substance seems to the eye to consist of bundles of fine fibres
closely packed-together; but on taking-out a small portion, and putting
it under the Microscpe with a little water under a thin glass-cover, it will
be found after a short time (if not immediately) to be a wriggling mass
of life, the apparent fibres being really Anguillulce, or 6 eels ' of the Micro-
scopist. If the seeds be soaked in water for a couple of hours before they
are laid open, the eels will be found in a state of activity from the first;
their movements, however, are by no means so energetic as those of the
A. glutinis or * paste-eel/ This last frequently makes its appearance
spontaneously in the midst of paste that is turning sour; but the best
means of securing a supply for any occasion, consists in allowing a portion
of any mass of paste in which they may present themselves to dry up,
and then, laying this by so long as it may not be wanted, to introduce
it into a mass of fresh paste, which if it be kept warm and moist, will be
found after a few days to swarm with these curious little creatures.

592. Besides the foregoing Orders of Entozoa, the Trematode group
must be named; of which the Distoma hepaticum or € fluke/ found in
the livers of Sheep affected with the 'rot,' is atypical example. Into
the details of the structure of this animal, which has the general form
of a sole, there is no occasion for us here to enter; it is remarkable, how-
ever, for the branching form of its digestive cavity, which extends
throughout almost the entire body, very much as in Planarige (Fig. 406);
and also for the curious phenomena of its development, several distinct
forms being passed through between one sexual generation and another.
These have been especially studied in the Distoma, which infests the
Lymnmus; the ova of which are not developed into the likeness of their
parents, but into minute worm-like bodies, which seem to be little else
than masses of cells inclosed in a contractile integument, no formed
organs being found in them; these cells, in their turn, are developed into
independent zooids, which escape from their containing cyst in the con-
dition of free ciliated Animalcules; in this condition they remain for
some time, and then imbed themselves in the mucus that covers the tail
of the Mollusk, in which they undergo a gradual development into true
Distomata; and having thus acquired their perfect form, they penetrate
the soft integument, and take-up their habitation in the interior of
the body. Thus a considerable number of Distomata may be produced
from a single ovum, by a process of cell -multiplication in an early stage of
its development. In some instances the free ciliated larva possesses dis-
tinct eyes; although these organ are wanting in the fully developed Dis-
toma, the peculiar * habitat ' of which would render them useless.

593. Turbellaria. — This group of animals, which is distinguished
by the presence of cilia over the entire surface of the body, seems inter-
mediate in some respects between the ' trematode ' Entozoa and the Leech-
tribe among Annelida. It deserves special notice here, chiefly on account

ANNULOSA, OR WORMS.

195

of the frequency with which the worms of the Planarian tribe present
themselves among collections both of marine and of fresh-water animals
(particular species inhabiting either locality), and on account of the curi-
ous organization which many of these possess. Most of the members of
this tribe have elongated flattened bodies, and move by a sort of gliding
or crawling action over the surfaces of aquatic Plants and Animals. Some
of the smaller kind are sufficiently transparent to allow of their internal
structure being seen by transmitted light, especially when they are slightly
compressed; and the accompanying figure
(Fig. 406) displays the general conforma- FlG- 406-

tion of their principal organs, as thus
shown. The body has the flattened sole-
like shape of the Trematode Entozoa; its
mouth, which which is situated at a consi-
derable distance from the anterior ex-
tremity of the body, is surrounded by a
circular sucker that is applied to the living
surface from which the animal draws its
nutriment; and the buccal cavity (b) opens
into a short oesophagus (c), which leads at
once to the cavity of the stomach. In the
true Planarice the mouth is furnished with
a sort of long funnel-shaped proboscis; and
this, even when detached from the body,
continues to swallow anything presented
to it. The cavity of the stomach does not
give origin to any intestinal tube, nor is it
provided with any second orifice; but a
large number of ramifying canals are pro-
longed from it, which carry its contents
into every part of the body. This seems
to render unnecessary any system of vessels
for the circulation of nutritive fluid; and
the two principal trunks, with connecting
and ramifying branches, which may be
observed in them, are probably to be re-
garded in the light of a water-vascular
system, the function of which is essentially
respiratory. Both sets of sexual organs
are combined in the same individuals;
though the congress of two, each impreg-
nating the ova of the other, seems to be
generally necessary. The ovaria, as in the
Entozoa, extend through a large part of
the body, their ramifications proceed-
ing from the two oviducts {k, Tc)y which have a dilatation (I) at their
point of junction. — There is still much obscurity about the history of
the embryonic development of these animals; as the accounts given
of it by different observers by no means harmonize with each other.1 —
The Planariae, however, do not multiply by eggs alone; for they occa-
sionally undergo spontaneous fission in a transverse direction, each seg-
ment becoming a perfect animal; and an artificial division into two or even

Structure of Polycelis levigatus (a
Planarian worm).— a, Mouth surround-
ed by its circular sucker; &, buccal
cavity; c, oesophageal orifice; d, stom-
ach; e, ramifications of gastric canals;
/, cephalic ganglia and their nervous
filaments; g, g, testes; h, vesicula semi-
nalis; i, male genital canal; fc, fc, ovi-
ducts; Z, dilatation at their point of
junction ; m, female genital orifice.

1 See Balfour's "Comparative Embryology," Vol. i., pp. 159-162.

196

THE MICROSCOPE AND ITS REVELATIONS.

more parts may be practised with a like result. In fact, the power of
the Planariae to reproduce portions which have been removed, seems but
little inferior to that of the Hydra (§ 515); a circumstance which is pecu-
liarly remarkable, when the much higher character of their organization
is borne in mind. They possess a distinct pair of nervous ganglia (f, f),
from which branches proceed to various parts of the body; and in the
neighborhood of these are usually to be observed a number (varying from
2 to 40) of ocelli or rudimentary eyes, each having its refracting body or
crystalline lens, its pigment-layer, its nerve bulb, and its cornea-like bulg-
ing of the skin. The integument of many of these animals is furnished
with 6 thread-cells ' or 'filiferous capsules,' very much resembling those
of Zoophytes (§ 528).

594. Annelids. — This Class includes all the higher kinds of Worm-
like animals, the greater part of which are marine, though there are
several species which inhabit fresh water, and some which live on land.
The body in this class is usually very long, and nearly always presents a
well-marked segmental division, the segments being for the most part
similar and equal to each other, except at the two extremities; but in
the lower forms, such as the Leech and its allies, the segmental division
is very indistinctly seen, on account of the general softness of the integu-
ment. A large proportion of the marine Annelids have special respiratory
appendages, into which the fluids of the body are sent for aeration; and
these are situated upon the head (Fig, 407), in those species which (like
the Serpula, Terebella, Sabellaria, etc. ) have their bodies inclosed by tubes,
either formed of a shelly substance produced from their own surface, or
built up by the agglutination of grains of sand, fragments of shell, etc.;
whilst they are distributed along the two sides of the body in such as
swim freely through the water, or crawl over the surfaces of rocks, as is
the case with the Nereidce, or simply bury themselves in the sand, as the
Arenicola or nob-worm.' In these respiratory appendages the circula-
tion of the fluids may be distinctly seen by Microscopic examination;
and these fluids are of two kinds, — first, a colorless fluid, containing
numerous cell-like corpuscles, which can be seen in the smaller and more
transparent species to occupy the space that intervenes between the outer
surface of the alimentary canal and the inner wall of the body, and to
pass from this into canals which often ramify extensively in the respira-
tory organs, but are never furnished with a returning series of passages,
— and second, a fluid which is usually red, contains few floating parti-
cles, and is inclosed in a system of proper vessels that communicates
with a central propelling organ, and not only carries away the fluid away
from this, but also brings it back again. In Terebella we find a distinct
provision for the aeration of both fluids; for the first is transmitted to
the tendril-like tentacles which surround the mouth (Fig. 407, b, b),
whilst the second circulates through the beautiful aborescent gill-tufts
(k, k), situated just behind the head. The former are covered with
cilia, the action of which continually renews the stratum of water in
contact with them, whilst the latter are destitute of these organs; and
this seems to be the general fact as to the several appendages to which
these two fluids are respectively sent for aeration, the nature of their
distribution varying greatly in the different members of the class. The
red fluid is commonly considered as blood, and the tubes through which
it circulates as blood-vessels; but the Author has elsewhere given his
reasons1 for coinciding in the opinion of Prof. Huxley, that the colorless

1 See his " Principles of Comparative Physiology," 4th Edit., 218, 219, 292.

ANNULOSA, OR WORMS.

197

Fig. 407.

corpusculated fluid which moves in the peri-visceral cavity of the body
and in its extensions, is that which really represents the blood of other
Articulated animals; and that the system of vessels carrying the red fluid
is to be likened on the one hand to the 6 water- vascular system ■ of the
inferior Worms, and on the other to the tracheal apparatus of Insects
(§ 634). — In the observation of the beauti-
ful spectacle presented by the respiratory
circulation of the various kinds of Anne-
lids which swarm on most of our shores,
and in the examination of what is going
on in the interior of their bodies (where
this is rendered possible by their trans-
parence), the Microscopist will find a most
fertile source of interesting occupation;
and he may easily, with care and patience,
make many valuable additions to our pre-
sent stock of knowledge on these points.
There are many of these marine Annelids,
in which the appendages of various kinds
put forth from the sides of their bodies fur-
nish very beautiful microscopic objects; as
do also the different forms of teeth, jaws,
etc., with which the mouth is commonly
armed in the free or non-tubicolar species,
these being eminently carnivorous.

595. The early history of the Develop-
ment of Annelids, too, is extremely curi-
ous; for they come forth from the egg in a
condition very little more advanced than
the ciliated gemmules of Polypes, consist-
ing of a globular mass of untransformed
cells, certain parts of whose surface are
covered with cilia; in a few hours, how-
ever, this embryonic mass elongates, and
the indications of a segmental division be-
come apparent, the head being (as it were)
marked off in front, whilst behind this is
a large segment thickly covered with cilia,
then a narrower and non-ciliated segment,
and lastly the caudal or tail-segment, which
is furnished with cilia. A little later, a
new segment is seen to be interposed in
front of the caudal; and the dark internal
granular mass shapes itself into the out-
line of an alimentary canal. 1 The number
of segments progressively increases by the
interposition of new ones between the caudal
and its preceding segments; the various-internal organs become more and
more distinct, eye-spots make their appearance, little bristly appendages are

Circulating Apparatus of Terebella
conchilega:—a^ labial ring; b, b, ten-
tacles; c, first segment of the trunk;
d, skin of the back; e, pharynx; /,
intestine; g, longitudinal muscles of
the inferior surface of the body; hy
glandular organ (liver ?) ; i, organs of
generation; j, feet; fc, fc, branchiae;
i, dorsal vessel acting as a respira-
tory heart; m, dorso-intestinal vessel;
n, venous sinus surrounding oesopha-
gus; n', inferior intestinal vessel; o,
o, ventral trunk; p, lateral vascular
branches.

1 A most curious transformation once occurred within the Author's experience
in the larva of an Annelid, which was furnished with a broad collar or disk
fringed with very long cilia, and showed merely an appearance of segmentation
in its hinder part; for in the course of a few minutes, during which it was not
under observation, this larva assumed the ordinary form of a marine Worm three

198

THE MICROSCOPE AND ITS REVELATIONS.

put forth from the segments, and the animal gradually assumes the like-
ness of its parent; a few days being passed by the tubicolar kinds, how-
ever, in the actively moving condition, before they settle down to the
formation of a tube.1

596. To carry out any systematic observations on the embryonic
development of Annelids, the eggs should be searched for in the situa-
tions which these animals haunt; but in places where Annelids abound,
free-swimming larvae are often to be obtained at the same time and in the
same manner as small Medusae (§ 522); and there is probably no part of
our coasts, off which some very curious forms may not be met with.
The following may be specially mentioned as departing widely from the
ordinary type, and as in themselves extremely beautiful objects. — The
Actinotrocha (Fig. 408) bears a strong resemblance in many particulars
to the * bipinnarian * larva of a Star-fish (§ 543), having an elongated
body, with a series of ciliated tentacles (d) symmetrically arranged;
these tentacles, however, proceed from a sort of disk which somewhat
resembles the ' lophophore' of certain Polyzoa (§ 549). The mouth (e)
is concealed by a broad but pointed hood or 6 epistome ' (a), which some-
times close down upon the tentacular disk, but is sometimes raised and
extended forwards. The nearly cylindrical body terminates abruptly at
the other extremity, where the anal orifice of the intestine (i) is sur-
rounded by a circlet of very large cilia. This animal swims with great
activity, sometimes by the tentacular cilia, sometimes by the anal circlet,
sometimes by both combined; and besides its movement of progression,
it frequently doubles itself together, so as to bring the anal extremity
and the epistome almost in contact. It is so transparent that the whole
of its alimentary canal may be as distinctly seen as that of Laguncula
(§ 549); and, as in that Polyzoon, the alimentary masses often to be seen
within the stomach (c) are kept in a continual whirling movement by
the agency of cilia with which its walls are clothed. This very interest-
ing creature was for a longtime a puzzle to Zoologists; since, although
there could be little doubt of its being a larval form, there was no clue
to the nature of the adult produced from it, until this was discovered by
Krohn in 1858 to be a Gephyrean Worm.2 An even more extraordinary
departure from the ordinary type is presented by the larva which has
received the name Pilidium (Fig. 409) ; its shape being that of a helmet,
the plume of which is replaced by a single long bristle-like appendage
that is in continual motion, its point moving round and round in a
circle. This curious organism, first noticed by Muller, has been since
ascertained to be the larva of the well-known JVemertes, a Turbellarian

or four times its previous length, and the ciliated disk entirely disappeared. An
accident unfortunately prevented the more minute examination of this Worm,
which the Author would have otherwise made; but he may state that he is cer-
tain that there was no fallacy as to the fact above stated; this larva having been
placed by itself in a cell, on purpose that it might be carefully studied, and having
been only laid aside for a short time whilst other selections were being made
from the same gathering of the Tow-net.

1 For further information on this subject, see Balfour's " Comparative Embry-
ology," Chap, xii., and the Memoirs there cited.

2 4 Ueber Pilidium und Actinotrocha7 in " Miiller's Archiv," 1858, p. 293. —
For more recent observations upon this interesting creature, see Balfour's " Com-
parative Embryology," Vol. i., pp. 299-302, and a paper on 6 The Origin and Sig-
nificance of the Metamorphosis of Actinotrocha,' by Mr. E. B. Wilson (of
Baltimore), in " Quart, Journ. Microsc. Sci," April, 1881.

ANOTLOSA, OR WORMS.

199

worm of enormous length, which is commonly found entwining itself
among the roots of Algae. 1

597. Among the animals captured by the Tow-net, the marine Zoolo-
gist will be not unlikely to meet with an Annelid which, although by no
means Microscopic in its dimensions, is an admirable subject for Micro-
scopic observation, owing to the extreme transparence of its entire body,
which is such as to render it difficult to be distinguished when swimming
in a glass jar, except by a very favorable light. This is the T omopteris,
so named from the division of the lateral portions of its body into a suc-
cession of wing-like segments (Plate xxiii., b), each of them carrying at
its extremity a pair of pinnules, by the movements of which it is rapidly

Fig. 408. Fig. 409.

Actinotrocha branchiata: — a, Epi- Pilidium gyrans:—A, young, showing at a the ali-

stome or hood ; 6, anus; c, stomach; d, mentary canal, and at b the rudiment of the Ne-

ciliated tentacles; e, mouth, mertid; b, more advanced stage of the same; c,

newly-freed Nemertid.

propelled through the water. The full-grown animal, which measures
nearly an inch in length, has first a curious pair of * frontal horns ' pro-
jecting laterally from the head, so as to give the animal the appearance
of a ' hammer-headed ' Shark; behind these there is a pair of very long
antennae, in each of which we distinguish a rigid bristle-like stem or seta,
inclosed in a soft sheath, and moved at its base by a set of muscles con-
tained within the lateral protuberances at the head. Behind these are

1 See especially Leuckart and Pagenstecher's ' Untersuchungen iiber niedere
Seethiere,' in Muller's " Archiv," 1853, p. 569, and Balfour, op. cit, p. 165. The
Author has frequently met With Pilidium in Lamlash Bav.

200

THE MICROSCOPE AND ITS REVELATIONS.

PLATE XXIIL

STRUCTURE AND DEVELOPMENT OP TOMOPTERIS ONI SCIPORMIS (Original).

A. Portion of caudal prolongations, containing the spermatic sacs, a, a.

b. Adult Male specimen.

c. Hinder part of adult Female specimen, more enlarged, showing ova lying freely in the perivis
ceral cavity and its caudal prolongation.

d. Ciliated canal, commencing externally in the larger and smaller rosette-like disks, a, b.

e. One of the pinnulated segments, showing the position of the ciliated canal, c, and its rosette-
like disks, a, 6; snowing also the incipient development of the ova, d, at the extremity of the seg-
ment.

p. Cephalic Ganglion, with its pair of auditory (?) vesicles, «, a, and its two ocelli, 6, b.
g. Very young Tomopteris, showing at a, a the larval antennae; 6, 6, the incipient long antennas
of the adult; c, d, e, /, four pairs of succeeding pinnulated segment, followed by the bifid tail.

ANNULOSA, OR WORMS.

201

about sixteen pairs of the ordinary pinnulated segments, of which the
hinder ones are much smaller than those in front, gradually lessening in
size until they become almost rudimentary; and where these cease, the
body is continued onwards into a tail-like prolongation, the length of
which varies greatly according as it is contracted or extended. This pro-
longation, however, bears four or five pairs of very minute appendages,
and the intestine is continued to its very extremity; so that it is really to
be regarded as a continuation of the body. In the head we find, between
the origins of the antennae, a ganglionic mass, the component cells of
which may be clearly distinguished under a sufficient magnifying power,
as shown at f; seated upon this are two pigment-spots b), each bear-
ing a double pellucid lens-like body, which are obviously rudimentary
eyes: whilst imbedded in its anterior portion are two peculiar enucleated
vesicles, a, a, which are probably the rudiments of some other sensory
organs. On the under side of the head is situated the mouth, which,
like that of many other Annelids, is furnished with a sort of proboscis
that can be either projected or drawn-in; a short oesophagus leads to an
elongated stomach, which, when distended with fluid, occupies the whole
cavity of the central portion of the body, as shown in fig. b, but which
is sometimes so empty and contracted as to be like a mere cord, as shown
in fig. c. In the caudal appendage, however, it is always narrowed into
an intestinal canal; this, when the appendage is in extended state as at
c, is nearly straight; but when the appendage is contracted, as seen at b,
it is thrown into convolutions. The perivisceral cavity is occupied by
fluid in which some minute corpuscles may be distinguished; and these
are kept in motion by cilia which clothe some parts of the outer surface
of the alimentary canal and line some part of the wall of the body. No
other more special apparatus, either for the circulation or for the aeration
of the nutrient fluid, exists in this curious Worm; unless we are to regard
as subservient to the respiratory function the ciliated canal which may be
observed in each of the lateral appendages except the five anterior pairs.
This canal commences by two orifices at the base of the segment, as
shown at fig. e, b, and on a larger scale at fig. d; each of these orifices
(d, a, b) is surrounded by a sort of rosette; and the rosette of the larger
one (a) is furnished with radiating ciliated ridges. The two branches
incline towards each other, and unite into a single canal, that runs along
for some distance in the wall of the body, and then terminates in the
perivisceral cavity; and the direction of the motion of the cilia which line
it, is from without inwards.

598. The Keproduction and Developmental history of this Annelid
present many points of great interest. The sexes appear to be distinct,
ova being found in some individuals, and spermatozoa in others. The
development of the ova commences in certain i germ-cells ' situated within
the extremities of the pinnulated segments, where they project inwards
from the wall of the body; these, when set free, float in the fluid of the
perivisceral cavity, and multiply themselves by self-division; and it is
only after their number has thus been considerably augmented, that they
begin to increase in size and to assume the characteristic appearance of
ova. In this stage they usually fill the perivisceral cavity not only of the
body, but of its caudal extension, as shown at c; aud they escape from it
through transverse fissures which form in the outer wall of the body, at
the third and fourth segments. The male reproductive organs, on the
other hand, are limited to the caudal prolongation, where the sperm-cells
are developed within the pinnulated appendages, as the germ-cells of the

202

THE MICROSCOPE AND ITS REVEL ATIOtfS-

female are within the appendages of the body. Instead of being set free,
however, into the perivisceral cavity, they are retained within a saccular
envelope forming a testis (a, a, a) which fills up the whole cavity of each
appendage; and within this the spermatozoa may be observed, when ma-
ture, in active movement. They make their escape externally by a pas-
sage that seems to communicate with the smaller of the two just-men-
tioned rosettes; but they also appear to escape into the perivisceral cavity
by an aperture that forms itself when the spermatozoa are mature.
Whether the ova are fertilized while yet within the body of the female,
by the entrance of spermatozoa through the ciliated canals, or after
they have made their escape from it, has not yet been ascertained. — Of
the earliest stages of embryonic development nothing whatever is yet
known; but it has been ascertained that the animal passes through a
larval form, which differs from the adult not merely in the number of
the segments of the body (which successively augment by additions at the
posterior extremity), but also in that of the antennae. At g is repre-
sented the earliest larva hitherto met-with, enlarged as much as ten times
in proportion to the adult at B; and here we see that the head is destitute
of the frontal horns, but carries a pair of setigerous antennae, a, a, be-
hind which there are five pairs of bifid appendages, 5, c, d, e, f, in the
first of which, Z>, one of the pinnules is furnished with a seta. In more
advanced larvae having eight or ten segments, this is developed into a
second pair of antennae resembling the first; and the animal in this stage
has been described as a distinct species, T. quadricomis. At a more
advanced age, however, the second pair attains the enormous develop-
ment shown at b; and the first or larval antennae disappear, the setigerous
portions separating at a sort of joint (g, a, a), whilst the basal projec-
tions are absorbed into the general wall of the body. — This beautiful
creature has been met-with on so many parts of our coast, that it cannot
be considered at all uncommon; and the Microscopist can scarcely have
a more pleasing object for study.1 Its elegant form, its crystal clear-
ness, and its sprightly, graceful movements render it attractive even to
the unscientific observer; whilst it is of special interest to the Physiolo-
gist, as one of the simplest examples yet known of the Annelid type.

599. To one phenomenon of the greatest interest, presented by vari-
ous small Marine Annelids, the attention of the Microscopist should be
specially directed; this is their luminosity, which is not a steady glow
like that of the Glow-worm or Fire-fly, but a series of vivid scintillations
(strongly resembling those produced by an electric discharge through a
tube spotted with tin-foil), that pass along a considerable number of seg-
ments, lasting for an instant only, but capable of being repeatedly ex-
cited by any irritation applied to the body of the animal. These scin-
tillations may be discerned under the Microscope, even in separate
segments, when they are subjected to the irritation of a needle-point or
to a gentle pressure; and it has been ascertained by the careful observa-
tions of M. de Quatrefages, that they are given out by the muscular fibres
in the act of contraction.*2

600. Among the fresh-water Annelids, those most interesting to the
Microscopist are the worms of the Nais tribe, which are common in our

1 Seethe Memoirs of the Author and M. Claparede in Vol xxii. of the 44 Lin-
neean Transactions," and the authorities there referred to; also a recent Memoir
by Dr. F. Vejdovsky in 44 Zeitschrift f. wiss. Zool.," Bd. xxxi., 1880.

2 See his Memoirs on the Annelida of LaManche, in 44 Ann. des Sci. Nat.," Ser.
2, Zool., Tom. xix., and Ser. 3, Zool., Tom. xiv.

ANNULOSAj OR WORMS.

203

rivers and ponds, living chiefly amidst the mud at the bottom, and espe-
cially among the roots of aquatic plants. Being blood-red in color, they
give to the surface of the mud, when they protrude themselves from it
in large numbers and keep the protruded portion of their bodies in con-
stant undulation, a very peculiar appearance; but if disturbed, they with-
draw themselves suddenly and completely. These Worms, from the
extreme transparency of their bodies, present peculiar facilities for Mi-
croscopic examination, and especially for the study of the internal circu-
lation of the red liquid commonly considered as blood. There are here
no external respiratory organs; and the thinness of the general integu-
ment appears to supply all needful facility for the aeration of the fluids.
One large vascular trunk (dorsal) may be seen lying above the intestinal
canal, and another (ventral) beneath it; and each of these enters a con-
tractile dilatation, or heart-like organ, situated just behind the head.
The fluid moves forwards in the dorsal trunk as far as the heart, which
it enters and dilates; and when this contracts, it propels the fluid partly
to the head, and partly to the ventral heart, which is distended by it.
The ventral heart, contracting in its turn, sends the blood backwards
along the ventral trunk to the tail, whence it passes towards the head as
before. In this circulation, the stream branches-oif from each of the
principal trunks into numerous vessels proceeding to different parts of
the body, which then return into the other trunk; and there is a peculiar
set of vascular coils, hanging down in the perivisceral cavity that con-
tains the corpusculated liquid representing the true blood, which seems
specially destined to convey to it the aerating influence received by the red
fluid in its circuit, thus acting (so to speak) like internal gills. — The
Naiad-worms have been observed to undergo spontaneous division during
the summer months; a new head and its organs being formed for the
posterior segment behind the line of constriction, before its separation
from the anterior. It has, been generally believed that each segment
continues to live as a complete worm; but it is asserted by Dr. T. Wil-
liams that from the time when the division occurs, neither half takes-in
any more food, and that the two segments only retain vitality enough to
enable them to be (as it were) the ' nurses y of the eggs which both in-
clude.— In the Leech tribe, the dental apparatus with which the mouth
is furnished, is one of the most curious among their points of minute
structure; and the common 6 medicinal 9 Leech affords one of the most
interesting examples of it. What is commonly termed the 6 bite 9 of the
leech, is really a saw-cut, or rather a combination of three saw-cuts, radi-
ating from a common centre. If the mouth of a leech be examined with
a hand-magnifier, or even with the naked eye, it will be seen to be a tri-
angular aperture in the midst of a sucking disk; and on turning back
the lips of that aperture, three little white ridges are brought into view.
Each of these is the convex edge of a horny semicircle, which is bor-
dered by a row of eighty or ninety minute hard and sharp teeth; whilst
the straight border of the semicircle is imbedded in the muscular sub-
stance of the disk, by the action of which it is made to move back-
wards and forwards in a saw-like manner, so that the teeth are enabled
to cut into the skin to which the suctorial disk has affixed itself.1

1 Among the more recent sources of information as to the Anatomy and Phy-
siology of the Annelids, the following may be specially mentioned: — The " His-
toire Naturelle des Anneles Marins et d'Eau douce" of M. de Quatrefages, forming
part of the " Suites a Buffon; " the successive admirable Monographs of the late
Prof. Ed. Claparede, ' 4 Recherches Anatomiques sur les Annelides, Turbellaries,

204

THE MICROSCOPE AND ITS REVELATIONS.

Opalines, et Gregarines, observes dans les Hebrides" (Geneva, 1861); "Recherches
Anatomiques sur les Oligochetes" (Geneva, 1862); 44 Beobachtungen iiber Anato-
mie und Entwickelurigsgeschichte Wirbelloser Thiere an der Kiiste von Norman-
die" (Leipzig, 1863); and 4 4 Les Annelides Chetopodes du Golf e de Naples" (Ge-
neva, 1868-70); the Monograph of Dr. Ehler's, 44 Die Borstenwtirmer (Annelida
Chsetopoda)," 1864-8; and lastly, Dr. Macintosh's 44 Monograph of the British An-
nelids," now in course of publication by the Ray Society.

CRUSTACEA.

205

CHAPTEK XVIII.
CRUSTACEA.

601. Passing from the lower division of the Articulated series to
that of Arthropods, in which the body is furnished with distinctly articu-
lated or jointed limbs, we come first to the Class of Crustacea, which in-
cludes (when used in its most comprehensive sense) all those animals
belonging to this group, wThich are fitted for aquatic respiration. It thus
comprehends a very extensive range of forms; for although we are accus-
tomed to think of the Crab, Lobster, Cray-fish, and other well-known
species of the order Decapoda (ten-footed) as its typical examples, yet
all these belong to the highest of its many orders; and among the lower
are many of a far simpler structure, and not a few which would not be
recognized as belonging to the class at all, were it not for the information
derived from the study of their development as to their real nature, which
is far more apparent in their early than it is in their adult condition.
Many of the inferior kinds of Crustacea are so minute and transparent,
that their whole structure may be made-out by the aid of the Microscope
without any preparation; this is the case, indeed, with nearlV the whole
group of Entomostraca (§ 603), and with the larval forms even of the
Crab and its allies (§ 614); and we shall give our first attention to these,
afterwards noticing such points in the structure of the larger kinds as
are likely to be of general interest.

602. A curious example of the reduction of an elevated type to a
very simple form is presented by the group of Pycnogonida, some of the
members of which may be found by attentive search in almost every
locality where sea-weeds abound; it being their habit to crawl (or rather
to sprawl) over the surfaces of these, and probably to imbibe as food the
gelatinous substance with which they are invested.1 The general form
of their bodies (Fig. 410) usually reminds us of that of some of the long-
legged Crabs; the abdomen being almost or altogether deficient, whilst
the head is very small, and fused (as it were) into the thorax; so that the
last-named region, with the members attached to it, constitutes nearly
the whole bulk of the animal. The head is extended in front into a
probosis-like projection, at the extremity of which is the narrow orifice
of the mouth; which seems to be furnished with vibratile cilia, that serve
to draw into it the semi-fluid aliment. Instead of being furnished (as in
the higher Crustaceans) with two pairs of antennae and numerous pairs of
'feet-jaws/ it has but a single pair of either; it also bears four minute
ocelli, or rudimentary eyes, set at a little distance from each other on a

1 It is remarkable that very large forms of this group, sometimes extending to
more than -twelve inches across, have been brought up from great depths of the
sea.

206

THE MICROSCOPE AND ITS REVELATIONS.

sort of tubercle. From the thorax proceed four pairs of legs, each com-
posed of several joints, and terminated by a hooked claw; and by these
members the animal drags itself slowly along, instead of walking actively
upon them like a crab. The mouth leads to a very narrow oesophagus
(a), which passes back to the central stomach (b) situated in the midst
of the thorax, from the hinder end of which a, narrow intestine (c)
passes-off, to terminate at the posterior extremity of the body. From
the central stomach five pairs of caecal prolongations radiate; one pair (d)
entering the feet-jaws, the other four (e> e) penetrating the legs, and
passing along them as far as the last joint but one; and those extensions
are covered with a layer of brownish-yellow granules, which are prob-

of the digestive apparatus; since, whenever the caecum of any one the
legs undergoes dilatation, a part of the circumambient liquid will be
pressed-out from the cavity of that limb, either into the thorax, or into
some other limb whose stomach is contracting. The fluid must obtain
its aeration through the general surface of the body, as there are no
special organs of respiration. The nervous system consists of a single
ganglion in the head (formed by the coalescence of a pair), and of another
in the thorax (formed by the coalescence of four pairs), with which the
cephalic ganglion is connected in the usual mode, namely, by two nerv-
ous cords which diverge from each other to embrace the oesophagus. —
In the study of the very curious phenomena exhibited by the digestive
-apparatus, as well as of the various points of internal conformation
which have been described, the Achromatic Condenser will be found use-

Ammothea pycnogonoides.'—a, narrow oesophagus; &•
stomach; c, intestine; dy digestive caeca of the feet-jaws;
e, e, digestive caeca of the legs .

Fig. 410.

ably to be regarded as a dif-
fused and rudimentary con-
dition of the liver. The
stomach and its caecal pro-
longations are continually
executing peristaltic move-
ments of a very curious
kind; for they contract and
dilate with an irregular al-
ternation, so that a flux
and reflux of their contents
is constantly taking place
between the central portion
and its radiating extensions,
and between one of these
extensions and another.
The perivisceral space be-
tween the widely-extended
stomach and the walls of
the body and limbs is oc-
cupied by a transparent
liquid, in which are seen
floating a number of minute
transparent corpuscles of
irregular size; and this fluid,
which represents the blood,
is kept in continual motion,
not only by the general
movements of the ani-
mal, but also by the actions

CRUSTACEA.

207

ful, even with the 1 inch, 2-3d inch, or $ inch Objective; for the imper-
fect transparence of the bodies of these animals renders it of importance
to drive a large quantity of light through them, and to give to this light
such a quality as shall sharply define the internal organs.1

603. Entomostraca. — This group of Crustaceans, nearly all the ex-
isting members of which are of such minute size as to be only just visible
to the naked eye, is distinguished by the inclosure of the entire body
within a horny or shelly casing; which sometimes closely resemble a bi-
valve shell in form and in the mode of junction of its parts, whilst in
other instances it is formed of only a single piece, like the hard envelope
of certain Rotifera (§ 453, III.). The segments into which the body is
divided, are frequently very numerous, and are for the most part similar
to each other; but there is a marked difference in regard to the append-
ages which they bear, and to the mode in which these minister to the lo-
comotion of the animals. For in the Lophyropoda, or ' bristly-footed '
tribe, the number of legs is small, not exceeding five pairs, and their
function is limited to locomotion, the respiratory organs being attached
to the parts in the neighborhood of the mouth; whilst in the Branchio-
poda, or 6 gill-footed 9 tribe, the same members (known as 6 fin-feet')
serve both for locomotion and for respiration, and the number of these is
commonly large, being in Apus not less than sixty pairs. The character
of their movements differ accordingly; for whilst all the members of the
first named tribe dart through the water in a succession of jerks, so as to
have acquired the common name of ' water-fleas,' those among the latter
which possess a great number of 6 fin-feet/ swim with an easy gliding move-
ment, sometimes on their back alone (as in the case with Branchipus), and
sometimes with equal facility on the back, belly, or sides (as is done by
Artemia salina, the 6 brine shrimp'). — Some of the most common forms
of both tribes will now be briefly noticed.

604. The tribe of Lophyropoda is divided into two Orders; of which
the first, Ostracoda, is distinguished by the complete inclosure of the
body in a bivalve shell, by the small number of legs, and by the absence
of an external ovary. One of the best known examples is the little Cypris,
which is a common inhabitant of pools and streams: this may be recog-
nized by its possession of two pairs of antennae, the first having numerous
joints with a pencil-like tuft of filaments, and projecting forwards from
the front of the head, whilst the second has more the shape of legs, and
is directed downwards; and by the limitation of its legs to two pairs, of
which the posterior does not make its appearance outside the shell, being
bent upwards to give support to the ovaries. The valves are generally
opened widely enough to allow the greater part of both pairs of antennae
and of the front pair of legs to pass-out between them; but when the ani-
mals are alarmed, they draw these members within the shell, and close
the valves firmly. They are very lively creatures, being almost constantly
seen in motion, either swimming by the united action of their foot-like
antennae and legs, or walking upon plants and other solid bodies floating
in the water. — Nearly allied to the preceding is the Cythere, whose body
is furnished with three pairs of legs, all projecting out of the shell, and
whose superior antennae are destitute of the filamentous brush; this genus

1 Certain points of resemblance borne by Pycnogonida to Spiders, makes the
careful study of their development a matter of special interest and importance;
as there is some reason to regard them rather as Arachnida adapted to a marine
habitat, than as Crustacea.— See Balfour's " Comparative Embryology," pp. 448,
449, and the authorities there referred to.

208

THE MICROSCOPE AND ITS REVELATIONS.

is almost entirely marine, and some species of it may almost invariably be
met- with in little pools among the rocks between the tide-marks, creep-
ing about (but not swimming) amongst Confervas and Corallines. — There
is abundant evidence of the former existence of Crustacea of this group,
of larger size than any now existing, to an enormous extent; for in cer-
tain fresh-water strata, both of the Secondary and Tertiary series, we find
layers, sometimes of great extent and thickness, which are almost entirely
composed of the fossilized shells of Cyprides; whilst in certain parts of
the Chalk, which was a marine deposit, the remains of bivalve shells re-
sembling those of Cythere present themselves in such abundance as to
form a considerable part of its substance.

605. In the order Copepoda, there is a jointed shell forming a kind
of buckler or carapace that almost entirely incloses the head and thorax,

is soft and gelatinous, and it is composed of two distinct parts, a thorax
(Pig. 411, a) and an abdomen (S), of which the latter, being compara-
tively slender, is commonly considered as a tail, though traversed by the
intestine which terminates near its extremity. The head, which coa-
lesces with the thorax, bears one very large pair of antennae (c), possess-
ing numerous articulations and furnished with bristly appendages, and
another small pair (d); it is also furnished with a pair of mandibles or
true jaws, and with two pairs of * feet-jaws/ of which the hinder pair is
the longer and more abundantly supplied with bristles. The legs (e) are
all beset with plumose tufts, as is also the tail (/,/) which is borne at
the extremity of the abdomen. On either side of the abdomen of the
female, there is often to be seen an egg-capsule or external ovarium (b);

a, Female of Cyclops quadricornis:—a, body ;
5, tail; c, antenna; d, antennule; e, feet; /, plu-
mose setae of tail; — b, tail, with external egg-
sacs: — c, d, e, f, g, successive stages of develop-
ment of young.

Fig. 411.

an opening being left beneath,
through which the members pro-
ject; and there are five pairs of
legs, mostly adapted for swimming,
the fifth pair, however, being rudi-
mentary in the genus Cyclops, the
commonest example of the group.
This genus receives its name from
possessing only a single eye, or
rather a single cluster of ocelli;
which character, however, it has in
common with the two genera already
named, as well as with Daphnia
(§ 606), and with many other En-
tomostraca. It contains numerous
species, some of which belong to
fresh- water, whilst others are ma-
rine. The Fresh-water species often
abound in the muddiest and most
stagnant pools, as well as in the
clearest springs; the ordinary water
with which London is supplied fre-
quently contains large numbers of
them. Of the marine species, some
are to be found in the localities in
which the Cythere is most abun-
dant, whilst others inhabit the open
ocean, and must be collected by the
Tow-net. The body of the Cyclops

CRUSTACEA.

209

within which the ova, after being fertilized, undergo the earlier stages of
their development. — The Cyclops is a very active creature, and strikes the
water in swimming, not merely with its legs and tail, but also with its
antennae. The rapidly-repeated movements of its feet-jaws serve to create
a whirlpool in the surrounding water, by which minute animals of various
kinds, and even its own young, are brought to its mouth to be devoured.

606. The tribe of Branchiopoda also is divided into two Orders, of
which the Cladocera present the nearest approach to the preceding, hav-
ing a bivalve carapace, no more than from four to -six pairs of legs, two
pairs of antennae, of which one is large and branched and adapted for swim-
ming, and a single eye. The commonest form of this is the Daphnia pulex,
sometimes called the c arborescent water-flea/ from the branching form
of its antennae. It is very abundant in many ponds and ditches, coming
to the surface in the mornings and evenings and in cloudy weather, but
seeking the depths of the water during the heat of the day. It swims by
taking short springs; and feeds on minute particles of vegetable sub-
stances, not, however, rejecting animal matter when offered. Some of
the peculiar phenomena of its reproduction will be presently described
(§ 609).

607. The other order, Phyllopoda, includes those Branchiopoda
whose body is divided into a great number of segments, nearly all of
which are furnished with leaf-like members, or 'fin-feet.' The two
Families which this order includes, however, differ considerably in their
conformation; for in that of which the genera Apus and Nebalia are rep-
resentatives, the body is inclosed in a shell, either shield-like or bivalve,
and the feet are generally very numerous; whilst in that in which contains
Brancliipus and Artemia> the body is entirely unprotected, and the
number of pairs of feet does not exceed eleven. The Apus cancriformis,
which is an animal of comparatively large size, its entire length being
about 2 J inches, is an inhabitant of stagnant waters; but although occa-
sionally very abundant in particular pools or ditches, it is not to be met-
with nearly so commonly as the Entomostraca already noticed. It is .
recognized by its large oval carapace, which covers the head and body like
a shield; by the nearly cylindrical form of its body, which is composed of
thirty articulations; and by the multiplication of its legs, which amount
to about sixty pairs. The number of joints in these and in the other ap-
pendages is so great, that in a single individual they may be safely esti-
mated at not less than two millions. These organs, however, are for the
most part small; and the instruments chiefly used by the animal for loco-
motion are the first pair of feet, which are very much elongated (bearing
such a resemblance to the principal antennae of other Entomostraca, as to
be commonly ranked in the same light), and are distinguished as rami or
oars. With these they can swim freely in any position; but when the
rami are at rest and the animal floats idly on the water, its fin-feet may
be seen in incessant motion, causing a sort of whirlpool in the water, and
bringing to the mouth the minute animals (chiefly the smaller Entomos-
traca inhabiting the same localities) that serve for its food. — The Bran-
chipus stagnalis has a slender, cylindriform, and very transparent body
of nearly an inch in length, furnished with eleven pairs of fin-feet, but is
destitute of any protecting envelope; its head is furnished with a pair of
very curious prehensile organs (which are really modified antennae),
whence it has received the name of Cheirocephalus; bat these are not
used by it for the seizure of prey, the food of this animal being vegetable,
and their function is to clasp the female in the act of copulation. The

210

THE MICROSCOPE AND ITS REVELATIONS.

Branchipus or Cheirocephalus is certainly the most beautiful and elegant
of all the Entomostraca, being rendered extremely attractive to the view
by " the uninterrupted undulatory wavy motion of its graceful branchial
feet, slightly tinged as they are with a light reddish hue, the brilliant
mixture of transparent bluish-green and bright red of its prehensile
antennae, and its bright red tail with the plumose setae springing from
it;" unfortunately, however, it is a comparatively rare animal in this
country. — The Artemia salina or i brine shrimp 9 is an animal of very
similar organization, and almost equally beautiful in its appearance and
movements, but of smaller size, its body being about half an inch in
length. Its ' habitat 9 is very peculiar; for it is only found in the salt-
pans or brine-pits in which sea- water is undergoing concentration as at
Lymington) ; and in these situations it is sometimes so abundant as to
communicate a red tinge to the liquid.

608. Some of the most interesting points in the history of the
JSntromostraca lie in the peculiar mode in which their generative f unc-
tion is performed, and their tenacity of life when desiccated, in which
last respect they correspond with many Eotifers (§ 452). By this pro-
vision they escape being completely exterminated, as they might other-
wise soon be, by the drying-up of the pools, ditches, and other small
collections of water which constitute their usual ' habitats.5 It does not
appear, however, that the adult Animals can bear a complete desiccation,
although they will preserve their vitality in mud that holds the smallest
quantity of moisture; but their eggs are more tenacious of life, and there
is ample evidence that these will become fertile on being moistened,
after having remained for a long time in the condition of fine dust.
Most Entomostraca, too, are killed by severe cold, and thus the whole
race of adults perishes every winter; but their eggs seem unaffected by
the lowest temperature, and thus continue the species, which would be
otherwise exterminated. — Again, we frequently meet in this group with
that agamic reproduction, which we have seen to prevail so extensively
among the lower radiata and Mollusca. In many species there is a double
mode of multiplication, the sexual and the non-sexual. The former
takes-place at certain seasons only; the males (which are often so differ-
ent in conformation from the females, that they would not be supposed
to belong to the same species, if they were not seen in actual congress)
disappearing entirely at other times. The latter, on the other hand,
continues at all periods of the year, so long as warmth and food are sup-
plied; and is repeated many times (as in the Hydra) so as to give origin
to as many successive ' broods.' Further, a single act of impregnation
serves to fertilize not merely the ova which are then mature or nearly so,
but all those subsequently produced by the same female, which are
deposited at considerable intervals. In these two modes, the multiplica-
tion of these little creatures is carried-on with great rapidity, the young
animal speedily coming to maturity and beginning to propagate; so that
according to the computation of J urine, founded upon data ascertained
by actual observation, a single fertilized female of the common Cyclops
quadricornis may be the progenitor in one year of 4,442,189,120 young.

609. The eggs of some Entomostraca are deposited freely in the
w^ter, or are carefully attached in clusters to aquatic Plants; but they
are more frequently carried for some time by the parent in special recep-
tacles developed from the posterior part of the body; and in many cases
Ihey are retained there until the young are ready to come-forth, so that
these animals may be said to be ovo-viviparous. In Daphnia, the eggs

CRUSTACEA.

211

are received into a large cavity between the back of the animal and its
shell, and there the young undergo almost their whole development, so
as to come-forth in a form nearly resembling that of their parent. Soon
after their birth, a moult or exuviation of the shell takes-place; and the
egg-coverings are cast-off with it. In a very short time afterwards,
another brood of eggs is seen in the cavity, and the same process is
repeated, the shell being again exuviated after the young have been
brought to maturity. At certain times, however, the DapJmia may be
seen with a dark opaque substance within the back of the shell, which
has been called the ephippium, from its resemblance to a saddle. This,
when carefully examined, is found to be of dense texture, and to be com-
posed of a mass of hexagonal cells; and it contains two oval bodies, each
consisting of an ovum covered with a horny casing, enveloped in a capsule
which opens like a bivalve shell. From the observations of Sir J. Lub-
bock,1 it appears that the ephippium is really only an altered portion of
the carapace; its outer valve being a part of the outer layer of the epider-
mis, and its inner valve the corresponding part of the inner layer. The
development of the ephippial eggs takes-place at the posterior part of the
ovaries, and is accompanied by the formation of a greenish-brown mass
of granules; and form this situation the eggs pass into the receptacle
formed by the new carapace, where they become included between the two
layers of the ephippium. This is cast-off, in process of time, with the rest
of the skin, from which, however, it soon becomes detached; and it con-
tinues to envelop the eggs, generally floating on the surface of the water
until they are hatched with the returning warmth of spring. This curious
provision obviously affords protection to the eggs which are to endure
the severity of winter cold; and an approach to it may be seen in the re-
markable firmness of the envelopes of the ' winter eggs ' of some Eotifera
(§ 451). There seems a strong probability, from the observations of Sir
J. Lubbock, that the 6 ephippial ' eggs are true sexual products, since
males are to be found at the time when the ephippiaare developed; whilst
it is certain that the ordinary eggs can be produced non-sexually, and
that the young which spring from them can multiply the race in like
manner. The young produced from the ephippial eggs seem to have the
same power of continuing the race by non-sexual reproduction, as the
young developed under ordinary circumstances.

610. In most Entomostraca, the young at the time of their emersion
from the egg differ considerably from the parent, especially in having
only the thoracic portion of the body as yet evolved, and in possessing
but a small number of locomotive appendages (see Fig. 411, c-g); the
visual organs, too, are frequently wanting at first. The process of devel-
opment, however, takes place with great rapidity; the animal at each
successive moult (which process is very commonly repeated at intervals
of a day or two) presenting some new parts, and becoming more and
more like its parent, which it very early resembles in its power of multi-
plication, the female laying eggs before she has attained her own full
size. Even when the Entomostraca have attained their full growth, they
continue to exuviate their shell at short intervals during the whole of
life; and this repeated moulting seem to prevent the animal from being
injured, or its movements obstructed, by the over-growth of uarasitic
Animalcules and Confervae; weak and sickly individuals being frequently

1 An account of the two methods of Reproduction in Daphnia, and of the
structure of the Ephippium,' in " Philosophical Transactions,'' 1857, p. 79.

212

THE MICROSCOPE AND ITS REVELATIONS.

seen to be so covered with such parasites, that their motion and life are
soon arrested, apparently because they have not strength to cast-off and
renew their envelopes. The process of development appears to depend
in some degree upon the influence of light, being retarded when the ani-
mals are secluded from it; but its rate is still more influenced by heat;
and this appears also to be the chief agent that regulates the time which
elapses between the moultings of the adult, these, in Daphnia, taking-
place at intervals of two days in warm summer weather, whilst several
days intervene between them when the weather is colder. The cast shell
carries with it the sheaths not only of the limbs and plumes, but of the
most delicate hairs and setae which are attached to them. If the animal
have previously sustained the loss of a limb, it is generally renewed at
the next moult, as in higher Crustacea.1

611. Closely connected with the Entomostracous group is the tribe
of suctorial Crustacea; which for the most part live as parasites upon the
exterior of other animals (especially Fish), whose juices they imbibe by
means of the peculiar proboscis-like organ which takes in them the place
of the jaws of other Crustaceans; whilst other appendages, representing
the feet-jaws, are furnished with hooks, by which these parasites attach
themselves to the animals from whose juices they derive their nutriment.
Many of the suctorial Crustacea bear a strong resemblance, even in their
adult condition, to certain Entomostraca; but more commonly it is
between the earlier forms of the two groups that the resemblance is the
closest, most of the suctoria undergoing such extraordinary changes in
their progress towards the adult condition, that, if their complete forms
were alone attended-to, they might be excluded from the class altogether,
as has (in fact) been done by many Zoologists. — Among those Suctorial
Crustacea which present the nearest approach to the ordinary Entomos-
tracous type, may be specially mentioned the Argulus foliaceus, which
attaches itself to the surfaces of the bodies of fresh-water Fish, and is
commonly known under the name of the ' fish louse/ This animal has
its body covered with a large firm oval shield, which does not extend,
however, over the posterior part of the abdomen. The mouth is armed
with a pair of styliform mandibles; and on each side of the proboscis
there is a large short cylindrical appendage, terminated by a curious sort
of sucking-disk, with another pair of longer jointed members, terminated
by prehensile hooks. These two pairs of appendages, which are probably
to be considered as representing the feet-jaws, are followed by four pairs
of legs, which, like those of the Branchiopods, are chiefly adapted for
swimming; and the tail, also, is a kind of swimmeret. This little animal
can leave the fish upon which it feeds, and then swims freely in the
water, usually in a straight line, but frequently and suddenly changing
its direction, and sometimes turning over and over several times in suc-
cession. The stomach is remarkable for the large caecal prolongations
which it sends out on either side, immediately beneath the shell; for
these subdivide and ramify in such a manner, that they are distributed
almost as minutely as the caecal prolongations of the stomach of the
Planaria (Fig. 406). The proper alimentary canal, however, is con-
tinued backwards from the central cavity of the stomach, as an intestinal
tube, which terminates in an anal orifice at the extremity of the abdo-
men.— A far more marked departure from the typical form of the class

1 For a systematic and detailed account of this group, see Dr. Baird's " Natu-
ral History of the British Entomostraca," published by the Ray Society.

CRUSTACEA.

213

is shown in the Ler?icea, which is found attached to the gills of Fishes.
This creature has a long suctorial proboscis; a short thorax, to which is
attached a single pair of legs, which meet at their extremities, where
they bear a sucker which helps to give attachment to the parasite; a large
abdomen; and a pair of pendent egg-sacs. In its adult condition it buries
its anterior portion in the soft tissue of the animal it infests, and appears
to have little or no power of changing its place. But the youngs when
they come forth from the egg, are as active as the young of Cyclops
(Fig. 411, c, d), which they much resemble; and only attain the adult
form after a series of metamorphoses, in which they cast-off their loco-
motive members and eyes. It is curious that the original form is retained
with comparatively slight change by the males, which increase but little
in size, and are so unlike the females that no one would suppose the two
to belong to the same family, much less to the same species, but for the
Microscopic study of their development.1

612. From the parasitic Suctorial Crustacea, the transition is not
really so abrupt as it might at first sight appear to the group of Cirrhi-
peda, consisting of the Barnacles and their allies: for these, like many of
the Suctoria, are fixed to one spot during the adult portion of their lives,
but come into the world in a condition that bears a strong resemblance
to the early state of many of the true Crustacea. The departure from
the ordinary Crustacean type in the adults, is, in fact, so great that it is
not surprising that Zoologists in general should have ranked them in a
distinct Class; their superficial resemblance to the Mollusca, indeed,
having caused most systematists to place them in that series, until due
weight was given to those structural features which mark their 6 articu-
lated 9 character. We must limit ourselves, in our notice of this group,
to that very remarkable part of their history, the Microscopic study of
which has contributed most essentially to the elucidation of their real
nature. The observations of Mr. J. V. Thompson,2 with the extensions
and rectifications which they have subsequently received from others
(especially Mr. Spence Bate3 and Mr. Darwin4) show that there is no
essential difference between the early forms of the sessile (Balanidse or
6 acorn-shells ') and of the pedunculated Cirrhipeds (Lepadidaeor ' barna-
cles'); for both are active little animals (Fig. 412, a), possessing three
pairs of legs, and a pair of compound eyes, and having the body covered
with an expanded carapace, like that of many Entomostracous Crusta-
ceans, so as in no essential particular to differ from the larva of Cyclops
(Fig. 411, c). After going through a series of Metamorphoses, one
stage of which is represented in Fig. 412, B, c, these larvae come to pre-
sent a form, D, which reminds us strongly of that of Daphnia; the body
being inclosed in a shell composed of two valves, which are united along
the back, whilst they are free along their lower margin, where they sepa-
rate for the protrusion of a large and strong anterior pair of prehensile
limbs provided with an adhesive sucker and hooks, and of six pairs of
posterior legs adapted for swimming. This Bivalve shell, with the

1 As the group of Suctorial Crustacea is rather interesting to the professed
Naturalist than to the amateur Microscopist, even an outline view of it would be
unsuitable to the present work; and the Author would refer such of his readers
as may desire to study it, to the excellent Treatise by Dr. Baird already referred to.

2 4 'Zoological Researches," No. iv., 1830, and Philos. Transact., 1835, p. 355.

3 4 On the Development of the Cirripedia,' in " Ann. of Nat. Hist.," Ser. 2, Vol.
viii. (1851), p. 324.

4 44 Monograph of the Sub-Class Cirripedia," published by the Ray Society.

214

THE MICROSCOPE AND ITS REVELATIONS.

members of both kinds, is subsequently thrown-off; the animal then
attaches itself by its head, a portion of which, in the Barnacle, be-
comes excessively elongated into the ' peduncle' of attachment, whilst
in Balanus it expands into a broad disk of adhesion; the first thoracic
segment sends backwards a prolongation which arches over the rest of
the body so as completely to inclose it, and of which the exerior layer is
consolidated into the 'multi valve' shell; whilst from the other thoracic
segments are evolved the six pairs of cirrhi, from whose peculiar char-
acter the name of the group is derived. These are long, slender, many-
jointed, tendril-like appendages, fringed with delicate filaments covered
with cilia, whose action serves both to bring food to the mouth, and to
maintain aerating currents in the water. The Balani are peculiarly inter-
esting objects in the Aquarium, on account of the pumping action of their
beautiful feathery appendages, which may be watched through a Tank*

Fig. 412.

Development of Balanus balanoides;—x, earliest form; b, larva after second moult; c, side
view of the same; d, stage immediately preceding the loss of activity; a, stomach (?); 6, nucleus
of future attachment (?).

Microscope; and their cast skins, often collected by the Tow-net, are
well worth mounting.

613. Malacostraca. — The chief points of interest to the Micro-
scopist in the more highly organized forms of Crustacea, are furnished
by the structure of the shell, and by the phenomena of metamorphosis,
both which may be best studied in the commonest kinds. — The Shell of
the Decapods in its most complete form consists of three strata — namely,
1, a horny structureless layer covering the exterior; 2, an areolated
stratum; and 3, a laminated tubular substance. The innermost and
even the middle layers, however, may be altogether wanting; thus, in
the Phyllosomce or ' glass-crabs/ the envelope is formed by the trans-
parent horny layer alone; and in many of the small crabs belonging to
the genus Portuna, the whole substance of the carapace beneath the
horny investment presents the areolated structure. It is in the large
thick-shelled Crabs that we find the three layers most differentiated.

CRUSTACEA.

215

Thus, in the common Cancer pagnrvs, we may easily separate the struc-
tureless horny covering after a short maceration in dilute acid; the
areolated layer, in which the pigmentary matter of the colored parts of
the shell is chiefly contained, may be easily brought into view by grind-
ing away from the inner side as flat a piece as can be selected, having
first cemented the outer surface to the glass slide, and by examining this
with a magnifying power of 250 diameters, driving a strong light through
it with the Achromatic Condenser; whilst the tubular structure of the
thick inner layer may be readily demonstrated, by means of sections
parallel and perpendicular to its surface. This structure, which resem-
bles that of dentine (§ 655), save that the tubuli do not branch, but
remain of the same size through their whole course, may be particularly
well seen in the black extremity of the claw, which (apparently from
some peculiarity in the molecular arrangement of its mineral particles) is
much denser than the rest of the shell; the former having almost the
semi-transparence of ivory, whilst the latter has a chalky opacity. In
a transverse section of the claw, the tubuli may be seen to radiate from
the central cavity towards the surface, so as very strongly to resemble
their arrangement in a tooth; and the resemblance is still further in*
creased by the presence, at tolerably regular intervals, of minute sinuosi-
ties corresponding with the laminations of the shell, which seem, like
the 6 secondary curvatures' of the dentinal tubuli, to indicate successive
stages in the calcification of the animal basis. In thin sections of the
areolated layer it maybe seen that the apparent walls of the areolae are
merely translucent spaces from which the tubuli arc absent, their orifices
being abundant in the intervening spaces.1 The tubular layer rises up
through the pigmentary layer of the Crab's shell in little papillary eleva-
tions, which seem to be concretionary nodules; and it is from the deficiency
of the pigmentary layer at these parts, that the colored portion of the
shell derives its minutely-speckled appearance. — Many departures from
this type are presented by the different species of Decapods; thus, in the
Prawns, there are large stellate pigment-spots (resembling those of
Frogs, Fig. 465, c), the colors of which are often in remarkable con-
formity with those of the bottom of the rock-pools frequented by these
creatures; whilst in the Shrimps there is seldom any distinct trace of
the areolated layer, and the calcareous portion of the skeleton is disposed
in the form of concentric rings, which seem to be the result of the con-
cretionary aggregation of the calcifying deposit (§ 713).

614. It is a very curious circumstance, that a strongly-marked differ-
ence exists between Crustaceans that are otherwise very closely allied, in
regard to the degree of change to which their young are subject in their
progress towards the adult condition. For whilst the common Crab,
Lobster, Spiny Lobster, Prawn, and Shrimp undergo a regular meta-
morphosis, the young of the Cray -fish and some Land-crabs come forth
from the egg in a form which corresponds in all essential particulars
with that of their parents. Generally speaking, a strong resemblance
exists among the young of all the species of Decapods which undergo a

1 The Author is now quite satisfied of the correctness of the interpretation
put by Prof. Huxley (see his Article, 4 Tegumentary Organs,' in the " Cyclop, of
Anat. and Phys.," Vol. v., p. 487) and by Prof. W. C. Williamson (' On some
Histological Features in the Shells of Crustacea,' in " Quart. Journ. of Microsc.
Science," Vol. viii., 1860, p. 38), upon the appearances which he formerly
described (''Reports of British Association " for 1847, p. 128) as indicating a cellu-
lar structure in this layer.

216

THE MICROSCOPE AND ITS REVELATIONS.

metamorphosis, whether they are afterwards to belong to the macrourous
(long-tailed) or to the brachyourous (short-tailed) division of the group;
and the forms of these larvae are so peculiar, and so entirely different
from any of those into which they are ultimately to be developed, that
they were considered as belonging to a distinct genus, Zoea, until their
real nature was first ascertained by Mr. J. V. Thompson. Thus, in the
earliest state of Carcinus mmnas (small edible Crab), we see the head and
thorax, which form the principal bulk of the body, included within a
large carapace or shield (Fig. 413, a) furnished with a long projecting
spine, beneath which the fin-feet are put forth: whilst the abdominal
segments, narrowed and prolonged, carry at the end a flattened tail-fin,
by the strokes of which upon the water, the propulsion of the animal is
chiefly effected. Its condition is hence comparable, in almost all essen-
tial particulars, to that of Cyclops (§ 605). In the case of the Lobster,
Prawn, and other /macrourous' species, the metamorphosis chiefly con-
sists in the separation of the locomotive and respiratory organs; true legs
being developed from the thoracic segments for the former, and true gills
(concealed within a special chamber formed by an extension of the cara-
pace beneath the body) for the latter; while the abdominal segments

Pig. 413.

Metamorphosis of Carcinus Mcenas : — a, first or Zoea stage ; b, second or Megalopa stage ; c,
third stage, in which it begins to assume the adult form; D, perfect form.

increase in size, and become furnished with appendages (false feet) of
their own. In the Crabs, or f brachyourous 9 species, on the other hand,
the alteration is much greater; for besides the change first noticed in the
thoracic members and respiratory organs, the thoracic region becomes
much more developed at the expense of the abdominal, as seen at B, in
which stage the larva is remarkable for the large size of its eyes, and
hence received the name of Megalopa when it was supposed to be a dis-
tinct type. In the next stage, c, we find the abdominal portion reduced
to an almost rudimentary condition, and bent under the body; the
thoracic limbs are more completely adapted for walking, save the first
pair, which are developed into chelce or pincers; and the little creature
entirely loses the active swimming habits which it originally possessed,
and takes on the mode of life peculiar to the adult.1

615. In collecting minute Crustacea, the Eing-net should be used for
the fresh-water species, and the Tow-net for the marine. In localities
favorable for the latter, the same * gathering 9 will often contain multi-

1 On the Metamorphosis of Crustacea and Cirripedia, see especially the
recent 4< Untersuchungen iiber Crustaceen" of Prof. Claus; Vienna, 1876.

CRUSTACEA. 217

tudes of various species of Entomostraca, accompanied, perhaps, by the
larvae of higher Crustacea, Echinoderm larvae, Annelid larvae, and the
smaller Medusae. The water containing these should be put into a large
glass jar, freely exposed to the light; and, after a little practice, the eye
will become so far habituated to the general appearance and modes of
movement of these different forms of animal life, as to be able to distin-
guish them one from the other. In selecting any specimen for Micro-
scopic examination, the Dipping-tube (§ 126) will be found invaluable.
The collector will frequently find Megalopa larvae, recognizable by the
brightness of their two black eye-spots, on the surface of floating leaves of
Zostera. — The study of the Metamorphosis will be best prosecuted, how-
ever, by obtaining the fertilized eggs which are carried about by the
females, and watching the history of their products. — For preserving
specimens, whether of Entomostraca, or of larvae of the higher Crustacea,
the Author would recommend Glycerine-jelly as the best medium.

218

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XIX.

INSECTS AND AKACHNIDA.

616. There is no Class in the whole Animal Kingdom which affords
to the Microscopist such a wonderful variety of interesting objects, and
such facilities for obtaining an almost endless succession of novelties, as-
that of Insects. For, in the first place, the number of different kinds
that may be brought together (at the proper time) with extremely little
trouble, far surpasses that which any other group of animals can supply
to the most painstaking collector; then again, each specimen will afford,
to him who knows how to employ his materials, a considerable number
of Microscopic objects of very different kinds; and thirdly, although some
of these objects require much care and dexterity in their preparation, a
large proportion may be got out, examined, and mounted, with very little
skill or trouble. Take, for example, the common House-fly: — its eyes
may be easily mounted, one as a transparent, the other as an opaque object
(§ 626); its attennce, although not such beautiful objects as those of
many other Diptera, are still well worth examination (§ 628) ; its tongue
or 6 proboscis' (§ 629) is a peculiarly interesting object, though requiring
some care in its preparation ; its spiracles, which may be easily cut off
from the sides of its body, have a very curious structure (§ 635); its ali-
mentary canal affords a very good example of the minute distribution of
the tracliece (§ 634); its wing, examined in a living specimen newly come
forth from the pupa state, exhibits the circulation of the blood in the
'nervules' (§ 633), and when dead shows a most beautiful play of iri-
descent colors, and a remarkable areolation of surface, when examined
by light reflected from its surface at a particular angle (§ 638); its foot
has a very peculiar conformation, which is doubtless connected with its
singular power of walking over smooth surfaces in direct opposition to
the force of gravity, and on the action of which additional light has
lately been thrown (§ 640); while the structure and physiology of its
sexual apparatus, with the history of its development and metamorphoses,
would of itself suffice to occupy the whole time of an observer who should
desire thoroughly to work it out, not only for months but for years.1
Hence, in treating of this department in such a work as the present, the
Author labors under the embarras des richesses; for to enter into such a
description of the parts of the structure of Insects most interesting to
the Microscopist, as should be at all comparable in fulness with the
accounts which it has been thought desirable to give of other Classes,,
would swell out the volume to an inconvenient bulk; and no course
seems open, but to limit the treatment of the subject to a notice of the

1 See Mr. Lowne's valuable Treatise on " The Anatomy and Physiology of the
Blow-fly," 1870.

INSECTS AND ARACHNID A.

219

kinds of objects which are likely to prove most generally interesting,
with a few illustrations that may serve to make the descriptions more
clear, and with an enumeration of some of the sources whence a variety
of specimens of each class may be most readily obtained. And this
limitation is the less to be regretted, since there already exist in our
language numerous elementary treatises on Entomology, wherein the
general structure of Insects is fully explained, and the conformation of
their minute parts as seen with the Microscope is adequately illustrated.

617. A considerable number of the smaller Insects — especially those
belonging to the Orders Coleoptera (Beetles), Neuroptera (Dragon-fly,
May-fly, etc)., Hymenoptera (Bee, Wasp, etc.), and Diptera (two-winged
Flies) — may be mounted entire as opaque objects for low magnifying
powers; care being taken to spread out their legs, wings, etc., so as
adequately to display them, which may be accomplished, even after they
have dried in other positions, by softening them by stepping them in hot
water, or, where this is objectionable, by exposing them to steam. Full
directions on this point, applicable to small and large Insects alike, will
be found in all Text-books of Entomology. There are some, however,
whose translucence allows them to be viewed as transparent objects; and
these are either to be mounted in Canada balsam or in Deane's medium,
Glycerine-jelly, or Farrant's gum, according to the degree in which the
horny opacity of their integument requires the assistance of the balsam
to facilitate the transmission of light through it, or the softness and deli-
cacy of their textures render an aqueous medium more desirable. Thus,
an ordinary Flea or Bug will best be mounted in balsam; but the various
parasites of the Louse, kind, with some or other of which almost every
kind of animal is affected, should be set-up in some of the ' media.'
Some of the aquatic larvae of the Diptera and Neuroptera, which are so
transparent that their whole internal organization can be made-out with-
out dissection, are very beautiful and interesting objects when examined
in the living state, especially because they allow the Circulation of the
blood and the action of the dorsal vessel to be discerned (§ 632). Among
these, there is none preferable to the larva of the Ephemera marginata
(Day-fly), which is distinguished by the possession of a number of beauti-
ful appendages on its body and tail, and is, moreover, an extremely com-
mon inhabitant of our ponds and streams. This insect passes two or
even three years in its larval state, and during this time it repeatedly
throws-off its skin; the cast skin, when perfect, is an object of extreme
beauty, since, as it formed a complete sheath to the various appendages
of the body and tail, it continues to exhibit their outlines with the ut-
most delicacy; and by keeping these larvae in an Aquarium, and by
mounting trie entire series of their cast skins, a record is preserved of
the successive changes they undergo. Much care is necessary, however,
to extend them upon slides, in consequence of their extreme fragility;
and the best plan is to place the slip of glass under the skin whilst it is
floating on water, and to lift the object out upon the slide. — Thin sections
of Insects, Caterpillars, etc., which bring the internal parts into view in
their normal relations, maybe cut with the Microtome (§ 184), by first
soaking the body (as suggested by Dr. Halifax) in thick gum-mucilage,
which passes into its substance, and gives support to its tissues, and then
inclosing it in a casing of melted paraffin, made to fit the cavity of the
Section-instrument.

618. Structure of the Integument. — In treating of those separate parts
of the organization of Insects which furnish the most interesting objects

220

THE MICROSCOPE AND ITS REVELATIONS.

of Microscopic study, we may most appropriately commence with their
Integument and its appendages (scales, hairs, etc). The body and mem-
bers are closely invested by a hardened skin, which acts as their skeleton,
and affords points of attachment to the muscles by which their several
parts are moved; being soft and flexible, however, at the joints. This
skin is usually more or less horny in its texture, and is consolidated by
the animal substance termed Chitine, as well as, in some cases, by a sma.l
quantity of mineral matter. It is in the Coleoptera that it attains its
greatest development; the 6 dermo-skeleton ' of many Beetles being so firm
as not only to confer upon them an extraordinary power of passive resist-
ance, but also to enable them to put forth enormous force by the action
of the powerful muscles which are attached to it. It may be stated as a
general rule, that the outer layer of this dermo-skeleton is always cellular,
taking the place of an epidermis; and that the cells are straight-sided
and closely-fitted together, so as to be polygonal (usually hexagonal) in
form. Of this we have a very good example in the superficial layers
(Pig. 427, b) of the thin horny lamellae or blades which constitute the
terminal portion of the antenna of the Cockchafer (Fig. 426); this layer
being easily distinguished from the intermediate portion (a) of the lamina
by careful focussing. In many Beetles, the hexagonal areolation of the
surface is distinguishable when the light is reflected from it at a particu-
lar angle, even when not discernible in transparent sections. The integu-
ment of the common Red Ant exhibits the hexagonal cellular arrangement
very distinctly throughout; and the broad flat expansion of the leg of
the Crabro (' sand-wasp ') affords another beautiful example of a distinctly-
cellular structure in the outer layer of the integument. The inner layer,
however, which constitutes the principal part of the thickness of the
horny casing of the Beetle-tribe, seldom exhibits any distinct organiza-
tion; though it may be usually separated into several lamellae, which are
sometimes traversed by tubes that pass into them from the inner surface,
and extend towards the outer without reaching it.

619. Tegumentary Appendages.- — The surface of Insects is often
beset, and is sometimes completely covered, with appendages, having
either the form of broad flat Scales, or that of Hairs more or less
approaching the cylindrical shape, or some form intermediate between
the two. — The scaly investment is most complete among the Lepidoptera
(Butterfly and Moth tribe); the distinguishing character of the insects
of this order being derived from the presence of a regular layer of
scales upon each side ot their large membranous wings. It is to the
peculiar coloration of the scales that the various hues and figures are
due, by which these wings are so commonly distinguished; all the scales
of one patch (for example) being green, those of another red, and so on:
for the subjacent membrane remains perfectly transparent and colorless,
when the scales have been brushed off from its surface. Each scale
seems to be composed of two or more membranous lamellae, often with
an intervening deposit of pigment, on which, especially in Lepidoptera,
their color depends. Certain scales, however, especially in the Beetle-
tribe, have a metallic lustre, and exhibit brilliant colors that vary with
the mode in which the light glances from them; and this ' iridescence/
which is specially noteworthy in the scales of the Curculio imperialis
('diamond-beetle '), seems to be a purely optical effect, depending
either (like the prismatic hues of a soap-bubble) on the extreme thinness
of the membranous lamellae, or (like those of 'mother-of-pearl/ § 565)
on a lineation of surface produced by their corrugation. Each scale is

INSECTS AND ARACHNIDA.

221

furnished at one end with a sort of handle or f pedicle ? (Figs. 414, 415),
by which it is fitted into a minute socket attached to the surface of the
insect; and on the wings of Lepidoptera these sockets are so arranged
that the scales lie in very regular rows, each row overlapping a portion
of the next, so as to give to their surface, when sufficiently magnified,
very much the appearance of being tiled like the roof of a house. Such
an arrangement is said to be ' imbricated.7 The forms of these scales are
often very curious, and frequently differ a good deal on the several parts
of the wings and of the body of the same individual; being usually more
expanded on the former, and narrower and more hair-like on the latter.
A peculiar type of scale, which has been distinguished by the designation
plumule, is met with among the Pieridce, one of the principal families
of the Diurnal Lepidoptera. The 6 plumules ' are not flat, but cylin-
drical or bellows-shaped, and are hollow; they are attached to the wing
by a bu]b, at the end of a thin elastic peduncle that differs in length in
different species, and proceeds from the broader, not from the narrower
end of the scale; whilst the free extremity usually tapers off, and ends
in a kind of brush, though sometimes it is broad and has its edge fringed
with minute filaments. These ' plumules/ which are peculiar to the
males, are found on the upper surface of the wings, partly between and
partly under the ordinary scales. They seem to be represented among
the Lyccenidce by the ' battledore ' scales to be presently described
(§621).' . . .

620. The peculiar markings exhibited by many of these Scales, very
early attracted the attention of Opticians engaged in the application of
Achromatism to the Microscope (§ 15); for, as the clearness and strength
with which they could be shown, were found to depend on the degree to
which the angular aperture of an Objective could be opened without sac-
rifice of perfect correction for spherical and chromatic aberration, such
scales proved very serviceable as ' tests.7 The Author can well remember
the time when those of Morpho menelaus (Fig. 414), the ordinary and
6 battledore7 scales of the Polyommatus argus (Figs. 415, 416), and the
scales of the Lepisma saccharina (Fig. 417), which are now only used
for testing Objectives of low or medium power (§ 159, I., n.), were the
recognized tests for objectives of high power; while the exhibition of
alternating light and dark bands on a Poctora-scale was regarded as a
first-rate performance. The resolution of these bands into the ' notes of
admiration 7 (Plate II., fig. 2) now clearly shown by every good 6 Stu-
dents 7 l-4th, marked the next step in advance; and though the intro-
duction of the Diatom-tests greatly promoted the enlargement of angular
aperture, yet the Author has the authority of the ablest constructors of
high-power Objectives in this county for stating, that they still regard
the Podura-scale as the best test for definition, and consequently for that
combination of qualities which is most required in Objectives to be used
for Biological investigations of the greatest difficulty (§ 158, vi.).a As
the real structure of this scale, of which the ' notes of admiration,7 or the
' exclamation-markings 7 constitute the optical expression, has been a
matter of much controversy, the question requires special consideration;

1 See Mr. Watson's Memoirs ' On the Scales of Battledore Butterflies/ in
" Monthly Microscopical Journal," Vol. ii., pp. 73, 314.

2 The Author is assured that it is by no means an uncommon experience, on
first putting together an Objective of wide aperture, to find it capable of resolv-
ing a difficult Diatom, whilst, when tested on a Podura-scale, it utterly fails, on
account of its imperfect ' definition.'

222

THE MICROSCOPE AND ITS REVELATIONS.

and in discussing it, regard should bo had to what we are taught by the
study of the larger and more strongly marked forms of Insect-scales, as
to what scales are. — That they are in reality flattened cells, analogous to
the Epidermic cells of higher animals (§ 671), can scarcely be doubted
by any Physiologist. Their ordinary flattening is simply the result of
their drying up; and the exception presented by the ' plumules 9 and
' battledore ' scales (Fig. 416), which have the two surfaces separated by
a considerable cavity, helps to prove the rule. It is perfectly clear in
some of these, that the membranous wall of the cell is strengthened by
longitudinal ribs, which diverge from the peduncle; as is particularly
well seen in the plumules of two West African butterflies, Pieris Aga-
thina and Pieris Phloris, in which the plumules are as much as l-300th
of an inch in length (large enough to be studied under the Binocular
Microscope), and are of cylindrical form, save that they are drawn in as

Fig. 414.

Fig. 415.

Fig. 416.

Scale of Morpho Menelaus. Scales of Pelyommatus argus (Azure- Battledore Scale of

blue);— a, battledore-scale; 6, inerfer- Polyommatus argus
ence striae. (Azure-blue).

if by a cord at about one-half or one-third of their length, the ribs
curving inwards to this constriction.1 In ordinary scales we find similar
ribs, sometimes running parallel to each other, or nearly so (Figs. 414,
415), and occasionally connected by distinct cross-bars (Pig. 418) but
sometimes diverging from the 'quill;' and where, as in Lepisma (Fig
417), the ribs are parallel on one surface and divergent on the other, a
very curious set of appearances is presented by their optical intersection
which throws considerable light on the meaning of the Podura-msxk-
mgs.

621. The easier test-scales are furnished by the order Lepidoptera
(Butterflies and Moths); and among the most beautiful of these, both
for color and for regularity of marking, are those of the Morpho Mene-
laus (Fig. 414). These are of a rich blue tint, and exhibit strong longi-

1 See Watson, loc. cit., p. 75.

INSECTS AND ARACHNIDA.

223

tudinal striae, which seem due to ribbed elevations of one of the superfi-
cial layers. There is also an appearance of transverse striation, which
cannot be seen at all with an inferior objective, but becomes very decided
with a good objective of medium focus; and this is found, when sub-
mitted to the test of a high power and good illumination, to depend
upon the presence of transverse thickenings or corrugations (Fig. 414),
probably on the internal surface of one of the membranes.— The large
scales of the Polyommatus argus (' azure-blue ' butterfly) resemble those
of the Menelaus in form and structure, but are more delicately marked
(Fig. 415). Their ribs are more nearly parallel than those of the
Menelaus scale, and do not show the same transverse striation. When
one of these scales lies partly over another, the effect of the optical inter-
section of the two sets of ribs at an oblique angle is to produce a set of
interrupted striations (£), very much resembling those of the Podura-
scale. The same Butterfly furnishes smaller scales, which are commonly
termed the ' battledore ' scales, from their resemblance in form to that
object (Fig. 415, a). These scales, which occur in the males of several
genera of the family Lyccenidce, and present a considerable variety of
shape,1 are marked by narrow longitudinal ribbings, which at intervals
seem to expand into rounded or oval elevations that give to the scales a
dotted appearance (Fig. 416); at the lower part of the scale, however,
these dots are wanting. Dr. Anthony describes and figures them as
elevated bodies, somewhat resembling dumb-bells or shirt-studs, ranged
along the ribs, and standing out from the general surface.2 Other good
observers, however, whilst recognizing the stud-like bodies described by
Dr. Anthony, regard them as not projecting from the external surface
of the scale, but as interposed between its two lamellae;3 and this view
seems to the author to be more conformable than Dr. Anthony's to gen-
eral probability.

622. The more difficult ' test-scales 9 are furnished by little wingless
insects ranked together by Latreille in the order Thysanura, but now
separated by Sir John Lubbock,4 on account of important differences in
internal structure, into the two groups Collembola and true Thysanura.
Of the former of these, the Lepismidm constitute the typical family; and
the scale of the common Lepisma saccliarina, or 6 sugar-louse,5 very early
attracted the attention of Microscopists on account of its beautiful shell-
like sculpture. When viewed under a low magnifying power, it presents
a beautiful 6 watered silk ' appearance, which, with higher amplification,
is found to depend (as Mr. E. Beck first pointed out)6 upon the intersec-
tion of two sets of striae, representing the different structural arrange-
ments of its two superficial membranes. One of its surfaces (since ascer-
tained by Mr. Joseph Beck7 to be the under or attached surface of the

1 See Watson, loc. cit.

2 4 The Markings on the Battledore Scales of some of the Lepidoptera,' in
44 Monthly Microsc. Journal," Vol. vii. (1872), pp. 1, 250.

3 See 44 Proceedings of the Microscopical Society," op. cit., p. 278.

4 See his 44 Monograph of the Collembola and Thysanura" published by the
Kay Society, 1872.

5 This insect may be found in most old houses, frequenting damp warm cup-
boards, and especially such as contain sweets; it may be readily caught in a small
pill-box, which should have a few pin-holes in the lid; and if a drop of chloro-
form be put over the holes, the inmate will soon become insensible, and may be
then turned out upon a piece of clean paper, and some of its scales transferred to
a slip of glass by simply pressing this gently on its body.

6 44 The Achromatic Microscope," p. 50.

7 See his Appendix to Sir John Lubbock's 44 Monograph."

224

THE MICROSCOPE AND ITS REVELATIONS.

scale) is raised, either by corrugation or thickening, into a series of
strongly-marked longitudinal ribs, which run nearly parallel from one
end of the scale to the other, and are particularly distinct at its margins
and at its free extremity; whilst the other surface (the free or outer,
according to Mr. J. Beck) presents a set of less definite corrugations,
radiating from the pedicle, where they are strongest, towards the sides
and free extremity of the scale, and therefore crossing the parallel ribs at
angles more or less acute (Pig. 417). It was further pointed out by Mr.
K. Beck, that the intersection of these two sets of corrugations at differ-
ent angles produces most curious effects upon the appearances which
optically represent them. For where the diverging ribs cross the longi-
tudinal ribs very obliquely, as they do near the free extremity of the

Fig. 417. • Fig. 418.

Scale of Lepisma saccharina, [Scale of Machilis polypodia.

scale, the longitudinal ribs seem broken up into a series of ' exclamation-
markings/ like those of the Podura; but where the crossing is transverse
or nearly so, as at the sides of the scale, an appearance is presented as of
successions of large bright beads. The conclusion drawn by the Messrs.
Beck, that these interrupted appearances are "produced by two sets of
uninterrupted lines on different surfaces," has been confirmed by the
careful investigations of Mr. Morehouse.1 The minute beaded structure
observed by Dr. Koyston-Pigott2 alike in the ribs and in the intervening
spaces, may now be pretty certainly regarded as an optical effect of dif-
fraction (§ 156). In the scale of a type nearly allied to Lepisma, the
Macliilis polypoda, the very distinct ribbing (Pig. 418) is produced by the

1 " Monthly Microsc. Journal," Vol. xi. (1874), p. 13, and Vol. xviii. (1877),
p. 31.

2 "Monthly Microsc. Journ.," Vol. ix. (1873), p. 63.

INSECTS AND ARACHNID A.

225

corrugation of the under membranous lamina alone; the upper or exposed
lamina being smooth, with the exception of slight undulations near the
pedicle; and the cross-markings being due to structure between the super-
posed membranes, probably a deposit on the interior surface of one or
both of them.1

623. Although the Poduridce and Lepismidm now rank as distinct
Families, yet they approximate sufficiently in general organization, as
well as in habits, to justify the expectation that their scales would be
framed upon the same plan. The Poduridm are found amidst the saw-
dust of wine-cellars, in garden tool-houses, or near decaying wood; and
derive their popular name of ' spring-tails ' from the possession by many
of them of a curious caudal appendage, by which they can leap like fleas.
This is particularly well developed in the species now designated Lepido-
cyrtus curvicollis, which furnishes what are ordinarily known as ( Podura *-

Fig. 419. Fig. 420.

Test-scales of Lepidocyrtus curvicollis:— Ordinary scale of

a, large, strongly-marked scale: b, small Lepidocyrtus curvicollis,

scale, more faintly marked.

scales. "When full-grown and unrubbed," says Sir John Lubbock,
"this species is very beautiful, and reflects the most gorgeous metallic
tints. " Its scales are of different sizes and of different degrees of strength
of marking (Fig. 419, a, b), and are therefore by no means of uniform
value as tests. The general appearance of their surface, under a power
not sufficient to resolve their markings, is that of watered silk, — light
and dark bands passing across it with wavy irregularity; but a well-cor-
rected Objective of very moderate angular aperture now suffices to resolve
every dark band into a row of distinct ' exclamation marks' (Plate n.,
fig. 2). If, however, they are illuminated by oblique light from above
(the scales being placed under the objective without any cover, so as to
avoid the loss of light by reflection from its surface), the appearances
presented are those shown in fig. 4 when the markings are at right angles

1 See Mr. Joseph Beck, in Sir J. Lubbock's " Monograph," p. 255.
15

226

THE MICROSCOPE AND ITS REVELATIONS.

to the direction of the light, and in fig. 5 when they lie in the same direc-
tion as the light with their narrow ends pointing to it. When this last
direction is reversed, the light from the points is so slight, that the scales
appear to have lost their markings altogether. If moisture should insin-
uate itself between the scale and the covering-glass, the markings disap-
pear entirely, as shown in fig. 3; and this is true also of the scale of
Lepisma. A certain longitudinal continuity may be traced between the
6 exclamation-marks 9 in the ordinary test-scale; but this is much more
apparent in other scales from the same species (Fig. 420), as well as in
the scales of various allied types, which were carefully studied by the late
Mr. R. Beck.1 In certain other types, indeed, the scales have very dis-
tinct longitudinal parallel ribs, sometimes with regularly disposed cross-
bars; these ribs, being confined to one surface only (that which is in con-
tact with the body), are not subject to any such interference with their
optical continuity as has been shown to occur in Lepisma; but more or
less distinct indications of radiating corrugations often present them-
selves. The appearance of the interruptod ' exclamation-marks ' Mr. J.
Beck (op. cit., p. 254) considers to be due "to irregular corrugations of
the outer surface of the under membrane, to slight undulations on the
outer surface of the upper membrane, and to structure between the super-
posed membranes." It has been recently stated by Mr. Joseph Beck,
that the scales of a Lepidopterous insect belonging to the genus Mormo,
which under a low power present the watered-silk appearance seen in the
Podura-scale, under a l-5th show the 6 exclamation ' markings, whilst
under a l-10th they exhibit distinct ribs from pedicle to apex; thus show-
ing in one scale how the appearances run from one scale into the other.2
On the other hand, we are assured by Dr. Royston-Pigott, not only that
what a lens most perfectly corrected for spherical aberration ought to show,
is a minute beaded structure, alike in the 6 exclamation-markings 9 and in
the spaces between them; but that the markings whose perfect definition
had been previously considered the aim of all constructors of high-power
Objectives, are altogether illusory, these markings representing nothing
else than the manner in which the rouleaux of beads lie with reference
to one another.3 The Author has fully satisfied himself by his own
study, under an oil-immersion l-25th of Messrs. Powell and Lealand, of
a Podura-scale illuminated by the ' immersion paraboloid 9 (which gives
a view of it entirely different than any that can be obtained either by
transmitted or reflected light), that the 4 exclamation-markings 9 are — as
maintained by the Messrs. Beck — the optical expression of a corrugated
or ribbed arrangement of the lower membrane of the scale, slightly
modified by the internal structure of the upper membrane, and probably
also (as confirmed by Mr. Wenham) by a structure interposed between
the two membranes.4 And this conclusion is borne out, in opposition to
the doctrine of Dr. Royston Pigott, by two unrivalled Photographs taken
of the Podura-scale by Col. Dr. Woodward. One of these, taken with a
magnifying power of 3200 diameters, central monochromatic light, im-
mersion l-16th, and amplifier, shows the ' exclamation-marks 9 better

1 "Trans, of Microsc. Soc.," N.S., Vol. x. (1862), p. 83. See also Mr. Joseph
Beck, in the Appendix to Sir John Lubbock's "Monograph," and in "Monthly
Microsc. Journ.," Vol. iv., p. 253.

2 "Journ. Roy. Microsc. Soc," Vol. ii. (1879), p. 810.

3 See his paper 'On High Power Definition,' in " Monthly Microscopical Jour-
nal," Vol. ii. (1869), p. 295, and several subsequent papers.

4 " Monthly Journ. of Microsc. Sci.," Vol. xi. (1874), p. 75.

INSECTS AND ARACHNIDA.

227

than any photographic representation previously obtained; and it is clear
that Dr. Woodward regards this as the truest view. " Immediately after-
wards/'he says, "with the same optical combination and magnifying
power, without any change in the cover-correction, by simply rendering
the illuminating pencil oblique, and slightly withdrawing the objective
from its first focal position, I obtained a negative which displays the
' bead-like 9 or varicose appearance of the ribbing more satisfactorily than
I had previously been able to do."1 The beaded appearance shown in
this photograph, a copy of a portion of which is given in Fig. 421, cor-
responds so entirely with that which Dr. Woodward afterwards found to
be producible in the scale of the Gnat by a like alteration in the illumina-
tion (§ 156), that the Author feels fully justified in adhering to his ori-
ginal opinion that it does not represent real structure, but is an optical
effect of diffraction.2

624. The Hairs of many Insects, and still more of their larvae, are
very interesting objects for the microscope, on account of their branched
or tufted conformation: this being particularly remarkable in those

Fig. 421.

Portion of a Podura-scale, from a Photograph by Col. Dr. Woodward.

with which the common hairy Caterpillars are so abundantly beset.
Some of these afford very good tests for the perfect correction of Objec-
tives. Thus the hair of the Bee is pretty sure to exhibit. strong prismatic
colors, if the Chromatic aberration should not have been exactly neutral-
ized; and that of the larva of a Dermestes (commonly but erroneously
termed the i bacon-beetle5) was once thought a very good test of defining
power, and is still useful for this purpose. It has a cylindrical shaft
(Fig. 422, b) with closely-set whorls of spiny protuberances, four or five;

1 44 Monthly Microscopical Journal," Vol. v., p. 246.

2 The successive Volumes of the ' 4 Monthly Microscopical Journal," from the
2d (in which Dr. Royston-Piggott's views were first promulgated) to the present
date, teem with Papers on this subject from Mr. Jos. Beck, Mr. Mclntire, Dr.
Maddox, Dr. Royston-Pigott, Mr. Wenham, and Col. Dr. Woodward; which,
with a Paper by Mr. Slack in 44 The Student," Vol. v., p. 49, and a Paper by Mr.
Morehouse, giving the results of his examination of the scales of Lepisma and
Podura as opaque objects, under very high immersion objectives, with Beck's
Vertical Illuminator (44 Monthly Microsc. Journ.," Vol. xviii., 1877, p. 31), should
be consulted by such as wish to follow out the inquiry.

228

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 422.

in each whorl; the highest of these whorls is composed of mere knobby
spines: and the hair is surmounted by a curious circle of six or seven large
filaments, attached by their pointed ends to its shaft, whilst at their free
extremities they dilate into knobs. An approach to this structure is seen
in the hairs of certain Myriapods (centipedes, gally-worms, etc.), of
which an example is shown in Fig. 422, a; and some minute forms of this
class are most beautiful objects under the Binocular Microscope, on ac-
count of the remarkable structure and regular arrangement of their hairs.

625. In examining the Integument of Insects, and its appendages,
parts of the surface maybe viewed either by reflected or transmitted light,
according to their degree of transparence and the nature of their cover-
ing. The Beetle and Butterfly tribes furnish the greater number of the
specimens suitable to be viewed as opaque objects: and nothing is easier
than to mount portions of the elytra of the former
(which are usually the most showy parts of their
bodies), or of the wings of the latter, in the manner
described in § 175. The tribe of Ciircidionidce, in
which the surface of the body is beset with scales hav-
ing the most varied and lustrous hues, is distinguished
among Coleoptera for the brilliancy of the objects
it affords; the most remarkable in this respect being
the well-known Curcitlio imperialis, or ' diamond-
beetle 9 of South America, parts of whose elytra,
when properly illuminated and looked-at with a low
power, show like clusters of jewels flashing against
a dark velvet ground. In many of the British Cur-
culionidae, which are smaller and less brilliant, the
scales lie at the bottom of little depressions of the
surface; and if the elytra of the 6 diamond beetle ' be
carefully examined, it will be found that each of the
clusters of scales which are arranged upon it in rows,
seems to rise out of a deep pit which sinks-in by its
side. The transition from Scales to Hairs is" ex-
tremely well seen by comparing the different parts
of the surface of the diamond-beetle with each other.
The beauty and brilliancy of many objects of this
kind are increased by mounting them in cells in
Canada balsam, even though they are to be viewed
with reflected light; other objects, however, are ren-
dered less attractive by this treatment; and in order
to ascertain whether it is likely to improve or to
deteriorate the specimen, it is a good plan first to test some other portion
of the body having scales of the same kind, by touching it with turpen-
tine, and then to mount the part selected as an object, either in balsam
or dry, according as the turpentine increases or diminishes the brilliancy
of the scales on the spot to which it was applied. Portions of the wings
of Lepidoptera are best mounted as opaque objects, without any other
preparation then gumming them flat down to the disk of the wooden
slide (§ 175); care being taken to avoid disturbing the arrangement of the
scales, and to keep the objects, when mounted, as secluded as possible
from dust. In selecting such portions, it is well to choose those which
have the brightest and the most contrasted colors, exotic butterflies being
in this respect usually preferable to British; and before attaching them to
slides, care should be taken to ascertain in what position, with

a, Hair of Myriapod.
B, Hair of Dermestes.

INSECTS AND ARACHNIDA.

229

the arrangement of light ordinarily used, they are seen to the best
advantage, and to fix them there accordingly. — Whenever portions of the
integument of Insects are to be viewed as transparent objects, for the
display of their intimate structure, they should be mounted in Canada
balsam, after soaking for some time in turpentine; since this substance
has a peculiar effect in increasing their translucence. Not only the
horny casings of perfect Insects of various orders, but also those of their
pupae, are worthy of this kind of study; and objects of great beauty (such
as the chrysalis case of the Emperor-moth), as well as of scientific
interest, are sure to reward such as may prosecute it with any assiduity.
Further information may often be gained by softening such parts in
potash, and viewing them in fluid. — The scales of the wings of Lepidop-
tera, etc., are best transferred to the slide, by simply pressing a portion
of the wing either upon the slip of glass or upon the cover; if none should
adhere, the glass may first be gently breathed-on. Some of them are best
seen when examined 1 dry,' whilst others are more clear when mounted in
fluid; and for the determination of their exact structure, it is well to have

recourse to both these methods. Hairs, on the other hand, are best
mounted in Balsam.

626. Parts of the Head. — The eyes of Insects, situated upon the upper
and outer part of the head, are usually very conspicuous organs, and are
frequently so large as to touch each other in front (Fig. 423). We find
in their structure a remarkable example of that multiplication of similar
parts, which seems to be the predominating 'idea' in the conformation
of Articulated animals; for each of the large protuberant bodies which
we designate as an eye, is really a ' compound ' eye, made up of many
hundred or even many thousand minute conical ocellites (b). Approaches
to this structure are seen in Annelida and Entomastraca; but the number
of ' ocellites' thus grouped-together is usually small. In the higher
Crustacea, however, the 6 ocellites ' are very numerous; and their com-
pound eyes are constructed upon the same general plan as those of In-
sects, though their shape and position are often very peculiar (Fig. 491).
The individual ocellites are at once recognized, when the 6 compound

Fig. 423.

Fig. 424.

Head and Compound Eyes of the Bee,
showing the ocellites in situ on one side (a),
and displaced on the other (b) ; a, a, a, stem-
mata, b,b, antennas.

Section of the Composite Eye of
Melolontha vulgaris (Cockchafer):
— a, facets of the cornea; 6, trans-
parent pyramids surrounded with
pigment; c, fibres of the optic nerve;
d, trunk of the optic nerve.

230

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 425.

eyes ' are examined under even a low magnifying power, by the 6 facetted f
appearance of the surface (Fig. 423, a), which is marked-out by very
regular divisions either into hexagons or into squares: each facet is the
'corneule 9 of a separate ocellite, and has a convexity of its own; hence by
counting the facets, we can ascertain the number of ocellites in each ' com-
pound eye.' In the two eyes of the common Fly, there are as many as
4,000; in those of the Cabbage Butter-fly there are about 17,000; in the
Dragon-fly, 24,000; and in the Mar delta Beetle, 25,000. Behind each
f corneule ' is a layer of dark pigment, which takes the place and serves
the purpose of the 'iris' in the eyes of vertebrate animals; and this is
perforated by a central aperture or c pupil/ through which the rays of
light that have traversed the corneule gain access to the interior of the
eye. The further structure of these bodies is best examined by vertical
sections (Fig. 424); and these show that the shape of each ocellite (b) is
conical, or rather pyramidal, the corneule forming its base (a), whilst its
apex abuts upon the extremity of a fibre (c) proceed-
ing from the termination of the optic nerve (d). The
details of the structure of each ocellite are shown in
Fig. 425; in which it is shown that each corneule is
a double-convex lens, made up by the junction of two-
plano-convex lenses, a a and a' a', which have been
found by Dr. Hicks to possess different refractive-
powers; by this arrangement (it seems probable) the-
aberrations are diminished, as they are by the combina-
tion of 6 humors ' in the Human eye. That each ' cor-
neule 9 acts as a distinct lens, may be shown by de-
taching the entire assemblage by maceration, and then
drying it (flattened out) upon a slip of glass; for when
this is placed under the Microscope, if the point of a-
knife, scissors, or any similar object, be interposed
between the mirror and the stage, the image of this
point will be seen, by a proper adjustment of the focus-
of the microscope, in every one of the lenses. The
focus of each ' corneule 9 has been ascertained by;
experiment to be equivalent to the length of the pyra-
mid behind it; so that the image which it produces
will fall upon the extremity of the filament of
the optic nerve which passes to the latter. The
pyramids (b, b) consist of a transparent substance,,
which may be considered as representing the 6 vitreous humor;' and
they are separated from each other by a layer of dark pigment df d\
which closes-in at d d between their bases and the corneules, leaving &
set of pupillary apertures c, c, for the entrance of the rays which pass to>
them from the ' corneules.' After traversing these pyramids, the rays
reach the bulbous extremities e, e of the fibres of the optic nerve, which
are surrounded, like the pyramid, by pigmentary substance. Thus the
rays which have passed through the several ' corneules' are prevented
from mixing with each other; and no rays, save those which pass in the
axes of the pyramids, can reach the fibres of the optic nerve. Hence, it
is evident, that, as no two ocellites on the same side (Fig. 424) have ex-
actly the same axis, no two can receive their rays from the same point of
an object; and thus, as each compound eye is immovably fixed upon the
head, the combined action of the entire aggregate will probably only afford
but a single image, resembling that which toe obtain by means of our

Minute structure of
the Eye of the Bee:— a
a, anterior lenses of
corneule; a' a', its pos-
terior lenses; c c, pupil-
lary apertures, separat-
ed by intervening pig-
ment d d;bb% pyramids
separated by pigment
d' d\ and abutting on
e e, bulbous extremities
of nerve-fibres.

INSECTS AND ARACHNID A.

231

single eyes. — Although the foregoing may be considered as the typical
structure of the Eyes of Insects, yet there are various departures from it
(most of them slight) in the different members of the Class. Thus in
some cases the posterior surface of each 6 corneule ' is concave; and a space
is left between it and the iris-like diaphragm, which seems to be occupied
by a watery fluid or ' aqueous humor;' in other instances again, this space
is occupied by a double-convex body, which seems to represent the 1 crys-
talline-lens;' and this body is sometimes found behind the iris, the num-
ber of ocellites being reduced, and each one being larger, so that the
cluster presents more resemblance to that of Spiders, etc. — Besides their
' compound ' eyes, Insects usually possess a small number of < simple '
eyes (termed ocelli or stemmata) seated upon the top of the head (Fig.
423, a, a, a). Each of these consists of a single very convex corneule; to
the back of which proceeds a bundle of rods that are in connection with
fibrils of the optic nerve. Such ocelli are the only visual organs of the
Larvae of insects that undergo complete metamorphosis; the 6 compound '
eyes being only developed towards the end of the Pupa-stage.1

627. Various modes of preparing and mounting the Eyes of Insects
may be adopted, according to the manner wherein they are to be viewed.
For the observation of their external facetted surface by reflected light,
it is better to lay down the entire head, so as to present a front-face or
a side-face, according to the position of the eyes; the former giving a
view of both eyes, when they approach each other so as nearly or quite
to meet (as in Fig. 423); whilst the latter will best display one, when the
eyes are more situated at the sides of the head. For the minuter examina-
tion of the 'corneules/ however, these must be separated from the hemi-
spheroidal mass whose exterior they form, by prolonged maceration; and
the pigment must be carefully washed away, by means of a fine camel-
hair brush, from the inner or posterior surface. In flattening them out
upon the glass-slide, one of two things must necessarily happen; either
the margin must tear when the central portion is pressed-down to a level;
or, the margin remaining entire, the central portion must be thrown into
plaits, so that its corneules overlap one another. As the latter condition
interferes with the examination of the structure much more than the
former does, it should be avoided by making a number of slits in the
margin of the convex membrane before it is flattened-out. Vertical sec-
tions, adapted to demonstrate the structure of the ocelli and their rela-
tions to the optic nerve, can be only made when the insect is fresh, or
or has been preserved in strong spirit. Mr. Lowne (loc. cit.) recommends
that the head should be hardened in a 2 per cent solution of chromic
acid, and then imbedded in cacoa-butter; the sections must be cut very
thin, and should be mounted in Canada balsam. The following are some
of the Insects whose eyes are best adapted for Microscopic preparations: —
Coleoptera, Cicindela, Dytiscus, Melolontha (Cockchafer), Lucanus (Stag-
beetle) ; — Orthoptera, Acheta (House and Field Crickets), Locusta; —
Hemiptera, Notonecta (Boat-fly); — Neuroptera, Libellula (Dragon-fly),
Agrion; — Hymenoptera, Vespidse (Wasps) and Apidse (Bees) of all kinds;
— Lepidoptera, Vanessa (various species of Butterflies), Sphinx ligustri
(Privet Hawk-moth), Bombyx (Silk-worm moth, and its allies); — Dip-
tera, Tabanus (Gad-fly), Asilus, Eristalis (Drone-fly), Tipula (Crane-fly),
Musca (House-fly), and many others.

1 For minute details as to the structure of the Eyes of Insects, see the admira-
ble Memoir by Mr. Lowne. in "Phil. Trans.," 1878, p. 577.

232

THE MICROSCOPE AND ITS REVELATIONS.

628. The Ante?inc&, which are the two jointed appendages arising from
the upper part of the head of Insects (Fig. 423, b b), present a most
wonderful variety of conformation in the several tribes of Insects; often
differing considerably in the several species of one genus, and even in the
two sexes of the same species. Hence the characters which they afford
are extremely useful in classification; especially since their structure
must almost necessarily be in some way related to the habits and general
economy of the creatures to which they belong, although our imperfect
acquaintance with their function may prevent us from clearly discerning
this relation. Thus among the Coleoptera we find one large family, in-
cluding the Glow-worm, Fire-fly, Skip-jack, etc., distinguished by the
toothed or serrated form of the antennae, and hence called Serricornes;
in another, of which the Burying-beetle is the type, the antennae are ter-
minated by a club-shaped enlargement, so that these beetles are termed

Fig. 426. Fig. 427.

Antenna of Melolontha (Cockchafer).

Clavicornes; in another, again, of which the Hydrophilus or large "Water-
beetle is an example, the antennae are never longer and are commonly
shorter than one of the pairs of palpi, whence the name of Palpicornes
is given to this group; in the very large family that includes the Lucani
or Stag-beetles with the Scarabm, of which the Cockchafer is the com-
monest example, the antennae terminate in a set of leaf-like appendages,
which are sometimes arranged like a fan or the leaves of an open book
(Fig. 426), are sometimes parallel to each other like the teeth of a comb,
and sometimes fold one over the other, thence giving the name Lamelli-
comes; whilst another large family is distinguished by the appellation
Longicornes, from the great length of the antennae, which are at least as
long as the body, and often longer. Among the Lepidoptera, again, the
conformation of the antennae, frequently enables us at once to distin-
^ guish the group to which any specimen belongs. As every treatise on
Entomology contains figures and descriptions of the principal types of

INSECTS AND ARACHNIDA.

233

conformation of tnese organs, there is no occasion here to dwell upon
them longer than to specify such as are most interesting to the Micro-
scopist: — Coleoptera, Brachinus, Calathus, Harpalus, Dytiscus, Staphyli-
nus, Philonthus, Elater, Lampyris, Silpha, Hydrophilus, Aphodius,
Melolontha, Cetonia, Curculio; — Ortlioptera, Forncula (Earwig), Blatta
(Cockroach) ; — Lepidoptera, Sphinges (Hawk-moth), and Nocturna
(Moths) of various kinds, the large ' plumed ' antennae of the latter being
peculiarly beautiful objects under a low magnifying power; — Diptera,
Culicidse (Gnats of various kinds), Tipulidae (Crane-flies and Midges),
Tabanus, Eristalis, and Muscidae (Flies of various kinds). All the larger
antennae, when not mounted € dry' as opaque objects, should be put up
in Balsam, after being soaked for some time in turpentine; but the small
feathery antennae of Gnats and Midges are so liable to distortion when
thus mounted, that it is better to set them up in fluid, the head with
its pair of antennae being thus preserved together when not too large. —
A curious set of organs has been recently discovered in the antennae of
many Insects, which have been supposed to constitute collectively an
apparatus for Hearing. Each consists of a cavity hollowed out in the
horny integument, sometimes nearly spherical, sometimes flask-shaped,
and sometimes prolonged into numerous extensions formed by the folding
of its lining membrane; the mouth of the cavity seems to be normally
closed-in by a continuation of this membrane, though its presence can-
not always be satisfactorily determined; whilst to its deepest part a nerve-
fibre may be traced. The expanded lamellae of the antennae of Melolontha
present a great display of these cavities, which are indicated in Fig. 427,
A, by the small circles that beset almost their entire area; their form,
which is very peculiar, can here be only made out by vertical sections; but
in many of the smaller antennae, such as those of the Bee, the cavities can
be seen sideways without any other trouble than that of bleaching the
specimen to render it more transparent.1

629. The next point in the organization of Insects to which the
attention of the Microscopist may be directed, is the structure of the
mouth. Here, again, we find almost infinite varieties in the details of
conformation; but these maybe for the most part reduced to a small
number of types or plans, which are characteristic of the different orders
of Insects. It is among the Coleoptera, or Beetles, that we find the
several parts of which the mouth is composed, in their most distinct
form; for although some of these parts are much more highly developed
in other Insects, other parts maybe so much altered or so little developed
as to be scarcely recognizable. The Coleoptera present the typical con-
formation of the mandibulate mouth, which is adapted for the prehen-
sion and division of solid substances; and this consists of the following
parts: — 1, a pair of jaws, termed mandibles, frequently furnished with

1 See the Memoir of Dr. Hicks 4 On a new Structure in the Antennae of Insects,'
in 44 Trans, of Linn. Soc," Vol. xxii., p. 147; and his 4 Further Remarks,' at p. 383 of
the same volume. See also the Memoir of M. Lespes, 4 Sur l'Appareil Auditif des
Insectes,' in 44 Ann. des Sci. Nat.," Ser. 4, Zool., Tom. ix;, p. 258; and that of M.
Claparede, 4 Sur les pretendus Organes Auditif s des coleopteres lamellicornes et
autres Insectes,' in 44 Ann. des. Sci. Nat.," Ser. 4, Zool., Tom. x., p. 236. Dr. Hicks
lays great stress on the 4 bleaching process,' as essential to success in this investi-
gation: and he gives the following directions for performing it: — Take of Chlorate
of Potass a drachm, and of Water a drachm and a half; mix these in a small wide
bottle containing about an ounce; wait five minutes, and then add about a drachm
and a half of strong Hydrochloric Acid. Chlorine is thus slowly developed; and
the mixture will retain its bleaching power for some time.

234

THE MICROSCOPE AND ITS REVELATIONS.

powerful teeth, opening laterally on either side of the mouth, and serv-
ing as the chief instruments of manducation; 2, a second pair of jaws,
termed maxillce, smaller and weaker than the preceding, beneath which
they are placed, and serving to hold the food, and to convey it to the back
of the mouth; 3, an upper lip, or labrum; 4, a lower lip or labium; 5,
one or two pairs of small jointed appendages termed palpi, attached to
the maxillae, and hence called maxillary palpi; 6, a pair of labial palpi.
The labium is often composed of several distinct parts; its basal portion
being distinguished as the mentum or chin, and its anterior portion being
sometimes considerably prolonged forwards, so as to form an organ which
is properly designated the ligida, but which is more commonly known as
the * tongue/ though not really entitled to that designation, the real
tongue being a soft and projecting organ which forms the floor of the

Fig. 428.

Tongue of common Fly:— a, lobes of ligula; b, portion inclosing the lancets, formed by the
metamorphosis of the maxillae; c, maxillary palpi: — a, portion of one of the pseudotracheae
enlarged.

mouth, and which is only found as a distinct part in a comparatively
small number of Insects, as the Cricket. — This ligula is extremely devel-
oped in the Fly kind, in which it forms the chief part of what is com-
monly called the ' proboscis 9 (Pig. 428) ;' and it also forms the c tongue'
of the Bee and its allies (Fig. 429). The ligula of the common Fly
presents a curious modification of the ordinary tracheal structure

1 The representation given in the figure is taken from one of the ordinary prep-
arations of the Fly's proboscis, which is made by slitting it open, flattening it out,
and mounting it in Balsam. For representations of the true relative positions of
the different parts of this wonderful organ, and for minute descriptions of them,
the reader is referred to Mr. Suffolk's Memoir ' On the Proboscis of the Blow-fly/
in ' 6 Monthly Microsc. Journ.," Vol. i.. p. 331; and to Mr. Lowne's Treatise on
" The Anatomy and Physiology of the Blow-fly," p. 41.

INSECTS AND ARACHNID A.

235

(§ 634), the purpose of which is not apparent; for instead of its tra-
cheae being kept pervious, after the usual fashion, by the winding of a
continuous spiral fibre through their interior, the fibre is broken into
rings, and these rings do not surround the whole tube, but are termi-
nated by a set of arches that pass from one to another (Fig. 428, a).1 —
In the Diptera or two-winged Flies generally, the labrum, maxillae,
mandibles, and the internal tongue (where it exists) are converted into
delicate lancet-shaped organs termed setce, which, when closed-together,
are received into a hollow on the upper side of the labium (Fig. 428, 5),
but which are capable of being used to make punctures in the skin
of Animals or the epidermis of Plants, whence the juices may be drawn
forth by the proboscis. Frequently, however, two or more of these
organs may be wanting, so that their
number is reduced from six, to four, fig.429.
three, or two. — In the Hymenoptera (Bee
and Wasp tribe), the labrum and the
mandibles (Fig. 429, J) much resemble
those of Mandibulate Insects, and are
used for corresponding purposes; the
maxillae (c) are greatly elongated, and
form, when closed, a tubular sheath
for the Ligida or 'tongue/ through
which the honey is drawn up; the labial
palpi (cl) also are greatly developed,
and fold together, like the maxillae, so
as to form an inner sheath for the
'tongue;' while the 'ligula' itself (e)
is a long tapering muscular organ,
marked by an immense number of short
annular divisions, and densely covered
over its own length with long hairs (b).
It is not tubular, as some have stated,
but is solid; when actively employed in
taking food, it is extended to a great
distance beyond the other parts of the
mouth; but when at rest it is closely
packed-up and concealed between the
maxillae. ' ' The manner," says Mr. New-
port, "in which the honey is obtained
when the organ is plunged into it at the bottom of a flower, is by e lapping/
or a constant succession of short and quick extensions and contractions of
the organ, which occasion the fluid to accumulate upon it and to ascend
along its upper surface, until it reaches the orifice of the tube formed by
the approximation of the maxillae above, and of the labial palpi and this
part of the ligula below."

630. By the plan of conformation just described, we are led to that

1 According to Dr. Anthony (" Monthly Micros. Journ.," Vol. xi., p. 242), these
* pseudo-tracheae ' are suctorial organs, which can take-in liquid alike at their ex-
tremities and through the whole length of the fissure caused by the interruption
of the rings; the edges of this fissure being formed by the alternating series of
4 ear-like appendages,' connected with the terminal 4 arches,' the closing- together
of which converts the pseudo-trachea into a complete tube. Dr. A. considers
each of these ear-like appendages to be a minute sucker, 44 either for the adhesion
of the fleshy tongue, or for the imbibition of fluids, or perhaps for both purposes."
— The point is well worthy of further investigation.

a, Parts of the Mouth of Apis mellifica
(Honey-bee):— a, mentum; o, mandibles;
c, maxilko; d, labial palpi; e, ligula, or
prolonged labium, commonly termed the
tongue:— b, portion of the surface of the
ligula, more highly magnified.

236

THE MICROSCOPE AND ITS REVELATIONS.

which prevails among the Lepidoptera or Butterfly tribe, and which,
being pre-eminently adapted for suction, is termed the hanstellate mouth.
In these Insects, the labrum and mandibles are reduced to three minute
triangular plates; whilst the maxillae are immensely elongated, and are
united together along the median line to form the haustellium or true
'proboscis,' which contains a tube formed by the junction of the two
grooves that are channelled out along their mutually applied surfaces,
and which serves to pump-up the juices of deep cup-shaped flowers, into
which the size of their wings prevents these insects from entering. The
length of this haustellium varies greatly: thus in such Lepidoptera as
take no food in their perfect state, it is a very insignificant organ; in
some of the white Hawk-moths, which hover over blossoms without
alighting, it is nearly two inches length; and in most Butterflies and
Moths it is about as long as the body itself. This ' haustellium,' which,
when not in use, is coiled- up in a spiral beneath the mouth, is an extremely
beautiful Microscopic object, owing to the peculiar banded arrangement
it exhibits (Fig. 430), which is probably due to the disposition of its mus-
cles. In many instances, the two halves may be seen to be locked together

Fig. 430.

Haustellium (proboscis) of Vanessa.

by a set of hooked teeth, which are inserted into little depressions between
the teeth of the opposite side. Each half, moreover, may be ascertained
to contain a trachea or air-tube (§ 634); and it is probable, from the
observations of Mr. Newport, that the sucking-up of the juices of a
flower through the proboscis (which is accomplished with great rapidity)
is effected by the agency of the respiratory apparatus. The proboscis of
many Butterflies is furnished, for some distance from its extremity, with
a double row of small projecting barrel-shaped bodies (shown in Pig.
430), which are surmised by Mr. Newport (whose opinion is confirmed
by the kindred inquiries of Dr. Hicks, § 628) to be organs of taste. —
Numerous other modifications of the structure of the mouth, existing in
the different tribes of Insects, are well worthy of the careful study of the
Microscopist; but as detailed descriptions of most of these will be found
in every Systematic Treatise on Entomology, the foregoing general ac-
count of the principal types must suffice.

631. Parts of the Body. — The conformation of the several divisions
of the alimentary cayial presents such a multitude of diversities, not only

INSECTS AND ARACHNID A.

237

in different tribes of Insects, but in different states of the same individual,
that it would be utterly vain to attempt here to give even a general idea of it;
more especially as it is a subject of far less interest to the ordinary Micro-
scopist, than to the professed Anatomist. Hence we shall only stop to
mention that the 6 muscular gizzard ' in which the oesophagus very com-
monly terminates, is often lined by several rows of strong horny teeth for
the reduction of the food, which furnish very beautiful objects, espe-
cially for the Binocular. These are particularly developed among the
Grasshoppers, Crickets, and Locusts, the nature of whose food causes
them to require powerful instruments of its reduction.

632. The Circulation of Blood may be distinctly watched in many
of the more transparent larvae, and may sometimes be observed in the
perfect insect. It is kept up, not by an ordinary heart, but by a 6 dorsal
vessel' (so named from the position it always occupies along the middle
of the back), which really consists of a succession of muscular hearts or
contractile cavities, one for each segment, opening one into another from
behind forwards, so as to form a continuous trunk divided by valvular
partitions. In many larvae, however, these partitions are very indistinct;
and the walls of the ' dorsal vessel ' are so thin and transparent, that it
can with difficulty be made-out, a limitation of the light by the dia-
phragm being often necessary. The blood which moves through this
trunk, and which is distributed by it to the body, is a transparent and
nearly-colorless fluid, carrying with it a number of 'oat shaped 9 corpus-
cles, by the motion of which its flow can be followed. The current enters
the ' dorsal vessel ' at its posterior extremity, and is propelled forwards
by the contractions of the successive chambers, being prevented from
moving in the opposite direction by the valves between the chambers,
which only open forwards. Arrived at the anterior extremity of the ' dor-
sal vessel/ the blood is distributed in three principal channels; a central
one, namely, passing to the head, and a lateral one to either side; de-
scending so as to approach the lower surface of the body. It is from the
two lateral currents that the secondary streams diverge, which pass into
the legs and wings, and then return back to the main stream; and it is
from these also, that, in the larva of the Ephemera marginata (Day-fly),
the extreme transparence of which renders it one of the best of all sub-
jects for the observation of Insect Circulation, the smaller currents diverge
into the gill-like appendages with which the body is furnished (§ 636).
The blood-currents seem rather to pass through channels excavated among
the tissues, than through vessels with distinct walls; but it is not improb-
able that in the perfect Insect the case may be different. In many aqua-
tic larvae, especially those of the Culicidce (Gnat tribe), the body is almost
entirely occupied by the visceral cavity; and the blood may be seen to
move backwards in the space that surrounds the alimentary canal, which
here serves the purpose of the channels usually excavated through the
solid tissues, and which freely communicates at each end with the 6 dor-
sal vessel. ' This condition strongly resembles that found in many Anne-
lida.1

633. The circulation may be easily seen in the wings of many Insects
in their pupa state, especially in those of the Neuroptera (such as Dragon-
flies, and Day-flies), which pass this part of their lives under water in a

*See the Memoirs on Corethra plumicornis, bv Prof. Rymer Jones, in ' * Trans-
act, of Microsc. Soc," N.S., Vol. xv. (1867), p. 99; by Prof. E. Ray Lankester, in
the " Popular Science Review" for October, 1865; and by Dr. A. Weissmann, in
"Siebold and Kolliker's Zeitschrift," Bd. xvi., p. 45.

238

THE MICROSCOPE AND ITS REVELATIONS.

condition of activity; the pupa of Agrion paella, one of the smaller dra-
gon-flies, being a particularly favorable subject for such observations.
Each of the 'nervures* of the wings contains a 6 trachea' or air-tube (§
634), which branches-off from the trached system of the body; and it is
in a space around the trachea that the blood may be seen to move, when
the hard framework of the nervure itself is not too opaque. The same
may be seen, however, in the wings of pupa3 of Bees, Butterflies, etc.,
which remain shut-up motionless in their cases; for this condition of
apparent torpor is one of great activity of their nutritive system, — those
organs, especially, which are peculiar to the perfect Insect, being then
in a state of rapid growth, and having a vigorous circulation of blood
through them. In certain insects of nearly every order, a movement of
fluid may be seen in the wings for some little time after their last meta-
morphosis; but this movement soon ceases, and the wings dry-up. The
common Fly is as good a subject for this observation as can be easily
found; it must he caught within a few hours or days of its first appear-
ance; and the circulation maybe most conveniently brought into view by
inclosing it (without water) in the aquatic box, and pressing-down the
cover sufficiently to keep the body at rest without doing it any injury.

634. The Respiratory apparatus of Insects affords a very interesting
series of Microscopic objects; for, with great uniformity in its general
plan there is almost infinite variety in its details. The aeration of the
blood in this class is provided-for, not by the transmission of the fluid to
any special organ representing the lung of a Vertebrated animal (§ 692)
or the gill of a Mollusk (§ 586), but by the introduction of air into every
part of the body, through a system of minutely-distributed trachece or
air-tubes, which penetrate even the smallest and most delicate organs.
Thus, as we have seen, they pass into the haustellium or proboscis ' of
the Butterfly (§ 630), and they are minutely distributed in the elongated
labium or ' tongue ' of the Fly (Fig. 428). Their general distribution is
shown in Fig. 431; where we see two long trunks (f) passing from one
end of the body to the other, and connected with each other by a trans-
verse canal in every segment; these trunks communicate on the one hand,
by short wide passages, with the 6 stigmata/ ' spiracles/ or ' breathing
pores' (g), through which the air enters and is discharged; whilst they
give off branches to the different segments, which divide again and again
into ramifications of extreme minuteness. They usually communicate
also with a pair of air-sacs (h) which is situated in the thorax; but the
size of these (which are only found in the perfect Insect, no trace of them
existing in the larvae) varies greatly in different tribes, being usually
greatest in those insects which (like the Bee) can sustain the longest and
most powerful flight, and least in such as habitually live upon the ground
or upon the surface of the water. The structure of the air-tubes reminds
us of that of the 6 spiral vessels' of Plants, which seem destined (in part
at least) to perform a similar office (§ 362); for within the membrane
that forms their outer wall, an elastic fibre winds round and round, so as
to form a spiral closely resembling in its position and functions the spiral
wire-spring of flexible gas-pipes; within this again, however, there is
another membranous wall to the air-tubes, so that the spire winds between
their innner and outer coats. — When a portion of one of the great trunks
with some of the principal branches of the tracheal system has been dis-
sected-out, and so pressed in mounting that the sides of the tubes are
flattened against each other (as has happened in the specimen represented
in Fig, 432), the spire forms two layers which are brought into close

INSECTS AND ARACHNID A.

239

apposition; and a very beautiful appearance, resembling that of watered
silk, is produced by the crossing of the two sets of fibres, of which one
overlies the other. That this appearance, however, is altogether an opti-
cal illusion, may be easily demonstrated by carefully following the course
of any one of the fibres, which will be found to be perfectly regular.

Fig. 431. Fig. 432.

one of the stigmata; h, air-sac.

Spiracle of Common Fly.

635. The i stigmata ' or 6 spiracles ' through which the air enters the
tracheal system, are generally visible on the exterior of the body of the
insect (especially on the abdominal segments) as a series of pores along
each margin of the under surface. In most larvae, nearly every segment
is provided with a pair; but in the perfect insect several of them remain
closed, especially in the thoracic region, so that their number is often
considerably reduced. The structure of the spiracles varies greatly in re-
gard to complexity in different insects; and even wrhere the general plan is
the same, the details of conformation are peculiar, so that perhaps in
scarcely any two species are they alike. Generally speaking they are fur-
nished with some kind of sieve at their entrance, by which particles of

240

THE MICROSCOPE AND ITS REVELATIONS.

dust, soot, etc., which would otherwise enter the air-passages, are filtered
out; and this sieve may be formed by the interlacement of the branches
of minute arborescent growths from the border of the spiracle, as in the
common Fly (Fig. 433), or in the Dytiscus; or it may be a membrane
perforated with minute holes, and supported upon a framework of bars
that is prolonged in like manner from the thickened margin of the aper-
ture (Fig. 434), as in the larva of the Melolontha (Cockchafer). Not
unfrequently, the centre of the aperture is occupied by an impervious
disk, from which radii proceed to its margin, as is well seen in the spira-
cle of Tipula (Crane-fly). — In those aquatic Larvae which breathe air,
we often find one of the spiracles of the last segment of the abdomen
prolonged into a tube, the mouth of which remains at the surface while the
body is immersed; the larvae of the Gnat tribe may frequently be observed
in this position.

636. There are many aquatic Larvae, however, which have an entirely-
different provision for respiration; being furnished with external leaf -like
or brush-like appendages into which the tracheae are prolonged, so that,

by absorbing air from the water that
bathes them, they may convey this into
the interior of the body. We cannot have
a better example of this than is afforded
by the larva of the common Ephemera
(Day-fly), the body of which is furnished
with a set of branchial appendages resem-
bling the 6 fin-feet * of Branchiopods (§
603), whilst the three-pronged tail also
is fringed with clusters of delicate hairs
which appear to minister to the same
function. In the larva of the Libellula
(Dragon-fly), the extension of the surface
for aquatic respiration takes place with-
Spiracie of Larva of Cockchafer. in the termination of the intestine;

the lining membrane of which is folded
into an immense number of plaits, each containing a minutely ramified
system of tracheae; the water, slowly drawn-in through the anus for
bathing this surface, is ejected with such violence that the body is
impelled in the opposite direction; and the air taken-up by its tracheae
is carried, through the system of the air-tubes of whicli they form-part,
into the remotest organs. This apparatus is a peculiarly interesting
object for the Microscope, on account of the extraordinary copiousness
of the distribution of the tracheae in the intestinal folds.

637. The main trunks of the tracheal system, with their principal
ramifications, may generally be got-out with little difficulty, by laying-
open the body of an Insect or Larva under water in a Dissecting-trough
(§ 180), and removing the whole visceral mass, taking care to leave as
many as possible of the branches which will be seen proceeding to this
from the two great longitudinal tracheae, to whose position these branches
will serve as a guide. Mr. Quekett recommends the following as the
most simple method of obtaining a perfect system of tracheal tubes from
a larva: — a small opening having been made in its body, this is to be
placed in strong acetic acid, which will soften or decompose all the vis-
cera; and the tracheae may then be well-washed with the syringe, and
removed from the body with the greatest facility, by cutting away the
connections of the main tubes with the spiracles by means of fine pointed

INSECTS AND ARACHNID A.

241

scissors. In order to mount them, they should be floated upon the slide,
on which they should then be laid-out in the position best adapted for
displaying them. If they are to be mounted in Canada balsam, they
should be allowed to dry upon the slide, and should then be treated in
the usual way; but their natural appearance is best preserved by mount-
ing them in fluid (weak spirit or Goadby's solution), using a shallow cell
to prevent pressure. The finer ramifications of the tracheal system may
generally be seen particularly well in the membranous wall of the stom-
ach or intestine; and this, having been laid-out and dried upon the
glass, may be mounted in balsam so as to keep the tracheae full of air
(whereby they are much better displayed), if care be taken to use balsam
that has been previously thickened, to drop this on the object without
liquefying it more than is absolutely necessary, and to heat the slide and
the cover (the heat may be advantageously applied directly to the cover,
after it has been put-on, by turning-over the slide so that its upper face
shall look downward) only to such a degree as to allow the balsam to
spread and the cover to be pressed-down. — The spiracles are easily dis-
sected-out by means of a pointed knife or a pair of fine scissors; they
should be mounted in glycerine-jelly when their texture is soft, and in
balsam when the integument is hard and horny.

638. Wings, — These organs are essentially composed of an extension
of the external membranous layer of the integument, over a framework
formed by prolongations of the inner horny layer, within which prolon-
gations tracheae are nearly always to be found, whilst they also include
channels through which blood circulates during the growth of the wing
and for a short time after is completion (§ 633). This is the simple
structure presented to us in the Wings of Neuroptera (Dragon-flies, etc.),
Hymenoptera (Bees and Wasps), Diptera (two-winged-Flies, and also of
many Homoptera (Cicadae and Aphides); and the principal interest of
these wings as Microscopic objects lies in the distribution of their ' veins y
or 6 nervures ' (for by both names are the ramifications of their skeleton
known), and in certain points of accessory structure. The venation of
the wings is most beautiful in the smaller Keuroptera; since it is the dis-
tinguishing feature of this order that the veins, after subdividing, reunite
again, so as to form a close network; whilst in the Hymenoptera and
Diptera such reunions are rare, especially towards the margin of the
wings, and the areolae are much larger. Although the membrane of which
these wings are composed appears perfectly homogeneous when viewed by
transmitted light, even with a high magnifying power, yet, when viewed
by light reflected obliquely from their surfaces, an appearance of cellular
areolation is often discernible; this is well se,en in the common Fly, in
which each of these areolae has a hair in its centre. In order to make
this observation, as well as to bring-out the very beautiful iridescent hues
which the wings of many minute Insects (as the Aphides) exhibit when
thus viewed, it is convenient to hold the wing in the Stage-forceps for
the sake of giving it every variety of inclination; and when that position
has been found which best displays its most interesting features, it should
be set up as nearly as possible in the same. For this purpose it should
be mounted on an opaque slide; but instead of being laid down upon its
surface, the wing should be raised a little above it, its ' stalk' being held
in the proper position by a little cone of soft wax, in the apex of which
it may be imbedded. — The wings of most Hymenoptera are remarkable
for the peculiar apparatus by which those of the same side are connected
together, so as to constitute in flight but one large wing; this consists of
16

242

THE MICROSCOPE AND ITS REVELATIONS.

a row of curved hooklets on the anterior margin of the posterior wing,
which lay hold of the thickened and doubled-down posterior edge of the
anterior wing. These hooklets are sufficiently apparent in the wings of
the common Bee, when examined with even alow magnifying power; but
they are seen better in the Wasp, and better still in the Hornet. — The
peculiar scaly covering of the wings of the Lepidoptera has already been
noticed (§ 619); but it may here be added that the entire wings of many
of the smaller and commoner insects of this order, such as the TineidcB
or 6 clothes-moths/ form very beautiful opaque objects for low powers;
the most beautiful of all being the divided wings of the Fissipeanes or
6 plumed moths/ especially those of the genus Pterophoras.

639. There are many Insects, however, in which the Wings are more
or less consolidated by the interposition of a layer of horny substance
between the two layers of membrane. This plan of structure is most
fully carried-out in the Coleoptera (Beetles), whose anterior wings are
metamorphosed into elytra or ' wing-cases;' and it is upon these that the
brilliant hues by which the integument of many of these insects is dis-
tinguished are most strikingly displayed. In the anterior wings of the
ForficulidcB or Earwig-tribe (which form the connecting link between
this order and the Orthoptera), the cellular structure may of ten be readily
distinguished when they are viewed by transmitted light, especially after
having been mounted in Canada balsam. The anterior wings of the
Orthoptera (Grasshoppers, Crickets, etc.), although not by any means so
solidified as those of Coleoptera, contain a good deal of horny matter;
they are usually rendered sufficiently transparent, however, by Canada
balsam, to be viewed with transmitted light; and many of them are so
colored as to be very showy objects (as are also the posterior fan-like
wings) for the Electric or Gas-microscope, although their large size, and
the absence of any minute structure, prevent them from affording much
interest to the ordinary Microscopist. — We must not omit mention, how-
ever, the curious Sound-producing apparatus which is possessed by most
insects of this order, and especially by the common House-cricket. This
consists of the * tympanum 9 or drum, which is a space on each of the
upper wings, scarcely crossed by veins, but bounded externally by a large
dark vein provided with three or four longitudinal ridges; and of the
' file' or 'bow/ which is a transverse horny ridge in front of the tym-
panum, furnished with numerous teeth: and it is believed that the sound
is produced by the rubbing of the two bows across each other, while its
intensity is increased by the sound-board action of the tympanum. — The
wings of the Fulgoridce (Lantern-flies) have much the same texture with
those of Orthoptera, and possess about the same value as Microscopic
objects; differing considerably from the purely membranous wings of the
Cicadse and Aphides, which are associated with them in the order Hornop-
tera. In the order Hemiptera, to which belong various kinds of land
and water Insects that have a suctorial mouth resembling that of the
common bag, the wings of the anterior pair are usually of parchmenty
consistence, though membranous near their tips, and are often so richly
colored as to become very beautiful objects, when mounted in Balsam
and viewed by transmitted light; this is the case especially with the ter-
restrial vegetable-feeding kinds, such as the Pentatoma and its allies,
some of the tropical forms of which rival the most brilliant of the Beetles.
The British species are by no means so interesting; and the aquatic kinds,
which, next to the bed-bugs, are the most common, always have a dull
brown or almost black hue: even among these last, however, — of which

INSECTS AND ARACHNIDA.

243

the Notonecta (water-boatman) and the Nepa (water-scorpion) are well-
known examples,— the wings are beautifully variegated by differences in
the depth of that hue. The halteres of the Diptera, which are the
representatives of the posterior wings, have been shown by Dr. J. B.
Hicks to present a very curious structure, which is found also in the
elytra of Coleoptera and in many other situations; consisting in a multi-
tude of vesicular projections of the superficial membrane, to each of
which there proceeds a nervous filament, that comes to it through an
aperture in the tegumentary wall on which it is seated. Various con-
siderations are stated by Dr. Hicks, which lead him to the belief that
this apparatus, when developed in the neighborhood of the spiracles or
breathing-pores, essentially ministers to the sense of smell, whilst, when
developed upon the palpi and other organs in the neighborhood of the
mouth, it ministers to the sense of taste.1

640. Feet. — Although the feet of Insects are formed pretty much on
one general plan, yet that plan is subject to considerable modifications,
in accordance with the habits of life of different species. The entire
limb usually consists of five divisions, namely the coxa or hip, the tro-
chanter, the femur or thigh, the tibia
or shank, and the tarsus or foot;
and this last part is made up of
several successive joints. The typical
number of these joints seems to be
five; but that number is subject to
reduction; and the vast order Cole-
optera is subdivided into primary
groups, according as the tarsus con-
sists of five, four, or three segments.
The last joint of the tarsus is usually
furnished with a pair of strong
hooks or claws (Figs. 435, 436); and
these are often serrated (that is, fur-
nished with saw-like teeth), especially
near the base. The under-surface
of the other joints is frequently
beset with tufts of hairs, which are
arranged in various modes, sometimes
forming a complete 'sole;' this is
especially the case in the family Ourculionidce; so that a pair of the feet
of the * diamond- bettle/ mounted so that one shows the upper surface
made resplendent by its jewel-like scales, and the other the hairy cushion
beneath, is a very interesting object. In many Insects, especially of the
Fly kind, the foot is furnished with a pair of membranous expansions
termed pulvilli (Fig. 435); and these are beset with numerous hairs, each
of which has a minute disk at its extremity. This structure is evidently
connected with the power which these Insects possess of walking over
smooth surfaces in opposition to the force of gravity; yet there is still
considerable uncertainty as to the precise mode in which it ministers to

1 See his Memoir * On a new Organ in Insects,' in "Journal of Linnaean
Society," Vol. i. (1856), p. 136; his 1 Further Remarks on the Organs found on the
bases of the Halteres and Wings of Insects,' in " Trans, of the Linn. Society,"
Vol. xxii., p. 141; and his Memoir ' On certain Sensory Organs in Insects, hitherto
undescribed,' in " Trans of Linn. Soc," Vol. xxiii., p. 189.

Fig. 435.

Foot of Fly.

244

THE MICROSCOPE AND ITS REVELATIONS.

this faculty. Some believe that the disks act as suckers, the Insect being
h eld-up by the pressure of the air against their upper surface, when a
vacuum is formed beneath; whilst others maintain that the adhesion is
the result of the secretion of a viscid liquid from the under side of the
foot. The careful observations of Mr. Hepworth have led him to a con-
clusion which seems in harmony with all the facts of the case— namely,
that each hair is a tube conveying a liquid from a glandular sacculus
situated in the tarsus; and that when the disk is applied to a surface, the
pouring-forth of this liquid serves to make its adhesion perfect. That
this adhesion is not produced by atmospheric pressure alone, is proved by
the fact that the feet of Flies continue to hold-on to the interior of an
exhausted receiver; whilst, on the other hand, that the feet pour-forth a
secreted fluid, is evidenced by the marks left by their attachment on a
clean surface of glass. Although, when all the hairs have the strain put
upon them equally, the adhesion of their disks suffices to support the
insect, yet each row may be detached separately by the gradual raising of
the tarsus and pulvilli, as when we remove a piece of adhesive plaster by

lifting it from the edge or
corner. Flies are often found
adherent to window-panes in
the autumn, their reduced
strength not being sufficient
to enable them to detach
their tarsi.1 — A similar ap-
paratus on a far larger scale,
presents itself on the foot of
the Dytiscus (Fig. 436, a).
The first joints of the tarsus
of this insect are widely ex-
panded, so as to form a
nearly-circular plate: and
this is provided with a very
remarkable apparatus of
suckers, of which one disk
(a) is extremely large, and
is furnished with strong rad-
iating fibres, a second (b) is
a smaller one formed on the
same plan (a third, of the like
kind, being often present),
whilst the greater number are comparatively small tubular club-shaped
bodies, each having a very delicate membranous sucker at its extremity, as
shown on a larger scale at b. These all have essentially the same structure ;
the large suckers beingfurnisheJ, like the hairs of the Fly's foot, with secret-
ing sacculi, which pour forth fluid through the tubular footstalks that carry
the disks, whose adhesion is thus secured; whilst the small suckers form
the connecting link between the larger suckers and the hairs of many
beetles, especially Curculionidce.2 The leg and foot of the Dytiscus, if

1 See Mr. Hep worth's communications to the " Quart. Journ. of Microsc.
Science," Vol. ii. (1854;, p. 158, and Vol. iii. (1855), p. 312. See also Mr. Tuffen
West's Memoir 4 On the Foot of the Fly,' in " Transact, of Linnaean Society," Vol.
xxii., p. 393, and Mr. Lowne's "Anatomy of the Blow-fly," p. 19.

2 See Mr. Lowne ' On the so-called Suckers of Dytiscus and the Pulvilli of
Insects,' in "Monthly Microscopical Journal," Vol. v., p. 267.

INSECTS AND ARACHNID A. 245

mounted without compression, furnish a peculiarly beautiful object for
the Binocular Microscope. — The Feet of Caterpillars differ consider-
ably from those of perfect Insects. Those of the first three segments,
which are afterwards to be replaced by true legs, are furnished with strong
horny claws; but each of those of the other segments, which are termed
* pro-legs/ is composed of a circular series of comparatively slender curved
hooklets, by which the Caterpillar is enabled to cling to the minute rough-
nesses of the surface of the leaves, etc., on which it feeds. This structure
is well seen in the pro-legs of the common Silkworm.

641. Stings and Ovipositors. — The insects of the order Hymenopiera
are all distinguished by the prolongation of the last segment of the abdo-
men into a peculiar organ, which in one division of the order is a 6 sting/
and in the other is an ' ovipositor ' or instrument for the deposition of
the eggs, which is usually also provided with the means of boring a hole
for their reception. The former group consists of the Bees, Wasps, Ants,
etc. ; the latter of the Saw-flies, Gall-flies, Ichneumon-flies, etc. These
two sets of instruments are not so unlike in structure, as they are in func-
tion.— The 'sting' is usually formed of a pair of darts, beset with barbed
teeth at their points, and furnished at their roots with powerful muscles,
whereby they can be caused to project from their sheath, which is a
horny case formed by the prolongation of the integument of the last seg-
ment, slit into two halves, which separate to allow the protrusion of the
of the sting; whilst the peculiar 'venom' of the sting is due to the ejec-
tion, by the same muscular action, of a poisonous liquid, from a bag situ-
ated near the root of the sting, which passes down a canal excavated
between the darts, so as to be inserted into the puncture which they
make. The stings of the common Bee, Wasp, and Hornet, may all be
made to display this structure without much difficulty in the dissection.
— The 'ovipositor' of such insects as deposit their eggs in holes ready-
made, or in soft animal or vegetable substances (as is the case with the
Jckneumomdw), is simply a long tube, which is inclosed, like the sting,
in a cleft sheath. In the Gall-flies (Cynipidce), the extremity of the ovi-
positor has a toothed edge, so as to act as a kind of saw whereby harder
substances may be penetrated; and thus an aperture is made in the leaf,
stalk, or bud of the plant or tree infested by the particular species, in
which the egg is deposited, together with a drop of fluid that has a pecu-
liarly irritating effect upon the vegetable tissues, occasioning the produc-
tion of the ' galls,' which are new growths that serve not only to protect
the larvae, but also to afford them nutriment. The oak is infested by
by several species of these Insects, which deposit their eggs in different
parts of its fabric; and some of the small 'galls' which are often found
upon the surface of oak-leaves, are extremely beautiful objects for the
lower powers of the Microscope. In the Tenthredinidce, or 'saw-flies,'
and in their allies the Siricidce, the ovipositor is furnished with a still
more powerful apparatus for penetration, by means of which some of
these Insects can bore into hard timber. This consists of a pair of
'saws' which are not unlike the 'stings' of Bees, etc., but are broader,
and toothed for a greater length, and are made to slide along a firm piece
that supports each blade, like the 'back' of a carpenter's 'tenon-saw;'
they are worked alternately (one being protruded while the other is drawn
back) with great rapidity; but, when not in use, they lie in a fissure be-
neath a sort of arch formed by the terminal segment of the body. When
a slit has been made by the working of the saws, they are withdrawn into
this sheath; the ovipositor is then protruded from the end of the abdo-

246

THE MICROSCOPE AND ITS REVELATIONS.

men (the body of the insect being curved downwards); and , . being guided
into the slit by a pair of small hairy feelers, there deposits an egg.1 —
Many other insects, especially of the order Diptera, have very prolonged
ovipositors, by means of which they can insert their eggs iuto the integu-
ments of animals, or into other situations in which the larvae will obtain
appropriate nutriment. A remarkable example of this is furnished by
the Gad-fly {Tabanus), whose ovipositor is composed of several joints,
capable of being drawn together or extended like those of a telescope, and
is terminated by boring instruments; and the egg being conveyed by its
means, not only into but through the integument of the Ox, so as to be
imbedded in the tissue beneath, a peculiar kind of inflammation is set-up
there, which (as in the analogous case of the gall-fly) forms a nidus appro-
priate both to the protection and to the nutrition of the larva. Other
insects which deposit their eggs in the ground, such as the Locusts, have
their ovipositors so shaped as to answer for digging holes for their recep-
tion.— The preparations which serve to display the foregoing parts, are
best seen when mounted in Balsam; save in the case of the muscles and
poison-apparatus of the sting, which are better preserved in fluid or in
glycerine-jelly.

642. The Sexual organs of Insects furnish numerous objects of
extreme interest to the Anatomist and Physiologist; but as an account
of them would be unsuitable to the present work, a reference to a copious
source of information respecting one of their most curious features, and
to a list of the species that afford good illustrations, must here suffice.2 —
The eggs of many Insects are objects of great beauty, on account of the
regularity of their form, and the symmetry of the markings on their sur-
face (Fig. 437). The most interesting belong for the most part to the
order Lepidoptera; and there are few among these that are not worth
examination, some of the commonest (such as those of the Cabbage butter-
fly, which are found covering large patches of the leaves of that plant)
being as remarkable as any. Those of the Puss moth (Cirura vinula),
the Privet hawk-moth {Sphinx ligustri), the small Tortoiseshell butterfly
( Vanessa urticce), the Meadow-brown butterfly {Hipparchia j antra) , the
Brimstone-moth (Eumia cratcegata), and the Silkworm (Bombyx mori),
may be particularly specified: and from other orders, those of the Cock-
roach (Blatta orientalis), Field Cricket (Acheta campestris), Water-scor-
pion (JVepa ranatra), Bug (Cimex lectularius), Cow-dung-fly (Scatophaga
stercoraria), and Blow-fly (Musca vomitoria). In order to preserve these
eggs, they should be mounted in fluid in a cell; since they will otherwise
dry up and may lose their shape. — They are very good objects for the
6 conversion ^of relief ' effected by Nachet's Stereo-pseudoscopic Binocular
(§38).

643. The remarkable mode of Eeproduction that exists among the
Aphides must not pass unnoticed here, from its curious connection with

1 The above is the account of the process given by Mr. J. W. Gooch ; who has
informed the Author that he has repeatedly verified the statement formerly made
by him (" Science Gossip," Feb. 1, 1873), that the eggs are deposited, not as origi-
nally stated by Reaumur, by means of a tube formed by the coaptation of the
saws, but through a separate ovipositor, protruded when the saws have been with-
drawn.

2 See the Memoirs of M. Lacaze-Dutheirs, * Sur Tarmure genitale des Insectes,'
in " Ann. des Sci. Nat.," Ser. 3, Zool., Tomes xii., xiv., xvii., xviii., xix.; and M.
Ch. Robin's " Memoire sur les Objets qui peuvent etre conserves en Preparations
Microscopiques " (Paris, 1856), which is peculiarly full in the enumeration of the
objects of interest afforded by the Class of Insects.

INSECTS AND ARACHNID A.

247

the non-sexual reproduction of Entomostraca (§ 609) and Rotifera (§ 451)
as also of Hydra (§ 515) and Zoophytes generally; all of which fall spe-
cially, most of them exclusively, under the observation of the Microscopist.
The Aphides which may be seen in the spring and early summer, and
which are commonly but not always wingless, are all of one sex, and
give birth to a brood of similar Aphides, which come into the world
alive, and before long go through a like process of multiplication. As
many as from seven to ten successive broods may thus be produced in the
course of a single season; so that from a single Aphis, it has been calcu-
lated that no fewer than ten thousand million millions, may be evolved
within that period. In the latter part of the year, however, some of these
viviparous Aphides attain their full development into males and females;
and these perform the true Generative process, whose products are eggs,
which, when hatched in the succeeding spring, give origin to a new vivi-
parous brood that repeat the curious life-history of their predecessors.
It appears from the observations of Prof. Huxley,1 that the broods of
viviparous Aphides originate in ova which are not to be distinguished
from those deposited by the perfect winged female. Nevertheless, this
non-sexual or agamic reproduction must be considered analogous rather
to the ' gemmation 9 of other Animals and Plants, than to their sexual

Fig. 437.

6 generation;' for it is favored, like the gemmation of Hydra, by warmth
and copious sustenance, so that by appropriate treatment the viviparous
reproduction may be caused to continue (as it would seem) indefinitely,
without any recurrence to the sexual process. Further, it seems now
certain that this mode of reproduction is not at all peculiar to the
Aphides, but that many other Insects ordinarily multiply by 6 agamic 9
propagation, the production of males and the performance of the true
generative act being only occasional phenomena; and the researches of
Prof. Siebold have led him to conclude that even in the ordinary economy
of the Hive-bee the same double mode of reproduction occurs. The
queen, who is the only perfect female in the hive, after impregnation by
one of the drones (or males), deposits eggs in the 6 royal' cells., which are
in due time developed into young queens; others in the drone-cells, which
become drones; and others in the ordinary cells, which become workers or
neuters. It has long been known that these last are really undeveloped
females, which, under certain conditions, might become queens; and it
has been observed by bee-keepers that worker-bees, in common with

1 ' On the Agamic Reproduction and Morphology of Aphis,' in ' ' Transact, of
Linn. Soc," Vol. xxii., p. 193.

248

THE MICROSCOPE AND ITS REVELATIONS.

virgin or unimpregnated queens, occasionally lay eggs, from which
eggs none but drones are ever produced. From careful Microscopic
examination of the drone eggs laid even by impregnated queens, Siebold
drew the conclusion that they have not received the fertilizing influence
of the male fluid, which is communicated to the queen-eggs and worker
eggs alone; so that the products of sexual generation are always female,
the male being developed from these by a process which is essentially one
of gemmation.1

644. The Embryonic Development of Insects is a study of peculiar
interest, from the fact that it may be considered as divided (at least in
such as undergo a 'complete metamorphosis') into two stages that are
separated by the whole active life of the larva; that, namely, by which
the Larva is produced within the egg, and that by which the Imago of
perfect insect is produced within the body of the Pupa. Various circum-
stances combine, however, to render the study a very difficult one; so
that it is not one to be taken up by the inexperienced Microscopist.
The following summary of the process in the common Blow-fly, however,
will probably be acceptable. — A gastrula with two membranous lamellae
(§ 391) having been evolved in the first instance, the outer lamella very
rapidly shapes itself into the form of the larva, and shows a well-marked
segmental division. The alimentary canal, in like-manner, shapes itself
from the inner lamella; at first being straight and very capacious, includ-
ing the whole yolk; but gradually becoming narrow and tortous, as addi-
tional layers of cells are developed between the two primitive lamellae,
from which the other internal organs are evolved. When the larva comes
forth from the egg, it still contains the remains of the yolk; it soon
begins, however, to feed voraciously; and in no long period it grows to
many thousand times it original weight, without making any essential
progress in development, but simply accumulating material for future
use. An adequate store of nutriment (analogous to the 6 supplemental
yolk ' of Purpura, § 584) having thus been laid up within che body of
the larva, it resumes (so to speak) its embryonic development, its pas-
sage into the pupa state, from which the imago is to come forth, involv-
ing a degeneration of all the larval tissues: whilst the tissues and organs
of the imago " are re-developed from cells which originate from the dis-
integrated parts of the larva, under conditions similar *,o those apper-
taining to the formation of the embryonic tissues from fche yolk." The
development of the segments of the head and body in Insects generally
proceeds from the corresponding larval segments; but according to Dr.
Weissnian, there is a marked exception in the case ot the Diplera and
other insects whose larvae are unfurnished with legs — their head and
thorax being newly formed from 'imaginal disks' which adhere to the
nerves and tracheae of the anterior extremity of the larva;2 and, strange
as this assertion may seem, it has been confirmed by the subsequent in-
vestigations of Mr. Lowne.

645. Arachnida. — The general remarks which have been made in
regard to Insects, are equally applicable to this Class; which includes,
along with the Spiders and Scorpions, the tribe of Acarida, consisting
of Mites and Ticks. Many of these are parasitic, and are popularly

1 See Prof. Siebold's Memoir 4 'On true Parthenogenesis in Moths and Bees,"
translated by W. S. Dallas : London, 1857.

2 See his ' Entwickelung der Dipteren,' in " Kolliker and Siebold's Zeitschrif t, "
Bande xiv.-xvi.; and Mr. Lowne's " Anatomy of the Blow-fly " pp. 6-9, 113-121.

INSECTS AND ARACHNID A.

249

associated with the wingless parasitic Insects, to which they bear a strong
general resemblance, save in having eight legs instead of six. The true
'mites' (AcarincB) generally have the legs adapted for walking, and
some of them are of active habits. The common clieese-mite, as seen by
the naked-eye, is familiar to everyone; yet few who have not seen it
under a Microscope have any idea of its real conformation and move-
ments; and a cluster of them, cut out of the cheese they infest, and
placed under a magnifying power sufficiently low to enable a large num-
ber to be seen at once, is one of the most amusing objects that can be
shown to the young. There are many other species, which closely re-
semble the Cheese-mite in structure and habits, but which feed upon
different substances; and some of these are extremely destructive. To
this group belongs a small species, the Sarcoptes scabiei, whose presence
appears to be the occasion of one of the most disgusting diseases of the
skin — the itch — and which is hence commonly termed the ' itch-insect.'
It is not found in the pustule itself, but in a burrow which passes-off
from one side of it, and which is marked by a red line on the surface;
and if this burrow be carefully examined, the creature will very com-
monly, but not always, be met-with. It is scarcely visible to the naked
eye; but when examined under the microscope, it is found to have an
oval body, a mouth of conical form, and eight feet, of which the four
anterior are terminated by small suckers, whilst the four posterior end
in very prolonged bristles. The male is only about half the size of the
female. The Ricinice or 6 ticks 9 are usually destitute of eyes, but have
the mouth provided with lancets, that enable them to penetrate more
readily the skins of animals whose blood they suck. They are usually
of a flattened, round, or oval form; but they often acquire a very large
size by suction, and become distended like a blown-bladder. Different
species are parasitic upon different animals; and they bury their suckers
(which are often furnished with minute recurved hooks) so firmly in the
skins of these, that they can hardly be detached without pulling away
the skin with them. It is probably the young of a species of this group",
which is commonly known as the ' harvest-bug/ and which is usually
designated as the Acarus autumnalis; this is very common in the
autumn upon grass or other herbage, and insinuates itself into the skin
at the roots of the hair, producing a painful irritation; like other Acar-
ida, it possesses only six legs for some time after its emersion from the
egg (the other pair being only acquired after the first moult), so that its
resemblance to parasitic Insects becomes still stronger. — It is probable
that to this group also belongs the Demodex folliculorum, a creature which
is very commonly found parasitic in the sebaceous follicles of the Human
skin, especially in those of the nose. In order to obtain it, pressure
should be made upon any one of these that appears enlarged and whitish
with a terminal black spot; the matter forced-out will consist principally
of the accumulated sebaceous secretion, having the parasites with their
eggs and young mingled with it. These are to be separated by the addi-
tion of oil, which will probably soften the sebaceous matter sufficiently
to set free the animals, which may be then removed with a pointed brush;
but if this mode should not be effectual, the fatty matter may be dis-
solved-away by digestion in a mixture of alcohol and ether. The pus-
tules in the skin of a Dog affected with the ' mange' were found by
Mr. Topping to contain a Demodex, which seems only to differ from that
of the human sebaceous follicles in its somewhat smaller size; and M.
Gruby is said to have given to a dog a disease resembling the mange, if

250

-THE MICROSCOPE AND ITS REVELATIONS.

not identical with it, by inoculating it with the Human parasite. — The
Acarida are best preserved, as Microscopic objects, by mounting in one
or other of the * media' described in § 206.

646. The number of objects of general interest furnished to the
Microscopist by the Spider tribe, is by no means considerable. Their
Eyes exhibit a condition intermediate between that of Insects and Crus-
taceans, and that of Vertebrata; for they are simple, like the 6 stemmata'
of the former (§ 626), usually number from six to eight, are sometimes
clustered-together in one mass, though sometimes disposed separately;
while they present a decided approach in internal structure to the type
characteristic of the visual organs of the latter. — The structure of the
Mouth is always mandibulate, and is less complicated than that of the
' mandibulate 9 insects. — The Eespiratory apparatus, which, where devel-
oped at all among the Acarida, is tracheary like that of Insects, is here
constructed upon a very different plan; for the ' stigmata 9 which are usu-
ally four in number on each side, open into a like number of respiratory
sacculi, each of which contains a series of leaf-like folds of its lining
membrane, upon which the blood is distributed so as to afford a large
surface to the air. — In the structure of the limbs, the principal point

worthy of notice is the peculiar appendage with which they usually ter-
minate; for the strong claws, with a pair of which the last joint of the
Foot is furnished, have their edges cut into comb-like teeth (Fig. 438),
which seem to be used by the animal as cleansing-instruments.

647. One of the most curious parts of the organization of the Spiders,
is the ' spinning-apparatus 9 by means of which they fabricate their elab-
orately constructed webs. This consists of the ( spinnerets/ and of the
glandular organs in which the fluid that hardens into the thread is elab-
orated. The usual number of the spinnerets, which are situated at the
posterior extremity of the body, is six; they are little teat-like promi-
nences, beset with hairy appendages; and it is through a certain set of
these appendages, which are tubular and terminate in fine-drawn points,
that the glutinous secretion is forced-out in a multitude of streams of
extreme minuteness. These streams harden into fibrils immediately on
coming into contact with the air; and the fibrils proceeding from all the
apertures of each spinneret coalesce into a single thread. It is doubtful,
however, whether all the spinnerets are in action at once, or whether
those of different pairs may not have dissimilar functions; for whilst the
radiating threads of a spider's web are simple (Fig. 439, a) those wThich

Fif?. 438.

Foot, with comb-like claws, of the common Spider (Epeira).

INSECTS AND AKACHNIDA.

251

lie across these, forming its concentric circles, or rather polygons, are
studded at intervals with viscid globules (b), which appear to give to
these threads their peculiarly adhesive character; and it does not seem
by any means unlikely that each kind of thread should be produced by
its own pair of spinnerets. It was observed by Mr. R. Beck, that these
viscid threads are of uniform thickness when first spun; but that undu-
lations soon appear in them, and that the viscid matter then accumulates
in globules at regular intervals. — The total number of spinning-tubes va-
ries greatly, according to the species of the Spider, and the sex and age of

Fig. 439.

4 -

Ordinary thread (a), and viscid thread (b), of the common Spider,

the individual; being more than 1000 in some cases, and less than 100 in
others. The size and complexity of the secreting glandulae vary in like
manner: — Thus in the Spiders which are most remarkable for the large
dimensions and regular construction of their webs, they occupy a large
portion of the abdominal cavity, and are composed of slender branch-
ing tubes whose length is increased by numerous convolutions; whilst
in those which have only occasional use for their threads, the secreting
organs are either short and simple follicles, or undivided tubes of moder-
ate length.

252

THE MICROSCOPE AND ITS KEVELATIONS.

OHAPTEE XX.
VERTEBRATED ANIMALS.

648. We are now arrived at the highest division of the Animal King-
dom, in which the bodily fabric attains its greatest development, not
only as to completeness, but also as to size; and it is in most striking
contrast with the Class we have been last considering. Since not only
the entire bodies of Vertebrated animals, but, generally speaking, the
smallest of their integral parts, are far too large to be viewed as Micro-
scopic objects, we can study their structure only by a separate examina-
tion of their component elements; and it seems, therefore, to be a most
appropriate course to give under this head a sketch of the microscopic
characters of those Primary Tissues of which their fabric is made-up,
and which, although they may be traced with more or less distinctness in
the lower tribes of Animals, attain their most complete development in
this group.1 — For some time after Schwann first made public the remark-
able results of his researches, it was very generally believed that all the
Animal tissues are formed, like those of Plants, by a metamorphosis of
cells; an exception being taken, however, by some Physiologists in regard
to the ' simple fibrous' tissues (§ 668). There can be no longer any
doubt, however, that this doctrine must be greatly modified;2 so that,
whilst the Vegetable Physiologist may rightly treat the most highly organ-
ized Plant as a mere aggregation of cells, analogous in all essential par-
ticulars to those which singly constitute the ' unicellular 9 Protophytes
(§ 227), the Animal Physiologist does wrong in seeking a cellular origin
for all the component parts of the Animal fabric; and may best interpret
the phenomena of tissue-formation in the most complicated organisms,
by the study of the behavior of that apparently-homogenous 6 protoplasm 9
of which the simplest Protozoa are made up, and by tracing the progres-
sive 6 differentiation 9 which presents itself as we pass from this through
the ascending series of Animal forms.3

1 This sketch is intended , not for the Professional student, but only for the
amateur Microscopist, who wishes to gain some general idea of the elementary
structure of his own body and of that of Vertebrate animals generally. Those
who wish to go more deeply into the inquiry are referred to the following as the
most recent and elaborate Treatises that have appeared in this country:— The
translation of Striker's 44 Manual of Histology," published by the New Sydenham
Society; the "Handbook for the Physiological Laboratory," by Drs. Burdon-
Sanderson, Michael Foster, Brunton, and Klein; the translation of the 4th edition
of Prof. Frey's "Histology and Histo-chemistry of Man;" the 4 General Anatomy'
of the 8th edition of 44 Quain's Anatomy" (1874); and the 44 Atlas of Histology,"
by Prof. Klein and Mr. Noble Smith (1880-1).

2 The important 'Review of the Cell-Theory,' by Prof. Huxley, in the 44 Brit,
and For. Med.-Chir. Review," Vol. xii. (Oct, 1853), p. 285, may be considered the
starting-point of many later inquiries.

3 The study of Comparative Histology, prosecuted on this basis, promises to be

VERTEBRATED ANIMALS.

253

649, Although tnere would at first sight appear but little in common
between the simple bodies of those humble Monerozoa which constitute
the lowest types of the Animal series (§ 392), and the complex fabric of
Man or other Vertebrates, yet it appears from recent researches, that in
the latter, as in the former, the process of ' formation' is essentially
carried-on by the instrumentality of protoplasmic substance, universally
diffused through it in such a manner as to bear a close resemblance to the
pseudopodial network of the Ehizopod (Fig. 283); whilst the tissues pro-
duced by its agency lie, as it were, on the outside of this, bearing' the
same kind of relation to it as the Foraminiferal shell (Fig. 314) does to
the sarcodic substance which fills its cavities and extends itself over its
surface. For, as was first pointed out by Dr. Beale,1 the smallest living
' elementary part' of every organized fabric is composed Qf organic mat-
ter in two states: the protoplasmic (which he termed germinal matter),
possessing the power of selecting pabulum from the blood, and of trans-
forming this either into the material of its own extension, or into some
product which it elaborates; whilst the other, which may be termed
formed material, may present every gradation of character from a mere
inorganic deposit to a highly organized structure, but is in every case
altogether incapable of self -increase. A very definite line of demarcation
can be generally drawn between these two substances, by the careful use
of the staining-process (§ 200); but there are many instances in which
there is the same gradation between the one and the other, as we have
have formerly noticed between the 6 endosarc ' and the 6 ectosarc ' of the
Amoeba (§403). — Thus it is on the protoplasmic component that the
existence of every form of Animal organization essentially depends; since
it serves as the instrument by which the nutrient material furnished by
the blood is converted into the several forms of tissue. Like the sarco-
dic substance of the Ehizopods, it seems capable of indefinite extension;
and it may divide and subdivide into independent portions, each of which
may act as the instrument of formation of an ' elementary part.' Two
principal forms of such elementary parts present themselves in the fabric
of the higher Animals — namely, cells and fibres ; and it will be desirable
to give a brief notice of these, before proceeding to describe those more
complex tissues which are the products of a higher elaboration.

650. The cells of which many Animal tissues are essentially composed,
consist, when fully and completely formed, of the same parts as the typi-

exceedingly fertile in results of this most intereating character. Thus Dr N.
Kleinenberg, in his admirable 44 Anatomische entwickelungsgeschichtliche Un-
tersuchung" (1872), on Hydra, gives strong reason for regarding a particular set
of cells in the body of that animal as combining the functions of Nerve and
Muscle. And the Author has been led by his study of Comatula to recognize
the most elementary type of Nerve-trunk in a simple protoplasmic cord, not yet
separated into distinct fibres with insulating sheaths.

1 Prof. Beale's views are most systematically expounded in his lectures 4 On
the Structure of the simple Tissues of the Human Body," 1861; in his 44 How to
Work with the Microscope," 5th edition, 1880; and in the Introductory portion
of his new edition of 44 Todd and Bowman's Physiological Anatomy," 1867. The
principal results of the inquiries of German Histologists on this point are well
stated in a Paper by Dr. Duffin on * Protoplasm, and the part it plays in the
actions of Living Beings,' in 44 Quart. Journ. of Microsc. Science," Vol. iii., N.S.,
(1863), p. 251.— The Author feels it necessary, however, to express his dissentfrom
Prof. Beale's views in one important particular — viz., his denial of 4 vital' en-
dowments to the 4 formed material' of any of the tissues; since it seems to him
illogical to designate contractile muscular fibre (for example) as 4 dead,' merely
because it has not the power of self -reparation.

254

THE MICROSCOPE AND ITS REVELATIONS.

cal cell of the Plant (§ 223); — viz., a definite 4 cell- wall/ inclosing cell-
contents (of which the nature may be very diverse), and also including a
i nucleus/ which is the seat of its formative activity. It is of such cells,
retaining more or less of their characteristic spheroidal shape, that every
mass of fat, whether large or small, is chiefly made up (Fig. 468). And
the internal cavities of the body are lined by a layer of epithelium- cells
(Fig. 466), which, although of flattened form, present the like combina-
tion of components. But there is a large number of cases in which the
■cell shows itself in a form of much less complete development; the ' ele-
mentary part ? being a corpuscle of protoplasm, of which the exterior has
undergone a slight consolidation, like that which constitutes the ' pri-
mordial utricle 5 of the Vegetable cell (§ 223) or the 'ectosarc' of the
Amoeba (§ 403), but in which there is no proper distinction between
4 cell- wall 9 and ' cell-contents.5 This condition, which is characteristi-
cally exhibited by the nearly globular colorless corpuscles of the Blood
(§ 666), appears to be common to all cells in the incipient stage of their
formation: and the progress of their development consists in the gradual
differentiation of their parts, the ' cell-wall' becoming distinctly sepa-
rated from the * cell-contents/ and these from the ' nucleus; 9 and the ori-
ginal protoplasm being very commonly replaced more or less completely
by some special product (such as fat in the cells of adipose tissue, or
haemoglobin in the red corpuscles of the blood), in which cases the
nucleus often disappears altogether. — In the earlier stages of cell-develop-
ment, multiplication takes place with great activity by a duplicative sub-
division that corresponds in all essential particulars with that of the Plant-
cell (§ 226); as is well seen in Cartilage, a section of which will often
exhibit in one view the successive stages of the process1 (compare Fig.
470 with Fig. 139). Whether 'free' cell -multiplication ever takes place
in the higher Animals, is at present uncertain.

651. A large part of the fabric of the higher Animals, however, is
made up of fibrous tissues, which serve to bind together the other com-
ponents, and which, when consolidated by calcareous deposit, constitute
the substance of the skeleton. In these, the relation of the ' germinal
matter' and the 6 formed material' presents itself under an aspect which
seems at first sight very different from that just described. A careful
examination, however, of those 6 connective-tissue-corpuscles ' (Fig. 461)
that have long been distinguished in the midst of the fibres of which
these tissues are made up, shows that they are the equivalents of the
corpuscles of 6 germinal matter,' which in the previous instance came to
constitute cell-nuclei; and that the fibres hold the same relation to them,
that the 6 walls ' and ' contents ' of cells do to their germinal corpuscles.
The transition from the one type to the other is well seen in Fibro-cartilage,
in which the so-called ' intercellular substance ' is often as fibrous as ten-
don. The difference between the two types, in fact, seems essentially
to consist in this — that, whilst the segments of ' germinal matter' which
form the cell-nuclei in cartilage (Fig. 470) and in other cellular tissues,
are completely isolated from each other, each being completely sur-

1 Great attention has lately been given by many able observers, to the changes
which take place in the nucleus before and during its cleavage. A full account
of these is contained in the recently-published third Edition of Prof. Strassbur-
ger's " Zellbiidung und Zelltheilung " (1880). See also Dr. Klein's 4 Observations
on the Structure of Cells and Nuclei,' in "Quart. Journ. Microsc. Science," N.S.,
Vol. xviii. (1878), p. 315, and Vol. xix. (1879), pp. 125, 404; and Chap. xliv. of his
"Atlas of Histology."

VERTEBRATE D ANIMALS.

255

rounded by the product of its own elaborating action, those which form
the ' connective-tissue-corpuscles ' are connected together by radiating
prolongations (Pig. 461) that pass between the fibres, so as to form a
continuous network closely resembling that formed by the pseudopodia
of the Rhizopod (Fig. 283). — Of this we have a most beautiful example
in Bone; for whilst its solid substance may be considered as connective
tissue solidified by calcareous deposit, the 6 lacunae' and 'canaliculi'
which are excavated in it (Fig. 441) give lodgment to a set of radiating
corpuscles closely resembling those just described; and these are centres
of ' germinal matter/ which appear to have an active share in the for-
mation and subsequent nutrition of the osseous texture. In Dentine (or
tooth-substance) we seem to have another form of the same thing; the
walls of its 'tubuli' and the ' intertubular substance' (§ 655) being the
6 formed material' that is produced from thread-like prolongations of
'germinal matter' issuing from its pulp, and continuing during the life
of the tooth to occupy its tubes; just as in the Foraminifera we have
seen a minutely-tubular structure to be formed around the individual
threads of sarcode which proceded from the body of the contained ani-
mal (Figs. 314, 335). It may now be stated, indeed, with considerable
confidence, that the bodies of even the highest Animals are everywhere
penetrated by that sarcodic substance of which those of the lowest and
simplest are entirely composed; and that this substance, which forms
a continuous network through almost every portion of the fabric, is the
main instrument of the Formation, Nutrition, and Reparation of the
more specialized or differentiated Tissues. — As it is the purpose of this
work not to instruct the professional student in Histology (or the Sci-
ence of the Tissues), but to supply scientific information of general inter-
est to the ordinary Microscopist, no attempt will here be made to do more
than describe the most important of those distinctive characters which
the principal tissues present when subjected to Microscopic examination;
and as it is of no essential consequence what order is adopted, we may
conveniently begin with the structure of the skeleton,1 which gives sup-
port and protection to the softer parts of the fabric.

652. Bone. — The Microscopic characters of osseous tissue may some-
times may be seen in a very thin natural plate of bone, such as in that
forming the scapula (shoulder-blade) of a Mouse; but they are displayed
more perfectly by artificial sections, the details of the arrangement being
dependent upon the nature of the specimen selected, and the direction
in which the section is made. Thus when the shaft of a ' long ' bone of
a Bird or Mammal is cut-across in the middle of its length, we find it to
consist of a hollow cylinder of dense bone, surrounding a cavity which
is occupied by an oily marrow; but if the section be made nearer its ex-
tremity, we find the outside wall gradually becoming thinner, whilst the
interior, instead of forming one large cavity, is divided into a vast num-
ber of small chambers, partially divided by a sort of 6 lattice-work ' of
osseous fibres, but communicating with each other and with the cavity
of the shaft, and filled, like it, with marrow. In the bones of Keptiles
and Fishes, on the other hand, this 6 cancellated ' structure usually ex-
tends throughout the shaft, which is not so completely differentiated
into solid bone and medullary cavity as it is in the higher Vertebrata.

1 This term is used in its most general sense, as including not only the proper
vertebral or internal skeleton, but also the hard parts protecting the exterior of
the body, which form the dermal skeleton.

256

THE MICROSCOPE AND ITS REVELATIONS.

In the most developed kind of 'flat' bones, again, such as those of the
head, we find the two surfaces to be composed of dense plates of bone,
with a 'cancellated' structure between them; whilst in the less perfect
type presented to us in the lower Vertebrata, the whole thickness is usu-
ally more or less 4 cancellated,' that is, divided-up into minute medullary
cavities. — When we examine, under alow magnifying power, a longitu-
dinal section of a long bone, or a section of a flat bone parallel to its
surface, we find it traversed by numerous canals, termed Haversian after
their discoverer Havers, which are in connection with the central cavity,
and are filled, like it, with marrow: in the shafts of 'long' bones these
canals usually run in the direction of their length, but are connected
here and there by cross-branches; whilst in the flat-bones they form an
irregular network.— On applying a higher magnifying power to a thin
transverse section of a long bone, we observe that each of the canals
whose orifices present themselves in the field of view (Fig. 440), is the
centre of a rod of bony tissue (1), usually more or less circular in its

Fig. 440. Fig. 441.

Minute structure of Bone, as seen in transverse Lacunae of Osseous substance:— a, cen-
section:— 1, a rod surrounding an Haversian canal, tral cavity; 6, its ramifications
3, showing the concentric arrangement of the lam-
ellae; 2, the same, with the lacunae and canaliculi; 4,
portions of the lamellae parallel with the external
surface.

form, which is arranged around it in concentric rings, resembling those
of an Exogenus stem (Fig. 254). These rings are marked out and di-
vided by circles of little dark spots, which, when closely examined (2),
are seen to be minute flattened cavities excavated in the solid substance
of the bone, from the two flat sides of which pass forth a number of ex-
tremely minute tubules, one set extending inwards, or in the direction of
the centre of the system of rings, and the other outwards, or in the direc-
tion of its circumference; and by the inosculation of the tubules (or canalU
cull) of the different rings with each other, a continuous communication
is established between the central Haversian canal and the outermost part
of the bony rod that surrounds it, which doubtless ministers to the nu-
trition of the texture. Blood-vessels are traceable into the Haversian
canals, but the 'canaliculi' are far too minute to carry blood-corpuscles;
they are occupied, however, in the living bone, by threads of sarcodic
substance, which bring the segments of 'germinal matter' contained
in the lacunae into communication with the Avails of the blood-vessels.

VERTEBRATED ANIMALS.

257

653. The minute cavities or lacuna (sometimes, but erroneously-
termed ' bone-corpuscles/ as if they were solid bodies), from which the
canaliculi proceed (Fig. 441), are highly characteristic of the true osse-
ous structure; being never deficient in the minutest parts of the bones
of the higher Vertebrata, although those of Fishes are occasionally des-
titute of them. The dark appearance which they present in sections of
a dried bone is not due to opacity, but is simply an optical effect, depen-
dent (like the blackness of air-bubbles in liquids) upon the dispersion
of the rays by the highly refracting substance that surrounds them
(§ 153). The size and form of the lacunae differ considerably in the sev-
eral Classes of Vertebrata, and even in some instances in the Orders; so
as to allow of the determination of the tribe to which a bone belonged,
by the Microscopic examination of even a minute fragment of it (§ 705).
The following are the average dimensions of the lacunae, in characteris-
tic examples drawn from the four principal Classes expressed in frac-
tions of an inch : —

Long Diameter. Short Diameter.

Man 1-1440 to 1-2400 1-4000 to 1-8000

Ostrich 1-1333 to 1-2250 1-5425 to 1-9650

Turtle 1-375 to 1-1150 1-4500 to 1-5840

Conger-eel 1-550 to 1-1135 1-4500 to 1-8000

Fig. 442.

Section of the Bony Scale of Lepidosteus :— a. showing the regular distribution of the lacunae
and of the connecting canaliculi ; 6, small portion more highly magnified.

The lacunae of Birds are thus distinguished from those of Mammals by
their somewhat greater length and smaller breadth; but they differ still
more in the remarkable tortuosity of their canaliculi, which wind back-
wards and forwards in a very irregular manner. There is an extraordi-
nary increase in length in the lacunae of Reptiles, without a corresponding
increase in breadth; and this also seen in some Fishes, though in general
the lacunae of the latter are remarkable for their angularity of form
and the fewness of their radiations, — as shown in Fig. 442, which rep-
resents the lacunae and canaliculi in the bony scale of the Lepidosteus
('bony pike' of the North American lakes and rivers), with which the
bones of its internal skeleton perfectly agree in structure. The dimen-
sions of the lacunae in any bone do not bear any relation to the size of
the animal to which it belonged ; thus there is little or no perceptible
difference between their size in the enormous extinct Iguanodon, and in
the smallest Lizard now inhabiting the earth. But they bear a close rela-
tion to the size of the Blood-corpuscles in the several Classes; and this rela-
tion is particularly obvious in the ' perennibranchiate ? Batrachia, the ex-
traordinary size of whose blood-corpuscles will be presently noticed
(§ 665):-

258

THE MICROSCOPE AND ITS REVELATIONS.

Long Diameter.

Short Diameter.

Proteus
Siren .

1-570 to 1-980
1-290 to 1-480
1-450 to 1-700
1-375 to 1-494
1-445 to 1-1185

1-885 to 1-1200
1-540 to 1-975
1-1300 to 1-2100
1-980 to 1-2200
1-4000 to 1-5225 1

Menopoma .
Lepidosiren
Pterodactyle

654. In preparing Sections of Bone, it is important to avoid the
penetration of the Canada balsam into the interior of the lacunae and
canaliculi; since, when these are filled by it, they become almost invisible.
Hence it is preferable not to employ this cement at all, except it may be,
in the first instance; but to rub-down the section beneath the finger,
guarding its surface with a slice of cork or a slip of gutta-percha (§ 196);
and to give it such a polish that it may be seen to advantage even when
mounted dry. As the polishing, however, occupies much time, the bene-
fit which is derived from covering the surfaces of the specimen with
Canada balsam may be obtained, without the injury resulting from the
penetration of the balsam into its interior, by adopting the following
method: — a quantity of balsam proportioned to the size of the specimen
is to be spread upon a glass slip, and to be rendered stiffer by boiling,
until it becomes nearly solid when cold; the same is to be done to the
thin-glass cover; next, the specimen being placed on the balsamed sur-
face of the slide, and being overlaid by the balsamed cover, such a degree
of warmth is to be applied as will suffice to liquefy the balsam without
causing it to flow freely; and the glass-cover is then to be quickly pressed-
down, and the slide to be rapidly cooled, so as to give as little time as
possible for the penetration of the liquefied balsam into the lacunar sys-
tem.— The same method maybe employed in making sections of Teeth.
The study of the organic basis of Bone (commonly, but erroneously
termed cartilage) should be pursued by macerating a fresh bone in dilute
Nitro-hydrochloric acid, then macerating it for some time in pure water,
and then tearing thin shreds from the residual substance, which will
be found to consist of an imperfectly-fibrillated material, allied in its
essential constitution to the 6 white fibrous' tissue (§ 668).

655. Teeth. — The intimate structure of the Teeth in the several
Classes and Orders of Vertebrata, presents differences , which are no less
remarkable than those of their external form, arrangement, and succes-
sion. It will obviously be impossible here to do more than sketch some
of the most important of these varieties.— The principal part of the
substance of all teeth is made-up of a solid tissue that has been appro-
priately termed dentine. In the Shark tribe, as in many other Fishes,
the general structure of this dentine is extremely analogous to that of
bone; the tooth being traversed by numerous canals, which are con-
tinuous with the Haversian canals of the subjacent bone, and receive
blood-vessels from them (Fig. 443); and each of these canals being
surrounded by a system of tubuli (Fig. 444), which radiate into the sur-
rounding solid substance. These tubuli, however, do not enter lacunae,
nor is there any concentric annular arrangement around the medullary
canals; but each system of tubuli is continued onwards through its own

1 See Prof. J. Quekett's Memoir on this subject, in the Transac. of the Microsc.
Soc," Ser. 1, Vol. ii.; and his more ample illustration of it in the " Illustrated
Catalogue of the Histological Collection in the Museum of the Eoyal College of
Surgeons," Vol. ii.

2 Some useful hints on the mode of making these preparations will be found
in the ' 4 Quart. Journ. of Microsc. Science," Vol. vii. (1859), p. 258.

VERTEBRATED ANIMALS.

259

division of the tooth, the individual tubes sometimes giving-off lateral
branches, whilst in other instances their trunks bifurcate. This arrange-
ment is peculiarly well displayed, when sections of teeth constructed upon
this type are viewed as opaque objects (Fig. 445).— In the teeth of the
higher Vertebrata, however, we usually find the centre excavated into a
single cavity (Fig. 446), and the remainder destitute of vascular canals;
but there are intermediate cases (as in the teeth of the great fossil
Sloths) in which the inner portion of the dentine is traversed by pro-
longations of this cavity, conveying blood-vessels, which do not pass into
the exterior layers. The tubuli of the 'non-vascular' dentine, which
exists by itself in the teeth of nearly all Mammalia, and which in the
Elephant is known as 6 ivory/ all radiate from the central cavity, and
pass towards the surface of the tooth in a nearly parallel course. Their
diameter at their largest part averages l-10,000th of an inch; their
smallest branches are immeasurably fine. The tubuli in their course
present greater and lesser undulations; the former are few in number;

Fig. 443. Fig. 444.

Fig. 443. Perpendicular section of Tooth of Fig. 443. Transverse section of portion of

Lamna, moderately enlarged, showing network Tooth of Pristis, more highly magnified, show-
of medullary canals. ing orifices of medullary canals, with systems

of radiating and inosculating tubuli.

but the latter are numerous, and as they occur at the same part of the
course of several contiguous tubes they give rise to the appearance of
lines concentric with the centre of radiation. These ' secondary curva-
tures ' probably indicate, in dentine, as in the Crab's shell (§ 613), suc-
cessive stages of calcification. — The tubuli are occupied, during the life
of the tooth, by delicate threads of protoplasmic substance, extending
into them from the central pulp.

656. In the Teeth of Man and most other Mammals, and in those of
many Reptiles and some Fishes, we find two other substances, one of
them harder, and the other softer, than dentine; the former is termed
enamel; and the latter cementum or crusta petrom. — The enamel is com-
posed of long prisms, closely resembling those of the 6 prismatic ' Shell-
substance formerly described (§ 563), but on a far more minute scale;
the diameter of the prisms not being more in Man than l-5600th of an
inch. The length of the prisms corresponds with the thickness of the
layer of enamel; and the two surfaces of this layer present the ends of

260

THE MICROSCOPE AND ITS REVELATIONS.

the prisms, the form of which usually approaches the hexagonal. The
course of the enamel-prisms is more or less wavy; and they are marked
by numerous transverse striae, resembling those of the prismatic shell-
substance, and probably originating in the same cause, — the coalescence
of a series of shorter prisms to form the lengthened prism. In Man and
in Carnivorous animals the enamel covers the crown of the tooth only,
with a simple cap or superficial layer of tolerably uniform thickness
(Fig. 446, a), which follows the surface of the dentine in all its inequali-
ties; and its component prisms are directed at right angles to that surface,
their inner extremities resting in slight but regular depressions on the ex-
terior of the dentine. In the teeth of many Herbivorous animals, however,
the enamel forms (with the cementum) a series of vertical plates, which
dip down into the substance of the dentine, and present their edges alter-
nately with it, at the grinding surface of the tooth; and there is in such
teeth no continuous layer of enamel over the crown. This arrangement
provides, by the unequal wear of these three substances (of which the
enamel is the hardest, and the cementum the softest), for the constant

Fig. 445. Fig. 446.

Transverse section of Tooth of Myliobates
(Eagle Ray) viewed as an opaque object.

Vertical section of Human Molar Tooth:
a, enamel; b, cementum or crusta petrosa;
c, dentine or ivory ; d, osseous excrescence,
arising from hypertrophy of cementum; e,
pulp-cavity ; /, osseous lacunae at outer part
of dentine.

maintenance of a rough surface, adapted to triturate the tough vegetable
substances on which these animals feed. The enamel is the least constant
of the dental tissues. It is more frequently absent than present in the
teeth of Fishes; it is entirely wanting in the teeth of Serpents; and it
forms no part of those of the Edentata1 (sloths, etc.) and Cetacea
(whales) among Mammals. — The cementum, or crusta petrosa, has the
characters of true bone; possessing its distinctive stellate, lacunae and
radiating canaliculi. Where it exists in small amount, we do not find it
traversed by medullary canals; but, like dentine, it is occasionally
furnished with them, and thus resembles bone in every particular.
These medullary canals enter its substance from the exterior of the tooth,

1 It has been shown by Mr. Charles Tomes, however, that the 'enamel organ'
is originally present within the tooth-capsule of the Armadillo, though it under-
goes an early degeneration; — a fact of no little interest in connection with the
general doctrine of 1 Descent with modification.'

VERTEBRATED ANIMALS.

261

and consequently pass towards those which radiate from the central cav-
ity in the direction of the surface of the dentine, where this possesses a
similar vascularity,- — as was remarkably the case in the teeth of the great
extinct Megatherium. In the Human tooth, however, the cementum has
no such vascularity; but forms a thin layer (Fig. 446, which envelops
the root of the tooth, commencing near the termination of the cap of
enamel. In the teeth of many herbivorous Mammals, it dips down with
the enamel to form the vertical plates of the interior of the tooth; and
in the teeth of the Edentata, as well as of many Reptiles and Fishes, it
forms a thick continuous envelope over the whole surface, until worn-
away at the crown.

657. Dermal skeleton. — The skin of Fishes, of most Reptiles, and ot
a few Mammals, is strengthened by plates of a horny, cartilaginous, bony,
or even enamel-like texture; which are sometimes fitted-together at their
edges, so as to form a continuous box-like envelope; whilst more com-
monly they are so arranged as partially to overlie one another, like the
tiles on a roof; and it is in this latter case that they are usually known
as scales. Although we are accustomed to associate in our minds the
6 scales' of Fishes with those of Reptiles, yet they are essentially-different
structures; the former being developed in the substance of the true skin
(with a layer of which, in addition to the epidermis, they are always cov-
ered), and bearing a resemblance to cartilage and bone in their texture
and composition; whilst the latter are formed upon the surface of the
true skin, and are to be considered as analogous to nails, hoofs, etc., and
other ' epidermic appendages/ In nearly all the existing Fishes the scales
are flexible, being but little consolidated by calcareous deposit; and in
some species they are so thin and transparent, that, as they do not pro-
ject obliquely from the surface of the skin, they can only be detected by
raising the superficial layer of the skin, and searching beneath it, or
by tearing off the entire thickness of the skin, and looking for them near
its under surface. This is the case, for example, with the common Eel,
and with the viviparous Blenny; of either of which fish the skin is a
very interesting object when dried and mounted in Canada balsam, the
scales being seen imbedded in its substance, whilst its outer surface is
studded with pigment-cells. Generally speaking, however, the posterior
extremity of each scale projects obliquely from the general surface, carry-
ing before it the thin membrane that incloses it, which is studded with
pigment-cells; and a portion of the skin of almost any Fish, but especially
of such as have scales of the ctenoid kind (that is, furnished at their pos-
terior extremities with comb-like teeth, Fig. 448), when dried with its
scales in situ, is a very beautiful opaque object for the low powers of the
Microscope (Fig. 447), especially with the Binocular arrangement. Care
must be taken, however, that the light is made to glance upon it in the
most advantageous manner; since the brilliance with which it is reflected
from the comb-like projections entirely depends upon the angle at which
it falls upon them. The only appearance of structure exhibited by the
thin flat scale of the Eel, when examined microscopically, is the presence
of a layer of isolated spheroidal transparent bodies, imbedded in a plate
of like transparence; these, from the researches of Prof. W. C. William-
son1 upon other scales, appear not to be cells (as they might readily be

1 See his elaborate Memoirs * On the Microscopic Structure of the Scales and
Dermal Teeth of some Ganoid and Placoid Fish,' in "Philos. Transact.," 1849; and
* Investigations into the Structure and Development of the Scales and Bones of
Fishes,' in " Philos. Transact.," 1851.

262

THE MICROSCOPE AND ITS REVELATIONS.

supposed to be), but concretions of Carbonate of Lime. When the scale
of the Eel is examined by Polarized light, its surface exhibits a beautiful
St. Andrew's cross; and if a plate of Selenite be placed behind it, and
the analyzing prism be made to revolve, a remarkable play of colors is
presented.

658. In studying the structure of the more highly developed scales,
we may take as an illustration that of the Carp; in which two very dis-
tinct layers can be made-out by a vertical section, with a third but incom-
plete layer interposed between them. The outer layer is composed of
several concentric laminae of a structureless transparent substance, like
that of cartilage; the outermost of these laminae is the smallest, and the
size of the plates increases progressively from without inwards, so that
their margins appear on the surface as a series of concentric lines; and
their surfaces are thrown into ridges and furrows, which commonly have
a radiating direction. The inner layer is composed of numerous laminae

Portion of Skin of Sole, viewed as an opaque object. Scale of Sole, viewed as a trans-

parent object.

of a fibrous structure, the fibres of each lamina being inclined at various
angles to those of the lamina above and below it. Between these two
layers is interposed a stratum of calcareous concretions, resembling those
of the scale of the Eel: these are sometimes globular or spheroidal, but
more commonly * lenticular/ that is, having the form of a double-convex
lens. The scales which resemble those of the Carp in having a form
more or less circular, and in being destitute of comb-like prolongations,
are called cycloid; and such are the characters of those of the Salmon,.
Herring, Koach, etc. The structure of the ctenoid scales (Fig. 448),.
which we find in the Sole, Perch, Pike, etc., does not differ essentially
from that of the cycloid, save as to the projection of the comb-like teeth
from the posterior margin; and it does not appear that the strongly-
marked divisions which Prof. Agassiz has attempted to establish between
the ' cycloid' and the 6 ctenoid' Orders of Fishes, on the basis of this
difference, is in harmony with their general organization. Scales of every
kind may become consolidated to a considerable extent by the calcifica-
tion of their soft substance; but still they never present any approach to

VERTEBKATED ANIMALS,

263

the true Bony structure, such as is shown in the two Orders to be next
adverted-to.

659. In the ganoid Scales, on the other hand, the whole substance of
the scale is composed of a substance which is essentially bony in its nature:
its int-imate structure being always comparable to that of one or other of
the varieties which present themselves in the bones of the Vertebrate
skeleton; and being very frequently identical with that of the bones of
the same fish, as is the case with the Lepidosteus (Fig. 442), one of the
few existing representatives of this Order, which, in former ages, of the
Earth's history, comprehended a large number of important families.
Their name (from yavo5y splendor) is bestowed on account of the smooth-
ness, hardness, and high polish of the outer surface of the scales; which
is due to the presence of a peculiar layer that has been likened (though
erroneously) to the enamel of teeth, and is now distinguished as ganoin.
The scales of this order are for the most part angular in their form; and
are arranged in regular rows, the posterior edges of each slightly over-
lapping the anterior ones of the next, so as to form a very complete
defensive armor to the body. — The scales of the placoid type, which
characterizes the existing Sharks and Kays, with their fossil allies, are
irregular in their shape, and very commonly do not come into mutual
contact, but are separately imbedded in the skin, projecting from its sur-
face under various forms. In the Eays each scale usually consists of a
flattened plate of a rounded shape, with a hard spine projecting from its
centre; in the Sharks (to which tribe belongs the ' dog-fish 9 of our own
coast) the scales have more of the shape of teeth. This resemblance is
not confined to external form; for their intimate structure strongly resem-
bles that of dentine, their dense substance being traversed by tubuli,
which extend from their centre to their circumference in minute ramifi-
cations, without any trace of osseous lacunae. These tooth-like scales are
often so small as to be invisible to the naked eye; but they are well seen
by drying a piece of the skin to which they are attached, and mounting
it in Canada balsam; and they are most brilliantly shown by the assistance
of polarized light. — A like structure is found to exist in the 6 spiny rays '
of the dorsal fin, which, also, are parts of the dermal skeleton; and these
rays usually have a central cavity filled with medulla, from which the
tubuli radiate towards the circumference. This structure is very well
seen in thin sections of the fossil c spiny rays/ which, with the teeth and
scales, are often the sole relics of the vast multitudes of Sharks that must
have swarmed in the ancient seas, their cartilaginous internal skeletons
having entirely decayed away. — In making sections of bony Scales,
Spiny rays, etc., the method must be followed which has been already de-
tailed under the head of Bone (§ 654).

660. The scales of Keptiles, the feathers of Birds, and the hairs, hoofs,
nails, claivs, and horns (when not bony) of Mammals, are all epidermic
appendages; that is, they are produced upon the surface, not within the
substance, of the true Skin, and are allied in structure to the Epidermis
(§ 671); being essentially composed of aggregations of cells filled with
horny matter, and frequently much altered in form. This structure may
generally be made-out in horns, nails, etc. - with little difficulty; by treating
thin sections of them with a dilute solution of soda; which after a short time
causes the cells that had been flattened into scales, to resume their globu-
lar form. The most interesting modifications of this structure are pre-
sented to us in Hairs and in Feathers; which forms of clothing are very
similar to each other in their essential nature, and are developed in the

264

THE MICROSCOPE AND ITS REVELATIONS.

same manner — namely, by an increased production of epidermic cells at
the bottom of a flask-shaped follicle, which is formed in the substance of
the true skin, and which is supplied with abundance of blood by a spe-
cial distribution of vessels to its walls. When a hair is pulled-out i by its
root/ its base exhibits a bulbous enlargement, of which the exterior is
tolerably firm, whilst its interior is occupied by a softer substance, which
is known as the 'pulp;' and it is to the continual augmentation of this
pulp in the deeper part of the follicle, and to its conversion into the pe-
culiar substance of the hair when it has been pushed upwards to its nar-
row neck, that the growth of the hair is due. — The same is true of feath-
ers, the stems of which are but hairs on a larger scale; for the ' quill ' is
the part contained within the follicle answering to the ' bulb' of the hair;
and whilst the outer part of this is converted into the peculiarly-solid
horny substance forming the ' barrel ' of the quill, its anterior is occupied,
during the whole period of the growth of the feather, with the soft pulp,

Fig. 449. Fig. 450. Fig. 451.

A B 0

interior, covered by lygonal cells,
imbricated scales or A, Small Hair of Squirrel t — b, Large Hair

flattened cells. of Squirrel: — c, Hair of Indian Bat.

only the shrivelled remains of which, however, are found within it after
the quill has ceased to grow.

661. Although the hairs of different Mammals differ greatly in the
appearances they present, we may generally distinguish in them two ele-
mentary parts — namely, a cortical or investing substance, of a dense horny
texture, and a medullary or pith-like substance, usually of a much softer
texture, occupying the interior. The former can sometimes be distinctly
made out to consist of flattened scales arranged in an imbricated manner,
as in some of the hairs of the Sable (Fig. 449); whilst, in the same hairs,
the medullary substance is composed of large spheroidal cells. In the
Musk-deer, on the other hand, the cortical substance is nearly undistin-
guishable; and almost the entire hair seems made up of thin- walled poly-
gonal cells (Fig. 450). The hair of the Reindeer, though much larger,
has a very similar structure; arid its cells, except near the root, are occu-
pied with hair alone, so as to seem black by transmitted light, except
when penetrated by the fluid in which they are mounted. In the hair of
the Mouse, Squirrel, and other small Kodents (Fig. 451, A, b), the corti-

VERTEBRATED ANIMALS.

265

Fig. 452.

cal substance forms a tube, which we see crossed at intervals by partitions
that are sometimes complete, sometimes only partial; these are the walls
of the single or double line of cells, of which the medullary substance is
made-up. The hairs of the Bat tribe are commonly distinguished by the
projections on their surface, which are formed by extensions of the com-
ponent scales of the cortical substance: these are particularly well seen in
the hairs of one of the Indian species, which has a set of whorls of long
narrow leaflets (so to speak) arranged at regular intervals on its stem (c).
In the hair of the Pecari (Pig. 452), the cortical
envelope sends inwards a set of radial prolonga-
tions, the interspaces of which are occupied by
the polygonal cells of the medullary substance;
and this, on a larger scale, is the structure of
the 'quills' of the Porcupine; the radiating
partitions of which, when seen through the
more transparent parts of the cortical sheath,
give to the surface of the latter a fluted appear-
ance. The hair of the Ornithorhynchus is a
very curious object; for whilst the lower part of
it resembles the fine hair of the Mouse or Squirrel, this thins away and
then dilales again into a very thick fibre, having a central portion com-
posed of polygonal cells, inclosed in a flattened sheath of a brown fibrous
substance.

662. The structure of the human Hair is in certain respects peculiar.

' Transverse section of Hair of
Pecari.

Fig. 453.

Structure of Human Hair:— a, external surface of the shaft, showing the transverse striae and
jagged boundary caused by the imbrications of the cuticular layer; b, longitudinal section of the
shaft, showing the fibrous character of the cortical substance, and the arrangement of the pig-
mentary matter; c, transverse section, showing the distinction between the cuticular envelope, the
cylinder of cortical substance, and the medullary centre ; d, another transverse section, showing
deficiency of the central cellular substance.

When its outer surface is examined, it is seen to be traversed by irregular
lines (Fig. 453, a), which are most strongly marked in foetal hairs; and
these are the indications of the imbricated arrangement of the flattened
cells or scales which form the cuticular layer. This layer, as is shown by
transverse sections (c, d), is a very thin and transparent cylinder; and it
incloses the peculiar fibrous substance that constitutes the principal part
of the shaft of the hair. The constituent fibres of this substance, which
are marked-out by the delicate striae that may be traced in longitudinal
sections of the hair (b), may be separated from each other by crushing

266

THE MICROSCOPE AND ITS REVELATIONS.

the hair, especially after it has been macerated for some time in sulphuric
acid; and each of them, when completely isolated from its fellows, is found
to be a long spindle-shaped cell. In the axis of this fibrous cylinder there
is very commonly a band which is formed of spheroidal cells; but this
6 medullary 9 substance is usually deficient in the fine hair scattered over
the general surface of the body, and is not always present in those of the
head. The hue of the Hair is due partly to the presence of pigmentary
granules, either collected into patches, or diffused through its substance;
but partly also to the existence of a multitude of minute air-spaces, which
cause it to appear dark by transmitted and white by reflected light. The
cells of the medullary axis in particular, are very commonly found to con-
tain air, giving it the black appearance shown at c. The difference be-
tween the blackness of pigment and that of air-spaces may be readily de-
termined by attending to the characters of the latter as already laid-down
(§§ 153, 154); and by watching the effects of the penetration of Oil of
Turpentine or other liquids, which do not alter the appearance of pig-
ment-spots, but obliterate all the markings produced by air-spaces, these
returning again as the hair dries. — In mounting Hairs as Microscopic
preparations, they should in the first instance be cleansed of all their fatty
matter by maceration in ether; and they may then be put up either in
weak Spirit or in Canada balsam, as may be thought preferable, the
former menstruum being well adapted to display the characters of the
finer and more transparent hairs, while the latter allows the light to pen-
etrate more readily through the coarser and more opaque. Transverse
sections of Hairs are best made by gluing or gumming several together,
and then putting them into the Microtome; those of Human hair may
be easily obtained, however, by shaving a second time, very closely, a part
of the surface over which the razor has already passed more lightly, and
by picking-out from the lather, and carefully washing the sections thus
taken-off.

663. The stems of feathers exhibit the same kind of structure as
Hairs; their cortical portion being the horny sheath that envelops the
shaft, and their medullary portion being the pith-like substance which
that sheath includes. In small feathers, this may usually be made very
plain by mounting them in Canada balsam; in large feathers, however,
the texture is sometimes so altered by the drying up of the pith (the cells
of which are always found to be occupied by air alone), that the cellular
structure cannot be demonstrated save by boiling thin slices in a dilute
solution of potass, and not always even then. In small feathers, especially
such as have a downy character, the cellular structure is very distinctly
seen in the lateral barbs, which are sometimes found to be composed of
single files of pear-shaped cells, laid end-to-end; but in larger feathers it
is usually necessary to increase the transparence of the barbs, especially
when these are thick and but little pervious to light, either by soaking
them in turpentine, mounting them in Canada balsam, or boiling them
in a weak solution of potass. In feathers which are destined to strike
the air with great force in the act of flight, we find each barb fringed on
either side with slender flattened filaments or 'barbules;' the barbules of
one side of each barb are furnished with curved hooks, whilst those of
the other side have thick turned-up edges; and as the two sets of barbules
that spring from two adjacent barbs cross one another at an angle, and *
as each hooked barbule of one locks into the thickened edge of several
barbules of the other, the barbs are connected very firmly, in a mode very
similar to that in which the anterior and posterior wings of certain Hy-

VERTEBRATED ANIMALS.

267

Fig. 454.

menopterous Insects are locked together (§ 638). — Feathers or portions
of feathers of Birds distinguished by the splendor of their plumage are
very good objects for low magnifying powers, when illuminated on an
opaque ground; but care must be taken that the light falls upon them at
the angle necessary to produce their most brilliant reflection into the
axis of the Microscope; since feathers which exhibit the most splendid
metallic lustre to an observer at one point, may seem very dull to the eye
of another in a different position. The small feathers of Humming-birds,
portions of the feathers of the Peacock, and others of a like kind, are well
worthy of examination; and the scientific Microscopist, who is but little
attracted by mere gorgeousness, may well apply himself to the discovery
of the peculiar structure which imparts to these objects their most remark-
able character.

664. Sections of horns, hoofs, clmos, and other like modifications of
Epidermic structure, — which can be easily made by the Microtome
(§ 184), the substance to be cut having been softened, if necessary, by
soaking in warm water, — do not in general afford any very interesting
features when viewed in the ordinary mode; but there are no objects on
which Polarized light produces more
remarkable effects, or which display
a more beautiful variety of colors
when a plate of Selenite is placed be-
hind them and the analyzing prism
is made to rotate. A curious modi-
fication of the ordinary structure of
Horn is presented in the appendage
borne by the Rhinoceros upon its
snout, which in many points resem-
bles a bundle of hairs, its substante
being arranged in minute cylinders
around a number of separate centres,
which have probably been formed
by independent papillae (Fig. 454).
When transverse sections of these
cylinders are viewed by polarized
light, each of them is seen to be
marked by a cross, somewhat resem-
bling that of Starch-grains; and the

light and shadow of this cross are replaced by contrasted colors when the
Selenite plate is interposed. — The substance commonly but erroneously
termed whalebone, which is formed from the surface of the membrane
that lines the mouth of the Whale, and has no relation to its true bony
skeleton, is almost identical in structure with Ehinoceros horn, and is
similarly affected by polarized light. The central portion of each of its
component threads, like the medullary substance of Hairs, contains cells
that have been so little altered as to be easily recognized; and the outer
or cortical portion also may be shown to have a like structure, by macer-
ating it in a solution of potass, and then in water. — Sections of any of
the Horny tissues are best mounted in Canada balsam.

665. Blood. — Carrying our Microscopic survey, now, to the elemen-
tary parts of which those softer tissues are made up, that are subservient
to the active life of the body rather than to its merely-mechanical re-
quirements, we shall in the first place notice the isolated floating cells
contained in the Blood, which are known as Blood-corpuscles. These

Transverse section of Horn of Ehinoceros,
viewed by Polarized Light.

268

THE MICROSCOPE AND ITS REVELATIONS.

are of two kinds; the ' red/ and the 'white' or ' colorless/ — The red
present, in every instance, the form of a flattened disk, which is circular
in Man and most Mammalia (Fig. 456), but is oval in Birds, Reptiles
(Fig. 455), and Fishes, as also in a few Mammals (all belonging to the
Camel tribe). In the one form, as in the other, these corpuscles seem to
be flattened cells, the walls of which, however, are not distinctly differ-
entiated from the ground-substance they contain; as appears from the
changes of form which they spontaneously undergo when kept by means
of a ' warm stage ' 1 at a temperature of about 100°, and from the effects
of pressure in breaking them up. The red corpuscles in the blood of
Oviparous Vertebrata are distinguished by the presence of a central spot
or nucleus; this is most distinctly brought into view by treating the
blood-disks with acetic acid, which causes the nucleus to shrink and be-
come more opaque, whilst rendering the remaining portion extremely
transparent (Fig. 455, d). By examining unaltered red corpuscles of the
Frog or Newt under a sufficiently high magnifying power, the nucleus is
seen to be traversed by a network of filaments, which extends from it

Fig. 455. Fig. 456.

Red Corpuscles of Frog's Blood:— a a,
their flattened face; 6, particle turned
nearly edgeways ; c, colorless corpuscle ; c£,
red corpuscles altered by diluted acetic acid.

Red Corpuscles of Human Blood;
represented at a, as they are seen when
rather within the focus of the Microscope,
and at b as they appear when precisely in
the focus.

throughout the ground-substance of the corpuscle, constituting an intra-
cellular reticulation. — The red corpuscles of the blood of Mammals, how-
ever, possess no distinguishable nucleus; the dark spot which is seen in
their centre (Fig. 456, b) being merely an effect of refraction, consequent
upon the double-concave form of the disk. When these corpuscles are
treated with water, so that their form becomes first flat, and then double-
convex, the dark spot disappears; whilst, on the other hand, it is made

1 A very simple mode of applying continued warmth to an object under obser-
vation, is to lay the slide on a thin plate of brass or tin, about 3 inches longer
than the breadth of the stage, and about 2 inches broad; which must be perfor-
ated with a hole about l~4th inch in diameter, at the distance of half the breadth
of the stage from one end of it. When this plate is laid on the stage, and its hole
is brought into the optic axis, so as to allow the light reflected upwards from the
mirror to pass to the slide laid upon it, the plate will project about 8 inches on
one side of the stage, — preferably the right. By placing a small lamp beneath
this projection and keeping the finger of the left hand on the part of the plate
close to the object (so as to feel the degree of warmth imparted to it), the heat
given by the lamp may be regulated by varying its position. — For more exact and
continuous regulation of the temperature, recourse may be had to the 4 warm
stage 9 devised by Prof. Schaf er and made by Mr. Casella, which is traversed by a
current of warm water. See " Quart. Joiirn. of Microsc. Sci.," N.S., Vol. xiv.
(1874), p. 394.

VERTEBRATED ANIMALS.

26&

more evident when the concavity is increased by the partial shrinkage of
the corpuscles, which may be brought about by treating them with fluids
of greater density than their own substance. When floating in a suffi-
ciently thick stratum of blood drawn from the body, and placed under a
cover-glass, the red corpuscles show a marked tendency to approach one
another, adhering by their discoidal surfaces so as to present the aspect
of a pile of coins; or, if the stratum be too thin to admit of this, partially
overlapping, or simply adhering by their edges, which then become
polygonal instead of circular. The size of the red corpuscles is not alto-
gether uniform in the same blood; thus it varies in that of Man from
about the l-4000th to the l-2800th of an inch. But we generally find
that there is an average size, which is pretty constantly maintained
among the different individuals of the same species; that of Man may be
stated at about l-3200th of an inch. The following Table 1 exhibits the
average dimensions of some of the most interesting examples of the red
corpuscles in the four classes of Vertebrated Animals, expressed in frac-
tions of an inch. Where two measurements are given, they are the long
and the short diameters of the same corpuscles. (See also Fig. 45?).

MAMMALS.

Man. 1-3200

Dog 1-3542

Whale 1-3099

Elephant 1-2745

Mouse 1-3814

Camel 1-3254, 1-5921

Llama 1-3361, 1-6294

Java Musk-Deer 1-12325

Caucasian Goat 1-7045

Two-toed Sloth 1-2865

BIRDS.

Golden Eagle 1-1812, 1-3832

Owl 1-1830, 1-3400

Crow 1-1961, 1 4000

Blue-Tit 1-2313, 1-4128

Parrot 1-1898, 1-4000

Ostrich 1-1649, 1-3000

Cassowary 1-1455, 1-2800

Heron 1-1913, 1-3491

Fowl 1-2102, 1-3466

Gull 1-2097, 1-4000

REPTILES AND BATRACHIA.

Turtle 1-1231, 1-1882

Crocodile 1-1231, 1-2286

Green Lizard 1-1555, 1-2743

Slow-worm 1-1178, 1-2666

Viper 1-1274, 1-1800

Frog 1-1108, 1-1821

Water-Newt 1-8014, 1-1246

Siren 1-420, 1-760

Proteus 1 -400, 1-727

Amphiuma 1-345, 1-561

FISHES.

Perch 1-2099, 1-2824

Carp 1-2142, 1-3429

Gold-Fish 1-1777, 1-2824

Pike 1-2000, 1-3555

Eel 1-1745, 1-2842

Gymnotus 1-1745, 1-2599

Thus it appears that the smallest red corpuscles known are those of the
Musk-deer; whilst the largest are those of that curious group of Ba-
trachia (Frog-tribe) which retain the gills through the whole of life; and
one of the oval blood-disks of the Proteus, being more than 30 times as
long and 17 times as broad as those of the Musk-deer, would cover no
fewer than 510 of them. — Those of the Amphiuma are still larger.2 — Ac-
cording to the estimate of Vierordt, a cubic inch of Human blood con-

1 These measurements are chiefly selected from those given by Mr. Gulliver,
in his edition of Hewson's Works, p. 236 et seq.

2 A very interesting account of the 4 Structure of the Red Corpuscles of the
Amphiuma tridactylum' has been given bv Dr. H. D. Schmidt, of New Orleans,
in the " Journ. of the Royal Microsc. Society," Vol. i. (1879;, pp. 57, 97.

270

THE xMICROSCOPE AND ITS REVELATIONS.

Fig. 457.

tains upwards of eighty millions of red corpuscles, and nearly a quarter
of a million of the colorless.

666. The white or ' colorless ' corpuscles are more readily distin-v
guished in the blood of Eeptiles than in that of Man; being in the for-
mer case of much smaller size, as well as having a circular outline (Fig. ,
455, c); whilst in the latter their size and contour are so nearly the
same, that, as the red corpuscles themselves, when seen in a single layer,
have but a very pale hue, the deficiency of color does not sensibly mark
their difference of nature. The proportion of white to red corpuscles
being scarcely ever greater (in a healthy Man) than 1 to 250, and often
as low as from one-half to one-quarter of that ratio, there are seldom

many of them to be seen in the field
at once; and these may be recog-
nized rather by their isolation than
their color, especially if the glass
cover be moved a little on the slide,
so as to cause the red corpuscles to
become aggregated into rows and
irregular masses. — It is remarkable
that, notwithstanding the great
variations in the sizes of the red cor-
puscles indifferent species of Verte-
brated animals, the size of the white
is extremely constant throughout,
their diameter being seldom much
greater or less than l-3000th of an
inch in th e warm-blooded classes, and
l-2500th in Eeptiles. Their ordin-
ary form is globular; but their aspect
is subject to considerable variations,
which seem to depend in great part
upon their phase of development.
Thus, in their early state, in which
they seem to be identical with the
corpuscles found floating in chyle
and lymph, they seem to be nearly
homogeneous particles of protoplas-
mic substance; but in their more
advanced condition, according to Dr.
Klein, their substance consists of a
reticulation of very fine contractile
protoplasmic fibres, termed the ' in-
tracellular network;' in the meshes
of which a hyaline interstitial mate-
rial is included; and which is contin-
uous with a similar network that can be discerned in the substance of
the single or double nucleus, when this comes into view after the with-
drawal of these corpuscles from the body. In their living state, how-
ever, whilst circulating in the vessels, the white corpuscles, although
clearly distinguishable in the slow-moving stratum ift contact with their
walls (the red corpuscles rushing rapidly through the centre of the tube),
do not usually show a distinct nucleus. This may be readily brought
into view by treating the corpuscles with water, which causes them to
swell up, become granular, and at last disintegrate, with the emission of

Jl. i Li

Comparative sizes of Red Blood-Corpuscles :
— 1. Man; 2. Elephant; 3. Musk-Deer; 4. Drome-
dary; 5. Ostrich; 6. Pigeon; 7. Humming Bird;
8. Crocodile; 9. Python; 10. Proteus, 11. Perch;
2. Pike; 13. Shark.

VERTEBRATED ANIMALS.

271

granules which may have been previously seen in active molecular move-
ment within the corpuscle. — When the white corpuscles in a drop of
freshly drawn blood are carefully watched for a short time, they may be
observed to undergo changes of form, and even to move from place to
place, after the manner of Amcebce (§ 403). When thus moving, they
engulf particles which lie in their course — such as granules of vermilion
that have been injected into the blood-vessels of the living animal, — and
afterwards eject these, in the like fashion. Such movements will continue
for some time in the colorless corpuscles of cold-blooded animals, but
still longer if they are kept in a temperature of about 75°. The move-
ment will speedily come to an end, however, in the white corpuscles of
Man or other warm-blooded animals, unless the slide is kept on a warm
stage at the temperature of about 100° F. A remarkable example of an
extreme change of form in a White corpuscle of Human blood, is repre-
sented in Fig. 458. Similar changes have been observed also in the cor-
puscles floating in the circulating fluid of the higher Invertebrata, as the
Crab, which resemble the ' white ' corpuscles of Vertebrated blood,
rather than its 'red' corpuscles, —

these last, in fact, being altogether fig. 458.

peculiar to the circulating fluid of
Vertebrated animals.

667. In examining the Blood mi-
croscopically, it is, of course, impor-
tant to obtain as thin a stratum of
it as possible, so that the corpuscles
may not overlie one another. This
is best accomplished by selecting a
piece of thin glass of perfect flatness,
and then, having received a small
drop of Blood upon a glass slide,
to lay the thin-glass cover not upon
this, but with its edge just touching
the edge of the drop; for the blood Altered White Corpuscles of Blood, an

Will then be drawn-Ill by Capillary hour after having been drawn from the finger.

attraction, so as to spread in a uni-
formly-thin layer between the two glasses. Such thin films may be pre-
served in the liquid state by applying a cover-glass and cementing it with
gold size before evaporation has taken place; but it is preferable first to
expose the drop to the vapor of Osmic acid, and then to apply a drop of
a weak solution of Acetate of Potass; after which a cover-glass may be
put on, and secured with gold-size in the usual way. It is far simpler,
however, to allow such films to dry without any cover, and then merely
to cover them for protection; and in this condition the general charac-
ters of the corpuscles can be very well made-out, notwithstanding that
they have in some degree shrivelled by the desiccation they have under-
gone. And this method is particularly serviceable, as affording a fair
means of comparison, when the assistance of the Microscopist is sought
in determining, for Medico-legal purposes, the source of suspicious
blood-stains; the average dimensions of the dried blood-corpuscles of the
several domestic animals being sufficiently different from each other, and
from those of Man, to allow the nature of any specimen to be pro-
nounced-upon with a high degree of probability.

668. Simple Fibrous Tissues, — A very beautiful example of a tissue
of this kind is furnished by the membrane of the common Fowl's egg;

272

THE MICROSCOPE AND ITS REVELATIONS.

which (as may be seen by examining an egg whose shell remains soft for
want of consolidation by calcareous particles) consists of two principal
layers, one serving as the basis of the shell itself, and the other forming
that lining to it which is know as the membrana putaminis. The latter
may be separated by careful tearing with needles and forceps, after pro-
longed maoeration in water, into several matted lamellae resembling that
represented in Fig. 459; and similar lamellae may be readily obtained
from the shell itself, by dissolving away its lime by dilute acid.1 — The
simply-fibrous structures of the body generally, however, belong to one
of two very definite kinds of tissue, the ' white ' and the * yellow/ whose ap-
pearance, composition, and properties are very different. The white fibrous
tissue, though sometimes apparently composed of distinct fibres, more
commonly presents the aspect of bands, usually of a flattened form, and
attaining the breadth of 1 -500th of an inch, which are marked by nume-
rous longitudinal streaks, but can seldom be torn-tip into minute fibres
of determinate size. The fibres and bands are occasionally somewhat
wavy in their direetion; and they have a peculiar tendency to fall into

Fig. 459. Fig. 460.

Fibrous membrane from Egg-shell. White Fibrous Tissue from Ligament.

undulations, when it is attempted to tear them apart from each other
(Fig. 460). This tissue is easily distinguished from the other by the
effect of Acetic acid, which swells it up and renders it transparent, at
the same time bringing into view certain oval nuclear particles of 6 ger-
minal matter/ which are known as ' connective-tissue corpuscles 9 (§ 651).
These are relatively much larger, and their connections more distinct,
in the earlier stages of the formation of this tissue (Fig. 461). It is per-
fectly inelastic; and we find it in such parts as tendons, ordinary ligaments,
fibrous capsules, etc., whose function it is to resist tension without yield-
ing to it. It constitutes, also, the organic basis or matrix of bone; for
although the substance which is left when a bone has been macerated
sufficiently long in dilute acid for all its Mineral components to be re-
moved, is commonly designated as cartilage, this is shown by careful
Microscopic analysis not to be a correct description of it; since it does
not show any of the characteristic structure of cartilage, but is capable
of being torn into lamellae, in which, if sufficiently thin, the ordinary
structure of a fibrous membrane can be distinguished. — The yellow

1 For an account of the curious form in which the Carbonate of Lime is dis-
posed in the Egg shell, see§ 710.

VERTEBRATED ANIMALS.

273

fibrous tissue exists in the form of long, single, elastic, branching fila-
ments with a dark decided border; which are disposed to curl when not
put on the stretch (Fig. 462), and frequently anastomose, so as to form
a network. They are for the most part between l-5000th and 1-10, 000th
of an inch in diameter; but they are often met with both larger and
smaller. This tissue does not undergo any change, when treated with
Acetic acid. It exists alone (that is without any mixture of the white)
in parts which require a peculiar elasticity, such as the middle coat of
arteries, the ' vocal cords/ ' ligamentum nuchal of Quadrupeds, the elas-
tic ligament which holds together the valves of a Bivalve shell, and that
by which the claws of the Feline tribe are retracted when not in use;
and it enters largely into the composition of areolar or connective tis-
sue.

669. The tissue formerly known to Anatomists as 6 cellular,' but now
more properly designated connective or areolar tissue, consists of a net-

Fig. 461. Fig. 462.

Portion of young Tendon, show- Yellow Fibrous Tissue from Ligamentum

ing the corpuscles of Germinal Mat- Nuchse of Calf,
ter, with their stellate prolongations,
interposed among its fibres.

work of minute fibres and bands, which are interwoven in every direction,
so as to leave innumerable areolce or little spaces that communicate freely
with one another. Of these fibres, some are of the 6 yellow 9 or elastic
kind, but the majority are composed of the 'white ; fibrous tissue; and,
as in that form of elementary structure, they frequently present the con-
dition of broad flattened bands or membranous shreds in which no dis-
tinct fibrous arrangement is visible. The proportion of the two forms
varies, according to the amount of elasticity, or of simple resisting power,
which the endowments of the part may require. We find this tissue in
a very large proportion of the bodies of higher Animals ; thus it binds to-
gether the ultimate muscular fibres into minute fasciculi, unites these
fasciculi into larger ones, these again into still larger ones which are
obvious to the eye, and these into the entire muscle; whilst it also forms
the membranous divisions between distinct muscles. In like manner
it unites the elements of nerves, glands, etc., binds together the fat-cells
into minute masses (Fig. 468), these into large ones, and so on; and in this
18

274

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 463.

way penetrates and forms part of all the softer organs of the body. But
whilst the fibrous structures of which the ' formed tissue' is composed
have a purely mechanical function, there is good reason to regard the ' con-
nective-tissue-corpuscles ' which are everywhere dispersed among them, as
having a most important function in the first production and subsequent
maintenance of the more definitely organized portions of the fabric (§ 650).
In these corpuscles, distinct movements, analogous to those of the sarco-
dic extensions of Khizopods, have been recognized in transparent parts,
such as the cornea of the eye and the tail of the young Tadpole, by ob-
servations made on these parts whilst living.— For the display of the
characters of the fibrous tissues, small and thin shreds may be cut with
the curved scissors (§ 183) from any part that affords them; and these

must be torn asunder with needles under
the simple Microscope, until the fibres are
separated to a degree sufficient to enable
them to be examined to advantage under a
higher magnifying power. The difference
between the ' white' and the 'yellow' com-
ponents of connective tissue is at once
made apparent by the effect of Acetic acid;
whilst the ' connective-tissue-corpuscles 9
are best distinguished by the staining-pro-
cess (§ 200), especially in the early stage of
the formation of these tissues (Fig. 461).

670. Skin; Mucous and Serous Mem-
branes.— The Skin which forms the external
envelope of the body, is divisible into two
principal layers ; the cutis vera or * true
skin,' which usually makes up by far the
larger part of its thickness, and the 'cuticle/
'scarf-skin/ or epidermis, which covers it.
At the mouth, nostrils, and the other orifices
-^i^X^elPS of Reopen cavities and canals of the body,
shows depressions a, a, between the the skin passes into the membrane that lines
p^^?atoiy 'ducts?, a^mVseen thl these, which is distinguished as the mucous
deeper layer of the epidermis, or membrane, from the peculiar glairy secretion

stratum Malpighu: — b, cutis vera, in „ ,7 , . , . *f fi 0 . J . ,

which are imbedded the perspiratory 01 mUCUS by Which its SUrtace IS protected.

But those great closed cavities of the body,
which surround the heart, lungs, intes-
tines, etc., are lined by membranes of
different kind; which, as they secrete
only a thin serous fluid from their surfaces, are known as serous membranes.
Both Mucous and Serous membranes consist, like the skin, of a proper
membranous basis, and of a thin cuticular layer, which, as it differs in
many points from the epidermis, is distinguished as the Epithelium
(§ 673). — The substance of the ' true skin ' and of the ' mucous ' and ' serous '
membranes is principally composed of the fibrous tissues last described;
but the skin and the mucous membranes are very copiously supplied with
Blood-vessels and with Glandulae of various kinds; and in the skin we
also find abundance of Nerves and Lymphatic vessels, as well as, in some
parts, of Hair-follicles. The general appearance ordinarily presented by
a thin vertical section of the skin of a part furnished with numerous sen-
sory papillce (§ 682), is shown in Fig. 463: where we see in deeper layers of
the cutis vera little clumps of fat-cells, /, and the perspiratory glandulae,

glands d, with their ducts e, and ag-
gregations of fat-cells /; g, arterial
twig supplying the vascular papillae
p; t, one of the tactile papillae with
its nerves.

VERTEBRATED ANIMALS.

275

d9 d, whose ducts, e, e, pass upwards: whilst on its surface we distinguish
the vascular papillae, p, supplied with loops of blood-vessels from the trunk,
g> and a tactile papilla, t, with its nerve twig. The spaces between the
papillae are filled-up by the soft ' Malpighian layer/ m, of the epidermis,
A, in which its coloring matter is chiefly contained, whilst this is cov-
ered by the horny layer, h, which is traversed by the spirally twisted con-
tinuations of the perspiratory ducts, opening at s upon the surface, which
presents alternating depressions, a, and elevations, b. — The distribution
of the blood-vessels in the Skin and Mucous membranes, which is one of
the most interesting features in their structure, and which is intimately
connected with their several functions, will come under our notice here-
after (Figs. 479, 482, 483). In Serous membranes, on the other hand,
whose function is simply protective, the supply of Blood-vessels is more
scanty.

671. Epidermic and Epithelial Cell-layers. — The Epidermis or 'cuti-v
cle ' covers the whole exterior of the body, as a thin semi-transparent pelli-
cle, which is shown by Microscopic examination to consist of a series of
layers of cells, that are continually wearing-off at the external surface,
and being renewed at the surface of the true skin; so that the
newest and deepest layers gradually become the oldest and most super-
ficial, and are at last thrown-off by slow desquamation. In their progress
from the internal to the external surface of the epidermis, the cells
undergo a series of well-marked changes. When we examine the inner-
most layer, we find it soft and granular; consisting of germinal corpuscles
in various stages of development into cells, held together by a tenacious
semi-fluid substance. This was formerly considered as a distinct tissue,
and was supposed to be the peculiar seat of the color of the skin; it
received the designation of Malpighian layer or rete mucosum. Passing
outwards, we find the cells more completely formed; at first nearly
spherical in shape, but becoming polygonal where they are flattened one
against another. As we proceed further towards the surface, we perceive
that the cells are gradually more and more flattened until they become
mere horny scales> their cavity being obliterated; their origin is indi-
cated, however, by the nucleus in the centre of each. This change in
form is accompanied by a change in the chemical composition of the
tissue, which seems to be due to the metamorphosis of the contents of
the cells into a horny substance identical with that of which hair, horn,
nails, hoofs, etc., are composed. — Mingled with the epidermic cells, we
find others which secrete coloring matter instead of horn; these, which
are termed ' pigment-cells/ are especially to be noticed in the epidermis
of the Negro and other dark races, and are most distinguishable in the
Malpighian layer, their color appearing to fade as they pass towards the
surface. — The most remarkable development of pigment cells in the
higher animals, however, is on the inner surface of the choroid coat of
the Eye, where they have a very regular arrangement, and form several
layers, known as the pigmentum nigrum. When examined separately,
these cells are found to have a polygonal form (Fig. 464, a), and to have
a distinct nucleus (b) in their interior. The black color is given by the
accumulation, within each cell, of a number of flat rounded or oval
granules, of extreme minuteness, which exhibit an active movement
when set free from the cell, and even whilst inclosed within it. The
pigment-cells are not always, however, of this simply rounded or poly-
gonal form; they sometimes present remarkable stellate prolongations,
under which form they are well seen in the skin of the Frog (Fig. 478,

276

THE MICROSCOPE AND ITS REVELATIONS.

c, c). The gradual formation of these prolongations may be traced in
the pigment-cells of the Tadpole during its metamorphosis (Fig. 465).
Similar varieties of form are to be met-with in the pigmentary cells of
Pishes and small Crustacea, which also present a great variety of hues;
and these seem to take the color of the bottom over which the animal
may live, so as to serve for its concealment.

672. The structure of the Epidermis may be examined in a variety of
ways. If it be removed by maceration from the true Skin, the cellular
nature of its under surface is at once recognized, when it is subjected to
a magnifying power of 200 or 300 diameters, by light transmitted
through it, with this surface uppermost; and if the epidermis be that of
a Negro or any other dark-skinned race, the pigment- cells will be very
distinctly seen. This under-surface of the epidermis is not flat, but

Fig. 464 Fig. 465. Fig. 466.

is excavated into pits and channels for the reception of the papillary
elevations of the true Skin; an arrangement which is shown on a large
scale in the thick cuticular covering of the Dog's foot, the subjacent
papilla being large enough to be distinctly seen (when injected) with
the naked eye. The cellular nature of the newly-forming layers is best
seen by examining a little of the soft film that is found upon the surface
of the true Skin, after the more consistent layers of the cuticle have been
raised by a blister. The alteration which the cells of the external layers
have undergone, tends to obscure their character; but if any fragment of
epidermis be macerated for a little time in a weak solution of Soda of
Potass, its dry scales become softened, and are filled-out by imbibition
into rounded or polygonal cells. The same mode of treatment enables
us to make out the cellular structure in warts and corns, which are
epidermic growths -from the surface of papillae enlarged by hypertrophy.
673. The Epithelium may be designated as a delicate cuticle, cover-

VERTEBRATED ANIMALS.

277

ing all the free internal surfaces of the body, and thus lining all its
cavities, canals, etc. Save in the mouth and other parts in which it
approximates to the ordinary cuticle both in locality and in nature,
its cells (Fig. 466) usually form but a single layer"; and are so de-
ficient in tenacity of mutual adhesion, that they cannot be detached in
the form of a continuous membrane. Their shape varies greatly. Some-
times they are broad, flat, and scale-like, and their edges approximate
closely to each other, so as to form what is termed a 6 pavement ' or
' tessellated ' epithelium : such cells are observable on the web of a Frog's
foot, or on the tail of a Tadpole; for, though covering an external
surface, the soft moist cuticle of these parts has all the characters of an
epithelium. In other cases the cells have more of the form of cylinders,
standing erect side-by-side; one extremity of each cylinder forming part
of the free surface, whilst the other rests upon the membrane to which
it serves as a covering. If the cylinders be closely pressed together,
their form is changed into prisms; and such epithelium is often known
as ' prismatic. ' On the other hand, if the surface on which it rests be
convex, the bases or lower ends of the cylinders become smaller than
their free extremities; and thus each has the form of a truncated cone
rather than of a cylinder, and such epithelium (of which that covering
the villi of the intestine, Fig. 479, is a peculiarly-good example) is termed
' conical.' But between these primary forms of epithelial cells, there
are several intermediate gradations; and one often passes almost in-
sensibly into the other. — Any of these forms of epithelium may be
furnished with cilia; but these appendages are more commonly found
attached to the elongated, than to the flattened forms of epithelium cells
(Fig. 467). Ciliated epithelium is found upon the lining membrane of
the air-passages in all air-breathing Vertebrata: and it also presents itself
in many other situations, in which a propulsive power is needed to pre-
vent an accumulation of mucous or other secretions. Owing to the very
slight attachment that usually exists between the epithelium and the
membranous surface whereon it lies, there is usually no difficulty what-
ever in examining it; nothing more being necessary than to scrape the
surface of the membrane with a knife, and to add a little water to what
has been thus removed. The ciliary action will generally be found to
persist for some hours or even days after death, if the animal has been
previously in full vigor;1 and the cells that bear the cilia, when detached
from each other, will swim freely about in water. If the thin fluid that
is copiously discharged from the nose in the first stage of an ordinary
'cold in the head,' be subjected to microscopic examination, it will com-
monly be found to contain a great number of ciliated epithelium-cells,
which have been thrown-off from the lining membrane of the nasal
passages.

674. Fat, — One of the best examples which the bodies of higher
animals afford, of a tissue composed of an aggregation of cells, is pre-
sented by Fat; the cells of which are distinguished by their power of
drawing into themselves oleaginous matter from the blood. Fat-cells
are sometimes dispersed in the interspaces of areolar tissue; whilst in
other cases they are aggregated in distinct masses, constituting the
proper Adipose substance. The individual fat-cells always present a

1 Thus it has been observed in the lining of the windpipe of a decapitated
criminal, as much as seven days after death; and in that of the river Tortoise it
has been seen fifteen days after death, even though putrefaction had already far
advanced.

278

THE MICROSCOPE AND ITS REVELATIONS.

nearly spherical or spheroidal form; sometimes, however^ when they are-
closely pressed together, they become somewhat polyhedral, from the
flattening of their walls against each other (Fig. 468). Their intervals
are traversed by a minute network of blood-vessels (Fig. 480), from
which they derive their secretion; and it is probably by the constant
moistening of their walls with a watery fluid, that their contents are
retained without the least transudation, although these are quite fluid at
the temperature of the living body. Fat-cells, when filled with their
characteristic contents, have the peculiar appearance which has been
already described as appertaining to oil-globules (§ 154), being very
bright in their centre, and very dark towards their margin, in conse-
quence of their high refractive power; but if, as often happens in prepa-
rations that have been long mounted, the oily contents should have
escaped, they then look like any other cells of the same form. Although
the fatty matter which fills these cells (consisting of a solution of
Stearine or Margarine in Oleine) is liquid at the ordinary temperature

Fig. 468.

Fig. 469.

Areolar and Adipose tissue; a,
a, fat-cells; bt b, fibres of areolar
tissue.

Cellular Cartilage of Mouse's ear.

of the body of a warm-blooded animal, j^et its harder portion sometimes
crystallizes on cooling; the crystals shooting from a centre, so as to form
a star-shaped cluster. — In examining the structure of Adipose tissue, it
is desirable, where practicable, to have recourse to some specimen in
which the fat-cells lie in single layers, and in which they can be
observed without disturbing or laying them open; such a condition is
found, for example, in the mesentery of the Mouse; and it is also occa-
sionally met with in the fat-deposits which present themselves at inter-
vals in the connective tissues of the muscles, joints, etc. Small collec-
tions of fat-cells exist in the deeper layers of the true skin, and are
brought into view by vertical sections of it (Fig. 463,/). And the
structure of large masses of fat may be examined by thin sections, these
being placed under water in thin cells, so as to take-off the pressure of
the glass-cover from their surface, which would cause the escape of the
oil-particles. No method of mounting (so far as the Author is aware) is
successful in causing these cells permanently to retain their contents.

675. Cartilage. — In the ordinary forms of Cartilage, also, we have an
example of a tissue essentially composed of cells; but these are commonly

VERTEBR ATED ANIMALS.

279

separated from each other by an c intercellular substance/ which is so
closely adherent to the outer walls of the cells as not to be separable from
them. The thickness of this substance differs greatly in different kinds
of cartilage, and even in different stages of the growth of any one. Thus
in the cartilage of the external ear of a bat or mouse (Fig. 469), the cells
are packed as closely together as are those of an ordinary Vegetable paren-
chyma (Fig. 236, a); and this seems to be the early condition of most
cartilages that are afterwards to present a different aspect. In the ordi-
nary cartilages, however, that cover the extremities of the bones, so as to
form smooth surfaces for the working of the joints, the amount of inter-
cellular substance is usually considerable; and the cartilage-cells are com-
monly found imbedded there in clusters of two, three, or four (Fig. 470),
which are evidently formed by a process of ' binary subdivision.' The
substance of these cellular cartilages is entirely destitute of blood-vessels;
being nourished solely by imbibition from the blood brought to the mem-
brane covering their surface. Hence they may be compared, in regard

Fig. 470, Fig. 471.

Section of the branchial Cartilage of Tad- Ultimate Follicles of Mam-
pole: — a, group of four cells, separating mary Gland, with their secret-
f rom eaeh other ; 6, pair of cells in apposition ; ing cells a, a, containing nuclei
c, c, nuclei of cartilage-cells; d, cavity con- 6, b.
taining three cells (the fourth probably
behind).

to their grade of organization, with the larger Algae; which consist, like
them, of aggregations of cells held together by intercellular substance,
without vessels of any kind, and are nourished by imbibition through
their whole surface. — There are many cases, however, in which the struc-
tureless intercellular substance is replaced by bundles of fibres, sometimes
elastic, but more commonly non-elastic; such combinations, which are
termed /?#r(?-cartilages, are interposed in certain joints, wherein tension
as well as pressure has to be resisted, as, for example, between the verte-
brae of the spinal column and the bones of the pelvis. — In examining the
structure of Cartilage, nothing more is necessary than to make very thin
sections with a sharp razor or scalpel, or, if the specimen be large and
dense (as the cartilage of the ribs), with the Microtome. These sections
maybe mounted in weak spirit, Goadby's solution, or glycerine-jelly; but
in whatever way they are mounted, they undergo a gradual change by
lapse of time, which renders them less fit to display the characteristic
features of their structure.

676. Structure of the Glands. — The various Secretions of the body (as

280

THE MICROSCOPE AND ITS REVELATIONS.

the saliva, bile, urine, etc.), are formed by the instrumentality of organs
termed Glands; which are, for the most part, constructed on one funda-
mental type, whatever be the nature of their product. The simplest idea
of a gland is that which we gain from an examination of the 4 follicles ' or
little bags imbedded in the wall of the stomach; some of which secrete
mucus for the protection of its surface, and others gastric juice. These
little bags are filled with cells of a spheroidal form, which may be con-
sidered as constituting their epithelial lining; these c :11s, in the progress
of their development, draw into themselves from the blood the constitu-
ents of the particular product they are to secrete; and they then seem to
deliver it up, either by the bursting or by the melting-away of their walls,
so that this product may be poured-forth from the mouth of the bag into
the cavity in which it is wanted. The Liver itself, in the lowest animals
wherein it is found, presents this condition. Some of the cells that form
the lining of the stomach in the Hydra and Actinia, seem to be distin-
guished from the rest by their power of secreting bile, which gives them
a brownish-yellow tinge; in many Polyzoa, Compound Tunicata, and
Annelida, these biliary cells can be seen to occupy follicles in the walls of
the stomach; in Insecta these follicles are few in number, but are im-
mensely elongated so as to form biliary tubes, which lie loosely within
the abdominal cavity, frequently making many convolutions within it,
and discharge their contents into the commencement of the intestinal
canal; whilst in the higher Mollusca, and in Crustacea, the follicles are
vastly multiplied in number, and are connected with the ramifications of
glancl-ducts, like grapes upon the stalks of their bunch, so as to form a
distinct mass which now becomes known as the Liver. The examination
of the biliary tubes of the Insect, or of the biliary follicles of the Crab,
which may be accomplished with the utmost facility, is well adapted to
give an idea of the essential nature of glandular structure. Among Ver-
tebrated animals the Salivary glands, the Pancreas (sweet-bread), and
the Mammary glands, are well adapted to display the follicular structure
(Pig. 471); nothing more being necessary than to make sections of these
organs, thin enough to be viewed as transparent objects. The Liver of
Vertebrata, however, presents certain peculiarities of structure, which
are not yet fully understood; for although it is essentially composed, like
other glands, of secreting cells, yet it has not been determined beyond
doubt whether these cells are contained within any kind of membranous
investment. The Kidneys of Vertebrated animals are made-up of elon-
gated tubes, which are straight, and are lined with a pavement-epithelium
in the inner or ' medullary 9 portion of the kidney, whilst they are con-
voluted and filled with a spheroidal epithelium in the outer or 'corti-
cal.' Certain flask-shaped dilatations of these tubes include curious little
knots of blood-vessels, which are known as the ' Malpighian bodies 9 of
the kidney; these are well displayed in injected preparations. — For such
a full and complete investigation of the structure of these organs as the
Anatomist and Phosiologist require, various methods must be put in prac-
tice which this is not the place to detail. It is perfectly easy to demon-
strate the cellular nature of the substance of the Liver, by simply scraping
a portion of its cut surface; since a number of its cells will be then de-
tached. The general arrangement of the cells in the lobules may be dis-
played by means of sections thin enough to be transparent; whilst the
arrangement of the blood-vessels can only be shown by means of Injections
(§ 687). Fragments of the tubules of the Kidney, sometimes having the
Malpighian capsules in connection with them, may also be detached by

V EJRTEB K ATED ANIMALS.

281

scraping its cut surface; but the true relations of these parts can only be
shown by thin transparent sections, and by injections of the blood-vessels
and tubuli. The simple follicles contained in the walls of the Stomach
are brought into view by vertical sections; but they may be still better
examined by leaving small portions of the lining membrane for a few
days in dilute nitric acid (one part to four of water), whereby the fibrous
tissue will be so softened, that the clusters of glandular epithelium lining
the follicles (which are but very little altered) will be readily separated.

677. Muscular Tissue. — Although we are accustomed to speak of this
tissue as consisting of ' fibres/ yet the ultimate structure of the ' muscu-
lar fibre ' is very different from that of the ' simple fibrous tissues 9 al-
ready described. When we examine an ordinary muscle (or piece of
' flesh ') with the naked eye, we observe that it is made-up of a number
of fasciculi or bundles of fibres (Fig. 472), which are arranged side-by-
side with great regularity, in the direction in which the muscle is to act,
and are united by connective tissue. These fasciculi may be separated
into smaller parts, which appear like simple fibres; but when these are

Fig. 472. Fig 473.

examined by the Microscope, they are found to be themselves fasciculi,
composed of minuter fibres bound together by delicate filaments of con-
nective tissue. By carefully separating these, we may obtain the ulti-
mate muscular fibre. This fibre exists under two forms, the striated and
the non-striated. The former is chiefly distinguished by the transversely-
striated appearance which it presents (Fig. 473), and which is due to an
alternation of light and dark spaces along its whole extent; the breadth
and distance of these striae vary, however, in different fibres, and even in
different parts of the same fibre, according to their state of contraction
or relaxation. Longitudinal striae are also frequently visible, which are
due to a partial separation between the component fibrillae into which the
fibre may be broken up. — When a fibre of this kind is more closely ex-
amined, it is seen to be inclosed within a delicate tubular sheath, which
is quite distinet on the one hand from the connective tissue that binds
the fibres into fasciculi, and equally distinct from the internal substance
of the fibre. This membranous tube, which is termed the sarcolemma, is
not perforated by capillary vessels, which therefore lie outside the ulti-
mate elements of the muscular substance; whether it is penetrated by the

282

THE MICROSCOPE AND ITS REVELATIONS.

ultimate fibres of nerves, is a point not yet certainly ascertained. — The
diameter of the fibres varies greatly in different kinds of Vertebrated
animals. Its average is greater in Reptiles and Fishes than in Birds and
Mammals, and its extremes also are wider; thus its dimensions vary in
the Frog from l-100th to l-1000th of an inch, and in the Skate from
l-65th to l-300th; whilst in the Human subject the average is about
l-400th of an inch, and the extremes about l-200th and l-600th.

678. The substance of the fibre, when broken up by 'teazing' with
needles, is found to consist of very minute fibrillae, which, when exam-
ined under a magnifying power of from 250 to 400 diameters, are seen to
present a slightly-beaded form, and to show the same alternation of light
and dark spaces as when the fibrillae are united into fibres or into small
bundles (Fig. 473). The dark and light spaces are usually of nearly
equal length: each light space is divided by a transverse line, called
'Dobie's line;' while each dark space is crossed by a lighter band, known
as * Hensen's stripe.' It has been generally supposed that these markings
indicate differences in the composition of the fibre; but Mr. J. B. Hay-
croft has recently revived an idea which originated with Mr. Bowman,
that. they are the optical expressions of its shape. The borders of the
striated fibre (he truly states) present wavy margins, indicative of a trans-
verse ridging and furrowing; the whole fibre (or a single fibril) thus con-
sisting of a succession of convex bead-like projections with intermediate
concave depressions. When the axis of the fibre is in true focus, Dobie's
line, d, crosses the deepest part of the concavity, while Hensen's stripe,
H, crosses the most projecting part of the convexity; and it can be shown,
both theoretically and experimentally, that this alternation of lights and
shades will be produced by the passage of light through a similarly-shaped
homogenous rod of any transparent substance. If, on the other hand,
the surface of the fibre be brought into focus, the convex ribbings appear
light and the intervening depressions dark, — which is the aspect origin-
allly represented by Bowman. The appearances are the same in the ex-
tended and contracted states of the fibre; with the exception that the
alternation of light and dark striae is closer in the contracted state,
while the breadth (representing the thickness) of the fibre is correspond-
ingly increased.1

679. In the examination of Muscular tissue, a small portion may be
cut-out with the curved scissors; this should be torn up into its compo-
nent fibres; and these, if possible, should be separated into their fibrillae,
by dissection with a pair of needles under the Simple Microscope. The
general characters of the striated fibre are admirably shown in the large
fibres of the Frog; and by selecting a portion in which these fibi'es spread
themselves out to unite with a broad tendinous expansion, they may often
be found so well displayed in a single layer, as not only to exhibit all
their characters without any dissection, but also to show their mode of
connection with the ' simple fibrous 9 tissue of which that expansion is
formed. As the ordinary characters of the fibre are but little altered by
boiling, recourse may be had to this process for their more ready separa-
tion, especially in the case of the tongue. Dr. Beale recommends Gly-
cerine for the preparation, and Glycerine-media for the preservation, of
objects of this class; and states that the alternation of light and dark
spaces in the fibrillae is rendered more distinct by such treatment. The
fibrillae are often more readily separable when the muscle has been

1 ''Quart, Journ. Microsc. Science," N.S., Vol. xxi., p. 307.

VERTEBRATE D ANIMALS.

283

macerated in a weak solution of Chromic acid. — The shape of the fibres
can only be properly seen in cross sections; and these are best made by
the Freezing Microtome (§ 191). — Striated fibres, separable with great
facility into their component fibrillae, are readily obtainable from the
limbs of Crustacea and of Insects; and their presence is also readily dis-
tinguishable in the bodies of Worms, even of very low organization; so
that it may be regarded as characteristic of the Articulated series gener-
ally. On the other hand, the Molluscous classes are for the most part
distinguished by the non-striation of their fibre; there are, however, two
remarkable exceptions, strongly striated fibre having been found in the
Tereiratula and other Brachiopods (where, however, it is limited to the
anterior adductor muscles of the shell), and also in many Polyzoa. Its
presence seems related to energy and rapidity of movement; the non-
striated presenting itself where the movements are slower and feebler in
their character.

Fig. 474.

Diagram of Striated Fibrilla.

Structure of non-stri-
ated Muscular Fibre: — a,
portion of tissue showing
fusiform cells a, a, with
elongated nuclei 6, 6;— b, a
single cell isolated and
more highly magnified ; c,
a similar cell treated with
acetic acid.

680. The ' smooth ' or non-striated form of Muscular fibre, which is
especially found in the walls of the stomach, intestines, bladder, and
other similar parts, is composed of flattened bands whose diameter is
usually between l-2000th and l-3000th of an inch; and these bands are
collected into fasciculi, which do not lie parallel with each other, but
cross and interlace. By macerating a portion of such muscular sub-
stance, however, in dilute nitric acid (about one part of ordinary acid to
three parts of water) for two or three days, it is found that the bands
just mentioned may be easily separated into elongated fusiform cells, not
unlike ' woody fibre' in shape (Fig. 474, a, a); each distinguished, for
the most part, by the presence of a long staff-shaped nucleus, b, brought
into view by the action of acetic acid, c. These cells, in which the distinc-
tion between cell-wall and cell-contents can by no means be clearly seen,
are composed of a soft yellow substance often containing small pale
granules, and sometimes yellow globules of fatty matter. In the coats of
the Blood-vessels are found cells having the same general characters, but
shorter and wider in form; and although some of these approach very

284

THE MICROSCOPE AND ITS REVELATIONS.

closely in their general appearance to epithelium-cells, yet they seem to
have quite a different nature, being distinguished by their elongated
nuclei, as well as by their contractile endowments.

681. Nerve-substance* — Wherever a distinct Nervous System can be
made out, it is found to consist of two very different forms of tissue —
namely, the cellular, which are the essential components of the ganglionic
centres, and the fibrous, of which the connecting trunks consist. The
typical form of the nerve-cells or ' ganglion-globules' may be regarded as
globular; but they often present an extension into one or more long pro-
cesses, which give them a ' caudate ' or 6 stellate 9 aspect. These pro-
cesses'have been traced into continuity, in some instances, with the axis-
cylinders of nerve-tubes (Fig. 475); whilst in other cases they seem to
inosculate with those of other vesicles. The cells, which do not seem to
possess a definite cell-wall, are for the most part composed of a finely-
granular substance, which extends into their prolongations; and in the
midst of this is usually to be seen a large well-defined nucleus. They also

Fig. 475. Fig. 476. Fig. 477.

Ganglion-cells and Nerve- Gelatinous Nerve- the branches of the cutaneous nerves, a, 6,
fibres from a ganglion of fibres, from Olfac- inosculating to form a plexus, of which the ulti-
Lamprey. tory Nerve. mate fibres pass into the cutaneous papillae, c, c.

generally contain pigment-granules, which give them a reddish or yellow-
ish-brown color, and thus impart to collections of ganglionic cells in the
warm-blooded Vertebrata that peculiar hue, which causes it be known as
the cineritious or gray matter, but which is commonly absent among the
lower animals. — Each of the tubular nerve-fibres, on the other hand, of
which the trunks are made up, consists, in its fully developed form, of a
delicate membranous sheath, within which is a hollow cylinder of a
material known as the ' white substance of Schwann/ whose outer and
inner boundaries are marked-out by two distinct lines, giving to each
margin of the nerve-tube what is described as a 6 double contour.' The
contents of the membranous envelope are very soft, yielding to slight
pressure: and they are so quickly altered by the contact of water or of
any liquids which are foreign to their nature, that their characters can
only be properly judged-of when they are quite fresh. The centre or axis
of the tube is then found to be occupied by a transparent substance
which is known as the ' axis-cylinder:' and there is reason to believe that

VERTEB RATED ANIMALS

285

this last, which is a protoplasmic substance, is the essential component
of the nerve-fibre, while the function of the hollow cylinder that sur-
rounds it, which is composed of a combination of fat and albuminous
matter, is simply protective. The diameter of the nerve-tubes differs in
different nerves; being sometimes as great as l-1500th of an inch, and as
small in other instances as 1-12, 000th. — In many of the lower Invertebrata,
such as MeduscB (§ 523) and Comatulcs (§ 546), we seem fully justified by
physiological evidence in regarding as Nerves certain protoplasmic fibres
which do not possess the characteristic structure of 4 nerve-tubes;' and
fibres destitute of the ' double contour ' are found also in certain parts of
the body of even the highest Vertebrates. These fibres, which are known
as 'gelatinous/ are considerably smaller than the preceding, and do not
exhibit any differentiation of parts (Fig. 476) . They are flattened, soft,
and homogenous in their appearance, and contain numerous nuclear
particles which are brought into view by acetic acid. They can some-
times be seen to be continuous with the axis-cylinders of the ordinary
fibres, and also with the radiating prolongations of the ganglion-cells; so
that their nervous character, which has been questioned by some anato-
mists, seems established beyond doubt.

682. The ultimate distribution of the Nerve-fibres is a subject on
which there has been great divergence of opinion, and which can only be
successfully investigated by observers of great experience. The Author
believes that it may be stated as a general fact, that in both the motor
and the sensory nerve-tubes, as they approach their terminations in the
muscles and in the skin respectively, the protoplasmic axis-cylinder is
continued beyond its envelopes; often then breakmg-up into very minute
fibrillae, which inosculate with each other so as to form a network closely
resembling that formed by thepseudopodial threads of Bhizopods (Pig. 283.)
Recent observers have described the tibrillae of motor nerves as terminating
in' motorial end-plates 5 seated upon or in the muscular fibres; and these
seem analogous to the little ' islets 9 of sarcodic substance, into which
those threads often dilate. — Where the Skin is specially endowed with
tactile sensibility, we find a special papillary apparatus, which in the
skin may be readily made out in thin vertical sections treated with solu-
tion of soda (Fig. 477). It was formerly supposed that all the cutaneous
papillae are furnished with nerve-fibres, and minister to sensation: but it
is now known that a large proportion (at any rate) of those that are fur-
nished with loops of blood-vessels (Figs. 463, p, 483), being destitute of
nerve-fibres, must have for their special office the production of Epider-
mis; whilst those which, possessing nerve-fibres, have sensory functions,
are usually destitute of blood-vessels. • The greater part of the interior of
each sensory papilla (Fig. 477, c, c) of the skin is occupied by a peculiar
'axile body,' which seems to be merely a bundle of ordinary connective
tissue, whereon the nerve-fibre appears to terminate. The nerve-fibres are
more readily seen, however, in the ' fungiform 9 papillae of the Tongue,
to each of which several of them proceed; these bodies, which are very
transparent, may be well seen by snipping- off minute portions of the
tongue of the Frog; or by snipping-off the papillae themselves from the
surface of the living Human tongue, which can be readily done by a dex-
terous use of the curved scissors, with no more pain than the prick of a
pin would give. The transparence of these papillae also is increased by
treating them with a weak solution of soda. — Nerve-fibres have also been
found to terminate on sensory surfaces in minute 6 end-bulbs * of spher-
oidal shape and about l-600th of an inch in diameter; each of them being

286

THE MICROSCOPE AND ITS REVELATIONS.

composed of a simple outer capsule of connective tissue, filled with clear
soft matter, in the midst of which the nerve-fibre, after losing its dark
border, ends in a knob. The ' Pacinian corpuscles,' which are best seen
in the mesentery of the Cat, and are from 1-15 th to 1-10 of an inch long,
seem to be more developed forms of these ' end-bulbs.'

683. For the sake of obtaining a general acquaintance with the
Microscopic characters of these principal forms of Nerve-substance, it is
best to have recourse to minute nerves and ganglia. The small nerves
which are found between the skin and the muscles of the back of the
Frog, and which become apparent when the former is being stripped-off,
are extremely suitable for this purpose; but they are best seen in the
Hyla or 'tree-frog,' which is recommended by Dr. Beale as being much
superior to the common Frog for the general purposes of minute histo-
logical investigation. If it be wished to examine the natural appearance
of the nerve-fibres, no other fluid should be used than a little blood-
serum; but if they be treated with strong acetic acid, a contraction of
their tubes takes place, by which the axis-cylinders are forced-out from
their cut extremities, so as to be made more apparent than they can be
in any other way. On the other hand, by immersion of the tissue in
a dilute solution of Chromic acid (about one part of the solid crystals to
two hundred of water), the nerve-fibres are rendered firmer and more
distinct. Again, the axis- cylinders are brought into distinct view by the
staining-process (§ 202 a), being dyed much more quickly than their
envelopes; and they may thus be readily made-out by reflected light, in
transverse sections of nerves that have been thus treated. The gelatinous
fibres are found in the greatest abundance in the Sympathetic nerves;
and their characters may be best studied in the smaller branches of that
system. — So, for the examination of the ganglionic cells, and of their
relation to the nerve-tubes, it is better to take some minute ganglion as a
whole (such as one of the sympathetic ganglia of the Frog, Mouse, or
other small animal), than to dissect the larger ganglionic masses, whose
structure can only be successfully studied by such as are proficient in this
kind of investigation. The nerves of the orbit of the eyes of Fishes, with
the ophthalmic ganglion and its branches, which may be very readily
got-at in the Skate, and of which the components may be separated
without much difficulty, form one of the most convenient objects for the
demonstration of the principal forms of nerve-tissue, and especially for
the connection of nerve-fibres and ganglion-cells. — For minute inquiries,
however, into the ultimate distribution of the nerve-fibres in Muscles,
and Sense-organs, certain special methods must be followed, and very
high magnifying powers must be employed. Those who desire to follow
out this inquiry should acquaint themselves with the methods which
have been found most successful in the hands of the able Histologists
whose works have been already referred to.

684. Circulation of the Blood. — One of the most interesting spectacles
that the Microscopist can enjoy, is that which is furnished by the Circu-
lation of the Blood in the capillary blood-vessels which distribute the
fluid through the tissues it nourishes. This, of course, can only be
observed in such parts of Animal bodies as are sufficiently thin and
transparent to allow of the transmission of light through them, without
any disturbance of their ordinary structure; and the number of these is
very limited. The web of the Frog's foot is perhaps the most suitable
for ordinary purposes, more especially since this animal is to be easily
obtained in almost every locality; and the following is the simple

VERTEBRATED ANIMALS.

28T

arrangement preferred by the Author: — A piece of thin Cork is to
be obtained, about 9 inches long and 3 inches wide (such pieces are
prepared by Cork-cutters, as soles), and a hole about 3-8th of an inch in
diameter is to be cut at about the middle of its length, in such a position
that, when the cork is secured upon the stage, this aperture may corre-
spond with the axis of the Microscope. The body of the Frog is then to
be folded in a piece of wet calico, one leg being left free, in such a man-
ner as to confine its movements, but not to press to tightly upon its body;
and being then laid down near one end of the cork-plate, the free leg is
to be extended, so that the foot can be laid over the central aperture.
The spreading-out of the foot over the aperture is to be accomplished,
either by passing pins through the edge of the web into the cork beneath,
or by tying the ends of the toes with threads to pins stuck into the cork
at a small distance from the aperture; the former method is by far the
least troublesome, and it may be doubted whether it is really the source
of more suffering to the animal than the latter, the confinement being
obviously that which is most felt. A few turns of tape, carried loosely
around the calico bag, the projecting leg, and the cork, serve to prevent
any sudden start; and when all is secure, the cork-plate is to be laid
down upon the stage of the Microscope, where a few more turns of the
tape will serve to keep it in place. The web being moistened with water
(a precaution which should be repeated as often as the membrane ex-
hibits the least appearance of dryness), and an adequate light being
reflected through the web from the mirror, this wonderful spectacle is
brought into view on the adjustment of the focus (a power of from 75 to
100 diameters being the most suitable for ordinary purposes), provided
that no obstacle to the movement of the blood be produced by undue
pressure upon the body or leg of the animal. It will not unfrequently
be found, however, that the current of blood is nearly or altogether stag-
nant for a time; this seems occasionally due to the animal's alarm at its
new position, which weakens or suspends the action of its heart, the
movement recommencing again after the lapse of a few minutes, although
no change has been made in any of the external conditions. But if the
movement should not renew itself, the tape which passes over the body
should be slackened; and if this does not produce the desired effect, the
calico envelope also must be loosened. When everything has once been
properly adjusted, the animal will often lie for hours without moving, or
will only give an occasional twitch; and even this may be avoided by
previously subjecting it to the influence of chloroform, which may be
renewed from time to time whilst it is under observation. — The move-
ment of the Blood will be distinctly seen by that of its corpuscles (Fig.
478), which course after one another through the network of Capillaries
that intervenes between the smallest arteries and the smallest veins; in
those tubes which pass most directly from the veins to the arteries, the
current is always in the same direction; but in those which pass across
between these, it may not unfrequently be seen that the direction of the
movement changes from time to time. The larger vessels with which
the capillaries are seen to be connected, are almost always veins, as may
be known from the direction of the flow of blood in them from the
branches (b, h) towards their trunk (a); the arteries, whose ultimate
subdivisions discharge themselves into the capillary network, are for the
most part restricted to the immediate borders of the toes. When a
power of 200 or 250 diameters is employed, the visible area is of course
greatly reduced; but the individual vessels and their contents are much

288

THE MICROSCOPE AND ITS REVELATIONS.

more plainly seen: and it may then be observed that whilst the "'red'
corpuscles (§ 655) flow at a very rapid rate along the centre of each tube,
the*' white' corpuscles (§ 666), which are occasionally discernible, move
slowly in the clear stream near its margin.

685. The Circulation may also be displayed in the tongue of the Frog,
by laying the animal (previously chloroformed) on its back, with its head
close to the hole in the cork-plate, and, after securing the body in this
position, drawing-out the tongue with the forceps, and fixing it on the
other side of the hole with pins. So, again, the circulation may be
examined in the lungs — where it affords a spectacle of singular beauty,
— or in the mesentery, of the living Frog, by laying open its body, and,
drawing forth either organ; the animal having previously been made
insensible by chloroform. The tadpole of the Frog, when sufficiently
young, furnishes a good display of the capillary circulation in its tail;
and the difficulty of keeping it quiet during the observation may be over-
come by gradually mixing some warm water with that in which it is

Fig. 478.

Capillary Circulation in a portion of the web of a Frog's foot:— a, trunk of vein; 6, 6, its
branches; c, c, pigment-cells.

swimming, until it becomes motionless; this usually happens when it has
been raised to a temperature of between 100° and 110°; and notwith-
standing that the muscles of the body are thrown into a state of spas-
modic rigidity by this treatment, the heart continues to pulsate, and the
circulation is maintained.1 The larva of the Water-neivt, when it can be
obtained, furnishes a most beautiful display of the circulation, both in
its external gills and in its delicate feet. It may be inclosed in a large
Aquatic-box or in a shallow cell, gentle pressure being made upon its
body, so as to confine its movements without stopping the heart's action.
— The circulation may also be seen in the tails of small Fish, such as the
minnow or the stickleback, by confining these animals in tubes, or in
shallow cells, or in a large Aquatic-box;2 but although the extreme

1 A special form of Live-box for the observation of living Tadpoles, etc. , con-
trived by F. E. Schultze, of Rostock, is described and figured in the " Quart.
Journ. of Microsc. Science," N.S., Vol. vii. (1867), p. 261.

2 A convenient Trough for this purpose is described in the " Quart. Journ. of
Microsc. Science," Vol. vii. (1859), p. 113.

VEKTEBRATED ANIMALS.

289

transparence of these parts adapts them well for this purpose in onfc
respect, yet the comparative scantiness of their blood-vessels prevents thens
from being as suitable as the Frog's web in another not less important
particular. — One of the most beautiful of all displays of the circulation,
however, is that which may be seen upon the yolk-bag of young Fish
(such as the Salmon or Trout) soon after they have been hatched; and as
it is their habit to remain almost entirely motionless at this stage of their
existence, the observation can be made with the greatest facility by means
of the Zoophyte-trough, provided that the subject of it can be obtained.
Now that the artificial breeding of these Fish is largely practised for the
sake of stocking rivers and fish-ponds, there can seldom be much diffi-
culty in procuring specimens at the proper period. The store of yolk
which the yolk-bag supplies for the nutrition of the embryo, not being
exhausted in the Fish (as it is in the bird) previously to the hatching of
the egg, this bag hangs-down from the belly of the little creature on its
emersion; and continues to do so until its contents have been absorbed
into the body, which does not take place for some little time afterwards.
And the blood is distributed over it in copious streams, partly that it
may draw into itself fresh nutritive material, and partly that it may be
subjected to the aerating influence of the surrounding water.

686. The Tadpole serves, moreover, for the display, under proper
management, not only of the capillary but of the general Circulation;
and if this be studied under the Binocular Microscope, the observer
not only enjoys the gratification of witnessing a most wonderful specta-
cle, but may also obtain a more accurate notion of the relations of the
different parts of the circulating system than is otherwise possible.1 The
Tadpole, as every naturalist is aware, is essentially a Fish in the early
period of its existence, breathing by gills alone, and having its circulating
apparatus arranged accordingly: but as its limbs are developed and its tail
becomes relatively shortened, its lungs are gradually evolved in prepara-
tion for its terrestrial life, and the course of the blood is considerablj
changed. In the Tadpole as it comes forth from the egg, the gills are
external, forming a pair of fringes hanging at the sides of the head
(Plate xxiv., fig. 1); and at the bases of these, concealed by opercula or
gill-flaps resembling those of Fishes, are seen the rudiments of the inter-
nal gills, which soon begin to be developed in the stead of the preceding.
The external gills reach their highest development on the fourth or fifth
day after emersion; and they then wither so rapidly (whilst being at the
same time drawn-in by the growth of the animal), that by the end of the
first week only a remnant of the right gill can be seen under the edge of
the operculum (fig. 2, c), though the left gill (b) is somewhat later in its
disappearance. Concurrently with this change, the internal gills are
undergoing rapid development; and the beautiful arrangement of their
vascular tufts, which originate from the roots of the arteries of the exter-
nal gills, as seen at g, fig. 5, is shown in fig. 4. It is requisite that the
Tadpole subjected to observation should not be so far advanced as to have
lost its early transparence of skin; and it is further essential to the trac-

1 See Mr. "Whitney's account of ' The Circulation in the Tapdole,' in " Transact,
of Microsc. Soc," N. S., Vol. x. (1862), p. 1, and his subsequent paper ' On the
Changes which accompany the Metamorphosis of the Tadpole ' in the same Trans
actions, Vol. xv., p. 43. — In the first of these Memoirs Mr. W. described the inter-
nal gills as lungs, an error which he corrected in the second.
19

PLATE XXIV.

circulation in the tadpole (after Whitney).

Fig. 1. Anterior portion of young Tadpole, showing the external gills, with the incipient tufts of
the internal gills, and the pair of minute tubes between the heart and the spirally-coiled intestine,
which ire the rudiments of the future lungs.

2. More advanced Tadpole, in which the external gills have almost disappeared :— a, remnant of
external gills on the left side; b, operculum; c, remnant of externa) gill on the right side, turned in.

3. Advanced Tadpole, showing the course of the genera) Circulation:— a, heart; 6, branchial
arteries; c, pericardium: d, internal gill; e, first or cephalic trunk; /, branch to lip; gr, branches to
head; h, second or branchial trunk ; i, third trunk, uniting with its fellow to form the abdominal
aorta, which is continued as the caudal artery k, to the extremity of the tail ; I, caudal vein ; m,
kidney ; n, vena cava ; o, liver ; p, vena portse ; q, sinus venosus, receiving the jugular vein, r,
and the abdominal veins, t, u, as also the branchial vein, v.

4. The branchial Circulation on a larger scale:— a, b, c, three primary branches of the branchial
artery; a, cartilaginous arches; 6, additional framework; c, e, twigs of branchial artery; d, /, root-
lets of branchial vein.

5 Origin of the vessels of the internal gills, gr, from the roots of those of the external.

6. The heart, systemic arteries, pulmonary arteries and veins, and lungs, in the adult Frog; the
heart being turned up in the rigrht-hand figure, to show the junction of the Pulmonary veins and
their entrance into the left auricle.

VEBTEBRATED ANIMALS.

291

ing-out the course of the abdominal vessels, that the creature should have
been kept without food for some days, so that the intestine may empty
itself. This starving process reduces the quantity of red corpuscles, and
thus renders the blood paler; but this, although it makes the smaller
branches less obvious, brings the circulation in the larger trunks into
more distinct view. " Placing the Tadpole on his back," says Mr. Whit-
ney, " we look, as through a pane of glass, into the chamber of the chest.
Before us is the beating heart, a bulbous-looking cavity, formed of the
most delicate transparent tissues, through which are seen the globules of
the blood, perpetually, but alternately, entering by one orifice and leaving
it by another. The heart (Plate xxiv., fig. 3, a) appears to be slung, as
it were, between two arms or branches, extending right and left. Prom
these trunks (b) the main arteries arise. The heart is inclosed within an
envelope or pericardium (c), which is, perhaps, the most delicate,|and is,
certainly, the most elegant beauty in the creature's organism. Its ex-
treme fineness makes it often elude the eye under the single Microscope,
but under the Binocular its form is distinctly revealed. Then it is seen
as a canopy or tent, inclosing the heart, but of such extreme tenuity that
its folds are really the means by which its existence is recognized. Passing
along the course of the great vessels to the right and left of the heart, the
eye is arrested by a large oval body (d) of a more complicated structure
and dazzling appearance. This is the internal gill, which, in the Tad-
pole, is a cavity formed of most delicate transparent tissue, traversed by
certain arteries, and lined by a crimson network of blood-vessels, the in-
terlacing of which, with their rapid currents and dancing globules, forms
one of the most beautiful and dazzling exhibitions of vascularity." Of
the three arterial trunks which arise on each side from the truncus arte-
riosus, b, the first, or cephalic, e, is distributed entirely to the head, run-
ning first along the upper edge of the gill, and giving off a branch, /, to
the thick- fringed lip which surrounds the mouth; after which it suddenly
curves upwards and backwards, so as to reach the upper surface of the
head, where it dips between the eye and the brain. The second main
trunk, h, seems to be chiefly distributed to the gill, although it freely
communicates by a network of vessels both with the first or cephalic and
with the third or abdominal trunk. The latter also enters the gill and
gives off branches; but it continues its course as a large trunk, bending
downwards and curving towards the spine, where it meets its fellow to
form the abdominal aorta, i, which, after giving-off branches to the ab-
dominal viscera, is continued, as the caudal artery, h, to the extremity of
the tail. The blood is returned from the tail by the caudal vein, I, which
is gradually increased in size by its successive tributaries as it passes to-
wards the abdominal cavity; here it approaches the kidney, m, and sends
olf a branch which incloses that organ on one side, while the main trunk
continues its course on the other, receiving tributaries from the kidney as
it passes. (This supply of the kidney by venous blood is a peculiarity of
the lower Vertebrata. ) The venous blood returned from the abdominal
viscera, on the other hand, is collected into a trunks, known as the por-
tal vein, which distributes it through the substance of the liver, o, as in
Man; and after traversing that organ it is discharged by numerous fine
channels, which converge towards the great abdominal trunk, or vena
cava, n, as it passes in close proximity to the liver, onwards to the sinus
venosus, q, or rudimentary auricle of the heart. This also receives the
jugular vein, r, from the head, which first, however, passes downwards
ti front of the gill close to its inner edge, and meets a vein, t, coming up

292

THE MICROSCOPE AND ITS REVELATIONS.

from the abdomen, after which it turns abruptly in the direction of the
heart. Two other abdominal veins, u, meet and pour their blood direct
into the sinus venosus; and into this cavity is also poured the aerated
blood returned from the gill by the branchial vein, v, of which only the
one on the right side can be distinguished. — The lungs may be detected
in a rudimentary state, even in the very young tadpole; being in that
stage a pair of minute tubular sacs, united at the upper extremities, and
lying behind the intestine and close to the spine. They may be best
brought into view by immersing the tadpole for a few days in a weak so-
lution of chromic acid, which renders the tissue friable, so that the parts
that conceal them may be more readily peeled away. Their gradual en-
largement may be traced during the period of the tadpole's transparence;
but they can only be brought into view by dissection when the metamor-
phosis has been completed. The following are Mr. Whitney's directions
for displaying the Circulation in these organs: — "Put the young Frog
into a wineglass, and drop on him a single drop of chloroform. This
suffices to extinguish sensibility. Then lay him on the back on a piece
of cork, and fix him with small pins passed through the web of each foot.
Kemove the skin of the abdomen with a fine pair of sharp scissors and
forceps. Turn aside the intestines from the left side, and thus expose
the left lung, which may now be seen as a glistening transparent sac,
containing air bubbles. With a fine camel-hair pencil the lung may now
be turned-out, so as to enable the operator to see a large part of it by
transmitted light. Unpin the frog, and place him on a slip of glass, and
then transmit the light through the everted portion of lung. Eemember
that the lung is very elastic, and is emptied and collapsed by very slight
pressure. Therefore, to succeed with this experiment, the lung should
be touched as little as possible, and in the lightest manner, with the brush.
If the heart is acting feebly, you will see simply a transparent sac, shaped
according to the quantity of air-bubbles it may happen to contain, but
void of red vascularity and circulation. But should the operator succeed
in getting the lung well placed, full of air, and have the heart still beat-
ing vigorously, he will see before him a brilliant picture of crimson net-
work, alive with the dance and dazzle of blood-globules, in rapid chase of
one another through the delicate and living lace-work which lines the
chamber of the lung." The position of the lungs in relation to the heart
and the great vascular trunks, is shown in Plate xxiv., fig. 6.

687. Injected Preparations. — Next to the Circulation of the Blood in
the living body, the varied distribution of the CapiKc ries in its several
organs, as shown by means of 6 injections ' of coloring matter thrown into
their principal vessels, is one of the most interesting subjects of Micro-
scopic examination. The art of making successful preparations of this
kind is one in which perfection can usually be attained only by long
practice, and by attention to a great number of minute particulars; and
better specimens may be obtained, therefore, from those who have made
it a business to produce them, than are likely to be prepared by amateurs
for themselves. For this reason, no more than a general account of the
process will be here offered; the minute details which need to be atteuded-
to, in order to attain successful results, being readily accessible elsewhere
to such as desire to put it in practice.1 Injections may be either opaque

1 See especially the article 'Injection,' in the " Micrographic Dictionary,-" M.
Robin's work, "Du Microscope et des Injections;" Prof. H. Frey's Treatise "Das
Mikroscop und die Mikroskopische Technik;" Dr. Beale's " How to Work with the

VERTEBRATED ANIMALS.

293

or transparent, each method having its special advantages. The former
is most suitable where solid form and inequalities of surface are especially
to be displayed, as in Figs. 479 and 485; the latter is preferable where
the injected tissue is so thin as to be transparent (as in the case of the
retina and other membranes of the eye), or where the distribution of its
blood-vessels and their relation to other parts may be displayed by sec-
tions thin enough to be made transparent by mounting either in Canada
balsam or Dammar (Plate xxv.). — The injection is usually thrown into
the vessels by means of a brass syringe expressly constructed for the pur-
pose, which has several jet-pipes of different sizes, adapted to the differ-
ent dimensions of the vessels to be injected; and these should either be
furnished with a stop-cock to prevent the return of the injection when
the syringe is withdrawn, or a set of small corks of different sizes should
be kept in readiness, with which they may be plugged. The pipe should
be inserted into the cut end of the trunk which is to be injected, and
should be tied therein by a silk thread. In injecting the vessels of Fish,
Mollusks, etc., the softness of the vessels renders them liable to break in
the attempt to tie them; and it is therefore better for the operator to
satisfy himself with introducing a pipe as large as he can insert, and with
passing it into the vessel as far as he can without violence. All the ves-
sels from which the injection might escape should be tied, and sometimes
it is better to put a ligature round a part of the organ or tissue itself;
thus, for example, when a portion of the Intestinal tube is to be injected
through its branch of the Mesenteric artery, not only should ligatures be
put round any divided vessels of the mesentery, but the cut ends of the
intestinal tube should be firmly tied. — For making those minute injec-
tions, however, which are needed for the purposes of anatomical investi-
gation, rather than to furnish ' preparations ' to be looked-at, the Author
has found the glass-syringe (Fig. 106), so frequently alluded-to, the most
efficient instrument; since the Microscopist can himself draw its point to
the utmost fineness that will admit of the passage of the injection, and
can push this point without ligature, under the Simple Microscope, into
the narrowest orifice, or into the substance of the part into which the in-
jection is to be thrown. — Save in the*cases in which the operation has to
be practised on living animals, it should either be performed when the
body or organ is as fresh as possible, or after the expiry of sufficient time
to allow the rigor mortis to pass-off; the presence of this being very ini-
mical to the success of the injection. The part should be thoroughly
warmed, by soaking in warm water for a time proportionate to its bulk;
and the injection, the syringe, and the pipes should also have been sub-
jected to a temperature sufficiently high to insure the free flow of the
liquid. The force used in pressing-down the piston should be very mod-
erate at first, but should be gradually increased as the vessels become
filled; and it is better to keep up a steady pressure for some time, than to
attempt to distend them by a more powerful pressure, which will be cer-
tain to cause extravasation. This pressure should be maintained1 until
the injection begins to flow from the large veins, and the tissue is thor-
oughly reddened, and if one syringeful of injection after another be re-
quired for this purpose, the return of the injection should be prevented

Microscope;" the " Handbook to the Physiological Laboratory;" and Rutherford's
and Schafer's treatises on " Practical Histology."

1 Simple mechanical arrangements for this purpose, by which the fatigue of
maintaining this pressure with his hand is saved to the operator, are described in
the works referred-to in the preceding note.

294

THE MICROSCOPE AND ITS REVELATIONS.

by stopping the nozzle of the jet-pipe when the syringe is removed for
refilling. When the injection has been completed, any openings by which
it can escape should be secured, and the preparation should then be placed
for some hours in cold water, for the sake of causing the size to * set.'1

688. For opaque injections, the best coloring-matter, when only one
set of vessels is to be injected, is Chinese vermilion. This, however, as.
commonly sold, contains numerous particles of far too large a size; and
it is necessary first to reduce it to a greater fineness by continued tritu-
ration in a mortar (an agate or a steel mortar is the best) with a small
quantity of water, and then to get rid of the larger particles by a process
of ' levigation/ exactly corresponding to that by which the particles of
coarse sand, etc., are separated from the Diatomacecs (§ 300). The fine
powder thus obtained, ought not, when examined under a magnifying
power of 200 diameters, to exhibit particles of any appreciable dimen-
sions. The size or gelatine should be of a fine and pure quality, and
should be of sufficient strength to form a tolerable firm jelly when cold,,
whilst quite limpid when warm. It should be strained, whilst hot,
through a piece of new flannel; and great care should be taken to pre-
serve it free from dust, which may be best done by putting it into clean
jars, and covering its surface with a thin layer of alcohol. The propor-
tion of levigated vermilion to be mixed with it for injection, is about 2
oz. to a pint; and this is to be stirred in the melted size, until the two
are thoroughly incorporated, after which the mixture should be strained
through muslin. — Although no injections look so well by reflected light
as those which are made with vermilion, yet other coloring substances,
may be advantageously employed for particular purposes. Thus a bright
yellotv is given by the yellow chromate of lead, which is precipitated when
a solution of acetate of lead is mixed with a solution of chromate of po-
tass; this is an extremely fine powder, which ' runs 'with great facility
in an injection, and has the advantage of being very cheaply prepared.
The best method of obtaining it is to dissolve 200 grains of acetate of
lead and 105 grains of chromate of potass in separate quantities of
water, to mix these, and then, after the subsidence of the precipitate,
to pour-off the supernatant fluid so as to get-rid of the acetate of potash
which it contains, since this is apt to corrode the walls of the vessels if
the preparation be kept moist. The solutions should be mixed cold,
and the precipitate should not be allowed to dry before being incorpo-
rated with the size, four ounces of which will be the proportion appro-
riate to the quantity of the coloring-substance produced by the above
process. The same materials may be used in such a manner that the de-
composition takes-place within the vessels themselves, one of the solutions
being thrown-in first, and then the other; and this process involves so
little trouble or expense, that it may be considered the best for those
who are novices in the operation, and who are desirous of perfecting
themselves in the practice of the easier methods, before attempting the
more costly. By M. Doyere, who first devised this method, it was sim-
ply recommended to throw-in saturated solutions of the two salts, one

1 The Kidney of a Sheep or Pig is a very advantageous organ for the learner
to practise-on; and he should first master the filling of the vessels from the arte-
rial trunk alone, and then, when he has succeeded in this, he should fill the tu-
buli uriniferi with white injection, before sending colored injection into the renal
artery. The entire systemic circulation of small animals, as Mice, Rats, Frogs,,
etc., may be injected from the aorta; and the pulmony vessels from the pulmo-
nary artery.

VERTEBRATED ANIMALS.

295

after the other; but Dr. Goadby, who had much experience in the use of
it, advised that gelatine should be employed in tl e proportion of 2 oz.
dissolved in 8 oz. of water, to 8 oz. of the saturated solutions of each
salt. This method answers very well for the preparations that are to be
mounted dry; but for such as are to be preserved in fluid, it is subject
to the disadvantage of retaining in the vessels the solution of acetate of
potash, which exerts a gradual corrosive action upon them. Dr. Goadby
has met this objection, however, by suggesting the substitution of ni-
trate for acetate of lead; the resulting nitrate of potash having rather a
preservative than a corrosive action on the vessels. — When it is desired
to inject two or more sets of vessels (as the arteries, veins, and gland-
ducts) of the same preparation, different coloring substances should be
employed. For a white injection, the carbonate of lead (prepared by
mixing solutions of acetate of lead and carbonate of soda, and pouring-
off the supernatant liquid when the precipitate has fallen) is the best
material. No Hue injections can be much recommended, as they do
not reflect light well, so that the vessels filled with them seem almost
black; the best is freshly precipitated
prussian blue (formed by mixing solu-
tions of persulphate of iron and ferro-
cyanide of potassium), which, to avoid
the alteration of its color by the free
alkali of the blood, should be triturated
with its own weight of oxalic acid and
a litte water, and the mixture should
then be combined with size, in the pro-
portion of 146 grains of the former to 4
oz. of the latter.

689. Opaque injections may be pre-
served either dry or in fluid. The former
method is well suited to sections of many
solid organs, in which the disposition of
the vessels does not sustain much alte-
ration by drying; for the colors of the ves-
sels are displayed with greater brilliancy
than by any other method, when such slices, after being well dried, are mois-
tened with turpentine and mounted in Canada balsam. But for such an
injection as that shown in Fig. 479, in which the form and disposition
of the intestinal villi would be completely altered by drying, it is indis-
pensable that the preparation should be mounted in fluid, in a cell deep
enough to prevent any pressure on its surface. Either Goadby's solution
or weak Spirit answers the purpose very well; or by careful manage-
ment even such may be mounted in Canada balsam or Dammar.

690. Within the last few years, the art of making transparent Injec-
tion has been much cultivated, especially in Germany; and beautiful
preparations of this description have been sent over from that country
in large numbers. The coloring-matter is chiefly employed is Carmine,
which is dissolved in liquid ammonia; the solution (after careful filtra-
tion) being added in the requisite amount to liquid gelatine.

The following is given by Dr. Carter as a formula for a carmine injection
which will run freely through the most minute capillaries, and which will not
tint the tissues beyond the vessels themselves, a point of much importance: — Dis-
solve 60 grains of pure carmine in 120 grains of strong liquor ammoniae (Pharm.
Brit.), and filter if necessary ; with this mix thoroughly 1£ oz. of a hot solution

•296

THE MICROSCOPE AND ITS REVELATIONS.

PLATE XXV.

DISTRIBUTION OP CAPILLARY BLOOD-VESSELS AS SHOWN IN TRANSPARENT INJECTIONS (Original).

Fig. 1. Transverse section of Small Intestine of Rat, showing the villi in situ.

2. Section of the Toe of a Mouse:— a, a, a, tarsal bones; 6, digital artery; c, vascular loops in
the papillae forming the thick epidermic cushion on the under surface, d, distribution of vessels in
the matrix of the claw.

3. Distribution of Blood-vessels in the cortical of layer of the Brain, showing the manner in which
the arteries, carried-in by the pia mater, dip-down into the furrows of the convolutions.

VERTEBR ATED ANIMALS.

297

of gelatine (1 to 6 of water); mix another £ oz. of the gelatine solution with
86 minims of glacial acetic acid; and drop this, little by little, into the solution of
carmine, stirring briskly the whole time. After the part has been injected, and
has been hardened either by partial drying or by immersion in the Chromic acid
solution or in Alcohol, thin sections are cut with a sharp razor; and these are usu-
ally dried and mounted in Canada balsam.

Many of these transparent injections (Plate xxv.) are peculiarly well
seen under the Binocular Microscope, which shows the capillary net-
work not only in two dimensions (length and breadth), but also in its
third dimension, that of its thickness; this is especially interesting in
such injections as that (fig. 1) of the villi of the Intestine (seen in sitio
in a transverse section of its tube), a thin section of the Mouse's toe
(fig. 2), or the convoluted layer of the Brain (fig. 3). The Stereoscopic
effect is best seen, if the light reflected through the object be moderated
by a ground-glass, or even by a piece of tissue-paper, placed behind it.
— This method, however, does not serve to display anything well, save
the distribution of the Capillary vessels; the structures they traverse
being imperfectly shown. For the purpose of scientific research, there-
fore, the method followed by Dr. Beale (for full details of which the
reader is referred to his Treatise) is much to be preferred.

The material recommended by him for the finest injections is prepared as fol-
lows:— Mix 10 drops of the tincture of perchloride of iron (Pharm. Brit.) with 1
oz. of glycerine: and mix 3 grains of ferrocyanide of potassium, previously dis-
solved in a little water, with another 1 oz. of glycerine. Add the first solution
very gradually to the second, shaking them well together; and lastly, add 1 oz.
of water, and 3 drops of strong hydrochloric acid. This 'prussian blue fluid,'
though not a solution, deposits very little sediment by keeping; and it appears
like a solution even when examined under high magnifying powers, in conse-
quence of the minuteness of the particles of the coloring matter. Where a second
color is required, a carmine injection may be used, which is to be prepared as
follows: — Mix 5 grains of carmine with a few drops of water, and, when they are
well incorporated, add about 5 drops of strong liquor ammoniae. To this dark-red
solution add about £ oz. of glycerine, shaking the bottle so as to mix the two
fluids thoroughly; and then very gradually pour in another J oz. of glycerine acidu-
lated with 8 or 10 drops of acetic or hydrochloric acid, frequently shaking the
bottle. Test the mixture with blue litmus paper; and mix with it another i oz.
of glycerine, to which a few drops more acid should be added, if the acid reaction
of the liquid should not have previously been decided. Finally, add gradually 2
drachms of alcohol previously well mixed with 6 drachms of water, and incor-
porate the whole by thorough shaking after the addition of each successive
portion.

The staining process (§ 202) may be combined with the injecting; but Dr.
Beale has now come to prefer the following method, when such a combination is
desired. An alkaline carmine fluid rather stronger than that ordinarily employed
(carmine 15 grs., strong liq. ammoniae J drachm, glycerine 2 oz., alcohol 6
drachms) is first to be injected carefully with very slight pressure; the ammonia
having a tendency to soften the walls of the vessels. When they are fully dis-
tended, the preparation is to be left for from 12 to 24 hours, in order that time may
be allowed for the carmine liquid which has permeated the capillaries, to soak
through the different tissues and stain the germinal matter fully. Next a little
pure glycerine is to be injected, to get rid of the carmine liquid ; and the prussian
blue fluid is then to be injected with the utmost care. When the vessels have
been fully distended, the injected preparation is to be divided into very small pieces;
and these are to be soaked for an hour or two in a mixture of 2 parts of glycerine
and 1 of water, and then for three or four days in strong glycerine acidulated with
acetic acid (5 drops to 1 oz.). Preparations thus made are best mounted in Gly-
cerine jelly; and may then be examined with the highest powers of the Micro-
scope.

A well-injected preparation should have its vessels completely filled
through every part; the particles of the coloring matter should be so

298

THE MICROSCOPE AND ITS REVELATIONS

closely compacted together, that they should not be distinguishable
unless carefully looked for; and there should be no patches of pale unin-
jected tissue. Still, although the beauty of a specimen, as a Microscopic
object, is much impaired by any deficiency in the filling of its vessels,
yet to the Anatomist the disposition of the vessels will be as apparent
when they are only filled in part, as it is when they are fully distended;
and in thin sections mounted as transparent objects, imperfectly injected
capillaries may often be better seen than such as have been completely
filled.

691. A relation may generally be traced between the disposition of
the Capillary vessels, and the functions they subserve; but that relation
is obviously (so to speak) of a mechanical kind; the arrangement of the
vessels not in any way determining the function, but merely administer-

Fig. 480. Fig. 481.

Capillary network around Fat-cells.

Capillary network of Muscle.

ing to it, like the arrangement of water or gas-pipes in a manufactory.
Thus in Fig. 480 we see that the capillaries of adipose substance are dis-
posed in a network with rounded meshes, so as to distribute the blood
among the Fat-cells (§ 674); whilst in Fig. 481 we see the meshes

Fig. 482.

Fig. 483.

Distribution of Capillaries in
Mucous Membrane.

Distribution of Capillaries in

Skin of Finger.

enormously elongated, so as to permit the Muscular fibres (§ 677) to lie
in them. Again, in Fig. 482 we observe the disposition of the Capillaries
around the orifices of the follicles of a Mucous membrane; whilst in Fig.
483 we see the looped arrangement which exists in the papillary surface
of the Skin, and which is subservient to the nutrition of the epidermis
and to the activity of the sensory nerves (§ 682).

692. In no part of the Circulating apparatus, however, does the dis-
position of the capillaries present more points of interest, than it does in

VERTEBRATED ANIMALS.

299

the Respiratory organs. In Fishes the respiratory surface is formed by
an outward extension into fringes of gills, each of which consists of an
arch with straight laminae hanging down from it; and every one of these
laminae (Fig. 484) is furnished with a double row of leaflets, which is most
minutely supplied with blood-vessels, their network (as seen at a) being
so close that its meshes (indicated by the dots in the figure) cover less space
than the vessels themselves. The gills of Fish are not ciliated on their sur-
face, like those of Mollusks and of the larva of the Water-Newt; the ne-
cessity for such a mode of renewing the fluid in contact with them being
superseded by the muscular apparatus with which their gill-chamber is
furnished. — But in Eeptiles the respiratory surf ace is formed by the walls
of an internal cavity, that of the lungs: these organs, however, are con-
structed on a plan very different from that which they present in higher

Fig. 484. Fig. 485.

Two branchial processes of the Gill of Interior of upper part of Lung of Frog,

the Eel, showing the branchial lamellae:
— a, portion of one of these processes
enlarged, showing the capillary network
of the lamellae.

Vertebrata, the great extension of surface which is effected in the lat-
ter by the minute subdivision of the cavity not being here necessary. In
the Frog (for example) the cavity of each lung is undivided; its walls,
which are thin and membranous at the lower part, there present a sim-
ple smooth expanse; and it is only at the upper part where the extensions
of the tracheal cartilage form a network over the interior, that its
surface is depressed into sacculi, whose lining is crowded with blood-
vessels (Fig. 485). In this manner a set of air-cells is formed in the
thickness of the upper wall of the lung, which communicate with the
general cavity, and very much increase the surface over which the blood
comes into relation with the air; but each air-cell has a capillary network
of its own, which lies on one side against its wall, so as only to be exposed
to the air on its free surface. In the elongated lung of the Snake the

300

THE MICROSCOPE AND ITS REVELATIONS.

same general arrangement prevails; but the cartilaginous reticulation of
its upper part projects much further into the cavity, and incloses in its
meshes (which are usually square, or nearly so) several layers of air-
cells, which communicate, one through another, with the general cavity.
— The structure of the lungs of Birds presents us with an arrangement of a
very different kind, the purpose of which is to expose a very large amount
of capillary surface to the influence of the air. The entire mass of each
lung may be considered as subdivided into an immense number of
* lobules 9 or 'luhglets' (Fig. 486, b), each of which has its own bron-
chial tube (or subdivision of the windpipe), and its own system of blood-
vessels, which have very little communication with those of other lobules.
Each lobule has a central cavity, which closely resembles that of a Frog's
lung in miniature, having its walls strengthened by a network of carti-
lage derived from the bronchial tube, A, in the interspaces of which are
openings leading to sacculi in their substance. But each of these cavi-
ties is surrounded by a solid plexus of blood-vessels, which does not seem
to be covered by any limiting membrane, but which admits air from the
central cavity freely between its meshes; and thus its capillaries are in

Fig. 486.

Interior structure of Lung of Fowl, as displayed by a section, a, passing in the direction of a
bronchial tube, and by another section, b, cutting it across.

immediate relation with air on all sides, a provision that is obviously very
favorable to the complete and rapid aeration of the blood they contain.
— In the lung of Man and Mammals, again, the plan of structure differs
from the foregoing, though the general effect of it is the same. For its
whole interior is divided-up into minute air-cells, which freely commu-
icate with each other, and with the ultimate ramifications of the air-tubes
into which the trachea subdivides; and the network of blood-vessels (Fig.
487) is so disposed in the partitions between these cavities, that the blood
is exposed to the air on both sides. It has been calculated that the num-
ber of these air-cells grouped around the termination of each air-tube in
Man is not less than 18,000; and that the total number in the entire
lungs is six hundred millions.

693. The following list of the parts of the bodies of Vertebrata, of
which injected preparations are most interesting as Microscopic objects,
may be of service to those who may be inclined to apply themselves to
their production — Alimentary Canal; stomach, showing the orifices of
the gastric follicles, and the rudimentary villi near the pylorus ; small
intestine, showing the villi and the orifices of the follicles of Lieberktthn,

VERTEBRATED ANIMALS.

301

and ai its lower part the Peyerian glands ; large intestine, showing the
various glandular follicles : — Respiratory Organs ; lungs of Mammals,
Birds, and Eep tiles ; gills and swimming-bladder of fish ; Glandular
Organs; liver, gall-bladder, kidney, parotid : — Generative Organs; ovary
of Toad ; oviduct of Bftd and Frog ; Mammalian placenta ; uterine and
foetal cotyledons of Euminants : — Organs of Sense ; retina, iris, choroid,

Fig. 487.

Arrangement of the Capillaries on the walls of the Air-cells of the Human Lung.

and ciliary processes of eye, pupillary membrane of foetus ; papillae of
tongue ; mucous membrane of nose, papillae of skin or finger ; Tegumen-
tary Organs ; skin of different parts, hairy and smooth, with vertical
sections showing the vessels of the hair-follicles, sebaceous glands, and
papillae; matrix of nails, hoofs, etc. : — Tissues; fibrous, muscular, adipose,
sheath of tendon : — Nervous Centres ; sections of brain and spinal cord.

302

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XXI.

APPLICATION OF THE MICROSCOPE TO GEOLOGICAL INVESTIGATION.

694. The utility of the Microscope is by no means limited to the deter-
mination of the structure and actions of the Organized beings at present
living on the surface of the Earth ; for a vast amount of information is
afforded by its means to the Geological inquirer, not only with regard to
the minute characters of the many Vegetable and Animal remains that
are entombed in the successive strata of which its crust is composed, but
also with regard to the essential nature and composition of many of those
strata themselves. — We cannot have a better example of its value in both
these respects, than that which is afforded by the results of Microscopic
examination of lignite or fossilized wood, and of ordinary coal, which
we now assuredly know to be a product of the decay of wood.

695. Specimens of fossilized wood, in a state of more or less complete
preservation, are found in numerous strata of very different ages, — more
frequently, of course, in those whose materials were directly furnished by
the dry land, and were deposited in its immediate proximity, than in
those which were formed by the deposition of sediments at the bottom of
a deep ocean. Generally speaking, it is only when the wood is found to
have been penetrated by silex, that its organic structure is well preserved;
but instances occur every now and then, in which penetration by carbon-
ate of lime has proved equally favorable. In either case, transparent sec-
tions are needed for the full display of the organization; but such sections,
though made with great facility when lime is the fossilizing material,
require much labor and skill when silex has to be dealt with. Occasion-
ally, however, it has happened that the infiltration has filled the cavities
of the cells and vessels, without consolidating their walls ; and as the latter
have undergone decay without being replaced by any cementing material,
the lignite, thus composed of the internal 6 casts ' of the woody tissues, is
very friable, its fibres separating from each other like those of asbestos ;
and laminae split asunder with a knife, or isolated fibres separated by
rubbing-down between the fingers, exhibit the characters of the woody
-structure extremely well, when mounted in Canada balsam. — Generally
speaking, the lignites of the Tertiary strata present a tolerably close
resemblance to the woods of the existing period: thus the ordinary struc-
ture of dicotyledonous and monocotyledonous stems may be discovered in
such lignites in the utmost perfection ; and the peculiar modification pre-
sented'by coniferous wood is also most distinctly exhibited (Eig. 259).
As we go back^ however, through the strata of the Secondar y period, we
more and more rarely meet with the ordinary dicotyledonous structure

THE MICROSCOPE IK GEOLOGICAL INVESTIGATION.

303

and the lignites of the earliest deposits of these series are, almost uni-
versally, either Gymnosperms1 or Palms.

696. Descending into the Palaeozoic series, we are presented in the
vast coal formations of our own and other countries with an extraordinary
proof of the prevalence of a most luxuriant vegetation in a comparatively-
early period of the world's history; and the Microscope lends the Geolo-
gist essential assistance, not only in determining the nature of much of
that vegetation, but also in demonstrating (what had been suspected on
other grounds) that Coal itself is nothing else than a mass of decomposed
vegetable matter, derived from the decay of an ancient vegetation. The
determination of the characters of the Ferns, Sigillarice, Lepidodendra,
Catamites, and other kinds of vegetation whose forms are preserved in
the shales or sandstones that are interposed between the strata of Coal,
has been hitherto chiefly based on their external characters; since it is
seldom that these specimens present any such traces of minute internal
structure as can be subjected to Microscopic elucidation. But persever-
ing search has recently brought to light numerous examples of Coal-
plants, whose internal structure is sufficiently well preserved to allow of
its being studied microscopically: and the careful researches of Prof. W.
C. Williamson have shown that they formed a series of connecting links
between Cryptogamia and Flowering plants; being obviously allied to
Equisetacece, Lycopodiacece, etc., in the character of their fructifications
whilst their stem-structure foreshadowed both the ' endogenous' and
' exogenous ' types of the latter.2 Notwithstanding the general absence
of any definite form in the masses of decomposed wood of which Coal
itself consists (these having apparently been reduced to a pulpy state by
decay, before the process of consolidation by pressure, aided perhaps by
heat, commenced), the traces of structure revealed by the Microscope are
of ten sufficient — especially in the ordinary 6 bituminous' coal — not only
to determine its vegetable origin, but in some cases to justify the Botan-
ist in assigning the character of the vegetation from which it must have
been derived; and even where the stems arid leaves are represented by
nothing else than a structureless mass of black carbonaceous matter, there
are found diffused through this a multitude of minute resinoid yellowish-
brown granules, which are sometimes aggregated in clusters and inclosed
in sacculi; and these may now be pretty certainly affirmed to represent
the spores, while the sacculi represent the sporangia, of gigantic Lyco-
podiacece (§ 347) of the Carboniferous Flora. The larger the proportion
of these granules, the brighter and stronger is the flame with which the
coal burns; thus in some blazing cannel-coals they abound to such a de-
gree as to make up the greater proportion of their substance; whilst in
anthracite or ' stone-coal/ the want of them is shown by its dull and slow
combustion. It is curious that the dispersion of these resinoid granules
through the black carbonaceous matter is sometimes so regular, as to give
to transparent sections very much the aspect of a section of vegetable
cellular tissue, for which they have been mistaken even by experienced
rnicroscopists; but this resemblance disappears under a more extended
scrutiny, which shows it to be altogether accidental.

697. In examining the structure of coal, various methods may be fol-

1 Under this head are included the Cycadece, along with the ordinary Conifer ce
or pine and fir tribe.

a See his succession of Memoirs on the Coal-plants, in the recent volumes of
the "Philosophical Transactions."

304

THE MICROSCOPE AND ITS REVELATIONS.

lowed. Of those kinds which have sufficient tenacity, thin sections may
be made; but the opacity of the substance requires that such sections
should be ground extremely thin before they become transparent; and its
friability renders this process one of great difficulty. It may, however,
be facilitated by using Marine Glue, instead of Canada balsam, as the
cement for attaching the smoothed surface of the coal to the slip of glass
on which it is rubbed-down. Another method is recommended by the
authors of the " Micrographic Dictionary" (2d edit., p. 178): — "The
coal is macerated for about a week in a solution of carbonate of potass;
at the end of that time, it is possible to cut tolerably thin slices with a
razor. These slices are then placed in a watch glass with strong nitric
acid, covered, and gently heated; they soon turn brownish, then yellow,
when the process must be arrested by dropping the whole into a saucer
of cold water, or else the coal would be dissolved. The slices thus treated
appear of a darkish amber-color, very transparent, and exhibit the struc-
ture, when existing, most clearly. We have obtained longitudinal and
transverse sections of Coniferous wood from various coals in this way.
The specimens are best preserved in glycerine, in cells; we find that
spirit renders them opaque, and even Canada balsam has the same de-
fect."— When the coal is so friable that no sections can be made of it by
either of these methods, it may be ground to fine powder, and the parti-
cles may then, after being mounted in Canada balsam, be subjected to
Microscopic examination: the results which this method affords are by no
means satisfactory in themselves, but they will often enable the organic
structure to be sufficiently determined, by the comparison of the appear-
ances presented by such fragments with those which are more distinctly
exhibited elsewhere. Valuable information may often be obtained, too,
by treating the ash of an ordinary coal-fire in the same manner, or (still
better) by burning to a white ash a specimen of coal that has been pre-
viously boiled in nitric acid, and then carefully mounting the ash in
Canada balsam; for mineral 6 casts' of vegetable cells and fibres may of-
ten be distinctly recognized in such ash; and such casts are not unfre-
quently best afforded by samples of coal in which the method of section
is least successful in bringing to light the traces of organic structure, as
is the case, for example, with the anthracite of Wales.

698. Passing on now to the Animal kingdon, we shall first cite some
parallel cases in which the essential nature of deposits that form a very
important part of the Earth's crust, has been determinined by the assist-
ance of the Microscope; and shall then select a few examples of the most
important contributions which it has afforded to our acquaintance with
types of Animal life long since extinct. — It is an admitted rule in Geolo-
logical science, that the past history of the Earth is to be interpreted, so
far as may be found possible, by the study of the changes which are still
going on. Thus, when we meet with an extensive stratum of fossilized
Diatomacece (§ 299) in what is now dry land, we can entertain no doubt
that this siliceous deposit originally accumulated either at the bottom of
a fresh-water lake or beneath the waters of the ocean; just as such de-
posits are formed at the present time by the production and death of suc-
cessive generations of these bodies, whose indestructible casings accu-
mulate in the lapse of ages, so as to form layers whose thickness is only
limited by the time during which this process has been in action (§ 298).
In like manner, when we meet with a Limestone-rock entirely composed
of the calcareous shells of Forarnmifera, some of them entire, others
broken-up into minute particles (as in the case of the Fusulina-limestone

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION.

305

of the Carboniferous period, § 485, and the Nummulitic limestone of the
Eocene, § 489), we interpret the phenomenon by the fact that the dredg-
ings obtained from certain parts of the ocean-bottom consist almost en-
tirely of remains of existing Foraminifera, in which entire shells, the
animals of which may be yet alive, are mingled with the debris of others
that have been reduced by the action of the waves to a fragmentary state.
Such a deposit consisting chiefly of Orbitolites, § 466, is at present in
the act of formation on cer-
tain parts of the shores of Fig.488.
Australia, as the Author was
informed by Mr. J. Beete
Jukes; thus affording the
exact parallel to the stratum
of Orbitolites (belonging, as
his own investigations have
led him to believe, to the
very same species), that
forms part of the ' calcaire
grossier 9 of the Paris basin.
So in the fine white mud
which is brought up from
almost every part of the
sea-bottom of the Levant,
where it forms the stratum
that is continually undergo-
ing a slow but steady in-
crease in thickness, the Mi-
croscopic researches of Prof.
"Williamson1 have shown, not
only that it contains multi-
tudes of minute remains of
living organisms, both Ani-
mal and Vegetable, but that
it is entirely or almost wholly
composed of such remains.
Amongst these were about
26 species of Diatomaceae
(siliceous), 8 species of Fora-
minifera (calcareous), and a
miscellaneous group of ob-
jects (Fig. 488), consisting

d, siliceous
spicules of Geodia; c, sponge-

snicilles of SDOno-es and GrOr- sp^cuielunknown);'E, 'calcareous spicule of Grantia; f, g,
bpiuuitJb yi ouuuges ctnu vxui f q ^tions of caicareous skeleton of Echinodermata; h,

gOniae, and fragments 01 the i, calcareous spicule of Gorgonia ;k, l, n, siliceous spicules

Calcareous skeletons Of Echi- gi^^* ■> Portion of prismatic layer of shell of

noderms and Mollusks. A

collection of forms strongly resembling that of the Levant mud, with
the exception of the siliceous Diatomaceae, is found in many parts of
the * calcaire grossier 9 of the Paris basin, as well as in other extensive
deposits of the same early Tertiary period .

699. It is, however, in regard to the great Chalk Formation, that
the information afforded by the Microscope has been most valuable

: Memoirs of the Manchester Literary and Philosophical Society,'
20

1 Vol. vii.

306

THE MICROSCOPE AND ITS REVELATIONS.

Mention has already been made (§ 480) of the fact that a large propor-
tion of the North Atlantic sea-bed has been found to be covered with an
' ooze ' chiefly formed of the shells of Globigeri7ice; and this fact, first deter-
mined by the examination of the small quantities brought up by the sound-
ing apparatus, has been fully confirmed by the results of the recent ex-
ploration of the Deep-sea with the dredge; which, bringing up half a ton
of this deposit at once, has shown that it is not a mere surface-film,
but an enormous mass whose thickness cannot be even guessed at.
" Under the Microscope," says Prof. Wyville Thomson1 of a sample
of 1^ cwt. obtained by the dredge from a depth of nearly three miles,
"the surface-layer was found to consist chiefly of entire shells of Gloibi-
gerina bidloides, large and small, and of fragments of such shells mixed
with a quantity of amorphous calcareous matter in fine particles, a little
fine sand, and many spicules, portions of spicules, and shells of Eadio-

Fig. 489.

Microscopic Organisms in Chalk from Gravesend: a, 6, c, d, Textularia globulosa; «, e, e, Rota-
liaaspera; /, Textularia aculeata; g, Planulariahexas; h, Navicula.

laria, a few spicules of Sponges, and a few frustules of Diatoms. Below
the surface-layer the sediment becomes gradually more compact, and a
slight gray color, due, probably, to the decomposing organic matter, be-
comes more pronounced, while perfect shells of Globigerina almost dis-
appear, fragments become smaller, and calcareous mud, structureless,
and in a fine state of division, is in greatly preponderating proportion.
One can have no doubt, on examining this sediment, that it is formed
in the main by the accumulation and disintegration of the shells of Glo-
bigerina; the shells fresh, whole, and living, in the surface-layer of the
deposit; and in the lower layers dead, and gradually crumbling down by
the decomposition of their organic cement, and by the pressure of the
layers above." This white calcareous mud also contains in large amount

1 " The Depths of the Sea," p. 410.

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION.

307

the 'coccoliths' and ( coccospheres \ formerly described (§ 409). — Now
the resemblance which this Globigerina-mud, when dried, bears to
Chalk, is so close as at once to suggest the similar origin of the latter,
and this is fully confirmed by Microscopic examination. For many sam-
ples of it consist in great part of the minuter kinds of Foraminifera,
especially Globigerince (Figs. 489, 490), whose shells are imbedded in a
mass of apparently amorphous particles, many of which, nevertheless,
present indications of being the worn fragments of similar shells, or of
larger calcareous organisms. In the Chalk of some localities, the disin-
tegrated prisms of Pinna (§ 563), or of other large shells of the like struc-
ture (as Inoceramus), form the great bulk of the recognizable compo-
nents; whilst, in other cases, again, the chief part is made up of the
shells of Cytherina, a marine form of Entomostracous Crustacean (§ 604).
Different specimens of Chalk vary greatly in the proportion which the
distinctly organic remains bear to the amorphous residuum, and which

Fig. 490.

Microscopic Organisms in Chalk from Meudon; seen partly as opaque, and partly as transpa-
rent objects.

the different kinds of the former bear to each other; and this is quite
what might be anticipated, when we bear in mind the predominance of one
or another tribe of Animals in the several parts of a large area; but it
may be fairly concluded from what has been already stated of the amor-
phous component of the Globigerina-mud, that the amorphous constitu-
ent of Chalk likewise is the disintegrated residuum of Foraminif eral shells.
— But further, the Globigerina-mud now in process of formation is in
some places literally crowded with Sponges having a complete siliceous
skeleton (§ 511); and some of them bear such an extraordinarily close
resemblance, alike in structure and in external form, to the Ventriculites
which are well known as Chalk-fossils, as to leave no reasonable doubt
that these also lived as siliceous sponges on the bottom of the Cretace-
ous sea. Other sponges, also, are found in the Globigerina-mud, the
structure of whose horny skeleton corresponds so closely with the sponge-

308

THE MICROSCOPE AND ITS REVELATIONS.

tissues which can be recognized in sections of nodular Flints, Agates,1
etc., as to make it clear — when taken in connection with correspondence
of external form — that such flints are really fossilized sponges, the sili-
cifying material having been furnished by the solution of the skeletons of
the siliceous sponges, or of deposits of Diatoms or Radiolaria. Further,
in many sections of Flints there are found minute bodies termed Xan-
thidia, which bear a strong resemblance to the sporangia of certain Des-
onidiacece (Fig. 158, d); and the Author has found similar bodies in
the midst of what appears to be sponge-tissue imbedded in the Globige-
rina-mud. And (as was first pointed out by Mr. Sorby) the coccoliths
and coccospheres at present found on the sea-bottom (§ 409), are often to
be discovered by the Microscopic examination of Chalk.2 All these corre-
spondences show that the formation of Chalk took place under condi-
tions essentially similar to those under which the deposit of Globigerina-
mud is being formed over the Atlantic sea-bed at the present time.

700. In examining Chalk or other similar mixed aggregation, whose
component particles are easily separable from each other, it is desirable
to separate, with as little trouble as possible, the larger and more defi-
nitely organized bodies from the minute amorphous particles; and the
mode of doing this will depend upon whether we are operating upon the
large or upon the small scale. If the former, a quantity of soft Chalk
should be rubbed to powder with water, by means of a soft brush; and
this water should then be proceeded with according to the method of lev-
igation already directed for separating the Diatomaceae (§ 300). It will
usually be found that the first deposits contain the larger Foraminifera,
fragments of Shell, etc., and that the smaller Foraminifera and Sponge-spi-
cules fall next; the fine amorphous particles remaining diffused through the
water after it has been standing for some time, so that they may be
poured-away. The organisms thus separated should be dried and mounted
in Canada balsam. — If the smaller scale of preparation be preferred, as
much Chalk scraped fine as will lie on the point of a knife is to be laid
on a drop of water on the glass slide, and allowed to remain there for
a few seconds; the water, with any particles still floating on it, should
then be removed; and the sediment left on the glass should be dried and
mounted in Balsam. — For examining the structure of Flints, such chips
as may be obtained with a hammer will commonly serve very well: a
clear translucent flint being first selected, and the chips that are "obtained
being soaked for a short time in turpentine (which increases their trans-
parence), those which show organic structure, whether Sponge- tissue or
Xanthidia, are to be selected and mounted in Canada balsam. The most
perfect specimens of Sponge-structure, however, are only to be obtained
by slicing and polishing, — a process which is best performed by the lapi-
dary.

701. There are various other deposits, of less extent and importance
than the great Chalk-formation, which are, like it, composed in great
part of Microscopic organisms, chiefly minute Foraminifera; and the
presence of animals of this group may be largely recognized, by the
assistance of this instrument, in sections of Calcareous rocks of various
dates, whose other materials were fragments of Corals, Encrinite-stems,

1 See Dr. Bowerbank's Memoirs in the * 4 Trans, of the Geolog. Society," 1840,
and in the " Ann. of Nat. Hist.," 1st Ser., Vols, vii., x.

2 On the Organic origin of the so-called " Crystalloids " of Chalk; in " Ann.
of Nat. Hist.," Ser. 3, Vol. viii. (1861), pp. 193-200.

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION. 309

or the shells of Mollusks. In the formation of the Coralline Crag' (Ter-
tiary) of the eastern coast of England, Polyzoaries (§ 548) had the
greatest share; but the Tertiary limestone of which Paris is chiefly built
consists almost exclusively of the shells of Miliolida (§ 462), and is thus
known as Miliolite (millet-seed) limestone. In the vast stratum of Nu-
mulitic limestone (Fig. 333), which was formed at the commencement
of the Tertiary period, the Microscope enables us to see that the matrix
in which the large entire Nummulites are imbedded, is itself composed
of comminuted fragments and young of the same, together with minuter
Foraminifera. In the Oolitic (Secondary) formation, again, there are
many beds which are shown by the Microscope to have been chiefly com-
posed of Foraminiferal shells; and in those portions which exhibit the
6 roe-stone ' arrangement from which the rock derives its name (such as is
beautifully displayed in many specimens of Bath-stone and Portland-
stone), it is found by Microscopic examination of transparent sections,
that each rounded concretion is composed of a series of concentric
spheres formed by successive calcareous deposits upon a central nucleus,
which nucleus is often a Foraminiferal shell. In these and similar calca-
reous formations, the entire materials of which were obviously furnished
by the accumulation of animal remains, it not unfrequently happens
that all traces of their origin are obliterated by local ' metamorphic '
action usually dependent upon neighboring Volcanic heat; and thus a
crystalline marble, whose particles present not the least evidence of or-
ganic arrangement, may have been formed by the metamorphosis of
Chalky, Oolitic, or Nummulitic limestone. INow there is very strong evi-
dence that the vast mass of sub-crystalline * Carboniferous ' limestone,
which forms our coal-basins, has had a similar origin in Foraminiferal
and Zoophytic life; the traces of which have been for the most part re-
moved by the metamorphic action involved in its upheaval. For where
it has sustained but little disturbance, the evidences of its organic
(chiefly Foraminiferal) origin are unmistakable. Thus in the great
plains of Russia, there are certain bands of limestone of this epoch, vary-
ing in thickness from fifteen inches to five feet, and frequently repeated
through a vertical depth of two hundred feet over very wide areas, which
are almost entirely composed of the extinct genus Fusulina (Fig. 331).
Again, those parts of the Carboniferous limestone of Ireland which have
undergone least disturbance, can be plainly shown, by the examination
of Microscopic sections, to consist of the remains of Foraminifera, Poly-
zoa, fragments of Coral, etc. And where, as not unfrequently happens,
beds of this limestone are separated by clay seams, these are found to
be loaded with ' Microzoa ' of various kinds, particularly Foraminifera
(of which the Saccamina, Fig. 319, a, has come down to the present
time), and the beautiful Polyzoaries known as ' lace-corals/

702. Mention has been already made (§ 487 note) of Prof. Ehrenberg's
very remarkable discovery, that a large proportion (to say the least) of
the green sands which present themselves in various stratified deposits,
from the Silurian epoch to the Tertiary period, and which in certain
localities constitute what is known as the Greensand formation (beneath
the Chalk), is composed of the casts of the interior of minute shells of
Foraminifera and Mollusca, the shells themselves having entirely disap-
peared. The mineral material of these casts has not merely filled the
chambers and their communicating passages (Fig. 328, A, b), but has
also penetrated, even to its minutest ramifications, the canal-system of
the intermediate skeleton (Figs. 332, 337). The precise parallel to these

310

THE MICROSCOPE AND ITS REVELATIONS.

deposits presents itself in certain spots of the existing sea-bottom, such
as the Agulhas bank near the Cape of Good Hope; where the dredge
comes up laden with a green sand, which, on microscopic examination,
proves to consist almost entirely of 4 internal casts ' of existing Foramini-
fera, that must have been formed by the chemical replacement of their
protoplasmic bodies by ferruginous silicates precipitated from the Sea-
water. And this fact gives the clue to the interpretation of the condi-
tions under which the 'Eozoic Limestone' of Canada (§ 497), formed on
the sea-bottom of the Laurentian epoch by the extension of continuous
Foraminiferal growth resembling a Coral reef, became interpenetrated
with a like deposit of green silicate of magnesia (serpentine), of whose
presence in large amount in the sea-water of that period there is ample
evidence. — The determination of the organic nature of this Serpentine-
limestone, which is one of the lowest members of a series of strata so far
below those in which organic remains had previously been detected, that,
to use the words of Sir William Logan, the appearance of the so* called
' Primordial Fauna 9 is a comparatively modern event, — may be regarded as

the most remarkable achievement of
fig. 491. Microscopic inquiry as applied to

Geology.

703. It is obvious that, under or-
dinary circumstances, only the hard
parts of the bodies of Animals that
have been entombed in the depths of
the earth are likely to be preserved;
but from these a vast amount of in-
Eye ot Triiobite. formation maybe drawn; and the in-

spection of a microscopic fragment
will often reveal, with the utmost certainty, the entire nature of the organism
of which it formed part. Minute fragments of the tests or spines of all Echi-
nodermata, and of all such Molluscous shells as present distinct appearances
of structure (this being especially the case with the Brachiopods, and
with certain families of Lamellibranchiate bivalves), may be unerringly
identified by its means, when the external forms of these fragments
would give no assistance whatever.— In the study of the important
ancient group of TriloMtes, not only does a Microscopic examination of
the * casts ' which have been preserved of the surface of their Eyes (Fig.
491) serve to show the entire conformity in the structure of these organs
to the ' composite ' type which is so remarkable a characteristic of the
higher Articulata (§ 626), but it also brings to light certain peculiarities
which help to determine the division of the great Crustacean series with
which this group has most alliance.1

704. It is, however, in the case of the Teeth, the Bones, and the Der-
mal skeleton of Vertebrated animals, that the value of Microscopic
inquiry becomes most apparent; since their structure presents so many
characteristics which are subject to well-marked variations in their several
Classes, Orders, and Families, that a knowledge of these characters fre-
quently enables the Microscopist to determine the nature of even the
most fragmentary specimens, with a positiveness which must appear
altogether misplaced to such as have not studied the evidence. It was
in regard to teeth, that the possibility such determinations was first made

1 See Prof. Burmeister " On the Organization of the Trilobites ," published
the Ray Society, p. 19.

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION.

311

clear by the laborious researches of Prof. Owen;1 and the following may-
be given as examples of their value: — A rock-formation extends over
many parts of Russia, whose mineral characters might justify its being
likened either to the Old or to the New Red sandstone of this country,
and whose position relatively to other strata is such that there is great
difficulty in obtaining evidence from the usual sources as to its place in
the series. Hence the only hope of settling this question (which was one
of great practical importance, — since, if the formation were neio Red,
Coal might be expected to underlie it, whilst if old Red, no reasonable
hope of Coal could be entertained) lay in the determination of the Organic
remains which this stratum might yield; but unfortunately these were
few and fragmentary, consisting chiefly of teeth which are seldom per-
fectly preserved. From the gigantic size of these teeth, together with
their form, it was at first inferred that they belonged to Saurian Reptiles,
in which case the Sandstone would have been considered as New Red;
but Microscopic examination of

their intimate structure unmis- fig. 492.

takably proved them to belong
to a genus of Fishes (Dendrodus)
which is exclusively Palaeozoic,
and thus decided that the forma-
tion must be Old Red. — So
again, the Microscopic examina-
tion of certain fragments of
teeth found in a sandstance of
Warwickshire, disclosed a most
remarkable type of tooth-struc-
ture (shown in Fig. 492), which
was also ascertained to exist in
certain teeth that had been dis-
covered in the 6 Keupersand-
stein ' of Wurtemberg; and the
identity or close resemblance of
the animals to which these

teeth belonged haying been Section of Tooth of Labyrinthodon.

thus established, it became

almost certain that the Warwickshire and Wurtemberg sandstones were
equivalent formations, a point of much Geological importance. The
next question arising out of this discovery, was the nature of the animal
(provisionally termed Labyrinthodon, a name expressive of the most pecu-
liar feature in its dental structure) to which these teeth belonged. They
had been referred, from external characters merely, to the order of Sau-
rian Reptiles; but it is now clear that they were gigantic Salamandroid
Amphibia, having many points of relationship to Ceratodus (the Austra-
lian ' mud-fish '), which shows a similar though simpler dental organiza-
tion.

705. The researches of Prof. Quekett on the minute structure of bone2
have shown that from the average size and form of the lacunae, their dis-
position in regard to each other and to the Haversian canals, and the

1 See his magnificent " Odontography."

2 See his Memoir on the ' Comparative Structure of Bone,' in the " Transact, of
the Microsc. Soc.," Ser. 1, Vol.' ii.; and the " Catalogue of the Histological
Museum of the Roy. Coll. of Surgeons," Vol. ii.

312

THE MICROSCOPE AND ITS REVELATIONS.

number and course of the canaliculi (§ 653), the nature of even a minute
fragment of Bone may often be determined with a considerable approach
to certainty; as in the following examples, among many which might be
cited: — Dr. Falconer, the distinguished investigator of the fossil remains
of the Himalayan region, and the discoverer of the gigantic fossil Tor-
toise of the Sivalik hills, having met with certain small bones about
which he was doubtful, placed them for minute examination in the hands
of Prof. Quekett, who informed him, on Microscopic evidence, that they
might certainly be pronounced Eeptilian, and probably belonged to an
animal of the Tortoise tribe : and this determination was fully borne-out
by other evidence, which led Dr. Falconer to conclude that they were
toe-bones of his great Tortoise. — Some fragments of Bone were found,
many years since, in a Chalk-pit, which were considered by Prof. Owen
to have formed part of the wing-bones of a long- winged sea-bird allied to
the Albatross. This determination, founded solely on considerations
derived from the very imperfectly-preserved external forms of these frag-
ments, was called in question by some other Palaeontologists; who thought
it more probable that these bones belonged to a large species of the extinct
genus Pterodactylus, a flying lizard whose wing was extended upon a
single immensely-prolonged digit. No species of Pterodactyle, however,
at all comparable to this in dimensions, was at that time known; and the
characters furnished by the configuration of the bones not being in any
degree decisive, the question would have long remained unsettled, had
not an appeal been made to the Microscopic test. This appeal was so
decisive, by showing that the minute structure of the bone in question cor-
responded exactly with that of Pterodactyle bone, and differed essentially
from that of every known Bird, that no one who placed much reliance
upon that evidence could entertain the slightest doubt on the matter.
By Prof. Owen, however, the validity of that determination was ques-
tioned, and the bone was still maintained to be that of a Bird; until the
question was finally set at rest, and the value of the Microscopic test
triumphantly confirmed, by the discovery of undoubted Pterodactyle
bones of corresponding and even of greater dimensions, in the same and.
other Chalk quarries.

706. The application of the Microscope to Geology is not, however,
limited to the discovery or determination of Organic structure; for, as
has been now satisfactorily demonstrated, very important information
may be acquired by its means respecting the mineral composition of Rocks,
and the mode of their formation. The Microscopic examination of the
sediments now in course of deposition on various parts of the great
Oceanic area, and especially of the large number of samples brought up
in the ' Challenger 9 soundings, has led to this very remarkable conclu-
sion,— that the debris resulting from the degradation of Continental
land-masses are not carried far from their shores, being entirely absent
from the bottom of the deep Ocean-basins. The sediments there found,
where not of Organic origin, mainly consist of volcanic sands and ashes,
which are found in Volcanic areas, and of clay that seems to have been
produced by the disintegration of masses of pumice (vesicular lava),
which, after long floating, and dispersion by surface-drift or ocean cur-
rents, have become water-logged and have sunk to the bottom. As no
ordinary siliceous sand is found anywhere save in the neighborhood of
Continents and Continental islands, and as all Oceanic islands are the
products of local Volcanic outbursts, this absence of all trace of submerged
Continental land over the great Oceanic area, affords strong confirmation

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION. 313

to the belief which Geological evidence has been gradually tending to
establish, that the sedimentary rocks which form the existing land, were
deposited in the immediate neighborhood of pre-existing land, whose de-
gradation furnished their materials; and consequently that the original
disposition of the great Continental and Oceanic areas was not very dis-
ferent from what it now is.1 Further, the microscopic examination of
these Oceanic sediments reveals the presence of extremely minute parti-
cles, which seem to correspond in composition to meteorites, and which
there is strong reason for regarding as ' cosmic dust ' pervading the inter-
planetary spaces. — Thus the application of the Microscope to the study
of these deposits, brings us in contact with the greatest questions not only
of Terrestrial but also of Cosmical Physics; and furnishes evidence of the
highest value for their solution.

707. The application of the Microscope to the determination of the
materials of the sediments now in process of deposition on the Ocean-
bottom, leads us to another great department of Microscopic inquiry now
being extensively prosecuted, — namely, Microscopic Petrology, or the
study of the Mineral materials and Physical structure of Eocks. For
although the Geologist has no difficulty in determining by his unaided eye,
with the use of simple chemical tests, the mineral composition of rocks
of coarse texture, and in distinguishing the fragments of previously exist-
ing rocks of which they have been built-up, the case is different with
those of extremely fine grain, still more with such as present an appa-
rently homogeneous, compact, and glassy character. For it is only by
the microscopic study of these, that any trustworthy conclusions can be
arrived at in regard to the mode in which they have originated, and the
changes they have subsequently undergone; and such study often reveals
facts of the most unexpected kind and the most striking significance. —
Thus, many compact sedimentary rocks, whose homogeneous appearance
to the eye or the hand-magnifier gives no clue to their origin, are found,
when thin sections of them are examined microscopically, to be aggrega-
tions of minute rounded and water- worn grains (often less than l-1000th of
an inch in diameter) of Quartz, Felspar, Mica, soft and hard Clays, Clay-
slate, Oxide of Iron, Iron-pyrites, Carbonate of Lime, fragments of fossil
Organisms, etc., arranged without any trace of decided structure or crys-
tallization. In rocks exhibiting slaty cleavage, again, the direction in
which the pressure has been applied is indicated in a microscopic section
by the elongation or flattening out of some of the particles, with a sliding
movement of others. In regard to eruptive or igneous rocks, on the
other hand, the results of microscopic examination enable it to be stated
that whether possessing the hardest and most compact substance, and
presenting the most homogeneous and even glassy aspect, or existing
under the form of the softest and finest powder (like the dust-ash of vol-
canoes), the rocks of this class are characterized — as a rule — by the
minutely-crystalline character of their mineral conponents; and this even
when their vitrification seems to the eye so complete, as to forbid the
expectation of any such recognition. And in this manner a clue is ob-
tained to the sources of these rocks; which (there is now strong reason
to believe) have been formrd for the most part, if not universally, by the
melting-down of the rocks pre-existing in the neighborhood, and not
ejected (as according to the older theory) from the general molten inte-

!See Prof. Geikie's Lecture on 'Geographical Evolution,' in the ' 'Proceedings
of the Royal Geograpical Society," July, 1879.

314

THE MICROSCOPE AND ITS REVELATIONS.

rior of the earth. — Again, we are often enabled by the same means to
trace-out the 6 metamorphic ' action by which one kind of rock has been
converted into another subsequently to its first deposition as a sediment.
Of this the change of a calcareous deposit made-up of the remains of
Foraminifera with fragments of shells, corals, etc., into a crystalline
Limestone, is one of the most common; occurring wherever the rock has
been subjected to pressure and contortion, and especially in the near
neighborhood of igneous outbursts. And there can now be little hesita-
tion in attributing much of this conversion to the solvent action of water
raised to a very high temperature under enormous pressure. A very
curious piece of evidence, moreover, has now been furnished by Micro-
scopic study, in support of the doctrine which other considerations render
probable, that some forms of Granite (to say the least) have been gen-
erated from sedimentary rocks by metamorphic agency of a like nature.
For it has been shown by Mr. Sorby that the quartz-crystals of Granite
often inclose water or other liquids (sometimes liquid carbonic acid) in
cavities in their interior; which cavities, however, are not filled with the
liquid, the remaining spaces being occupied by vapor. This fact cannot
be otherwise accounted for, than by supposing that the crystallization must
have taken place in the presence of water; and that this water, though
liquid, must have been so hot as at that time to fill the cavities which it
now occupies only partially, the size of the present vacuity marking the
amount of its subsequent shrinkage during the cooling of the mass.

708. As this study, however, can only be successfully prosecuted by
such as have previously obtained a considerable knowledge of Mineralogy,
further details would obviously be unsuitable to our present purpose;
which is only to excite an interest in these researches, and to give such
general directions as will be of service to beginners who may be disposed
to follow them out. — The mode in which Eock -sections are to be cut, is
essentially the same as that for which directions have already been given
(§§ 192-196); but it will be found desirable to use broader and thicker
glasses than the ordinary 3x1 inch size, so that the sections may be
about an inch square. The emery-plate should only be used for the
hardest rocks, as the softer will be disintegrated when rubbed upon it.
For these last, a fine corundum-file, or a piece of pumice-stone, is to be
preferred in the first instance, and a fine Water-of-Air stone for finish-
ing. When the rock is very friable, it may be saturated with hardened
Canada balsam before rubbing down. As sections of the thinness usually
required may not bear being transferred from the glasses to which they
are cemented, it will be desirable that the attachment of a flattened and
polished surface to the glass on which any section is to remain, should be
finally made before the reduction of its thickness has been such as to in-
volve the risk of its fracture in the process.1

1 An "Elementary Text-book of Petrology " has lately been published by Mr.
F Rutley, of H. M. Geological Survey. The more advanced Student should have
recourse to the successive Memoirs published by Mr. Sorby in the Journal of the
Geological Society, the Proceedings of the Yorkshire Geological Society and else-
where, especially the following: — 4 On some Peculiarities in the Microscopic Struc-
ture of Crystals,' in " Journ. of Geolog. Society," Vol. xiv., p. 242; 'On the Mi-
croscopic Structure of Crystals, indicating the Origin of Minerals and Rocks/ Op,
tit, p. 453; * On the Original Nature and subsequent Alteration of Mica-Schist/
Op. cit., Vol. xix., p. 401; 4Sur 1' Application du Microscope a l'Etude de la
Geologie Physique, in 4 4 Bull. Soc. Geol. de Paris," 1859-60, p. 568; and his Presi-
dential Addresses to the Geological Society, 1879 and 1880. — Also the Memoir by
Mr. David Forbes, 4 The Microscope in Geology,' in the 44 Popular Science Review,"

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION.

315

Fig. 493.

709. In the application of the Microscope to Petrological and Minera-
logical research, the employment of Polarized light is constantly re-
quired; and various means and appliances are needful for its most advan-
tageous application, which are not required by the ordinary Microscopist.1
An instrument having been recently brought out by M. Nachet, which
combines all that the large experience of MM. Fouque and Michel Levy
has led them to think desirable for Mineralogical and Petrological invest-
igation, an account of it is here subjoined. — In all Microscopes previously
constructed for this purpose, the rotation of the object on the Stage be-
tween the Polarizing and the Analyzing prisms was liable to put it out
of position in regard to the cross- threads in the eye-piece; as the center-
ing of the Objective is scarcely
ever so perfect as not to pro-
duce some displacement, and,
if the centering be adjusted
so as to be perfect for one
Objective, it is likely to be
faulty for another. Now, the
peculiarity of M. Nachet's con-
struction is, that the Eye-piece,
with its cross-threads and ana-
lyzing prism, remains fixed
above (being carried upon a
separate arm), whilst the Body
and Stage (with the object it
carries) can be made to rotate
altogether around the optic
axis, above the Polarizing
prism which remains fixed be-
neath; the angular amount of
this rotation being measured
by a graduated ring, arid a ver-
nier attached to the stage. By
this arrangement, the object is
made to rotate between the
two prisms of the Polarizing
apparatus, without changing
its position beneath the Ob-
jective, and therefore without
displacing its image from its
contact with the cross-threads
of the Eye-piece. The mode
in which this plan is worked-

Oct., 1867; the Treatise of Vogelsang, * 4 Philosophie der Geologie und Mikrosko-
pische Gesteinsstudien," Bonn, 1867; various subsequent Memoirs by the same; the
Treatises of Zirkel, 4 4 Mikroskopische Beschaffenheit der Mineralien u. Gesteine,"
1873, and * 4 Microscopic Petrography " (U. S. Geological Exploration of Fortieth
Parallel), 1876; the Treatises of Rosenbusch, 44 Mikroskopische Physiographie der
petrographisch-wichtigen Mineralien," 1873 and 44 Mikroskopische Physio-
graphie der massigen Gesteine," 1877; that of Jenzsch, 4 * Mikroskopische Flora
u. Fauna Krystallinischer Massengesteine," 1868; that of Von Lasaulx, "Elemente
der Petrographie," 1875; and the great work of MM. Fouque and Levy, 44 Mine-^
ralogie Micrographique, Roches Eruptives Franchises," Paris, 1879.

1 The description of a Microscope specially devised for this purpose by Mr.
Rutley, and made by Mr. Watson (of Pall Mall), will be found at p. 307 of his Text-
book.

Nachet" s Small Mineralogical Microscope.

316

THE MICROSCOPE AND ITS REVELATIONS.

out in the ordinary small Continental model, is shown in Fig. 493;
whilst, on the other hand, Fig. 494 represents the largest and most
complete form of the instrument. In this last, the upper part of the
body, carrying the eye-piece and analyzing prism, can be raised or low-
ered by the pinion attached to the fixed arm that carries it. At m, im-
mediately beneath the eye-piece, is a small mirror, so placed as to illu-
minate the cross- wires when the field is dark. The analyzing prism is

Fig. 494*

Nachet's Large Mineralogical Microscope.

inserted at A, in such a manner as to allow of being readily withdrawn
when its action is not required. The Stage, with its traversing object-
platform D, is made to rotate in the optic axis by the pinion e; which
can be thrown out of gear so as to enable the rotation to be made by
hand; and the object-platform which is graduated in both directions, is
fitted with a square against which the slide abuts, so that any particular
point in a section, whose place has been once noted by the scales, can be
readily found again. The Polarizing prism N, is mounted quite inde-

THE MICROSCOPE IN GEOLOGICAL INVESTIGATION.

317

pendently of the stage, and can be precisely centered by the two milled-
heads, c and c'. In the lower (rotating) part of the body, there is a
horizontal slit at b for the introduction of laminae of gypsum, quartz,
etc., and into the lower end of the ocular tube can be fitted a cone that car-
ries the converging lenses necessary to transform the instrument into an
Amici microscope, its distance from the objective being regulated by the
rack near the top of the eye-tube.

318

THE MICROSCOPE AND ITS REVELATIONS.

CHAPTER XX.

CRYSTALLIZATION. — POLARIZATION. — MOLECULAR COALESCENCE.

710. Although by far the most numerous and most important appli-
cations of the Microscope are those by which the structure and actions of
Organized beings are made known to us, yet there are many Mineral
substances which constitute both interesting and beautiful objects; being
remarkable either for the elegance of their forms or for the beauty of
their colors, or for both combined. The natural forms of Inorganic
substances, when in any way symmetrical, are so in virture of that pecu-
liar arrangement of their particles which is termed crystallization; and
each substance which crystallizes at all, does so after a certain type or
plan, — the identity or difference of these types furnishing characters of
primary value to the Mineralogist. It does not follow, however, that the
form of the crystal shall be constantly the same for each substance; on
the contrary, the same plan of crystallization may exhibit itself under a
great variety of forms; and the study of these in such minute crystals as
are appropriate subjects for observation by the microscope, is not only a
very interesting application of its powers, but is capable of affording
some valuable hints to the designer. This is particularly the case with
crystals of Snow, which belong to the ' hexagonal system/ the basis of
every figure being a hexagon of six rays; for these rays "become in-
crusted with an endless variety of secondary formations of the same kind,
some consisting of thin laminae alone, others of solid but translucent
prisms heaped one upon another, and others gorgeously combining
laminae and prisms in the richest profusion;" 1 the angles by which these
figures are bounded being invariably 00° or 120°. Beautiful arborescent
forms are not unfrequently produced by the peculiar mode of aggregation
of individual crystals: of this we have often an example on a large scale
on a frosted window; but microscopic crystallizations sometimes present
the same curious phenomenon (Pig. 495). — In the following list are
enumerated some of the most interesting natural specimens which the
Mineral kingdom affords as Microscopic objects; these should be viewed
by reflected light, under a very low power: —

Antimony, sulphuret Iron, ilvaite or Elba-ore

Asbestos pyrites (sulphuret)

Aventurine Lapis lazuli

1 See Mr. Glaisher's Memoir on ' Snow-Crystals in 1855,' with numerous beau-
iful figures, in " Quart. Journ. of Microsc. Sci ," Vol. iii. (1855), p. 179.

Ditto, artificial
Copper, native

Lead, oxide (minium)
sulphuret (galena)

arseniate
malachite-ore
peacock-ore
pyrites (sulphuret)
ruby-ore

Silver, crystallized
Tin, crystallized

oxide

sulphuret

Zinc, crystallized.

CRYSTALLIZATION. POLARIZATION.

319

Fig. 495.

Thin sections of Granite and other rocks of the more or less regularly-
crystalline structure adverted to in the preceding paragraph, also of
Agate, Arragonite, Tremolite, Zeolite, and other Minerals, are very
beautiful objects for the Polariscope.

711. The actual process of the Formation of Crystals may be watched
under the Microscope with the greatest facility; all that is necessary
being to lay on a slip of glass, previously warmed, a saturated solution of
the Salt, and to incline the stage in a slight degree, so that the drop
shall be thicker at its lower than at its upper edge. The crystallization
will speedily begin at the upper edge, where the proportion of liquid to
solid is most quickly reduced by eva-
poration, and will gradually extend
downwards. If it should go on too
slowly, or should cease altogether,
whilst yet a large proportion of the
liquid remains, fhe slide may be again
warmed, and the part already solidified
may be re-dissolved, after which the
process will recommence with in-
creased rapidity. — This interesting
spectacle may be watched under any
Microscope; and the works of Adams
and others among the older observ-
ers testify to the great interest
which it had for them. It becomes
far more striking, however, when
the crystals, as they come into being,
are made to stand out bright upon
a dark ground, by the use of the Spot
lens, the Paraboloid, or any other
form of Black-ground illumination;
still more" beautiful is the spectacle

when the Polarizing apparatus is employed, so as to invest the crystals
with the most gorgeous variety of hues. Very interesting results may
often be obtained from a mixture of two or more Salts; and some of the
Double Salts give forms of peculiar beauty.1 A further variety may be
produced by fusing the film of the substance which has crystallized from its

Crystallized Silver,

1 The following directions have been given by Mr. Davies (" Quart. Journ. of
Microsc. Sci.," Vol. ii., 1862, p. 128, and Vol. v., p. 205) for obtaining these.
" He makes a nearly saturated solution, say of the double Sulphate of Copper and
Magnesia; he dries rapidly a portion on a glass slide, allowing it to become hot,
so as to fuse the salt in its water of crystallization; there then remains an amor-
phous film on the hot glass. On allowing the slide to cool slowly, the particles of
the salt will absorb moisture from the atmosphere, and begin to arrange them-
selves on the glass, commencing from points. If then placed under the Micro-
scope, the points will be seen starting up here and there; and from those centres
the crystals may be watched as they burst into blossom and spread their petals
on the plate. Starting-points may be made at pleasure, by touching the film
with a fine needle, to enable the moisture to get under it; but this treatment
renders the centres imperfect. If allowed to go on, the crystal would slowly
cover the plate, or if breathed-on they form immediately; whereas if it is desired
to preserve the flower-like forms on a plain ground, as soon as they are large
enough development is suspended by again applying gentle heat; the crystals are
then covered with pure Canada balsam and thin glass, to be finished off as usual.
The balsam must cover the edges of the film, or moisture will probably get under
it, and crystallization go creeping on."

320 THE MICROSCOPE AND ITS REVELATIONS.

solution; since on the temperature of the glass slide during the solidifica-
tion will depend the size and arrangement of the crystals. Thus Santo-

a. 496,

Radiating Crystallization of Santonine.

nine, when crystallizing rapidly on a very hot plate, forms large crystals
radiating from centres without any undulations; when the heat is less

Fig. 497.

Radiating Crystallization of Sulphate of Copper and Magnesia,

considerable, the crystals are smaller, and show concentric waves of very

CRYSTALLIZATION. POLARIZATION.

321

decided form (Fig. 496); but when the slip of glass is cool, the crytals
are exceedingly minute. It would seem as if these last results were due
to interruptions in the formative process at certain points, consequent
upon the hardening influence of cold, and the starting of a fresh forma-
tion at those points.1 A curious example of the like kind in the crystal-
lization of Sulphate of Copper to which a small quantity of Sulphate of
Magnesia has been added, is shown in Pig. 497. The same principle has
been carried out to a still greater extent in the case of Sulphate of Copper
alone, by Mr. E. Thomas,2 who has succeeded, by keeping the slide at a
temperature of from 80Q to 90°, in obtaining most singular and beautiful
forms of spiral crystallization, such as that represented in Fig. 498.
Mr. Slack has shown that a great variety of spiral and curved forms can
be obtained by dissolving metallic salts, or Salicine, Santonine, etc., in
water containing 3 or 4 per cent of colloid Silica. The nature of the
action that takes place may be understood by allowing a drop of the
Silica-solution to dry upon a slide; the result of which will be the pro-

Fig. 498.

Spiral Crystallization of Sulphate of Copper.

duction of a complicated series of cracks, many of them curvilinear.
When a group of crystals in formation tend to radiate from a centre, the
contractions of the Silica will often give them a trangential pull.
Another action of the Silica is to introduce a very slight curling with
just enough elevation above the slide to exhibit fragments of Newton's
rings, when it is illuminated with Powell and Lealand's modification of
Prof. Smith's dark-ground illuminator for high powers, and viewed with
a l-8th Objective. With crystalline bodies, these actions add to the
variety of colors to be obtained with the Polariscope, the best slides

1 See Davies on * Crystallization and the Microscope,' in "Quart. Journ. of
Microsc. Sci.," Vol. iv., p. 251.

2 See his paper ' On the Crystallization at various Temperatures of the Double
Salt, Sulphate of Magnesia and Sulphate of Zinc,' in "Quart. Journ. of Microse.
Sci.," N.S., Vol. vi., pp. 137, 177. See also H. N. Draper on 4 Crystals for the
Micro-Polariscope,' in "Intellectual Observer," Vol. vi. (1865), p. 437.

322

THE MICROSCOPE AND ITS REVELATIONS.

exhibiting a series of tertiary tints.1 — The following List specifies the
Salts and other substances whose crystalline forms are most interesting.
When these are viewed with Polarized light, some of them exhibit a beauti-
ful variety of colors of their own, whilst others require the interposition
of the Selenite plate for the development of color. The substances
marked d are distinguished by the curious property termed dichroism,
which was first noticed by Dr. Wollaston, but has been specially investi-
gated by Sir D. Brewster.2 This property consists in the exhibition of
different colors by these crystals, according to the direction in which the
light is transmitted through them; a crystal of Chloride of Platinum,
for example, appearing of a deep red when the light passes along its axis,
and of a vivid green when the light is transmitted in the opposite direc-
tion, with various intermediate shades. It is only possessed by doubly-
refracting substances; and it depends on the absorption of some of the
colored rays of the light which is polarized during its passage through
the crystal, so that the two pencils formed by double refraction become
differently colored, — the degree of difference being regulated by the in-
clination of the incident ray to the axis of double refraction.

Acetate of Copper, d

■ of Manganese

of Soda

of Zinc

Alum

Arseniate of Potass

Asparagine

Aspartic Acid

Bicarbonate of Potass

Bichromate of Potass

Bichloride of Mercury

Binoxalate of Chromium and Potass

Bitartrate of Ammonia

of Lime

of Potass

Boracic Acid
Borate of Ammonia

of Soda (borax)

Carbonate of Lime (from urine of horse)
Carbonate of Potass

of Soda

Chlorate of Potass
Chloride of Barium

of Cobalt

of Copper and Ammonia

of Palladium, d

of Sodium

Cholesterine
Chromate of Potass
Cinchonoidine
Citric Acid
Cyanide of Mercury
Hippuric Acid
Hypermanganate of Potass
Iodide of Potassium

of Quinine

Mannite
Margarine

Murexide

Muriate of Ammonia
Nitrate of Ammonia

of Barytes

— of Bismuth

of Copper

of Potass

of Soda

of Strontian

of Uranium

Oxalic Acid
Oxalate of Ammonia

of Chromium

of Chromium and Ammonia, d

of Chromium and Potass, d

of Lime

of Potass

of Soda

Oxalurate of Ammonia
Phosphate of Ammonia

Ammoniaco-Magnesian (triple

of urine)

of Lead, d

of Soda

Platino-chloride of Thallium
Platino-cyanide of Ammonia, d
Prussiate of Potass (red)

Ditto ditto (yellow)
Quinidine
Salicine
Saliginine
Santonine
Stearine
Sugar

Sulphate of Ammonia

of Cadmium

of Copper

of Copper and Ammonia

1 ' On the Employment of Colloid Silica in the preparation of Crystals for the
Polariscope,' in " Monthly Microscopical Journal," Vol. v., p. 50.

2 ' ' Philosophical Transactions," 1819.

CRYSTALLIZATION. POL ARIZ ATION.

323

Sulphate of Copper and Magnesia Sulphate of Soda

of Copper and Potass of Zinc

of Iron Tartaric Acid

of Iron and Cobalt Tartrate of Soda

of Magnesia Uric Acid

of Nickel Urate of Ammonia

of Potassa of Soda

It not unfrequently happens that a remarkably-beautiful specimen of
Crystallization develops itself, which the observer desires to keep for dis-
play. In order to do this successsully, it is necessary to exclude the air;
and Mr. Warrington recommends Castor-oil as the best preservative. A
small quantity of this should be poured on the crystallized surface, a
gentle warmth applied, and a thin glass cover then laid upon the drop
and gradually pressed down; and after the superfluous oil has been re-
moved from the margin, a coat of Gold-size or other varnish is to be ap-
plied.— Although most of the objects furnished by Vegetable and Animal
structures, which are advantageously shown by Polarized light, have
been already noticed in their appropriate places, it will be useful here to
recapitulate the principal, with some additions.

Vegetable.

Cuticles, Hairs, and Scales, from

Leaves (§§ 877-380)
Fibres of Cotton and Flax
Raphides (§ 359)

Spiral cells and vessels (§§ 357-362)
Starch-grains (§ 358)
Wood, longitudinal sections of, mount-
ed in balsam (§ 368)

Animal.

Fibres and Spicules of Sponges (§ 510)
Polypidoms of Hydrozoa (§ 521)

Spicules of Gorgoniae (§ 529)
Polyzoaries (§ 248)

Tongues (Palates) of Gasteropods mounted

in balsam (§§ 576-579)
Cuttle-fish bone (§ 575)
Scales of Fishes (§ 657, 658)
Sections of Egg-shells (§ 712)

of Hairs (§§ 661, 662)

of Quills (§ 660)

of Horns (§ 664)

of Shells (§§ 563-574)

of Skin (§ 670)

of Teeth (§§ 655, 656)

of Tendon, longitudinal (§ 668)

712. Molecular Coalescence. — Kemarkable modifications are shown in
the ordinary forms of crystallizable substances, when the aggregation of
the inorganic particles takes place in the presence of certain kinds of or-
ganic matter; and a class of facts of great interest in their bearing upon
the mode of formation of various calcified structures in the bodies of
Animals, was brought to light by the ingenious researches of Mr. Eainey,1
whose method of experimenting essentially consisted in bringing-about a
slow decomposition of the salts of Lime contained in Gum-arabic, by the
agency of Subcarbonate of Potash. The result is the formation of spher-
oidal concretions of Carbonate of Lime, which progressively increase in
diameter at the expense of an amorphous deposit which at first inter-
venes between them; two such spherules sometimes coalescing to produce
6 dumb-bells/ whilst the coalescence of a larger number gives rise to the
mulberry-like body shown in Pig. 499, b. The particles of such compo-
site spherules appear subsequently to undergo re-arrangement according
to a definite plan, of which the stages are shown at c and d; and it is
upon this plan that the further increase takes place, by which such

1 See his Treatise " On the Mode of Formation of the Shells of Animals, of
Bone, and of several other structures, by a process of Molecular Coalescence,
demonstrable in certain artificially-formed products" (1858); and his 'Further
Experiments and Observations,' in "Quart. Journ. of Microsc. Sci.," N.S., Vol. i.
(1861), p. 23.

324

THE MICROSCOPE AND ITS REVELATIONS.

larger concretions as are shown at a, a, are gradually produced. The
structure of these, especially when examined by Polarized light, is found
to correspond very closely with that of the small calculous concretions
which are common in the urine of the Horse, and which were at one time
supposed to have a matrix of cellular structure. The small calcareous
concretions termed 6 otoliths,' or ear-stones, found in the auditory sacs of
Fishes, present an arrangement of their particles essentially the same.
Similar concretionary spheroids have already been mentioned (§ 613) as
occurring in the skin of the Shrimp and other imperfectly-calcified shells
of Crustacea; they occur also in certain imperfect layers of the shells of
Mollusca; and we have a very good example of them in the outer layer of
the envelope of what is commonly known as a 'soft egg/ or an 'egg-
without shell/ the calcareous deposit in the fibrous matting already
described (§ 668) being here insufficient to solidify it. In the external
layer of an ordinary egg-shell, on the other hand, the concretions have
enlarged themselves by the progressive accretion of calcareous particles,
so as to form a continuous layer, which consists of a series of polygonal
plates resembling those of a tessellated pavement. In the solid 6 shells '

Fig. 499.

it it

Artificial Concretions of Carbonate of Lime.

of the eggs of the Ostrich and Cassowary, this concretionary layer is of
considerable thickness; and vertical as well as horizontal sections of it
are very interesting objects, showing also beautiful effects of color under
Polarized light. And from the researches of Prof. W. C. Williamson on
the scales of Fishes (§ 657), there can be no doubt that much of the cal-
careous deposit which they contain is formed upon the same plan.

713. This line of inquiry has been contemporaneously pursued by
Prof. Harting, of Utrecht, who, working on a plan fundamentally the
same as that of Mr. Eainey (viz., the show precipitation of insoluble salts
of Lime in the presence of an Organic 6 colloid'), has not only confirmed
but greatly extended his results; showing that with animal colloids (such
as egg-albumen, blood-serum, or a solution of gelatine) a much greater
variety of forms may be thus produced, many of them having a strong
resemblance to Calcareous structures hitherto known only as occurring
in the bodies of Animals of various classes. The mode of experimenting
usually followed by Prof. Harting, was to cover the hollow of an ordi-
nary porcelain plate with a layer of the organic liquid, to the depth of
from 0.4 to 0.6 of an inch; and then to immerse in the border of the

CRYSTALLIZATION. POLARIZATION.

325

liquid, but at diametrically opposite points, the solid salts intended to
act on one another by double decomposition, such Muriate, Nitrate, or
Acetate of Lime, and Carbonate of Potass or Soda; so that, being very
gradually dissolved, the two substances may come slowly to act upon
each other, and may throw down their precipitate in the midst of the
* colloid.' The whole is then covered with a plate of glass, and left for
some days in a state of perfect tranquillity; when there begin to appear
at various spots on the surface, minute points reflecting light, which
gradually increase and coalesce, so as to form a crust that comes to adhere
to the border of the plate; whilst another portion of the precipitate sub-
sides, and covers the bottom of the plate. Bound the two spots where
the salts are placed in the first instance, the calcareous deposits have a
different character; so that in the same experiment several very dis-
tinct products are generally obtained, each in some particular spot. The
length of time requisite is found to vary with the temperature, being gen-
erally from two to eight weeks. By the introduction of such a coloring
matter as madder, log-wood, or carmine, the concretions take the hue
of the one employed. When these concretions are treated with dilute
acid, so that their calcareous particles are wholly dissolved-out, there is
found to remain a basis-substance which preserves the form of each;
this, which consists of the 'colloid5 somewhat modified, is termed by
Harting calco-globuline. — Besides the globular concretions with the pecu-
liar concentric and radiating arrangement obtained by Mr. Bainey (Fig.
499), Prof. Harting obtained a great variety of forms bearing a more or
less close resemblance to the following: — 1. The 'discoliths' and ' cya-
tholiths' of Prof. Huxley (Pig. 293). 2. The tuberculated ' spicules'
of Alcyonaria (Figs. 362, 363), and the very similar spicules in the man-
tle of some species of Doris (§ 573). Lamellae of ' prismatic shell-sub-
stance' (§ 363), which are very closely imitated by 'crusts formed of
flattened polyhedra, found on the surface of the 6 colloid.' 4. The
spheroidal concretions which form a sort of rudimentary shell within
the body of Limax (§ 573). 5. The sinuous lamellae which intervene
between the parallel plates of the 'sepiostaire' of the Cuttle-fish (§ 575);
the imitation of this being singularly exact. 6. The calcareous concre-
tions that give solidity to the 'shell' of the bird's egg: the semblance of
which Prof. Harting was able to produce in situ, by dissolving away the
calcareous component of the egg-shell by dilute acid, then immersing
the entire egg in a concentrated solution of chloride of calcium, and trans-
ferring it thence to a concentrated solution of carbonate of potass, with
which, in some cases, a little phosphate of soda was mixed.1 Other forms
of remarkable regularity and definiteness> differing entirely from anything
that ordinary crystallization would produce, but not known to have their
parallels in living bodies, have been obtained by Prof. Harting. Look-
ing to the relations between the calcareous deposits in the scales of Fishes
(§§ 657-659) and those by which Bones and Teeth are solidified, it can
scarcely be doubted that the principle of 6 molecular coalescence ' is appli-
cable to the latter, as well as to the former; and that an extension and
variation of this method of experimenting would throw much light on
the process of ossification and tooth-formation. — The inquiry has been

1 See Prof. Harting' s "Recherches de Morphologie Synthetique sur la produc-
tion artificielle de quelques Formations Calcaires Inorganiques, publiees par
l'Academie Royale Nederlandaise des Sciences," Amsterdam, 1872; and il Quart.
Journ. of Microsc. Sci.," Vol. xii., p. 118.

326

THE MICROSCOPE AND ITS REVELATIONS.

further prosecuted by Dr. W. M. Ord, with express reference to the for-
mation of Urinary and other Calculi.2

714. Micro -Chemistry of Poisons. — By a judicious combination of
Microscopical with Chemical research, the application of re-agents may
be made effectual for the detection of Poisonous or other substances, in
quantities far more minute than have been previously supposed to be
recognizable. Thus it is stated by Dr. Wormley,2 that Micro-Chemical
analysis enables us by a very few minutes' labor to recognize with unerr-
ing certainty the reaction of the 100,000th part of a grain of either
Hydrocyanic Acid, Mercury, or Arsenic; and that in many other in-
stances we can easily detect by its means the presence of very minute
quantities of substances, the true nature of which could only be other-
wise determined in comparatively large quantity, and by considerable
labor. This inquiry may be prosecuted, however, not only by the appli-
cation of ordinary Chemical Tests under the Microscope, but also by the
use of other means of recognition which the use of the Microscope affords.
Thus it was originally shown by Dr. Guy3 that by the careful sublimation
of Arsenic and Arsenious Acid, — the sublimates being deposited upon
small disks of thin-glass, — these are distinctly recognizable by the forms
they present under the Microscope (especially the Binocular) in extremely
minute quantities; and that the same method of procedure may be applied
to the volatile metals, Mercury, Cadmium, Selenium, Tellurium, and some
of their Salts, and to some other volatile bodies, as Sal-Ammoniac, Cam-
phor, and Sulphur. The method of sublimation was afterwards extended
by Dr. Helwig4 to the Vegetable Alkaloids, such as Morphine, Strychnine,
Veratrine, etc. And subsequently Dr. Guy, repeating and confirming Dr.
Helwig's observations, has shown that the same method may be further
extended to such Animal products as the constituents of the Blood and of
Urine, and to volatile and decomposable Organic substances generally.5
By the careful prosecution of Micro-Chemical inquiry, especially with the
aid of the Spectroscope (where admissible), the detection of Poisons and
other substances in very minute quantity can be accomplished with such
facility and certainty as were formerly scarcely conceivable.

1 See his Treatise " On the Influence of Colloids upon Crystalline Form and
Cohesion," London, 1879.

2 "Micro-Chemistry of Poisons," New York, 1867.

3 ' On the Microscopic Characters of the Crystals of Arsenious Acid,' in
" Trans, of Microsc. Society," Vol. ix. (1861), p. 50.

3 6 ' Das Mikroskop in der Toxikologie," 1865.

5 ' On Microscopic Sublimates; and especially on the Sublimates of the Alka
loids,' in "Trans of Royal Microsc. Soc," Vol. xvi. (1868),p. 1; also " Pharma.
ceutical Journal," June to September, 1867.

APPENDIX.

327

APPENDIX.

* NUMERICAL APERTURE ' AND * ANGULAR APERTURE.'

The introduction of the 6 immersion system J has rendered necessary a
considerable modification in the mode of determining the real ' Aper-
tures 7 of Achromatic Objectives; which were formerly estimated entirely
by their respective * angles of aperture,' — such angles being (as formerly
explained, § 10), those contained, in each case, between the most
diverging of the rays issuing from the axial point of an object, that can
enter the lens and take part in the formation of an image. A careful
investigation of the whole subject of 'Aperture/ both theoretically and
practically, has of late been carried out with the greatest ability by Prof.
Abbe, of Jena; of whose important discovery of the dependence of ' re-
solving power 9 upon effraction — not refraction — an account has been
already given (§ 157). This investigation has enabled him to place the
question on an exact basis; and not only to clear up a great deal that was
formerly obscure, but to formulate a definite principle for the compari-
son of 'immersion' with 6 dry' or ' air ' objectives, which shows that the
advantages obtainable from the use of the former are much greater than
had been previously conceived.

Prof. Abbe has also made an important contribution to the practical
part of this inquiry, by the invention of an ' Apertometer ' for the pre-
cise measurement of angular apertures/ by which more exact and definite
results can be obtained than by any of the methods previously in use:
and he has further shown that a comparison of 'dry' and of 'immer-
sion ' lenses by their respective ' angles ' alone is so completely fallacious,
as to necessitate the introduction of a new scale of ' numerical apertures/
to which, as to a common standard, both could be referred. — It is the
object of this Addendum, in the first place, to explain to the readers of
this treatise the precise meaning of Prof. Abbe's term; and then to put
before them the new views in regard to the capacities of ' immersion '
Objectives, to which his investigations have led him. As (for obvious
reasons) conclusions only can be here stated, those who desire to master
the train of reasoning by which those conclusions have been worked-out,
are recommended to study the two most recent expositions of the doc-
trine; one given by Prof. Abbe himself in his Paper ' On the Estimation
of Aperture/ and the other by his disciple, Mr. Frank Crisp (one of the
Secretaries of the Koyal Microscopical Society) in his 'Notes on Aper-

1 " Journ. of Roy. Microsc. Soc.," Vol. i. (1878), p. 19. Another method devised
by Prof. Hamilton Smith (Op. cit., Vol. ii., 1879, p. 775), gives nearly the same
results as that of Prof. Abbe. And yet another has been proposed by Mr. Tolles
(Op. cit., Vol. iii., 1880, p. 887), who does not, however, give any reason to ques-
tion the accuracy of Prof. Abbe's instrument.

328 THE MICROSCOPE AND ITS REVELATIONS.

ture, Microscopical Vision, and the Value of Wide-angled Immersion
Objectives; ' contained in the " Journal of the Koyal Microscopical
Society/' for April and June, 1881.

It can be easily demonstrated mathematically, that the ' aperture ' of
a single lens used as a magnifying glass — that is, its capacity for receiv-
ing, and bringing to a remote conjugate focus, the rays emanating from
the axial point of an object brought very near to it — is determined by
the ratio between its absolute diameter (or clear c opening') and its focal
length; while that of an ordinary Achromatic Objective, composed of
several lenses, is determined by the ratio of the diameter of its back lens
(so far as this is really utilized) to its focal length. This ratio is most
simply expressed, when the medium is the same, by the sine of its semi-
angle of aperture (sin u); and we hence see how different are the propor-
tionate ' apertures' of different lenses from their proportionate ' angles
of aperture.' For as the sine of half 180°, — the largest possible theoreti-
cal angle, whose two boundaries lie in the same straight line, — is equal
to radius, and as the sine of half 60° is equal to £ radius, it follows that
a lens having an angle of 60° has an aperture equal to half (instead of
being only one-tliird) of the theoretical maximum. And as the sines of
angles beyond 60° increase very slowly, an objective whose angle is 120°
will have (instead of only two-thirds) as much as about 87-100ths of the
aperture given by the theoretical maximum.

When, however, the medium in which the Objective works is not air,
but a liquid of higher refractive index — such as water or oil — an addi-
tional circumstance has to be taken into consideration; for we may now
have three angles of aperture expressed by the same number of degrees,
which yet denote quite different c apertures.' For instance, an ' angle'
of 90° in oil will give a greater * aperture ' than one of 90° in water; and
the latter a greater aperture than 90° in air. For since, when light is
transmitted from any medium into another of greater refractive index
(§ 1), its rays are bent towards the perpendicular, the rays forming a
pencil of given angular extension in air, will, when they pass into water
or oil, be closed-together or compressed; so that in comparing (for
instance) an object mounted in balsam with one mounted dry, the
balsam angle, though much reduced, may nevertheless contain all the
rays that were spread-out over the whole hemisphere when the object was
in the less dense medium. It follows, therefore, that a given € angle '
in oil or water represents an increase in ' aperture ' over the same angle
in air. The amount of this increase having been determined by Prof.
Abbe to be proportional, in each case, to the index of refraction of the
interposed medium, the comparative 'apertures' of lenses working in
different media are in the compound ratio of two factors, — the sines of
their respective semi-angles of aperture, and the refractive indices of
the interposed fluids.

It is the product of these (n sin u) that gives what is termed by Prof.
Abbe the Numerical Aperture; which serves, therefore, as the standard
of comparison not only between ' immersion' and ' dry ' objectives, but
also between objects of like kind. For, when the medium is the same,
the factor (n) which represents the refractive index may, of course, be
neglected; the ' numerical apertures' of such objectives then being
simply the sines of their respective semi-angles.

Thus, taking as a standard of comparison a ( dry ' objective of the
maximum theoretical angle of 180,° whose ' numerical aperture ' is the

APPENDIX.

329

sine of 90%=radius or 100, we find this standard to be equalled by a
( water ' immersion objective of only 96% and by an ' oil' or * : homogene-
ous ' immersion lens of only 82°; the ' numerical apertures 'of these,
obtained by multiplying the sines of their respective semi-angles by the
refractive index of water in one case and of oil in the other, being 1.00
in both. Each, therefore, will have as great a power of receiving and
utilizing divergent rays, as any ' dry ' lens can even theoretically possess,
— an angle of nearly 70° being the limit of what is practically attainable.
But as the actual angle of an ' immersion ' Objective can be opened-out
to the same extent as that of an * air 9 objective, it follows that the ' aper-
ture 9 of the former can be augmented far beyond even the theoretical
maximum of the latter; the maxima of numerical aperture being 1.52
for Oil-immersion, and 1.33 for Water-immersion objectives, as against
1.00 for ' dry; ' and these being nearly attainable in practice.1

So, if we have four Objectives, two of which are ' dry/ the third a
water-immersion, and the fourth an oil-immersion, their apertures have
hitherto been designated, on the angular aperture notation, by (for
instance) 47° and 74° air-angle; 85° water-angle; and 117° oil-angle; so
that it is difficult without calculation to judge of their relative apertures.
By the numerical notation, however, the apertures of the four are seen
to be as .40, .60, .90 and 1.30; so that a comparison is readily made,
and it is seen whether the two latter have larger or smaller apertures than
the maximum of a dry objective.

This important doctrine may be best made practically intelligible by
a comparison (Fig. 500) of the relative diameters of the back lenses of
' dry 5 with those of 6 water 9 and ' oil 9 immersion Objectives of the same
power, from an ' air-angle 9 of 60° to an 6 oil-angle ' of 180°; these diam-
eters expressing in each case, the opening between the extreme pencil-
forming rays at their issue from the posterior surface of the combination,
to meet in its conjugate focus for the formation of the image; the extent
of which opening in relation to focal length (not that of the rays entering
the Objective), is the real measure of the Aperture of the combination.
The dotted circles in the interior of 1 and 2 are of the same diameter as
3 ; and therefore show the excess in the diameters of the back lenses of
the ' oil 5 and ' water 3 immersion-objectives, over that of the 6 dry 9 at
their respective theoretical limits.

Now this difference is capable of being practically tested by a simple
experiment originally suggested by Mr. Stephenson, and thus described
by Prof. Abbe: — "Take any immersion-objective of balsam angle exceed-
ing the critical angle, and focus it on a balsam-mounted object, which is
illuminated by any kind of immersion-condenser, in such a way that the
whole range of the aperture-angle is filled by the incident rays. Kemove
the eye-piece, and place the pupil of the eye at the place where the air-
image is projected by the objective, and look down on the lens. You see
a uniformly bright circle of well-defined diameter, which is the true cross
section of the image-forming pencil emerging from the Microscope (for
the eye receives now all rays which have been transmitted through a
small central portion of the object — that portion which is conjugate to
the pupil — and receives no other rays). After this, focus the same objec-

1 At p. 325 of Vol. L, Ser. 2 (1881) of the " Journ. of the Roy. Microsc. Soc.,"
will be found a Table calculated by Mr. Stephenson of the Equivalent Angles of
Aperture of Dry, Water-immersion, and Oil (or homogeneous) immersion Objec-
tives, with their respectiye Illuminating powers, and Theoretical Resolving
powers, for every 0.02 of Numerical Aperture, from 0.40 to 1.52.

330

THE MICROSCOPE AND ITS REVELATIONS.

Fig. 500.

180° Oil-angle.
(1.52 Num. Ap.)

live on an ordinary dry-mounted preparation (or on one which is con-
nected with the slide, the cover-glass being put on dry), and repeat the
observation; you will now see a well-defined circle, a cross section of the
emergent pencil, but of less diameter than in the former case, surrounded
by a dark annulus, visible by faint diffused light only."1 The explana-
tion of this experiment is, that in focussing an immersion-objective on an
object with air above it (i. e., between itself and the cover-glass), the
under-surface of the cover-glass acts as the plane front surface of the
system, converting it into a true ' dry ' lens of 180° angular aperture,
which gathers-in almost the whole hemisphere of light from the radiant
in air* and yet the emergent pencil of rays is much narrower than when

the same objective is used as an im-
mersion, and f ocussed on an object in
balsam, the extreme divergence of
whose rays is not more than 138°.

A wide-angled 6 immersion 9 Ob-
jective can therefore utilize rays from
an object mounted in a dense medium,
such as balsam, which are entirely
lost for the image (since they do not
exist, physically) when the same
object is in air, or is observed through
a film of air. And this loss can-
not be compensated-for by an in-
crease of illumination; because the
rays which are lost are different rays,
physically, from those obtained by
any illumination, however intense, in
a medium like air.

It is by increasing the number of
6 diffraction-spectra/ that the rays
admitted from the object contribute
to the ' resolving power ' of the Ob-
jective for lined and dotted objects;
the truth of the image formed by the
recombination of these spectra, being,
as formerly shown (§ 157), essen-
tially dependent upon the augmenta-
tion of the number which the objec-
tive can be made to receive.

Upon the i aperture ' of an objec-
tive are dependent (1) its illuminating
power, (2) its resolving power, and (3) its penetrating power; — the first
varying as the square of the numerical aperture, the second being in
direct, and the third in inverse proportion to the numerical aperture.

Whilst Prof. Abbe's investigation has made it clear that the 6 aper-
ture' of an immersion objective may exceed the maximum of that of a
dry objective, it is hardly necessary to point out that the act of the excess
is a distinct question from that of the value of the excess for particular
cases. As the penetrating power of the objective is diminished in pro-
portion as the aperture is increased, it is seen that large apertures can

1 The diameter of the emergent pencil may be accurately measured by the use
of an eye-piece Micrometer with the 4 'auxiliary Microscope" of Prof. Abbe's
Apertometric apparatus, already referred to

180° Water-angle.
U.33 Num. Ap.)

180° Air-angle.
96° Water-angle.
82° Oil-angle.
1.00 Num. Ap.)

97° Air-angle.
(0.75 Num. Ap.)

0° Air-angle.
(0.50 Num. Ap.)

APPENDIX.

331

only be obtained at the expense of a great reduction of penetration or
local depth, and consequently also of working distance, — qualities which
are essential in some of the most important kinds of Biological investiga-

Fig. 501.

tion; and the Author, therefore, still holds to the opinion, that for
objectives intended to be used for such purposes, ' moderate angles ' are

332

THE MICROSCOPE AND ITS REVELATIONS.

preferable; objectives of wide angle being kept for ' critical ' investiga-
tions upon objects specially demanding their use. In this view he is
entirely supported by Mr. Dallinger, whose unrivalled experience in
Biological work of the highest kind, entitles his opinion on such a point
to the highest respect. See Preface, pp. v., vi.

Microscopes, Etc.

Messrs. Watson's Neiv Models. — A new form of Large Compound
Microscope (Fig. 501) has lately been brought out by Messrs. Watson (of
Holborn), the peculiarity of which essentially consists in this, — that the
horizontal axis on which it is suspended passes through the axial point of
the plane in which the object lies; so that by inclination of the body and
stage — the source of light remaining fixed, — illuminating rays may be
made to fall on the object at any degree of obliquity. The mechanical
stage is so constructed (by placing the entire movement above the object
platform) as to give it a thinness not otherwise attainable with the power
of making a complete revolution. The mirror with its frame may be
slipped off the swinging arm that ordinarily carries it, and slid into a fit-
ting on the foot, on which it can be readily centred so as to reflect light
upon the centre of the stage, whatever may be the inclination of the
latter. And a further variety of illumination may be obtained by rotat-
ing the whole instrument on its foot, the mirror retaining its fixed posi-
tion in the centre. — The principle of these ingenious arrangements is to
give to the stage, and all that is above it, every variety of position in rela-
tion to a fixed source of light, instead of varying the position of the light
in relation to the object. — Experience alone can test its advantages over
the old models.

The above-named Makers have also adapted a 6 swinging sub-stage/
not merely to this large instrument, but to a smaller one on the scale of
the ' Student's Microscope 9 of Messrs. Boss (Fig. 43); which is furnished,
in addition, with a graduated disk for the precise measurement of the
obliquity given to the illuminating apparatus. Having carefully exam-
ined this instrument, with the Objectives supplied by the makers, the
Author is able to speak favorably of its workmanship; and would desire
to add the name of Messrs. Watson to those of whose Students' micro-
scopes he has spoken with approval at p. 67.

Messrs. Swiff s New Students9 Microscope. — These excellent Makers,
having adopted the general plan of the ' Wale' model (Fig. 44), of which
the Author has spoken in terms of high commendation, have applied to
it a new fine adjustment of their own, which gives to the ring that carries
the objective a very delicate and steady movement;1 replacing the iris-
diaphragm of the Wale model with their own ' calotte 9 diaphragm.

M. Nachetfs Objective-carrier. — Every working Microscopist has de-
sired a ready means of varying his ' powers/ without the trouble of un-
screwing one Objective and screwing on another. This difficulty has
been partly met by the use of the ' nose-piece;' but this cannot be conve-
niently made (at least, in the case of the heavily-mounted English
objectives) to carry more than two powers. By Messrs. Parkes, of
Birmingham, as already mentioned § 53, sliding tubes are substituted
for screws; but the use of them requires the withdrawal of the nose of
the microscope to a considerable distance above the stage. — The attention

1 See 44 Journ. of Roy. Microsc. Soc," Vol. i., N.S. (1881), p. 297.

APPENDIX.

333

of M. Nachet having been long directed to this point, he has recently
brought out a form of ' porte-objectif ' (an improvement on a suggestion
originally made by Prof. Thury) which allows the change of objectives to
be readily made without as much raising of the body from the stage as is
required in screwing and unscrewing. It consists (Pig. 502) of a fixed
inner cylinder, whose top screws into the bottom of the body; this being
embraced by a movable outer cylinder (a), that is kept closely pressed up
to its lower end by a strong spiral spring between the two. The bottom
of this outer cylinder is formed by a shoulder that is cut away for about
one-fourth of its circumference, so as to allow a (foliar (b) at the top of
the objective to be slipped into the opening as shown at c. When this is

Fig. 502.

Nachet's Objective carrier.

done, the objective is held firmly in place by the pressure of the spring;
and all that is needed to remove it is a slight pulling down of the outer
cylinder, which enables the collar of the objective to be slipped out again.
The inner cylinder is supplied by M. Nachet (when desired) with the
Society's screw, and the ' collar 9 can be adapted to receive either M.
Nachet's or any other Objectives. — Having been enabled, by the kindness
of M. Nachet, to make a trial of this little apparatus, the Author is glad
to be able to speak most favorably both of its simplicity and its effective-
ness.

INDEX.

Abbe, Prof., on Homogeneous immer-
sion, i. 17; on Diffraction spectra,
i. 156-160; on Penetration of objec-
tives, i. 163 note; on Numerical aper-
ture of objectives, ii. 327; on Aper-
tometer, ii. 327.

Aberration, Chromatic, i. 8, 9.

Spherical, i. 6, 7.

means of reducing and cor-
recting, i. 7-14.

Absorption bands, i. 89-93.

Acalephs, see Medusoz.

Acanthometrina, ii. 113.

Acarida, ii. 248, 249.

Achlya prolifera, i. 251, 253.

Achnanthes, i. 296, 297.

Achromatic Condenser, i. 102, 103; use
of, i. 144, 145.

Achromatic Correction, i. 10, 11.

Achromatic Objectives, see Objectives.

Acinetina, ii. 39, 40.

Acrocladia, spines of, ii. 143.

Actinia, ii. 135; thread-cells of, ii. 135,
136.

Actinocyclus, i. 291.

Actinomma, ii. 113.

Actinophrys, ii. 10-12.

Actinoptychus, i. 292.

Actinosphcerium, ii. 13.

Actinotrocha, ii. 198.

Actinozoa, ii. 134-137.

Adjustment of Focus, i. 82, i. 137-139.

Adjustment of Object-glass, i. 11-15;

i. 139-141.

JEcidium tussilaginis, i. 324.
Agamic eggs, of Rotifera, ii. 58-60; of
Entomostraca, ii. 210, 211; of Insects,

ii. 246, 247.

Agrion% circulation in larva of, ii. 238. ,
Air-bubbles, microscopic appearances

of, i. 152; in microscopic preparations,

i. 198, i. 216-217.
Albuminous substances, tests for, i.

208, 209.
Alburnum, i. 364, 370.
Alcohol, as hardening agent, i. 202; as

test, i. 209.
Alcyonian Zoophytes, ii. 136, 137.
Alcyonidium, ii. 161.
Alg^e, higher, microscopic structure of,

i. 331-335 (see Protophyta).

Airman, Prof., on Sarcode organisms,
ii. 22 note; on Noctiluca, ii. 34; on
Peridinium, ii. 37; on Myriothela,
ii. 122; on Tubularida, ii. 129 note; on
fresh-water Polyzoa, ii. 162 note; on
Appendicularia, ii. 169, 170.

Alternating Circulation of Ascidians,
ii. 166, 168.

Alternation of Generations, ii. 134.

Alveolina, ii. 73.

Amaranthus, seeds of, i. 386.

Ambulacral disks of Echinida, ii. 141.

Amici, Prof., his early construction of
Achromatic lenses, i. 11, 15; his in-
vention of the immersion system, i.
16; his drawing Camera, i. 97; his
Prism for oblique illumination, i. 106.

Amoeba, ii. 15-17.

Amceboids of Vol vox, i. 244; of proto-
plasm of Chara, i. 262 note; of proto-
plasm of roots of Mosses, i. 339; of
Myxomycetes, i. 326; of Sponges, ii.
117-119; of Polypes, etc., ii. 122, 123;
of colorless Blood-corpuscles, ii. 271.

Amoroucium, ii. 165.

Amphipleura pellucida, resolution of,
i. 171.

Amphistegina, ii. 91.

Amphitetras, i. 295.

Amplifiers, i. 86.

Anacharis alsinastrum, formation of
cells in, i. 356; cyclosis in, i. 356, 357.

Anagallis, petal of, i. 383.

Androspores of QEdogonium, i. 258.

Angle of Aperture, i. 8; limitation of,
for Binocular, i. 35-38; its relation to
Angular Aperture, i. 160 note; to
Numerical Aperture, ii. 327.

Anguillulce, ii. 193.

Angular Apperture of Object Glasses,

i. 160 note; its relation to resolving
power, i. 157, 163; its real meaning,

ii. 327; limits to its value, Preface, v.
Anguliferece, i. 295.

Aniline dyes, as staining agents, i. 206.
Animal Tissues, formation of, ii. 252-
255.

Animalcule-cage, i. 123.
Animalcules, ii. 24 (see Infusoria,
Monerozoa. Rhizopoda, and Rotifera).
Animals, distinction of, from Plants,

336

INDEX.

i. 222, 223; links connecting with I
Plants, i. 325-328. I

Annelida, ii. 192-204; marine, circu- I
lation in, ii. 196, 197; metamorphoses
of, ii. 197, 198; remarkable forms of,

ii. 199-202; luminosity of, ii. 202;
fresh-water, ii. 202, 203.

Annual layers of Wood, i. 369-371.

Annular Ducts, i. 365, 366.

Annulosa, ii. 192— see Entozoa, Turbel-
laria, and Annelida.

Anodon, shell of, ii. 174; parasitic em-
bryo of, ii. 183; ciliary action on gills
of, ii. 189.

Anomia, fungi in shell of, i. 321.

Ant, red, integument of, ii. 220.

Antedon, development of, ii. 152-154.

Antennae of Insects, ii. 232, 233.

Antheridia, of Chara, i. 262; of Mar-
chantia, i. 337; of Mosses, i. 340; of
Ferns, i. 347; — see Antherozoids.

Antherozoids, i. 229; of Vol vox, i. 242;
of Yaucheria, i. 251; of Sphaeroplea,
i. 255, 256; of (Edogonium, i. 258; of
Characeae, i. 261, 266; of Fuci, i. 333;
of Marchantia, i. 337; of Mosses, i.
339; of Ferns, i. 347.

Anthers, structure of, i. 388, 384.

Anthony, Dr., on scale of Gnat, i. 155;
onbattledoor scales, ii. 223; on tongue
of Fly, ii. 235 note.

Antirrhinum, seeds of, i. 386.

Apertometers, ii. 327.

Aperture, Angular, see Angular Aper-
ture; Numerical, ii. 327.

Aphides, agamic reproduction of, ii. 246.

Aphthae, fungus of, i. 320.

Aplanatic Searcher, i. 8 note.

Apothecia of Lichens, i. 330.

Appendicular ia, ii. 169, 170.

Apple, cuticle of, i. 376.

Apus, ii. 209.

Aquatic Box, i. 123.

Arachnida, microscopic forms of, ii.
248, 249; eyes of, ii. 250; respiratory
organs of, ii. 250; feet of, ii. 250;
spinning apparatus of, ii. 250, 251.

Arachnoidiscus, i. 293.

Arachnosphcera, ii. 114.

Aralia, cellular parenchyma of, i,
354.

Arcella, ii. 18, 19.

Archegonia, of Marchantia, i. 336; of
Mosses, i. 340; of Ferns, i. 347.

Archer, Mr., on zoospores of Desmi-
diacese, i. 267 note; on Chlamido-
myxis, i. 327-328; on Clathrulina, ii.
14.

Arenaceous Foraminifera, ii. 77-85.
Arenicola, ii. 196.
Areolar tissue, ii. 273.
Argulus, ii. 212.
Aristolochia, stem of, i. 375.
Artemia, ii. 207, 210.
Ascaris, ii. 193; fungous vegetation on,
i. 319.

Asci, of Lichens, i. 330; of Fungi, i.
322, 323.

Ascidia parallelogramma, ii. 164.
Ascidians, solitary, ii. 164; compound

ii. 165-167; social, 166-167; develop.

ment of, ii. 168-170.
Ascogonia, of Fungi, i. 322; of Lichens,

i. 330.
Ascomycetes, i. 322.
Asph alt e- varnish, i. 178.
Aspidisca-ioi'ia of Trichoda, ii. 48.
Aspidium, fructification of, i. 345.
Asplanchna, ii. 57, 58.
Astasia, ii. 33.

Asteriada, skeleton of, ii. 145; meta-
morphoses of, ii. 150, 151.
Asterolampra, i. 291.
Aster omphalus, i. 291,
Astromma, ii. 112.
Astrophyton, ii. 145.
Astrorhiza, ii. 78.

Auditory vesicles of Mollusks, ii. 190;

development of, ii. 186.
Aulacodiscus, i. 293.
Auxospores of Diatomaceae, i. 283.
Avicula, nacre of, ii. 174.
Avicularia of Polyzoa, ii. 162.
Axile bodies of sensory papillae, ii. 285.
Axis-cylinder of Nerve-fibres, ii. 284-

286.

Azure blue butterfly, scales of, ii. 222,
223.

Bacillariaparadoxa, i. 287; movements

of, i. 283.
Bacillus, i. 308-311.
Bacteria, i. 308-315.
Bacteriastrum, i. 296.
Badcock, Mr., on metamorphosis of

Acinetina, ii. 40.
Bailey, Prof., his Diatomaceous tests,

i. 171; on siliceous cuticle, i. 349; on

internal casts of Foraminifera, ii. 93

note.

Baker, Mr., his Students' Microscope,

i. 59; his Students' Binocular, i. 6">;
his Travelling Microscope, i. 81, 82;
his Pond-stick, i. 219.

Balanus, metamorphosis of, ii. 213. 214.
Balbiani, M., on generation of Infu-
soria, ii. 49-52.
Balsam, Canada, see Canada Balsam.
Banksia, stomata of, i. 380.
Barbadoes, Polycystina of, ii. 109, 114.
Bark, structure of, i. 373.
Barnacle, metamorphosis of, ii. 213, 214.
Basidia of Fungi, i. 322.
Bat, hair of, ii. 264; cartilage of ear of,

ii. 279.

Batrachospermeoe, i. 258, 259.
Battledoor scale of Polyommatus, ii*

222 223.
Bathybius, ii. 20.

Beading of Diatom-valves, i. 277-279;
of Insect-scales, Dr. Eoyston Pigott
on, ii. 224, 226.

INDEX.

337

Beale, Prof., his Pocket Microscope,
i. 80; his Demonstrating Microscope,

i. 81; his views of viscid media, i.
210-212; his Views of Tissue-forma-
tion, ii. 253-255.

Beck, Messrs., their Economic Micro-
scopes, i. 67; their Popular Micro-
scope, i. 68; their Large Compound
Microscope, i. 77; their improved
ditto, i. 80; their Achromatic Con-
densers, i. 102, 103; their arrange-
ment of Polarizing apparatus, i. 113;
their Compressors, i. 126, 127; their
Binocular Magnifier, i. 187 note; their
Microtome, i. 192.

Mr. Joseph, on scales of Thysa-

nurge, ii. 223-226.

Mr. Richd., his Dissecting Micro-
scope, i. 48; his Disk-holder, i. 121;
his Side-Reflector, i. 116; his Vertical
Illuminator, i. 118, 119; on scales of
of Thysanurse, ii. 224; on Spider's
threads, ii. 251.

Bee, eyes of, ii. 229, 230; hairs of, ii. 227;
proboscis of, ii. 235; wings of, ii. 242;
sting of, ii. 245; reproduction of,

ii. 247.
Berg-mehl, i. 302.
Bermuda-earth, i. 292, 302.
Beroe, ii. 137, 138.

Biddulphia, i. 293; growth of, i. 275
note; surf ace-marking of , i. 276; self-
division of, i. 280, 281.

Bignonia, seed of, i. 386.

Biliary Follicles, ii. 280.

Biloculina, ii. 71.

Binary subdivision of Vegetable Cells,
i. 227, 228; of Animal Cells, ii. 253;
see Cells, Animal and Vegetable.

Binocular Eye-piece, i. 33.

Magnifier, Nachet's, i. 48, 49;

Beck's, i. 187 note.

Microscopes, Stereoscopic,

principles of construction of, i. 25-28;
advantages of, i. 35-38; Objectives
suitable for, i. 35-37; different forms
of, Nachet's, i. 28-29; Wenham's, i.
29-31; Stephenson's, i. 30-33.

Non-Stereoscopic, Powell and

Lealand's, i. 84; Wenham's, i. 85.

Stereo-Pseudoscopic, Nachet's,

i. 33-35.

Vision, i. 25-28.

Bipinnaria-l&rvsi of Star-fish, ii. 151.

Bird, Dr. Golding, on preparation of
Zoophytes, ii. 131.

Birds, bone of, ii. 257; feathers of, ii.
266; blood of, ii. 269; lungs of, ii. 300,

Bird's-head processes of Polyzoa, ii. 162.

Bisulphide of Carbon, mounting Dia-
toms in, i. 291.

Bivalve Mollusks, shells of, ii. 171-178.

Black ground illuminators, i. 106-110,
i. 147.

Blackham, Dr., on Focal Depth, i. 163
note.

Blankley, Mr., his Selenite Stage, i. 113.
Blenny, viviparous, scales of, ii. 261.
Blights of Corn, i. 323.
Blood, Absorption-bands of, i. 92, 93.
Blood-disks of Vertebrata, ii. 267-271;

mode of preserving, ii. 271; circula-
tion of, see Circulation.
Blood-vessels, injection of, ii. 292-297;

disposition of, in different parts, ii.

297-301.
Bocket Lamp, i. 131.
Bone, structure of, ii. 255-258; mode of

making sections of, i. 196-199, ii. 258.
Bones, fossil, examination of, ii. 311.
Botryllians, ii. 160.
Botrytis, of Silkworms, i. 317-326.
Botterill, Mr., his Growing-slide, i. 122,

123; his Zoophyte- trough, i. 125.
Bowerbankia. ii. 161.
Brachionus, ii. 54, 62.
Brachiopoda, Shell-structure of, ii.

177, 178.

Brady, Mr. H. B., on Saccammina, ii.
78; on Loftusia, ii. 84; on Globigerina,
ii. 87.

Braithwaite, Dr., on Sphagnaceee, i. 344.
Branchiopoda, ii. 207-209.
Branchipus, ii. 209.

Braun, Prof., on development of Pedi-
astrese, i. 270-272.

Brittan, Dr., on Fungus-germs, i. 321.

Brownian Movement, i. 153, 154.

Browning, Mr., his Platyscopic Lens,
i. 21 ; his smaller Stephenson Binocu-
lar, i. 72-73; his Rotating Microscope,
i. 65; his Micro-Spectroscope, i. 89-
91.

Bryozoa, see Polyzoa.

Buccinum, palate of, ii. 182; egg cap-
sules of, ii. 184; development of, ii.
187.

Buckthorn, stem of, i. 369.

Bugs, ii. 219; wings of, ii. 242.

Bugula avicularia, ii. 162, 163.

Built-up Ceils, i. 182.

Bulbels, of Chara, i. 261 ; of Marchantia,

i. 336, 337.
Bulimina, ii. 89.

Bull's-eye Condenser, i. 114, 115; use

of, 148-150.
Burdock, stem of, i. 375.
Busk, Mr. G., on Vol vox, i. 238-243; on

Polyzoa, ii. 162. 163.
Butterflies, see Lepidoptera.

Cabinet for Microscopic Apparatus,

i. 130; for Objects, i. 218.
Cacao-butter, for imbedding, i. 195.
Cactus, raphides of , i. 363.
Calcaire Grossier, ii. 305, 307.
Calcareous Deposits, organic origin of,

ii. 308, 309.
Calcareous Sponges, ii. 120.
Calcarina, ii. 90.
Calycanthus, stem of, i. 374.
Calyptra of Mosses, i. 339.

338

INDEX.

Cambium-layer i. 373, 374.

Camera Lucida, i. 96-98; use of, in

Micrometry, i. 99.
Campanularidce, ii. 129.
Campy lodiscus, i. 288.
Canada Balsam, use of, as Cement, i.

176, i. 197-199; mounting of objects

in, i. 209, 214, 215.
Canaliculi of Bone, ii. 256, 257.
Canal-system of Foraminifera, ii. 70,

90-99.

Capillaries, circulation in, ii. 286-292;
injection of, ii. 293-298; distribution
of, ii. 298-300.

Capsule of Mosses, i. 340.

Carbolic Acid, as preservative, i. 210;
use of for dehydration, i. 215.

Carmine, as staining agent, i. 205; in-
jection with, ii. 295r 297.

Carp, scales of, ii. 262.

Carpenteria, ii. 88.

Carrot, seeds of, i. 387.

Cartilage, structure of, ii. 278, 279.

Caryophyllia, ii. 135.

Caryophyllum, seeds of, i. 386.

Caterpillars, feet of, ii. 245.

Cedar, stem of, i. 371.

Cells for mounting objects, i. 179-183;
mounting objects in, i. 215-217.

Cells, Animal, formation, of, ii. 253;
binary subdivision of, ii. 253, 279; in
Protozoa, ii. 1, 9, 12, 16, 26-30, 37, 38,
45, 47.

Vegetable, i. 224-227; origin and

multiplication of, i. 227, 228; binary
subdivision of, in protophyta, i. 230,
233, 241, 246, 254, 264-266, 279; in
Phanerogamia, i. 352-356; cyclosisin,
i. 260, 263, 356-359; thickening de-
posits in, i. 359-361; spiral deposits in,
i. 361; starch-grains in, i. 361, 362;
raphides in, i. 363.

Cellular Tissue, Animal, ii. 273; Vege-
table, ordinary forms of, i. 353-356;
stellate, i. 354, 355; formation of, i.
356.

Cellulose, i. 225; tests for, i. 208, 209.

Cements, Microscopic, i. 178, 179.

Cement-Cells, i. 180.

Cementum of Taeth, ii. 259.

Cephalopods, shell of, ii. 180; chroma-
tophores of, ii. 191.

Ceramiacece, i. 334.

Ceratium, ii. 38, 39.

Cercomonas, development of, ii. 29, 30.

Cestoid Entozoa, ii. 192, 193.

Chcetocerece, i. 295.

Chcetophoracece, i. 257, 258.

Chalk, formation of, ii. 305-308.

* Challenger' Expedition, use of tow-
net in, i. 221 note; collection of Glo-
bigerinae in, ii. 86, 87; observations
in, on Bathybius, ii. 20: on deep-sea
sediments, ii. 312, 313.

Characece, i. 259-262; cyclosis of fluid
in, i. 260, 261; multiplication of, by

gonidia, i. 262; sexual apparatus of.

i. 260-262.
Cheilostomata, ii. 162.
Chemical Microscope, i. 82-83.

Re-agents, i. 208, 209.

Chemistry, microscopic, ii. 326.
Cherry-stone, cells of, i. 360.
Chilodon, teeth of, ii. 43; self-division

of, ii. 46.

Chirodota, calcareous skeleton of, ii.
149.

Chitine of Insects, ii. 220.

Chlamidomyxis, i. 327, 328.

Choroid, pigment of, ii. 275.

Chromatic Aberration, i. 8, 9; means of
reducing and correcting, i. 10-16; re-
sidual, in high-angled Objectives, i.
173.

Chromatophores of Cephalopods, ii.
191.

Chromic acid, as solvent, i. 201 ; use of,
for hardening, i. 203.

Chyle, corpuscles of, ii. 270.

Cienkowski, on Myxomycetes, £* 327;
on Noctiluca, ii. 37.

Cidaris, spines of, ii. 135.

Ciliary action, nature of, ii. 41; in Pro-
tophytes, i. 250; in Infusoria, ii. 41;
on gills of Mollusks, ii. 189; on epithe-
lium of Vertebrata, ii. 277.

Ciliate Infusoria, ii. 41.

Cilio-flagellata, ii. 37-39.

Circulation of Blood, in Vertebrata, ii.
286-292; in Insects, ii. 237, 238; alter-
nating, in Tunicata, ii. 164, 167

Circulation, Vegetable, see Cyclosis.

Cirrhipeds, metamorphosis of, ii. 213,
214.

Cladocera, ii. 209.

Clark, Prof. H. James, on flagellate In-
fusoria, ii. 32; on Sponges, ii. 118
note.

Clathrulina elegans, ii. 13, 15.

Clavellinidce, ii. 166-168.

Cleanliness, importance of, to Micro-
scope, i. 134; in mounting objects, i.
217.

Clematis, stem of, i. 368, 376.
Closterium, cyclosis in, i. 264; binary

subdivision of , i. 264, 265; conjugation

of, i. 267-269.
Clypeaster, spines of, ii. 144.
Coal, nature of, ii. 303, 304.
Coalescence, molecular, ii. 323-325.
Cobweb-Micrometer, i. 92, 93.
Coccoliths and Coccospheres, ii. 19, 20,

325.

Cocconeidce, i. 296.

Cockchafer, cellular integument of, ii.

220; eyes of, ii. 229; antenna of, ii.

232, 233; spiracle of larva of, ii. 240.
Cockle of Wheat, ii. 193.
Coddington lens, i. 20.
Codosiga, life history of, ii. 32, 33.
Coelenterata, ii. 2.
Coenurus, ii. 192, 193.

INDEX.

339

Cohn, Dr. , his researches on Protococ-
cus, i. 232-236; on Volvox, i. 242,243; on
Stephanosphaera, i. 242 note; on Sphae-
roplea, i. 255; on Schizomycetes, i.
307, 308; on reproduction of Rotifera,
ii. 59; his cultivation-solution, i. 307
note.

Coleoptera, integument of, ii. 220; an-
tennae of, ii. 232, 233; mouth of, ii.
233, 234.

Collection of Objects, general direc-
tions for, i. 219-221.

Collins, Mr., his Harley Binocular, i.
70-71; his Eye-piece caps, i. 70; his
Students' Microscope, i. 59; his Grad-
uating Diaphragm, i. 102, 104.

Collomia, spiral libres of, i. 361.

Collozoa, ii. 115.

Colonial nervous system of Polyzoa, ii.
160.

Colorless corpuscles of Blood, ii. 270,
271.

Columella of Mosses, i. 342.

Comatida, metamorphosis of, ii. 152-
156; nervous system of, ii. 285.

Compound Microscope, optical princi-
ples of, i. 22-25; mechanical construc-
tion of, i. 40-42, 51, 52; Educational,
i. 52-55; Students', i. 55-67; Second
Class, i. 67-73; First class, i. 73-80;
for special purposes, i. 80-85.

Compressor, i. 126, 127; use of, i. 142.

Concave lenses, refraction by, i. 5, 6;
use of, in Achromatic combinations,
i. 10-15.

Conceptacles of Marchantia, i. 337.

Concretions, calcareous, ii. 323-325.

Condensers, Achromatic, i. 102-104:
Webster, i. 103; Swift's new combi-
nation, i. 113.

for Opaque objects, ordinary,

i. 114; Bull's-eye, i. 115; mode of
using, i. 147-150.

Confervacece, i. 253; self -division of, i.
254; zoospores of, i. 255; sexual re-
production of, i. 254, 255.

Conidia of Fungi, i. 322.

Coniferce, peculiar woody fibre of, i.
364; absence of ducts in, i. 369; struc-
ture of stem in, i. 371, 372; pollen-
grains of, i. 385 note; fossil, ii. 302.

Conjugatece, i. 236, 237.

Conjugation, of Palmoglaea, i. 232; of
Desmidiaceae, i. 267, 268; of Diato-
maceae, i. 281, 282; of Conjugateae, i.
236, 237; of Monadina, ii. 28-31; of
Noctiluca, ii. 37; of Vorticellina, ii.
52; — see Zygosis.

Connective Tissue, ii. 273; corpuscles
of, ii. 254, 273, 274.

Contractile vesicle, of Volvox, i. 238;
of Actinophrys, ii. 11; of Amoeba, ii.
16; of Infusoria, ii. 25, 45.

Conversion of Relief, i. 27, 28, 33, 34.

Convex lenses, refraction by, i. 3-5;
formation of images by, i. 6.

Copepoda, ii. 208.
Coquilla-nut, cells of, i. 360.
Coral, cutting sections of, with animal,
i. 200.

Corallines, true, i. 335; Zoophytic, ii.

129.
Cork, i. 373.

Corn, blights of, i. 323; ii. 193.

Corn-grains, husk of, i. 388.

Corns, structure of, ii. 276.

Cornuspira, ii. 70.

Corpuscles of Blood, ii. 267 271.

Correction of Object-glasses, for Sphe-
rical Aberration, i. 8, 9, 173; for Chro-
matic Aberration, i. 10, 11, 173; for *
thickness of covering glass, i. 11, 14,
135-141.

Coscinodiscece, i. 289-291.

Cosmarium, binary subdivision of, i.
265; conjugation of, i. 267; develop-
ment of, i. 268.

Cover-correction of Objectives, i. 11,
14, 135-141.

Covering-glass, i. 176, 177.

Crab, shell-structure of, ii. 214, 215;
metamorphosis of, ii. 216.

Crabro, integument of, ii. 220.

Crag-Formation, ii. 309.

Cricket, gastric teeth of, ii. 237; sounds
produced by, ii. 242.

Crinoidea, skeleton of, ii. 146; meta-
morphosis of, ii. 153-156.

Cristatella, ii. 162.

Cristellaria. ii. 85.

Crouch, Mr., his Educational Micro-
scope, i. 53; his Students' Binocular,

i. 65, 66; his stage-centering adjust-
ment, i. 80; his adapter for Beck's
side-reflector, i. 116.

Crusta Petrosa of Teeth, ii. 259.
Crustacea, ii. 205-217; lower forms of,

ii. 205-206; Entomostracous, ii. 206-
211; Suctorial, ii. 212; Cirrhiped, ii.
213, 214; Decapod, shell of, ii. 214,
215; metamorphosis of , ii. 215, 216.

Cryptogamia, general plan of structure
of, i. 331, 351, 352; — see Protophyta,
Algae, Lichens, Fungi, Hepaticae,
Mosses, Ferns, etc.

Crystallization, Microscopic, ii. 318, 323.

Ctenoid scales of Fish, ii. 261, 262.

Ctenophora, ii. 137-139.

Culture of Protophytic Fungi, i. 123
note, i. 307; of Flagellate Infusoria,
ii. 31. 1

Curculionidce, scales of, ii. 220, 228;

elytra of, ii. 128; foot of, ii. 244.
Cuticle of Animals, ii. 275-277.
of Equisetaceae, i. 349; of leaves,

i. 379.
Cutis Vera, ii. 274.

Cuttle-fish, shell of, if. 180; chromato-

phore of, ii. 191.
Cyanthus, seeds of, i. 387.
Cyclammina, ii. 82.
Cycloclypeus, ii. 70.

310

INDEX.

Cycloid scales of Fish, i. 261, 262.
Cyclops, ii. 208, 209; fertility of, ii. 210.
Cyclosis, in Vegetable cells, i. 226; in

Closterium, i. 263; in Diatomaceee, i.

273; in Chara, i. 259, 260; in cells of

Phanerogamia, i. 356-359; in Rhizo-

pods, ii. ti.
Cydippe, ii. 137, 138.
Cymbellece, i. 297.
Cynipidce, ovipositor of, ii. 245.
Cypris, ii. 207.

Cyprcea, structure of shell of, ii. 179.
Cystic Entozoa. ii. 192, 193.
Cysticerctts, ii. 192, 193.
Cytherina, ii. 207.

Dactylocalyx, ii. 121.

Dallinger, Mr., on flagellum of Bacte-
rium termo, i. 309; his Microscope
Lamp, i. 133; on qualities of Objec-
tives, i. 162, 165; Preface, v., vi.

Dallinger and Drysdale, their researches
on Monadina, ii. 26-32.

Dallingeria Drysdali, ii. 26-28.

Dalyell, Sir J. G., on development of
Medusae, ii. 132-134.

Dammar- Varnish, i. 178, 213.

Daphnia, ii. 209, 210.

Darker's Selenites, i. 113.

Davies, Mr., on Microscopic Crystalliza-
tion, ii. 319-321 note.

Dawson, Dr., on Eozoon, ii. 102.

Deane's Gelatine, i. 211.

De Bary, Dr., on Myxomycetes i. 327
note.

Decalcification, i. 201.

Decapod Crustacea, shell of, ii. 214, 215;

metamorphosis of, ii. 215, 216.
Defining power of Objectives, i. 161-

163, 173.

Dehydration, by Alcohol, i. 195; by
Carbolic Acid, i. 215.

Delsaux, Rev. J., on Brownian move-
ments, i. 154 note.

Demodex folliculorum, ii. 249.

Demonstrating Microscope, Beale's, i.
81.

Dendritina, ii. 72.

Dendrodus, teeth of, ii. 311.

Dentine of Teeth, ii. 258-260.

Depressions, distinction of, from eleva-
tions, i. 151.

Dermestes, hair of, ii. 228.

Desiccation, tolerance of, by Proto-
phytes, i. 235; by Infusoria, li. 31, 49;
by Rotifera, ii. 59, 60; by Entomos-
traca, ii. 210.

Desmidiaceai, general structure of, i.
262-264; cyclosis in, i. 263; binary
subdivision of, i. 264-266; formation
of gonidia in, i. 267; conjugation in,
i. 267, 268; classification of, i. 268,
269; collection of, i. 269, 270.

Deutzia, stellate hairs of, i. 379.

Development, of Annelids, ii. 197-201;
of Anodon, ii. 183, of Ascidians, ii.

168; of Cirrhipeds, ii. 213, 214; of
Crab, ii. 215; of Desmidiacese, i. 267;
of Diatomacese, i. 279-281; of Echin-
odermata, ii. 150-156; of Embryo( Ani-
mal), ii. 1, 122, of Embryo (Vegeta-
ble), i. 351, 352; of Entomostraca, ii.
211-213; of Ferns, i. 348; of Gastero-
pods, ii. 184-189; of Insects, ii. 247,
248; of Leaves, i. 356; of Medusse, ii.
126, 127; of Mosses, i. 342; of Nudi-
branchiata, ii. 185; of Palmoglsea, i.
230; of Pollen-grains, i. 384; of Pro-
tococcus, i. 232; of Sponges, ii. 118;
of Stem, i. 374; of Vegetable-cell, i.
227, 228; of Volvox, i. 238-241.

Diagonal Scales, i. 94, 99.

Diamond-beetle, scales of, ii. 220; elytra
of, ii. 228; foot of, ii. 243.

Diaphragm Eye-piece, Slack's, i. 95.

Diaphragm-Plate, i, 101-103.

Diatoma, i. 286.

Diatomacece, general structure of, i.
273, 274; silicified valves of, i. 274-
276; surface-markings of, i. 276-279;
binary subdivision of, i. 279, 280; con-
jugation of, i. 281, 282; gonidia of,
i. 282; auxospores of, i. 282; move-
ments of, i. 283; classification of, i.
284; general habits of, i. 301, 302; fos-
silized deposits of, i. 302, 303, ii. 304;
collection of, i. 302-304; mounting of,
i. 305, 306.

Diatoms, as Tests, i. 169-172, i. 276-279.

Dichroism, ii. 322.

Dicotyledonous Stems, structure of, i.

369-375.
Dictyoloma, seeds of, i. 387.
Didemnians, ii. 166.
Didymoprium, i. 269; self-division of,

i. 265; conjugation of, i. 269.
Difflugia, ii. 18.

Diffraction, errors arising from, i. 154-
157 ; production of microscopic images
by, i. 157-160.

Diphtheria, fungus of, i. 320.

Dipping-tubes, i. 127.

Diptera, mouth of, ii. 235; halteres of,

ii. 243; ovipositors of, ii. 246.
Discorbina, ii. 89.

Disk-holder, Beck's, i. 121; Morris's, i.
122.

Disk-illuminator, Wenham's, i. 105.
Dispersion, chromatic, i. 8, 9.
Dissecting Instruments, i. 187; Trough,

i. 187 ; Microscopes, i. 44-50.
Dissection, Microscopic, i. 186-188.
Distoma, ii. 194.

Dog, epidermis of foot of, ii. 276.
Doris, palate of, ii. 182; spicules of, ii.

179; development of, ii. 185.
Dorsal Vessel of Insects, ii. 237.
Double-staining, i. 207.
Doublet, Wollaston's, i. 20; Steinheil's,

i. 21.

Dragon-fly, eyes of, ii. 230; larva of, ii.
238-240.

INDEX.

341

Drawing Apparatus, i. 96-99.
Draw-Tube. i. 87.
Dropping Bottle, i. 211.
Drosera, hairs of, i. 379.
Dry-mounting of Objects, i. 179, 183.
Diysdale, Dr., see Dallinger.
Ducts, of Plants, i. 365, 366.
Dujardin, M., on Sarcode of Foramini-

fera, etc., i. 222 note; on Eotifera, ii.

60-62.

Dunning's Turn-Table, i. 184.
Duncan, Dr., on Fungi in coral, i.
321.

Duramen, i. 370.

Dytiscus, foot of, ii. 244; trachea and
spiracle of, ii. 339.

Eagle-Ray, teeth of, ii. 260.
Earwig wings of, ii. 242.
Eccremocarpus seeds of, i. 386.
Echinida, shell of, ii. 140, 141 ; ambula-

cral disks of, ii. 141, 142; spines of, ii.

142, 143; pedicellarise of, ii. 144; teeth

of, ii. 144, 145; metamorphosis of, ii.

151, 152.

Echinodermata, skeleton of, ii. 140-
145; metamorphoses of, ii. 150-153.

Echinus-spines, cutting sections of, i.
196-200, ii. 146-148.

Ectocarpacece, i. 332.

Ectoderm, ii. 1.

Ectosarc of Rhizopods, ii. 7, 15.

Ectoplasm of Vegetable cell, i. 225.

Edmunds, Dr., his immersion-parabo-
loid, i. 109; his parabolized gas-slide,
i. 125.

Educational Microscopes, i. 53-55.
Eel, scale of, ii. 262; gills of, ii. 299.
Eels, of paste and vinegar, ii. 193.
Eggs of Insects, ii. 246; — see Winter-
Eggs.

Egg-shell, fibrous structure of, ii. 272;
calcareous deposit in, ii. 324.

Ehrenberg, Prof. , his researches on In-
fusoria, ii. 24, 25; on Rotifera, ii. 24;
on Polycystina, ii. 109, 116; on com-
position of Greensands, ii. 93 note, ii.
309

Elastic Ligaments, ii. 272.

Elaters of Marchantia, i. 338.

Elementary Parts of Animal body, ii.
253-255 ; — see Tissues.

Elevations, distinction of, from depres-
sions, i. 151.

Elytra of Beetles, ii. 242.

Embryo, see Development.

Embryo-sac of Phanerogamia, i. 352.

Empusa musci, i. 318.

Enamel of Teeth, ii. 259.

Encrinites, see Crinoidea.

Encysting process, of Protophvtes, i.
230-236; of Infusoria, ii. 47-49.

End-bulbs of sensory Nerves, ii. 285.

Endochrome, of Vegetable cell, i. 225;
of Diatomaceae, i. 273.

Endoderm, ii. 1.

Endogenous Stems, structure of, i. 367,
375.

Endoplasm of Vegetable cell, i. 225.

Endosarc of Rhizopods ii. 7, 15.

Endosperm of Phanerogams, i. 353.

Enterobryus, i. 319, o20.

Entomostraca (Crustacea), ii. 205-211;
classification of, ii. 207-210; repro-
duction of, ii. 210-212.

Entophytic Fungi, i. 323, 324.

Entozoa, ii. 192-194; Cestoid, ii. 192;
Cystic, ii. 192; Nematoid, ii. 193, 194;
Trematode, ii. 194.

Eosin, as staining agent, i. 206.

Eozoic Limestone, ii. 310.

Eozoon Canadense, ii. 101-106.

Ephemera, larva of, ii. 219, 237, 240.

Ephippium of Daphnia, ii. 211.

Epidermis, Animal, ii. 275, 276.

Vegetable, i. 377-380.

Epithelium, ii. 276; ciliated, ii. 277.

Epithemia, i. 285; conjugation of, i.
281.

Equisetaceoz, cuticle of, i. 349; spores
of, i. 349.

Erecting Binocular, see Stephenson.
Erecting Prism, Nachet's, i. 88.
Erector, Listers, i. 87.
Errors of Interpretation, i. 150-156.
Euglena, ii. 33.
Eunotiece, i. 285.
Euplectella, ii. 121.
Euryale, skeleton of, ii. 145.
Ewart, Prof., on Bacillus, i. 311-313.
Exogenous Stems, structure of, i. 369-
375.

Eyes, care of, i. 134; Preface, vi., vii.

Eyes of Mollusks, ii. 190, 191; of Insects,
ii. 229-231; of Trilobite, ii. 310.

Eye-piece, i. 22; Huyghenian, i. 23, 24;
Kellner's, i. 24, 25; solid, i. 25; Rams-
den's, i. 25; Binocular i. 33; Erecting,
i. 88; Spectroscopic, i. 89; Microme-
tric, i. 92-95; Diaphragm i. 95.

Collins's shades for, i. 70.

Eve-piecing, deep, disadvantage of,

i. 136, 137, Preface, vi.

Falconer, Dr., on bones of fossil Tor-
toise, ii. 312.

Fallacies of Microscopy, i. 150-156.

Farrant's Medium, i. 211, 213.

Farre, Dr. Arthur, his researches on
Bowerbankia, ii. 161.

Fat-cells, ii. 278; capillaries of, ii. 298.

Feathers, structure of, ii. 263, 266.

Feet of Insects, ii. 243-245; of Spiders,

ii. 250.

Fermentation, influence of vegetation

on, ii. 315.
Ferns, i. 344-349; scalariform ducts

of, i. 344; fructification of, i. 344-346;

spores of, i. 346; prothallium of, i.

347; antheridia and archegonia of, i.

347; generation and development of,

i. 347, 348.

342

INDEX-.

Fertilization of ovule, in Flowering

plants, i. 352, 385.
Fibre-cells of anthers, i. 384; of seeds,

i. 360, 361.

Fibres, Muscular, ii. 281-283.

Nervous, ii. 284-286.

Spiral, of Plants, i. 360, 361, i.

364-366.

Fibrillar of Muscle, structure of ii. 281.

Fibro-Cartilage, ii. 279.

Fibro- Vascular Tissue of Plants, i. 363.

Fibrous Tissues of Animals, ii. 271-273;
formation of, ii. 254.

Field's Dissecting and Mounting Micro-
scope, i. 49, 50; his Educational Mi-
cx-oscope, i. 53.

Filiferous Capsules of Zoophytes, ii.
135.

Finders, i. 99; Maltwood's, i. 100.
Fine Adjustment, i. 40; uses of, i. 137-
139.

Fishes, bone of, ii. 257, 258; teeth of,

ii. 258, 259; scales of. ii. 261-263; blood
of, ii. 268, 269; circulation in, ii. 288;
gills of, ii. 299.

Fishing tubes, i. 127.

Flagella, of Protococcus, i. 233; of Vor-
vox, i. 237; of Bacteria, i. 308.

Flagellata (Infusoria), ii. 26-37; their
relation to Sponges, ii. 117.

Flatness of field of Objectives, i. 164.

Flints, organic structure in, ii. 308; ex-
amination of, ii. 308.

Flint Glass, dispersive power of, i. 10;
use of, in Objectives, i. 15, 16.

Floridece, i. 334.

Floscularians, ii. 60, 61.

Flowers, small, as Microscopic objects,
i 382; structure of parts of, i. 382-385.

Fluid, mounting objects in, i. 215-217.

Fluke, ii. 194.

Flustra, ii. 157-161.

Fly, fungous disea.se of, i. 318; number
of objects furnished by, ii. 218; eye of
ii. 230; circulation in, ii. 238; tongue
of, ii. 234; spiracle of, ii. 239; wing of,
ii. 241; foot of, ii. 243; development
of, ii. 248.

Focal Adjustment, i. 137-139; errors
arising from imperfection of, i. 151-
153.

Focal Depth of Objectives, i. 163; in-
crease of, with Binocular, i. 38.

Follicles of Glands, ii. 280.

Foot of Fly, ii. 243: of Dytiscus, ii. 244;
of Spider, ii. 250.

Foraminifera, ii. 64-106; their relation
to Rhizopods, ii. 7, 66; their general
structure, ii. 66-70; porcellanous, ii.
70-77; arenaceous, ii. 77-85; vitreous,
ii. 85-106; collection and mounting of,
ii. 107-109; fossil deposits of, see Fos-
sil Foraminifera; mode of making
sections of, i. 198 note.

Forceps, i. 128; Stage, i. 120; Slider, i.
185.

Forficulidce, wings of, ii. 242.
Formed Material, Dr. Beale on, ii. 253-
255.

Fossil Bone, ii. 311.

Diatoms, i. 302, 303, ii. 304, 305.

Foraminifera, ii. 72, 73, 78, 82-84,

90, 96-106, 304-310.

Radiolaria, ii. 109.

Sponges, ii. 307, 308.

Teeth, ii. 310, 311.

■ Wood, i. 371, 373, ii. 302-304.

Fowl, lung of, ii. 300.
Fragillariece, i. 286.

Free Cell formation in Plants, i. 227r
228.

Freezing Microtome, i. 191, 192.

Frog, blood of, ii. 268-271; pigment,
cells of, ii. 275, 276; circulation in
web of, ii. 286-288; in tongue of, ii.
288; in lung of, ii. 288; structure of
lung of, ii. 299, 300.

Fructification, of Chara, i. 260-262; of
Fuci, i. 332-334; of Florideae, i. 334-
335; of Lichens, i. 329; of Fungi, i.
321. 324; of Marchantia, i. 337, 338; of
Mosses, i. 339-342; of Ferns, i. 344-
348; of Equisetaceae, i. 349; of Lyco-
podiaceae, i. 350.

Fucacece, i. 331-334; sexual apparatus,
of, i. 332-334; development of, i. 334.

Fungi, relation of, to Algae, i. 229, 307;
to Animals, i. 307, 325-329; to Li-
chens, i. 329; simplest forms of, i. 307-
316; in bodies of living Animals, i.
316-320; in substance, or on surface,
of Plants, i. 323, 324; amoeboid states
of, i. 325, 326; universal diffusion of
sporules of, i. 313-321; culture of, u
..23 note, i. 307.

Furcularians, ii. 62.

Fusulina, ii. 90, 91.

Gad-flies, ovipositor of, ii. 246.

Gall-flies, ovipositor of, ii. 245.

Galls of Plants, ii. 245.

Ganglion-Cells, ii. 284.

Ganoid scales of Fish, ii. 263.

Gasteropoda, structure of shells of, ii.
178; palates of, ii. 180-183; develop-
ment of, ii. 183-189; organs of sense
of, ii. 190, 191.

Gastrula, ii. 1.

Geikie, Prof., on Geographical evolu-
tion, ii. 313 note.
Gelatine, see Glycerine jelly.
Gelatinous Nerve fibres, ii. 284.
Generation, distinguished from Growth,

i. 227-229; in Cryptogams, i. 350; in
Phanerogams, i. 352.

Geology, applications of Microscope to,,

ii. 302-314.

Geranium-petal, peculiar cells of, i.
383.

Germ-cell of Cryptogams, i. 350; of

Phanerogams, i. 352.
Germinal Matter, Dr. Beale on, ii. 253.

INDEX.

343

Gills, of Mollusks, ciliary motion on,
ii. 189, 190; of Fishes, distribution of
vessels in, ii. 299; of Water-newt, cir-
culation in, ii. 288.

Gizzard of Insects, ii. 237.

Glands, structure of, ii. 279, 280.

Glandular woody fibre of Conifers, i.
364.

Glass Slides, i. 175, 176.

Stage-plate, i. 122.

Thin, i. 176, 177.

Glaucium, cyclosis in hairs of, i. 359.
Globigerina, ii. 86, 87.
Globigerina-mud, ii. 86; its relation to

Chalk-formation, ii. 305-309.
Globigerinida, ii. 86-91.
Glochidium, ii. 183.
Glue, Liquid, i. 179.

, Marine, uses of, i. 179, 181.

Glycerine, for mounting objects, i. 210-

213.

Glycerine Jelly, i. 211; mounting in, i.
212.

Glvcerine and Gum medium, i. 211,
213.

Gnat, scale of, i. 155: transparent larva

of, ii. 237.
Gold-Size, use of, i. 178.
Gomphonemece, i. 298.
Goniometer, i. 95.

Gonidia, i. 229 note, i. 230; multiplica-
tion by, in Desmidiacese, i. 267; in
Pediastrese, i. 270; in Diatomaceaa, i,
280; inHydrodictyon, i. 253; inChara,
i. 261; in Lichens, i. 329; in Fungi, i.
322, 324; in Vol vox, i. 241.

Gordius, ii. 193.

Gorgonia, spicules of, ii. 136, 137.

Gosse, Mr., on mastax of Rotifers, ii.
56, 57; on sexes of Rotifers, ii. 58; on
Melicerta, ii. 61; on thread-cells of
Zoophytes, ii. 136.

Grammaiophora, i. 288; its use as test,

i. 171.

Grantia, structure of, ii. 120, 121.
Grasses, silicified cuticle of, i. 379.
Gray, Dr., on palates of Gasteropods,

ii. 182; on development of Buccinum,
ii, 187.

Green Sands, Foraminiferal origin of,
ii. 309, 310; Prof. Ehrenberg on com-
position of, ii. 93 note, ii. 309.

Gregarinida, ii. 21, 22.

Gromia, ii. 8-10.

Growing-Slide, i. 122.

Growth, distinguished from Generation,

i. 227-229.

Guano, Diatomaceae of, i. 303.
Gulliver, Mr., on Raphides, i. 363; on

sizes of Blood-disks, ii. 269-271.
Gum Arabic, i. 179.

Guy, Dr., on sublimation of Alkaloids,

ii. 326.
Gymnosperms, i. 352, 353.

Haeckel, Prof., on Gastraea theory, ii.

22 note; on Monerozoa, ii. 2 ; on Ba-
thybius, ii. 19; on Radiolaria, ii. 110;
on Infusoria, ii. 26 note; on Calcare-
ous Sponges, ii. 120 note.

Ho3matococeust i. 245; its relations to
Protococcus, i. 233.

Hematoxylin, as staining agent, i. 206.

Hairs, of Insects, ii. 227; of Mammals,
ii. 263-266.

of Vegetable cuticles, i. 378; rota-
tion of fluid in, i. 358, 359.

Halichondria, spicules of, ii. 119.

Halifax, Dr., on making Sections of
Insects, ii. 219.

Haliomma, ii. 113.

Haliotis, palate of, ii. 182.

Haliphysema, ii. 80.

Halodactylus, ii. 161.

Halophragmium, ii. 81.

Halteres of Diptera, ii. 243.

Hand-Magnifiers, i. 19-22, 43, 44.

Hard Substances, cutting Sections of,
i. 196-199.

Hardening of Animal Substances, i. 202.

Harley Binocular, i. 70.

Harting, Prof., on Calcareous Concre-
tions, ii. 324.

Hartnack, M. , his diagonal Micrometer,

i. 94; on Surirella, i. 171.
Harvest-bug, ii. 249.
Haversian Canals of Bone, ii. 256.
Haustellate Mouth, ii. 236.
Haycraft, Mr., on Muscular fibre, ii.

286.

Hazel, stem of, i. 370.
Hearing, organs of (?), in Insects, ii.
233.

Heart-wood, i. 370.

Heat, tolerance of, by Bacteria, etc., i.

313; by Infusoria, ii. 31, 32.
Heliopelta, i. 292.
Heliozoa, ii. 8, 11-14.
Helix, palate of, ii. 181.
Hemiptera, wings of, ii. 242.
Hepaticce, i. 335-338; see Marchantia.
Hepworth, Mr., on feet of Insects, ii. 244.
Hertwig, Dr., on Rhizopods, ii. 8 note,

ii. 9; on Foraminifera, ii. 64 note.
Heteromita, ii. 30.
Heterostegina, ii. 99.
Hexiradiate Sponges, ii. 121.

Hicks, Dr., on Vol vox, i. 244; on Amoe-
boid production in root -fibres of
Mosses, i. 339; on eyes of Insects, ii.
230; on peculiar organs of sense in
Insects, ii. 233 note, ii. 243.

Hincks, Rev. T., on Hydroid Zoophytes,
ii. 126; on Polyzoa, ii. 162 note.

Hippocrepian Polyzoa, ii. 161, 162.

Hogg, Mr., on development of Lym-
naeus, ii. 186.

Hollyhock, pollen-grains of, i. 37, 167,
i. 385.

Holothurida, skeletons of, ii. 148-150.
Holtenia, ii. 121.

Homogeneous Immersion, i. x7 18.

34:4

INDEX.

Hoofs, structure of, ii. 267.

Hooker, Sir J. D., on Antartic Dia-
toms, i. 301.

Hoop, of Diatoms, i. 275, 279, 280.

Hormosina, ii. 81.

Hornet, wings of, ii. 242.

Horns, structure of, ii. 267.

Houghton, Rev. W., on Glochidium,
ii. 183.

Hudson, Dr., on in Pedalio, ii. 58, 63.

Huxley, Prof., on Protoplasm, i. 222; on
cell formation in Sphagnaceae, i. 342;
on Bathybius, ii. 19; on Coccoliths,
ii. 19, 20; on Rotifera, ii. 59, 63, on
Thalassicolla, ii. 116 note; on Nocti-
luca, ii. 34 note; on Shell of Moliusca,
ii. 173; on Appendicularia, ii. 169; on
Blood of Annelida, ii. 197; on Shell
of Crustacea, ii. 214 note; on Repro-
duction of Aphides, ii. 246.

Huyglienian eye piece, i. 23, 24.

Hyalodiscus. i. 171, i. 289.

Hydatina, ii. 62; reproduction of, ii.
58.

Hydra, life-history of, ii. 122-126.
Hydra tuba, developments of Acalephs

from, ii. 132-134.
Hydrodictyon, i. 252, 253.
Hydrozoa, simple, ii. 123; composite,

ii. 126-131; their relation to Medusas,

ii. 126, 131-134.
Hyla, preparation of nerves of, ii. 286.

lee-Plant, cuticle of, i. 378.

Ichneumonidce, ovipositor of, ii. 245.

Illumination of Opaque objects, i. 147-
150; of Transparent objects, i. 144-
147: diverse effects of, on lined ob-
jects, i. 146-147.

Illuminators, Black-ground, i. 106-110,
i. 147.

Oblique, i. 104, 105, i. 145-

147.

Parabolic, i. 107, 108.

Reflex, i. 109, 110.

Side, i. 114-117.

Vertical, i. 117-119.

Wenham's Disk, i. 105; his

Reflex, i. 109, 110.

White Cloud, i. 111.

Imbedding processes, i. 194-196.

Immersion-Lenses, i. 16-18.

Images, formation of, by convex lenses,

i. 6.

Index of Refraction, i. 1-3.

Indigo-carmine, as staining agent, i.207.

Indian Corn, cuticle of, i. 377, 380.

Indicator, Quekett's, i. 96.

Indusium of Ferns, i. 346.

Infusoria, ii. 25-53; Flagellate, ii. 26;
Suctorial, ii. 39; Ciliate, ii. 41; move-
ments of, ii. 43, 44; internal struc-
ture of, ii. 44, 45; binary subdivision
of, ii. 46; encysting process of, ii. 47-
49; sexual generation (?) of, ii. 49-52.

Infusorial Earths, i. 302.

Injections of Blood-vessels, mode of
making, ii. 292-298.

Insects, great numbers of objects
furnished by, ii. 218; microscopic
forms of, ii. 219; antennae of, ii. 232,
233; circulation of blood in, ii. 237,
238; eggs of, ii. 246, 247; eyes of, ii.
229-231; feet of, ii. 243-245; gastric
teeth of, ii. 237; hairs of, ii. 227; in-
tegument of, ii. 219, 229; mouth of,
ii. 233-236; organs of hearing in, ii.
233; of smell in, ii. 243; of taste in,
ii. 236; ovipositors of, ii. 245, 246;
scales of, ii. 220-228; spiracles of, ii.
239, 240; stings of, ii. 245; tracheae of,
ii. 238-240; wings of, ii. 241-243.

Interference-spectra, i. 156-160.

Intermediate Skeleton of Foraminif era,
ii. 70, 86, 91, 94, 103.

Internal Casts of Foraminif era, ii. 89,
92, 93, 99, 100, 105, 309.

Interpretation, errors of, i. 150-155.

Inverted Microscope, Dr. L. Smith's,
i. 82.

Iodine, as test, i. 208.

Iris, structure of leaf of, i. 380, 381.

Iris-diaphragm, i. 102.

Isthmia, i. 293; markings on, i. 276;

self-division of, i. 280.
Iteh-Aearus, ii. 249.
lulus, fungous vegetation in, i. 319.

Jackson, Mr. G., his model for Com-
pound Microscope, i. 52; his Eye-piece
Micrometer, i. 93, 94.

Jevons, Prof., on Brownian movement,

i. 154.

Jukes, Prof., on Foraminif eral reef,

ii. 305.

Kellner's Eye-piece, i. 24, 25.

Kerona silurus, ii. 42.

Kent, Mr. S., on Flagellate Infusoria,

ii. 32, 33; on Sponges, ii. 118 note.
Kidney, structure of, ii. 280.
Klein, Dr., on Cells and Nuclei, ii. 252

note.

Kleinenberg, Prof., on Hydra, ii. 126
note, ii. 253 note; his preparing fluid,
i. 203; his staining fluid, i. 206.

Koch, on Sections of hard and soft sub-
stances, i. 200.

Kolliker, Prof., on Fungi in Shells, etc.,
i. 320 note.

Kovalevsky, on development of Asci-
dians, ii. 169 note.

Kiihne, on contraction of Vorticella-
stalk, ii. 44.

Labelling of Objects, i. 218, 219.
Laboratory Dissecting Microscope, i. 47.
Labyrinthodon, tooth of, ii. 311.
Lachmann, see Claparede and Lach-
mann.

Lacinularia, Prof. Huxley on, ii. 58
note.

INDEX.

345

Lacunae of Bone, ii. 256, 257.

Lagena, ii. 66, 85.

Laguncula, ii. 157-160.

Lamellicornes, antennae of, ii. 232.

Lamps for Microscope, i. 131, 132.

Lankester, Prof. E. Ray, on amoeboids
in fresh- water Medusa, ii. 122; on de-
velopment of Limnaeus, ii. 186.

Larvae of Echinoderms, ii. 150-156.

Laurentian Formation of Canada, ii.
101, ii. 310; of Europe, ii. 101 note.

Leaves, structure of, i. 380-382.

Leech, teeth of, ii. 203.

Leeson, Dr. , his double-refracting Go-
niometer, i. 95; his Selenite-plate, i.
112.

Legg, Mr., on collection of Foramini-
fera, ii. 107, 108.

Leidy, Dr., on Enterobryus, i, 319; on
Rhizopods, ii. 19 note.

Lenses, refraction by, i. 3, 4.

Lepidocyrtus, scales of, see Podura.

Lepidoptera, scales of, ii. 220-229; pro-
boscis of, 236, 237; wings of, ii. 220,
242; eggs of, ii. 247.

Lepidosteus, bony scales of, ii. 257,
263.

Lepidostrobi, i. 350.

Lepisma, scales of, ii. 223, 224; diffrac-
tion-spectrum of, i. 159.
Lepralia, ii. 158, 162.
Lerncea, ii. 213.

Levant-Mud, microscopic organisms of,

ii. 305.
Lever of Contact, i. 177.
Lewis, Mr. B., his freezing Microtome,

i. 192.

Libellula, eyes of, ii. 230; respiration of

larva of, ii. 240.
Liber, i. 374.

Lichens, composite nature of, ii. 329,
330.

Lichmophorece i. 286.

Lieberkiihn (speculum), i. 117, 118;
mode of using, i. 150.

Lieberkuhnia, ii. 6, 7.

Ligaments, structure of, ii. 272.

Light, for Microscope, i. 131-134; ar-
rangement of, for Transparent ob-
jects, i. 143-147; for Opaque objects,
i. 147-150.

Light-modifiers, i. 110.

Ligneous Tissue, i. 363, 364.

Limax, shell of, ii. 179; palate of, ii.
181.

Limestones, organic origin of, ii. 308,
309; Fusuline, ii. 90, 91, 309; Nummu-
litic, ii. 94, 96, 309; Milioline, ii. 309;
Orbitoidal, ii. 100; Eozoic, ii. 101, 102,
310.

Limiting Angle, i. 3.
Limpet, palate of, ii. 182.
Liquid Glue, i. 179.

Lined Objects, diverse effects of Illumi-
nation on, i. 146, 147.
Tests, resolution of, i. 169-172.

Lister, Mr. J. J., his improvements in
Achromatic lenses, i. 14; his Erector,

i. 87; his observations on Zoophytes,

ii. 127; on Social Ascidians, ii. 167,
168.

Lister, Prof., on Bacteria, etc., i. 314.

Lituolida, ii. 81-85.

Live-box, i. 123.

Liver, structure of, ii. 280, 281.

Liverwort, i. 335-338.

Lobb, Mr., on binary subdivision in

Micrasterias, i. 266.
Lobosa, ii. 8, 14-19.
Loftusia, ii. 84.

Logan, Sir W., on Laurentian Forma-
tion, ii. 101 note, ii. 310.

Lophophore of Polyzoa, ii. 158.

Lophyropoda, ii. 207, 208.

Lowne, Mr., on feet of Insects, ii. 244
note; on eyes of Insects, ii. 231 note;
on development of Insects, ii. 248.

Lubbock, Sir J., on Daphnia, ii. 211; on
Thysanura, ii. 223.

Luders, Mad., on fermentation, i. 316.

Luminosity of Noctiluca, ii. 33, 36; of
Anelida, ii. 202.

Lungs of Reptiles, ii. 299; of Birds, ii.
300; of Mammals, ii. 300.

Lyccenidce, scales of, ii. 221, 223.

Lycopodiaceoe, i. 350.

Lymnceus, development of, ii. 184, 186.

Lymph, corpuscles of, ii. 270.

Machilis, scale of, ii. 224.
Macro-gonidia, i. 229 note; of Volvox,

i. 241 ; of Pediastreae, i. 271 ; of Hydro-

dictyon, i. 252.
Maddox, Dr., his Growing-Slide, i. 123;

on cultivation of Microscopic Fungi,

i. 123 note.
Magnifying power, augmentation of,

i. 136, 137; determination of, i. 173,
174.

Magenta, as staining agent, i. 206.
Mahogany, section of, i. 372.
Malpighian bodies of Kidney, ii. 280.

layer of Skin, ii. 275.

Maltwood's Finder, i. 100.

Malvacece, pollen-grains of, i. 385; their

use as tests, i. 37, 167.
Mammals, bone of, ii. 255-258; teeth of,

ii. 259-261; hairs, hoofs, etc., of, ii.
263-267; blood of, ii. 267-271; lungs
of, ii. 300.

Man, teeth of, 259-261; hair of, ii. 265,

266; blood of, ii. 267-271.
Mandibulate m5uth of Insects, ii. 233.
Marchantia, general structure of, i. 335;

stomata of, i. 336; conceptacles of, i.

337; sexual apparatus of, i. 338.
Margaritacece, shells of, 173, 174.
Marine Glue, uses of, i. 179, 181.
Marsh, Dr. S., his section-lifter, i. 205;

on Section-cutting, etc., i. 194, 213.
Mastax of Rotifera, ii. 56.
Mastogloia, i. 299, 300.

316

INDEX.

Matthews, Dr., his Micro-megascope, i.
88; his saw for Section-cutting, i.
197.

Media, Preservative, i. 209-211.
Medullary Rays, i. 354, 371-273.

Sheath, i. 364, 369.

Medusae, their relation to Polypes, ii.

126, 131-134; fresh- water, amoeboids

in, 122.

Megalopa-\a,Yv& of Crab, ii. 216.
Megatherium, teeth of, 261.
Melanospermece, i. 332.
Melieertians, ii. 60, 61.
Melolontha, see Cockchafer.
Melosira, i. 289; auxospores of, i. 282.
Menelaus, scale of, ii. 221, 222.
Meniscus Lenses, refraction by, i. 6.
Meridion circular e, i. 285.
Mesembryanthemum, cuticle of, i. 378.
Mesocarpus, i. 236.

Metamorphosis, of Annelids, ii. 198-
201; of Ascidians, ii. 168-170; of Cir-
rhipeds, ii. 213, 214; of higher Crus-
tacea, ii. 215, 216; of Entomostraca,
ii. 211; of Echinoderms, ii. 150-153; of
Infusoria, ii. 47-49; of Insects, ii. 248;
of Mollusks, ii. 183-189.

Metazoa, ii. 2.

Mica-Selenite Stage, i. 113.

Micrasterias, binary sub-division of, i.
266; stato-spores of, i. 267.

Micro-Chemistry, ii. 326.

Micrococcus, i. 308.

Micro-gonidia, i. 229 note; of Protoc-
cus, i. 234; of Desmidiacese, i. 267; of
Hydrodictyon, i 253.

Micro-megascope, i. 88.

Micrometers, Ramsden's, i. 92, 93; Jack-
son's, i. 93, 94; Hartnack's, i. 95.

Micrometry, by Micrometer, i. 93-95;
by Camera Lucida, i . 99.

Micropyle of Vegetable Ovule, i. 353,
386.

Microscope, support required for, i.
130, 131; care of, i. 134, 135; focal ad-
justment of, i. 137-141; arrangement
of, for Transparent objects, i. 141-
147; for Opaque objects, i. 147-150.

Binocular, see Binocular

Microscope.

Compound, see Compound

Microscope.

Simple, see Simple Micro-
scope.

Chemical, i. 82, 83.

Demonstrating, i. 81.

Dissecting^ i. 44-50.

Educational, i. 53-55.

Inverted, i. 82-84.

Mineralogical, ii. 315-317.

Pocket, i. 8( .

Popular, i. 68.

Portable. Binocular, i. 83.

Student's, i. 55-67, ii. 332.

Travelling, i. 81, 82.

Microscopic Dissection, i. 186-188.

Micro-Spectroscope, i. 89-92.

Microtome, Simple, i. 189; Hailes's, i.
190, 191; Strassburg, i. 191; freezing,
i. 192; Rivet-Leiser, i. 192, 193.

Microzymes, i. 314.

Mildew of Corn, i. 323.

Miliolida, ii. 70.

Millon's test for Albuminous substances,

i. 208. 1

Milne-Edwards, M., on Compound As-
cidians, ii. 166, note.

Mineral Objects, ii. 313-326.

Minnow, circulation in, ii. 288.

Misinterpretation of microscopic ap-
pearances, causes of, i. 150-156.

Mites, ii. 249.

Mivart, Prof., on Radiolaria, ii. 110.
Moderator, Rainey's, i. 110.
Molecular Coalescence, ii. 323-325.

Movement, i. 153, 154.

Mollusca, shells of, ii. 171-180; palates-

of, ii. 180-183; development of, ii.

183-189; ciliary motion on gills of,

ii. 189, 190; organs of sense of, ii. 190,
191.

Molybdate of Ammonia, i. 207.
Monadina, ii. 26-32.
Monerozoa, ii. 2-7.

Monocotyledonous -Stems, structure of ,

i. 367, 368..
Monothalamous Foraminifera, ii. 66.
Morula, ii. 1.

Morehouse, Mr., on Lepisma-scale, ii.

224, ii. 227 note,
Morris, Mr., his Object-holder, i. 121,

122; on mounting Zoophytes, ii. 131.
Mosses, structure of, i. 338, 339; sexual

apparatus of, i. 340-342; development

of spores of, i. 341.
Mother-of-Pearl, structure of, ii. 174.
Moths, see Lepidoptera.
Moulds, fungous, i. 321, 322.
Mounting of objects, i. 211; in Canada

Balsam, i. 214, 215; in cement cells,

i. 215; in deep cells, i. 216.
Mounting-Instrument, Smith's, i. 186.

Microscope, Field's, i. 49, 50.

Mounting-Plate, i. 185.

Mouse, hair of, ii. 264; cartilage of ear

of, ii. 278; vessels of toe of, ii. 297
Mouth of Insects, ii. 233-236.
Mucor, i. 323.

Mucous Membranes, structure of, ii.
275; capillaries of, ii. 298.

Miiller, Dr. Fritz, on Polyzoa, ii. 160.

Miiller, Prof. J., on Radiolaria, i. 110;
on Echinoderm-larvse, ii. 150-153.

Miiller s fluid, for hardening, i. 203.

Muscardine, of Silk-worms, i. 317, 318.

Muscular Fibre, structure of, ii. 281-
284; mode of examining and prepar-
ing, ii. 282; capillaries of, ii. 298.

Musk-deer, hair of, ii. 264; minute blood-
corpuscles of, ii. 269.

Mussel, ciliary action on gills of, ii. 189;
development of, ii. 183.

INDEX.

34:7

Mya, structure of hinge-tooth of, ii. 175.
Mycelium of Fungi, i. 320-325.
Myliobates, teeth of, ii. 258, 259.
Myriapods, hairs of, ii. 228.
Myriothela, amceboids in, ii. 122.
Myxomycetes, i. 325-327.

Nachet, M. , his Stereoscopic Binocular,
i. 28, 29; Stereo-pseudoscopic Binocu-
lar, i. 33-35; Binocular Magnifier, i.
48, 49; Student's Microscope, i. 63, 64;
Chemical Microscope, i. 82, 83; Min-
eralogical Microscope, ii. 315-317;
Erecting Prism, i. 88; Camera, i. 98.
Porte-Objectif, ii. 333.

Nacre, structure of, ii. 173, 174.

Nais, ii. 202, 203.

Nassida, teeth of, ii. 43.

Navicellee of Gregarinida, ii. 22.

Navicular, i. 298; movements of, i. 283.

Needles for Dissection, i. 188.

Nematoid Entozoa, ii. 193, 194.

Nemertes, larva of, ii. 198, 199.

Nepa, tracheal system of, ii. 239.

Nepenthes, spiral vessels of, i. 364.

Nervous Tissue, structure of, ii. 284,
285; mode of examining, ii. 286.

Net, Collector's, i. 219-221.

Nettle, sting of, i. 379.

Neuroptera, circulation in, ii. 237, 240;
wings of, ii. 241.

Neutral-tint Reflector, i. 98.

Newt, circulation in larva of, ii. 288.

Nicol-Prism, i. 111.

Nitella, i. 259.

Nitzschiece, i. 287.

Nobert's Test, i. 169, 170.

Noetiluca, ii. 33-37.

Nodosaria, ii. 85.

Nonionina, ii. 94.

Nose piece, i. 99.

Nostochacece, i. 249.

Nucleus, of Vegetable cells, i. 225-228;

of Animal cells, ii. 254.
Nudibranchs, development of, ii. 185,

186.

Numerical Aperture of Objectives, ii.
327.

Nummulinida, ii. 69, 91-101.
Nnmmulite, structure of, ii. 94-98.
Nummulitic Limestone, ii. 94, ii. 309.
Nuphar lutea, parenchyma of, i. 854,
355.

Oak, galls of, ii. 245.

Object-Glasses, Achromatic, principle
of, i. 7-10; Angular aperture of, i. 8,
i. 161-163; ii. 327; Numerical aperture
of, ii. 327; construction of, i. 11-16;
immersion, i. 16-18; adjustment of,
for covering glass, i. 14, i. 139-141;
adaptation of, to Binocular, i. 35-38;
working distance of, i. 161; defining
power of, 161-163; focal depth of, i.
163; increase of, with Binocular, i. 38;
resolving power of, i. 164; flatness of

field of, i. 164; comparative value of
i. 161-165; Preface, v., vi.; different
powers of, tests for, i. 165-173; de-
termination of magnifying power of,
i. 173, 174.

Object-Holder, i. 121, 122.

Objects, mode of mounting, dry, i. 179,
183; in Canada balsam, i. 213, 214;
in preservative media, i. 209-213; in
cells, i. 215-217; see Opaque and
Transparent Objects.

labelling and preserving of,

i. 218, 219.

collection of, i. 219-221.

Oblique Illuminators, i. 104, 105.

Ocelli of Insects, ii. 229-231.

Octospores of Fuci, i. 333.

CEdogoniece, i. 257, 258.

Oidium, i. 323.

Oil-globules, microscopic appearances

of, i. 152, 153.
Oil-immersion Objectives, i. 17, 18; ii.

329.

Oleander, cuticle of, i. 378; stomata of,
i. 380.

Oncidium, spiral cells of, i. 361.

Onion, raphides of, i. 363.

Oogonia of Fucacese, i. 333.

Oolite, structure of, ii. 282.

Oospores, i. 228, 229; of Volvox, i. 243;
of Achlya, i. 251; of Sphseroplea, i. 255;
of CEdogonium, i. 258; of Batracho-
spermeae, i. 259; of Chara, i. 262; of
Fucaceae, i. 333.

Opaque Objects, arrangement of Micro-
scope for, i. 147-150; modes of mount-
ing, i. 179, 183.

Operculina, ii. 94-96.

Ophioeoma, teeth and spines of, ii. 145.

Ophioglossece, prothallium of, i. 348.

Ophiurida, skeleton of, ii. 145; develop-
ment of, ii. 151.

Ophrydince, ii. 46.

Orbiculina, ii. 72, 73.

Orbitoides, structure of, ii. 100, 101.

Orbitolina, ii. 90.

Orbitolites, structure and development

of, ii. 70, 73-77; fossil, ii. 305.
Orbulina, ii. 86.
Orchideous Plants, i. 360.
Ord, Dr. W. M., on Calculi, ii. 326.
Ornithorynehus, hair of, ii. 265.
Orthoptera, wings of, ii. 242.
Osmic acid, uses of, i. 203.
Osmunda, prothallium of, i. 348 note.
Oscillatoriaeece, i. 247, 249.
Ostracece, shells of, ii. 175, 176.
Ostracoda, ii. 207.

Otoliths of Gasteropods, ii. 190; of
Fishes, ii. 324.

Ovipositors of Insects, ii. 245, 246.

Ovules of Phanerogamia, i. 352; fertili-
zation of, i. 385; mode of studying,
i. 385, 386.

Owen, Prof., on fossil Teeth, ii. 311; on
fossil Bone, ii. 312.

348

INDEX.

Oxytricha form of Trichoda, ii. 47-49.
Oyster, shell of, ii. 176, 177.

Pachymatisma, spicules of, ii. 120.

Pacinian corpuscles, ii. 286.

Palates of Gasteropods, ii. 180-183.

Palm, stem of, i. 367, 368.

Palmellacece, i. 245, 246.

Palmodictyon, i. 246.

Palmoglcea macrococca, life-history of,

i. 230, 231.

Papillae of Skin, structure of, ii. 274,
285; capillaries of, ii. 298; of Tongue,

ii. 285.

Parabolic Speculum, i. 116.
Parabolized Gas-Slide, i. 125.
Paraboloid, i. 107, 108; immersion, i.
108, 109.

Paraffin, imbedding in, i. 194-196.
Paramecium, ii. 42; contractile vesicles

of, ii. 45; binary subdivision of, ii. 46;

sexual generation (?) of, ii. 49.
Parasitic Fungi in Animal bodies, i.

317-321; in Plants, i. 323, 324.
Parker, Mr. Jeffery, on Hydra, ii. 122.
Parkeria, ii. 83-85.

Passulus, fungous vegetation in, i. 321.

Paste, Eels of, ii. 93.

Pasteur, M., his researches on ferments,

i. 313; on pebrine, i. 315.
Patella, palatal tube of, ii. 182.
Pearls, structure of, ii. 174.
Pebrine, i. 315.
Pecari, hair of, ii. 265.
Pecten, eyes of, ii. 190; tentacles of, ii.

191.

Pedalion, ii. 58, 63.

Pedesis, Prof. Jevons on, i. 154.

Pediastrece, structure of, i. 270-273;

multiplication and development of,

i. 270, 271; varieties of, i. 272.
Pedicellariae of Echinoderms, ii. 144.
Pedicellina, ii. 162.
Pelargonium, cells of petal of, i. 383.
Pelomyxa palustris, ii. 17.
Peneroplis, ii. 66, 71.
Penetrating power of Object-glasses, i.

163, increase of, with Binocular, i.

38.

Penicillium, i. 323.

Pentacrinoid larva of Comatula, ii. 152-
156.

Pentacrinus, skeleton of, ii. 146.

Perennibranchiata, bone of, ii. 257;
blood-corpuscles of, ii. 269, 270.

Peridinium, ii. 37, 38.

Peristome of Mosses, i. 389-342.

Peronospora, i. 323.

Perophora, ii. 167, 168.

Petals of Flowers, structure of, i. 383.

Petrology, Microscopic, ii. 312-317.

Pettenkofer's test, i. 208.

Phanerogamia, distinctive peculiari-
ties of, i. 352, 353; elementary tissues
of, i. 353-367 (see Tissues of Plants);
Stems and Roots of, i. 367-377; Cuti-

cles and Leaves of, i. 377-382; Flowers
of, i. 382-386; Seeds of, i. 386-388.

Phyllopoda, ii. 209.

Picric acid, for hardening, i. 203.

Picro-aniline, as staining agent, i. 207.

Picro-carmine, as staining agent, i. 206.

Pieridce, scales of, ii. 221, 222.

Pigott, Dr. Royston, his Aplanatic
Searcher, i. 8 note; his Micrometers,
i. 92 note; on angle of aperture, i.
162; on scales of Insect?, ii. 224, 226.

Pigment-cells, ii. 275, 276; of Cuttle-
fish, ii. 191; of Crustacea, ii. 215.

Pigmentum nigrum, ii. 275.

Pilidium-\ixrv8L of Nemertes, ii. 199.

Pillischer, Mr., his International Micro-
scope, i. 59, 60.

Pilulina, ii. 79.

Pinna, structure of shell of, ii. 171-173;

fossil, in Chalk, ii. 307.
Pinnularia, i. 298.
Pistillidia, see Archegonia.
Pith, structure of, i. 354, 368.
Placoid scales of Fish, ii. 263.
Planaria, ii. 194, 195.
Planorbulina, ii. 89.
Plantago, cyclosis in hairs of, i. 359.
Plants, distinction of, from Animals,

i. 222-224.

Plasmodium, of Myxomocetes, i. 326;

of Protomyxa, ii. 3.
Plate-glass Cells, i. 182.
Pleuro sigma, i. 298; nature of markings

on, i. 274-279; value of, as Test, i. 170-

172; diverse aspects of, i. 146-151;

diffraction-spectrum of, i. 160.
Pluteus-\2Lrva,of Echinus, ii. 152.
Plumules of Butterflies, i. 221.
Pocket Microscope, Beale's, i. 80.
Podophrya quadripartita, ii. 39-41.
Podura, scale of, ii. 223-227; use of, as

Test object, i. 172, 173.
Poisons, detection of, ii. 326.
Polarization, Objects suitable for, i.

318-323.

Polarizing Apparatus, i. 111-114.
Polistes, fungous vegetation in, i. 318.
Pollen-grains, development of, i. 383;

structure and markings of, i. 383-

385.

Pollen-tubes, fertilizing action of, i.
386.

Polycelis, ii. 195.
Polyclinians, ii. 165.
Polycystina, ii. 109, 113-116.
Polygastrica, see Infusoria.
Polymorphina, ii. 85.
Polyommatus argus, scale of, ii. 222,
223.

Polypes, see Hydra and Zoophytes.
Polypide of Polyzoa, ii. 157.
Polypodium, fructification of, i. 345.
Polystomella, ii. 92-94.
Polythalamous Foraminifera, ii. 66-68.
Polytoma uvella, ii. 29.
Polytrema, ii. 90.

INDEX.

349

Polyzoa, general structure of, ii. 157-
163; classification of, ii. 162.

Polvzoaiy, ii. 157.

Pond-Stick, Baker's, i. 219.

Poppy, seeds of, i. 386, 387.

Popular Microscope, Beck's, i. 68.

Porcellanous Foraminifera, ii. 68, 70-
77.

Porcellanous shells of Gasteropods, ii.
178.

Porcupine, quill of, ii. 265.

Porifera, see Sponges.

Portable Binocular, i. 83.

Potato-disease, i. 323.

Powell and Lealand's Microscopes, i.
67, 68, 77, 79; their non-stereoscopic
Binocular, i. 85; their Achromatic
Condenser, i. 103; their Light-modi-
fier, i. 110; their Oil-immersion objec-
tives, i. 18; their Vertical Illuminator,
i. 116.

Prawn, shell of, ii. 215.

Preservative Media, i. 209-211

Primordial Utricle, i. 225, 356.

Pringsheim, Dr., his observations on
Vaucheria, i. 251; on Hydrodictyon,
i. 252; on CEdogonium, i. 258.

Prismatic Shell-substance, ii. 171, 172.

Prism, Amici's, i. 106; Nachet's Erect-
ing, i. 88; Wenham's Binocular, i. 30,
85; Stephenson's Binocular, i. 31;
Camera Lucida, i. 96-98; Spectro-
scope, i. 90; Polarizing, 111, 112.

Proboscis, of Bee, ii. 234, 235; of Butter-
fly, ii. 236; of Fly, ii. 234.

Proteus, blood- corpuscles of, ii. 269,
270.

Prothallium of Ferns, i. 346-348.
Protocoecus, life-history of, i. 231-236.
Protomyxa, ii. 2, 3.

Protoplasm, i. 222; of Vegetable cell, i.
224-228; of Animals, ii. 253-255.

Protophyta, general characters of, i.
222-228.

Protophytic Algae, i. 229-306.

Protophy tic Fungi, i. 229, 307; relation
of, to Protozoa, i. 307; cultivation of,
i. 123, 307.

Protozoa, ii. 1, 2; their relations to
Protophyta, i. 224.

Pseud-embryo of Echinoderms, ii. 150.

Pseudo-navicellse of Gregarinida, ii. 21.

Pseudopodia of Rhizopods, ii. 2-19, dif-
ferent forms of, ii. 7.

Pseudoscope, i. 27, 28.

Pseudoscopic Microscope of MM.
Nachet, i. 33-36.

Pteris, fructification of, i. 345; prothal-
lium of, i. 346.

Pterodactyls bone of, ii. 312.

Puccinia, i. 323. ! '

Purpura, egg-capsules of, ii. 184; devel*
opment of, ii. 187-189.

Pycnogonidce, ii. 205-207.

Quadrula symmetrica, ii. 19.

Quatrefages, M. de, on luminosity of
Annelids, ii. 202.

Quekett, Prof. J., his Dissecting Micro-
scope, i. 45; his Indicator, i. 96; on
Raphides, i. 363; on structure of Bone,
ii. 258, 311.

Quinqueloculina, ii. 71.

Radiating Crystallization, ii. 320, 321.

Radiolaria, ii. 109, 110; their relation
to Heliozoa, ii. 109; their general
structure, ii. 110, 111; their classifica-
tion, ii. 112, 113; collection and
mounting of , ii. 115, 116.

Rainey, Mr., his Light modifier, i. 110;
on Molecular coalescence, ii. 313-325.

Ralfs, Mr., on Desmidiacese, i. 263 note;
on Diatomaceae, i. 284 note.

Ralph, Dr., his mode of mounting, i.
215.

Ramsden's Micrometer, i. 92, 93.
Raphides, i. 363.

Re-agents, Chemical, use of, in Micro-
scopic research, i. 208, 209, ii. 326.

Red Corpuscles of blood, ii. 267-270.

Red Snow, i. 245.

Reflection by Prisms, i. 2, 3,

Reflex Illuminator, Wenham's, i. 109.

Refraction, laws of, i. 1-3; by convex
lenses, i. 3-5; by concave and menis-
cus lenses, i. 5-6.

Reindeer, hair of, ii. 264.

Reophax, ii. 82.

Reptiles, bone of, ii. 257, 258, 311;
teeth of, ii. 259, 311; scales of, ii. 263;
blood of, ii. 268-271; lungs of, ii. 299,
300.

Resolving power of Object-glasses, i.
158, 164.

Reticular ia, ii. 7-11.

Reticulated Ducts, i. 366.

Rhabdammina, ii. 80.

Rhinoceros, horn of, ii. 267.

Rhizocarpece, i. 350.

Rhizopoda, ii. 7-19; their subdivions,
ii. 7, 8; their relation to higher Ani-
mals, ii. 252, 253.

Rhizosolenia, i. 296.

Rhizostoma, ii. 134.

Rhodospermece, i. 334.

Rhubarb, raphides of, i. 363.

Rhynchonellidce, structure of Shell of,
ii. 178.

Rice, starch-grains of, i. 362.

Rice-paper, i. 354, 355.

Ricinice, ii. 249.

Ring-Cells, i. 181.

Ring-Net, i. 219-221.

Rivet-Leiser Microtome, i. 192, 193.

Roasted Corn, detection of, in Chicory,

■ i^38g. ,.a >e ,

i^QMnj^.; oi> N.xti}ucaw, ifc $1 note.: iL

; ss"? . • * i ;

Rochea, epidermis of, i. 378.
Rocks, structure of, ii. 304-310 313-,
31^; ! 1

350

INDEX.

Roots, structure of, i. 375, 376; mode of
making sections of, i. 376.

Ross, Mr., on correction of Object-
glass, i. 14, 15; his First-class Micro-
scopes, i. 73-76; his Achromatic Con-
denser, i. 103; his Students' Micro-
scope, i. 60, 61; his Simple Microscope,
i. 43-45; his Lever of contact, i. 177;
his Compressor, i. 126.

Ross-Model for Compound Microscope,

i. 51 52.

Rotalia, ii. 67, 68, 89, 90.
Rotaline Foraminifera, ii. 67, 89, 90.
Rotating Microscope, Browning's, i. 64,
65.

Rotifer, anatomy of, ii. 55-58; repro-
duction of, ii. 58, 59; tenacity of life
of, ii. 59; occurrence of, in leaves of
Sphagnum, i. 343, ii. 53.

Rotifeka, general structure of, ii. 53-
63; reproduction of, ii. 58, 59; desic-
cation of, ii. 59; classification of, ii.
60-63.

Royston-Pigott, Dr., see Pigott.
Rush, stellate parenchyma of, i. 354,
355.

Rust, of Corn, i. 323.
Rutherford, Prof., his freezing Micro-
tome, i. 192, 196.

Sable, hair of ii 264.
Saccammina, ii. 78, 79.
Saceharomyces, i 315.
Saccolobium, spiral cells of, i. 361.
Safety-stage, Stephenson's, i. 120.
Salpingceca, ii. 32.

Salter, Mr. Jas., on teeth of Echinida,

ii. 144.

Salts, crystallization of, ii. 318-323.
Salvia, spiral fibres of seed of, i. 361.
Salicylic Acid, as preservative, i. 210.
Sand-wasp, integument of. ii. 220.
Sandy tests of Foraminifera, ii. 77-85.
Sarcina ventriculi, i. 316.
Sarcode, of Protozoa, i. 222 note, i. 222.
Sarcoptes scabiei, ii. 249.
Sarsia, ii. 127.

Saw-flies, ovipositor of, ii. 245. 246.
Scalariform ducts of Ferns, i. 344, 366.
Scales, of cuticle of Plants, i. 378, 379.

of Fish, ii. 261-263.

of Insects, ii. 220-228; their use

as Test-objects, i. 167-173.
of Reptiles and Mammals, ii.

263.

Schiek's Compressor, i. 126.
Schizomycetes, i 307-313: their Zymotic

action, i. 313-315.
Schizonemece, i. 299.
Schultz's test, i. 208.
Schultze, Prof. Max, on Protoplasm., i.

222- note; hn, movement of^tfuia in

BiatonlVi. 2?3; on surf ace markings

of Diatoms, i. 277 note.
SchvuzerMr. A ... on use of Illuminators,

ic 110. I c « • c °% ' ? ' -

Schwann, doctrines of, ii. 252.

Schwendener, on Lichens, i. 329.

Scissors, for microscopic dissection, i.
188; for cutting thin sections, ii. 188.

Sclerogen, deposit of, on walls of Cells,
i. 359, 360.

Scolopendrum, sori of, i. 345.

Sea Anemone, ii. 135, 136.

Section-cutting Instruments, i. 189-193.

Section-lifter, Marsh's, i. 205.

Sections, thin, mode of making, of Soft
substances, i. 188-196; modes of
mounting, L 212-214; of Hard Sub-
stances, i. 196-200. of Foraminifera,
i. 198 note; of Leaves, i. 382; of Wood,

i. 376; of Echinus-spines, ii. 146, 147;
of Insects, ii. 219; of Bones and
Teeth, ii. 258; of Hairs, ii. 266.

Seeds, testae of, i. 386-388; spiral cells
in, i. 361.

Segmentation of Yolk-mass, ii. 185, 187.

Selaginellece, i. 350.

Selenite Stages, i. 112-114.

Sepiola, eggs of, ii. 191.

Sepiostaire of Cuttle-fish, ii. 180, 325.

Serialaria, colonial nervous system of,

ii. 160.

Serous Membranes, structure of, ii,
274.

Serpentine-Limestone, ii. 101-107, 310.

Sertularidce, ii. 129-131.

Sexual Generation, lowest forms of, in

Protophytes, i. 229, 230, 236, 237; in

Infusoria, ii. 26-30.
Shadbolt, Mr., on Arachnoidiscus, i.

293: his Annular condenser, i. 107

note; his Turn-table, i. 184.
Shark, teeth of, ii. 258,259; scales, etc.,

of, ii. 263.

Shell, of Crustacea, ii. 214, 215; of
Echinida, ii. 140, 141; of Foramini-
fera, ii. 68-70; of Mollusca, ii. 172-
180; Fungi in, i. 321.

Shrimp, shell of, ii. 215.

Side Illuminators, i. 114-116.

Side-Reflector, Beck's, i. 116, 117.

Siebert and Kraft's Dissecting Micro-
scope, i. 46.

Siebold, Prof., on reproduction of Bee,
ii. 247.

Silica crack-slide, i. 152, 162, ii. 321.

Siliceous Epiderms, i. 349, 379.

Sponges, ii. 120, 121.

Silk-worm diseases, i. 315-317.

Silver, crystallized, ii. 319.

Simple Microscope, optical principles of,
i. 18-22; various forms of, i. 43-51.

Siphonaceoz, i. 250, 251.

Siricido3, ovipositors of, ii. 245, 246.

Skin, structure of, ii. 274, 275; papillae
/of, ii. 284, 285, 298.

Slack, Mr., on Pinnularia, i. 298; on
< artificial Diatoms, i. 277 note; his
Diaphragm-Eyepiece, i. 95; his Light-
modifier, i. Ill; his Stage-vice, i. 121;
his Compressors, i. 126, 127; his Silica

INDEX.

351

crack-slide, i. 152, 162; his crystalliza-
tions from silicated solutions, ii. 321.

Sladen, Mr. P., on preserving Echino-
derm larvae, ii. 153.

Slider-Forceps, i. 185.

Slides, Glass, i. 175, 176.

Wooden, i. 183.

Slug, rudinientarv shell of, ii. 179; pal-
ate of, ii. 181, 182; eyes of, ii. 190.

Smith, Mr. Jas., his Mounting Instru-
ment, i. 186; his use of Bull's-eye
Condenser, i. 118.

Smith, Dr. Lawrence (U. S.), his In-
verted Microscope, i. 82.

Smith, Prof. H. L. (U. S.), on Binocular
Eyepiece, i. 33; his vertical Illumin-
ator, i. 118; his cells for dry-mounting,

i. 180; on mounting Diatoms, i. 306.
Smith, Prof. J. Edwards (U. S.), on de-
velopment of (Edogonium, i. 257; on
wide-angled Objectives, Preface, vi.f
vii.

Smith, Prof. W., on Diatomaceae, i.

170, 273, 301 note.
Smith and Beck, see Beck, Messrs.
Smut, of Wheat, i. 323.
Snail, palate of, ii. 181, 182; eyes of, ii.

190.

Snake, lung of, ii. 299.
Snow crystals, ii. 318.
Social Ascidians, ii. 166-168.
Soemmering's speculum, i. 97.
Sole, skin and scales of, ii. 261, 262.
Sollitt, Mr., on Diatom-tests, i. 170.
Sorby, Mr., on skeleton of Echinoderms,

ii. 146 note; his Spectroscope Eye-
piece, i. 90; his Microscopic examina-
tion of Rocks, ii. 314, 315 note.

Soredia of Lichens, i. 329.
Sori of Ferns, i. 344-346.
Spatangidium, i. 291.
Spatangus, spines of, ii. 143.
Spectacles, for Dissection, i. 187.
Spectro-Micrometer, Brownings, i. 91.
Spectroscope Eye-piece, i. 90.
Spectroscopic Analysis, principles of, i.
89-92.

Speculum, Parabolic, i. 116, 117.
Spermogonia of Fungi, i. 322; of Li-
chens, i. 330.
Sphacelaria, i. 332.

Sphozria, development of, within Ani-
mals, i. 318.

Sphazroplea, sexual reproduction of, i.
255.

Sphcerosira volvox, i. 243.

Splicer ozosma, i. 266.

Splicer ozoum, ii. 115.

Sphagnacece, peculiarities of, i. 342-344;

occurrence of parasites in leaf -cells

of, i. 327, ii. 53.
Spherical Aberration, i. 6, 7; means of

reducing and correcting, i. 7, 8.
Spicules of Sponges, ii. 120-122; Alcyo-

nian Zoophytes, ii. 136; of Doris, ii.

179.

Spiders, eyes of, ii. 250; respiratory
organs of, ii. 250; feet of, ii. 250; spin-
ning apparatus of, ii. 251.

Spines of Echinida, ii. 142, 143; mode
of making sections of, ii. 146, 147; of
Spatangus, ii. 143.

Spinning apparatus of Spiders, ii. 251.

Spiracles of Insects, ii. 239-241.

Spiral Cells of Sphagnum, i. 343; of
Orchideae, i. 360; of anthers, i. 384.

Crystallization, ii. 321.

■ Ducts, i. 366.

Fibres, i. 361.

Vessels, i. 364; in petals, i. 383.

Spiriferidce, Shell-structure of, ii. 178.

Spirillina, ii. 85.

Spirillum, i. 312.

Spirolina, ii. 72.

Spiroloculina, ii. 71.

Sponges, general structure and relations
of, ii. 117, 118; reproduction of , ii. 118;
skeleton of, ii. 119-122; fossil, ii. 307,
308.

Spongilla, ii. 118, 121.

Spongiole of Root, i. 375.

Spores, different kinds of, i. 228-230;
of Fungi, general diffusion of, i. 321-
323; of Hepaticae, i. 338; of Mosses,
i. 342; of Ferns, i. 345-348; of Equise-
taceae, i. 349; — see Oospores and Zy-
gospores.

Spot-Lens, i. 107.

Spring-Clip, i. 186.

Press, i. 186.

Scissors, i. 188.

Squirrel, hair of, ii. 264.

Siage-centering adjustment, i. 80.

Stage, Glass, i. 63.

Stage, Safety, i. 120.

Stage-Forceps, i. 120.

Stage-Plate, glass, i. 122.

Stage- Vice, i. 121.

Staining Processes, i. 204-208.

Stanhope Lens, i. 21.

Stanhoscope, i. 21.

Star- Anise, seed- coat of, i. 360.

Starch-granules, in Cells, i. 361, 362;
appearance of, by Polarized light,
i. 362.

Star-fish, Bipinnarian larva of, ii. 150,
151.

Stato-spores, i. 230 note; of Volvox, i.

244; of Hydrodictyon, i. 253.
Staurastrum, prominences of, i. 263;

self -division of, i. 265; varieties of,

i. 272.
Stauroneis, i. 299.

Steenstrup, Prof., on Alternation of
generations, ii. 134.

Stein, Dr., his doctrine of Acineta
forms, ii. 41 note, ii. 52 note; his re-
searches on Infusoria, ii. 63 note.

Steinheil Doublet, i. 21.

Stellaria, petal of, i. 343.

Stellate cells, of Rush, i. 354, 355; of
Water lily, i. 354, 355.

352

INDEX.

Stemmata of Insects, ii. 231.

Stem, i. 367; Monocotolydonous, struc-
ture of, i. 367, 367 ; Exogenous, struc-
ture of, i. 368-374; development of,
i. 374, 375; mode of making sections
of, i. 376.

Stentor, ii. 44; its conjugation, ii. 52.

Stephanoceros Eichornii, ii. 60, 61.

Stephanosphcera, i. 243 note, i. 244 note.

Stereoscope, i. 25.

Stereoscopic Spectacles, i. 187.

Vision, principles of, i. 25-

28; application of, to Compound Mi-
croscope, i. 27-39; to Simple Micro-
scope, i. 48, 49.

Stephenson, Mr., his suggestion of
homogeneous immersion Objectives,
i. 17; on diffraction-doctrine, i. 157-
160; his Binocular Microscope, i. 31-
33; his safety-stage, i. 120; on mount-
ing in bisulphide of carbon, i. 279;
on Coscinodiscus, i. 290.

Stewart, Mr., on internal skeleton of
Echinodermata, ii. 148.

Stick-net, i. 220.

Stigmata of Insects, ii. 239, 240.

Stings of Plants, structure of, i. 379; of
Insects, ii. 245, 246.

Stokes, Prof., on Absorption bands of
blood, i. 91, 92.

Stomata/of Marchantia, i. 336; of Flow-
ering Plants, i. 379, 380.

Stones, for polishing Sections, i. 198.

Stones, of Fruit, structure of, i. 360.

Strassburger, Dr., on cell-division, ii.
254 note.

Striatellece, i. 288.

Student's Microscopes, principles of
construction of, i. 55-57; Objectives
suitable for, i. 57-58; various forms,
of, i. 59-67.

Suctorial Crustacea, ii. 212, 213.

Suctorial Infusoria, ii. 39.

Sulphate of Copper and Magnesia,
radiating crystallization of, ii. 320.

Sulphate of Copper, spiral crystalliza-
tion of, ii. 321.

Sulphuric Acid, as test, i. 208.

Sundew, hairs of, i. 379.

Sunk Cells, i. 182.

Surirella, i. 287; conjugation of, i. 281;
use of, as test, i. 171.

Swift, Mr., his Challenge Microscope,
i. 71; his Portable Binocular, i. 82, 83;
his swinging Sub-stage, i. 71 note;
his combination Sub-stage, i. 113, 114;
his Aquatic box, i. 124; his Micro-
scope lamp, i. 122; his Wale Students'
Microscope, ii. 332.

Synapta, calcareous skeleton of, ii. 149.

Syncoryne, ii. 127.

Syncrypta, i. 244.

Synedveai, i. 287.

Syringe, small glass, i. 128; uses of,

i. 142, 204, 208, 212, 217, ii. 188 note,

ii. 293.

Syringe, injecting, ii. 293.

Tabanus, ovipositor of, ii. 246.
Table for Microscope, i. 130.
Tadpole, pigment cells of, ii. 276; circu-
lation in, ii. 288-292.
Taenia, ii. 192, 193.
Tardigrada, ii. 62.

Teeth, of Echinida, ii. 144, 145; of
Ophiocoma, ii. 145; of Mollusks, ii.
181-183; of Leech, ii. 203; of Verte-
brata, structure of, ii. 258-261; fossil,
ii. 311, 312; mode of making sections
of, ii. 258.

Tendon, structure of, ii. 273.

Tenthredinido3, ovipositor of, ii. 245.

Terebella, circulation and respiration
in, ii. 196, 197.

Terebratula, shell-structure of, ii. 177,
178; muscular fibre of, ii. 283.

Terpsinoe, i. 288.

Tests, of Rhizopods, ii. 18, 19; of

Foraminifera, ii. 77-85.
Test-Liquids, i. 208, 209.
Test-Objects, i. 16">; for low powers, i.

166, 167; for medium powers, i. 167-

169; for high powers, i. 169-173.
Tetramitus rostratus, ii. 30, 31.
Tetraspores of Ceramiacese, i. 334.
Textularia, ii. 68, 88.
Thalassicolla, ii. 115.
Thallus of lower Cryptogamia, i. 246,

329, 331.
Thaumantias, ii. 131.
Thecse, of Ferns, i. 345; of Equisetaceae,

i. 349.

Thin Glass, i. 176, 177.
Thomas, Mrs. H., on Cosmarium, L
266.

Thomas, Mr. R., on microscopic crys-
tallization, ii. 321.

Thompson, Mr. J. V., on development
of Comatula, ii. 153; on metamor-
phosis of Cirrhipeds, ii. 213; on meta-
morphosis of Crustacea, ii. 216.

Thomson, Sir Wyville, on Globigerina,

ii. 87; on Siliceous Sponges, ii. 121;
on development of Pentacrinoid larva,
ii. 156; on Chalk-formation, ii. 306.

Thread-cells of Zoophytes, ii. 137, 138.

Thrush, fungous vegetation of, i. 320.

Thurammina, ii. 81.

Thwaites, Mr., on conjugation of Dia-
toms, i. 281, 282; on filamentous ex-
tensions of Palmellese, i. 246 note.

Ticks, ii. 248.

Tinea favosa, fungus of, i. 320.

Tinoporus, ii. 89, 90.

Tipula, larva of, ii. 240.

Tissues, Elementary, of Animals, mi-
croscopic study of, ii. 252; formation
of, ii. 253-255; see Blood, Bone, Ca-
pillaries, Cartilage, Epidermis, Epi-
thelium, Fat, Feathers, Fibrous Tis-
sues, Glands, Hair, Horn, Mucous
Membranes, Muscle, Nervous Tissue,

•

INDEX.

353

Pigment-cells, Scales, Serous Mem-
branes, Teeth.

Tissues, Elementary, of Plants, i. 353;
Cellular, i. 353-363; Woody, i. 363,
364; Vascular, i. 365, 366; dissection
of, i. 366; preparation of, i. 201.

Toiles, Mr., his Binocular Eye-piece, i.
33; his Amplifier, i. 86; his vertical
Illuminator, i. 119.

Tomopteris, ii. 199-201.

Tongues of Gasteropods, ii. 181-183; of
Insects, ii. 234-236.

Torula cerevisice, i. 315.

Tous-les-mois, Starch-grains of, i. 362.

Tow-net, i. 220.

Tracheae of Insects, ii. 238-240; mode of

preparing, ii. 240, 241.
Tradescantia, cyclosis in hairs of, i.

358.

Transparent Objects, arrangement of
Microscope for, i. 141-145; various
modes of Illuminating, i. 141-146.

Travelling Microscopes, i. 81, 82.

Trematode, Entozoa, ii. 194.

Triceratium, i. 295; markings on, i. 277.

Trichoda, bristles of, ii. 43; metamor-
phosis of, ii. 47-49.

Trichogyne, of Lichens, i. 330; of Flori-
deae, i. 335.

Trilobite, eye of, ii. 310.

Triloculina, ii 71.

Triple Staining, i. 207.

Trochus, palate of, ii. 181.

Trout, circulation in young of, ii. 289.

Tube-cells, i. 180.

Tubular Nerve-substances, ii. 284, 285.
Tubularia, ii. 127.

Tunicata, general organization of, ii.

163, 164: see Ascidians.
Turbellaria, ii. 194-196.
Turn-tables, i. 184.

Tyndall, Prof., on Bacteria, etc., i. 313,
314, 321.

Ulvacece, i. 246, 247.

Unicellular nature of Infusoria, ii. 25.

Unicellular Plants, i. 229.

Unionidce, shells of, ii. 174-176.

Uredo, i. 323.

Urns of Mosses, i. 340.

Uvella, i. 235.

Vacuoles, i. 225; microscopic appear-
ances of, i. 153.
Vallisneria, cyclosis in, i. 356, 357.
Vampyrella, ii. 3-5.

Van Beneden, Prof. Ed., on gigantic

Gregarina, ii. 21.
Vanessa, haustellium of, ii. 236.
Variation, tendency to, in Desmideaceae,

i. 271; in Diatomaceae, i. 282; in For-

aminifera, ii. 72, 77, 96; in Polycys-

tina, ii. 112, 113 note.
Varnishes and Cements, i. 178, 179.
Vaucheria, zoospores of, i. 250; sexual

reproduction of, i. 251.

Vegetable Ivory, i. 360.

Vegetable Kingdom, differentiated

from Animal, i. 222-233.
Vegetable substances, preparation of,

i. 201.
Ventriculites, ii. 307.
Vermilion injections, ii. 294, 295.
Vertebrata, elementary structure of,

ii. 252 (see Tissues); blood of, ii. 267-
271 circulation in, ii. 286-292.

Vertical Illuminators, i. 118, 119;
Vesicular Nerve Substance, ii. 284.
Vessels of Plants, i. 365, 366.
Vibracula of Polyzoa, ii. 163.
Vibrio, i. 311, 312.

Villi of intestine, injections of, ii. 295.

Vine-disease, i. 323.

Vinegar, Eels of, ii. 193.

Vitreous For ami nif era, ii. 69, 85-107.

Volvox, structure of, i. 237-240; devel-
opment and multiplication of, i. 240,
241; generation of, i. 241-243; amoe-
boid state of, i. 241-243.

Vorticella, ii. 43, 46; encysting process
in, ii. 47; conjugation of, ii. 52.

Wale's New Working Microscope, i. 61-
63.

Wallich, Dr., on making sections of
Foraminifera, i. 198 note; on Diatoms,

i. 275 note, i. 277 note; on Cocco-
spheres, ii. 19; on nucleus in Gromia,

ii. 9; on Globigerinae, ii. 86; on Poly-
cystina, ii. 113 note.

Warts, structure of, ii, 276.
Water-Bath, i. 185.

Water-immersion Objectives, i. 16, 17;

ii. 327, 330.
Water-Lily, stellate cells of, i. 354, 355;

leaf of, i. 382.
Water-newt, circulation in larva of, ii.

288.

Water- Vascular system, of Rotifera, ii.
57 ; of Planaria, ii. 195.

Watson, Messrs., their new form of
Microscope, ii. 331, 332.

Weber's Annular Cell, i. 124.

Webster-Condenser, 1. 103, 104.

Wenham, Mr., his new Achromatic
combination, i. 15; his suggestion of
homogeneous immersion, i. 17; his
Binocular Microscope, i. 19-31; his
Non-Stereoscopic Binocular, i. 84; his
Disk-illuminator, i. 105; his Parabolic
Illuminator, i. 107, 108; his Reflex
Illuminator, i. 109; on adjustment of
Object-glasses, i. 140; his observations
on Pleurosigma, i. 277 note; on Cyclo-
sis, i. 358, 359; on Podura scale, ii.
226.

Whalebone, structure of, ii. 267.

Wheat, blights of, i. 323, ii. 193.

Wheatstone, Sir C, his invention of the
Stereoscope, i. 25-27; of the Pseudo-
scope, i. 27, 28.

Wheel-animalcules, see Rotifera.

354

LNDEX.

White-cloud Illuminator, i. 111.

White Corpuscles of blood, ii. 270, 271.

White Fibrous tissue, ii. 272.

Whitney, Mr., on circulation in Tad-
pole, ii. 289-292.

Williamson, Prof. W. C, on Vol vox, i.
243 note; on shells of Crustacea, ii.
215 note; on scales of Fishes, ii. 261,
262; on Coal -plants, ii. 303; on Levant-
mud, ii. 305.

Wings of Insects, ii. 241-243.

Winter-eggs, of Rotifera, ii. 59; of
Hydra, ii. 125; of Entomostraca, ii.
210.

Wollaston, Dr., his Camera Lucida, i.
96.

Wood, of Exogenous stems, i. 369,
370.

Woodward, Col. Dr., his Prism, i. 105;
his resolution of Amphipleura pellu-
cida, i. 171; of Surirella gemma, i.
172; on scale of Gnat, i. 155, on Podu-
ra-scale, ii. 227.

Woody Fibre, i. 363; glandular, of Con-
ifers, i. 364.

Working-distance of Objectives, i. 161.

Wormlev, Dr., on Micro-Chemistry, ii.
32H.

Wyth's Amplifier, i. 86.

Xanthidia of Flints, i. 267 note, ii.
308.

Yeast-plant, i. 315.
Yellow Fibrous tissue, ii. 273.
Yucca, epidermis of, i. 377; stomata of,
i. 380.

Zeiss's oil-immersion Objectives, i. 17,
18; his adjusting Low-power, i. 18t>.
166; his Sub-stage Condenser, i. 104
note.

Zentmayer, Mr., on defining power, i.
162 note; his swinging tail-piece, i.
61, 75; his glass stage, i. 63.

Zoea-lnxva, of Crab, ii. 216.

Zoantharia, ii, 135.

Zooglcea, i. 308.

Zoophyte-Trough, i. 125.

Zoophytes, ii. 122-137; see Actinozoa,
Alcyonaria, and Hydrozoa.

Zoospores, i. 230; note; of Protococcus,
i. 2o3, 234; of Ulvacese, i. 247; of Vau-
cheria, i. 250; of Achlya, i. 251; of
Confervacese, i. 254; of Chsetophora,
i. 258; of Pediastreae, i. 271; of Fuca-
ceas, i. 334.

Zygnemaceoe, i. 236, 237.

Zygospores, i. 229; of Conjugates, i.
232, 236; of DesmidiaceaB, i. 267, 268;
of Diatomacese, 281, 282.

Zygosis of Actinophrys, ii. 12; of Amoe-
ba; ii. 17; of Gregarina, ii. 22.

Zymotic action of Bacillus-organisms,
313-315.

ERRATUM.

The first sentence in the Note to p. 163. vol. i., should run thus: —
The Author is informed by Prof. Abbe, that the ' penetration ' of Objectives de-
creases in a corresponding ratio with the increase of their respective Numerical
Apertures; or, when Objectives of the same class are compared, with the increase
in the sines of their respective semi-angles of aperture.

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